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Record of Decision System (RODS)



City & State:  NEW LONDON  CT  06349
EPA ID:  CTD980906515
EPA Region:  01
NPL Status:  Currently on the Final NPL
ROD Type:  Record of Decision
ROD ID:  EPA/541/R-00/001
ROD Date:  06/29/2000
Operable Unit(s):  07
Abstract:  The United States Navy Submarine Base New London (NSB-NLON) consists of approximately 547 acres of land and associated buildings in southeastern Connecticut in the towns of Ledyard and Groton. NSB-NLON is situated on the east bank of the Thames River, approximately 6 miles north of Long Island Sound, and is bounded to the east by
Connecticut Route 12, to the south by Crystal Lake Road, and to the west by the Thames River.

In 1867, the State of Connecticut donated a 122-acre parcel on the east bank of the Thames River to the Navy. The
Navy began using the property in 1868 when it was officially designated as a Navy Yard. The Navy designated the site a Submarine Base in 1916. Between 1935 and 1945, the Navy built in excess of 180 buildings and expanded NSB-NLON from 112 to 497 acres through the acquisition of adjacent land.

NSB-NLON currently serves as a major support center for the U.S. Atlantic fleet. Additionally, NSB-NLON includes housing for Navy personnel and their families, submarine training facilities, military offices, medical facilities, and facilities designed for the maintenance, repair, and overhaul of submarines. Land use adjacent to the NSB-NLON is generally residential or commercial.

The Groton Water Department supplies potable water to NSB-NLON. The primary sources of the Groton water supply are reservoirs that are supplemented with wells. The water supplies are located within the Poquonock River Watershed, located east of NSB-NLON, which is not within the NSB-NLON watershed. Groundwater at NSB-NLON is not used for potable water.

In 1975, the Department of Defense developed a program, known as the Installation Restoration Program (IRP) to investigate and clean up problem areas involving contamination at federal facilities such as the NSB-NLON. The NSB-NLON was placed on the National Priority List (NPL) in August 1990.

Site 20 is located in the northeast potion of the base. The site includes Building 524, located near the top of a bedrock high, and the southern bunker area, located southeast and downhill of Building 524 adjacent to the Area A Wetland.
Site 20 consists of three drainage areas. Soils at site 20 consist primarily of coarse sand, gravel, and rock fill underlain by up to 17 feet of fine-grained dredge spoils. Ground water as site 20 is located in both the overburden soil and the underlying bedrock and flows to the southwest. Ground water is classified as GB, indicating the area has been used for long-term, intense industrial or commercial development. Ground water is not used as a source of drinking water.

Building 524 was constructed in 1990. Prior to construction, the area was primarily woodlands. Portions of the site were blasted to remove bedrock during construction. The building was historically used for administration, minor torpedo assembly, and storage of simulator torpedoes. Chemicals, including cleaning and lubricating compounds, paints, adhesives; and liquid fuels, were used and stored in relatively small amounts at the site. Although building 524 is part of OU 7, remedial action in this area is not expected because no impacted soil or sediment has been identified.

The southern bunkers are first evident in aerial photographs from 1969, and the northern area bunker is evident in photographs from 1974. The southern bunkers were reconstructed in the mid-1980's, including removal of structurally unsuitable soils (most likely dredge spoils associated with the Area A Wetlands) and subsequent analytical testing of soils, excavations, and ground water was performed. Drainage Areas 1, 2, and 3 are located in the southern bunker area. Currently, the bunkers are used for the storage of live and simulator torpedoes and missiles.

Future land use at site 20 is likely to remain the same. NSB NLON has no plans to cease active base status. However, should the base close or transfer, it is possible that site 20 may become part of a residential area.

In 1982, an initial assessment study was completed as part of the Navy Assessments and Control of Installation Pollutants, to assess the potential for environmental contamination. At that time, site 20 was not identified as a potential contaminated site and was not investigated. In 1992, the navy completed a Phase I RI. Site 20 was not included in this investigation, although samples were collected in the Area A Wetlands, which is adjacent to site 20. The Phase II RI was completed in 1997 and recommended that this site proceed to a Feasibility Study to evaluate a "limited action" effort consisting of a ground water monitoring program and possibly access / use restrictions. In June 2000, a final FS for site 20 was completed identifying potential remedial alternatives. In May 2000, the navy published a Proposed Remedial Action Plan and a public hearing was held on the plan, presenting the selected remedial alternatives for site 20. A Record of Decision addressing OU7 was completed in June 2000.
Remedy:  Alternative 3b, Selective Excavation and Asphalt Batching or Offsite Disposal (Residential Scenario), is the selected remedy for Site 20. An expected outcome of the selected remedy is that Site 20 will no longer present an unacceptable risk to humans or the environment. The selected remedy will treat the low level threats associated with site contaminants. The amount of time necessary to achieve the goals consistent with potential future residential use is within 1 year.

Soil and sediment cleanup levels have been established to be the more stringent of either the Remediation Standard Regulations (Pollutant Mobility Criteria, Residential Direct Exposure Criteria, or Industrial/Commerial Direct Exposure Criteria), or the 10-5 risk based Preliminary Remediation Goals as calculated in the Feasibility Study.

Selective excavation will be conducted to remove contaminated soil and sediment. The following soils and sediments will be excavated in order to achieve the residential scenario cleanup levels:

Drainage Area 1 - Sediment with PAH (benzo[a]pyrene) concentrations in excess of cleanup levels is located at 2WCSD3 from 0 to 1 foot bags. Soil with PAH concentrations in excess of cleanup levels is located at 2WCTB2 from 0 to 2 foot bags. Soil with arsenic concentrations in excess of cleanup levels is located at 2WCTB3 from 4 to 6 bags, and at 2WCTB5 from 6 to 8 feet.

Drainage Area 2 - Soil concentrations are not expected to exceed cleanup levels but will be sampled to ensure that the remediation goals are met.

Drainage Area 3 - Soil concentrations are not expected to exceed cleanup levels but will be sampled to ensure that the remediation goals are met.

Based on the locations and depths of the Contaminants of Concern, it is anticipated that a total of approximately 199 yd3 of soil and sediment will be removed under Alternative 3b to achieve compliance with the cleanup levels under the future residential land use scenario.

Collection of confirmatory soil and sediment samples from the bottom and sidewalls of the excavation will occur. Samples will be analyzed for PAHs and inorganics to confirm that material exceeding the media-specific cleanup levels has been removed.

The excavated area will be backfilled with clean fill, the drainage swales will regraded, and disturbed asphalt will be repaired. Excavated soil will either be disposed at an offsite, licensed disposal facility or treated using thermoplastic stabilization/solidification, depending on the actual total volume that is excavated and the results of the waste characterization samples. Asphalt batching is the preferred disposal option.

Under Alternative 3b, contamination above media specific cleanup levels will be removed from the site. Therefore, 5 year reviews will not be required.

Estimated Capital Costs: $63,300 or $81,200
Estimated Annual O&M: $0
Estimated Present Worth: $63,300 or $81,200
Text:  View full-text ROD [ 628K ]
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