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California R , �''onal Water Quality �ntrol Board <br /> Nlmo <br /> Central Valley Region 4, <br /> Peter M.Rooney Sacramento Main Office' ; <br /> Ed J.Schnabel <br /> 5ecretaryfor Internet Addmss: http:/lwww.swrcb.r-a.gov/—rwgcbSIhome.htmi Chair <br /> Environmental 3443 Routier Road,Suite A,Sacramento,California 95827-3003 <br /> Protection Phone(916 255-3000•FAX(916)255-3015 ; <br /> !� <br /> a FROM:` �,1Vlark R. List <br /> TO: 'Gordon L. Boggs .... <br /> Engineering Geologist .. <br /> UST Program Manager. ! g g g . <br /> DATE: 18 December 1998 SIGNATURE: E' <br /> SUBJECT: FORMER TOWN& COUNTRY CHEVRON SITE; 13336 E. HIGHWAY 88,_,. .. <br /> LOCKEFORD, SAN JOAQUIN COUNTY; <br /> Via"*- ;1 <br /> Background: <br /> On 29 December 1997, San Joaquin County Environmental Health'Division (SJCEHD) sent a Case ; <br /> 1�1%1a <br /> Closure Summary" and site chronology to the Regional Board, for!concurrence on this site. Regional <br /> Board staff did not concur with the NFAR decision by SJCEHD, and in a 13 February 1998 letter, we <br /> requested that the Responsible Party determine the lateral and vertical extent of contamination and <br /> calculate the remaining contaminant mass. Additionally, one groundwater sample was to be collected to <br /> determine if petroleum contamination had impacted groundwater. <br /> In response to our request,the responsible party agreed to collect soil and groundwater samples <br /> sufficient to demonstrate that the vertical distribution of contaminants will not adversely impact water <br /> quality or human health. Between 26 June and 1 July 1998 one soil baring (B7) was advanced to 100 <br /> feet bgs. Sixteen soil samples and one grab groundwater sample were submitted and analyzed for TPHg, <br /> BTEX and the fuel oxygenates. The analytical results show soil contamination extends to approximately <br /> 45 feet bgs for TPHg (55 mg/Kg) and to 60 feet bgs for benzene (0.;011 mg/kg} in S$7;with the highest 1 <br /> concentrations of TPHg and benzene detected, 3,300 mglKg and 1,3 mg/K, respectively, at 40 feet bgs. <br /> Selected samples were analyzed by Toxicity Characteristic Leaching Procedure (TCLP) with the highest ,* <br /> leachable.benzene concentration.of.460 µgLL detected in.thesample collected from 40 feet bgs-This <br /> r �. <br /> leachable contaminant fraction represents a threat to water quality.'The single groundwater sample was <br /> analyzed and contained 210 Rg/L(ppb)TPHg,4.3 Rg/L benzene and 16.0 Rg/L toluene. Mr. Goldman <br /> of GeoSoly attributed the elevated concentrations of petroleum constituents in groundwater to leaching f <br /> of contaminants through the vertical soil profile through another migratory pathway, vapor phase <br /> migration, or cross-contamination of the bailer during its descent down the center of the augers. .. <br /> The site is underlain by sandy clay, from the surface to 22 fee[bgs" The highest concentrations of soil <br /> contamination are present in clayey sand and silty sand,between 22 and 42 feet bgs. Between 42 and 60 <br /> feet bgs, sandy silt and silt are present,'with silty sand and clayey ssand logged between 60 feet and <br /> approximately 87 feet bgs. Groundwater was encountered in soil-boring B7 in sandy silt, at 96.4 feet bgs <br /> on 1 July 1998. <br /> California Environmental Protection Agency . <br /> ��Recycled Paper <br />