SITE INFORMATION AND CORRESPONDENCE

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- 2- 18 April 2012 Michael Oliphant NFAR— Catellus, Tracy The findings of SAI C's October 2010 human health screening evaluation considered a residential land use scenario for exposure to chemicals of potential concern in onsite soil. The risk evaluation was conducted using a methodology and approach described in the Preliminary Endangerment Assessment (PEA) Guidance Manual, California Environmental Protection Agency, Department of Toxic Substances Control, 1999 (CaIEPA-DTSC). Given that the most of the project lies within a utility corridor, shallow groundwater is unlikely to be used at the Site, so the screening evaluation did not consider a groundwater exposure pathway. SAIC estimated the cancer risk and non-cancer hazard from exposure to onsite soil using a residential exposure scenario, following equations and assumptions provided in the CaIEPA-DISC PEA Guidance Manual. SAIC estimated the exposure routes for incidental soil ingested and dermal contact with soil, inhalation of windblown dust for non-volatile constituents, and inhalation of chemical vapors from soil. The aggregate cancer risk for oral, dermal, and inhalation exposure to onsite soil was 4E-06, which is within the acceptable risk range of 1 E-06 to 1 E-04, and does not present an unacceptable risk for a residential exposure scenario. Given the current Site development, the future onsite use will likely be by construction/trench workers. The aggregate non-cancer hazard was 3E-03 which is well below the acceptable health hazard value of 1. The Report estimated that both the cancer risk and non-cancer hazard indicate the present Site conditions do not pose a health risk for a hypothetical resident. SAIC's review of the California Department of Fish and Game 2009 Natural Diversity Database for wildlife indicates that six threatened or sensitive species in the vicinity. The Swainsons' Hawk reported in 2004 was about 900 feet from the northern property boundary. As noted in the risk screening evaluation, based on the planned use of the property, the Site is not considered suitable habitat for sensitive ecological receptors and that a threat does not appear to exist. Consistent with State Water Resources Control Board (SWRCB) Resolution No. 92-049, Section ill, A through C, SAIC evaluated alternative cleanup technologies and determined that any process other than natural attenuation would be ineffective, infeasible, and disproportionally costly. Residual crude oil concentrations naturally degrade with time, likely over a period of several years. Issues: In the early 1990's, a release of non-hazardous crude oil to soil and groundwater from the historical TAOC and/or OVP pipelines that transected the project, was discovered. Soil and groundwater impacts consist of TPHc constituents. Fuel fingerprint evaluation confirmed the TPH present was consistent residual weathered San Joaquin Valley crude oil. Setting: The Site use, described above and surrounding area currently includes some undeveloped and agriculture land, but has been designated as Urban Reserve 4 in the City of Tracy's General Plan. The General Plan notes that nearby areas will be developed for industrial, commercial, and office uses near Interstate 205. Some low density residential use is noted for areas farther from the Interstate. Source: Historical leaks from crude oil pipeline(s) installed in the early 1900's, and removed from service during the late 1960's to early 1970's. Actions: Field investigations were conducted between 2003 and 2008. • In 2006, 31 soil borings were advanced to collect soil and groundwater samples for TPH determination. Depth to groundwater ranged from approximately S to 15 feet bgs. The results for the soil samples submitted for analysis reported TPHc from ND, to a maximum concentration of 24,000 mg/kg in a sample from a depth of eight feet bgs. Some separate phase crude oil was noted at this same approximate interval. The majority of TPH detections were in samples at depths from 5 to about 13 feet bgs. With one exception of 2,300 mg/kg in a sample from 21.5 feet bgs, analysis of samples from deeper depths of 15 to 29 feet bgs was ND for TPH compounds, and/or did not exceed respective environmental screening levels. Some detection's of benzene, toluene, ethylbenzene, and xylenes (BTEX) and some polynuclear aromatic hydrocarbons (PAHs) were above screening levels, and/or were ND to low concentrations, not exceeding screening levels. Higher concentrations of the TPH compounds coincide with elevated concentrations of TPHc in samples.