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Mr. Ron Valladao �. January 13, 2000 Page 3 (including no nearby water supply wells), if the source has been removed, if the extent of contamination has been established, and if it can be shown that contamination levels are r stable and/or decreasing with time. In this case, the risk levels are low based on low BTEX concentrations. The source has been removed. However,:the extent of contamination has not been established on the adjoining property. Costs for this'would include those associated with construction of three to five monitoring wells to verify contamination degree and extent and to evaluate trends over time, or$10,000 to $20,000. Excavation The contaminated soil can be excavated and disposed of or treated onsite to acceptable levels. This is a viable remedial option. However, if the subject property is remediated and the adjoining is not, there is a significant risk that contaminants will migrate back onto the subject property, unless an intervening slurry wall is constructed to separate the two sites. Costs for this are tentatively estimated at $100,000.to $125,000, and would be doubled if the adjoining property is remediated at the same time. A slurry wall would cost approximately $20,000. In Situ Remedial Action i The contaminated soil can be treated onsite by injecting appropriate nutrient to enhance natural degradation of the hydrocarbons. Similar to excavation, if the subject property is remediated and the adjoining is not, contaminants will migrate back onto the subject property, unless an intervening slurry wall is constiucted to separate the two sites. This risk is reduced by the nature of the remedial action, which would actually tend to mitigate diesel concentration on both sides of the fence. Costs for this are tentatively estimated at$50,000 to $75,000, and would be doubled if the adjoining property is remediated at the same time. 9015-025