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• Laboratory Control Sample/ Laboratory Control Sample Duplicate (LCS/LCSD) Performance • Matrix Spike/Matrix Spike Duplicate (MS/MSD) Sample Performance • Field Duplicate Comparison • Detection Limits Summary of Findings: All samples were analyzed according to the accompanying chains of custody and all analytical holding times were met. QC data were reviewed for laboratory and instrument precision and accuracy from LCS/LCSD recoveries and relative percent differences (RPDs) and MS/MSD sample recoveries and RPDs. All quality control elements were found to be within acceptable limits with the following exceptions: • The MS/MSD percent recoveries associated with the analysis of Equipment Rinse, collected July 19, were greater than the upper control limit for dissolved manganese; the result was not detected in the parent sample, so no data were qualified. • The MS/MSD percent recoveries associated with the analysis of MW-450S and MW-450S Dup were less than the lower control limit for dissolved chromium; dissolved chromium was qualified as estimated (J) in both samples. • The MS/MSD percent recoveries and RPD associated with the analysis of MW-211 and TW-14 were not meaningful for sulfate. The concentration of sulfate in the parent samples was greater than four times the concentration used for the spike. Therefore, the criteria were not evaluated. • The MS/MSD percent recoveries and RPD associated with the analysis of TW-15 were not meaningful for dissolved manganese. The concentration of manganese in the parent sample was greater than four times the concentration used for the spike. Therefore, the criteria were not evaluated. • The MS/MSD percent recoveries and RPD associated with the analysis of MW-102 were not meaningful for hexavalent chromium and sulfate. The concentration of hexavalent chromium and sulfate in the parent sample was greater than four times the concentration used for the spike. Therefore, the criteria were not evaluated. • The MS/MSD percent recoveries and RPD associated with the analysis of MW-213 (1-7) were not meaningful for dissolved chromium and manganese. The concentration of the chromium and manganese in the parent sample was greater than four times the concentration used for the spike. Therefore, the criteria were not evaluated. Field sampling precision was also evaluated by using the calculated RPD between results reported for the field duplicate pairs, which are listed above. All RPD results were found to be within the acceptable limits for precision for all methods with the following exception: • The field duplicate pairs MW-214(1-8) and MW-214 (1-8) Dup, and MW-104 (S-2) and MW-104 (S-2) Duplicate, and TW-13 and TW-13 (Duplicate) had RPDs that was greater than the control limit for dissolved chromium; chromium was qualified as estimated (J) in the parent samples. Page 2of6