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' that the corrective actions proposed will attain an acceptable risk or permanently <br />break pathways. <br />E-21 proposes a multi-faceted remediation program to remove or reduce BTEX <br />compounds in soil and groundwater to below the soil and groundwater cleanup <br />levels discussed in Section IV. A. <br />Phase I - Hazardous Waste Removal (Slurry Holding Trench) <br />' Based on the benzene and TCLP results, E-21 recommends gross removal of <br />the slurry, and sidewall and bottom wall soils in the SHT. Cement has been <br />added to approximately half the slurry for use as an absorbent. The cement also <br />helped to solidify the slurry to improve transport conditions. There has been <br />' minimal leaching or migration of contaminants from the SHT. Excavation will <br />proceed and confirmation sampling will be performed from the sidewall and <br />bottom of the excavation until the material is no longer considered a hazardous <br />' waste. This is the only area where gross removal and disposal of hazardous <br />waste is necessary. There was approximately 375 cubic yards of "slurry" in the <br />trench. We estimate 600 to 700 cubic yards will be excavated for off-site <br />' disposal at a hazardous waste disposal facility after contaminated sidewall and <br />bottom soils are removed. <br />Phase II - Non-Hazardous Waste Removal <br />' After material classified as hazardous waste is removed from the SHT, E-21 <br />recommends removal of soils around the perimeter of the SHT that contain BTEX <br />' levels in excess of the CHPHE Soil Cleanup Standards (Protective of <br />Groundwater) be excavated for off-site disposal as a special "petroleum <br />contaminated" waste. Excavation will be performed and confirmation samples <br />' will be collected at regular intervals until groundwater is encountered or <br />excavation becomes impractical. However, in the area of the SHT, lateral or <br />vertical migration of contaminants appears to the limited. We estimate <br />approximately 1,200 to 1,500 cubic yards of soils may require excavation in this <br />phase from the SHT area. <br />There is approximately 300 cubic yards of material in the slurry wall excavation to <br />' the west of the release area that is impacted with gasoline. This material does <br />not contain BTEX concentrations in excess of the CDPHE Soil Cleanup <br />Standards (Protective of Groundwater), however it may continue to be a source <br />' of contamination to groundwater. E-21 recommends gross removal of this <br />material for off-site disposal. The excavation extends over 25 feet bgs and <br />groundwater is approximately 12 feet bgs. Sandy and gravelly deposits range <br />from 8 to 12 feet bgs in this area. Excavation of the backfill will extend to <br />' groundwater, if the excavation does not cave in. If caving occurs at shallower <br />depths, excavation may be discontinued. It is expected that in both these areas, <br />a significant amount of uncontaminated overburden may need to be excavated <br />' and backfilled. Soils will be segregated for waste disposal and backfill <br />determination. <br />' Phase III - In-Situ Soil and Groundwater Remediation <br />After soil excavation, disposal and backfilling is completed, the slurry wall <br />construction will resume. Due to the need for equipment and soil staging during <br />19