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STATE OF CALIFORNIA GEORGE DEUKMEJIAN Governor <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD- r: <br /> CENTRAL VALLEY REGION <br /> 3443 ROUTIER ROAD <br /> SACRAMENTO,CA 95827-3098 <br /> 4 March 1988 <br /> Mr. Tim Ross <br /> Unocal Corporation r <br /> 2175 North California Blvd. I = <br /> Suite 650 <br /> Walnut Creek, Ca. 94596 <br /> UNOCAL SITE AT PACIFIC AVE. AND ROBINHOOD IN STOCKTON, SAN <br /> JOAQUIN COUNTY <br /> You may proceed with the proposed interim cleanup at the subject <br /> site. The design and implementation of a final remedial action <br /> alternative must be accomplished in compliance with the time <br /> schedule discussed below. The proposal for abandoning monitoring <br /> well No. 1 (MW-1) and replacing it with MW-8 can proceed with <br /> appropriate changes. <br /> According to information received from Kleinfelder and Associates <br /> (KA) the interim cleanup will consist of five extraction wells. <br /> These wells will be constructed directly south of the proposed <br /> building at 25 foot intervals and will be screened across the <br /> water table. Construction and sampling of a deeper monitoring <br /> well has revealed contamination in deeper water bearing zones <br /> yet, the proposed interim extraction system is designed to <br /> capture a segment of the contamination existing in the top <br /> portion of the aquifer only. We feel a more efficient cleanup <br /> plan could be developed with a more complete assessment into the <br /> extent of the contamination. <br /> The KA proposal for abandoning MW-1 and constructing MW-8 <br /> directly to the west must be modified. Prior to abandoning MW-1, <br /> a monitoring well must be constructed to the north of it. The <br /> exact placement and construction details of this well must be <br /> approved by this office prior to construction. This well to the <br /> north may be constructed in lieu of or in addition to the <br /> originally proposed MW-8. Placement of a well north of MW-1 will <br /> provide a greater distance between north-south well placement <br /> thus allowing for a more accurate measurement of the southerly <br /> gradient. In addition a northerly well is needed to confirm the <br /> ground water is not contaminated in this direction also. <br /> After construction of the monitoring well (s) two sets of water <br /> level elevation measurements must be collected at 30 day <br /> intervals before MW-1 abandonment will be considered. <br />