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Ge0logfeal Technics 14c. Page 5 ' IRAP—Pilot Test Project No. 425.2 March 21,2005 ' • As pore water is displaced by vapors groundwater mounding could occur and cause lateral spreading of contaminants. ' • The effect of mounding is minimized by using ozone verses air, since the volume of ozone sparged to the groundwater is significantly less than what is needed to ' accomplish the same task when using air. Ozone: • Ozone is toxic to humans (inhalation and absorption hazard). ' • Ozone enhances the flammability of other materials (source of oxygen). • Ozone sparging may alter the Eh/pH of the system, causing metals in soils to become more mobile. However, this influence is temporary and only exists in the immediate ' area of the altered state of the natural groundwater chemistry. ' 3.0 SOIL VAPOR EXTRACTION Previous Remedial Action Work ' A soil excavation was performed in July 2001 to remove the contaminated soil from core contamination area. Total depth of excavation was about 11 feet bgs. Figure 2 shows the excavation boundaries. The excavation activities were documented in the soil excavation ' report dated January 28, 2002. The excavation pit was backfilled with 1.5-inch drain rock to depth of 5 feet bgs and compacted with a vibrating compactor. Two 4-inch diameter drainpipes were installed at the west and east ends of the excavation site to a depth of 10-feet ' bgs for the anticipated future use in vapor extraction. Pea gravel was used to fill the excavation pit to 1.5 feet bgs and compacted with a vibrating compactor. Class 2 base-rock was used to fill the pit to 4-inchs bgs and was capped with asphalt after compaction. ' Proposed Remedial Action Work GTI proposes to install the ozone injection points along the sides of excavation pit as shown ' in Figure 2. The ozone sparging may produce the contamination vapors of volatile hydrocarbons and push these vapors towards the excavation pit. Therefore, to extract these contaminant vapors, soil vapor extraction system is necessary to install. The proposed soil ' vapor extraction system will use the pipes for vapor extraction already installed at the time of excavation backfill as described above. The following section describes the soil vapor extraction technology review. ' GTI proposes to install two activated carbon units to pass the vapors extracted through vapor extraction system to remove the contaminants. ' 3.1 Soil Vapor Extraction Technology Review ' Soil vapor extraction (SVE) is the process of removing volatile organic compounds in the subsurface by drawing air through the subsurface sediments, which allow a transfer of chemical mass from the liquid state to the vapor state. As vapor, the chemicals are removed 1