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GeosyntecD consultants 2. BACKGROUND Historical waste disposal practices and documented spills from dry cleaning businesses resulted in the contamination of soil and groundwater beneath the Site. Tetrachloroethene (PCE), trichloroethene (TCE), 1,2-dichloroethene (c-1,2-DCE and t- 1,2-DCE), and vinyl chloride (VC) are the main constituents historically reported in groundwater, soil, and soil vapor at the Site. Interim Remedial Actions have been implemented at the Site in phases starting in 1998: Phase I - groundwater extraction and treatment system (GWETS); Phase II - SVE; Phase III — GWETS expansion; Phase IV —AS; and Phase V. The GWETS, including wells installed as part of Phase I and Phase III remedial actions, and the subsurface conditions associated with the Phase V - enhanced reductive dechlorination (EDR). GWETS implementation is ongoing to control the dissolved phase impacts at the Site. The current extent of the dissolved phase plume was described in the 2013 Groundwater Monitoring Report Semiannual Sampling—June 2013 by Environmental Resource Management (ERM). In general the upgradient dissolved impacts extend to N. Gettysburg Drive west of the Site as defined by concentrations below the reporting limit in well MW-004A and downgradient by MW-117A. The northern extent of dissolved impacts is defined by concentrations below detection limits at wells MW-106 and MW-107A and southern by MWOOIA and MW-003A. The general extent of the dissolved phase impacts in groundwater are shown on Figure 2. The SVE and AS systems were installed to remediate impacts related to the source areas. The SVE system was installed as part of the Phase II Interim Remedial Action (IRA) for the Site in 1999 and included 37 SVE wells (SVE-1 thorough SVE-35 and SVMWE-001 and SVMWE-002) screened from approximately 10 to 30 feet below grade. The SVE system was designed to address soil source area impacts adjacent to the former dry cleaner locations and below the sanitary sewer located within Benjamin Holt Drive. As such, the SVE system extends across the Site on both sides of Benjamin Holt Drive (Figure 2). The SVE treatment equipment associated with the system is located in the treatment system compound in the southwest portion of the Site. The SVE system was in continuous operation from September 1999 through June 2009 and removed approximately 7,500 pounds of PCE over 10 years of operation (Geosyntec, 2013). The mass removal rate decreased significantly within the first few years of operation and remained relatively low thereafter. At the request of the CVRWQCB, optimization of the SVE system was conducted in 2012 and 2013. Based on post optimization soil vapor sampling, closure of the SVE system was requested in System Decommissioning and Well Destruction Work Plan 3 07/18/2014