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FSB-18-99 THU 08.54 AN P. 08 <br /> V 99(THUD IS=18 UNOCAL %-�T NORTH RE TEL:510 94*--,"!81 F, 007 <br /> DRAFT <br /> W'nh regard to the wafer quality objec&ves for orPnic chemicals. the State <br /> Departn=t ofHcalth Services(DHS)has set MCLS for baaene, toluene, cthylb e, <br /> &std xylene,(BTM in drinking waxer of 1 ppb, 100 ppb, 680 pp1h and 1,750 ppb, <br /> IesPecdvely(Cal. Code of Rcgs., cit-22, § 64444)- Although DMS has not yrt set an <br /> MC.for rnethyl-t=Uary-butyl-cdxr(MME), DHS has sex sn We= atsian level of 35 <br /> Ppb(r)HS Manorandum from 103eph P. Browny PRD-,Acting Chie& Water Toxicology <br /> Unit to Alexis M Mae,,P.E., Acdng Supervisor, Standards and Technology Unit, Office <br /> of Drinking Water(February 19, 1991)at P. 4 DHS has adopted a 5 ppb MME <br /> costcer xratinn as a 3=ondwy dam$water andard for uste attd odor. The threshold <br /> odor co-mcwzdon of commerdtai 5005 tc(tnaasuted as total pc rolctsut hydrocarbon <br /> gasoliue, or TPH-M is tater is commonly accepwd to be 5 ppb,with 10 ppb giving a <br /> smong odor. <br /> The following is a brief historical semMWY of PeddOD is site at 1665 Padfic <br /> Avenue in the City of Sumiaon. The site is looted is a com==e a tesidedW area of the <br /> coy and was aa.operating sm v=station from about 1947 to 1988;gas EM was d Pensed <br /> fi'oM two 10,000 gallon capacity USTs. Since dmooHtiou of the stadc'm aril r=wvs+l of the <br /> USTs in 1988,the site bas remabwd vacaw- <br /> The site is tmderiaitt by flood plain sed norm(day,silt and sand)of the <br /> PUestocene Victor Formation. In the vtctpdty of the site,mer in the more <br /> permeable strata of Victor Fortttstion is generally of kXerior 9uafitY(cnacentrativas of <br /> nitrate greater than 45,000 ppb,chloride greats than 300,000 lib,and TDs greaser than <br /> 1,000,OOQ ppb) and is not viewed by local water purveyors as a source of drinking wow. <br /> Lrndedying the V ctor Forestation are the alluvW sediments(clay, silt; sand, and gravel)of <br /> the Plies-Phestocene Laguna Fatmation. Groundwater in the La V=Formation is used <br /> =a3,sively throughout the arra for m=dpal,Wust ial, and agd=Wiral supply_ There <br /> are no water supply wells within Soo tcet of dw site and UK=municipal welts located in <br /> the general area are routinely constructed with atmt,tlar seals which ex wd to deptlu of <br /> 150 to 200 feed so as to exclude the shallower poor guality.grotmdwater in the Victor <br /> Formation. The nearest surface water, a canal which extends eastedty from the Port of <br /> 4 <br />