SITE INFORMATION AND CORRESPONDENCE 1993-1995

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Pacific Gas and Electric Company Environmental Services P.O.Box 7640 San Francisco,CA 94120 415/973-7000 Direct Dial 415/973- / �p Telecopy 415/973-9201 H �.3 February 23, 1995 0 James L. Tjosvold, P.E. Acting Chief, Site Mitigation Branch r California Environmental Protection Agency 10151 Croydon Way, Suite 3 Sacramento, CA 95827 Attention: Mr. Fernando Amador Dear Mr. Tjosvold: Re: Docket #HSA 90/91-008 -Proposed Revisions to the Groundwater Monitoring Program for the Stockton Former Manufactured Gas Plant Site Pacific Gas and Electric Company(PG&E) proposes to revise the quarterly groundwater monitoring program at its Stockton Former Manufactured Gas Plant Site. The proposal includes reducing the sampling frequency of some existing wells installed prior to the Phase III investigation from the groundwater monitoring program described in the DTSC approved"Final Workplan, Phase III Groundwater Investigation, PG&E Former Manufactured Gas Plant Site" (Workplan). The Workplan states that the groundwater monitoring program will be revised as appropriate and that the program will be continued for two years from the start of Phase IIIc or until the submittal of the Remedial Action Plan(RAP). Phase IIIc began in January 1994, therefore monitoring is required through December 1995 or through RAP submittal. The completion of the Phase III groundwater investigation is an appropriate time to discuss appropriate revisions to the groundwater monitoring program with your agency. Because the next quarter sampling must be completed by March 31, 1995, any changes to the sampling program should be in place by March 15, 1995. Proposed revisions are described below. Proposed Approach: PG&E recommends the following groundwater monitoring program: • All wells installed during Phase III would be sampled quarterly for one year. The new wells are MW-1R and MW-18 in Zone A, MW-17 and MW-19 in Zone B, and MW-14, MW-15 and MW-16 in Zone C.