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V 3.0 Contaminant Fate and Transport The data collected through investigations and testing indicates that the site poses minimal risks to human health and the environment because the petroleum hydrocarbon plume has stabilized and passive bioremediation is occurring at the site. To further support this conclusion, a contaminant fate and transport model was performed. The model was used to simulate the transport of BTEX constituents through the saturated zone to a downgradient imaginary well at the southwestern property boundary. The contaminant fate and transport model documentation is L. presented in Appendix D. 3.1 Pathways of Exposure 60 The Stockton Service Center is located on the southeast corner of the intersection of West Main Street and Los Angeles Street. As shown on Figure 8, the L" site is located within one-quarter mile of the McCormick-Baxter Superfund site and the Port of Stockton. LO The most likely exposure pathway for contamination to reach human receptors is via domestic wells. This exposure assessment not only focusses on the existing extent of the plume, but also on the area that may be influenced by the plume in the ~ future. Historical monitoring has shown that the primary direction of groundwater flow is to the southwest (Figure 9). Figure 8 shows the locations of drinking water L' wells nearest to the site. There is only one known drinking water well within 0.5 miles of the site, located at 215 South Los Angeles Street. Based on historic Le monitoring data, this location south-southeast of the site is not downgradient of the plume. Table 1 presents a summary of information for the four drinking water wells LO shown on Figure 8. The data indicates there are no existing drinking water wells within 0.5 miles downgradient of the property. Site conditions preclude direct contact (dermal), inhalation of volatile emissions, L' or ingestion of contaminated dust. The entire site is covered with asphalt paving which prohibits exposure to contaminants via inhalation, dermal contact, and >`. ingestion routes. The site is completely surrounded by a 6-foot chain link fence topped with barbed wire. Thus, site conditions minimize onsite exposures from petroleum hydrocarbons in the groundwater to District employees and the general public. Furthermore, East Bay Municipal Utility District has no intention of selling the site in the future. As stated in the Introduction section of this report, the site 9687 Fast Bay Municipal Utility District 40429700.fcr 10 Final Closure Report 1� it