SITE INFORMATION AND CORRESPONDENCE

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O�evron Chevron JUN 2 4 1993 Chevron U.S.A.Products Company 2410 Camino Ramon June 22, 1993 ENVIRONMENTAL REAM San Ramon,CA 94583 PERMITlSERVICES Marketing Department Phone 510 842 9500 Ms. Margaret Lagorio San Joaquin County Environmental Health P.O. Box 2009 Stockton, CA 95201 Re: Chevron Station#9-6465, 5608 North Pershing Avenue, Stockton, CA Attached soil excavation and remediation report(Touchstone, 6115193) Dear Ms. Lagorio: Attached is a report dated June 15, 1993, which was prepared by Chevron's consultant, Touchstone Developments (Touchstone), to describe soil remediation activities performed between April 23 and May 20, 1993,at the subject site. At the request of the current property owner, Chevron conducted soil remediation activities to fulfill site closure requirements as specified by the San Joaquin County Public Health Services (SJCPHS). Extensive soil overexcavation was performed to remove all potential sources of groundwater contamination that had been identified during two previous underground storage tank removal operations. As a result of the soil overexcavation activities, all potential sources of groundwater contamination were removed from the former waste oil tank, fuel tanks, and product piping areas. During the overexcavation activities groundwater monitoring wells MW-2 and MW-7 were properly removed under the guidance and supervision of SJCPHS personnel. In discussing the complete requirements for case closure, Ms. Linda Turkatte of SJCPHS expressed the concern that dissolved hydrocarbons may still be bound in soils at shallow depths outside of the overexcavated areas and that groundwater contamination could occur if present water levels rise and come into contact with these shallow soils. A review of the historic site data has been performed to evaluate Ms. Turkatte's concerns. The following observations are presented: 1.) Ten groundwater monitoring wells outside of the overexcavated area have had detectable concentrations of dissolved hydrocarbons. The historic groundwater data from MW-8 demonstrates that if there are any residual hydrocarbons bound in the shallow soils they do not exist as potential sources of groundwater contamination. In January, 1991 dissolved concentrations of TPHGas and benzene (250 and 2 ppb) were detected at a depth of 40.1 feet. Groundwater levels then dropped 0.67 feet over the following six months. In October, 1991 groundwater levels had risen 1.70 feet and come back in contact with the soils at 40.1 feet. The subsequent groundwater samples at this depth did not contain any detectable concentrations of dissolved hydrocarbons and have not to this date. Further support of this has been demonstrated in monitoring wells MW-4A, 5A, 9, 10, and MW 11. 5