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Record of Decision System (RODS)

NAVAL SURFACE WARFARE CENTER - DAHLGREN

Abstract

Site Name:  NAVAL SURFACE WARFARE CENTER - DAHLGREN
Address:  2 MI E OF INTER 301 & 206 
City & State:  DAHLGREN  VA  22448
County:  KING GEORGE
 
EPA ID:  VA7170024684
EPA Region:  03
 
NPL Status:  Currently on the Final NPL
 
ROD Type:  Record of Decision
ROD ID:  EPA/541/R-98/069
ROD Date:  09/30/1998
Operable Unit(s):  03
 
Media:  Debris, Groundwater, Other, Sediment, Soil, Surface Water
 
Contaminant:  Base Neutral Acids, Inorganics, Metals, PAH, PCBs, Pesticides, VOC
 
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 Naval Surface Warfare Center Dahlgren site (NSWCDL) is located in Dahlgren, Virginia.
Operable Unit 1 (OU1):

Site 12, the Chemical Burn Area, is one of several Installation Restoration (IR) sites located at the NSWCDL facility. Site 12 is situated on the Mainside of the base and is bounded on its western side by Gambo Creek. Groundwater production wells supplying potable water to NSWCDL are over 600 feet deep and located over 4,000 feet south of Site 12. These wells are unaffected by contaminants related to Site 12. The closest residences, on-base Navy housing consisting of over 150 homes, are within 6,000 feet southwest of Site 12.
Activity in the vicinity of Site 12 first began about 1952 when a 600 by 600-foot area was cleared of vegetation. Later, around 1964, two pits were observed in the cleared area. It was reported that fuel had been used to burn laboratory materials and metallic hardware and equipment at the pit. The last burn was conducted in the fall of 1982. By 1986, the pit and fence at Site 12 were no longer visible due to the amount of vegetation present in the area. By late 1986, the fence was removed and the pit was filled in by regrading the area. Known or potential wastes disposed of at Site 12 include fuel oils, spent solvents, metals, caustics, hypochlorite, polymers, glues, and decontaminated chemical warfare agent solution.

Site 12 was identified as a potential area of contamination in the initial investigation performed in the early 1980s. Confirmation of contamination at Site 12 occurred between 1983 and 1984. Results of sampling at the site were reported in 1986. One of the two Records of Decision (RODs) issued in September 1997 address Site 12.

OU2:
Site 2, the Fenced Ordnance Area, is one of several Installation Restoration (IR) sites located at the NSWCDL facility. Site 2 is situated on the Mainside of the base and is bounded on its western side by Gambo Creek. Groundwater production wells supplying potable water to NSWCDL are located over 4,000 feet south of Site 2. The closest residences, on-base Navy housing consisting of over 150 homes, are within 6,000 feet southwest of Site 2.

Evidence shows that activity at Site 2 began around 1943, when a small cleared area was observed in a photo. By 1952, the area had grown larger and a pile of dark-colored dirt was present in the northwest corner. In the early 1970s, a fenced landfill area was excavated and reportedly used for the disposal of metal ordnance materials that may have contained explosive residue. In addition, asbestos pipe wrappings, rinsed pesticide containers, ordnance hardware, and machine parts were buried in this area. Trenching operations also occurred at the site in the 1980s.

The initial assessment on the site was conducted in 1981 and concluded that radioactive monitoring should be completed. Other studies were performed and have been completed in 1991-1992. One of the two RODs issued in September 1997 address Site 2.

OU3:
The Disposal/Burn Area (Site 9) is an inactive landfill, approximately 5 acres in size, located off Caskey Road in the central portion of the Mainside, adjacent to the southwestern shore of Gambo Creek and associated marsh area. Gambo Creek and its associated marsh area border approximately two-thirds of the site to the east and north. The majority of the remaining area surrounding Site 9 is wooded. Historic information indicates that the facility used this area as a sanitary landfill from the early 1940s until 1971. However, dumping and occasional burial of construction debris and tree stumps continued until 1984. Site 58, also called the Building 1350 Landfill, is an extension of Site 9 to the southwest and is approximately 0.7 acre in size. This landfill was in use during a later period than Site 9. A ROD addressing contaminated soil, groundwater, and sediments associated with Site 9 and Site 58 was completed in September 1998.

OU5:
The 1400 Area Landfill (Site 17) is an inactive landfill located in the northwest corner of the NSWCDL. Two unnamed drainage tributaries form the western and eastern boundaries of the site. A small pond is located in the western portion of the site with a marsh on the eastern portion. The site was used as a landfill, where municipal solid waste and construction debris were deposited, compacted, and covered on a periodic basis during the early 1970s and possibly until 1978. The landfill is fully vegetated with tall grass. Soil cover exists over the majority of the landfill. The area bordering the site to the north and west is undeveloped and heavily wooded. A ROD addressing contaminated soil and groundwater at Site 17 was completed in September 1998.
 
Remedy:  Alternative 3 with option A (upgradient groundwater control), option B2 to the north (shoreline protection), and B3 to the south (fill Gambo Creek and restore as wetlands) is the selected remedial alternative utilizing capping to address both soils and sediments.

The selected remedy for Site 9 is to utilize capping to address both soils and sediments, and to provide institutional controls, as well as groundwater, surface water, and sediment monitoring. The major components of the selected remedy include the following. Landfill wastes in the southern area, estimated at approximately 250 cubic yards (cy), shall be excavated until bare soil is exposed. These wastes and surface soils shall be consolidated and stabilized on the landfill portion of the site. The landfill, estimated to be approximately 5 acres upon completion of closure activities, will be covered with a multilayer cap meeting the requirements of the Virginia Solid Waste Management Regulations. The final cap components will be determined during the final design for Site 9. The multilayer cap will be revegetated, and the closure completed consistent with sanitary landfill closure requirements. An impermeable slurry wall will be installed on the hydraulically upgradient (west) side of the landfill, which shall effectively redirect groundwater movement around the capped landfill. The slurry wall will be installed to a depth below grade and key into the clay confining unit beneath the site.

Surface debris will be removed (excavated) from the marshy area of the site and consolidated and stabilized on the landfill. It is estimated that approximately 260 cy of surface debris will be removed from the marsh. Vegetation in the marshy area of the site will be cut back. Upon completion of the placement of the marsh cap, appropriate vegetation will be re-introduced and maintained. Installation of the marsh cap will raise the elevation of the marsh and will likely turn the capped area into an upland environment. The wetland loss will be mitigated elsewhere at the Naval Surface Warfare Center Dahlgreen (NSWCDL) facility. Where Gambo Creek is within 100 feet of the waste/fill material in the marsh, on the northeastern portion of the site, the shoreline of Gambo Creek will be protected against erosion to provide a benefit equivalent to moving waste 100 feet away from Gambo Creek. It is conservatively assumed that the shoreline protection will consist of spot regrading of the Gambo Creek stream bank. It is anticipated that 560 linear feet of shoreline protection will be required. Portions of Gambo Creek on the southeastern portion of the site will be filled, and established as wetlands.

Institutional controls, including limiting site access through gates and limiting future land use, will be implemented to eliminate or reduce pathways of exposure to contaminants at the site. Monitoring will also be instituted to determine if contaminants are migrating at significant rates and concentrations.

Institutional controls will be implemented to limit future site land use. An institutional control plan will be developed as part of the remedial action design and include: access controls, signs along the perimeter of the site, restrictions on shallow groundwater use for drinking water, description of land use controls in the base master plan, periodic inspection, monitoring, and re-evaluation of land use controls, annual certification that institutional controls are in place, notification to the U.S. Environmental Protection Agency (EPA) and state regulators whenever the Navy anticipates any major changes in land use restrictions, public notice, and a deed notification.

The Navy shall institute the following institutional controls within 90 days of installation of the capping system: a real property description notation, Base Master Plan notations, and limited site access. The Navy shall institute groundwater monitoring to ensure remedial action objectives arebeing maintained. The Navy shall also monitor the surface waters and sediments at Site 9.

Estimated Capital Costs of Option B2 with Option A: $3,547,067
Estimated Capital Costs of Option B3 with Option A: $4,342,404
Estimated Annual O&M Costs: $33,350 plus $15,500 every 5 years
Estimated Present Worth Costs of Option B2 with Option A: $3,994,325
Estimated Present Worth Costs of Option B3 with Option A: $4,789,662
 
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