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A S S O C I A T E S I N C o- ow POTENTIAL EXPOSURE PATHWAYS General Pathways of exposure are the means through which an individual may come into contact with a chemical. Exposure pathways are determined by environmental conditions, potential for a chemical to move from one medium to another, and the population's general lifestyles. Although several potential pathways may exist 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: sr... • A source and mechanism for chemical release, • An environmental transport medium(i.e., air,water, soil), • A point of potential human contact with the medium, and • A route of exposure(e.g., inhalation, ingestion, dermal contact). U. Gasoline may migrate from soil to ground water and may be subjected to ground water transport. Additionally, gasoline compounds readily volatilize from soil into the ambient air. The potential pathways of exposure to gasoline present in the soils and ground water generally include ingestion of soil and ground water, dermal �. contact with soil, and inhalation of vapors. Site Specific Pathways r.. DIRECT CONTACT WITH SOIL - Gasoline contaminated soil beneath the site exists beneath an asphalt paved parking lot. No direct contact with the impacted soil is expected without removing the paving and excavating L' the soil. ' DIRECT CONTACT WITH GROUND WATER — On October 20, 2003, ground water was measured at an +•+ average depth of 56.4 feet below the site in the seven on-site wells. Access to the wells is protected by bolted metal well boxes and locking well caps. .L. OFF-SITE MIGRATION POTENTIAL TO DRINKING WATER - In 1998, ATC conducted a sensitive receptor survey within a 2,000-foot radius of the site. Groundwater well construction logs obtained from the t Department of Water Resources (DWR) were reviewed to assist in identifying wells located within 2,000 feet LO of the site. Seven wells were identified within 2,000 feet of the site. The two closest identified wells are located approximately 700 feet west and approximately 900 feet south of the site. According to the information obtained from the DWR, the well located to the west is approximately 176 feet deep and is screened from 165 to 176 feet bgs. The well located to the south is approximately 578 feet deep and is screened from 188 to 578 feet bgs. The five other wells are located at least 1,200 feet northeast of the site. 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 south. Based on information in the San Joaquin County Flood Control and Water Conservation District's Spring 1997 Groundwater Report, the regional groundwater gradient is tot e northeast. Based on distance, topography, groundwater gradient, and subsurface geology, it is unlikely that the W Diesel Performance January 5,2004 ATC Project Number 5462577 Page 4 1..