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(arsenic, barium, bicarbonate, calcium, carbonate, chloride, gasoline -range petroleum
<br />hydrocarbons, hexavalent chromium, magnesium, nitrate, oil and grease, potassium, sodium,
<br />strontium, sulfate, TDS, and VOCs).
<br />2.1 Detection Monitoring
<br />During the second quarter 2011 monitoring event, Del -Tech collected groundwater samples from
<br />the background well (AMW-2) and detection monitoring wells (AMW-6, AMW-7, AMW-12,
<br />AMW-13, and AMW-14). The field results provided by Del -Tech and laboratory results
<br />provided by BC Labs for the second quarter 2011 groundwater detection monitoring event are
<br />summarized on Table 2.2. The historical groundwater data for the detection monitoring wells are
<br />presented in Appendix D. Times series concentration plots of historical groundwater data for the
<br />detection monitoring wells are presented in Appendix E. For VOCs, only those compounds that
<br />exhibited detections at detection monitoring wells during the second quarter 2011 monitoring
<br />event were plotted. The concentration limits presented on Table 2.2 were calculated by Herst &
<br />Associates, Inc. from data collected through the second quarter 2011 monitoring event. The
<br />statistical analysis calculations for detection monitoring wells are presented in Appendix E.
<br />Information on the development of the concentration limits can be found in the Fourth
<br />Quarter/Annual 1999 Monitoring Report, Austin Road Landfill, prepared by C112M Hill in
<br />January 2000. A copy of the statistical analysis methodology is presented in Appendix C.
<br />As presented on Table 2.2, the following constituents exceeded their respective concentration
<br />limits during the second quarter 2011: barium at AMW-12, AMW-13, and AMW-14; chloride at
<br />AMW-14; and hexavalent chromium at AMW-6 and AMW-7.
<br />During the second quarter 2011 monitoring event, no VOCs were detected above the laboratory
<br />reporting limit (RL) in samples collected from detection monitoring wells AMW-2, AMW-7, or
<br />AMW-12. Tetrachloroethene was detected above the laboratory RL at AMW-6.
<br />Dichlorodifluoromethane, tetrachloroethene, and trichloroethene were detected above the
<br />laboratory RL at AMW-13. Tetrachloroethene was detected above the laboratory RL at AMW-
<br />14.
<br />Historical data from the detection monitoring wells were analyzed for temporal trends using
<br />Mann -Kendall / Sen's Slope trend analysis. Graphs and summary tables of the Mann -Kendall /
<br />Sen's Slope analyses for detection monitoring wells are presented in Appendix E.
<br />Mann -Kendall / Sen's Slope analysis identified significant increasing statistical trends in the
<br />following inorganic constituents: barium AMW-6 and AMW-14, bicarbonate alkalinity at AMW-
<br />2, AMW-7, and AMW-13, calcium at AMW-7 and AMW-14, chloride at AMW-6 and AMW-7,
<br />hexavalent chromium at AMW-14, magnesium at AMW-6, AMW-7, and AMW-14, nitrate at
<br />AMW-2, AMW-6, AMW-7, and AMW-14, potassium at AMW-14, sodium at AMW-14, field
<br />specific conductance at AMW-2, AMW-6, and AMW-7, strontium at AMW-6 and AMW-14,
<br />sulfate at AMW-7 and AMW-14, and TDS at AMW-6 and AMW-7. Carbonate at AMW-2,
<br />AMW-12, and AMW-13 exhibited apparent increasing trends according to the Mann -Kendall /
<br />Sen's Slope analysis, but these trends are due to a historical increase in the laboratory RL.
<br />Given that bicarbonate alkalinity, nitrate, and field specific conductance exhibit significant
<br />increasing trends at upgradient well AMW-2, the increasing trends for these constituents at
<br />downgradient wells are likely due to ongoing changes in the natural groundwater geochemistry at
<br />the site.
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