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ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> Q 2� Donna K Heran,R E H S Unit Supervisors <br /> Director 304 East Weber Avenue, Third Floor Carl Borgman,R E H S <br /> 9 <br /> Al Olsen,R E H S Stockton, California 95202-2708 Mike Huggins,R E H S , R DDouglas W Wilson, R E H S <br /> �4�r�oa� pProgram Manager Telephone (209) 468-3420 Margaret Lagorio,R E H S <br /> Laurie A Cotulla,R E H S <br /> Program Manager Fax (209) 464-0138 Robert McCielion,R E H S <br /> Mark Barcellos,R E H S <br /> ' r <br /> I0u2, 1 <br /> EDWARD C RALSTON JAN 0 2 2004 <br /> CONOCOPHILLIPS BY "------------------ <br /> 76 BROADWAY COPY SACRAMENTO CA 95812 <br /> RE Tosco (former Unocal) Service Station #4409 Site Code 508431 <br /> 1502 N EI Dorado St RO# 0000664 <br /> Stockton, CA , 95204 <br /> San Joaquin County Environmental Health Department (EHD) has reviewed <br /> Results of Offsite Assessment and Site Conceptual Model (SCM) dated <br /> September 30, 2003 as submitted by your consultant, SECOR, on October 3, <br /> 2003 and has the following comments <br /> I <br /> Conclusions included in the SCM detailed the subsurface investigations from the <br /> UST removal in 1999 up to and including the installation of four offsite monitoring <br /> wells (MW-11 thru MW-14) Exposure potential was evaluated and <br /> recommendations for continued quarterly sampling and monitoring of the existing <br /> monitoring wells were included Recommendations also included future <br /> preparation of a Feasibility Study/Corrective Action Plan (FS/CAP). EHD <br /> concurs with the data and recommendations and looks forward to your evaluation <br /> of remedial options that could return this site to `pre-release' conditions <br /> EHD has researched the ground water sampling data included within the SCM <br /> for MW-5, MW-6, and MWA0, all screened in the 70'-80' below ground surface <br /> (bgs) interval These wells continue to contain elevated levels of petroleum and <br /> EHD cannot consider the vertical extent of the petroleum release onsite as <br /> defined Prior to completing your evaluation of remedial alternatives, you should <br /> gather soil and ground water data onsite beyond the 70'-80' interval Prior to <br /> installing these required deeper monitoring wells, the vertical extent of the <br /> petroleum migration should be determined Only repeatable, non-detect ground <br /> water samples can be used as support for delineation conclusions <br /> A work plan should be submitted to EHD to collect this data by February 27, <br /> 2004 <br /> i <br /> In discussions with other EHD staff, it was discovered that SECOR is also the <br /> consultant for the ARCO site discussed in the SCM Since there is a great <br /> amount of ARCO and ConocoPhillips (CP) data currently being shared in reports <br /> submitted to EHD, data to support the discussions of a 'commingled' plume <br /> should be presented in future reports <br />