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TAOC 6th Street Property -2 - 7 February 2014 Human Health Screening Evaluation crude oil pipelines, including the adjacent separate off-site projects are being conducted with regulatory oversight by Central Valley Regional Water Quality Control Board staff (Staff). For the most part, petroleum hydrocarbons in soil and groundwater have been delineated primarily on the Site property. On-site, petroleum hydrocarbons in soil and groundwater are outlined primarily along the trace of the former OVP/TAOC alignments. However, petroleum hydrocarbons leaks attributable to the historical crude oil pipelines extend off-site to the east, south, and west of the Site. The off-site investigations are being addressed separately with regulatory oversight provided by Staff. Depth to groundwater is approximately 12 to 21 feet below ground surface (bgs) and the gradient is toward the north-northwest. Human Health Screening Evaluation Since the depth to groundwater occurs at about 12 to 21 feet bgs, dermal contact with the water in trenches is unlikely in the event of future redevelopment. As such, the shallow groundwater pathway was considered incomplete and thus was not evaluated as a potential exposure pathway. The following residential exposure routes were quantitatively evaluated: • Incidental ingestion of soil. • Dermal contact with soil. • Inhalation of wind-blown dust (non-volatile constituents). • Inhalation of chemical vapors from soil (volatile constituents). The potential also exits for migration into indoor air from chemicals detected in soil vapor if OU-2 and OU-5 are redeveloped with buildings. Therefore, potential future residents and commercial/industrial workers in these two units were evaluated for inhalation of vapors in indoor air. Results of groundwater samples collected from Site borings reported total dissolved solids (TDS) values at or above drinking water standards to over 27,000 mg/L. A City of Tracy municipal ordinance prohibits the use of the shallow aquifer for domestic purposes and all new developments are required to use a water supply provided by the City. According to AMEC's HHESE report, the non-cancer hazard index and cancer risk estimate for each receptor evaluated was well below the de minimus target levels of 1 and 1 E-06 (i.e., one in one million) respectively for the OU-2 investigation area. The non-cancer hazard and cancer risk values estimated are below acceptable values established by California Environmental Protection Agency (CaIEPA) and United States EPA agencies. Within OU-5, the non-cancer hazard index for each receptor evaluated was well below the target level of 1 for potential exposure. However, the estimated cancer risk at 7E-05, 1 E-05, and 3E-04, for commercial/industrial, construction workers, and residents, respectively, were above the acceptable risk threshold of 1 E-06. This unacceptable cancer risk is attributed entirely to elevated concentrations of polyaromatic hydrocarbon (PAH) compounds reported in the five feet bgs sample from boring TRY-29. According to the HHESE, if the risk exposure is re-evaluated without using the TRY-29 PAH results, the non-cancer hazard index and cancer risk for each receptor evaluated were well below the de minimus target levels of 1 and 1 E-06, respectively, including the residential scenario. AMEC's report concluded that...site-related chemicals are unlikely to result in unacceptable non- cancer hazards or cancer risk if future exposure to soil located at TRY-29 is mitigated. Mitigation is only applicable if OU-5 is redeveloped for unrestricted commercial or residential land use evaluated