SITE INFORMATION AND CORRESPONDENCE FILE 2

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ENVIRONMENTAL HEALTH DEPARTMENT SAN JOAQUIN COUNTY so._�-coG Unit Supervisors Donna K. Heran, R.E.H.S. Carl Bergman, R.E.H.S. < Director 304 East Weber Avenue, Third Floor Mike Huggins, R.E.H.S., R.D.I. At Olsen, R.E.H.S. Stockton, California 95202-2708 Douglas W. Wilson, R.E.H.S. • �q , �_ . .�c • Program Manager Telephone: (209) 468-3420 Margaret Lagorio, R.E.H.S. �rFOR`' Laurie A. Cotulla, R.E.H.S. Robert McClellon, R.E.H.S . Program Manager Fax: (209) 464-0138 Mark Barcellos, R.E.H.S. APR 17 2003 RODGER LISTON DARPETRO INC USA SERVICE STATION 3450 EL CAMINO CERES CA 95307 RE: DARPETRO, INC Site Code : 1060 749 E CHARTER WAY STOCKTON, CA 95206 San Joaquin County Environmental Health Department (EHD) reviewed the revised Work Plan (WP) , prepared by California Geophysical Group , Inc. (CGG ) on your behalf on 06 January 2003 (received by this office 03 February 2003) , and has discussed its provisions with Mr. James Barton of the Central Valley Regional Water Quality Control Board (CVRWQCB ) . The WP is a revision of the undirected work plan for a soil gas investigation dated 04 October 2001 , prepared in response to EHD's comment letter of 03 December 2002 , The WP lists the historical stages of the site investigation , references the reports containing the results of the various investigations , and proposes to advance a soil boring/monitoring well and seven soil gas borings to identify the source(s) of contamination on the site . Specifically, the work plan proposes to install a ground water monitoring well on the west side of the site and seven soil gas test borings around the underground storage tank (UST) pit and west dispenser to 23 feet bsg to collect soil gas samples for laboratory analysis . It is the consensus of EHD and CVRWQCB that soil gas investigations are of use as a screening tool to identify areas of concern , but would not be a proper technique to utilize at this stage of investigation for this site. EHD and CVRWQCB infer that the purpose of the soil gas investigation at this time is to determine if an ongoing release is occurring from the current UST system operating on the site. EHD and CVRWQCB believe that this would be more accurately determined by performing an enhanced leak detection test. This test is not usually a reimbursable expense from the UST Cleanup Fund , but may be worthwhile and provide you useful information . EHD does not approve the soil gas investigation portion of the WP. Installation of the proposed monitoring well on the western margin of the site would be useful for delineating the upgradient extent of contamination on the site and may help resolve the potential commingled plume issue raised by your consultant, but is not adequate to address the overall directive issued you by EHD letter dated 11 June 2001 to: I