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' Geofogicaf7ecknics Inc. • • Page 5 Feasibility Study Work Plan ' ProjectNo.425.2 August 17,2000 ' 4. The depth to water at the site ranges from 8 to I 1 feet bgs, this is only a few feet over the minimum depth required. Shallow depths to groundwater would make capturing and ' controlling vapors difficult and very problematic in fine-grained soils. 5. Due to the air sparging wells needing to be installed 5 to 15 feet below the deepest ' contamination, it would be required that they are installed into the sand layer below a depth of 40-feet bgs. This presents two problems at the site: • The sand is located beneath a low permeability silty/clayey layer that would impede if ' not stop, the vertical migration of air. It could also encourage the lateral spread of the contamination away from the source area. • The saturated thickness of the aquifer is reaching the maximum recommended thickness. ' 3.0 ASSESSMENT OF REMEDIAL EFFECTIVENESS In order to determine the success of the remedial alternative that will be chosen, different ' testing plans will be implemented. This work will show how the remaining contamination in the aquifer responds to the removal of the heavy contamination from the source area. ' If excavation is used, confirmation soil samples will be collected on the excavation side walls and pit bottom and water samples will be collected in the areas of the pit that goes below the ' water table. If Air Sparging/Vapor Extraction is used, remedial effectiveness will be determined by the ' performance of a spike test, confirmation boring and groundwater monitoring. If a limited excavation is chosen as the remedial alternative then the effectiveness will be judged by groundwater monitoring. 4.0 RECOMMENDATIONS Based on the information provided above and the preliminary cost comparison between the two remedial alternatives, GTI recommends that the highly contaminated soil on the north ' side of the building be excavated to a depth of 15 feet. We highly recommend that Air Sparging/Vapor Extraction System not be considered. The conditions at Georges are not suitable for this technology. It is our professional opinion that site conditions restrict the use ' Air Sparging/Vapor Extraction and that it would be very costly to operate such a system.