Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Prepared in cooperation with the Maryland Department of the Environment Maryland Department of Natural Resources Maryland Department of Agriculture Dorchester Soil Conservation District U.S. Fish and Wildlife Service

Scientific Investigations Report 2011–5054

U.S. Department of the Interior U.S. Geological Survey Cover. Aerial view of Little Blackwater River looking north. The Key Wallace Drive bridge is in the foreground. Photograph by Jane Thomas, IAN Image Library (www.ian.umces.edu/imagelibrary/). Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

By Brandon J. Fleming, Benjamin D. DeJong, and Daniel J. Phelan

Scientific Investigations Report 2011–5054

U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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Suggested citation: Fleming, B.J., DeJong, B.D., and Phelan, D.J., 2011, Geology, hydrology, and water quality of the Little Blackwater River watershed, Dorchester County, Maryland, 2006–09: U.S. Geological Survey Scientific Investigations Report 2011–5054, 82 p.

ISBN 978-1-4113-3123-5 iii

Contents

Abstract...... 1 Introduction...... 1 Purpose and Scope...... 2 Description of Study Area...... 2 Methods...... 2 Groundwater and Surface-Water Monitoring Methods...... 2 Groundwater and Surface-Water Sampling Methods...... 5 Geology...... 5 Miocene Stratigraphy...... 6 Pleistocene-Holocene Stratigraphy...... 6 Hydrology...... 9 Groundwater-Flow System...... 9 Surface-Water System...... 15 Water Quality...... 17 Data Quality Assurance...... 17 Blanks ...... 17 Duplicates...... 18 Ion Balances...... 18 Groundwater Quality...... 18 Inorganic Constituents...... 18 Organic Constituents...... 25 Surface-Water Quality...... 25 Inorganic Constituents...... 25 Organic Constituents...... 25 Summary and Conclusions...... 28 Acknowledgments...... 29 Selected References...... 29 Appendix 1: Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland...... 32 Appendix 2: Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland...... 37 Appendix 3: Concentrations of inorganic and organic constituents in equipment blanks, Little Blackwater River watershed, Dorchester County, Maryland, 2007–08...... 57 Appendix 4: Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland...... 60 Appendix 5: Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland...... 68 Appendix 6: Lithologic and geophysical logs of DO Cd 58 core, Little Blackwater River watershed, Dorchester County, Maryland...... 77 Appendix 7: Lithologic and geophysical logs of DO Cd 66 core, Little Blackwater River watershed, Dorchester County, Maryland...... 78 Appendix 8: 2-D resistivity survey along the Egypt Road well transect B-B’, Little Blackwater River watershed, Dorchester County, Maryland...... 82 iv

Figures

1–2. Maps showing— 1. Location of Little Blackwater River watershed study area, Dorchester County, Maryland...... 3 2. Location of the Little Blackwater River drainage area and monitoring sites...... 4 3–4. Photographs showing— 3. Miocene formations observed in cores collected in the study area: (A) Calvert Formation (97.9–99-feet depth in Kentuck core), and (B) Choptank Formation (approximately 69–70.25-feet depth in Kentuck core)...... 9 4. Examples of facies seen in Pleistocene sequences from the DO Dd 12 core: (A) fluvial (approximately 4–5.25-feet depth), (B) rising-stage (approximately 20–21.25-feet depth), and (C) estuarine-marine (41.75–43-feet depth)...... 10 5. Diagram showing stratigraphic contrast between DO Cd 58 (left) and DO Cd 66 (right)...... 11 6. Photographs showing the Parsonsburg Sand as expressed in (A) 2.25–4-feet depth in the DO Dd 12 core, and (B) 8.5–9.5-feet depth in the Maintenence Yard core...... 12 7. Diagram showing generalized north-south hydrogeologic cross section through the Little Blackwater River watershed, Dorchester County, Maryland...... 13 8. Graphs showing groundwater levels in (A) wells DO Cd 64 (screen interval 3–13 feet below land surface [fbls]), DO Cd 65 (screen interval 70–75 fbls), DO Cd 66 (screen interval 124–129 fbls), May 2008–August 2009, (B) wells DO Dd 12 (screen interval 95–100 fbls) and DO Dd 13 (screen interval 2–12 fbls), September 2007–September 2009, and (C) well DO Cd 1, 1960–2010, Dorchester County, Maryland...... 15 9. Graph showing (A) Groundwater levels in water-table wells, and cross sections showing (B) winter and (C) summer groundwater- flow directions, October 2007–July 2009, Little Blackwater River watershed, Dorchester County, Maryland...... 16 10–12. Graphs showing— 10. Groundwater levels in wells DO Cd 58 and DO Cd 63, and surface-water elevations at the gage on the Little Blackwater River at Cambridge, Maryland, November 2007–May 2008...... 17 11. Comparison of (A) specific conductance at the Cambridge gage and Key Wallace Drive gage, Maryland, and (B) temperature and specific conductance at the Key Wallace Drive gage, Maryland, November 2006–November 2009...... 17 12. Discharge to and from the Little Blackwater River at Seward, Maryland on Key Wallace Drive, Dorchester County, Maryland, November 2006–September 2009...... 17 v

13. Trilinear diagrams showing chemical characteristics of inorganic constituents in surface water and groundwater, Little Blackwater River watershed, Dorchester County, Maryland...... 23 14. Boxplots showing inorganic constituents in surface water and groundwater, Little Blackwater River watershed, Dorchester County, Maryland...... 24 15. Graph showing pH compared to well depth for all groundwater wells sampled, Little Blackwater River watershed, Dorchester County, Maryland...... 25 16–17. Boxplots showing— 16. Inorganic constituents at surface-water sites, Little Blackwater River watershed, Dorchester County, Maryland...... 26 17. Summer (June through November) and winter (December through May) inorganic constituents in the upper and lower basin, Little Blackwater River watershed, Dorchester County, Maryland...... 27

Tables

1. Geologic units described in previous investigations in the Coastal Plain of Delaware, Maryland, and Virginia...... 7 2. Thickness and depth of geologic units in the Little Blackwater River watershed, Cambridge, Maryland...... 8 3. Locations and descriptions of wells installed and monitored during the Little Blackwater River study, Dorchester County, Maryland...... 14 4. Concentrations of organic compounds detected in surface-water and groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland, June 2008...... 19 5. Dissolved organic compounds analyzed for, but not detected, in surface-water and groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland...... 22 vi

Conversion Factors and Datums

Multiply By To obtain Length inch (in.) 2.54 centimeter (cm) foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) Area square foot (ft2) 0.09290 square meter (m2) square mile (mi2) 2.590 square kilometer (km2) Volume gallon (gal) 3.785 liter (L) cubic foot (ft3) 0.02832 cubic meter (m3) Flow rate cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s) gallon per minute (gal/min) 0.06309 liter per second (L/s) gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F = (1.8 × °C) + 32 Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88). Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 25 °C). Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L) or micrograms per liter (μg/L). The term “water year” is defined as the 12-month period from October 1 of any given year through September 30 of the following year. The water year is designated by the calendar year in which it ends and which includes 9 of the 12 months. Thus, the year ending September 30, 2002, is called the “2002 water year.”

Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

By Brandon J. Fleming, Benjamin D. DeJong, and Daniel J. Phelan

Abstract from 9 surface-water sites to characterize pre-development conditions and the seasonal variability of inorganic constituents and nutrients. The highest mean values of nitrogen are The Little Blackwater River watershed is a low-lying found in the deep groundwater system, with relatively low tidal watershed in Dorchester County, Maryland. The poten- values in the water table. Surface-water-quality samples in the tial exists for increased residential development in a mostly lower half of the basin show a significant increase in inorganic agricultural watershed that drains into the Blackwater National seawater constituents, especially in summer, corresponding Wildlife Refuge. Groundwater and surface-water levels were with net negative discharge from the Little Blackwater River. collected along with water-quality samples to document Samples also were collected from nine wells and four hydrologic and geochemical conditions within the watershed surface-water sites for pesticides in June 2008. The herbicides prior to potential land-use changes. atrazine, metolachlor, and simazine, and the insecticide fipro- Lithologic logs were collected in the Little Blackwater nil were detected at each of the four surface-water sites, with River watershed and interpreted with existing geophysical concentrations less than 2 micrograms per liter. Concentrations logs to conceptualize the shallow groundwater-flow system. A of pesticides found in groundwater were typically one to two shallow water table exists in much of the watershed as shown orders of magnitude lower than pesticide concentrations found by sediment cores and surface geophysical surveys. Water- in surface water of the Little Blackwater River. table wells have seasonal variations of 6 feet, with the lowest Seasonal hydraulic-gradient reversals between the shal- water levels occurring in September and October. Seasonally low groundwater system and the Little Blackwater River, low water-table levels are lower than the stage of the Little coincident with the inflow of brackish water from Fishing Bay Blackwater River, creating the potential for surface-water and Blackwater National Wildlife Refuge, indicate a potential infiltration into the water table. for saltwater intrusion into the water table. The likelihood of Two stream gages, each equipped with stage, velocity, saltwater intrusion into the water table is further supported specific conductance, and temperature sensors, were installed by high chloride concentrations observed in water-table wells at the approximate mid-point of the watershed and near the near the Little Blackwater River. mouth of the Little Blackwater River. The gages recorded data continuously and also were equipped with telemetry. Discharge calculated at the mouth of the Little Blackwater River showed a seasonal pattern, with net positive discharge in Introduction the winter and spring months and net negative discharge (flow into the watershed from Blackwater National Wildlife Refuge The U.S. Geological Survey (USGS), in cooperation with and Fishing Bay) in the summer and fall months. Continuous the Maryland Department of the Environment, the Maryland water-quality records showed an increase in specific conduc- Department of Natural Resources, the Maryland Department tance during the summer and fall months. of Agriculture, the Dorchester Soil Conservation District, Discrete water-quality samples were collected during and the U.S. Fish and Wildlife Service, began a study of 2007–08 from 13 of 15 monitoring wells and during 2006–09 the hydrology of the Little Blackwater River watershed in 2 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Dorchester County, Maryland in September 2006. The study forested and marshy riparian areas, and tidal wetlands (James was designed to document the local geologic setting, mea- Newcomb, Dorchester Soil Conservation District, oral com- sure seasonal groundwater and surface-water conditions, and mun., 2007). The watershed is relatively flat, with an elevation analyze water quality in the drainage area of the Blackwater of 30 ft (feet) near Cambridge, to sea level at the confluence National Wildlife Refuge (BNWR) planned for municipal with the Blackwater River. The Little Blackwater River is development. tidally affected for much of its reach, and flows generally The BNWR is located 12 mi (miles) south of Cambridge southward to discharge to the Blackwater River (fig. 2). in Dorchester County, Maryland, and consists of over 25,000 acres of freshwater impoundments, brackish tidal wetlands, open fields, and mixed evergreen and deciduous forests (fig. 1). The refuge was established in 1933 primarily as a Methods wildlife sanctuary for migratory birds but is the home of other Groundwater and surface-water levels were measured threatened species such as the Delmarva fox squirrel and bald over a multi-year period to describe the seasonal hydrologic eagle. In the 20th century, wetland plants have disappeared variation within the Little Blackwater River watershed. from the wetlands for a variety of reasons including the pres- Water-quality parameters including major ions, nutrients, and ence of nutria (Myocastor coypus)—non-native semi-aquatic pesticides were collected from groundwater and surface-water rodents that overgraze native wetland plants. Residential sampling sites to characterize water quality prior to changes in development is planned in the Little Blackwater River land use. watershed between the refuge and the City of Cambridge (fig. 2). County, State, and Federal regulators and agencies as well as public civic groups are concerned that an increase in Groundwater and Surface-Water Monitoring development could have detrimental effects on the BNWR by Methods changing groundwater-flow patterns, increasing runoff from areas treated with fertilizers, and increasing discharges from River conditions in the Little Blackwater River were on-site wastewater systems into the tidal Little Blackwater monitored using two USGS gaging stations, station number River that flows into the Blackwater River and the BNWR. 1490120 (Little Blackwater River near Cambridge, Md.), In an effort to minimize the potential effects of development located at the approximate mid-point of the watershed with on the BNWR, the State of Maryland purchased part of the a drainage area of 15.3 mi2, and station number 1490140 proposed development area that directly borders the Little (Little Blackwater River at Seward, Md.), near the confluence Blackwater River, and no development will be allowed on the of the Little Blackwater River and the Blackwater River at state-owned property (fig. 2). Key Wallace Drive, with a drainage area of 30.2 mi2 (fig. 2) as calculated from a 30-m (meter) digital elevation model. Purpose and Scope These sites will hereafter be referred to as the Cambridge and the Key Wallace Drive gages. Both gages measured specific This report describes (1) the geology of the Little conductance, temperature, velocity, and river stage at 6-minute Blackwater River watershed based on the drilling results from intervals. Discharge was calculated at Key Wallace Drive with concurrent regional geological investigations, (2) the ground- an acoustic Doppler current profiler (ADCP), which measures water-flow system in areas adjacent to proposed development, both the velocity and the direction of flow. (3) streamflow characteristics, and (4) groundwater and The USGS installed a transect of three monitoring well nests (multiple wells screened at different depths at the loca- surface-water quality in the Little Blackwater River watershed tion) consisting of eight wells, DO Cd 56-63, on the east side from 2006 through 2009. Data presented in this report will of Egypt Road in 2007, between the proposed development provide a baseline of preexisting conditions for comparison area and the Little Blackwater River (fig. 2). Another monitor- with future post-development conditions. ing nest consisting of three wells, DO Cd 64-66, was installed about 0.4 mi farther south on the west side of Egypt Road in Description of Study Area 2008. The USGS also installed a pair of monitoring wells (DO Dd 12 and DO Dd 13) in the Kentuck Swamp near the The Little Blackwater River watershed is in Dorchester BNWR in 2007 as part of a more regional assessment of the County, Maryland, on the Eastern Shore of the Chesapeake hydrogeology of the basin (fig. 2). Two wells, DO Cd 67 and Bay. The watershed extends from the south side of Cambridge DO Cd 68, were installed prior to the start of the study and to the Blackwater River in the BNWR (fig. 2). The Little were only monitored for water levels. Continuous sediment Blackwater River watershed drains approximately 27,748 core was recovered from the deep well at each nest site and acres [43.3 mi2 (square miles)] that are used primarily for was used in this study as the basis for the geologic inter- agriculture. Land use in the watershed in 2005 included pretation. Once the wells were installed, water levels were approximately 1,276 acres of residential, commercial, and measured monthly and selected wells were instrumented with light industrial land, and 26,472 acres of cropland, woodland, continuous pressure transducers. Methods 3

Figure 1. Location of Little Blackwater River watershed study area, Dorchester County, Maryland. 4 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Figure 2. Location of the Little Blackwater River drainage area and monitoring sites. Geology 5

Groundwater and Surface-Water Sampling Surface-water-quality samples were collected using Methods vertically integrated samplers at the approximate mid-stream location at each of the sampling points. Horizontal integration Groundwater samples were generally collected using was not used due to the narrowness of the sampling locations. standard USGS sampling protocols (U.S. Geological Survey, At two sampling locations (1490113 and 1490108) culverts variously dated) that were modified slightly because of the low were present under the roadways at each location. The culvert permeability of the materials in which many of the wells were that had the most visual flow was sampled. Beginning on screened. Fultz groundwater sampling pumps were used and March 16, 2006, samples were collected from three surface- pumped at low-flow rates to minimize the drawdown in the water sampling sites (1490112, 1490116, and 1490120) and wells so that well screens were not exposed to the atmosphere analyzed for nutrients, major ions, and field parameters during the purging and sampling. For water-table wells, which (fig. 2) in cooperation with the USGS Priority Ecosystems had well screens that straddled the water table, the drawdown Science (PES) Program. was minimized as much as possible, but some aquifer materi- Two additional sampling locations (1490113 and als were exposed to the atmosphere. The intermediate-depth 1490140) were added for the next quarterly sampling effort wells sampled in October 2007 along the transect (wells DO (June 22, 2006, fig. 2). Additional sampling locations Cd 57, 60, and 62) had such low recovery rates that groundwa- (1490108, 1490110, and 1490130) were added and quarterly ter sampling pumps could not maintain flow rates high enough sampling was maintained until October 29, 2007. A final to recover sufficient volume for sampling. These wells were sampling was conducted June 10, 2008 at eight of the surface- sampled with bailers during this sampling event, and were not water sites. Two storm-sampling events were also conducted sampled in June 2008. on October 6, 2006 and April 16, 2007 to evaluate the impacts The sampling procedure involved lowering the pump of major rain events when storm or wind surge was not bring- intake to the desired depth, and then pumping at a low-flow ing higher saline water from the Blackwater River or Fishing rate. Water-quality parameters were collected for pH, tem- Bay into the Little Blackwater River watershed. The storm perature, specific conductance, and dissolved oxygen during samples were collected following evaluations of the real-time purging as the water was pumped through a flow-through discharge and specific conductance data in consultation with cell. Parameter readings were taken every 5 minutes using visual observations from staff from the BNWR. Groundwater YSI 6920 water-quality sondes until the change in parameter and surface-water sampling sites, dates, and results of sam- values between intervals reached stable values. Once stabi- pling are listed in Appendix 1 and 2. Also presented in lization was attained, defined as parameter values with less Appendix 1 and 2 are the results of duplicate environmental than a 5-percent change in six successive 5-minute intervals, samples and ion balances, with equipment blank results pre- sampling bottles for total (unfiltered) analyses were filled, then sented in Appendix 3 and described later in this report. bottles for dissolved (filtered) analyses, followed by those requiring special sample-handling procedures, such as organic compounds. In-line filtration capsules were used to prevent Geology atmospheric contact until the sample bottles were filled. All bottles were preserved, iced and processed, and shipped to the The Little Blackwater River watershed on the central USGS National Water Quality Laboratory in Denver, Colorado Delmarva Peninsula is situated in the Atlantic Coastal Plain. within 48 hours. The Coastal Plain is underlain by a wedge of Cenozoic and Mesozoic sediments that range in thickness from zero at the Fall Line west of the Chesapeake Bay in Virginia Number of and Maryland to approximately 8,000 ft under the coast of Number of ground- surface-water water samples in Maryland at Ocean City (fig. 1), and is approximately 3,300 ft Constituent group samples in study study (including thick under the study area (Trapp and others, 1984). A study sampled for in study (including replicates and by Ator and others (2005) divides the surficial hydrogeology replicates and equipment blanks) of the Mid-Atlantic Coastal Plain into seven sub-regions. The equipment blanks) study area lies entirely within the coastal lowlands sub-region Inorganic constituents described by Ator and others (2005). The geological part including major 20 71 of the current study is focused on both Pleistocene marine ions, nutrients, and and non-marine deposits and Miocene substrates, which field parameters the Pleistocene deposits unconformably overlie. The subtle Organic constituents geomorphology of the area belies a complex stratigraphic including pesticides, 9 4 sequence of laterally variable lithologies. The Delmarva fungicides, and Peninsula is highly sensitive to shifts in sea level because of insecticides its low relief and close proximity to the Atlantic. The complex sedimentology and stratigraphy of the region are evidence of 6 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 constantly alternating processes of erosion and deposition. lenses. Two dinoflagellate samples collected from SDB-1 Quaternary deposits lie unconformably on middle Miocene bracket this unit. These well-preserved samples contain an sediments, a relation that reflects both deep erosion during assemblage that fits in the DNZ DN6 of de Verteuil and the Pleistocene and a potential long (approximately 10–12 Norris (1996), which in turn correlates with Shattuck beds million years) hiatus in deposition. The Miocene sediments 17–18 (Drumcliff and St. Leonard Members of the Choptank are commonly shallow marine shelf facies with interbedded Formation; middle Miocene) of Gernant (1970) (Lucy pro-delta deposits. The Miocene substrate is cut by numerous Edwards, U.S. Geological Survey, oral/written commun., paleochannels of the Proto Chesapeake Bay and its tributar- 2008). ies. The channels are filled with the Pleistocene Kent Island The upper Miocene St. Mary’s and Eastover Formations Formation, an assemblage of cut-and-fill fluvial-to-marine, conformably overlie the Choptank Formation on the western transgressive-regressive sequences locally overlain by a thin side of the Bay (Gernant, 1970), but have not been observed in blanket of cold-climate modified sediments. This thin assem- the study area east of the Bay. The absence of these overlying blage of surficial deposits is an artifact of a former landscape units indicates that they were stripped off the full extent of the that was constructed, eroded, and modified by cold-climate Little Blackwater River watershed during repeated episodes of processes during the late Pleistocene. When climate warmed falling sea level in the Pleistocene. at the beginning of the Holocene, the deeply incised drainages began to fill with fluvial-to-estuarine sediments as sea levels rebounded. Holocene sedimentation continues to fill the lower Pleistocene-Holocene Stratigraphy topography. Climate variability during the Pleistocene was the dominant controlling factor on the stratigraphy and sedi- Miocene Stratigraphy mentology in the Little Blackwater River watershed. The sea level was lowered as much as about 400 ft during glacial A core drilled to basement approximately 2 mi north periods (Waelbroeck and others, 2002). These lower base of the study area placed the basal contact of the Miocene at levels greatly increased the erosive power of streams on 345 ft (Trapp and others, 1984; table 1). Miocene deposits in the Delmarva Peninsula and caused deep incision of major this area include the fossiliferous sand, silt, and clay beds of rivers and their tributaries. Cold-climate processes and eolian the Calvert and Choptank Formations. These units have low sedimentation became extremely active while these cold, dry permeability, and have even been referred to as the “upper climatic conditions prevailed. During subsequent interglacial confining unit” of the Piney Point aquifer (see Klohe and periods, climates warmed and sea level rose. River channels Feehley, 2001). aggraded in response and filled the previously incised topogra- The Calvert Formation is the oldest unit in the phy. The Pleistocene stratigraphy within the Little Blackwater Chesapeake Group (table 1). The top of this unit was pen- River watershed is therefore largely defined by a variably etrated in several of the cores in the study area at elevations thick package of transgressive-regressive sequences represent- ranging from 48–87 ft bsl (below sea level) (table 2). In the ing facies that range from cut-and-fill stream deposits to full study area, the Calvert Formation is generally composed estuarine fill, and have been capped with cold-climate-modi- of dark gray to olive gray very fine to medium sand with a fied sediments. variable abundance of fossils, including Chesapectinnefrens, Complete transgressive sequences from low stand barnacles, and small clams (fig. 3A). In a concurrent study, (fluvial) to high stand (full estuarine) systems tracts can be a sediment sample collected from this unit and analyzed for seen in cores drilled near the center of paleochannels in the dinoflagellates in a core approximately 14 mi to the north of Little Blackwater River watershed (for example, DO Dd 12 the study area (South Dover Bridge; SDB-1) (fig. 1), places core, 17–30 ft; Appendix 4). The fluvial facies are generally this unit in the dinoflagellate cyst zone (DNZ) DN5 of characterized by open-water, very fine to coarse sand with silt, deVerteuil and Norris (1996), and correlates this unit with pebbles, and sparse cobbles (fig. 4A). Bedforms range from Shattuck beds 14–16 (upper Calvert Formation; middle coarse lag deposits and braided channel cross-beds to silty, Miocene) of Gernant (1970) (Lucy Edwards, U.S. Geological laminated fining-upward sequences on tops of flood plains. Survey, oral commun., 2008). Intermediate, or rising stage, facies are predominantly silt and The Choptank Formation unconformably overlies the clay with thin sand lenses throughout, and local burrows and Calvert Formation as an onlap in this area and has a variable organic materials (fig. 4B). The fully estuarine facies is com- thickness (2–53 ft) that is attributed to local scouring by monly characterized by burrowed-to-massive silty clay with Pleistocene channels. A distinctive local facies in the upper local concentrations of organic materials (fig. 4C). Although part of this unit (“red and green bed”) ranges from gray fine these full, orderly fining-upward transgressive sequences are sand to greenish, or reddish, gray silty clay or silty fine sand present near the center of paleochannels in the Kent Island with local concentrations of whitish silty concretions and bur- Formation, small lenses of sand, silt, and clay facies are often rows; woody fragments and unoxidized iron sulfide growths interfingered with one another on channel margins and are also occur (fig. 3B). The lower part of this unit is generally not laterally continuous (for example, Maintenance Yard core, a massive, dark gray clay with small (less than 1 inch) sand 26–35 ft; Appendix 5). Geology 7

Calvert

Choptank Formation Formation Group

Holocene this study sediments This study Chesapeake Not penetrated in Calvert Choptank Formation Formation

2010

Aquia Aleman Group

Marlboro this study Nanjemoy Formation Formation Formation Formation

Piney Point Corner beds Drummonds Chesapeake Not penetrated in written commun., and others, USGS, deposits this study Delaware) Tidal marsh Tidal Walston Silt Walston (Maryland and Omar Formation Beaverdam Sand Not penetrated in Parsonsburg Sand Parsonsburg Chesapeake Group Calvert Formation] Ironshire Formation Yorktown Formation Yorktown Choptank Formation, Pensauken Formation Sinepuxent Formation Kent Island Formation [St. Mary’s Formation, [St. Mary’s Owens and Denny (1979)

Eastover Formation Formation St. Mary’s St. Mary’s Yorktown Yorktown

Calvert Formation Formations

(West side of (West Group undifferentiated Potomac Group, Aquia Formation

Chesapeake Bay) Bacons Castle and

Marlboro Formation Chesapeake Nanjemoy Formation Piney Point Formation Old Church Formation Mixon and others (1989) .] Calvert Formation Arundel Formation Patuxent Formation Patapsco Formation Choptank Formation Yorktown Formation Yorktown St. Mary’s Formation St. Mary’s

Columbia Group Aquia Formation

(Maryland names) Group Raritan Formation

Magothy Formation Group

Brightseat Formation Nanjemoy Formation Monmouth Formation

Piney Point Formation Chesapeake ?Brandywine Formation? Potomac Cushing and others (1973)

(1984) (lower part) Formations, No name listed undifferentiated undifferentiated Potomac Group, Trapp and others Trapp Aquia Formation Chesapeake Group Magothy Formation Severn and Matawan Brightseat Formation Nanjemoy Formation Piney Point Formation Upper Lower Series Eocene Pliocene Miocene Holocene Paleocene Oligocene Cretaceous Cretaceous Pleistocene Geologic units described in previous investigations the Coastal Plain of Delaware, Maryland, and Virginia.

System Tertiary Cretaceous Quaternary Table 1. Table [USGS, U.S. Geological Survey; shaded areas indicate geologic units not included in study 8 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Table 2. Thickness and depth of geologic units in the Little Blackwater River watershed, Cambridge, Maryland (from Trapp and others, 1984).

Thickness Depth System Series Group or Formation (feet) (feet to base) Quaternary Pleistocene/Holocene 48 48 Chesapeake Group Miocene 297 345 (lower part) Piney Point Formation 192 537 Tertiary Eocene Nanjemoy Formation 128 665 Aquia Formation 124 789 Paleocene Brightseat Formation 30 819 Severn and Matawan Formations, 46 865 Upper Cretaceous undifferentiated Cretaceous Magothy Formation 132 997 Potomac Group, Lower Cretaceous 2,302 3,299 undifferentiated Precambrian Basement complex

The lithologic contrast between two cores that were accommodation space (fig. 5). However, the elevation of dis- drilled less than 0.5 mi from one another (DO Cd 58 and tinctive shell beds within the Calvert Formation in these cores DO Cd 66; Appendixes 6 and 7) clearly illustrates the high indicates that if there were ever any structures offsetting these subsurface variability in this area. DO Cd 58 is located about cores, it would be opposite from the one that was described one third of a mile from the Little Blackwater River and has above, as this datum is about 13.5 ft lower in DO Cd 66 than an approximately 60-ft-thick section of Kent Island sediments, in DO Cd 58 (fig. 5). including a full transgressive sequence, a partial falling-stage As stated above, the uppermost Pleistocene sediments sequence, and some minor wind-blown sands on the surface. (the Parsonsburg Sand) were heavily impacted by cold-climate These sediments rest unconformably over about 2 ft of the processes during glacial maxima. Cold, dense winds originat- shallow, open-water facies of the middle Miocene Choptank ing at the terminus of the Laurentide ice sheet (less than 150 Formation below. The Choptank Formation is conformable on mi to the north) froze large parts of the emergent topography the Calvert Formation at about 48 ft bsl. By contrast, DO Cd and transformed the central Delmarva Peninsula into a perigla- 66 is about 0.5 mi from the Little Blackwater River channel cial landscape that has been well documented by French and and only includes about 14 ft of Kent Island fill that includes others (2009). Thermal-contraction cracks filled with eolian a partial rising-stage sequence capped by minor wind-blown material have been observed in gravel pits about 15 mi to the sands. This thin package rests unconformably on about 55 ft north of the study area in Easton, Maryland and about 25 mi of the shallow, open-water facies of the middle Miocene to the southeast near Salisbury, Maryland, for example. These Choptank Formation. The Choptank Formation at DO Cd 66 cracks are found in association with thermokarst structures is conformable on the Calvert Formation at about 61 ft bsl. such as deformed and involuted near-surface soil horizons that There are two possible explanations for the obvious lithologic result from thermal subsidence of underlying frozen ground contrast between these sediment records. The first explanation (French and others, 2009; Smoot and others, 2009). The sur- is that there could be a paleo-valley wall separating these two face materials in which these phenomena occur are generally cores. In this scenario, the Kent Island sediments in DO Cd 58 composed of silty sand containing scattered small pebbles filled a paleochannel that had previously eroded the missing (figs. 6A and B), and have been interpreted as a cover-sand Miocene record in this location, but not the one located at DO unit and considered an analog to the cover sands found in Cd 66. Alternatively, geologic structure may be interpreted Europe. This suite of cold-climate-derived features is indica- from the shallow geology between the two cores; a fault could tive of permafrost and (or) deep seasonal frost (French, 2007). be offsetting these cores so that DO Cd 66 is on the headwall Additionally, large, currently inactive dune fields have long and DO Cd 58 is on the footwall. If this were the case, the been recognized across the central Delmarva and attributed thicker Kent Island package in DO Cd 58 indicates more to processes active during colder, drier climates (Denny and Hydrology 9

(A) (B) Hydrology

The hydrology within the Little Blackwater River watershed is complex and variable, primarily due to lateral and vertical lithologic variability in the subsurface. Repeated climate oscillations during the Pleistocene caused both major stream incision into the existing Miocene land surface and subsequent backfilling of these channels with fluvial-to-estuarine sediments. Sediments that filled these stream channels represent a full range of sandy fluvial deposits to clayey estuarine-marine deposits that are interfingered throughout. The preferential flowpaths for shallow groundwater flow in this stratigraphy are extremely discontinuous. Although these sediments are young and non-indurated, they provide avenues for groundwater flow that are generally thin and lack significant lateral continuity (fig. 7). In many locations, erosion and deposition in the Pleistocene did not have an impact on the deeper strata. These locations have a thicker and more complete section of low permeability red and green beds of the upper Choptank Formation and are likely to create confining conditions in the Piney Point aquifer below. Extensive ditching along agricultural fields can create artificial flowpaths that circumvent the typical topographically driven groundwater-flow system. The tidal nature of the Little Blackwater River affects groundwater fluxes, and because of the wide expanse of open water within the BNWR, southerly winds can increase river stage well into the headwater areas of the basin, creating temporary localized reversals in shallow groundwater-flow directions close to the river. Combined with the potential uptake of water during the growing season, all of these factors create a complex and dynamic hydrologic setting on the Delmarva Peninsula.

Groundwater-Flow System

The USGS installed a transect of three monitoring well nests (multiple wells screened at different depths at the same location) consisting of eight wells, DO Cd 56-63 on the east side of Egypt Road in 2007, between the proposed develop- Figure 3. Miocene formations observed in cores collected ment area and the Little Blackwater River (fig. 2). Another in the study area: (A) Calvert Formation (97.9–99-feet depth monitoring nest consisting of three wells, DO Cd 64-66 was in Kentuck core), and (B) Choptank Formation (approximately installed about 0.4 mi farther south on the west side of Egypt 69–70.25-feet depth in Kentuck core). [Photographs by Road in 2008 (table 3). The USGS installed a pair of moni- B.D. DeJong, USGS.] toring wells (DO Dd 12 and 13) in the Kentuck Swamp near the BNWR in 2007 as part of a more regional assessment of others, 1979; Sirkin and others, 1977). Recent Light Detection the hydrogeology of the basin. The groundwater levels from and Ranging (LIDAR)-based investigations carried out in both September 2007 through September 2009 in wells DO Dd the central Delmarva Peninsula and west of the Chesapeake 12-13, and from May 2008 through September 2009 in wells Bay confirm these observations and highlight the regional DO Cd 64-66 have consistently shown downward vertical impact of these climates during this period (Markewich and gradients, indicating the potential for movement of shallow others, 2009; Newell and Clark, 2008). groundwater towards the deeper flow system (figs. 8A and B). Sea level has continued to rise since the Wisconsinan gla- Monitoring well DO Cd 1, located just west of the basin ciation. As sea levels rose, the eroded Wisconsinan landscape (fig. 2) and screened at 320 ft bls (below land surface) in the filled with organic-rich silty peat, which is thickest in major Piney Point aquifer, has water levels that are typically river channels but also present in surficial wetlands. 45–55 ft bsl (fig. 8C). These lower water levels, caused by 10 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

(A) (B) (C)

Figure 4. Examples of facies seen in Pleistocene sequences from the DO Dd 12 core: (A) fluvial (approximately 4–5.25-feet depth), (B) rising-stage (approximately 20–21.25-feet depth), and (C) estuarine-marine (41.75–43-feet depth). [Photographs by B.D. DeJong, USGS.] Hydrology 11

Depth DO Cd 58 DO Cd 66 [feet below land Lithology Lithology surface (BLS)] 0

20 Pleistocene Fill

40 “Red/ Green Beds” of the upper Miocene Choptank Formation 50

70 Distinctive shell bed layer in the Calvert Formation

100

110

120

130 .47 mi

Figure 5. Stratigraphic contrast between DO Cd 58 (left) and DO Cd 66 (right). 12 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

(A) (B)

Figure 6. The Parsonsburg Sand as expressed in (A) 2.25–4-feet depth in the DO Dd 12 core, and (B) 8.5–9.5-feet depth in the Maintenence Yard core. [Photographs by B.D. DeJong, USGS.] Hydrology 13

Figure 7. Generalized north-south hydrogeologic cross section through the Little Blackwater River watershed, Dorchester County, Maryland.

regionally extensive water withdrawals from the Piney Point The response of the deeper wells to changes in tides may aquifer, indicate a large downward gradient between the shal- be caused by pressure loading as the high tides press down low and deeper groundwater systems. on the system, forcing water levels to rise in confined-aquifer The water-table wells, screened in the Parsonsburg Sand, wells. The same type of responses are typical in coastal areas generally have water levels slightly above sea level, with sea- and are observed in monitoring wells along tidal areas under sonal variations of several feet (fig. 9A). In winter and spring both non-pumping and pumping conditions, such as in the months, water-table well observations show groundwater Ocean City and Manokin aquifers (about 250–400 ft bls) near gradients driven by the subtle topography, indicating potential Ocean City, Maryland (Phelan, 1987, fig. 26). flow towards the Little Blackwater River (fig. 9B). In summer Geophysical (gamma) logs were collected in the deeper and fall months, water-table well observations show ground- wells, and a 2-dimensional electrical resistivity survey was water levels that drop below the stage of the Little Blackwater performed parallel to the well transect between Egypt Road River. These lower groundwater levels create gradient rever- and the Little Blackwater River. These logs (Appendixes 6 sals with the potential for the Little Blackwater River to lose and 7) and results from the survey (Appendix 8), combined water into the water-table system (fig. 9C). This in turn creates with geologic core descriptions, are the basis for the cross- the potential for infiltration of brackish river water into the sectional conceptual flow model of the water-table system shallow groundwater system close to the river, as evidenced for the Little Blackwater River (figs. 9B and C). In Appendix by elevated chloride concentrations in monitoring wells DO Cd 61 and DO Cd 68 (see Appendix 1). 8, red colors indicate higher electrical resistivity, typically The deeper wells, screened in the Miocene sediments (at sands saturated with fresh water. Blue colors indicate values depths above the Piney Point aquifer, which is the primary of lower electrical resistivity, typically of silts and clays. This groundwater supply in the area), generally have water levels interpretation is consistent with the sediment cores collected that are several feet below sea level. Continuous water-level from the drilling of the wells along this cross section, however, records from the deeper wells show a muted but instantaneous the sands are poorly sorted and contain some silts and clays. pressure response to tidal fluctuations observed at the The interpretation using gamma logs, electrical resistivity Cambridge gage (fig. 10). Well DO Cd 58 is approximately surveys, and lithologic logs confirms the presence of thin 2,500 ft from the Little Blackwater River and screened at sandy deposits (10–20 ft) of the Parsonsburg Sand, which has 89–94 ft bls, whereas well DO Cd 63 is 500 ft from the Little a relatively higher permeability than the underlying silts and Blackwater River and screened at 47–52 ft bls. clays in this part of the watershed. 14 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

bottom 13.00 21.00 94.00 13.00 19.00 13.00 19.00 52.00 13.00 75.00 15.00 15.00 12.00 interval Depth to (feet bls) of screen 129.00 100.00 3.00 3.00 3.00 3.00 5.00 5.00 2.00 16.00 89.00 14.00 14.00 47.00 70.00 95.00 interval (feet bls) of screen 124.00 Depth to top

11.59 13.45 21.98 94 13.11 19.19 13.20 19.37 53.2 13.0 75 15 15 Depth of (feet bls) 129.5 100 borehole

9.50 9.85 9.43 7.28 7.11 3.68 3.81 3.12 2 5 5.26 5.31 surface Altitude 10.18 10.00 10.34 NAVD88) of ground (feet above wire-wound wire-wound wire-wound wire-wound wire-wound wire-wound wire-wound wire-wound wire-wound wire-wound wire-wound wire-wound wire-wound wire-wound wire-wound Type of screen Type

of Type Type PVC PVC PVC PVC PVC PVC PVC PVC PVC PVC PVC PVC PVC PVC PVC casing

2 2 2 2 2 2 2 2 2 2 2 4 4 2 2 Casing (inches) diameter NAD83) degrees, (decimal Longitude -76.096111 -76.096111 -76.099167 -76.099167 -76.099167 -76.093056 -76.093056 -76.093056 -76.103333 -76.103333 -76.103333 -76.092500 -76.095278 -76.105556 -76.105556 NAD83) Latitude degrees, (decimal 38.522778 38.522778 38.522778 38.521667 38.521667 38.520000 38.520000 38.520000 38.516667 38.516667 38.516667 38.527778 38.514167 38.455000 38.455000

Local DW-1 DW-2 ERN-1-A ERN-1-B ERN-1-C ERN-2-A ERN-2-B ERN-3-A ERN-3-B ERN-3-C ERN-4-A ERN-4-C ERN-4-D Kentuck-1 Kentuck-2 well name

USGS well number 383118076054601 383118076054602 383112076053501 383112076053502 383112076053503 383100076061101 383100076061102 383100076061103 383122076055701 383122076055702 383122076055703 383139076053301 383051076054201 382718076062001 382718076062002

Locations and descriptions of wells installed and monitored during the Little Blackwater River study, Dorchester County, Maryland. Dorchester County, Locations and descriptions of wells installed monitored during the Little Blackwater River study,

USGS DO Cd 56 DO Cd 57 DO Cd 58 DO Cd 59 DO Cd 60 DO Cd 61 DO Cd 62 DO Cd 63 DO Cd 64 DO Cd 65 DO Cd 66 DO Cd 67 DO Cd 68 DO Dd 12 DO Dd 13 well name Table 3. Table Datum of 1988; PVC, polyvinylchloride; bls, below land surface] Vertical American North American Datum of 1983; NAVD88, [USGS, U.S. Geological Survey; NAD83, North Hydrology 15

Figure 8. Groundwater levels in (A) wells DO Cd 64 (screen interval 3–13 feet below land surface [ft bls]), DO Cd 65 (screen interval 70–75 ft bls), DO Cd 66 (screen interval 124–129 ft bls), May 2008–August 2009, (B) wells DO Dd 12 (screen interval 95–100 ft bls) and DO Dd 13 (screen interval 2–12 ft bls), September 2007–September 2009, and (C) well DO Cd 1, 1960–2010, Dorchester County, Maryland.

Surface-Water System portion of the Choptank River on the Delmarva Peninsula in 685 samples between 1980 and 2009 ranged from 46 to 307 Over the period of record, specific conductance varies µS/cm, with a median of 133 µS/cm (U.S. Geological Survey, seasonally at the Cambridge and Key Wallace Drive gages, 2010). with maximum values in late October, and minimum values Discharge calculated at Key Wallace Drive varies in May (figs. 11A and B). Annual peaks in specific conduc- seasonally, with net negative discharge (more water flowing tance are observed approximately 2 months after annual peaks upstream than downstream) during the summer and fall in surface-water temperature. These specific conductance seasons, and net positive discharge from the Little Blackwater patterns reflect the same seasonal trends typically seen in the River in the winter and spring (fig. 12). In water years 2008 Chesapeake Bay as the saltwater front moves up the Bay in and 2009 (October 1, 2007 through September 30, 2009), the summer and out of the Bay in the spring in response to annual net discharge was negative, meaning more water seasonal changes in freshwater inflow to the Bay. Specific conductance at the Key Wallace Drive and flowed into the watershed from the Blackwater River than Cambridge gages ranged from 200 to 24,000 and 120 to flowed out to the Blackwater River. The annual net discharge 13,000 µS/cm (microsiemens per centimeter), respectively in water year 2007 was positive, however. Given the high (fig. 11A). For comparison, the specific conductance of percentage of agricultural land use and significant amounts of seawater is typically about 50,000 µS/cm (Hem, 1985), and riparian wetland vegetation, evapotranspiration (ET) is likely a the range of specific conductance values in the freshwater major cause of groundwater flux out of the watershed. 16 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Figure 9. (A) Groundwater levels in water-table wells, and cross sections of (B) winter and (C) summer groundwater-flow directions, October 2007–July 2009, Little Blackwater River watershed, Dorchester County, Maryland. Water Quality 17

Figure 10. Groundwater levels in wells DO Cd 58 and DO Cd 63, and surface-water elevations at the gage on the Little Figure 12. Discharge to and from the Little Blackwater River Blackwater River at Cambridge, Maryland, November 2007– at Seward, Maryland on Key Wallace Drive, Dorchester County, May 2008. Maryland, November 2006–September 2009.

Water Quality

Water-quality samples were collected during 2007–08 from 13 monitoring wells and during 2006–09 from 9 surface- water sites to characterize pre-development conditions and seasonal variability. Continuous water-quality monitors were installed at both gaging stations (Cambridge and Key Wallace Drive) to measure temperature and specific conductance and observe the seasonality of brackish-water conditions in the Little Blackwater River between 2006 and 2009.

Data Quality Assurance

Quality-assurance samples were collected during this study. Equipment blanks were collected to determine the potential for contamination of samples during the sampling, shipping, and laboratory handling procedures. Duplicate samples were collected to determine reproducibility, and ion balances were calculated to determine whether all appropriate major ions had been analyzed, and whether the analytical results were acceptable, and within generally accepted guidelines.

Blanks Three field equipment blanks were collected during groundwater sampling, and one field equipment blank was collected during surface-water sampling to determine if there was Figure 11. Comparison of (A) specific conductance at the a potential for contamination from the sampling equipment Cambridge gage and Key Wallace Drive gage, Maryland, and and filters, or if there was carryover contamination from previ- (B) temperature and specific conductance at the Key Wallace ous samples (Appendix 3). One of the three blanks collected at Drive gage, Maryland, November 2006–November 2009. the groundwater sites was analyzed for inorganic constituents 18 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 only, and the other two blanks were analyzed for both organic constituents ranged from 0 to 16.4 percent, with an average of and inorganic constituents. The surface-water blank was ana- 5.1 percent, indicating good reproducibility even after 15 lyzed for inorganic constituents only. minutes of pumping. These results show good reproducibility The inorganic blank groundwater samples had detectable at the non-detect levels, but cannot address the reproducibility concentrations of dissolved calcium that ranged from 0.02 of the detected concentrations as found in other samples. to 0.1 mg/L (milligrams per liter) (Appendix 3) whereas the environmental calcium sample concentrations ranged from 1.1 to 95.5 mg/L. This indicates that up to about 10 percent Ion Balances of only the lowest calcium concentration may have been The accuracy of major dissolved-constituent values in affected by sampling, handling, or laboratory procedures. Four a reasonably complete chemical analysis of a water sample other inorganic compounds were detected in concentrations can be checked by calculating the cation-anion balance (Hem, near detection levels in at least one of the four blank samples 1985). If the analytical work has been performed accurately, for potassium, alkalinity, silica, and ammonia plus organic and if all major ions were analyzed, the difference between nitrogen. The potassium detection in the blank was less than the two sums will generally not exceed approximately plus or 0.5 percent of the lowest environmental concentration. The minus 5 percent. The cation-anion balances, given in per- acid-neutralizing capacity (ANC) in two blanks was detected cent differences between total cations and total anions when at estimated concentrations (4 mg/L) below the minimum converted to milliequivalents per liter (meq/L), are presented reporting level of 5 mg/L, but was about half of the concentra- for each groundwater and surface-water sample (inorganic tion of the lowest environmental sample at 9 mg/L, indicating constituents) from the Little Blackwater River watershed in that very low ANC concentrations may be reported at almost Appendixes 1 and 2, respectively. Ion balances for 69 surface- twice the actual value. water samples ranged from -15.4 to 10.9 percent, and averaged Dissolved organic carbon (DOC) was detected in one 1.7 percent. Nine surface-water samples had ion balances that surface-water blank at a concentration of 0.6 mg/L, whereas exceeded 5 percent. Ion balances for 20 groundwater samples environmental concentrations in surface water ranged from ranged from -6.9 to 3.8 percent, with an average of -2 percent. 7.4 to 47 mg/L, indicating the potential to add greater uncer- Five of the 20 samples had ion balances between 5 and 6.9 tainty in samples with very low DOC concentrations. There percent. were no detections of any organic compounds from the two groundwater equipment blanks. The lack of detections indi- cated that there was no contamination, but the unexpected Groundwater Quality analytical results of sulfometuron-methyl in a groundwater sample from DO Dd 12 may suggest otherwise. Groundwater-quality samples were collected from nine monitoring wells in October 2007. Several wells were installed in the winter and spring of 2008, and nine wells, Duplicates including the newest, were sampled during June 2008. The sets of parameters analyzed varied between the groundwater Two duplicate groundwater sample pairs were collected sampling rounds, but both included major ions and nutrients. to determine reproducibility of the inorganic analyses The samples collected during June 2008 also were analyzed (Appendix 1). Both duplicate pairs were sampled within 15 for concentrations of pesticides, pesticide degradates, and minutes after the original sample. Most constituents were other organic compounds. Concentrations of inorganic con- consistent between the duplicate samples, with the exception stituents in the groundwater samples are shown in of well DO Cd 63, when sulfate concentrations nearly doubled Appendix 1. Concentrations of organic compounds detected (from 4.7 to 7.4 mg/L) between the first and second samples. in groundwater and surface-water samples are shown in Relative percent differences (RPDs) were calculated between table 4. A list of organic compounds that were analyzed for, duplicate pairs for each inorganic parameter that had measur- but not detected, is shown in table 5 along with detection able concentrations in both sample pairs to describe the repro- levels. ducibility of the values. The formula for calculating RPD is: Inorganic Constituents C − C 1 2 100 (C − C ) * Results from all major ion analyses from both groundwa- 1 2 ter and surface-water samples are shown in trilinear diagrams 2 (1) (fig. 13). Several patterns are apparent. Samples are grouped into four categories: shallow groundwater, deep groundwa- where C1 is the concentration of the parameter in the original ter, surface water in the upper basin and surface water in the sample and C2 is the concentration of the same parameter lower basin. Deep groundwater samples (black squares) have from the duplicate sample. With the exception of the one higher values of bicarbonate, whereas shallow groundwater sulfate concentration mentioned above, RPDs from inorganic samples (red squares) have little to no bicarbonate. Boxplots Water Quality 19 0.07 0.08 2,4-D <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 (µg/L)

0.07 0.08 basis, <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 2,4-D plus 2,4- (µg/L as 2,4-D) D methyl ester, D methyl ester, sum on a molar

------759 759 759 759 766 sure, pres Baro- metric (mm Hg) - --, data not available; dark shaded couplets ------0 0 9.5 11.5 13.1 13.2 51.5 15 90 pling Sam (feet) depth

) 2 ------8.29 1.46 4.19 (mi area 15.3 Drainage ------0.5 period 50 prior to Pumping sampling (minutes)

------rate Flow T-MDL) but below the laboratory reporting level (LRL) with higher uncertainty] T-MDL) 0.29 0.73 0.572 0.83 4.68 0.88 1.09 (gal/min)

------point (feet) 6.44 4.05 5.52 15.04 measuring Water level, Water depth below Groundwater sites Surface-water sites

5 2.9 6 9.5 7.28 3.68 3.12 3.12 5 5.26 5.31 -1.25 (feet) 10.18 10.34 of land surface Altitude

, square miles; mm, millimeters; Hg, mercury; µg/L, micrograms per liter; %, percent; ------2 well 13.5 13.1 13.2 53.2 53.2 13 15 99.7 12 129.5 surface) Depth of (feet be low land Time 1230 0740 1245 1130 0815 1520 1100 1030 1045 1555 1500 1050 1345 1610 Date 6/10/2008 6/10/2008 6/10/2008 6/10/2008 06/11/2008 6/10/2008 6/10/2008 6/10/2008 6/10/2008 06/11/2008 06/11/2008 06/11/2008 06/09/2008 06/09/2008

USGS 01490112 01490113 01490116 01490120 station number 383122076055701 383118076054601 383112076053501 383112076053503 383112076053503 383100076061101 383100076061103 383051076054201 382718076062001 382718076062002

hester County, Maryland, Concentrations of organic compounds detected in surface-water and groundwater samples, Little Blackwater River watershed, Dorc hester County,

name Station Bridge Cambridge, Md. Cambridge, Md. Christ’s Rock Christ’s Maple Dam near Tributary River near DO Cd 56 DO Cd 59 DO Cd 61 DO Cd 63 DO Cd 63 DO Cd 64 DO Cd 66 DO Cd 68 DO Dd 12 DO Dd 13 Table 4. Table June 2008.—Continued [USGS, U.S. Geological Survey; ft., feet; gal/min, gallons per minute; mi indicate duplicate samples; Md., Maryland; <, less than; E, quantified above the long-term method detection limit (L 20 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 - µg/L Desulfi <.012 <.012 <.012 <.012 <.012 <.012 <.012 <.012 <.012 <.012 E.002 E.007 E.002 E.002 nylfipronil, nylfipronil,

- (µg/L) on-ethyl <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 E.02 E.02 Chlorimur -

ran (µg/L) <.02 <.02 <.02 <.02 <.02 <.02 <.0210 <.02 <.02 <.02 <.02 <.02 <.02 <.02 Carbofu , 2 --, data not available; dark shaded couplets (µg/L) <.06 <.06 <.06 <.06 <.06 <.06 <.06 <.06 <.06 <.06 <.06 E.01 E.01 E.01 Carbaryl , 1 (µg/L) <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 E.01 Carbaryl 0.07 0.13 <.06 <.06 <.06 <.06 <.06 <.06 <.06 <.06 <.06 <.06 <.06 E.05 (µg/L) Caffeine T-MDL) but below the laboratory reporting level (LRL) with higher uncertainty] T-MDL) (µg/L) Atrazine 0.732 0.044 0.917 1.100 0.009 0.019 <.007 <.007 <.007 <.007 <.007 <.007 <.007 <.007 - Ala chlor (µg/L) 0.016 0.014 <.006 <.006 <.006 <.006 <.006 <.006 <.006 <.006 <.006 <.006 <.006 <.006 Groundwater sites Surface-water sites chlor (µg/L) Aceto- 0.028 <.0164 <.006 <.006 <.006 <.006 <.006 <.006 <.006 <.006 <.006 <.006 <.006 <.006 - - -triazine s (µg/L) , square miles; mm, millimeters; Hg, mercury; µg/L, micrograms per liter; %, percent; 0.88 0.84 0.76 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 2 amino- pylamino-6-ethyl 2-Hydroxy-4-isopro - (µg/L) <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 E.030 E.050 E.055 -triazine s amino-4-amino- 2-Chloro-6-ethyl -triazine, s <.014 <.014 <.014 <.014 <.014 <.014 <.014 <.014 <.014 E.167 E.023 E.210 E.239 E.009 (µg/L CIAT) 2-Chloro-4- amino- isopropylamino-6-

hester County, Maryland, Concentrations of organic compounds detected in surface-water and groundwater samples, Little Blackwater River watershed, Dorc hester County,

(µg/L) <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 <.08 E.0571 Triclopyr

(µg/L) 0.10 <.06 <.06 <.06 <.06 <.06 <.06 <.06 <.06 <.06 <.06 <.06 <.06 methyl E.08 Sulfometuron- (µg/L) 0.239 0.015 0.309 0.391 <.006 <.006 <.006 <.006 <.006 <.006 <.006 <.006 <.006 E.005 Simazine Simazine --, data not available; dark shaded couplets 0.04 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 (µg/L) Siduron (µg/L) 0.034 0.064 <.008 <.008 <.008 <.008 <.008 <.008 <.008 <.008 <.008 <.008 <.008 Prometon <.008 ------<.12 <.12 <.12 <.12 <.12 (µg/L) Picloram

T-MDL) but below the laboratory reporting level (LRL) with higher uncertainty] T-MDL) (µg/L) 1.240 0.058 1.210 1.260 0.030 0.020 0.026 <.010 <.010 <.010 <.010 <.010 <.010 <.010 Metolachlor Groundwater sites (µg/L) Surface-water sites <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 E.005 E.027 E.006 E.006 Fipronil (µg/L) sulfone Fipronil <.024 <.024 <.024 <.024 <.024 <.024 <.024 <.024 <.024 <.024 E.017 E.019 E.015 E.011 , square miles; mm, millimeters; Hg, mercury; µg/L, micrograms per liter; %, percent; 2

(µg/L) sulfide Fipronil <.013 <.013 <.013 <.013 <.013 <.013 <.013 <.013 <.013 <.013 E.010 E.008 E.008 E.007 (µg/L) amide <.029 <.029 <.029 <.029 <.029 <.029 <.029 <.029 <.029 <.029 fipronil E.002 E.005 E.002 E.002 Desulfinyl

(µg/L) Diuron <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 E.0139 E.0255 E.0217

(µg/L) <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.0863 <.0863 <.04 <.04 <.04 <.04 <.04 Disulfoton

hester County, Maryland, Concentrations of organic compounds detected in surface-water and groundwater samples, Little Blackwater River watershed, Dorc hester County,

name Station Carbaryl concentration from high-performance liquid chromatography (HPLC). Carbaryl concentration from gas chromatography-mass spectrometry (GCMS). Note: See table 5 for list of compounds that were not detected. Bridge Cambridge, Md. Cambridge, Md. 1 2 Christ’s Rock Christ’s Maple Dam near Tributary River near DO Cd 56 DO Cd 59 DO Cd 61 DO Cd 63 DO Cd 63 DO Cd 64 DO Cd 66 DO Cd 68 DO Dd 12 DO Dd 13 Table 4. Table June 2008.—Continued [USGS, U.S. Geological Survey; ft., feet; gal/min, gallons per minute; mi indicate duplicate samples; Md., Maryland; <, less than; E, quantified above the long-term method detection limit (L 22 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Table 5. Dissolved organic compounds analyzed for, but not detected, in surface-water and groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland.

[<, less than; all concentrations in micrograms per liter, filtered through glass-fiber filter with 0.7-micron opening; see Appendixes 1 and 2 for detected concentrations]

Mini- Mini- Mini- Mini- mum mum mum mum Compound Compound Compound Compound report- reporting report- report- ing limit limit ing limit ing limit 2,4-D methyl ester <.04 cis-Permethrin <.01 Lindane <.006 Parathion <.010 2,4-DB <.02 Cyanazine <.02 Linuron1 <.04 Pebulate <.004 2,6-Diethylaniline <.002 Cycloate <.02 Linuron2 <.06 Pendimethalin <.012 3-Hydroxy carbofuran <.04 Dacthal mono- <.02 Malathion <.016 Phorate <.04 acid Acifluorfen <.04 DCPA <.003 MCPA <.06 Propyzamide <.004 Aldicarb sulfone <.08 Diazinon <.005 MCPB <.06 Propachlor <.006 Aldicarb sulfoxide <.06 Dicamba <.04 Metalaxyl <.02 Propanil <.006 Aldicarb <.12 Dichlorprop <.02 Methiocarb <.04 Propargite <.04 alpha-HCH <.002 Dieldrin <.009 Methomyl <.12 Propham <.04 Azinphos-methyl <.12 Dinoseb <.04 Methyl parathion <.008 Propiconazole <.04 Bendiocarb <.04 Diphenamid <.04 Metribuzin <.012 Propoxur <.04 Benfluralin <.004 EPTC <.002 Metsulfuron-methyl <.14 Tebuthiuron <.016 Benomyl <.04 Ethalfluralin <.009 Molinate <.002 Terbacil2 <.018 Bensulfuron-methyl <.06 Ethoprop <.012 N-(4-Chlorophenyl)-N’-methyl- <.12 Terbacil1 <.04 urea Bentazon <.04 Fenuron <.04 Napropamide <.018 Terbufos <.018 Bromacil <.02 Flumetsulam <.06 Neburon <.02 Thiobencarb <.010 Bromoxynil <.12 Fluometuron <.04 Nicosulfuron <.1 Triallate <.006 Butylate <.002 Fonofos <.01 Norflurazon <.02 Trifluralin <.006 Chloramben methyl <.1 Imazaquin <.04 Oryzalin <.04 ester Chlorpyralid <.06 Imazethapyr <.04 Oxamyl <.12 Chlorpyrifos <.005 Imidacloprid <.06 p,p’-DDE <.003 1 Concentration from high-performance liquid chromatography (HPLC). 2 Concentration from gas chromatography-mass spectrometry (GCMS). Water Quality 23

Figure 13. Trilinear diagrams showing chemical characteristics of inorganic constituents in surface water and groundwater, Little Blackwater River watershed, Dorchester County, Maryland.

of samples grouped into the same categories in figure 13 are weathered organic matter and higher quartz content in sedi- shown in figure 14. Silica shows the highest mean and range ments. These characteristics, along with the low observed dis- in both groundwater groups, as would be expected. Manganese solved oxygen and reducing conditions contribute to the low and iron are highest in shallow groundwater. Calcium has the values of nitrate in the shallow groundwater. highest mean in deep groundwater, which is consistent with Chloride concentrations in the shallow groundwater the shell material found in the deep cores. Deep wells (greater increase with proximity to the Little Blackwater River. The than 15 ft bls) have higher nitrogen concentrations (2.32–6.89 wells closest to the river, DO Cd 61 and DO Cd 68, located mg/L) than shallow (less than 15 ft bls) wells (0.26–0.95 500 and 250 ft from the Little Blackwater River, respectively, mg/L). The exception is well DO Cd 66, screened from have chloride concentrations over 381 mg/L and 219 mg/L. 124–129 ft bls with a nitrogen concentration of 0.66 mg/L. For reference, the U.S. Environmental Protection Agency The other inorganic constituents in figure 14 are relatively low Secondary Maximum Contaminant Level (SMCL) for chloride compared to the lower basin surface-water samples. based on taste is 250 mg/L (U.S. Environmental Protection The pH in shallow groundwater is relatively low—around Agency, 2009). In observed monthly water-level measure- 4—and increases with depth to over 7 at 130 ft deep (fig. 15). ments, there are seasonal gradient reversals between the water Several samples collected from water-table wells screened levels in wells DO Cd 61 and DO Cd 68 and the stage of the in more silty sediments have pH values around 5 (fig. 15). Little Blackwater River. These higher chloride concentrations As noted in Ator and others (2005), shallow groundwater are likely caused by infiltration of brackish river water into the quality in Coastal Plain lowlands can be acidic in areas with shallow groundwater-flow system close to the river. 24 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Figure 14. Boxplots showing inorganic constituents in surface water and groundwater, Little Blackwater River watershed, Dorchester County, Maryland. Water Quality 25

Inorganic Constituents Major ions were sampled in surface water at several sites within the watershed (fig. 2). Results of surface-water and groundwater inorganic analyses are plotted on a trilinear diagram (fig. 13). The samples are separated into four groups: shallow groundwater, deep groundwater, surface water from the upper basin, and surface water from the lower basin. Surface-water samples from the lower half of the Little Blackwater River watershed have consistently higher chloride concentrations than the upper part of the watershed, with a maximum concentration of 5,870 mg/L at the southernmost site, 01490140. The lower (southern) part of the watershed is under a strong tidal influence, not only in stage but also in terms of brackish-water mixing. Daily and seasonal variations in specific conductance at the mouth of the river (site 1490140) and near the middle of the watershed (site 1490120) are shown in figure 11A. Both gage sites have strong seasonal Figure 15. pH compared to well depth for all groundwater variations in specific conductance, but the magnitude of the wells sampled, Little Blackwater River watershed, seasonal variation decreases further upstream in the water- Dorchester County, Maryland. shed. Boxplots of selected inorganic constituents for surface- water sampling sites are shown in figure 16. Sites 1490140, 1490130, and 1490120, in the lower basin, show the greatest range of values for constituents associated with seawater. Ranges of silica, iron, and manganese are greatest at the surface-water sites in the upper basin where base flow from shallow groundwater contributes more significantly to overall Organic Constituents streamflow. Surface-water samples are further grouped into summer Groundwater samples were collected and analyzed for (June through November) and winter (December through pesticides from nine wells on June 9–11, 2008 (table 4). The May) samples in the upper and lower basin (fig. 17). During commonly used herbicides atrazine, metolachlor, simazine, the winter months, when the water table is higher, the Little sulfometuron-methyl, and the atrazine degradate 2-chloro-4- Blackwater River is discharging freshwater. As such, upper isopropylamino-6-amino-s-triazine (CIAT) were detected at and lower basin inorganic constituents do not vary signifi- low concentrations (0.03 mg/L or less) in up to three of nine cantly. However, in summer months, the upper basin has shallow wells that ranged in depth from 12 to 15 ft (table 4). higher mean values for iron, manganese, and silica, likely One deeper well (DO Dd 12, 99.7 ft) had a single detection caused by a greater portion of total streamflow coming from (0.10 mg/L) of the herbicide sulfometuron-methyl. The groundwater. detection of sulfometuron-methyl in well DO Dd 12 may be There is a significant change in water chemistry in the due to contamination during sampling or laboratory analysis, lower basin from winter to summer. Constituents typically and should be confirmed with subsequent sampling because found in seawater are observed in much greater concentra- sulfometuron-methyl is used far less than the other herbicides tions in the lower basin during summer (fig. 17). The source of in Dorchester County (Maryland Department of Agriculture, seawater in the Little Blackwater River is from Fishing Bay, 2002), and no other herbicides or insecticides were detected in which flows through the BNWR. that well. The detection was probably not caused by drilling because the shallow well at that location showed no concentrations of that compound. Organic Constituents Surface-water samples were collected and analyzed for Surface-Water Quality pesticides only once at four surface-water sites on June 10, 2008 (table 4). This single sampling effort cannot address Surface-water-quality samples were collected during either variability or seasonality of the results, and is only rep- storm events and also on a seasonal basis. Storm event resentative of conditions at that time. The herbicides atrazine, sampling occurred on October 6, 2006 and again on April 16, metolachlor, and simazine, and the insecticide fipronil, were 2007. Quarterly samples were taken from March 2006 through detected at each of the four surface-water sites. Atrazine, October 2007. A final sampling effort was conducted in June metolachlor, and simazine were 3 of 16 pesticides that were 2008. commonly found in surface waters of the Mid-Atlantic region 26 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Figure 16. Boxplots showing inorganic constituents at surface-water sites, Little Blackwater River watershed, Dorchester County, Maryland. Water Quality 27

Figure 17. Boxplots showing summer (June through November) and winter (December through May) inorganic constituents in the upper and lower basin, Little Blackwater River watershed, Dorchester County, Maryland. 28 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 by Ferrari and others (1997), and were commonly used in stratigraphy have a thicker and more complete section of the Dorchester County in 2000, the latest date for which county low-permeability beds of the upper Choptank Formation. pesticide usage data are available (Maryland Department of Much of the complexity within the shallow groundwater Agriculture, 2002). system is due to the heterogeneous nature of the surficial sedi- Atrazine is a commonly detected herbicide in surface ments. Extensive ditching along agricultural fields can create water and was detected at concentrations up to 1.1 mg/L. artificial flowpaths that circumvent the typical topographically In addition, three compounds that are atrazine degradates driven groundwater-flow system. The tidal nature of the Little (2-Chloro-4-isopropylamino-6-amino-s-triazine [CIAT], Blackwater River also affects groundwater fluxes, and because 2-Chloro-6-ethylamino-4-amino-s-triazine, and 2-Hydroxy-4- of the wide expanse of open water within the Blackwater isopropylamino-6-ethylamino-s-triazine) also were detected at National Wildlife Refuge, southerly winds can increase river three of the four sites. For comparative purposes, the USEPA stage well into the headwater areas of the basin, creating Maximum Contaminant Level (MCL) for atrazine in drink- temporary, localized reversals in shallow groundwater-flow ing water is 3 mg/L (U.S. Environmental Protection Agency, directions close to the river. 2009). Commonly used pesticides in Dorchester County in Water-table wells in the study area generally have water 2000 that were also detected in surface water during this study levels slightly above sea level, with seasonal variations of were alachlor, atrazine, metolachlor, and simazine (Maryland several feet. Horizontal hydraulic gradients are persistent Department of Agriculture, 2002). Metalachlor and simazine throughout all seasons and indicate groundwater flow towards are pre-emergent herbicides and are commonly used in much the Little Blackwater River. Lower seasonal groundwater of the Delmarva Peninsula (Ator and others, 2004; Maryland levels in shallow wells close to the river during late summer Department of Agriculture, 1999, 2002). Fipronil is an insec- and fall indicate a localized gradient reversal from the Little ticide commonly used on termites and fleas, and was found at Blackwater River. estimated concentrations below the minimum reporting level. Discharge calculated at the lower gage varies seasonally, Fipronil was not reported to have been used in the County in with net negative discharge (more water flowing upstream than 2000, but was reported to have been used in adjacent counties downstream) from June through November and net positive (Maryland Department of Agriculture, 2002). Usage patterns discharge from the Little Blackwater River from December may have changed between 2000, when the latest county-wide through May. Given the high percentage of agricultural land data on pesticide usage are available, and 2008, when samples use and significant amounts of riparian wetland vegetation, were collected in the Little Blackwater River watershed. evapotranspiration is likely the major flux of freshwater out Ator and others (2004) analyzed the seasonal variability of the watershed during the summer. In the summer months, of atrazine and metalachlor in two streams on the Delmarva brackish water encroaches up the Little Blackwater River from Peninsula, and found that seasonal variability in pesticide the Blackwater National Wildlife Refuge and Fishing Bay. concentrations in surface water is related to application pat- Water samples were collected during 2007–08 from 13 terns and that concentrations were generally highest in the monitoring wells and during 2006–09 from 9 surface-water growing season but were detectable throughout the year. sites to characterize pre-development conditions and seasonal Concentrations of pesticides found in the Little Blackwater variability of inorganic constituents and nutrients. Pesticide River during this study were similar to concentrations found samples were collected from nine wells and four surface- by Ator and others (2004) in the Pocomoke River between water sampling sites in June 2008. The herbicides atrazine, Wicomico and Worcester Counties, and in Chesterville Branch metolachlor, and simazine, and the insecticide fipronil, were in Kent County, Maryland. detected at each of the four surface-water sampling sites. With the exception of sulfometuron-methyl, concentrations of pesticides found in the groundwater were typically one to two Summary and Conclusions orders of magnitude lower than pesticide concentrations found in the Little Blackwater River during the same time period. The goals of this study were to (1) document geochemi- Concentrations and the type of compounds found in the Little cal conditions in the shallow groundwater system and the Blackwater River were similar to concentrations and com- Little Blackwater River prior to potential land-use changes, pound types found in other investigations in the Pocomoke and (2) characterize the hydrology of the watershed, looking River between Wicomico and Worcester Counties, and in at both the tidal and seasonal variability of surface water and Chesterville Branch in Kent County, Maryland. Nitrogen con- groundwater. The lithologic variability in the subsurface of the centrations were higher in deep groundwater than in shallow Little Blackwater watershed suggests an inherently complex groundwater. Chloride concentrations in the water-table wells hydrogeologic regime. Preferential pathways for groundwater increase with proximity to the Little Blackwater River. flow in the shallow sediments are generally quite thin and It is unclear what implications land-use change from lack significant lateral continuity. Areas where Pleistocene agricultural to residential would have on the water quality in erosion and deposition did not have an impact on the deeper the Little Blackwater River watershed. Changes in land use Selected References 29 will likely affect the applications of pesticides, road salts, and Cole, W.D., 2008, The Little Blackwater River watershed nutrients within the watershed. These potential impacts are management plan: From city headwaters to National subjects for future studies. Wildlife Refuge: Cambridge, Maryland, Dorchester Soil Seasonal hydraulic-gradient reversals between the Little Conservation District, 58 p., accessed October 27, 2009, at Blackwater River and the water table, coincident with a http://www.ci.cambridge.md.us/uploads/images/Planning_ Zoning/Draft_Little_Blackwater_Mgmt_Plan.pdf. seasonal increase in specific conductance and chloride in the Little Blackwater River, along with elevated chloride in near- Cushing, E.M., Kantrowitz, I.H., and Taylor, K.R., 1973, river water-table wells indicate saltwater intrusion into the Water resources of the Delmarva Peninsula: shallow groundwater system during summer and fall months. U.S. Geological Survey Professional Paper 822, 58 p. Sea level rise could exacerbate the impacts to saltwater deVerteuil, L., and Norris, G., 1996, Miocene dinoflagellate intrusion in the future. However, the mechanisms affecting stratigraphy and systematics of Maryland and Virginia: saltwater intrusion into the shallow groundwater system are Micropaleontology, v. 42, supplement, p. 1–172. beyond the scope of this study and can be the subject of further investigations. Denny, C.S., and Owens, J.P., 1978, Sand dunes on the central Delmarva Peninsula, Maryland and Delaware: U.S. Geological Survey Professional Paper 1067–C, 15 p. Acknowledgments Denny, C.S., Owens, J.P., Sirken, L.A., and Rubin, M., 1979, The Parsonsburg Sand in the central Delmarva Peninsula, The authors would like to thank the Edgar family for Maryland and Delaware: U.S. Geological Survey allowing us to install and maintain a stream gage on their Professional Paper 1067–B, 16 p. property, and USGS employees Jessica Teunis, Deborah Ferrari, M.J., Ator, S.W., Blomquist, J.D., and Dysart, J.E., Bringman, Michael Brownley, Anthony Tallman, and Douglas 1997, Pesticides in surface water of the Mid-Atlantic Yeskis for their sampling and data-collection efforts, and Region: U.S. Geological Survey Water-Resources Wayne Newell for technical input for the geologic interpreta- Investigations Report 97–4280, 12 p. tion. The authors would also like to thank Michael Brayton French, H.M., 2007, The periglacial environment (3d ed.): and Gary Lauben of the USGS for assistance with geophysical Chichester, United Kingdom, John Wiley and Sons Ltd., surveys. The authors also thank the following personnel from 458 p. other agencies and organizations who assisted in field logisti- cal support and provided technical input during the completion French, Hugh, Demitroff, Mark, and Newell, W.L., 2009, of this project: Diane Cole and James Newcomb (Dorchester Past permafrost on the Mid-Atlantic Coastal Plain, eastern Soil Conservation District); Rebecca Fox and Thomas Fisher United States: Permafrost and Periglacial Processes v. 20, (University of Maryland, Horn Point Laboratory); William no. 3, p. 285–294, DOI: 10.1002/ppp.659. Giese, Dixie Birch, and Suzanne Baird (U.S. Fish and Wildlife Gernant, R.E., 1970, Paleoecology of the Choptank Formation Service, Chesapeake Marshlands Wildlife NWR Complex); (Miocene) of Maryland and Virginia: Maryland Geological and Gary Setzer (Maryland Department of the Environment). Survey Report of Investigations No. 12, 90 p. Hem, 1985, Study and interpretation of the chemical characteristics of natural water: U.S. Geological Survey Water- Selected References Supply Paper 2254, 263 p. Klohe, C.A., and Feehley, C.E., 2001, Hydrogeology and Ator, S.W., Denver, J.M., and Brayton, M.J., 2004, Hydrologic ground-water quality of the Piney Point-Nanjemoy and and geochemical controls on pesticide and nutrient transport Aquia aquifers, Naval Air Station Patuxent River and to two streams on the Delmarva Peninsula: U.S. Geological Webster Outlying Field, St. Mary’s County, Maryland: U.S. Survey Scientific Investigations Report 2004–5051, 34 p., Geological Survey Water-Resources Investigations Report available online at http://pubs.usgs.gov/sir/2004/5051/. 01–4029, 51 p., available online at http://pubs.usgs.gov/wri/ wri01–4029/. Ator, S.W., Denver, J.M., Krantz, D.E., Newell, W.L., and Martucci, S.K., 2005, A surficial hydrogeologic framework Larsen, Curt, Clark, Inga, Guntenspergen, Glenn, Cahoon, for the Mid-Atlantic Coastal Plain: U.S. Geological Survey Don, Caruso, Vincent, Hupp, Cliff, and Yanosky, Tom, Professional Paper 1680, 44 p., available online at 2004, The Blackwater NWR inundation model. Rising sea http://pubs.usgs.gov/pp/2005/pp1680/. level on a low-lying coast: Land use planning for wetlands: U.S. Geological Survey Open-File Report 04–1302, online only, available at http://pubs.usgs.gov/of/2004/1302/. 30 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Markewich, H.W., Litwin, R.J., Pavich, M.J., and Brook, Trapp, Henry, Jr., Knobel, L.L., Meisler, Harold, and Leahy, G.A., 2009, Late Pleistocene eolian features in southeastern P.P., 1984, Test Well DO-Ce 88 at Cambridge, Dorchester Maryland and Chesapeake Bay region indicate strong County, Maryland: U.S. Geological Survey Water-Supply WNW–NW winds accompanied growth of the Laurentide Paper 2229, 48 p. Ice Sheet: Quaternary Research, v. 71, no. 3, p. 409–425, doi: 10.1016/j.yqres.2009.09.003. U.S. Environmental Protection Agency, 2009, 2009 Edition of the drinking water standards and health advisories: U.S. Maryland Department of Agriculture, 1999, Maryland Environmental Protection Agency, EPA 822-R-09-011, pesticide statistics for 1997: Maryland Department of Office of Water, accessed February 02, 2011, at http://water. Agriculture Report MDA–265–99, 56 p. epa.gov/action/advisories/drinking/drinking_index.cfm. Maryland Department of Agriculture, 2002, Maryland U.S. Geological Survey, variously dated, National field man- pesticide statistics for 2000: Maryland Department of ual for the collection of water-quality data: U.S. Geological Agriculture Report MDA–265–02, 45 p. Survey Techniques of Water-Resources Investigations, book 9, chaps. A1–A9, available online at http://pubs.water.usgs. Milheim, L.E., Jones, J.W., and Barlow, R.A., 2007, gov/twri9A. Development of an impervious-surface database for the Little Blackwater River watershed, Dorchester County, U.S. Geological Survey, 2010, National Water Information Maryland: U.S. Geological Survey Open-File Report System data available on the World Wide Web (Water 2007–1308, 6 p., available online at http://pubs.usgs.gov/ Data for the Nation), accessed January 20, 2010, at http:// of/2007/1308/ofr2007-1308.pdf. waterdata.usgs.gov/nwis/. Mixon, R.B., Berquist, C.R., Jr., Newell, W.L., Johnson, Waelbroeck, C., Labeyrie, L., Michel, E., Duplessy, J.C., G.H., Powars, D.S., Schindler, J.S., and Rader, E.K., 1989, McManus, J.F., Lambeck, K., Balbon, E., and Labracherie, Geological map and generalized cross sections of the M., 2002, Sea-level and deep water temperature changes Coastal Plain and adjacent parts of the Piedmont, Virginia, derived from benthic foraminifera isotopic records: IMAP: U.S. Geological Survey Numbered Series, 1 sheet. Quaternary Science Reviews, v. 21, nos. 1–3, p. 295–305, doi: 10.1016/S0277-3791(01)00101-9. Newell W.L., and Clark Inga, 2008, Geomorphic map of Worcester County, Maryland, interpreted from a LIDAR- based digital elevation model: U.S. Geological Survey Open-File Report 2008–1005, 34 p., 2 pls., available online at http://pubs.usgs.gov/of/2008/1005/. Owens, J.P., and Denny, C.S., 1979, Upper Cenozoic deposits of the central Delmarva Peninsula, Maryland and Delaware: U.S. Geological Survey Professional Paper 1067–A, 28 p. Owens, J.P., and Denny, C.S., 1986, Geologic map of Dorchester County, Maryland: Baltimore, Maryland, Maryland Geological Survey, 1 sheet, scale 1:62,500. Phelan, D.J., 1987, Water levels, chloride concentrations, and pumpage in the coastal aquifers of Delaware and Maryland: U.S. Geological Survey Water-Resources Investigations Report 87–4229, 106 p. Sirkin, L.A., Denny, C.S., and Rubin, M., 1977, Late Pleistocene environment of the central Delmarva Peninsula, Delaware-Maryland: Geological Society of America Bulletin, v. 88, no. 1, p. 139–142, doi: 10.1130/0016-7606(1977)88<139:LPEOTC>2.0.CO;2 Smoot, J.P., Newell, W.L., and DeJong, B.D., 2009, Investigation into the origin and character of surficial sedimentary deposits at the Midshore Regional Solid Waste Facility near Easton, Maryland: U.S. Geological Survey Open-File Report 2009–1052, 64 p., available online only at http://pubs.usgs.gov/of/2009/1052/. Appendixes 1–8 31

Appendixes 1–8 32 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 3.8 3.9 6.5 7.2 3.7 4.1 6.2 3.9 3.9 4.0 6.5 7.5 7.3 7.3 5.8 7.5 3.9 7.4 7.3 5.6 lab pH, -- 4.2 4.1 6.3 7.3 5.1 4.2 6.2 4.0 3.8 6.3 7.1 7.1 7.1 5.3 7.4 4.3 7.3 7.1 5.2 pH, field ------1.2 0.9 2.8 0.1 0.4 0.9 2.3 0.2 0.0 0.7 0.1 0.3 0.3 0.4 (mg/L) oxygen Dissolved ------95 46 64 97 (mg/L) Carbon 124 dioxide, dissolved ------7.8 9 6 (FNU) Turbidity Turbidity

------(ft) 5.47 9.5 11.5 13.1 13.2 46.18 51.5 51.5 90 depth Sampling ------0.5 50 65 Pump period (minutes) ------0.3 0.3 0.1 0.7 0.2 0.6 1.1 0.8 0.1 4.7 0.4 0.9 1.1 rate min) flow (gal/ Pump - Water Quality Laboratory] Water ------(ft) , °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms 8.48 6.44 8.4 8.53 7.75 4.05 4.61 8.01 5.52 level, depth Water Water below 14.9 16.01 15.04 measur ing point , nitrate; P, phosphorus; <, less than; E, estimated; M, present but not quantified; U, deleted value by lab; --, data not phosphorus; <, less than; E, estimated; M, present but not , nitrate; P, 3 (ft) 9.50 9.50 9.85 9.43 7.28 7.28 7.11 3.68 3.68 3.68 3.81 3.12 3.12 3.12 5.00 5.26 5.26 5.31 of land 10.18 10.34 surface Altitude , nitrite; NO

2 11.6 land well (feet 13.5 13.5 22.0 94.0 13.1 13.1 19.2 13.2 13.2 13.2 19.4 53.2 53.2 53.2 13.0 15.0 99.7 99.7 below 129.5 surface) Depth of , ammonia; NO 4 1110 1115 Time 1135 1158 1100 0815 1240 1515 1445 1520 1029 1225 1030 1045 1555 1500 1050 0915 1345 1610 Date 06/11/2008 06/11/2008 06/11/2008 06/11/2008 10/30/2007 10/31/2007 10/30/2007 10/30/2007 06/10/2008 10/31/2007 10/31/2007 10/31/2007 06/10/2008 10/31/2007 10/31/2007 06/10/2008 06/10/2008 10/31/2007 06/09/2008 06/09/2008 , silica; N, nitrogen; NH 2

USGS well name DO Cd 56 DO Cd 56 DO Cd 57 DO Cd 58 DO Cd 59 DO Cd 59 DO Cd 60 DO Cd 61 DO Cd 61 DO Cd 61 DO Cd 62 DO Cd 63 DO Cd 63 DO Cd 63 DO Cd 64 DO Cd 66 DO Cd 68 DO Dd 12 DO Dd 12 DO Dd 13 Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland. Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County,

, calcium carbonate; SiO 3 USGS well number 383122076055701 383122076055701 383122076055702 383122076055703 383118076054601 383118076054601 383118076054602 383112076053501 383112076053501 383112076053501 383112076053502 383112076053503 383112076053503 383112076053503 383100076061101 383100076061103 383051076054201 382718076062001 382718076062001 382718076062002 Appendix 1. [ft, feet; gal/min, gallons per minute; FNU, formazin nephelometric units; mg/L, milligrams liter liter; CaCO available; USGS, U.S. Geological Survey; shaded couplets indicate duplicate samples; NWQL, National Appendixes 1–8 33 -- -- 26.9 54.7 34.7 26.3 39.2 41.9 38.1 74.6 74.1 82.4 66.1 65.4 47.6 74.6 64.2 67.2 52.7 83.5 Sodium cations) of major fraction of cations (% equivalent -- -- 1.0 2.7 1.3 1.6 1.4 1.6 1.3 6.1 6.9 9.1 6.1 6.0 1.3 7.8 3.6 5.9 3.5 3.4 ration Sodium, adsorption 4.0 2.9 8.3 3.9 2.4 6.1 4.4 4.4 4.7 6.8 2.6 2.9 0.3 22.6 17.4 18.7 19.0 12.6 12.9 15.3 (mg/L) dissolved Potassium, 7.0 1.8 30.4 20.0 16.6 55.2 16.0 18.3 13.4 16.1 16.8 22.8 10.4 26.4 27.7 28.8 16.9 16.8 18.3 22.1 (mg/L) dissolved Magnesium, 5.7 1.1 11.8 19.1 14.9 19.9 95.5 19.1 15.6 18.9 13.5 15.4 13.6 36.1 36.5 37.7 28.7 10.6 37.8 46.1 (mg/L) Calcium, dissolved ) 3 ------34.2 Non- lab (mg/L as CaCO hardness, dissolved, carbonate ) 3 Water Quality Laboratory] Water ------55.2 99.1 Non- , °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms as CaCO hardness, dissolved, carbonate field (mg/L ) 3 - , nitrate; P, phosphorus; <, less than; E, estimated; M, present but not quantified; U, deleted value by lab; --, data phosphorus; <, less than; E, estimated; M, present but not , nitrate; P, 3 96 77 43 96 10 -- -- 118 114 115 173 120 466 103 132 199 205 141 170 206 ness Hard CaCO (mg/L as , nitrite; NO 2 -- (°C) 14.7 19.8 17.1 15.1 16.7 22.2 18.0 18.9 21.4 18.5 15.2 19.6 19.6 23.2 15.6 19.2 15.8 18.0 21.9 ature, water Temper- Temper- -

-- , ammonia; NO 4 field 606 677 443 546 542 439 231 762 907 161 tance, (µS/cm) 1,192 1,059 1,320 1,048 1,217 1,241 1,240 1,089 1,063 conduc Specific

- 657 724 400 626 518 376 231 795 917 150 (µS/cm) conduc Specific 1,110 1,204 1,062 1,060 1,370 1,013 1,205 1,220 1,230 1,070 tance, lab , silica; N, nitrogen; NH 2 1110 1115 Time 1135 1158 1100 0815 1240 1515 1445 1520 1029 1225 1030 1045 1555 1500 1050 0915 1345 1610 Date Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, 06/11/2008 06/11/2008 06/11/2008 06/11/2008 10/30/2007 10/31/2007 10/30/2007 10/30/2007 06/10/2008 10/31/2007 10/31/2007 10/31/2007 06/10/2008 10/31/2007 10/31/2007 06/10/2008 06/10/2008 10/31/2007 06/09/2008 06/09/2008

, calcium carbonate; SiO 3

USGS well name Appendix 1. [ft, feet; gal/min, gallons per minute; FNU, formazin nephelometric units; mg/L, milligrams liter liter; CaCO not available; USGS, U.S. Geological Survey; shaded couplets indicate duplicate samples; NWQL, National DO Cd 56 DO Cd 56 DO Cd 57 DO Cd 58 DO Cd 59 DO Cd 59 DO Cd 60 DO Cd 61 DO Cd 61 DO Cd 61 DO Cd 62 DO Cd 63 DO Cd 63 DO Cd 63 DO Cd 64 DO Cd 66 DO Cd 68 DO Dd 12 DO Dd 12 DO Dd 13 34 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 ------285 357 286 668 155 (mg/L) E822 E754 E777 E161 E716 E634 E541 Residue, stituents dissolved, sum of con 1.2 4.7 7.4 0.5 1.1 E.17 14.9 44.9 37.4 39.0 49.8 48.4 17.8 37.3 (mg/L) 146 199 244 138 174 238 Sulfate, dissolved

) 2 70.2 56.3 57.4 50.4 58.1 59.0 50.1 51.4 49.7 49.7 47.6 56.4 58.3 57.6 41.8 59.8 17.8 29.0 29.6 66.4 SiO Silica, (mg/L as dissolved 0.60 0.41 0.27 0.30 0.15 0.19 0.16 0.71 0.77 0.92 0.27 0.32 0.32 0.32 0.19 0.41 0.22 0.29 0.20 0.15 (mg/L) Fluoride, dissolved 9.7 93.9 80.7 18.2 16.8 58.1 47.1 21.4 61.0 51.0 49.6 49.0 25.6 20.0 68.5 67.7 (mg/L) 285 297 381.1 219.6 Chloride, dissolved ------0.07 0.09 0.06 0.08 0.11 1.02 1.05 0.31 <.02 E.016 (mg/L) Bromide, dissolved - Water Quality Laboratory] Water

------17.6 ate, field, 209 500.6 157.7 194.4 712.6 577.1 (mg/L) , °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms dissolved Bicarbon - ) 3 - -- , nitrate; P, phosphorus; <, less than; E, estimated; M, present but not quantified; U, deleted value by lab; --, data phosphorus; <, less than; E, estimated; M, present but not , nitrate; P, 3 ------14.3 dis 411.2 172 129.3 159.5 585.6 474.4 solved CaCO Alkalin (mg/L as ity, field, ity, - ) 3 , nitrite; NO 2 9 ------13 606 614 603 392 CaCO ity, lab, ity, Alkalin (mg/L as dissolved - ) 3 8 ------11 , ammonia; NO 4 605 621 605 397 CaCO tralizing (mg/L as lab, total capacity, capacity, Acid-neu 30.0 68.5 31.5 81.0 35.1 39.0 31.2 19.4 82.0 24.5 (mg/L) 116 137 138 181 184 198 199 200 212 176 Sodium, dissolved , silica; N, nitrogen; NH 2 1110 1115 Time 1135 1158 1100 0815 1240 1515 1445 1520 1029 1225 1030 1045 1555 1500 1050 0915 1345 1610 Date Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, 06/11/2008 06/11/2008 06/11/2008 06/11/2008 10/30/2007 10/31/2007 10/30/2007 10/30/2007 06/10/2008 10/31/2007 10/31/2007 10/31/2007 06/10/2008 10/31/2007 10/31/2007 06/10/2008 06/10/2008 10/31/2007 06/09/2008 06/09/2008

, calcium carbonate; SiO 3

USGS well name Appendix 1. [ft, feet; gal/min, gallons per minute; FNU, formazin nephelometric units; mg/L, milligrams liter liter; CaCO not available; USGS, U.S. Geological Survey; shaded couplets indicate duplicate samples; NWQL, National DO Cd 56 DO Cd 56 DO Cd 57 DO Cd 58 DO Cd 59 DO Cd 59 DO Cd 60 DO Cd 61 DO Cd 61 DO Cd 61 DO Cd 62 DO Cd 63 DO Cd 63 DO Cd 63 DO Cd 64 DO Cd 66 DO Cd 68 DO Dd 12 DO Dd 12 DO Dd 13 Appendixes 1–8 35 ------0.11 0.15 0.20 0.13 0.10 0.33 (mg/L) Organic nitrogen, dissolved N) Nitrite, 0.00 0.00 0.00 0.00 0.00 <.002 <.002 <.002 E.00197 E.001 E.00122 E.002 E.00128 E.002 E.002 E.002 E.001 E.002 E.00148 E.001 (mg/L as dissolved ------0.01 0.01 0.01 0.01 0.01 E.006 E.003 E.004 E.004 E.005 E.006 E.003 E.006 E.005 E.004 (mg/L) Nitrite, dissolved

------0.12 0.13 E.043 E.041 E.112 Nitrate, dissolved (mg/L as N) ------0.52 0.57 E.186 E.176 E.488 (mg/L) Nitrate, dissolved 0.11 0.12 0.13 0.04 0.04 0.14 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 <.04 E.03 Nitrate dissolved (mg/L as N) plus nitrite, Water Quality Laboratory] Water 0.47 0.22 2.75 3.55 0.72 0.29 2.07 0.24 0.28 0.32 2.38 6.20 6.27 6.36 0.15 0.48 0.12 2.48 2.50 0.16 dissolved Ammonia, (mg/L as N) as (mg/L , °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms ) 4 -- -- 0.61 0.28 3.55 4.57 0.93 0.37 2.66 0.31 0.41 3.07 7.99 8.08 0.19 0.62 0.16 3.20 3.22 0.21 NH , nitrate; P, phosphorus; <, less than; E, estimated; M, present but not quantified; U, deleted value by lab; --, data phosphorus; <, less than; E, estimated; M, present but not , nitrate; P, (mg/L as 3 dissolved Ammonia, ------, nitrite; NO 2 0.39 0.37 0.43 6.85 6.90 0.30 0.65 0.21 3.09 1.06 as N) nitrogen, Ammonia total (mg/L plus organic ------, ammonia; NO 412 287 853 397 269 542 575 679 764 678 4 (mg/L) ration, Residue dissolved on evapo ------0.39 1.16 0.54 0.37 0.92 1.04 0.92 0.21 E.22 E.97 E.74 E1.1 Residue, (tons per dissolved acre-foot) , silica; N, nitrogen; NH 2 1110 1115 Time 1135 1158 1100 0815 1240 1515 1445 1520 1029 1225 1030 1045 1555 1500 1050 0915 1345 1610 Date Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, 06/11/2008 06/11/2008 06/11/2008 06/11/2008 10/30/2007 10/31/2007 10/30/2007 10/30/2007 06/10/2008 10/31/2007 10/31/2007 10/31/2007 06/10/2008 10/31/2007 10/31/2007 06/10/2008 06/10/2008 10/31/2007 06/09/2008 06/09/2008

, calcium carbonate; SiO 3

1.4 0.5 3.8 -6.5 -6.7 -1.5 -0.7 -2 -6.9 -3.9 -5.3 -3.7 -0.2 -0.7 -0.7 -0.5 -0.8 -5.9 -0.1 -0.3 anion ence) Cation/ balance (% differ - 18.5 49.6 62.6 27.7 Man (µg/L) 511 404 233 729 122 954 569 772 416 454 606 379 546 577 223 890 ganese, dissolved

Iron, (µg/L) 2,496 2,900 7,477 5,081 5,100 2,217 2,550 4,870 6,660 2,617 4,990 5,090 4,240 2,680 5,860 3,160 4,020 4,290 18,690 18,190 dissolved

------U U M M M total (mg/L) sulfide, Hydrogen

------3.4 2.0 2.3 8.3 9.8 2.5 7.1 1.1 total (mg/L) 10.2 14.4 carbon, Organic Organic

-- -- .000 0.06 0.09 0.00 0 0.01 0.07 0.00 0.10 0.15 0.00 0 0.00 0.01 0.00 0.06 0.00 0.01 (mg/L) ion, total, Hydrogen calculated - P) ------0.01 1.98 2.14 0.02 0.06 0.31 <.008 E.0071 E.0057 (mg/L as rus, total Phospho Water Quality Laboratory] Water 0.11 0.01 0.01 0.96 0.14 0.01 0.02 0.01 0.01 0.01 0.13 1.91 1.87 2.20 0.01 0.06 0.01 0.19 0.67 0.05 Ortho- , °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms dissolved (mg/L as P) phosphate, , nitrate; P, phosphorus; <, less than; E, estimated; M, present but not quantified; U, deleted value by lab; --, data phosphorus; <, less than; E, estimated; M, present but not , nitrate; P, 3 -- -- 0.03 0.04 2.95 0.43 0.04 0.05 0.33 0.02 0.04 0.41 5.87 5.72 0.03 0.18 0.02 0.60 2.05 0.14 (mg/L) Ortho- dissolved phosphate, , nitrite; NO

2 ------0.52 0.42 0.32 1.20 total Total Total (mg/L) nitrogen, nitrogen,

+ 3 , ammonia; NO 4 +N), 4 -- +NO 2 0.75 0.55 3.18 3.93 0.95 0.44 2.32 0.41 0.47 0.45 2.80 6.53 6.89 0.26 0.66 0.34 2.88 3.05 0.64 Total Total (mg/L) NH nitrogen dissolved, (NO determined analytically ------0.18 0.08 0.12 0.57 0.15 0.17 0.09 0.59 0.90 total (mg/L) Organic nitrogen, , silica; N, nitrogen; NH 2 1110 1115 Time 1135 1158 1100 0815 1240 1515 1445 1520 1029 1225 1030 1045 1555 1500 1050 0915 1345 1610 Date Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, 06/11/2008 06/11/2008 06/11/2008 06/11/2008 10/30/2007 10/31/2007 10/30/2007 10/30/2007 06/10/2008 10/31/2007 10/31/2007 10/31/2007 06/10/2008 10/31/2007 10/31/2007 06/10/2008 06/10/2008 10/31/2007 06/09/2008 06/09/2008

, calcium carbonate; SiO 3

53 76 65 ------186 330 171 169 309 130 353 128 202 537 169 142 121 125 353 553 143 field (µS/cm) Specific conductance,

57 78 lab 192 313 316 171 164 320 320 295 129 352 124 201 544 173 108 142 133 134 369 565 137 (µS/cm) Specific , square miles; mm Hg, conductance, 2 6.7 7.1 6.3 7.2 7.0 7.1 6.9 7.3 7.1 7.1 6.9 7.0 7.0 7.0 6.9 7.1 7.1 7.2 7.7 7.1 7.1 6.8 7.2 lab pH, -- 6.6 6.5 6.3 6.5 6.9 6.4 6.5 6.8 6.6 6.5 6.5 6.1 6.5 6.1 6.7 6.5 6.6 6.7 6.3 6.4 6.3 6.1 pH, field -- 9 3 ------75 79 46 12 75 79 65 22 17 10 74 53 61 30 38 104 Dissolved oxygen (% saturation) -- 9.5 9.3 0.7 4.7 0.9 9.3 9.1 6.8 1.8 0.3 8.5 1.4 0.9 7.2 6.5 6.6 2.3 4.2 0.2 , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 11 11.6 3 12.7 (mg/L) oxygen Dissolved ------7.7 7.4 7.2 , nitrite; NO 11.2 2 12.9 29.9 10.1 30.1 26.8 40.5 13.5 55.0 45.6 16.7 13.8 10.7 12.0 30.0 19.6 52.0 (mg/L) Carbon dioxide, dissolved ------770 768 741 762 769 759 770 768 741 769 759 767 767 757 772 741 762 769 759 , ammonia; NO 4 (mm Hg) pressure Barometric Barometric

) 2 -- -- 3.7 3.7 3.7 3.7 3.7 3.7 0.2 0.2 0.2 0.2 0.2 8.3 8.3 8.3 8.3 8.3 8.3 8.3 8.3 8.3 8.3 (mi area Drainage Drainage , falling; ND, no data] Little Blackwater River near Christs Rock, Md. /s) ------3 1.36 0.321 0.6 0.108 0.08 0.076 , silicate; N, nitrogen; NH (ft 2 12.4 177 Discharge Little Blackwater River at Maple Dam Rd. near Cambridge, Md. Little Blackwater River at Stone Boundary Rd. near Cambridge, Md. ------Little Blackwater tributary at Stone Boundary Rd. near Cambridge, Md. (ft) Gage height 7 5 5 5 5 5 5 5 5 5 5 (ft) 12 12 12 12 12 12 14 14 14 14 14 14 of land surface Altitude , calcium carbonate; SiO 3 F F L L L L L L L L L L R R R R R R H H H H H Tidal Tidal cycle Time 1400 0900 0915 1045 1300 0910 1300 1305 1000 1030 1330 0710 0815 1215 1050 1030 1310 1045 1226 1215 0945 1015 1230 Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 12/06/2006 03/13/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 12/06/2006 12/06/2006 03/13/2007 04/16/2007 10/29/2007 06/10/2008 06/10/2008 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008

91 78 -- 248 220 100 254 309 335 188 209 182 191 180 136 210 209 444 167 field (µS/cm) 4,220 Specific conductance,

90 81 lab 110 246 218 262 319 319 187 203 180 204 186 151 215 231 465 150 153 (µS/cm) Specific 2,030 , square miles; mm Hg, conductance, 2 7.7 7.2 7.1 7.2 7.8 7.5 7.4 7.3 7.1 7.0 7.1 7.0 7.1 7.1 7.8 6.8 7.5 6.8 7.5 7.2 lab pH, -- 6.4 7.0 7.0 6.8 7.1 6.7 7.0 6.9 6.6 6.7 6.1 6.7 6.6 6.8 7.0 6.6 6.4 6.2 6.3 pH, field 8 7 ------28 10 83 68 78 72 64 17 17 68 57 73 35 20 108 Dissolved oxygen (% saturation) ------2.3 0.98 8.2 8.8 9 5.6 6.7 0.6 1.4 1.5 6.8 7.1 7.9 2.7 2.2 0.5 , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3 12.3 (mg/L) oxygen Dissolved ------5.0 5.1 7.6 5.3 9.1 , nitrite; NO 11.5 2 10.4 13.6 19.6 10.4 26.4 10.4 13.2 10.2 28.8 27.5 36.1 (mg/L) Carbon dioxide, dissolved ------767 767 770 768 741 762 769 759 767 767 757 772 741 762 769 759 , ammonia; NO 4 (mm Hg) pressure Barometric Barometric

) 2 -- 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 4.2 4.2 4.2 4.2 4.2 4.2 4.2 4.2 4.2 4.2 (mi area Drainage Drainage , falling; ND, no data] /s) Maple Dam Branch at Rt. 16 Cambridge, Md. 3 ------1.26 0.475 , silicate; N, nitrogen; NH (ft 2 11.2 Little Blackwater River tributary near Cambridge, Md. Discharge ------(ft) Gage height (ft) 2.9 2.9 2.9 2.9 2.9 2.9 2.9 2.9 2.9 6 6 6 6 6 6 6 6 6 6 6 of land surface Altitude , calcium carbonate; SiO 3 F F F L L L L R R R R R R R R R R H H ND Tidal Tidal cycle Time 1615 1300 1430 1210 1030 1100 1135 1400 0740 1250 1110 1000 1320 1100 1242 1225 0930 1000 1245 1250 Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/13/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 06/10/2008

69 -- 298 509 219 223 171 175 705 574 147 field 4,110 2,160 1,460 6,210 2,940 7,000 (µS/cm) 14,910 Specific conductance,

73 297 519 225 226 186 155 169 736 542 149 lab 2,140 4,140 6,130 2,940 7,020 7,020 (µS/cm) Specific E14,900 , square miles; mm Hg, conductance, 2 6.7 7.3 7.2 7.1 7.1 7.4 6.7 7.9 6.9 7.4 7.3 7.5 7.0 7.4 7.2 8.6 8.9 7.2 lab pH, -- 6.8 5.8 7.5 7.0 6.9 6.9 6.3 7.2 6.6 6.6 9.3 8.1 7.2 7.8 7.0 9.3 7.7 pH, field -- -- 73 77 88 85 87 79 80 62 41 93 92 68 89 90 101 138 Dissolved oxygen (% saturation) -- 9 5.7 6.8 8.5 9.9 8.9 5.8 6.4 3 8.2 9.8 7.8 9.6 8.9 , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 11.3 3 10.5 10 (mg/L) oxygen Dissolved -- -- , nitrite; NO 6.9 2.3 5.9 7.9 4.5 8.7 3.5 0.0 0.9 4.1 0.5 2.4 0.0 2.7 2 15.3 16.4 (mg/L) Carbon dioxide, dissolved -- -- 767 757 772 741 767 762 769 759 767 757 773 741 762 769 , ammonia; NO 4 (mm Hg) pressure Barometric Barometric

) 2 -- 15.3 15.3 15.3 15.3 15.3 15.3 15.3 15.3 15.3 15.3 28.2 28.2 28.2 28.2 28.2 28.2 28.2 (mi area Drainage Drainage , falling; ND, no data] Little Blackwater River near Seward, Md. /s) 3 ------, silicate; N, nitrogen; NH -7.48 (ft 2 Discharge Little Blackwater River near Cambridge, Md. gaging station ------(ft) 0.37 2.3 1.44 0.71 2.06 Gage height (ft) 5 5 5 5 5 5 5 5 -1.25 -1.25 -1.25 -1.25 -1.25 -1.25 -1.25 -1.25 -1.25 -1.25 of land surface Altitude , calcium carbonate; SiO 3 F F F F F L R R R R R R R R R R H H Tidal Tidal cycle Time 1130 1020 0915 1245 1000 1204 1240 1230 1030 1130 0845 1230 0940 1138 1300 1510 1515 1100 Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 07/10/2007 10/29/2007

215 5,225 4,840 2,450 1,870 field 15,470 15,660 13,000 12,900 17,500 (µS/cm) Specific conductance,

287 lab 5,230 4,880 2,603 1,784 (µS/cm) Specific E15,300 E15,300 E12,900 E12,970 E17,540 , square miles; mm Hg, conductance, 2 7.2 8.0 7.3 7.5 7.7 7.3 7.4 7.8 7.4 7.6 lab pH, -- 5.2 7.7 8.6 7.5 8.5 7.2 7.5 7.1 7.6 pH, field 81 99 89 82 91 98 88 93 145 141 Dissolved oxygen (% saturation) 6.1 8.5 8.3 7.9 9.9 6.5 , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 11.1 11.4 3 10 10 (mg/L) oxygen Dissolved ------, nitrite; NO 0.3 3.5 0.3 5.4 1.5 1.9 2.3 2 (mg/L) Carbon dioxide, dissolved -- 767 767 767 757 772 741 762 769 759 , ammonia; NO 4 (mm Hg) pressure Barometric Barometric

) 2 30.2 30.2 30.2 30.2 30.2 30.2 30.2 30.2 30.2 30.2 (mi area Drainage Drainage , falling; ND, no data] /s) 18 3 ------450 356 , silicate; N, nitrogen; NH -283 -195 (ft 2 Discharge ------(ft) 2.18 1.52 2.68 2.44 Gage height Little Blackwater River at Seward, Md. gaging station (at Key Wallace Drive) Little Blackwater River at Seward, Md. gaging station (at Key Wallace 5 5 5 5 5 5 5 5 5 5 (ft) of land surface Altitude , calcium carbonate; SiO 3 F F F F R R R R R ND Tidal Tidal cycle Time 0900 1520 1200 1215 0901 1045 1340 1730 1115 1050 Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 06/22/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008

3.1 8.3 4.9 6.1 8.0 9.9 7.0 7.9 13.6 31.9 21.4 10.6 28.7 28.9 29.6 10.2 30.0 18.3 66.0 12.7 10.5 43.4 73.4 (mg/L) Sodium, dissolved -- 34.6 47.0 25.7 32.2 23.2 28.3 43.2 46.7 30.5 37.4 38.9 22.5 46.2 63.7 36.7 37.8 33.8 37.6 25.8 58.8 61.4 26.5 Sodium cations) of major fraction of cations (% equivalent , square miles; mm Hg, 2 -- ratio 0.83 1.61 0.34 1.02 0.53 0.64 1.43 1.54 0.47 0.78 1.32 0.44 1.25 3.43 0.90 0.79 0.73 0.80 0.50 2.54 3.38 0.56 Sodium, adsorption 3.6 3.2 2.4 9.7 4.5 4.5 4.4 3.0 2.9 3.9 3.8 7.3 4.3 9.2 8.0 7.1 5.7 3.7 5.1 8.5 8.5 7.7 11.2 (mg/L) dissolved Potassium, 4.9 6.9 1.4 7.1 3.9 4.7 6.9 6.9 6.6 1.8 2.8 8.6 3.5 4.6 8.8 4.1 2.1 3.8 3.4 3.6 6.3 9.8 3.8 , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3 (mg/L) dissolved Magnesium, , nitrite; NO 2 -- 4.4 5.3 8.3 8.9 8.7 8.1 4.4 7.7 7.6 8.8 8.9 11.7 12.5 18.2 21.9 12.8 13.4 19.3 17.0 25.0 13.5 19.6 (mg/L) Calcium, dissolved

) 3

, ammonia; NO 4 ------6.6 6.0 4.9 4.5 0.6 2.4 2.3 25.5 32.4 13.9 10.3 23.4 10.4 15.0 25.0 hardness, dissolved, lab Noncarbonate (mg/L as CaCO

) 3 , falling; ND, no data]

Little Blackwater River near Christs Rock, Md. ------2.7 , silicate; N, nitrogen; NH 2 26.0 25.7 29.6 16.6 14.2 26.0 18.4 10.4 16.0 15.1 hardness, Noncarbonate Little Blackwater River at Maple Dam Rd. near Cambridge, Md. dissolved, field (mg/L as CaCO Little Blackwater River at Stone Boundary Rd. near Cambridge, Md. Little Blackwater tributary at Stone Boundary Rd. near Cambridge, Md. ) 3 -- 51.5 74.1 16.6 83.7 47.8 52.6 76.6 69.5 20.5 32.3 97.8 36.5 40.8 70.0 37.2 19.6 35.0 33.2 37.0 55.3 89.3 37.7 CaCO (mg/L as Hardness , calcium carbonate; SiO 3 -- -- 5.5 9 7 6.5 7.5 8 6 (°C) 11 11 29 15 28.5 14 24 25.5 26.5 20 14 10.5 30 27.5 ature, water Temper- Temper-

------9 9 9.5 8.5 air (°C) 11 13.5 10 31.5 10 14 31 12 21 ature, Temper- Temper- Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 12/06/2006 03/13/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 12/06/2006 12/06/2006 03/13/2007 04/16/2007 10/29/2007 06/10/2008 06/10/2008 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008

/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi per liter; °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms /s, cubic feet per second; mg/L, milligrams liter, 3 USGS station number 01490108 01490108 01490108 01490108 01490108 01490108 01490110 01490110 01490110 01490110 01490110 01490110 01490111 01490112 01490112 01490112 01490112 01490112 01490112 01490112 01490112 01490112 01490112 Appendix 2. [ft, feet; ft millimeters mercury; --, data not available; CaCO Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F 42 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 3.8 4.5 9.1 4.2 9.0 9.1 19.7 14.4 20.0 27.6 40.4 13.6 13.1 14.1 16.6 14.3 14.6 18.5 56.7 (mg/L) 295.8 Sodium, dissolved -- 36.7 32.0 16.2 36.6 42.7 22.3 55.9 34.4 30.0 37.9 40.0 39.6 30.5 33.4 38.9 24.3 63.2 72.9 28.5 Sodium cations) of major fraction of cations (% equivalent , square miles; mm Hg, 2 -- 1.04 0.81 0.28 1.03 1.37 0.35 2.23 0.84 0.73 0.92 1.06 1.02 0.69 0.84 1.05 0.36 3.14 8.71 0.63 ratio Sodium, adsorption 5.0 4.7 6.3 3.3 2.7 2.2 5.4 5.1 4.6 4.7 6.3 8.0 9.1 5.0 3.7 2.4 8.0 7.8 7.9 16.2 (mg/L) dissolved Potassium, , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3.7 2.2 5.4 6.6 2.0 4.0 3.0 3.7 4.7 4.5 4.3 3.3 5.3 5.5 1.9 7.3 3.9 4.0 3.8 3 (mg/L) 32.5 dissolved Magnesium, , nitrite; NO 2 -- 9.1 7.8 7.9 7.1 9.3 11.0 18.1 10.1 19.5 19.9 18.3 15.0 18.2 10.1 14.1 14.4 12.6 33.9 20.8 (mg/L) Calcium, dissolved ) 3

, ammonia; NO 4

lab ------5.2 8.2 7.1 0.6 7.5 2.1 27.5 44.1 12.0 10.2 23.8 31.8 hardness, dissolved, Noncarbonate (mg/L as CaCO ) 3 , falling; ND, no data]

Maple Dam Branch at Rt. 16 Cambridge, Md. ------, silicate; N, nitrogen; NH field 8.5 8.8 2.7 2 Little Blackwater River tributary near Cambridge, Md. 29.9 43.4 24.9 34.1 22.1 hardness, dissolved, Noncarbonate (mg/L as CaCO ) 3 - -- 44.3 67.6 60.2 34.3 70.9 77.0 31.1 62.4 49.8 60.9 46.1 37.1 33.6 56.9 58.7 25.4 61.5 39.5 ness, Hard CaCO 218.4 (mg/L as , calcium carbonate; SiO 3 -- 5 8.5 8 6 (°C) 26 18.5 16 28 14 26.5 24 21 15 10 10.5 29.5 10 30 ature, water Temper- Temper-

------air 8.5 9 9 (°C) 21 10.5 14 32 12 20 ature, Temper- Temper- Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 09/13/2006 10/06/2006 12/06/2006 03/13/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 06/10/2008 06/22/2006

52.0 75.5 64.0 50.4 44.4 46.2 30.5 75.4 75.3 36.7 76.8 74.5 68.3 67.5 47.8 75.8 76.7 cations Sodium cations) fraction of (% equiva lent of major , square miles; mm Hg, 2 ratio 1.81 9.71 3.37 1.63 1.28 1.22 0.46 8.12 0.92 4.54 3.82 1.19 13.42 17.46 10.93 18.02 28.82 Sodium, adsorption 5.2 9.9 9.1 6.3 4.0 3.0 7.9 9.7 6.3 4.6 16.6 14.8 28.9 41.1 22.5 52.3 53.0 99.6 (mg/L) dissolved Potassium, 6.7 9.7 4.7 5.5 4.4 1.9 4.6 3.9 , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 11.1 3 33.9 21.6 70.4 56.4 15.2 mg/L 116 133 131 328.2 dissolved, Magnesium, , nitrite; NO 2 8.8 7.0 9.5 8.6 4.2 8.2 8.8 8.7 5.3 11.4 25.8 18.7 47.9 43.6 23.1 56.8 (mg/L) 121.3 Calcium, dissolved

) 3

, ammonia; NO 4 ------5.9 6.0 24.3 14.0 21.4 10.2 48.9 49.5 15.9 541.6 237.8 hardness, dissolved, lab Noncarbonate (mg/L as CaCO

, falling; ND, no data]

Little Blackwater River near Seward, Md. ) 3 ------, silicate; N, nitrogen; NH 27.5 17.0 24.1 52.7 48.4 2 CaCO 115.9 384.0 544.4 658.7 (mg/L as hardness, 1,599.5 Little Blackwater River near Cambridge, Md. gaging station Noncarbonate dissolved, field ) 3 -- 55.9 61.9 36.7 46.5 39.7 18.4 39.4 84.7 67.3 29.3 204.1 135.6 409.5 586.2 289.9 689.1 CaCO (mg/L as Hardness 1,654.4 , calcium carbonate; SiO 3 -- 6 9 6 9 (°C) 11.5 28 21.5 17 10 32.5 14 31.5 21 17 10 33.5 14 ature, water Temper- Temper-

------9 8.5 9 air (°C) 12 20 10.5 12 34 20 13 ature, Temper- Temper- Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 07/10/2007 10/29/2007

75.9 76.1 76.1 75.5 75.9 75.7 63.0 75.9 77.0 76.3 cations Sodium cations) fraction of (% equiva lent of major , square miles; mm Hg, 2 2.47 9.35 ratio 26.88 27.81 25.04 15.11 14.69 10.83 25.38 31.39 Sodium, adsorption 5.3 94.2 98.6 82.4 35.0 32.0 17.6 98.7 18.3 (mg/L) 115.1 dissolved Potassium, 6.2 , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3 92.2 49.1 31.3 (mg/L) 315.7 330.9 266.0 100.2 272.0 380.3 dissolved, Magnesium, , nitrite; NO 2 5.0 90.7 37.9 32.1 21.6 98.6 12.8 111.9 116.7 135.9 (mg/L) Calcium, dissolved

) 3

, ammonia; NO 4 ------23.0 112.0 455.4 416.0 229.9 hardness, 1,264.8 dissolved, lab Noncarbonate (mg/L as CaCO

, falling; ND, no data]

) 3 ------, silicate; N, nitrogen; NH 418.1 233.9 2 CaCO (mg/L as 1,269.3 1,317.9 1,842.3 hardness, Noncarbonate dissolved, field ) 3 Little Blackwater River at Seward, Md. gaging station (at Key Wallace Drive) Little Blackwater River at Seward, Md. gaging station (at Key Wallace 37.8 507.3 459.9 256.0 160.7 CaCO 1,579.5 1,654.1 1,321.8 1,366.3 1,905.5 (mg/L as Hardness , calcium carbonate; SiO 3 5.8 9 9 (°C) 28 33 21 17 32 14.5 33 ature, water Temper- Temper-

8.5 9.5 ------air 21 13 37 (°C) ature, Temper- Temper- Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 06/22/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008

-- -- total 1.07 0.84 1.19 3.11 1.43 2.53 0.93 0.94 1.35 0.75 1.77 2.16 1.67 0.80 1.02 0.99 2.46 2.87 0.93 2.09 E1.006 nitrogen, Ammonia (mg/L as N) plus organic

- -- -- 38 24 54 52 42 12 15 32 24 26 36 due, total 118 Resi <10 <20 <20 <20 <16.7 <20 <10 <10 <20 (mg/L)

, square miles; mm Hg, 2 -- -- 33.5 74.3 96.7 92.8 82.8 66.6 76.0 81.7 116 172 179 161 (mg/L) E43.0 E73.2 E55.4 sum of Residue, E167 E103 E105 E204 E182 E386 dissolved, constituents 5.5 6.9 6.0 7.3 6.6 6.8 3.4 8.2 5.7 5.1 11.9 22.8 35.9 37.8 26.1 10.4 27.7 27.7 34.5 21.6 24.1 14.6 59.2 (mg/L) Sulfate, dissolved ) 2 7.70 4.26 2.04 8.07 7.71 2.95 4.79 8.31 1.16 3.32 6.67 2.92 0.65 4.88 3.16 6.58 8.41 SiO 19.46 16.2 17.0 16.9 17.75 12.41 Silica, (mg/L as dissolved, , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3 0.18 0.18 0.32 0.16 0.21 0.22 0.15 0.25 0.12 0.15 0.18 0.12 0.10 0.12 0.11 0.19 0.14 <.10 E.110 E.065 E.076 E.084 E.101 (mg/L) Fluoride, dissolved , nitrite; NO 2 -- 4.7 8.0 11.8 11.2 21.3 38.1 30.1 15.9 35.3 35.6 12.5 34.2 34.5 22.4 15.9 18.3 17.6 12.9 76.6 13.7 (mg/L) 132 195 Chloride, dissolved dissolved , ammonia; NO 4 ------0.598 (mg/L) <.02 E.0149 Bromide, dissolved

, falling; ND, no data] ------31 59 66 38 76 77 53 17 42 30 21 49 field, (mg/L) dissolved Little Blackwater River near Christs Rock, Md. Bicarbonate, , silicate; N, nitrogen; NH 2 - ) 3 Little Blackwater River at Maple Dam Rd. near Cambridge, Md. ------25 49 54 31 63 63 43 14 34 25 18 40 Little Blackwater River at Stone Boundary Rd. near Cambridge, Md. CaCO Little Blackwater tributary at Stone Boundary Rd. near Cambridge, Md. Alkalin (mg/L as ity, field, ity, dissolved - ) 3 ------26.0 41.7 10.0 38.6 66.2 46.1 14.5 92.8 32.0 36.6 17.2 24.7 18.2 12.0 35.4 , calcium carbonate; SiO CaCO ity, lab, ity, 3 Alkalin (mg/L as dissolved ) 3 -- -- 26.5 48.8 10.4 49.1 31.5 34.7 66.2 67.0 44.1 15.2 18.2 89.8 31.8 27.2 35.7 17.5 24.7 18.5 38.9 20.2 33.8 Acid- CaCO (mg/L as lab, total capacity, capacity, neutralizing Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 12/06/2006 03/13/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 12/06/2006 12/06/2006 03/13/2007 04/16/2007 10/29/2007 06/10/2008 06/10/2008 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008

------0.76 1.26 1.07 0.64 0.94 1.53 0.99 1.80 1.85 0.89 0.87 0.74 0.96 3.00 1.27 2.05 2.00 total nitrogen, Ammonia (mg/L as N) plus organic ------11 30 46 30 12 66 32 46 20 24 20 20 20 total 158 <20 <10 <10 (mg/L) Residue, Residue,

, square miles; mm Hg, 2 ------88.7 97.1 87.2 122 155 191 174 106 E62.2 E52.7 E78.5 E46.3 (mg/L) sum of E119 E121 E122 E227 Residue, dissolved, E1,043 constituents 9.9 6.8 6.2 9.4 8.6 6.8 7.1 11.7 11.5 29.4 26.0 39.6 58.7 29.4 30.1 23.5 10.9 24.4 31.9 66.1 (mg/L) Sulfate, dissolved ) 2 2.78 4.47 4.36 3.18 4.06 0.53 5.54 6.45 4.46 1.89 3.55 2.39 5.83 7.41 7.50 SiO Silica, 10.06 18.79 15.72 10.59 14.91 (mg/L as dissolved , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3 0.26 0.16 0.18 0.19 0.33 0.16 0.15 0.15 0.21 0.12 0.12 0.14 0.22 0.13 0.17 0.16 E.074 E.074 E.077 E.073 (mg/L) Fluoride, dissolved , nitrite; NO 2 -- 5.3 6.1 8.3 5.6 14.6 13.4 21.4 37.0 16.4 12.4 25.9 24.0 25.9 22.5 23.3 27.4 15.5 (mg/L) 105 576 Chloride, dissolved dissolved , ammonia; NO 4 ------0.029 1.828 (mg/L) Bromide, dissolved

, falling; ND, no data] ------63 50 41 50 42 39 30 48 field, (mg/L) 113 dissolved Maple Dam Branch at Rt. 16 Cambridge, Md. Bicarbonate, , silicate; N, nitrogen; NH 2 Little Blackwater River tributary near Cambridge, Md. - ) 3 ------52 41 34 93 41 34 32 25 40 CaCO Alkalin (mg/L as ity, field, ity, dissolved

- ) 3 ------55.0 26.1 43.4 32.9 19.1 53.8 36.5 23.4 33.1 26.9 17.9 37.5 , calcium carbonate; SiO CaCO ity, lab, ity, 3 Alkalin (mg/L as dissolved

) 3 -- -- 53.5 26.0 44.3 33.4 19.7 42.8 54.3 27.0 34.1 23.7 33.2 27.2 18.7 37.3 22.5 37.2 37.0 Acid- CaCO 101.1 (mg/L as lab, total capacity, capacity, neutralizing Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/13/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 06/10/2008

-- -- total 2.45 1.61 1.41 1.13 1.36 4.26 2.35 1.75 3.64 2.90 2.65 1.47 2.70 5.58 2.40 2.74 nitrogen, Ammonia (mg/L as N) plus organic -- -- 22 15 98 62 40 32 82 45 92 24 total 200 100 <20 <20 E23.3 E36.7 (mg/L) Residue, Residue,

, square miles; mm Hg, 2 -- -- 94.3 77.8 113 148 251 358 E41.1 E92.9 (mg/L) sum of E120 E751 E273 Residue, dissolved, E2,160 E3,260 E1,470 E3,720 E8,810 constituents 4.4 9.3 7.6 7.4 23.0 36.0 12.8 17.6 30.1 83.2 23.6 30.9 13.8 (mg/L) 611.5 103.4 219.5 261.5 261.0 Sulfate, dissolved ) 2 SiO 0.77 2.64 4.79 4.50 2.91 4.86 4.05 3.26 5.92 3.98 0.84 9.88 1.85 2.24 5.49 5.60 0.26 Silica, 13.27 (mg/L as dissolved , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3 0.17 0.21 0.13 0.12 0.13 0.11 0.23 0.14 0.15 0.25 0.15 0.14 0.12 0.10 0.31 0.30 0.34 E.063 (mg/L) Fluoride, dissolved , nitrite; NO 2 7.5 55.6 41.1 36.4 28.9 22.2 23.8 -- 629 122 431 821 174 131 (mg/L) 1,256 1,837 2,101 4,906 Chloride, dissolved dissolved , ammonia; NO 4 ------4.076 (mg/L) 16.395 Bromide, dissolved

, falling; ND, no data] ------42 36 19 24 31 51 39 23 37 67 field, (mg/L) Little Blackwater River near Seward, Md. dissolved Bicarbonate, , silicate; N, nitrogen; NH 2 - ) Little Blackwater River near Cambridge, Md. gaging station 3 ------35 30 16 20 26 42 32 19 30 55 CaCO Alkalin (mg/L as ity, field, ity, dissolved - ) 3 ------8.2 37.6 30.8 32.5 18.3 33.4 44.7 52.1 35.8 17.8 13.5 , calcium carbonate; SiO CaCO ity, lab, ity, 3 Alkalin (mg/L as dissolved ) 3 -- 9.0 22.4 37.5 30.4 32.6 18.6 28.4 31.4 33.7 50.2 55.3 33.3 17.4 12.2 41.5 42.0 71.3 Acid- CaCO (mg/L as lab, total capacity, capacity, neutralizing Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 07/10/2007 10/29/2007

-- -- total 2.22 2.95 1.93 1.98 3.27 2.41 1.87 3.08 nitrogen, Ammonia (mg/L as N) plus organic plus -- -- 26 48 13 48 32 62 total 330 E46.0 (mg/L) Residue,

, square miles; mm Hg, 2 -- -- E140 E901 (mg/L) sum of Residue, E7,180 E2,680 E2,490 E1,360 E7,330 dissolved, E10,500 constituents 18.3 56.0 (mg/L) 680.6 692.0 514.0 167.5 165.4 109.2 583.6 738.1 Sulfate, dissolved ) 2 SiO 0.52 0.40 2.01 1.38 4.35 1.70 1.99 1.15 0.63 <.20 Silica, (mg/L as dissolved , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3 0.37 0.38 0.35 0.19 0.21 0.15 0.40 0.35 0.23 E.099 (mg/L) Fluoride, dissolved , nitrite; NO 2 57.6 750 479 (mg/L) 1,411 4,974 5,058 4,099 1,522 4,094 5,874 Chloride, dissolved , ammonia; NO 4 ------(mg/L) 19.525 Bromide, dissolved

, falling; ND, no data] ------64 51 27 59 77 field, (mg/L) dissolved Bicarbonate, , silicate; N, nitrogen; NH 2 - ) 3 ------53 42 23 48.3 63 CaCO Alkalin (mg/L as ity, field, ity, dissolved Little Blackwater River at Seward, Md. gaging station (at Key Wallace Drive) Little Blackwater River at Seward, Md. gaging station (at Key Wallace - ) 3 ------56.9 51.9 43.9 26.1 14.9 48.6 , calcium carbonate; SiO CaCO ity, lab, ity, 3 Alkalin (mg/L as dissolved ) 3 -- -- 58.5 56.7 44.4 24.5 12.3 46.9 72.3 51.1 Acid- CaCO (mg/L as lab, total capacity, capacity, neutralizing Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 06/22/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008

------total 1.274 0.931 1.362 1.79 1.21 1.53 0.874 4.83 0.973 E.768 (mg/L) E1.10 E1.80 E3.16 E2.56 Total nitrogen, Total

+N), 4 , square miles; mm Hg, +NH 2 3 1.34 0.98 1.28 3.83 1.79 2.40 1.25 1.21 1.05 1.53 0.80 1.69 2.08 1.40 2.63 1.70 0.97 0.96 1.04 4.84 3.06 1.00 1.98 (mg/L) +NO 2 determined Total nitrogen Total (NO dissolved, analytically

------total (mg/L) 0.901 1.112 1.819 1.505 0.947 2.07 0.882 1.73 1.053 0.823 1.057 1.325 0.867 E.803 Organic nitrogen, E1.39 E2.82 E2.06 , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3 -- 0.003 0.007 0.003 0.006 0.003 0.010 0.003 0.004 0.004 0.002 0.064 0.004 0.005 0.005 0.003 0.005 0.012 0.020 0.006 0.006 <.008 Nitrite, E.0018 dissolved (mg/L as N) , nitrite; NO 2 -- -- (mg/L) 0.011 0.022 0.011 0.021 0.011 0.034 0.009 0.013 0.014 0.007 0.209 0.012 0.015 0.018 0.011 0.016 0.039 0.067 0.02 0.019 E.006 Nitrite, dissolved , ammonia; NO 4 ------0.086 0.168 0.068 2.307 0.038 0.203 0.093 0.165 0.341 0.275 E.017 E.025 E.040 E.023 Nitrate, dissolved (mg/L as N) , falling; ND, no data] ------0.379 0.746 0.301 0.17 0.897 0.41 0.732 1.508 1.218 (mg/L) E.074 E.109 E.178 E.101 Nitrate, 10.214 dissolved Little Blackwater River near Christs Rock, Md. , silicate; N, nitrogen; NH 2 Little Blackwater River at Maple Dam Rd. near Cambridge, Md. Little Blackwater River at Stone Boundary Rd. near Cambridge, Md. 0.089 0.175 0.072 2.371 0.042 0.208 0.096 0.17 0.361 0.281 0.28 Nitrate <.04 <.060 <.060 <.060 <.060 <.060 <.060 <.04 E.052 E.029 E.020 E.031 Little Blackwater tributary at Stone Boundary Rd. near Cambridge, Md. dissolved (mg/L as N) plus nitrite, 0.064 0.247 0.301 0.338 0.198 0.163 0.069 0.403 0.072 0.365 0.083 0.061 0.048 1.009 0.102 0.337 0.103 0.101 , calcium carbonate; SiO <.04 <.04 <.02 <.02 E.017 3 dissolved Ammonia, (mg/L as N) ) 4 ------NH 0.11 0.08 0.06 1.30 0.13 0.43 0.13 0.08 0.32 0.39 0.44 0.26 0.21 0.09 0.52 0.09 0.47 E.022 (mg/L as dissolved Ammonia, Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 12/06/2006 03/13/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 12/06/2006 12/06/2006 03/13/2007 04/16/2007 10/29/2007 06/10/2008 06/10/2008 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008

------0.819 1.59 1.372 0.933 1.14 1.2 1.11 E.932 E.907 total (mg/L) E1.83 E1.30 Total nitrogen, Total

, square miles; mm Hg, 2 1.11 3.07 1.14 1.48 1.35 0.87 1.16 1.70 1.16 2.12 1.33 1.61 2.02 1.05 0.81 0.74 2.66 1.33 1.89 2.07 (mg/L) determined Total nitrogen Total (NO2+NO3+NH4+N), dissolved, analytically

------total 1.031 1.013 0.558 0.949 1.454 0.823 1.667 0.924 1.73 E.663 (mg/L) Organic E1.76 E1.254 nitrogen, , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3 0.004 0.003 0.008 0.007 0.004 0.004 0.002 0.010 0.005 0.003 0.003 0.005 0.005 0.003 0.008 0.008 <.006 <.008 E.0013 E.0019 Nitrite, dissolved (mg/L as N) , nitrite; NO 2 ------0.012 0.008 0.025 0.022 0.014 0.014 0.007 0.033 0.017 0.009 0.008 0.017 0.017 0.01 0.026 (mg/L) E.004 E.006 Nitrite, dissolved , ammonia; NO 4 ------0.057 0.327 0.295 0.286 0.187 0.208 0.146 E.036 E.035 E.032 Nitrate, dissolved (mg/L as N) , falling; ND, no data] ------0.255 1.449 1.307 1.265 0.826 0.921 0.646 (mg/L) E.161 E.154 E.141 Nitrate, dissolved Maple Dam Branch at Rt. 16 Cambridge, Md. , silicate; N, nitrogen; NH 2 Little Blackwater River tributary near Cambridge, Md. 0.06 0.335 0.302 0.29 0.191 0.218 0.151 <.060 <.060 <.060 <.060 <.060 <.060 <.060 <.04 <.04 E.034 E.039 E.040 E.035 Nitrate dissolved (mg/L as N) plus nitrite, , calcium carbonate; SiO 0.039 0.047 0.032 0.021 0.021 0.073 0.119 0.354 0.466 0.178 0.146 0.033 0.076 0.320 0.349 <.04 <.04 <.02 <.02 <.02 3 dissolved Ammonia, (mg/L as N) ) 4 ------0.05 0.06 0.04 0.03 0.03 0.10 0.15 0.46 0.60 0.23 0.19 0.04 0.10 0.41 NH (mg/L as dissolved Ammonia, Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/13/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 06/10/2008

------1.68 1.74 2.74 2.81 total (mg/L) E1.45 E2.38 E2.77 Total nitrogen, Total

+N), 4 , square miles; mm Hg, +NH 2 3 1.88 4.33 2.28 1.70 1.44 1.34 2.02 4.56 2.51 1.71 3.56 3.44 2.33 2.00 4.59 2.81 mg/L) +NO 2 determined Total nitrogen Total (NO dissolved, analytically

------2.439 1.078 1.574 4.228 3.615 1.695 4.296 total (mg/L) E1.181 E2.419 E1.75 E2.901 E2.035 Organic nitrogen, , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3 0.002 0.004 0.007 0.003 0.014 0.004 0.003 0.014 0.008 0.008 <.008 <.002 E.0014 E.0017 E.0013 E.0016 Nitrite, dissolved (mg/L as N) , nitrite; NO 2 -- -- 0.007 0.013 0.022 0.011 0.046 0.012 0.01 0.047 0.026 0.026 E.005 E.006 E.004 E.005 (mg/L) Nitrite, dissolved , ammonia; NO 4 ------0.069 0.365 0.073 0.103 E.036 E.025 E.024 Nitrate, dissolved (mg/L as N) , falling; ND, no data] ------0.306 1.615 0.321 0.456 (mg/L) E.161 E.113 E.106 Nitrate, Little Blackwater River near Seward, Md. dissolved , silicate; N, nitrogen; NH 2 Little Blackwater River near Cambridge, Md. gaging station 0.073 0.379 0.087 0.111 <.060 <.060 <.060 <.060 <.060 <.04 <.060 <.060 <.060 E.043 E.029 E.032 Nitrate dissolved (mg/L as N) plus nitrite, 0.010 0.012 0.261 0.047 0.068 0.031 0.088 0.024 0.543 0.180 0.774 <.04 <.04 <.02 , calcium carbonate; SiO E.013 E.028 3 dissolved Ammonia, (mg/L as N) ) 4 ------NH 0.01 0.02 0.34 0.06 0.09 0.04 0.11 0.03 0.70 0.23 1.00 E.02 E.036 (mg/L as dissolved Ammonia, Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 10/29/2007

------3.01 3.51 total (mg/L) E1.98 E1.89 Total nitrogen, Total

+N), 4 , square miles; mm Hg, +NH 2 3 2.06 2.07 1.89 3.14 1.96 2.22 6.71 2.36 2.14 3.21 (mg/L) +NO 2 determined Total nitrogen Total (NO dissolved, analytically

------6.218 2.349 total (mg/L) E2.217 E1.726 E1.975 E1.726 E3.077 Organic nitrogen, , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3 0.002 0.007 0.013 0.005 0.003 <.002 E.0014 E.0013 E.0015 E.0014 Nitrite, dissolved, (mg/L as N) , nitrite; NO 2 -- 0.007 0.023 0.041 0.016 0.009 E.005 E.004 E.005 E.004 (mg/L) Nitrite, dissolved , ammonia; NO 4 ------0.063 0.228 E.046 E.019 Nitrate, dissolved (mg/L as N) , falling; ND, no data] ------0.278 1.011 (mg/L) E.204 E.085 Nitrate, dissolved , silicate; N, nitrogen; NH 2 0.065 0.241 Nitrate <.060 <.060 <.060 <.060 <.060 <.04 E.053 E.024 dissolved (mg/L as N) plus nitrite, Little Blackwater River at Seward, Md. gaging station (at Key Wallace Drive) Little Blackwater River at Seward, Md. gaging station (at Key Wallace 0.021 0.022 0.231 0.248 0.062 0.412 <.04 E.028 E.011 E.015 , calcium carbonate; SiO 3 dissolved Ammonia, (mg/L as N) ) 4 -- NH 0.03 0.03 0.30 0.32 0.08 0.53 E.036 E.015 E.020 (mg/L as dissolved Ammonia, Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 06/22/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008

5.0 2.7 8.7 3.4 1.7 0.8 0.1 3.4 2.4 5.3 2.1 7.5 2.2 7.8 3.2 3.6 5.0 5.4 4.6 2.4 7.2 10.9 -15.4 balance Cation/anion (% difference) (% (µg/L) 92.3 37.8 69.5 77.2 77.1 14.6 10.1 80.4 33.1 26.3 31.8 43.9 149.9 361.6 452.3 145.2 586.9 374.4 343.1 154.9 225.2 317.3 500.0 dissolved Manganese, , square miles; mm Hg, 2

383 543 591 292 405 370 514 312 407 785 394 402 515 343 797 713 Iron, (µg/L) 1,411 4,412 2,860 1,815 1,474 1,069 2,340 dissolved

-- -- 9.2 total, 26.4 22.4 22.7 28.7 15.4 44.9 16.3 16.2 17.2 23.7 30.3 22.2 15.5 25.0 22.4 21.4 34.6 19.3 34.8 (mg/L) carbon, Organic E14.8

, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3 -- -- 11.9 11.3 11.2 21.3 16.6 22.0 21.0 12.5 38.4 12.0 13.3 14.0 22.0 28.7 17.1 22.1 18.9 17.3 22.8 13.9 27.3 (mg/L) carbon, Organic dissolved, , nitrite; NO 2

-- 0 0 0.001 0 0 0 0 0 0 0 0 0.001 0 0.001 0 0 0 0 0.001 0 0.001 0.00 total, (mg/L) , ammonia; NO calculated 4 Hydrogen ion,

, falling; ND, no data] total 0.274 0.219 0.232 1.197 0.647 0.865 0.298 0.295 0.226 0.302 0.166 0.587 0.972 0.362 0.849 0.762 0.275 0.304 0.150 0.599 0.856 0.221 0.999 (mg/L as P) Phosphorus, Little Blackwater River near Christs Rock, Md. , silicate; N, nitrogen; NH 2

Little Blackwater River at Maple Dam Rd. near Cambridge, Md. Little Blackwater River at Stone Boundary Rd. near Cambridge, Md. Little Blackwater tributary at Stone Boundary Rd. near Cambridge, Md. 0.067 0.012 0.101 0.162 0.368 0.317 0.021 0.021 0.019 0.084 0.061 0.230 0.355 0.156 0.216 0.482 0.154 0.186 0.061 0.134 0.346 0.077 0.530 dissolved (mg/L as P) Orthophosphate, , calcium carbonate; SiO 3

-- (mg/L) 0.206 0.037 0.31 0.496 1.13 0.971 0.066 0.057 0.257 0.186 0.705 1.09 0.478 0.662 1.48 0.472 0.571 0.187 0.41 1.06 0.235 1.62 dissolved Orthophosphate, Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 12/06/2006 03/13/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 12/06/2006 12/06/2006 03/13/2007 04/16/2007 10/29/2007 06/10/2008 06/10/2008 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008

- -- -- 3.9 2.6 4.4 3.3 0.7 1.2 4.7 1.6 3.3 2.6 3.4 2.4 4.5 7.1 -0.1 -2.5 -0.1 -1.1 ence) balance (% differ Cation/anion (µg/L) 95.5 37.3 59.0 71.4 51.0 55.1 73.9 23.6 259.1 203.3 212.3 174.7 147.4 334.0 274.1 162.8 285 663.0 371 353 dissolved Manganese, , square miles; mm Hg, 2

56 97 64 80 Iron, 511 121 613 468 316 956 379 245 238 218 420 (µg/L) 1,480 1,049 1,070 1,870 2,000 dissolved

------8.2 8.8 7.4 total, 12.8 13.2 13.9 15.2 25.2 14.0 14.3 32.0 15.3 30.7 32.2 (mg/L) carbon, Organic E16.4 E15.3

, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3 ------6.4 8.9 7.5 6.6 (mg/L) 11.9 10.6 15.3 13.3 13.2 18.1 12.1 12.3 21.8 13.0 22.8 23.4 carbon, Organic dissolved , nitrite; NO 2

-- 0 0 0 0 0 0 0 0 0.00 0 0.001 0 0 0 0 0 0 0.001 0.00 total, (mg/L) , ammonia; NO calculated 4 Hydrogen ion,

, falling; ND, no data] total 0.480 0.235 0.544 0.205 0.108 0.252 0.465 0.267 0.407 0.362 0.881 0.830 0.450 0.224 0.123 0.261 0.749 0.354 0.930 0.990 (mg/L as P) Phosphorus, Maple Dam Branch at Rt. 16 Cambridge, Md. , silicate; N, nitrogen; NH 2 Little Blackwater River tributary near Cambridge, Md.

0.010 0.009 0.378 0.018 0.010 0.064 0.031 0.084 0.107 0.175 0.587 0.444 0.294 0.054 0.031 0.095 0.336 0.044 0.668 0.680 dissolved (mg/L as P) Orthophosphate, , calcium carbonate; SiO 3

-- (mg/L) 0.03 0.028 1.16 0.055 0.03 0.197 0.094 0.257 0.33 0.537 1.8 1.36 0.903 0.165 0.094 0.291 1.03 0.134 2.05 dissolved Orthophosphate, Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/13/2007 04/16/2007 7/10/2007 10/29/2007 06/10/2008 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 06/10/2008

- 2.4 2.5 4.3 5.4 7.8 5.5 0.7 4.5 0.2 -0.3 -2.8 -2.5 -2.7 -2.0 -1.9 -0.8 -2.3 -2.3 ence) balance (% differ Cation/anion 3.4 3.6 6.2 11.5 95.3 79.8 90.1 64.0 43.5 30.0 27.3 10.9 119 382 129 777 198 322 (µg/L) dissolved Manganese, , square miles; mm Hg, 2

41 Iron, 119 484 439 498 842 455 549 386 299 380 203 271 <30 <30 E21.6 (µg/L) <120 1,480 dissolved

-- -- total, (mg/L) carbon, 25.0 25.4 26.3 18.0 39.5 28.5 29.7 28.1 28.8 29.7 21.6 47.2 35.2 35.7 24.1 Organic E25.6

, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P, 3 -- -- 15.6 14.3 20.8 16.1 18.7 23.1 16.2 21.0 16.0 14.8 18.1 15.3 16.8 22.4 24.4 20.0 (mg/L) carbon, Organic dissolved , nitrite; NO 2

-- 0 0.002 0 0 0 0 0.001 0 0 0.00 0 0 0 0 0 0 0 total, (mg/L) , ammonia; NO calculated 4 Hydrogen ion,

, falling; ND, no data] total 0.351 0.591 0.650 0.410 0.452 0.185 0.369 0.586 0.344 0.745 0.307 0.441 0.372 0.231 0.717 0.730 0.720 0.194 Little Blackwater River near Seward, Md. (mg/L as P) Phosphorus, , silicate; N, nitrogen; NH 2 Little Blackwater River near Cambridge, Md. gaging station

0.072 0.049 0.372 0.195 0.265 0.042 0.062 0.171 0.031 0.527 0.009 0.042 0.144 0.011 0.091 0.273 0.295 0.057 dissolved (mg/L as P) Orthophosphate, , calcium carbonate; SiO 3

(mg/L) 0.221 0.149 1.14 0.599 0.814 0.129 0.192 0.526 0.095 1.62 0.028 0.13 0.443 0.034 0.278 0.837 0.176 dissolved Orthophosphate, Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 03/16/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 07/10/2007 10/29/2007

- 2.0 -4.7 -2.8 -3.2 -2.6 -3.0 -2.2 -2.0 -1.2 -0.4 ence) balance (% differ Cation/anion 6.8 7.0 9.5 6.5 (µg/L) 51.8 38.8 36.5 75.4 <9.0 104 dissolved , square miles; mm Hg, 2 Manganese,

21 96 Iron, 112 289 299 <60 <60 <90 <60 (µg/L) <120 dissolved

-- -- total, (mg/L) 21.6 23.9 23.8 23.9 17.7 39.2 carbon, Organic E25.8 E66.6 , nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological , nitrate; P,

3 -- -- 13.9 13.7 14.3 12.9 17.3 15.4 14.8 21.1 (mg/L) carbon, Organic dissolved , nitrite; NO 2

-- 0.006 0 0 0 0 0 0 0 0 total, (mg/L) , ammonia; NO 4 calculated Hydrogen ion,

, falling; ND, no data] total 0.156 0.140 0.094 0.316 0.184 0.200 0.848 0.186 0.128 0.587 (mg/L as P) Phosphorus, , silicate; N, nitrogen; NH 2

Little Blackwater River at Seward, Md. gaging station (at Key Wallace Drive) Little Blackwater River at Seward, Md. gaging station (at Key Wallace 0.009 0.132 0.012 0.012 0.262 E.004 E.003 E.005 E.004 E.005 dissolved (mg/L as P) Orthophosphate, , calcium carbonate; SiO 3

(mg/L) 0.027 0.404 0.037 0.038 0.803 E.013 E.010 E.015 E.012 E.017 dissolved Orthophosphate, Date Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, 06/22/2006 06/22/2006 09/13/2006 10/06/2006 12/06/2006 03/12/2007 04/16/2007 07/10/2007 10/29/2007 06/10/2008

USGS station number Appendix 2. [ft, feet; ft millimeters mercury; --, data not available; CaCO Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F 01490140 01490140 01490140 01490140 01490140 01490140 01490140 01490140 01490140 01490140 Appendixes 1–8 57 - - - - ne gen ------carb sium Total Total Aldi Mag nitro (µg/L) (mg/L) (mg/L) <.014 <.020 <.020 <.020 <.06 <.12 <.12 ------Total Total 0.1 0.08 0.05 <.06 <.06 <.060 <.060 (µg/L) E.02 E.03 (mg/L) (mg/L) Calcium nitrogen Aldicarb sulfoxide

------rus total <.008 <.008 <.008 <.08 <.08 (µg/L) (mg/L) (mg/L) sulfone Residue, Aldicarb Phospho <10 ------P) <10 <.006 <.006 <.006 <.006 <.006 <.006 phosphate (µg/L) (mg/L) Ortho Residue (mg/L as Alachlor - N) ------(%) d10 116 123 rfen <.002 <.002 <.002 <.002 <.040 <.040 (µg/L) Nitrite Acifluo (mg/L as Diazinon- 2 - +NO N) 3 ------(%) 13C 87.2 81.8 Ace (µg/L) <.06 <.04 <.04 <.04 <.006 <.006 tochlor NO (mg/L as Caffeine- -

- -- -- N) ran (%) -- -- 85.3 94.2 3-Hy droxy (µg/L) <.020 <.020 <.020 <.020 <.040 <.040 Barban (mg/L as carbofu Ammonia ------N) +orgN (%) 113 3 105 0.49 <.14 <.14 <.040 <.040 OIET (µg/L) (mg/L as a-HCH-d6 NH ------(%) <.18 <.18 <.18 <.18 <.08 <.08 CEAT (µg/L) 89.1 77.7 (mg/L) 2,4,5-T Sulfate

-- -- 6 4 <.2 <.2 <.02 <.014 <.014 E.1 CIAT <8 <8 tance (µg/L) Silica (mg/L) (µS/cm) conduc- Specific 3 ------<5 E4 E4 1230 1234 1500 1023 2,4-D ester <.040 <.040 (µg/L) CaCO (mg/L) methyl Sample start time Date <.20 <.12 <.12 <.12 <.2 <.4 <.4 <.4 (µg/L) (mg/L) Sodium 03/12/2007 06/09/2008 06/09/2008 10/30/2007 Manganese

<.04 <.02 <.02 Iron Md. E.01 Little Local (µg/L) (mg/L) <6 <8 <8 <8 River at Seward, identifier DO Cd 58 DO Dd 12 DO Dd 13 Potassium Blackwater Concentrations of inorganic and organic constituents in equipment blanks, Little Blackwater River watershed, Dorchester County, Maryland, 2007–08. Concentrations of inorganic and organic constituents in equipment blanks, Little Blackwater River watershed, Dorchester County,

Date Date 1490140 03/12/2007 06/09/2008 06/09/2008 10/30/2007 03/12/2007 06/09/2008 06/09/2008 10/30/2007 Station number 382718076062001 382718076062002 383122076055703 Appendix 3. —Continued °C, degrees Celsius; µS/cm, microsiemens per centimeter at 25°C; %, percent; µg/L, micrograms liter; <, less than; --, data not available; E, estimated] [mg/L, milligrams per liter, 58 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 ------Di ME mid Ne ben ------Lin ram dane Chlo (µg/L) (µg/L) (µg/L) (µg/L) buron <.10 <.10 <.04 <.04 <.006 <.006 <.02 <.02 phena ------ran <.020 <.020 <.04 <.04 <.018 <.018 (µg/L) (µg/L) (µg/L) (µg/L) <.060 <.060 amide Imida- cloprid Dinoseb Naprop Carbofu ------pyr ran urea <.020 <.020 <.009 <.009 <.04 <.04 <.12 <.12 (µg/L) (µg/L) (µg/L) (µg/L) phenyl) Dieldrin Carbofu N’methyl- Imazetha N(4Chloro- 2 ------quin prop <.060 <.060 <.02 <.02 <.04 <.04 <.002 <.002 (µg/L) (µg/L) (µg/L) (µg/L) Imaza- Dichlor- Dichlor- Molinate Carbaryl 1 ------<.04 <.04 <.04 <.04 <.010 <.010 <.14 <.14 (µg/L) (µg/L) (µg/L) (µg/L) furon- methyl Fonofos Metsul Dicamba Carbaryl ------turon (µg/L) (µg/L) (µg/L) (µg/L) <.002 <.002 <.005 <.005 <.04 <.04 <.012 <.012 Fluome Butylate Diazinon Metribuzin ------Bro (µg/L) (µg/L) (µg/L) (µg/L) pronil sulam Meto <.12 <.12 <.012 <.012 <.06 <.06 <.010 <.010 finylfi- Desul lachlor Flumet- moxynil ------<.02 <.02 <.029 <.029 <.020 <.020 <.008 <.008 (µg/L) (µg/L) (µg/L) (µg/L) amide Methyl Fipronil Desulfi Bromacil parathion nylfipronil ------<.04 <.04 <.003 <.003 <.024 <.024 <.120 <.120 (µg/L) (µg/L) (µg/L) (µg/L) DCPA DCPA sulfone Fipronil Bentazon Methomyl ------<.06 <.06 <.02 <.02 <.013 <.013 <.040 <.040 carb (µg/L) (µg/L) (µg/L) (µg/L) furon- methyl sulfide Fipronil Bensul Methio Dacthal monoacid - -Per ------EPTC <.120 <.120 <.010 <.010 <.002 <.002 <.016 <.016 (µg/L) (µg/L) (µg/L) (µg/L) methyl methrin cis Azinphos- Malathion ------<.007 <.007 <.005 <.005 <.04 <.04 <.060 <.060 (µg/L) (µg/L) (µg/L) (µg/L) Chlor- Diuron pyrifos Linuron Atrazine ------<.002 <.002 <.080 <.080 <.04 <.04 <.02 <.02 (µg/L) (µg/L) (µg/L) (µg/L) Linuron on-ethyl Disulfoton Chlorimur alpha-HCH Concentrations of inorganic and organic constituents in equipment blanks, Little Blackwater River watershed, Dorchester County, Maryland, 2007–08. Concentrations of inorganic and organic constituents in equipment blanks, Little Blackwater River watershed, Dorchester County,

Date Date Date Date 03/12/2007 06/09/2008 06/09/2008 10/30/2007 03/12/2007 06/09/2008 06/09/2008 10/30/2007 03/12/2007 06/09/2008 06/09/2008 10/30/2007 03/12/2007 06/09/2008 06/09/2008 10/30/2007 Appendix 3. —Continued °C, degrees Celsius; µS/cm, microsiemens per centimeter at 25°C; %, percent; µg/L, micrograms liter; <, less than; --, data not available; E, estimated] [mg/L, milligrams per liter, Appendixes 1–8 59 - - - Or ------con azole (µg/L) ganic Propi (mg/L) 0.6 <.04 <.04 carbon ------<.040 <.040 <.060 <.060 (µg/L) (µg/L) Caffeine Propham ------<.04 <.04 <.02 <.02 (µg/L) (µg/L) Sum 2,4-D Propargite + 2,4-D ME ------lin <.006 <.006 <.006 <.006 (µg/L) (µg/L) Triflura Propanil - lor ------<.006 <.006 <.08 <.08 (µg/L) (µg/L) Triclopyr Triclopyr Propach ------(µg/L) (µg/L) <.01 <.01 <.006 <.006 Triallate Triallate Prometon ------carb (µg/L) (µg/L) <.12 <.12 <.010 <.010 Thioben Picloram ------<.040 <.040 <.02 <.02 (µg/L) (µg/L) Phorate Terbufos Terbufos

2 ------<.012 <.012 <.040 <.040 (µg/L) (µg/L) Pendi methalin Terbacil

1 ------<.004 <.004 <.018 <.018 (µg/L) (µg/L) Terbacil Pebulate ------<.04 <.04 <.02 <.02 (µg/L) (µg/L) Siduron Oryzalin ------mide <.02 <.02 <.004 <.004 (µg/L) (µg/L) Propyza Norflurazon ------ron <.10 <.10 <.040 <.040 (µg/L) (µg/L) Propoxur Nicosulfu Concentrations of inorganic and organic constituents in equipment blanks, Little Blackwater River watershed, Dorchester County, Maryland, 2007–08. Concentrations of inorganic and organic constituents in equipment blanks, Little Blackwater River watershed, Dorchester County,

Date Date 03/12/2007 06/09/2008 06/09/2008 10/30/2007 03/12/2007 06/09/2008 06/09/2008 10/30/2007 Concentrations from high-performance liquid chromatography (HPLC). Concentrations from gas chromatography-mass spectrometry (GCMS). 1 2 Appendix 3. —Continued °C, degrees Celsius; µS/cm, microsiemens per centimeter at 25°C; %, percent; µg/L, micrograms liter; <, less than; --, data not available; E, estimated] [mg/L, milligrams per liter, 60 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland. Depth [feet below land surface (BLS)] Lithology Features Comments 0 LEGEND 0-0.5 Yellowish brown (10YR 5/4) f-vc subangular- subrounded quartz sand (roadfill) Silt and clay Silt 0.5-1.2 Very dark grayish brown (10YR 3/2) organic-rich silty clay. Small pods of dark gray (10YR 4/2) silt Sandy clay Peat 1.2-1.6 Gradual transition to black (10YR 4/2) peaty silt Coarse sand/ gravel 1.6-2.5 Very dark grayish brown (10YR 4/2) to Medium sand gray (10YR 5/1) organic-rich clay. Abundant 2 oxidized zones; detrital limonite? Fine sand and silt Clay 2.5-3.0 Gray (10YR 5/1) sandy (vf) clay. Abundant Burrows roots No data 3.0-3.9 Gray (10YR 5/1) to dark gray (10YR 4/1) silty vf-f sand. Granules common and less silt Iron stains/mottles toward base Wood fragments Shells/shell fragments 4 3.9-5.5 Light brownish gray (10YR 6/2) open- Pebbles work f-m angular-subangular quartz sand Roots

5.5-7.0 Color change to dark brown (10YR 3/3); appears stained by humate. Horizontally bedded and alternates between more brown and more gray colors 6

8 No recovery

9.3-10.0 Pebble gravel in a matrix of dark gray m sand fining upwards to dominantly m sand

10 10.0-14.7 Very dark gray (10YR 3/1) clayey silt. Large sand-filled burrows in upper ~5 in.

12 Appendixes 1–8 61

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Depth [feet below land surface (BLS)] Lithology Features Comments 12

14.7-15.0 Dark gray (2.5 Y 4/0) clayey silt. Large sand-filled burrows in upper ~.4 in. 15.0-15.2 Small lag of c sand to pea gravel composed of rounded-well rounded quartz and chert with silt between clasts 15.2-16.2 Dark gray (2.5Y 4/0) silty m-vc subangular-well rounded quartz sand and ~7% black chert. Several pea gravel clasts in lower ~.5 in.

16 16.2-16.4 Gravel lag composed of well-rounded quartz clasts up to 4 cm in diameter 16.4-17.0 Dark gray (2.5Y 4/0) silty m-vc subangular-well rounded quartz sand and ~7% black chert

17.0-18.0 Dark gray (2.5Y 4/0) heavily burrowed silt. Burrows filled with sand from above; also abundant macro organic fragments

18 18.0-20.0 Dark gray (2.5Y 4/0) silty clay with several accumulations of peaty material

20 20.0-22.6 Very dark gray (10YR 3/1) peaty silty clay (~30% peat)

22.6-24.0 Very dark gray (10YR 3/1) silty clay with ~15% peat

24 62 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Lithology Features Depth [feet below land surface (BLS)] Comments 24 24.0-24.4 Very dark gray clay with few small shell fragments near base

28 27.9-28.4 Black (10YR 2/1) peat

28.4-28.7 Dark gray (10YR 4/1) peaty silty clay 28.7-29.2 Gravel lag (to 28.9) composed of .4-1.2 in. well-rounded quartz and black chert with a matrix of grayish brown (2.5Y 5/2) silty f-vc subangular-well rounded quartz sand w/ few black chert fragments 29.2-44.3 Gray (5Y 4/1; more blue in upper ~7.0 ft) clay with abundant roots. ~2 in. concretion at 31 ft

36 Appendixes 1–8 63

36.1-44.0 Color varies to gray (10YR 5/1; 5Y 5/1) to dark gray (5Y 4/1)

44.3-45.0 Olive gray (5Y 4/2) clay

45.0-46.5 Olive gray (5Y 4/2) clay with abundant organics

46.5-47.8 Gray (5Y 5/1) clay. Silty near the middle of unit, and oxidized in lower ~10 in., possibly in association with small limonite concretions

47.8-49.6 Gray (5Y 5/1) silty f angular-subangular quartz sand with few mica flakes. Color changes to dark gray (5Y 4/1) at 48.5 ft 48 64 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Depth [feet below land surface (BLS)] Lithology Features Comments 48

49.6-64.8 Color changes to dark grayish brown (2.5Y 4/2) and silt disappears

60 Appendixes 1–8 65

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Lithology Depth [feet below land surface (BLS)] Features Comments 60

64.8-64.9 Gravel lag composed of rounded, but chipped, red-stained quartz pebbles, with a .8-in. clay lense directly underlying 64.9-65.4 Dark grayish brown (2.5Y 4/2) micaceous vf-f sand. No opaques

19.93-20.13 Dark gray (5Y 4/1 - 10YR 4/1) clay (alternates between more red and more green hues) with small vf sand lenses composed of above sand. Small light brownish gray (2.5Y 6/2) mud balls present from ~65.5 to 69.0 ft

72 66 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Lithology Features Depth [feet below land surface (BLS)] Comments 72

-reddish color fades and disappears here

79.2-84.0 Very dark grayish brown (10YR 3/2) clay with several vf sand stringers and numerous mud balls (”little white balls”)

84 Appendixes 1–8 67

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Lithology Depth [feet below land surface (BLS)] Features Comments 84 84.0-91.7 Dark gray (5Y 4/1) clay continues without sand, except that which fills burrows

-alternations between red and green reappears

91.7-92.0 Dark gray (5Y 4/1) heavily oxidized sandy clay - clayey vf-f angular-subangular quartz sand with minimal mica; small fragments of pectin shells near base 92 92.0-92.3 Dark grayish brown (2.5Y 4/2) vf-f angular-subangular quartz sand with minimal mica; micro and macro organics 92.3-96.0 Dark olive gray (2.5Y 3/2) vf-m angular-rounded quartz sand with minimal chert grains. Abundant pectin shell fragments down to 95.6 ft; potentially burrowed

96 68 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland. Core Section Depth [feet below land surface (BLS)] Lithology Features Comments 0 0-.70 Grayish brown peat rich in LEGEND grasses and roots with vf-m quartz sand and silt. Soil has a medium-thick platy structure Peat Clay with some silt .70-2.0 Gray vf sand with silt and traces of m-c sand, heavily mottled Medium sand Silt with some clay

Clay Coarse sand/ gravel 2 2.0-4.0 Gray vf sand and silt coarsening upwards to dominantly vf sand No data Fine sand and silt

Wood fragments Burrows

Pebbles Iron stains/mottles

4 4.0-4.5 Gray vf-m angular-well rounded sand coated with silt fining upwards to Roots Shells/shell fragments vf sand and silt

6 NO RECOVERY NO

7.4-9.3 Gray f-m subangular-well rounded quartz sand with evidence of redox features

9.3-10.0 Pebble gravel in a matrix of dark gray m sand fining upwards to dominantly m sand

10 10.0-10.7 Pebble gravel in a matrix of dark gray m sand fining upwards to m sand

10.7-11.5 Rounded-well rounded and flattened pebble gravel with interstitial dark gray subangular-well rounded vf-vc silt coated sand

11.5-11.8 Dark gray silty clay and vf sand mixed with vf-c sand fining up to dark gray clay with a pocket of vf-c sand, likely from sediment overloading 11.8-12.6 Dark gray clay with a pocket of f sand-pebbles, likely from sediment overloading 12 Appendixes 1–8 69

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Depth [feet below land surface (BLS)] Lithology Features Comments 12

12.6-12.9 Dark gray clay rich in root fragments;. This layer dries out much more quickly than the underlying clay; sharp boundary between them 12.9-17.7 Dark gray clay with a small amount of organic material and associated redox features. small roots observed in core interior

22.9-23.9 Dark gray clay continues with abundant oyster shell fragments (>60%) with no apparent preferred orientation

24 70 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Depth [feet below land surface (BLS)] Lithology Features Comments 24 23.9-24.4 Very dark gray clay with few small shell fragments near base

24.4-24.8 Dark gray clay with abundant oyster shell fragments (>60%) with no apparent preferred orientation 24.8-28.1 Very dark gray clay with abundant organic material and charcoal

28 28.1-28.2 Lense of angular-subangular vf-c sand 28.2-28.4 Black clay coarsening up to sandy peat

28.4-29.2 Black peat with charcoal fragments interrupted by a 1 cm sand lense of dark gray vf-vc subangular-well rounded sand

29.2-30.2 Black vf-vc subangular-rounded sand rich in opaque minerals and likely stained by humate. Small charcoal fragments present. Fine silt binds grains together

* 29.5-29.9 Very dark grayish brown 30 *29.9-30.2 Light gray-dark gray; sharp basal contact 30.2-31.0 Light gray vf-m angular-subrounded sand with sharp basal contact

31.0-31.2 Dark gray - gray clay with small non-extensive sand laminae

31.2-31.3 Dark gray angular-subrounded vf-f sand 31.3-31.33 Dark gray clay bed with two thin sand lenses 31.33-31.6 Dark gray angular-subrounded vf-f sand 31.6-31.7 Dark gray clay and vf-f sand alternating every 1/2 cm 31.7-31.8 Dark gray clay with small vertical sand inclusions, possibly from burrow infilling 32 31.8-32.3 Dark gray clay and light gray finely laminated vf-f sand alternating every .2-.8 in.

32.3-32.4 Light gray vf sand and silt; oxidized

*32.4-34.9 Missing 2.5’ of core according to labels on rods

34 DATA NO

34.9-35.1 Light gray vf sand and silt; oxidized 35.1-35.5 Dark gray clay with finely laminated beds of light gray sand; overall coarsening upward trend. Heavily oxidized disturbed laminae shows evidence of sediment loading 35.5-36.0 Dark gray with very thin (.25-.5 cm) fine sand & silt laminae

36 Appendixes 1–8 71

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Lithology Depth [feet below land surface (BLS)] Features Comments 36 36.0-36.1 Dark gray fine sand/silt 36.1-36.5 Dark gray clay with non-continuous sand pockets ~.4-.6 in. in diameter. Sharp basal contact 36.5-36.7 Dark gray sand bed with small interstitial clay pockets 36.7-36.9 Dark gray clay with .1-in. thick vf sand beds spaced 1.5 cm apart 36.9-37.2 Dark gray sand bed with coarse mottling (~.4 in.) 37.2-37.5 Dark gray clay with small vertical sand inclusions; likely infilled burrows 37.5-38.0 Discrete packages of dark gray clay alternating with dark gray sand with sharp contacts

38 38.0-38.4 Gray vf-f sand bed with a 1.5-cm clay horizon diagonally bedded

38.4-38.6 Dark gray clay with small sand pockets; overall fines up. Possible bivalve traces 38.6-39.0 Gray vf-f sand bed with slight fining upward trend and bioturbated (vertical oxidized zones)

39.0-39.3 Dark gray clay interfingering with/coarsening upward to vf-f sand

39.3-39.5 Dark gray clay 39.5-39.7 Discontinuous light gray vf-f sand locally pinching to 0 thickness surrounded by dark gray clay 39.7-39.9 Dark gray clay with vertical sand intrusions (filled burrows?) 40 39.9-40.1 Light gray vf-f sand 40.1-40.6 Gray clay that oxidizes quickly upon exposure; possible bivalve trace

40.6-41.0 Dark gray clay; massive

41.0-41.8 Dark gray f sand with possible bioturbation (discolored) bound by abrupt contacts

41.8-44.8 Very dark gray clay with repeating flasers of vf-f very dark gray sand 42

44.8-44.9 Dark gray vf-f sand

46 NO DATA- BETWEEN VIBRACORE AND B40 AND VIBRACORE BETWEEN DATA- NO

48 72 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Depth [feet below land surface (BLS)] Lithology Features Comments 48

52 NO DATA- BETWEEN VIBRACORE AND B40 AND VIBRACORE BETWEEN DATA- NO

55.0-60.0 Very dark gray (5Y 3/1) angular-rounded f quartz sand

*Begin B40 Auger Hole Data

60 Appendixes 1–8 73

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Depth [feet below land surface (BLS)] Lithology Features Comments 60

60.0-66.0 Very dark grayish brown (2.5Y 3/2) clay with vf-f quartz sand stringers (oxidized)

66.0-70.0 Very dark gray (5Y 3/1) clay with vf-f quartz sand stringers

70 70.0-72.0 Very dark gray (5Y 3/1) silty vf-f sand

72 74 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Depth [feet below land surface (BLS)] Lithology Features Comments 72 72.0-75.0 Very dark grayish brown (2.5Y 3/2) clay with abundant m-vc sand grains

75.0-77.0 Very dark grayish brown (2.5Y 3/2) clay

77.0-80.0 Dark gray (10YR 4/1) clay with small sand lenses/stringers

80 80.0-96.8 Very dark grayish brown (10YR 3/2) clay with several vf sand stringers and numerous mud concretions

84 Appendixes 1–8 75

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Lithology Depth [feet below land surface (BLS)] Features Comments 84

96.8-94.0 Dark gray (5Y 4/1) - very dark gray (5Y 3/1) clay

96 76 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued

Depth [feet below land surface (BLS)] Lithology Features Comments 96 94.0-99.0 Very dark gray (5Y 3/1) well-laminated silty vf sand

99.0-100.0 Black (5Y 2.5/2) vf sand

100

100.0-101.5 Very dark grayish brown (2.5Y 3/2) clay

101.5-103.0 Very dark grayish brown (2.5Y 3/2) well-laminated sand

102

103.0 Very dark grayish brown (2.5Y 3/2) clay 103 BOC Appendixes 1–8 77

Appendix 6. Lithologic and geophysical logs of DO Cd 58 core, Little Blackwater River watershed, Dorchester County, Maryland.

Depth [feet below land surface (BLS)] Gamma Log Lithology Description 0 API-GR 100 0 1.0-2.0 Plowed horizon

2.0-11.8 Silty vf sand transitioning to silty sand and gravel

*6.0-8.0 Possible limonite nodules oxidizing

10 11.8-12.0 Small pea gravel lag 12.0-12.4 Silty sand continues 12.4-16.0 Silty clay

16.0-18.5 Dark brown clay

18.5-19.5 Poorly sorted f-fc sand and granules 19.5-21.5 Dark brown clay continues 20 21.5-22.0 vf-m sand and silt 22.0-28.0 Brown clay rich in organics

28.0-43.0 Gray clay with variable organic content 30

43.0-50.0 Gray silty/sandy clay package

*Wet; Small aquifer in upper part

50 50.0-53.0 Open-work sand package rich in quartz and black chert

53.0-55.0 Brownish gray clay

55.0-89.5 Gray silty/sandy clay with large shell hash to 64.7 ft Diminishing shells 64.7-89.5 ft

90 78 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 7. Lithologic and geophysical logs of DO Cd 66 core, Little Blackwater River watershed, Dorchester County, Maryland.

ERN-4 Depth [feet below land surface (BLS)] GAMMA Lithology Description 0 API-GR 200 0 0-6” Black (10YR 2/1) plowed horizon 6”-2’4” Yellowish-grayish brown (10YR 6/2-5/6) locally oxidized, rooted, and burrowed silt. More oxidized towards the base 2’4”-4’9” Dark yellowish brown (10YR 3/4) diamict. Vf-f sand matrix with increasing amounts of floating pebbles towards the base. Pebbles are generally angular-well rounded quartz and chert. Several are tubular, a couple flattened. 4’9”-6’6” Dark grayish brown-v. dark grey (10YR 4/1-2) silty vf-f micaceous sand with several matrix supported granules and one 1-cm rounded quartz pebble. Upper ~8” mottled, several oxidized zones. 6’6”-9’1” Dark olive heavily burrowed silty clay and sand. Several .4-.6 in pebbles in matrix.

10 9’6”-11’10” Dark olive gray (5Y3/2) silty f-m sand with few clay rip-ups. Several small (<.5 cm) pebbles from 9’7”-9’9”. Fines increase at 11’10” (vf sand and clayey silt). 12’6”-14’3” : Unconformity lag; several large (.4-.2.75 in.) angular-rounded pebbles and many clay rip-ups.

14’3”-30’8” Gray (5YR 5.5/1) clay unit with many flaser beds begins (For details, see inset 1). * First occurence Pterocarya pollen grains; MIOCENE

20 Inset 1

30 30’8”-34’6” Very dark grayish brown (2.5Y3/2)-dark olive gray (5Y3/2) laminated and heavily burrowed vf sand and silty clay.

34’6”-36’10” Grayish brown (2.5Y 5/2) open work fine sand package. Angular quartz sand with ~5% unidentified opaques.

36’10”-47’2” Dark olive gray (5Y3/2) silty f sand. Heavily burrowed/bioturbated with burrows oxidizing upon exposure. Well-laminated unit with a couple of ~1-2” clay horizons around 40’. Fines increase to the base.

40 -41’6”-41’8.5” V. dark grayish brown (2.5Y3/2) well-sorted f quartz sand. Well-laminated and angular; possibly some small bits of charcoal.

47’2”-62’6” “Red clay” unit returns: V. dark grayish brown (2.5Y3/2) - dark grayish brown (10YR 4/2) silty clay. Heavily burrowed (filled with sand) with many flasers. Sand component is micaceous angular quartz (either rosy or stained) silty vf sand (for details, see inset 2). 50

Inset 2

62’6”-62’11” Sandy (f-m) silt with several floating angular-rounded granules (white and black quartz) 62’11”-64’2” Dark gray (5Y4/1) clay with floating granules and vf micaceous quartz sand flasers 64’2”-67’11.5” Olive gray (5Y5/2) silty vf-f sand and clay. Heavily bioturbated/burrowed

67’11.5”-68’5” vf-m angular-well rounded quartz sand with ~3% opaques and ~3% shell fragments in the sand fraction. Shell fragments appear at 68’ and remain minimal to 68’5”. Clay horizon from 68’3”-68’5”. Several sand-filled 70 burrows precipitating sulfates.

68’5”-75’11”* Dark grayish brown (2.5Y4/2) shell hash. Dense shell layer in silty vf sand. Shells include pectin, isognomen, barnacles, and more. (*missing 69’6”-74’6”; assume shell hash continues)

75’11”-79’6” Dark greyish brown (2.5Y4/2) angular vf-m massive sand. Shells are minimal, but few horizontally lying clams “float” in matrix.

79’6”-82’6” Dark grayish brown (2.5Y4/2) angular vf-m massive sand continues, with shell proportion increasing once again to 80 become a dense shell hash. Appendixes 1–8 79

Appendix 7. Lithologic and geophysical logs of DO Cd 66 core, Little Blackwater River watershed, Dorchester County, Maryland. —Continued Depth [feet below land surface (BLS)] GAMMA Lithology Description 0 API-GR 200 80 82’6”-89’6” Olive gray (5Y4/2) angular-subrounded m quartz sand with few clams and other bivalves in matrix suspension. Small clay films throughout.

89’6”-100’10”* Olive gray (5Y4/2) massive/bioturbated m quartz sand with minimal shells (*99’6”-100’10”. missing). 90

100’10”-104’6”* Olive gray (5Y4/2) m quartz sand with high proportion of shells. Appears fragmented; storm surge? 100 (*101’-104’6” missing)

104’6”-107’ Olive gray (5Y4.5/2) silty vf-f quartz sand with high proportion of shells. The fine fraction appears to be made up largely of ground-up shell material that fizzes violently with HCL. -Top ~3” indurated fossiliferous limestone clast (likely small portion of 101‘-104’6” interval).

107’-108’9” Dark gray (5Y4/1) f-m silty quartz sand with several shell fragments in suspension; mostly pectin and isognomen.

108’9”-113’6”* Grayish brown (2.5Y5/2) vf-f quartz sand with fewer shells. Some organic material (roots?) (*113’6”-115’6” missing)

110 -110’4”-111’6” ~50% shells with long axes in horizontal position. -111’6”-111’11” Open-work concentration of organics with oxidation stains and a couple of small pectin fragments.

113’6”-116’1” Brown (10YR4/3) Indurated zone; disaggregated shells. 116’1”-119’6” Olive gray (5Y4/2) f angular quartz sand with many large clams both stacked and in suspension in horizontal orientation. Indurated from 117’-117’8”; shells minimal below 118’4” 119’6”-123’8” Sand continues with increasing shell accumulation. Dense pectin and pearly isognomen.

120

123’8”-127’5” Dark greyish brown (2.5Y4/2) silty vf-f sand. Massive or structure destroyed by drilling. Shells minimal.

127’-129’6” Olive gray (5Y5/2) silty vf-f sand with variable induration. Generally well-laminated with bioturbation.

130

EXPLANATION

Pebbles Soft Sediment Deformation Sand

Silty clay and sand Burrows/Bioturbation Glauconite

Silty sand

Oxidation stain Shells/Shell Fragments Clay 80 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 7. Lithologic and geophysical logs of DO Cd 66 core, Little Blackwater River watershed, Dorchester County, Maryland. —Continued Depth [feet below land surface (BLS)] GAMMA Lithology Description 0 API-GR 200 14 14’3”-14’11” Gray (5YR5.5/1) clay with several small flasers.

14’11”-15’3” Dark grayish brown (2.5Y4/2) vf sand 15’3”-15’6” Heavily burrowed gray (5YR5.5/1) clay. ~2 cm burrows and many flaser beds 15’6”-16’11” Gray (5YR5.5/1) clay. ~2 cm burrows and many flaser beds. Large burrows drop out. 16

16’11”-17’3” Light olive brown (2.5Y5/4) well-laminated, vf, angular quartz sand. 17’3”-18’2” Interbedded clay and sand; sand has very clear laminae.

18 18’2”-19’5” Dark gray (5YR4/1) clay cyclically interrupted by oxidized silty vf sand beds.

19’5”-19’11.5” Light olive brown (2.5Y5/4) vf well-laminated sand. 19’11.5”-21’10.5” Dark gray (5YR4/1) clay with sand flasers throughout. 20

22 21’10.5”-22’9” Interbedded clay and sand on ~3’ intervals. Some charcoal bits at the base. Sand part is well laminated.

22’9”-26‘ Dark gray (5YR4/1) clay with multiple vf sand flasers and ~1” sand beds.

26 26‘-26’1” Dark olive gray (5Y3/2) angular-subrounded micaceous vf quartz sand. 26’1”-27’6” Clays and vf sands with soft-sediment deformation (due to drilling?)

27’6”-30’8” Dark gray (5YR4/1) clay. The most “pure” clay in the package; flasers throughout, but less common and smaller. Colors vary from above to grayish brown (2.5Y4/2). 28

30 Appendixes 1–8 81

Appendix 7. Lithologic and geophysical logs of DO Cd 66 core, Little Blackwater River watershed, Dorchester County, Maryland. —Continued Depth [feet below land surface (BLS)] GAMMA Lithology Description 0 API-GR 200 47 47’2”-51’6” Very dark grayish brown (2.5Y3/2) silty clay. Heavily burrowed, multiple flasers, two sand excursions.

54’6”-52’8” Very dark grayish brown (2.5Y3/2) vf sand and silt.

52’8”-54’1” Very dark grayish brown (10YR3/2) heavily burrowed clay. Filling sands 53 are micaceous angular quartz silty vf sand.

54’1”-54’8” Dark brown (10YR3/3) angular micaceous f sand excursion; possibly glauconitic.

54’8”-55’6” Very dark grayish brown (10YR3/2) clay with 2 small well-laminated silty f sand 55 beds.

55’6”-56’ Dark brown (10YR3/3) vf sand package. Micaceous quartz with possible charcoal in upper ~1”. 56’-57’6” Dominant clays and sands “swirled” together. Bioturbated? Soft sediment deformation? Disturbed by drilling?

57’6”-62’6” Brown (10YR4/3) clay with less sand/silt; also slightly less “red”. Few burrows.

63 82 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 8. 2-D resistivity survey along the Egypt Road well transect B-B', Little Blackwater River watershed, Dorchester County, Maryland. Prepared by USGS West Trenton Publishing Service Center. Edited by Valerie M. Gaine. Graphics and layout by Timothy W. Auer.

For additional information, contact: Director, MD-DE-DC Water Science Center U.S. Geological Survey 5522 Research Park Drive Baltimore, MD 21228 or visit our Web site at: http://md.water.usgs.gov Fleming, B.J., and others—Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09—Scientific Investigations Report 2011–5054 r Printed on recycled pape