SITE INFORMATION AND CORRESPONDENCE_CASE 1

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a r w 14800 W. Frontage Rd (Hwy. 99) - 3 - 4 September 1998 Manteca, San Joaquin County An off-site domestic well is to be installed at 14852 S. Hwy. 99, Manteca. The new well is being provided to replace the former domestic well, which has been impacted by contamination from the Moore Petroleum site. Based on discussions with Ms. Quynh Hoa of the State Water Resources Control Board (SWRCB), UST Cleanup Fund, the cost of installation of the off-site domestic well is to be reimbursed by the Cleanup Fund, pending Regional Board staff concurrence with site closure. APEX completed a fate and transport study for the site. The purpose of the study was to determine the potential impact to the on-site and off-site domestic wells. Based on the model, no contamination is projected to impact the new domestic wells for the 10 years period (1997 to 2006), that was modeled. The assumptions used in the model, although in some cases less conservative than they could have been, appear adequate, based on sampling data. Summary: Significant remedial activities have been completed at the site, bringing the TPHg and benzene concentrations to below laboratory reporting limits. Low concentrations of TPHd, MTBE, and 1,2-DCA remain in the soil and groundwater below the site. Contamination from the site has impacted two domestic wells, which have been, or will be replaced with new, deeper domestic wells. The cost of installation of the new domestic well at the 14852 S. Hwy. 99, is to be reimbursed by the SWRCB UST Cleanup Fund. Fate and transport modeling suggests that contamination from the site will not impact the new on-site domestic well, or the proposed off-site domestic well within the 10 year period modeled. The mass of contamination remaining in the soil and groundwater was calculated. Calculations were based on the assumption that if a contaminant was not detected above the laboratory reporting limit,then it was assumed to have zero concentration. The subsurface volume of impacted water was calculated, based on the groundwater sample concentrations. Mass and volume calculations and contaminant concentrations appear to be small, and the fate and transport model suggests that an impact to the domestic wells is unlikely. Based on the information reviewed, provided the data are accurate and representative of site conditions, concurrence with the SJCEHD determination for no further action appears appropriate.