A.1 Aberdeen Proving Ground, MD
A.1.1 Contacts
Moshood Oduwole
215-814-3362
Yazmine Yap-Deffler
215-814-3369
A.1.2 Summary
|
Environment: |
Tidal wetland |
|
Scale: |
Pilot |
|
Contaminants of Concern: |
Chloroform, carbon tetrachloride, tetrachloroethene, 1,1,2,2-tetrachloroethane, hexachloroethane, pentachloroethane |
|
Final Remedy: |
Active capA covering over material (contaminated sediment) used to isolate the contaminants from the surrounding environment. (reactive mat with mixture of peat and compost bioaugmented with dechlorinating microbes) |
A.1.3 Site Description
The Aberdeen Proving Ground (APG) is a 72,500 acre Army installation located off Route 40 in Edgewood (Harford County), on the western shore of the upper Chesapeake Bay. The Bush River divides APG into two distinct areas: the Edgewood Area to the west and the Aberdeen Area to the east. Beginning in 1917, the Edgewood Area of the site was used to conduct chemical research programs, to manufacture chemical agents, and to test, store, and dispose of toxic materials. Contaminants may have been introduced to the surficial aquifer at the site as multiple nonpoint source releases of solvents during site operations, resulting in a plume of contaminated groundwater that flows toward the tidal wetland. The site was formally added to the National Priorities List February 21, 1990.
Seep areas have been identified in the tidal wetland, where natural attenuation of chlorinated solvents by anaerobic biodegradation is hindered by the increase in vertical seepage flux and the resulting decrease in residence time in the wetland sediments. The area of concern is located in a tidal wetland along West Branch Canal Creek, where localized areas of preferential discharge (seeps) transport contaminated groundwater. Groundwater contaminated with chlorinated VOCs discharges from a 30–50 ft aquifer to the wetlands and tidal creek.
CSM summary: The CSM for the site noted that the major transport mechanism for VOCs was preferential seepage of contaminated groundwater from the aquifer to West Branch Canal Creek. The pilot study divided the seeps into two categories:
- Focused seeps: locations with the highest concentrations of chlorinated parent compounds, relatively low concentrations of chlorinated degradation products, and insignificant concentrations of methane in shallow pore-water samples (primarily occurring along the creek edge or forming a dendritic-like pattern between the wetland and creek channel).
- Diffuse Seeps: locations characterized by relatively high concentrations of chlorinated degradation products (or a mixture of compounds and their degradation products) and detectable methane concentrations in shallow pore-water samples primarily occurring along the wetland boundary.
The seep used during the pilot study (seep 3-4W) was characterized as a focused seep.
A.1.4 Remedial Objectives
Remediation risks included adverse effects to wetland water quality from nutrients or metals mobilization. RAOs/project objectives included:
- achieve 90% removal of VOCs in mat
- establish and maintain conditions conducive to WBC-2 survival (redox, pHA measure of the acidity or alkalinity of a solution, numerically equal to 7 for neutral solutions, increasing with increasing alkalinity and decreasing with increasing acidity. The pH scale commonly in use ranges from 0 to 14.)
- achieve hydraulic compatibility
- achieve geotechnical stability (settlement 0.4–1 ft)
- cause no adverse effects to wetland water quality from nutrients or metals mobilization
A.1.5 Remedial Approach
Final selected remedy: Active cap (reactive mat with mixture of peat and compost bioaugmented with dechlorinating microbes).
A pilot study was conducted using a permeable reactive mat placed at the groundwater/surface water interface, which encouraged anaerobic biodegradation. The mat consisted of a mixture of peat and compost bioaugmented with dechlorinating microbes. Performing a pilot study before launching a full-scale remedy allowed necessary modifications to be made at a much lower cost.
The top 1 ft of wetland sediment was removed with a vacuum truck. Mixtures for the reactive mat were put down (22 inches total). The mat initially extended above the wetland surface to allow for settling. The reactive mat was designed to optimize chlorinated volatile organic compound degradation efficiency without altering geotechnical and hydraulic characteristics, or creating undesirable water quality in the surrounding wetland area.
A.1.6 Monitoring
Monitoring by the USGS over a one-year period (October 2004 to October 2005) showed consistent mass removal in the mat, even during the cold winter months. The success of the remedy in meeting remedial goals was shown through performance monitoring that involved several aspects of the remedy. Groundwater and surface water were sampled to monitor contaminant concentrations. The reactive mat matrix was sampled to monitor microbial activity. Because a permeable reactive mat was used, groundwater level and hydraulic head surrounding the mat were monitored to ensure the placement of the mat did not create new seeps.
RAOs/project objectives achieved? The pilot study was deemed a success based on data gathered through performance monitoring. Total chloromethanes decreased as the plume moved from the base of the mat upward to the mat surfaces. Mass removal was estimated at 95–99.99%. Chlorinated ethenes and ethanes were similarly reduced.
A.1.7 References
USGS. 2011. MD-DE-DC Water Science Center: Enhanced Bioremediation of Chlorinated Solvents in Wetland Seep Areas, Aberdeen Proving Ground: WBC-2 Dechlorinating Culture and Reactive Mat Pilot Test. http://md.water.usgs.gov/posters/biomat/index.html.
Majcher, E.H., Lorah, M.M., Phelan, D.J., and McGinty, A.L., 2009. "Design and performance of enhanced bioremediation pilot test in a tidal wetland see, West Branch Canal Creek, Aberdeen Proving Ground, Maryland". U.S. Geological Survey Scientific Investigations Report 2009-5112, 70pp.
Publication Date: August 2014