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petroleum hydrocarbons occur at the site between 17 and 42 feet bgs The performance of the <br /> SVE/AS system is documented in quarterly groundwater monitoring reports <br /> In November 1996, a vacuum vaporizer well system, known as UVB (Underdruck Verdampfer <br /> Brunnen), was installed for groundwater remediation at the site The installation of the UVB <br /> system consisted of overdnllmg existing groundwater recovery well RW3 to install the dual- <br /> screen UVB well for groundwater extraction-infection, and the installation of adjacent <br /> monitoring wells UVB-MW1 and UVB-MW2 to monitor system performance (EA 1997) This <br /> remedial option was selected as it prevented migration from an upgradient offsite source, while <br /> remediating the onsite groundwater hydrocarbon concentrations <br /> IUVB technology was designed and developed by IE GmbH of Germany as a method for the in <br /> situ treatment of groundwater, and was first introduced in the United States in 1992 The UVB <br /> system is an in situ groundwater remediation system which removes petroleum hydrocarbons <br /> using a combination of physical and biological processes The UVB system creates a circulation <br /> cell that transports the mobile, dissolved-phase and residual-phase hydrocarbons to a central well <br /> casing for treatment The treatment methodology is primarily air stripping, and secondarily <br /> bioremediation for the light and middle range hydrocarbon fractions <br /> Between 6 February 1997 and 22 September 2000, a total of 1,890 2 pounds of petroleum <br /> hydrocarbons as gasoline (TPH-g) was removed from groundwater by the UVB system based on <br /> laboratory analytical results, and 821 5 pounds based on field measurements (ETIC 2000a) The <br /> operational measurements of the UVB system showed that it had reached the asymptotic stage of <br /> operation The UVB system was therefore shut down as referenced in ETIC's letter dated 29 <br /> October 2000 (ETIC 2000b) The shutdown of the UVB system was approved by the SJCEHD <br /> in a letter received in December 2000 <br /> i <br /> G 1Proleets%73942VMA5TEM WP%IPR 1204\IPRtcxt doc 5 <br />