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• <br /> ADDENDUM TO WORKPLAN FOR SOIL CONTAMINATION INVESTIGATION AT 1500 <br /> SHAW ROAD, STOCI:TON, CA - DATED JANUARY 12, 1993 <br /> Prepared by <br /> No. J. Hunter & Associates <br /> April 15, 1993 <br /> PURPOSE OF ADDENDUM: <br /> To place four (4) soil borings an abo,/e site , and complete as <br /> groundwater monitoring wells. Recent investarative work <br /> performed under the above workplan revealed the presence of <br /> hydrocarbons below 45 ' , which was the approximate depth of the <br /> water table during the Spring of 1986. <br /> BRIEF REVIEW OF RECENTLY COMPLETED WORK: <br /> On February 1 & 2, 1993, five (5) soil borings were placed at the <br /> locations shown on the attached Exhibit A - thev are Ldentiiied <br /> as SB-1 , SS-2, etc. Total depths are indicated ne:t to the aiger <br /> • hale symbol . Each soil boring was continously cored using wire- <br /> line operated equipment; selected samples were screener with a <br /> PID meter , & cores were retained at 5 ' intervals from 11 bgl to <br /> total depth; they were briefl / described, prop2r1y preserved and <br /> preserved pending transport to the laboratory for anal .rsis. <br /> Refer to Exhibits BrC,D,E,,& F for details of that wore. <br /> Upon completion of augerzng operations, the soil samples were <br /> transferred under proper chain of castody to FGL laboratory, wz th <br /> instructions to test for STEX qy TPH-G. The results of that <br /> analysis is summarized on Table V. <br /> A review of that analysis revealed that measureabl a amounts of <br /> petroleum hydrocarbon components we-e aetected in all 3 sa;. 1 <br /> bearings, and below 45 'bgl , (Spring 1986 water tabic, ) in SOLI <br /> borings #2, 3, & 4. The levels of contamination wera generally <br /> highest in the sandier sediments. No water was encountered in <br /> any of the soil borings. <br /> As a result of the above work, it is apparent tnat contamination <br /> has migrated downward from the site of the removed UST, and is <br /> present at depths below recent high water levels. It is possible <br /> that the groundwater may have been degrades, although invest- <br /> igative work to date has not determined if that is the case. <br /> Because contamination was measured in all 5 o+ the soil borings, <br /> work to date has not defined either- the vertical or horizontal <br /> • limits of the plume, and additional worK is reauared. <br /> Therefore, it is proposed to place four .43 additional zoi l <br /> 1 <br />