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• • <br /> Fox River Paper Company June 23,2006 <br /> Background Water Quality Concentrations Page 2 of 5 <br /> Table A. Background TDS Concentration Estimates <br /> Fox River Site, Ripon, CA <br /> Aquifer(s) Well Numbers Type of Analysis Distribution Q95) Type of Cl <br /> mg/L <br /> Semiperched OB-10,OB-14, Medians for each date Non-normal 713 Nonparametric <br /> OB-16,OB-17, <br /> OB-21,OB-22 <br /> Upper TH-4,TH-5,TH-9 Medians for each date Non-normal 1030 Nonparametric <br /> Intermediate TH-6,TH-10 Medians for each date Non-normal 470 Nonparametric <br /> In addition to the TDS analyses, L&A calculated background concentrations for the other <br /> FR discharge parameters (individual anions and cations) in accordance with Title 27 of <br /> the California Code of Regulations (27 CCR; Table B; attached). <br /> Statistical Analysis of TDS Data <br /> L&A examined the data set and identified that each aquifer had 17 sampling events at 6 <br /> wells, 3 wells, and 2 wells, respectively, for the semiperched, upper, and intermediate <br /> zones, respectively. First, L&A calculated the median value across each aquifer zone for <br /> each sampling date. Calculating background concentrations using median values for each <br /> date is desirable because it reduces the influence of extreme values on the analysis. The <br /> resulting 17 median values for each aquifer zone for each sampling event were analyzed <br /> for their distribution characteristics, and the 95th percentile upper confidence limit was <br /> calculated based on the appropriate distribution. L&A selected the 95th percentile value <br /> as representative of background conditions because it is the published procedure of other <br /> California practitioners calculating background concentrations of inorganic compounds in <br /> groundwater. <br /> The analysis of the FR data did not show sufficient correlation with normal distribution <br /> for any of the aquifers for TDS. This is likely due to the small sample sizes (two to six <br /> wells) per event. As a result, a nonparametric analysis was used to calculate the upper <br /> limit of the 95th percentile confidence interval. These calculations generated background <br /> TDS concentration estimates as follows (Table A): <br /> • Semiperched: 713 mg/L <br /> • Upper: 1030 mg/L <br /> • Intermediate: 470 mg/L <br /> 003044.00 Lawrence&Associates <br /> W.1C1ients\FoxR1ver\Fina1 background tds.doc <br />