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FEB-I8-99 ?HU 09:55 API P. iB <br /> FEB. -11' 99(THU) IS: 18 UNOCAL�T ,NORTH RE TEL-510 941md%81 P. a09 <br /> DRAFT <br /> pump island had been while the third well was positioned at the fb mer location of the <br /> site's second, westerly pump island_ One of the new groundwater monitor' wills was <br /> constructed about 300 feet down-gradient of tate site while the other was positioned oo- <br /> site <br /> and up-gradient, aboin 60 batt southvma at the pair ofvapor cm-action wells. <br /> Analyses of soil sariVies colleaed during the drilling of these wells indicated an absence of <br /> gaSOEm consdWevis in the vicinity of the westaty pump Wand and at the locations of the <br /> two newly inwiled groundwater mvrdtnr wells. Hawevet, in the vicit* of the eLsteriy <br /> PUMP rslane, xYn-g and benzene Frere aeiecred at tas high as 7,300 ppm <br /> and 3.4 ppm, respectively, at a depth of 26 feet;the data indicated tkm conc>,nuv ions <br /> dimini +ed to I20 ppm and 0.083 ppnl,respec&*,at a depth of 51 bees. <br /> In July 19%.two more gr+ ndwaw monitor weRs'were installed southeast and <br /> smuhwest of the site to complete definition of the plug. Water quality data from the <br /> array of nine gro=dwata moeitnr wells shaved that the dissolved phase berme Morley <br /> centered at the loran of the easterly pump island,extem 9ed down-gradient about 120 <br /> feet,no more than 50 to 60 feet off-sine. <br /> Iu Jkwary 1996, recovery of residual petrateum hydrocarbons in the vadose zone <br /> was=bated ted using Sail Vapor Exuaction(SVE)teolnalogy. The SVE system was <br /> operational through November 1996 and recovered an estimated 404 gallons of IFIL-g, <br /> including about two g4a=of Mazene. <br /> Bening in May 1996, MTBE was analyzed for in gun rtedy groundwater <br /> samples from site monkor wells. These analyaea have not detected MTBE in mer <br /> front any site monitor wells. <br /> By letter to petitioner dried Ianuory 9, 1997,County staff concluded that"...the <br /> assessment of the lateral extent of groundwater contamination is complete, the a seam eut <br /> of soil contarzf=tion is complete, and the plums appear to be stable." The County <br /> recommeaded that a feasibility study and convolve action pian (CAF) be submirted, <br /> Quarterly groundwater monitoring ccm6nue, and data in support of the presence of natural. <br /> attenuation be collected. <br /> By letter to the County dated February 7, 1997, petitioner summarized the extent <br /> Of remedial activities undertaken at the site and the findings of its'investigative efforts. <br /> 6 <br />