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Ms. Shelby Lathrop - 2 - 18 January 2011 <br /> Former Tosco Bulk Terminal No. J13 <br /> Our comments are presented below. <br /> 1. We concur with ConocoPhillips' proposal to prepare an HHRA. However, we do not concur <br /> with ConocoPhillips' assessment that an evaluation of the risk presented by groundwater is <br /> not warranted since there is no current or anticipated potable use. The Water Quality Control <br /> Plan for the Sacramento River and San Joaquin River Basins (Basin Plan) states that the <br /> existing and potential beneficial uses of groundwater in the Site vicinity include Industrial <br /> Service Supply and Industrial Process Supply. In addition, the Port of Stockton <br /> communicated its intention to develop the area south of the Site. As such, potential indoor <br /> and outdoor exposure pathways for groundwater that merit evaluation include ingestion, <br /> dermal contact, and inhalation of volatiles. <br /> 2. The HHRA Work Plan contains no discussion about evaluating data from soil or soil gas. <br /> Evaluation of soil and soil gas data is necessary to assess the risk to construction workers <br /> and the migration of volatile chemicals from soil to indoor air. If ConocoPhillips considers <br /> data from these media to be unusable for this assessment, the rationale must be presented <br /> in the HHRA Work Plan. <br /> 3. Page 4 of the HHRA Work Plan proposes to apply the upper tolerance limit (UTL) statistical <br /> method to determine whether 95% of the dissolved concentrations of TBA fall below the <br /> UTL with 95% confidence. We concur with the proposed confidence limit and coverage of <br /> the statistical method. However, the UTL method is restricted to the analysis of normally <br /> distributed data. To prove that soil or groundwater data are normally distributed, <br /> ConocoPhillips may present the data as a semi-log probability plot. The soil and <br /> groundwater data may include a considerable amount of censored data. If soil or <br /> groundwater concentration data for any chemical being proposed for statistical analysis are <br /> not normally distributed and/or consist of a high percentage of non-detects, Central Valley <br /> Water Board staff will meet ConocoPhillips to formulate a non-parametric alternative for <br /> determining baseline and compliance concentrations for all applicable CDCs. <br /> 4. Although Comment No. 5 in our 30 July letter specifically addressed TBA and methanol, the <br /> HHRA must address all applicable COCs identified in investigation reports prepared for this <br /> Site. ConocoPhillips must provide the rationale for CDCs deemed not applicable, and <br /> cancer risks and hazard quotients must be summed to assess the cumulative risk for <br /> exposure to multiple chemicals in the same exposure pathways. Total petroleum <br /> hydrocarbons as diesel (TPHd) was detected at 1,900 micrograms per liter (Ng/L) in <br /> groundwater monitoring conducted in September 2010. For assessing the risk presented by <br /> TPHd, we understand that this compound is generally identified by the carbon range of a <br /> middle distillate which is C10-C24- <br /> 5. The HHRA Work Plan does not include a discussion about,ecological risk assessment. If <br /> ConocoPhillips has determined that the remedial strategy will result in little or no effect on <br /> wildlife, a section must be included in the HHRA presenting this rationale. <br /> Pursuant to ConocoPhillips' previous requests, an outline of our preferred presentation of the <br /> HHRA is attached. By 14 February 2010, please submit a revised HHRA Work Plan that <br /> addresses the comments enumerated above. <br />