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Stantec Consulting Services Inc. <br /> 3017 Kilgore Road,Suite 100 <br /> Rancho Cordova CA 95670-6150 <br /> Sta me c tel(916)861-0400;fax(916)861-0430 <br /> October 21, 2015 <br /> Attention: Mr. William Brattain, P.E. <br /> Water Resource Control Engineer <br /> Private Sites Cleanup Unit <br /> 1 1020 Sun center Drive #200 <br /> Rancho Cordova, CA 95870 <br /> Subject: Response to California Regional Water Quality Control Board, Central Valley <br /> Regional Letter dated June 15, 2015 and Request for Additional Methane and Soil <br /> Gas VOC Investigation <br /> L&M Operable Unit <br /> 666 West Weber Avenue <br /> Stockton, San Joaquin County <br /> Stantec Job #: 185750217 <br /> Dear Mr. Brattain, <br /> Stantec Consulting Services Inc. (Stantec), on behalf of Chevron Environmental Management <br /> Company (CEMC) and Phillips 66 (P66), is submitting this letter in response to the June 15, 2015 <br /> letter from the California Regional Water Quality Control Board, Central Valley Region (CRWQCB) <br /> which was prepared in response to Stantec's May 15, 2015 Soil Vapor Assessment Report, L&M <br /> Operable Unit, 666 West Weber Avenue, Stockton, San Joaquin County. In addition, Stantec is <br /> including a work plan for additional soil gas sampling for methane, fixed gases, and volatile <br /> organic compounds to address data gaps that were brought up following CRWQCB's review of <br /> the Soil Vapor Assessment Report Submitted May 15, 2015 as well as RWQCB response #3 below. <br /> The following bullets provide the CVRWQCB's comment in italics followed by Stantec's responses <br /> to the comment below: <br /> 1. We note that there is no longer a screening level being proposed for TPH-g in the soil vapor <br /> probes. A screening level for TPH-g is necessary for this site given detections of TPH-g in <br /> certain probes where other constituents for which proposed screening levels remain (BTEX <br /> and naphthalene) are generally not detected. TPH-g in soil vapor at levels above the <br /> Region 2 screening level does remain a potential health concern and is also potentially a <br /> concern for nuisance odors given its low odor threshold. The previously proposed Region 2 <br /> screening level for TPH-g of 295,000 ug/m3 for shallow soil gas (that is based on dividing the <br /> residential indoor air criterion for TPH-g by a 0.002 attenuation factor) is acceptable and <br /> should be used for this site since there is no other relevant health-based criterion for TPH-g. <br /> Without a relevant screening level for TPH-g in shallow soil gas, gasoline constituents could <br /> remain at unacceptably high levels and prevent us from finding that human health has <br /> been protected in any future request for no further action. <br /> t'os!�n wLn c;c-nmonty in mir: <br />