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SEQMATRIX <br /> Mr.Robert Mihalovich <br /> Chevron.Euvironmental Management Company <br /> May% W2 <br /> Page 4 T <br /> hydrocarbop,sla it c lly trade and/or fuel tail,from ChevranTexac 's uma OVP <br /> bD.d*p ong the northers btrundary of the site adjacent to the railroad right ofwgy, <br /> 3. .Fourscreen rg,level risk assessments were inc�usitng eitlterm r>rtsum detected <br /> conor 95th percentile upper con,fde�ree limit o tJre ru't7nic.tneen <br /> 053o <br /> UCL, ag a Wosure point concentrations,raid assuming groundr!►,ater ether used as <br /> Mnkirrg water source or not used as a.drinking water sourc4. <br /> No response xequ rod. <br /> 4,"With cx roxrn water samples,it is not apPt�oinri'ate Flo cars tea#S%&A oA the <br /> mean;�r�r.,VOvxibt►ater,.due to the,large.unce4a(aty w s o*s»iall.sar pile <br /> The faxes:a e ee�mg:l�vPC tisk asses�rnent that�npifaj�+. �I ',r not <br /> . techs <br /> 1.2 <br /> C�at; t :The assessment using 9MUCL for$mundwo wasp ri.ed for <br /> compatispn:purposes. <br /> S. In a absenceafa-designadon by the R0gionat T�a#er>�uali�y:Cur�tisril Bthat <br /> dh w hw u►+ r ie rto a beneflad use,I3TSC lERD recomprtnaTs assumfiig all <br /> ground�.;' a pratendd futura di u ki water;sp <br /> Geornatnx:acknowledges that the Regional Water Quality Control Board considers <br /> virtually.a.groundwater as a potential drinking water source and our-screening level risk <br /> evaluation included a scenario where groundwater would potentially be used as future <br /> drinidug water source; In reality,it is extremely unlikely that a dome stieTwatc r well will <br /> t7c ha led at or�near:the property,.which is within the+City of Tzar.. Tlu<Cult of Tracy <br /> it pal a ectian l'I=1<l d)requires.the use ofwatex SWP. hy.-the Cites and <br /> declaze .vrater wells:tp ciiiasti#u#e a public nuisance that; nstabaTO-col satier this <br /> more realistic scenario,Geomatrix also estimated`.risk asooing thatzrDun water is not <br /> ingested. <br /> 6. Acceptable riskforProposition bS and theA&T'oxicsffet Spots Programs are not <br /> applicable to the DISCSite iWitigation Program. In accordance with the National <br /> C'ontinge�ncy.Pi an(7VCP), use Ixl g6 as thepoint,ofdeparture when sling <br /> whether a human receptor is "at risk".asperRiskAssessment GuidanceforSuperfund <br /> {RAGS).- Volumel-Haman.Wealth.Evaluation MWtual,Part B;Development ofR&k» <br /> Based Pireliminury Remediation Goals(PitGs) (U.S EPA.,1991). As stated in 40 C&F <br /> 3110.430: "For known or suspected carcinogens,acceptable exposure levels are <br /> generally concentration levels that represent an excess upper bound life-time.cancer <br /> risk to an individual of between.104 and 1'0 using-JuIbirmation on the relationship <br /> betweeu,dose and response. The 10*4 risk level shall be used us the polat of <br /> departure for determining remediation goals for alternatives when AltAlts are not <br /> available or are not sufficiently protective because of the presence of multiple f <br />