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fi{ 404 WEST FREMONT STREET <br /> '':'% WKA No. 1628.09 <br /> k=, August 31, 2001 <br /> Page 7 <br /> 1 WKA conducted ninegroundwater-monitoring events at the site during 1995 through 1997. In <br /> November 1997 WKA installed monitoring well MW7 and Vapor Extraction/Air Sparging wells <br /> VEWl/ASI, VEW2/AS2, and VEW3/AS3. Early groundwater samples from MW7 showed low <br /> >a concentrations of petroleum hydrocarbons,but the hydrocarbons have subsequently attenuated to <br /> 3 non-detectable concentrations. <br /> In February 2000 WKA conducted soil vapor extraction and air sparging pilot tests. Test data <br /> indicated that both vapor extraction and air sparging are physically feasible at the site. Vapor <br /> extraction showed an effective radius of influence of at least 23 feet, and likely greater,using a <br /> vacuum pressure of 36 inches H2O and a flow rate of 250 scfm. Air samples collected during the <br /> test, however, did not contain significant concentrations of petroleum hydrocarbons. The air- <br /> sparging radius of influence was approximately 10 feet. <br /> On September 12, 2000, WKA advanced three geoprobe borings (HP 1,HP 2, and MW8) into <br /> groundwater at off-site locations northeasterly of the site. One boring was subsequently <br /> converted to monitoring well MW8. Groundwater samples obtained from the borings did not <br /> contain detectable concentrations of the target analytes (petroleum hydrocarbons and fuel <br /> oxygenates). <br /> Proposed Scope of Work <br /> An air sparging/soil vapor extraction system is proposed for removal of petroleum hydrocarbons <br /> and VOCs in the saturated zone,vadose zone and unsaturated zone beneath the site. The chief <br /> advantage of the combined air sparging/soil vapor extraction system is its ability to remediate <br /> residual and adsorbed contamination below and above the water table. Existing vapor extraction <br /> wells VEWI and VEW2 and existing air sparging points AS 1,AS2 and AS3 will be incorporated <br /> into the treatment system(Plate 2). <br /> .1 <br /> General Deseription of Air Sparging System <br /> `�- The air sparging system will consist of a 7.5 horsepower, single-phase, 230-volt, 60 hertz industrial <br /> - duty electrical motor. The air sparging unit will be equipped with a totallyenclosed fan cooled <br /> r-�J <br /> IOWA ACX KUHL <br /> INC <br /> k�E <br />