ARCHIVED REPORTS_CONCEPTUAL SITE MODEL

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r • Between January and April of 1988, a soil vapor survey was conducted in the impoundment area (PEG, ' 1995). • In May 1989, two monitoring wells (MW-12 and MW-13) were installed to a depth of approximately 60 feet bgs. The wells are screened from approximately 48 to 50 feet bgs to the total depth of the boring in a presumed lower water bearing zone (PEG, 1995). • In May 1990, a Problem Assessment Report (PAR) and Work Plan were submitted (PEG, 1995). The PAR included a '/z-mile radius well search, fate and transport modeling, and summary of previous site work. • In July 1993, five extraction wells (MW-14 through MW-16, MW-18 and MW-19) and three groundwater monitoring wells (MW-17, MW-20, and MW-21) were installed. Wells MW-14 through MW-16 were used for separate phase hydrocarbon (SPH) recovery and wells MW-18 and MW-19 were used for hydraulic containment(PEG, 1995). • In August 1993, additional site assessment was performed. Twenty soil borings were drilled in the farm field adjacent to the site. The results of groundwater samples collected from all 20 borings indicated total petroleum hydrocarbons as diesel (TPHd), total petroleum hydrocarbons as gasoline (TPHg), benzene and toluene concentrations were all non-detect(PEG, 1995). • In June 1994, one 10,000-gallon double walled fiberglass underground storage tank (UST), pump island, and associated piping was removed from the Keylock area. Two soil samples were collected from the former pump island area. Groundwater was observed in the tank excavation at approximately 8 feet bgs (PEG, 1995). I • A PAR was submitted on May 15, 1995 (PEG, 1995). The principal findings of the PAR are listed below: 1. The lateral and vertical extent of dissolved-phase hydrocarbons in the lower water bearing zones was adequately defined. 1 2. Continued operation of the containment system, including the pumping of groundwater from the extraction wells, maintained the shallow groundwater plume onsite. 1 3. Continued SPH recovery and extraction of dissolved-phase hydrocarbons, from three wells within the SPH plume onsite, reduced hydrocarbon mass in groundwater. • In July 2001, an assessment report and work plan for additional assessment was submitted as part of the ongoing investigation of hydrocarbon-impacted groundwater and soil at the site (SECOR, 2001). Data collected in April of 2001 and May of 2001 indicated the extent of the methyl tertiary butyl ether (MtBE) within shallow groundwater (northeast of the site on private property) was not defined. Offsite groundwater analysis results in May of 2001 reported MtBE concentrations ranging from 6.1 micrograms per liter (pg/L) to 95 pg/L. Microbiological analysis of soil and groundwater samples collected on April 12, 2001 suggested a healthy population of hydrocarbon degraders exists with good natural attenuation potential at the offsite sample locations. • BLASLAND, BOUCK &LEE,INC. 3124106 engineers,scientists,economists 2-2 J:\D0006\44634_00161022_ConceptuaI Site Model.doc