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- <br /> ` 5900 Hollis Street, Suite A,Emeryville, Calfornia 94808 <br /> Telephone: 510.420.0700 Facsimile: 510.420.9170 <br /> CONESTOGA-ROVERS +Ivww.CRAworldxom <br /> &ASSOCIATES <br /> June 19, 2009 Reference No. 241660 <br /> Ms.Victoria McCartney <br /> San Joaquin County Environmental Health Department E j! �j E 11: <br /> 600 East Main Street <br /> Stockton,California 95202-3029 JUN 2 3 2009 <br /> Dear Ms. McCartney: ENVIRONMENT HEALTH <br /> PERMIT/SERVICES <br /> Re: Response to Agency Letter <br /> Former Shell Service Station <br /> 1160 West Yosemite Avenue <br /> Manteca,California <br /> SAP Code 166801 <br /> Incident No. 97422510 <br /> Agency No. 1284 <br /> Conestoga-Rovers &Associates (CRA) prepared this letter on behalf of Equilon Enterprises LLC <br /> dba Shell Oil Products US (Shell) to respond to San Joaquin County Environmental Health <br /> Department(SJCEHD)'s April 6, 2009 letter,which requested that Shell submit a corrective <br /> action plan (CAP) for site remediation by June 19, 2009. <br /> SJCEHD concluded that a CAP is warranted because there may be a correlation between <br /> groundwater depths and petroleum hydrocarbon concentrations in wells MW-1,MW-3, and <br /> MW-4, a fate and transport model (VLEACH,Version 2.2.0.3) submitted in Cambria <br /> Environmental Technology, Inc.'s (Cambria's) October 26, 2006 Agency Response and Site <br /> Investigation Plan predicted elevated total petroleum hydrocarbon as gasoline (TPHg) <br /> concentrations in groundwater for an extended period of time,and there is a lack of site <br /> investigation west and northwest of the source. CRA addresses these concerns below. <br /> CRA prepared a vicinity map (Figure 1) and a site plan showing soil borings and groundwater <br /> monitoring wells (Figure 2). This map shows that a number of soil borings have been advanced <br /> west and n rthwest of the source areas. From 2001 to 2004, Cambria advanced borings GP-1, <br /> GP-2, GP-3'and B-1 through B4 and installed wells MW-1,MW-3, and MW-5,which are west <br /> and northwest of the source areas. <br /> The above-referenced VLEACH model output predicted that after 3 years (in 2006) the MW-1 <br /> TPHg concentration would reach 3,326 micrograms per liter (µg/L), that the concentration <br /> would peak at 25,122 µg/L in 20 years (2023), and that concentrations would begin decreasing <br /> thereafter. After 100 years (in 2103),the model predicted that the TPHg concentration would <br /> decline to 1.,732 µg/L. To test the modeling results, Cambria recommended periodic evaluation <br /> Equal <br /> Employment <br /> Opportunity Employer <br /> Worldwide Engineering,Environmental,Construction,and IT Services <br />