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{ 404 WEST FREMONT STREET WKA No. 1628,09 August 31 , 2001 Page 7 F 1 WKA conducted nine groundwater-monitoring events at the site during 1995 through 1997. In November 1997 WKA installed monitoring well MW7 and Vapor Extraction/Air Sparging wells VEWI /AS1, VEW2/AS2, and VEW3/AS3 . Early groundwater samples from MW7 showed low concentrations of petroleum hydrocarbons, but the hydrocarbons have subsequently attenuated to --, non-detectable concentrations, In February 2000 WKA conducted soil vapor extraction and air sparging pilot tests. Test data indicated that both vapor extraction and air sparging are physically feasible at the site. Vapor extraction showed an effective radius of influence of at least 23 feet, and likely greater, using a 7 vacuum pressure of 36 inches H2O and a flow rate of 250 sef n, Air samples collected during the IJ test, however, did not contain significant concentrations of petroleum hydrocarbons. The air- sparging radius of influence was approximately 10 feet. i f On September 12, 2000, WKA advanced three geoprobe borings (HPI , HP2, and MW8) into IJ groundwater at off-site locations northeasterly of the site. One boring was subsequently converted to monitoring well MW8. Groundwater samples obtained from the borings did not contain detectable concentrations of the target analytes (petroleum hydrocarbons and fuel oxygenates). I rl Proposed Scope of Work - An air sparging/soil vapor extraction system is proposed for removal of petroleum hydrocarbons - and VOCs in the saturated zone, vadose zone and unsaturated zone beneath the site. The chief advantage of the combined air sparging/soil vapor extraction system is its ability to remediate residual and adsorbed contamination below and above the water table. Existing vapor extraction wells VEWI and VEW2 and existing air sparging points AS 1 , AS2 and AS3 will be incorporated into the treatment system (Plate 2), 'LJ General Description of Air Sparging System The air sparging system will consist of a 7.5 horsepower, single-phase, 230-volt, 60 hertz industrial duty electrical motor. The air sparging unit will be equipped with a totally enclosed fan cooled , I v uvni L.oee = [<ocrw_ i:.,�, 1; �,:,•.:, Ff ACISOCIAI US INC.