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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 and AMW- I 9BR; nitrate at
<br />AMW-4 and AMW-5R; field pH at AMW-4, AMW-5R, AMW- 11, and AMW-1 9BR; potassium
<br />at AMW-5R; sodium at AMW-5R; field specific conductance at AMW-I and AMW-5R; sulfate
<br />at AMW-5R and AMW-10; field temperature at AMW-5R; TDS at AMW-5R; and field turbidity
<br />at AMW-5R and AMW-10. Carbonate alkalinity exhibited an apparent increasing trend at
<br />AMW-5R according to the Mann -Kendall / Sen's Slope analysis, but this trend is due to a
<br />historical 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-I 1; bicarbonate alkalinity at
<br />AMW-10; calcium at AMW-4 and AMW-10; chloride at AMW-4, AMW-10, AMW-11, and
<br />AMW-18; hexavalent chromium at AMW-19 and AMW-19BR; magnesium at AMW-4, AMW-
<br />10, and AMW-11; nitrate at AMW-I, AMW-10, AMW-18, AMW-19, and AMW-19BR; field pH
<br />at AMW-1; potassium at AMW-4, AMW-10, AMW-I 1, and AMW-18; sodium at AMW-10 and
<br />W-18; field specific conductance at AMW-4, AMW- 10, and AMW- 11; strontium at AMW-4
<br />and AMW-10; sulfate at AMW-I, AMW-18, AMW-19, and AMW-19BR; field temperature at
<br />AMW-11; TDS at AMW-4, AMW-10, AMW-11, and AMW-18; and field turbidity at AMW-4.
<br />Carbonate alkalinity exhibited an apparent increasing trend at AMW-18 according to the Mann -
<br />Kendall / Sen's Slope analysis, but this trend is 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- I and AMW- 10.
<br />Mann -Kendall / Sen's Slope analysis identified significant decreasing statistical trends in the
<br />following VOCs: 1, 1 -dichloroethane at AMW-4, AMW-1 0, and AMW-1 1; 1,2 -dichlorobenzene
<br />at AMW-1; 1,4 -dichlorobenzene at AMW-4; benzene at AMW-4; chloroethane at AMW-1; cis-
<br />1,2-dichloroethene at AMW-4 and AMW- 11; dichlorodifluoromethane at AMW-I, AMW-4,
<br />AMW-10, and AMW-11; tetrachloroethene at AMW-4, AMW-5R, AMW-10, and AMW-11;
<br />trans- 1,2-dichloroethene at AMW-4; trichloroethene at AMW-4, AMW-10, and AMW-1 1; and
<br />vinyl chloride at AMW-4.
<br />The third quarter 2012 concentration of arsenic at AMW-1 (0.013 mg/L) is above the National
<br />Primary Drinking Water Standard of 0.01 mg/L, but is within the range of concentrations
<br />observed at that well since April 1995 (<0.01 to 0.019 mg/L). The increasing trend for dissolved
<br />arsenic at AMW-1 is not observed when the data are limited to the period of November 2007 to
<br />0 August 2012, indicating that concentrations have stabilized in the past five years.
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