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amec— <br /> TCE <br /> concentrations near the former Decaffeination Building. Approximately <br /> 10 pounds of TCE were removed after three months of operation (Fluor Daniel GTI, <br /> 1998). <br /> The SVE operations removed approximately 200 pounds of TCE, primarily from the area near <br /> the former Decaffeination Building and approximately 690 pounds of chloroform from the area <br /> near the former Chemical Storage building (RUST, 1994c; Fluor Daniel GTI, 1998). <br /> Groundwater Extraction and Treatment <br /> Hydraulic containment of CDCs by pumping at plant production wells, as discussed in Section <br /> 3.1.2, was likely ongoing throughout the entire history of TCE use by the plant. Although there <br /> were no site monitoring wells installed and monitored in the 1950's and 1960's to document <br /> hydraulic gradients, the plant production wells were pumped at rates several times higher than <br /> when N-1 was pumping between 1986 and 1995. In 1994, hydraulic gradients in the Upper <br /> and Intermediate Aquifers, including the B-zone, were towards N-1 beneath the site (RUST, <br /> 1995); that information, in conjunction with documented mass removal rates from N-1 (Table <br /> 2) is an indication that hydraulic containment by N-1 was occurring at an average pumping <br /> rate of 140 gpm. Therefore, it is very likely that hydraulic containment of groundwater beneath <br /> the entire site was established by historical pumping at N-1 and N-3, at average annual rates <br /> that ranged from approximately 239 to 632 gpm (Table 1). <br /> Following the detection of CDCs in water samples from plant production wells, a GAC <br /> treatment system was installed, and groundwater extraction and treatment at N-1 continued <br /> from July 1986 until 1995 when N-1 was replaced with A-zone extraction well EI-1. During this <br /> time, TCE mass recovery rates at well N-1 ranged from approximately 1 —2 pounds per day <br /> (lbs/day) in 1987 and to approximately 0.3 to 0.8 lbs/day in 1993 (Table 2). Approximately <br /> 1,800 lbs of TCE mass were estimated to have been recovered by pumping well N-1 between <br /> January 1987 and August 1993 (RUST, 1994a). Prior to the installation of the GAC treatment <br /> system, removal of TCE from extracted groundwater likely occurred at the water treatment <br /> towers, where influent water was heated to precipitate dissolved carbonates, and a portion of <br /> TCE in pumped groundwater likely volatilized during this process. <br /> After N-1 was decommissioned in 1995, hydraulic containment of A-zone groundwater was <br /> continued by groundwater extraction at nearby wells EW-1 (screened from 99— 119 feet bgs) <br /> and EI-1 (screened from 96 — 116 feet bgs)(in absence of historical pumping records, we have <br /> assumed that the combined extraction rate from wells EW-1 and EI-1 was approximately 140 <br /> to 200 gpm). These extraction wells targeted the depth interval where high TCE <br /> concentrations were reported in samples from nearby monitoring well M-11 A. Groundwater <br /> extraction from EI-1 and EW-1 continued until February 13, 2008, when shallower-depth <br /> extraction wells EU-3 and EU-4 were installed (ECM, 2008a). Both of these wells were <br /> AMEC Geomatrix, Inc. <br /> I:\Doc_Safe\9000s\9837.005\4000 REGULATORY\SCM_01.30.09\1_text\SCM Report Final.doc 15 <br />