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LAWRENCE <br /> & ASSOCIATES <br /> ENGINEERING GEOLOGY .l01i S 7 2006 <br /> ( I Y I L ENGINEERING <br /> GROUNDWATER HYDROLOGY ENVIRONroJENI HEALTH <br /> PERIA T/SERVICES <br /> 003044.00 <br /> June 23, 2006 <br /> Mr. Todd Del Frate <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> 11020 Sun Center Drive#200 <br /> Rancho Cordova, CA 95670-6114 <br /> Dear Mr. Del Frate: <br /> SUBJECT: BACKGROUND GROUNDWATER QUALITY <br /> CONCENTRATIONS FOR MONITORED PARAMETERS AT FOX <br /> RIVER PAPER COMPANY, RIPON, CALIFORNIA <br /> On behalf of Fox River Paper (FR), Lawrence & Associates (L&A) evaluated data <br /> specified by the California Regional Water Quality Control Board, Central Valley Region <br /> (CVRWQCB) to develop total dissolved solids (TDS)background concentrations for <br /> three water bearing zones, the semiperched, upper, and intermediate aquifers in the <br /> vicinity of the FR Site. The data that the CVRWQCB specified for this purpose were 17 <br /> quarterly sampling events from January 2002 through January 20061. The wells selected <br /> as representative of background conditions by the CVRWQCB were as follows: <br /> • Semiperched: OB-10, OB-14, OB-16, OB-17, OB-21, OB-22 <br /> • Upper: TH-4, TH-5, TH-9 <br /> • Intermediate: TH-6, TH 10 <br /> Because the data set shows substantial variation in analyte concentrations with respect to <br /> well location, screened interval (aquifer zone), and date of sample, L&A evaluated <br /> various ways to statistically analyze the data to appropriately reflect spatial and temporal <br /> variations and their effects on background concentration calculations. The following <br /> sections describe the procedures and rationale for the calculated estimates of background <br /> TDS concentrations for each aquifer zone (Table A). This evaluation is considered <br /> adequate for a basic estimate of current background concentrations given the specified <br /> data. <br /> 1 CVRWQCB, 19 May 2006,Review and Comments for the Fourth Quarter 2005 Groundwater <br /> Monitoring,Annual Summary Report, and Addendum to Amended Report of Waste Discharge, Fox River <br /> Paper Company's Ripon Mill, San Joaquin County, Facility No. 5B392011002,p.2. <br /> 2001 Market Street • Room 523 • Redding, California 96001 • (530)244-9703 • fax (530)244-5021 • www.lwrnc.com <br />