SITE INFORMATION AND CORRESPONDENCE

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through November 1996 and recovered an estimated 400 gallons of TPH-g, including about two gallons of benzene. Beginning in May 1996, MTBE was analyzed in quarterly groundwater samples from site monitor wells. To date, analyses (EPA Method 8260) have detected low concentration of MTBE, generally 2 to 10 ppb, in groundwater samples collected during the winter of 1998/1999 from up-gradient, cross-gradient, and down-gradient monitor wells. These occurrences of MTBE are consistent with United States Geological Survey findings that atmospheric "washout" can result in concentrations of MTBE in excess of 20 ppb in shallow groundwater. By letter to Petitioner dated January 9, 1997, County staff concluded that "...the assessment of the lateral extent of groundwater contamination is complete, the assessment of soil contamination is complete, and the plume appears to be stable." The County recommended that a feasibility study and corrective action plan(CAP)be submitted, quarterly groundwater monitoring continue, and data in support of the presence of natural attenuation be collected. By letter to the County dated February 7, 1997, Petitioner summarized the extent of remedial activities undertakers at the site and the findings of its investigative efforts. Petitioner then concluded that the site was suitable for closure as a low-risk groundwater case and that further site assessment or corrective action was not necessary. By letter to Petitioner dated March 3, 1997, County staff concluded that the plume of dissolved phase petroleum hydrocarbons was about 130 feet long and 60 feet wide, that the average benzene concentration within the limits of the plume was 32 ppb, and that the plume was stable and declining. However, the County also concluded that site closure at that time was not appropriate without additional information that demonstrated that natural attenuation was occurring and an explanation that natural attenuation would restore the beneficial use of groundwater. By letter to the UST Cleanup Fund Manager dated June 13, 1997, Petitioner requested that its case be reviewed for closure. Petitioner contended that petroleum hydrocarbon sources (USTs and piping) had been removed from the site, impacted soil had been excavated, SVE had removed additional residual petroleum hydrocarbons in soil, free product had never been observed, MTBE had never been detected in groundwater, the nearest public water supply well is approximately 800 feet from the site, and the County had determined that assessment of the extent of affected soil and groundwater was complete. 6