ARCHIVED REPORTS_2007_5 - Laserfiche WebLink

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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 fourth quarter 2007 monitoring event. The field and laboratory results provided by BC Laboratories, Inc. for the fourth quarter 2007 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 fourth quarter 2007 monitoring event were plotted. The concentration limits presented on Table 2.2 were calculated by Herst&Associates, Inc. from data collected through the fourth quarter 2007 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 fourth quarter 2007 monitoring event, barium at AMW-13 and hexavalent chromium at AMW-7 exceeded their respective concentration limits. The fourth quarter 2007 barium concentration at AMW-13 (0.29 mg/L) is comparable to concentrations observed at that well since May 1995, and is well below the National Primary Drinking Water Standard(2 mg/L). The fourth quarter 2007 hexavalent chromium concentration at AMW-7 (0.0056 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 fourth quarter 2007 monitoring event, no VOCs were detected above the laboratory PQL in samples collected from detection monitoring wells AMW-6, AMW-7 or AMW-12. cis- 1,2-Dichloroethene, tetrachloroethene, and trichloroethene were detected above the PQL at AMW-13 during the fourth quarter 2007. Tetrachloroethene and trichloroethene were detected above the PQL at AMW-14 during the fourth quarter 2007. The fourth quarter 2007 concentration of cis-l,2-dichloroethene at AMW-6 (0.60 ug/L) is comparable to concentrations observed at that well intermittently since March 2003, and is well below the National Primary Drinking Water Standard (70 ug/L). The fourth quarter 2007 concentration of tetrachloroethene at AMW-13 (12 ug/L) is comparable to concentrations observed at that well intermittently since March 1996, and is above the National Primary Drinking Water Standard(5 ug/L). The fourth quarter 2007 concentration of tetrachloroethene at AMW-14 (16 ug/L) is comparable to concentrations observed at that well intermittently since March 1996, and is above the National Primary Drinking Water Standard (5 ug/L). The fourth quarter 2007 concentration of trichloroethene at AMW-13 (3.8 ug/L) is comparable to concentrations observed at that well intermittently since February 2000, and is below the National Primary Drinking Water Standard (5 ug/L). The fourth quarter 2007 concentration of 2