ARCHIVED REPORTS_2008_14 - Laserfiche WebLink

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0 wells. Corrective action monitoring well AMW-5R is a replacement for corrective action monitoring well AMW-5. The analytical results from samples collected at the corrective action wells are used to evaluate improvements in groundwater quality as a result of previously implemented corrective action measures. ATC Associates, Inc. reported that corrective action monitoring well AMW-3 has been abandoned. Groundwater samples are scheduled to be analyzed quarterly for field parameters (groundwater elevation, pH, specific conductance, temperature, and turbidity) and monitoring parameters (arsenic, barium, bicarbonate, calcium, carbonate, chloride, gasoline-range petroleum hydrocarbons, hexavalent chromium, magnesium, nitrate, oil and grease, potassium, sodium, strontium, sulfate,TDS, and VOCs). 2.1 Detection Monitoring Groundwater samples were collected from the background well (AMW-2) and detection monitoring wells (AMW-6, AMW-7, AMW-12, AMW-13, and AMW-14) during the third quarter 2008 monitoring event. The field results provided by ATC Associates, Inc. and laboratory results provided by BC Laboratories, Inc. for the third quarter 2008 detection monitoring sampling are summarized on Table 2.2. The historical groundwater data for the detection monitoring wells are presented in Appendix D. The data are graphed on time series concentration plots, included in Appendix E. For VOCs, only those compounds that exhibited detections for the third quarter 2008 monitoring event were plotted. The concentration limits presented on Table 2.2 were calculated by Herst & Associates, Inc. from data collected through the third quarter 2008 monitoring event. The statistical analysis calculations for detection monitoring wells are included in Appendix E. A copy of the statistical analysis methodology is included in Appendix C. During the third quarter 2008 monitoring event, barium at AMW-13 and hexavalent chromium at AMW-6 and AMW-7 exceeded their respective concentration limits. The third quarter 2008 barium concentration at AMW-13 (0.26 mg/L) is comparable to concentrations observed at that well consistently since May 1995, and is well below the National Primary Drinking Water Standard (2 mg/L). The third quarter 2008 hexavalent chromium concentration at AMW-6 (0.0055 mg/L) is comparable to concentrations observed at that well intermittently since February 1997, and is well below the National Primary Drinking Water Standard for chromium (0.1 mg/L). The third quarter 2008 hexavalent chromium concentration at AMW-7 (0.006 mg/L) is comparable to concentrations observed at that well intermittently since July 1995, and is well below the National Primary Drinking Water Standard for chromium(0.1 mg/L). During the third quarter 2008 monitoring event, no VOCs were detected above the laboratory PQL in samples collected from detection monitoring well AMW-12. Bromoform was detected above the PQL at AMW-2. Tetrachloroethene was detected above the PQL at AMW-6. Bromoform and dibromochloromethane were detected above the PQL at AMW-7. Tetrachloroethene was detected above the PQL at AMW-13. Dichlorodifluoromethane, tetrachloroethene,and trichloroethene were detected above the PQL at AMW-14. The third quarter 2008 concentration of bromoform at AMW-2 (1.3 ug/L) is comparable to concentrations observed at that well intermittently since August 2006. The third quarter 2008 concentration of tetrachloroethene at AMW-6 (0.96 ug/L) is comparable to concentrations observed at that well intermittently since September 1996, and is below the National Primary 2