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Fost-ti.Fax We 7671 Dom ° n�' '2– • �`� <br /> ni� vF-L— irl Health Hazard Assessment <br /> ta,Sacra ento,Direcor SACRAMENTO <br /> Phone a Phone a�q(/ )zsr-31 t� �?' t•Sacramento,Califoruie 95814 <br /> Pax a 7 b •Sxcnmento,Cagf°ruia 95812-4010 0 V R WOOD <br /> S^ � ` ay Street,1C"Floor• <br /> _ _ .._ _ Oakland <br /> RANDUM JCAA „H i 25 <br /> Winton H.H1d= <br /> Agency Secnal;v <br /> TO: Phillip S. Isorena <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> 3443'Roti ier lt04 Suite A <br /> Sacramento,Ci ifernia 95827-3003 <br /> James G. arlisle,D V. ., Ch <br /> It1ief k <br /> Appli ad,RiskAssessment Unit <br /> Integrated Risk Assessment Sect' <br /> DATE: April 18, 2002 <br /> SUBJECT: RESPONSE TO COMMENTS ON TI-iE HEALTH RISK ASSESSMENT <br /> FORMER LYOTH LOADIND STATION.TRACY, CALIFORNIA. <br /> Three principal issues were identified in an April 20, 2000, memorandum from <br /> Susan Knadle, and again in our January 16, 1002, meeting; 1) The adequacy of the <br /> characterization of the distribution of benzene, 2) The model used to estimate indoor exposure to <br /> volatile compounds,and 3)'fhe alpha level used in calculating the confidence interval for <br /> polycyclic aromatic hydrocarbons (PAHs). These issues arc discussed below: <br /> 1. Four soil samples from the GP-3 area were analyzed for benzene. Benzene was detected in <br /> one of these samples (GP-3)at a depth of 12 feet and a concentration of 0.12 mg/kg. This <br /> sample was also the only one that was positive for total petroleum hydrocarbons (TPH) and <br /> also.contained 36 ing/kg PAHs. Five other samples from beneath the.tank..were analyzed.,for <br /> PAH. All were below 0.2 mg/kg except one that contained 26 mg/kg PAH, The latter was <br /> just a few feet away from GP-3. Givelt the fact that the single sample containing benzene <br /> was below the center of the tank, and that the negative samples surrounding the tank indicate <br /> that significant migration has not occurred, l believe that this constitutes reasonable evidence <br /> that the maximum concentration has been captured and used to assess risk. The fact that <br /> there is a rough correlation between benzene and TPH and that the other samples are <br /> negative for TPH also supports this line of reasoning. Additional sampling reveals that the <br /> only significant concentrations of PAH in this area are at or very near the center of the tank. <br /> 2. Indoor concentrations have been re-calculated using the Johnson and Ettinger(1999)model. <br /> 3. The 0.01 P value in the report was a typographical error. The actual value used was 0.1, <br /> which is the appropriate value for a two-tailed test. <br /> California Environmental Protection Agency <br /> The energy cbelleagc fadng Calt fornia is r"L Every Californian needy m take immediate action to reduce energy Consumption, <br /> Printed on Recycled Paper <br /> 9162553015 => CHEVRON ENC TEL=9258420213 06/05 '02 16:18 <br />