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i <br /> r' <br /> 2255 Airport, Stockton <br /> March, 2006 <br /> Page 2 <br /> limited as rises in DO concentrations were not detected in VW-2-which is 15 <br /> feet south of SW-1. Horizon has calculated a mass of 1,182 gallons of Total <br /> Petroleum Hydrocarbons as gasoline (TPH-g) and 1.1 gallons of benzene left <br /> remaining in the soil, and 37 gallons of dissolved TPH-g, 4.1 gallons of <br /> benzene, and 0.23 gallons of 1,2-dicholroethane (1,2-DCA) in groundwater. <br /> Horizon estimated the rate of migration of the contamination plume in <br /> groundwater at 6.5 feet per year (ft/yr), 7 ft/yr for benzene, and 9 ft/yr for <br /> 1,2-DCA. Two domestic wells and one municipal well were identified on a <br /> map survey within 2,000 feet of the site, but the physical locations of the two <br /> domestic wells have not been verified. Horizon reported that according to <br /> California Water Service (CWS) potable water for residents in the area is being <br /> serviced by CWS. <br /> Based on the result of the pilot test report, E14D concurs with Horizon that <br /> SVE and AS appear to be viable remediation alternatives. To bring the site <br /> toward final closure status, Horizon recommends continual monitoring, and <br /> installing a remediation system for source removal and plume migration <br /> control. Please submit a Corrective Action Plan (CAP) that will evaluate the <br /> most cost-effective remedial alternatives to EHD by May 20, 2006. If you <br /> have any questions contact Jeffrey Wong at (209) 468-0335. <br /> Donna Heran, REHS, Director <br /> Environmental Health Division <br /> . <br /> effr <br /> e ong, Senior REHS Nuel C. Henderson,Jr. PG <br /> /Site Mitigation Unit LOP/Site Mitigation Unit <br /> c: CRWQCB, Central Valley Region —James L.L. Barton, PG <br /> c: Horizon Environmental, Inc. — Rexford K. Smith, PG. <br /> I <br /> i <br />