Laserfiche WebLink
19449 Riverside Drive,Suite 230,Sonoma,California 95476 <br /> CONESTOGA-ROVERS Telephone: 7079354850 Facsimile: 7079358649 <br /> &ASSOCIATES www.CRAworld.com <br /> July 2,2009 _ <br /> u �Co.11 <br /> 241729 <br /> _J� <br /> Mr. Brian Taylor,P.G. <br /> JUL 0 Ci 2009 <br /> Regional Water Quality Control Board-Central Valley Region ENVIRON[ANT HEA FH <br /> 11020 Sun Center Drive,Suite#200 PERMIT/SERVICES <br /> Rancho Cordova,California 95670 <br /> Dear Mr.Taylor: <br /> Re: Response to RWQCB Review of April 30,2009 Work Plan to Monitor Baseline <br /> Concentrations and Response to Infiltration Study Work Plan <br /> Shell Stockton Terminal <br /> 3515 Navy Drive <br /> Stockton,California <br /> SAP Code 356164 <br /> Incident No.300002 <br /> Conestoga-Rovers&Associates(CRA)has prepared this response on behalf of Equilon Enterprises LLC <br /> dba Shell Oil Products US(Shell)regarding the California Regional Water Quality Control Board- <br /> Central Valley Region(RWQCB)review dated June 10,2009 of the referenced Work Plan for the Shell <br /> Stockton Terminal,3515 Navy Drive,Stockton,San Joaquin County,California(Site). <br /> Based on RWQCB comments,it is our understanding that RWQCB concurs with the proposed list of <br /> analytes,monitoring frequency and numerical modeling approach,however,the RWQCB requests <br /> additional information on the following:1)the proposed data analysis methods to be used for <br /> implementing the background study for non-constituents of concern(non-COOS),in accordance with the <br /> methods listed in CCR,Title 27 S.20415(e)(8)(A-E),and 2) the list of constituents that will require <br /> updating to calculate background conditions. Our response to these requests is as follows. <br /> 1.0 PROPOSED STRATEGY FOR <br /> CALCULATING BACKGROUND CONCENTRATIONS <br /> Background calculations will be undertaken on a per-parameter basis,utilizing historical and ongoing <br /> monitoring data from four background monitoring wells(MW-19,MW-25,MW-26,and MW-31). Per the <br /> Title 27 S. 20415(e)(6)requirements,a minimum of 1 year of quarterly sampling results for each <br /> background monitoring well will be used in background concentration calculations. For monitoring <br /> parameters monitored historically in the background wells,all available data will be considered. <br /> Background values will be reassessed on an annual basis with ongoing monitoring data. <br /> The background concentrations will be calculated as Upper Tolerance Limits(UTLs)with 95 percent <br /> coverage and 95 percent confidence,using the Tolerance Interval statistical data analysis method,per <br /> Title 27 S.20415(e)(8)(C)and 27 S.20415(e)(9)(D). Such values are 95 percent upper confidence limits on <br /> the 95th percentile of the population of background concentrations for the given monitoring parameter. <br /> Thus,no more than one in twenty samples from groundwater consistent with background would be <br /> Equal <br /> Employment <br /> Opportunity Employer <br /> Worldwide Engineering, Environmental, Construction, and IT Services <br />