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Record of Decision System (RODS)



Address:  OFF RTE 40 
City & State:  EDGEWOOD  MD  21010
County:  HARFORD
EPA ID:  MD2210020036
EPA Region:  03
NPL Status:  Currently on the Final NPL
ROD Type:  Record of Decision
ROD ID:  EPA/ROD/R03-95/187
ROD Date:  10/11/1994
Operable Unit(s):  04
Media:  Air, Groundwater
Contaminant:  Arsenic, volatile organic compounds, 1,4-dithiane, semi-volatile compounds
Abstract:  Please note that the text in this document summarizes the Record of Decision for the purposes of facilitating searching and retrieving key text on the ROD. It is not the officially approved abstract drafted by the EPA Regional offices. Once EPA Headquarters receives the official abstract, this text will be replaced.

The U.S. Army Aberdeen Proving Ground (APG) is a 72,516 acre installation locate in southeastern Baltimore County and southern Harford County, Maryland, on the western shore of the upper Chesapeake Bay. The installation is bordered to the east and south by the Chesapeake Bay, to the west by Gunpowder Falls State Park, the Crane Power Plant and residential areas, and to the north by the towns of Edgewood, Magnolia, Perryman, and Aberdeen. APG is divided into two areas by th Bush River: the Edgewood Area of APG lies to the west of the river and the Aberdeen Area lies to the east.

APG was established in 1917 as the Ordnance Proving Ground and was designated a formal military post in 1919. Testing of ammunition and other equipment and operation of training schools began at APG in 1918. Between this time and the onset of WWII, activities at APG included research and development and large-sca wide variety of munitions, weapons, and other equipment.

APG's primary mission continues to be the testing and development of weapons, munitions, vehicles, and a wide variety of support equipment. Within the Edgewood area, chemical warfare research, development, and related activities have occurred.

Many areas of the Gunpowder Neck of the Edgewood Area have been used as impact areas for the testing of ordnance. Ordnance have been tested and fired into various areas and there is the potential for encountering unexploded ordnance and/or intact or leaking liquid-filled rounds deposited during testing and firing. Disposal and testing activities have also taken place in areas along th Gunpowder Neck.

The O-Field area is an area of approximately 259 acres located on the Gunpowder Neck peninsula in the Edgewood Area. It is bordered on the north and east by Wilson Creek, on the south by H-Field, and on the west by Gunpowder River. Watson Creek drains into the Gunpowder River through a narrow culvert under Wastson Creek Road. The Gunpowder River, in turn, drains into Chesapeake Bay.

The O-Field area contains two known disposal areas and one suspected disposal area. The northern disposal area is designated as Old O-Field, and this area wa used for disposal activities from the late 1930s to 1953. The second area is known as New O-Field. It was used from the mid-1950s to the early 1980s as a destruction and disposal area. The suspected disposal area known as the "Pit Site" is on the west side off Watson Creek Road near the Gunpowder River. The "Pit Site" was reportedly used from the late 1930s to mid-1950s as a disposal area.

Old O-Field is a four and a half acre site that was used by the Army for storage handling, disposal, and destruction of chemical warfare materials (CWM), decontaminating chemicals, ordnance, laboratory samples, and contaminated equipment. The site is located within a restricted area of APG, and access to the site is strictly controlled. The site is surrounded by a chain-link fence, which is supplemented by other physical security countermeasures, and is patrolled on a 24-hour basis.

At present, Old O-Field is heavily vegetated. There are trees and smaller bushes. Small animals such as foxes have been observed inside the fenced area. The surface of the field is highly irregular; there are areas where deep subsidence has occurred indicating that the trenches and pits are eroding and collapsing. A large number of ordnance items, drums, pipes, ammunition crates, canisters, and miscellaneous scrap metal items are visible on the surface of the field and within the open trenches.

The residential areas closest to Old O-Field lie approximately two and seven tenths miles north, three miles to the west, and four and a half miles to the north-northwest. In addition, Kent County lies six miles west of Old O-Field.
Remedy:  This remedial action addresses the principal threat posed by this site, which ha the potential for an accidental release of chemicals into the air. The function of this operable unit is to reduce the risk of an accidental release of chemical warfare materials (CWM) from the site by minimizing the possibility of a fire at the site, reducing the likelihood and potential effects of an unplanned detonation of ordnance, and minimizing both the likelihood and the potential effects of evaporative release of CWM from a subsurface release.

The selected remedy consists of five components. The first is a Permeable Infiltration Unit (PIU)which will be constructed on top of the site. The PIU will be constructed principally of sand and other granular materials. Construction of the PIU will reduce the threat of a release of CWM by covering the site with non-flammable materials, which will serve to cut off the air flow to the surface of Old O-Field, stop erosion and stabilize the soil, provide a blast-resistant layer on top of the ordnance, and provide a vapor barrier to reduce the emission of CWM from an underground release.

The second component is the installation of an air monitoring system within the PIU to detect the presence of CWM within the pore spaces of the sand.

The third component is the construction of a sprinkler system on top of the PIU that will be capable of quickly spraying water or other solutions on the PIU. I a CWM release is detected by the air monitoring system, then the sprinkler syste will be activated. The water sprayed onto the PIU will form a vapor barrier within the sand to prevent an air release of CWM and will also hasten the degradation of CWM.

The fourth component is the conduction of treatability studies using the sprinkler system to apply water or other solutions to the PIU. The results of these studies will be used to evaluate the feasibility of enhanced leaching of the contaminants from soil and buried containers to the groundwater. In addition, the surface of the PIU will be monitored to evaluate the rate of subsidence of Old O-Field.

The fifth component is verification of the ability of the groundwater extraction and treatment system that is under construction for OU-1 to capture and treat th contaminated groundwater emanating from Old O-Field. In addition, the effectiveness of the groundwater monitoring program to detect changes in the sit hydrogeology and groundwater chemistry will be verified.
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