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2012 Annual Groundwater Monitoring and Evaluation Report
<br /> Full-Scale In Situ Hexavalent Chromium Reduction Treatment Implementation
<br /> Former Marley Cooling Tower Site, Stockton,California February 2013
<br /> 3.1.3 Northern Injection Area Wells
<br /> Baseline well sampling results represent conditions within and around the established Cr plume
<br /> boundary and areas of treatment. Quarterly well sampling results track the performance of the
<br /> treatment by quarter.
<br /> Consistent with the WDR, the third and fourth quarter 2012 monitoring and sampling events
<br /> included EW-3, MW-1, MW-2, MW-4, MW-6, MW-8, MW-101, MW-102, MW-104 (S-2),
<br /> MW-105, MW-106, MW-207, MW-208, MW-213 (I-7), MW-214 (I-8), MW-300, MW-320,
<br /> MW-323, MW-361, MW-449S, MW-449D, TW-12, and TW-13 in the northern area of the Site
<br /> to obtain information on groundwater quality. Monitoring well MW-206 was scheduled to be
<br /> sampled during both quarters, but field samplers reported that no water was produced by the
<br /> dedicated well pump.
<br /> 3.1.4 Southern Injection Area Wells
<br /> Consistent with the WDR, the third and fourth quarter 2012 monitoring and sampling events
<br /> included EW-1, I-11, MW-9, MW-204 (S-8), MW-205 (S-7), MW-301, MW-303, MW-321 (I-
<br /> 9), MW-322, MW-324 (I-10), MW-447S, MW-447D, MW-448S, MW-448D, MW-4505, MW-
<br /> 450D, TW-14, TW-15, TW-16, TW-17, to obtain information on groundwater quality.
<br /> Additionally, monitoring well MW-363 was sampled in third and fourth quarter 2012 in
<br /> accordance with a response to a DTSC comment in the Final Work Plan for Focused
<br /> Supplemental Hexavalent Chromium Reduction as Part of the In Situ Remedial Action Plan
<br /> Amendment Activities (MWH, 2012).
<br /> 3.2 GROUNDWATER ELEVATION, ESTIMATED GRADIENT, AND
<br /> LINEAR VELOCITY
<br /> Depth-to-groundwater and groundwater-elevation measurements are presented in Table 4.
<br /> Potentiometric surface maps were prepared by Dudek for the Shallow, 100-Foot Sand, and
<br /> Intermediate zones using groundwater data collected in July and October 2012; those maps are
<br /> presented in Appendix A. Interpretation of the groundwater gradient is complicated by the
<br /> effects of the groundwater extraction (for treatment) in an area with an otherwise relatively flat
<br /> water-table surface. Groundwater elevations, estimated gradients, and linear velocities during
<br /> (D MWH,:
<br /> 3-3
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