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comparable to values observed at that well since August 2003. The fourth quarter 2006 field pH <br />values at AMW-1 and AMW-3 are both within the National Secondary Drinking Water Standard <br />range (6.5 - 8.5). <br />The following organic parameters exhibited an increasing trend according to the Sen's Slope <br />analysis: cis-l,2-dichloroethene at AMW-1 and AMW-10, and vinyl chloride at AMW-1. <br />The fourth quarter 2006 concentration of cis-l,2-dichloroethene at AMW-1 (2.5 ug/L) is <br />comparable to concentrations observed at that well intermittently since October 2001. The fourth <br />quarter 2006 concentration of cis-1,2-dichloroethene at AMW-10 (5.6 ug/L) is comparable to <br />concentrations observed at that well intermittently since February 2005. The concentration of cis- <br />1,2-dichloroethene at both AMW-1 and AMW-10 is below the National Primary Drinking Water <br />Standard (70 ug/L). The fourth quarter 2006 concentration of vinyl chloride at AMW-1 (0.76 <br />ug/L) is comparable to concentrations observed at that well intermittently since October 2001, <br />and is below the National Primary Drinking Water Standard (2 ug/L). <br />Sen's Slope analysis identified decreasing trends in the following organic parameters: cis-1,2- <br />dichloroethene at AMW-11, dichlorodifluoromethane at AMW-1, AMW-4, and AMW-11, <br />tetrachloroethene at AMW-11, and trichloroethene at AMW-11. <br />Piper diagrams of the first through fourth quarter 2006 results for the corrective action monitoring <br />wells are included in Appendix H. Hydrographs of the corrective action monitoring wells, <br />illustrating historic groundwater elevations, well screen elevations, and pump intake elevations, <br />are included in Appendix I. <br />.7 <br />6 <br />