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Stantec Addendum Work Plan for Human Health Risk Assessment Former Tosco Bulk Terminal #10013 February 14,2011 COMMENT 1 "We concur with the proposed confidence limit and coverage of the statistical method. However, the UTL method is restricted to the analysis of normally distributed data. To prove that soil or groundwater data are normally distributed, ConocoPhillips may present the data as a semi- log probability plot. The soil and groundwater data may include a considerable amount of censored data. If soil or groundwater concentration data for any chemical being proposed for statistical analysis are not normally distributed and/or consist of a high percentage of non-detects, Central Valley Water Board staff will meet ConocoPhillips to formulate a non-parametric alternative for determining baseline and compliance concentrations for all applicable COCs." RESPONSE: Prior to application of the approved UTL statistical method, Stantec proposes to run the historical data through the USEPA developed ProUCL 4.0 software program. The ProUCL 4.0 software is a widely accepted tool used to address various statistical issues arising in risk assessment studies, in background evaluations, and in background versus site comparison applications. Most of the statistical methods described and recommended in USEPA guidance documents to compute 95% upper confidence limits have been incorporated in ProUCL 4.0. ProUCL 4.0 will help calculate the mean and standard deviation of the data and provide a determination of the normalcy of the data. Stantec proposes to use the outputs of the ProUCL 4.0 software usage to present to the RWQCB to evaluate whether the soil or groundwater data meets USEPA definitions of normally distributed. A USEPA fact sheet for the ProUCL 4.0 statistical software is included as Attachment 3. Additional details and functions of the program can also be reviewed on the USEPA website. Additionally, if through use of the software it is determined that the data are not normally distributed or are deemed censored, the ProUCL 4.0 software is able to recommend and apply several non- parametric testing approaches,which would be presented to the Central Valley Water Board staff for consideration. COMMENT 4: "Although Comment No. 5 in our 30 July letter specifically addressed TBA and methanol, the HHRH must address all applicable CDCs identified in investigation reports prepared for this Site. ConocoPhillips must provide the rationale for COCs deemed not applicable, and cancer risks and hazard quotients must be summed to assess the cumulative risk for exposure to multiple chemicals in the same exposure pathways. ..." RESPONSE:Stantec will consider all detected analytes as potential CDCs in the Tier 1 HHRA and compare them to applicable screening levels. COMMENT 5: "The HHRA Work Plan does not include a discussion about ecological risk assessment. If ConocoPhillips has determined that the remedial strategy will result in little or no effect on wildlife, a section must be included in the HHRA presenting this rationale." RESPONSE: Stantec will consider potential exposures to ecological receptors as part of the Tier 1 HHRH, taking into consideration the selected remedial strategy. The rationale for our conclusions regarding potential effects on wildlife will be presented as part of the HHRH. 4