SITE INFORMATION AND CORRESPONDENCE_FILE 2

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500 East Grant Line Page 2 The soil samples which were collected during installation of AW10, AW11, and AW12 indicated significant petroleum hydrocarbon contamination; however, neither the vertical nor horizontal extent of this contamination was defined. The deepest sample from AW10 which underwent field screening or petroleum hydrocarbon analysis was collected at 11 feet and evidenced contamination up to 3,200 ppb benzene, 507 ppm TPH-gas and 3,700 ppm TPH-diesel. The deepest sample from AW11 was collected at 12 feet and evidenced contamination up to 17 ppm TPH-diesel. The deepest sample from AW12 was collected at 11 feet and evidenced contamination up to 4,000 ppb benzene, 590 ppm TPH-gas and 3,000 ppm TPH-diesel. It is unfortunate that better characterization of the extent of petroleum hydrocarbon contamination was not attempted. Further investigation will be necessary to determine the extent of residual soil contamination after the 1990 soil excavation attempt. Disposal documentation was not included in the report, please verify the disposition of contaminated soil, from drilling activities, and of contaminated water, from pump testing and purging activities. Human Health Risk Assessment for Petroleum Hydrocarbons PHSIEHD indicated in correspondence dated April 2, 1993 that a health based risk assessment would have Iimited value since groundwater quality had already been impacted. The final remedial plan involving quarterly groundwater monitoring is inadequate given the still unknown extent of on-site soil contamination and the residual contamination evidenced to date. Additional investigation will be necessary prior to the development of a remedial action plan which will address both the soil and groundwater contamination. Quarterly Monitoring Report, October through December 1993 The results of groundwater sampling of October 28, 1993 were reported. The sampling results indicated detectable groundwater contamination (benzene and TPH-diesel) in samples collected from monitoring wells AW3 and AW9. Please note that purging records were not included and should be submitted as an addendum. Alton correspondence Alton responded to a letter forwarded to PHS/EHD that was prepared by Geomatrix and dated September 29, 1993.