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1 Report-Sot]and Groundwater investigation Canepa s Car Wash 5320 Pacific St Stockton CA June Page9- 9- Soil and groundwater samples were collected at the same depths at 70 feet in SBA and at 50 and 70 feet ' in SB-2 A review of the laboratory analysis indicates that the difference in concentrations is the result of the soil solubility of the gasoline components in groundwater 5 CONCLUSIONS Inter-bedded clay, silt, and sand are present in the shallow subsurface geology at the Canepa's Car Wash site Groundwater was encountered at approximately 40 feet bgs Groundwater yields are greater in the ' inter-bedded silty and sandy sequences from 40 feet to at least 70 feet(total drilling depth) Weathered gasoline odor was noted beginning at 23 5 feet and a fresh gasoline odor was noted beginning at approximately 26 feet and continuing the depth of the borings ' The Simulprobe soil gas screening samples were collected in the vadose zone and indicated that significant gasoline vapor is present in the pore space of the non-saturated soils A comparison of the ' soil gas screening samples and the laboratory analysis of soil samples collected in the vadose zone indicates that hydrocarbons contained in pore space may be as much as an order of magnitude greater than those detected by laboratory analysis An array of nine SVE wells have been installed at the site in the immediate vicinity of the soil borings SBA and SB-2 The SVE wells are screened from approximately 8 to 50 feet bgs Significant hydrocarbons were detected in the vadose zone beginning at 22 feet bgs and extending to the water table located at approximately 40 feet Approximately 20 feet of the contaminated soil column is in direct contact with the screened portion of the SVE wells Soil and groundwater samples were collected at various depths in the saturated zone Field observations and laboratory analysis indicate that the highest concentration of gasoline contamination is at about 55 ' feet bgs, the depth of the water table when the monitor wells at the site were installed in 1993 Hydrocarbons were detected at 70 feet, the termination depth of the soil borings The eight monitor wells installed at the site have screened intervals well below the current water table and provide little information pertaining to the vadose zone/groundwater interface A comparison of the groundwater analyses from this investigation with the most recent Quarterly Groundwater Monitoring results indicates an order of magnitude increase in gasoline and gasoline components t6. RECOMMENDATION Condor recommends that the SVE system approved for this site be installed and operated The SVE ' system was originally described in Work Plan - Catalytic Oxidation (CAT-OA9 System—Installation and Monitoring, dated May 28, 1997, prepared by Condor Mr Ron Rowe of the PHS/EHD approved the Work Plan on July 16, 1997 The San Joaquin Valley Unified Air Pollution Control District granted an 1 Authority to Construct document on March 16 1998 It is Condor's understanding that the investigation 1 and findings reported herein satisfy the provisions of the California Underground Storage Tank Clean-Up Fund (UST-CF) for pre-approval of corrective action costs for the installation of an interim SVE system ' proposed for this site The provisions were outlined in a letter dated October 23, 1997 and prepared by Mr Chuck Arnold In order to proceed with the installation of the SVE system Condor will require a tetter from the PHS/EHD confirming Condor's understanding of the site and address the conditional nature of the UST-CF's letter {�� CONDOR