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r <br /> STATF AF f`AI IFORNIA -FnvirnnmPntA Prnrnn AgAnPV V <br /> PFTF rnvfbrnnr <br /> ~CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD liEA!_T}1 "ate <br /> CENTRAL VALLEY REGION ; ,.. �; ct,1�i,F — - <br /> 3443 Routier Road,Suite A e <br /> Sacramento,CA 95827-3098 e 4 p l }. O � <br /> PHONE:(916) 255-3000 No! 21 <br /> FAX: (916) 255-3015 rn <br /> 24 January 1994 <br /> = X3(.11 <br /> Mr. Robert Boust o a <br /> Unocal Refining and Marketing Division <br /> Unocal Corporation -` <br /> P. O. Box 5155 <br /> San Ramon, California 94583 <br /> OPERATIONAL HISTORY, FORMER UNOCAL BULK PLANT, PORT OF STOCKTON, <br /> SAN JOAQUIN COUNTY <br /> Thank you for your letter of 20 December 1993 which provided a summary of the operational <br /> history of the subject site. My comments are presented below. <br /> 1. Your letter states that the northeast section of the site was subleased by ST Services, ST <br /> Services installed a vapor recovery unit (VRU) and apparently an underground tank, and the <br /> VRU still exists at the site. Please submit a map with a convenient scale showing the <br /> locations of the VRU and the alleged underground tank. Since ST may have installed the <br /> alleged underground tank during the term of the sublease, why is there an uncertainty <br /> regarding its existence? I request that you provide me with more information about the <br /> underground tank. <br /> 2. Your letter states that the 10,000- and 20,000-gallon tanks constructed in the mid-1970s at <br /> Unocal were predominantly used to store diesel. Since the tanks were not used exclusively <br /> for storing diesel, what other fuel products or chemicals were stored in these tanks? <br /> Kleinfelder's September 1988 Problem Assessment Report stated that the 10,000-gallon tank <br /> contained stoddard solvent at the time of the investigation. <br /> The report also showed that the soil samples from all monitoring well (MV) borings except <br /> MW-1 contained trans-1,2-dichloroethylene (trans-1,2-DCE) and trichlorethylene (TCE). <br /> The ground water sample from MW-5 contained 20 µg/l of 1,2-dichloroethane (1,2-DCA). <br /> The maximum contanimant level for drinking water for 1,2-DCA is 0.5 ,ug/1. Trans-1,2- <br /> DCE, 1,2-DCA, and TCE are all degradation products of tetrachloroethylene (PCE). The <br /> Board's investigations of dry cleaners have shown that some facilities which have used only_. <br /> stoddard solvent as a dry cleaning agent are showing contamination by PCE or its breakdown <br /> products. The investigations also suggest that some stoddard solvent formulations contain <br /> PCE. Thus, Unocal is a potential source of the chlorinated hydrocarbons which were <br />