ASSESSMENT AND COMPARISON OF TWO PHYTOREMEDIATION SYSTEMS
TREATING SLOW-MOVING GROUNDWATER PLUMES OF TCE
A thesis presented to
the faculty of
the College of Arts and Sciences of Ohio University
In partial fulfillment
of the requirements for the degree
Master of Science
Amy C. Lewis
June 2006
© 2006
Amy C. Lewis
All Rights Reserved
This thesis entitled
ASSESSMENT AND COMPARISON OF TWO PHYTOREMEDIATION SYSTEMS
TREATING SLOW-MOVING GROUNDWATER PLUMES OF TCE
by
AMY C. LEWIS
has been approved for
the Program of Environmental Studies
and the College of Arts and Sciences by
Guy Riefler
Assistant Professor of Civil Engineering
Benjamin M. Ogles
Dean, College of Arts and Sciences
Abstract
LEWIS, AMY C., M.S., June 2006. Environmental Studies
ASSESSMENT AND COMPARISON OF TWO PHYTOREMEDIATION SYSTEMS
TREATING SLOW-MOVING GROUNDWATER PLUMES OF TCE (158 pp.)
Director of Thesis: Guy Riefler
This study assessed the impact of the X-740 Phytoremediation System, located at
the Portsmouth Gaseous Diffusion Plant, on a TCE plume. Differences in planting
technique and tree species used at the site were analyzed. In addition, groundwater
uptake and TCE removal were determined. The X-740 Phytoremediation System was
planted in 1999 and was calculated over the following years. The phytoremediation
system was initially expected to take two years to reach maturity, however, the
groundwater data presented in this paper documents that actually it was four years before
the phytoremediation system began noticeably influencing the groundwater. The
phytoremediation system does not show a decrease in water elevations until 2003, even
though it was expected to have occurred in 2001 or 2002. Increased hydraulic gradient
across the site indicates by 2005 the system trees were extracting 75,000 gallons per day
(gpd) or 98 gpd per tree. The total mass of TCE in the phytoremediation area in 1999
was 425 g when compared to 2005 the TCE mass was 394 g showing a slight decrease particularity in the final two years of sampling. Furthermore, the TCE concentration is
demonstrating fluctuating results. During the growing season the TCE concentrations are lower than during the dormant season. This occurrence is also evident in the byproducts of TCE consistently from 2001 through 2005. BIOCHLOR simulations also indicate that
the TCE concentrations are below what would be expected due to natural attenuation.
The results of this evaluation indicate that the trees are having a positive effect on the groundwater at the X-740 Area, although the effect is slight and not apparent until the fourth year of growing. It is expected that TCE contaminant and removal will continue to improve as the trees mature.
Approved:
Guy Riefler
Assistant Professor of Civil Engineering
Acknowledgement
I would like to begin by clearly stating my involvement in the phytoremediation study at the Portsmouth Gaseous Diffusion Plant (PORTS) facility. I started working at
PORTS in June of 1999 as an intern for my undergraduate degree. In September I was hired full time after graduation. During the summer of 1999, the X-740
Phytoremediation Area was installed which I missed due to my hire date. I immediately began groundwater sampling for the contaminants of concern required by the Integrated
Groundwater Monitoring Plan (IGWMP). A total of 18 wells at the X-740 Area are sampled on a semiannual (twice a year) basis. In addition to collecting, I also evaluated the data in order to create isoconcentration and potentiometric surface maps which illustrate the flow of the groundwater as well as the plume migration. This allows the prediction of the effectiveness of the phytoremediation system pertaining to the groundwater flow and uptake by trees. I used this information to generate the visual extent of the contamination via the isoconcentration illustrations as well as the visual groundwater flow changes initiated by the phytoremediation system. Also, I monitored tree growth, health, and mortality rates, well casings, groundwater levels, and in-well pressure transducer/data loggers. All of these monitoring options were instituted to demonstrate that the phytoremediation system was working effectively. I compared the isoconcentration and potentiometric surface diagrams each quarter to the previous quarters, sequentially to illustrate the effects of the chosen remediation options.
In relation to the X-749 Phytoremediation Area, I acted as the Field Quality
Engineer during the installation of the project. In collaboration with a construction
business my company helped to install the X-749 Phytoremediation System in January of
2003. During the implementation my involvement included the daily field tasks of ensuring the trenches were aligned according to the drawings as well as excavated to the correct depth, the materials were the specified brand, the amended soils were mixed with the correct amount of each material such as peat moss, coarse sand, fertilizer, and lime, along with the proper thickness of sand in the trenches. When this phase was complete the installation of the tree species began. At this phase, my tasks included the assurance that the trees were the correct species, size, and planted according to drawings and specifications. I also ensured the total number of trees were planted according to the design, installation, and the total number of watering tubes were installed in relation to the total number of trees installed. Once this phase was completed, the monitoring phase began which included the extended version of the IGWMP (a total of 79 groundwater wells are sampled on a semiannual basis). Prior to this, the X-749 Area was monitored, however, not as extensively. Also, similar to the X-740 Phytoremediation Area, I conducted surveillance and maintenance inspections.
I have worked at the PORTS facility for over 6 years monitoring these areas as well as others. Some activities on-site require a two man crew, others do not. A total of five other individuals have assisted in portions of the data collection. I did not participate in the background data collection; although it will be used as a means of comparison.
My thesis will include the knowledge and experience I have gained during my professional career and monitoring data I collected during my employment. However, the evaluation and analysis of data that will be completed for this thesis results from my
individual academic research and goes well beyond what is required for my employment at PORTS.
Additionally, I would like to thank everyone involved for their time throughout my research. I would especially like to thank Dr. Guy Riefler for his efforts during my last months of research who offered guidance and direction in the completion of this paper. I would also like to thank Dr. Stuart and Dr. Miles for being members of my committee.
9
Table of Contents
Page
Abstract...... 4
Acknowledgement ...... 6
List of tables...... 11
List of figures...... 12
1.0 Trichloroethylene contamination...... 17 1.1 Trichloroethylene history...... 17 1.2 Public health effects...... 18 1.3 Regulations ...... 19
2.0 Phytoremediation...... 20 2.1 Plant selection ...... 21 2.2 Phytoremediation process ...... 22 2.3 Advantages...... 28 2.4 Disadvantages ...... 30 2.5 Economical benefits...... 31 2.6 Determinate factors of phytoremediation ...... 33 2.7 Evidence of TCE uptake ...... 34 2.8 Evidence of volatile organic compound (VOC) transpiration ...... 36 2.9 Evidence of VOC degradation...... 38 2.10 Evidence of groundwater uptake ...... 39 2.11 Implications for this study ...... 40
3.0 Site description ...... 41 3.1 Plant history ...... 41 3.2 Population distribution and site location...... 42 3.3 Site hydrology and geology ...... 45 3.4 X-740 Area...... 48 3.5 X-749/X-120 Area ...... 50
4.0 Remediation options ...... 52 4.1 X-740 Remedial Plan...... 52 4.2 X-749 Remedial Plan...... 54
5.0 Research question ...... 56 5.1 Tree growth and mortality rates...... 57 5.1.1 Planting methods...... 57 10
5.1.2 Impact pf planting method, TCE exposure, and species selection ...... 62 5.1.3 TCE accumulation in tree tissue ...... 70 5.2 Groundwater flow ...... 73 5.2.1 Depth to water...... 73 5.2.2 Groundwater flow potentiometric surface maps...... 78 5.2.3 Hydraulic gradient ...... 95 5.2.4 X-749 depth to water ...... 97 5.2.5 Hourly water level measurements...... 100 5.3 TCE groundwater plume...... 105 5.4 Total mass of TCE ...... 135 5.5 BIOCHLOR simulation ...... 138
6.0 Conclusions...... 150
7.0 Literature cited...... 155 11
List of Tables
Table Page
Table 2-1. Relation of plant species to specific contaminants...... 27
Table 2-2. A comparison of phytoremediation costs to standard technologies...... 32
Table 2-3. Estimated cost savings through the use of phytoremediation versus conventional treatment...... 33
Table 5-1. X-740 Area TCE concentrations in µg/L from third quarter 1997 through second quarter 2005...... 107
Table 5-2. X-740 Area 1,1-DCE concentrations in µg/L from third quarter 1997 through second quarter 2005...... 108
Table 5-3. X-740 Area cis-1,2-DCE concentrations in µg/L from third quarter 1997 through second quarter 2005...... 109
Table 5-4. X-740 Area trans-1,2-DCE concentrations in µg/L from third quarter 1997 through second quarter 2005...... 110
Table 5-5. X-740 Area vinyl chloride concentrations in µg/L from third quarter 1997 through second quarter 2005...... 111
Table 5-6. X-740 Area second and fourth quarter average TCE concentrations in µg/L from 2002 through 2005...... 112
Table 5-7. X-740 Area second and fourth quarter average 1,1-DCE concentrations in µg/L from 2002 through 2005...... 112
Table 5-8. Total dissolved mass and sorbed mass of TCE concentrations of the X-740 groundwater plume from concentration data collected fourth quarter of 2005...... 136 12
List of Figures
Figure Page
Figure 2-1. Phytoremediation process as inorganic and organic constituents cycle through vegetation...... 25
Figure 3-1. Portsmouth Gaseous Diffusion Plant with five TCE contaminant plumes... 44
Figure 3-2. Location of the Portsmouth Gaseous Diffusion Plant...... 45
Figure 3-3. Geology diagram of the Portsmouth Gaseous Diffusion Plant...... 47
Figure 5-1. Planting scheme implemented at the X-740 Area...... 59
Figure 5-2. X-740 groundwater plume in 2001, planting pattern, and hybrid poplar tree layout of the X-740 Phytoremediation Area...... 61
Figure 5-3. X-740 phytoremediation tree growth and mortality study 2003...... 63
Figure 5-4. X-740 phytoremediation tree growth and mortality study 2005...... 64
Figure 5-5. X-740 phytoremediation species pattern and planting technique and growth results from 2005 survey...... 65
Figure 5-6. Percentage of the trees planted in trenches versus trees planted in boreholes, 2003 X-740 phytoremediation tree growth and mortality study...... 67
Figure 5-7. Percentage of the trees planted in trenches versus trees planted in boreholes, 2005 X-740 phytoremediation tree growth and mortality study...... 67
Figure 5-8. Tree species growth and mortality percentage 2003...... 69
Figure 5-9. Tree species growth and mortality percentage 2005...... 69
Figure 5-10. X-740 Phytoremediation tree coring study TCE concentration results...... 72
Figure 5-11. X-740 Area well locations used for the water level and gradient study. .... 75
Figure 5-12. Average groundwater levels from wells in the X-740 Phytoremediation Area (X740-03G, X740-08G, X740-10G, X740-PZ10G, and X740-PZ12G) and outside the area (X740-05G, X740-06G, F-13G, X326-04G, X330-PZ01G)...... 76
13
Figure 5-13. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 1998...... 79
Figure 5-14. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 1998...... 80
Figure 5-15. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 1999...... 81
Figure 5-16. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 1999...... 82
Figure 5-17. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 2000...... 83
Figure 5-18. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 2000...... 84
Figure 5-19. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 2001...... 85
Figure 5-20. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 2001...... 86
Figure 5-21. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 2002...... 87
Figure 5-22. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 2002...... 88
Figure 5-23. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 2003...... 89
Figure 5-24. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 2003...... 90
Figure 5-25. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 2004...... 91
Figure 5-26. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 2004...... 92
Figure 5-27. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 2005...... 93 14
Figure 5-28. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 2005...... 94
Figure 5-29. Annual gradient fluctuations between 1998-2005 at the X-740 Area. Wells X740-04G-03G, X740-04G-10G, X740-05G-03G, and X740-05G-10G...... 96
Figure 5-30. X-749 Area well locations used for the water level study...... 99
Figure 5-31. Average groundwater levels from wells in the X-749 Phytoremediation Area (X749-37G, X749-38G, STSW-101G, STSW-102G, and X749-32G) and outside the area (X749-13G, X120-08G, X120-10G, X749-PZ05G, X749-PZ06G)...... 100
Figure 5-32. X740-03G and X740-PZ17G hydrograph data from July 2003...... 102
Figure 5-33. X740-03G and X740-PZ17G hydrograph data from July 2004...... 103
Figure 5-34. X740-03G and X740-PZ17G hydrograph data from July 2005...... 104
Figure 5-35. 1,1-DCE concentrations of wells X740-03G and X740-10G, two of the four designated monitoring wells at the X-740 Phytoremediation Area...... 113
Figure 5-36. 1,1-DCE concentrations of wells X740-PZ10G and X740-PZ12G, two of the four designated monitoring wells at the X-740 Phytoremediation Area...... 113
Figure 5-37. TCE concentrations of wells X740-03G and X740-10G between 1997 and 2005, two of the four designated monitoring wells at the X-740 Phytoremediation Area...... 114
Figure 5-38. TCE concentrations of wells X740-PZ10G and X740-PZ12G between 1997 and 2005, two of the four designated monitoring wells at the X-740 Phytoremediation Area...... 115
Figure 5-39. X-740 Area TCE concentration 5 years after tree majority...... 117
Figure 5-40. X-740 Area TCE concentration 10 years after tree majority...... 118
Figure 5-41. X-740 Area TCE concentration 15 years after tree majority...... 119
Figure 5-42. X-740 Area TCE concentration 1997 and 1998...... 120
Figure 5-43. X-740 Area TCE concentration second quarter 1999...... 121
Figure 5-44. X-740 Area TCE concentration fourth quarter 1999...... 122 15
Figure 5-45. X-740 Area TCE concentration second quarter 2000...... 123
Figure 5-46. X-740 Area TCE concentration fourth quarter 2000...... 124
Figure 5-47. X-740 Area TCE concentration second quarter 2001...... 125
Figure 5-48. X-740 Area TCE concentration fourth quarter 2001...... 126
Figure 5-49. X-740 Area TCE concentration second quarter 2002...... 127
Figure 5-50. X-740 Area TCE concentration fourth quarter 2002...... 128
Figure 5-51. X-740 Area TCE concentration second quarter 2003...... 129
Figure 5-52. X-740 Area TCE concentration fourth quarter 2003...... 130
Figure 5-53. X-740 Area TCE concentration second quarter 2004...... 131
Figure 5-54. X-740 Area TCE concentration fourth quarter 2004...... 132
Figure 5-55. X-740 Area TCE concentration second quarter 2005...... 133
Figure 5-56. X-740 Area TCE concentration fourth quarter 2005...... 134
Figure 5-57. Total mass TCE concentrations between 1999 and 2005...... 138
Figure 5-58. First-order sequential decay process...... 139
Figure 5-59. BIOCHLOR 2005 simulation data input screen...... 142
Figure 5-60. TCE concentrations along plume centerline, 1999 simulation...... 143
Figure 5-61. DCE concentrations along plume centerline, 1999 simulation...... 144
Figure 5-62. TCE concentrations along plume centerline, 2001 simulation...... 145
Figure 5-63. DCE concentrations along plume centerline, 2001 simulation...... 145
Figure 5-64. TCE concentrations along plume centerline, 2003 simulation...... 146
Figure 5-65. DCE concentrations along plume centerline, 2003 simulation...... 147
Figure 5-66. PCE concentrations along plume centerline, 2003 simulation...... 147 16
Figure 5-67. TCE concentrations along plume centerline, 2005 simulation...... 148
Figure 5-68. DCE concentrations along plume centerline, 2005 simulation...... 149
Figure 5-69. PCE concentrations along plume centerline, 2005 simulation...... 149 17
1.0 Trichloroethylene contamination
1.1 Trichloroethylene history
Trichloroethylene (TCE) is a man-made organic compound which does not occur in the natural environment. It is a clear, colorless, nonflammable liquid with a sweet smell that evaporates quickly (EPA, 2005b). It is used primarily as an industrial solvent and as a large volume degreasing agent for metals and electronic parts (EPA, 2005b).
TCE can be found in industrial products such as dry cleaning fluid, fumigant, and refrigerant and heat exchange fluid. TCE can also be found in many household products for instance typewriter correction fluid, paint, spot removers, carpet-cleaning fluids, metal cleaners, and varnishes (EPA, 2005b; EPA, 2006). The main contributors to TCE contamination in the environment are industrial processes associated with tool and automobile production. Industrial waste landfills that do not implement proper disposal practices as well as wastewater from industrial discharges are also a contributing source of TCE contamination entering the environment (EPA, 2005b). Once TCE is released into the atmosphere it can break down within one week. TCE in surface water breaks down more slowly. However, both media are excellent transporters of TCE delivering it to the soil where it passes into groundwater (EPA, 2005b). The United States has multiple drinking water supplies that are contaminated with TCE (EPA, 2005b). 18
1.2 Public health effects
TCE has varying health effects depending on the concentration of TCE as well as the duration and quantity of exposure. Levels of TCE in the environment are typically well below levels of those in the workplace (EPA, 2005b). Individuals who live or work near factories that use TCE or TCE related products may be exposed to low levels of this chemical in the environment. Additionally, individuals who use any of the above listed household products may be exposed to significant amounts of TCE via inhalation, absorption, or ingestion. Health effects that could occur either immediately or shortly after TCE exposure greater than 50 mg/L include cardiac arrhythmias; nausea and vomiting; serious liver damage; eye, nose and throat irritation; and dizziness, headaches, and neurological problems. Chronic exposure to TCE may result in several forms of cancer including liver, kidney, lung, testicular, cancerous tumors, and leukemia. Chronic exposure to TCE may also have reproductive effects relating to maternal exposure and heart defects in offspring (EPA, 2006). Depending on the level of TCE exposure, this chemical can be associated with several serious adverse health effects, including neurotoxicity, immunotoxicity, endocrine effects, developmental, liver, and kidney toxicity (EPA, 2005b). TCE will affect the same organ systems in every individual which is exposed. However, due to the individual’s health, genes, previous chemical and medical history, and personal habits such as smoking and/or drinking can vary the seriousness of the effects of TCE from person to person (EPA, 2006). 19
1.3 Regulations
Chemicals which are believed to cause health problems within the population have a predetermined safe level which is determined by the Environmental Protection
Agency (EPA). The EPA sets the safe level of these chemicals by evaluating the possible health risks and exposures. These levels are referred to as Maximum Contaminant Level
Goals (MCLG). The EPA has determined the safe level of TCE in drinking water is 0.
This is believed to the best level of protection for the public, this number should not cause any health problems within the population. The EPA has also set a Maximum
Contaminant Level (MCL). The MCL’s are set as close to the MCLG’s as reasonably possible due to the ability of public water systems ability to detect and remove the chemicals of concern. The MCL for TCE is 5 µg/L. This is the lowest level in which water systems can remove or treat the chemical of concern should it occur in drinking water. The regulations and drinking water standards for ensuring these policies are the
National Primary Drinking Water Regulations in which all public water systems must abide by (EPA, 2005a).
Among the listed National Priorities List (NPL) sites, TCE is the most widely detected organic chemical. The NPL is a numerically based screening system that uses data from investigations to assess hazardous waste sites that may pose a potential threat to human health and the environment. The most common volatile organic detected in a
1999 study of public drinking water systems was TCE. The Superfund Amendments and
Reauthorization Act (SARA) under the Right to Know provisions recently reported that
“525 facilities nationwide released over 8 million pounds of TCE to the air, 400 pounds 20 to surface water, and 12,600 pounds to the land” which will likely seep into the groundwater (EPA, 2005b). In 1981 TCE production was slightly over 260,000 lbs, in
1991 an increase of 60,000 lbs was reported totaling 320,000 lbs. A Toxics Release
Inventory reported over a six year span a total slightly over 291,000 lbs of TCE was released into the environment entering the groundwater and soil (EPA, 2005a).
Trichloroethylene is listed as a priority pollutant under the Clean Water Act
(CWA) and has a Safe Drinking Water Act (SDWA) MCL of 5 µg/L. It is regulated under RCRA as a spent solvent process waste and as a characteristically toxic waste
(EPA, 2005b).
2.0 Phytoremediation
Phytoremediation technology is based on the ability of certain plant species and their associated rhizospheric microorganisms to remove, degrade, or sequester contaminants located in the soil, sediment, surface water and groundwater (EPA, 2001a).
Phytoremediation is a promising clean-up solution for a wide variety of pollutants and
sites. It is a passive, in-situ technology which is entirely solar driven while producing no
waste during installation or implementation (EPA, 1998). Phytoremediation is a natural
process which allows for the easy adaptation, remediation and redevelopment of various
locations such as residential, industrial, commercial, government owned areas, and even brownfield sites. Organic compounds can be captured in the trees’ root systems, and possibly degraded by tree enzymes or ultraviolet light as they are transpired along with
the water vapor through the leaves of the trees (EPA, 2001a). As compared to other
remediation technologies phytoremediation is minimally invasive since the site can be 21 cleaned without removing the existing soil (Tucker, 2001). It is also considered highly beneficial since it is much less expensive than traditional methods of remediation such as pump-and-treat or “dig-and-dump” (Auliff, 2005).
2.1 Plant selection
A phytoremediation system can only be effective if the appropriate plant species are matched to the site’s specific needs regarding the plants ability to remediate the contaminant of concern and the plants physiology matches the area and environmental climate (Isebrands and Westphal, 2001). Plant species are chosen for a phytoremediation project based on site-specific factors including; adaptability to local conditions, native or non-native to the area, ease of planting and maintenance, rate of absorption of water through evapotranspiration, degradative enzymes produced, growth rate and yield, depth of the root zone concerning the contaminant of concern, and the ability to bioaccumulate contaminants (EPA, 1998; EPA, 2001a). Each area selected for phytoremediation is
different based on region, site geology, and the contaminants of concern (EPA, 2001a).
A diverse number of species thrive in various conditions and remediate different
types of contaminants (Isebrands and Westphal, 2001). Phytoremediation can be used to
treat diverse contaminants, including crude oil, polynuclear aromatic hydrocarbons
(PAHs), chlorinated solvents, metals, radionuclides, and explosives (Zynda, 2001). For
instance, the garden-variety clover can consume nearly 80% of petroleum toxins within three years at a moderately contaminated site; the yucca plant can absorb 10 times the amount of munitions at a heavily contaminated site than previously tested plants; the
Indian mustard lowered lead levels in a community garden that initially exceeded 1000 22 mg/L by half; mulberry & Osage orange trees have recently been discovered to break down polychlorinated biphenyls (PCBs); sunflowers have demonstrated the ability to absorb radioactive elements; and poplar trees have prevented the spread of groundwater contamination in areas around the country (Auliff, 2005; Frazer, 2005; Helman, 2001;
Northwestern University, 2004; Washington State University, 2005). Thus far, 400 plant species have been discovered which have the ability to degrade contaminants (Helman,
2001).
2.2 Phytoremediation process
The phytoremediation process occurs naturally in the environment as inorganic and organic constituents cycle through vegetation as shown in figure 2-1.
Phytoremediation is an extended version of the natural process. The phytoremediation process can be utilized to restore soil, sediment, or groundwater to its natural state by removing contamination in numerous ways (EPA, 2001a). The phytoremediation process can be further classified by the physical and biological processes involved which include; phytodegradation, phytoextraction, phytostabilization, phytovolatilization, rhizodegradation, rhizofiltration, hydraulic control, and microorganism stimulation
(Northwestern University, 2004; DOE, 2002; EPA, 2001a).
♦ Phytodegradation: The breakdown of contaminants external to the plant via
enzymes produced by the plant.
♦ Phytoextraction: The uptake of a contaminant and the translocation of that
contaminant into the shoots of the plant. This method is typically used for metal
contamination (DOE, 2002; EPA, 2001a; Zynda, 2001). 23
♦ Phytostabilization: The immobilization of the contaminant via absorption and
adsorption in order to prevent future migration. This method is typically used for
large surface areas reducing contaminant migration by reducing runoff, surface
erosion, groundwater flow rates, and human exposure to the contaminants (EPA,
2001a; Northwestern University, 2004).
♦ Phytovolatilization: The uptake and transpiration of a contaminant via a plant
while releasing the contaminant or a less toxic form of the contaminant into the
atmosphere.
♦ Rhizodegradation: The break down of a contaminant in soil through microbial
activity which is otherwise unreachable. Microbial activity in the root zone of a
plant is approximately 1,000 times higher than in soil alone (EPA, 2001a; Frazer,
2001).
♦ Rhizofiltration: The adsorption or precipitation of a contaminant into or onto the
plant roots in the root zone.
♦ Hydraulic control: The uptake of a large volume of water by plants to control
migration of the contaminant. Trees normally used for this process are the
willow, cotton wood, or poplar tree (EPA, 2001a).
♦ Microorganism stimulation: Plants excrete and provide natural enzymes which
stimulate the growth of microorganisms such as fungi and bacteria. The organic
contaminants are then metabolized by the microorganisms in the root zone (DOE,
2002; EPA, 2001a; Zynda, 2001). 24
These qualities possessed within plants allow the remediation of soil, sediments, groundwater, surface water, and wastewater ranging in types of contamination including heavy metals, organic compounds, and radioactive waste (Frazer, 2001). 25
Figure 2-1. Phytoremediation process as inorganic and organic constituents cycle through vegetation. 26
Additionally, phytoremediation can treat a wide variety of contaminants (EPA,
2001a). The majority of contaminated locations are often polluted with a multitude of
contaminants, and research has shown that the phytoremediation process can treat
multiple contaminants at the same time (Stanley, 1998). Phytoremediation provides in- situ remediation, which does not disturb the soil and therefore is suitable for urban and residential areas (Auliff, 2005). For most contaminated sites phytoremediation offers a permanent solution. A phytoremediation system can eliminate the majority if not all of the contamination located at a site (EPA, 2001a). Table 2-1 demonstrates the relationship between plant species and specific contaminants (Alliance for Nuclear Accountability,
2004). 27
Vegetation Treatment Contaminant Process Prairie grasses Completely PAHs Rhizodegradation remediated soil with a concentration of 10 mg/kg. Aquatic plants Decreased Munitions (RDX, TNT) Phytodegradation (canary grass, concentration to wool grass, <50 µg/L from sweetflag, initial ranges of parrotfeather) 1250-4440 µg/L. Indian mustard Levels initially Lead, Selenium, Sulfur, Phytoextraction and Broccoli exceeded 1000 Cadmium, Nickel, mg/L was Chromium, Zinc, Copper, reduced by half Cesium, and Strontium Mulberry and Supports growth PCBs Rhizodegradation Osage orange of PCB- trees degrading bacteria. Sunflowers Cesium was Radioactive elements Rhizofiltration decreased from (Cesium, Strontium, 200 µg/L to Uranium) 3µg/L within 24 hours. Strontium was decreased from 200 µg/L to 35µg/L within 48 hours. Poplar trees Average uptake Trichloroethylene Phytodegradation during first Phytovolatilization season 50 mg/L and second season 14.5 mg/L.
Table 2-1. Relationship of plant species to specific contaminants (Alliance for Nuclear Accountability, 2004; Auliff, 2005; Belz, 1997; EPA 2001b; Frazer, 2005; Helman, 2001; Washington State University, 2005). 28
2.3 Advantages
Phytoremediation can be used as the sole technology, as an interim solution, or in combination with multiple treatments in order to create a unified clean-up strategy
(Auliff, 2005; EPA, 2001a). This strategy is sometimes implemented in order to reduce overall project costs and to lessen the associated risks to an untreated site before the final redevelopment begins while reaching achievable clean-up goals (EPA, 2001a).
Phytoremediation offers an aesthetically pleasing environment by providing views
of trees and green spaces which has social and psychological benefits to the public.
Research has shown that vegetation can have dramatic impacts on human health. For
instance, views of green spaces have significant healing impacts in hospitals requiring
less medication and fewer complications signifying shorter hospital stays; views of green
spaces in public housing developments reduces stress, and domestic violence, views of
green spaces improve productivity on the job; and business districts with trees and
landscaping are perceived to distribute higher quality merchandise (Isebrands and
Westphal, 2001).
Additionally, phytoremediation can be easily integrated into the natural
environment. A phytoremediation system can be incorporated through a variety of
natural landscapes such as; wetlands, forests, or grasslands. Implementing
phytoremediation as a natural environment can enhance or restore the physical
appearance of a site. The majority of remediation methods are invasive and the clean-up
employs heavy, noisy, large construction equipment that is costly and can potentially
spread the contamination (EPA, 2001a). Phytoremediation presents a minimally to non- 29 invasive treatment that reduces contamination without further environmental pollution, greens possibly barren areas, and is aesthetically pleasing to the community as well as passerby’s (Isebrands and Westphal, 2001). A summary of advantages to a phytoremediation system are presented below;
Advantages
♦ Can be either in-situ or ex-situ technology
♦ Passive system
♦ Works on a variety of organic and inorganic compounds
♦ High public acceptance
♦ Generates less secondary waste, soils remain in place and are reusable
♦ Easy to implement and maintain
♦ Fewer air and water emissions; reduces exposure risk to the community
♦ Costs 10% to 20% of mechanical treatments
♦ Utilizes natural organisms; preserves natural state of the environment
♦ Valuable metals can be reclaimed and reused
♦ Mitigates greenhouse gas production, reduces urban heat island effects
♦ Solar driven
♦ Environmentally friendly and aesthetically pleasing to the public
(EPA, 1998; Frazer, 2001; Isebrands, 2001; Northwestern University, 2004).
30
2.4 Disadvantages
In order to implement a successful phytoremediation system the appropriate plant species must be chosen to remediate the contaminant of concern as well as the appropriate planting location. The planting location must yield the appropriate climatic conditions and temperature variances so the chosen plant species will have the ability to adapt to the regional area (Isebrands and Westphal, 2001). For instance, the Yucca plant is successful in the desert conditions remediating munitions and the poplar tree is successful in the Midwest remediating volatile organics. Neither species would be able to thrive and produce a successful phytoremediation system if the locations were reversed
(Isebrands and Westphal, 2001; Washington State University, 2005).
Additionally, the phytoremediation process is slow (EPA, 1998). Many years are needed in order to remediate a contaminated site using phytoremediation, whereas other methods like “dig and dump” are completed immediately. These other methods may also require less planning, implementation, and long-term maintenance than phytoremediation
(Auliff, 2005).
Furthermore, there is a possibility that the food chain could be affected. If a small animal were to eat the toxic plant the animal’s predator could in turn be affected by the plant’s contamination. It is possible this chain of events could continue until it reaches a human (Zynda, 2001). A summary of disadvantages of a phytoremediation system is presented below; 31
Disadvantages
♦ Restricted to sites with shallow contamination within rooting zone
♦ Remediation rate and effectiveness is temperature dependent, nutrient dependent,
dependent on climatic conditions, and soil fertility
♦ High concentrations of certain materials can be toxic to plants
♦ May take several years to remediate due to slow growth rate
♦ Harvested biomass from phytoextraction may be classified as a hazardous waste
♦ Potential contamination of food chain, dependent upon contaminant type and
chosen plant species
♦ Unfamiliar to many regulators
♦ Slower than mechanical treatments
♦ Genetically modified plants could potentially cross with wild plants
♦ Mass transfer limitations
♦ Hyperaccumulator plants (absorb heavy metals) must be treated as a toxic waste
(EPA, 1998; Frazer, 2001; Isebrands, 2001; Northwestern University, 2004).
2.5 Economical benefits
It is of a relatively low cost to install and operate a phytoremediation system as compared to other common remediation methods (Helman, 2001). Standard agricultural and landscaping equipment, materials, and practices are used to install and maintain these systems. These techniques are less expensive regarding up-front and long-term costs
(EPA, 2001a). Table 2-2 provides a comparison of phytoremediation costs to standard technologies (EPA, 1998). 32
Contaminant Phytoremediation Costs Estimated Cost using Other Technologies (In- situ Bioremediation, Soil Washing, Solvent Extraction, Soil Venting, Incineration) Metals $80 per cubic yard $250 per cubic yard Site contaminated with $70,000 $850,000 petroleum hydrocarbons 10 acres lead contaminated $500,000 $12 million land Radionuclides in surface $2 to $6 per thousand water gallons treated None listed 1 hectare to a 15 cm depth $2,500 to $15,000 None listed (various contaminants)
Table 2-2. A comparison of phytoremediation costs to standard technologies (EPA, 1998).
The overall cost of a phytoremediation system is extremely site specific (Frazer,
2001). The entire remedial process must be considered in the cost estimate of the system
including the initial growing of the plants, continued maintenance, harvesting, and finally
the disposal or recycling of the plants (Northwestern University, 2004). Traditional
clean-up methods range from $10 to $100 per cubic meter of on-site soil. That can raise an estimated three times if the soil is taken to a hazardous waste facility.
Phytoremediation can cost as little as five cents per cubic meter with no involvement of a hazardous waste facility (Frazer, 2001). Table 2-3 provides an estimated cost savings through the use of phytoremediation rather than conventional treatment (EPA, 2001a). 33
Contaminant Phytoremediation Conventional Treatment Projected and Matrix Savings
Application Estimated Application Estimated Cost Cost
Lead in soil Extraction, $150,000 - Excavate and $500,000 50-65 % (1 acre) harvest, and $250,000 landfill disposal Solvents in Degradation $200,000 for Pump and $700,000 50 % cost groundwater and installation treat annual savings by (2.5 acres) hydraulic and initial operating third year control maintenance cost Total In-situ $50,000 - Excavate and $500,000 80 % petroleum degradation $100,000 landfill or hydrocarbons incinerate in soil (1 acre)
Table 2-3. Estimated cost savings through the use of phytoremediation versus conventional treatment (EPA, 2001a).
2.6 Determinate factors of phytoremediation
The low cost of phytoremediation has attracted a lot of attention for remediation efforts in industry and government. So much attention, that a study regarding the uncertainty of potential costs has been conducted (Angle et al., 2005). The actual cost of a phytoremediation project is extremely difficult to predict. The three considerations stakeholders need to take into consideration are the likelihoods of success, the time of remediation, and the cost effectiveness of the entire system. This article (Angle et al.,
2005) considers the uncertainty in projects with various characteristics and uses a model to predict the actual costs of a phytoremediation system. Typically, when phytoremediation is compared to other more invasive remediation options only accounting cost estimates for these options are compared to phytoremediation which is 34 costed as an agricultural concern. Items such as overhead, management, and salaries are not normally considered in these estimates for the phytoremediation project which results in an unfair comparison. This model bases investment decisions on a combination of the net value of profits, the payback period, and the probability of success. Factors such as the life expectancy of the project, the contaminant, and the species selection all factor into the model. Each phytoremediation system is different and the real numbers associated with each system can be plugged into the model to determine the estimated costs of the project enabling more accurate investment decisions.
2.7 Evidence of TCE uptake
Phytoremediation has been extensively tested in the laboratory, in some cases using soils and/or water from contaminated sites. Numerous species of plants have been grown in the laboratory to evaluate their phytoremediation potential to treat contaminated soil and/or groundwater (Cherian and Oliveira, 2005). The outcome of one particular study was to determine if hybrid poplar trees were capable of metabolizing TCE in the soil (Choe et al., 1997). The first experiment conducted involved cell cultures derived from the Populus trichocarpa x P. deltoides species. The cells were studied to determine if they alone were capable of metabolizing TCE without the dynamics of soil and surrounding vegetation. The cells were housed in sealed flasks and tested for their ability to remain viable and sensitivity to TCE. The cells cultured in 260 mg/L TCE grew at the same rate as cells with no TCE exposure.
The second experiment conducted involved the entire plant of the Populus trichocarpa x P. deltoides and Populus trichocarpa x P. maximowiczii species grown 35 hydroponically (Choe et al, 1997). Two trees received water containing 50 mg/L of TCE and the remaining trees received only water. After week 20 and week 31 the trees were tested to determine TCE uptake. The leaves, stems, upper, middle, and lower roots were analyzed for TCE. The trees exposed to TCE only grew to 85% of the trees not exposed to TCE and did not develop as many minor roots as the non-exposed trees. Significant amounts of TCE were detected in the stems; however minimal amounts were detected in the leaves. TCE was also detected in all three sections of the collected roots. These results confirmed the rationale in order to use plants, especially the hybrid poplar tree, as an alternative to current remediation methods.
Additionally, experiments have been conducted in order to study specific plants that have the ability to enhance the natural attenuation of chemicals (Bankston et al.,
2001). A study was conducted to observe the fate of TCE in a surface aquifer that discharges into a wetland. The two primary plant species evaluated were the eastern cottonwood (Populus deltoides) and the broad-leaved cattail. The surface aquifer was contaminated with TCE which flows into the wetland. Groundwater samples were collected every four months throughout the entire length of the plume. The concentration of TCE located in the furthest well from the source and closest to the wetland increased from 89 µg/L to 240 µg/L over the course of the study, and TCE byproducts were detected in the aquifer which indicates plume migration by natural attenuation and biotransformation of TCE.
Young cattails obtained from the center of the wetland and cottonwood saplings obtained from the wetland edge were collected. The samples were housed in a 36 microcosm with native soil and water to assess microbial transformation of TCE. TCE was added to a total concentration of 35 µg TCE per kilogram of soil and water. The cottonwood saplings were found to have TCE in the roots (2.3%), stems (3.2%), and leaves (4.9%). The observations of this study provide evidence that native species such as the eastern cottonwood can accelerate the natural attenuation of TCE.
Similar studies have been conducted to determine the fate and transport of TCE and additional volatile organic compounds in hybrid poplar trees (Burken and Ma, 2002).
Tree cores were collected from an uncontaminated 8-year-old hybrid poplar tree (Populus deltoids x P. nigra) trunk and tree cuttings were collected from the branches. The air-biomass experiments for both tree core and cuttings showed that contaminants were sorbed in the relative order of 1,1,2,2,-tetrachloroethane (TeCA) > TCE > carbon tetrachloride (CT). Also, all of the volatile organics in the study were shown to be sorbed by the water-wood experiments. The TCE uptake experiments did not demonstrate any signs of toxicity, wilting, or reduction in water usage. The calculated transpiration shared a linear relationship with a known solution. This provides evidence that the aqueous contaminant was taken up by the trees, and that the concentration in the transpiration stream was directly proportional to the concentration at the roots.
2.8 Evidence of volatile organic compound (VOC) transpiration
Phytoremediation has been successfully implemented at contaminated field sites to reduce the concentration and mobility of contaminants. Field test results are few and sporadic. However, the results of a few field tests have been published. 37
A full-scale field study conducted in 2003 demonstrated the transpiration of volatile organic compounds by a phytoremediation system (Burken and Ma, 2003). The experiment involved hybrid poplar whips, Populus deltoides x P. nigra, approximately
30 cm in length, growing over a groundwater plume of 1,1,2,2,-tetrachloroethane and
TCE. This system had been an active phytoremediation system since 1996. Each whip was fitted with two diffusion traps. One towards the bottom portion of the tree and the other towards the top portion of the tree. TCE was collected in both the upper and lower diffusion traps. However, the lower diffusion trap collected a greater TCE concentration than the upper trap. The mass of TCE collected in the lower trap was 14.8 mg and in the upper trap was 8.3 mg after 28 days. TCE concentrations in the 5-year old phytoremediation system demonstrated decreasing TCE concentrations with the height up the tree with the greatest TCE concentration root level. This study provided evidence that TCE is indeed volatilized into the atmosphere via transpiration which is the primary fate of TCE after uptake.
Additionally, studies have been conducted to determine the potential for phytoremediation of CT using poplar trees. A field study conducted in 2004 assessed the transpiration of CT from leaves, soil, tree trunks, and surface roots (Dossett et al., 2004).
The experiment was conducted around field test beds that were 1.5 m deep by 3.0 m wide by 5.7 m long and lined with double-walled 1.5 mm polyethylene. The study began in
1995 with 15 hybrid poplar trees (Populus trichocarpa x P. deltoides) planted in the bed spaced approximately 1 m apart. Beginning in 1996 the bed received influent water containing CT during the growing season between 1996 and 2002. 38
In order to extract the amount of CT transpired by the plant during the growing season, single leaves were collected and analyzed in 2002. No CT was detected in any of the leaf bag samples. These results suggest that transpiration was not a significant removal for CT. Tree trunk cores, soil, and surface root samples were obtained in 2002 and calculated concentrations were compared with external standards. The results indicated a greater concentration in the upper portions of the tree trunks than in the lower portions which is inconsistent with the transpiration process. In 2002, the effluent water from the test bed was found to have a lower CT concentration than the influent water representing a 99.8% removal of CT. Overall, this study implied that poplar trees can effectively break down CT with minimal transpiration occurring during this process.
2.9 Evidence of VOC degradation
During the phytoremediation process VOC degradation is hypothesized to be the dominant fate of TCE (Dossett et al., 2004). A field study was conducted to determine the degradation rate considering the seasonal variation, contaminated versus uncontaminated areas, and treed versus untreed areas (Andersen et al., 2005). The study site consisted of a phytoremediation plantation of 1146 hybrid poplar trees (Populus deltoids x P. nirga) planted over contaminated groundwater of PAHs. Ten push-pull wells were installed at five locations. Locations were chosen based on the ability to compare contaminated versus uncontaminated areas and treed versus untreed areas. The push-pull method included bromide, dissolved oxygen (DO), and naphthalene in a solution that was injected (push) into each well. Groundwater sampling occurred immediately after the injection of solution. Groundwater extraction (pull) continued until 39 three times the injected volume was collected. The uncontaminated areas without trees demonstrated little to no oxygen consumption, however, substantial DO consumption was observed at the contaminated areas with trees. The treed areas demonstrated a higher DO consumption rate than the untreed areas. The DO and naphthalene consumption rates showed an increase in the summer months as compared to the winter months. This study established that the push-pull test can indicate differences between treed versus untreed areas as well as seasonal variations. These findings suggest that a phytoremediation plantation remains active during the winter season but at a lower rate. Additionally, increases in microbial activity in uncontrolled areas compared to controlled areas during the winter months indicate that phytoremediation is not limited to the summer growth.
2.10 Evidence of groundwater uptake
The design of a phytoremediation system is essential to the success of the system.
In order to assess the effectiveness of a phytoremediation system and to understand the water-use habits, a study was conducted to evaluate the uptake of groundwater, surface water, and soil water in a phytoremediation system (Clinton et al., 2004). The study was conducted on the Populus deltoides species to measure the uptake of groundwater versus the uptake of irrigation water. Tree sap flow rates were utilized to estimate transpiration rates of the individual trees. Two trees were selected that grew over TCE and cis-1,2- dichloroethene plumes in the groundwater. Additionally, irrigation was implemented two consecutive days during the morning. Twenty-four tree core samples were collected as well as groundwater and ambient air samples in order to determine TCE analyses. The sap flow rate increased by 11% the first day of watering and 61% the second day of 40 watering. Since the temperature remained constant throughout the two day experiment sap flow rates were most likely increased by the water availability. TCE concentrations before the applied irrigation were 977 µg/L, after irrigation TCE concentrations were 767
µg/L. The decrease in TCE concentrations implies the trees utilized the available surface water rather than the groundwater. This experiment provides evidence that if a phytoremediation system has a larger than normal increase in surface water via irrigation or precipitation the system will utilize the surface source of water rather than the contaminated groundwater.
2.11 Implications for this study
Phytoremediation of TCE by poplar trees has been studied at great length in the laboratory and recently a small portion of field tests have begun reporting their findings.
Hydroponic studies have shown rapid TCE uptake from water (Choe et al., 1997; Burken and Ma, 2003). In some studies, TCE accumulates in leaves, stems, and/or trunk samples
(Dossett et al., 2004) while in others transpiration of TCE appears to be significant (Choe et al., 1997). Transformation of TCE within the tree tissue has also been observed by both tree enzymes and bacteria (Choe et al., 1997). Additionally, seasonal variations have proven TCE uptake occurs both in the growing season as well as the dormant season
(Andersen et al., 2005). The varying results depend on the site conditions as well as the regional location, the contaminant of concern, the size of the study area, and whether the study is conducted in the laboratory or in the field. Full-scale field results are important because laboratory studies tend to neglect the environmental conditions the system might be exposed too. 41
PORTS is a large phytoremediation project that is being conducted as a full-scale field study not as a pilot study. This phytoremediation study encapsulates a total combined area of approximately 45 acres with TCE concentrations up to 9700 µg/L. The site has also been extensively monitored via approximately 250 groundwater monitoring wells located on-site. The size of this study area combined with the field planting techniques, regional location, and chemical concentration of concern creates a unique system suitable for investigation on the effectiveness of phytoremediation.
While it is established that phytoremediation of TCE by poplars is feasible, there are few published reports of the results of full scale implementation. In this study the performance of a full-scale capture phytoremediation system will be assessed. Questions that cannot be assessed in the laboratory will be addressed such as impact on groundwater flow and contaminant plume, seasonal variations in performance, and longevity and health of trees.
3.0 Site description
3.1 Plant history
PORTS, a Department of Energy (DOE) Facility, enriched uranium from the early
1950s until 2001. This facility is one of two uranium enrichment facilities in the United
States (DOE, 2005a). The PORTS facility operated for 47 years in sequence with the
Paducah Gaseous Diffusion Plant (PGDP) (Alliance for Nuclear Accountability, 2004).
The principal process at PORTS was uranium enrichment production and operations facilities. The uranium isotopes are separated by gaseous diffusion for U-235 enrichment
(DOE, 2005a). Enriched uranium, which is used in commercial nuclear power reactors, 42 was produced at PORTS until 2001 when production was ceased. Natural uranium consists of 0.7% of U-235. The uranium required for use in commercial nuclear power reactors must be 3-4% enriched. However, a byproduct of uranium is also produced during the enrichment process, namely uranium hexafluoride. The materials are both hazardous and radioactive, during the operating life of the PORTS facility “11,000 lbs of uranium was buried on site, 17,000 lbs of uranium was dumped into local streams and
23,000 lbs was released into the atmosphere.” The facilities which produced highly- enriched uranium were closed in 1991, however low-enriched uranium continued to be produced (Alliance for Nuclear Accountability, 2004). The PORTS facility currently stands in cold standby mode which will allow the plant to be maintained in a condition so that uranium enrichment production could restart within 18-24 months, if necessary
(DOE, 2005a). Also, the process to support a new centrifuge enrichment facility began in
2005. In addition to cold standby mode the PORTS facility is currently involved in environmental restoration, waste management activities, and the indefinite surveillance and maintenance of contaminated facilities (Alliance for Nuclear Accountability, 2004).
3.2 Population distribution and site location
The PORTS facility is situated on 3,714 acres of land as shown in figure 3-1. It is located approximately 4 miles south of the Village of Piketon (population 1,907), 20 miles north the city of Portsmouth (population 20,909), 70 miles south of Columbus
(population 711,470), and 1 mile east of the Scioto River as shown in figure 3-2 (Alliance for Nuclear Accountability, 2004). Eight hundred (800) acres of the 3,714 acre reservation is a fenced area which contains the former production facilities. The 43 remaining 2,914 acres of land includes “restricted buffers, waste management areas, plant management and administrative facilities, gaseous diffusion plant support facilities and vacant land” (DOE, 2000). Surrounding the PORTS facility boundaries is the Wayne
National Forest to the east and southeast, Brush Creek State Forest to the southwest, with the majority of the remaining adjoining land consisting of farmland and rural developments (DOE, 2000). 44
Figure 3-1. Portsmouth Gaseous Diffusion Plant with five TCE contaminant plumes (Childers et al., 2005). 45
Figure 3-2. Location of the Portsmouth Gaseous Diffusion Plant (Alliance for Nuclear Accountability, 2004).
3.3 Site hydrology and geology
The site hydrology consists of four primary geologic and hydraulic units the unconsolidated Minford, unconsolidated Gallia, Sunbury Shale, and the Berea Sandstone
as shown in figure 3-3. The Gallia and Berea are the two water-bearing units while the
Sunbury and Minford are considered aquitards since they yield a lower amount of water
(Alliance for Nuclear Accountability, 2004). The Gallia aquifer located approximately 46
25 ft below the surface, ranges in thickness between 0 and 10 ft with an average thickness of 4 ft (Alliance for Nuclear Accountability, 2004; Rieske, 2005b). The Gallia acts like a semi-confined aquifer which is an aquifer that is fully saturated with a semi-impervious upper layer and an impervious lower layer. In a semi-confined aquifer the water is held under pressure, the installation of the wells or sand stacks to bedrock initiates the vertical upward flow of groundwater. The potentiometric surface (water level) is typically 10 to
15 feet below the land surface (Rieske, 2005b). Plant-wide, the hydraulic conductivity of the aquifer material, the ability of the subsurface materials to allow fluid flow, in the
Gallia ranges between 0.11 to 150 feet per day averaging 4.2 feet per day at the X-749 and X-740 Phytoremediation Areas (Alliance for Nuclear Accountability, 2004). The
Gallia groundwater flow velocity in the X-749 and X-740 Phytoremediation Areas is approximately 0.1 and 0.2 feet per day, respectively. The uppermost bedrock aquifer
(Berea Sandstone) is located approximately 40 feet below the surface, with an average thickness of 30 feet. Hydraulic conductivity in the Berea Sandstone at the X-749 and X-
740 Phytoremediation Areas is approximately 1.0 and 2.0 feet per day, respectively and groundwater flow velocity is approximately 0.1 and 0.3 feet per day, respectively
(Rieske, 2005b). The Berea aquifer is continuous throughout the site unlike the Gallia aquifer. Thus far most of the contamination at the PORTS facility has been located in the
Gallia aquifer as well as minor amounts in the Berea aquifer (Alliance for Nuclear
Accountability, 2004). 47
Figure 3-3. Geology diagram of the Portsmouth Gaseous Diffusion Plant (Alliance for Nuclear Accountability, 2004).
48
The PORTS facility consists of four quadrants (separate flow regions). These four quadrants were established based on groundwater flow in order to assist with remediation activities (DOE, 2000). Within these four quadrants five groundwater contaminant plumes have been identified beneath the site as shown in Figure 3-1. These five groundwater plumes are contaminated with the volatile organic compound TCE
(DOE, 2000). TCE was used as a solvent for degreasing metal parts and equipment at the
PORTS site. Additionally, TCE generated onsite was stored in drums at locations which are now considered contaminated areas (DOE, 2000; DOE, 2002). The early disposal methods at the plant site regarding TCE are unknown (DOE, 2000).
Phytoremediation has been implemented in order to assist in the removal of TCE in the groundwater at two locations at the PORTS facility: the X-740 Area and the X-
749/X-120 Area. Currently at both locations the TCE levels in the groundwater are above the action level of 1 µg/L (DOE, 1998; DOE, 2000). The highest concentration at the X-
740 Area reported as of fourth quarter 2005 is 5,500 µg/L. Additionally, the highest concentration at the X-749 Area reported as of fourth quarter 2005 is 4,200 µg/L (DOE,
2005a).
3.4 X-740 Area
The X-740 Waste Oil Handling Facility is located in the western section of the site within Quadrant III as shown in Figure 3-1. The West Drainage Ditch, numerous holding ponds, and two of the main process buildings lie within this quadrant.
Groundwater flows to the west in Quadrant III, while the West Drainage Ditch and the numerous holding ponds direct all of the surface water to the west as well. 49
The X-740 Waste Oil Handling Facility was used as a switchyard during plant construction and was also in operation between 1982 and 1992. The facility was primarily used for the drum-staging of non-radionuclide contaminated waste oils and solvents generated by various activities on plant site. The drums were staged at the facility pending analysis of their contents before their final disposition. Empty drums resulting from combining partially full drums were crushed in a hydraulic drum crusher.
The effluent from the drum crusher was discharged to a tank/sump located beneath the drum crusher pad. These activities may have lead to the contamination of the area.
Sampling of the groundwater and soil was conducted in 1992 to evaluate the extent of the contamination (DOE, 1998).
The facility underwent Resource Conservation and Recovery Act (RCRA) closure in 1993. The RCRA closure decontamination activities included the decontamination of the floor and walls of the facility, the removal of the tank/sump, and the removal of the surrounding contaminated soil (DOE, 1998). However, a VOC groundwater plume is located in the Gallia and Berea aquifers. The groundwater plume is located west of the
X-740 building; the approximate extent is 3.5 acres (Brandt et al., 2002). The remaining contamination exists at detectable levels in the groundwater, consisting primarily of TCE.
The past TCE concentration reached a maximum value of 11,000 µg/L as reported in
1993 (DOE, 2003b). More recently, the TCE concentration reached a maximum value of
5,500 µg/L as reported in 2005 (DOE, 2005a). The Quadrant III Decision Document for
PORTS contained the selected remediation option for the X-740 Area which was 50 approved by Ohio EPA and U.S. EPA in 1998. The X-740 Phytoremediation System was installed in the summer of 1999 (DOE, 2003b).
3.5 X-749/X-120 Area
The X-749 Landfill and the X-120 Former Goodyear Training Facility is located in the southern section of the site within Quadrant I as shown in Figure 3-1. The Peter
Kiewit Landfill as well as other landfills lie within Quadrant I along with processing areas and administrative buildings. The groundwater in Quadrant I flows to the east toward Big Run Creek. The X-749 Landfill also known as the Contaminated Materials
Disposal Facility is believed to be a continuing source of TCE contamination. The materials contained within the X-749 Landfill possess trace quantities of neptunium, plutonium, and technetium, all are extremely water-soluble. It is suspected that the majority of this waste was buried with no preventive packaging (Alliance for Nuclear
Accountability, 2004).
During plant construction the X-120 Goodyear Training Facility operated as a machine shop, paint shop, and two warehouses. It is highly probable that the machine and metal shops used solvents and degreasers (TCE) while in operation (DOE, 2002).
Again, the disposal procedures for these substances are unknown. The X-120 facilities have since been demolished and removed during construction activities of the Gas
Centrifuge Enrichment Plant. Several investigations, however, have identified various
VOCs, primarily TCE, at detectable levels in the groundwater (DOE, 2000).
Located approximately 500 feet to the southeast of the X-120 Goodyear Training
Facility is the X-749 Landfill. The X-749 Landfill is comprised of both northern and 51 southern segments. The northern segment was utilized from 1955 to 1989 and is approximately 7.5 acres in size. The northern segment was used for the disposal of low- level radioactive contaminated equipment and materials. This waste was contaminated with low-level radioactivity, chlorinated solvents, metal hydroxide sludge, and waste oils.
The southern segment was utilized from 1986 to 1989 and is approximately 4 acres in size. The southern segment was used for the disposal of a variety of demolition debris and scrap metals. This waste was contaminated with low-level radioactivity, alumina, sodium fluoride, incinerator ash, and asbestos (DOE, 2002).
The X-749 Landfill is currently treated as a single unit due to the groundwater plume which lies under both segments of the landfill. The 11.5-acre landfill underwent closure in compliance with RCRA in 1989 (DOE, 2002). This closure activity included the installation of slurry walls along the north and west sides of the landfill as well as the installation of groundwater trenches along the east and southwest sides of the landfill.
These installed features operate, as a source control for groundwater contamination. In addition, a multi-layered landfill cap was installed over the complete facility. The captured contaminated groundwater is treated at an on-site groundwater treatment facility
(DOE, 2000).
The X-120 facilities are no longer considered a source of contamination. It is extremely probable, however, that the X-749 Landfill is a continuing source of contamination to the groundwater (DOE, 2002). The groundwater plume is located in all four directions (north, east, south, and west) of the X-749 landfill; the approximate extent is 41 acres (Rieske, 2005a). The remaining contamination exists at detectable levels in 52 the groundwater, consisting primarily of TCE (DOE, 2002). The past TCE concentration reached a maximum value of 4,300 µg/L as reported in 1998 (DOE, 1999). The current
TCE concentration reached a maximum value of 4,200 µg/L as reported in 2005 (DOE,
2005b). The Quadrant I Decision Document for PORTS contained the selected remediation option for the X-749/X-120 Area which was approved by Ohio EPA and
U.S. EPA in 2001. The X-749 Phytoremediation System was installed in 2003 (DOE,
2002).
4.0 Remediation options
The U.S. EPA has developed a response strategy which identifies response
actions and remedies for sites with contaminated groundwater. This strategy also
identifies response strategies for ex-situ (to treat extracted contaminated groundwater in
order to remove contaminants by using aboveground treatment options) and in-situ
treatment of contaminated groundwater. The response strategy implements the
Superfund program to “streamline site investigations, selection of cleanup actions, and
the remediation selection process.” These presumptive remedies are the best available
selection of technologies for treatment of extracted groundwater (DOE, 2000).
4.1 X-740 Remedial Plan
Five treatment options were considered to remove TCE from groundwater at the
X-740 Area. These options included no action, institutional controls and monitoring, institutional controls and phytoremediation, institutional controls and extraction wells,
institutional controls and Vacuum Enhanced Recovery (VER). The third option was
selected which proposed a phytoremediation system of approximately 3 acres of hybrid
poplar trees to be planted in the X-740 Area. This system would act as a hydrologic sink 53
(extraction system). Once implemented the phytoremediation process would directly take up various contaminants, compounds that stimulate bacterial growth would be released, and fungi growth would increase due to additional carbon sources. This method would reduce contaminant mobility and TCE concentration after several years of operation (DOE, 1998). Concerning reliability, the phytoremediation system is expected to remove the contaminants of concern from the contaminated groundwater exceeding the preliminary remedial goal. The size of the contaminant plume will decrease with time decreasing the rate of migration. The total cost would be $271,000 with an annual operation and maintenance cost of $16,000 (EPA, 1999).
The primary factor involved in selecting phytoremediation was based on the ability of the phytoremediation system to use the “natural growth process of the biological systems to attenuate and reduce contaminants in groundwater”. Additionally, several other positive factors resulted in the selection of phytoremediation; (1) young hybrid poplar trees, the species of choice in this instance, if planted 10 to 15 feet below ground surface have the ability to develop strong, mature roots; (2) within 2 years this strong, mature root system would be developed; (3) within the initial 2 years natural attenuation (natural processes to clean up contamination in soil and groundwater) would take place; (4) metals are not a contaminate of concern, in turn, metals bioaccumulation in tree leaves are not foreseen; (5) estimated annual water consumption is 6,000 gallons per day per acre of trees; and (6) minimal changes will be required for additional monitoring activities (DOE, 1998). 54
A phytoremediation system of 766 hybrid poplar trees was planted in order to manage the VOC contaminant plume over an area of 2.6 acres during the summer of
1999. Two distinct planting methods were utilized as well as three hybrid poplar tree species. Monitoring and maintenance activities included inspections of the condition of the trees, condition of the ground cover, and the condition of the monitoring wells.
Groundwater level collection as well as the frequency of groundwater sampling was also increased to monitor the remediation effort (DOE, 2003b).
4.2 X-749 Remedial Plan
Six treatment options were available for implementation at the X-749 Area, including no action, no further action, pump-and-treat, pump-and-treat with subsequent phytoremediation, phytoremediation, and enhanced bioremediation and phytoremediation
(DOE, 2000). Alternative 5, phytoremediation, was selected which required several acres of land to be planted with one-year-old hybrid poplar trees incorporating a significant amount of the plume area. However, to allow the root system to mature at least two years of initial growing was expected. Monitoring will continue throughout the life of the phytoremediation system. The design layout of the phytoremediation system of hybrid poplar trees would ensure maximum efficiency to capture and remove the contaminated groundwater. This method would reduce the over all plume size and TCE concentration after several years of operation. The highest concentration of TCE, approximately 4,200
µg/L, was expected to decrease to 48 µg/L within 30 years of implementation. The phytoremediation system is expected to remove the contaminants of concern from the 55 contaminated groundwater below the preliminary remedial goal. The total cost would be
$689,000 with an annual operation and maintenance cost of $334,000 (DOE, 2000).
The primary factor involved in selecting phytoremediation was based on the ability of the phytoremediation system to use the “natural growth process of the biological systems to attenuate and reduce contaminants in groundwater” (DOE, 1998).
Additionally, several other positive factors resulted in the selection of phytoremediation;
(1) the young hybrid poplar trees, the species of choice, if planted 10 to 15 feet below ground surface have the ability to develop strong, mature roots; (2) within 2 years this strong, mature root system would be developed; (3) within the initial 2 years natural attenuation (natural processes to clean up contamination in soil and groundwater) would take place; (4) metals are not a contaminate of concern, in turn, metals bioaccumulation in tree leaves are not foreseen; (5) estimated annual water consumption is 6,000 gallons per day per acre of trees; (6) minimal changes will be required for additional monitoring activities; (7) the total size of the plume will be reduced as well as the total concentration; and (8) contaminants will be contained within the boundaries of the area with additional support from barrier walls and containment trenches (DOE, 1998; DOE, 2000).
A phytoremediation system of 2,640 hybrid poplar trees was planted in seven areas/zones to manage the VOC contaminant plume, over an area of 28 acres during the winter of 2003. One planting method was utilized as well as one hybrid poplar tree species (DOE, 2002). This single planting method and tree species was selected due to the knowledge and data gained from the X-740 Phytoremediation System (Rieske,
2005b). Monitoring and maintenance activities included inspections of the condition of 56 the trees, condition of the ground cover, and the condition of the monitoring wells.
Groundwater level collection, the frequency of groundwater sampling, and the analysis of the groundwater samples increased to monitor the remediation effort (DOE, 2004a).
5.0 Research question
What impact does a phytoremediation system have on the groundwater flow and
chemistry in a TCE plume, and how do design choices such as species selection and
planting technique affect those results?
The performance of the X-740 and X-749 Phytoremediation Areas will be
evaluated and compared with design differences to identify any correlation. Further, new
results that have not and cannot be assessed in the laboratory will be determined such as
plume capture, seasonal variations in performance, and longevity and health of trees.
First, the overall performance of the systems to prevent offsite migration of TCE
and reduce plume size and concentration will be assessed. Information available for this
analysis will include groundwater elevations and chemical analysis data. In addition,
surveys have been repeatedly done to monitor the health of the trees. Reporting these
results for a full-scale system itself is a significant contribution to the field. Next,
performance results will be overlaid with design differences between and within the two
systems to determine if any correlation can be proven. Guidance on design specifications
may also be a significant contribution from this work. 57
5.1 Tree growth and mortality rates
5.1.1 Planting methods
The X-740 Area incorporates 3.5 acres of the PORTS reservation. Two inventive planting methods were implemented at the X-740 Area in order to construct a unique remediation system of hybrid poplar trees: a trench and sand stack method and a borehole method. Figure 5-1 represents both of the planting schemes implemented at the X-740
Area. Both planting methods implemented for the X-740 Phytoremediation System included three multi-species hybrid poplar trees (Populus nigra x Populus nigra, Populus nigra x Populus maximowiczii, and Populus deltoides x Populus nigra) planted in rows perpendicular to groundwater flow. These two techniques alternated throughout 2.6 acres of the X-740 Area (DOE, 2003b). The remaining 0.9 acres has a lower TCE concentration and was not treated by phytoremediation.
The first method of planting utilized was the trenching method, which included trees planted in rows of trenches typically 2-feet wide and 10-feet deep. The groundwater table at the X-740 Area is between 10-15 feet below ground surface (bgs).
The intention was to ensure the trees were planted within the groundwater table (Rieske,
2005b). Excavated soils from the trench installation were combined with fertilizer, lime, coarse sand, and peat moss to create an environment in which the trees would prosper.
The trees were planted in the trench with the backfill material throughout the entire length of the trench (DOE, 2003b). Prior to the trench installation, 8-inch diameter boreholes were drilled to 30-foot, approximately to bedrock, and filled with coarse sand to initiate the vertical flow of groundwater. Each boring was positioned between trees in 58 the row. These “sand stacks” provide a conduit for the contaminated groundwater to flow upwards to the trees in the trenches promoting the use of the natural groundwater
(DOE, 2003b).
59
Figure 5-1. Planting scheme implemented at the X-740 Area (DOE, 2003b). The trench and sand stack method is shown on the left and right set of trees. The borehole method is shown in the middle set of trees. 60
The second method of planting utilized was the boring method which included trees planted in 2-foot diameter, 10-foot deep borings. Borings 24 inches in diameter were drilled to the water table, approximately 10 feet bgs. After reaching the water table, the trees were planted in the boreholes along with the excavated soils combined with fertilizer, lime, coarse sand, and peat moss to ground surface (DOE, 2003b).
The X-740 hybrid poplar trees were spaced 10-feet apart in rows 10-feet to 20- feet apart (Rieske, 2005b). The planting pattern consisted of 36 rows, 11 rows implementing the trench and sand stack design, and 25 rows implementing the boring design. Figure 5-2 illustrates the planting pattern and tree layout design of the X-740
Phytoremediation Area as well as the X-740 groundwater plume (DOE, 2003b). The designs were alternated within the first 25 rows of the 36 row planting scheme. A total of
240 trees were planted with the trench and sand stack design and 526 trees were planted with the borehole design (DOE, 2003b). The tree species layout alternated between each genus. The trees were planted densely with the intention that the competition for water would force the trees roots to extend further into the ground thereby utilizing the groundwater. Additionally, the intention of the alternating planting pattern was for the trees planted in the borings to consume the surface water from precipitation while the trees planted in the trenches would consume the majority of the groundwater from the
Gallia aquifer via the sand stacks (Rieske, 2005b). 61
Figure 5-2. X-740 groundwater plume in 2001, planting pattern, and hybrid poplar tree layout of the X-740 Phytoremediation Area (DOE, 2003b). 62
5.1.2 Impact of planting method, TCE exposure, and species selection
The X-740 Phytoremediation System included three multi-species hybrid poplar trees (Populus nigra x Populus nigra, Populus nigra x Populus maximowiczii, and
Populus deltoides x Populus nigra) (DOE, 2002). In 2003 and 2005 tree growth and mortality studies were conducted at the X-740 Phytoremediation Area.
Tree diameters were measured at approximately 55 inches above ground surface or measured at the largest part of the tree if it was not 55 inches or greater. Items of interest regarding the trees were recorded during this survey such as dead trees, partially dead trees, missing trees, and tree height. A schematic of this data was created in order to illustrate a visual determination of the growth pattern at the X-740 Area for 2003 and
2005 as shown in figure 5-3 and figure 5-4 (DOE, 2003b).
A total of 766 hybrid poplar trees were planted at the X-740 Area, 240 trees were planted via the trench and sand stack method, the remaining 526 trees were planted using the borehole design as shown in figure 5-2 and the schematic representation in figure 5-5.
The survey conducted in 2003 concluded that among the 240 trees planted in the trenches, 15 (6.2%) were dead, 9 (3.8%) had diameters less than 3 cm, 55 (22.9%) had diameters greater than or equal to 3 and less than 8 cm, and 161 (67.1%) had diameters of
8 cm or greater. The trees planted within the trenches were thriving with the majority larger than 8 cm in diameter. Of the 526 trees planted in the boreholes, 44 (8.4%) were dead, 91 (17.3%) had diameters less than 3 cm, 369 (70.1%) had diameters greater than or equal to 3 and less than 8 cm, and 22 (4.2%) had diameters of 8 cm or greater.
63
Figure 5-3. X-740 phytoremediation tree growth and mortality study 2003 (DOE, 2003b). 64
Figure 5-4. X-740 phytoremediation tree growth and mortality study 2005. 65
Figure 5-5. X-740 phytoremediation species pattern and planting technique and growth results from 2005 survey. 66
The survey conducted in 2005 concluded that within the 240 trees planted in the trenches, 8 (3.3%) were dead, 8 (3.3%) had diameters less than 3 cm, 20 (8.3%) had diameters greater than or equal to 3 and less than 8 cm, and 204 (85%) had diameters of 8 cm or greater. Within the 526 trees planted in the boreholes, 29 (5.5%) were dead, 43
(8.2%) had diameters less than 3 cm, 293 (55.7%) had diameters greater than or equal to
3 and less than 8 cm, and 161 (30.6%) had diameters of 8 cm or greater. After the 2003 survey dead trees were removed, so trees recorded as dead in 2005 died after the 2003 survey.
Results from the 2003 and 2005 surveys are plotted in figures 5-6 and 5-7. For both monitoring periods the trees planted within the boreholes were not as large in diameter as the trees planted within the trenches. For both surveys, the majority of trees planted in trenches were greater than 8 cm in diameter, while the majority of trees planted in boreholes were between 3 and 8 cm in diameter. Overall, the trees planted in the trenches have a more successful growth rate than the trees planted in the boreholes.
Because both planting methods used the same soil amendments, were mixed to the same depth of 10 feet, and were approximately the same width (2-foot diameter hole versus 2- foot width trench), the difference in growth rates is most likely due to more water availability through the trenches and sand stacks. 67
80.0%
70.0%
60.0%
50.0%
Trees planted in Trenches 40.0% Trees planted in Boreholes
30.0%
20.0%
10.0%
0.0% Dead < 3 cm 3-8 cm >8 cm 2003 Growth and mortality study
Figure 5-6. Percentage of the trees planted in trenches versus trees planted in boreholes, 2003 X-740 phytoremediation tree growth and mortality study.
90.0%
80.0%
70.0%
60.0%
50.0% Trees planted in Trenches Trees planted in Boreholes 40.0%
30.0%
20.0%
10.0%
0.0% Dead < 3 cm 3-8 cm >8 cm 2005 Growth and mortality study
Figure 5-7. Percentage of the trees planted in trenches versus trees planted in boreholes, 2005 X-740 phytoremediation tree growth and mortality study. 68
Throughout the phytoremediation system the tree mortality of 2003 and 2005 appears to be random. The largest trees in diameter were located in the northeastern and center sections of the plantation. The TCE concentrations in these areas were between
100-1000 µg/L or greater than 1000 µg/L as shown in figure 5-2. The mortality rate appears to be random and not attributed to the TCE concentration.
The hybrid poplar tree species Populus nigra x Populus nigra and Populus nigra
X Populus maximowiczii were very similar in tree diameter and mortality (figures 5-8 and
5-9). The hybrid poplar tree species Populus deltoides x Populus nigra in 2003 and 2005 were smaller in diameter and had a higher mortality rate. This was in part due to a fungal infection which infected only the Populus deltoides x Populus nigra species. Once infected, the tree develops a large canker on the trunk. This is common in several trees of this species in the X-740 Phytoremediation Area (Rieske, 2005b). This damage results in the tree tops breaking thereby stunting the growth of not only the damaged tree but the growth and health of the surrounding trees (Rieske, 2005b). The other two hybrid poplar tree species, Populus nigra x Populus nigra and Populus nigra X Populus maximowiczii, were not affected by the infestation. 69
Populus nigra x P. maximowiczii Populus nigra x P. nigra Populus deltoides x P. nigra
25.0%
20.0%
15.0%
10.0%
5.0%
0.0% Dead < 3 cm 3-8 cm >8 cm 2003 species growth and mortality study
Figure 5-8. Tree species growth and mortality percentage 2003.
Populus nigra x P. maximowiczii Populus nigra x P. nigra Populus deltoides x P. nigra
20.0%
18.0%
16.0%
14.0%
12.0%
10.0%
8.0%
6.0%
4.0%
2.0%
0.0% Dead < 3 cm 3-8 cm >8 cm 2005 Species growth and mortality study
Figure 5-9. Tree species growth and mortality percentage 2005. 70
5.1.3 TCE accumulation in tree tissue
A tree coring study was conducted at the X-740 Phytoremediation Area in 2003.
Core samples were collected from a total of 16 hybrid poplar trees for the study (DOE,
2003b). Eleven core samples were collected from species Populus nigra x Populus maximowiczii (NM-6), three core samples were collected from Populus nigra x Populus nigra (NE-19), and two core samples were collected from species Populus deltoides x
Populus nigra (DN-34). A 0.4 inch diameter hole was bored into each tree trunk with a small hand auger (incremental core sampler). A core sample of 0.25 inches in diameter and 2 to 4 inches in length was collected approximately 18 inches above ground level for all sixteen trees. Once collected the tree core samples were placed in a pre-weighed
TeflonTM-lined rubber septum and tightly secured with a crimp-top seal. Once the
samples reached the laboratory a 250 µL headspace sample was extracted from each
sample container via a gas-tight syringe and injected into a gas chromatograph for TCE
and TCE byproduct analysis (DOE, 2003b).
TCE was detected at measurable levels in only three of the 16 core samples
collected at the X-740 Phytoremediation Area (figure 5-10). A TCE concentration of 3.3
µg/L was detected in the headspace sample of species NM-6 planted with the trench and
sand stack combination planting method. Also, TCE concentrations of 6.9 µg/L and 2.8
µg/L were detected in the headspace sample of species NM-6 planted with the borehole
planting method. TCE was not detected in the majority of cored trees, however, the
detected TCE indicates that some of the trees are accumulating TCE and are clearly
utilizing contaminated groundwater within the phytoremediation system (DOE, 2003b). 71
One of the detections was in an area of TCE concentrations above 1,000 µg/L, but the other two were in lower concentration regions between 5 and 100 µg/L. There does not appear to be any relationship between groundwater TCE concentration and detection in the plant tissue. Additionally, there were not enough detections to discern any correlation based on tree planting method or tree species.
A tree coring study has not been conducted at the X-749 Phytoremediation Area due to the young age of the system. A five-year evaluation of the X-749
Phytoremediation System will be conducted in 2008 incorporating tree growth, diameter studies, mortality rates, transducer/data loggers data, and core samples to determine TCE uptake of the area (DOE, 2004a). 72
Figure 5-10. X-740 Phytoremediation tree coring study TCE concentration results (DOE, 2003b). 73
5.2 Groundwater flow
5.2.1 Depth to water
During 1999 prior to the tree installation at the X-740 Phytoremediation Area water level measurements were collected from ten Gallia monitoring wells in the area.
During the tree installation throughout the summer of 1999 four new Gallia monitoring wells were installed at the X-740 Area. Manual water level measurements were collected quarterly at a total of fourteen Gallia monitoring wells in the X-740 Area between 1998 and 2001. These manual water level measurements were collected in order to monitor the combined impact of the trees on the groundwater prior to root development (DOE,
2003b). The water level measurement data included ten Gallia wells installed during the early 1990’s as well as the four Gallia wells installed in 1999. Beginning in 2001 water level measurements were collected monthly during the growing season (April-
September) and quarterly during the dry season (October-March). A total of eight water level measurements are provided annually to monitor the phytoremediation system's effect on the groundwater in the X-740 Area (DOE, 2003b).
The primary function of the X-740 Phytoremediation Area is to hydraulically prevent further spreading of the TCE plume. This process utilizes deep rooted plants, such as the poplar trees, to pump large quantities of water from the saturated zone. The focal point of any phytoremediation system is to develop a cone of depression under the entire plantation area. This occurrence can halt migration of the contaminant plume and create a hydraulic barrier maintaining plume capture (Van Den Bos, 2002). A cone of depression is not evident at the X-740 Phytoremediation Area as of yet, however, water 74 level measurements and water elevations demonstrated uncharacteristic behavior in 2004 and 2005 than in previous years indicative of the mature trees influencing groundwater flow at the site.
Water level depths as well as water elevations for 1998 through 2005 were examined for wells X740-03G, X740-08G, X740-10G, X740-PZ10G, and X740-PZ12G, all five wells are located within the X-740 Phytoremediation System of trees as shown on figure 5-11. Additionally, water level depths as well as water elevations for 1998 through
2005 were examined as background measurements for wells X740-05G, X740-06G, F-
13G, X326-04G, and X330-PZ01G, each located between 100 ft and 1500 ft upgradient from the X-740 Phytoremediation System as shown in figure 5-11. Figure 5-12 illustrates the increase in depth to groundwater in the five wells installed within the phytoremediation area versus the five wells installed outside of the area. The water level measurements were plotted twice for each year from 1998 to 2005, once for the dormant season and once for the growing season. The dormant season points are the averages of the months of October through March (average of 2 values). The growing season points are the averages of the months of April through September (average of 6 values). 75
Figure 5-11. X-740 Area well locations used for the water level and gradient study.
76
18.00
16.00
14.00 X740-03G 12.00 X740-08G X740-10G X740-PZ10G 10.00 X740-PZ12G X740-05G X740-06G 8.00 F-13G X326-04G Depth to water (ft) to water Depth 6.00 X330-PZ01G
4.00
2.00
0.00 98D 98G 99D 99G 00D 00G 01D 01G 02D 02G 03D 03G 04D 04G 05D 05G 1998-2005 Dormant and Growing Seasons
Figure 5-12. Average groundwater levels from wells in the X-740 Phytoremediation Area (X740-03G, X740-08G, X740-10G, X740-PZ10G, and X740-PZ12G) and outside the area (X740-05G, X740-06G, F-13G, X326-04G, X330-PZ01G).
Water level measurements collected from 1998 and 1999, prior to root development of the trees in the phytoremediation area (the trees were planted in the summer of 1999), demonstrate greater water level depths during the dormant season than during the growing season. These depths, for example, vary between a dormant season measurement of 14.15 ft and a growing season measurement of 12.41 ft for well X740-
08G placed within the trees, and a dormant season measurement of 13.67 ft and a growing season measurement of 12.37 ft for well X330-PZ01G a background well approximately 1500 ft upgradient of the phytoremediation system. This information signifies a lower water elevation at the X-740 Phytoremediation Area during the winter 77 season, and a higher water elevation at the X-740 Phytoremediation Area during the summer season. This cyclic trend is apparent in water level measurements collected from the five wells installed within the phytoremediation plantation of trees and the five background wells installed from 250 ft to 1500 ft upgradient of the X-740
Phytoremediation System.
However, water level measurements collected from 2003-2005 from wells in the
X-740 Phytoremediation Area show a markedly different trend then measurements obtained before this time period. Depth to water steadily increases in the X-740
Phytoremediation System from 2003 to 2005. Over that time period and average groundwater table drop of 0.30 ft was observed. The five background wells outside of the phytoremediation area continue the cycle or have a decreasing depth to water during the dormant season than during the growing season from 1998 and 2005. In these wells, there has been no apparent change in the annual groundwater fluctuations since 1998 unlike the wells within the phytoremediation system. It is most apparent in wells X330-
PZ01G and X326-04G which are both up to 1,500 feet away from the site,
The X-740 Phytoremediation System was predicted to be mature within two to three years of the initial planting, which would have been by 2001 or 2002. However, according to the water level measurements, the X-740 Phytoremediation System appears to have no observable impact on groundwater levels until 2004. Thus the phytoremediation system required four to five years to mature instead of the estimated two to three.
78
5.2.2 Groundwater flow potentiometric surface maps
Potentiometric surface maps of the X-740 Area from April (second quarter) and
October (fourth quarter) of 1998 through 2005 are provided in figures 5-13 through 5-28.
Groundwater consistently flows from east to west across the site. The phytoremediation system was installed in 1999 between figures 5-15 and 5-16. It was expected that groundwater contours would change significant over the site as the trees matured.
Obvious signs of significant groundwater extraction would indicate the formation of a cone of depression or increased head gradient across the site, compared to the flow upgradient. These trends are not apparent from analysis of these figures. It does appear that the head gradient across the site is higher during the spring sampling events (as shown by the contour lines being closer together) while the head gradient upgradient of the site and during the fall is lower. However, the figures do not clearly show that this trend was initiated by the installation of the phytoremediation system. Because of the unclear data provided here, an effort to develop a groundwater model to reproduce these figures was abandoned. However, the change in gradient was analyzed further. 79
Figure 5-13. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 1998. 80
Figure 5-14. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 1998. 81
Figure 5-15. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 1999. 82
Figure 5-16. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 1999. 83
Figure 5-17. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 2000. 84
Figure 5-18. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 2000. 85
Figure 5-19. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 2001. 86
Figure 5-20. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 2001. 87
Figure 5-21. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 2002. 88
Figure 5-22. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 2002. 89
Figure 5-23. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 2003. 90
Figure 5-24. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 2003. 91
Figure 5-25. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 2004. 92
Figure 5-26. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 2004. 93
Figure 5-27. Potentiometric surface map of X-740 Area from levels measured in April (second quarter) 2005. 94
Figure 5-28. Potentiometric surface map of X-740 Area from levels measured in October (fourth quarter) 2005. 95
5.2.3 Hydraulic gradient
The hydraulic gradient is the driving force of fluid flow in a porous medium
calculated as the change in hydraulic head (pressure) per unit distance. The difference in
the hydraulic gradient from 1998 (before the phytoremediation system was installed)
through 2005 was calculated between two wells upgradient of the X-740
Phytoremediation Area, X740-04G and X740-05G, and two wells planted within the trees near the center of the plume, X740-03G and X740-10G, as shown in figure 5-11. The gradients in the well pairs steadily increase over time, although there is some scatter in the data (see figure 5-29). The data was plotted based on a yearly average, combining both growing and dormant seasons. It appears that as the trees mature the increasing groundwater withdrawal can be seen by the increasing gradient across the site. In fact
there is a statistically significant difference (α=0.05) between average gradients for the
four well pairs in 1998 and 1999 to the average gradient for the four well pairs in 2004
and 2005. 96
0.015
0.01
0.005 04G-03G 04G-10G 05G-03G
Gradients 05G-10G 0 98 99 00 01 02 03 04 05
-0.005
-0.01 1998-2005
Figure 5-29. Annual gradient fluctuations between 1998-2005 at the X-740 Area. Wells X740-04G-03G, X740-04G-10G, X740-05G-03G, and X740-05G-10G.
Poplar trees only transpire between 4-6 months (April-September) of the year, therefore it is extremely difficult to determine the amount of groundwater taken up in a phytoremediation system (Schnoor, 2002). Additionally, groundwater uptake and transpiration rates depend on many factors as discussed previously such as plant species, plant size and diameter, climatic factors, and precipitation. Further, surface water from precipitation can also be absorbed and transpired by the phytoremediation system inhibiting groundwater use and remediation efforts (Schnoor, 2002).
Groundwater flow to the phytoremediation system can be estimated using the calculated gradient over the X-740 Area and the Darcy’s equation:
dh Q = −KA dx 97
Where, Q is the groundwater flow rate (ft3/s), K is the hydraulic conductivity of the
dh aquifer (ft/s), A is the cross sectional area of the aquifer (ft2), and is the hydraulic dx gradient of the aquifer (ft/ft). The gradients from four well combinations of X740-05G &
10G, X740-05G & 03G, X740-04G & 10G, and X740-04G& 03G were used to calculate the annual groundwater consumption of the phytoremediation system. The hydraulic conductivity of the site (0.0000491 ft/s) was multiplied by the cross sectional area of the phytoremediation system (2400 ft2), the thickness of the aquifer (30 ft), and the change in the gradient from the average gradient in 1998 and 1999 to the average gradient in 2004
and 2005. The difference in gradients between the well combinations were X740-05G &
10G - 0.98 ft/ft, X740-05G & 03G - 0.44 ft/ft, X740-04G & 10G - 1.53 ft/ft, and X740-
04G& 03G - 0.99 ft/ft. Based on these results, the X-740 Phytoremediation Area is
estimated to transpire an average 75,000 gallons per day (gpd) of groundwater. This is an
average daily consumption rate of 98 gallons per tree during an average growing season.
Groundwater uptake rates for four to five-year old poplar trees were estimated at 26 gpd
to 53 gpd (EPA, 2001b), while six to seven year old poplar were estimated to take up 80
gpd (EPA, 2001b). The poplar trees at the X-740 Phytoremediation Area are seven years old, though somewhat higher, 98 gpd is consistent with these reported values.
5.2.4 X-749 depth to water
The water levels and water elevations at the X-749 Phytoremediation Area have
demonstrated comparable behavior to the early stages of the X-740 Phytoremediation
Area water levels and water elevations. Water level depths as well as water elevations
for 2002 through 2005 were examined for wells X749-37G, X749-38G, STSW-101G, 98
STSW-102G, and X749-32G, all five wells are located within the X-749
Phytoremediation System of trees as shown in figure 5-30. Additionally, water level depths and water elevations were examined for wells X749-13G, X120-08G, X120-10G,
X749-PZ05G, and X749-PZ06G, each located between 150 ft and 1000 ft upgradient from the X-749 Phytoremediation System.
The X-749 Phytoremediation Area was installed in 2003, and based on results from the X-740 Phytoremediation Area; changes in groundwater levels should be detectable in 2007 or 2008. Water level measurements collected from 2002 to 2005, demonstrate greater water level depths during the dormant season than during the growing season (figure 5-31). This cyclic trend is apparent in water level measurements from the five wells installed within the phytoremediation area and some of the upgradient wells installed. This behavior is consistent with the X-740 Phytoremediation Area during the first four years following installation (figure 5-12). A decreasing groundwater elevation due to phytoextraction should become apparent in the X-749 Phytoremediation
Area within the next two years. 99
Figure 5-30. X-749 Area well locations used for the water level study. 100
25.00
20.00
X749-37G X749-38G 15.00 STSW-101G STSW-102G X749-32G X749-13G X120-08G 10.00 X120-10G
Depth to water (ft) X749-PZ05G X749-PZ06G
5.00
0.00 02D 02G 03D 03G 04D 04G 05D 05G 2002-2005 Dormant and Growing Seasons
Figure 5-31. Average groundwater levels from wells in the X-749 Phytoremediation Area (X749-37G, X749-38G, STSW-101G, STSW-102G, and X749-32G) and outside the area (X749-13G, X120-08G, X120-10G, X749-PZ05G, X749-PZ06G).
5.2.5 Hourly water level measurements
Hourly groundwater level measurements were collected routinely at the X-740
Phytoremediation Area via transducer and data loggers during the month of July (DOE,
2004a). Transducer and data loggers were installed in 2003 through 2005 in two Gallia
groundwater monitoring wells in the X-740 Phytoremediation Area to monitor the
performance of the system during one month of the growing season. The groundwater
level measurements collected by the transducer and data loggers indicated a fluctuation in
the readings between daybreak and nightfall (figures 5-32, 5-33, and 5-34). This could
be due to groundwater uptake by the tree root system during the day and subsequent 101 groundwater recharge at night. However, it could also be due to evaporation or evapotranspiration from other native vegetation on the site. Water level measurements were not collected with the transducer and data loggers during the dormant season so if a change occurred in the water levels during the growing season it cannot be identified.
Also, water level measurements were not collected with the transducer and data loggers in upgradient wells to determine if the diurnal changes were more prominent under the phytoremediation area. The hydrographs in figures 5-32, 5-33, and 5-34 demonstrate the diurnal water level measurement fluctuations during the month of July from 2003-2005 for wells X740-03G and X740-PZ17G. The major grid lines on the x-axis represents midnight. The water level recharge during the night-time hours can be identified as well as the water level drawdown during the daylight hours.
664.00 102
X740-PZ17G X740-03G
663.00
662.00
661.00
660.00
659.00 Groundwater elevation (ft)
658.00
657.00
M 0 A M 0 AM 2:0 0 A M 2:0 0 AM 03 1 2:0 0 A M 03 1 2:0 7/1/ 03 1 2:0 00 AM 0 A 7/2/ 03 1 2: 0 AM M 7/3/ 03 1 2:0 0 AM A M 7/4/ 2:0 A M 7/5/ 6/03 1 03 1 2:0 :00 A M 7/ 03 1 :00 A M July 2003 7/7/ 03 1 3 12 :00 A M 7/8/ /0 3 12 :00 A M 7/9/ /0 3 12 :00 A M /0 3 12 :00 A M 7/10 /0 3 12 :00 A M 7/11 /0 3 12 :00 A M 7/12 /0 3 12 :00 A M 7/13 /0 3 12 :00 A M 7/14 3 12 :00 A M Figure 5-32. X740-03G and X740-PZ17G hydrograph data from July 2003. 7/15 /0 3 12 :00 A M 7/16 17/0 /0 3 12 :00 A M 7/ /0 3 12 :00 A M 7/18 3 12 :00 A M 7/19 3 12 :00 A M 7/20 21/0 /0 :00 A M 7/ 3 12 :00 A M 7/22 23/0 /0 3 12 :00 A M 7/ 3 12 A 7/24 25/0 /0 3 12 :00 7/ 3 12 12:00 :00 7/26 27/0 /0 3 7/ 3 12 7/28 /0 3 12 7/29/0 7/30 31/0 7/ 662.00 103
X740-PZ17G X740-03G
661.00
660.00
659.00
658.00
657.00 Groundwater elevations (ft)
656.00
655.00
M M M M M M 7/1/04 12:00 AM A 7/2/04 12:00 AM 0 7/3/04 12:00 A 0 AM 7/4/04 12:00 A M 7/5/04 12:00 A 12:0 M 7/6/04 12:00 A M 7/7/04 12:00 A 04 JulyM 2004 7/8/04 12:0 M 7/9/ M 7/10/04 12:00 AM 0 A M 7/11/04 12:00 AM :0 0 A A M 7/12/04 12:00 AM :0 A 7/13/04 12:00 A :00 7/14/04 12:00 A :00 7/15/04 12:00 A 7/16/04 12:00 A 4 12 Figure 5-33. X740-03G and X740-PZ17G hydrograph data from July 2004. 7/17/04 12 /0 4 12 7/18/04 12 /0 7/19 /04 12:00 AM 7/20 21 /04 12:00 AM 7/ 22 7/ 7/23/04 12:00 AM 7/24/04 12:00 AM 7/25/04 12:00 AM 7/26/04 12:00 AM 7/27/04 12:00 AM 7/28/04 12:00 AM 7/29/04 12:00 AM 7/30/04 12:00 AM 7/31/04 12:00 AM 660.50 104
660.00 X740-PZ17G X740-03G
659.50
659.00
658.50
658.00
657.50
657.00
656.50 Groundwater elevations (ft)Groundwater
656.00
655.50
655.00
M A M 0 A M :0 0 A M 2 0 0 A M 1 2: :0 0 A M 5 1 2 :0 0 A M /0 5 1 2 :0 0 A M /1 /0 5 1 2 :0 0 A M 7 /2 /0 5 1 2 0 0 A M 7 /3 /0 5 1 2: 0 A 7 /0 5 1 : 00 M 7/4 0 12 A M /5 / 05 2: :00 0 A M 7 /6 / 5 1 2 :0 0 A M 7 /7 /0 5 1 2 :0 0 A M July 2005 7 /8 /0 5 1 2 :0 0 A M 7 /9 /0 5 1 2 0 A 7 0 /0 5 : 00 M /1 1 0 1 2 : 0 A M 7 / 05 1 2 :0 0 A M /1 12 / 5 1 2 :0 0 A M 7 / 3 /0 5 1 2 0 0 A M 7 /1 4 /0 5 1 2: 0 7 /1 5 0 5 : 0 A M 7 6/ 0 1 2 :0 0 A M 7/1 1 / 5 1 2 :0 A M / 7 /0 5 1 2 :00 0 A M Figure 5-34. X740-03G and X740-PZ17G hydrograph data from July 2005. 7 /1 8 /0 5 1 2 0 A 7 /1 9 /0 5 1 : 00 M 7 /1 0 0 2 : 0 A M 7 / 05 1 2 :0 0 A M /2 21 / 5 1 2 :0 0 A M 7 / 2 /0 5 1 2 0 0 A M 7 /2 3 /0 5 1 2: 0 7 /2 4 0 5 : A M 7 5/ 0 1 2 :00 0 A 7/2 / 5 1 2 :0 /2 6 /0 5 1 2 :00 7 /2 7 /0 5 1 2 7 /2 8 /0 5 1 7 /2 9 /0 5 7 /2 0 0 7 3 1/ 7/ 7/3 105
5.3 TCE groundwater plume
The preliminary groundwater study began in 1989 at the PORTS facility. X-740 groundwater samples are collected on a semiannual basis from 14 Gallia monitoring wells. These samples are analyzed for volatile organic compounds, TCE and its byproducts cis-1,2-dichloroethene (cis-1,2-DCE), trans-1,2-dichloroethene (trans-1,2-
DCE), 1,1-dichloroethene (1,1-DCE), and vinyl chloride. TCE has been detected in 10 of the 14 Gallia monitoring wells at the X-740 Area. The X-740 Gallia groundwater wells with TCE detections are X740-02G, X740-03G, X740-04G, X740-08G, X740-10G,
X740-11G, X740-PZ10G, X740-PZ12G, X740-PZ14G, and X740-PZ17G. The X-740
Gallia groundwater wells with non-detection concentrations or concentrations less than
0.5 µg/L are X740-01G, X740-05G, X740-06G, and X740-13G. TCE, 1,1-DCE, cis-1,2-
DCE, trans-1,2-DCE, and vinyl chloride concentrations of the 10 Gallia groundwater monitoring wells where TCE was detected are provided in tables 5-1, 5-2, 5-3, 5-4, and
5-5.
At the X-740 Phytoremediation Area four monitoring wells (X740-03G, X740-
10G, X740-PZ10G, and X740-PZ12G) were identified for assessment evaluations due to their high TCE concentrations.
Well X-740-03G is located in the center of the plume with the highest reported
TCE concentration. The TCE concentration appears to be increasing from 1200 µg/L in
1997 to 5500 µg/L in 2005. The TCE byproduct of 1,1-DCE also appears to be increasing from 240 µg/L in 1997 to 930 µg/L in 2005. As well, the TCE byproduct of 106 cis-1,2-DCE appears to be increasing from 4 µg/L in 1997 to 15 µg/L in 2005. The TCE byproducts of trans-1,2-DCE and vinyl chloride were not detected.
Well X-740-10G is located approximately 100 ft south of well X740-03G in the moderate concentration range of the TCE plume. The TCE concentration appears to be increasing from 26 µg/L in 1997 to 380 µg/L in 2005. The TCE byproduct of 1,1-DCE also appears to be increasing from 7.4 µg/L in 1997 to 92 µg/L in 2005. As well, the
TCE byproduct of cis-1,2-DCE was detected at low concentrations, and trans-1,2-DCE and vinyl chloride were not detected.
Well X-740-PZ10G is located approximately 80 ft west of well X740-03G in the low concentration range of the TCE plume. The TCE concentration appears to be increasing from 9 µg/L in 2000 to 50 µg/L in 2005. The TCE byproduct of 1,1-DCE also appears to be increasing from an undetected concentration in 2000 to 7.6 µg/L in 2005.
As well, the TCE byproduct of cis-1,2-DCE was detected at low concentrations, and trans-1,2-DCE and vinyl chloride were not detected.
Well X-740-PZ12G is located approximately 125 ft west of well X740-03G in the moderate concentration range of the TCE plume. The TCE concentration appears to be increasing from 25 µg/L in 2000 to 170 µg/L in 2005. The TCE byproduct of 1,1-DCE also appears to be increasing from 7 µg/L in 2000 to 26 µg/L in 2005. As well, the TCE byproduct of cis-1,2-DCE was detected at low concentrations, and trans-1,2-DCE and vinyl chloride were not detected.
107
Sampling X740- X740- X740- X740- X740- X740- X740- X740- X740- X740- event 02G 03G 04G 08G 10G 11G PZ10G PZ12G PZ14G PZ17G 4Q-2005 NS 5500 NS NS 380 17 50 170 67 45 2Q-2005* 4.8 3500 6.2 20 200 16 39 150 110 38 4Q-2004 NS 4500 NS NS 580 21 62 170 98 18 2Q-2004* NS 3100 7.2 16 210 17 37 190 82 52 4Q-2003 NS 3600 NS NS 480 16 65 180 53 460 2Q-2003* 4.5 2700 16 21 150 22 17 180 83 29 4Q-2002 NS 3800 NS NS 570 20 73 280 80 56 2Q-2002* NS 1900 30 25 150 19 52 200 65 54 4Q-2001 NS 2700 NS NS 560 23 70 230 87 48 2Q-2001* 3.0 2200 27 29 200 20 61 220 80 16 4Q-2000 3.0 3000 18 24 520 18 9.0 25 7.0 ND 2Q-2000* 2.0 1500 36 34 140 19 NS NS NS NS 4Q-1999 ND 2100 11 34 490 26 NS NS NS NS 2Q-1999 ND 2200 12 29 320 16 NA NA NA NA 2Q-1998 NS NS NS 44 NS 13 NA NA NA NA 3Q-1997 2.3 1200 22 39 26 NS NA NA NA NA
Table 5-1. X-740 Area TCE concentrations in µg/L from third quarter 1997 through second quarter 2005. *=data collected during growing season (April through September) ND=not detected, NS=not sampled, NA=not applicable Quarters are based on calendar year
108
Sampling X740- X740- X740- X740- X740- X740- X740- X740- X740- X740- event 02G 03G 04G 08G 10G 11G PZ10G PZ12G PZ14G PZ17G 4Q-2005 NS 930 NS NS 92 5.2 7.6 26 22 14 2Q-2005* 4.7 510 1.2 1.4 41 6.4 5.1 32 27 15 4Q-2004 NS 930 NS NS 140 8.8 9.5 36 28 2.3 2Q-2004* NS 560 1.4 0.91 44 6.1 5.6 41 17 15 4Q-2003 NS 630 NS NS 110 6.1 11 40 17 12 2Q-2003* 3.8 NS 2.4 0.66 31 8.2 3.1 41 22 12 4Q-2002 NS 770 NS NS 140 9.0 12 51 26 23 2Q-2002* NS 350 6.0 ND 40 8.0 9.0 50 21 22 4Q-2001 NS 550 NS NS 160 10 13 71 29 19 2Q-2001* 3.0 490 8.0 ND 62 10 12 69 33 7.0 4Q-2000 3.0 660 4.0 ND 150 9.0 ND 7.0 3.0 ND 2Q-2000* ND 260 9.0 ND 37 8.0 NS NS NS NS 4Q-1999 ND 520 3.0 ND 150 13 NA NA NA NA 2Q-1999 ND 580 3.0 ND 110 8.0 NA NA NA NA 2Q-1998 NS NS NS ND NS 6.0 NA NA NA NA 3Q-1997 ND 240 3.9 ND 7.4 NS NA NA NA NA
Table 5-2. X-740 Area 1,1-DCE concentrations in µg/L from third quarter 1997 through second quarter 2005. *=data collected during growing season (April through September) ND=not detected, NS=not sampled, NA=not applicable Quarters are based on calendar year
109
Sampling X740- X740- X740- X740- X740- X740- X740- X740- X740- X740- event 02G 03G 04G 08G 10G 11G PZ10G PZ12G PZ14G PZ17G 4Q-2005 NS 15 NS NS 2.4 ND ND 0.28 0.28 0.16 2Q-2005* ND NR ND 27 1.0 ND ND ND ND ND 4Q-2004 NS 14 NS NS 2.9 ND ND ND ND ND 2Q-2004* NS ND ND 24 ND ND 0.21 ND ND 0.16 4Q-2003 NS ND NS NS 2.7 ND ND ND ND ND 2Q-2003* ND NS ND 38 0.77 ND 0.58 0.41 0.31 ND 4Q-2002 NS ND NS NS ND ND ND ND ND ND 2Q-2002* ND ND ND 34 ND ND ND ND ND ND 4Q-2001 NS ND NS NS ND ND ND ND ND ND 2Q-2001* ND ND ND 52 ND ND ND ND ND ND 4Q-2000 ND ND ND 34 ND ND ND ND ND ND 2Q-2000* ND ND ND 48 ND ND NS NS NS NS 4Q-1999 ND NS ND 43 ND ND NA NA NA NA 2Q-1999 ND 20 ND 47 ND ND NA NA NA NA 2Q-1998 NS NS NS 62 NS 6.0 NA NA NA NA 3Q-1997 ND 4.0 ND 56 ND NS NA NA NA NA
Table 5-3. X-740 Area cis-1,2-DCE concentrations in µg/L from third quarter 1997 through second quarter 2005. *=data collected during growing season (April through September) ND=not detected, NS=not sampled, NA=not applicable Quarters are based on calendar year
110
Sampling X740- X740- X740- X740- X740- X740- X740- X740- X740- X740- event 02G 03G 04G 08G 10G 11G PZ10G PZ12G PZ14G PZ17G 4Q-2005 NS ND NS NS ND ND ND ND ND ND 2Q-2005* ND ND ND 11 ND ND ND ND ND ND 4Q-2004 NS ND NS NS ND ND ND ND ND ND 2Q-2004* NS ND ND 7.5 ND ND ND ND ND ND 4Q-2003 NS ND NS NS ND ND ND ND ND ND 2Q-2003* ND NS ND 16 ND ND ND ND ND ND 4Q-2002 NS ND NS NS ND ND ND ND ND ND 2Q-2002* ND ND ND 15 ND ND ND ND ND ND 4Q-2001 NS ND NS NS ND ND ND ND ND ND 2Q-2001* ND ND ND 21 ND ND ND ND ND ND 4Q-2000 ND ND ND 15 ND ND ND ND ND ND 2Q-2000* ND ND ND 20 ND ND NS NS NS NS 4Q-1999 ND NS ND 18 ND ND NA NA NA NA 2Q-1999 ND ND ND 19 ND ND NA NA NA NA 2Q-1998 NS NS NS 23 NS ND NA NA NA NA 3Q-1997 ND ND ND 21 ND NS NA NA NA NA
Table 5-4. X-740 Area trans-1,2-DCE concentrations in µg/L from third quarter 1997 through second quarter 2005. *=data collected during growing season (April through September) ND=not detected, NS=not sampled, NA=not applicable Quarters are based on calendar year
111
Sampling X740- X740- X740- X740- X740- X740- X740- X740- X740- X740- event 02G 03G 04G 08G 10G 11G PZ10G PZ12G PZ14G PZ17G 4Q-2005 ND ND ND ND ND ND ND ND ND ND 2Q-2005* NS ND NS NS ND ND ND ND ND ND 4Q-2004 NS ND NS NS ND ND ND ND ND ND 2Q-2004* NS ND ND ND ND ND ND ND ND ND 4Q-2003 NS ND NS NS ND ND ND ND ND ND 2Q-2003* ND NS ND 0.42 ND ND ND ND ND ND 4Q-2002 NS ND NS NS ND ND ND ND ND ND 2Q-2002* ND ND ND ND ND ND ND ND ND ND 4Q-2001 NS ND NS NS ND ND ND ND ND ND 2Q-2001* ND ND ND ND ND ND ND ND ND ND 4Q-2000 ND ND ND ND ND ND ND ND ND ND 2Q-2000* ND ND ND ND ND ND NS NS NS NS 4Q-1999 ND ND ND ND ND NA NA NA NA NA 2Q-1999 ND ND ND ND ND NA NA NA NA NA 2Q-1998 NA NA NA NA NA NA NA NA NA NA 3Q-1997 NA NA NA NA NA NA NA NA NA NA
Table 5-5. X-740 Area vinyl chloride concentrations in µg/L from third quarter 1997 through second quarter 2005. *=data collected during growing season (April through September) ND=not detected, NS=not sampled, NA=not applicable Quarters are based on calendar year
These results seem to indicate that phytoremediation has failed to cleanup the plume. In fact, contaminant concentrations have increased since installation of the phytoremediation system. It is possible that the boring, trenching, soil mixing, and change in groundwater flow due to and following the installation of the phytoremediation system liberated some sequestered contaminants. However, second quarter (summer) concentrations are characteristically lower than fourth quarter (winter) concentrations in all four selected monitoring wells for the volatile organic compounds of TCE and 1,1-
DCE. This could be due to the influence on the trees in the phytoremediation area during the growing season. The average concentrations of TCE and 1,1-DCE for second and fourth quarters are provided in tables 5-6 and 5-7. Figure 5-35 represents the 1,1-DCE 112 concentrations of wells X740-03G and X740-10G between 1997 and 2005. Figure 5-36 represents the 1,1-DCE concentration of wells X740-PZ10G and X740-PZ12G between
1997 and 2005.
Sampling X740- X740- X740- X740- X740- X740- X740- X740- X740- X740- event 02G 03G 04G 08G 10G 11G PZ10G PZ12G PZ14G PZ17G 4Q/2002- NA 4350 NS NS 502.5 18.5 62.5 200 74.5 144.8 2005 2Q/2002- 4.7 2800 14.9 20.5 177.5 18.5 36.3 180 85 43.3 2005*
Table 5-6. X-740 Area second and fourth quarter average TCE concentrations in µg/L from 2002 through 2005. *=data collected during growing season (April through September) NA=not applicable Quarters are based on calendar year
Sampling X740- X740- X740- X740- X740- X740- X740- X740- X740- X740- event 02G 03G 04G 08G 10G 11G PZ10G PZ12G PZ14G PZ17G 4Q/2002- NA 815 NA NA 120.5 7.3 10 38.3 23.3 17.5 2005 2Q/2002- 4.3 355 2.3 0.74 39 7.2 5.7 41 21.8 16 2005*
Table 5-7. X-740 Area second and fourth quarter average 1,1-DCE concentrations in µg/L from 2002 through 2005. *=data collected during growing season (April through September) NA=not applicable Quarters are based on calendar year 113
1000
900
800
700 g/L) m 600
X740-03G 500 X740-10G
400
1,1-DCE concentration1,1-DCE ( 300
200
100
0 3Q- 2Q- 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 1997 1998 1999 1999 2000* 2000 2001* 2001 2002* 2002 2003* 2003 2004* 2004 2005* 2005 Sampling event
Figure 5-35. 1,1-DCE concentrations of wells X740-03G and X740-10G, two of the four designated monitoring wells at the X-740 Phytoremediation Area.
80
70
60 g/L)
m 50
X740-PZ10G 40 X740-PZ12G
30 1,1-DCE concnetration1,1-DCE (
20
10
0 3Q- 2Q- 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 1997 1998 1999 1999 2000* 2000 2001* 2001 2002* 2002 2003* 2003 2004* 2004 2005* 2005 Sampling event
Figure 5-36. 1,1-DCE concentrations of wells X740-PZ10G and X740-PZ12G, two of the four designated monitoring wells at the X-740 Phytoremediation Area. 114
The TCE concentrations are below the Ohio EPA preliminary performance goal of 495 µg/L in three of the four selected monitoring wells at the X-740 Area. Well
X740-03G is the only well above the target concentration. Figure 5-37 provides an overview of the TCE concentrations versus the EPA preliminary performance goal of wells X740-03G and X740-10G . Figure 5-38 provides an overview of the TCE concentrations versus the EPA preliminary performance goal of wells X740-PZ10G and
X740-PZ12G.
5000
4500
4000
3500 g/L)
m 3000
X740-03G 2500 X740-10G EPA Goal
2000 TCE concentration ( TCE 1500
1000
500
0
7 7 8 8 8 9 9 0 0 1 1 2 2 2 3 4 4 9 -9 -9 0 0 0 -0 0 -9 v- l-9 v r-9 v-00 -0 v- l-0 v r-0 v-04 ul o ar u a ul- o ul ar- u a ul-03 ul- o J N M J No M Jul-99Nov-9 Mar-0 J N Mar-01 J No M J No M J Nov-03 Mar-0 J N Mar-05 X740 Sampling Events 1997-2005
Figure 5-37. TCE concentrations of wells X740-03G and X740-10G between 1997 and 2005, two of the four designated monitoring wells at the X-740 Phytoremediation Area.
115
600
500
400 g/L) m
X740-PZ10G 300 X740-PZ12G EPA Goal
200 TCE concentration ( TCE
100
0
7 8 9 0 0 0 1 2 3 3 3 4 5 9 9 -99 99 9 -0 0 -0 0 -02 02 0 -0 0 -0 0 -0 v- l- - v- r l- l- - v- r l- l- v-04 r o u ul o a u u ul o a u u o a Jul-97N Mar-98 J Nov-98 Mar J N M J Nov Mar-01 J Nov-01 Mar J N M J Nov Mar-04 J N M X740 sampling events 1997-2005
Figure 5-38. TCE concentrations of wells X740-PZ10G and X740-PZ12G between 1997 and 2005, two of the four designated monitoring wells at the X-740 Phytoremediation Area.
In 1999 prior to the installation of the phytoremediation area, groundwater flow and transport modeling was performed at the X-740 Area to assess the impacts of the phytoremediation remedial activity. The model was unable to predict the actual TCE concentration at a given point in the future due to insufficient historical data. The model simulated natural attenuation as a constant rate decay. The groundwater extraction rate, estimated at 50 to 350 gallons per tree per day, was annualized to account for the tree density, growing season, and tree maturity within two years. The model predicted the
TCE concentrations being reduced below the maximum contaminant level of 5 µg/L within 10.5 years for the Gallia aquifer after the development of a mature root system.
The groundwater flow and solute transport modeling figures were developed using
FRAC3DVS modeling software (DOE, 2003c). Figures 5-39, 5-40, and 5-41 represent 116 the model predicted TCE in the Gallia aquifer in 5, 10, and 15 years after phytoremediation installation (DOE, 2003c). The predicted five-year groundwater model of the X-740 groundwater plume is similar to the actual 2005 groundwater plume (figure
5-56. There has not been a significant change in the X-740 groundwater plume between
1998 and 2005, as predicted by the model. The moderate concentration range seems to be extending further west which was predicted in the five-year model. This migration is consistent with the groundwater flow from east to west. However, the isoconcentration maps of the X-740 groundwater plume present minor changes in the second quarter maps due to lower TCE concentrations than in the fourth quarter. Figures 5-42 through 5-56 demonstrate the actual TCE extent of the X-740 Area ranging between third quarter 1997 and fourth quarter 2005. The plume contours were originally produced using Surfer 7.0 contouring and surface mapping software; currently changes in the contour plumes are adjusted manually. 117
Figure 5-39. X-740 Area TCE concentration 5 years after tree majority (DOE, 2003c). 118
Figure 5-40. X-740 Area TCE concentration 10 years after tree majority (DOE, 2003c).
119
Figure 5-41. X-740 Area TCE concentration 15 years after tree majority (DOE, 2003c).
120
Figure 5-42. X-740 Area TCE concentration 1997 and 1998. 121
Figure 5-43. X-740 Area TCE concentration second quarter 1999. 122
Figure 5-44. X-740 Area TCE concentration fourth quarter 1999. 123
Figure 5-45. X-740 Area TCE concentration second quarter 2000. 124
Figure 5-46. X-740 Area TCE concentration fourth quarter 2000. 125
Figure 5-47. X-740 Area TCE concentration second quarter 2001. 126
Figure 5-48. X-740 Area TCE concentration fourth quarter 2001. 127
Figure 5-49. X-740 Area TCE concentration second quarter 2002. 128
Figure 5-50. X-740 Area TCE concentration fourth quarter 2002. 129
Figure 5-51. X-740 Area TCE concentration second quarter 2003. 130
Figure 5-52. X-740 Area TCE concentration fourth quarter 2003. 131
Figure 5-53. X-740 Area TCE concentration second quarter 2004. 132
Figure 5-54. X-740 Area TCE concentration fourth quarter 2004. 133
Figure 5-55. X-740 Area TCE concentration second quarter 2005. 134
Figure 5-56. X-740 Area TCE concentration fourth quarter 2005. 135
5.4 Total mass of TCE
The mass of dissolved TCE in the groundwater at the X-740 Phytoremediation
Area can be estimated using the TCE concentration contour maps. Average concentration between contour lines was computed and multiplied by average aquifer pore space. For example using the fourth quarter 2005 contours from figure 5-56, the average TCE concentration of the X-740 groundwater plume was calculated using the highest concentration value (5500 µg/L) and the largest contour interval (1000 µg/L) of the plume. This process was used to calculate the average for each contour interval of
1000 µg/L, 100 µg/L, and 5 µg/L. The mass of dissolved TCE was then calculated by multiplying the area between the contour intervals (2750 sq ft), the average concentration
(3250 µg/L), the aquifer thickness (30 ft), and by the effective porosity (0.2) resulting in a sum of 54 g as shown in table 5-8.
The mass of sorbed TCE in the groundwater at the X-740 Phytoremediation Area was estimated using the same calculation as the mass of dissolved TCE and multiplying the results by one minus the effective porosity (0.2), the bulk density (1.6 kg/L), the fraction of organic carbon (foc) (1.8E-3), and by the organic carbon partition coefficient of TCE (Koc) (130 L/kg). The total mass of TCE was then be calculated by adding each result for the dissolved TCE and the sorbed TCE as shown in table 5-8.
136
Contours (µg/L) Area (sq ft) Area Average Mass Dissolved Mass Between Concentration (g) Sorbed (g) (sq ft) (µg/L) 5500 - - - - - 1000 2750 2750 3250 54 16 100 57330 54580 550 180 54 5 275120 217790 52.5 69 21 Total Mass = 394 g
Table 5-8. Total dissolved mass and sorbed mass of TCE concentrations of the X-740 groundwater plume from concentration data collected fourth quarter of 2005.
The mass of dissolved TCE and the mass of sorbed TCE was calculated between
1999 and 2005 for the second and fourth quarters. The mass of dissolved TCE and sorbed TCE was lower during the second quarter than the fourth quarter between1999 and 2004. However, in 2005 the results for mass of dissolved TCE and sorbed TCE was higher during the fourth quarter than the second quarter. Additionally, the same results were apparent for the total mass of TCE for 1999-2004. The total mass of TCE is lower during the second quarter than the fourth quarter. Again, during 2005 the total mass of
TCE is higher during the fourth quarter than the second quarter. Figure 8-57 demonstrates the total mass TCE concentrations between 1999 and 2005. Overall the mass of dissolved TCE, the mass of sorbed TCE, and the total mass of TCE between
2000 and 2005 initially decreased, then gradually increased, and now appear to be on a decreasing trend. However, it is not clear if these variations are statistically significant and may just be scatter in the data. Unlike the concentrations in the selected wells in which concentrations increased over time, the total mass in the contamination plume appears to have remained relatively constant. This is consistent with the modeling results 137 that predicted 5 years elapsing after completion of the phytoremediation system before a decrease in concentrations was observed. 138
500
450
400
350
300
250 Total Mass of TCE
200 TCE concentration (g)TCE
150
100
50
0 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 2Q- 4Q- 1999 1999 2000* 2000 2001* 2001 2002* 2002 2003* 2003 2004* 2004 2005* 2005 Sampling event
Figure 5-57. Total mass TCE concentrations between 1999 and 2005. *=data collected during growing season (April through September) Quarters are based on calendar year
5.5 BIOCHLOR simulation
BIOCHLOR is a screening model that simulates remediation by natural
attenuation of dissolved solvents at contaminated sites. Natural attenuation is a naturally
occurring process in soil and groundwater that reduces the mass, toxicity, mobility, volume, or concentration of the contaminant. The software is implemented in a
Microsoft Excel spreadsheet based on the Domenico analytical solute transport model.
The BIOCHLOR software has the ability to simulate 1-D advection, 3-D dispersion,
linear adsorption, and biotransformation of chlorinated solvents (EPA, 2000).
BIOCHLOR uses sequential first-order decay for simulating in-situ biotransformation.
The sequence of the first-order decay process is shown in figure 5-58.
139
Figure 5-58. First-order sequential decay process.
Phytoremediation is a more active process than natural attenuation (EPA, 2000).
Phytoremediation can be used as a stand alone process or it can be used as a means to supplement natural degradative processes. VOC’s which are highly chlorinated such as
TCE and PCE are better degraded anaerobically while byproducts such as DCE and vinyl chloride are better degraded aerobically. A phytoremediation plantation can promote a
change in subsurface conditions from an aerobic to mostly anaerobic state by the
production of root exudates and root decomposition (Van Den Bos, 2002). Additionally,
evidence of degradation can be detected by soil and groundwater monitoring. Indications
of contaminant degradation are lower dissolved oxygen concentrations and higher
concentrations of TCE byproducts such as DCE and vinyl chloride (Van Den Bos, 2002).
The X-740 Phytoremediation System has increasing DCE concentrations as well as low
dissolved oxygen concentrations indicating an anaerobic system.
First a BIOCHLOR model was developed for the site and calibrated to match concentration data collected in 1999. The initial contamination was set to based upon
historical records at the site. Concentration values from wells along the centerline of he 140 plume were used for calibration of the model, namely X740-03G, X740-10G, X740-11G,
X740-PZ12G, and X740-PZ17G. This calibrated model was used to project concentrations to more recent dates with collected data. BIOCHLOR simulations were modeled for the years of 1999, 2001, 2003, and 2005 to assess whether the plume changes over time are consistent with natural attenuation or if the phytoremediation system is accelerating plume shrinkage.
The BIOCHLOR simulations require seven areas of general information in order to simulate natural attenuation. These seven items are advection, dispersion, adsorption, biotransformation, general items (simulation time, area length, and area width), source data, and field data for comparison. Advection at the site was determined to be 699.6 ft/yr using the hydraulic conductivity (1.5E-02 cm/sec), hydraulic gradient (0.009 ft/ft), and effective porosity (0.2) of the site. The default values from the software were used for the dispersion and adsorption estimations. The first-order biotransformation estimations for PCE, TCE, and DCE were changed from the default values to 3.0 λ(1/yr),
3.5 λ(1/yr), and 7.0 λ(1/yr). The default values for vinyl chloride were used for the first- order biotransformation estimates. The general information used was the simulation times of 17, 19, 21, and 23 years corresponding to the pertinent years of 1999, 2001,
2003, and 2005. The modeled area width of 200 ft and the modeled area length of 600 ft were used in the simulation. The contaminant thickness was estimated at 2.5 ft and the width was estimated at 12.5 ft. The average data from well X740-03G was used as the source data since it is the well with the highest TCE concentration and located in the center of the plume. Field data from wells X740-10G, 11G, PZ12G, and PZ17G were 141 used given that these wells are along the plume centerline. An example of the BIOCHOR simulation data input file is represented in figure 5-59. 142
Figure 5-59. BIOCHLOR 2005 simulation data input screen. 143
The modeled simulation of 1999 (simulation 17 years) reveals the TCE and DCE concentrations are in succession with the sequential first-order decay process within the simulated 0-600 ft of the collection point (figures 5-60 and 5-61). No PCE or vinyl chloride concentrations were available for the 1999 simulation.
No Degradation/Production Sequential 1st Order Decay Field Data from Site
10.000 0 1.000 60 120 180 240 360 420 480 540 600 0.100
0.010
Concentration (mg/L) Concentration 0.001 0 100 200 300 400 500 600 700
Distance From Source (ft.)
Figure 5-60. TCE concentrations along plume centerline, 1999 simulation. 144
No Degradation/Production Sequential 1st Order Decay Field Data from Site
1.000 0
0.100 60 120 180 240 360 420 480 540 600
0.010
Concentration (mg/L) Concentration 0.001 0 100 200 300 400 500 600 700
Distance From Source (ft.)
Figure 5-61. DCE concentrations along plume centerline, 1999 simulation.
The modeled simulation of 2001 (simulation 19 years) reveals that two of the four
field data points for TCE concentrations are below the sequential first-order decay
process within the simulated 0-600 ft of the collection point (figure 5-62). Three of the
four field data points for DCE concentrations are below the sequential first-order decay process within the simulated 0-600 ft of the collection point (figure 5-63). No PCE or vinyl chloride concentrations were available for the 2001 simulation. 145
No Degradation/Production Sequential 1st Order Decay Field Data from Site
10.000 0 1.000 60 120 180 240 360 420 480 540 600 0.100
0.010
Concentration (mg/L) Concentration 0.001 0 100 200 300 400 500 600 700
Distance From Source (ft.)
Figure 5-62. TCE concentrations along plume centerline, 2001 simulation.
No Degradation/Production Sequential 1st Order Decay Field Data from Site
1.000 0
0.100 60 120 180 240 360 420 480 540 600
0.010
Concentration (mg/L) Concentration 0.001 0 100 200 300 400 500 600 700
Distance From Source (ft.)
Figure 5-63. DCE concentrations along plume centerline, 2001 simulation.
The modeled simulation of 2003 (simulation 21 years) reveals that two of the four field data points for TCE concentrations are below the sequential first-order decay 146 process within the simulated 0-600 ft of the collection point (figure 5-64). All four field data points for DCE concentrations are below the sequential first-order decay process within the simulated 0-600 ft of the collection point (figure 5-65). Only one field data point was available for PCE and it is located below the sequential first-order decay process within the simulated 0-100 ft of the collection point (figure 5-66). No vinyl chloride concentrations were available for the 2003 simulation.
No Degradation/Production Sequential 1st Order Decay Field Data from Site
10.000 0 1.000 60 120 180 240 360 420 480 540 600 0.100
0.010
Concentration (mg/L) Concentration 0.001 0 100 200 300 400 500 600 700
Distance From Source (ft.)
Figure 5-64. TCE concentrations along plume centerline, 2003 simulation.
147
No Degradation/Production Sequential 1st Order Decay Field Data from Site
1.000 0
0.100 60 120 180 240 360 420 480 540 600
0.010
Concentration (mg/L) Concentration 0.001 0 100 200 300 400 500 600 700
Distance From Source (ft.)
Figure 5-65. DCE concentrations along plume centerline, 2003 simulation.
No Degradation/Production Sequential 1st Order Decay Field Data from Site
1.000
0.100 0
60 120 0.010 180 240 360 420 480 540 600
Concentration (mg/L) Concentration 0.001 0 100 200 300 400 500 600 700
Distance From Source (ft.)
Figure 5-66. PCE concentrations along plume centerline, 2003 simulation.
The modeled simulation of 2005 (simulation 23 years) reveals that two of the four field data points for TCE concentrations are below the sequential first-order decay 148 process within the simulated 0-600 ft of the collection point (figure 5-67). All four field data points for DCE concentrations are below the sequential first-order decay process within the simulated 0-600 ft of the collection point (figure 5-68). Two field data points were available for PCE and both are located below the sequential first-order decay process within the simulated 0-100 ft of the collection point (figure 5-69). No vinyl chloride concentrations were available for the 2005 simulation.
No Degradation/Production Sequential 1st Order Decay Field Data from Site
10.000 0 1.000 60 120 180 240 360 420 480 540 600 0.100
0.010
Concentration (mg/L) Concentration 0.001 0 100 200 300 400 500 600 700
Distance From Source (ft.)
Figure 5-67. TCE concentrations along plume centerline, 2005 simulation.
149
No Degradation/Production Sequential 1st Order Decay Field Data from Site
1.000 0
0.100 60 120 180 240 360 420 480 540 600
0.010
Concentration (mg/L) Concentration 0.001 0 100 200 300 400 500 600 700
Distance From Source (ft.)
Figure 5-68. DCE concentrations along plume centerline, 2005 simulation.
No Degradation/Production Sequential 1st Order Decay Field Data from Site
1.000
0.100 0
60 120 0.010 180 240 360 420 480 540 600
Concentration (mg/L) Concentration 0.001 0 100 200 300 400 500 600 700
Distance From Source (ft.)
Figure 5-69. PCE concentrations along plume centerline, 2005 simulation. 150
The 2001 BIOCHLOR simulation reveals that two of the four TCE data points are below the sequential first-order decay process. As well, three of the four DCE data points are below the sequential first-order decay process for the 2001 simulation. The
2003 BIOCHLOR simulations are consistent with the 2001 results for TCE and DCE.
Also, the 2005 BIOCHLOR simulations are consistent with the 2001 results for TCE.
However, the 2005 simulations indicate all of the four of the DCE concentrations are below the sequential first-order decay process. This is an increase from the 2001 and
2003 simulations. As a result of the model concentrations being higher than the field concentrations it appears that natural attenuation as well as phytoremediation is occurring in the groundwater plume. It seems that the phytoremediation system is having a positive influence on the X-740 groundwater plume, although inconsistent with the previous data.
6.0 Conclusions
While it is established that phytoremediation of TCE by poplars is feasible, there are few published reports of the results of full scale implementation. PORTS is a large phytoremediation project that is being conducted as a full-scale field study. The size of this study area (45 acres) combined with the field planting techniques, regional location, and chemical concentration of concern creates a unique system suitable for investigation on the effectiveness of phytoremediation. The study results are summarized below.
The data obtained from the tree species selection, growth, diameter and mortality rate survey conducted in 2003 and 2005 implicate that the trees planted in the trenches have an overall more successful growth rate the trees planted in the boreholes. However, the overall results were similar; from 2003 through 2005 the trees planted in the trenches 151 and in the boreholes decreased in mortality as well as the trees with a diameter less than 8 cm. Additionally, trees with a diameter greater than 8 cm increased. Throughout the phytoremediation system the tree mortality of 2003 and 2005 appears to be random and not attributed to the TCE concentration.
As well, the results of the tree coring study evaluation detected TCE at measurable levels in three of the 16 core samples collected at the X-740
Phytoremediation Area. The detection of TCE could indicate the that trees are using some of the contaminated groundwater within the phytoremediation system
The X-740 Phytoremediation System was predicted to be mature within two to three years of the initial planting, which would have been by 2001 or 2002. However, according to the water level measurements, the X-740 Phytoremediation System appears to have no observable impact on groundwater levels until 2003. A cyclic trend is apparent in 2003 through 2005 from water level measurements. Groundwater elevations steadily decrease in the X-740 Phytoremediation System from 2003 to 2005. Over that time period an average groundwater table drop of 0.30 ft was observed. Thus, it was expected the system required four to five years to mature instead of the estimated two to three years. These trends are not apparent from analysis of the potentiometric surface contours. It does appear that the head gradient across the site is higher during the spring sampling events while the head gradient upgradient of the site and during the fall is lower. However, it is not clear if this trend was initiated by the installation of the phytoremediation system. 152
The difference in the hydraulic gradient from 1998 (before the phytoremediation system was installed) through 2005 was calculated between two wells upgradient of the
X-740 Phytoremediation Area and two wells planted within the trees near the center of the plume. The gradients in the well pairs steadily increase over time, although there is some scatter in the data. It appears that as the trees mature the increasing groundwater withdrawal can be seen by the increasing gradient across the site. In fact there is a statistically significant difference (α=0.05) between average gradients for the four well pairs in 1998 and 1999 to the average gradient for the four well pairs in 2004 and 2005.
The X-740 Phytoremediation Area was estimated to transpire an average 75,000 gallons per day (gpd) of groundwater. This is an average daily consumption rate of 98 gallons per tree during an average growing season. Groundwater uptake rates for four to five-year old poplar trees were estimated at 26 gpd to 53 gpd, while six to seven year old poplar were estimated to take up 80 gpd. The poplar trees at the X-740 Phytoremediation
Area are seven years old, though somewhat higher, 98 gpd is consistent with these reported values.
There has not been a significant change in the X-740 groundwater plume between
1998 and 2005. The X-740 groundwater plume seems to be migrating to the west which is consistent with the groundwater flow. The TCE and TCE byproduct concentrations seem to indicate that phytoremediation has failed to cleanup the plume. However, second quarter concentrations are characteristically lower than fourth quarter concentrations in all four designated monitoring wells for the volatile organic compounds of TCE and 1,1- 153
DCE; this could be attributed to the influence on the trees in the phytoremediation area during the growing season.
The mass of dissolved TCE, the mass of sorbed TCE, and the total mass of TCE between 2000 and 2005 appears to have decreased from the calculated values of 1999; although the estimates between the 2000 and 2005 seem to fluctuate somewhat sporadically.
The 2001, 2003, and 2005 BIOCHLOR simulations indicate the TCE, DCE, and
PCE concentrations are below the sequential first-order decay process which signifies natural attenuation as well as phytoremediation is occurring. It appears that the phytoremediation system is having a positive influence on the X-740 groundwater plume, although inconsistent with the previous data.
The X-740 Phytoremediation Area, with time, will continue to grow, maturing, and developing a more extensive root system. The phytoremediation system appears to be influencing the groundwater at the X-740 Area as demonstrated with the cyclic trend in the water levels, the increase in gradient across the site, and the increase in TCE byproduct concentration occurring in the later years of the system. The X-740
Phytoremediation Area is not currently demonstrating signs of a cone of depression.
However, the groundwater flow at the X-740 Phytoremediation Area is demonstrating encouraging trends, only time will tell if the development of a cone of depression capable of capturing the TCE plume is achievable. The next five-year evaluation of the X-740
Phytoremediation System is scheduled in 2008. 154
The groundwater flow at the X-749 Phytoremediation Area is demonstrating the same cyclic trend as the X-740 Phytoremediation Area in its early stages of root development. Due to the young age of the system it is difficult to distinguish whether the phytoremediation system is having a positive result. A five-year evaluation of the X-749
Phytoremediation System will be conducted in 2008 incorporating tree growth, diameter studies, mortality rates, water levels, transducer/data loggers data, and tree core samples to determine the effectiveness of the system.
155
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