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` APPENDIX D <br /> ASSUMPTIONS, CONDITIONS, AND CALCULATIONS <br /> Alternative 1: Excavation/Off-Site Disposal and Air Sparging <br /> Assumptions/Conditions <br /> 1 Lateral extent of petroleum hydrocarbon impact is approximately 2,400 square <br /> feet <br /> 2 The plume thickness ranges in depth from 35 to 50 feet Excavated volume of soil <br /> is approximately 4,000 cubic yards <br /> 3 An attenuation factor was developed utilizing historical groundwater monitoring <br /> data from Monitoring Well MW-11 (Figure C-1) This attenuation factor was <br /> applied to the most heavily impacted well on the site, Well MW-13, for the <br /> purpose of determining the total time for the groundwater monitoring effort <br /> Therefore, utnlizmg the attenuation factor obtained from Morutonng Well MW-11, <br /> the total time for groundwater monitoring at the site until water quality goals can <br /> be attained at Well MW-13 was calculated to be 3 years <br /> 4 A 6-foot diameter bucket auger foundation ng will be utilized to excavate soils to <br /> a depth of 50 feet <br /> 5 Assume 68 days to complete excavation <br /> 6 Excavated souls will be manifested and transported to a Class II landfill <br /> 7 Assume backfiH will be composed of lean grout <br /> 8 Assume landfill requirement of 1-4 point composite sample for each 200 cubic <br /> yards and regulatory requirement of 1 sample for every 10-foot grid from the <br /> invert and sidewalls of the excavation <br /> Capital <br /> • Excavation Crew(68 days at $2,500/day) $170,000 <br /> 3201337BICAP_AMD DOC D - 1 November 30, 1995 <br />