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'f <br /> ENVIRONMENTAL HEALTEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> Unit Supervisors <br /> r ?, Donna K.Heran,R.E.H.S. Carl Bor man,R.E.H.S. <br /> { Director <br /> 304 East Weber Avenue, Third Floor ii Borg <br /> man, <br /> Olsen,R.E.H.S. Stockton, California 95202-2708 Mike Huggins,R.E.H.S.,R.D.I. <br /> �q:=,. ,, X v • <br /> Douglas W.Wilson,R.E.H.S. <br /> Program Manager <br /> 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 McClellon,R.E.H.S. <br /> Mark Barcellos,R.E.H.S. <br /> MAY 18 2005 <br /> DENIS L. �!BROWN <br /> SHELL OIL PRODUCTS US <br /> HSE — ENVIRONMENTAL SERVICES <br /> 20945 SOUTH WILMINGTON AVENUE <br /> CARSON CA 90810-1039 <br /> RE: Interstate Shell SITE CODE: 1058124 <br /> 620 West Charter Way <br /> Stockton, California 95206 <br /> San Joaquin County Environmental Health Department (EHD) has reviewed Site <br /> Conceptual Model, dated October .7, 2004, which was submitted by Cambria <br /> Environmental Technology, Inc. (CETI) on your behalf for the above-referenced site. <br /> CETI estimates that there are approximately 192 pounds total petroleum hydrocarbons as <br /> gasoline (TPH-g), 23 pounds benzene, and 2 pounds methyl tertiary-butyl ether (MTBE) <br /> remaining in groundwater at this site, and CETI further concludes: <br /> • Vertical and lateral soil delineation is complete. <br /> • Vertical groundwater delineation is complete. <br /> • The shallow plume at approxiniately 20 to 40 feet below surface grade (bsg) is <br /> shrinking as a result of the soil vapor extraction (SVE) system that operated at this <br /> site between 1992 and 1996 removing chemicals of concern (COC) from the <br /> subsurface soil. <br /> • No sensitive receptors are identified within 2,000 feet of this site. <br /> Based on these conclusions, CETI recommends the following: <br /> • A reduction in sampling schedule from quarterly to annually for monitoring wells`- <br /> MW-1, MW-2, MW-3, MW-4, MW-5, MW-6, and MW-10. <br /> • Advancement of five cone penetrometer test (CPT) borings to further assess the <br /> lateral extent of COC in groundwater; two CPT borings are to be located across <br /> Charter Way, two CPT borings are to be located on the adjacent property to the <br /> east, and one CPT boring is proposed to be located down-gradient of MW-9. <br /> EHD comments on CETI's conclusions and recommendations as follows: <br /> • It appears that the vertical extent of impacted soil has been adequately <br /> characterized. Significant impact to soil in the area apparently most intensely <br /> impacted, the present underground storage tank (UST) area, was encountered in <br />