Pilot-scale phytoremediation of pesticide-contaminated groundwater near Columbia, SC airport (CAE)
A pilot-scale phytoremediation system is being implemented to address shallow groundwater contaminated by residual pesticides from a landfill near West Columbia, South Carolina. The pilot-scale phytoremediation system will test the idea that fast growing hybrid poplar trees will take up shallow groundwater that contains organochlorine pesticides, such as β-BHC compounds and toxaphene, at higher rates than native trees. The goal is to keep the contaminants from moving away from the landfill.
Background
An old landfill is located east of South Carolina Highway 302 in West Columbia, Lexington County, South Carolina and adjacent to an unnamed tributary to Sixmile Creek, a tributary to the Congaree River. Historical sampling activities at the landfill include groundwater from monitoring wells, surface water in the tributary, and porewater from the bed sediments (hyporheic zone) of the tributary. This sampling indicated the presence of organochlorine pesticides (“pesticides”) in groundwater, surface water, and porewater.
U.S Geological Survey (USGS) reviewed this historical groundwater-quality data collected at the site since 1996 and determined that an increased loss of pesticides (higher attenuation) occurred near the tributary compared to slower losses near the source areas in the old landfill. For example, the loss of total pesticides was 22 times greater in groundwater in the tributary floodplain relative to pesticide concentrations in groundwater leaving the source area. Similarly, the loss of other pesticides, such as β-BHC and toxaphene, were 48 and 8 times greater, respectively, near the tributary.
It was hypothesized that the observed faster rate of pesticide mass loss could be attributed to the use of groundwater by trees growing in the riparian zone where the water table is closer to land surface. Since then, the plans are to increase the rate of pesticide removal from groundwater by uptake though trees. This will be accomplished by planting a pilot-scale plot of fast, growing hybrid poplar trees that have more extensive root systems and are more capable of removing these contaminants from groundwater.
The pilot-scale system will comprise of about 200 hybrid poplar trees, which have been specially designed to take up groundwater and dissolved contaminants such as organochlorine pesticides (Landmeyer, 2011). The phytoremediation system is envisioned to be roughly 50- by 100-ft and will be installed in the spring of 2024, after existing scrub trees and vines in the selected area are grubbed and removed. Over at least a 2-year period, the performance of the pilot-scale trees will be evaluated using a monitoring system comprised of point surface-water flow measurements; collection and analyses of groundwater from existing monitoring wells by the existing site consultant; collection and analyses of pore-water samples and analyzed for twenty-one pesticides using EPA Method 8081A by the existing site consultant; and, collection and analyses of passive samplers installed in the pilot-scale trees, by the USGS.
Goals
The goals of the pilot-scale phytoremediation system are to provide data to evaluate the extent that the trees will:
- Decrease pesticide concentrations in groundwater at a greater rate than native trees, and
- Decrease groundwater discharge to a Sixmile Creek tributary. This is expected to be protective of the surface-water quality.
The hydrogeology and geomorphic characteristics of the site favors the success of a riparian zone phytoremediation system over other remedial technologies, because the riparian zone is characterized by:
- A shallow water table, often near land surface, which maximizes the survival of the trees after installation and eliminates the need to provide costly irrigation, and
- A climate with high evapotranspiration (ET) rates (greater than 4 inches/month in summer) that maximizes groundwater uptake by trees.
Project Schedule
- Clear 100 foot by a 50-foot area for planting of trees. Erosion controls will be installed between planting area and Sixmile Creek tributary to decrease overland flow of sand and silt into the tributary.
- One year performance monitoring using existing wells.
- Hybrid poplar trees will be planted and multiple clones will be utilized to ensure plant diversity and overall grove resistance to infestation. Each hole and/or trench will be backfilled with uncontaminated clean organic-rich loam from a local nursery. The location of each tree will be documented by using a global positioning (GPS) device. This information will be added into an ARC GIS base map.
- Two-year performance monitoring measuring concentrations of organochlorine pesticides in the hybrid poplar trees will be compared to the level of pesticides detected in native trees. The concentrations of organochlorine pesticides in groundwater before and after the planting will be compared. Concentrations are anticipated to decrease over time in the well near the planted area.
Reference Cited
Landmeyer, J.E., 2011, Introduction to Phytoremediation of Contaminated Groundwater. Springer. 415 p. ISBN 978-94-007-1956-9.
A pilot-scale phytoremediation system is being implemented to address shallow groundwater contaminated by residual pesticides from a landfill near West Columbia, South Carolina. The pilot-scale phytoremediation system will test the idea that fast growing hybrid poplar trees will take up shallow groundwater that contains organochlorine pesticides, such as β-BHC compounds and toxaphene, at higher rates than native trees. The goal is to keep the contaminants from moving away from the landfill.
Background
An old landfill is located east of South Carolina Highway 302 in West Columbia, Lexington County, South Carolina and adjacent to an unnamed tributary to Sixmile Creek, a tributary to the Congaree River. Historical sampling activities at the landfill include groundwater from monitoring wells, surface water in the tributary, and porewater from the bed sediments (hyporheic zone) of the tributary. This sampling indicated the presence of organochlorine pesticides (“pesticides”) in groundwater, surface water, and porewater.
U.S Geological Survey (USGS) reviewed this historical groundwater-quality data collected at the site since 1996 and determined that an increased loss of pesticides (higher attenuation) occurred near the tributary compared to slower losses near the source areas in the old landfill. For example, the loss of total pesticides was 22 times greater in groundwater in the tributary floodplain relative to pesticide concentrations in groundwater leaving the source area. Similarly, the loss of other pesticides, such as β-BHC and toxaphene, were 48 and 8 times greater, respectively, near the tributary.
It was hypothesized that the observed faster rate of pesticide mass loss could be attributed to the use of groundwater by trees growing in the riparian zone where the water table is closer to land surface. Since then, the plans are to increase the rate of pesticide removal from groundwater by uptake though trees. This will be accomplished by planting a pilot-scale plot of fast, growing hybrid poplar trees that have more extensive root systems and are more capable of removing these contaminants from groundwater.
The pilot-scale system will comprise of about 200 hybrid poplar trees, which have been specially designed to take up groundwater and dissolved contaminants such as organochlorine pesticides (Landmeyer, 2011). The phytoremediation system is envisioned to be roughly 50- by 100-ft and will be installed in the spring of 2024, after existing scrub trees and vines in the selected area are grubbed and removed. Over at least a 2-year period, the performance of the pilot-scale trees will be evaluated using a monitoring system comprised of point surface-water flow measurements; collection and analyses of groundwater from existing monitoring wells by the existing site consultant; collection and analyses of pore-water samples and analyzed for twenty-one pesticides using EPA Method 8081A by the existing site consultant; and, collection and analyses of passive samplers installed in the pilot-scale trees, by the USGS.
Goals
The goals of the pilot-scale phytoremediation system are to provide data to evaluate the extent that the trees will:
- Decrease pesticide concentrations in groundwater at a greater rate than native trees, and
- Decrease groundwater discharge to a Sixmile Creek tributary. This is expected to be protective of the surface-water quality.
The hydrogeology and geomorphic characteristics of the site favors the success of a riparian zone phytoremediation system over other remedial technologies, because the riparian zone is characterized by:
- A shallow water table, often near land surface, which maximizes the survival of the trees after installation and eliminates the need to provide costly irrigation, and
- A climate with high evapotranspiration (ET) rates (greater than 4 inches/month in summer) that maximizes groundwater uptake by trees.
Project Schedule
- Clear 100 foot by a 50-foot area for planting of trees. Erosion controls will be installed between planting area and Sixmile Creek tributary to decrease overland flow of sand and silt into the tributary.
- One year performance monitoring using existing wells.
- Hybrid poplar trees will be planted and multiple clones will be utilized to ensure plant diversity and overall grove resistance to infestation. Each hole and/or trench will be backfilled with uncontaminated clean organic-rich loam from a local nursery. The location of each tree will be documented by using a global positioning (GPS) device. This information will be added into an ARC GIS base map.
- Two-year performance monitoring measuring concentrations of organochlorine pesticides in the hybrid poplar trees will be compared to the level of pesticides detected in native trees. The concentrations of organochlorine pesticides in groundwater before and after the planting will be compared. Concentrations are anticipated to decrease over time in the well near the planted area.
Reference Cited
Landmeyer, J.E., 2011, Introduction to Phytoremediation of Contaminated Groundwater. Springer. 415 p. ISBN 978-94-007-1956-9.