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2011 Annual Groundwater Monitoring and Evaluation Report <br /> Full-Scale In Situ Hexavalent Chromium Reduction Treatment Implementation <br /> Former Marley Cooling Tower Site, Stockton,California January 2012 <br /> 3.0 GROUNDWATER MONITORING AND SAMPLING <br /> This section summarizes the groundwater monitoring and sampling events, and presents and <br /> discusses the results of the groundwater monitoring and sampling performed between July 1 and <br /> December 31, 2011 (2011 third- and fourth-quarter monitoring and sampling events). <br /> 3.1 MONITORING AND SAMPLING PLAN <br /> Groundwater monitoring and sampling associated with the full-scale in situ Cr+6 reduction <br /> treatment implementation were performed before, in conjunction with, and after the full-scale <br /> injection program. Table 2 lists the wells included in this sampling period. Supplemental <br /> sampling was performed at several Intermediate Zone monitoring wells (including wells not <br /> specified in the MRP)in August to track remedial progress. <br /> 3.1.1 Analytical Methods and Field Parameters <br /> Analytical methods used were selected in accordance with requirements stated in the WDR, as <br /> listed in Table 3. Methods included: <br /> • U.S. Environmental Protection Agency(EPA) 7196A and 7199 (Cr+6) <br /> • EPA 601013/6020 (Cr, As, iron(Fe), and manganese (Mn)) <br /> • EPA 300.0 (sulfate (SO4)) <br /> • SM 2540C (total dissolved solids (TDS)) <br /> • SM 5310C (total organic carbon(TOC)) <br /> Groundwater samples analyzed for metals by EPA Methods 6010B and 6020 were filtered in the <br /> laboratory using 0.45-micron membrane filters before preservation and analysis. <br /> In May 2009, the CVRWQCB approved, by electronic mail, a program modification proposal to <br /> discontinue nitrate analyses as part of the in situ RAP Amendment activities (CVRWQCB, <br /> 2009). This change to the sampling program was incorporated into the third quarter of 2009 and <br /> subsequent sampling events. <br /> Groundwater samples were collected from monitoring wells using a combination of portable and <br /> dedicated down-hole pumps. All groundwater samples were collected and field parameters <br /> 1) MWH,, <br /> 3-1 <br />