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�� 2000 Opportunity Dr,Suite 110, Roseville,California 95678 CONESTOGA-ROVERS Telephone: 9166773407,ext.100 Facsimile: 916.6773687 &ASSOCIATES www.CRAworld.com October 1, 2007 Ms. Victoria McCartney San Joaquin County Environmental Health Department RECEUOV 600 East Main Street S� OC Stockton, California 95202 3 2007 ENVIR0141E .., CES Re: Soil Vapor Sampling Work Plan PERMITjS R�EA Th' Chevron Station 9-1452 334 East Main Street Ripon, California Y� Dear Ms. McCartney: On behalf of Chevron Environmental Management Company (Chevron), Conestoga-Rovers & Associates (CRA) is submitting this Soil vapor Sampling Work Plan for the site referenced above. This document was prepared in response to the San Joaquin County Environmental Health Department (SJCEHD) letter dated September 13, 2007 (Attachment A). CRA proposes advancing three shallow soil vapor Geoprobe borings to assess the potential for vapor intrusion into buildings on-site. Vapor sample concentrations will be compared to California Health Hazard Screening Levels (CHHSLs) and/or Regional Water Quality Control Board (RWQCB) Region 2 Environmental Screening Levels(ESLs)for soil vapor to assess risk. The site is an active Chevron branded service station located on Main Street just north of Highway 99 in Ripon, California (Figure 1). Land use in the site vicinity is primarily agricultural. The nearest large body of surface water is the Stanislaus River, located approximately 2,000 feet to the east of the site (Figure 1). Current site facilities include three 12,000-gallon gasoline underground storage tanks (USTs), two dispenser islands under a common canopy, and a station building containing two hydraulic hoists (Figure 2). Historical information indicates that the site was originally constructed as a service station in June 1969. SITE BACKGROUND Site Geology and Hydrogeology: The elevation of the site is approximately 70 feet above mean sea level; the topography surrounding the site is relatively flat. Boring logs indicate soil beneath the site consists of silt with interbedded sand and silty sand lenses ranging in thickness from approximately 1 to 8 feet to approximately 40 feet below grade(fbg). A review of the boring log for CYT-1 indicates soil below 49 fb consists of clay and stiff fine-grained sediments om 40 to approximately 0'fbg, a sand layer f pm'S to fbg, stiff fine-grained sediment from 8Sto fbg, and sand and sand mixtures with silt from Ito to the total depth explored of 120 fbg. Review of CPT-2 indicates silt and clay mixtures with altegiatin tiff fine-grained sediments from surfac grade an approximate depth of 64 fbg, a sand layer between-&4 and g, stiff fine-grained sediment from to �fbg, and a sand layer from.1-1-50 fbg to the total depth explored of-1-29 fbg. Equal Employment Opportunity Employer ,..,.,,:.a,u_ nor w.M. nwews�w;.�.....-_•Mu.sawcr.�eurK�-M.w Worldwide Engineering,Environmental,Construction,and IT Services