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HEM Tit i9;i T�� I AMI1� 48 November 1, 1995 Project 131420.01.04 Margarett Lagorio San Joaquin County Health Department P.O. Box 388 Stockton, CA 95201-0388 Subject Well Permits for SVE system at Del Monte Disco Site j Dear Margarett: I This letter is being submitted per the directive issued in the PHS/EHD letter dated 10/2/95 requiring the submittal of a work plan for additional wells by November 10, 1995 at the Del Monte site (former Disco Gas Station) located at 110 North Filbert Street, Stockton, California. In a telephone conversation with Margarett Lagorio, PHS/EHD expressed a i concern about the effectiveness of dual soil vapor extraction and air sparging well completions in the same borehole. The PHS/EHD suggested Del Monte install an additional vapor extraction well without an air sparging component. The non-aqueous phase liquid (NAPL) encountered in the construction of piezometer clusters NP-1 and NP-2 shows that vadose zone contamination may extend beyond the present radius of vapor extraction influence. We originally assumed that the extent of vadose zone NAPL was limited to the i area beneath the three former USTs described in the RDFS (CH2M HILL, February 1992). Piping removed from the site, that formerly conveyed gasoline from tanks to pump islands, was found to be thoroughly corroded. Leakage from the piping may have been the source of the NAPL phase contamination found in the vadose soils at NP-1 and NP-2. Del Monte proposes the drilling of 2 additional borings and the conversion one or both of the borings into SVE wells (Figure 1). The attached figure shows the proposed locations for the borings. These borings are being drilled to further characterize the extent of impacted soil at the site. In addition the conversion of one or both of these borings will expedite the remediation procedures and increase the radius of capture of the existing system. Boring SB- c:\work\word\delmonte\p1an03\svedril.doc t