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r 19449 Riverside Drive,Suite 230,Sonoma,California 95476 <br /> CONESTOGA-ROVERS Telephone: 707.935.4850 Facsimile: 7079356649 <br /> &ASSOCIATES www.CRAworld.com <br /> April 5,2011 t nV <br /> tU <br /> Mr. Brian Taylor, P.G. APR 0 7 2011 <br /> California Regional Water Quality Control Board ENVIRONMENTAL HEALTH <br /> Central Valley Region PERMIT/SERVICES <br /> 11020 Sun Center Drive#200 <br /> Rancho Cordova,California 95670 <br /> Re: Agency Response to RWQCB's 15 February 2011 Letter <br /> Shell Oil Products US-Former Shell Central Valley Crude Oil Pipelines <br /> Hansen Road near Schulte Road (Cordes Ranch) <br /> Tracy,California <br /> SAP Code 805248 <br /> Incident No.300562 <br /> Dear Mr. Taylor: <br /> Conestoga-Rovers&Associates (CRA)has prepared this letter on behalf of Equilon Enterprises <br /> LLC dba Shell Oil Products US(Shell)for the Former Shell Central Valley Crude Oil Pipelines <br /> site located at Hansen Road near Schulte Road,Tracy,California (site). This letter is being <br /> submitted in response to the Central Valley Regional Water Quality Control Board's (CVWB) <br /> 15 February 2011 letter to Shell (Letter). The CVWB's letter provides comments to CRA's <br /> 17 January 2011 Site Assessment Work Plan. <br /> The following is in response to CVWB's Letter: <br /> Page 2, Comment 1: "We do not concur that collecting depth discrete groundwater samples is not a <br /> viable option during borehole advancement for the deep wells. Shell has proposed using roto-sonic <br /> equipment to drill the boreholes. This drilling method uses telescoping drill casings and permits <br /> sampling equipment to be lowered to the bottom of the boreholes without having to withdraw the drill <br /> string. This effectively eliminates the possibility of spreading contaminants vertically downwards <br /> through cross contamination." <br /> "Collecting depth discrete groundwater samples will be of particular strategic importance when drilling <br /> the well cluster northeast of Area 3. The proposed location of this well probably will not define the <br /> groundwater plume laterally to the northeast because it is southwest of B-78, a boring from which <br /> polluted groundwater samples were collected. Furthermore, neither of the screened intervals for the <br /> Equal <br /> Employment <br /> Opportunity Employer <br /> Worldwide Engineering, Environmental, Construction,and IT Services <br />