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2018 ANNUAL GROUNDWATER MONITORING REPORT FORMER KEARNEY—KPF FACILITY-STOCKTON,CALIFORNIA
<br /> 4.1 Constituent Concentrations
<br /> 4.1.1 Shallow Zone
<br /> Five shallow zone monitor wells located inside the Trigger Boundary were sampled for VOCs and 1,4-dioxane
<br /> during the annual sampling event. The five wells inside the Trigger Boundary had detections of one or more of
<br /> the following constituents: chloroform, 1,1-dichloroethane, 1,1-dichloroethylene (DCE), tetrachloroethylene
<br /> (PCE), trichloroethylene (TCE), and 1,4-dioxane, but exceedances of the CL occurred solely for concentrations of
<br /> PCE, TCE, 1,1-DCE, and 1,4-dioxane (Table 4).
<br /> The CL exceedances in the shallow zone were primarily within and around Pond 2 North(Figures 7-11).Comparison
<br /> of water quality results between October 2017 (Appendix G, Water Quality Hydrographs, Well vs. Constituents)
<br /> and October 2018 shows that concentrations of detected CDCs decreased in well SMW-1 and were comparable
<br /> (or in a few cases, slightly higher) in wells TP-1A, SMW-2, SMW-4, and SMW-5.
<br /> 4.1.2 Intermediate Zone
<br /> Three intermediate zone monitor wells located inside the Trigger Boundary were sampled for VOCs and 1,4-dioxane
<br /> during the annual sampling event. The three wells sampled within the Trigger Boundary (KI-5, KEW-3U, and KEW-
<br /> 41,J) had detections above the CL for one or more of the following constituents: TCE, 1,1-DCE, and 1,4-dioxane.
<br /> The CL exceedances in the intermediate zone were limited to a small area east of Pond 2 North and at the southern
<br /> end of Pond 2 South (Table 4 and Figures 13-16).Concentrations in October 2018 were similar to those observed in
<br /> October 2017.The distributions of the CDCs are discussed further in Section 4.3,Discussion of Remediation Progress,
<br /> with respect to where the CDCs exceed the CLs. Figures 12-16 also show the distribution of the CDCs to the extent
<br /> that they were detected at levels less than or equal to the CLs.
<br /> 4.1.3 Deep Zone
<br /> No deep zone wells were sampled in October 2018. Results from previous sampling events are shown in Table 4
<br /> and on Figure 17,VOCs in the Deep Zone.
<br /> 4.2 Long-Term Trends in Constituent Concentrations
<br /> Compared to 1994 and earlier (and, in the case of 1,4-dioxane, 1996), the concentrations of COCs that have
<br /> exceeded their respective CLs have decreased in all wells(Appendix G).There is a period from 1999 through 2002,
<br /> which corresponds with interrupted treatment system operation,during which COC concentrations largely remained
<br /> constant. There is also a short period when CDCs increased at some locations, corresponding to startup activities
<br /> of the enhanced treatment system in 2003. However,since then, concentrations have declined.
<br /> Between March 2012 and January 2015, the treatment system was shut down for a rebound study. During the
<br /> rebound study, concentrations of 1,4-dioxane increased to above the CL in four shallow zone wells and four
<br /> intermediate zone wells.Since the treatment system was restarted in January 2015, concentrations of 1,4-dioxane
<br /> remain above the CL in several shallow and intermediate zone wells within the Trigger Boundary and above the
<br /> D U D E K 10886-1
<br /> 14 March 2019
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