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Lee Higgins -2 - 7 December 2010 <br /> Chevron, TAOC Tracy Rail Yard <br /> Board (Central Valley Water Board) staff is providing regulatory oversight for Chevron's <br /> investigations. A Site investigation workplan was approved by Central Valley Water Board <br /> staff in a 22 May 2009 letter to Chevron, amended 8 March 2010. In conjunction, the DTSC <br /> staff reviewed the workplan and requested that the OVP/TAOC investigation include the <br /> collection of soil vapor samples from onsite locations where elevated concentrations of <br /> petroleum hydrocarbons were previously detected in soil and groundwater. In particular, at <br /> locations along the southern Site boundary where the former TAOC pipeline alignment is <br /> adjacent to residential areas. <br /> The purpose of the current investigation included: <br /> • Additional borings to collect samples where results of previous soil and/or groundwater <br /> samples indicated the presence of total petroleum hydrocarbon (TPH) compounds. <br /> • Drill borings and collect samples from areas lacking data, to evaluate/delineate the <br /> lateral and vertical extent of crude oil affected soil and/or groundwater. <br /> • Complete borings along the projected alignment of the former OVP/TAOC pipelines to <br /> determine the presence of crude oil leaks. Evaluate the extent of any crude oil affected <br /> soil and/or groundwater. <br /> • Submit samples for fuel fingerprint evaluation to determine whether petroleum <br /> hydrocarbons are associated with the historical crude oil pipelines or another source. <br /> • At the request of the DTSC, collect soil vapor samples from borings within areas of <br /> known affected soil along the TAOC pipelines adjacent to the residential <br /> neighborhoods. Vapor samples will be analyzed for TPH compounds of concern <br /> attributable to crude oil, including the volatile organic compounds (VOCs) — benzene, <br /> toluene, ethylbenzene, and xylenes (BTEX) and naphthalene — a polynuclear aromatic <br /> hydrocarbon (PAH) compound. <br /> CURRENT INVESTIGATION <br /> In August 2009 and March 2010, AMEC drilled 32 soil borings within OU's 2 through 5 for <br /> collection of soil and groundwater samples which were submitted for analysis of the TPH <br /> compounds of potential concern. Five borings were completed for collection of soil vapor <br /> samples from depths of five and ten feet below ground surface (bgs) at each location for <br /> analysis of BTEX and naphthalene. One groundwater and six soil samples were submitted for <br /> fuel fingerprint determination to evaluate if the TPH compounds present are related to the <br /> historical crude oil pipelines. <br /> According to AMEC, PAHs are frequently detected in soil and/or groundwater samples, <br /> particularly when elevated TPHc concentrations are present. Since several individual PAHs <br /> are considered to be carcinogenic. When detected, the concentrations are included when <br /> estimating the potential health risk exposure for a site. In accordance with various State and <br /> Federal regulatory health guidelines, when PAHs are present, all values detected are <br /> combined to estimate the overall "additive" health risk for PAHs. When at least one <br /> carcinogenic PAH is detected in a sample, the equivalent is calculated using a toxicity <br /> equivalent factor (TEF) for each PAH present, adjusting the toxicity of carcinogenic PAHs to <br />