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� y I <br /> IBM Wright <br /> ron <br /> . Envimerital <br /> Services, Inc. <br /> .2395 East Pescadero Avenue <br /> Tracy,CAS 95304 <br /> January 28, 2011 <br /> Project No, 4509 <br /> Mr. Paul Verma <br /> City of Tracy . <br /> 325 Civic Center Plaza <br /> Tracy, California 95376 <br /> Re: Response Letter for Soil Vapor Sampling Workplan for Addendum to <br /> y. Closure Summary Report to .Support a No Further Action Required <br /> `6961 Sitt'°at^99?6th Street, Trac��K, <br /> sP <br /> r're• � W'`.L�T X 4. '� k°Y �' . 3f in^.7.P.r e"' .�of .:�A `1.'A 4 �` 7 <br /> r <br /> , <br /> Dear.Mr. Verma, . <br /> Wright Environmental',Services; Inc. (Wright) has issued a Closure Summary:Report -- <br /> (CSR) dated September 17,,2010 for Case Closure No Further.Action Required (NEAR) z: <br /> for the above referencedsite.: As.you know the site assessment and groundwater. <br /> quarterly monitoring work was performed as requested by the San Joaquin County <br /> Environmental Health Department (EHD) who also requested a CSR in their letter <br /> September 24, 2009. The purpose,of this letter is Jo respond to,the EHD letter dated <br /> December 21, 2010 for comments of the CSR to'address the potential soil vapor threat.' <br /> The CSR report is used by EHD to comprehensively review the site data and determine,if <br /> it is, or is not, appropriate to.consider,approval for site closure at.this time. , <br /> Technical Approach,' <br /> The`EHD has reviewed the referenced CSR report'Wright has prepared and needs ,a <br /> technical justification for soil vapor threat to the site as a part of the CSR to support "site <br /> closure" (see References). Wright had noted that soil vapor samples had not been <br /> collected on this site,., Some residual fuel contaminants are present near the edge,of the ' <br /> site and whether these pose a soil vapor threat is not clear. Some guidance is given in the <br /> Regional Water Quality Control Board Environmental Screening Levels (RWQCB ESLs, <br /> May 2008 revision):regarding residual soil contaminants,and possibly estimating a soil <br /> vapor threat. However, it is our understanding the RWQCB (and other agencies) may not ; <br /> accept this indirect estimate 'for soil vapor threat estimates `based on residual soil ' <br /> contaminants data alone. ,Theiefore soil vapor.-sampling is needed to ascertain presence <br /> and possible implications of soil vapor and on this basis Wright could not supply,an <br /> opinion as to soil vapor presence or risk in the CSR. ,., - <br /> ' ,.Page 1 of 8 I <br />