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-ort-It`FU Note 7671 �� �n� 71- <br /> To <br /> '"N � 41— LSof?�it/�j Health Hazard Assessment <br /> Cia./Dept Co. - <br /> Pnane ai In,Ph.D.,Director _ <br /> rnonae�y(6 z6r-53y8 teSacramento,California 95914 SACRAMENTO <br /> FM e Q S� � YO FaX N e Slicflmenta,California 95912-4010 C V R W 0'C"9 <br /> ay street, 16'"rtoor• M ' 2S OaklandQCa{if gals 44 tf 12_ <br /> RANDUM UULL AWFR <br /> Wimton a.aickox <br /> Agency Sc--v enyux.1. <br /> Q rnor <br /> TO: Phillip S. Isorena <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> 3443RDutier Road, Suite A <br /> Sacramento,Califbrnia 95827-3003 <br /> F°�E�14f: Jat�les�. Catli:sle,D.V.iV[., 4��-P" <br /> Applied Risk,Aasessm t Unit Chief ` <br /> Integrated Risk Assessment Sect" <br /> DATE: April 18, 2002 <br /> SUBJECT. RESPONSE TO COMMENTS ON THE 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) The 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 nig/k.-PAHs. Five other samples from beneath the.tank.wcre 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. Given 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, 1 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 rc-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,d�e(lrrtse facing Coit(o nio u r.L Every CaUforntan aeedf to take immediafe action to reduce energy wnfumption. <br /> Printed"Recycled Paper <br />