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amec— <br /> Ripon. <br /> Note: This conclusion may have been representative for the regional <br /> groundwater flow system, but groundwater flow to depths of at least 200 feet bgs <br /> beneath the Site would have been controlled by pumping at the onsite production <br /> wells. These early assumptions on historical groundwater flow established in the RI <br /> are inconsistent with known historical water use in Ripon and have formed the <br /> basis for earlier conceptual models of TCE migration beneath the Study Area, <br /> leading to serious misconceptions about how CDCs came to be detected in <br /> groundwater samples collected south and west of the Site. <br /> • The water table (B-unit) has been impacted by higher concentrations of TCE <br /> (above 1,000 pg/L) southwest and offsite of the former Nestle plant (based on <br /> groundwater samples from well M-813 at 519 Stockton Avenue near the corner of <br /> 4th Street and Stockton Avenue). The highest concentrations of TCE reported for <br /> samples collected from onsite monitoring wells were from a deeper monitoring well <br /> (M-1 A; 101 — 121 feet bgs), near former plant well N-1, where a groundwater <br /> sample from this well was reported to contain TCE at a concentration of <br /> 10,000 pg/L in July 1987 (RUST, 1994a). Groundwater samples from all other Site <br /> wells were reported to contain TCE, but at concentrations that were generally less <br /> than 100 pg/L. <br /> • The distribution of TCE in the A-level and Intermediate Aquifer water bearing zones <br /> was greater in areal extent than for the B-Aquifer, but COCs were typically reported <br /> at lower concentrations, and the breakdown products of TCE in the deeper zones <br /> indicates that TCE was degrading naturally. <br /> Although not a specific conclusion of the RI Report, the six phases of investigations included <br /> the collection of six soil samples from depths ranging from 15 to 40 feet bgs, including three <br /> samples from near the former Decaffeination Building (the soil boring for VE-4) and three <br /> samples from near the former chemical storage building (the soil boring for VE-5). Of these <br /> soil samples, the highest concentrations of COCs were chloroform at concentration of <br /> 0.41 milligrams per kilogram (mg/kg) from a depth of approximately 15 feet bgs at VE-5; the <br /> highest TCE concentration reported was 0.04 mg/kg from approximately 40 feet bgs at VE-4 <br /> (RUST, 1994a). None of the soil or groundwater samples were reported to have TCE <br /> concentrations that would be indicative of non-aqueous phase liquid (NAPL). <br /> Post-Ri Characterization Activities <br /> A fourth soil vapor survey was completed in July 1995 after the plant was decommissioned <br /> and the Decaffeination Building was demolished. The survey targeted the vadose zone <br /> beneath the former Decaffeination Building, the Chemical Storage building, and the <br /> 519 Stockton Avenue offsite area. Elevated levels of TCE were reported for soil vapor samples <br /> collected from beneath the former Decaffeination Building area, where vapor concentrations <br /> as high as 1,500 pg/L were reported. <br /> At the time the RI Report was completed, there were no onsite wells deeper than <br /> approximately 121 feet (M-1 A; note M-6 cluster wells are considered to be offsite in this SCM). <br /> AMEC Geomatrix, Inc. <br /> hDoc_Safe\9000s\9837.005\4000 REGULATORY\SCM_01.30.09\1_text\SCM Report Final.doc 12 <br />