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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 /> 4.0 LABORATORY AND FIELD SAMPLE RESULTS AND DISCUSSION <br /> This section presents a summary and discussion of laboratory and field sample results for the <br /> different Site areas. Field sampling logs and calibration logs are presented in Appendix B. <br /> Laboratory analytical packages are provided in Appendix C. A Data Validation Report for all <br /> laboratory analytical data is provided in Appendix D. <br /> 4.1 DATA VALIDATION AND QUALITY ASSISTANCE/QUALITY <br /> CONTROL <br /> The Data Validation Report is part of the quality assurance/quality control (QA/QC) program for <br /> the full-scale in situ Cr+6 reduction treatment implementation, which includes steps to evaluate <br /> the precision and accuracy of the laboratory analytical results and to assess the integrity of the <br /> field procedures, sample handling, and laboratory procedures. Data review is conducted on the <br /> final laboratory reports to assess the quality of the reported analytical results for the injection <br /> program. All data submitted for this project are of known and acceptable quality as qualified in <br /> the Data Validation Report (see Appendix D), based on laboratory-established control limits and <br /> the data quality objectives. These data are considered acceptable for their intended purposes. <br /> 4.2 ANALYTICAL RESULTS <br /> Analytical results for the quarterly and supplemental sampling performed from January through <br /> June 2012 are summarized in Table 5 for all chemical analytes. Additionally, Table 6 presents <br /> proposed upper background concentration limits in comparison to Water Quality Objectives <br /> (WQO) and individual historical data for the background and compliance wells. Graphs 1 <br /> through 53 present concentrations of primary constituents of interest over time at the wells <br /> included in the quarterly sampling program. The following sections discuss results for primary <br /> constituents of interest for the full-scale in situ Cr+6 reduction treatment implementation: <br /> • Total and hexavalent Cr(primary constituents of concern at the Site) <br /> • Fe (indicator of reduction/oxidation [redox] conditions in the treatment zone) <br /> • Mn(indicator of redox conditions in the treatment zone) <br /> • As (can be temporarily mobilized within the reduced treatment zone) <br /> (D MWK, <br /> 4-1 <br />