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1 INTRODUCTION <br /> 1.1 Soil Vapor Extraction <br /> Soil vapor extraction (SVE) is a well-recognized and widely used method of remediating <br /> vadose zone soils impacted by volatile organic compounds (VOCs). The SVE process <br /> works by promoting the transfer of VOCs in the vadose zone from adsorbed, dissolved, <br /> or non-aqueous phase within the pore-space of affected soils to the vapor phase. The <br /> SVE process is accomplished by applying a vacuum to vapor extraction wells where the <br /> extracted vapors are conveyed to an above-ground treatment system and removed from <br /> the vapor stream prior to discharge to the atmosphere. Treatment processes for VOCs <br /> may include carbon adsorption, catalytic or thermal oxidation and/or cryogenic <br /> compression. The success of a SVE system is significantly dependent on the airflow <br /> characteristics of the targeted treatment subsurface zone, and the mass transfer <br /> characteristics of the VOCs. TCE and chloroform were the major VOCs) targeted for <br /> removal at the 230 Industrial Avenue (the Site; Figure A.3-1). As a result of TCE and <br /> TCE daughter products detected in soil vapor near the former on-site decaffeination <br /> facility at the Site, Nestle implemented a series of SVE pilot studies and installed SVE <br /> systems beginning in 1986. An overview of the historical operation and effectiveness of <br /> these efforts at the Site are detailed in the sections below. <br /> 1.2 Background Information at 230 Industrial Avenue Site <br /> Nestle initiated SVE activities at the Site in 1986. The initial application of SVE at the <br /> Site was centered in the area of the former decaffeination facility in response to results <br /> of soil gas detections of TCE in this area'. Camp Dresser & McKee (CDM) installed the <br /> first soil vapor extraction wells (VE-1 through VE-5) in 1986. A pilot SVE program was <br /> initiated to test the efficiency of the system in removing TCE from the vadose zone2. <br /> CDM installed two additional vapor extraction wells (VE-6 and VE-7) in the vicinity of a <br /> chemical storage shed in 1992. These two wells were sited in the area of a suspected <br /> chloroform spill. <br /> In 1995, Weiss Associates prepared a Vadose Zone Source Investigation Results and <br /> Remedial Action Plan for the Site 3. This report presented results of recent vadose zone <br /> vapor sampling in the SVE treatment area and developed an approach for remediating <br /> the remaining areas still exhibiting VOC impacts. Weiss Associates recommended three <br /> new vapor extraction wells in the vicinity of the area the highest TCE concentrations <br /> detected in previous soil vapor surveys. <br /> Nestle contracted Fluor Daniel GTI (Fluor Daniel) in 1997 to analyze SVE operational <br /> data and soil vapor sampling data, and to provide recommendations for SVE <br /> enhancement at the Site4. In the September 1997 Revised Soil Vapor Extraction Plan, <br /> Fluor Daniel recommended installing four additional SVE wells (VE-9 through VE12) and <br /> two additional soil gas monitoring points (013-1 and 013-2) (Figure A.3-2). This updated <br /> system was installed in January 1998 and operated through December 1999. In <br /> February 2000, the IT Group proposed discontinuing SVE activities based on laboratory <br /> data which documented concentrations below the shutdown criteria established by the <br /> California Regional Water Quality Control Board (RWQCB) Central Valley Region. <br /> The shutdown criteria established by the RWQCB required that soil vapor could not <br /> exceed 350 parts per billion by volume (ppbv) (1881 pg/m3) for TCE. Soil gas samples <br /> collected from wells VE-9, VE-10, VE-11, and VE-12 during the pulsed operation period <br /> showed that TCE was the only chlorinated VOC detected, with the highest concentration <br />