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AMW-2, AMW-6, AMW-7, and AMW-14, potassium at AMW-14, sodium at AMW-14, field
<br />specific conductance at AMW-7, strontium at AMW-6 and AMW-14, sulfate at AMW-7, and
<br />TDS at AMW-7. Carbonate at AMW-2 exhibited an apparent increasing trend according to the
<br />Sen's Slope analysis, but this trend is due to a historical increase in the laboratory RL.
<br />There was only one constituent that exhibited a statistically significant increasing trend during the
<br />fourth quarter 2009 and also exceeded a concentration limit: barium at AMW-14. As described
<br />above, the fourth quarter 2009 barium concentration at AMW-14 (0.25 mg/L) is comparable to
<br />concentrations observed at that well since August 2006, and is well below the National Primary
<br />Drinking Water Standard (2 mg/L).
<br />Sen's Slope analysis identified decreasing trends in the following inorganic parameters: calcium
<br />at AMW-12, chloride at AMW-12, magnesium at AMW-12, nitrate at AMW-13, potassium at
<br />AMW-12, strontium at AMW-12, and field turbidity at AMW-2.
<br />None of the VOCs that were detected in detection monitoring wells during the fourth quarter
<br />2009 monitoring event exhibited a significant increasing trend according to the Sen's Slope
<br />analysis. One VOC that was detected in detection monitoring wells during the fourth quarter
<br />2009 exhibited a significant decreasing trend: dichlorodifluoromethane at AMW-14.
<br />Piper diagrams of the first through fourth quarter 2009 results for the detection monitoring wells
<br />are presented in Appendix H. Hydrographs of the detection monitoring wells, illustrating
<br />historic groundwater elevations, well screen elevations, and pump intake elevations, are included
<br />in Appendix I.
<br />2.2 Corrective Action Monitoring
<br />During the fourth quarter 2009 monitoring event, ATC associates, Inc. collected groundwater
<br />samples from corrective action monitoring wells (AMW-1, AMW-4, AMW-5R, AMW-10,
<br />AMW-11, AMW-18, AMW-19, and AMW-1913R). Corrective action monitoring well AMW-5R
<br />is a replacement for corrective action monitoring well AMW-5. Corrective action monitoring
<br />well AMW-19BR is a replacement for corrective action monitoring well AMW-19B. The field
<br />results provided by ATC Associates, Inc. and laboratory results provided by BC Laboratories,
<br />Inc. for the fourth quarter 2009 corrective action monitoring event are summarized on Table 2.3.
<br />The historical groundwater data for the corrective action monitoring wells are presented in
<br />Appendix F. Times series concentration plots of historical groundwater data for the detection
<br />monitoring wells are presented in Appendix G. For VOCs, only those compounds that exhibited
<br />detections at corrective action monitoring wells during the fourth quarter 2009 monitoring event
<br />were plotted.
<br />VOCs have been consistently detected in samples from corrective action monitoring wells AMW-
<br />1, AMW4, AMW-10, and AMW-11. AMW-5/5R, AMW-18, AMW-19, and AMW-19BR have
<br />previously exhibited sporadic VOC detections.
<br />Historical data from the corrective action monitoring wells from March 1994 to the present were
<br />analyzed for temporal trends using Sen's Slope trend analysis. Graphs and summary tables of the
<br />Sen's Slope analyses for corrective action monitoring wells are presented in Appendix G. Table
<br />2.4 summarizes the results of the corrective action monitoring well trend analysis. The following
<br />inorganic constituents exhibited an increasing trend according to the Sen's Slope analysis: barium
<br />at AMW-1 and AMW-5R, bicarbonate at AMW-1, AMW-5R, and AMW-18, chloride at AMW-
<br />5R, nitrate at AMW-4 and AMW-5R, sodium at AMW-5R, field specific conductance at AMW-1
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