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2012 Semiannual Groundwater Monitoring and Evaluation Report
<br /> Full-Scale In Situ Hexavalent Chromium Reduction Treatment Implementation
<br /> Former Marley Cooling Tower Site, Stockton,California October 2012
<br /> 3.1.3 Northern Injection Area Wells
<br /> Baseline well sampling results represent conditions within and around the current established Cr
<br /> plume boundary and areas of treatment. Quarterly well sampling results track the performance
<br /> of the treatment by quarter.
<br /> Consistent with the WDR, the first two 2012 quarterly monitoring and sampling events included
<br /> MW-1, MW-2, MW-8, MW-101, MW-102, MW-104 (S-2), MW-105, MW-106, MW-207,
<br /> MW-208, MW-213 (I-7), MW-300, MW-323, MW-361, TW-12, and TW-13 in the northern area
<br /> of the Site to obtain information on groundwater quality. Wells MW-6, MW206, MW214 (I-8)
<br /> and MW-320 continued with quarterly sampling and well EW-3 was sampled during the first
<br /> quarterly event, though they are not required by the MRP. EW-3 was sampled during the second
<br /> quarterly event for dissolved chromium and field parameters as part of the overall groundwater
<br /> monitoring program, which will be reported on by Dudek.
<br /> 3.1.4 Southern Injection Area Wells
<br /> Consistent with the WDR, the first two 2012 quarterly monitoring and sampling events included
<br /> MW-9, MW-204 (S-8), MW-205 (S-7), MW-301, MW-303, MW-321 (1-9), MW-322, MW-324
<br /> (I-10), TW-14, TW-15, TW-16, TW-17, MW-4475, MW-447D, MW-4485, and MW-448D to
<br /> obtain information on groundwater quality. Wells EW-1 and I-11 continued with quarterly
<br /> sampling, though they are not required by the MRP. Due to the presence of steel 1-beams, which
<br /> could not be moved before or during the noted sampling period, despite repeated requests to
<br /> move the steel, wells TW-14 and TW-15 could not be sampled during the first quarterly event
<br /> and wells TW-14 and MW-204 could not be sampled during the second quarterly event. These
<br /> wells were sampled as part of the third quarter 2012 sampling event, which will be reported in
<br /> the 2012 Annual Report and is due by February 2013.
<br /> 3.2 GROUNDWATER ELEVATION, ESTIMATED GRADIENT, AND
<br /> LINEAR VELOCITY
<br /> Potentiometric surface maps were prepared by Dudek for the Shallow, 100-Foot Sand, and
<br /> Intermediate zones using groundwater data collected in January and April 2012. Depth-to-
<br /> groundwater and groundwater-elevation measurements are presented in Table 4. Potentiometric
<br /> (D IVBWH,
<br /> 3-3
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