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i C*ATC ASS O C I ATE S INC • A quarterly groundwater monitoring program was initiated in February 1992 with the installation of wells MW-1 through MW-3 and the monitoring program was subsequently expanded following the installation of additional monitoring wells. The most recent groundwater analyses available from samples collected in May 1997, indicate a dissolved hydrocarbon plume is located in the vicinity of the former product islands, primarily near MW-2. Petroleum hydrocarbon constituents detected included: benzene (1,200 parts per billion [ppb]), toluene (28,000 ppb), ethylbenzene (3,900 ppb), xylenes (18,000 ppb), and TPHg (77,000 ppb) (MPDS, June 2, 1997). • Monitoring wells MW-1, 9, 8, 7 and 5 have always been clean. Wells MW-2, 3, and 4 have always been contaminated (PHS/EHD Investigative Officers Report). + Groundwater elevations have changed significantly since the monitoring program was implemented. In 1988, static groundwater was 30 feet bgs; in 1992, static groundwater was 50 feet bgs; and the May 1997 groundwater monitoring data indicates water has rebounded to approximately 30 feet bgs (PHS/EHD Investigative Officers Report). • PHS/EHD requested a Corrective Action Plan (CAP) using the feasibility of SVE and natural attenuation, continuance of quarterly monitoring and a receptor survey closure (PHS/EHD Investigative Officers Report). • On June 7, 1997, UNOCAL requested site closure based, in part, on the State's guidance letter dated January 3, 1997 and works performed at the subject site. (PHS/EHD Investigative Officers Report). • PHS/EHD denied site closure on February 7, 1997 and requested a Corrective Action Plan (CAP) using the feasibility of SVE and natural attenuation, continuance of quarterly monitoring and a receptor survey closure (PHS/EHD Investigative Officers Report). • UNOCAL appealed to the State Water Resources Control Board (SWRCB) for site closure. UNOCAL representatives did not appear for a scheduled PHS/EHD office hearing and the site has been referred to the San Joaquin County District Attorney's office (PHS/EHD Investigative Officers Report). On February 25, 1998, Mr. Tom Lutterman of ATC contacted Ms. Margaret Lagorio, Lead Senior Registered Environmental Heath Specialist, of PHS/EHD. Ms. Lagorio indicated: • Contaminant vertical definition has never been addressed at the site. W A17292.051summaryrpldoc 6