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Record of Decision System (RODS)

PATUXENT RIVER NAVAL AIR STATION

Abstract

Site Name:  PATUXENT RIVER NAVAL AIR STATION
Address:  OPPOSITE LEXINGTON PARK (STATE HWY 235) 
City & State:  PATUXENT RIVER  MD  20670
County:  ST. MARY'S
 
EPA ID:  MD7170024536
EPA Region:  03
 
NPL Status:  Currently on the Final NPL
 
ROD Type:  Record of Decision
ROD ID:  EPA/541/R-00/008
ROD Date:  02/08/2000
Operable Unit(s):  01, 02
 
Abstract:  Disposal operations at the landfill began in April 1974 , which consisted of placing solid waste in 10-foot lifts and 50 foot working faces. Once the solid waste was placed in lifts, it was covered with soil from the borrow area next to the landfill. The borrow area for the landfill during its operation is the area now known as the Current Sanitary Landfill. It is estimated that the landfill received approximately 22,000 tons of plastic and paper trash. It is estimated that the landfill received approximately 43 tons of oil contaminated soils and liquid wastes consisting of petroleum-oil lubricants, solvents, thinners, paints, small amounts of pesticides, and photographic wastes. The liquid wastes were predominantly residues left in cans, rags, and absorbents. The landfill operated under Maryland Department of Environment (MDE) Solid Waste Permit number 79-18-08-04A from March 1, 1979 until September of 1980 when the landfill was closed.

Located next to the landfill is the 10-acre Current Sanitary Landfill. Disposal operations began at the Current Sanitary Landfill when the landfill closed in 1980. The Current Sanitary Landfill is regulated under the Resource Conservation and Recovery Act (Subtitle D) (Solid Waste Disposal Act), as administrated by the MDE Solid Waste Program. An estimated 145,000 tons of municipal solid waste was disposed of at the Current Sanitary Landfill. The Current Sanitary Landfill received waste as defined under its Refuse Disposal Permit for municipal landfills from September 1, 1980 to November 17, 1991. In October 1991, the NAS began transporting municipal wastes to the St. Andrews Landfill in St.
Mary's County Maryland. From November 18, 1991 to May 27, 1994, the Current Sanitary Landfill accepted rubble fill only as per Code of Maryland Regulation (COMAR) 26.04.07.13. From May 28, 1994 to September 30, 1994, the Current Sanitary Landfill accepted clean fill only. The purpose of this waste acceptance policy change was due to the amount of fill area remaining. On November 14, 1994, NAS provided verbal notification to the State that the Current Sanitary Landfill was closed on September 30, 1994.

During construction of the Current Sanitary Landfill, a leachate collection system was extended along the down gradient perimeter of the landfill. The leachate collection system is intended to intercept leachate generated by the wastes as a result of groundwater intrusion and precipitation infiltration. The system connects the two landfills, therefore, any monitoring of the system includes leachate from both landfills. The leachate is sent via underground piping to the St. Mary's Metropolitan Commission, Pine Hill Run Wastewater Treatment Facility, for treatment and discharge. Monthly monitoring of the leachate began in January 1985. Flow varies from a low of 12,000 gallons per day to a high of 25,000 gallons per day. Currently, the leachate is sampled and analyzed quarterly.

In May of 1985 four 4-inch PVC monitoring wells were constructed as part of a Confirmation Study performed by CH2M Hill. All four wells are permitted with the State of Maryland (SM-81-1568 through 1571). The wells range (three down gradient and one up gradient) in depth from 32 to 43 feet. On March 13, 1986 NAS began submitting a Landfill Annual Report to the State of Maryland. The report included monthly groundwater elevations, leachate data, and the amount of waste deposited. During the time period of February 7 to March 14 and June 26 to July 21, 1989, five additional monitoring wells were installed as part of the Hygrologic Study of the Former and Current Landfills, conducted
by CH2M Hill. Two wells were installed in the first clay layer 32 to 43 feet below ground surface and the remaining three were installed in the next lower clay layer approximately 80 to 85 feet below ground surface. All five wells were permitted by the State of Maryland (SM-81-40-16 through 4020).

Initially (August 1985), the State of Maryland periodically sampled the wells. Then on September 23, 1992, the State of Maryland requested the submission of a Landfill Sampling and Analysis Plan. The State of Maryland decided to no longer collect and analyze from the groundwater monitoring wells, and on November 2, 1992, NAS submitted a revised landfill sampling and analysis plan. On January 1, 1993, NAS began quarterly sampling of the wells. Since 1993, the monitoring well information has been included in the Landfill Annual Report. Surface water monitoring date was collected in June 1974 from the seasonal streams on either side of the landfill. Additional surface water samples were collected in 1985 and
1987.

The Department of the Navy, (DON) issued guidance in the 1980's for all installations to perform hazardous waste assessments of sites as a result of past disposal activities. In March 1984, an Initial Assessment Study of Naval Air Station Patuxent River, Maryland was completed. The landfill was one of 31 sites identified in the 1984 report, and it was recommended for further study because of it potential contribution to surface water and/or groundwater contamination.

The first Groundwater Monitoring Plan and Quality Report was completed on March 20, 1986. This report contained the water level elevation and water quality data from sampling events. The State acknowledged receipt of this report and requested additional information about the ground water. This led to the eventual development of a hydrologic investigation.

The first sanitary landfill utilization report entitled Sanitary Landfill Utilization Report was completed on March 5, 1986. The Current Sanitary Landfill is underlain with a clay liner and the slopes are covered with a synthetic liner.

The Confirmation Study Report (site investigation) was conducted in 1987 to verify the presence of contamination based on the Initial Assessment study. The investigation supports the previous study and the site was recommended for the next phase of the Navy's Installation Restoration Program.

On April 4, 1987 MDE issued a Notice of Violation (NOV) for the Current Sanitary Landfill for not complying with the terms and conditions of the permit. As a result of the NOV, stricter monitoring controls were enforced.

In 1988, a RCRA Facility Assessment of the NAS was initiated. The RCRA Facility Assessment (RFA) Phase II Report identified the Former Sanitary Landfill as Solid Waste Management Unit (SWMU) 47. The RFA noted that paper, plastics, cardboard, hospital wastes, cesspool/sewage sludge, demolition/construction debris, landscaping wastes, petroleum-oil lubricant (POL) products, paints, antifreeze, solvents, pesticides, asbestos, and photo lab wastes were deposited in the Former Sanitary Landfill from 1974 to 1980.

In 1990, a Hydrological Investigation of the Current and Former Sanitary Landfills was conducted to determine groundwater flow, elevation, conductivity, pH, and temperature.

The Interim Remedial Investigation (IRI) was part one of the two phase Remedial Investigation of the Installation Restoration Program. The IRI was conducted in 1991 to determine the human health risk posed by the site. The IRI only partially characterized risk to human health at the site because insufficient information was collected to evaluate environmental risk. EPA subsequently supplemented the human health risk assessment at the site to complete the human health risk assessment. The IRI report was finalized in February,1994.

In August, 1995, a soil gas survey was conducted. The total number of samples taken was 57. The information from this sampling event will be used to determine the need for possible treatment of landfill gases and new monitoring well locations.

To date, no Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) and /or RCRA enforcement actions have been taken at Site 11, the Former Sanitary Landfill (CERCLA Landfill).

The thirty-day public comment period was held from September 6, 1995 through October 6, 1995 and the public meeting was held on September 15, 1995. A summary of the site conditions and the interim remedial alternatives under consideration (EPA/ROD/R03-96/222), were presented to the public.
 
Remedy:  The selected remedy for sites 1 and 12 is Alternative 2: Institutional Controls and Long-term monitoring; Installation of a Soil Cover over Areas B and D; Excavation of Contaminated Material and Debris from Area C, and Offsite Disposal. Alternative 2 was selected as the remedy for site 1 and 12 because it offers the best balance of the nine NCP criteria based on available information and a current understanding of site conditions. Alternative 2 is protective of human health and the environment because it prevents exposure to landfill wastes through the construction of a soil cover over sites 1 and 12. The selected alternative is readily implementable and cost-effective. The construction
of soil cover, instead of a more elaborate RCRA Subtitle D cap, reduces construction and O&M costs while maintaining a similar level of effectiveness. The selected alternative considers the publics' desire dire restoring limited recreational use of sites 1 and 12. Stabilization measures along the northwestern portion of site 1 will allow for public access while maintaining habitat in the area.

Under Alternative 2, a soil cover with minimum 2 percent and maximum 3 horizontal: 1 vertical side grades will be placed over the landfill area of sites 1 and 12. The soil cover will consist of a minimum of 18 inches of subsoil and minimum of 6 inches of topsoil capable of supporting vegetative growth. The base for the soil cover will be obtained from the area east of site 1 (Area F). Approximately 2.6 acres of wetlands will be eliminated in site 1 as a result of installing the soil cover. In addition, approximately 1 acre of the marsh west of site 12 will be disturbed during the soil cover. These emergent wetlands will be mitigated, one-for-one, elsewhere on the NAS. Surface debris and contaminated soil will be excavated from a ravine (Area C) and disposed in an offsite permitted landfill. Shoreline stabilization will be implemented along the northeastern portion of site 1, in order to stabilize current erosion.

Institutional controls will consist of the following: (1) access to restrictions to prevent trespassing and disturbance to the soil cover, and (2) deed notices and land use controls to limit size development and access to groundwater. Monitoring will be performed to access the migration of contaminants into the environment and to evaluate the effectiveness of the remedy. Routine operation and maintenance activities will be performed to promote long-term stability of the soil cover. A review will be conducted every 5 years to evaluate whether human health and the environment continues to be protected.

Costs:
Estimated Capital Cost: $3,720,000
Estimated Annual O&M Cost: $56,564
Estimated Present Worth Cost: $4,590,000
O&m Duration: 5 years
Discount Rate: 5%
 
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