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~ Pacific Gas and EleCW mpany Environmental Services • <br /> P.O.Box 7640 <br /> San Francisco,CA 94120 <br /> 415/972-7000 <br /> Direct Dial 415/972- <br /> July 31, 1990 Telecopy415/972-9201 <br /> Mr. Val Siebal <br /> Regional Administrator <br /> California Department of Health Services <br /> r & Toxic Substances Control Division <br /> Region 1 <br /> 10151 Croydon Way <br /> Sacramento, CA 95827-2106 <br /> Attention: Mr. Hector Magallanes <br /> Dear Mr. Siebal : <br /> Re: PG&E's Stockton Former Manufactured Gas Plant Site <br /> Thank you for your comments on the preliminary remedial investigation <br /> report prepared for PGBE's Stockton Former Manufactured Gas Plant Site <br /> ("site") . Our responses to your comments are given below by topic. <br /> o Subsurface Surveys <br /> We plan to perform a ground penetrating radar, seismic refraction, or <br /> other comparable non-invasive subsurface survey as part of our <br /> upcoming supplemental remedial studies at the site. <br /> o Retention of Soil Borings <br /> We are investigating whether any cores from the 1987 sampling are <br /> still available. Representative cores from future studies will be <br /> archived as a lithologic record or for reanalysis of non-volatile <br /> constituents, within the limitations of holding times established <br /> pursuant to the analytical guidelines set forth in EPA Publication <br /> SW-846. <br /> o Off-Site Soil Borings, Off-Site Groundwater Monitoring Wells <br /> We agree that off-site soil and groundwater sampling will be <br /> necessary, both to determine the extent of potential sources of <br /> residues and their extent in groundwater, and to establish <br /> "background" conditions. We look forward to working closely with <br /> your staff in formulating the details of the off-site investigation. <br /> o Presentation of Lithologic, Analytic, and Hydrologic Results <br /> Future reports will present soils data and findings as stratigraphic <br /> cross-sections. <br />