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1 Geologl at reckntcs Inc. Page 8 ' IRAP—Pilot Test Project No. 425.2 March 21,2005 ' 4.4 Screening for Proposed Technology Effectiveness GTI compared various remediation technologies in the Feasibility Study dated April 28, 2004. In situ chemical oxidation was found to be most effective according to the site specific ' geology. Ozone sparging was found to be very effective for the remediation of gasoline spill sites in literature. 'r W a 4o , (A rAr i l L-'4,5 g-Fr /) ' A pilot test to install and operate an OS (Ozone Sparging) system is proposed in the following sections. ' 4.5 Ozone Sparging Pilot Test ' It is proposed to operate the ozone sparging system for a period of six (6) months. The data will be reviewed at the end of this period and a final Corrective Action Plan (CAP) will be developed to address the residual contamination (if necessary). ' 4.6 Ozone Sparging Wells ' Ozone sparging (OS) wells containing gas diffusers are needed to inject ozone into the subsurface. GTI proposes installing eight OS wells as shown in Figure 2. All the OS wells will be installed up to equal depths of 23 feet bgs, and a diffusion point will be installed (20' ' to 221) to target the silty sand layer. This phase for pilot testing will target the most contaminated zone represented by the shallow wells (screen intervals 5' to 22' bgs). Figure 4D and Figure 4E indicate that approximately 18' to 22' is the silty sand unit, above this unit ' various layers of sandy silt, silt, sand, and clay exists. Diffused ozone will also migrate upwards to oxidize shallower contamination zones. I If .�" I t The ozone sparging and VETS will run in alternating pulses so extraction wells do not immediately remove the injected ozone. ' 4.7 Well Borehole Installation The well borings will be drilled by a licensed driller and will use an 8-inch outside diameter, ' continuous flight, hollow stem auger. The OS wells will be constructed using 1.0 inch diameter PVC casing with flush threads. The sparge point will consist of an 18 — 24" long diffuser designed to produce fine bubbles with maximum surface area. A #12 sand filter pack will surround and extend 1 foot above and below the sparge point. A three-foot transition seal will be installed above the sand pack by adding weighted bentonite pellets. A surface seal will be achieved by pumping a neat cement grout (augmented with < 4% t bentonite) via a tremie tube. The tops of the wells will be provided with a T- shaped joint. See Figure 5 for a schematic of OS well construction.