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M. Scott Mansholt -2 - 22 May 2009 <br /> Chevron <br /> TAOC 6th Street Tracy Rail Yard <br /> California Regional Water Quality Control Board, Central Valley Region (Central Valley Water <br /> Board) staff will provide regulatory oversight for Chevron's investigation activities associated <br /> with the Site. According to the Workplan Site map, the OVP extends approximately 400 feet <br /> north into and ends at the approximate center of OU-2. The TAOC pipelines extend southeast <br /> to northwest approximately 1,750 feet along the southern boundary of OU-2 and 3, and <br /> crosses beneath the SPRR tracks. From this point, the TAOC lines continue approximately <br /> 800 feet into/through the southern part of OU-5 continuing west offsite into the adjacent <br /> residential neighborhood. <br /> PROPOSED SITE INVESTIGATION <br /> According to the Workplan, AMEC's proposed boring and sampling locations are intended to <br /> investigate: a) offset borings where previous soil/groundwater samples results indicated the <br /> presence of total petroleum hydrocarbon (TPH) compounds; b) drill borings within areas <br /> lacking data that are between earlier borings, in order to evaluate the lateral and vertical extent <br /> of affected soil and/or groundwater; c) drill exploratory borings along the projected alignment <br /> of the former OVP/TAOC pipelines to determine if crude oil leaks may have occurred and if <br /> affected soil and/or groundwater is present; and, d) collect soil vapor samples from borings <br /> with known affected soil that are near the TAOC pipelines and adjacent to the residential <br /> neighborhoods. <br /> AMEC proposes drilling 26 onsite soil borings within the five OUs for collection of soil and/or <br /> groundwater samples to characterize the affected areas and to determine if petroleum <br /> hydrocarbons present at the Site are related to the historical pipelines. Samples collected will <br /> be submitted for analysis of the Site petroleum hydrocarbons of concern attributed to crude oil, <br /> including volatile organic compounds (VOCs) and polynuclear aromatic hydrocarbons (PAHs). <br /> Samples will be submitted for fuel fingerprint evaluation to determine whether petroleum <br /> hydrocarbons detected are associated with the historical OVP - TAOC pipelines or possibly <br /> attributable to another source. <br /> Analytical results for samples from the earlier investigation reported detections of <br /> tetrachloroethene (PCE), trichloroethene (TCE), naphthalene, and low concentrations of other <br /> VOCs present in soil and groundwater samples from borings in OU-2. These VOCs were not <br /> associated with the transport of crude oil in the historical pipelines. Five borings will be drilled <br /> for collection of soil vapor samples as outlined above and submitted for determination of <br /> benzene, toluene, ethylbenzene, xylenes, and naphthalene. <br /> Based on the field observations and analytical results, additional borings may be drilled to <br /> further delineate the extent of affected soil. Central Valley Water Board staff concurs with <br /> AMEC's proposal to conduct the Site investigation described in the Workplan. <br /> By 5 November 2009, please submit the soil and groundwater investigation report. <br />