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Record of Decision System (RODS)



Address:  33RD AND DAHLIA 
City & State:  COMMERCE CITY  CO  80022
County:  ADAMS
EPA ID:  COD980717953
EPA Region:  08
NPL Status:  Deleted from the Final NPL
ROD Type:  Record of Decision
ROD ID:  EPA/ROD/R08-93/072
ROD Date:  06/30/1993
Operable Unit(s):  03
Media:  GW, SW, Air
Contaminant:  VOCs, Metals
Abstract:  The 150-acre Sand Creek Industrial (Operable Units 3 and 6) site is an inactive landfill located on the 300-acre Sand Creek Industrial site in Commerce City, Colorado. The site is situated within the Sand Creek floodplain and borders a 1-acre wetlands area. Land use in the area is predominantly industrial, with some agricultural uses. There are an estimated 25 people who reside within a one-mile radius of the site, and a daytime population that reaches several hundred due to the local businesses and industrial nature of the area. Municipal water is supplied for the metropolitan area surrounding the site through ground water and surface water from alluvial and bedrock wells and outside sources. In 1990, a State inventory indicated that only two properties used private wells for drinking water. Prior to 1967, the site was used primarily for agricultural purposes, but from 1956 to 1964, the southern boundary of the landfill was used for sand and gravel mining operations. In 1967, the landfill began accepting both demolition and domestic refuse. Known hazardous and pathological wastes reportedly were excluded from disposal at the landfill; however, the method used to exclude these wastes, and the consistency with which this practice was employed, is not known. In 1975, the landfill was closed, and the area was revegetated. In 1977, a State investigation of an explosion at the landfill concluded that methane gas was migrating from the landfill. In response, two methane gas venting systems were installed at the landfill in 1978. In 1981, the State determined that the passive venting system was ineffective, and as a result, one of the PRPs installed an active venting system that collected gases and vented them to the surface through three stacks. EPA investigations conducted from 1982 to 1988 indicated the presence of several VOCs and inorganic compounds in the ground water and surface water. In 1987, air and soil analyses indicated VOC contamination in the gas samples, but no indication of contamination in the soil samples from the landfill cover was found. In 1990, EPA required the PRPs to address the potential for explosion and health risks associated with gaseous emissions released from the landfill, as OU6. In 1991, as part of the EPA-initiated removal action for OU6, the PRPs installed and began operating an active landfill gas-extraction system (LFGES), replacing the previously installed systems. Due to the complex nature of the site, EPA has divided it into six operable units in order to more effectively address specific contamination problems. A 1989 ROD addressed contaminated soil, buildings, and tanks, as OU1, and a 1990 ROD addressed contaminated soil at the COC area, as OU5. Other 1993 RODs address OU2 and provide an amendment for OU5. This ROD addresses the contaminated ground water, surface water, and air at the 48th and Holly Landfill, as OUs 3 and 6. Soil and sediment were eliminated from the original scope since investigations indicated that they were not contaminated significantly. Future RODs will address remediation of the ground water at the landfill, if subsequent evaluations determine that the landfill is responsible for unacceptable ground water contamination. The primary contaminants of concern affecting the ground water, surface water, and air are VOCs, including benzene, PCE, TCE, and toluene; and metals, including arsenic. SELECTED REMEDIAL ACTION: The selected remedial action for this site includes continuing the operation and maintenance of the OU6 LFGES, including treating the condensate offsite at a POTW, with improvements as required during the normal course of operation and maintenance activities; continuing maintenance of the soil cover system, the perimeter fence, and the warning signs; continuing existing institutional controls and implementing additional institutional controls, as necessary; monitoring ground water and landfill gas; and conducting periodic site reviews; and providing additional remedial action, as necessary, if monitoring indicates that the landfill contributes to unacceptable contamination of the ground water. The estimated present worth cost for this remedial action is $7,283,000, which includes an estimated annual O&M cost of $240,000 for 30 years. PERFORMANCE STANDARDS OR GOALS: Not applicable. INSTITUTIONAL CONTROLS: Land use and ground water restrictions will be implemented to prevent dermal or direct contact with the landfill contents, impede the use of ground water underlying the landfill as a drinking water source, and protect the integrity of the soil cover system and the LFGES operating at the landfill. Additional institutional controls may be implemented, as necessary, and include zoning and subdivision regulations, building permits, recording requirements, State statutes, and local ordinances.
Remedy:  The remedial action selected for OU3/OU6 will address the principal threats existing at the Landfill and will ensure that: (1) emissions of landfill gas are controlled to prevent inhalation at levels that pose an endangerment to human health or the environment, (2) accumulation of landfill gas is minimized in order to prevent explosion hazards, (3) dermal contact with the landfill contents is prevented, and (4) the use of ground water underlying the Landfill as a drinking water source is prevented.

The major components of the selected remedy include:
* Continued operation and maintenance of the OU6 landfill gasextraction system (LFGES) with improvements as required during the normal course of operation and maintenance activities;
* Continued maintenance of the soil cover system with improvements as required during the normal course of operation and maintenance activities;
* Continued maintenance of the perimeter fence and warning signs;
* Continuation of existing institutional controls, and implementation of additional institutional controls, as necessary;
* Implementation of the OU3 monitoring program and periodic site reviews.
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