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ENVIRONMENTAL HEALTDEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> � _,�f•.oG Unit Supervisors <br /> c --ted i a Donna K.Heran,R.E.H.S. 304 East Weber Avenue, Third Floor Carl Borgman,R.E.H.S. <br /> Director Mike Huggins,R.E.H.S.,R.D.I. <br /> 1 LgC7, Al Olsen,R.E.H.S. StOC1CtOri, California 95202-2708 Douglas W.Wilson,R.E.H.S. <br /> • :, — = �P • Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> Laurie A.Cotulla,R.E.H.S. Fax: (209) 464-0138 Robert McClellon,R.E.H.S. <br /> Program Manager - Mark Bar""cellos,R.E.H.S. <br /> KAREN PETRYNA JUL O 2 2004 <br /> SHELL OIL PRODUCTS US <br /> 20945 SOUTH WILMINGTON AVENUE <br /> CARSON CA 90810 <br /> RE: Interstate Shell SITE CODE: 1058124 <br /> i <br /> 620 West Charter Way <br /> Stockton, California 9520-6 <br /> EHD <br /> San Joaquin County Environmental Health Department (EHD) has reviewed Site Investigation <br /> Report dated January 21, 2003, along with quarterly groundwater monitoring reports for years <br /> 2002, 2003, and the first quarter of 2004, prepared and submitted on your behalf by Cambria <br /> Environmental Technology, Inc. (Cambria). Briefly summarized, Cambria's findings and <br /> interpretations were as follows: <br /> • Soil and groundwater results from cone penetrometer test (CPT) boring CPT-5 delineate <br /> the "vertical extent of total petroleum hydrocarbons as gasoline (TPH-g), benzene, and <br /> methyl tertiary-butyl ether(MTBE) at this site. <br /> • Groundwater analytical data collected from CPT-6, CPT-7, and CPT-8 define the lateral <br /> extent of petroleum hydrocarbons to the west, southwest, and south of the source area. <br /> • Groundwater samples from CPT-9, CPT-10, and CPT-11 contain TPH-g, benzene, and <br /> MTBE. <br /> • The highest concentrations of gasoline constituents were detected between 65 and 73 feet <br /> below surface grade (bsg). <br /> • The highest concentrations of TPH-g and benzene were detected in CPT-11 at 65 feet bsg. <br /> Based on these findings, interpretations, and conclusions, Cambria proposes to advance two <br /> additional CPT borings east of borings CPT-10 and CPT-11 to a depth of approximately 80 feet bsg <br /> to delineate _the lateral extent of petroleum hydrocarbons in groundwater east of the site. EHD <br /> approves the.advancement of the two CPT borings east of borings CPT-10 and CPT-11. However, <br /> EHD recommends that the borings be advanced to 100 feet bsg instead of 80 feet bsg for the <br /> following reasons: <br /> • Groundwater samples collected recently from monitoring well MW-8 have had - <br /> significantly increased concentrations of MTBE and TBA - as high as 23,000 µ/L and <br /> 7,300 p/L,respectively. <br /> ,t <br />