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San Joaquin County DIRECTOR <br /> OPpU�N' C Environmental Health Department Donna Heran, RENS <br /> M ASSISTANT DIRECTOR <br /> ' �' .. JI600 East Main Street Laurie Cotulla,REHS <br /> Stockton California 95202-3029 <br /> � PROGRAM COORDINATORS <br /> Carl Borgman, REHS <br /> Mike Huggins, REHS, RDl <br /> Website: www.sjgov.org/ehd Margaret.Lagorio.REHS <br /> ° Phone: (209) 468-3420 Robert McClellon,REHS <br /> Fax: (209) 464-0138 Jeff Carruesco, REHS, RDI <br /> Kasey Foley, REHS <br /> October 29, 2008 <br /> Arthur L Wyatt Jr. <br /> 6265 Crooked Stick <br /> Stockton CA 95219 <br /> Subject: Former Arco Am/Pm Site Code: 1216 <br /> 4511 Pacific Avenue <br /> Stockton CA, 95207 <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed Soil <br /> Remediation Confirmation Report (SRCR) dated February 18, 2008, Remediation <br /> Update Report -- Third and Fourth Quarter 2007 (RUR) dated February 26, 2008, and <br /> Quarterly Report — First Quarter 2008 (QR) dated May 26, 2008, all submitted by your <br /> consultant Advanced GeoEnvironmental, Inc. (AGE) and comments as follows: <br /> During October and November 2007, five confirmation soil borings, designated B-20 <br /> through B-24, were advanced on-site to a total depth of 50 feet below surface grade <br /> (bgs) to evaluate the effectiveness of the soil vapor extraction (SVE) system, which had <br /> operated at the site from January 2005 to August 2007, by assessing the hydrocarbon <br /> contamination remaining in soil; the purpose of the work was to evaluate the necessity <br /> for reinitiating the remedial operation. <br /> In the SRCR, AGE indicates that the confirmation soil samples taken above 35 feet bsg <br /> in the vadose zone (the depth to groundwater was approximately 31 feet bsg in <br /> December 2007) did not contain detectable concentrations of contaminants except for <br /> sample B-20-10 (at 10 feet bsg) which contained 2.2 milligrams .per kilogram (mg/kg) <br /> total petroleum hydrocarbon quantified as gasoline (TPH-g). AGE concluded that the <br /> impacted soil above 35 feet bsg does not pose a threat through vapor intrusion, or <br /> human exposure risk, and does not exceed gross contamination level. Soil samples from <br /> borings B-21, B-23, and B-24 collected between 35 and 50 feet bsg in the saturated <br /> zone were impacted by petroleum hydrocarbons at concentrations as high as 440 mg/kg <br /> TPH-g (sample B-23-40, collected at 40 feet bsg); the detected THP-g 'concentration <br /> exceeded the San Francisco Bay Regional Water Quality Control Board (SFBRWQCB) <br /> Environmental Screening Levels (ESLs) for leaching potential into groundwater. <br /> EHD concurs with AGE's conclusion that the confirmation soil boring data for borings <br /> B-20 through B-24 in the vadose zone appear to indicate no residual impact above 35 <br /> feet bsg, except for sample B-20-10, which contained low concentrations of <br /> contaminants, suggesting that the SVE had effectively removed contaminants; however, <br /> there is very little historical data with which to directly compare the soil confirmation data <br /> above 35 feet bsg and thereby directly demonstrate the effectiveness of the SVE system <br /> operation. From 1992 to 2004, soil samples were taken primarily between 25 and 70 feet <br /> bsg. Only two soil borings, (B-4 and B-7) out of a total of"14 soil borings encountered <br /> impacted soil above 35 feet bsg. The remaining boring samples collected above 35 feet <br /> 081429directive <br />