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San Joaquin County <br /> Environmental Health Department DIRECTOR <br /> Donna Heran, REHS <br /> 1868 East Hazelton Avenue <br /> " e! Stockton , California 95205-6232 PROGRAM COORDINATORS <br /> I L11'? Tip Robert McClellan, RENS <br /> /--: Jeff Carruesce, REHS, RDI <br /> °ti . . . `� P Website: wwwsjgov. org/ehd Kasey Foley, REHS <br /> F o R Linda T urkatte, REHS <br /> Phone : (209) 468 -3420 Rodney Estrada, REHS <br /> Fax: (209) 464-0138 Adrienne Ellsaesser, REHS <br /> November 3 , 2014 <br /> Ms. Sharon Evans <br /> Phillips 66 Company <br /> 1380 San Pablo Avenue <br /> Rodeo, CA 94572 <br /> Subject: Former Circle K Store No. 08671 /Phillips 66 Company <br /> 8606 Thornton Road <br /> Stockton, California 95209 <br /> Dear Ms. Evans: <br /> The San Joaquin County Environmental Health Department (EHD) has received the additional <br /> information requested by EHD letter dated 21 July 2014 in the report titled No Further Action <br /> Request ( NFAR) dated 22 September 2014, prepared by your consultant Cardno ATC (Cardno) . <br /> In the NFAR, Cardno presented the calculations for the residual methyl tert-butyl ether (MTBE) <br /> masses in soil and groundwater, a professional evaluation of the threat to nearby water supply <br /> wells from the residual dissolved MTBE mass, and pertinent construction details for the former <br /> municipal water supply well, which has been destroyed . Construction details for three domestic <br /> water supply wells apparently are not available . The EHD reviewed the data and discussed <br /> possible case closure with a representative of the Central Valley Regional Water Quality Control <br /> Board (CVRWQCB) on 08 October 2014. <br /> The CVRWQCB representative was concerned that the plume of impacted groundwater has not <br /> been adequately delineated , noting an apparent increase of concentrations in the downgradient <br /> well MW-7 potentially indicative of a plume migrating past the down-gradient well . The <br /> CVRWQCB was specifically concerned that <br /> ® The lateral extent of impacted groundwater downgradient of MW4 has not been <br /> delineated; <br /> • The vertical extent of impacted groundwater in the source area is poorly characterized <br /> by existing data ; and <br /> The water supply wells reported to be approximately 180 feet north of the subject site <br /> (8732 Davis Road) and 281 feet north of the site (8855 Das Road) have not been <br /> sampled for analysis for the chemicals of concern . i ; , , <br /> The EHD has reviewed the site data and reports and has concluded that the site soil analytical <br /> data are not suggestive of a large residual contaminant mass since the maximum contaminant <br /> concentration detected was 2 . 8 milligrams per kilogram (mg/kg) MTBE, and is limited in areal <br /> extent at shallow depth in the dispenser area, locally to deeper soil , and Cardno has calculated <br /> the residual mass in soil to consist of 0. 013 pounds of MTBE. Although there can be significant <br /> error in such estimates, it would appear that there is minimal residual mass in soil to continue to <br /> impact groundwater, <br />