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amec�9 <br /> well were reported to contain TCE, cDCE, and vinyl chloride at concentrations ranging from <br /> 7.1 — 27 pg/L, 3 — 10 pg/L and 2.6— 10 pg/L, respectively, with the highest concentrations <br /> reported in April 2008, before steadily decreasing to the lowest concentrations in September <br /> 2008, based on monthly sampling (ECM, 2008b). <br /> Nestle replaced the Kiernan well with a deeper well installed beneath the Corcoran Clay in <br /> August 2008. Depth-discrete sampling was conducted during well replacement. No COCs <br /> were detected in the samples collected above the Corcoran Clay at depths of approximately <br /> 80 and 120 feet bgs (Figure 36). Five groundwater samples were collected beneath the <br /> Corcoran Clay, at depths of approximately 220, 282, 305, 322 and 342 feet bgs (Figure 36). Of <br /> these samples, those from depths of 282 and 305 feet bgs were reported to contain TCE and <br /> cDCE at total COC concentrations of 2.74 pg/L and 0.59 pg/L (cDCE only), respectively. <br /> These detections are likely related to the former Fiscalini irrigation well 25, which was a <br /> conduit well to the Lower Aquifer; it was decommissioned by Nestle in May 2008. <br /> 4.6.6 Timing and Location of Offsite TCE Releases <br /> There are three reported areas of industrial sewer discharge: 1) industrial sewer leaks, as <br /> discussed in Section 3.6, 2) direct infiltration of untreated industrial wastewater (Section 4.3.2 <br /> and 4.5.2), and direct discharge of industrial wastewater to the Stanislaus River (Section <br /> 4.5.2). In North America, TCE was the industrial solvent of choice in the 1950's and 1960's <br /> particularly for metal fabrication before 1,1,1-TCA became more popular due to its lower <br /> toxicity (Mohr, 2001). Prior to the 1950, TCE was the preferred solvent for dry cleaning (Mohr, <br /> 2007). It is likely that and older dry cleaning operations and manufacturing operations in Ripon <br /> used TCE and likely discharged TCE to the industrial and sanitary sewer systems. <br /> Additionally, discharge of water containing TCE to the industrial sewer system reportedly <br /> occurred between 1957 and 1970 from the former Nestle facility (RUST, 1994a); it is unknown <br /> whether TCE or other COCs have recently been discharged by other industries to the sanitary <br /> or industrial sewer. <br /> Sewer Leaks: Discharge from the industrial sewer can explain the distribution of TCE in B- <br /> Zone wells. Vapor impacts from sewer line discharges provide a likely explanation for the <br /> distribution of CDCs. Non-aqueous phase (vapor and liquid) releases of PCE have been <br /> associated with widespread groundwater contamination throughout the Central Valley (Izzo, <br /> 1992); similarly, the industrial sewer in Ripon is a likely mechanism of discharge. By <br /> comparison, discharges of TCE from the industrial sewer appear to have also affected <br /> groundwater. It is unknown whether historical or recent dry cleaners in Ripon discharged PCE <br /> to the sanitary or industrial sewer system, although the detections of PCE at municipal supply <br /> well MW-4 have been attributed to a dry cleaner release on Main Street (RUST, 1994a), so the <br /> AMEC Geomatrix, Inc. <br /> hDoc_Safe\9000s\9837.005\4000 REGULATORY\SCM_01.30.09\1_text\SCM Report Final.doc 49 <br />