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Cteologtcal reds gics i c. Page 6 ' IRAP—Pilot Test Project No. 425.2 March 21,2005 ' from the subsurface in the extraction air stream and destroyed above ground via thermal oxidation or removed with the activated carbon. ' Soil vapor extraction has proven to be an effective in situ remedial method for soils of a permeable nature and can also be used to mitigate volatile hydrocarbons in groundwater by ' drawing air through permeable geologic units above the capillary fringe. 3.2 Concerns and Limitations ' • The system is more likely to extract the vapors from the excavation pit area, and will not affect the ozone sparging system. • The system is unlikely to show any limitations for this specific site. 7 ' 4.0 INTERIM REMEDIAL ACTION—In Situ Pilot Test ' 4.1 Proposed Ozone Sparging (OS) Pilot Testing Zone A Monitoring wells (MW-1 thru MW-8) have screen intervals between 5 feet to 22 feet ' bgs. MW-1, MW-2, MW- 4 and MW-5 have historically shown contamination during the quarterly monitoring events (Table 1). MW-3, MW-7 and MW-8 appear to not be affected by contamination. MW-1 and MW-2 shows the highest TPH-G contamination in the ' historical data, and MW-4 and MW-5 also contains significant amounts of gasoline concentrations historically. ' GTI proposes to conduct a pilot study to utilize ozone sparging to address the groundwater plume in the vicinity of MW-1, MW-2, MW-4 and MW-5 as shown in Figure 2. If the results of the pilot test show that ozone sparging is an effective groundwater remedial ' alternative, the system will continue to be operated during the remedial phase with some alterations to the system developed for the pilot test. The alterations can be new injection points and/or other necessary changes to address the contamination plume. ' As Shown in Figure 2, GTI proposes eight ozone sparging points. Eight ozone sparging points as shown in Figure 2 will cover the core area of contamination site. The sparging ' points will also act like a barrier to control the off site movement of the contamination plume. Figure 3 indicates the presence of gasoline plume under the Durham Ferry Road in the downward gradient of groundwater. Table 1 indicates that the gasoline plume did not hit ' MW-6 and MW-7. GTI will propose to install more ozone sparging points in the groundwater downward gradient if the pilot testing achieves the expected results to remove the contamination. f, i The initial decision to utilize ozone sparging (OS) is analogous to determining if the site is suitable for air sparging. This is because the basic mechanics of delivering the gas to the ' subsurface is the same regardless of the gas used.