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Fox River Paper Company Background Water Quality Concentrations June Page a 3 of of5 5 These background concentrations indicate a higher water quality in near-surface water (semiperched) relative to water at greater depth. The trend reverses at depths beyond the upper aquifer. The trend in the shallow zones may reflect the overall improvement in the quality of recharge water in the FR site vicinity over time. Shallower groundwater would likely have infiltrated into the subsurface more recently than deeper water. Statistical Analysis of Other Analytes In accordance with 27 CCR, L&A calculated estimates for the background concentrations for the other discharge parameters in FR's Waste Discharge Requirements (WDRs). This analyte list includes: • Bicarbonate • Calcium • Chloride • Electrical conductance (EC) • Magnesium • Nitrate • pH • Potassium • Sodium • Sulfate The procedure used for this analysis was the same as that described above for the TDS data for each separate aquifer zone. L&A calculated median values for each analyte for each sampling event by aquifer zone. The resulting 17 median values for each analyte in each aquifer zone were evaluated for distribution characteristics. The majority of median value data sets for the three aquifer zones showed normal distributions except: • For all zones, EC, pH, chloride, and nitrate had non-normal distributions. • For the intermediate zone, sulfate had a non-normal distribution. Parametric (for normal distributions) and nonparametric (for non-normal distributions) analyses yielded the following values for the upper limit of the 95`x'percentile confidence interval, which is used as the estimate for background concentration or value. Table B presents background concentration values for all analytes listed in Fox River's WDRs Order No. 5-01-148. 003044.00 Lawrence&Associates W:1CZients\FoxRiverTina1 background tds.doc