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In December 1987 to January 1988, six groundwater monitoring wells (OW-1 through OW-6) were installed associated with the UST investigation in AOI 4, and five additional groundwater wells (TW-1 through TW-4 and TP-1) were installed during the ISA in October 1988. One additional groundwater monitoring well (TW-5) was installed in the vicinity of the former UST during Parsons' Remedial Investigation in 2008. Wells OW-1 through OW-6 were subsequently abandoned following regulatory case closure for the UST investigation in 1997. Additionally, well TW-5 was abandoned in 2011 prior to excavation of the surrounding soil impacts at AOI 4 during implementation of the soil removal action workplan. Soil impacts identified during historical investigations led to the soil removal action at the Site, which occurred in late 2011 to early 2012. During the removal action, impacted groundwater was encountered in AOI 3 and 4 in locations where excavations extended below the water table. Floating heavy hydrocarbon product was observed on the groundwater surface during the excavation of AOI 3. The product was found to consist primarily of TPHd and TPHmo, with low concentrations of TPHg, PAHs, and metals. Groundwater samples from AOI 4 were found to contain concentrations of methyl tertiary butyl ether(MTBE) and TPH below the site remedial goals and, therefore, didn't require remediation. Subsequently, the impacts at the Site were split into operable units(OUs); shallow soil was designated as OU 1, and groundwater was designated as OU 2. Following remedial excavation activities, regulatory case closure for OU 1 was granted in May 2013 (DTSC 2013). Six groundwater extraction points (designated EP-1 through EP-6) were installed during backfill operations following the remedial excavation at AOIs 3 and 4. These were placed at a depth of approximately 12 feet below ground surface (bgs), or 4 feet below groundwater. Extraction point locations are provided in Figures 2 through 4. Six ozone injection points (OIPs) were also constructed at the bottom of the AOI 3 excavation at approximately 1I to 15 feet bgs. Each OIP consisted of 1-inch diameter polyvinyl chloride (PVC) riser piping fitted with 1-inch diameter, perforated PVC laterals extending from each riser. Figure 3 shows the locations of the OIPs (designated OIP-1 through OIP-6). As detailed in Parsons' Monitoring Well Completion Report (Parsons 2012a), ten additional groundwater monitoring wells were installed in May 2012 (seven at AOI 3 and three at AOI 4)to serve as compliance monitoring wells during ozone injection. Wells TW-8 through TW-14 were installed around the perimeter of AOI 3, and wells TW-5R (the replacement well for TW-5 that was abandoned prior to soil remediation activities), TW-6, and TW-7 were installed within and downgradient of groundwater impacts noted at AOI 4. Monitoring well construction details for these wells and the five previously-installed monitoring wells are summarized in Table 1. The locations of these wells are provided in Figures 2 through 4. Groundwater monitoring was conducted at AOI 4, and monitoring and remediation via ozone injection was implemented in AOI 3 from June 2012 to June 2014. Details regarding implementation of groundwater remediation can be found in Parsons' April 18, 2012 Groundwater Installation, Monitoring, and Remediation Workplan (GWIMR) (Parsons 2012b) and subsequent quarterly groundwater monitoring reports for the Site. 2