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2013 Semiannual Groundwater Monitoring and Evaluation Report
<br /> Full-Scale In Situ Hexavalent Chromium Reduction Treatment Implementation
<br /> Former Marley Cooling Tower Site,Stockton,California August 2013
<br /> background wells are presented in Table 6. Proposed upper background concentration limits are
<br /> based on historical data available on an individual basis by well. The wide range in
<br /> concentrations of some historical data supports the proposed changes from the WDR/MRP
<br /> criteria.
<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 MRP No. R5-2012-0814, the first quarter 2013 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-4495, 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 the first quarter, but field samplers reported that no water was produced by the
<br /> dedicated well pump. During the second quarter 2013 monitoring and sampling events included
<br /> EW-3, MW-4, MW-213, MW-320, MW-449S, and MW-449D. The twenty wells that were not
<br /> sampled during the second quarter 2013 event were identified as not requiring continued MRP
<br /> Section II monitoring based on (1) the last set of North Yard groundwater amendment injections
<br /> occurred in October 2010, (2) chromium concentrations at many locations are stable below the
<br /> water quality objective (WQO) (Table 5), and (3) 20 of the 24 wells would continue to be
<br /> sampled under the MRP Section I monitoring. The rationale for individual well reduction is
<br /> outlined in the notification letter provided to CVRWQCB and DTSC on June 4, 2013 (MWH,
<br /> 2013b).
<br /> 3.1.4 Southern Injection Area Wells
<br /> Consistent with MRP No. R5-2012-0814, the first and second quarter 2013 monitoring and
<br /> sampling events included EW-1, I-11, MW-9, MW-204 (S-8), MW-205 (S-7), MW-301, MW-
<br /> 303, MW-321 (I-9), MW-322, MW-324 (I-10), MW-447S, MW-447D, MW-448S, MW-448D,
<br /> (a MWK,
<br /> 3-3
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