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r ! (YVATt 41" ASSOCIATES I NC . at a property, usually only a few contribute significantly to the total exposure. For a complete exposure pathway to exist, each of the following elements must be present: �.. 0 A source and mechanism for chemical release, 0 An environmental transport medium(i.e., air,water, soil), • A point of potential human contact with the medium, and .1 • A route of exposure (e.g., inhalation, ingestion, dermal contact). Gasoline may migrate from soil to groundwater and may be subjected to groundwater transport. 6o Additionally, gasoline compounds readily volatilize from soil into the ambient air. The potential pathways of exposure to gasoline present in the soils and groundwater generally include ingestion of soil and groundwater, dermal contact with soil, and inhalation of vapors. �,. Site Specific Pathways DIRECT CONTACT WITH SOIL, - Gasoline contaminated soil beneath the site exists beneath an asphalt paved surface. No direct contact with the impacted soil is expected without removing the paving and excavating the soil. v DIRECT CONTACT WITH GROUNDWATER–On November 26, 2003,groundwater was measured at an average depth of 5.9 feet below the site in the eight on-site wells. Access to the wells is protected by bolted metal well boxes and locking well caps. 6" OFF-SITE MIGRATION POTENTIAL TO DRINKING WATER - In 1998, Kleinfelder conducted a sensitive receptor survey within a 2,000-foot radius of the site. Groundwater well construction logs obtained from the Department of Water Resources (DWR)were reviewed to assist in identifying wells located within j! 2,000 feet of the site. According to Kleinfelder's Ground Water Assessment Report, dated April 12, 1998, "Eleven wells were located using the original Well Driller's Reports. Of the 11, two were located within the 2,000-foot perimeter—one is an irrigation well, and the other is a public well. The remaining nine wells are too located outside the 2,000-foot perimeter and are city and privately owned wells. The visual survey revealed an additional five private wells. The owner of the private well closest to the site stated the well was shut down and no longer used." A copy of Kleinfelder's Plate 4 showing the location of the wells is included in 6W Appendix B of this SCM. Historical groundwater monitoring data collected at the site indicate the hydraulic gradient beneath the site is very flat with the gradient direction generally towards the north. Only one of the wells identified by Kleinfelder is located north of the site in a downgradient position with respect to the site. INHALATION OF VAPORS–The potential for inhalation of gasoline vapors at the site involves the ability of the gasoline components to partition from the groundwater into the soil and from the soil into the ambient air. Gasoline contaminated soil beneath the site exists beneath an asphalt paved surface and groundwater was recently measured at an average depth of 5.9 feet below the site in the eight on-site wells. No direct contact with the impacted soil or water and ambient air is expected without removing the paving and excavating the soil. ar Former Cheaper#37 January 29 2004 ATC Project Number 5425847.0037 Page 6