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UNOCAL <br /> Page 3 <br /> NPI-22, NP1-111, NP2-60 and NP2-116 all of which have lower groundwater <br /> contaminant concentrations. <br /> Quarterly sampling of the monitoring wells must continue and analysis for <br /> oxygenates using EPA Method 8260 must be performed. In addition, a work <br /> plan to define the lateral and vertical extent of the soil and groundwater <br /> contamination should be submitted by November 15, 1999. <br /> Vapor extraction and air sparging have proven to be effective methods of <br /> remediation in areas of Stockton. PHS/EHD recommends on site installation of <br /> these types of wells be included in the above requested work plan so that <br /> feasibility tests for these remedial alternatives can be conducted. <br /> If you have any questions contact me at (209) 468-3449. <br /> Donna Heran, REHS, Director <br /> Environmental Health Division <br /> --rYkAA1_ � <br /> Margaret Lagorio, Supervising REHS <br /> Site Mitigation Unit <br /> c: CVRWQCB - Mark List <br /> ARCADIS Geraghty & Miller -Dr. Stephen Cullen <br /> UNOCAL - Bob Boust <br /> SJCADA - David Irey <br />