ARCHIVED REPORTS HUMAN HEALTH SCREENING EVALUATION

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' Human Health Screening Evaluation Surland Homes—Bridle Creek February 12,2009 2. EXPOSURE PATHWAYS AND MEDIA OF CONCERN An early step of the screening evaluation process is to construct a CSM for the site. The CSM identifies the on-site contaminant sources, release mechanisms, transport media, exposure pathways, exposure routes, and potential future human receptors associated with the site. An on- site residential land use scenario was evaluated for this site as required in the PEA Guidance Manual. The CSM for this site is shown on Figure 3. The 2003 DTSC letter noted that a residential exposure scenario risk assessment may not be protective of construction worker exposure. Consequently, this HHSE also includes a construction worker exposure scenario utilizing the same data set as the residential exposure assessment. The CSMP rovided in the 2006 SAIC work plan identified soil ingestion and soil dermal contact exposure pathways. As discussed below, the groundwater exposure pathway is considered 1 incomplete. The inhalation of vapors and dust emissions was also considered an incomplete exposure pathway based on comments from DTSC noting that site data collected did not warrant quantitative evaluation of indoor air exposures. However, naphthalene was detected in two soil samples during the 2007 investigation, and inhalation of dust and vapor pathways were therefore evaluated in this HHSE for both the residential and construction worker exposure scenarios. The groundwater exposure pathway was eliminated based on a City of Tracy ordinance prohibiting installation of private water-supply wells. The closest surface water is 1/2 mile south (up gradient) of the site; therefore, the surface water exposure pathway is not complete, and groundwater and surface water exposure routes were not evaluated quantitatively in this HHSE (see Figure 3). 3. CONSTITUENTS OF POTENTIAL CONCERN AND EXPOSURE CONCENTRATIONS I The site characterization studies conducted to date indicate that on-site soils are affected by low levels of benzene, toluene, ethylbenzene, and total xylenes (BTEX), and polynuclear aromatic hydrocarbons (PAHs). The DTSC requested that exposure to metals be included in the HHSE. SAIC and CEMC consider that the presence of crude oil in the subsurface does not contribute to increased concentrations of metals in soil, and presented data to support this position in a May 2007 letter (SAIC, 2007). Nonetheless, the DTSC requested an evaluation of risk associated with exposure to metals, and that evaluation has been included in this HHSE. The area of crude- oil affected soils is shown on Figure 2. Site-related groundwater investigations have shown that groundwater has not been affected much beyond the former location of well TW-2. Groundwater samples from wells TW-1 and TW-3 did not exhibit detections of BTEX or PAHs, and only low concentrations of TPH (Appendix B). Samples of soils potentially affected by historic on-site, crude-oil pumping operations were collected and analyzed for TPH quantified as crude oil (TPHc). The samples were also analyzed for BTEX and PAHs, critical hydrocarbon constituents of crude oil identified in the PEA ' Guidance Manual. The samples were also analyzed for metals as part of the 2007 investigation. The COPCs for the site were identified during the site characterization process. All analytes detected in at least one sample were included in the HHSE. Analytes that were not detected in any sample—and therefore not considered COPCs—are benzene, acenaphthylene, ' 4 =ai In From Science to Solutions