SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Michael Oliphant . -2 - 26 September 2012 Chevron TAOC TRY stn Street Offsite-West,Tracy Screening Evaluation. Analytical data for 17 soil samples collected from 12 boring locations were evaluated for the Report. TPHc represents a mixture of highly variably composition, and has typically not had descriptive health criteria. However, health criteria for the VOCs and PAHs concentrations reported do exist, and those values are considered for the Screening Evaluation. The only VOC/PAH chemical reported was the PAH compound benzo(g, h, i)perylene detected in the 0 to 10 feet bgs interval and thus was considered a COPC for the Screening Evaluation. • Low concentrations of TPHc previously reported in shallow soil in the 0 to 10 feet bgs interval ranged from non detect (ND) to 850 milligrams per kilogram (mg/kg). Low concentrations of BTEX and some PAH compounds noted at depths at/below upper groundwater (13 to 18 feet bgs) were not considered for the Screening Evaluation. The California Department of Toxic Substances Control (DTSC) Preliminary Endangerment YAssessment (PEA) Guidance Manual (1999)`describes that the 0 to 10 feet bgs"interval is considered appropriate to evaluate potential risk at a site containing affected soil. • Data provided describes development of exposure point concentration (EPC) for the reported detection of benzo(g, h, I,)perylene. Since only a single detection was reported, rather than using the upper confidence level (UCL) of the mean concentration, the concentration detected in soil (0.03 mg/kg) was considered. This approach is consistent with provisions provided in DTSC's PEA Guidance Manual. • The Site is in a predominately mixed residential and commercial area and presently is used for residential and/or vacant land. At this time land use changes are not anticipated. Thus, the Screening Evaluation considered a residential risk scenario which also included the UPRR right-of-way and vacant.land. Potential receptors would be onsite adults or children, which is considered a conservative estimate of risk. • Potential direct exposure to the COPCs in onsite soils by oral ingestion, dermal, and particulate inhalation routes were considered potentially complete exposure pathways in the Screening Evaluation. Based on soil vapor data of shallow soil at the adjacent TAOC TRY 6th Street project with a similar source, and only a single low concentration of a COPC reported, inhalation exposure is assumed to be an insignificant exposure pathway. • Groundwater at the Site, from about 13 to 18 feet bgs_, is not used as a source of drinking water. Based on a City of Tracy ordinance for water quality..parameters unrelated to the historical pipelines, shallow groundwater in the Tracy area is not to be utilized as a source of drinking water. Thus, the potential exposure to groundwater is considered an incomplete pathway. • Toxicity values for benzo(g, h, i)perylene were used to quantitatively estimate potential current and future health impacts. Reference doses are used to estimate non-cancer health hazards and cancer slope factors estimate potential cancer risks. However, a reference dose or cancer slope factor is not available for benzo(g, h, i) perylene. Values for a reference dose (0.06 mg/kg) of a similar PAH compound, acenaphthalene was used as a surrogate to establish/determine a non-cancer health hazard value. A hazard value of 1.6E-05 determined is well below the acceptable non-cancer health hazard quotient of 1. I I