SITE INFORMATION AND CORRESPONDENCE_FILE 1

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i and human receptors. Once the significant pathways .were identified, these \ pathway end points were analyzed to identify receptor locations. Finally, these pathways were assessed to determine expected indicator chemical concentrations at the receptor resulting from indicator chemical concentrations on-site. The reciprocal relation is then used to determine what acceptable contaminant concentrations may remain on-site based on the ARAR chosen. 4.1 Source Characterization Based on site investigations, the spill sites at the former AFPC site are located beneath and surrounding a maintenance shop. The initial focus of the site investigation was an apparent leak from a 10,000 gallon underground diesel tank located on the west side of the building. Subsequent site investigation have shown the presence of two, apparently separate sources of subsurface diesel contamination originating from both the eastern and western sides of the building. The areas of contaminated subsurface soil extend from approximately 10 to 35 feet below ground. Lateral migration of diesel is observed to increase to a depth of 25 .feet and then decrease significantly by 35 feet. The maximum TPH diesel concentration measured on site was 28,000 ppm at a depth of 15 feet below ground surface adjacent to the diesel tank on the west side of the shop. The highest concentration measured adjacent to the underground tank on the east side of the building was 22,000 ppm TPH diesel measured at 20 feet. 4.2 Selection of Indicator Chemicals In order to assess health and environmental effects from sites with multiple contaminant species, indicator chemicals are chosen to represent health effects and transport of materials on-site. Chemicals may become . indicator species based on their toxicity, mobility, or prevalence on--site. Those species are then used to assess site cleanup criteria on the basis that 4-2 GGA/0179b