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Case Study:  Aberdeen Proving Ground  

     Aberdeen Proving Ground (APG) was founded on October 20, 1917; six months after the United States entered World War I, and is still active today.  Its purpose was to serve as a location where design and testing of weaponry material could occur in close proximity to the nation's industrial and shipping centers [37]. The location covers more than 72,500 acres in Harford County, Md and is bordered by the union of the Susquehanna River and the Chesapeake Bay to the north and the Gunpowder River to the south (Figure 11) [37].   Within the compound there are two principal areas which are separated by the Bush River; the Aberdeen Area to the north and the Edgewood Area to the south.  In addition to designing and testing weapons, APG trains Army ordinance personnel and has been a center for chemical warfare research and development since the Edgewood Area was established [37].

Figure 11: Map of Aberdeen Proving Ground taken from [38].

     The activities at APG have led to two main areas of contamination listed on the (National Priority List) NPL as Superfund sites; the Edgewood Area and the Michaelsville Landfill on the Aberdeen Area.   Both locations were proposed to the NPL of the most serious uncontrolled or abandoned hazardous waste sites requiring long term remedial action on April 10, 1985 [39, 40].   The Michaelsville Landfill site was formally added to the list October 4, 1989 [39]and the Edgewood area was added a short time later on October 4, 1989 [40].

A.    Edgewood Area

     From 1917 to the present, the Edgewood Area was used for chemical research programs to develop, manufacture, and test chemical agent munitions [40].  In the process toxic materials have been stored and disposed of causing large areas of known or suspected land and water contamination as well as contamination in numerous buildings [40]. Substances disposed of in the area include significant quantities of napalm, white phosphorus, and chemical agents.  On-site groundwater sampling has identified various metals, volatile organic compounds (VOCs) and chemical warfare agent degradation products. On-site soil contamination in surface and subsurface soil and surface water contamination have also been identified.  There are 38,600 people living within three miles of the site and two separate operational well fields, causing the risk of people accidentally ingesting or coming in direct contact with contaminated groundwater, surface water, soil, or sediments  [40].

     Cleanup of this site is the responsibility of the Federal government and has consisted of initial actions (removals) and 15 long-term remedial phases focusing on cleanup of the entire site [40].   Of the long-term cleanup measures there have been several dealing with groundwater.  The following is a chronological summary taken from the EPA [40] of the groundwater actions and written according to the specific area.

     A ROD was written for hydraulic containment of contaminated groundwater at the Old-O-Field Chemical Munition Landfill in the fall of 1991.  This was followed by the construction of an extraction and chemical treatment system in fall of 1995 and continuous automated biomonitoring to ensure the treated effluent is not toxic to fish.   Both are still operational.  A ROD was written for the extraction and treatment of groundwater contaminated with TCE at the Old Nike Site (a former missile base) in 1996.  A treatment plant was installed at the Nike Site and is currently treating groundwater.  Tests were performed and completed at J-Field (a former open burning area for chemical agents, white phosphorus, high explosives, and riot control agents) to determine if phytoremediation with trees could effectively contain the contaminated groundwater and remove contaminants. 

     A ROD was issued at Carroll Island/Graces Quarters (areas used for testing lethal and nonlethal chemical surety materials and for open air testing of various chemical materials) and a groundwater remediation system was installed to address solvent contaminated groundwater.  It is completed, operational and has dramatically reduced VOC levels in the aquifer. A water treatment plant was constructed for the Canal Creek and is operational.  In the summer of 2001, a decision was reached requiring the Army to pump and treat lead and zinc contaminated groundwater in the Canal Creek Area of the facility. Design work and construction was completed and since then the treatment system has reduced contamination almost tomaximum contaminant levels  (MCLs). There are numerous other investigations that have been conducted at the Edgewood Areas but need to wait for completion due to limited financial and human resources. There are also numerous other investigations underway and many RODs needed to complete the site work. Most of this work is being performed under performance based contracts.

B.     Michaelsville Landfill

     The Michaelsville Landfill is a 20-acre landfill in the Aberdeen Area.  The Landfill operated as a sanitary landfill from the 1970s until 1980 and received household garbage, industrial waste, solvents, waste motor oils, polychlorinated biphenyl (PCB) transformer oils, wastewater treatment sludge, pesticides containing thallium, selenium, and antimony [39]. Also in this area are the Phillips Field Disposal Area, the White Phosphorous Munition Burial Site, and numerous known or suspected solid waste management units that may be sources of contamination. The area contains firing ranges, impact areas, vehicle test tracks, a fire training area, and laboratories in support of testing these activities. Groundwater and surface water sampling identified various heavy metals, phosphorous, and VOCs and explosives. There is also soil contamination with pesticides and PCBs, VOCs and petroleum hydrocarbons. 38,600 people live within 3 miles of the site with water supply wells near the site boundaries [39].  This creates the risk of people coming into direct contact with or accidentally ingesting contaminated groundwater, surface water, soil, or sediments.

     Cleanup of this site is the responsibility of the federal government and has included excavation of contaminated soils and removal of storage tanks.  As far as the groundwater is concerned, the EPA [39] reported that an investigation of the Michaelsville Landfill (source) was completed in 1992 . In late 1997 a ROD was issued requiring institutional controls and long-term monitoring for the groundwater associated with the landfill. In July of 2000 a ROD was signed requiring construction of a groundwater treatment plant to protect the Perryman Wellfield which is the source of drinking water for most of Harford County. The plant construction was completed in Summer of 2003 and is operational. The investigation of contaminated areas has been completed and RODs have been issued for six groundwater plumes.

C.    Financial Responsibility

     Since the contaminated areas are on government property and due to military activities, the US Army is financially responsible for the contamination.  In addition, the APG installation and its tenants are actively involved in a wide variety of environmental compliance, pollution prevention, conservation, and restoration programs [37]. APG is participating in the Installation Restoration Program (IRP), established in 1978. Under this program, the Department of Defense (DOD) seeks to identify, investigate, and clean up contamination from hazardous materials [41, 42]. APG reported spending a total of $31 million on environmental programs, installation programs and installation restoration activities in 1994.  The total cost of remediation up to 1999 was reported as $386.2 million [43].  The estimated cost of future total remediation was $650.1 million in 2042 [43].

D.    Research Conducted

     Research has been conducted to determine the fate of chlorinated VOCs in a freshwater tidal wetland located at APG[44-46].  The study site is a natural wetland located along the West Branch Canal Creek.  Nested piezometers and porous-membrane sampling devices were installed in the wetland study area on the eastern side of West Branch Canal Creek where the contaminated groundwater discharges (Figure 12).  The contaminated aquifer, known as the Canal Creek aquifer, is about 12-14 m and consists mainly of medium- to coarse grained sand and gravel. Wetland sediments on top of the aquifer consist of two distinct layers; the lower layer is silty to sandy clay or clayey sand and the upper layer is peat mixed with variable amounts of clay and silt [44].  The layers have a combined thickness of about 1.8 m and the average linear groundwater flow velocity in the wetland sediments is estimated to be about 0.6 m/yr [44].

Figure 12:  Wetland at APG taken from Lorah and Olsen [44]. 

     Field evidence demonstrated that anaerobic biodegradation naturally attenuated a plume of chlorinated VOCs as it discharged from the aerobic sand aquifer through the wetland sediments [45].   Footprints of the natural attenuation processes responsible for the degradation of two parent contaminants, trichloroethylene (TCE) and 1,1,2,2-tetrachloroethane (PCA) were measured from the nested piezometers and porous-membrane sampling devices.   The decreases in TCE and PCA occurred simultaneously with the production of their less-chlorinated daughter products as the groundwater flowed through the increasingly reduced wetland sediments [44, 45].   Possible reductive degradation pathways include hydrogenolysis of TCE and hydrogenolysis and dichloroelimination of PCA, which were evidenced by the formation of daughter products: 1,2-dichloroethylene, vinyl chloride, 1,1,2-trichloroethane, and 1,2-dichloroethane (see Figure 13).

Figure 13:  Dechlorination pathways for PCA and TCE taken from Lorah and Olsen [45].

     Lorah and Olsen [44] found that initial concentration of PCA at about 1.5 umol/L transformed into daughter products that decreased to below detection within 34 days in the microcosms and within a 1.0-m vertical distance in the wetland sediments. Detection levels were reached within 0.15-0.30 m of land surface for PCA as well as TCE and their daughter products [45]. The naturally higher concentrations of dissolved organic carbon in the wetland sediments and the lower redox state of the groundwater compared to the aquifer allowed for the enhanced reductive dechlorination of TCE and PCA [45].   These field and laboratory studies provide evidence that the ground/surface-water interfaces in wetlands allow natural attenuation through complete anaerobic biodegradation to naturally reduce concentration and toxicity of chlorinated VOC-contaminated groundwater before humans or sensitive environments are reached.

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