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2012 Semiannual Groundwater Monitoring and Evaluation Report Full-Scale In Situ Hexavalent Chromium Reduction Treatment Implementation Former Marley Cooling Tower Site, Stockton,California October 2012 1.0 INTRODUCTION MWH Americas, Inc. (MWH) has prepared this 2012 Semiannual Groundwater Monitoring and Evaluation Report on behalf of SPX Corporation (SPX) for the former Marley Cooling Tower Company (MCTC) facility (the Site) in Stockton, California (Figure 1). This report summarizes the results of groundwater monitoring during the first semiannual period (January through June) of 2012, and presents an evaluation of groundwater trends associated with the full-scale in situ hexavalent chromium (Cr+6) groundwater remediation at the Site. A facility site plan, illustrating the groundwater remediation area, is provided as Figure 2. The full-scale in situ Cr+6 remediation was implemented in 2008, conforming to the Final Remedial Action Plan (RAP) Amendment (MWH, 2007a) accepted by the California Department of Toxic Substances Control (DTSC). A supplemental Cr+6 remediation effort was implemented during the second semiannual period of 2010, as described in the 2010 annual performance monitoring report (MWH, 2011a). This semiannual report was prepared according to Waste Discharge Requirements (WDR) Order No. R5-2007-0126 and the associated Monitoring and Reporting Program (MRP) issued by the California Central Valley Regional Water Quality Control Board(CVRWQCB) (2007). The full-scale in situ treatment program was implemented based on the successful results of two pilot studies conducted at the Site. The pilot studies, which evaluated the effectiveness of treatment and methods of implementation, consisted of two phases (I and II). The phases are discussed in detail in the 2008 Semi-Annual Groundwater Monitoring Report(MWH, 2008a). The injection-boring phase of the RAP Amendment In Situ Cr+6 Reduction Treatment Implementation Program began on January 16, 2008, and was completed on June 5, 2008, as summarized in Table 1. The injection-boring phase consisted of 509 remedial injection borings throughout the Site to deliver reductant solution into impacted Shallow Zone portions of the aquifer and create reactive (reductive) barriers across accessible areas of the Cr+6 plume. Five horizontal flushing wells and two horizontal treatment wells were also installed beneath the former retort pit source area between February 25 and March 21, 2008. The horizontal wells have since been used to inject treatment solution and water (to flush the vadose zone) in the source area (twice), as summarized in Table 1. Details of the program are presented in the Remedial Action Implementation Completion Report (RAICR) (MWH, 2008b). Supplemental (D MWH, 1-1