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Trichloroethene was detected at AMW-10 above the laboratory RL. Dichlorodifluoromethane,
<br /> tetrachloroethane, and trichloroethene were detected at AMW-19BR above the laboratory RL.
<br /> Historical data from the corrective action monitoring wells from March 1994 to the present were
<br /> analyzed for temporal trends using Mann-Kendall / Sen's Slope trend analysis. Graphs and
<br /> summary tables of the Mann-Kendall / Sen's Slope analyses for corrective action monitoring
<br /> wells are presented in Appendix G. For constituents whose historical data consist primarily of
<br /> non-detects (carbonate alkalinity, oil and grease, volatile petroleum hydrocarbons, and VOCs),
<br /> trend evaluation was performed on data from the earliest detection through the present. Wells
<br /> with no historical detections for a constituent were not evaluated for trends.
<br /> Table 2.4 summarizes the results of the corrective action monitoring well trend analysis. Mann-
<br /> Kendall / Sen's Slope analysis identified significant increasing statistical trends in the following
<br /> inorganic constituents: arsenic at AMW-1; barium at AMW-1 and AMW-19; bicarbonate
<br /> alkalinity at AMW-1, AMW-5R and AMW-18; chloride at AMW-5R; nitrate at AMW-4 and
<br /> AMW-5R; field pH at AMW-4, AMW-5R, AMW-11, and AMW-19BR; potassium at AMW-5R;
<br /> sodium at AMW-5R; field specific conductance at AMW-1 and AMW-5R; sulfate at AMW-5R
<br /> and AMW-10; field temperature at AMW-5R; TDS at AMW-5R; and field turbidity at AMW-5R
<br /> and AMW-10. Oil and grease exhibited apparent increasing trends at AMW-10 and AMW-11
<br /> according to the Mann-Kendall / Sen's Slope analysis, but these trends are due to a historical
<br /> increase in the laboratory RL.
<br /> Mann-Kendall / Sen's Slope analysis identified significant decreasing statistical trends in the
<br /> following inorganic constituents: barium at AMW-10 and AMW-11; bicarbonate alkalinity at
<br /> AMW-4 and AMW-10; calcium at AMW-4 and AMW-10; chloride at AMW-4, AMW-10,
<br /> AMW-11, and AMW-18; hexavalent chromium at AMW-19 and AMW-19BR; magnesium at
<br /> AMW-4, AMW-10, and AMW-11; nitrate at AMW-1, AMW-10, AMW-18, AMW-19, and
<br /> AMW-19BR; field pH at AMW-1; potassium at AMW-4, AMW-10, AMW-11, and AMW-18;
<br /> sodium at AMW-1, AMW-10, AMW-18, and AMW-19BR; field specific conductance at AMW-
<br /> 4, AMW-10, and AMW-11; strontium at AMW-4 and AMW-10; sulfate at AMW-1, AMW-18,
<br /> AMW-19, and AMW-19BR; field temperature at AMW-11; TDS at AMW-4, AMW-10, AMW-
<br /> 11, and AMW-18; and field turbidity at AMW-4. Carbonate exhibited apparent decreasing trends
<br /> at AMW-11 and AMW-18 according to the Mann-Kendall/Sen's Slope analysis,but these trends
<br /> are due to a historical decrease in the laboratory RL.
<br /> Mann-Kendall / Sen's Slope analysis identified significant increasing statistical trends in the
<br /> following VOCs: 1,1-dichloroethane at AMW-1; chlorobenzene at AMW-1; and cis-1,2-
<br /> dichloroethene at AMW-1.
<br /> Mann-Kendall / Sen's Slope analysis identified significant decreasing statistical trends in the
<br /> following VOCs: 1,1-dichloroethane at AMW-4, AMW-10, and AMW-11; 1,2-dichloroethane at
<br /> AMW-1; 1,2-dichloropropane at AMW-4 and AMW-11; 1,4-dichlorobenzene at AMW4; cis-
<br /> 1,2-dichloroethane at AMW4 and AMW-11; dichlorodifluoromethane at AMW-1, AMW4,
<br /> AMW-10, and AMW-11; tetrachloroethene at AMW4, AMW-5R, AMW-10, and AMW-11;
<br /> trans-l,2-dichloroethene at AMW-4 and AMW-11; trichloroethene at AMW-4, AMW-10, and
<br /> AMW-11; and vinyl chloride at AMW-4.
<br /> The second quarter 2012 concentration of arsenic at AMW-1 (0.006 mg/L) is below the National
<br /> Primary Drinking Water Standard of 0.01 mg/L. The increasing trend for dissolved arsenic at
<br /> AMW-1 is not observed when the data are limited to the period of November 2007 to May 2012,
<br /> indicating that concentrations have stabilized in the past five years.
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