STORMWATER PONDS IN COASTAL SOUTH CAROLINA
2019 State of Knowledge Full Report
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 1 STORMWATER PONDS IN COASTAL SOUTH CAROLINA
2019 State of Knowledge Full Report
A report sponsored by the South Carolina Sea Grant Consortium and the State of South Carolina pursuant to National Oceanic and Atmospheric Administration Award No. NA10OAR4170073.
Suggested citation: Cotti-Rausch, B.E., Majidzadeh, H., and DeVoe, M.R., eds., Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Full Report. S.C. Sea Grant Consortium, Charleston, S.C.
Cover photo by Grace Beahm Alford.
SCSGC-T-20-02 Table of Contents
Acknowledgements...... iv
Preface...... v
Chapter 1 – A Pond Inventory for the Eight Coastal Counties of South Carolina...... 1
Chapter 2 – Environmental Factors and Design Features that Control Stormwater Transport and Contaminant Fate in Ponds...... 15
Chapter 3 – An Assessment of Nonpoint Source Pollution in Stormwater Pond Systems in Coastal South Carolina...... 41
Chapter 4 – The Ecological Function of South Carolina Stormwater Ponds within the Coastal Landscape...... 81
Chapter 5 – A Policy Lens of South Carolina Coastal Stormwater Management...... 103
Chapter 6 – An Economic Assessment of Coastal Stormwater Management...... 123
Chapter 7 – Communication Recommendations for Improved Stormwater Pond Maintenance in Coastal South Carolina...... 143
Chapter 8 – Synthesis of Our Current Understanding of Stormwater Ponds in Coastal South Carolina...... 159
Glossary of Acronyms...... 185
Participating Institutions ACKNOWLEDGEMENTS
We gratefully acknowledge all contributors who volunteered their time to provide comments and make contributions in their specific field of expertise to the work of the Stormwater Ponds Research and Management Collaborative, and ultimately to the synthesis of our current understanding of stormwater ponds in coastal South Carolina. A total of 32 individuals contributed to the preparation of this report (20 listed below and 12 anonymous, external reviewers):
Jeff Adkins* Ed Oswald* NOAA Office for Coastal Management Charleston Trident Association of Realtors Lee Bundrick Richard Peterson, Ph.D. S.C. Sea Grant Consortium (former) Coastal Carolina University Currently at the Kiawah Conservancy Andrea Sassard David Fuss* S.C. Sea Grant Consortium (former) Horry County Stormwater Management Department Currently at the National Oceanic and Atmospheric (former) Administration Currently at the Indian River Land Trust Calvin Sawyer, Ph.D.* Shannon Hicks* Cooperative Extension, Clemson University S.C. Department of Health and Environmental Control Norm Shea* Dan Hitchcock, Ph.D. S.C. Department of Natural Resources Clemson University Allen Smith* Melody Hunt, Ph.D. Estate Management Services S.C. Sea Grant Consortium (former)
Currently at the U.S. National Park Service Lisa Swanger Coastal Waccamaw Watershed Education Blaik Keppler Program ACE Basin National Estuarine Research Reserve April Turner* Michelle LaRocco S.C. Sea Grant Consortium North Inlet-Winyah Bay National Estuarine Research Reserve
(former) John Weinstein, Ph.D. The Citadel Currently at Georgetown County, S.C. David Whitaker* Eric Larson* S.C. Department of Natural Resources (former) Beaufort County Stormwater Management Department Currently a member of the South Atlantic Fishery (former) Management Council Currently at EOM Operations Chris Marsh, Ph.D.* The LowCountry Institute *Stormwater Ponds Advisory Council members
Special thanks to the S.C. Sea Grant Consortium Communications team: Joey Holleman, technical editor; Susan Ferris Hill, copy editor and proofreader; and Crystal Narayana, designer.
EDITORS Bridget Cotti-Rausch, Ph.D. Coastal Environmental Quality Program Specialist (former), S.C. Sea Grant Consortium, Charleston, S.C. Currently an Environmental Protection Specialist, U.S. Environmental Protection Agency, Washington, D.C.
Hamed Majidzadeh, Ph.D. Coastal Environmental Quality Program Specialist (former), S.C. Sea Grant Consortium, Charleston, S.C. Currently an Assistant Professor, Southern New Hampshire University, Manchester, NH
M. Richard “Rick” DeVoe Executive Director, S.C. Sea Grant Consortium, Charleston, S.C.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report iv ACKNOWLEDGEMENTS PREFACE
The state of South Carolina has seen some of the most rapid coastal population growth rates and overall rates of urbanization in the nation. Its upward trend in population growth is expected to continue with a projected population in the coastal zone of over 1.5 million by the year 2030. The resulting urban and suburban growth in the region increases the amount of impervious surfaces (e.g., roofs, roads, parking lots) to support the associated development. As impervious surface area in a watershed increases so does the amount of stormwater runoff. In coastal South Carolina, the most common best management practice to control runoff is stormwater ponds.
The S.C. Sea Grant Consortium, in collaboration with various stakeholders, identified ponds as a growing topic of concern throughout the eight coastal counties (Figure A.1). In October 2014, the Consortium initiated the S.C. Stormwater Ponds Research and Management Collaborative, an effort that gathered scientists and resource managers to investigate and address the challenges associated with these systems. The long-term vision of the Collaborative is to (1) satisfy the information needs and concerns of local communities, homeowners’ associations (HOAs), businesses, and industries surrounding pond design, maintenance, and management; (2) characterize coastal ponds to understand their functionality, durability, benefits, and costs; and (3) ultimately develop new and innovative engineering and
Grand Strand
Tri-County
Lowcountry
Figure A.1 South Carolina’s eight coastal counties with the three coastal regions designated as follows: (1) Grand Strand (Horry and Georgetown), (2) Tri-County (Berkeley, Charleston, and Dorchester), and (3) Lowcountry (Colleton, Beaufort, and Jasper).
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report v construction practices to ensure that current and future ponds function efficiently without negative ecological impacts or economic costs due to inadequate maintenance.
What follows is the Collaborative’s initial product, a scientific state-of-knowledge report on stormwater ponds in coastal South Carolina organized in eight chapters. This report presents an inventory of existing ponds, a comprehensive literature review and gap analysis, and recommendations for research, outreach, and management. Twenty researchers from Consortium member institutions collaborated on this project, which was funded by the State of South Carolina and the National Sea Grant College Program.
Each project team worked to ensure that any information on ponds from coastal South Carolina was included in the report. When coast-specific data were lacking on a given topic, studies from other regions or states were incorporated, as appropriate. The project was guided by the Stormwater Ponds Advisory Council (SPAC) comprised of regulatory agents, private sector representatives, and nonprofits. To satisfy the informational needs of our diverse stakeholder groups, we produced a series of products to convey the information gathered by our project teams. This technical report was written for the following audiences: researchers, the stormwater management community, and local and state decision-makers. To share this report with nontechnical groups, specifically individual property owners and HOAs, the Consortium will produce a pamphlet and booklet series written for general audiences.
The results of this initial work by the Collaborative provide the foundation for the generation of additional science- based information, which fills critical information gaps to address key management and policy questions and provides for more efficient and cost-effective stormwater pond retrofits and design for the future. An executive summary of this report on stormwater ponds in coastal South Carolina is available on the S.C. Sea Grant Consortium’s website at www.scseagrant.org/spsok.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report vi CHAPTER 1 – A POND INVENTORY FOR THE EIGHT COASTAL COUNTIES OF SOUTH CAROLINA
Authors
Erik M. Smith, Ph.D. Belle W. Baruch Institute for Marine and Coastal Sciences, University of South Carolina North Inlet-Winyah Bay National Estuarine Research Reserve
Denise M. Sanger, Ph.D. Marine Resources Research Institute, S.C. Department of Natural Resources ACE Basin National Estuarine Research Reserve
Andrew Tweel, Ph.D. and Erin Koch Marine Resources Research Institute, S.C. Department of Natural Resources
Corresponding Author Erik M. Smith, Ph.D. ([email protected])
1.1 Background The use of stormwater ponds as a best management practice (BMP) to control surface runoff became a widespread practice in South Carolina due to stormwater control regulations passed in 1992 (Drescher et al. 2007). Since then ponds have become highly utilized as stormwater BMPs and are associated with all forms of commercial, residential, and golf-course development along the S.C. coast. Knowledge of the total number, relative distribution, and cumulative surface area of ponds within coastal S.C. is, however, currently poorly constrained. This represents a key information gap in determining how the creation and use of ponds as a stormwater management practice have changed the hydrology and associated material transport within the coastal zone.
There have been various attempts to quantify the occurrence of ponds in S.C. over the years. Siewicki et al. (2007) estimated there were over 8,100 ponds within the five 14-digit Hydrologic Unit Codes of the S.C. coastal zone based on 1999 aerial imagery. Another analysis by Lewitus et al. (2008) determined that ponds greater than 0.4 hectares occurring east of Highway 17, the major coastal highway that serves as the regulatory dividing line between fresh and marine waters, numbered 1,174 in 1994, but by 1999 this number had increased by 70% to a total of 1,997 ponds. A more recent and higher resolution inventory of coastal ponds, based on 2006 color aerial imagery identified 14,446 ponds, representing a cumulative surface area of 21,397 acres, within the coastal watersheds of S.C. (E. Smith, unpublished data). Given continued high rates of coastal development, previous pond inventories are likely outdated and a potentially large underestimate of the current inventory of coastal ponds. In addition, the previous inventories of coastal ponds implicitly assumed all ponds identified in aerial imagery were constructed expressly for the purposes of stormwater control and can thus be classified as “stormwater ponds.” This has likely skewed estimates of the number of true stormwater ponds, given the known popularity of recreational fishing ponds along the coast of S.C. as well as the prevalence of agricultural irrigation ponds in the western portion of some of the coastal counties. To address this
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 1 information gap, the objectives of this project were to:
1. Create an updated inventory of the number, size, and geographic distribution of all small artificial water bodies (“ponds”) in the eight coastal counties of S.C. through interpretation and manual digitization of 2013 aerial imagery. 2. Attempt to classify ponds by visually interpreting surrounding land use during pond digitization to distinguish between ponds associated with coastal development, and thus likely created for stormwater control, from rural ponds associated with agricultural or recreational uses. 3. Conduct a retrospective inventory analysis for select regions of the coastal zone to better understand rates of pond construction and its association to land-use change.
1.2 Framework
1.2.1 Pond Digitization Methods
The identification and geolocation of existing ponds for the eight coastal counties of S.C. were based on United States Department of Agriculture (USDA) National Agriculture Imagery Program (NAIP) 2013-Natural Color 1-meter resolution Imagery, which was the most recent high-resolution imagery available for coastal S.C. (USDA 2013a). Heads-up digitization was conducted using a systematic grid review approach at a consistent scale of 1:3000 to provide a sufficient degree of resolution to delineate the perimeter and open water area of each pond. Details on digitization methods can be found in Appendix A1 (see www.scseagrant.org/spsok).
As ponds were identified and selected for digitization, the surrounding land use was visually interpreted to first ensure that the water body met the requirements for inclusion in the inventory and then to place the digitized ponds in one of seven visually defined land-use classifications (Table 1.1). Identified water bodies intentionally excluded from the pond inventory were those interpreted as any of the following:
• Marsh or riverine impoundments, including former rice fields, • Ponds or lagoons associated with wastewater treatment plants, • Any pond or lagoon associated with industrial facilities or power plants, • Open water within forested wetlands (swamps), and • Small water features created for fountains or other visual aesthetics, such as those associated with miniature golf sites.
Category Description Rural Ponds that are either associated with agricultural practices or associated with rural homesteads and which have presumably been created for irrigation or fishing and other recreational uses. Forest Ponds in the middle of woods with no structures in the relative vicinity. Mining Ponds located adjacent to borrow pits or sand mining operations. Residential Ponds located in residential neighborhoods and not adjacent to golf course land. Golf Ponds located on golf courses with no adjacent houses.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 2 Category Description Commercial Ponds located in or adjacent to shopping areas, office complexes, government properties, school properties, or downtown urban areas. Mixed Ponds adjacent to either residential or commercial properties combined with golf courses, which in most cases were residential developments that included golf courses.
Table 1.1 Visually defined land-use categories used to classify ponds. The first three categories are not considered to be associated with coastal development, while the last four classes are assumed to be the direct result of development and thus likely constructed as BMPs for stormwater control.
1.2.2 Associating Ponds with Location and Landscape Attributes
Each pond in the inventory was categorized by county as well as its United States Geological Survey (USGS) Watershed Boundary Dataset-HUC 12-digit watershed (USGS 2005) and whether or not it occurs within the boundary of the S.C. Department of Health and Environmental Control-Office of Ocean and Coastal Resource Management (DHEC-OCRM) Critical Area (DHEC 2008), which delineates the boundaries of coastal wetland systems where DHEC-OCRM has direct permitting authority and has established additional regulatory criteria to protect sensitive coastal waters. In addition, each pond was associated with several different data layers used to define the surrounding land-use, elevation, soil type, and distance to nearest major surface water body.
Specific data layers associated with the pond inventory were as follows. Coastal Change Analysis Program (C-CAP) Southeast Region land cover data from 2010 was used to identify the land cover data adjacent to the ponds (e.g., forested, developed, wetlands, etc.) at 30 m resolution (NOAA 2013). USGS National Land Cover Database – Percent Developed Imperviousness data from 2011 provided an estimate of the impervious cover surrounding each pond at 30 m resolution (MRLC 2014). The U.S. Department of Agriculture (USDA) Soil Survey Geographic SSURGO Database provided soil drainage classes surrounding each pond (USDA 2013b), which were merged into two classes: poorly drained (sum of very poorly drained, somewhat poorly drained, and poorly drained classes) and well-drained (sum of moderately well-drained, well-drained, excessively drained, and somewhat excessively drained classes). Elevation data referenced to the North American Vertical Datum of 1988 (NAVD88, feet) was associated with the perimeter area of each pond using the most recent LIDAR-derived digital elevation model (DEM) available (DNR 2016). To compute the distance of each pond to its nearest surface water, U.S. Fish and Wildlife Service National Wetlands Inventory (NWI) data for “Estuarine and Marine Deepwater” and “Riverine” surface categories were used (USFWS 1979). This dataset delineates freshwater and marine rivers, tidal creeks, and estuaries to a minimum width of approximately 20 m (66 feet).
1.2.3 Determining Rate of Increase in Pond Number and Cumulative Area
An assessment of change over time in pond number and cumulative area was conducted for two pilot areas: The “Grand Strand” area of Horry and Georgetown counties, and the greater Charleston area (Tri-County area) that comprises portions of Charleston, Berkeley, and Dorchester counties. The first pilot area is roughly the extent of the greater Myrtle Beach area covering approximately 421 square miles from the Waccamaw River east toward the Atlantic Ocean. This area was chosen for a pilot study because of its relatively high rate of development during the past two decades. The second pilot area is roughly the extent of the Charleston metropolitan area, covering about 595 square
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 3 miles, from the North Edisto River to just south of Bulls Bay and west into portions of Dorchester and Berkeley counties. This area was also chosen because of its relatively high rate of development in recent decades. To conduct the change analysis, ponds were identified on the 1994, 1999, and 2006 aerial imagery in addition to the 2013 imagery.
1.3 Results
1.3.1 Pond Number and Distribution
Based on available 2013 imagery, the eight coastal counties of S.C. contain a total of 21,594 ponds, which collectively comprise a cumulative area of 29,395 acres. Forty-three percent of these ponds (9,269 ponds) were determined to be associated with development-related land uses (i.e., residential or commercial development, golf courses, or some combination of each), and thus can be assumed to have been created specifically for stormwater management. These development-related ponds collectively comprise a cumulative area of 11,916 acres. The vast majority (93.7%) of ponds not associated with developed land were interpreted to be a combination of agricultural ponds and rural ponds presumably created for recreational fishing purposes, which is a common practice in the western portion of the coastal plain. Ponds classified as associated with mining operations represented just 1.4% of the undeveloped pond category, while forest ponds represented 5.1% of the undeveloped pond category.
Figure 1.1a Pond inventory for the eight coastal counties Figure 1.1b Pond inventory for the eight coastal counties of South Carolina with each pond classification identified of South Carolina with ponds grouped and color-coded as by color coding. Blue line denotes the upstream limit of either development-related or nondevelopment-associated the DHEC-OCRM Critical Area. land uses.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 4 Not surprisingly, the spatial distribution of development-related ponds tends to follow population density and development patterns along the coast (Figures 1.1a and 1.1b). As a result, Horry, Charleston, and Beaufort counties contain the highest number of ponds among S.C.’s eight coastal counties (Figure 1.2). Collectively, these three counties contain 64% of all ponds and 75% of the development-related ponds within the eight coastal counties. While the majority of ponds in Beaufort and Charleston counties are associated with development (74% and 56%, respectively), the large rural and agricultural areas in the western portion of Horry County result in development- related ponds accounting for just 40% of all ponds within this county. Nondevelopment-associated ponds dominate total pond numbers in the remaining five counties, with the largest ratio of nondevelopment to development ponds occurring in Colleton and Jasper counties. Across all counties, development-related ponds tend to be dominated by ponds associated with residential developments (Figure 1.3). The exception to this was Jasper and Beaufort counties, which have higher percentages of ponds associated with the “mixed” land-use category, represented overwhelmingly by residential golf course developments. Thus, across all eight coastal counties, the creation of ponds is overwhelmingly associated with residential development or residential developments that also include golf courses. Ponds were also identified relative to location of the DHEC-OCRM Critical Area, given its regulatory significance. Although the Critical Area accounts for just 26% of the total land area within the eight coastal counties, 33% of all ponds and 52% of all development-related ponds occur within it. These numbers are largely driven by Horry, Charleston, and Beaufort counties, which by themselves account for 90% of all development-related ponds within the Critical Area, and which contain 762, 1,831, and 1,784 Critical Area development-related ponds, respectively.
Horry
Georgetown
Berkeley
Dorchester
County Charleston
Colleton
Beaufort Development related Jasper Nondevelopment related
0 1000 2000 3000 4000 5000 6000
Count
Figure 1.2 Numbers of development-related and nondevelopment-associated ponds by county.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 5 Golf Residential Mixed Commercial
Horry
Georgetown
Berkeley
Dorchester
County Charleston
Colleton
Beaufort
Jasper
0 20 40 60 80 100
% of Total
Figure 1.3 Distribution of land-use categories associated with development-related ponds by county.
The total area of the coastal zone now represented by ponds (29,395 acres) is equivalent to 17% of the combined surface area of Lakes Marion and Moultrie. While this cumulative surface area of ponds is relatively small compared to the state’s major coastal reservoirs, these ponds, especially the development-related ponds, could represent a significant component of the coastal landscape at the local level. This is readily apparent in the spatial distribution of development-related pond area per unit upland area (Figure 1.4). The three major urbanizing areas of S.C.’s coast clearly stand out as locations in which the cumulative water surface represented by ponds comprise a measurable percentage of the total land area. In the Grand Strand area, for example, ponds comprise greater than 1% of the total land area across almost the entire coastal region east of the Waccamaw River and Intracoastal Waterway, and in many specific locations within this region they represent greater than 5% or even 10% of the total land area. Similar patterns are evident throughout the greater Charleston area and in concentrated areas of highly developed Hilton Head Island and Bluffton (Beaufort County).
1.3.2 Pond Size
Among all ponds within the eight coastal counties, individual pond area varies by almost four orders of magnitude, ranging from 0.016 to 149.6 acres. The distribution of pond size is very highly skewed, however, towards the small size classes. Among all ponds, median pond size is just 0.47 acres (i.e., 50% of ponds in all eight coastal counties
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 6 Figure 1.4 Spatial distribution of pond area expressed as a percentage of total upland area, calculated on a square kilometer basis. The darker the shade, the larger the percentage of land surface in that area that is pond water.
are less than 0.47 acres) and 98% of all ponds are less than 10.0 acres (Figure 1.5a). But because of this extreme skewness, the combined area of all ponds less than 0.47 acres is roughly just 5% of the cumulative area of all ponds, while those ponds larger than 10 acres account for almost a third (32%) of the cumulative area of all ponds (Figure 1.5b). Interestingly, almost identical size distribution patterns hold when considering just development-related ponds; although their numbers and cumulative areas are much lower (Figures 1.5c and 1.5d). For development-related ponds, median size is 0.54 acres, although because there are fewer very large development-related ponds, those over 10.0 acres account for just 20% of the cumulative area. Development-related ponds also exhibit differences in the median and range of pond size among the different counties (Figure 1.6). The two southern counties (Jasper and Beaufort), followed closely by the two northern counties (Georgetown and Horry), all have higher median pond areas and larger ranges in pond area than the four counties surrounding the greater Charleston metro area.
1.3.3 Pond Locations within the Landscape
As expected given the geography of the coastal counties and the location of the major urbanizing areas, ponds are positioned in relatively close proximity to coastal waters. Throughout all coastal counties, 57% of all development- related ponds (totaling 5,277 ponds) are within 1.0 miles of a river, tidal creek, or other coastal water body greater than 66 feet in width, as defined by the National Wetland Inventory, and fully one-third of all development-related
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 7 a) Number of ponds by size class; All ponds 6000 100 5000 80 4000 # of ponds 60 3000 Total (%) 40 Count 2000 1000 20 0 0
0 1 2 3 4 5 6 7 8 9 10 Cumulative total (%) Pond size (acre)
b) Pond area by size class; All ponds 3000 100 2500 80 2000 60 1500 Area 40 1000 Total (%)
Area (acre) Area 500 20 0 0
0 1 2 3 4 5 6 7 8 9 10 Cumulative total (%) Pond size (acre)
c) Number of ponds by size class; Development-related ponds 3000 100 2500 80 2000 60 1500 # of ponds Total (%) 40 Count 1000 500 20 0 0
0 1 2 3 4 5 6 7 8 9 10 Cumulative total (%) Pond size (acre)
1500 d) Pond area by size class; Development-related ponds 100 80 1000 60 Area 500 Total (%) 40
Area (acre) Area 20 0 0
0 1 2 3 4 5 6 7 8 9 10 Cumulative total (%)
Pond size (acre)
Figure 1.5 Histograms of pond numbers and cumulative areas by size class for all ponds (upper two panels) and just development-related ponds (lower two panels).
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 8 Horry
Georgetown
Berkeley
Dorchester
Charleston County
Colleton
Beaufort
Jasper
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Pond Area (acre)
Figure 1.6 Box plot of size distributions of development-related ponds, by county. Vertical lines represent median pond area; boxes contain the 25th to 75th percentile of the distribution; and the horizontal lines contain the 10th to 90th percentile of the distribution. Outliers (ponds that lie beyond either the 10th or 90th percentiles) not shown.
ponds are within just 0.5 miles of such waters. Median distance and the percentage of development-related ponds occurring close to coastal waters vary substantially by county (Figure 1.7). Given the proportion of ponds in Beaufort and Charleston counties that occur within the Critical Area, it is not surprising that 75% of all development-related ponds occur less than 1 mile from coastal waters. Most of these ponds are near tidal creeks and larger branches of Charleston Harbor and Port Royal Sound rather than near beaches. A similar percentage of ponds in Georgetown County occur within 1 mile of major receiving waters due to the extensive tidal rivers entering Winyah Bay. While Horry County has a number of development-related ponds in close proximity to its beaches, the extensive development inland and relative paucity of inland coastal waters results in a median distance between ponds and receiving waters of over 1 mile.
Despite their relatively close proximity to coastal waters, ponds occupy a rather large range in vertical elevation across the coastal counties. For the three counties with the most development-related ponds (Horry, Charleston, and Beaufort), there are pronounced differences in the range of their elevation, relative to mean sea level (Figure 1.8). Beaufort and, especially, Charleston counties have a preponderance of their development-related ponds distributed at lower elevations, while Horry County, which has a much smaller Critical Area, tends to have relatively few low-lying ponds. Assuming the tidal elevation of mean higher high water in each of these three counties might be an indication
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 9 Horry
Georgetown
Berkeley
Dorchester
County Charleston
Colleton
Beaufort
Jasper
0 1 2 3 4 5 6
Distance to Nearest Major Surface Water (miles)
Figure 1.7 Box plot showing the distribution of distances to nearest major surface water body (defined by the NWI, see methods) for development-related ponds, by county. All else as in Figure 1.6.
of the potential for tidal or saline groundwater exchange between pond and coastal surface waters, there are 2%, 17%, and 20% of development-related ponds at or below the elevation of mean higher high water in Horry, Charleston, and Beaufort counties, respectively. Thus, there are likely few brackish ponds in the northern portion of the state, but they may represent a non-trivial proportion of the ponds within the southern portion of the S.C. coast.
Based on USDA Soil Survey data, the S.C. coastal zone is characterized by a dominance of poorly drained soils, which cover approximately 73% of the total area. Critical Area soils tend to be more poorly drained (78%) than the coastal zone as a whole, reflecting lower elevations and a larger coverage of wetlands within the Critical Area. Not surprisingly then, ponds tend to be located in areas dominated by poorly drained soils. There is, however, a bimodal distribution to the data (not shown); while 68% of the development-related ponds are surrounded by land that contain greater than 80% poorly drained soils, there is also a significant fraction, 16%, of ponds that are surrounded by rather well drained soil, defined as those that are comprised of greater than 20% poorly drained soils.
1.3.4 Change in Pond Numbers Over Time in the Charleston and Myrtle Beach Areas
Horry and Charleston counties presently contain the largest number of all ponds and of development-related ponds. In both counties these ponds are concentrated in the greater Charleston metropolitan area and the greater Myrtle Beach metropolitan area, also known as the Grand Strand. There has been a marked increase in the number of development-
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 10 a) Horry County 500
400
300
200 Pond Count 100
0 -10 0 10 20 30 40 50 60 70 80 90 100
b) Charleston County 500
400
300
200 Pond Count 100
0 -10 0 10 20 30 40 50 60 70 80 90 100
c) Beaufort County 500
400
300
200 Pond Count 100
0 -10 0 10 20 30 40 50 60 70 80 90 100 Pond Elevation Relative to Mean Sea Level (feet)
Figure 1.8 Histogram distributions of pond elevation relative to mean sea level for development-related ponds in a) Horry County, b) Charleston County, and c) Beaufort County. Elevations of mean sea level were based on NOAA tidal datums for Springmaid Pier, Charleston Harbor, and Skull Creek (Hilton Head) for plots a, b, and c, respectively.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 11 related ponds and cumulative surface area between 1994 and 2013 in both areas (Figure 1.9). The trends over time in cumulative surface area track trends in pond number fairly closely, indicating that average pond size has stayed relatively constant over this time period. Fitting a simple linear trend to the pond number data indicates that the rate of pond construction has been rather similar between the two regions, with 101 ponds created per year, on average, in the greater Myrtle Beach area and 108 ponds per year created, on average, in the greater Charleston area. Taking into account the difference in size of the Myrtle Beach area (421 sq. miles) versus the Charleston area (595 sq. miles), the annual increase in pond number is approximately a third greater in Myrtle Beach, compared to the Charleston area. Of course, these simple linear trends mask the higher rates of increase that occurred between 1999 and 2006, which was followed by a relative slowdown in pond construction between 2006 and 2013, presumably associated with the housing market crash and lack of new development that occurred within this same broad period of time.
Concurrent with increases in pond numbers and cumulative areas, land development in both pilot areas also increased over time, with higher rates in the greater Myrtle Beach area, compared to the greater Charleston area (data not shown). In both areas, rates of development tended to increase in each of the three development density categories, although exponential increases were greatest for the medium density development category in both regions. The greater Myrtle Beach area also had a significant increase in the percentage of developed open land (e.g., golf course lands) during 1994 to 2010, but this was not the case for the greater Charleston area. In both areas, the rate of increase among all developed land categories combined was roughly paralleled by a concomitant decrease in the percentage of total forest land cover.
Direct comparisons between development rates and rates of pond increases are problematic, however, because the two data sets span slightly different years and have different sampling intervals. Such a comparison can be made, however, if one assumes that overall increases in cumulative pond area for the development-related ponds can reasonably be described by an exponential curve, similar to land development rates (and r2 values for 4-point exponential curve fit for cumulative pond area were 0.94 and 0.96 for Myrtle Beach and Charleston pilot areas, respectively). In this case, the
a) Myrtle Beach Area b) Charleston Area
Figure 1.9 Change over time in pond number (squares) and cumulative surface area (triangles) of development-related ponds for the greater a) Myrtle Beach area and b) Charleston area.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 12 long-term average increase in cumulative pond area was 4.40% per year in the greater Myrtle Beach area and 4.36% per year in the greater Charleston area. For the Myrtle Beach area, this mean annual increase is only slightly higher than the mean annual increase in total developed land area (3.66% per year). In contrast, the mean annual increase in pond area for the greater Charleston area is more than twice as great as the area’s mean annual increase in total developed land (1.71% per year).
1.4 References
DHEC (2008) Critical Area Boundary for Permitting Regulations. Charleston, South Carolina: S.C. Department of Health and Environmental Control – Ocean and Coastal Resource Management. (Accessed: 3/2016) http://www. scdhec.gov/HomeAndEnvironment/maps/GIS/GISDataClearinghouse
DNR (2016) LiDAR Data by County – Various Years. Columbia, South Carolina: S.C. Department of Natural Resources and the Lidar Consortium. (Accessed: 3/2016) http://www.dnr.sc.gov/GIS/lidarstatus.html
Drescher SR, Messersmith MJ, Davis BD, Sanger DM (2007) State of Knowledge: Stormwater Ponds in the Coastal Zone. S.C. Department of Health and Environmental Control – Ocean and Coastal Resource Management
Lewitus AJ, Brock LM, Burke MK, DeMattio KA, Wilde SB (2008) Lagoonal stormwater detention ponds as promoters of harmful algal blooms and eutrophication along the South Carolina coast. Harmful Algae 8:60-65
MRLC (2014) National Land Cover Database 2011 – Percent Developed Imperviousness. U.S. Geological Survey (USGS) – Multi-Resolution Land Characteristics Consortium (MRLC). (Accessed: 3/2016) http://www.mrlc.gov/ nlcd11_data.php
NOAA (2013) C-CAP Southeast Region 2010-Era Land Cover. Charleston, South Carolina: National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), Coastal Services Center (CSC). (Accessed: 3/2016) https://coast.noaa.gov/dataregistry/search/collection/info/ccapregional
Siewicki TC, Pullaro T, Pan W, McDaniel S, Glenn R, Stewart J (2007) Models of total and presumed wildlife sources of fecal coliform bacteria in coastal ponds. Journal of Environmental Management 82:120-132
USDA (2013a) National Agriculture Imagery Program (NAIP), Natural Color 1-meter resolution Imagery for South Carolina. Salt Lake City, Utah: U.S. Department of Agriculture (USDA), FSA Aerial Photography Field Office. (Accessed throughout the project) http://gis.apfo.usda.gov/arcgis/services
USDA (2013b) Soil Survey Geographic (SSURGO) database. Fort Worth, Texas: U.S. Department of Agriculture (USDA) – Natural Resources Conservation Service (NRCS). (Accessed: 3/2016) http://websoilsurvey.nrcs.usda.gov
USGS (2005) National Watershed Boundary Dataset (WBD) – Hydrologic Unit Codes (HUC) 12-digit. Denver, Colorado: U.S. Department of Interior (DOI), U.S. Geological Survey (USGS) – National Geospatial Technical Operations Center. (Accessed: 3/2016) http://nhd.usgs.gov/wbd.html
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 13 USFWS (1979) Classification of Wetlands and Deepwater Habitats of the United States. Washington, DC: U.S. Department of the Interior (DOI), Fish and Wildlife Service – National Wetlands Inventory Program. (Accessed: 3/2016) http://www.fws.gov/wetlands/index.html
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 14 CHAPTER 2 – ENVIRONMENTAL FACTORS AND DESIGN FEATURES THAT CONTROL STORMWATER TRANSPORT AND CONTAMINANT FATE IN PONDS
Authors
Vijay M. Vulava, Ph.D., Barbara A. Beckingham, Ph.D., and Timothy J. Callahan, Ph.D. Department of Geology and Environmental Geosciences, College of Charleston, Charleston, S.C.
Corresponding Author Vijay M. Vulava, Ph.D. ([email protected])
2.1 Background Stormwater ponds are recognized as serving both water quantity and water quality functions. Traditionally engineered with the objective to control flooding, they act as reservoirs to collect water and eroding soil from the surrounding landscape and to dampen the storm pulse to receiving water bodies. This function is important for the integrity of downstream structures, and ecosystems therein (Persson & Wittgren 2003). Over time, it has been shown that ponds can also serve other functions; they provide ecological habitat for birds and aquatic life (Hassall & Anderson 2015), either trap or act as a gateway to the transport of various environmental pollutants to receiving bodies (Van Metre et al. 2000; Thapalia et al. 2010), sequester carbon and provide cultural and ecosystem services (Moore & Hunt 2012), and can serve as a valued, aesthetic feature of a community (Ghermandi & Fichtman 2015). By averting and storing runoff on-site, ponds open up the possibility for rainwater use, such as for landscape irrigation, saltwater intrusion barriers, drinking water aquifer recharge, augmentation of potable water reservoirs, non-potable water use in buildings, and baseflow augmentation to improve freshwater habitat and recreational use depending on water quality and need (Grebel et al. 2013). Thus, how ponds perform hydrologically and geochemically influence how they are viewed as either environmental assets or liabilities.
2.2 Framework The primary focus of this chapter is the fate and transport of environmental contaminants in ponds. Due to the complex interdisciplinary nature of the problem, this chapter includes multiple objectives:
1. Hydrology: to describe the roles that surface water and groundwater play in transporting water and contaminants to and within ponds in different geographical and geological settings across the Southeastern U.S., with a focus on the conditions found in the eight coastal S.C. counties. 2. Nature of contaminants: to identify key contaminants of concern associated with runoff and how their properties can influence their fate in pond environments.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 15 3. Biogeochemical processes: to describe the relevant mechanisms and reactions that influence contaminants and water quality in stormwater and pond systems.
This study includes an extensive review of appropriate studies that outline current state of knowledge from a hydrological and contaminant fate and transport perspective. Our citations include 194 references as 159 primary literature sources, 12 books, four conference presentations, nine technical reports, and six student theses. Gaps in our current knowledge are identified and specific research priorities are offered.
2.3 Physical Hydrology of Stormwater Systems
2.3.1 Climate, Geography, and Geology
The water balance in S.C., derived from the most recently available 30-year climatological average, is dominated by precipitation (average annual precipitation is 48 inches [1,200 mm]) and evaporation and transpiration, often expressed as evapotranspiration, or ET (average annual ET is 34 inches [865 mm]) (Wachob et al. 2009). Only a few site-specific studies address seasonal and longer-term impacts of hydrologic processes (e.g., runoff, sedimentation) on ponds (Drescher et al. 2007). In the lower gradient areas of the Southeastern Coastal Plain (SECP), referred to as the Lowcountry, hydrology is strongly influenced by the flat topography and shallow depths to the water table (Tufford & Marshall 2002; Callahan et al. 2012; Hitchcock et al. 2014). Dry detention basins are recommended for higher- permeability sandy soils compared to wet detention basins (ponds described here) in lower-permeability soils and/or shallow water table conditions, yet there appear to be no studies in the lower SECP on how the conveyed stormwater flows into and through different ponds. Identifying the geographic distribution of ponds is a major effort of this state of knowledge report (see Chapter 1), but an additional set of indices could be useful for exploring their hydrologic functioning, such as comparing water balance details (duration and fluctuations of pond water level) with underlying soils and geology data for mapped ponds. There may be important links between the substrate and the vulnerability of ponds to flooding and contaminant accumulation (Fletcher et al. 2013).
2.3.2 Water Balance and Flow
Hydrological processes are better understood in the lower SECP as a result of studies conducted over the past few decades (e.g., Sun et al. 2000, 2002, 2006; Messersmith 2007; Tufford & Marshall 2002; La Torre Torres et al. 2011; Callahan et al. 2012). These studies have collectively confirmed the importance to the overall water balance of (a) forest health and productivity through ET as a water demand process and (b) permeable cover in the watershed for groundwater recharge. In S.C. and across the SECP, topographic slope, soils, and land use/land cover are important site factors controlling water flow. Runoff includes overland flow (also called sheetwash) and shallow subsurface flow (soil interflow), which ultimately delivers stormwater to receiving water bodies. If those systems are dynamic – if the overland flow and interflow are focused into a channel – it is referred to as concentrated flow and moves across the landscape as small rills, moderate-sized creeks, and larger streams and rivers.
In the built environment, ditches, culverts, and other engineered systems are designed to move this water away from infrastructure to reduce flooding hazards. Construction of ponds and the associated engineered infrastructure such as ditches and culverts serve to intercept and sequester surface runoff (Fennessey et al. 2001; Fletcher et al. 2013). These developed and developing landscapes in the Southeast U.S. have altered water balance because of reduced ET caused by
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 16 deforestation, and decreased groundwater infiltration caused by larger coverage of impervious surfaces (hardscapes such as roofs, parking lots, and roads). The net result is increased surface water discharge. This surface water has traditionally been managed through engineered structures such as drainage ditches and storm sewers, and in the past few decades, through routing the stormwater to detention ponds, lagoons, and basins. Urbanized settings have a new water balance that is now dominated by runoff rather than ET or infiltration (Garrett et al. 2012; Fletcher et al. 2013). Ponds and dry basins are structures that are designed to buffer natural receiving waters from runoff (Wachob et al. 2009).
Subsurface-surface connections, as affected by shallow water table conditions, can contribute groundwater inflow into the pond and/or reduce infiltration and recharge due to the small hydraulic head differences between the pond water and the adjacent water table. However, there is a lack of detailed research on the importance of subsurface - surface water exchange in the modern landscape that contains thousands of ponds. Evidence is emerging that groundwater may be a conduit for the movement of constituents in/out of ponds (Bunker 2004; Wisniewski 2014), and potentially from ponds to aquifers (Bunker 2004).
2.3.3 Pond Design and Hydrology
Another classification of stormwater basins is those in which plants play an integral function, such as buffers between the sources and the pond, as well as engineered bioretention cells or constructed wetlands built and permitted to receive runoff. Addition of vegetation within the stormwater pond’s watershed acts to increase demand through plant transpiration and increase surface roughness to reduce runoff velocity (Bettez & Groffman 2012; Hitchcock et al. 2014). Separate from ponds (wet detention basins), bioretention cells are typically very shallow, landscaped, depressional areas and thus do not classify as a pond. While outside the scope of the current review, bioretention cells are a potentially effective low impact development (LID) practice. Constructed wetlands are also shallow vegetated depressions, but with variations in elevation to create environments for slow water flow, a diversity of vegetation, and biogeochemical conditions that can assist in water quality improvements. They are also subject to design and regulation criteria that govern wet detention ponds (Ellis et al., 2014). In a S.C. Department of Health and Environmental Control-Office of Ocean and Coastal Resource Management (DHEC-OCRM) study of 511 ponds, wet detention was the most frequently used type (Drescher et al. 2007), and is the focus of this entire report accordingly.
Ponds are generally classified according to the way they store and route runoff. In the broadest terms, stormwater basins are either wet or dry – having a permanent pool of water or not. Whether a pool is permanently wet or dries up between rain events is a function of connectivity with surface and ground waters, soil properties, and design of outlet structures. For instance, under similar geologic settings, a permanent pool of water can be retained by setting outlet structures at higher elevations than for a dry detention basin (Persson & Wittgren 2003; Weiss et al. 2007). For wet basins, the pond is sized to have a temporary storage volume above a permanent pool of water (DHEC 2005). For dry basins, stormwater peak flow is attenuated, with the runoff draining over the course of at least 24 hours and typically less than 48 hours (Weiss et al. 2007; Ellis et al. 2014).
Nuisance flooding is a hazard to property near ponds (Fennessey et al. 2001) that may result from a lack of understanding of the hydrology of ponds in the coastal zone. Property can flood following the construction of a large adjacent impervious area when a pond is constructed directly upslope, as is done for in-fill residential or commercial development. This may instigate a local increase in the water table if the pond is not lined with low permeability clay or geotextile to minimize groundwater seepage, or if an extreme event causes pond overflow or bank failure. These
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 17 hazards can occur when the site plan over-predicts the predevelopment runoff of a watershed and/or uses property boundaries to define the catchment area for the ponds, as is commonly done (Fennessey et al. 2001). The ultimate result of improperly sized stormwater basins may be an additional financial burden on community residents impacted by flooding or increased maintenance.
The role of engineering design on water detention with respect to size and volume is well-studied. However, in the dynamic and rapidly-developing coastal zone of S.C., combining site details such as topography, pond design details, and runoff predictive models that include soil data such as the Curve Number approach (Fennessey et al. 2001) would inform best management practices for stormwater managers to plan for and mitigate stormwater inputs. A needed area of investigation is the design “lifetime” of ponds with respect to sedimentation. Rapid urbanization and increase in impervious cover are likely to result in increased sedimentation in ponds. A site-specific study at a development on Daniel Island, Berkeley County near Charleston, S.C. found that in just a few years a single stormwater pond lost 36% of its usable volume and a series of linked ponds lost 15% of the system’s total usable volume (Messersmith 2007). It is not known if this is a widespread issue for the entire region or a site-specific exception. Existing studies have identified potential threats to pond life associated with these sediments and other particles as a mode to convey pollutants into ponds (Zoumis et al. 2001; Weinstein et al. 2010a; Frost et al. 2015).
Research Gaps
• Investigate the role of soils and geology of the SECP on pond design and function. • Understand which management practices are important to help avoid sedimentation problems in ponds. • Examine the time scales required for stormwater retention to protect water quality. • Determine the implications of reduced pond holding capacity and potential surface–groundwater interactions due to sedimentation. • Evaluate the impacts of pond design elements (e.g., lined vs. unlined, pond size relative to catchment area) on stormwater management efficacy. • Examine the capacity of ponds to effectively function in the future under scenarios of changing precipitation patterns and temperature.
2.4 Transport of Contaminants in Runoff
2.4.1 Particulate Matter
Suspended particulate matter (PM) makes up a significant portion of surface runoff contaminant load. Major nonpoint sources that result in PM in runoff include roads, construction and urban developments, soil erosion, deforestation, agricultural activities, and aerial deposits. Urban areas contribute significantly to runoff pollution load to ponds due to higher human density (Wong et al. 2012). Particles can have a distinct geochemical or anthropogenic composition (e.g. mineral, organic, or synthetic) depending on the source (Frost et al. 2015). Size and morphology of these particles in runoff are highly variable depending on the intensity of rainstorms as well as the catchment type (Characklis & Wiesner 1997; Sansalone & Buchberger 1997a, b; Sansalone et al. 1998; Kim & Sansalone 2008).
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 18 Emerging contaminants such as nanomaterials (e.g., Das et al. 2012) and microplastics (e.g., Teuten et al. 2007; Andrady 2011; Cole et al. 2011) are becoming ubiquitous in estuarine and coastal environments from anthropogenic sources, but these types of particles have been understudied thus far in ponds (see Chapter 3). Larger-sized materials including garbage and trash are also often part of runoff in highly developed areas, leading to clogged water conveyances or compromised pond function. In addition to PM itself being a potential hazard to aquatic life, the nature of the suspended particles in stormwater and the sediment bed in stormwater ponds influences contaminant transport, fate, and effects.
2.4.2 Inorganic Chemicals
Trace metals are common contaminants in urban environments and can be present in dissolved form or associated with PM in runoff (Wong et al. 2006; Fletcher et al. 2013). The most common trace metals in dissolved forms reported in runoff include lead, copper, cadmium, and zinc (Characklis & Wiesner 1997; Sansalone & Buchberger 1997a, b; Davis et al. 2001; Kamalakkannan et al. 2004; Brown & Peake 2006; Bentzen & Larsen 2009; Karlsson et al. 2010; Frost et al. 2015). Specific sources reported include building siding and roofs (e.g., Quek & Förster 1993) and automobile brakes and tires (Laxen & Harrison 1977; Ellis et al. 1987; Sansalone & Buchberger 1997b; Davis et al. 2001). Dry and wet deposition can be significant sources of trace metals in urban areas (Nriagu 1989; Sabin et al. 2005; Fulkerson et al. 2007; Eckley & Branfireun 2008). Radioisotopes and stable isotopes of trace metals are often employed in source-tracking of trace metals found in various environments, including soils and lake sediment, and may apply to ponds (Quast et al. 2006; Thapalia et al. 2010; Louchouarn et al. 2012; Wiederhold 2015).
Other inorganic chemicals in stormwater include major elements and ions such as sodium (Na), potassium (K),
calcium (Ca), magnesium (Mg), chloride (Cl), and sulfate (SO4), as well as nitrate (NO3) and phosphate (PO4), which are important nutrients. These chemicals are often present in relatively high concentrations and may be derived from the weathering of inorganic minerals present in dry deposits, road dust, eroded soils, road applied salts (in the case of inclement weather), and fertilizer applications (Göbel et al. 2007). In addition to dissolved forms, certain inorganic chemical species are often associated with sediment particles, which can be major vectors in transport of these chemicals (Bryan & Revitt 1982; Sansalone et al. 1995; Characklis & Wiesner 1997; Sansalone & Buchberger 1997a, b; Kamalakkannan et al. 2004; Jartun et al. 2008).
2.4.3 Organic Chemicals
Fate and transport of organic chemicals is more complex compared with that of inorganic chemicals and sediment due to their chemistry, which can include transformations and distribution between solid, dissolved, and gaseous forms (Jaffé 1991). Common organic chemicals in urban areas that are ubiquitous in runoff are derived from automobile- and other combustion-derived oil and gas residues, asphalt, and coal tar-coated pavement and roofs (Fam et al. 1987; Van Metre et al. 2000; Mahler et al. 2012). These organic mixtures can be predominately comprised of polycyclic aromatic hydrocarbons (PAHs), a class of nonpolar organic chemicals which exhibit relatively low vapor pressure and low aqueous solubility (Hoffman et al. 1985; Stout et al. 2001; Menzie et al. 2002; Kamalakkannan et al. 2004; Brown & Peake 2006; Hwang & Foster 2006; Boving & Neary 2007; Göbel et al. 2007; Jartun et al. 2008; Bentzen & Larsen 2009; Watts et al. 2010; Birch et al. 2012; Mahler et al. 2012). Because of these properties, PAHs are more likely to be associated with PM in surface runoff (Kamalakkannan et al. 2004; Jartun et al. 2008; Bentzen & Larsen 2009; Birch et al. 2012).
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 19 Other non-polar organic chemicals, such as polychlorobiphenyls (PCBs), polychlorinated dibenzodioxins (dioxins), and polychlorinated dibenzofurans have similar chemical properties as PAHs, are anthropogenic in origin, and are often found in industrial-urban runoff (Eriksson et al. 2007; Cornelissen et al. 2008; Howell et al. 2011a, b). These chemicals are also more likely to be associated with sediment in runoff (Zgheib et al. 2011). Fire retardant chemicals such as polybrominated diphenyl ethers (PBDEs) are another class of chemicals that are being increasingly found in urban runoff associated with organic-rich particles (Oram et al. 2008; Gasperi et al. 2014). Herbicides such as atrazine, alachlor, and glyphosate are relatively common in agricultural runoff (e.g., Leonard et al. 1979; Thurman et al. 1991; Logan et al. 1994), but herbicides are also commonly used in urban areas to control unwanted vegetation among commercial and residential developments and along public roads and highways (e.g., Revitt et al. 2002; Huang et al. 2004). Pesticides and insecticides such as diazinon, carbaryl, and malathion are also increasingly found in urban runoff (e.g., Hoffman et al. 2000; Weston et al. 2009). Concentrations of pesticides in ponds in coastal S.C. have been positively correlated with high temperatures and rainfall, and also correlated with concentrations in adjacent tidal creeks (e.g., pyrethroids, imidacloprid), which demonstrates potential connections between runoff, ponds, and receiving waters (Serrano & DeLorenzo 2008; DeLorenzo et al. 2012).
Emerging contaminants such as pharmaceutical chemicals, hormones, and sunscreen/ultraviolet filters are now ubiquitous in runoff (Richardson & Ternes 2011). These chemicals are structurally very complex and are increasingly found in natural waters resulting in ecosystem disruption (Kümmerer 2004), yet studies on the transport of these chemicals to ponds are needed.
2.4.4 Pathogens
Pathogenic organisms are increasingly common in runoff (Geldreich 1996; Mallin et al. 2000; Grant et al. 2001; Han et al. 2006; Arnone & Walling 2007; Mallin et al. 2009; Parker et al. 2010; Rich & Maier 2015). These organisms include bacteria, enteric viruses, protozoa, and parasites and come from a variety of sources, including humans (e.g., septic system failure), pet animals, farm animals, and wildlife. Because of the range of origins for these organisms in the environment, there are a variety of source-tracking methods available to identify specific sources (Whitlock et al. 2002; Meays et al. 2004; Webster et al. 2004; Siewicki et al. 2007; Parker et al. 2010; Rock et al. 2015). Due to the wide variety of pathogenic organisms present in these environments, common fecal-sourced organisms such as fecal coliforms, E. coli, and enterococcus are often used as indicators of contaminated surface runoff (Arnone & Walling 2007; Gerba 2015b). Enteric viruses such as enterovirus and adenoviruses are more difficult to track, but specific viruses may also be used as indicators of compromised water quality (Fong & Lipp 2005). Studies have shown that environmental pathogens are often naturally associated with soil in the landscape and are mobilized by runoff (Ahn et al. 2005; Surbeck et al. 2006; Parker et al. 2010). Survival of these organisms is greatly dependent on the environmental conditions such as water temperature, UV light penetration, pH, dissolved salts, organic matter, and biological factors such as existing microflora (Gerba 2015a). Adding to the complexity, dynamic communities of bacteria and viruses are highly variable in individual ponds, even those in close proximity (Saxton et al. 2016).
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 20 Research Gaps
• Understand the nature of contaminants carried by runoff and the sources of those contaminants in order to better design and manage ponds. • Understand the interaction of contaminants in ponds, which is crucial considering trends in increasing urbanization in the coastal region.
2.5 Transformation and Fate of Contaminants in Ponds
2.5.1 Biological Processes
Biological processes leading to biological uptake and transformation of chemicals alter the budget of contaminants in ponds. These processes are highly dependent on the specific contaminant as well as other conditions in the water column (e.g., pH, dissolved oxygen, salinity, organic carbon content, redox status, temperature) and biological community structure (Mihelcic & Luthy 1988; Mueller et al. 1989; Leahy & Colwell 1990; Das & Chandran 2010). Different microorganisms can adapt to contaminated environments, resulting in the creation of specific conditions that biodegrade complex organic chemicals (Das & Chandran 2010; Maier & Gentry 2015) or alter the bioavailability of organic and inorganic chemicals, including toxic metals (Roane et al. 2015).
Contaminants may also be removed from the water column via uptake into plants near or within ponds by a process commonly referred to as phytoremediation (Alkorta & Garbisu 2001; Susarla et al. 2002; Pulford & Watson 2003); however, for chemicals that are simply stored on or within the plants to be effectively removed from the system and not re-released following plant turnover, vegetation needs to be harvested at the end of the growing season. Vegetation can also aid contaminant removal in ponds by reduction of water velocity and entrainment of sediment, or adhesion to plant surfaces. Although ponds have been observed to remove bacteria from runoff, in-pond conditions favorable for bacterial growth could lead to a proliferation of harmful species and higher concentrations in the effluent of ponds (DeLorenzo & Fulton 2009; Hathaway et al. 2009; Grebel et al. 2013). Ponds may also attract wildlife, leading to in- pond sources (Hathaway et al. 2009), which may show seasonality depending on wildlife migration patterns (Phillips 2014).
Biological processes contributing to contaminant removal depend on the habitat the pond provides. Ponds in coastal S.C. that are tidally influenced have been observed to range from low brackish to marine salinities, and this affects specific bacteria assemblages (DeLorenzo & Fulton 2009). Benthic invertebrate communities will also be affected by salinity tolerance. Action by these invertebrate communities to bioturbate sediments in detention ponds could impact hydraulic conductivity (and therefore water infiltration through sediment bed), oxygen availability in sediment pore waters, and sediment-water pollutant exchange (Nogaro & Mermillod-Blondin 2009).
2.5.2 Chemical Transformations
Values for chemical transformation rates under specified conditions may be found for a small subset of potential pollutants in the literature (e.g., wastewater treatment, environmental chemistry, and engineering) or may be modeled
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 21 based on chemical structure (e.g., U.S. EPA EPI Suite). Chemical transformation in stormwater treatment structures has been modeled using first-order kinetic decay assumptions, with removal mechanisms (e.g., physical, chemical, or biological) not treated individually (Elliott & Trowsdale 2007). However, pond design characteristics, such as dimensions, that influence environmental conditions (e.g., temperature and redox conditions) should also affect the transformation rate, and therefore these rates should not be applied universally. Stratification and eutrophication can impact the availability of oxygen in pore waters and subsequently the redox conditions, which control the processing of nutrients, speciation of metals, and degradation of organic compounds. The depth of the pond permanent pool will influence light penetration for the photochemical transformation of certain organic contaminants. Shallow open- water treatment cells have been designed for photolytic degradation of certain organic contaminants, but may not be applicable to ponds due to low light penetration to sediment bottoms and growth of shading, floating vegetation such as duckweed (Jasper & Sedlak 2013). For contaminants with relatively high vapor pressures for which volatilization is a potential removal pathway from pond waters, important pond features are the surface area of the pond and surrounding open area generating wind across the pond surface, since these factors will influence evaporation of water and temperature which affect volatilization. While there are few studies that measure rates of photodegradation and volatilization from ponds, lessons can be applied from studies that have focused on the treatment of chemicals in wastewater treatment ponds and constructed wetlands (Oulton et al. 2010; Jelic et al. 2011).
2.5.3 Sorption Processes and Role of Particles in Contaminant Removal within Ponds
The basic environmental geochemistry that explains sorption and complexation processes is well established (Stumm & Morgan 1996; Langmuir 1997; Schwarzenbach et al. 2003; Appelo & Postma 2005; Luoma & Rainbow 2008). Sorption processes include surface complexation, ion exchange, fixation, surface precipitation, and partitioning (Schwarzenbach et al. 2003; Bradl 2004; Brown & Calas 2012). Because of the versatility of some of the different sorption mechanisms, chemical sorption occurs in a wide range of sorbent material, from suspended materials to bed sediment, and including particulate and dissolved organic matter, mineral phases, and tissue of living organisms (McCarthy & Zachara 1989; Schwarzenbach et al. 2003; Brown & Calas 2012). Dissolved and particulate organic carbon fractions of natural organic matter (NOM) from disparate sources are likely to be found in runoff and ponds. While these forms of NOM are not primary contaminants in water, increased presence in runoff can behave as vectors for other contaminants or eventually impact contaminant fate in streams and ponds, due to sorption and complexation of sparingly soluble chemicals (e.g., Chiou et al. 1986; Allen-King et al. 2002). “Black” carbon, particles formed by incomplete combustion such as soot, also impacts contaminant fate due to strong sorptive interactions.
Trace metals can form strong complexes to specific components in sediment such as clay minerals, mineral oxides (iron [Fe], aluminum [Al], or manganese [Mn] oxides), and organic fractions. Relative sorption control or strength in the matrix depends on factors such as relative availability of the different sediment components, sorption kinetics, bulk solution conditions (e.g., pH, ionic strength or salinity, redox conditions) and particle surface characteristics (Stumm & Morgan 1996; Langmuir 1997; Appelo & Postma 2005; Du Laing et al. 2009; Frost et al. 2015). Ionic forms of trace metals, inorganic ions, and also organic ions in aqueous environments readily complex with other ions present in water and to a variety of inorganic mineral or organic surfaces.
Nonpolar and/or neutral organic chemicals strongly sorb to PM surfaces and/or partition into nonpolar phases including soils, suspended organic matter and sediment, and organisms (Karickhoff 1984; Schwarzenbach et al. 2003). The exact nature of sorption depends on the chemical structure of the sorbate in addition to the material sorbent and is typically related to aqueous solubility (Allen-King et al. 2002). In addition to the sorption mechanisms, reaction
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 22 kinetics play a significant role in the distribution of chemicals in dynamic environmental systems, such as stormwater ponds. Temperature, salinity, and dissolved humic substances can additionally strongly impact the sorption of nonpolar and neutral organic molecules (Tremblay et al. 2005).
Pathogens are also more likely to be sorbed, or attached as biofilms, to PM in aquatic environments (Ahn et al. 2005; Cizek et al. 2008; Jenkins et al. 2012). This association with sediment increases the survival of the pathogenic organisms and lowers predation by other microorganisms (Gerba & McLeod 1976; Schillinger & Gannon 1985; Evanson & Ambrose 2006; Jeng et al. 2005; Bonilla et al. 2007; Jenkins et al. 2012;). The type of sediment (presence of certain mineral oxide surfaces and organic matter), aqueous geochemical conditions (e.g., pH, salinity, dissolved oxygen, water temperature, alkalinity, and redox conditions), and seasonal conditions also play a significant role in survival of pathogens in the sediment (Van Donsel et al. 1967; Scholl & Harvey 1992; Jimenez-Sanchez et al. 2015). These geochemical conditions in stormwater ponds can be highly variable and can impact storage versus further transport of pathogens out of ponds and downstream. Stormwater runoff has been shown to transport enough fecal bacteria loads to close coastal S.C. shellfisheries, and high levels of bacteria have been recorded in runoff and S.C. ponds following heavy rainfall events (Drescher et al. 2007).
Physical and chemical characteristics of particles, such as size, mineral makeup, organic content, surface area, and bulk density, impact mobility and sorption and therefore also impact transport of contaminants associated with particles (Zanders 2005). For example, small and less dense particles (compared with quartz mineral grains, whose density is approximately 2.65 g/cm3) are often more mobile as they are not easily trapped by vegetation and can be carried by flowing water at lower velocities. Smaller-sized particles (e.g., less than 300 µm diameter) are often associated with high concentration of contaminants (Vaze & Chiew 2004; Zanders 2005). Silt and clay fractions are two common classes of inorganic suspended particles in streams and ponds (Slattery & Burt 1997). While silt-sized fractions can be a combination of quartz and other silicate minerals, clay-sized fractions (less than 2 µm diameter) tend to be predominantly aluminosilicates (Langmuir 1997). Specific mineralogy is reflective of the soil mineralogy of the region subject to erosion by surface runoff (Wall & Wilding 1976; Carter et al. 2003; Taylor & Owens 2009). These properties also control the affinity and kinetics of interactions between the contaminant and solid phase (via chemical interactions or biological niche in the case of biological agents), as well as particle settling potential. Contaminants may originate on PM, become particle-bound during transport, or sorb once within the ponds. And given the sorption processes described, PM phases play a significant role in transporting, sequestering, or mobilizing contaminants in freshwater, estuarine, and coastal waterbodies (Turner & Millward 2002; Walling 2005; Fries et al. 2006; Taylor & Owens 2009; Crompton 2015; Frost et al. 2015).
2.5.4 Sedimentation Processes
Once runoff reaches ponds, the water velocity slows, allowing ponds to serve as basins that trap particles by sedimentation and filtration. As described above, it is the ability of ponds to trap particles and associated contaminants that largely determines whether ponds improve water quality. According to the International Stormwater Best Management Practice (BMP) Database, median pollutant removal rates range from 17 to 96%, depending on the pollutant type (Clary et al. 2017). Pond performance is often better with particulate than dissolved pollutants, and ponds are better at removing suspended solids than some other types of BMPs (Barrett 2008). The removal efficiency of suspended solids, total nitrogen (N), and total phosphorus (P) may be greater in eutrophic than mesotrophic ponds (Borden et al. 1997; Winston et al. 2013), potentially due to phytoplankton N and P uptake.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 23 Sedimentation of particles in ponds is an important process (U.S. EPA 1999; Bentzen & Larsen 2009; Hathaway et al. 2009) and is a function of the density, size, and buoyancy of particles and the flow regime in relation to the size, depth, and pathways that water takes in the pond. Thus, where particles and associated contaminants drop out or are filtered out is dependent on both particle source and pond design traits affecting hydrodynamics. Large and dense particles are more likely to be deposited in ponds and near inlets since they typically have faster-settling velocities. However, other conditions such as fluid density and viscosity, laminar vs. turbulent flow conditions, particle shape, and current flow have to be explicitly considered when making quantitative predictions of transport of sediment and associated contaminants in water (Julien 2010). Organic particles are generally slower to settle and less effectively removed, depending on pond design. Pollutant distribution between dissolved and particulate phases and the ability of ponds to capture particles strongly control pollutant removal within ponds. For instance, Crawford et al. (2010), in a survey of 16 coastal S.C. ponds, found that levels of Al and Cd were higher in pond inlets, while levels of Cu, Pb, and Zn were higher in the center of the ponds. This suggests the affinity for certain metals to adsorb to finer clay-sized particles and thus travel further from the inlet before sedimentation occurs. Clay and organic carbon content also were generally seen to be higher near the center of ponds than near the inlet (Crawford et al., 2010).
Although some removal occurs during the dynamic period when runoff enters the pond, the U.S. EPA reports that 90% of pollutant removal occurs during the quiescent period between rainfall events when particles settle to the bottom of the detention pond (U.S. EPA 1999). Generally, hydrocarbon removal is related to suspended sediment removal and, in one study, ponds had a median removal rate of 80 - 90%, again illustrating the importance of sedimentation (Schueler 2000).
2.5.5 Role of Pond Design in Contaminant Fate
Hydraulic residence time (RT) is a parameter that controls sedimentation and biogeochemical transformation. It is determined by pond dimensions and water discharge. Residence time has been cited as the factor that is most limiting to water quality improvement in ponds (although other factors, such as redox environment and plants are notable for certain constituents) (Mallin et al. 2002; Weiss et al. 2007, 2008). For instance, Comings et al. (2000) found that a pond that retained stormwater seven times longer (RT = 1 week) than a reference pond allowed for superior pollutant removal. Carpenter et al. (2014) found that adding a sluice gate to the outlet of a detention pond allowed for a longer RT, which resulted in improvement of removal efficiency for total suspended solids from 39 to 90%, ammonia- nitrogen from 10 to 84%, and zinc from 20 to 42%. It has also been suggested that stormwater structures with low flow conditions maximize protection of downstream assets from pesticides (Howitt et al. 2014).
Although RT in S.C. ponds is generally long according to some previous studies (Lewitus et al. 2003; Bunker 2004; Brock 2006), performance assessments of ponds elsewhere in VA indicated that the holding capacity of these systems were often less than 24 hours (Hancock et al. 2010). However, this is an area of needed research to substantiate the conditions leading to vulnerable conditions. While many of the above studies have shown ponds to be broadly effective at removing and retaining pollutant loadings, specific removal efficiencies among studies are highly variable. The reasons for this variability are not well understood but are likely at least partially driven by pond geometry (Wu et al. 1996; Borden et al. 1997; Mallin et al. 2002), proximity to rural vs. urban areas (Tufford & Marshall 2002), and hydrology (Persson & Wittgren 2003; Huda & Meadows 2010). Size, depth, and shape are important design criteria that have been observed to affect pollutant removal in ponds. In a study on Daniel Island, S.C. researchers found a series of linked ponds had longer RT and superior pollutant removal capabilities as compared to a single pond on the site (Messersmith et al. 2007). Comings et al. (2000) found that the larger a pond is in relation to the area it drains,
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 24 the better it performs at removing pollutants, and furthermore, that pollutant removal can be improved by moving weirs to direct flow in a tortuous pathway through treatment cells. As shown in this study and other work on the basic functioning of water treatment facilities in general, the path of stormwater through a pond should not be in a direct line, which promotes short-circuiting. Ellis et al. (2014) and S.C. DHEC (2005) designate the criteria for pond dimension as at least a ratio of 1.5:1 for pond length to width, although a ratio of 3:1 affords better water quality treatment. Pond surface area was able to explain trapping efficiency for PAHs in coastal S.C. ponds, although whether the effects were due to larger ponds being able to settle solids more effectively or larger size reducing the susceptibility of sediment bottom to scour during high flow events was undetermined (Weinstein et al. 2010a). Adequate wet detention pond depth allows for effective sediment gravity settling (Weiss et al. 2007). An additional advantage is that the sediment bottom, which potentially stores high levels of nutrients and sediment-bound contaminants, is buffered against washout of sediments during the next storm event by the overlying water column, or “permanent wet pool.” A pool depth of 4 to 6 feet is ideal as per S.C. DHEC (2005). Vegetated ponds and stormwater wetlands have the additional advantage of plants providing a buffer to slow water flow and structure to hold sediments in place through the growth of root systems. However, periods of high flow create turbulence or shear force, which leads to sediment resuspension and can cause the release of contamination to receiving waters (Julien 2010).
Hydrophobic organic contaminants with strong sorption and low water solubility have been observed to concentrate in sediments (Weinstein et al. 2010a; Roinas et al. 2014); however more polar and water soluble organics will be increasingly mobile and may pass through the pond depending on how water is routed (Neary & Boving 2011; Roinas et al. 2014). Pond design often includes a forebay to trap the majority of the coarse suspended solids fraction prior to flow entering the main body of the pond, although finer sediments will pass through.
Wet Detention Pond Wet Retention Pond Pollutant (S.C. DHEC, 2005) (International Database) Total Suspended Solids 65-80% *75% Total Copper 40-65% *52% Total Zinc 50-75% *56% Metals 35-75% **17-75% Total Lead 60-85% *67% Total Phosphorus 50-70% *55% Total Nitrogen 35-45% *23% Bacteria 45-75% *54-96%
*Indicates that the median removal capability of wet ponds was found to be significant (p < 0.05; non-parametric Mann Whitney test) (Clary et al. 2017). **With the exception of arsenic, all metals were found to be removed at significant rates.
Table 2.1 Average pollutant removal capabilities summarized from S.C. DHEC (2005) and the International BMP Database (Clary et al. 2017), which classifies basins with a permanent pool as retention ponds. The S.C. DHEC manual cites the range of average removal capabilities while the International database provides median values. For “metals” the range is provided because the removal efficiency differed depending on the type (e.g., nickel, chromium) and the range for “bacteria” represents differing measures (e.g., E. coli, fecal coliform).
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 25 The overall performance of ponds in removing or sequestering contaminants is very site-specific – there is no clear formula for how all ponds behave. For example, S.C. DHEC (2005) lists the large ranges of pond removal capabilities for a number of common stormwater pollutants (Table 2.1). The International BMP database, which synthesizes data from hundreds of pond samples, also shows there is much variability in removal capabilities, which is difficult to constrain due to site differences (Clary et al. 2017).
Regular removal of the accumulated sediments from ponds is necessary to minimize the risk of contaminated sediments affecting benthic habitat quality, in-pond and downstream ecosystem health, and groundwater quality, and to maximize the operational efficiency of the pond (Durand et al. 2005). Dredging of sediments is recommended when the permanent pool volume is significantly reduced beyond useful design specifications, but there are no state regulations requiring dredging (Rollins & Powell 2013). Further illustrating the role of sediments to capture contaminants in ponds, Weinstein et al. (2010b) report that, depending on local and state regulations, excavated pond sediments are typically treated as either solid waste or hazardous waste and transported to either landfills or hazardous waste facilities for disposal, respectively. Currently, in S.C. there are no requirements that pond sediments be tested for chemical or biological contaminants prior to sediment removal (Ellis et al. 2014). This topic is covered in more detail in Chapter 3 of this report.
2.5.6 Modeling of Stormwater Processes at the Landscape Scale
Knowledge of transport, transformation, and storage has been translated into models that aim to predict pollutant concentrations and loads in stormwater systems to inform engineering and management (Elliott & Trowsdale 2007; Vezzaro et al. 2011, 2012; Fletcher et al. 2013). Integrated modeling of stormwater quality involves simulating source generation, the flush of pollutants from catchment surfaces and how they are channeled through surface water drainage systems, and final treatment in ponds. These steps are modeled as functions of hydrologic factors and pollutant characteristics, emphasizing that hydrology and biogeochemistry are fundamentally linked. The majority of existing models on stormwater treatment include contaminant settling in ponds using sediment settling theory, first or second order decay, removal fractions or output concentrations, or other variables such as flow rate (Elliott & Trowsdale 2007). It has been shown that improvement of models will require more monitoring data for calibration and field testing and improved understanding of fate processing for a wider selection of environmental contaminants (Bertrand-Krajewski 2007; Elliott & Trowsdale 2007; Scholes et al. 2008). A study of micropollutant removal abilities by stormwater ponds found the most sensitive model parameters were those related to physical processes such as flow and settling/resuspension (e.g., total suspended solids) (Vezzaro et al. 2011). However, at present, research has not identified an optimum set of parameters for employing stormwater quality models (Bertrand-Krajewski 2007). Increasingly, models are also considering stormwater as a resource, though the performance of stormwater technologies in restoring water quality remains poorly quantified. As models improve, they will also consider the uncertainty associated with climate change that requires all water management systems to be resilient to change (Fletcher et al. 2013).
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 26 Research Gaps
• Understand the major controls that influence contaminant fate in pond systems, specifically for the Southeastern coastal region. • Assess nutrient and biological exchanges between ponds and tidal creeks. • Integrate knowledge on hydrologic function with engineering principles, contaminant behavior, and biological interactions to advance our understanding of pond systems. • Explore the role of groundwater for nutrient transport, and concurrent influence of soil type and landscape on subterranean movement.
2.6 Summary and Recommendations Significant portions of the SECP have been altered due to development, affecting the hydrology and water balance through re-routing of water from infiltration and evapotranspiration to surface runoff and storage in wet detention ponds constructed in the landscape. This review summarizes various processes and mechanisms that are likely to occur in ponds using our best understanding of hydrology and biogeochemical principles. Hydrology and contaminant behavior in ponds is very complex and, as summarized in the sections above, there is still more research that needs to be done to more fully understand the dynamic behavior of these systems. For instance, we were unable to clearly establish contributions of ponds to groundwater contamination, though it is of growing concern and requires investigation (Walsh et al. 2005; Roy & Bickerton 2012). While a basic understanding of pond hydrology is fundamental to our conceptual understanding of runoff and pond function, no systems-level studies that address all relevant mechanisms were identified over the course of our literature review.
Since the implementation of federal control regulations and guidelines in the 1990s to manage stormwater, careful calculations of pond design have been enacted in the field based on straightforward engineering principles. However, while it is widely recognized that ponds can reduce contamination of the ultimate receiving water bodies for certain classes of contaminants (S.C. DHEC 2005), ponds were not specifically designed for post-construction phase water quality improvements (Ghermandi & Fichtman 2015). Pond designs that include elements that actively reduce water contamination could help address the growing need for contaminant reductions of nonpoint sources to final receiving water bodies (Walsh et al. 2005; Clary et al. 2008; Collins et al. 2010). Pond water quality and the ability to remove pollutants and protect downstream water bodies are affected by pond location in the landscape. We need a better understanding of how diverse engineered features impact hydrological and biogeochemical processes in order to inform policies and/or regulations that govern pond design and management practices (Chiandet & Xenopoulos 2016; Johnson & Sample 2017). Because of the variability in pollutant removal efficiencies, an audit of design details to measured performance is needed, as is an analysis of how changing precipitation patterns in the future may impact functionality. Studies that categorize the strengths, weaknesses, and vulnerabilities of stormwater ponds in the southeastern coastal zone are progressing, but more comprehensive work is needed. Therefore, we recommend concerted, stepwise approaches to integrate and improve the understanding of stormwater pond functioning as it pertains to the unique biological, hydrological, and geochemical settings in each region of coastal S.C.
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Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 40 CHAPTER 3 – AN ASSESSMENT OF NONPOINT SOURCE POLLUTION IN STORMWATER POND SYSTEMS IN COASTAL SOUTH CAROLINA
Authors
Mohammed Baalousha, Ph.D., Samantha McNeal, and Geoffrey I. Scott, Ph.D. Department of Environmental Health Sciences, Arnold School of Public Health, University of South Carolina, Columbia, S.C.
Corresponding Author Geoffrey I. Scott, Ph.D. ([email protected])
3.1 Background In this chapter, we seek to demonstrate why urban nonpoint source (NPS) pollutants carried by stormwater runoff are a major concern for human health and the health of coastal ecosystems, as well as the role ponds can play in mitigating this impact. Water quality in the United States is well monitored particularly around point sources of pollution. However, data from current monitoring programs indicate that NPS pollution is a growing problem and causes two-thirds of the total amount of pollution impacting water quality. This is attributed to various contaminants including metals, organic materials, and microbes (Wang 2015). Runoff results in approximately 40% of U.S. rivers, lakes, and estuaries falling below the basic standards for recreational uses, and South Carolina is no exception (Sparling et al. 2007). Contaminants are generated from various anthropogenic activities and are transferred from urban, industrial, commercial, agricultural, and rural areas into estuaries and surface waters via runoff (Good 2014). Ponds are engineered Best Management Practices (BMPs) that protect downstream systems, though low water circulation and the high pollutant load contribute to water quality problems within pond basins (Novotny 1995). The Figure 3.1 Some major sources of NPS pollution loading within urban coastal NPS runoff discharged into ponds areas of the U.S. that can contribute to runoff, some of which is discharged into may emanate from fertilizer and ponds. www.sciencedirect.com/science/article/pii/S0048969716305587 pesticide applications, fecal material
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 41 input from humans, pets, and wildlife, and runoff from domestic wastewater, driveways, and roads (WHO 1999) (Figure 3.1).
Urban runoff pollution can have many deleterious effects on plants, fish, animals, and humans. For example, untreated urban runoff from an auto recycling facility into waterways near Los Angeles, California over several years killed 20% or more of the exposed minnows (Swamikannu 1994). And a study in San Francisco Bay found higher levels of both legacy pollutants and Contaminants of Emerging Concern (CECs) in NPS runoff than in waste water treatment plant (WWTP) effluent (SFEI 2013).
3.2 Framework Here, we review chemical and microbial pollution sources within coastal S.C. To assess the scope of each group of contaminants, data on concentrations and location (ponds vs. natural systems) in addition to a range of environmental parameters were extracted from the peer-reviewed literature and government sources (e.g., NOAA, USGS). A database was then developed using these data for each group of contaminants in surface waters and sediments, as appropriate. The topic sections that follow summarize information about the major pollutants found in ponds and what risks these contaminants may pose to environmental and human health.
3.2.1 Literature Review
Most pond chemistry data were taken from a study conducted by researchers at The Citadel and reported in a National Oceanic and Atmospheric Administration (NOAA), S.C. Sea Grant Consortium (SCSGC), and S.C. Department of Health and Environmental Control (DHEC) joint report by Weinstein et al. (2008) and later published in a series of peer-reviewed papers (Crawford et al. 2010; Weinstein et al. 2010a, 2010b). This work constituted a detailed analysis of pond sediments from 16 of the 112 ponds reported on in the DHEC 2007 state of knowledge report (Drescher et al. 2007). Samples were taken from two locations: the pond inlet and pond center. Here, the different pond types reported in these studies were converted into the current pond classification system developed by Smith et al. (Chapter 1) and include the following urban site types: residential, mixed land use, golf course, and commercial ponds. We also retained a fifth type, which was reference ponds located in rural or undeveloped areas (two of these ponds were sampled in the report). According to the 2013 inventory, these rural ponds comprise 57% of all ponds in the eight coastal counties (Chapter 1). Microbial pollutant data from South Carolina Urbanization and Southeastern Estuarine Systems (USES), and the Land Use Coastal Ecosystem Study (LUCES) summarized in Scott et al. (2008), along with studies by Johnston et al. (2009), Serrano & DeLorenzo (2008), Berquist et al. (2010), and DeLorenzo et al. (2012), are discussed in the context of the older studies by Drescher et al. (2007) and Messersmith (2007). A number of references on contaminant levels in estuarine and tidal creek sites in S.C. are also included and used for comparison with pollutant levels reported in ponds. Data – including location, land use types, chemical, or microbial pollution data, and any other relevant information from each study – was entered into a database. In total, our citations include 111 references as 66 primary literature sources, nine books, four conference presentations, 30 technical reports, and two student theses.
3.2.2. Analysis
An environmental risk assessment was conducted using methods described by the Environmental Protection Agency
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 42 (EPA 2004), Holland et al. (2004), and the Interstate Shellfish Sanitation Conference (ISSC) (2004). Simply put, NPS contaminants quantified in runoff, surface waters, and sediments were ordered from lowest to highest concentration to generate a cumulative frequency exposure curve for each pollutant type. This curve was plotted versus environmental standards or guidelines in water or sediments for each contaminant, including published EPA water quality criteria (Acute and Chronic Water Quality Criteria) and Sediment Quality Guidelines (SQGs) (Long & Morgan 1990; Long et al. 1995; MacDonald et al. 1996; Long & MacDonald 1998) (Table 3.1). Both Probable Effect Level (PEL), the concentration above which adverse effects on survival or growth are expected to occur frequently, and the Threshold Effect Level (TEL), the concentration below which adverse effects are expected to occur only rarely, are reported for each contaminant listed. In our discussion we mainly use the designations of Effects Range Low (ERL), the threshold concentration where adverse effects begin to occur, and Effects Range Median (ERM), the median concentration where adverse effects are more certain to occur. These threshold levels correspond to the Incidence of Adverse Effects (IAE), which is the estimated toxicity observed in sediment toxicity tests by Long et al. (1995). The IAE is expressed as a percentage (%IAE), and this value corresponds to the number of data entries within each concentration range in which biological effects were observed in benthic indicator species, divided by the total number of entries within each range.
SQG concentrations1 % Incidences of Adverse Effects Chemicals TEL PEL ERL ERM < ERL > ERL and < ERM > ERM
Trace metals (mg/kg dry weight or ppm)
Arsenic 5.9 1.7 8.2 70 5% 11.1% 63% Cadmium 0.6 3.5 1.2 9.6 6.6% 36.6% 65.7% Chromium 37.3 90.0 81 370 2.9% 21.1% 95% Copper 35.7 197 34 270 9.4% 29.1% 83.7% Lead 35 197 46.7 218 8% 35.8% 90.2% Mercury 0.2 0.5 0.2 0.7 8.3% 23.5% 42.3% Nickel 18 36 20.9 51.6 1.9% 16.7% 16.9% Silver NG NG 1 3.7 2.6% 32.3% 92.8% Zinc 123 315 150 410 6.1% 47% 69.8%
Pesticides/PCBs (µg/kg dry weight or ppb) p,p’-DDE NG4 NG 2.2 27 5% 50% 50% TOTAL DDT 7 4,450 1.6 46.1 20% 75% 53.6% TOTAL PCBs 34.1 277 22.7 180 18.5% 40.8% 51%
PAHs (µg/kg dry weight or ppb)
Acenapthene NG NG 16 500 20% 32.4% 84.2% Acenaphthylene NG NG 44 640 14.3% 17.9% 100% Anthracene NG NG 85.3 1,100 25% 44.2% 85.2% Fluorene NG NG 19 540 27.3% 36.5% 86.7% 2-Methyl Naphthalene NG NG 70 670 12.5% 73.3% 100% Naphthalene NG NG 160 2,100 16% 41% 88.9%
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 43 SQG concentrations1 % Incidences of Adverse Effects Phenanthrene 41.9 515 240 1,500 18.5% 46.2% 90.3% SUM LMW PAH2 NG NG 552 3,160 13% 48.1% 100% Benz(a)anthracene 31.7 385 261 1,600 21.1% 43.8% 92.6% Benzo(a)pyrene 31.3 782 430 1,600 10.3% 63% 80% Chrysene 57.1 862 384 2,800 19% 45% 88.5% Dibenzo(a,h)anthracene NG NG 63.4 260 11.5% 54.5% 66.7% Fluoranthene 111 2,355 600 5,100 20.6% 63.6% 92.3% Pyrene 53 875 665 2,600 17.2% 53.1% 87.5% SUM HMW PAH3 NG NG 1,700 9,600 10.5% 40% 81.2% TOTAL PAHs NG NG 4,022 44,792 14.3% 36.1% 85%
1SQG= Based on NOAA’s national Sediment Quality Guidelines 2SUM LMW PAH = Concentration of all low molecular weight PAHs 3SUM HMW PAH = Concentration of all high molecular weight PAHs 4NG = No guideline values
Table 3.1 The Sediment Quality Guidelines (SQGs) concentrations and Incidences of Adverse Effects as shown by Long et al. (1995) and used in this report to predict adverse effects on benthic and epibenthic estuarine/marine fauna.
For legacy pollutants and fecal coliform bacteria (FCB), we have both SQGs and Water Quality Criteria to compare reported concentrations and to provide an initial assessment of risk and hazards. For select CECs, there are reported best available risk assessment guidelines provided by Anderson et al. (2012), as analyzed by an expert panel in California (CA). These are useful for a first order approximation of risks (comparison of maximum measured concentration with estimated bioeffects). These benchmark environmental metrics were used as thresholds to predict bio-effects criteria for each chemical contaminant and to indicate when shellfish harvest or contact recreation guidelines were exceeded. Determinations were then made as to the extent and magnitude of expected effects that will occur within the environment for each major class of contaminants for which there are existing environmental quality guidelines.
For microbial pollutants we utilized the South Carolina Estuarine and Coastal Assessment Program’s (SCECAP) water quality index to evaluate the concentrations of bacteria found in stormwater runoff, pond surface samples, and estuarine water samples (Sanger et al. 2016).
Finally, we compared our literature findings with a 2016 NOAA National Status and Trends (herein, “NOAA NST”) Program report. In this report NOAA published data from 161 estuarine sites in coastal S.C. and Georgia (GA). These included evaluations for metals, pesticides, and polycyclic aromatic hydrocarbons. Where applicable we have included a summary table comparing data from the published works described above with those from this NOAA study.
3.3 Chemical Contaminants
3.3.1 Trace Metals
Metals in the environment at trace (or low) concentrations include any metal that can leech from sediments into the
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 44 environment naturally (e.g., aluminum and iron) or is discharged into the environment from a point source or as an NPS pollutant. Anthropogenic sources include but are not limited to: mining, leechate from solid waste sites, energy production (e.g., coal-fired power plants), emissions from transportation sources (cars, trucks, and trains), animal and human wastes, and paint pigments. The top 20 substances from the federal Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) Priority List of Hazardous Substances include five metals of concern often found in trace concentrations at Superfund sites across the U.S.: arsenic (As), lead (Pb), mercury (Hg), cadmium (Cd) and chromium (Cr). Trace metals are a major cause of water quality impairments in the U.S., causing more than 11,000 impairments nationwide. Some of the most common metal impairments were: mercury (Hg; 4,476 impairments), iron (Fe; 774), copper (Cu; 620), arsenic (As; 593), lead (Pb; 485), zinc (Zn; 326), aluminum (Al; 297), cadmium (Cd; 241), and nickel (Ni; 61) (EPA 2015). Additionally, in 2010, trace metals were responsible for
100
90 ERM = 270 mg/Kg) 80 IAE = >83.7% 70 ERL = 34 mg/Kg) 60 IAE = >29.1-83.7% 50 - Reference Ponds 40 - Residential Ponds - Mixed Ponds 30 - Golf Course Ponds Cumulative Frequency (%) Cumulative Frequency 20 - Commercial Ponds - Unclassified Ponds 10 - Tidal Creeks 0
0.000 200.000 400.000 600.000 800.000
Cu Concentration (ppm)
Figure 3.2 Cumulative frequency plot for Cu concentrations in pond sediments and estuarine/tidal creek sites in S.C., where different colored symbols represent different pond types versus tidal creek sites shown in gray. To interpret the figure: recall that for concentrations above the ERL point the %IAE, or estimated potential for toxicity in benthic indicator species, is 29 to 83.7%, while above the ERM the likelihood for negative biological effects is greater than 83.7%. Additionally, the cumulative frequency demonstrates that ~80% of all samples fall below the ERL threshold while < 5% exceeded the ERM. However, we see that more pond samples fall above the ERL relative to the tidal creek samples, indicating that ponds are hot spots for these chemical contaminants. This plot is generally representative of results for Cd and Zn as well, which exceeded SQGs, and concentrations were generally higher in ponds than estuarine sites.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 45 more than 21% of the 1,103 water quality impairments in S.C. (Mehta 2010). Mercury is one of the major causes of fish advisories in 40 out of 50 states, including S.C. And these trace metals are of environmental and/or public health concerns in shellfish (Scott et al. 1984). While Al and Fe are largely derived from natural sources, other trace metals including Cu, Pb, and Zn are commonly discharged from anthropogenic sources. All of these metals were included in our analysis of pollution in ponds. The elemental symbols are used throughout the following text.
Results
Results of sediment trace metal chemistry analyses (Table 3.2) and environmental risk assessments showed that a number of samples from S.C. exceeded SQGs for eight of the nine trace metals assessed (Table 3.3). Metal concentrations in S.C. ponds can be classified into three groups: 1) metals that do not exceed ERL or ERM, 2) metals that exceeded ERL, but not ERM, and 3) metals that exceeded both ERL and ERM levels. A total of eight ERL exceedances were observed for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, with 8.7 to 65% of all samples exceeding the respective ERL. Similarly, three ERM exceedances were observed for Cr, Cu, and Zn, though only 1.1 to 3.7% of all samples exceeded the respective ERM. For three of the eight ERL exceedances (Cd, Cu, and Zn) and two of the three ERM exceedances (Cu and Zn), the highest concentrations were observed in ponds. The second highest concentration for chromium was observed in ponds. These results suggest that ponds serve their design function and remove some trace metals from runoff before it reaches downstream systems.
Al Cd Cr Land Use ERL = n/a ERL = 1.2 mg/kg dw ERL = 81 mg/kg dw Classification ERM = n/a ERM = 9.6 mg/kg dw ERM = 370 mg/kg dw
Mean ± Mean ± Mean ± Range # Range # Range # SE SE SE 9324 ± < 1,181 – 1.32 ± < DL – Reference sites 4 4 < DL < DL 4 4604 17,491 0.76 2.68 8,265 ± 926 – 2.08 ± < DL – Residential 10 11 11.1 ± 7.4 < DL – 58 10 2,746 25,512 0.35 4.14 10,549 ± 1,006 – 2.22 ± 1.61 – Golf course 6 6 < DL < DL 6 4,134 26,977 0.38 2.79 10,596 ± 1,947 – 2.19 ± 1.73 – Mixed land use 6 6 < DL < DL 6 3,170 20,010 0.21 3.12 7,882 ± 1,830 – 2.11 ± < DL – Commercial 10 10 < DL < DL 10 1,707 19,693 0.62 2.62 3,417 ± 0.02 – 0.43 ± < DL – 98.8 ± Creeks/Estuaries 114 153 4 - 2,873 152 679 22,488 0.05 5.50 22.6 Creeks/estuaries w/o 67.4 ± 4 - 270 150 Shipyard Creek 3.04
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 46 Cu Fe Pb Land Use ERL = 34 mg/kg dw ERL = n/a ERL = 46.7 mg/kg dw Classification ERM = 270 mg/kg dw ERM = n/a ERM = 218 mg/kg dw Mean ± Mean ± Mean ± Range # Range # Range # SE SE SE 9.72 ± 4,471 ± 1013 – 3.37 ± 2.17 – Reference sites < DL – 20 4 4 4 5.60 3,122 13,848 0.69 5.17 154.54 ± < DL – 4,128 ± 721 – 1.82 ± < DL – Residential 10 10 10 48.82 465 1,396 15,050 1.71 6.48 89.13 ± < DL – 5,031 ± 682 – 0.91 ± < DL – Golf course 6 6 6 25.59 161 1,851 12,061 0.64 3.81 15.27 ± 5,831 ± 520 – 4.05 ± < DL – Mixed land use < DL – 32 6 6 6 4.36 1,709 10,833 1.72 10.74 181.28 ± < DL – 4,301 ± 1,118 – 5.00 ± < DL – Commercial 10 10 10 77.30 589 1,035 11,549 1.30 13.81 22.28 ± 5,203 ± 0.42 – 29.74 ± 1.67 – Creeks/Estuaries 1 – 271 154 114 148 2.06 3,385 320,799 2.02 153.6
Zn Land Use ERL = 150 mg/kg dw Classification ERM = 410 mg/kg dw Mean ± Range # SE 40.52 ± Reference sites < DL – 89 4 2.36 37.64 ± Residential < DL – 81 10 10.89 30.04 ± Golf course < DL – 61 6 10.94 91.93 ± < 2.37 – Mixed land use 6 37.65 244 224.0 ± < 6.07 – Commercial 10 58.14 573 92.21 ± 8.60 – Creeks/Estuaries 148 5.03 422
Table 3.2 Comparison of concentrations of metal in sediments (units = mg/kg dry wt.) from ponds, tidal creeks, and estuaries in South Carolina. Where # = number of samples; SE = standard error; < DL = below detection limit; Shipyard Creek = Superfund site (placed on the EPA list in 2000); Reference sites = pristine sediments. The ERL and ERM concentrations (in mg/kg dry weight) are provided as references; n/a = no ERL or ERM established for the given metal.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 47 Trace Metals % Samples compared to SQG < ERL > ERL > ERM As 35% 65% Cd 77.8% 22.2% Cr 75% 25% 1.1% Cu 79.5% 20.5% 3.7% Hg 90.5% 9.5% Ni 69.1% 30.9% Pb 91.3% 8.7% Zn 87.2% 12.8% 1.6%
Table 3.3 Summary of sediment trace metal chemistry results in ponds and tidal creeks compared to SQGs. Note ponds had highest concentrations of cadmium, copper, and zinc that exceeded ERMs in some samples. Gray shading indicates ponds have highest concentration, and bolding indicates ponds have second highest concentrations.
Discussion
Some trace metals were detected at concentrations that exceeded SQGs in both ponds and tidal/estuarine sites in coastal S.C. There were ERL exceedances for arsenic (65% of all samples), Cd (8.2%), Cr (30.7%), Cu (14.7%), Hg (9.5%), Ni (30.9%), Pb (11.4%), and Zn (12.4%) in all S.C. sites. Pond sediments had the highest levels of Cd, Cu, and Zn as compared to any natural site; concentrations of Zn were especially elevated in sediments from commercial ponds (Weinstein et al. 2008). There were no reported sediment contaminant levels in stormwater ponds for three trace metals: As, Hg, and Ni, indicating a current data gap that future monitoring studies should address. Overall, metals have been correlated with various pond characteristics including pond age, pond surface area, extent of drainage area, and the percent of surrounding impervious cover (Weinstein et al. 2008). With the exception of cadmium, metal concentrations in ponds were positively correlated with percent clay content of sediments and total organic carbon (TOC). In general, metals associate with fine-grain sediments (e.g., clay). The accumulation of copper in pond sediments has been previously linked to known applications of Cu-based algaecides, especially in golf course and residential ponds (Weinstein et al. 2008). Also, it was found that for several metals, concentrations were higher at the pond inlet as compared to the center, while other metals were concentrated at the pond center (Weinstein et al. 2008), indicating sedimentation does not necessarily occur uniformly throughout the basin.
The levels of trace metals in sediments may pose significant ecotoxicological risk to benthic organisms in ponds, with the predicted %IAE for trace metals ranging from 6 to 95, including for Cd (6 to 36%), Cr (21 to 95%), Cu (29 to 84%), and Zn (47 to 70%). These risks would be primarily concentrated within the endemic benthic fauna within ponds; though many of the ponds in coastal S.C. do have tidal exchange with nearby creeks. Additional impacts of flow from these ponds to estuaries and tidal creeks may occur when there is significant discharge from the ponds, which would involve increased suspended sediment loads. This occurs during heavy precipitation events or tropical disturbances. It is worth noting that some of the ponds in S.C. (those with higher salinity) are natural habitats for benthic/epibenthic organisms such as oysters, crabs, and shrimp. Residents may fish these organisms for food, resulting in human exposure which may be a potential public health concern. We compared exceedances of SQGs trace metals summarized in this report versus levels reported by NOAA NST at 161 estuarine sites randomly sampled and analyzed
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 48 in S.C. and GA. This comparison indicated very similar results for some trace metals (Hg and Ni) between the states, while S.C. had much higher levels of exceedance for As, Cd, Cr, Cu, Pb, and Zn (Table 3.4).
Trace Metals NOAA NST S.C. NOAA NST S.C. > ERL > ERL > ERM > ERM As 39.8% 65% 0% 0% Cd 4.9% 8.2% 0% 0% Cr 5.6% 30.7% 0% 1.3% Cu 3.1% 14.7% 0% 0.6% Hg 13.0% 9.5% 1.2% 0% Ni 20.4% 30.8% 0% 0% Pb 2.5% 11.4% 0% 0% Zn 1.9% 12.4% 0% 0.7%
Table 3.4 Comparison of trace metal ERL/ERM exceedances of SQGs for estuarine/tidal creeks and pond sites in S.C. (this study) versus estuarine sites in the southeastern (SE) U.S. (S.C. and GA). Gray shading indicates ponds have highest concentration, and bold text indicates ponds have second highest concentrations (out of 186 samples).
Research Gaps
Most measurements in ponds have been of total metal concentrations with little attention given to metal speciation. Metals can occur as free ions, complex with ligands such as organic matter, and anions sorbed to nanoparticles, colloids, and particulate matter, or occur as nanomaterials (more details in sub-section 3.5.3). The environmental and health risk of metals depend on their speciation, with free/labile metals generally being the most toxic species. Therefore, future research should consider:
• Speciation of metals in pond ecosystems and the impact of metal speciation on their environmental behavior, fate, sequestration in sediments and potential for later release to surface waters, and cumulative mixture toxicity. • Processes should be studied in the context of land use and the variability of storm events.
3.3.2 Pesticides and Polychlorinated Biphenyls (PCBs)
Worldwide, more than 1,000 organic chemicals are registered for use as active ingredients in pesticides, which are often ubiquitously present in the environment (Aprea et al. 2002). Approximately one billion pounds of active ingredient pesticides are used in the U.S. each year (Nowell et al. 1999). Because of this widespread use, there are several monitoring programs put in place by governmental agencies, including the Food and Drug Administration (FDA), the EPA, and the Department of the Interior.
Inputs are derived from residential coastal development, such as termiticide treatment of dwellings, residential lawn
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 49 and turf management, golf courses, or antifouling agents, as well as industrial, municipal, and groundwater inflows. In fact, one third of the pesticide used in the U.S. is attributed to urban use, and this is reflected by concentrations of elevated organochlorine pesticides in urban influenced streams, which frequently exceed samples from intensive agricultural sites (Paul & Meyer 2001). Urban areas were found by the EPA to have the greatest exceedance of chronic Aquatic Life Benchmarks (ALBs) for Pesticide Registration based on toxicity levels for various taxa. The ALBs are national guidelines of toxicity values for pesticides based on scientific studies for freshwater species. From 2002–2011 throughout the U.S. nearly two-thirds of agriculture land-use streams, 50% of mixed land-use, and 90% of urban streams exceeded ALBs (Figure 3.3). Primary pesticides found to exceed ALBs were fipronil, metolachlor, malathion, cis-permethrin, and dichlorvos, which exceeded chronic ALBs in more than 10% of streams sampled. Impervious surfaces in developed areas exacerbate the issue by increasing the direct loading of pesticides into waterways (Paul & Meyer 2001).
Federal monitoring programs are supplemented by regional and local studies, such as USES, LUCES, and SCECAP. Wickliffe (2013) reported that more than 80 of the 100 pesticides most frequently sold by Lowes and other retail outlets in S.C. are used on residential lawns and golf courses. This application was more than four times greater than
Agriculture Urban Mixed Atrazine
Deethylatrazine
Metolachlor
Simazine
Prometon
Tebuthiuron
Cyanazine
Herbicides Acetochlor
Alachlor
Metribuzin
EPTC
Dacthal
Diazinon 1992-2001 Carbaryl 2002-2011 Chlorpyrifos Insecticides 0 25 50 75 100 0 25 50 75 100 0 25 50 75 100 Percentage of Time Detected
Figure 3.3 Results of national stream and river pesticide assessment reported by USGS (Stone et al. 2014). This study includes pesticide monitoring data from sediments, grain size, and total organic carbon measurements.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 50 the number of pesticides used for other coastal pesticide applications. These data are significant given the high levels of urbanization in coastal S.C., and underscore the importance of ponds to control NPS runoff that may contain pesticides used in urban areas.
Pesticides are manufactured so that they are toxic to a general pest, such as weeds, insects, fungi, and rodents. If not properly applied according to the label, pesticides may then affect non-target species, including aquatic life, wildlife, and humans, because most pesticides are not necessarily species-specific but are designed to be toxic to a broad array of organisms (Aprea et al. 2002). Pesticides have been found in the tissues of a wide variety of aquatic species, including oysters, shark, finfish, tuna, sea turtles, alligators, sea birds, and clams (O’Connor 1991; Mathews 1994; Lauenstein et al. 2002; Gelsleichter et al. 2005). Coastal wetland ecosystems are of particular interest for any coastal application of pesticides, but treatments upland will eventually be transported to these systems via runoff and stream flow (Clark et al. 1993; EPA 2000). Wetlands and their sediments act as a repository for pesticides. The major concern for adverse effects of pesticides in the environment is based on the transport of these compounds by NPS runoff following precipitation events. Spray drift from local mosquito control applications may also be a source of pesticide exposure. Several studies have linked land use and the occurrence of pesticides in associated runoff and receiving waters in S.C. (Scott et al. 1994; Corbett et al. 1997; Sanger et al. 1999a, b; Graves et al. 2004; Weinstein et al. 2008; Crawford et al. 2010). Studies have also demonstrated chronic and acute toxicity for pesticides in low concentrations (from ng/L to mg/L) depending upon the pesticide class and the species exposed (Clark et al. 1993).
Results
PCBs
There were no published literature sources for PCBs in S.C. ponds at time of this report. Though there were no PCBs measured in pond sediments, 11.3% of the estuarine and tidal creek sites in this study exceeded ERLs. Similarly, NOAA NST reported that there were ERL exceedances for PCBs at 9.9% of the 161 estuarine sites surveyed in S.C. and GA, similar to the levels reported in S.C. tidal creeks (Sanger et al. 1999b).
Legacy Pollutants
Legacy pollutants refer to chemicals produced by industry that remain in the environment long after they are introduced. Chlordane was phased out by EPA in 1989 as a termiticide, the year Hurricane Hugo inundated much of the coast. This termiticide was detected in 11.1% of ponds, with concentrations ranging from DL (detection level) to 1.5 ng/g (average = 0.16 ng/g). Chlordane was only detected in residential ponds (range = DL - 15; average = 0.3 ng/g) and commercial ponds (range = DL - 1.3 ng/g; average = 0.22 ng/g). Sanger et al. (1999b) reported much higher concentrations of chlordane in S.C. tidal creeks, with highest concentrations in mixed land use residential areas (mean concentration ≤ 4.5 ng/g), and lower concentrations in agricultural, residential (urban lower density), and industrial areas (mean concentrations ≤1 ng/g). Concentrations in more pristine reference sites were much lower (< 0.75 ng/g).
Contemporary-Use Pesticides (CUPs)
Chlorpyrifos was the most frequently detected pesticide in S.C. pond sediments; nine out of 16 ponds (or 56% of total ponds surveyed) had detectable concentrations ranging up to 27.7 ng/g for a single high-density residential pond. Concentrations of chlorpyrifos in pond sediments, sampled from the center of ponds, were not significantly different among pond types (golf course = 9.46 ± 2.75 ng/g; low-density residential = 8.17 ± 2.01 ng/g; commercial = 10.97
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 51 ± 5.45 ng/g; Figure 3.4a). Chlorpyrifos sediment concentrations were found to be dependent on pond surface area (Weinstein et al. 2008). Holland et al. (2008) found lower concentrations of chlorpyrifos in S.C. tidal creeks (Figure 3.4b). The lowest levels were found in sediments from reference creeks (0.2 ng/g), while first order urban tidal creeks had the highest concentrations, as they were most closely associated with development (0.8 ng/g). DeLorenzo and Fulton (2009) found similar trends for the herbicide atrazine in estuarine surface water and ponds; maximum annual atrazine levels in ponds (1.00 μg/L) were nearly an order of magnitude higher than in tidal creeks (less than 0.05 μg/L). Weinstein et al. (2008) found several other pesticides in S.C. ponds including: endosulfan = 5.6% of ponds (6.2 ng/g in commercial ponds); fonofos = 5.6% of ponds (10.0 ng/g in low density residential ponds); and dichlorvos = 5.6% of ponds (25.9 ng/g in high population density mixed land use) ponds (Table 3.5).
a) Chlorpyrifos in Ponds b) Chlorpyrifos in Tidal Creeks 30.0 1
25.0 0.8 1st Order 2ndOrder 20.0 0.6 3rdOrder 15.0
0.4 10.0
0.2 5.0
0
Average Sediment Concentrations (ng/g) Average 0.0 Sediment Concentrations (ng/g) Average Golf LD Res HD Res Comm Forested Suburban Urban Course Land Use Class Land Use Class
Figures 3.4a and 3.4b A comparison of average sediment concentrations (± one standard deviation when replicates available) of the organophosphate insecticide chlorpyrifos in a) S.C. ponds (Weinstein et al. 2008) and b) S.C. tidal creeks (Holland et al. 2008). Ponds were distinguished by land use classes into: golf course, low density residential (LD Res), high density residential (HD Res), and commercial (Comm) ponds. First order creeks are those in closest proximity to the terrestrial or built environment.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 52 Site Description Chlordane (ng/g) Endosulfan (ng/g) Mean ± SE Range # Mean ± SE Range # Reference sites ND ND 2 ND ND 2 Residential 0.3 ± 0.3 < DL – 1.5 5 ND ND 5 Golf course ND ND 3 ND ND 3 Mixed land use ND ND 2 ND ND 2 Commercial 0.22 ± 0.22 < D L – 1.3 5 1.03 ± 0.22 < DL – 6.2 6 Creeks/Estuaries < 4.5a < DL – 4.5 NR NC < DL– 0.28b NR Fonofos (ng/g) Dichlorvos (ng/g) Mean±SE Range # Mean±SE Range # Reference sites ND ND 2 ND ND 2 Residential 2.00 ± 2.00 < DL – 10 5 ND ND 5 Golf course ND ND 3 ND ND 3 Mixed land use ND ND 2 12.95 < DL – 25.9 2 Commercial ND ND 5 ND ND 6 Creeks/Estuaries NA NA NA NA NA NA
Table 3.5 Sediment concentrations of pesticides as reported by where # = number of samples; SE = standard error; < DL = below detection limit; ND = not detected; NA = not assessed; NC = not calculated. Data taken from: a = Holland et al. (2008); b = Leight et al. (2005) and all other from Weinstein at al. (2008).
Discussion
The presence of legacy contaminants in pond sediments indicates that ponds do sequester these chemicals. Pesticides can have a long half-life when particle bound, and the anaerobic conditions in pond sediments may increase the life of these chemicals, leading to lower degradation rates (Bondarenko & Gan 2004). NOAA NST reported that there were ERL exceedances for DDT, another legacy pollutant, at 19.8% and for DDE, a breakdown product of DDT, at less than 1% of the 161 estuarine sites surveyed in S.C. and GA (Table 3.6). However, despite the persistence of these legacy pollutants, concentrations measured in ponds are lower when compared with levels of contemporary- use pesticides such as chlorpyrifos. This chemical replaced chlordane as a termiticide in residential areas until this usage was phased out by the EPA in 2001 due to risks to human health; this chemical is still utilized in commercial applications.
Chlorpyrifos has caused pervasive ecotoxicology issues in aquatic ecosystems. Stone et al. (2014) found that the organophosphate insecticide chlorpyrifos was one of several insecticides found in extremely high concentrations in urban areas and was one of the major causes of exceedances of ALBs nationally. There are no SQGs established by the EPA for this compound. However, Weinstein et al. (2008) found that sediments from nine ponds (50%) had levels of chlorpyrifos which exceeded ecological life criteria screening level benchmarks (derived by EPA 1996 and Jones et al. 1997), but none of the ponds had levels that were above the benchmarks for human health concern. Chlorpyrifos was identified by the state of CA Expert Panel on CECs (Anderson et al. 2012) as one of 12 Dirty Dozen Contaminants of Concern recommended for future monitoring and was reported by USGS (Stone et al. 2014) as one of several problematic insecticides, particularly in urban areas. Finally, this pesticide is known to be synergistically toxic to
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 53 aquatic invertebrates when found in the presence of the herbicide atrazine. The aquatic life criteria is 5.6 ng/L for the combination of these pesticides.
Contaminant NOAA NST S.C. > ERL > ERL Pesticides/PCBs Total PCBs 9.9% 11.3% Total DDT 19.8% 100%
Table 3.6 Comparison of DDT and PCBs to the SQG assessments of estuarine sites and ponds in S.C. (this study) versus estuarine sites reported by NOAA NST.
Research Gaps
Only limited data exists on pesticide levels in ponds, and PCB data is largely lacking. In particular, Contemporary Use Pesticides such as chlorpyrifos and pyrethroids should be monitored given their likelihood for acute and chronic toxicity to invertebrates (Maruya et al. 2013). Continued monitoring of these pesticides is warranted to evaluate the future hazards these pesticides pose to aquatic organisms. Specifically:
• Levels of chlorpyrifos, bifenthrin, fipronil, and pyethroids such as permethrin should be monitored in ponds as recommended by the State of CA Expert Panel on CECs, based on their environmental risk to aquatic organisms relative to measured concentrations. • Mosquito control pesticides should be further monitored, given the emphasis on prevention and control of West Nile and the Zika virus, as most of the recommended insecticides used for mosquito control have very narrow margins of safety. • Chlorpyrifos and atrazine should continue to be monitored due to their synergistic toxic effects on crustaceans and their widespread occurrences in ponds.
3.3.3 Polycyclic Aromatic Hydrocarbons (PAHs)
Polycyclic aromatic hydrocarbons are a ubiquitous group of chemical compounds that are predominately formed during the incomplete combustion of organic materials. PAHs may be formed three ways in the natural environment: high temperature pyrolysis of organic materials; low to moderate temperature diagenesis of sedimentary organic material to form fossil fuels, and direct biosynthesis by plants and microbes (Neff 1979). Fires occurring in nature are the largest contributing factor for natural sources of PAHs released in the atmosphere (Eisler 1987). Although PAHs can occur naturally in the environment, they are also considered an important group of pollutants associated with development and found in urban runoff (Sanger et al. 1999b; Walker et al. 1999; Van Dolah et al. 2005, 2006). PAHs are defined by their fused ring structure of two or more benzene rings. Those with two to five benzene rings are, in general, of the greater concern for human and environmental health (EPA 1999). These PAHs differ in their distribution and behavior in the environment and can be divided into low molecular weight PAHs and high
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 54 6000
5000 High Use Roads (>25,000 ADT) 4000 ER-L
3000
2000
1000
Mean Total PAH (ng/g) dry weight PAH Mean Total 0 Berm 3 meter 25 meter 50 meter 6000
5000 Moderate Use Roads (10,000 - 15,000 ADT) 4000 ER-L
3000
2000
1000
Mean Total PAH (ng/g) dry weight PAH Mean Total 0 Berm 3 meter 25 meter 50 meter 6000
5000 Low Use Roads (1,000 - 5,000 ADT) 4000 ER-L
3000
2000
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Mean PAH (ng/g) dry weight Mean PAH 0 Berm 3 meter 25 meter 50 meter
Transect
Figure 3.5 PAH concentrations measured in marsh sites adjoining major highway types in coastal areas of S.C. (taken from Van Dolah et al. 2005). The line indicates the ERL concentration. Note that highest PAH levels were found on moderate-use roads and not more heavily traveled roads due to road design and the distance to the adjoining marsh from the roadway. However, in all cases, concentrations were below the ERL.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 55 molecular weight PAHs. Solubility tends to decrease with increasing molecular weight. Low molecular weight PAHs (two to three rings and include fluorene and anthracene) are more likely to have significant acute toxicity on aquatic organisms. High molecular weight PAHs (four to seven rings) are known to be carcinogenic. The EPA identifies 34 PAH compounds as being the most abundant and frequently measured in sediments (EPA 2003) and of these, 16 are on an EPA priority pollutant list due to the fact these compounds are characterized as mutagenic or carcinogenic (EPA 2002a, b).
PAHs released in fires tend to adhere to suspended particulates and enter the terrestrial and aquatic environments when the particulates fall out (Eisler 1987). Based on their application and routes of disposal, PAHs will eventually be discharged into aquatic ecosystems. PAH concentrations are often elevated around roadways due to the significant discharge of auto emissions. Van Dolah et al. (2005) assessed these for S.C. coastal highways (Figure 3.5) and found the highest PAH levels originated from moderate-use roads. Because practically all incineration processes generate PAHs, several studies from S.C. compared PAH concentrations across a range of watershed-level land uses (Sanger et al. 1999b; Menzie et al. 2002; Brown & Peake 2006).
Results
Results of sediment PAH risk assessments indicated that SQGs were exceeded for 12 of the 13 PAHs evaluated.
100 90 80 ERM = 5100 µg/Kg IAE = >63% 70 60 ERL = 600 µg/Kg 50 IAE = >20.6-63.6% - Reference Ponds 40 - Residential Ponds - Mixed Ponds 30
Cumulative Frequency (%) Cumulative Frequency - Golf Course Ponds 20 - Commercial Ponds - Unclassified Ponds 10 - Tidal Creeks 0
0 10000 20000 30000 40000
Fluoranthene Concentration (ppb)
Figure 3.6 Fluoranthene concentrations (µg/kg dw) measured in sediments from ponds, tidal creeks, and other coastal estuarine locations in S.C. Note how pond concentrations exceeded the ERLs and ERMs and were generally higher than estuarine tidal creeks. Similar results were seen for phenanthrene and pyrene.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 56 Therefore, PAHs can be classified as those that exceeded ERLs or those that exceeded both ERLs and ERMs (e.g., Figure 3.6). Of the 12 ERL exceedances, 1.5 to 65% of all samples exceeded the respective ERL. Similarly, a total of eight ERM exceedances were observed for anthracene, fluorene, phenathrene, benzo(a)anthracene, benzo(a)pyrene, chrysene, fluoranthene, and pyrene, with 2.3 to 16.4% of samples exceeding their respective ERM (Table 3.8). For three of the 13 ERL and ERM exceedances (phenanthrene, fluoranthene, and pyrene) highest concentrations were measured in ponds. These results indicate that ponds may act as potential sinks for at least some PAHs. All four urban pond types: commercial, golf course, mixed land use, and residential had the highest concentrations measured for most contaminants as compared to ponds from reference (pristine) areas or with tidal creeks and estuarine ecosystems (Figure 3.6; Tables 3.7 and 3.8).
Site Description Acenapthene Anthracence Acenapthylene Mean ± SE Range # Mean ± SE Range # Mean ± SE Range # 31.6 – < DL – 364.1 ± < DL – Reference Sites 91.5 + 19.8 9 57.9 ± 19.1 9 9 161.6 125.8 153.7 1178.4 50.3 – < DL – < DL – Residential 91.4 ± 10.8 21 15.5 ± 6.1 21 30.6 ± 9.7 21 197.7 83.9 162.0 191.1 ± 62.2 – < DL – < DL – Golf Course 13 30.5 ± 10.0 13 9.4 ± 5.4 13 46.4 588.3 130.3 67.0 132.0 ± 55.1 – < DL – < DL – Mixed Land Use 13 95.1 ± 48.5 13 48.3 ± 26.8 13 13.3 197.6 491.6 284.1 424.8 ± 54.2 – 318.7 ± < DL – Commercial 21 0 - 1491.4 21 21.3 ± 10.0 21 126.9 1993.8 97.0 147.0 1.00 – Creeks/Estuaries 16.6 ± 5.7 3.0 – 273.0 55 42.6 ± 17.2 2.0 – 705.0 54 38.7 ± 32.1 55 1783.0
Site Description Fluorene Napthalene Phenathrene Mean ± SE Range # Mean ± SE Range # Mean ± SE Range # < DL – 290.8 ± 11.6 – Reference Sites 40.0 ± 4.8 27.8 – 64.8 9 1.9 ± 1.9 9 9 17.0 94.8 658.3 30.7 – < DL – 282.6 ± 12.0 – Residential 42.7 ± 4.6 21 44.7 ± 16.3 21 21 110.8 225.3 13.0 1591.2 30.3 – 528.2 ± 35.6 – Golf Course 81.5 ± 16.1 13 72.6 ± 16.5 4.8 – 193.3 13 13 178.4 147.3 1612.4 28.8 – 13.6 – 513.7 ± 39.8 – Mixed Land Use 49.1 ± 5.9 13 79.2 ± 24.1 13 13 103.1 241.3 210.4 2306.8 247.1 ± DL – 3701.2 ± 19.9 – Commercial 21 11.3 ± 26.6 DL – 353.5 21 21 88.3 1432.1 1111.0 16,345.1 2.0 – Creeks/Estuaries 16.7 ± 7.6 1.0 – 386.0 54 31.5 ± 5.7 5.0 – 227.0 57 97.1 ± 47.8 54 2534.0
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 57 Site Description Benzo(a)pyrene Chrysene Dibenzo(a,h)anthracene Mean ± SE Range # Mean ± SE Range # Mean ± SE Range # < DL – < DL – Reference Sites 18.7 ± 6.8 9 6.6 ± 2.6 9 1.8 ± 1.2 < DL – 9.5 9 50.7 20.9 207.8 ± 3,160 – 500.8 ± 5.3 – < DL – Residential 21 21 17.0 ± 7.1 21 98.8 1323.9 178.0 2253.2 94.8 104.2 ± 532.3 ± 8.5 – < DL – Golf Course 3.3 – 555.0 13 13 9.3 ± 4.1 13 45.5 176.0 1972.9 51.3 682.9 ± 5.2 – 728.2 ± 14.2 – < DL – Mixed Land Use 13 13 76.0 ± 39.8 13 3112.8 3013.8 239.2 2444.1 421.3 1888.4 ± < DL – 2,335.5 ± < DL – 209.9 ± < DL – Commercial 21 21 21 515.2 7126.5 525.7 7393.6 60.3 954.3 310.0 ± 5.0 – 172.6 ± 1.0 – Creeks/Estuaries 63 54 28.9 ± 14.9 1.0 – 818.0 59 128.2 7328.0 64.5 3171.0
Site Description Fluoranthene Pyrene Mean ± SE Range # Mean ± SE Range # 192.7 ± < DL – Reference Sites 53.0 ± 17.3 2.7 – 118.4 9 66.4 448.4 156.8 ± 11.2 – 797.5 ± < DL – Residential 21 492.3 6600.5 386.7 5140.3 445.4 ± 17.2 – 385.7 ± < DL – Golf Course 13 193.6 2329.5 175.3 2110.7 2214.3 ± 5.4 – 1871.6 ± 2.33 – Mixed Land Use 13 997.4 9359.2 869.5 8311.0 9652.9 ± 9.8 – 7361.8 ± < DL – Commercial 21 2687.5 37,612.0 2084.2 29,361.9 1009.4 ± 3.0 – 792.5 ± 2.00 – Creeks/Estuaries 63 623.3 36,123.0 451.5 27,910.0
Table 3.7 Concentrations of polycyclic aromatic hydrocarbons in sediments (μg/kg dry wt.) from ponds; creeks/ estuaries = all tidal creeks and estuaries in S.C. where # = number of samples; SE = standard error; < DL = below detection limit; Reference Sites = pristine sediments.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 58 % Samples compared to SQG Contaminant < ERL > ERL > ERM PAHs Acenaphthene 35% 65% Anthracene 79.4% 20.6% 2.3% Ancenapthylene 98.5% 1.5% Fluorene 37.4% 62.6% 2.3% 2-Methylynapthalene 91% 9% Napthalene 100% 0% Phenathrene 71% 29% 15.3% Benzo(a)anthracene 80.7% 19.3% 5% Benzo(a)pyrene 77.1% 22.9% 12.1% Chrysene 68.7% 31.3% 4.6% Dibenzo(ah)anthracene 94.1% 5.9% Fluoranthene 80.1% 19.9% 14% Pyrene 77.9% 22.1% 16.4%
Table 3.8 Summary of sediment PAH chemistry results in ponds and tidal creeks compared to SQGs. All ponds and many tidal creeks have contaminant concentrations > ERL. Gray shading indicates ponds have highest concentrations.
Discussion
Many PAHs in sediments were detected at levels that exceeded SQGs in both ponds and tidal creek/estuarine sites within coastal S.C. Ponds had the highest levels of several PAHs including phenanthrene, fluoranthene, and pyrene. Overall, PAHs were not highly correlated with clay or TOC content of the sediments, suggesting a different deposition pathway from metals, likely long-term atmospheric deposition (De Luca et al. 2005). Though PAHs from some ponds carried a distinct fuel signature (based on ratio of low to high molecular weight), the primary source for PAHs in all 16 ponds were pyrogenic sources (Weinstein et al. 2008). Commercial ponds had the highest PAH concentrations, and these were especially elevated in older ponds that had likely not been dredged (Fernandez & Hutchinson 1993). Residential and golf course pond sediments carried the highest motor oil signatures. Sediment-bound PAHs may pose significant ecotoxicological risk to benthic organisms within ponds, as the predicted %IAE for PAHs range from 10.3 - 73. The high %IAE values for all PAHs tested for suggest that at the reported concentrations there is potential for adverse effects in benthic organisms within coastal S.C. ponds.
Comparison of PAH exceedances summarized in this report versus levels reported by NOAA NST indicated very similar results for some PAHs (2-methylnapthalene, napthalene, benzo(a)anthracene, and dibenzo(a,h) anthracene), while S.C. had higher levels of acenapthene, fluorene, phenanthrene, benzo(a)pyrene, chrysene, fluoranthene, and pyrene (Table 3.9). NOAA reported that the mean estimated impact by PAHs in S.C. and GA based upon %IAE was 14.6 (at the 95% confidence level (CL) = 10.0 - 19.3%) while experimental sediment toxicity tests (based upon amphipod development and reproduction in sea urchins) provided estimates of 0.3 to 21.3%. Thus, the ranges of predicted and actual toxic effects overlapped between the two approaches. Comparisons of the potential for impacts predicted in S.C. similarly provide areal estimates of 5.8% (at the 95% CL = 0 - 18%) of tidal creek/estuarine sites
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 59 and 10.5% (95% CL = 3 - 17%) of pond samples, which have the highest concentrations of legacy pollutants. These predictions of ecotoxicological effects from legacy pollution in our S.C. study compares very favorably with NOAA results for the following watersheds: Charleston, Winyah Bay, and North Edisto River (in S.C.), and the Savannah and St. Simons Island (in GA).
NOAA NST S.C. NOAA NST S.C. Contaminant > ERL > ERL > ERM > ERM PAHs Acenapthene 13% 63% Anthracene 25% 15% 1% 2% Ancenapthylene 13% 7% Fluorene 39% 62% 2.2% 2-Methylnapthalene 10% 9% Napthalene 4% 3% Phenanthrene 21% 28% 15% Benzo(a)anthracene 12% 17% 3% Benzo(a)pyrene 6% 27% 16% Chrysene 12% 28% 4% Dibenzo(ah)anthracene 6% 7% Fluoranthene 11% 19% 1% 12% Pyrene 11% 17% 15%
Table 3.9 Comparison of PAH SQG Assessments of estuarine and pond sites in S.C. (this study) versus estuarine sites reported by NOAA NST. Gray shading = ponds had the highest concentrations. Note the higher PAH levels in S.C. when compared to other parts of the southeastern U.S.
Research Gaps
Because of the potential toxic effects for aquatic organisms of the various contaminants sequestered in ponds, whether these are potentially hazardous to wildlife needs to be better constrained. Specifically, we need to better understand:
• Ecotoxicological effects of PAHs discharged from ponds into estuarine ecosystems and the spatial extent of any downstream impacts. • Cumulative mixture ecotoxicological effects of different PAHs and other contaminants.
3.4 Microbial Pollutants Microbial pollution in coastal surface waters is a problem affecting recreational and commercial uses of rivers, beaches, and estuaries throughout the U.S. and is one of the major causes of water quality impairments in S.C. As development
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 60 alters landscapes and watershed hydrology, the major sources of bacterial pollution are human waste from inadequately maintained septic tanks and waste from wildlife, livestock, and pets. The standard solutions to this problem are to construct a central sewer collection system to reduce estuarine inputs from individual septic tank systems (Jolley 1978) and to construct stormwater BMPs to manage bacteria in NPS runoff.
In 2012, commercial fisherman in S.C. collected 9.9 million pounds of shellfish valued at $17.5 million in landing revenue (NMFS 2014). Microbial contamination can result in the closure of shellfish harvesting waters due to the presence of pathogenic bacteria and viruses (Scott et al. 2006). Bed closures can also decrease property values near the affected tidal creeks. Roughly 30 million tourists visit the state each year, and the majority of these visitors come to the coast. Any beach closures can have an economic impact on coastal S.C. It was estimated that in 2016, two million fewer tourists visited Myrtle Beach than in the previous year, and one of the reasons cited was the perception of bacteria-laden waters (Myrtle Beach Chamber of Commerce). Therefore, there is a strong need for tools that can help resource managers make timely and accurate decisions regarding closures, from both a public health and economic standpoint.
Limits in CFUs/100 mL1 Monthly Daily Type Indicator Used Class Approved Use Average Maximum 35 104 saltwater Enterococci SA2 recreational; heavy use 35 501 saltwater Enterococci SB3 recreational; infrequent use 14 43 saltwater FCB SA shellfish harvest 126 349 freshwater E. coli n/a recreational
1CFU = colony forming units; 2Salt Water A rating; 3Salt Water B rating.
Table 3.10 Current bacteria classifications and standards for waters of the State taken from DHEC’s Bureau of Water R.61-68 Water Classifications and Standards (effective June 27, 2014). Waters of the State as defined by the S.C. Pollution Control Act, and in compliance with the federal Clean Water Act, does not currently include stormwater conveyances, although there was some traction starting in 2014 at the federal level to include wetlands and other tributaries (such as wet ponds) as waters of the U.S. (see the Clean Water Rule in Chapter 5).
FCB concentrations are used to evaluate long-term water quality status of shellfish harvesting waters, shellfish tissues, and waters used for recreational contact. The coliform group is broad and consists of all aerobic and anaerobic, gram negative, non-spore forming, rod-shaped bacteria that grow and produce gas in broth when incubated at 35 - 37 °C (mammalian body temperature) within 24 hours. In general, FCB are associated with contamination from warm- blooded animals, and the FDA approves the measure of their abundances as an indicator of fecal pollution to protect shellfish consumption and recreational contact (Cabelli et al. 1983; Ruple et al. 1989; FDA 1989). FCB counts can indicate Escherichia coli, which is one of the more commonly measured bacteria in human feces (Kator & Rhodes 1996) and occurs with greater frequency in urban areas versus more pristine sites (Vernberg et al. 1996). In shellfish tissues, E. coli is the principal FCB present when water temperatures are less than 22°C (Cook & Ruple 1989), while at higher temperatures, Klebsiella species will dominate over other FCB. Vernberg et al. (1996) reported that K. pneumoniae was the most dominant member of the FCB group after E. coli in the evaluation of estuarine surface waters and oysters from pristine and urban estuaries in S.C. Klebsiella species are usually not a threat to human health
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 61 (Paille et al. 1987). Enterococcus and E. coli have been shown recently to more accurately predict acute gastrointestinal illness from contact by swimming than total levels of FCB. Therefore, DHEC now uses Enterococcus rather than FCB as the indicator for contact recreation in saltwater, while E. coli is the indicator used for recreational contact in freshwater. Note that limits based on Enterococcus concentrations are lower than those for E. coli or total FCB as this genus represents just 1% of the flora in saline systems (Layton et al. 2010). Results
Several studies of microbial pollution in S.C. ponds were identified, including the state of knowledge report on 112 ponds (Drescher et al. 2007). To recap, in this comprehensive review, most ponds were described as being freshwater with salinities less than 1 ppt. Approximately 20% had low dissolved oxygen concentrations (less than 4 mg/L), and some 23% of the ponds also had high FCB levels, greater than 400 colony-forming units (CFUs)/100 mL in surface water. The highest FCB levels were found after rain events.
Fecal Coliform Bacterial Density (cfus/100 ml) Source Water <43 >43 - <200 >200 - <400 >400 NPS Runoff 1% 9% 90% Ponds 54% 17% 5% 23% Estuarine Surface Water 34% 50% 13% 13%
Table 3.11 Comparison of fecal coliform levels (% of samples exceeding specific criteria) in NPS runoff in pond surface waters and in estuarine surface waters (after Scott et al., 2008). Geometric mean MPN values of <14-43 colony forming units (cfus)/100 ml are used as the standards for safe shellfish harvesting. MPN values of >43 cfus/100 ml are used as an indicator of shellfish harvest standard exceedances. Fecal coliform standards of 200cfus/100ml have been used as Class SA Water standards and were formerly the safe contact recreation standard. EPA Whole Body Water Contact Standards in marine waters today use an Enterococci level = 104cfus/100ml (single sample max). Fecal coliform standards of 400cfus/100ml have been used as Class SB Water Quality standards.
It is important to compare FCB levels in ponds to levels measured in adjoining estuarine ecosystems, as ponds are intended to intercept and remove pollutants. Scott et al. (2008) summarized results from two studies: DHEC-OCRM (2002) and the USES study. A comparison of FCB concentrations from NPS runoff, ponds, and estuarine surface waters indicated that the overall densities differ (USES 2004; Table 3.11), with FCB levels in runoff far exceeding that of ponds and estuarine waters. The USES data indicated that FCB densities in runoff source water from urbanized watershed in Murrells Inlet, S.C. ranged from 430 - 11,000 CFUs/100 mL (average = 4,610 CFUs/100 mL) versus densities ranging from 4,600 -11,000 CFUs/100 mL (average = 8,867 CFUs/100 mL) at the pristine NOAA National Estuarine Research Reserve (NERR) site in North Inlet, S.C. (Kelsey et al. 2003). Peak FCB densities of approximately 11,000 CFUs/100 mL measured in runoff were similar to peak levels at the NERR site and Murrells Inlet (USES 2004). These data far exceeded thresholds for recreational contact and shellfish harvesting standards (see Table 3.10 above for current water quality classifications). While overall there were no statistical differences detected between the two sites when data were pooled, monthly comparisons showed FCB levels were higher in the NERR system than Murrells Inlet (USES 2004). Similarly, the DHEC-OCRM study (2002) reported peak FCB densities as high as 35,000 CFUs/100 mL in NPS runoff flowing into estuarine areas of the East Cooper River near the Isle of Palms in Charleston County, S.C. Densities exceeding 10,000 CFUs/100 mL were measured in surface waters at eight other
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 62 Fecal Coliform Bacteria Counts
100
75
Poor Fair 50 Good % of Samples
25
0 NPS Runoff Pond Estuary Sample Sources
Figure 3.7 Data from coastal S.C. ponds and natural sites (Scott et al. 2008) and evaluated based on the S.C. Estuarine and Coastal Assessment Program (SCECAP; Sanger et al. 2016) criteria of poor (>400 CFU/mL), fair (43 < x ≤ 400 CFU/mL), and good (≤ 43 CFU/mL) water quality.
stream locations that receive runoff in the East Cooper river region, including Shem Creek.
Comparison of FCB levels in surface waters of ponds and estuarine samples were more comparable and generally indicate the importance of reducing levels in NPS runoff through sedimentation and other processes. Scott et al. (2008) analyzed FCB data from ponds in S.C. and compared these data with levels in estuarine surface waters and tidal creeks in S.C. These were plotted based on SCECAP’s water quality criteria (Figure 3.7; Sanger et al. 2016). Surface waters containing NPS runoff that flows into ponds generally contain very high levels of FCB (often >1000 CFUs/100 mL), which exceed shellfish harvest standards and standards for contact recreation in more than 99% of the samples. FCB levels were higher in residential and commercial ponds than in industrial and golf course ponds. In a comparison of a freshwater pond in the Charleston area with the receiving tidal creek, Serrano and DeLorenzo (2008) showed the tidal creek often had elevated FCB levels. The average creek levels were 1519 CFU/100 mL as compared to 181 CFU/100 mL in pond surface waters. Pond concentrations were often below the threshold for recreational contact while creek values far exceeded those allowed for contact and shellfish harvesting. Levels of FCB in waters decreased with decreasing water temperatures, with the exception of trends driven by introduction of bacteria from migratory birds in fall and winter. More recent S.C. pond studies found that FCB levels in surface waters of seven ponds of differing land use ranged from 1 to 2,600 CFUs/100 mL (average = 505.5 ± 361.5 CFUs/100 mL; Johnston
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 63 et al. 2009), and in two freshwater ponds from 86.2 to 469.2 CFUs/100 mL (average = 238.5 ± 41.3 CFUs/100 mL; DeLorenzo et al. 2012).
Discussion
More than 99% of FCB loadings to coastal waters occur during storm events due to direct deposition by runoff and sediment resuspension. During storms, FCB levels in downstream systems are most affected by erosion of sediments in pipes and channels that convey stormwater. Collectively, studies show the wide range of FCB measured in surface waters; some of this variance is due to differing rainfall amounts that drive increased bacterial loadings. In general, NPS runoff levels are higher than estuarine surface waters, and the mean estuarine surface water FCB levels were typically reduced by 10 - 100 fold. Levels in the middle and outer regions of most estuaries had much lower levels of FCB (1-100 CFU/100 mL range) due to tidal mixing and dilution from offshore seawater that is tidally exchanged.
Berquist et al. (2010) demonstrated the negative correlation between FCB levels and salinity in ponds and tidal creeks. Holland et al. (2004) found significant correlations between FCB levels in surface waters of estuarine tidal creeks and the extent of impervious surfaces and land use. A mechanistic model linked to flow (Holland et al. 2004) showed that when impervious cover exceeded 10 to 20% of a watershed we see increased FCB loadings to waterways. Peak flows in rain events (Cubic Feet per Second = cfs) and impervious surfaces were highly correlated with highly urbanized areas; where 40% cover had 271 cfs versus 175 cfs in moderately urbanized areas (defined as greater than 10% and less than 40% impervious area). In areas with low urbanization (less than 10% cover), peak flows were 100 cfs so the ratio of peak flows in high to low urbanized areas was 2.71. This value is very similar to enrichment levels measured by Van Dolah et al. (2008): 2.85 for chemical contaminants and 3.64 for FCB in highly urbanized areas. This underscores the importance of using BMPs to reduce chemical and microbial pollution in urban runoff and to reduce bacterial loadings to estuarine receiving waters used for shellfish and contact recreation. However, the North Inlet vs. Murrells Inlet comparison study and the results from Serrano & DeLorenzo (2008) demonstrate the potential for seasonal contributions from migratory waterfowl and wildlife at estuarine sites (Siewicki et al. 2007). These high FCB levels at even pristine sites demonstrate the need for management strategies to reduce bacterial source loadings with Poop-a- Scoop programs (e.g., pet waste reductions) and effective wildlife management strategies (e.g., Canada geese deterrents).
Overall, the higher bacterial concentrations found in NPS runoff near pond inflow sites compared to near pond outlets indicates that ponds do reduce FCB levels. Chapter 4 discusses some biogeochemical processes that occur in ponds which may remove some pollutants. In the 2007 state of knowledge report, Drescher et al. reported that FCB reductions in 112 coastal ponds ranged from -47 to 99% and Total Suspended Solids (TSS) were reduced from 79 to 91%. This close agreement between FCB and TSS reductions reinforces the importance of bacterial association with sediments. The EPA finds that 90% of materials settle out of the water column in ponds between rain events. Though the primary means of pollutant removal in ponds is via sedimentation, modeling indicates that other processes must also be involved (Borden et al. 1998). Multiple ponds connected in a series provided greater treatment potential than single pond designs as the cumulative sedimentation led to greater overall removal efficiencies (Messersmith 2007).
Weinstein et al. (2008) demonstrated that bacterial levels in ponds were positively correlated with the size of the pond’s drainage area, pond surface area, concentrations of total organic carbon, and percent clay particles. For ponds with low turbidity, significant UV treatment from solar radiation may also occur in the surface waters, which may further reduce FCB levels.
Overall these studies suggest that different mechanisms control and predict FCB densities during dry weather versus
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 64 storm periods and that the geometry of the stormwater conveyance system is an important control on sediment resuspension during storm events. Therefore, pond design should include features that prevent the disturbance of sediments during rain events. Otherwise ponds can discharge both chemical and microbial pollutants and become significant sources downstream.
Human Health
In general, risks from human sources are considered to be more dangerous than non-human sources due to greater chance for antibacterial resistance (DHEC-OCRM 2002; USES 2004). In the majority of studies, bacteria tested from ponds had low levels of antibiotic resistance, indicating wildlife sources. However, the co-occurrence of high levels of trace metals in sediments and high levels of FCB may result in the development of antibiotic resistance in the ambient communities. As reported by Luo (2015), surface waters in China were impacted by heavy metal pollution with the same trace metals we have found elevated in retention ponds sediments (sub-section 3.3.1). Bacteria can become resistant to antibiotics naturally through a series of mechanisms (Aminov 2009; Davies & Davies 2010), and resistance can be conferred by direct exposure to a number of environmental factors, including high temperatures, heavy metals (Baker-Austin et al. 2006; Seiler & Berendonk 2012), and exposure to antibiotics. With respect to antibiotic resistance, particular pathogens of concern include Vibrio species. Vibrio survive in brackish (1- 5 ppt) to full strength seawater (greater than 35 ppt) and may be introduced through tidal exchange, thus they likely reside in many coastal S.C. pond environments. Acquisition of resistance is significant, as V. vulnificus is responsible for more than 85% of deaths from seafood consumption. Additionally, between 1985 and 2008 the U.S. saw a greater than 100% increase in the rate of infection, and Vibrio was one of only three bacterial infections in the U.S. that saw increased rates of illness (Newton et al. 2012). Baker-Austin et al. (2008) isolated 350 V. parahaemolyticus strains from both water and sediments at three locations along the Atlantic coast of GA and S.C. and found that 99% of strains were resistant, with 24% of the isolates demonstrating resistance to 10 or more antibiotics. The increase in illnesses attributed to Vibrio strains are primarily due to these increased occurrences of wound infections (Weiss et al. 2012) caused by highly antibiotic resistant strains.
Research Gaps
Elevated FCB sediment levels in ponds can pose a risk to estuarine environments where molluscan shellfish are harvested if these sediments are resuspended and channeled during storm events. The sequestration of both metals and bacteria in ponds may have the potential to result in increased levels of antibiotic resistance in bacteria residing in these environments. Topics that should be further studied include:
• Alterations in genes of pond bacteria associated with exposure to different antibiotics and chemical contaminants. • Potential for lateral gene transfer among different bacterial species including E. coli (shellfish), Enterococcus (contact recreation), and Vibrio bacteria (shellfish and wound infections). • Potential for ponds to be hospitable environments for the propagation of antibiotic-resistant microbes, and the role, if any, legacy contaminants may play.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 65 3.5 Contaminants of Emerging Concern (CECs) CECs are those pollutants that are not currently included in mandated routine monitoring programs, therefore there are no SQGs or water quality guidelines for these contaminants. However, CECs are a growing environmental issue due to their high-volume usage, potential for toxicity in non-target species, and increasing occurrence in the environment. These include pharmaceuticals and personal care products (PPCPs), nanomaterials, and industrial chemicals such as flame retardants and poly- and perfluorinated alkyl substances (PFAs) (Shaw & Kannan 2009; Howard & Muir 2010; Scott et al. 2012). CECs could pose a significant risk, requiring future regulation, depending on their potential for ecotoxicological and other health effects.
The principal focus of the CEC research effort to date has been on diffuse agricultural runoff, while in terms of urbanization, research has almost exclusively addressed wastewater effluents and drinking water, with relatively little attention paid to runoff sources and discharges (Scott et al. 2012; Scott et al. 2016). The San Francisco Estuary Institute (SFEI) reported results of a collaborative study between the NOAA NST Program and the Southern California Coastal Water Research Program which found higher levels of CECs in runoff than in WWTP effluent (SFEI 2013). In addition, the co-occurrence of CECs with legacy pollutants such as trace metals, PAHs, and pesticides provides additional complexity in terms of mixture exposure to aquatic organisms. The flushing of CECs from impervious surfaces during wet weather conditions may be an important source, given the potential variety of everyday materials that contain or sequester xenobiotic pollutants (e.g., solvents in wood preservatives, garage services forecourts, industrial yards, discarded recreational drugs, drug syringes, leaching from weathered plastic materials).
The fate of CECs in the environment depends on their physicochemical properties, such as solubility in water and volatility; interaction with environmental components (e.g., sorption to nanoparticles, suspended sediments); degradation processes such as photolysis and microbial degradation; and environmental characteristics such as redox conditions (Anderson et al. 2012; SFEI 2013; Shaw & Kannan 2009). Sorption to organic matter and nanoparticles may result in the release of CECs to surface waters, while the affinity of CECs to associate with suspended sediments implies their potential for removal from the water column and subsequent concentration in pond sediments. Microbial degradation may then result in the formation of new metabolites, which may themselves be benign or harmful.
3.5.1 Pharmaceutical and Personal Care Products (PPCPs)
Pharmaceuticals are being used in large quantities by the medical community and in veterinary practices. After application, these compounds and their metabolites are released into the environment via various pathways such as WWTPs (primarily human use) or field runoff (veterinary or farm sources). As stated in several reviews (e.g., Daughton & Ternes 1999), the amount of PPCPs are equivalent to the mass quantities of agrochemicals, and a further complication of PPCPs in the environment is the constant introduction of new products. By design, PPCPs are biologically active, although in many cases the direct mode of action is unknown, so it can be assumed that organisms in the environment with similar targeted receptors are also affected. The task of predicting potential ecological effects is made even more difficult due to the fact that a single compound may have additional modes of actions at other target sites for which it was not intended. In fact, single PPCPs at low concentrations in the environment have been shown to cause measurable effects due to combination with other compounds (Daughton & Ternes 1999; Silva et al. 2002; Khetan & Collins 2007). Further challenges arise from the ability to observe adverse changes in ecosystems. Although acute toxicity is usually only reached at high, environmentally non-relevant concentrations, chronic effects should not be neglected, as these may be just as detrimental to a population in the long term (Fent et al. 2006; Vieno et al. 2007).
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 66 Results
PPCPs have also been measured in effluent from sewerage treatment plants in Charleston, S.C. and other locations around the U.S., with dominant contaminants measured including caffeine, triclosan, ibuprofen, and acetaminophen, all in the parts per trillion range (USGS 2002; Scott et al. 2016). Therefore, we may expect to measure these compounds in ponds where there is secondary treated effluent applied to land surfaces (e.g., golf courses and other spray irrigation locations). PPCPs pass through WWTPs without major degradation; current disinfection practices do not remove these compounds. Nationwide antibiotics were found at 48% of the sites sampled by USGS (2002). Cooper (2007) reported ponds reduced pharmaceuticals from sewage treatment plant effluent near Kiawah Island, S.C. No PPCPs were measured in sediments in S.C. ponds in any of the literature sources we reviewed for this study, but the antibiotic oxytetracycline was measured in surface waters in ponds (Scott et al. 2016). Oxytetracycline was Concentration (µg/L)
Figure 3.8 Oxytetracycline concentrations (µg/L) measured in secondary WWTP effluent land applied to a golf course in coastal S.C. (summarized in Scott et al. 2016). Note the detectable levels in the holding pond adjacent to the green and levels found in adjoining tidal creeks draining the golf course.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 67 a) View001 JEOL 1/1 Particle 9 Spot 2 2700 CrLa 2400 CKa SiKa 2100 NKa TiLa FeLa
1800 OKa FeLl TiLl AuMr 1500 SKa AgLb2 CrLl MnLa Counts AuMb 1200 AlKa AgLa MnLl CrKesc MnKesc AuMa 900 MgKa TiKesc AgMz AgLb KKb FKa CaKb FeKa PKa MnKa FeKesc NaKa AuMz
600 ClKa CrKa KKa CaKa AuLa MnKb FeKb AuLl CrKb TiKa TiKb 300
0 0.00 1.50 3.00 4.50 6.00 7.50 9.00
keV Acquisition Parameter Instrument : JEM-2100(HRP) b) Acc. Voltage : 200.0 kV JEOL 1/2 ProbeView000 Current: 1.00000 nA PHA mode Particles : T4 1 Spot 1 Real Time1000 : 86.05 sec Live Time : 58.11 sec Dead Time : 32 % 900 TiLa Counting Rate: 13067 cps Energy Range : 0 - 40 keV CKa TiLl 800 TiKa OKa 700 FeLa CrLl FeLl 600 NKa AgLb2 500 CrLa MnLa SiKa AuMr Counts AgLa MnLl CrKesc
400 AlKa FeKesc AuMa FKa TiKesc CaKa AgMz 300 FeKa MgKa PKa TiKb MnKesc MnKa AgLb KKb AnalysisStationAuMb ClKa
200 MnKb NaKa AuMz FeKb SKa KKa CaKb CrKb CrKa AuLl 100 AuLa
0 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 View000 keV JEOL 2/2 AcquisitionParticles Parameter 1 Spot 2 Instrument1000 : JEM-2100(HRP) Acc. Voltage : 200.0 kV Probe Current: 1.00000 nA PHA mode900 : MnLl T4 Real Time : 46.86 sec Live Time :CKa 38.65 sec
800 MnLa Dead Time : 17 %
Counting Rate: OKa 6209 cps
Energy 700Range : CrLa 0 - 40 keV FeKa 600 TiLl FKa AgLb2 CrLl
500 PKa Counts AuMr NKa AgLa FeLl CrKesc 400 SiKa TiLa FeLa AuMb AgMz TiKesc MnKb 300 CaKa MgKa AuMz MnKesc FeKesc MnKa AuMa ClKa AgLb KKb 200 FeKb AlKa NaKa CaKb SKa TiKb AuLl TiKa KKa CrKa CrKb AuLa 100 AnalysisStation
0 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 Figure 3.9 keV Acquisition Parameter Instrument : JEM-2100(HRP) Acc. Voltage : 200.0 kV Probe Current: 1.00000 nA PHA mode : T4 Real Time : 51.65 sec Stormwater Ponds in Coastal South Carolina: 2019Live TimeState of: 43.38Knowledge sec Report Dead Time : 15 % 68 Counting Rate: 5669 cps Energy Range : 0 - 40 keV
AnalysisStation View002c) JEOL 1/1
21000 TiLa 18000 CKa AlKa FeKa FeLl NKa SiKa 15000 OKa MnLa MnKb PKa AgLb2 TiLl
12000 AuMr 0.5 µm CrLl CrKesc Counts 9000 AuMb CrLa MgKa AgLb CaKa AuMa ClKa AuMz FeKb MnLl MnKa AgLa KKb 6000 MnKesc NaKa FeKesc 0.5 µm SKa FeLa CrKb KKa AgMz CaKb TiKesc TiKa TiKb CrKa AuLl
3000 AuLa
1.0 µm 0 0.5 µm 0.00 1.50 3.00 4.50 6.00 7.50 9.00 JEOL 1/1 View002 keV Date : 3/11/2016 Resolution : 512 x 384 ------21000 Instrument : JEM-2100(HRP) Acc. Volt. : 200 kV
Magnification18000 CKa TiLa : x 40,000 Dwell Time : AlKa 5.0 msec. FeKa
Sweep Count FeLl : 1 NKa SiKa 15000
Acquisition ParameterOKa MnLa Instrument : JEM-2100(HRP) MnKb PKa AgLb2
Acc. Voltage :TiLl 200.0 kV
Probe12000 Current: 1.00000 nA AuMr 0.5 µm PHA mode : T4 CrLl CrKesc RealCounts Time : 1211.91 sec Live Time9000 : 983.01 secAuMb CrLa MgKa
Dead Time : 19 % AgLb Counting Rate: 7848 cps CaKa AuMa ClKa AuMz
Energy Range : 0 - 40 keV FeKb MnLl MnKa AgLa KKb 6000 MnKesc NaKa FeKesc 0.5 µm SKa FeLa CrKb KKa AgMz CaKb TiKesc TiKa TiKb CrKa AuLl
3000 AuLa AnalysisStation
1.0 µm 0 0.5 µm 0.00 1.50 3.00 4.50 6.00 7.50 9.00
keV Date : 3/11/2016 Resolution : 512 x 384 ------Figure 3.9 Results of the transmission electron microscopy method for nanomaterials, which measures the difference Instrument : JEM-2100(HRP) Acc. Volt. : 200 kV in energy between the inner and outer electron shells, a characteristic of the atomic structure of the emitting element. Magnification : x 40,000 Dwell Time : 5.0 msec. Nanomaterials (NM) were detected in a) mixed land use pond in S.C. (Park Circle) associated with chromium and Sweep Count : 1 iron; b) a residential pond (Lake Edmond) associated with iron and titanium; and c) a golf course pond (Shadow Acquisition Parameter Moss) associated with titanium and iron. Instrument : JEM-2100(HRP) Acc. Voltage : 200.0 kV Probe Current: 1.00000 nA PHA mode : T4 Real Time : 1211.91 sec Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report Live Time : 983.01 sec Dead Time : 19 % 69 Counting Rate: 7848 cps Energy Range : 0 - 40 keV
AnalysisStation measured in ponds surrounding the fairway on a golf course where secondary treated sewerage was applied to the lawn (Figure 3.8). However, concentrations at these sites were well below those that pose a risk to the environment, as established for the broad class of tetracyclines (see Scott et al. 2016).
3.5.2 Environmental Nanomaterials (ENMs)
Nanotechnology is a rapidly growing, innovative technology that exploits the novel properties of ENMs to develop new products and enhance the performance of existing products (Christian et al. 2008; Baalousha et al. 2014). Outdoors, ENMs can be found in a wide range of applications such as scratch resistant surface coatings, fuel additives to enhance fuel efficiency, superior paints, hydrophobic surfaces to repel water and dirt, high-performance tires, antireflection layers for road signs and panels, and road markings (Adachi 2006; Van Broekhuizen 2009; Lee et al. 2010; Van Broekhuizen et al. 2011; Dylla & Hassan 2012; Yu et al. 2012; Ugwu 2013). As with any other technology, outdoor urban nanotechnologies are likely to create pollution and waste in receiving waters due to the degradation and erosion of nano-enabled products, and these streams may further aggravate pre-existing urban stressors (Wiek et al. 2013). Because ponds store sediments, this may lead to hot spots of ENMs in ponds and potentially in the sediments of receiving water bodies.
So far, most attention has been given to the characterization of occurrences and transformations of ENMs in WWTPs, as they are predicted to be one of the major conveyances of ENMs to the environment (Gottschalk et al. 2009, 2013). However, little attention has been given to the occurrence and transformations of ENMs and incidental nanomaterials, those unintentionally generated as a side product of anthropogenic processes, in urban runoff.
Results
No ENMs were measured in S.C. ponds in the published literature. Therefore, the authors of this chapter used transmission electron microscopy to conduct an exploratory analysis of nanomaterials in three Charleston ponds: a residential, a mixed land use, and a golf course pond. This revealed different types of nanomaterials including silica, iron oxides, and titanium dioxide in pond sediments (Figure 3.9). Silica NMs rich in chromium were found in the mixed land use pond (Figure 3.9a); titanium nanoparticles were identified in the residential (Figure 3.9b) and golf course ponds (Figure 3.9c). Further research is required to identify the different types of nanomaterials in ponds, their association with other contaminants such as trace metals and organics, the potential for these contaminants to be discharged into receiving water bodies, and their effect on these ecosystems.
3.5.3 Flame Retardants
Flame retardants are derived from anthropogenic sources and can be found in many applications. Currently, the largest source of these pollutants is brominated flame retardants that can be toxic and persist in the environment for long periods of time. At this time there is little information on how these chemicals impact microorganisms or their bioaccumulative effects within the food web (Segev et al. 2009).
Results
Weinstein et al. (2008) measured polybrominated diethylethers (PBDEs) flame retardants in sediments, which were detected in one out of 18 ponds (5.5%) and sampled at concentrations ranging from 30 to 72.8 ng/g. Higher concentrations have been measured in sediments (212 ng/g) and tissues (13,300 ng/g lipid weight in invertebrates)
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 70 from natural samples (Fair et al. 2007). The limited data has shown that generally PBDE concentrations in ponds are below analytical detection limits in most ponds, and higher concentrations were detected in estuarine sediments.
Research Gaps
With increased coastal flooding predicted due to sea level rise in the future (Union of Concerned Scientists, 2014), concerns have been raised about the potential for ponds to be impacted by sewerage overflows which may lead to additional CEC pollution sources within ponds.
• Identify, characterize, track, and quantify ENMs and NMs in all urban environmental compartments (i.e., air, impervious surfaces, and surface waters). • Investigate the fate, pathways, and transport of urban NMs into surrounding non-urban environments. • Develop analytical tools and methodologies to differentiate and quantify natural, engineered, and incidental NMs to determine the sources of NMs in the environment. • Assess the interaction and toxicity of NMs (and mixtures of NMs including microplastics carried by NMs) to all sectors of the biosphere within the urban environment. • Explore ways to mitigate and/or eliminate the most adverse bio-disrupting aspects of ENM and NM interactions within the urban environment. • Develop or revise regulations to protect environmental and human health in light of findings from these research areas on the occurrence of ENMs in the urban environment. • Re-investigate the geochemical cycle of metals, taking into account the significant occurrence of these metals in the form of NM components in the urban environment. • Assess the biological impacts of contaminant mixtures and their potential impact on human and ecosystem health in both ponds and estuarine habitats.
3.6 Summary and Recommendations Ponds in urban environments are often used as amenities by the public for boating, fishing, and swimming, and therefore have more uses other than designated BMPs for flood and water quality control. Risk assessment and routes of exposure to chemical, microbial, and emerging contaminants in ponds should receive more attention, as these BMPs are used throughout populated areas along the coast. Focus should be placed on management activities for both the environmental and public health risks posed by chemical and microbial contaminants. This review has shown there are environmental contaminants in ponds that may warrant action in terms of sediment loads, water quality concerns, and human exposure. For several chemical compounds, pond sediments had the highest concentrations when compared to concentrations measured in tidal creeks and estuarine ecosystems, indicating that they were somewhat effective in removing chemical pollutants and reducing loadings to estuarine ecosystems. Land use type was an indicator of contamination levels; all four types of urban ponds generally had higher contaminant concentrations for 29.1% of the contaminants assessed when compared to ponds from more pristine areas or to tidal creeks and estuarine systems. These urban ponds had the highest concentrations of 23% of PAHs and both legacy and contemporary use pesticides. Sediment contaminant levels varied among the urban pond types, with levels in commercial and residential
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 71 ponds often having higher levels as compared to mixed land use and golf course ponds. Residential areas and golf courses use over 80 different pesticides that have a wide range of safety, including some which should not be used near the water or in combination (e.g., chlorpyrifos and atrazine).
Fecal coliform levels in NPS runoff were generally higher than levels in both ponds and estuarine surface waters. Based on the available data, ponds can be effective in treating microbial contaminants in runoff via sedimentation processes. The high levels of chemical contaminants found in ponds may enhance antibiotic resistance in potentially pathogenic bacteria such as E. coli or Vibrio spp. The levels of antibiotic resistance in E. coli are three to four times higher in urban areas than in pristine waters, and future studies are warranted given the high rate of antibiotic resistance and increased rates of illness reported for Vibrio in coastal waters. Increased resistance may be conferred by interactions with trace metals or the loading of pharmaceuticals into our urban waterways. Only limited monitoring of CECs, including pharmaceutical products, has been conducted in S.C. ponds. Flame retardants were measured in one of 18 ponds sampled, and only at very low concentrations. Antibiotic oxytertacycline was found in golf course ponds where sewerage was applied via irrigation. Limited monitoring in S.C. showed the presence of iron, titanium, and chromium nanomaterials in ponds. We conclude that future studies should consider CEC monitoring; a potential program model would be the Southern California Coastal Water Research Program. Importantly, the cumulative ecotoxicological effects of contaminants concentrated in ponds on estuarine flora and fauna is largely unknown.
With regards to the question of whether ponds are effective structural BMPs for controlling downstream water quality, our review found ponds can be successful detention pools for particle-associated contaminants. Pond design can have much to do with the success of the pond at retaining these contaminants. Effective designs include: vegetated forebays that trap coarse sediments and allow small particles to be removed gradually in the main pond, vegetated littoral shelves, and multi-pond series as opposed to single pond designs. Additionally, soil type plays a role in pollutant removal. Though small particles may take longer to be removed from the water column, research indicates that some pollutants are disproportionately found to be associated with small particles; percent clay content was correlated with storage of several pollutant classes in S.C. pond sediments. The Lowcountry region of S.C.’s coast (Beaufort and Jasper counties) is typified by fine Class D soils, comprised of clay or silt with low infiltration rates, while in the Grand Strand region larger Class A soils that are sandy and have high infiltration rates dominate. Therefore, regional studies may prove beneficial for identifying how various stormwater BMPs perform under these diverse hydrological soil conditions. Because ponds are primarily designed to promote sedimentation and 90% of this occurs between storm events, we also need to consider the impact of increasing storm intensities and frequencies predicted as a result of climate change.
As shown in this review, pond sediment contaminant levels exceeded several SQGs, indicating the potential for toxicity to benthic and aquatic life if these sediments were discharged into the estuarine environment. Pond bottoms are especially vulnerable to resuspension during storms, and evidence from recent events, namely the 1,000-year flood in October 2015 and Hurricanes Matthew and Irma (2016 and 2017, respectively), have shown that stormwater systems can be overwhelmed by periods of intense rainfall. Therefore, pond designs should be required that effectively retain larger volumes, by increasing surface area to drainage volume, designing a meandering flow path, and allowing for depths sufficient to prevent sediment resuspension by winds. As discussed in Chapter 2, retention time is vital for ensuring ponds serve as both flood and water quality control structures. Additional potential for environmental or human exposure to pond sediments occurs during and following dredging operations. According to DHEC guidelines, ponds should be dredged when the volume of the permanent pool is reduced by 25% to ensure the basin can serve the
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 72 designed flood control. However, at present, there are no specific regulations in S.C. pertaining to the disposal of pond sediments, and dredged sediments are used for fill material. Thus, effective pond management strategies must evaluate the hazards posed by current sediment loads. This may include regulations that treat pond sediments as potentially hazardous wastes, because ponds can be “hot spots” for metals, pesticides, and other contaminants that have the potential to pose human health risks.
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Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 80 CHAPTER 4 – THE ECOLOGICAL FUNCTION OF SOUTH CAROLINA STORMWATER PONDS WITHIN THE COASTAL LANDSCAPE
Authors
Dianne I. Greenfield, Ph.D. Belle W. Baruch Institute for Marine and Coastal Sciences, University of South Carolina, Columbia, S.C. Marine Resources Research Institute, S.C. Department of Natural Resources, Charleston, S.C. Currently at the Advanced Science Research Center, City University of New York, New York, NY and the School of Earth and Environmental Sciences, Queens College, CUNY, Queens, NY
Erik M. Smith, Ph.D. Belle W. Baruch Institute for Marine and Coastal Sciences, University of South Carolina, Columbia, S.C. North Inlet-Winyah Bay National Estuarine Research Reserve, Georgetown, S.C.
Andrew W. Tweel, Ph.D. and Kimberly Sitta Marine Resources Research Institute, S.C. Department of Natural Resources, Charleston, S.C.
Denise M. Sanger, Ph.D. Marine Resources Research Institute, S.C. Department of Natural Resources, Charleston, S.C. ACE Basin National Estuarine Research Reserve
Corresponding Author Dianne I. Greenfield, Ph.D. ([email protected])
4.1 Background Development and increased impervious surface cover have numerous consequences for coastal ecosystems. One example, elevated runoff, increases the transport and volume of nonpoint source nutrient inputs, especially nitrogen (N) and phosphorus (P), into receiving watersheds and surface waters (Lewitus et al. 2003; Tufford et al. 2003; Drescher et al. 2007a; Sanger et al. 2015). Ponds control water quality impacts to adjacent receiving waters through the removal/retention of pollutants (nutrients, organic matter, sediments, bacterial pathogens, etc.), as they act as buffers between urban areas, residential and golf course communities, and surrounding water bodies (Lewitus & Holland 2003; Lewitus et al. 2003; Brock 2006; Guinn et al. 2014). In coastal S.C., ponds are typically small (< 1 – 10 acres; see Chapter 1), shallow (< 3 m maximum depth) (Drescher et al. 2007a, b; Smith 2012), and the waters span a wide range of salinities, fresh to estuarine, though freshwater ponds outnumber saline ponds (Lewitus et al. 2003, 2008; Drescher et al. 2007a, b), with salinity regime often related to the degree of direct (pipes) or subsurface (groundwater) connectivity with other ponds and/or nearby tidal creek estuaries (Bunker 2004; Brock 2006; Wisniewski 2014). The salinity and connectivities of these ponds directly impact the ecology of associated biota.
Ponds create unique ecosystems because they generally have reduced flushing capacity associated with high volume
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 81 residence times, making them susceptible to stagnation, particularly during warmer months, late summer through early fall (Lewitus et al. 2003, 2008; Bunker 2004; Vandiver & Hernandez 2009). Furthermore, they accumulate N and P from fertilizer runoff (Lewitus et al. 2003, 2008; DeLorenzo & Fulton 2009; Drescher et al. 2011b; DeLorenzo et al. 2012). As a result, they are natural “incubators” for the proliferation of algal blooms, many of which produce toxins or cause other adverse consequences, thus termed harmful algal blooms (HABs) (Lewitus et al. 2003, 2008; Siegel et al. 2011; Greenfield et al. 2013, 2014a). Ponds may also serve as valuable permanent and/or transient habitats for a wide range of species spanning multiple trophic tiers (microplankton to vertebrate predators). Given rapid and continued development, ponds have become integral features throughout the S.C. coastal landscape. Consequently, it is both timely and essential to evaluate ponds as functioning ecosystems (Sassard et al. 2014).
4.2 Framework In the “State of the Knowledge Report: Stormwater Ponds in the Coastal Zone” (Drescher et al. 2007a), information is provided regarding pond ecology, largely relating to nutrient loading and resultant eutrophication responses. Since that contribution, several advances have been made in our understanding of pond ecology that are directly relevant to ecosystem function within the coastal landscape and associated management strategies.
This chapter evaluates the current state of knowledge of ponds and their ecological function within the coastal landscape. To generate this updated review, a wide range of resource formats were evaluated, including primary literature, books, conference presentations (talk and/or poster format), technical reports, student theses, and websites. Citations were deemed appropriate for inclusion within this chapter if they met one or more of the following criteria pertaining to S.C. coastal ponds:
1. Described nutrient sources, inputs, or utilization, 2. Considered how abiotic factors (e.g., temperature, salinity) affect nutrient chemistry and/or biota, 3. Evaluated microorganism populations, dynamics, and/or food-web studies, 4. Assessed pond vegetation, 5. Evaluated invertebrate or vertebrate species and/or ponds as their habitats, 6. Considered how landscape characteristics drive biogeochemical cycling or biology within or among ponds, or 7. In cases where literature for Sotuh Carolina was limited, we addressed any item (1-6) using comparable regional pond systems (e.g., coastal Georgia, North Carolina, Virginia, and/or Maryland).
We realize that ponds are used as a Best Management Practice (BMP) for inland waters, other coastal states, the Midwest, and internationally. Thus, literature covered here is neither exhaustive nor may certain statements and conclusions herein apply to ponds in those systems. Accordingly, since the hydrology, landscape, and ecology of those systems differ markedly, only relevant studies from S.C. and regional states were included here. Our citations include 105 references as 67 primary literature sources, four books, eight conference presentations, 13 technical reports, three websites, and nine student theses. These are supported by an annotated bibliography (Appendix A4, see www. scseagrant.org/spsok). The following sections discuss how ponds act as ecosystems and their ecological relationships within the surrounding landscape. Highlights of major information gaps and associated recommendations for future directions are provided at the end of this chapter as well as at the end of individual sections.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 82 4.3 Ecological Function within the Coastal Landscape
4.3.1 Physical and Biogeochemical Processes
Ponds increase surface water volume and thus residence time, which has several consequences. For example, warm summer temperatures, shallow depths, and high residence times induce stagnation; this may result in depleted dissolved oxygen levels leading to hypoxia and even anoxia, particularly during the summer and early fall (Lewitus et al. 2008; Serrano & DeLorenzo 2008; Greenfield et al. 2009; Reed et al. 2016). Hypoxia is responsible for the majority (68%) of S.C. fish kills, followed by HABs (27%) then others (Greenfield et al. 2017). HABs and hypoxia may occur together, but blooms are associated with oxygen concentrations ranging from anoxic to hyperoxic (Lewitus et al. 2008; Greenfield et al. 2009, 2014b, 2015), depending on whether the bloom is developing, ongoing, or senescing. When phytoplankton cells actively divide during bloom development, they generate oxygen from photosynthesis (net autotrophy), but during senescence, bacterial remineralization increases and oxygen is consumed (net heterotrophy).
Pond biogeochemistry is highly complex, and recent work has helped transform our understanding of nutrient (notably N and P) cycling and associated microbial processes. For example, in urban ponds, particulate N and P contribute more to the total N (TN) and total P (TP) pools than forested creeks, which have relatively greater contributions of dissolved N and P to the total pools (Tufford et al. 2003). However, the availability of N and P to phytoplankton ultimately affects productivity because algae primarily utilize dissolved nutrient forms and ponds encompass a wide range of nutrient conditions (Drescher et al. 2011b; Smith 2012). For example, a study of 26 S.C. residential freshwater ponds spanning low- to high-density residential development, according to NOAA Coastal Change Analysis Program (C-CAP) land use classifications (Smith 2012, Smith et al. 2015), showed that average TN ranged from 287.9 to 3758.5 µg N L-1 while TP ranged from 3.7 to 394.0 µg P L-1. Though TN and TP concentrations were significantly correlated across these 26 ponds, TP was relatively more variable both across and within ponds. The relative contributions of particulate N and P to the total nutrient pools tended to increase with overall nutrient concentrations, likely due to a greater contribution of nutrients bound in phytoplankton biomass from the particulate pool.
While the relative importance of N and P to pond functioning was originally thought to be primarily driven by salinity, emerging evidence suggests that nutrient cycling processes are more similar in fresh and saline pond systems than previously believed. Specifically, in freshwater ecosystems, the classic paradigm is that lake productivity is usually limited by P availability (e.g., Dillion & Rigler 1974; Prarie et al. 1989), but more recent work suggests this is not always true (e.g., Abell et al. 2010). Consistent with the idea that freshwater productivity is often limited by P availability, phytoplankton biomass (chlorophyll a) in the above-mentioned 26 ponds was strongly correlated to TP concentrations, though experimental evidence suggests that the dependence of freshwater phytoplankton biomass on nutrient availability is more complex than a simple cause and effect relationship. As examples, during nutrient enrichment studies in several of the ponds described above, phytoplankton growth was stimulated by either N alone or, more commonly, by both N and P, rather than just P (Smith, unpubl. data). Similarly, Wisniewski (2014) found significant increases in phytoplankton numbers and biomass in response to N, but not necessarily P, additions using both inorganic (ammonium) and organic (urea) N-sources in fresh to brackish (0 – 5 psu) ponds, and responses were particularly augmented in urea-containing additions. These studies combined suggest that N can act as a limiting or co-limiting nutrient in fresh or nearly-freshwater pond systems. While bottle incubations, like any controlled
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 83 experimental design, have numerous well-known caveats (e.g., closed systems, limited duration, grazing), results are highly informative for assessing limiting nutrients and other trophic pathways in aquatic ecosystems.
Compared to freshwater ponds, brackish and saltwater ponds are primarily N-limited (e.g., Lewitus et al. 2008; Siegel et al. 2011; Greenfield et al. 2014a; Reed 2014; Reed et al. 2016), but growth and biomass of certain HAB species are enhanced by P (Greenfield et al. 2014a, 2015). Experimental evidence suggests that elevated N, especially urea, an organic N source, stimulates increases in phytoplankton biomass, particularly those of cyanobacteria, dinoflagellates, and other HAB species (Siegel et al. 2011; Reed et al. 2016). For example, Reed et al. (2016) conducted a two-year study of seasonal phytoplankton assemblage responses to three N-forms (ammonium, nitrate, and urea) with and without orthophosphate in a saline pond (mean 19.9 psu, range 11.3 to 32.7 psu). Results showed that N-additions, particularly urea, enhanced phytoplankton growth and HAB species abundances in ponds more than in less-developed landscapes (low to moderately developed tidal creeks), suggesting that ponds may be less resilient to nutrient loadings than comparatively less-developed systems. Furthermore, urea-fueled phytoplankton biomass resulted in greater contribution of phytoplankton-derived dissolved organic carbon (DOC) to the overall DOC pool in ponds and other developed systems than in less-developed tidal creeks (Reed et al. 2015). These findings have direct management relevance because greater than 50% of commercial fertilizers worldwide use urea (Glibert et al. 2006), so fertilization may alter the biogeochemical cycling of carbon in ponds. In sediments, total organic carbon (TOC) levels have been shown to vary widely among ponds (Weinstein et al. 2008), though this variability was not significantly related to land use or sampling location. Furthermore, the differences between fresh and salt water systems need exploration, particularly regarding N-cycling. For example, denitrification rates (reduction of nitrate to other N-forms, ultimately producing dinitrogen (N2) are more rapid in freshwater pond sediments than saline wetlands (Aelion & Warttinger 2010). However, denitrification may be enhanced by pond sediments in both fresh and brackish systems (Drescher 2005) because reaction rates are influenced by hydrology and N-loading (Strosnider et al. 2007), ultimately influencing the N-pool.
Research Gaps
• Elucidate the parameters (e.g., extent, duration) of hypoxic and anoxic events and their physical, biogeochemical, and climatic regulation. • Quantify heterotrophic remineralization and respiration rates. • Evaluate nutrient sources and inputs and nutrient biogeochemistry processing within and among ponds. • Understand the mechanisms by which management practices (including but not limited to fertilization) affect biogeochemical cycling (particularly N, P, and C) in ponds. • Integrate nutrient dynamics with hydrological factors (surface and groundwater inputs, flow rates, and retention times, etc.). • Nutrient (both form and concentration) utilization by algae and subsequent bloom dynamics and HAB/toxin proliferation.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 84 4.3.2 Vegetation
Managers commonly use vegetation around ponds to establish buffer zones, provide habitat for fauna, and enhance aesthetic value (e.g. Drescher et al. 2007, 2011a; Strosnider et al. 2007). Pond vegetation is broadly characterized as submerged, floating, or emergent (www.clemson.edu/extension/hgic/plants/other/landscaping/hgic1714.html; Rollins 2012; Rollins et al. 2012). Submerged plants (e.g., invasive Hydrilla, Eurasian watermilfoil) are rooted to the bottom of ponds and serve both management and ecological roles, such as stabilizing soils to prevent erosion and providing habitat for fish, turtles, and other macrofauna. Floating plants (e.g., alligatorweed, duckweed, water hyacinth) are common in S.C. and can rapidly cover a pond, thereby blocking sunlight to the benthos, potentially causing oxygen depletion within ponds. Monitoring and fish kill responses have shown positive associations between floating plants, such as duckweed, and hypoxia (Greenfield et al. unpubl. data). To control certain invasive vegetation, such as Hydrilla, non-native tilapia and/or triploid grass carp are commonly introduced to ponds (Rollins 2012). These fish species effectively graze several submerged and floating vegetation species, but they are comparatively less effective at controlling duckweed, except at salinities that are sub-optimal for rapid duckweed growth (N. Shea, pers. comm.). Consequently, herbicide application is the most commonly used method for duckweed management. Emergent vegetation, such as cattails and Phragmites, is the most commonly found pond vegetation category, and these species can sometimes cover expansive areas and mitigate shoreline erosion (N. Shea, pers. comm.). Beyond management, there is limited information on the ecological function(s) of vegetation in S.C. ponds, particularly how species (native and non-native plants) affect N and P cycling and faunal habitat. Studies in North Carolina have shown that pond and streamside vegetation can take up nutrients, thereby reducing levels in the water (Borden et al. 1997; Mallin & Wheeler 2000; Mallin et al. 2002), though removal efficiency is mediated by pond geometry (e.g., size, shape, depth) (Borden et al. 1997). Perimeter vegetation has also been shown to play an important role in carbon sequestration and increases macrofaunal diversity by creating vital habitat (Moore & Hunt 2012). Furthermore, the rhizosphere has been shown to be particularly important for N-cycling and removal through denitrification and ANAMMOX (ANaerobic AMMonium OXidation), particularly during summer (Song et al. 2014). However, the biogeochemical roles of plants in S.C. ponds are substantially understudied but likely highly important for nutrient cycling. Understanding the ecological role(s) of pond vegetation remains a notable gap in our knowledge of pond ecological function.
Research Gaps
• Thorough assessments of native vs. non-native plant species in coastal S.C. ponds. • Assessments of nutrient uptake by plants (forms and rates). • Influence of seasonality, drought, and/or flooding on vegetation. • Evaluations of how soil type and maintenance (dredging, erosion control, construction, etc.) affect the growth and productivity of surrounding vegetation. • Importance of vegetation as critical macrofaunal habitat. • Relative importance of herbaceous vs. woody vegetation as perimeter species for providing habitat and/or erosion control.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 85 4.3.3 Microflora and Fauna
Bacteria
Ponds commonly act as reservoirs for microscopic plankton (viruses, bacteria, algae, and zooplankton) because microorganisms often thrive in the water column and/or sediment environments that ponds provide (Lewitus et al. 2008; DeLorenzo & Fulton 2009; Greenfield et al. 2014b). No information was found on viruses in S.C. ponds during this review, but a Virginia study showed virus loads positively correlated with runoff (Williamson et al. 2014). Bacteria that pose concerns for public health, such as fecal coliform and pathogenic Vibrio spp., can reach high concentrations in S.C. ponds (Hathaway et al. 2009; DeLorenzo et al. 2012; Greenfield et al. 2014b, 2017b). In fact, Vibrio spp. levels in saline ponds can be enhanced by algal blooms and organic matter loading (Greenfield et al. 2014b, 2017b), suggesting that HABs at times act as a vector for Vibrio spp. proliferation. Bacteria, particularly fecal coliform, are also introduced to ponds by wildlife, such as the American alligator (Johnston et al. 2010), though other taxa, such as birds, are also likely contributors. Finally, some bacteria may be resistant to antimicrobial management, as DeLorenzo et al. (2012) found that 90% of 540 tested E. coli isolates collected from S.C. coastal ponds were attributed to pet waste and resistant to one or more antibiotics.
Algae
Pond algae have two major forms: filamentous and non-filamentous (phytoplankton). Filamentous algae are primarily cyanobacteria, such as fresh and saltwater species of Lyngbya. The frequency and geographic extent of filamentous cyanobacteria blooms is increasing dramatically across the East Coast (O’Neil et al. 2012; Paerl & Paul 2012). In addition, eukaryotic (often multi-nucleate) plant species (Viridiplantae) can produce substantial filamentous growth, and examples in S.C. ponds (usually freshwater) include Pythophora and Hydrodictyon. While well-studied elsewhere, research on filamentous algae is largely missing for S.C. ponds.
Phytoplankton are comparatively better studied because dense, pervasive, and often toxic blooms are a common feature of ponds (Lewitus & Holland 2003), and long-term monitoring has identified ponds as HAB hot spots, often linked with fish kills (Greenfield et al. 2017a). Blooms occur because ponds have poor flushing and accumulate runoff which makes them susceptible to eutrophication (Lewitus et al. 2003, 2008; Drescher et al. 2007b; DeLorenzo & Fulton 2009). HABs are most common from late spring through mid-fall (Hayes & Lewitus 2004; Hayes et al. 2008; Greenfield et al. 2009) and can present serious public health and environmental concerns. Blooms can cause fish kills and produce a range of toxins that induce gastroenteritis, dermal or respiratory ailments, and/or other health effects (reviewed in Chorus & Bartram 1999; Anderson et al. 2008; Heisler et al. 2008; O’Neil et al. 2012). Algal blooms and incidences of HAB species are more frequent in ponds surrounded by developed and/or managed land (e.g., residences, golf courses) than less developed land (Borden et al. 1997; Brock 2006; Reed 2014; Reed et al. 2016), likely due to higher nutrient inputs from fertilizers, pet waste, and wildlife (geese) (Lewitus et al. 2003, 2008; Serrano & DeLorenzo 2008; Siegel et al. 2011; Greenfield et al. 2014a). Although turf management and fertilizer application practices for areas draining into many pond networks are proprietary and consequently unavailable for this review, urea-based fertilizers comprise greater than 50% of nitrogenous fertilizers worldwide, and the use of urea in fertilizers is predicted to increase (Glibert et al. 2006). Thus, it is feasible that urea-based fertilizer application fosters HAB proliferation in S.C. ponds, but this hypothesis requires further testing. Overall, the capacity for microbes to utilize N and P, and their respective metabolic rates, is poorly studied but critical for understanding how nutrients are cycled
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 86 within and among pond systems. A mechanistic understanding of how nutrients drive blooms is lacking, as are further studies involving bloom management.
HABs
Major HAB taxa in S.C. ponds often include cyanobacteria, raphidophytes, dinoflagellates, and diatoms, though prymnesiophytes and euglenophytes are also common. HABs have been associated with 27% of fish kills in S.C. ponds (Greenfield et al. 2017a). Cyanobacteria are responsible for the largest number of toxic HABs worldwide (Chorus & Bartram 1999), and they thrive in warm, nutrient-rich, stagnant conditions, such as ponds (Paerl et al. 2001; Lewitus et al. 2008; Greenfield et al. 2014a). Cyanobacteria HABs span the entire range of coastal salinities (fresh to marine) and can produce numerous toxins. Commonly found genera/species include but are not limited to Anabaenopsis, Microcystis aeruginosa, M. flos-aquae, Oscillatoria, Cylindrospermopsis, Aphanizomenon, Anabaena, and Pseudanabaena (Lewitus et al. 2003; Brock 2006; Serrano & DeLorenzo 2008; Siegel et al. 2011; Greenfield et al. 2013, 2014a; Wisniewski 2014; Dearth 2017). Cyanobacteria toxins detected in S.C. lakes and ponds have been associated with human health effects. For example, during the summer of 2014, an adult male suffered a rash and swelling of the arm in response to a bloom of Lyngbya sp., a filamentous cyanobacterium in a freshwater lake that tested positive for lyngbyatoxin (Greenfield et al. unpubl. data). In ponds, the most commonly-detected toxin is microcystin, a hepatotoxin (Sivonen & Jones 1999) that can induce gastroenteritis, liver failure, and/or death (Pouria et al. 1998; Falconer 2005). During June 2000, a 7-year old girl waded in a S.C. coastal pond with a highly toxic (greater than 1,000 µg L-1 microcystin) M. aeruginosa bloom and subsequently developed a severe body rash and respiratory ailment leading to a S.C. Department of Health and Environmental Control (DHEC) water posting (R. Ball, pers. comm.). Microcystin values exceeding 1,000 µg L-1, though rare, have been reported elsewhere in coastal S.C. during dense M. aeruginosa blooms (Brock 2006; Dearth 2017), but more typical values range 1 to approximately 100 µg L-1 (Brock 2006; Greenfield et al. 2013). For reference, the provisional guideline for drinking water issued by the World Health Organization (WHO) of the most lethal and common toxin, microcystin-LR, is 1 µg L-1, and the WHO classifies microcystin concentrations ranging from 10 - 20 µg L-1 and 20 - 2,000 µg L-1 as posing moderate and high risks, respectively, for probable acute health effects in recreational waters (www.epa.gov/cyanohabs/world-health- organization-who-1999-guideline-values-cyanobacteria-freshwater).
Raphidophytes are commonly associated with fish kills, particularly the species Chattonella subsalsa, C. verriculosa, Fibrocapsa japonica, Heterosigma akashiwo, and Viridilobus marinus (Lewitus et al. 2003, 2004, 2008; Keppler et al. 2006; Reed 2014; Greenfield et al. 2015; Greenfield et al. 2017a). For example, raphidophytes were associated with 40 blooms and subsequent fish kill events between the months of June 2014 and August 2015 alone (Greenfield et al. 2015). Lysosomal destabilization (a sublethal effect) was observed in eastern oysters following exposure to C. subsalsa and F. japonica bloom water (Keppler et al. 2006), indicating that raphidophytes can exert deleterious effects on several animal taxa. In S.C. ponds, raphidophyte blooms are associated with low N to P ratios but high overall nutrient concentrations (Lewitus et al. 2004, 2008; Greenfield et al. 2015). Populations may be further regulated by microbes, as raphidophyte growth may be enhanced by certain bacterial assemblages (Liu et al. 2008a) or limited by algicidal species (Liu et al. 2008b). Dinoflagellates of the toxic genus Pfiesteria were documented in S.C. ponds and estuaries during the 1990s and 2000s, in some cases associated with fish kills (Lewitus et al. 2002, 2003; DeLorenzo & Fulton 2009). Pfiesteria blooms have not been reported in S.C. ponds since the previous DHEC State of the Knowledge report, but other dinoflagellate species, such as Karlodinium veneficum, Prorocentrum minimum, Protoperidinium quinquecorne, and Kryptoperidinium foliaceum, are common bloom-formers, either alone or as part of a multi-specific
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 87 assemblage (Kempton et al. 2002a, b; Lewitus et al. 2003, 2008; DeLorenzo & Fulton 2009; Greenfield et al. 2014a). Finally, blooms of the diatom Pseudo-nitzschia have been observed with increasing frequency in ponds and across the S.C. coast (Goodson et al. 2011; Reed 2014; Reed et al. 2016; Sitta et al. 2018). This is cause for substantial concern because several species of this genus produce the neurotoxin domoic acid, which is responsible for amnesic shellfish poisoning as well as the largest harvest closure for razor clams and Dungeness crabs along the Pacific coast in history (summer to fall of 2015).
Despite increasing knowledge of the extent of HABs in ponds, major gaps exist in our ability to accurately detect and predict a bloom’s onset. A more thorough understanding of bloom processes, as well as the development and application of tools and technologies that rapidly characterize HABs, microbes, and other pathogens, is badly needed to safeguard public health. Current algal bloom management practices include but are not limited to aerators, chemical algicides, and vegetation (Halfacre et al. 2007; Greenfield et al. 2014a; Hehman 2014). A before and after study of aerator installments in S.C. ponds showed that aerators improved (increased) water dissolved oxygen levels but did not significantly affect nutrient concentrations or phytoplankton assemblages (biomass, community composition, or primary productivity rates) (Hehman 2014). During a combined field and laboratory study using pond bloom water, Greenfield et al. (2014a) showed that both copper and peroxide-based algicides controlled cyanobacteria numbers and biomass. However, toxins (microcystins) merely transitioned from intracellular to extracellular fractions as cells lysed due to chemical exposure. Moreover, total water toxin levels were not significantly different from controls (no algicide), suggesting that algicides may visibly control blooms, but they do not mitigate toxicity.
Examples of future directions should include the development of technologies enabling early-warnings and characterization, such as by molecular methods that detect and quantify HABs and other microorganisms (Greenfield et al. 2008; Doll et al. 2014; Dearth 2017). An emerging research priority and management need is to understand how molecular and genetic factors drive species assemblages, population structure, and responses to environmental conditions. With the emergence of novel genomic and related “omic” technologies (e.g., metabolomics, proteinomics, transcriptomics), scientists have the capacity to elucidate a detailed, mechanistic understanding of species populations and processes, at population, individual, and sub-cellular levels. Studies using genomics tools to answer questions about S.C. pond ecosystems are currently sparse.
Zooplankton
It is widely known that larger zooplankton (mesozooplankton, > 200 µm in length), such as copepods, play major ecological roles in aquatic ecosystems by exerting “top-down” grazing pressure on phytoplankton and microzooplankton (20 to 200 µm). Surprisingly, during this review we found almost no information on mesozooplankton assemblages and grazing for S.C. ponds. Since grazing may be central to bloom regulation, this is a significant information gap. Hayes et al. (2008) showed that microzooplankton consume phytoplankton during dilution experiments, but otherwise, information on the ecological role(s) of zooplankton in S.C. ponds, or how their distribution(s) vary along environmental gradients (e.g., salinity, connectivity with other ponds and tidal creeks), is lacking. However, studies of Maryland ponds have shown that zooplankton community diversity is affected by salinity and dissolved oxygen concentrations (Sokol et al. 2015), suggesting that ambient environmental conditions are important.
The vast majority of information cited above is derived from monitoring and event-response activities. Despite the critical importance of such programs for evaluating pond water quality and identifying incidences of public and
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 88 environmental health concerns there remain numerous gaps in our understanding of microorganism processes. Virtually nothing is known about the role(s) of grazers on microbial and phytoplankton pond assemblages. New information shows that zooplankton grazing influences seasonal phytoplankton biomass and community composition in S.C. tidal creeks (Sitta et al. 2018), with microzooplankton grazing exerting a substantially greater influence on phytoplankton assemblages than mesozooplankton, but similar studies are lacking for ponds.
Research Gaps
• Population dynamics of bacterial pathogens. • Understanding of controls on filamentous algal growth. • Evaluations of microbial interactions and regulatory pathways, such as viral or bacterial-mediated control of algae or allelopathy. • Inter- and intra-specific competitive interactions. • Influence of seasonality and climate on algal and microbial processes. • Molecular and “omics” tools and other technologies enabling rapid assemblage characterizations, ecophysiology studies, and predictions of HABs and other pathogens. • Transcriptomics to elucidate species and genetic diversity within and among systems. • Greater understanding of the drivers of environmental compound production by microorganisms and/or other processes. • Understanding of the interactions between viruses, bacteria, algae, and potentially other trophic tiers. • Assessments of zooplankton communities, both meso- and micro-zooplankton species.
4.3.4 Macrofauna
Invertebrates
Ponds in coastal S.C. are not primarily designed to create habitat; however, they nevertheless support insects, invertebrates, fish, reptiles, and birds through infaunal, demersal, and pelagic food webs. A major finding from this review was that information on invertebrate and vertebrate ecology, including parasites, within S.C. ponds is generally lacking, highlighting this as an area where considerable research is needed. Few studies on insects were noted, though available literature suggests that mosquito larvae thrive in the warm, stagnant conditions offered by ponds (e.g., Hunt et al. 2005; Gingrich et al. 2006; Ellis et al. 2014). However, managers have suggested that mosquito larvae are not a major issue in S.C. ponds because they are often and effectively controlled by fish (e.g., Gambusia) (N. Shea, pers. comm.). Additionally, frogs are well-known consumers of mosquito larvae, but no literature was available describing their role consuming larvae specifically in S.C. ponds. These separate lines of evidence underscore that further investigation into the potential role of ponds as mosquito larval habitat is needed.
Amphibians and Reptiles
Amphibians are well-known to be sensitive to urbanization because they require both terrestrial and aquatic resources,
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 89 are sensitive to ecosystem disruption, and are often outcompeted by exotic species. Surveys have noted amphibians in S.C. ponds (Holt et al. 2015), but research is limited. However, other studies indicate that amphibians are impacted by pond construction. For example, frogs use ponds as breeding habitat (Brand & Snodgrass 2010), and ponds near Charlotte, N.C. were inhabited by up to 12 anuran species (Brix-Raybuck et al. 2010), including all but one species typically found in the region (Dorcas & Gibbons 2008). Presence of anurans in ponds is negatively associated with distance from the nearest riparian zone (Simon et al. 2009; Brix-Raybuck et al. 2010). Microcosm experiments comparing frog species tolerant of urbanization (American bullfrog, Bufo americanus) to non-tolerant species (wood frog, Rana sylvatica) exposed to pond sediments, containing elevated metals and chlorides, resulted in 100% mortality of R. sylvatica embryos compared to B. americanus, which only experienced sub-lethal effects (size reduction at metamorphosis) (Snodgrass et al. 2008). Although sediment characteristics may pose deleterious consequences, Massal et al. (2007) found that N-levels in Maryland ponds were not high enough to cause frog mortality. These studies underscore the importance of surrounding landscape characteristics for amphibian populations. Surveys of urban, golf course, and farm ponds in N.C. showed these systems host a range of turtle species, with relative abundances positively correlated with pond area, and nesting frequency negatively associated with extent of anthropogenic use (e.g., sidewalks, fairway) (Failey et al. 2007; Foley et al. 2012). Ponds are also commonly used as habitat for the American alligator (Alligator mississippiensis) (Johnston et al. 2010; N. Shea, pers. comm.).
Birds and Fish
The infaunal and demersal food webs are most likely the dominant components; however, ponds are often stocked with fish and attract wading birds and gulls (CIDEEP Report 2009; Rollins 2012; Ellis et al. 2014). In S.C., one unpublished study assessed bird usage of a select number of ponds (Nolan, pers. comm.). Similar research has been conducted in other states including Florida and Delaware (e.g., Wall 2006; Sloan 2008). Virtually nothing is known about how S.C. ponds affect bird habitat quality and use, particularly by migratory birds that may rely on S.C. coastal habitats during seasonal stop-overs. In one Maryland study, redwinged blackbirds (Agelaius phoeniceus) were found to nest in ponds located in commercial, residential, highway, and wetland (reference) areas, though nestling health was negatively impacted by sediment zinc concentrations (Sparling et al. 2004). Finally, it is well-known that ponds are commonly stocked with fish (Drescher et al. 2007a; Halfacre et al. 2007; Rollins 2012), often to mitigate growth of certain vegetation (described earlier), but little is known about how fish use ponds for breeding habitat. Some species, like the economically-important and catadromous American eel (Anguilla rostrata), have been collected from S.C. coastal ponds (S. Arnott, pers. comm.), though the extent to which eels use ponds as habitat is unknown.
Research Gaps
• The presence and impact of parasites on host populations and physiology. • Influence of bivalves and other suspension feeders on pond water quality. • The diversity and richness of macro-flora and fauna, including reproductive and migratory patterns. • Assessments of benthic faunal communities (annelids, nematodes, and others) and their influences on sedimentary processes. • The role of amphibians for regulating insect populations, especially given the global decline of amphibians and potential impact of management practices, such as pesticide use for mosquito control, on these taxa. • How habitat impacts reptiles and thus the presence of higher trophic tiers.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 90 • Assessments of ponds as nursery habitats or refugia for fish. • Tidal influences on animal migratory patterns (e.g., fish and invertebrate larvae). • Habitat quality for nesting and migratory bird species, including waterfowl. • Using biomarkers to identify responses including, but not limited to, stress responses across trophic levels.
4.3.5 Coastal Landscape
The construction of ponds has replumbed the way water moves in coastal S.C., as stormwater that previously flowed across the land surface or infiltrated through the soil is now directed through stormwater infrastructure designed primarily to dampen flow but also to improve water quality by retaining sediments and other pollutants, as discussed in the preceding section. The ecosystems and habitats represented by ponds are a direct result of the development of human systems, as there are essentially no natural, open-canopy ponds or lakes in the southeastern coastal plain. The typical hydrology of this area is one dominated by groundwater flow through a shallow surface aquifer, with upland surface waters largely limited to forested wetlands draining to blackwater creeks. Coastal development generally leads to the loss of pervious surfaces that allow rainwater to infiltrate to groundwater. Construction of ponds increases the volume of surface water and thus increases the overall residence time of surface water on the landscape.
Very little is known about how these ponds fit within the landscape, including their relationships to soil type and drainage or proximity to receiving water bodies and other sensitive coastal habitats. Their connectivity with receiving waterbodies and how their placement within the watershed might impact their ecologic function within the landscape is largely unknown and likely complex. Their role in altering ecological function within the broader coastal landscape may occur either indirectly through changes in hydrology or material transport, or directly through the creation of habitat types that previously did not exist in this region.
Transport of materials and organisms in and out of ponds has a number of consequences for adjacent systems. For example, levels of dissolved nutrients, HABs, and pathogenic Vibrio spp. in ponds can mimic concentration trends recorded in receiving tidal creeks (Greenfield et al. 2009, 2014, 2017), suggesting that ponds can be sources of these and potentially other constituents. Conversely, DeLorenzo et al. (2012) found that fecal coliform levels were higher in receiving tidal creeks than associated ponds, suggesting that ponds may have been removing bacteria. This is partially due to direct deposit of fecal bacteria in creeks by wildlife. Many studies show that ponds can exert significant removal rates for suspended sediments and fecal coliform (Wu et al. 1996; Borden et al. 1997; Comings et al. 2000; Mallin et al. 2002; Hogan and Walbridge 2007; Hathaway et al. 2009; Krometis et al. 2009; Huda & Meadows 2010; Moore 2010; Hathaway & Hunt 2012; Smith & Peterson, unpubl. data). Pollutant removal capabilities are discussed in more detail in Chapters 2 and 3. Ultimately, ponds are constructed aquatic ecosystems designed specifically to meet the stormwater management requirements associated with development or other land disturbing activities.
Detention ponds are, by far, the most frequently used stormwater management practice in the S.C. coastal zone, and they link upland runoff to coastal aquatic ecosystems through distinct outlet structures. In larger development projects, ponds are often created in linear series along natural drainage paths or are interconnected through a network of underground pipes. Recent stormwater runoff modeling work has allowed quantification of the relative effects of soil type, surrounding land use, elevation, and potential changes in climate on runoff volume and timing (Blair et al. 2014). In the context of coastal development and associated ponds, this modeling demonstrates the large effect that
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 91 position within the landscape (e.g., elevation gradient, soil type, vegetation) can have on the quantity and timing of stormwater inputs to ponds. For instance, the conversion of a forested coastal watershed to an urban watershed can, at a minimum, triple the volume of water flowing across the landscape that would have otherwise infiltrated or evapotranspired.
Of particular concern, from an environmental impacts perspective, are those ponds immediately adjacent to the land margin and having direct tidal exchange with coastal waters. The proportion of total water flow from uplands to the coastal zone that is collectively routed through ponds is currently unknown. Likewise, the extent to which groundwater exchange represents a significant biogeochemical link between ponds and other coastal aquatic ecosystems remains an open question. Coastal pond discharge is typically linked to tidal creek and open water sub- systems, although in certain areas, especially the greater Myrtle Beach region, ponds can be connected directly to open beach environments through coastal swashes and discharge pipes. Coastal S.C. water bodies, especially tidal creek headwaters, are sensitive to upstream inputs (Holland et al. 2004; Sanger et al. 2015) and the potential relationship between ponds and the receiving waterbodies has been discussed above.
Furthermore, these relationships between ponds and the surrounding landscape likely vary spatially. As a general trend in S.C. and other flood-prone landscapes, higher areas less vulnerable to flooding are generally developed first, with subsequent development expanding into wetlands (e.g., downtown Charleston, New Orleans). As these areas become developed, newer development often occurs in the previously undesirable lower-lying areas (Vandiver & Hernandez 2009). These low-lying ponds are more likely to be impacted by marine processes including tidal exchange, influx of seawater, and rising sea levels. Influx of seawater to freshwater systems, for instance, has been observed to significantly alter nitrogen cycling (Aelion & Warttinger 2010). This presents a major potential shift in pond function and performance, which may be exacerbated by aging stormwater infrastructure (S.C. Sea Grant Consortium 2009).
The identification of these low-lying ponds, and an improved understanding of how their function may change over time as tidal connectivity increases, is needed to better understand, plan, and manage pond function in the coming decades. Many of these questions could be addressed by assessing present pond function along elevation gradients with various levels of tidal connectivity. Some of these findings could be scaled up by means of a detailed analysis of pond placement and associated soil, land use, and proximity to other habitats within the landscape.
Research Gaps
• Understand the associations between ponds and surrounding landscape, especially coastal connectivity to ponds. • The landscape itself (elevation, flooding), and related consequences for biota. • Critical assessment of the impact of scale (pond size and related dimensions) on the ecological function.
4.4 The Future of Pond Ecosystems Water temperature, salinity, connectivity, and rates of exchange are primary factors regulating ponds and associated organisms, and the ranges of these parameters will likely shift in the future. For much of the Atlantic coast, climate predictions entail longer, warmer summers (e.g., Cronin et al. 2003; Najjar et al. 2010), and precipitation events may
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 92 be shorter and more intense (Meehl et al. 2007), affecting the rates and volumes of stormwater runoff as well as water column stability through buoyancy-increased stratification. Since ponds are prone to stagnation, these physical and climatic processes may enhance bottom hypoxia, particularly during summer, affect microbial processes rates, enhance HAB development, and increase the numbers of fish kills. In fact, numerous lines of evidence suggest that future climate scenarios favor algal bloom development. For example, the frequency and severity of HABs are increasing in response to warming and eutrophication (Paerl & Huisman 2009; O’Neil et al. 2012). Although nutrients, particularly N, are major drivers of bloom formation (Paerl et al. 2014), remarkably little is known about how climate and global change, alone or combined with nutrient enrichment, will impact HAB toxicity and the tendency for blooms to both form and persist. Moreover, the extent to which a changing climate will impact bacterial respiration rates and other higher trophic level processes, such as the reproductive cycles of macrofauna through earlier and warmer summers, is entirely unknown. These represent critical gaps in our understanding of ponds, and filling these gaps would provide critical information to inform effective coastal management strategies.
Changes in sea level, temperature, and precipitation patterns associated with climate change or other processes would be expected to further alter pond function and their relationships between adjacent ecosystems both upstream and downstream. Future management of these systems will need to address these changes, but in order to do so a number of unanswered questions remain regarding the associations between these pond systems and the surrounding landscape. Arguably, the most critical challenge facing researchers and managers in coastal low-lying regions, such as S.C., is how to adequately prepare for future climate and sea level scenarios. The relative influences of development patterns, landscape use, and climate change on pond processes are virtually unknown. Since sea level is predicted to continue to rise, and many coastal ponds are directly impacted by tides, salt water intrusion, and numerous other physical, chemical, and biological factors, this represents a key gap in our understanding of how managers and residents can prepare for future conditions. Related, a major information gap is understanding how climate change, including potential increases in the frequency and intensity of precipitation events, and sea level rise affect ponds.
Invasive Species
A serious concern is the potential for ponds to host exotic species and parasites, as they may alter aquatic food webs and overall ecosystem health. Invasive applesnails (Ampullairiidae spp.) are increasingly problematic across the Southeast due to high grazing rates on macrophytes (Horgan et al. 2014; www.dnr.sc.gov/invasiveweeds/snail.html). A survey of 200 coastal S.C. ponds found 18% were infested by applesnails, and population numbers are believed to be growing. Although their statewide distribution is not currently known, the extent to which applesnail, and other invasive species, populations may expand is an area of ecological concern.
Research Gaps
• Knowledge of how climate change will impact biogeochemical cycling and remineralization rates within pond waters and sediments. • Inter- and intra-specific population variability and associated responses to environmental factors (e.g., nutrients, temperature, salinity, toxin production). • Influence of global change and sea level rise on pond function.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 93 4.5 Summary and Recommendations Despite advances in our understanding of S.C. pond function since the Drescher et al. (2007a) State of the Knowledge report was issued, numerous and significant gaps remain in our understanding of pond ecology, and how they function within a complex coastal landscape. A surprising outcome from this review was just how little is known about the processes and both biological and physical linkages among and between ponds. For example, do S.C. ponds impact higher trophic levels and, conversely, the role of higher trophic tiers and food web interactions in pond function? Many gaps can be broadly described as needs for integrative studies evaluating the interactions between environmental parameters that drive pond ecosystems, such as research that considers seasonal and/or climate trends. Other notable gaps include studies integrating basic ecological principles. In particular, studies focusing on competitive and/or allelopathic interactions, predator/prey relationships, species’ migration, breeding, and invasions, diversity assessments (both species and genetic/population) are almost entirely absent. Numerous ongoing monitoring efforts collect static and bulk measurements of various water quality parameters. These programs are highly valuable for assessing long- term trends and identifying incidences where water quality becomes problematic for public and/or ecological health. However, monitoring programs are not designed to evaluate processes nor do they adequately achieve that goal. In fact, process studies to date are limited and thus represent a major gap in our understanding of pond ecological function.
A review of S.C. pond hydrology is provided in Chapter 2, but the extent to which surface and subterranean water movement transports nutrients and other materials to/from ponds is of primary concern because pond connectivity influences ecological function. Improved understanding of connectivities between ponds is a significant and open question due to the complex hydrology of ponds from direct (pipe) surface networks, groundwater exchange, and tides. As many ponds are either directly connected to a receiving tidal creek or indirectly connected through daisy- chain links, elucidating hydrological linkages will inform biological and chemical linkages between and among ponds. Since ponds serve numerous ecological functions (nutrient remineralization, provide habitat for fishes, birds, reptiles, and invertebrates, etc.), it is crucial to not only build upon existing programs but continue to understand and address these gaps. Also key will be communicating these processes and their outcomes to residents, managers, and other stakeholders. As ponds generally increase the property value of adjacent plots, it is essential that residents gain a broader understanding of their ecological and associated economic value and thus enact informed management decisions.
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Bunker KN (2004) A hydrological assessment of two detention pond watersheds in an urban coastal landscape. M.S. Thesis, College of Charleston, Charleston, S.C.
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Hayes KC, Lewitus AJ, Wilde SB (2008) Seasonal variations in phytoplankton growth and microzooplankton grazing in a eutrophic coastal lagoonal system in South Carolina. Ocean Sciences Meeting Orlando, FL
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Hehman L (2014) The effects of aeration on phytoplankton community composition and primary production in stormwater detention ponds near Myrtle Beach, S.C.. M.S. Thesis, University of South Carolina, Columbia, S.C.
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Holt C, Gould WJ, McSorley AJ, Oakley WF, Overcash JM, Watson MH (2015) Daimler stormwater pond survey- Spring 2015. The Citadel, Charleston, S.C.
Horgan FG, Stuart AM, Kudavidanage EP (2014) Impact of invasive apple snails on the functioning and services of natural and managed wetlands. Acta Oecologica 54:90-100
Hunt WF, Apperson CS, Kennedy SG, Harrison BA, Lord WG (2005) Occurrence and relative abundance of mosquitoes in stormwater retention facilities in North Carolina, USA. Water Science Technology 54:315-321
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Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 101 Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 102 CHAPTER 5 – A POLICY LENS OF SOUTH CAROLINA COASTAL STORMWATER MANAGEMENT
Authors
Lori A. Dickes, Ph.D. Master Public Administration Program, Strom Thurmond Institute, Clemson University, Clemson, S.C.
Jeffery Allen, Ph.D. South Carolina Water Resources Center, Clemson University, Clemson, S.C.
Monika Jalowiecka Environment and Sustainability Program, University of South Carolina, Columbia, S.C.
Katie Callahan Clemson University Center for Watershed Excellence, Clemson, S.C.
Bridget Cotti-Rausch, Ph.D. South Carolina Sea Grant Consortium, Charleston, S.C. Currently at the U.S. Environmental Protection Agency, Washington, D.C.
Corresponding Author Lori A. Dickes, Ph.D. ([email protected])
5.1 Background Ponds are often used as stormwater best management practices (BMPs), to minimize the impact of impervious surface cover and associated runoff. Stormwater BMPs are described by the Environmental Protection Agency (EPA) as “methods that have been determined to be the most effective, practical means of preventing or reducing pollution from nonpoint sources.” As most private developments are governed by homeowners’ associations (HOAs), these groups are largely responsible for the direct management, maintenance, and repair of BMPs on their properties. A 2007 study by the S.C. Department of Health and Environmental Control Office of Ocean and Coastal Resource Management (S.C. DHEC-OCRM) Stormwater Maintenance Program reported almost 15% non-compliance of permitted ponds following inspections of 511 residential development sites (Drescher et al. 2007). In the coastal region of S.C., non- compliance and poor pond performance can occur for many reasons, including: inappropriate vegetation, poor maintenance or control of vegetation, clogged intake or outtake pipes, and significant sediment buildup preventing effective water flow. Ponds are designed to achieve flood protection benefits and provide water quality treatment services. However, both their engineered purpose and the regulatory framework surrounding them are complex and often unknown to those that service them throughout their effective lifetimes. In this chapter we evaluate the current policy and regulatory landscape of stormwater management with the ultimate goal of providing recommendations to achieve greater levels of maintenance compliance and improved pond performance in the future. By starting at the federal stage and working to the local level, we sought to identify where, within the regulatory strata, scientific
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 103 information would best inform future decision-making. As S.C.’s coastal communities continue to experience rapid economic and population growth, ensuring that stormwater infrastructure functions effectively is a critical component to achieving sustainable growth and development.
5.2 Framework In this chapter we focused on S.C.’s coastal counties in order to understand the network of stormwater policies and regulations that govern these communities. Our research utilized a mixed-methods approach that allowed researchers to explore different components of a particular research question by deploying more than one methodological tool. This research employs three primary qualitative techniques: a policy instrument scan, a regional online survey, and a local focus group.
The United Nations Environmental Programme describes a policy instrument scan as one designed to go beyond understanding the broader regulatory and policy environment by attempting to describe the broadest mix and range of policy instruments that influence the policy environment of a specific issue (www.unep.org). A scan should address policy tools that are having a positive and/or a negative impact on the policy landscape, with particular focus on the chain of policy instruments and the hierarchy of regulatory and policy tools, along with external and/ or internal political or private pressures. This is a critical exercise for any complicated policy and regulatory area. For environmental issues, in particular, this analysis can be useful for policy-makers and researchers to inform future changes. Here, we outline the major federal, state, and local policies and regulations that directly impact stormwater management in S.C. Because stormwater management is a broad topic and our more specific goal is to understand and ultimately improve pond management, we focus here on pond BMPs with some mention of alternative low impact development (LID) practices.
5.3 Federal Policies Similar to many environmental issues, stormwater management lies within a network of federal, state, and local policies and regulations. United States environmental policy and regulation mimics the federalist system in general; with federal and state policies that set broad standards, have regulatory power, and provide funding streams to help state and local governments meet these requirements. Local governments are often then left to interpret, implement, and/or innovate within this larger policy context. In this policy environment, it is useful to identify the dominant, overlapping, and even conflicting policies or regulations that impact a particular issue.
5.3.1 The Clean Water Act (CWA)
At the federal level, the EPA is largely responsible for crafting broad policies and issuing guidance on issues related to water quality, including the impacts of stormwater on surface waters. In the area of water quality, the landmark policy is the CWA which was substantially amended from the 1948 Federal Water Pollution Control Act and ultimately signed into law in 1972. The CWA granted the EPA authority to implement water pollution control programs; at the heart of which was the establishment of water quality standards for various contaminants entering surface waters. Initially the CWA targeted point source pollutants, such as wastewater, but now includes guidelines on pollutants carried in stormwater runoff. Under the CWA, the states were granted the primary responsibility for managing water pollution within their borders.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 104 Several key sections of the CWA that impact stormwater policy and regulation are worth further explanation. Section 303(d) pertains to waters that remain polluted after attempted remediation efforts and includes the Total Maximum Daily Load (TMDL) program. The TMDL program aims to apportion waste load allocations to reduce the overall impact of pollutants on already impaired waterbodies. While TMDLs apply to a range of sources and outputs, stormwater discharges are an increasingly prevalent source of TMDLs to receiving waters (USNRC 2008), especially the input of sediments. Under the TMDL program, states are required to implement regular water quality monitoring programs, and every two years to use these data to identify which waterbodies do not meet established water quality standards, or are likely not to meet them in the next reporting cycle. These impaired waters are subject to further planning and management designed to bring them into compliance with federal standards.
As a 2015 extension to the CWA, the Clean Water Rule (CWR) states that if particularly large stormwater discharges flow into the nation’s waters downstream, stormwater is to be considered jurisdictional waters and must follow the practices set forth under the CWA (EPA 2015). Broadly, the CWR was intended to clarify water resource management issues and more specifically define the scope of federal protection, to include streams and wetlands. In 2017 the new administration suspended this rule, a decision that would remove federal protection from ~60% of U.S. streams.
5.3.2 National Pollutant Discharge Elimination System (NPDES)
Sections 301 and 402 of the CWA pertain to the controlled release of toxins and to stormwater management and permit programs in largely urban areas (USNRC 2008). For stormwater discharged into water bodies through storm drains, the CWA requires cities and counties meeting a certain population threshold to obtain a NPDES permit to monitor, reduce, and control pollutants contained in runoff within their jurisdictions. In addition, certain industrial and construction activities must also obtain permits to manage runoff (EPA 2015). The NPDES program is implemented in Section 402 of the CWA amendments and overseen federally by the EPA. It is this program that is largely responsible for the proliferation of ponds as stormwater control measures. Because the EPA in 1975 authorized the states to administer the NPDES program, further discussion of this process is reserved for Section 5.4.
5.3.3 Coastal Zone Management Act (CZMA)
This federal law passed in 1972, as Congress recognized the challenges associated with coastal population growth, and the need to protect the resources of the nation’s coastal zone. Under the CZMA, three national programs were authorized, including the National Coastal Zone Management Program, the National Estuarine Research Reserve (NERR) System, and the Coastal and Estuarine Land Conservation Program. There are two NERR Systems in S.C.: North Inlet-Winyah Bay located in Georgetown County in the Grand Strand, and the ACE Basin spanning Colleton and Beaufort counties in the Lowcountry. Both programs are heavily involved in research, education, and outreach activities that address, among other things, the impact of population growth on our natural coastal and marine resources.
Additionally, the CZMA requires that federal activities affecting water or land use within the coastal zone must receive permits that certify the proposed actions comply with its provisions (Ellis et al. 2014). This certification, known as the Coastal Zone Consistency Certification (CZC), is required before NPDES and any other state permit can be issued to a developer.
The policies described above are the primary federal regulations that impact stormwater management. However, there
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 105 are three additional federal policies that could potentially impact pond management: the Endangered Species Act, the National Environmental Policy Act, and the National Historic Preservation Act. These would apply on a case-by-case basis if a development site happens to meet criteria described under one of the acts.
5.4 State Regulations Federal agencies delegate how the states implement policy in a variety of ways: by authorizing states to enact specific policies or regulations as they see fit, by requiring the uses of specific intervention, or by mandating that precise planning, technology, or other best practices be implemented. This section reviews the state-level laws and regulations that impact stormwater management in S.C., all of which have clear links to federal programs. SC DHEC is the statewide regulatory agency assigned to protect the environment and implements all the policies described here; within S.C. DHEC stormwater management falls under the purview of the Bureau of Water.
5.4.1 Pollution Control Act (PCA)
This act, voted on by the state legislature in 1972, includes additional regulations above and beyond those called for in the CWA. The goal of the PCA is to protect public health, the environment, and employment from the negative effects of pollution. This policy grants S.C. DHEC the authority to enforce these standards and those set by the CWA, and the NPDES program is implemented under this act (Drescher et al. 2007; Ellis et al. 2014; R. Geer at DHEC pers. comm.). Under the PCA it is unlawful to directly or indirectly discharge point source pollutants into the environment unless authorization has been approved by compliance with a S.C. DHEC-issued permit (Ellis et al. 2014). To clarify, while the various individual sources of stormwater pollutants are “nonpoint sources,” the flow of stormwater runoff itself is classified as a “point source pollutant.” Therefore, S.C. DHEC issues permits designating effluent limits on these pollutants and guidance on required stormwater treatment programs, including the use of BMPs such as ponds for protecting downstream water quality (Ellis et al. 2014).
NPDES permits fall under several categories: Municipal Separate Storm Sewer System (MS4) permits, Construction General Permits (CGPs), and Multi-sector Industrial Stormwater General Permits (MSGPs). Depending on the size of the MS4 activity, these qualify as either General or Individual permits: General permits are allocated to Small MS4s, and Individual permits are allocated to Large and Medium MS4s and select industrial and construction activities (Ellis et al. 2014). For stormwater MS4s and General permits for industrial and construction activities, there are no effluent limitations.
Increasingly, smaller municipalities and smaller construction activities are required to meet NPDES stormwater regulations, thereby requiring additional policy guidelines and specification of TMDL allocations from the EPA and corresponding state agencies (EPA 2015). These permit types apply uniquely to Phase I (implemented in 1990) and Phase II (implemented in 2003) in the NPDES permitting process. In Phase I, the following required permits:
• MS4s serving municipalities of 100,000 or more people, • CGPs for all construction sites that disturb five or more acres, and • MSGPs for 11 specified industrial activities which disturb five or more acres of land.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 106 Phase II parameters are:
• MS4s serving municipalities of 10,000 to 100,000 people and a density of 1,000/square mile, • CGPs for construction sites that disturb between one and five acres, and • MSGPs for activities disturbing one to five acres.
Phase II also requires a Stormwater Pollution Prevention Plan (SWPPP) and a Notice of Intent be filed with S.C. DHEC. Currently, the S.C. Department of Transportation is the only large MS4 in S.C. and operates statewide under an Individual NPDES permit. In the coastal zone, there are no large or medium MS4 communities, while six counties and 19 municipalities are regulated under small MS4 General permits (Table 5.1). For example, Charleston County is a main permit holder while co-permittees are the City of Folly Beach, Isle of Palms, Sullivan’s Island, Lincolnville, incorporated James Island, and the City of Goose Creek. The most recent coastal MS4s were granted in 2017 to two municipalities in Beaufort County. MS4 status is an important consideration for stormwater management at the local level due to the rapid population growth rates in the coastal region.
Urbanized Area Small MS4 Berkeley County Charleston County Dorchester County City of Charleston City of Folly Beach City of Goose Creek City of Hanahan Charleston City of Isle of Palms Town of James Island Town of Lincolnville Town of Mount Pleasant City of North Charleston Town of Summerville Town of Sullivan's Island Georgetown County Horry County Town of Atlantic Beach Town of Briarcliffe Acres Myrtle Beach City of Conway City of Myrtle Beach City of North Myrtle Beach Table 5.1 All regulated small municipal Town of Surfside Beach separate storm sewer systems (Small MS4s) Beaufort County in the eight coastal counties (as of 2017). Beaufort Town of Bluffton* * Full implementation of these MS4 Town of Hilton Head Island* programs occurred in July 2017.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 107 To maintain compliance with the NPDES program, each MS4 community must develop programs that cover these six minimum control measures:
• Public education and outreach, • Public participation and involvement, • Illicit discharge detection and elimination, • Construction site runoff control, • Post-construction site runoff control, and • Pollution prevention and good housekeeping.
Often, MS4 communities contract with universities and extension programs to fulfill the first two requirements. They form local education consortia that provide numerous outreach materials, including information on appropriate pond management targeted at property owners and HOAs. These consortia also sponsor semi-annual regional stormwater pond conferences and teach Master Pond Manager courses that are open to the general public. In coastal S.C., there are three regional education consortia (Table 5.2).
Region Education Consortia Grand Strand Coastal Waccamaw Stormwater Education Consortium (CWSEC) cwsec-sc.org Tri-County Ashley Cooper Stormwater Education Consortium (ACSEC) www.clemson.edu/extension/carolinaclear/regional-consortiums/acsec/index.html Lowcountry Lowcountry Stormwater Partners (LSP) www.clemson.edu/extension/carolinaclear/regional-consortiums/lsp/index.html
Table 5.2 Coastal, regional stormwater education programs contracted through Coastal Carolina University (CWSEC) and Clemson University (ACSEC and LSP).
5.4.2 Coastal Management Program (CMP)
In the coastal zone, additional hurdles are faced by developers filing for permits to build near vital coastal resources such as tidal creeks and beaches. The state’s CMP was established in 1972 under the guidelines of the federal CZMA as a state-federal partnership. In 1977 this program was authorized by the state legislature under the Coastal Tidelands and Wetlands Act (CTWA). The CTWA was created in order to protect and ensure long-term sustainability of the vulnerable areas of the coast by encouraging state and local governments to protect coastal areas based on their unique ecological, economic, cultural, and social values (S.C. DHEC 2011 and 2014a). In 1977, S.C. adopted its own Coastal Zone Management Act, the purpose of which is to properly manage the natural, recreational, commercial, and industrial resources of S.C.’s coastal zone, as they were deemed by the legislature to be of current and future value to all citizens of the state. This legislation created the S.C. Coastal Council as a state agency to direct, develop, and implement a comprehensive management program. In 1993, S.C.’s CZMA was amended and the S.C. Coastal Council merged with S.C. DHEC, in the form of the Office of Ocean and Coastal Resource Management (OCRM). The jurisdiction of OCRM covers S.C.’s “critical areas,” which include coastal waters, tidelands, and beach/dune systems.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 108 Coastal Zone Consistency Certification
The consistency process ensures activities involving land and water uses within the eight coastal counties are consistent with the federal CZM Plan and the state’s plan through a Consistency Determination (Ellis et al. 2014). This requires S.C. DHEC-OCRM to review all state and federal permit applications for activities occurring in the eight coastal counties for consistencies with the state’s plan. Additionally, the federal CZM requires that S.C. DHEC-OCRM review federal funding assistance applications submitted by any state or local governments to determine if they are consistent with the state’s CZM plan. Because the state CZM plan is federally-approved, “federal consistency” also exists under the federal CZMA. This applies to activities in the coastal zone that may impact coastal resources and are classified as federal activities, require federal permits, or receive federal assistance. Projects approved under the federal consistency review process described above must comply with the state’s Coastal Tidelands and Wetlands Act (CTWA). Additional mitigation efforts must be taken to meet the requirements of the CZC to protect coastal waterways. Any stormwater BMP constructed in the coastal zone is required to retain the first ½ inch of runoff from an entire site or storage of the first inch of runoff from the built-upon portion of the property, whichever of these volumes is greater. If a development is located within 1,000 feet of shellfish beds, the first 1 ½ inches of runoff from the built-upon portion must be retained on site. There are additional requirements for outfalls from golf courses, mines, and landfills.
5.4.3 Stormwater Management and Sediment Reduction Act (SMSRA)
This act is broken into three components, the first of which, Erosion and Sediment Reduction and Stormwater Management, sets regulations for activities occurring on state land to avoid damage to property, land, and water caused by erosion, sediment, and stormwater. Part two contains the standards for the SMSRA, which dictates a statewide stormwater management and sediment reduction program as a preventative measure against current and future water quality and quantity problems. Part three is the Amendment to the Standards for SMSRA, tying highway construction, infringement permits, or easement, and/or right-of-way work to the S.C. Department of Transportation (Drescher et al. 2007). This program also established requirements for any development project located next to a receiving water body, shellfish bed, areas producing significant runoff, and other activities that may substantially influence surface waters. Under the SMSRA, the R.72-106(E) sets the standards and specifications that must be met to control erosion and stormwater for projects on state property. For example, one important regulatory consideration is the size of the area disturbed by the proposed project (Ellis et al. 2014; Geer 2015). Ponds are one of the tools identified in the SMSRA as a method to manage stormwater, erosion, and sediment control on state lands (Ellis et al. 2014).
5.5 Local Government: Direct Oversight The Stormwater Ponds Research and Management Collaborative evaluated the current role of local government in the eight coastal counties: Beaufort, Berkeley, Charleston, Colleton, Dorchester, Georgetown, Horry, and Jasper, and all but Colleton and Jasper are regulated MS4s. A flow diagram created by Beaufort County illustrates the role of the local government within the landscape of federal and state policies (www.bcgov.net/departments/Engineering-and- Infrastructure/stormwater-management/municipal-separate-storm-sewer-system-ms4.php). Below, we compare and contrast individual stormwater ordinances, stormwater management plans, and publicly available resources among the eight coastal counties and a selection of local governments.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 109 5.5.1 County Ordinances
MS4 Designated Counties
In reviewing the various ordinances related to stormwater management for the six coastal MS4s, we found the content was often similar among counties. Here, we focus especially on comparable language pertaining to inspections, maintenance responsibilities, and enforcement activities. As part of the NPDES permitting process, a developer must file a SWPPP with the county. Responsibility for following the SWPPP belongs first to the developer during the construction phase and then to the property owner. Upon transfer of ownership to the property owner or HOA, this entity then takes over the responsibility for maintaining ponds, or other stormwater structures, up to original design specifications. The county has authority to conduct enforcement procedures for violations and non-compliance during both the initial construction phase and post-construction period, equivalent to the effective lifetime of a pond. County stormwater programs responsible for carrying out these activities lie within broader Public Works or Engineering and Infrastructure departments. Each ordinance grants county inspectors access to inspect privately owned stormwater structures at any time; these inspections are conducted by a County Engineer, Public Works Director, or a designee. Failure to maintain stormwater infrastructure can result in legal ramifications. Steps the county can take in these cases vary and include issuance of a Notice of Violation, a Corrective Order, and potentially fines up to $1,000 per violation. In the most extreme cases, the county can press civil or even criminal charges. Additionally, the county reserves the right to correct any violation and bring the pond up to design specifications. Afterward, the property owner or HOA is held responsible for repaying the costs of the effort. Requirements laid out in the ordinance, including accepted BMPs for regulating stormwater, are described in detail in Stormwater Management Design Manuals. These manuals are written for, and formally adopted by, each county and assist in the design and evaluation of stormwater management facilities.
It is important to note that inspections for compliance with NPDES programs only cover ponds built after the issuance of an MS4 permit. The oldest permit in the coastal zone was issued in 2006 for Horry County; the most recent permit was for Beaufort County and issued in 2015. Therefore, the majority of ponds in the eight coastal counties are not regulated under the NPDES program. For example, aerial imagery estimates there were ~3,000 development-related ponds in Horry County as of 2006 (Figure 1.9 in Chapter 1), the year they received their MS4 permit. The entities that manage these older ponds are expected to maintain their BMPs at the original design standards and schedule frequent inspections to be conducted by licensed engineers. However, most of these communities lack formal stormwater management plans, and face additional challenges including reliance on paper as-built pond documents, frequent turnover at community leadership positions, and inconsistent record-keeping.
Non-MS4 Designated Counties
Though Jasper County is not a regulated MS4, stormwater management is included as Article 10 in the County’s Land Development Regulations. These regulations require that qualifying development activities (e.g., those that install > 5000 square feet of impervious surface, or major subdivisions) submit a Stormwater Management Plan to the county through the development application process. Additionally, the eventual property owners, termed “successors in interest,” must submit a maintenance agreement to the county that outlines specific management activities to be undertaken. These include annual pond inspections to be conducted by a licensed engineer and maintaining a reserve fund that can pay for any anticipated reconstruction costs or repairs required by the pond over a three-year period.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 110 Permanent Minimum flow Embankment Aquatic bench or pool depth dimensions Forebays Height and Littoral shelf (ft) (L:W) Slope (H:V) S.C. DHEC min = 4 – 6 1.5:1 barrier one foot below prepare planting no mention (2005) normal pool elevation plan by qualified and up to elevation landscape architect above permanent pool or wetland ecologist Beaufort mean = 3:1 storage capacity = 10% littoral zone to 3:1 County (2012) 3 – 7 of permanent pool promote growth of storage volume (hold wetland vegetation; sediment accumulation littoral shelf = 220 20 years) sq. feet per acre Berkeley min = 4 no mention all quantity BMPs also no mention < 15 feet; 3:1 County (2009) used for quality control must have a forebay to remove debris and coarse sediments Charleston min = 6 3:1 all ponds must have one no mention < 15 feet; 3:1 County (2016) or more forebays to trap coarse sediment Dorchester min = 6 no mention if BMP captures runoff for extended wet < 15 feet; 3:1 County (2014) from ≥ 5 acres detention ponds Georgetown min = 4 3:1 Hold 0.1 inch runoff permanently < 3:1 County (2006) from impervious inundated with drainage area; surface water (1-2 feet) area 15 - 25% total and planted with pond wet area hydrophytic vegetation Horry County min = 6 “must be no mention not required < 15 feet; 3:1 (2017) maximized to ensure sufficient time to allow for sedimentation of pollutants” Jasper County min = 3 – 4 3:1 forebay or “equivalent not required; < 15 feet; 3:1 (2011) upstream pretreatment” “wetland plants should be provided at should be each inlet encouraged…along the aquatic bench”
Table 5.3 Comparison of state (DHEC) and county design standards for wet detention ponds.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 111 Jasper County also adopted a Stormwater Management Design Manual in 2011, similar in content to Beaufort County’s manual. Both include large sections dedicated to green infrastructure. In contrast, Colleton County, the other non-regulated coastal county, has no ordinances or design manuals specifically pertaining to stormwater management.
Comparison of State vs. County Standards
In Table 5.3 we list the major design standards in S.C. DHEC’s Stormwater BMP Handbook (2005) and those from each county’s adopted design manual. Our review of these documents resulted in three major take-aways. First, county-specified design standards were often more stringent than those suggested by the state guidance. Secondly, requirements could vary substantially among the seven counties, especially with respect to language concerning forebays and aquatic vegetation. Finally, reading each manual clarified for us why wet detention ponds are a favorite of developers: they are the only accepted BMP that meets both water quantity mitigation and water quality protection needs.
5.5.2 Online County Resources
A review of available stormwater-related documents available on each county’s webpage was conducted, including:
• Stormwater webpage on the county’s website, • Stormwater management plan, • Link for ordinance document(s), and • Inclusion of stormwater management in Comprehensive Plans.
Table 5.4 provides a snapshot of each county’s online materials related to stormwater regulations and management. We included zoning in our scan because classifying land use and current/future building codes may serve as a proxy for stormwater management activities (USNRC 2008). Jasper County incorporated a section concerning zoning on their stormwater webpage. While no other county had a site dedicated to zoning, several referenced zoning in stormwater documents. For example, in Berkeley County’s Stormwater Design Standards Manual, zoning was mentioned under the Zoning and Land Development Regulations as well as the Building & Codes and Floodplain Ordinances (Berkeley County 2015).
Also, it is worth noting that the State’s Comprehensive Planning Act does not require local governments to incorporate stormwater management into their comprehensive plans (S.C. Code Ann. 6-29-510). Therefore, four of the coastal counties do not currently incorporate stormwater planning into their comprehensive plans (Table 5.4). Those counties with substantial text dedicated to future planning for stormwater management included Horry, Berkeley, Charleston, and Jasper counties. All comprehensive plans at least mention stormwater concerns or challenges but may not specifically address planning for future regulatory changes.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 112 Webpage Comprehensive Stormwater Stormwater Section Soley Stormwater Plan Map of the Management Management Devoted Extra Devoted to Manual Incorporating County Plan Ordinance to Zoning Stormwater Stormwater
Beaufort Berkeley Charleston Colleton Dorchester Georgetown Horry Jasper
Table 5.4 Online information pertaining to stormwater management for each coastal county. Check marks = information provided; x = information not provided.
5.5.3 Online Municipal Resources
Five municipalities (City of Beaufort, City of Charleston, Town of Mount Pleasant, City of Georgetown, and City of Myrtle Beach) were chosen for a website review of stormwater resources. Each municipality is regulated under the NPDES program and faces growing population and tourism demands, both of which heavily depend on proper stormwater management to be sustainable. Online, we found each municipality provides contact information for their respective stormwater departments. This is important for residents as these municipalities are responsible for maintaining and regulating the stormwater infrastructure within the area annexed to them. This additional layer adds to the regulatory complexity surrounding stormwater management; Figure 5.1 illustrates the multifaceted jurisdictions in the Tri-County region alone.
In most cases, the city websites are more limited in informational resources as compared to county stormwater pages. The exception was the City of Charleston, which has adopted and published its own Stormwater Management Design Manual and Stormwater Management Plan, in 2013 and 2014, respectively. The manual is similar to Charleston County’s, though differences between the two exist. For example, the city requires a minimum pond depth of three feet for mosquito control as compared to the six feet required by the county. These nuances require that developers, and also property owners, pay close attention to the design standards required for their site.
5.5.4 Council of Governments (COGs)
We also investigated the role of COGs in stormwater management. In the coastal zone there are three COGs (Waccamaw, Berkeley-Charleston-Dorchester, and Lowcountry) which provide planning and technical support to local governments in developing local and regional plans. While most COGs do not have staff trained specifically in the area of stormwater management, they do assist with comprehensive planning, which may include this component.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 113 Berkeley County (including jurisdictions of Hanahan and Goose Creek)
Charleston County (including jurisdictions of Isle of Palms, Sullivan’s Island, Lincolnville, incorporated James Island, and Folly Beach)
Dorchester County (including the jurisdiction of Summerville)
City of Charleston
Town of Mt. Pleasant
City of North Charleston
Figure 5.1 Map of SMS4 communities in the Tri-County region.
Therefore COGs rely on expertise provided by other agencies and/or consultants.
Additionally, COGs assist local government units in applying for Community Development Block Grants (CDBG) administered by S.C.’s Department of Commerce. These can be utilized to improve infrastructure, including water, sewer, and drainage activities. The CDBG program was designed to help local government address social and environmental problems, specifically in low income neighborhoods. These funds could be used to address issues related to stormwater infrastructure in coastal communities that are eligible to receive a CDBG. While we could not find evidence that these grants have been used to address stormwater needs in S.C., there are recent examples from other states (EPA 2017). In 2014, $8.9 million of CDBG funds were used in Detroit for infrastructure improvements to prevent flooding and build economic development. This included the planting of trees in 200 vacant lots to improve stormwater management. In Chicago, these funds were used to install a green roof on the historic Cultural Center.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 114 5.6 Survey and Focus Group We drew several conclusions after reviewing federal and state laws and local informational resources related to stormwater policy and regulation. Namely, that federal and state policies and regulations allow for creativity and innovation at the local level. While the federal NPDES program authorizes S.C. DHEC to implement stormwater regulation at the state level, counties and municipalities can meet these requirements by crafting their own unique ordinances. We did find that specific ordinance language, level of uniqueness, future planning, and the quality and availability of public information was highly variable across the eight coastal counties. To dig deeper into activities at the local level, we conducted a survey and held a focus group targeting stormwater professionals to gain insight on issues and concerns impacting local decision-makers and resource managers.
Methods
We employed both an online survey and in-person focus group methodology in order to gain a better understanding of local stormwater policies and regulatory activities. Respondents represented a range of professionals, including stormwater professionals from counties designated as MS4 NPDES permittees.
An online survey instrument was developed in conjunction with College of Charleston researchers focusing on the economics of stormwater management (Chapter 6). The survey instrument was sent to listservs of local stormwater managers and other stakeholders. The survey was distributed using the online survey platform, Qualtrics, to a wide range of stormwater managers and related professionals across the eight-county coastal zone. Reminders were sent to potential participants over a 4 - 6-week period in June - July, 2015. Ultimately, 58 individuals responded to the survey out of a total of 500 contacted.
Focus group methodology which allows researchers to explore critical issues in more depth by meeting directly with impacted stakeholders and providing an environment that allows for open-ended discussion and response cannot be achieved with a survey instrument. Our focus group was held in North Charleston, S.C. on July 22, 2015. Facilitators included researchers from Clemson University (this chapter) and the College of Charleston (Chapter 6). The Institutional Review Board (IRB) process was managed by the College of Charleston research team. Working together, each team developed 10-15 questions covering a range of economic and policy issues (Appendix A5, see www. scseagrant.org/spsok). To ensure responses from focus group members were properly noted, the entire conversation was recorded with the consent of all individuals in the focus group. The recording was then transcribed to ensure accurate documentation of the event discussions.
5.6.1 Survey Results
Policy questions focused on a range of issues including organizational responsibility, alternative technologies, community planning, and effective regulation and management. Almost 60% of respondents believe that stormwater management should be a shared responsibility among agencies. Further, about 70% of respondents stated that stormwater management is addressed in their community’s comprehensive plan. Of those that answered positively that stormwater is included in their comprehensive management plans, over 60% agreed or strongly agreed that the comprehensive plan is the most effective place to address stormwater issues, while 13% disagreed. We should note that while our respondents covered a range of professional affiliations, they did not necessarily represent an even geographic distribution from throughout the coastal zone of South Carolina.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 115 Stormwater ordinances are a tool that local governments can use to manage and enforce pond policy and specify best practices tailored to their unique geographic, hydrologic, and cultural conditions. The majority of respondents did not agree that stormwater ordinances are a barrier to economic development. Further, respondents had mixed responses as to whether the pressures associated with rapid population growth demand flexibility in stormwater ordinances and policy (Figure 5.2); overall, 47% either agree or strongly agree, while 31% disagree or strongly disagree. As coastal communities continue to grow, understanding how to manage growth with existing policy mechanisms is critical.
Figure 5.3 illustrates that respondents were split on whether ponds are the best tool for stormwater management. Just 24% agreed, while 26% disagreed, with 43% having no fixed opinion either way as to whether ponds are always an ideal BMP. This question underscores some of the inherent policy challenges with stormwater management, but it also demonstrates where scientific guidance may be used to inform a more definitive position on the effectiveness of ponds. Given that ponds are not necessarily the preferred BMP by those surveyed, it was perhaps not surprising that nearly 60% of survey respondents either agreed or strongly agreed that Low Impact Development (LID) tools can be more favorable management options than ponds. As defined by the EPA, LID is an alternative strategy to ponds that utilizes natural landscape features like soils, vegetation, rainwater harvesting, and other techniques that imitate nature’s processes. Practices mentioned by the EPA include bioretention areas, rain gardens, vegetated rooftops, installation of rain barrels, and use of permeable pavements (www.epa.gov/nps/urban-runoff-low-impact-development). The ultimate goal of LID practices is to minimize the impact of the built environment and facilitate a more natural movement of water.
A number of questions in our survey also addressed which organization(s) are best suited to manage and enforce stormwater policy (e.g., S.C. DHEC, local governments), and this topic was further discussed by the focus group (Section 5.6.2). Current state laws require S.C. DHEC to regulate and monitor ponds across the state, while local governments with stormwater NPDES permits are responsible for ponds within their jurisdictions, to ensure they meet state and federal regulations. When asked whether ponds are monitored adequately by S.C. DHEC, almost 60% either disagreed or strongly disagreed. When asked whether current county, state, and/or federal policies allow for the flexibility to make necessary changes to future stormwater management practices, results reveal another set of mixed responses: 30% agreed and 30% disagreed.
34% Agree 22% Disagree Neither Agree 20% nor Disagree 13% Strongly Agree
9% Strongly Disagree
Figure 5.2 Survey results: “Does population growth require flexible stormwater policies?” (n = 58).
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 116 Neither Agree 43% nor Disagree 26% Disagree
24% Agree
4% Strongly Disagree
3% Strongly Agree
Figure 5.3 Survey results: “Are ponds the best tool for stormwater management?” n = 58.
Final survey questions allowed for open-ended responses related to stormwater practices. Regarding policy and management, respondents were asked whether they believe there are any policy changes important for future stormwater management. Comments focused on the following issues that constitute opportunities for improvement in how stormwater is currently managed.
Potential Management Changes
• Require more LID practices both for new development and re-development. • Improve maintenance, and consider more progressive and restrictive design criteria. • Research and/or development of alternative management methods. • Institute strong prescriptive regulation. • Incorporate LID incentives into local and state development standards. • Create public-private partnerships. • S.C. DHEC should adapt new design criteria and provide regular training opportunities to engineers preparing stormwater plans and plan reviews.
Importantly, this survey did not include property developers, and a different view of ponds as ideal BMPs might have emerged if these professionals were questioned. While open-ended responses varied, additional education, more robust public-private partnerships, and the additional use of LID practices were each mentioned by multiple respondents. Overall, the survey highlights clear challenges in assigning responsibility for stormwater management, which underscores the importance of examining the current policy network and considering more effective policy organization for the future.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 117 5.6.2 Focus Group Results
Facilitators gathered eight community members in North Charleston, including:
• Commercial real-estate agent, • Public Services Department representative, • Board Accountant for a Stormwater Manager, • Stormwater Program Managers, • Assistant County Engineer, and • S.C. Sea Grant Consortium community representative.
These individuals were chosen based on their diverse knowledge of stormwater issues and management. The focus group team developed 10 key questions regarding stormwater policy and management (Appendix A5, see www. scseagrant.org/spsok). Each respondent was given an opportunity to answer each question in detail. A number of common themes emerged and are highlighted individually below. Focus group responses can be a helpful methodological tool to expand understanding of a specific set of issues and identify areas of concern. However, these conversations occurred within a small group of individuals at a single point in time. Therefore, these comments are not to be generalized to represent the opinions of entire groups of professionals. For the Stormwater Ponds Research and Management Collaborative and our community partners, these discussions will help us identify areas of need where we might be able to target our research and extension efforts.
1. Public Education
First and foremost, every member of the group agreed that public education for stormwater management is a critical best management practice. Education was further broken down into several layers, including the individual level and the HOA level. There was much discussion on how to ensure HOAs understand the maintenance requirements of ponds, the costs of maintenance, how ponds operate, as well as when to contact the county stormwater manager with a substantial pond issue. The importance of knowing the most effective methods of educating homeowners, the public, HOAs, and other stakeholders about ponds and best management of them was identified as critical.
2. HOAs
There were multiple comments and concerns associated with the issue of HOAs and stormwater management. A major concern is that HOAs lack knowledge of what their delegated pond responsibilities are. There is also a lack of long-term planning on behalf of HOA boards, so that the boards do not set aside finances from the yearly budget for pond maintenance. Additionally, when the pond is in desperate need of maintenance either five, 10, or even 20 years after the pond was initially built, the board often does not have sufficient funds to complete necessary management activities and receives opposition from the community when maintenance fees escalate. Additionally, HOAs have regular leadership changes and are often volunteer organizations with limited knowledge. All in all, the situation with HOAs and stormwater is a complex organizational and policy problem, which currently limits appropriate stormwater management.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 118 3. State Oversight
Another common theme discussed by nearly half of the group concerned S.C. DHEC and the agency’s role in stormwater management. Several respondents felt that they are in a constant battle with S.C. DHEC; that the agency offers little oversight to the management process. Often the agency will report to officials what they need to remain in compliance but will not offer solutions on how to meet these requirements. The group felt that S.C. DHEC was too focused on select items, such as TMDLs, but instead should provide a broader perspective on best practices in stormwater management. In contrast, several respondents did agree that while there is room for improvement, the agency is not overbearing at the county level of management and further find that S.C. DHEC’s vague language offers room for flexibility, which local officials have benefited from when addressing stormwater issues.
4. Coastal Concerns
Several individuals noted that they perceive some coastal counties are much more stringent with stormwater standards and regulations compared to the rest of the state. Respondents also noted that stormwater officials remain unsure of what constitutes a “failed” pond. The group identified the need for non-compliant ponds to be studied in order to analyze whether, given time, “failed” ponds in coastal zones may transform into productive, and still functional, wetland habitats given the shallow water table.
5. Land Uses and Pond Lifecycles
Stormwater managers are concerned about extending the effective life cycle of ponds by adjusting current pond design techniques and avoiding designs that serve as an attractant for geese and canine fecal matter. Related to this, local land use policies must complement and incorporate stormwater management, and policy changes should be made on the local, not state, level. It was also noted that ponds should be functional in that they should enable stormwater detention, flood control, and water quality if properly maintained.
6. Pond Alternatives
Focus group participants were open to alternatives to ponds such as implementing pervious pavers and other LID techniques into their stormwater management plans. However, participants discussed that LIDs require more maintenance than ponds once installed, are not necessarily cheaper, and require educating engineers, architects, and developers to inform and popularize the idea of implementing LIDs versus the standard pond for stormwater management. Regardless of the concerns with LIDs, focus group respondents clearly believed in the importance of encouraging and supporting LID use as a valuable, alternative tool for community stormwater management and one that would yield important environmental benefits.
5.7 Summary and Recommendations The information from the study described above confirms that, like many environmental issues today, pond management lies within a layered network of regulatory oversight. This review was designed to identify the dominant, overlapping policies or regulations that impact pond management in the eight coastal counties of S.C. The CWA and its constituent, the NPDES program, are the critical federal policies and regulatory documents that ultimately resulted in the construction and regulation of stormwater infrastructure, including ponds, that serve to re-route runoff and
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 119 protect downstream water quality. In S.C., the PCA grants S.C. DHEC the authority to regulate stormwater runoff. DHEC, in turn, gives authority to qualifying counties and municipalities to administer the NPDES program locally. Therefore, these communities craft local ordinances and provide design manuals for local control of ponds. Ultimately, the day-to-day maintenance of ponds in private communities falls to the property owner or HOA.
Understanding the flexibility of the policy environment is important in considering opportunities for policy change in the future, especially when coastal populations are growing exponentially, exacerbating the ongoing pressures from climate change that is altering weather patterns and driving sea level rise. As highlighted in our survey and by the focus group, coastal communities are presented with numerous challenges for ongoing management and enforcement related to pond issues. The key themes that emerged from our group discussion included: concern over enforcement of maintenance requirements for privately owned BMPs, communication avenues and provisioning of financial resources by HOAs, adequate communication between MS4s and S.C. DHEC, clarity on how to address impaired waterbodies, and improved research on whether design requirements for ponds are adequate or effective or whether LID practices are a preferred management strategy. To ensure that our coastal communities remain attractive, economically strong, and environmentally healthy in the future may require changes in the existing policy and regulatory environment impacting pond management. We conclude that due to the flexibility granted to local governments by S.C. DHEC, it is most likely that the necessary changes will occur at the county or municipal level.
5.8 References Beaufort County (2015) Stormwater Management Department. (Retrieved: 15 Oct., 2015) http://www.bcgov.net/ departments/Engineering-and-Infrastructure/stormwater-management//index.php
Beaufort County Stormwater Management Department (2015) Explanation of Regulatory Authority and Federal Mandate of the MS4 Permit. (Retrieved 28 Aug., 2017) http://www.bcgov.net/departments/Engineering-and- Infrastructure/stormwater-management/documents/MS4%20reg%20history%2008242015.pdf
Berkeley County Government (2015) Stormwater Management Program. (Retrieved: 28 Oct., 2015) https://www. berkeleycountysc.gov/drupal/engineering/storm
Charleston County Government (2015) Stormwater Management Program. (Retrieved: 21 Oct., 2015) http://www. charlestoncounty.org/departments/public-works/stormwater.php
City of Beaufort, S.C. (2015) City of Beaufort Government. (Retrieved: 04 Nov., 2015) http://www.cityofbeaufort. org/
City of Charleston, S.C. (2015) Stormwater. (Retrieved: 04 Nov., 2015) http://sc-charleston.civicplus.com/index. aspx?NID=350
City of Myrtle Beach, S.C. (2010) Welcome to Myrtle Beach. (Retrieved: 30 Oct., 2015) http://www. cityofmyrtlebeach.com
Colleton County, S.C. (2013) Documents. (Retrieved: 18 Oct., 2015) http://www.colletoncounty.org/documents
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 120 Committee on Reducing Stormwater Discharge Contributions to Water Pollution, Water Science and Technology Board, and National Research Council. (2008) Urban stormwater management in the United States. (Retrieved: 25 June, 2015) http://water.epa.gov/polwaste/npdes/stormwater/upload/nrc_stormwaterreport.pdf
Davis A, Pijanowski B, Robinson K, Kidwell P (2010) Estimating parking lot footprints in the Upper Great Lakes Region of the USA. Landscape and Urban Planning 96: 68-77
DHEC (2010) Fact Sheet: Industrial Storm Water (Except Construction) General NPDES Permit; SCR000000. http://www.scdhec.gov/Environment/ docs/sw_PNFSIGP.pdf (Retrieved: 28 July, 2015)
DHEC (2014a) Coastal Zone. (Retrieved: 17 July, 2015) http://www.scdhec.gov/Agency/RegulationsAnd Updates/ Laws AndRegulations/Coastal
DHEC (2014b) Stormwater Permitting: Overview. (Retrieved 16 July, 2015) https://www.scdhec.gov/Environment/ WaterQuality/Stormwater/Overview
DHEC (2011) South Carolina Coastal Zone Management Program Section 309 Assessment and Strategy 2011-2015. (Retrieved: 23 July, 2015) https://coast.noaa.gov/czm/enhancement/media/sc3092011.pdf
Dickes LA, Allen J, Jalowiecka M, Buckley K (2016) A policy lens of South Carolina coastal stormwater management. Journal of South Carolina Water Resources 3(1): 31 - 41
Dorchester County (2015) Stormwater Management. (Retrieved: 23 Oct., 2015) http://www.dorchestercounty.net/ index.aspx?page=90
Drescher SR, Messersmith M, Davis B, Sanger D (2007) State of the Knowledge Report: Stormwater Ponds in the Coastal Zone. S.C. DHEC-OCRM, S.C. Sea Grant Consortium
Ellis K, Berg C, Caraco D, Drescher S, Hoffmann G, Keppler B, LaRocco M, Turner A (2014) Low Impact Development in Coastal South Carolina: A Planning and Design Guide. (Retrieved: 18 June, 2015) http://www. scseagrant.org/pdf_files/LID-in-Coastal-SC-low-res.pdf
Gaba JM (2007) Generally Illegal: NPDES General Permits Under the Clean Water Act. Harvard Environmental Law Review 31:409 - 471
Georgetown County (2015) Welcome to Georgetown County Stormwater. (Retrieved: 19 Oct., 2015) http://www. georgetowncountycleanwater.com
Georgetown, S.C. (2014) Storm Drainage. (Retrieved: 6 Nov., 2015) http://cityofgeorgetownsc.com/water-utilities- department/storm-drainage
Horry County Stormwater Management (2014) Horry County Stormwater Management. (Retrieved 17 Oct., 2015) http://stormwater.horrycounty.org
Jasper County Government (2015) Zoning and Land Development Regulations. (Retrieved: 20 Oct., 2015) http:// www.jaspercountysc.org/secondary.aspx?pageID=248
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 121 Powell BA (2009) Stormwater ponds purposes and services of stormwater ponds. (Retrieved: 10 Nov., 2014) http:// www.clemson.edu/public/carolinaclear/cc_toolbox/pubs_pdfs/2011/pondseries_bpowell_010209.pdf
South Carolina Code of Laws: Title 6, Local Government Provisions Applicable to Special Purpose Districts and Other Political Subdivisions. (Retrieved: 12 Dec., 2015) http://www.scstatehouse.gov/code/t06c029.php
South Carolina Legislature (2014) South Carolina Code of Laws Unannotated Current through the End of the 2014 Session. (Retrieved 20 July, 2015) http://www.scstatehouse.gov/code/ t48c039.php
Town of Mt. Pleasant Municipal Complex (n.d.) Stormwater. (Retrieved: 01 Nov., 2015) https://www.tompsc.com/ index.aspx?nid=197
United Nations Environmental Programme. (n.d.) IEA Training Manual - Module 5 - 6.5 Step C: The policy instrument scan. (Retrieved: 15 Dec., 2016) http://www.unep.org/ieacp/iea/training/manual/module5/1235.aspx
U.S. EPA (2017) Federal and State Funding Programs – Stormwater & Green Infrastructure Projects. Water Infrastructure and Resiliency Finance Center (Retrieved 28 Aug., 2017) https://www.epa.gov/sites/production/ files/2017-05/documents/federal-and-california-sw-funding-programs.pdf
U.S. EPA (2015) The Final Clean Water Rule. (Retrieved: 01 Nov., 2015) http://www2.epa.gov/cleanwaterrule/final- clean-water-rule
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Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 122 CHAPTER 6 – AN ECONOMIC ASSESSMENT OF COASTAL STORMWATER MANAGEMENT
Authors
J. Wesley Burnett, Ph.D. and Christopher Mothorpe, Ph.D. Department of Economics, College of Charleston, Charleston, S.C.
Corresponding Author Christopher Mothorpe, Ph.D. ([email protected])
6.1 Background Over the past four decades, there has been a tremendous amount of population growth in the United States’ (U.S.) coastal regions. According to a recent National Oceanic and Atmospheric Administration (NOAA, 2013) report, approximately 39% of the current population is concentrated in coastal counties, which constitute less than 10% of the entire land area within the contiguous U.S. Further, approximately 52% of the population lives in counties that drain into coastal watersheds, which represent less than 20% of the total U.S. land area. Based on current trends, the population within coastal regions will grow from the current level of 123 million to 134 million people by the year 2020. The trends in population growth are no different for the South Atlantic coastal region of the U.S., which consists of the states of North Carolina, South Carolina, Georgia, and Florida. According to the U.S. Census Bureau (2010), approximately 23 million people moved to the coastal counties within the Southeastern Region between 1960 and 2008. The South Atlantic region, as a whole (i.e., coastal and non-coastal areas), is host to the most active and persistent inflow of domestic migrants in the U.S. Based on current trends, this area could soon become the nation’s most populous region (Kotkin 2013). In South Carolina alone, the coastal region has experienced a 22% increase in population and is expected to reach over 1.5 million people by 2030 (South Carolina Revenue and Fiscal Affairs Office 2015). The South Atlantic coastal region is highly susceptible to frequent, and often severe, flooding events and water impairment issues. This susceptibility is due to the region’s low-lying elevations, moderate year-round rainfall, increasing development, and highly complex watersheds. According to the U.S. Environmental Protection Agency (EPA), global climate change has arguably increased the frequency of heavy rain events as well as the intensity, frequency, duration, and strength of Atlantic hurricane activity (EPA 2016a).
The current study contributes to the literature by exploring one of the least studied but most widely used instruments to control stormwater runoff – retention ponds. Retention ponds or catchments are one of the more commonly employed best management practices used to collect and filter runoff, sediments, and other harmful pollutants before the water is discharged into the natural environment. Retention ponds are designed to fulfill two primary objectives. First, they act as a flood protection measure by collecting stormwater runoff and gradually releasing it into the watershed, which helps mitigate downstream flooding. Second, they filter runoff containing pollutants such as oils, fertilizers, and pesticides that could adversely impact environmental quality. According to Smith et al. (2017), there are approximately 21,600 stormwater retention ponds in the eight coastal counties of South Carolina. Without
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 123 proper management of these ponds, the South Atlantic coastal region will experience a continuing strain on its water resources, including intra-coastal waterways (and tributaries), marsh habitats, and other aquatic ecosystems.
Ponds, like any human-developed infrastructure, require regular monitoring and sustained maintenance throughout their useful lifecycle to ensure ongoing function and environmental effectiveness. The costs of maintaining many ponds ultimately fall on local, residential homeowners’ associations (HOAs). An HOA is a private organization within a community that makes and enforces rules within its jurisdiction. These collectives are composed of a relatively homogenous group of members (i.e., a club) within a residential development with well-defined boundaries (Groves 2006). Voter participant members who reside within a development generally manage HOAs, and the association operates to provide goods and services to its members. The purpose of the HOA is to enforce contractual land-use restrictions and provide services that would otherwise be offered by a municipal government or other entity. The association funds the provision of it services by collecting an annual or semi-annual HOA fee, which each of its members are required to pay. Within many jurisdictions, a residential developer initially constructs the ponds in accordance with local laws or ordinances. Developers often possess the requisite knowledge about pond construction and management. However, the ownership of common space within a development, including ponds, almost always passes to the HOA after development is complete. Therefore, HOAs may simply lack the knowledge to ensure their ponds are properly serving the designed function of mitigating harmful runoff and serving as flood protection (McKenzie 2005). This uncertainty can be compounded with deficient budgets to maintain many ponds.
6.2 Framework Despite the prevalence of water contamination issues associated with stormwater runoff, there has been little economics research addressing stormwater management. The existing economic literature is thin when compared to other scientific disciplines such as the marine sciences, engineering, hydrology, and ecology. For example, our search for the term “stormwater management” in the economics database, EconLit, resulted in only 18 studies published in peer-reviewed journal articles. Upon casting a wider net by using the search term “stormwater,” we identified 27 peer- reviewed journal articles, of which 19 loosely pertain to the current study. A search using Google Scholar generates several more results, although only some of the results come from peer-reviewed, scientific journals. Although not necessarily subject to the peer-review process, we also considered academic books and texts about stormwater management, and more specifically, stormwater pond management.
This chapter is organized as follows. In section 6.3, we offer a brief discussion of the relevant literature relating to quasi-public goods and stormwater management. In section 6.4, we discuss the local regulatory environment and industry practices, relevant to stormwater management in the South Atlantic coastal U.S. Section 6.5 offers an adaptation of a theoretical model, which outlines the social value and social cost of stormwater management in the context of retention ponds. Section 6.5 offers county-level data on stormwater pond fees, governmental expenditures, and enforcement. In section 6.6, we discuss the main findings and address policy implications within the context of a coastal watershed that is vulnerable to climate change and sea level rise.
6.3 Literature Review An interesting aspect of stormwater retention ponds is that they can be described as “impure” (or quasi-) public goods (Wichman 2016). These types of economic goods are labeled as impure because they provide both private and public
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 124 benefits. Salient analogs include green electricity, energy efficiency and renewable energy technology adoption, and fuel-efficient vehicles. Retention ponds fall within this category of goods because state or county laws and regulations assign private property rights of the ponds to private landowners, but the catchments provide benefits to the public. Homeowners within an HOA have legally assigned collective rights, which confer the rights to use and maintain all common areas in the development and such rights are governed by HOA covenants. Under these covenants, the HOA is the responsible party for the maintenance, repair, and replacement of the ponds. The construction and maintenance of a pond within one development may also provide flood and pollution mitigation benefits for downstream properties; however, downstream properties do not have to contribute to maintaining the pond. Put another way, environmental management problems must be treated in a spatial context, as nature links activities undertaken in one location with outcomes in another (Smith et al. 1997). These spatial links are especially true in low-lying elevations, such as coastal regions, that have complex, inter-connected watersheds.
The underlying problem with the private provision of public goods is that free-riding leads to an inefficient, underprovision of the good (Falkinger et al. 2000). In the case of retention ponds, the underprovision can take the form of under-development of the ponds or an inefficient level of maintenance activities over the life cycle of the pond. Free-riding can occur if neighboring houses outside of the development receive the downstream benefits of flood and pollution mitigation without having to contribute toward the costs of maintaining a retention pond. Historically, economic theory has addressed this phenomenon by viewing contributions to a public good as strategies in a non-cooperative game (Bergstrom et al. 1986; Cornes & Sandler 1986). Further, the literature has shown that the underprovision becomes stronger towards the end of a finite number of repetitions of a voluntary contributions game (Isaac et al. 1984; Ledyard 1995).
Incentive-based mechanisms have been proposed to induce efficient contributions to the public good (Varian 1994). For example, Falkinger (1996) designed a simple tax-subsidy scheme, which caused contributors to consider the relative size of their contributions in such a way that created an efficient level of the public good provision. Providing evidence from experimental trials, Falkinger et al. (2000) later showed this incentive-based mechanism performed quite well in a laboratory setting, leading to an immediate and significant shift, in the provision of the good, toward an efficient solution. Wichman (2016) built upon the early research by considering consumers with heterogeneous preferences over private and public components of environmental goods. He advocated for a combination of subsidy and credible punishments, which he posits lead to an incentive-compatible Nash equilibrium for the socially optimal provision of an impure public good.
It is challenging from a policymaking standpoint to determine the socially optimal provision of an impure good, such as the optimal level of flood or pollution mitigation provided by a stormwater retention pond. To establish such an arrangement, stakeholders first need some prerequisite knowledge of the economic costs and benefits of the services offered by stormwater retention ponds. The majority of the limited economic literature covering stormwater ponds is dedicated to assessing the costs or benefits, but not both, of the stormwater pond services.
The empirical benefit-analysis literature can be described as an assessment of the benefits provided by stormwater retention ponds, low impact development, land acquisition programs, or a combination thereof (Aminzadeh et al. 2013). The empirical cost-analysis literature, on the other hand, seeks to determine the economic or accounting costs associated with stormwater development, management, and maintenance. We reserve the discussion of the cost analysis to the next section, as it directly pertains to our discussion of the current regulatory environment within the South Atlantic coastal region.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 125 Among the benefit-analysis literature, the Cadavid and Ando (2013) study was one of the few studies that addressed the function, efficacy, and (separable) benefits of stormwater management in the U.S. Their research explored the willingness-to-pay (WTP) for stormwater control in the Champaign-Urbana region of Illinois. Since stormwater control is an impure public good, there is not necessarily an economic market to determine the price for offering the service or the quantity of stormwater control that should be provided. The authors estimated the benefits of stormwater control by conducting a stated-preference method (i.e., a choice experiment survey), and the authors found that households placed a positive monetary value on the following stormwater control services: reduction in basement flooding, improved water quality, and improved hydrological function and aquatic habitat. They estimated a $580,000 WTP value for stormwater control to reduce flooding (Cadavid & Ando 2013). Further, they estimated a WTP of $270 million to improve water quality. Since the authors only surveyed within one specific region of the Midwestern U.S., it would arguably be difficult to generalize their estimated results to other areas of the U.S., as households’ values of such services may differ by region.
A series of studies have conducted stated-preference evaluations to elicit the benefits of stormwater management in Australia (Jorgensen & Syme 2000; Jorgensen et al. 2004; Jorgensen et al. 2006). The goal of all three studies was to derive an accurate estimate of stormwater abatement benefits in Australia. For example, Jorgensen and Syme (2000) offered a contingent valuation survey in which they explicitly controlled for protest attitudes to elicit a more accurate WTP value for stormwater management. The authors estimated a total value of $13 million (in U.S. dollars) in benefits for stormwater management services. Brown et al. (2016) conducted a qualitative survey of private household participation in stormwater management in Australia. This particular study did not explicitly seek to estimate WTP for stormwater management; instead, the study sought to determine the factors that lead households to participate in a stormwater program. The authors found that the public is mainly uneducated about stormwater management practices, and they advocated for combining economic incentives with education programs to encourage mitigation behavior and other sustainability practices regarding stormwater management.
6.4 Retention Pond Maintenance Stormwater pond governance is enacted at the municipal level; however, state and federal requirements guide local ordinances. At the federal level, the Clean Water Act of 1972 regulates the discharge of pollutants into the nation’s waters and empowers the EPA to monitor surface water quality. Specifically, the Clean Water Act authorizes the EPA to implement programs and guidelines to control point and nonpoint sources of pollution. Section 402 of the Clean Water Act implements the National Pollutant Discharge Elimination System (NPDES), which requires all stormwater discharges from point sources from specific activities to have a permit and makes it illegal to discharge stormwater without a license.
Each state has enacted additional legislation aimed at regulating the release of pollutants into waterways. These acts include the Water Resources Act of 1972 in Florida, the Water Quality Control Act of 1964 in Georgia, the Pollution Control Act of 1972 in South Carolina, and the Clean Water Responsibility Act of 1997 in North Carolina. The acts work in conjunction with the federal Clean Water Act and provide additional regulations and guidelines for the collection and discharge of stormwater within each state. The statutes authorize the governing body to pursue legal actions such as civil and criminal penalties for ordinance violations. The legislation often places a maximum penalty per violation per day that a governing body may assess. For example, the maximum penalty in Georgia per violation per day is $27,500 (Water Quality Control Act, 1964) while the maximum penalty in South Carolina is $10,000 per
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 126 day (Pollution Control Act, 1972).
Municipal governments enact the final layer of stormwater ordinances, which often require developers to submit long-term maintenance plans before construction and operating permits are granted. The long-term maintenance plans serve as an agreement between the current and subsequent landowners and the municipal government regarding maintenance activities. Enforcement of stormwater pond ordinances is also the responsibility of municipal governments, which work to provide reasonable assurances that maintenance activities are performed. Reasonable safeguards include inspections, written violations, withholding and revoking of permits, and civil/criminal penalties for each violation. For example, the city of Savannah, Georgia may levy a sentence of up to $1,000 per day for each stormwater ordinance violation (Savannah Stormwater Management Ordinance, 2012).
The discussion thus far has focused on the use of civil and criminal penalties as negative incentives to uphold stormwater ordinances; however, municipalities may also use positive incentives to encourage best management practices. Positive incentive policies may include stormwater fee discounts, development incentives, grants, rebates and installation financing, and awards and recognition programs. In a survey of 43 cities, the EPA (2009a) found that 29 of the cities (approximately 67%) implemented a stormwater discount fee, which provides homeowners and landowners incentives to reduce impervious cover and stormwater runoff generated from their property. Incentives targeted towards community groups such as HOAs include grants, rebates, and installation financing, which mitigate the cost of implementing best management practices. The EPA’s survey of cities also found that only 6 of 43 (14%) provided grants while just 14 of 43 (33%) offered rebate and installation financing (U.S. EPA 2009a).
Our review of the literature found several survey-based case studies investigating the economic cost of stormwater pond management and maintenance. For example, Weiss et al. (2005), Weiss et al. (2007), and Erickson et al. (2010) all explored the economic cost of stormwater management for the Midwest Region of the United States. Based on their survey and literature analysis, the authors found that the maintenance cost for a relatively standard-sized pond (i.e., one-acre pond), with initial construction cost of $10,000, required annual maintenance that averaged approximately 8% of the initial construction cost (Erickson et al. 2010); therefore, the cumulative maintenance cost would approximately equal the initial construction cost after 12 years. Erickson et al. (2010) represent the costs of stormwater ponds in a particular manner because the ponds are generally constituted by relatively large upfront construction costs, whereas the annual maintenance costs are small in comparison. In their article, Erickson et al. (2010) do not explicitly list a discount rate nor define a useful life for a stormwater pond. Based on the lack of stated discount, it can only be presumed that the original authors posited a zero-discount rate, in which case the estimated annual maintenance costs are a lower bound of the actual annual maintenance costs. Further, stormwater ponds (depending on the type) generally require extensive maintenance after 20 to 35 years, and the useful life of a pond can exceed 50 years (U.S. EPA 2009b). For ponds approximately 10 acres in size, the annual maintenance cost constitutes 4% of the initial construction cost of $100,000, and the cumulative maintenance cost would roughly equal the total construction cost after 25 years of operation. Weiss et al. (2005) explored pond maintenance and construction cost estimates from the empirical literature, and their findings are presented in Figure 6.1. The figure indicates that operating and maintenance costs fall as pond size increases.
Wossink and Hunt (2003) explored the economic costs of best management practice (BMP) stormwater ponds in the state of North Carolina, including the Coastal Plain region. The authors use the term BMP to denote the “best” type of pond construction based on the environmental needs in which the pond is located. Their definition of a BMP is a relative term to denote the best type of pond given the stated needs; it does not connote a superior type of
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 127 100
10 O&M Cost as % of Total Const Cost O&M Cost as % of Total
1 1,000 10,000 100,000 1,000,000
Total Construction Cost ($)
Figure 6.1 Total operating and maintenance costs as a function of total construction cost in 2005 U.S. dollars for wet ponds. Notes: Diamond shaped points represent empirical estimates from the literature. The dashed line represents a line of best fit through the points. The two solid lines represent the 67% confidence interval for the estimates. Source: Weiss et al. (2005, p. 31).
maintenance or construction practice. The type of pond is determined by the size of the watershed, the imperviousness of the watershed, and the amount of available land for the pond construction (Wossink & Hunt 2003). For example, stormwater wetlands, a bio-retention pond, or a sand filter would be inappropriate for urban or suburban stormwater management because this type of watershed is probably relatively small, highly impervious, and has limited land available for construction of the pond. A structural wet pond would constitute a BMP for an urban or suburban region, because it is arguably the best solution based upon the environmental needs of the area.
Wossink and Hunt’s (2003) definition of the BMP cost includes the initial construction, land development, and annual operating expenses. Based on this definition, the authors estimated that a one-acre pond would cost approximately $14,000 to construct, whereas a 10-acre pond would require nearly $65,000 to build. Unlike Erickson et al. (2010), Wossink and Hunt (2003) estimated that the annual maintenance cost would run approximately 4% per year (as opposed to 8% cited in the previous study) of the initial construction cost. In other words, the cumulative maintenance cost would approximately equal the initial construction cost after 20 years. For a 10-acre pond, Wossink
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 128 and Hunt’s (2003) estimates imply that the annual maintenance cost would constitute approximately 2% of the initial construction cost; based on these calculations, it would take approximately 60 years for the cumulative maintenance cost to equal the initial construction cost. The differences in Erickson et al.’s (2010) estimates and Wossink and Hunt’s (2003) estimates arguably stem from the difference in regions and policies of stormwater ponds. In general, Wossink and Hunt’s research indicates that a one-acre pond requires a higher initial investment, but has a lower annual maintenance cost than those estimated by Erickson et al. (2010).
Cost Per Service Cost Per Service Maintenance Activity Lower Bound Upper Bound Annual Maintenance Activities Water Management $1,000 $5,000 Blue Tilapia $200 $500 Aeration $1,200 $1,500 Trash and Minor Debris $500 $1,000 Vegetation Removal $2,000 $5,000 Mosquito Control $1,500 $2,500 Tree and Branch Removal $5,000 $10,000 Total $11,400 $25,500 5-Year Maintenance Activities 1,000,000 Replace Fountain $2,000 $4,000 Engineering Consultation $500 $5,000 Trash Grates and Outfall Cove $400 $1,500 Inflow and Rip-Rap Repairs $7,000 $13,000 Clogged Pipe Cleaning $2,000 $5,000 Total $11,900 $28,500 30-Year Maintenance Activities Dredging $200,000 $400,000 Hauling $50,000 $70,000 Re-grade and Hydroseed $5,000 $10,000 Bare Root Aquatic Planting $3,000 $5,000 Total $258,000 $485,000 30-Year Aggregated Costs Total $671,400 $1,421,000
Table 6.1 Estimated 30-Year Maintenance Costs (USD) for Stormwater Retention Ponds. Notes: Service cost estimates based on a one-acre pond, 5-8 feet in depth, and 1,000 feet of shoreline. The 30-year aggregated cost consists of 30 annual maintenance activities, six five-year maintenance activities, and one 30-year maintenance activity.
Houle et al. (2013) conducted an engineering analysis of stormwater pond construction and maintenance costs in New Hampshire. The authors only calculated the costs for low impact development systems, which are arguably higher than the capital and maintenance costs of stormwater ponds. Nevertheless, the authors estimated that low
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 129 impact development systems would cost approximately $33,400 per acre in initial capital, and the annual maintenance cost would run approximately 19% of the initial capital cost. Based on these estimates, it would take approximately five years for the cumulative maintenance cost to equal the initial development cost. We obtained maintenance cost estimates from a stormwater pond developer and service manager located in the state of South Carolina. The estimates are provided for a one-acre pond with an approximate depth of five-to-eight feet and 1,000 feet of shoreline.
Table 6.1 contains two sets of cost estimates – a lower and upper bound estimate. The estimates are broken up into recommended annual, five-year, and 30-year maintenance costs. The forecast at the bottom indicates that maintenance activities for a one-acre pond can cost between $671,000 and $1,420,000 USD over a 30-year cycle of a pond. The total costs are relatively sensitive to the included service. For example, not all retention ponds will contain a fountain. Retention ponds vary in size from one to 15 acres (or larger), and the cost estimates are not levelized; nevertheless, a more extensive pond would scale the maintenance costs higher than what are provided (Table 6.1).
6.5 Theoretical Considerations for Stormwater Management Policies In the previous sections, we discussed the properties of stormwater control as an impure public good, which can lead to market failure and divergence between the marginal value of stormwater control to an individual and the marginal costs to society. Given this potential for free market failure, government intervention in terms of oversight, monitoring, and enforcement is arguably justified in order to bring the private and social value of stormwater management into equilibrium. This should, in turn, lead to the socially optimal level of runoff reduction.
In our theoretical models (Appendix A6-2, see www.scseagrant.org/spsok), we argue that if the demand for runoff is inelastic, then Figure 6.2 implies that the free market solution (Qf) for stormwater control results in high levels of runoff, and by extension risks for flooding and poor downstream water quality. Conversely, reducing the amount of runoff to the optimal level for social welfare (Qw) requires that the marginal social value is negative (high costs) and that the government would need to expend a tremendous amount of resources. These high government expenditures could further detract from social welfare. It is possible that the marginal social value of stormwater is negative based on the positive estimated benefits ascribed to stormwater management (i.e., runoff reduction), as evidenced by the recent economic literature (Cadavid & Ando 2013). However, this study was based in the Champagne-Urbana region of Illinois, so it is difficult to generalize the authors’ findings to other areas of the country. Further, Jorgensen and Syme (2000) found positive total estimated benefits associated with stormwater management. Jorgensen and Syme’s (2000) findings imply that runoff could generate negative marginal value to society, but not at a significant enough level to justify the costs of reducing runoff to the socially optimal level (Qw in Figure 6.2). As a result, government enforcement is likely to yield a level of runoff that is less than the social optimum (somewhere between Qf and Qw in Figure 6.2).
Therefore, we considered a third option for achieving the optimal level of stormwater management at lower costs to the individual. In this scenario (depicted in Figure 6.3), some government funds are delegated to actions that positively reinforce stormwater management, as derived from the recent economic literature pertaining to impure public goods. First, assume that current government enforcement activities (c(e)) raise the cost of stormwater management, so that the quantity of runoff results in level Qw, the intermediate runoff level predicted above. According to Figure 6.3, the government’s current activities induce a reduction of runoff, but the activities still do not
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 130 yield the socially optimal level achieved when costs are raised to c(E).
A government subsidy for stormwater management could arguably reduce the costs of additional enforcement carried by the pond manager and thus induce individuals to further reduce runoff through effective maintenance activities. If a local government can calculate the current level of runoff and also determine the socially optimal level of runoff for an area, then presumably they could offer a marginal subsidy to offset a community’s additional per-unit costs of stormwater management. In Figure 6.3, the marginal subsidy (shaded in gray) would provide the final inducement
to reduce the level of runoff to the socially optimal level, Qw. This suggested combination of a subsidy scheme and enforcement would arguably generate an incentive-compatible Nash equilibrium, as found within the game theoretic work by Wichman (2016) pertaining to impure public goods.
As outlined in section 6.4, positive incentives (such as subsidies) consist of stormwater fee discounts, development incentives, grants, tax rebates, installation financing, awards, and recognition programs. The EPA (2009) found
w welfare enhancing c(E)
Cost of Stormwater Management f free market c(0)
Qw Qf
High Quantity of Runoff Low Management = Management = Low Runoff High Runoff
Figure 6.2 Demand curve for pond maintenance that includes the costs (c) of both government enforcement (E) and free market (0) expenditures. We see that as the costs of management rise due to pricey government enforcement
practices, the quantity of runoff approaches the welfare enhancing “optimal level” (Q w ), while under the free market
the quantity of runoff is high (Q f ) due to low levels of management.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 131 w c(E) marginal unit of subsidies Cost of w’ Stormwater c(e) Management f c(0)
Qw Qw’ Qf High Quantity of Runoff Low Management = Management = Low Runoff High Runoff
Figure 6.3 Demand curve for pond maintenance including the costs of both government enforcement and incentives. The marginal unit of subsidies accounts for the additional cost of maintenance to achieve optimal levels of runoff by incentivizing managers to maintain their pond(s) at recommended levels.
that only 14% of surveyed cities provide grants and 33% of surveyed cities provide rebates or installation financing. Therefore, it appears that few cities in the U.S. currently offer stormwater management subsidies.
6.6 Stormwater Pond Management in South Carolina The objective of this section is to offer a series of descriptive statistics associated with stormwater pond management and enforcement for a vulnerable area within the South Atlantic coastal region. We only present descriptive statistics since there is little to no economic data pertaining to stormwater pond costs and benefits. Of course, an empirical analysis would allow us to test our model’s various predictions and provide the opportunity to draw inference from one or more hypothesis tests associated with stormwater pond management and enforcement. However, the objective of the current study is to push stormwater management to the fore so that research can be conducted in the future.
We examine stormwater management among South Carolina’s eight coastal counties. Figure 6.4 displays the coastal region of South Carolina, which consists of Jasper, Beaufort, Colleton, Dorchester, Charleston, Berkeley, Georgetown, and Horry counties. Characteristics of the coastal region include a generally flat terrain, slow moving rivers, widespread marshlands and swamps, and moderate year-round rainfall. The region contains two metropolitan
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 132 statistical areas (MSA): 1) the Charleston MSA; and 2) the Myrtle Beach MSA. Charleston County has the largest population followed by Horry, Berkeley, and Beaufort counties. The Charleston MSA consists of Charleston, Berkeley, and Dorchester counties. The Myrtle Beach MSA consists of Horry county.
6.6.1 Stormwater Pond Budget Data
As of 2013, there were approximately 21,600 ponds, encompassing around 30,000 acres, in South Carolina’s coastal counties (Smith et al. 2017). We obtained stormwater pond construction permit data from the S.C. Department of Health and Environmental Control (S.C. DHEC). Figure 6.5 shows the total number of stormwater best management practice (BMP) permits issued each year between 2009 and 2015. S.C. DHEC issued nearly 5,000 BMP permits between 2009 and 2015, and averaged 671 new BMP permits per year. The largest number of permits were issued in the most populated counties. Given the large population increase between 2006 and 2017, it is expected that the provision of BMP permits continued to increase in the years 2016 through 2018 (data not available).
As a proxy for the enforcement of stormwater pond ordinances, we use county-level expenditures on stormwater management. We focus on years between 2009 and 2015 due to the availability of S.C. DHEC permit data. Expenditures on stormwater management include personal and contractual services, supply and materials, capital outlay, and construction costs for publicly maintained ponds. These expenditures can loosely be interpreted as the costs of enforcement, identified as E in section 6.5. In Table 6.2, we explore the percentage change in stormwater
Myrtle Beach MSA
Charleston MSA
Horry
Georgetown
Berkeley
Charleston Dorchester Jasper Colleton
Beaufort
Figure 6.4 Map of South Carolina showing the eight coastal counties and the Charleston and Myrtle Beach MSAs.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 133 908 900 871
701 700 686 700
500 472
360
Number of BMP Permits Issued 300
2009 2010 2011 2012 2013 2014 2015
Year
Figure 6.5 Stormwater best management practice permits 2009 – 2015. Notes: The graph displays the annual number of stormwater best management practice permits issued by the S.C. Department of Health and Environmental Control between 2009 and 2015.
expenditures per pond permit, stormwater expenditures per person, total county government expenditures, government expenditures per person, stormwater expenditures as a percentage of total county expenditures, population, and median household income. We compare these statistics in the form of percentage changes, as there is a tremendous amount of variation between county-level population size and household income.
1 2 3 4 5 6 7 Stormwater Stormwater Stormwater Total County Total, Per- Expenditures Median Expenditures County Expenditures Gov’t. Capita Gov’t. (as percentage Population Household (per pond (per person) Expenditures Expenditures of total Income permit) expenditures) Beaufort -68.78 -20.67 4.08 -3.20 -18.05 7.52 3.63 Berkeley -11.74 464.12 27.24 14.85 391.18 10.79 2.10 Charleston -37.65 64.65 10.37 1.89 61.60 8.32 7.54 Dorchester -59.71 -19.58 8.99 0.92 -20.31 8.00 -1.06 Georgetown -25.90 130.46 6.19 5.15 119.17 0.99 -2.55 Horry -70.96 -19.69 3.66 -6.15 -14.42 10.45 -1.90
Table 6.2 Percentage Change in Stormwater Expenditures, Total County Government Expenditures, Population, and Household Income: 2009-2015. Notes: All numbers represent percent changes.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 134 Stormwater expenditures per pond permit (column 1) declined in all counties between 2009 and 2015. We contend that this reduction in stormwater expenditures represents a decline in enforcement activities relative to the number of ponds in a county, which leads to a movement away from the socially efficient level of stormwater abatement. Stormwater expenditures per person (column 2) declined in some counties but rose significantly in others. For example, Beaufort, Dorchester, and Horry County all experienced a 20% decline in stormwater expenditures per person. Conversely, Berkeley, Charleston, and Georgetown County all experienced large increases. Berkeley County’s per-person stormwater expenditures reveal a caveat to this story; that is, the average per-person stormwater management expenditures charged during the 2009-to-2015 period within the eight coastal counties was approximately $12 per person, whereas for Berkeley County it was less than $2 per person during this period. The large percent increase in stormwater expenditures per person in Berkeley County is driven by the fact that expenditures were at a relatively low level ($0.50 in 2009) and increased to $3 by 2015. A similar story can be told for Charleston and Georgetown counties, which initially had expenditures lower than the eight-county region average. These statistics suggest that the counties were operating at socially inefficient levels and sought to remedy the situation by raising per- person expenditures.
To demonstrate that the decline in stormwater expenditures per permit is not due to an overall reduction in government expenditures, we provide the percentage change in total county expenditures in column 3 of Table 6.2. Total, county-level expenses increased in each county, indicating that the decline in stormwater expenditures cannot be attributed to declining government expenditures. We include the percentage change in government expenditures per person, which remained relatively steady during this six-year period. Further, we show that stormwater expenditures as a percentage of total county expenditures (column 5) have declined in all but Berkeley, Charleston, and Georgetown counties. However, as we argued above, each county was leveeing an inefficient stormwater management fee during this period. As further evidence, we show that the population (column 6) has grown for each of these six counties during the six-year period. Finally, median household income increased for three of the counties and only marginally decreased for the remaining counties (Dorchester, Georgetown, and Horry). We include column (7) to demonstrate that the county-level governments did not reduce stormwater expenditures per permit due to economic hardship.
1 2 3 4 Residential Nonresidential Deviation from the Deviation from the Stormwater Fees County Stormwater Fees Mean of Mean of (Single Family (per acre) Residential Fees Commercial Fees Residence) Beaufort 100 328 42 64 Berkeley 48 288 -10 24 Charleston 72 418 14 154 Dorchester 45 208 -13 -56 Georgetown 52 240 -6 -24 Horry 29 102 -28 -162 Average 58 264 NA NA Standard Deviation 25 108 NA NA
Table 6.3 Residential and Nonresidential Stormwater Management Fees (USD): 2009-2015. Notes: Nonresidential (commercial) stormwater fees calculated as one acre of developed property with 40% of impervious surface.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 135 Table 6.3 offers the residential and nonresidential stormwater management fees for the six non-rural counties along the coastal region of South Carolina. Each county has slightly different methods for assessing the residential and nonresidential fees, and each county may have differentiated fees based on location within the county. Further, some counties use the stormwater fee revenues to pay for all of the county-level stormwater management expenditures, whereas other counties supplement the spending with other sources of income, such as taxes and fees through other county or municipal services. Beaufort County charged the highest residential fee, whereas Charleston County charged the highest non-residential fee on a per acre basis. As discussed above, Berkeley County had some of the lowest per- capita stormwater expenditures within the coastal region. This finding seems consistent with the county’s residential stormwater fee, which is $10 less than the average residential fee within this region. Horry County levied the lowest residential and non-residential fees; however, Horry County was one of the fastest growing counties in terms of population and economic development, which may have offset the need to charge higher fees.
In Table 6.4, we examine the change in developed areas between 2006 and 2011. The land development data is based on the National Land Cover Database (U.S. Geological Survey, 2017), which classifies land into 20 different classifications. Columns (1) and (2) report land classified as: Developed, Low Intensity; Developed, Medium Intensity; or Developed, High Intensity. Column (7) demonstrates that every county experienced an increase in development between 2006 and 2011. The change in land development is significant because the South Carolina Stormwater Management and Sediment Reduction Act (1993) requires that any new, land-disturbing development activity have a stormwater management and sediment control plan. Additionally, if the plan necessitates a retention pond, then the developer is required to file for a stormwater pond permit. Therefore, Table 6.4 can be construed as an additional robustness check on county-level stormwater expenditures per pond permit (offered in Table 6.2). In other words, population increases are driving land development in South Carolina coastal counties; therefore, the number of stormwater ponds is increasing as well. Despite the increase in development, the government expenditures per pond permit declined between 2009 and 2015.
1 2 3 4 5 6 7 % Change % % Level Developed Developed County Size Developed County Developed Developed Change 2006 (acres) 2011 (acres) (acres) Area 2006 (acres) 2011 (acres) (acres) (percent) Berkeley 22,810 24,499 786,701 2.90 3.11 7.14 1,689 Dorchester 13,026 13,837 368,516 3.53 3.75 6.04 811 Beaufort 15,069 16,519 590,968 2.55 2.80 9.18 1,449 Jasper 4,048 4,598 447,596 0.90 1.03 12.74 551 Charleston 44,954 46,838 869,111 5.17 5.39 4.10 1,883 Colleton 5,836 5,987 725,301 0.80 0.83 2.56 151 Georgetown 8,492 8,953 662,181 1.28 1.35 5.29 461 Horry 45,921 50,594 803,196 5.72 6.30 9.68 4,673
Table 6.4 South Carolina Coastal Region’s Change in Land Development: 2006-2011. Notes: Developed area represents area classified as: 1) Developed, Low Intensity; 2) Developed, Medium Intensity; or 3) Developed, High Intensity according to the National Land Cover Databases. Legend available at https://www.mrlc.gov/nlcd11_leg.php.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 136 6.6.2 Enforcement Data for Horry County, South Carolina
To provide additional evidence that counties are moving away from the efficient level, we collected data from the Horry County Stormwater Management Department (HCSMD). We chose Horry County for two reasons. First, among the coastal counties in South Carolina, it has the largest concentration of stormwater ponds (Chapter 1), and it experienced the greatest amount of land development between 2006 and 2011 (Table 6.4). Second, HCSMD utilizes the Cityworks and Energov platforms to manage, track, and analyze infrastructure assets. We used these platforms to collect inspection and compliance data on stormwater ponds.
According to the Horry County Stormwater Design Manual (Horry County, 2017), the stormwater management office will conduct periodic maintenance inspections over the useful life of a pond. The purpose of the inspections is to ensure that “…permanent maintenance is being performed by the maintenance schedules for the various stormwater management facilities in the County permit or approved stormwater management plan” (Horry County, 2017, p. 81). According to the HCSMD’s Best Management Practice Inspection Program, the goal is to conduct a post-construction inspection for each pond once every two years.
The HCSMD provided data on construction and post-construction inspections that occurred between 2010 and 2017. The HCSMD manages their post-construction inspection data using the Cityworks platform, and the data includes the date of the inspection, an itemized list of inspection criteria, and inspector recommendations. The inspection data lacks a field indicating if the pond is in compliance or not; therefore, we treat a pond as non-compliant under the following conditions: 1) the inspector listed recommended maintenance; 2) the inspector includes specific instructions or indicated routine maintenance for any of the inspection criteria. Given this definition, non-compliance suggests that the pond manager has not maintained the pond up to the level specified in the county permit or the approved stormwater management plan.
1 2 3 4 5 Post-Construction Count of All Percent of All Percent Year Count Compliant Inspections Inspections Compliant 2010 60 45 32 75 71 2011 357 144 109 40 76 2012 592 119 94 20 79 2013 584 30 26 5 87 2014 839 32 21 4 66 2015 1,407 85 65 6 76 2016 1,543 19 14 1 74 2017 1,391 10 9 1 90 Totals 6,773 484 370 7 76
Table 6.5 Horry County Stormwater Management Department’s Retention Pond Inspections. Notes: The “Count of All Inspections” column includes both construction and post-construction inspections.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 137 Table 6.5 presents inspection and compliance statistics occurring in Horry County, S.C. between 2010 and 2017. We calculated the percent of post-construction inspections relative to all inspections conducted, as well as the percent of post-construction inspections that resulted in a “compliant” status. During this period, the HCSMD conducted 6,773 inspections, of which, 484 (approximately 7%) were post-construction inspections. The number of inspections has increased over time; however, the number of post-construction inspections relative to the cumulative number of inspections conducted fell every year. We interpret this as declining government enforcement efforts targeted towards existing ponds. If the HCSMD were to meet its stated goal of inspecting each constructed stormwater pond every two years, then HCSMD would have to conduct 3,900 post-construction inspections each year. We interpret the information in Table 6.5 as evidence that the HCSMD is moving away from the efficient level, and, by extension, other municipalities are as well.
6.7 Summary and Recommendations In sum, we argue that current governmental enforcement of stormwater management leads to a reduction in stormwater runoff, but not at a level that maximizes social welfare. Due to the nature of retention ponds as an impure public good, it is difficult to regulate stormwater runoff efficiently. Based on the theoretical model, and examples from the South Atlantic coastal region, we demonstrated that government expenditures on stormwater management are costly. We also provided evidence, based on the limited economic literature, that stormwater management offers positive social benefits, and we claimed that these benefits are arguably diverging from the social costs of stormwater runoff. Given the high cost of enforcement, we posited that the government’s current disincentive structure (fees, penalties, and implementation, among others) is limited in affecting a reduction in stormwater runoff, so the disincentives should be combined with an incentive program, a potentially less-costly alternative. In other words, the government needs to offer a carrot in addition to a stick to induce the optimal management of stormwater runoff.
The optimal government program for reducing stormwater runoff is essential for the South Atlantic coastal region in particular, which is primarily vulnerable due to hurricane activity, low elevations, moderate year-round rainfall, and a growing population. This problem will arguably become exacerbated in the future due to climate change and sea level rise. In addition to well-designed government programs, future research is needed to estimate the social costs and benefits of stormwater management. Specifically, additional research is needed to better understand at least three aspects of stormwater management services. First, future research should offer a more comprehensive empirical analysis of the cost and benefits associated with stormwater ponds and stormwater management. For example, non- market valuation techniques, such as revealed preference or stated preference methods, could be used to continue analyzing the benefits of such services. Second, future research should attempt to better understand the supply side of stormwater management, why a potential underprovision of stormwater services may be offered, and the impacts of the underprovision of stormwater management on society. Three, additional research needs to further explore the funding needs and financial incentives offered by stormwater utility services. As a social science with a well- established literature of non-market valuation, the field of economics needs additional research dedicated toward better understanding stormwater runoff systems and mitigation.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 138 Research Gaps
• In addition to well-designed government programs, future research is needed to estimate the social costs and benefits of stormwater management. • Future research should attempt to better understand the supply side of stormwater management. • As a social science with a well-established literature of non-market valuation, the field of economics needs additional research dedicated towards a better understanding of runoff systems and mitigation.
6.8 References Aminzadeh, S, L Pendleton, S Bothwell, A Pickle, and AB Boehm (2013). U.S. coastal and estuarine stormwater management approaches. Choices Magazine, 28(3), 1-5
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Cornes, RC and T Sandler (1986). The theory of externalities, public goods, and club goods. Cambridge, MA: Cambridge University Press
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Espey, M, J Espey, and WD Shaw (1997). Price elasticity of residential demand for water: A meta-analysis. Water Resources Research, 33(6), 1369-1374
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Falkinger, J, E Fehr, S Gachter, and R Winter-Ebmer (2000). A simple mechanism for the efficient provision of public goods: Experiment evidence. American Economic Review, 90(1), 247-264
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 139 Groves, JR (2006). All together now? An empirical study of voting behaviors of homeowner association members in St. Louis County. Review of Policy Research, 23(6), 1199-1218
Horry County (2017). Horry County Stormwater Management Design Manual. Horry County Stormwater Management Department. Accessed online at http://stormwater.horrycounty.org/Portals/21/Documents/DesignManual/ Horry%20County%20SW%20Design%20Manual%20Enacted%20Jul%202017.pdf (November 2017)
Houle, JJ, RM Roseen, TP Ballestero, TA Puls, and J. Sherrard Jr. (2013). Comparison of maintenance cost, labor demands, and system performance for LID and conventional stormwater management. Journal of Environmental Engineering, 139, 932-938
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Jorgensen, BS, GJ Syme, LM Smith, and BJ Bishop (2004). Random error in willingness to pay measurement: A multiple indicators, latent variable approach to the reliability of contingent values. Journal of Economic Psychology, 25, 41-59
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Smith, EM, DM Sanger, A Tweel, and E Koch (2017). Chapter 1: A pond inventory for the eight coastal counties of South Carolina. In Stormwater Ponds in Coastal South Carolina: Inventory and State of Knowledge Report 2017, BE Cotti-Rausch, MR DeVoe (eds.)
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 140 Smith, VK, KA Schwabe, and C Mansfield (1997). Does nature limit environmental federalism? Discussion paper 97-30, Resources for the Future. Accessed online at http://www.rff.org/research/publications/does-nature-limit-environmental- federalism (February 2016)
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Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 141 Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 142 CHAPTER 7 – COMMUNICATION RECOMMENDATIONS FOR IMPROVED STORMWATER POND MAINTENANCE IN COASTAL SOUTH CAROLINA
Authors
Katie A. Callahan Center for Watershed Excellence, Clemson University, Clemson, S.C.
Amy E. Scaroni, Ph.D. and C. Guinn Wallover Clemson Extension Service, Charleston, S.C.
Melinda Weathers, Ph.D. Department of Communication Studies, Sam Houston State University, Huntsville, TX
Alex Neal College of Communication, North Greenville University, Tigerville, S.C.
Corresponding Authors Amy E. Scaroni, Ph.D. ([email protected]), C. Guinn Wallover ([email protected])
7.1 Background There are an estimated 9,269 development-related wet detention basins (herein referred to as stormwater ponds) in the coastal counties of S.C. (Chapter 1). As these ponds age, there is an increasing risk that poorly sized and poorly maintained ponds fail to control runoff effectively and export pollutants downstream (Mallin 2000; Mallin et al. 2001; Messersmith 2007). Despite variability in pond performance for treatment of multiple water quality parameters, regulations (i.e., requirement for seasonal high-water-table monitoring) could disincentivize low-impact development (LID) alternatives and maintain the status quo of wet detention ponds as the most frequently relied-on stormwater management control in coastal S.C. (e.g., 2012 S.C. DHEC Construction General Permit). With a rapidly growing coastal population, the number of ponds and the impervious areas they treat are expected to increase. In order to enhance effectiveness and efficiency of stormwater ponds, we need to ensure that our coastal residents and stormwater managers have access to tools and resources needed to make sound management decisions, communicate their efforts, and inform sustainable behaviors.
Crafting a consistent message that resonates will first involve identifying the level of awareness, knowledge, concern, and motivation of a specific audience. An analysis of what communication exists, how it is shared, and how it is interpreted in relation to stormwater pond ownership and responsibility is critical. Understanding audience values and motivations can then inform strategies to encourage sustainable behavior change toward performance of regular pond maintenance. Pond maintenance can reduce organic matter and sediment inputs to the pond, which can protect water quality in the pond and in downstream receiving waters. Education is an important component of any maintenance
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 143 strategy designed to mitigate the negative environmental impacts to, and from, ponds.
7.2 Framework
7.2.1 Recognizing Multiple Audiences
Multiple audiences directly influence the function and performance of ponds (Figure 7.1). These audiences often have different pond use and maintenance goals, which can lead to conflicts when establishing management regimes. Though the prevalence of ponds across coastal South Carolina is primarily driven by local regulation, and assisted in part by the ease of modeling and design, ponds are largely privately owned. For ponds within neighborhoods, stormwater pond ownership transfers from developer to the homeowners’ association (HOA) at the time of Transfer of Developer’s Rights. Homeowners, often with no training in pond management, are then responsible for all decision- making on pond management, from scheduling maintenance to budgeting for sediment removal. In some multi-use communities, residents and businesses may share a pond, which increases the complexity of ownership, responsibility, and expectations of performance.
Since 2006 under the National Pollutant Discharge Elimination System (NPDES) program Phase II initiative, local government staff of designated quality local programs are responsible for approving the design and engineering of ponds and stormwater-related infrastructure, as well as inspecting the maintenance of these systems, post-construction. These staff in engineering, public works, and stormwater departments are also often called upon by HOAs seeking assistance with their pond. Furthermore, per the NPDES General Permit for Stormwater Discharges (S.C. DHEC 2013), municipal separate storm sewer system (MS4) communities permitted for their stormwater discharges are required to address waterways that are not meeting standards for their designated use and are identified by the state’s List of Impaired Waterbodies, or 303(d) list (TMDL program; see Chapter 6 for more discussion). If poorly managed ponds are identified as contributing to the impairment of their receiving waters, MS4s may require additional maintenance action by a community or HOA.
7.2.2 Objectives
The goal of this project was to develop a targeted outreach strategy focused on pond management that could best be addressed with education and behavior change, through the following objectives:
1. Inventory recent and ongoing methodologies, needs, and successes of pond outreach efforts in coastal S.C. 2. Use research, surveys, and interviews with experts to prioritize pond problems that can be minimized or eliminated by widespread behavior change, brought about by educational efforts. 3. Use focus groups for audience analysis, including level of knowledge, awareness, and motivations related to pond management. Conduct an audience profile that also includes preferred methods of message delivery. 4. Use the Community-Based Social Marketing (CBSM) approach to conduct a barriers-and-benefits analysis (McKenzie-Mohr 2011) to evaluate the likelihood of adoption of priority behaviors (e.g., installation of vegetated buffer zones). 5. Use a panel to test audience response to messages, and modify messages based on feedback (Appendix A7-1, see www.scseagrant.org/spsok).
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 144 Stormwater Pond Audiences and Perceptions
s ager H an P om y M on e rt d M ow e n op an e r ag rs P A e , s, e m L t e st a n lu he e n e a t n d g V ic t , , C s A c R c ti ty o a e er P e m p t e p o c h o n e a t r r p t P d e r s , a s t a s e n L t n , E a i A o o i l r g e f o a r n s o e e t n R a
W Stormwater Ponds W
e P t D M B F e l t r o e e y t t s o n a i r d t l D io w a o n m t e C r u P to la s o ond S Q ig n r u tr e g n o at e e l R rs W , , rs R e e n gu g la si to e rs D
Audience Terminology
Perceived Primary Purpose
Audience Affecting Management Decision-Making
Figure 7.1 Multiple audiences and perceptions affect stormwater pond management and messaging.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 145 6. Develop an outreach strategy and initial outreach products for target audiences using the results of the evaluation in objectives 3 through 5 (Appendix A7-1 and A7-4, see www.scseagrant.org/spsok). 7. Develop a strategic outreach plan that includes activities and programs to increase awareness, instruct, and involve target audiences in sustainable actions to improve long-term stormwater pond management function.
7.2.3 Methods
Information was collected through a literature review, network query, expert interviews, and focus groups.
Network Queries
The Environmental Protection Agency-managed listserv NPSinfo, a community of more than 2,500 individuals from federal, state, and local government and numerous public and private organizations, was queried to gauge existing outreach efforts related to stormwater pond management and maintenance.
Expert Surveys
MS4 staff and representatives of pond management companies were surveyed in order to prioritize those stormwater pond issues that can best be minimized or eliminated by resident behavior change.
Surveys were implemented as recorded phone interviews; each survey participant was kept anonymous per university institutional review board policies and approval. Completion of the full survey required 30-45 minutes of the participant’s time (Appendix A7-2, see www.scseagrant.org/spsok). Seven experts were asked to participate in each of three regions (Beaufort area, Berkeley-Charleston-Dorchester tri-county area, and Myrtle Beach area), and from that group 10 experts participated in the survey (results presented in Appendix A7-3, see www.scseagrant.org/spsok).
Focus Groups
Focus groups were conducted in three different regions (North Myrtle Beach, Charleston, and Beaufort) between June and July of 2015. Focus group participants consisted of HOA board members, stormwater sub-committee members, and residents, and each survey participant was kept anonymous per university institutional review board policies and approval. Each focus group hosted five to 10 people, and the same 14 questions were asked at each event (Appendix A7-2, see www.scseagrant.org/spsok). Not every participant answered every question.
7.3 Recommendations for Outreach and Improved Communication Strategies Recommendation 1: Messages should help all residents feel a sense of ownership of the stormwater pond and responsibility for its maintenance and performance.
All residents, including renters, are an integral part of pond maintenance and performance, but it is important to recognize that property owners have a greater stake in neighborhood stormwater pond management and services. In order to develop a climate of shared responsibility and decision-making for improved pond maintenance, communities need to establish a sense of shared ownership and an understanding of the personal benefits they receive from the
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 146 pond(s) in their neighborhood. Focus group and expert survey feedback (detailed methods in Appendix A7-2 and Appendix A7-3, see www.scseagrant.org/spsok) indicated discrepancies in the level of awareness of pond ownership and maintenance responsibility between residents, those who were more highly involved in community decision- making (i.e., HOA board member), and those who live in close proximity to the pond itself.
For the majority of participants in our focus groups, their neighborhood Property Association/HOA owns the neighborhood stormwater pond and contracts with a pond management company for maintenance. Individual neighborhoods varied on the estimated percentage of residents aware of stormwater pond ownership. In most cases, few residents were aware of stormwater pond maintenance requirements and their responsibilities.
Almost all participants indicated that their HOA set aside funds annually for pond maintenance. Feedback was mixed on whether the amount set aside was adequate to cover maintenance costs. Anecdotal observations suggest that for many communities this funding is earmarked for short-term maintenance, and funds will be lacking when the stormwater pond reaches the end of its effective lifespan and needs to be dredged.
Recommendation 2: Communicate the pathways of stormwater; how it passes over impervious surfaces, collects contaminants, and ultimately is collected within the engineered pond.
The lack of consideration for, and awareness of, whole neighborhood responsibility may stem from the fact that in many cases residents are unfamiliar with stormwater management and are not aware that their pond is an engineered practice designed to capture and store stormwater runoff. When a resident moves into a neighborhood with a pond, it is often billed as an aesthetic feature providing waterfront property. Communication efforts should focus on the role of the stormwater pond and responsibilities for maintenance.
An official mechanism exists to communicate responsibility for stormwater best management practices (BMPs). The S.C. Department of Health and Environmental Control (S.C. DHEC), under the South Carolina Stormwater Management and Sediment Reduction Act of 1991 (48-14-10, et. seq.), requires and assigns stormwater system and BMP facility maintenance through Regulation 72-308. This document includes the following:
• Requires adequate maintenance of stormwater infrastructure and BMP facilities, including structures, improvements, and vegetation, defining this as good working condition so that facilities are performing to their design functions. • Requires and assigns inspection of all facilities and stormwater structures. • Grants access to S.C. DHEC and/or city or county of jurisdiction for inspection as deemed necessary and in response to reported deficiencies or citizen complaints. • Mandates that S.C. DHEC and/or county or city of jurisdiction provides inspection findings and directive for repairs to owner. • Commits owner to perform work necessary to keep facilities in working condition and following a maintenance schedule, if it exists. Failure to maintain may result in fines up to $1,000 per day. • Releases S.C. DHEC and the county or city of jurisdiction from liability of any kind for stormwater facility failures.
Through expert surveys and focus groups, we found that this document is rarely accompanied by a maintenance schedule for the pond and stormwater infrastructure for which ownership is being transferred. This presents a significant disconnect between those responsible for private stormwater infrastructure upkeep and those responsible
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 147 for maintaining and restoring surface waters that may be impacted by polluted stormwater discharges enforced by the MS4. Additionally, this lack of communication may handicap proactive efforts of MS4 communities to improve pond maintenance activities of neighborhoods within their jurisdiction through an education effort in advance of enforcement. Per the NPDES General Permit for Storm Water Discharges from Regulated Small MS4 regulation effective in January 2014, MS4 communities are mandated to identify if a waterway’s inability to effectively meet water quality standards is due to polluted stormwater runoff. If polluted runoff is identified as the cause for impairment, the MS4 must make specific and locally appropriate efforts to address impaired waterways (as identified in the 303(d) List of Impaired Waters) or in accordance with approved and established total maximum daily loads (TMDLs) within their MS4 jurisdiction.
Recommendation 3: Messages should recognize the complexity of stormwater pond management and offer specific management strategies for stormwater ponds. Messages should be proactive and include actionable behaviors.
Focus group discussions indicated that providing residents with knowledge and tools could influence their willingness and ability to address stormwater pond maintenance and performance. Participants were highly engaged in the discussions and expressed concern about stormwater pond maintenance and the impact of stormwater ponds on the local environment. Focus group participants included both HOA board members and residents of coastal communities with stormwater ponds. Specifically, the participants’ concerns focused on health of wildlife, public health, and health of the overall ecosystem, as well as property values and recreational opportunities.
Participants’ maintenance priorities included addressing eroding banks, invasive aquatic plants, water quality (including dissolved oxygen and clarity), algal blooms, water levels, nuisance wildlife, and general aesthetics. Some neighborhoods attempt pond maintenance themselves, while others subcontract out for individual maintenance actions or hire a pond management company. Results varied on whether or not their community had an inspection and maintenance plan for the pond, and those that did generally relied on a pond management company to provide maintenance and perform inspections. Several neighborhoods indicated a desire for specific maintenance recommendations from government or academic resources so they could take greater control over their pond’s maintenance plan, as opposed to relying on a pond management company to make all decisions.
The participants’ discussions showed that their willingness to manage ponds is connected to their ability to consider the whole system and all options for problem-solving pond issues over the life of the pond. Participants expressed a need for comprehensive guidance and solutions. Similarly, Casagrande (1997) identified that a traditional approach with residents (i.e., only periodically providing feedback on environmental planning decisions) is insufficient. A case study that evaluated community connection to ecosystem restoration found that neighborhoods, government agencies, private consultants, and/or industry must all participate in the restoration planning process as equals through the planning, implementation, and evaluation of the plan. Without this level of participation, a lack of ownership results (Casagrande 1997).
Beyond responsibility and ownership, participants in this research effort spoke of ambiguity in stormwater pond dredging time frames, requirements, and procedures. The S.C. Best Management Practice Manual (S.C. DHEC 2005) recommends dredging every 5-10 years or after 25% of the permanent pool volume has been lost due to accumulated sediment. Additionally, during a review of the policy recommendations (Chapter 5), we found no specific guidance for dredging activities in either county or municipal ordinances and BMP design manuals. The only manual that mentioned pond dredging was the City of Charleston manual, which stated there must be “adequate clearance…to
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 148 perform dredging” in the forebay and main pond, and that these activities should be “routine” (City of Charleston 2012). At this time, no testing parameters for contaminants in dredged material exists in South Carolina regulations. However, disposal of dredge material to waterways is illegal without permit approval from the U.S. Army Corps of Engineers, which may require analysis of bottom sediments and/or dredged material.
Recommendation 4: Messages should target audiences that influence stormwater pond design and maintenance as early in the process as possible. Messages should also include positive neighborhood feedback to challenge social norms.
The primary objective of our recommendations for improved communication practices is to encourage behaviors that will result in sustained and increased pond maintenance and performance. Increasing knowledge does not always equate to behavior change; therefore, bringing about a behavior change first requires an analysis of values, social norms, individual perceptions, and social institutions, and how these together influence behavioral decisions and interpretation of knowledge (Casagrande 1996). Focus group feedback provided insight into existing social norms, target audiences, and communication needs.
Case Study: Perception of Shoreline Aesthetic
To gauge both functionality and aesthetic perceptions related to three different types of shoreline design (vegetated buffer, mowed turf grass, and bulkhead), participants discussed each of these strategies, and then reflected on which one they preferred as the most attractive option. The responses and overall impressions from the group are summarized below.
Participants had mixed positive and negative views on vegetated buffers along the shoreline (Figure 7.2). While some participants voiced that shoreline plants help to stabilize the shoreline and filter pollutants, others raised concerns about nuisance wildlife habitat and fears of these plants spreading throughout the pond, raising additional maintenance concerns. Some communities have written into HOA covenants that the shoreline must be mowed and vegetated shorelines are not an option for them. Others worried about blocking water views, and the inconsistent “hodge podge” look of the assorted plants in the buffer photo, while expressing a preference for a monoculture of tall grasses for a more consistent look.
Participants were generally concerned about wave action and shoreline erosion impacts to a mowed turf grass shoreline (Figure 7.3). Opinions were divided on whether or not this was an attractive option, but many participants recognized that is wasn’t the best option for water quality protection or shoreline stabilization. Several assumed their neighbors would be receptive to this strategy, since it wouldn’t impede a water view, but also mentioned neighbors might not like this “uninteresting” look.
Many participants felt that bulkheads or a hardened shoreline were effective options for protecting the shoreline, but that they were not always feasible due to cost (Figure 7.4). Others pointed out the lack of habitat, expense of maintenance, and impact on adjacent soft shorelines.
Overall, participants were able to identify some of the impacts their stormwater pond has on coastal water quality, and were able to make the connection with ecosystem services that either directly or indirectly benefited themselves and their communities. Shellfish, finfish, general ecosystem health, and property values were the most commonly cited ecosystem services, although some participants did not make a connection between stormwater ponds and downstream
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 149 water quality. It was widely perceived that residences and golf courses, where applicable, have the largest impact on the water quality in their stormwater pond.
Participants’ perceptions of the acceptable social norm were identified as significant barriers in implementing a well-recognized BMP, the vegetated buffer. Vegetated shoreline buffers are commonly accepted as a best practice for preventing soil loss and erosion along ponds and lakes. Vegetated buffers along riparian areas filter and slow runoff, promote sedimentation and infiltration, enhance plant uptake of nutrients, and facilitate microbial decomposition of pollutants. Buffer use along stormwater pond shorelines may also assist in mitigating the impacts of overland flow
Attractiveness of Grand Beaufort Charleston Shoreline Strand
Perceived Benefits Perceived Drawbacks Limits trash Expensive Protects shoreline from erosion from wind and waves Easily damaged by muskrats Less mowing Threat of plants spreading into pond Attractive Potential for taller plants to limit viewscape Maintenance concerns (watering when water is low)
Figure 7.2 Schematic showing preference for vegetated buffer shoreline option by Beaufort and Charleston focus group participants relative to Grand Strand focus group participants.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 150 from properties adjacent to the pond. In coastal S.C., most pond banks are designed and installed with a monoculture of turf grass and maintained by mowing to the water’s edge or to the steep slope to the pond surface (Figure 7.5). This design and maintenance scheme often goes unchanged after pond ownership is transferred from the developer to the HOA.
Feedback from focus groups showed a variety of concerns and misperceptions that can be addressed to reduce barriers to adoption of vegetated shorelines. Concerns included the creation of habitat for undesirable wildlife (e.g., snakes), plant viability with fluctuating water levels, spread of shoreline plants throughout the pond similar to aquatic invasive
Attractiveness of Grand Beaufort Charleston Shoreline Strand
Perceived Benefits Perceived Drawbacks Meets HOA codes, convenents, and restrictions (CCRs) Wave action leads to failing banks No obstruction of view Turf is fertilized and results in excessive algal growth Expected aesthetic Turf requires additional chemicals to look healthy, which negatively effect water quality Minimal protection of pollution from parking lot runoff Property loss
Figure 7.3 Schematic showing preference for mowed turf shoreline option by Beaufort and Charleston focus group participants relative to Grand Strand focus group participants.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 151 Grand Beaufort Charleston Attractiveness of Strand Shoreline
Perceived Benefits Perceived Drawbacks Keeps water where it is supposed to be No mitigation of runoff volume Protects shoreline from erosion Easily damaged by muskrats Cost prohibitive for HOA Repairs are costly for homeowners No wildlife habitat (birds on shoreline, fish in water) Maintenance concerns (watering when water is low)
Figure 7.4 Schematic showing preference for a bulkheaded shoreline option by Grand Strand focus group participants.
plants, and obstructed views of the pond. Several participants lived in communities whose HOA’s Community Codes, Covenants, and Restrictions (CCRs) require a mowed turf grass shoreline, and they felt that it would be exceedingly difficult to change the CCRs to allow for the installation of vegetated buffers or even alternate mowing schedule zones.
To affect these perceptions, recognizing the weight that the social norm has in the likelihood of retrofitting an existing mowed shoreline or bulkhead to a shoreline with a vegetated buffer, we recommend using messages to highlight their neighbors’ preferences. For example, “Your neighbors prefer a vegetated shoreline over mowed turf to keep the shoreline from eroding, to protect the health of wildlife, and to reduce pond algae.” The message not only needs to overcome this social norm and perceived preference of residents, but it needs to address all barriers. Additional outreach on vegetated shoreline buffers should consider the focus group participants’ perceived benefits and drawbacks
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 152 Figure 7.5 Image of a stormwater pond typical of those found in coastal South Carolina, with mowed turf to the water’s edge.
of each shoreline option, identified in the table under each image (Figures 7.2 - 7.4).
The aesthetic of the vegetated shoreline buffer was considered acceptable and well-liked by many focus group participants, which suggests that this shoreline option could also be well-received by new homeowners. However, it should be noted that responses were mixed, with participants often providing multiple responses to a single prompt over the course of the conversation. Efforts to encourage vegetated buffer installation have a higher likelihood of success if they are incorporated early in the planning process and installed at the time of construction, before the Transfer of Developer’s Rights. Outreach should target developers or property managers prior to pond construction to ensure these recommendations are incorporated and shared with communities.
Recommendation 5: Messages should stress that stormwater pond maintenance will benefit health of residents, wildlife, the pond ecosystem, and recreational waters.
Secondary messaging should reference recreational activities that depend on clean water in the pond, or in downstream waterways. In a survey completed by residents within close geographic proximity to a restoration site on the West River in Connecticut, a high priority was placed on creating an environment suitable for relaxation and wildlife
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 153 XX Target Audience: Developers Communication Emphasis Areas, Actions
• To Engineers - consider all BMPs. Stormwater ponds are one option, but not the only practice that meets suspended sediment treatment criterion and can appeal to buyers. • To Contractors - emphasize careful construction, keeping with design depth and slopes. Engineering plans are the legal depiction of the final product of construction. • To HOA or Property Management Companies - • Express engineering and treatment objective of stormwater pond with new owners. • Provide engineering plans and maintenance requirements at time of Transfer of Developer’s Rights. • Explain the Statement of Responsibility Waiver to new owners. • Release responsibility intermittently to neighborhood HOA or property management company. • Surveyed residents find a vegetated shoreline appealing and more protective than turf. This is oftentimes limited by Codes, Covenants, and Restrictions (CCRs). Establishing a vegetated buffer after construction and creating the allowance for one in the CCR is of interest to new owners.
Suggested Emphasis Phrases and Topics Toward Achieving Actions
• Stormwater ponds serve three purposes - water quality treatment, minimal flood prevention, aesthetic. • Discharge from pond affects receiving water quality and ecosystem health. • Whole neighborhood benefit/whole neighborhood responsibility.
XX Target Audience: HOA Board and Property Managers Communication Emphasis Areas, Actions
• Have available your engineering plans for design depth and slope. • Annual inspection should be conducted, and inspection checklists are readily available. • Ensure runoff volume can easily flow through infrastructure, and there are no obstructions going into the pond (such as cattails and sediment accumulation). • Codes, Covenants, and Restrictions should be modified to allow for a vegetated shoreline, as this is appealing to many owners and protects shoreline from erosion and property loss. • Stormwater infrastructure throughout the neighborhood should be maintained. Recommend clean outs of catch basins and removal of debris and sediment that could terminate in the pond, as needed. • Budget for 5-7% of construction costs for annual maintenance.
Figure 7.6 Recommended target audiences, topics, and messages to improve stormwater pond maintenance.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 154 • Communicate purposes of neighborhood stormwater ponds and basic information about whole neighborhood maintenance responsibility.
Suggested Emphasis Phrases and Topics Toward Achieving Actions
• Stormwater ponds serve three purposes - water quality treatment, minimal flood prevention, aesthetic. • Every resident is integral in pond function. • Discharge from pond affects receiving water quality and ecosystem health. • Whole neighborhood benefit/whole neighborhood responsibility.
XX Target Audience: Residents Communication Emphasis Areas, Actions
• Your landscape decisions affect stormwater quality and the water quality of your pond. • Most South Carolina soils have high or excessive levels of phosphorus. Use of phosphorus-free and slow release fertilizers, and their proper application, will minimize nutrient rich runoff that encourages algal growth. • Understand the many purposes of a stormwater pond. • Consider a vegetated shoreline for greater bank protection and treatment of runoff. Most of your neighbors find a vegetated shoreline more appealing. • Minimize erosion and soil loss to pond by raising the mower deck and allowing grass to grow taller on slopes adjacent to the pond.
Suggested Emphasis Phrases and Topics Toward Achieving Actions
• Stormwater ponds serve three purposes – water quality treatment, minimal flood prevention, aesthetic – and serve your community. • Your community pond is purposed to treat runoff before discharge. • Pond maintenance benefits health of water quality and health of wildlife. • Minimizing nutrients in runoff (from fertilizer selection and application) can decrease the likelihood of excessive algae growth. • Community ponds in S.C. are generally owned by the neighborhood and are the responsibility of all owners. • Your neighborhood is tasked with responsibility of maintenance, liable to fines of up to $1000 per day if found non-compliant. • Healthy ponds can protect home values.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 155 enjoyment. These priority values were determined to support changes in behavior benefited by restoration activities (Casagrande 1997).
Similarly, focus group participants placed the greatest value on health – of community, of individuals, of wildlife, and of the ecosystem – as priorities for pond maintenance and design performance. This concern for human health and the health of wildlife has been referenced by other researchers as motivation for environmental responsibility and water quality protection (Naselli-Flores 2008). Secondly, participants were concerned about maintaining personal recreation opportunities through cleaner pond water and healthy discharges to recreational waters.
However, this emphasis likely varies by community. For example, in the Mount Pleasant community CCRs reviewed, the majority prohibited use of ponds for recreational activities such as fishing, boating, or swimming.
Recommendation 6: Messages should come from trusted sources; outreach should capitalize on electronic modes of communication.
Finally, focus group participants were asked where they first looked for assistance or resources for pond problems and questions; most commonly mentioned were the S.C. Department of Natural Resources (S.C. DNR), S.C. DHEC, and the Clemson University Cooperative Extension Service. Participants generally prefer to receive informational resources online. Several dozen agencies, universities, and organizations conduct environmental and natural resource education in coastal S.C. In order for these entities to affect change through consistent recommendations and communication, a stamp or symbol on outreach materials representing scientific, unbiased instruction and educational information could be used to brand outreach information. Participants also indicated that they would like to see additional resources made available, including funding opportunities, specific management recommendations, consistent messages, and a single portal to access information on all the rules and regulations related to stormwater pond management and maintenance. Additionally, information should be available online whenever possible, as per the preference of focus group participants.
7.4 Summary Overall Recommendation: Messages should recognize the multiple concerns, perspectives, and involvement of multiple audiences.
Multiple audiences directly influence the function and performance of stormwater ponds across their design, construction, and post-construction management stages (Figure 7.6). Identifying a consistent message that resonates with each audience will first involve understanding their level of knowledge, concern, and motivation. Understanding audience values, motivations, and concerns can then inform strategies to encourage sustainable behavior change. Education is a key component of any strategy designed to mitigate the negative environmental impacts to, and from, stormwater ponds. The success of ponds as BMPs to manage runoff, protect downstream water quality, and comply with regulations relies on several factors: recognition of ownership, awareness of the pond’s purpose, knowledge of pond function and maintenance needs, and responsible care of surrounding landscapes. These elements must factor into outreach messaging if it is to resonate with target audiences and ultimately protect S.C.’s vital coastal water resources. Arming residents with specific knowledge and tools will go a long way towards ensuring proper pond maintenance is carried out. HOAs want comprehensive instructions on pond maintenance to share with their residents. City and county staff in engineering, public works, and stormwater departments share common concerns,
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 156 mostly related to practices such as keeping infrastructure and conveyances clear of debris, managing erosion, and preventing flow obstructions from vegetation and sediment build-up (Appendix A7-4, see www.scseagrant.org/spsok). There are both real and perceived barriers to education and outreach. For example, failed attempts to implement widespread use of vegetated buffers are often due to misconceptions about cost and function, and to HOA covenants restricting planting on shorelines.
To promote positive behavioral changes, we recommend that visual campaigns use positive images of healthy ponds that are more likely to motivate homeowners, rather than those depicting algal blooms, stagnation, or other unsightly pond conditions. When discussing major obstacles to pond maintenance, participants cited money, lack of knowledge, and inability to influence or change residential lawn-care behaviors. Outreach messages addressing pond health should be specific, instructive, and connect all community residents’ actions to the performance of the pond. The greatest concerns voiced by residents were related to the health of people, wildlife, and the overall ecosystem. As the culmination of our research efforts, we presented our recommendations to the Stormwater Ponds Research and Management Collaborative for both short-term and long-term outreach strategies to create and disseminate outreach materials to increase awareness, instruct, and involve target audiences in sustainable actions to improve long-term pond management function.
7.5 References Casagrande DG (1996) A value based policy approach: The case of an urban salt marsh restoration. Coastal Management 24:327-337
Casagrande DG (1997) The human component of urban wetland restoration. Yale F&ES Bulletin 100: 254-270
Dietz ME, Abraham J (2011) Stormwater monitoring and resident behavior in a semi-arid region. Journal of Extension 49
Emmons and Olivier Resources (2007) Minnesota Low Impact Development: A Comparison
Fassman E (2011) Stormwater BMP Treatment Performance Variability for Sediment and Heavy Metals. Separation and Purification Technology no. 84:95-103
Mallin M (2000) Effect of human development on bacteriological water quality in coastal watersheds. Ecological Applications 10(4):1047-1056
Mallin MA, Ensign SH, McIver MR, Shank GC, Fowler PK (2001) Demographic, landscape, and meteorological factors controlling the microbial pollution of coastal waters. Hydrobiologia 460(1-3): 185-193
Messersmith MJ (2007) Assessing the coastal hydrology and pollutant removal efficiencies of wet detention ponds in South Carolina. M.S. Thesis, College of Charleston, Charleston, S.C.
McKenzie-Mohr D (2011) Fostering Sustainable Behavior. Canada: New Society Publishers
Naselli-Flores L (2008) “Urban lakes: Ecosystems at risk, worthy of the best care.” In: Sengupta M, Dalwani R (Eds.), Proceedings of Taal 2007 the 12th World Lake Conference, Taal (pp. 1333-1337)
S.C. DHEC (2005) Storm Water Management BMP Handbook. Columbia, S.C.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 157 S.C. DHEC (2012) Nonpoint Discharge Elimination System General Permit for Stormwater Discharges from Construction Activities. Permit No. SCR1000000. Columbia, S.C.
Smith E (2012) Nutrient-Organic Matter Dynamics in Stormwater Ponds: Implications for Stormwater Management and the Role of Ponds as Sources of Coastal Water Quality Impairment. Proceedings of the 2012 South Carolina Water Resources Conference, Columbia, S.C., October 10-11, 2012
Swann CP (2000) A survey of nutrient behavior among residents in the Chesapeake Bay Watershed. Oral. Presented at the National Conference on Tools for Urban Water Resource Management & Protection, Chicago, IL
Weinstein JE, Crawford KD, Garner TR (2008) Chemical and Biological Contamination of Stormwater Detention Pond Sediments in Coastal South Carolina. Final project report. S.C. Sea Grant Consortium and S.C. DHEC- OCRM, Charleston, S.C.
Witte K (1994) Fear control and danger control: A test of the extended parallel process model (EPPM). Communication Monographs 61:113-134
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 158 CHAPTER 8 – SYNTHESIS OF OUR CURRENT UNDERSTANDING OF STORMWATER PONDS IN COASTAL SOUTH CAROLINA
Author
Bridget E. Cotti-Rausch, Ph.D. S.C. Sea Grant Consortium, Coastal Environmental Quality Program Specialist, Charleston, S.C. Currently at the U.S. Environmental Protection Agency, Washington, D.C.
Corresponding Author Bridget E. Cotti-Rausch, Ph.D. ([email protected])
Synthesis In 2007, the S.C. Department of Health and Environmental Control-Office of Coastal Resource Management (SC DHEC-OCRM), in cooperation with the S.C. Sea Grant Consortium (SCSGC), published State of the Knowledge Report: Stormwater Ponds in the Coastal Zone (Drescher et al. 2007). This effort highlighted pond research topics including water quality, hydrology, pollutant removal, sedimentation, modeling, and social sciences. It also outlined research and informational needs. Here, we revisit 18 questions highlighted in the report, identify progress made in the past decade, and discuss past recommendations in the context of our current understanding. Throughout, we incorporate SCSGC-funded projects, and when appropriate, data from neighboring states and national studies. In the SCSGC Strategic Plan 2018-2021 (herein “Strategic Plan”) stormwater ponds are specifically identified as a priority area for ongoing research. Therefore, we cite how each topic corresponds to priorities outlined in the Strategic Plan. Ultimately, we seek to provide guidance that reflects the existing landscape of stormwater ponds in coastal South Carolina and advance efforts to refine stormwater pond practices to maximize functionality, effectiveness, and cost efficiency.
TOPIC 1. State Regulatory Standards in the Southeast U.S.
The 2007 State of the Knowledge report described stormwater management in the Southeast in order to provide context for South Carolina’s standards. In light of changes in North Carolina and Georgia, we begin by revisiting these standards here.
South Carolina (S.C.)
The regulatory standards for Stormwater Management and Sediment Reduction in South Carolina were last updated in June 2002. Briefly, these include water quantity (flood) controls on the post-development peak discharge rates that cannot exceed pre-development rates for the two- and 10-year frequency 24-hour storm event. Additionally, discharge velocities must be reduced. Water quality is also addressed: “When ponds are used for water quality protection, the
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 159 ponds shall be designed as both quantity and quality control structures.” Permanent ponds must store and release the first ½ inch of runoff over a 24-hour period from the site. Sediment storage must be calculated, but only for the duration of the construction activity. Additional regulations are in place for coastal counties, and for ponds constructed in the Critical Zone (Chapter 5). The statewide stormwater design manual provided by S.C. DHEC was last updated in June 2005, though a revision is anticipated. This manual states the designed permanent pool volume should be equal to one-inch of runoff per impervious acre on the development site. An average pool depth of four to six feet is described as “optimal” for water quality treatment. Additional design recommendations are described, including inclusion of forebays, and minimal flow length-to-width ratios of 1.5:1 to prevent runoff short-circuiting the basin. The manual provides a table of average pollutant removal efficiencies, though these are not for enforcement purposes.
North Carolina (N.C.)
In September 2016 the N.C. Department of Environment and Natural Resources, now the N.C. Department of Environmental Quality (NCDEQ), initiated changes to their statewide stormwater program (NCDEQ 2016). These included design requirements for wet ponds that reflect research on pollutant removal effectiveness. Major Design Standards include (deq.nc.gov/sw-bmp-manual):
• Basin discharges must be distributed over a vegetative filter strip. • Discharge rate of the treatment pool be drawn down over two to five days. • Average depth of permanent pool is calculated using a series of equations that considers pond surface area (top and bottom), volume of the permanent pool basin, and forebay. • Surface area to drainage area ratios adapted from Driscoll (1986) must be used to determine permanent pool surface areas based on pollutant removal efficiencies and calculated for individual regions (e.g., coastal, mountain), considering percent impervious cover. • The pond must include a forebay with a volume that is ~20% of the permanent pool. • A 10-foot wide vegetated shelf must be installed around the pond perimeter. • Short-circuiting of pond must be prevented; minimum length to width ratio of 1.5:1.
The NCDEQ program includes credits for removal of total suspended solids, total nitrogen, and total phosphorus, but no volume reduction credits. Bacterial removal is linked to the reduction in total suspended solids, but there are no specifications for reductions in fecal coliform counts or other microbial indicators. Stormwater regulations require that runoff is released over a period of two to five days; this increased residence time is intended to allow most suspended sediments and associated pollutants to settle out of the water. The basin is sized with additional volume to account for this sediment storage; at least one additional foot in addition to the permanent pool volume (main pond and forebay). These requirements must be met in order for a licensed engineer to receive a permit to construct a wet pond in the state. Major Design Elements must also be met in order to achieve pollutant removal rates for credit. The NCDEQ design manual also details maintenance requirements, including monitoring water clarity and algal growth. In the coastal counties, inspections should occur once a month, and within 24 hours of rainfall that exceeds 1.5 inches. Records should be made available upon request from an NCDEQ or local government inspector.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 160 Georgia (GA)
In the 2016 edition of the GA Stormwater Management Manual Volume 2: Technical Handbook (GA Environmental Protection Department 2016), a variety of practices were recommended to improve runoff volume reduction and water quality. This manual described the Unified Stormwater Sizing Criteria that is intended to holistically address stormwater impacts from development (atlantaregional.org/natural-resources/water/georgia-stormwater-management- manual). The statewide water quality treatment volume is equal to the runoff from the first 1.2 inches of rain (equal to an 85th percentile storm). Specifications for stormwater ponds include a forebay, a minimum length-to-width ratio for the pond of 1.5:1, and a maximum permanent pool depth of eight feet. The pollutant removal efficiencies described for ponds are similar to those found in the S.C. manual. There are no pollutant removal credits in GA, and wet ponds do not qualify for a runoff reduction volume credit.
In GA the above standards are only recommended, while in N.C. design specifications must be met in order to obtain a construction permit. Therefore, while the GA design manual has been updated more recently than in S.C., permit requirements for water quality improvements in both states have not progressed to the levels found in our northern neighbor. However, now that six of the eight coastal counties are regulated MS4s, additional guidance, including more strict design standards, can be found in their manuals, which are updated more regularly than the state’s (Chapter 5).
TOPIC 2. Inventory of Ponds
2007 State of the Knowledge Report Question 1: How many stormwater ponds exist in the coastal zone? Question 2: What is the cumulative volume/coverage of ponds? Question 3: At what rate are ponds expanding? Question 4: Do we need to classify ponds by size, land use, etc.?
Prior to the analysis presented in Chapter 1 of this report, the last comprehensive stormwater pond inventory for the South Carolina coast reported approximately 8,114 ponds, using aerial photography from 1999 (Siewecki et al. 2007). In the current contribution, Smith and colleagues utilized 2013 satellite imagery to quantify pond numbers, estimate pond acreage, and classify neighboring land uses. The researchers also calculated the rate of expansion in pond numbers over a nearly 20-year time span (1993 to 2013) and the coverage area relative to total development for the Charleston and Myrtle Beach metro areas. While development has increased by approximately 2% per year, cumulative pond aerial coverage has increased by roughly 4% over this period. Because stormwater ponds have proliferated so rapidly, tools that help stormwater departments meet the high demand for pond inspections can improve regulatory compliance and the lasting effectiveness of ponds as flood and water quality control measures.
Application: The 2013 geodatabase is available by request from the SCSGC. The Compliance Office of Berkeley County’s Stormwater Department requested and received the data in October 2017 to use this resource to improve their MS4 inspection program for private ponds.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 161 TOPIC 3. Pond Design and Management
Ponds work as water quality Best Management Practices (BMPs) largely by removing particles via sedimentation. As Chapter 2 describes, pollutant removal capability is dependent on particle density, size, chemical composition, and pond hydrodynamics. But basically, the longer stormwater is retained within a pond system, the more likely both large and fine grain particles will be removed through sedimentation and biological uptake can occur. A 2007 study compared sedimentation and pollutant removal efficiencies in a single residential pond and a multiple pond series (herein “pond series”), on Daniel Island, in Berkeley County (Messersmith 2007). In this study, the single pond demonstrated a greater loss of water storage capacity (36% loss) as compared to the terminal pond in the pond series (15% loss) over the sampling period. The Messersmith study also showed that the pond series drained more slowly than the single pond: 75% of water left the single pond in just seven hours while it took nearly 24 hours for the same amount to leave the pond series. Due to enhanced sedimentation and biological uptake, the pond series out-performed the single pond in terms of removal of nutrients (nitrogen and phosphorus), total suspended solids, and fecal coliform bacteria.
While those data are now a decade old, a recent article in The Daniel Island News (Bush 2017) demonstrated the development’s ongoing commitment to effective stormwater management, especially in terms of flood protection. The developers engineered their BMP systems to hold a 25-year storm event, as compared to the S.C. DHEC-mandated 10-year storm. Additionally, they credit much of their success in flood prevention in the wake of hurricanes Matthew in 2016 and Irma in 2017 on the interconnectedness of their pond systems. So that, in this case, superior pollutant removal appears to be linked to flood control. For more information on Daniel Island ponds’ system, see SCSGC’s fall 2017/winter 2018 issue of Coastal Heritage magazine (www.scseagrant.org/stormwater-ponds-the-coast-re-plumbed).
While the ponds described above are connected through an “intricate piping and drainage system” (Bush 2017), runoff enters ponds from multiple sources. To better understand pond water budgets, a year-long SCSGC-funded study by Smith and Peterson quantified inputs to three stormwater ponds in Horry County (from 2014 – 2016). The researchers found groundwater contributed between 2 and 5% of pond inflow during rain events and 6 to 26% over the course of the entire two-year study (Smith 2017). Overland sheetflow contributed between 15 and 18% of total input to the pond during rain events. In many residential areas, including those evaluated by this study, sheetflow travels over mowed turf grass and enters the pond carrying a pollutant load representative of the land use practices of the surrounding drainage area. In fact, between 40 and 50% of the nutrient loading to ponds was found to be delivered via sheetflow (Smith 2017). Excess nutrients lead to eutrophication and can result in algal blooms, with consequences for poor water quality in the pond. Another study of 14 residential ponds along the Grand Strand showed that sediment composition in ponds across the region was correlated to impervious surface cover and carried a largely terrestrial signature (Schroer et al. 2018). As the majority of fill materials are sourced from upland vegetation and other particle sources, algal growth is either remineralized within the pond or transported in the outflow (Schroer et al. 2018). These two studies reinforce the need for good upland management to maintain pond functionality. Beneficial activities include careful treatment with fertilizers to minimize excess nutrients flowing into ponds, as well as bagging and removal of lawn debris to prevent material introduction to pond systems that results in volume loss over time. As ponds receive particle loads from the surrounding area, a major issue for pond owners and managers is how quickly ponds lose storage volume and require dredging.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 162 2007 State of the Knowledge Report Question 5: How fast are ponds “filling in”?
The study by Schroer et al. (2018) addressed sedimentation rates and showed that accumulation ranged from just 0.05 to 0.57 cm/year and varied throughout the pond basin. Overall, the median time for these ponds to lose 25% of their volume was estimated to be 68 years (Schroer et al. 2018). Both this and the Smith and Peterson studies intentionally targeted ponds described as “typical” for the Grand Strand: those with no forebays, and little or no shoreline vegetation. These results differ markedly from those presented by Messersmith (2007) for the single pond on Daniel Island (near Charleston, S.C.) that lost nearly 40% of its storage volume in five years. According to Schroer’s estimates, sediment dredging operations would be required less frequently than the five to 10 years predicted by S.C. DHEC, while Messersmith’s study indicated 25% volume would be lost rapidly (S.C. DHEC 2005).
The contrast in fill rates between the Messersmith and Schroer studies could result from differing land uses, such as construction in the pond’s vicinity, and regional dissimilarities between the Tri-County and Grand Strand. These differences illustrate the difficulty in extrapolating broadly from a single study and the importance of defining a useful geographic range for data. For pond owners and managers, the range in possible sedimentation rates suggests the need to characterize individual sites in order to inform maintenance activities. Considering that dredging costs are calculated in terms of the volume of sediment removed and can exceed $700 per cubic yard, depending on the method used, pond managers should consider evaluating pond bathymetry to focus dredging in areas where sedimentation is greatest. We reached out to several pond professionals for their thoughts on dredging, and their universal recommendation was for pond owners to invest in bathymetric surveys. For a one-acre pond, these surveys can cost less than $1,000 (Quality Lakes Inc., pers. comm.).
Pond Bacterial Removal Capabilities
Bacterial removal efficiencies are linked to particle sedimentation. And as microbes can pose a major threat to shellfish, and bacteria such as Vibrio are associated with human illness, these microbes are heavily monitored in coastal waters. Ponds have been shown to be highly effective at removing microbial pollutants from runoff. However, in the Drescher (2007) review of 511 ponds, these removal efficiencies ranged from -47% (pond = source to receiving waters) to 99% (pond = sink). Results from two ponds studied in the Grand Strand showed that removal efficiencies for suspended sediments and E. coli averaged 75 and 90%, respectively (Smith 2017), supporting previous research in N.C. for E. coli (Hathaway et al. 2009; Krometis et al. 2009). According to the S.C. DHEC design manual, wet ponds can be expected to remove 45 to 75% of bacteria in runoff. Exploration of county and city stormwater design guides found that bacterial removal rates by wet ponds are classified as “moderate.” Compared with the local research, these design guides may be underestimating the upper limit on microbial removal efficiencies of ponds.
Broadly, the effectiveness of ponds as water and pollutant storage devices relies on enhancing runoff residence time. For example, the Smith and Peterson study found pollutant removal capabilities for the third pond in their study were non-significant based on the “short-circuiting” of water through the pond. Bacteria, and other pollutants, are often associated with small particles that take longer to settle out of the water column. The difference in settling times between very fine sand (100 µm diameter) and medium clay (1 µm) is seconds versus days. In the 2016 Final Report of the International Stormwater BMP Database, which compared the differences in influent and effluent concentrations for a variety of BMPs, wet ponds were shown to significantly reduce E. coli and fecal coliform bacteria
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 163 in the outflow leaving ponds. The median reductions in these pollutants ranged from 2.4 to 25-fold for the ponds evaluated. Because this is a national database, the specific characteristics that determined the effectiveness of a given BMP were poorly characterized. Much of the variability in pond removal capabilities likely stems from differences in the residence time of runoff within a given pond and associated land uses.
Pond size should also be appropriately scaled for the drainage area. During construction periods, to achieve more than 60% reductions in total suspended solids, the pond surface area should be at least 1.5% of the watershed drainage area (Pitt 2004). In Washington, a study by Comings et al. (2000) found that increasing pond surface area relative to the drainage basin from 1% to 5% allowed water to be retained seven times longer. The size, depth, and shape are therefore important design criteria. Pond designs that use horseshoe or snake-like paths to route runoff between the inflow and outfall structures are recommended. Considering that storm events can mobilize pond sediments, a S.C. study suggested that building a deeper permanent pool (8 to 10 feet) could help prevent resuspension of sediments on the pond bottom (Moore 2010). Additionally, as settling of fecal coliform bacteria and total suspended solid removal rates are linked, knowledge of critical particle sizes should factor into pond design. The majority of microbes studied by Krometis and colleagues (2009) in two N.C. ponds were found to be associated with particles less than 10 µm in diameter, while neither pond studied reduced concentrations of particles less than 5 µm. To evaluate pond placement within the landscape, they also compared particles in runoff, near the inflow of ponds and the outflow structures, as well as downstream locations. They found there were no fractionation differences between particle-associated microbes in runoff and inflow samples and concluded that ponds located in upland areas were most effective at trapping pollutants (Krometis et al. 2009).
TOPIC 4. Alternative BMP Designs
Returning to our previous example of Daniel Island, we learned from these developers that they closely considered the natural topography of the island in their stormwater management plan, taking advantage of different strategies depending on the specific site characteristics. Therefore, a freshwater wetland system runs through a portion of the island and is engineered to receive a large portion of runoff allowing stormwater to follow several paths through the system. Here we consider how the incorporation of diverse BMPs impacts stormwater management; as raised in the 2007 State of the Knowledge report.
2007 State of the Knowledge Report Question 6: What stormwater pre-treatment procedures are most effective?
A common critique of pond systems is their limitation on sedimentation efficiencies for small solids; the smallest particles that can be reliably removed by this process are found to be 2 to 5 µm in diameter (Camp 1952). Therefore, pond systems benefit from pre-treatments or post-treatments that can retain finer sediments. This especially concerns clay particles, that we understand from the work cited in Chapters 2 and 3 are often associated with a variety of potentially harmful contaminants (e.g., cadmium, copper, microbes). A study by Hathaway et al. (2009) in Charlotte, N.C. compared the bacterial removal efficiencies for a variety of stormwater BMPs. All BMPs tested removed fecal coliform bacteria at efficiencies greater than 50%, while a bioretention swale and wetland had removal efficiencies of 89 and 98%, respectively. These exceeded the capabilities of the wet pond studied (70%); this study supports the use of a variety of treatment practices to improve downstream water quality.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 164 Ponds also perform relatively poorly with respect to nitrogen; S.C. DHEC states the average removal capability of wet ponds to be between 30 and 45% (S.C. DHEC 2005). The Smith and Peterson study cited previously found total nitrogen was reduced by ~45% in two Grand Strand ponds. The 2016 International BMP Database Summary Statistics showed that ponds significantly reduce total nitrogen but at only a ~20% removal rate (inflow = 1.24 mg/L versus outflow = 1.00 mg/L) (Clary et al. 2017). Removal of nutrient pollutants is best accomplished by vegetated systems (Baker & Clark 2012; Lucas & Greenway 2008, 2011). Substantial uptake by plants can occur if low flow rates are achieved so that nutrients remain in contact with roots and soil microbes. Effective bioretention practices included those with underdrain systems that store water between storm events and allow denitrification to occur (Hunt et al. 2008). Phosphorus differs from nitrogen, as phosphate can be removed partially in ponds by sedimentation, with plant uptake serving as an additional treatment pathway. However, leaching of phosphate from sediments is possible if the environment turns anaerobic, as occurs in S.C. during periods of stratification, especially in summer. Therefore a properly aerated pond can help reduce this issue. Managers must consider both nitrogen and phosphorus loading when managing ponds, as research presented in Chapter 4 demonstrates both sources can promote unwanted and potentially toxic algal growth in fresh and saline systems. Unfortunately, the impact of vegetated buffers on nutrient uptake and cycling was identified as a major informational gap, as thorough studies on these topics are lacking for coastal S.C.
A retrofit to ponds that can be completed relatively inexpensively and may provide improved nutrient trapping ability is the addition of floating treatment wetlands (FTWs). In 2015, as part of the May River Action Plan, the Town of Bluffton used EPA 319 grant funds to build a 1.25-acre stormwater pond within the May River watershed in an area with elevated levels of fecal coliform bacteria (Jones et al. 2017). After the pond was built, the forebay exhibited algal blooms. The implementation of this BMP did not significantly reduce fecal coliform levels entering the watershed. Therefore, the town modified the pond using the “treatment train” approach, specifically, the addition of FTW and a filter sock at the outfall. Broadly, this approach uses a series of BMPs designed so that runoff flows from one to the next, which provides several opportunities to capture and treat runoff. Based on preliminary inspections, no blooms occurred following the implementation of FTWs, which the town attributed to uptake of nutrients by these plants (Jones et al. 2017). A study performed in Durham, N.C. evaluated the effectiveness of FTWs at removing nutrients and sediments in two ponds (Winston et al. 2013). In their study of pre- and post-retrofits, they found that the greater percent coverage achieved by the FTW resulted in better removal of pollutants. Overall, pollutant removal was modest for total phosphorus and total nitrogen, as the wetland plants took up a small fraction of these nutrients.
Low Impact Development Guidelines
In 2015, the S.C. Sea Grant Consortium and several partner institutions, including the North Inlet-Winyah Bay National Estuarine Research Reserve (NERR), the ACE Basin NERR, and the Center for Watershed Protection, published Low Impact Development in Coastal South Carolina: A Planning and Design Guide (herein “LID Design Guide”, www.scseagrant.org/wp-content/uploads/LID-in-Coastal-SC-low-res.pdf). This manual discusses how LID practices can be incorporated into stormwater management in coastal S.C. Its purpose is to enhance access to LID implementation by providing engineering tools, planning guidance, and case study examples specific to the coastal zone. In Chapter 4 of the LID Design Guide, the authors discuss stormwater BMPs and the treatment train approach which can be used to maximize the utility of a given BMP for improving water quality. While this method can be advantageous, as shown in Daniel Island, there are challenges because it is specialized for variable site characteristics, including natural topography and various land use types. These challenges include design complexity,
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 165 vegetation selections, and calculating practice depths. Most typically, the wet pond is the final step in a treatment train, while first-in-line BMPs include bioretention areas, green roofs, and mechanical stormwater filtering systems. A comprehensive national report by Clark and Pitt (2012) evaluated several general treatment mechanisms for removing particles in runoff, including sedimentation, physical filtration, and biological processes. This study also provided a useful table that summarizes notes for stormwater managers that can be used to determine effective pre-treatment and primary treatment options for a variety of pollutant classes.
From 2014 to 2016, researchers at Clemson University’s Baruch Institute of Coastal Ecology and Forest Science were funded by SCSGC to address the effectiveness of various stormwater treatment systems. Specifically, the work compared loading sources from forested land, natural wetlands, a wet detention pond, and a combined wetland-pond system (Hitchcock, unpubl. data). Both the pond and wetland-pond system reduced E. coli levels in discharge as compared to natural sites. Differences were also found between the basic pond and the modified pond-wetland system. They found that the addition of wetland plants and a baffle system (to increase retention times) to the pond resulted in significantly higher dissolved oxygen concentrations in the discharge. The pond had higher levels of solids discharged as compared to the pond-wetland system. The higher levels were attributed to the growth of algae in the pond but not present in the wetland-pond system, likely due to uptake of excess nutrients by the plants. This study also developed a GIS-based pilot LID Suitability Index for wetland (wet) and bioretention (dry) based applications in the coastal zone. Preliminary results showed that given varying soil types, topography, and seasonally high water tables, a larger percentage of land area favors bioretention systems in the Charleston area, while wetland-based systems were found to be preferable in the Myrtle Beach area. In the Beaufort area, bioretention is likely preferable on the sea islands, while the index recommends wetland systems to be used inland.
Application: This index can be found on Clemson’s Community Resource Inventory (CRI) data viewer at www. clemson.edu/cafls/research/baruch/cri and is being improved through ongoing research by a graduate student at Clemson. The pond inventory 2013 layer (Chapter 1) will be added to the CRI so that existing stormwater practices can provide context for potential future LID applications.
TOPIC 5. Pond Lifecycles and their Role within the Coastal Landscape
Sediment Contamination and Health Concerns
2007 State of the Knowledge Report Question 7: What is the level of sediment contamination? Question 8: How often is sediment dredged, and where is dredged material placed?
The research summarized in Chapter 3 shows that ponds can be hot spots for contaminants. Because pollutants such as heavy metals are often associated with particles and ponds largely improve water quality by sedimentation, pond sediments can show elevated levels of toxicity as compared to natural sites. Contaminants with the potential for negative impacts on aquatic life that have been shown to be elevated in S.C. pond sediments include: cadmium, copper, and both contemporary-use and legacy pesticides.
At present there are no overarching requirements that pond sediments be tested for chemical or biological
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 166 contaminants prior to excavation. In the absence of other regulatory mandates, recommended sediment testing guidelines are provided in Table 4.11 of the LID Design Guide, derived from the Wisconsin Administrative Code. However, this resource does not include guidance on copper or pesticide levels.
Sediment testing can be required if the dredging activity classifies for a Section 404 permit. Section 404 of the Clean Water Act, administered by the Army Corps of Engineers, regulates the discharge of dredged material into waters of the United States, including wetlands. We reviewed all public notices for Section 404 permits submitted statewide in 2016 and 2017 and found the majority of references to dredging stormwater ponds were as part of their initial construction phase. Over the two-year period we reviewed, a single permit was filed by the Sea Pines Plantation community (Hilton Head Island, Beaufort County) as part of a project to return their stormwater system to the original design standards. This permit concerned their network of 23 ponds, termed “lagoons,” constructed in the 1960s and 70s. The permit implied that this was the first effort by the community to dredge the accumulated sediments. From this information we can assume that these ponds were likely not filling in as rapidly as DHEC indicates. Though the Sea Pines permit for stormwater maintenance stated that the excavated material would be drained and hauled to “a suitable upland disposal site,” the permitting process was required in this case because this lagoonal system is tidally influenced and considered jurisdictional waterways. Our investigation into Section 404 permits, albeit narrow, suggests that dredged pond sediments are not regularly being used as fill material in areas that directly impact waters of the state.
However, we cannot draw from this record a comprehensive picture of what is happening with pond sediments. Perhaps private ponds are not being dredged often, or when dredging occurs the sediment is being disposed of in landfills or used as fill in ways that do not directly impact jurisdictional waterways. This information lies largely with pond management companies that are hired by communities to perform dredging operations. We learned through a local pond management company (Thomas Moore of Dragonfly Pond Works, pers. comm.) that they advise removing sediments when the pond has filled in and lost a third of its design capacity or when there is visible shallow water in the main body (< 1 feet). For this company, their preferred removal method is pump dredging as it is more efficient and environmentally friendly; this method also does not lower the water level or damage stocked fish populations. The costs of sediment removal per cubic yard typically run between $20 and $30, with nearby on-site disposal included. However, if the material needs to be transported to a further dump site, the costs can increase to between $55 and $65 per cubic yard. Disposal costs largely depend on where the dump site is located, with a ~$100 per hour charge associated with transport, and a roughly $75 fee for disposal at the landfill (per load; 14 to 15 cubic yards per load). For example, a disposal site located 30 minutes away that requires a 500 cubic yard dredge job adds up to $3,500 for hauling and $2,500 for disposal. Away from any wetlands or coastal waters, a dredge for a pond less than one acre would not require a permit. Echoing the recommendations of Quality Lakes, the representative from Dragonfly Pond Works also endorsed performing bathymetric mapping. As the research by Schroer et al. (2018) demonstrates, ponds do not necessarily fill in uniformly. Bathymetric mapping reveals where sediment has accumulated, allowing pond owners to target these operations and save the community money in the long run. Outside of dredging activities, we also considered the potential environmental impacts of accumulated pond sediments, discussed below.
2007 State of the Knowledge Report Question 9: What public and environmental health risks might ponds pose?
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 167 Chemical Pollutants
Based on analysis of existing data from ponds in S.C., the heavy metals cadmium, chromium, copper, and zinc are elevated to levels in pond sediments that may pose significant ecotoxicological risks to benthic organisms. Legacy pesticides, those no longer used in urban applications, can also persist in pond sediments many decades after their last use. This may be due to their association with particles and exposure to low oxygen conditions in pond bottoms that increase their half-lives. While legacy pesticides persist at low levels, the pesticide found in highest concentrations in coastal pond sediments is the contemporary-use pesticide, chlorpyrifos. This insecticide was found in nine of 16 S.C. ponds tested by Weinstein and colleagues (2008), at levels that exceeded the Environmental Protection Agency (EPA) ecological risk assessment screening benchmarks. Chlorpyrifos is also synergistically toxic to aquatic invertebrates when found in the environment with the herbicide atrazine, another chemical commonly found in coastal S.C. pond sediments. Nationally, the U.S. Geological Survey (USGS) identified chlorpyrifos as one of a handful of problematic pesticides found often in urban areas due to its potential to cause pervasive ecotoxicology issues in aquatic systems (Stone et al. 2014). A 2012 report by an expert panel in California identified the need to include this insecticide in future monitoring efforts (Anderson et al. 2012). The S.C. Coastal Pesticide Decision Making Tool developed by University of South Carolina and many partners (www.scpesticides.org) has Safety Rankings for the 100 most commonly used pesticides. This is a user-friendly, web-based tool designed for a broad range of audiences and can be used to improve upland management.
Sediment-associated pollutants derived from ponds are of greatest concern to human health if/when they become resuspended and transported into receiving waters, where they can come into direct contact with people engaging in various recreational activities. While chemical pollutants measured in S.C. ponds may be elevated to levels that pose a threat to benthic organisms, no published data show these sediments pose a risk to public health. However, much of the data presented in Chapters 2 and 3 of this report are derived from work published a decade ago. We can realistically hypothesize that contaminant levels in un-dredged ponds are likely higher now, as population growth and the associated increased coverage of impervious surfaces are linked to pollutant loading.
Harmful Algal Blooms (HABs)
Public health risks from exposure to stormwater ponds in coastal S.C. primarily include contact with HABs. Algal toxins in ponds have caused a variety of negative human health effects, including rashes, swelling, and respiratory ailments. Mycrocystins, a group of cyanobacteria toxins, have been found to be elevated in our coastal ponds to levels 10 to 100 times the World Health Organization limits for drinking water. From 2018 - 2020, mycrocystin (particularly the most potent form, LR) will be included in DHEC’s water quality monitoring in S.C.’s jurisdictional waters as part of the EPA initiative. While these do not now include ponds, broader guidance may result from these efforts.
Between the summers of 2014 and 2015, raphidophytes were associated with 40 blooms in coastal S.C. (Greenfield et al. 2015). Proliferation of these algae in ponds has been linked to nutrient loading and associated with certain bacterial species (Liu et al. 2008a, b). The diatom genus Pseudo-nitzschia is being reported more frequently in S.C.’s coastal stormwater ponds. This taxon is of particular concern because it produces the neurotoxin domoic acid, which has caused bivalve and dungeness crab fishery closures in other regions (Maine, west coast) of the U.S. A recent S.C. publication showed concentrations of the bacterial pathogen Vibrio were positively associated with dinoflagellate and raphidophyte blooms in coastal ponds (Greenfield et al. 2017). Vibrio was also positively associated with increased
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 168 temperature, a further indication that climate change may result in increased incidences of Vibrio and HABs.
Application: Acknowledging that HABs are a leading public health and environmental health concern, SCSGC recently funded several projects that seek to improve our ability to rapidly detect, quantify, and ultimately respond more effectively to these threats. Drs. Dianne Greenfield and Joe Jones were funded in 2014 - 2016 to develop a novel molecular tool to identify HAB species that have been linked to numerous coastal fish kills and other public health concerns. Following upon the success of this research, Dr. Greenfield and colleagues developed a tool that focuses on the cyanobacteria genus Microcystis, which produces microcystin. The products of this project will enhance monitoring efforts and early warning detection systems.
Pond Impacts on Waterways
2007 State of the Knowledge Report Question 10: What are impacts on receiving waters from pond discharges?
As ponds collect contaminants and promote HAB growth, there is concern over whether pond discharges are a source of pollutants to coastal waterways. As the inventory in Chapter 1 states, the majority of ponds in coastal S.C. are within the Critical Zone. This is an important issue along the coast. However, drawing from individual studies, it is not possible to provide a coast-wide answer as to whether ponds are a direct source of pollutants to waterways. The protection afforded by ponds to nearby receiving waters largely relies on the residence time of runoff within the pond. For flood control, the state requires that peak flows from two-year/24-hour and 10-year/24-hour storms be attenuated. The exact volume of runoff retained by a given pond then depends on the size of the development and proximity to nearby receiving waters and, in particular, shellfish beds. Some stormwater management programs have instituted stricter regulations, including the retention of a 25-year/24-hour storm event. However, in recent years S.C. has experienced heavy rain events that exceed even the 25-year storm event. In 2015 the state suffered a 1,000- year rain event, with some areas along the coast seeing rainfall that exceeded 28 inches in 24 hours. In these cases ponds can be overwhelmed, as indicated by measurements of fecal coliform concentrations and salinity of nearby tidal creeks. This has been noted by local stormwater managers and often attributed to poor pond designs. Some work by Greenfield and colleagues (2009, 2014b, 2017) shows that nutrient levels, HAB concentrations, and Vibrio spp. in ponds mimic trends recorded in receiving tidal creeks. On James Island, pesticide concentrations in a pond-tidal creek system were correlated, though pond chlorophyll and bacterial concentrations were not linked (Serrano & DeLorenzo 2008; DeLorenzo et al. 2012). This system demonstrated the importance of limiting introduction of pesticides and herbicides to ponds, as they can be a pathway to receiving waters.
Following up on her earlier work on stormwater and tidal creek systems (e.g., Blair et al. 2012; Sanger et al. 2013) Sanger and colleagues were funded by the SCSGC from 2014 - 2016 to evaluate the impact of 20 years of coastal development on tidal headwaters. These researchers also examined whether the widespread implementation of stormwater BMPs has a direct impact on tidal creek environmental quality within a watershed. Using models, the study found that use of BMPs in the suburbs does not alter the delivery of materials to tidal creeks as compared to what would be predicted based on the amount of impervious cover in a given area (Sanger et al. 2015).
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 169 Warning Signs
2007 State of the Knowledge Report Question 11: What water quality indicators/levels may indicate an impaired pond or potential pollution sources for receiving waters?
While there are no water quality criteria for stormwater ponds, standards do exist for bodies of water that are classified as waters of the state (DHEC 2014). These standards vary depending on the use of the waterways, such as for recreational contact or for sustaining shellfisheries. For lakes greater than 40 acres in size and other freshwaters, nutrient and chlorophyll criteria are based on an ecoregional approach. For lakes in the coastal counties, total phosphorus must be less than 0.09 mg/L, chlorophyll less than 40 µg/L, and total nitrogen less than 1.50 mg/L. There are additional metrics for microbial pollutants (summarized in Chapter 3). The S.C. Estuarine and Coastal Assessment Program (SCECAP) developed various thresholds for establishing water quality indices for estuarine ecosystems (Bergquist et al. 2009, Sanger et al. 2016). This includes physical parameters (dissolved oxygen, pH), as well as chemical (nitrogen, phosphorus), and biological measures (chlorophyll, fecal coliform bacteria). Sediment thresholds and index are also included in this program. Smith (2017), based on the SCECAP thresholds for estuarine waters, found that the outlet waters of the majority of ponds were classified as “good” for total phosphorus measurements (< 0.10 mg/L), while more were characterized as “fair” (0.81 to 1.05 mg/L) or “poor” (> 1.05) as pertaining to total nitrogen concentrations. In their study, the ponds with highest nutrient levels were found to be associated with the greatest development densities. Failure to meet either DHEC standards for coastal lakes or SCECAP thresholds for quality indicates that a natural waterway is impaired. The application of these metrics to ponds should be used with caution because part of their designed function is to collect and store pollutants. The main concern is if ponds become a source of pollutants to natural waterways, as discussed in the previous section.
TOPIC 6. Modeling
2007 State of the Knowledge Report Question 12: Which stormwater hydrological model is most applicable in coastal S.C.? Question 13: Which commonly used models have been validated for coastal S.C.?
Federal Tools
The EPA’s Storm Water Management Model (SWMM) is used globally for planning, analysis, and design as related to stormwater runoff. The most recent iteration, SWMM 5, includes the hydrologic performance of LID controls. In 2017, the EPA released the National Stormwater Calculator (SWC), which is a free software application that accesses national databases on soil type, topography, rainfall, and evaporation for a given site. The SWC was created to be user- friendly and site-specific, so that anyone that needs to calculate and reduce runoff from a property can use the tool. This tool can analyze site hydrology for LID controls, and it provides an LID cost estimation module. Finally, this model lets a user evaluate runoff based on both historic controls and climate scenarios.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 170 Local Models
Other commonly used stormwater modeling systems include the U.S. Department of Agriculture National Resources Conservation Service (USDA NRCS) curve number and unit hydrograph methods. These methods were modified by researchers in 2014 within NOAA’s National Centers for Coastal Ocean Science for coastal S.C.’s soil and topography to develop the stormwater runoff modeling system (SWARM) (Blair et al. 2014a, b). SWARM evaluates runoff for watersheds and sub-watersheds.
2007 State of the Knowledge Report Question 14: Are designed storm events (the two- or 10-year rain event) reducing peak rates of flow to pre- development conditions? Are pre-development rates accurate for our low topography? Question 15: What is the performance of ponds during small, frequent rain events versus large, infrequent events?
Managing Volume Control
During periods of high rainfall events in S.C., there is a possibility of ponds being overwhelmed by runoff. Managing runoff volume is an ongoing mission for Beaufort County, as shellfish are a valuable economic resource in the Lowcountry and fluctuations in salinity and the transport of microbial contaminants carried by runoff threaten the fishery. In 2006, Beaufort County evaluated pond basins in order to recommend improvements that addressed both volume control and water quality issues (tigerprints.clemson.edu/cgi/viewcontent.cgi?article=1128&context=scwrc Moore 2010). They proposed that ponds should be modeled for smaller, more frequent storm events rather than the large, less-frequent 10- and 25-year storms (EPA 2009). Ultimately this report concluded that the combination of wetland restoration and deeper permanent pools would improve volume controls and outflow concentrations. A recommended retrofit included the allowance for an eight to 10 foot permanent pool, and a freeboard that could detain a 25-year storm. The addition of a vegetated flood shelf was proposed to enhance volume control as well as promote evapotranspiration, sediment trapping, and bioretention of nutrients. As the proposed ponds would be designed to mimic nature, the study also indicated that the addition of wetlands would help retain microbial pollutants. By fall 2017, eight of the proposed projects were in process or had been completed. These were accomplished using 319 grants and public-private partnerships and the county plans to monitor these retrofits, including water quality indicators, as much as possible throughout their lifetime (Eric Larson of Beaufort County, pers. comm.).
A study for inland Richland County, S.C. was performed in 2010 to evaluate pond performance under seven design storm scenarios: one, two, five, 10, 25, 50, and 100-years with rainfall between 1.54 and 8.42 inches, along with storm durations of one, three, six, 12, and 24-hours (Huda & Meadows 2010). They found that during variable storm events the ponds frequently failed at protecting downstream waterways. In order to better prevent downstream flooding, the authors concluded that 24-hour extended detention of the one-year 24-hour storm is necessary and the permanent pool should be equivalent to the difference between post- and pre-development runoff volumes for the one-year 24- hour storm event (at least ½ inch from the entire watershed) in order to meet water quality standards. While models are powerful tools for determining effectiveness of stormwater management programs, they greatly benefit from ground-truthing with local data. Therefore the analyses of Huda & Meadows (2010) should be validated in the coastal
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 171 region in order to verify similar results for coastal plain.
Application: Tweel and colleagues (2015) evaluated the volume sensitivity of tidal creeks in Beaufort County, with varying levels of development, using in-stream salinity, rainfall, and SWARM. Ultimately, the study identified six particularly volume-sensitive watersheds and developed BMP and climate change scenarios that can be used by the county to focus policy and management actions. Volume-control measures have since been included in Beaufort County’s stormwater design manual. A similar study in Charleston County is being conducted from 2018-2020 to assess the applicability of the findings to another coastal location.
TOPIC 7. Costs and Benefits of Stormwater Management
First, we considered the approximate costs of maintaining stormwater ponds, as they are the standard BMP in coastal S.C. We utilized the information from the survey of pond professionals conducted by researchers from the College of Charleston and presented in Chapter 6. Based on these data the average costs of constructing a new private pond ranges between $17,000 and $33,000 per acre. The survey also indicated that average annual maintenance costs are between $230 and $760 per year, or between 1 and 8% of the initial construction costs. This back-of-the-envelope calculation was made by applying a fixed pond size of 0.54 acres, determined to be the average size of development- related coastal ponds (Chapter 1). These data, while provisional, do compare well with the costs for the published studies described in Chapter 6.
As development continues to boom on the S.C. coast, future stormwater management costs will likely be impacted by changes to existing policies and regulations on the volume of stormwater discharged from a site. For example, in 2009 Beaufort County commissioned several studies evaluating the cost of a proposed change to an ordinance that would require all new developments or redevelopments limit their stormwater rates and volumes to remain at or below pre-development levels (Ramsey 2010; Thomas & Hutton Engineering Co. 2009). To control post-development runoff to pre-development levels, several methods were proposed, including runoff to be diverted and reused, stored in underground tanks, or channeled through LID structures. Thomas & Hutton Engineering Co. (2009) found that constructing ponds with additional storage volume to use for irrigation purposes increased the cost of residential development by 10 to 35%, depending on the exact land-usage. While this is expensive, it was deemed not cost- prohibitive by the county.
LID Implementation
2007 State of the Knowledge Report Question 16: What are the comparative costs/benefits of more innovative practices?
Currently, nearly all design guides for S.C. coastal county stormwater programs include policies and standards to encourage developers to select LID practices such as bioswales, bioretention areas, rain gardens, and innovative technology BMPs like mechanical filtration devices. The level of detail provided in each guide varies by municipality. The LID Design Guide is directly cited by Horry and Georgetown counties as the recommended authority on implementing these practices. Specific LID requirements from individual county and municipal ordinances in coastal S.C. are briefly summarized in the LID Design Guide. Greater encouragement and/or direct incentivization of LID
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 172 stormwater management practices are stated in the Comprehensive Plans of Charleston, Dorchester, Georgetown, and Jasper counties. Full-scale implementation of incentive programs through local ordinances has not yet occurred. In the Jasper County Stormwater Design Manual, LID practices such as revegetation, green roofs, and permeable pavements do qualify for quantifiable stormwater management credits through reduction in runoff and improved water quality protection. The LID Design Guide outlines various strategies for local governments to encourage and incentivize more innovative green infrastructure, and it appears that many are moving to do so. The national Center for Watershed Protection also provides general guidance on how to implement better site designs and evaluate and change development rules (CWP 1998; EPA 2008). The Oak Terrace Preserve community located in North Charleston, S.C. is a model community for implementing LID practices.
Application: The cost of implementing and maintaining LID practices is highly variable, and at present there are little data on how they compare to traditional BMPs, namely ponds. Research by Dr. Marzieh Motallebi at Clemson University is currently (2018-2020) being funded to evaluate a variety of stormwater control measures (SCMs) over their life spans, calculate marginal costs of the selected SCMs, and evaluate costs of both their economic benefits and ecosystem services provided. The proposed research will build on the LID Design Guide and help to answer what the comparative costs and benefits are of utilizing innovative stormwater management practices in coastal S.C.
TOPIC 8. Societal Impacts
2007 State of the Knowledge Report Question 17: How can education and outreach to local government and homeowners be improved? Question 18: What are economic costs/benefits?
Importance of Education and Outreach
The 2007 DHEC-OCRM report was completed just as coastal counties and cities were taking over responsibility for stormwater infrastructure within their jurisdictions. As the shift to largely MS4-based management occurred, stormwater education and outreach programs grew rapidly to meet the requirements of the NPDES minimum control measures (MCMs). The first two of these require public outreach, education, and public involvement. SCSGC was a founding education partner to the first of the education consortia, the Coastal Waccamaw Stormwater Education Consortium (CWSEC), which was initialized in the Grand Strand in 2004. In 2007, CWSEC became more formalized as they went through their first NPDES Phase II permit cycle. The Ashley Cooper Stormwater Education Consortium (ACSEC) has operated in the Tri-County region since 2007, while the Lowcountry Stormwater Partners, recently revitalized in 2016, operates in Beaufort, Colleton, and Jasper counties. Clemson Extension directs the activities for both the ACSEC and the LSP, while Coastal Carolina University is the academic partner of CWSEC. The SCSGC remains a lead educational partner for all three programs.
These platforms unite highly skilled education providers and communicators with a variety of partners, each with their own expertise (e.g., DNR, the NERR programs). As the networks have grown, they have largely met the need to improve education and outreach to local governments and homeowners proposed in the 2007 DHEC report. Staff of each consortium works directly with the MS4 liaisons and their respective communities. Activities that each provide include regional conferences, focused workshops, mass media and targeted outreach, teacher and classroom trainings,
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 173 and formal professional training in pond management. The MS4 community relies heavily on these activities to educate homeowners and pond professionals in how to effectively manage the network of thousands of private ponds in the coastal zone. In Chapter 7 of this report, the authors discuss various strategies for communicating to a variety of groups on stormwater management.
As the economics chapter (Chapter 6) demonstrated through an international review of stormwater management practices, education is a best management practice for promoting improved, effective, and economically viable long-term strategies. Investing in educational programs, like those described above, is largely cost-effective for local government and can promote long-term behavioral changes. Because the majority of coastal S.C.’s programs are relatively new (< 10 years old), the long-term benefits of these programs have not yet been fully quantified.
Resources for Pond Owners
The EPA guidebook on stormwater wet ponds developed by the Center for Watershed Protection largely focuses on visual impairments related to the structure and functionality of the pond to retain water (EPA 2009). This guide focuses on pipe repairs and vegetation management, while water quality degradation related to bacteria, algal blooms, and low oxygen levels is only briefly addressed. Through the Master Pond Manager course offered by Clemson Extension, regional workshops, and local training efforts, pond owners are educated on what to look for that may indicate trouble in their own ponds. These programs cover topics related to dealing with nuisance animals, handling poor water quality, and managing plant growth and sedimentation around inflow and outflow structures. Primary water quality issues and causes include presence of algal blooms (= nutrients), fish kills (= toxins or low oxygen), and restricted flow (= sedimentation). Clemson Extension also provides soil testing services so if nutrients are a problem in ponds, the community can alter their fertilization routine to prevent nutrient over-loading to the system. These are vital programs, as private owners are responsible for the management and maintenance of the majority of coastal ponds. In 2018 Clemson Extension launched an online Master Gardener course that includes a variety of stormwater- related topics, such as planting and maintaining rain gardens.
Recognizing the need for ongoing education, Clemson Extension, in partnership with DNR, began hosting Stormwater Pond Working Group meetings entitled the “Healthy Pond Series” (www.dnr.sc.gov/marine/NERR/ pdf/HealthyPondSeriesFlyer9-14-17.pdf). This program was initiated in fall of 2017 and grew from an assessment performed after the 2016 Charleston Area Stormwater Ponds Conference. The content addresses informational needs that homeowners’ association (HOA) members and homeowners identified in a working group. Topics covered have included pond design and pond inspections. Each session features expert presentations, small group discussions, and a hands-on component, and they have proven to be popular free training opportunities for Charleston-area HOAs. Clemson Extension is evaluating whether they can expand the program to other regions.
Specialized Management Trainings
To promote good management practices, a variety of training options for pond professionals are available. Pond professionals, including those from out of state, benefit from Clemson Extension’s Master Pond Manager training. Clemson Extension also offers the Post-Construction BMP Inspector course that trains pond professionals to conduct routine, thorough inspections of stormwater BMPs. This is a statewide program that covers wet and dry ponds and green infrastructure practices.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 174 Additional technical trainings are offered through the Center for Watershed Protection, a national nonprofit based in Maryland that works to protect waterways from the negative impacts of land-use activities. They offer tailored workshops to meet a variety of audiences, including stormwater managers, public officials, and developers. Topics include: development site design, residential stormwater practices, and regulatory compliance. In 2017 in Baltimore, the Center for Watershed Protection piloted a workforce development program, entitled the Clean Water Certificate Training Program, that helps participants gain skills and knowledge in green infrastructure practices. Education and public involvement is shown to be an effective strategy for ensuring proper pond management, and communication efforts need to identify and target the individual groups responsible for pond management over their life cycle.
Measures of Success
Each regional stormwater education consortium in S.C. develops strategies for public outreach and involvement, and documents the activities it performs as a way to evaluate how well the consortium is meeting its goals. They publish records of these activities and annual reports that are available on their respective websites. However, establishing if and how the implemented programs result in behavioral changes and cleaner waterways is a challenge. The California Stormwater Quality Association (CASQA; www.casqa.org) found that an effective stormwater management program should meet six outcomes, including changes in attitudes, knowledge and awareness, as well as behavioral changes in BMP implementation practices. CASQA developed an online portal where members of the stormwater community can access materials that will assist them in assessing the effectiveness of individual programs. While many of these materials are tailored for California, the Effectiveness Assessment Baseline Report includes guidance and specific metrics that could be applied to the evaluation of any stormwater management program.
TOPIC 9. Recommendations for Future Action
The 2007 State of the Knowledge report outlined several management recommendations to improve stormwater management practices by DHEC-OCRM to ultimately benefit our coastal receiving waters. These included:
• Improve water quality by managing on a watershed basis. • Allow/encourage innovative stormwater management practices/standards (e.g., use vegetative options, install green infrastructure). • Research current use, feasibility, economic impact, and projected effectiveness of implementing pollutant removal efficiency standards for new systems. • Improve the Stormwater Maintenance Program (e.g., maintenance inspection procedures for emerging practices, sampling for sediment contaminants, include maintenance in realtor workshops, increase education to HOAs).
Over the past decade, the shift in responsibility from the state to the local level under the Phase II NPDES program means that direct management lies in the hands of county and municipal stormwater or public works departments. To better understand how stakeholders and decision-makers perceive current management needs, we convened a Stormwater Ponds Advisory Council (SPAC; Table 8.1), comprised of regulatory agents, private sector representatives, and nonprofits. Several of the issues listed above were addressed in preceding sections, including promotion of green infrastructure and educational practices. The remainder of the topics are addressed below, where we draw on conversations and feedback provided by SPAC members over a series of group and individual meetings, beginning in 2014.
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 175 Name Affiliation Subject Area Jeff Adkins NOAA NOS – Office for Coastal Resource Economist Management David Fuss Horry County Local Government – Stormwater Manager Shannon Hicks DHEC State Government – Resource Manager Eric Larson Beaufort County Local Government – Engineer Chris Marsh, Ph.D. The LowCountry Institute Environmental Science and Education Ed Oswald Private/Charleston Trident Real Estate Agent Association of Realtors Calvin Sawyer, Ph.D. Clemson Extension Water Quality Specialist Norm Shea Private Pond Management Allen Smith Private/S.C. Aquatic Plant Pond Manager Management Society April Turner S.C. Sea Grant Consortium Coastal Communities Extension Specialist David Whitaker, Ph.D. S.C. DNR – Marine Resources State Government – Resource Division Manager
Table 8.1 The Stormwater Ponds Advisory Council (SPAC).
Watershed Management
Ensuring that stormwater is managed on a watershed basis is a challenge, especially in the era of MS4 programs, where greater than five political entities may be managing a single watershed. In some cases these disparate entities work together to design and implement strategies that are appropriate across jurisdictions. Therefore, it is paramount that agencies like SCSGC work across a variety of stakeholders to ensure science-based information is generated and utilized. For example, SCSGC was involved in a study conducted in the Beaufort area to identify tidal creek systems that are especially vulnerable to volume of runoff (Tweel et al. 2015). This included a watershed analysis across all major Beaufort County watersheds, which scaled up the results of this single effort. Importantly, the study utilized a new model (described above under Topic 4) that can assist other coastal counties and municipalities manage runoff on a watershed scale.
In the Grand Strand, the Waccamaw Watershed Academy (WWA), established in 2004 by Coastal Carolina University, is a unique program in the state. The research arm of the WWA addresses technical study of environmental problems and is performed at the Environmental Quality Laboratory, the only lab in the region with regulatory-level standards. Their mission is to understand the sources, transport, and impacts of pollutants in the Waccamaw River watershed. This includes the Volunteer Water Monitoring Program, a successful long-term initiative which helps local municipalities meet NPDES Phase II stormwater program requirements. The work of the WWA incorporates coastal S.C. research including work performed in the Tidal Creeks Project, led by DNR and co-funded by SCSGC (Sanger
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 176 et al. 1999a, 1999b; Holland et al. 2004). This was seminal work in the field of evaluating and predicting pollution trends in tidal creek systems caused by development and associated increase in impervious surfaces.
Nationally, the EPA generates broad guidance for watershed management, while DHEC provides more specific watershed-based planning documents for the state. Additionally, DHEC has developed watershed-based plans for several specific watersheds, including the Savannah/Salkahatchie and the Broad/Edisto in the Lowcountry, and the Santee/Pee Dee in the Grand Strand. Section 319 grants, received from the EPA and administered through DHEC, are a source of funding for watershed-based planning activities that address NPS pollution. As part of the South Carolina Nonpoint Source Program, funds are dispensed through federal Section 319 grants and a state revolving fund; any state agency, local government, or public university is eligible to receive these grants.
Changes to Pond Design and Maintenance
Requiring that ponds, and other stormwater BMPs, meet minimal pollutant removal efficiency standards was proposed in 2007 and is still being discussed by DHEC and local managers. At this time there are no regulatory requirements for pond water quality, as mentioned previously in this synthesis. In meetings with the SPAC, we learned that information provided by the scientific community on water quality issues is valuable for agencies when proposing new policies to the legislature. Additionally, a better understanding of how effective (or not) ponds are at removing pollutants would be highly impactful. Our current report demonstrates that pollutant removal capabilities are highly variable and dependent on site characteristics and contaminant type. In order to provide more comprehensive management, we propose closer partnership with MS4 communities, as described under Recommended Priority 1 in the next section.
Other major challenges to proper pond maintenance, as cited by SPAC members, are related to the lack of knowledge of HOA members and property owners. Often, pond management decisions made by HOAs rely largely on aesthetic preferences, which in most places means clear cutting of grass to the pond’s edge. To combat misperceptions and promote positive changes, education is required at all stages of the pond life cycle as discussed previously. This opinion was reinforced by several SPAC members. In multiple conversations with stormwater managers, their greatest concern is about increasing awareness about ponds to the general public. At this time, BMP inspections required for Phase II MS4 programs cover structural function and not water quality measures. While structures can be a proxy for water quality issues, they cannot address function. And for many coastal counties and municipalities, even these inspection programs are in their infancy, so compliance rates are poorly characterized at this time. In Chapter 7 of this report, our communications team generated a detailed management booklet intended for a general audience and based on feedback from pond professionals. We describe additional strategies to address this issue below.
The Next Steps for the Stormwater Ponds Collaborative
Since 2006, SCSGC has funded 16 studies on stormwater BMPs, and an additional 11 studies on the impact of land use and runoff on downstream water quality issues. Not including the current effort, SCSGC and our partners have produced nine products that incorporate this science, including the LID Design Guide. At present, we are partnered with seven institutions and agencies working on stormwater management-related issues. Building on these successes, SCSGC now looks to the future and the next generation of stormwater management in order to best position ourselves so that we continue to serve as a helpful partner in the field. Because our involvement in stormwater is as both a research entity and educational partner, we work with a variety of stakeholders, each with unique relationships
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 177 to both our work and stormwater in general. Below we outline some potential activity priorities we identified during the preparation of this report.
First, Sea Grant’s path forward in both stormwater research and outreach would benefit from an official needs assessment of our diverse partner groups. These include:
• Coastal stormwater education consortia, • Academic institutions, • Local resource managers, • State agencies (e.g., DHEC, DNR), • Nonprofits (e.g., Charleston Waterkeeper, LowCountry Institute), • Private businesses, • Real estate professionals, • The development community, and • Local government stormwater managers.
The goal would be to identify priority needs and, together with the Homeowners’ Associations, to write a research prospectus for funding to address them. In the current report, knowledge or research gaps were identified by each project team and compiled in Appendix A8 (see www.scseagrant.org/spsok). Engaging our stakeholder communities to assist in prioritizing next steps from this curated list of knowledge gaps would be a useful step in creating a comprehensive and meaningful prospectus. An additional resource that may help to facilitate this process is a needs assessment used by the Consensus Building Institute in their evaluation of Ohio’s stormwater management programs (Consensus Building Institute 2012). We recommend the list of questions generated in this report be used by SCSGC as an interview guide, with pertinent topics including:
• Defining successful stormwater management, • Promoting positive behavioral changes, • Acknowledging citizen concerns, • Identifying inconsistencies and difficulties in implementation of various regulations, • Evaluating precipitation patterns and information needs, • Connecting users with trustworthy data sources, and • Determining an acceptable geographic range for projects.
The members of the collaborative and the SPAC are the appropriate first audiences to survey, but the process of preparing a prospectus can be extended to other partners with whom SCSGC regularly coordinates. Below we outline several priorities that were identified through previous meetings of the collaborative and SPAC that should be considered when developing the prospectus.
Recommended Priority 1
To evaluate the success of individual BMPs, as requested by stormwater managers, we believe the prospectus should continue and expand partnerships with local stormwater programs. Close partnerships with these programs would
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 178 avoid the difficulties faced in extrapolating broadly from studies performed on private land due to ignorance of pond history and current management. This challenge is illustrated throughout the report. By partnering with local stormwater departments that manage BMPs on public property, these knowledge gaps are removed. As mentioned earlier, a potential funding source for monitoring is the 319 program administered by DHEC. The State Revolving Fund can also be utilized to explore the effectiveness of green infrastructure and innovative retrofits (e.g., inclusion of vegetated forebays, floating wetlands), especially in MS4s that have already identified, or even incentivized, the use of LID practices in their stormwater management plans. A priority area for future research, as identified by state and local regulators, should be developing the scientific basis for water quality thresholds in stormwater ponds. As described under Topic 5, creating standards or thresholds based on what is expected for natural waterways is not necessarily appropriate as ponds are small, often stagnant water bodies designed to collect pollutants. Therefore, a unique system should be considered to assess the health of a stormwater pond over the course of its lifetime.
As an example the Stormwater Action Monitoring (SAM), an ambitious monitoring project in the Puget Sound region, united municipal groups for monitoring needs. This program is paid for by nearly 100 cities, counties, state and federal agencies, and businesses. A portion of the monitoring strategy, developed by the State of Washington’s Department of Ecology, evaluates the effectiveness of various BMPs. This includes LID practices, retrofits, and structural and non-structural BMPs. While large in scope, SAM may be a useful guide for creating regional monitoring programs in coastal S.C.
Recommended Priority 2
To incorporate the societal aspects of pond management, volunteer monitoring programs could also be implemented. Lee County, FL has sustained a successful Pond Watch Program which utilizes citizen volunteers to monitor ponds for conditions such as nutrients and chlorophyll a that indicate problems with aquatic weeds and algae. The data collected through this program are used to calculate the Trophic State Index, a tool used in Florida to determine the biological productivity of a lake or pond. Elsewhere, a long-term citizen science stormwater pond monitoring effort in Toronto, Canada found nutrient concentrations (phosphorus and nitrogen) were often elevated relative to Canadian water quality standards (Scott & Frost 2017). Alongside local guidance from the WWA, successful citizen science pond programs such as these can be used as guides for developing and implementing new pond monitoring initiatives in coastal S.C. These would likely rely on state and local funds but could seek public-private partnerships with communities and businesses.
Engagement Opportunities
As stated earlier, SCSGC has a unique role as a funding entity, science-based information generator, and information broker. Therefore, we ensure that the results of relevant studies are communicated directly to those groups that can utilize the information. At present, SCSGC is an education partner to the three coastal stormwater education consortia. This provides a direct pipeline by which we educate the educators. For instance, in 2017 the Coastal Environmental Quality program specialist spoke at the Coastal Waccamaw Stormwater Education Consortium winter meeting to share information on recent and ongoing SCSGC-funded studies. Audience members included educational partners and MS4 representatives. One- or two-page progress reports, written by SCSGC’s Communications department in a language that speaks to stormwater managers and pond professionals, would be useful products. These could be disseminated via a bi-annual newsletter or linked to a SCSGC-hosted GIS application that highlights active research projects. An additional tool to assist in the dissemination of information is the South Carolina Coastal
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 179 Information Network (SCCIN), a resource provided and maintained by SCSGC.
A final important aspect of communicating more frequently with our partners is to ensure we use a common language and reinforce a shared message. SCSGC will be partnering with Clemson Extension to create an interactive, online stormwater portal that will allow users to navigate science-based products alongside Clemson’s outreach and educational resources. We also are working with state and local agencies to revitalize a realtor training program. Through conversations with the real estate professional on the SPAC, we identified stormwater as an important issue facing agents and their clients along the coast.
Conclusion While each chapter of this 2019 State of Knowledge Report highlights specific research gaps for given topic areas, we found that by evaluating the field holistically, an overarching need arose. Because the proliferation of stormwater ponds along the Southeast coast has created new aquatic habitat that lies in residents’ backyards, social, economic, and ecological issues are thoroughly intertwined. For example, mitigating the impact of nutrients on ponds and downstream water quality relies strongly on the behavior of community members. Therefore, all future research must apply an interdisciplinary approach to characterize the role of ponds within the landscape and their associated management challenges. The mission for SCSGC is to facilitate comprehensive research projects and diverse outreach materials that address the complex interdependence of pond systems and human actions.
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Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 184 GLOSSARY OF ACRONYMS
ACSEC: Ashley-Cooper Stormwater Education Consortium BMP: Best Management Practice CASQA: California Stormwater Quality Association CBSM: Community-Based Social Marketing CDBG: Community Development Block Grants CECs: Contaminants of Emerging Concern CMP: Coastal Management Program (South Carolina) CWA: Clean Water Act (federal) CWSEC: Coastal Waccamaw Stormwater Education Consortium CZC: Coastal Zone Consistency (South Carolina) CZMA: Coastal Zone Management Act (federal) DHEC-OCRM: Department of Health and Environmental Control - Ocean and Coastal Resource Management (South Carolina) DL: Detection Level DOC: Dissolved Organic Carbon ENMs: Engineered Nanomaterials ERL: Effects Range Low ERM: Effects Range Median FCB: Fecal Coliform Bacteria FDA: Food and Drug Administration FTWs: Floating Treatment Wetlands HAB: Harmful Algal Bloom HCSMD: Horry County Stormwater Management Department HOA: Homeowners’ Association HUC: Hydrologic Unit Code IAE: Incidence of Adverse Effects INMs: Incidental Nanomaterials LID: Low Impact Development LSP: Lowcountry Stormwater Partners LUCES: Land Use – Coastal Ecosystem Study MS4: Municipal Separate Storm Sewer System MSA: Metropolitan Statistical Area NAIP: National Agriculture Imagery Program N.C. DEQ: North Carolina Department of Environmental Quality
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 185 NERR: National Estuarine Research Reserve NOAA: National Oceanic and Atmospheric Administration NOM: Natural Organic Matter NPDES: National Pollutant Discharge Elimination System NPS: Nonpoint Source (pollutants) PAH: Polycyclic Aromatic Hydrocarbons PBDE: Polybrominated Diphenyl Ethers PCB: Polychlorinated Biphenyls PM: Particulate Matter POC: Particulate Organic Carbon PPCPs: Pharmaceutical and Personal Care Products RT: Residence Time SAM: Stormwater Action Monitoring S.C. DHEC: South Carolina Department of Health and Environmental Control S.C. DNR: South Carolina Department of Natural Resources S.C. PCA: Pollution Control Act (South Carolina) S.C. SMSRA: Stormwater Management and Sediment Reduction Act (South Carolina) SCSGC or Consortium: South Carolina Sea Grant Consortium SPAC: Stormwater Ponds Advisory Council SQGs: Sediment Quality Guidelines SSURGO: Soil Survey Geographic Database (USDA) SWARM: Stormwater Runoff Modeling System (NOAA) SWPPP: Stormwater Pollution Prevention Plan TEL: Threshold Effect Level TMDL: Total Maximum Daily Load TN: Total Nitrogen TOC: Total Organic Carbon TP: Total Phosphorus U.S. EPA: United States Environmental Protection Agency USD: United States Dollar USDA: United States Department of Agriculture USGS: United States Geological Survey WHO: World Health Organization WTP: Willingness To Pay WWA: Waccamaw Watershed Academy WWTP: Waste Water Treatment Plant
Stormwater Ponds in Coastal South Carolina: 2019 State of Knowledge Report 186