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Duplicate analyses are performed by the laboratory to evaluate the precision of analytical <br /> procedures. Precision is evaluated by calculating a relative percent difference (RPD) using the <br /> following equation: <br /> Spike Concentration —Spike Duplicate Concentration <br /> RPD % = 1 x 100% <br /> Z(Spike Concentration+Spike Duplicate Concentration) <br /> The RPD and/or percent recovery for several MS or MSD samples were outside acceptable limits <br /> due to matrix interference. Sample results for the QC batch were accepted by the lab based on <br /> the percent recoveries and/or other acceptable QC data. The laboratory determined that the <br /> results were acceptable based on other quality control checks. <br /> Anion-Cation Charge Balance <br /> Anion-cation charge balance was calculated using concentrations of the major anions and <br /> cations in milliequivalents per liter (meq/L). The difference between the sum of anions and sum <br /> of cations was calculated as a percentage: <br /> Anions — Cations <br /> Anions + Cations x 100 <br /> We use +/- 5 percent as a guide for an acceptable percent difference. None of the samples <br /> collected during the 2023 First Semiannual monitoring event were analyzed for all of the <br /> constituents required to calculate the anion-cation charge balance. <br /> Ratio of Calculated Sum of Dissolved Solids to Specific Conductance <br /> The ratio of the calculated sum of dissolved solids (mg/L) to specific conductance was <br /> calculated.The ratio was calculated as follows: <br /> Sum of dissolved solids in mg/L <br /> Speci f is conductance <br /> The sum of dissolved solids divided by the specific conductance should fall within the range 0.55 <br /> to 0.812. None of the samples collected during the 2023 First Semiannual monitoring event were <br /> analyzed for all of the constituents required to calculate the ratio of calculated dissolved solids <br /> to specific conductance. <br /> Ratio of the Sum of Reacting Constituents to Specific Conductance <br /> The ratio of the sum of reacting cations (meq/L) to 0.01 times specific conductance, as well as <br /> the sum of reacting anions (meq/L) to 0.01 times specific conductance, should be within the <br /> range 0.92 to 1.242.This ratio was calculated as follows: <br /> 2 Friedman, L.C., and Erdmann, D.E., 1982, Quality assurance practices for the chemical and biological <br /> analyses of water and fluvial sediments: U.S. Geological Survey Techniques of Water-Resources <br /> Investigations, book 5,chap.A6, 181 p. <br /> D-3 <br />