SITE INFORMATION AND CORRESPONDENCE

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REMEDIAL ACTION PLAN ADDENDUM#1 USA PETROLEUM STATION#65 FEBRUARY, 1996 OPTION I Passive Soil Remediation Passive soil remediation relies on the principle that petroleum hydrocarbon compounds will naturally degrade or attenuate over time. Such degradation and/or attenuation can be attributed in part to metabolic and co-metabolic processes occurring between indigenous microorganisms found in soil and the hydrocarbon compounds of concern. Under proper circumstances,passive remediation can be an appropriate choice. Sites with soils having adequate populations of hydrocarbon degrading bacteria, nutrients and oxygen levels may be a good choice for this alternative. Additionally, sites in areas which pose little risk or threat for potential human contact may also be amenable to this alternative. Groundwater monitoring would still be required to assess the effectiveness of this RAA on hydrocarbon impacted soil and groundwater, and to assess potential off-site migration of the dissolved hydrocarbon plume. The cost of this option would be limited to performing regularly scheduled groundwater monitoring. Park anticipates groundwater monitoring will be continued for approximately four quarters at a cost of approximately $ 2,200.00 per quarter. OPTION H Soil Vapor Extraction With Off-Gas Treatment Soil vapor extraction (SVE)is designed to volatilize and remove hydrocarbon compounds present beneath the site as: • vapor in the vadose zone; and • to a limited degree, dissolved hydrocarbons in the groundwater. Petroleum hydrocarbon compounds beneath the site appear to the confined to a relatively small area immediately surrounding the tank cluster. Therefore, it appears that the hydrocarbon impacted zones beneath the site should be accessible by the use of soil vapor extraction. Analytical laboratory results of soil and groundwater samples collected from previously installed wells indicate that the hydrocarbon compounds are primarily in the gasoline hydrocarbon range. Analytical results of soil samples collected during previous investigations have failed to detect significant concentrations of hydrocarbons. SVE testing yielded relatively high concentrations. Hydrocarbon impacted soil is anticipated to extend to the water table approximately 47 to 50-feet below ground surface (bgs). While the vapor concentrations were high, the amount of actual hydrocarbon compounds present is believed to be small. Therefore, it appears possible to effectively remediate the site using vapor extraction by utilizing the existing wells in the area immediately surrounding the tank cluster, and to perform the remediation within a few month period. This option assumes the use of a hydrocarbon destruct unit of some type. 2