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2.3 Previous Investigations in the Vicinity Under the RWQCB's oversight, a number of site investigations and regulatory reviews were conducted in the vicinity of the Site. The site investigation results indicate that soil, soil gas, and groundwater samples were impacted with VOCs. Figures 3 and 4 depict the previous sampling locations. Detections of PCE in soil vapor and groundwater samples have been associated with historical dry-cleaning operations in the downtown area (Haley&Aldrich 2019; ECM 2012; Rust and CDM 1994), for example. • Two areas of higher PCE concentrations were identified based on soil gas samples collected from SV-101 and SV-108.SV-101 is near the Site, and SV-108 is in an area with a long industrial history of vehicle maintenance shops and dry-cleaning operations. • From 1989 to 2009, PCE was detected at concentrations up to 41 micrograms per liter (µg/L) in groundwater samples collected from City of Ripon municipal drinking water Well 04 (decommissioned in 2009). The well was located on North Walnut Avenue near the intersection with Pine Street in downtown Ripon, San Joaquin County(Figure 3). • As part of a TCE investigation for the Nestle USA - Beverage Division, Inc Facility Cleanup Program case (GeoTracker Global ID #SL205012989), PCE has been detected in samples from monitoring wells in downtown areas, including M-10A (between 1991 and 2003). PCE concentrations have recently been increasing in samples from monitoring well M-56A (7.8 to 12 µg/L in 2019). • In December 2011, Nestle detected PCE at concentrations ranging from 0.58 to 52 µg/L in grab groundwater samples collected from borings CPT-36, CPT37, and CPT 41, which were located along Pine Street and North Locust Avenue. Based on Nestle's history, PCE does not appear to be a chemical of concern (COC); however, anaerobic degradation of PCE leads to the production of TCE, cis-1,2 dichloroethene, and vinyl chloride, which are Nestle site related COCs. PCE is associated with industrial operations and dry cleaner operations. • In 2019, RWQCB directed Nestle to re-evaluate vapor intrusion pathways. For the evaluation, Nestle installed 17 soil gas probes in downtown Ripon. In addition to Site related COCs, Nestle detected PCE in 16 of the 17 soil gas probes. Nestle detected the highest soil gas PCE concentration (400 micrograms per cubic meter [µg/m3]) in a sample collected from 5 feet below ground surface (bgs) at probe SV-101, which was installed approximately 150 feet northeast of the Site (Figure 4). • In March 2021, the RWQCB initiated an investigation of the PCE source detected in soil gas collected from probe SV-101 and in groundwater samples collected from Nestle monitoring wells, Nestle temporary borings, and City of Ripon municipal drinking water Well 04. This investigation scope includes a sanitary sewer line video inspection, soil gas sampling, conditional sub-slab soil gas, indoor air, and outdoor air sampling, and a limited groundwater investigation at the former Ripon Cleaners. FINAL RIPON PCE INVESTIGATION WORK PLAN.DOCX 2-2 PROJECT NO.631021512