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Geosyntec Consullants 2017(Geosyntec,2018).The horizontal hydraulic gradient in the A-and B-zones is approximately 0.0025 foot-per-foot and varies depending on the proximity to the groundwater extraction and injection wells that comprise the groundwater treatment system at the Site(Geosyntec,2019). 2.4 Summary of Remedial Actions To date, a combination of soil and groundwater remediation activities have been implemented at the Site to address COC concentrations in the subsurface. A detailed description of historical remedial actions is provided in the FS (Geosyntec, 2015a) and the RAP (Geosyntec, 2015b). In the former source area, interim remedial actions for soil included soil vapor extraction and for groundwater included air and ozone sparging and groundwater extraction and treatment. In addition,an ISCO pilot test using potassium permanganate(KMnO4)was implemented in 2013 at to evaluate the feasibility of ISCO as a remedy for the downgradient impacts to groundwater (Geosyntec, 2014). A majority of the impacts in soil, soil vapor, and groundwater in the former source area have been addressed and current remediation efforts are focused on the area off-site and downgradient of the shopping center as described in Section 2.4 below(Figure 2). To address COC impacts in groundwater off-Site, an interim groundwater remedy comprising of groundwater extraction and treatment operated from 1998 to 2016. Based on the results of the ISCO pilot study, ISCO in combination with groundwater extraction and treatment was identified and selected as the final remedy in the RAP. The design of the final remedy was described in the RD/RA Work Plan(Geosyntec,2015c).The final remedy consists of an ISCO recirculation system with groundwater extraction from the downgradient edge of the plume along Inglewood Avenue, treatment with granular activated carbon (GAC), amendment with KMnO4, and re-injection upgradient into injection wells located along Pacific Avenue (Figure 2). The ISCO recirculation system commenced operation in 2016. In addition to the final remedy, the RAP and the RD/RA Work Plan identify contingency actions that may include additional ISCO injections to address residual impacts at the Site.This Work Plan describes the scope of a contingency action to address residual impacts in the former source area. 2.5 Nature and Extent of Impacts For the purposes of this report,discussion of nature and extent of impacts will focus on the former source area. A more detailed discussion of the historic nature and extent of chlorinated solvent impacts at the Site is presented in the FS (Geosyntec, 2015a) and updated in the most recent groundwater monitoring reports submitted to the CVRWQCB (Geosyntec, 2019). As of the most recent monitoring event(Geosyntec, 2019),the majority of the former source area and upgradient monitoring well sample results were low or below laboratory detection limits for Site COCs in all groundwater zones,except for elevated PCE concentrations in upper A-zone wells MW-006A, PT-I I and CHMW-005A, MW-130A-U, MW-131A-U. Lower A-zone impacts were limited to the area around wells MW-130A-L and MW-131A-L (Figure 3). No impacts were reported in the B-zone wells in the former source area (Geosyntec, 2019). This distribution suggests that laterally the residual impacts are limited to the area around the former release area in Fanner Source Area Injection Work Plan 4 August 08,2019