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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 /> 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 January 1 <br /> and June 30, 2013 (2013 first- and second-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. Note that sampling <br /> during first- and second-quarter 2013 was conducted in accordance with MRP No. R5-2012- <br /> 0814. The first quarter sampling was conducted as outlined for both the North and South Yards. <br /> The second quarter sampling was conducted on a reduced set of wells in the North Yard as <br /> permitted by MRP No. R5-2012-0814. A notification letter of the North Yard reduction was sent <br /> to both CVRWQCB and DTSC on June 4, 2013 (MWH, 2013b), verbal acceptance with <br /> comment was received in July 2013 from CVRWQCB and DTSC, and CVRWQCB to issue a <br /> joint acceptance with comment letter in July/August 2013. <br /> 3.1.1 Analytical Methods and Field Parameters <br /> Analytical methods used were selected in accordance with requirements stated in the MRP No. <br /> R5-2012-0814, as listed in Table 3. Methods included: <br /> • U.S. Environmental Protection Agency (EPA) 7199 (Cr+6) <br /> • EPA 6020 (Cr, As, iron(Fe), and manganese [Mn]) <br /> • EPA 300.0 (sulfate (SO4)) <br /> • EPA 160.1 (total dissolved solids [TDS]) <br /> • EPA 415.1 (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 /> (a MWH., <br /> 3-1 <br />