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George's Service Remedial Action Work Plan Project No.425.2 June 30,2011 the sparge wells, and will be successful in addressing contamination in the western portion of the site. The third air sparging well AS-3 is proposed to be located south of the existing pump island, and is expected to assist with addressing soil contamination that is south of the excavation area. 6.1.1. Air Sparging Operation a1tY It is proposed to operate the o e sparging system for a period of twelve (12) months. The data will be reviewed at the end of this period and report of remedial effectiveness and further recommendations as appropriate will be prepared. 6.1.2. Air Sparging Wells Air sparging (AS) wells containing gas diffusers are needed to inject air into the subsurface. GTI proposes installing three (3) AS wells around the former service station as shown in the Remedial Improvement Plans. All AS wells will be installed into the sand unit that forms Zone A and a diffusion point will be installed to target the sand layer that extends to the north at about 22 ft bgs. The air sparging and VETS (as discussed below) will run in alternating pulses so extraction wells do not immediately remove the injected air. 6.1.3. Well Borehole Installation The air sparge (AS) well boreholes will be drilled by a licensed driller, using an 8-inch outside diameter, continuous flight, hollow stem auger. The AS wells will be constructed using 1.0 inch diameter PVC casing with flush threads. The sparge point will consist of a 24"long fine screened interval designed to produS�Ane bubbles vvMaximum surface area. A#12 sand filter pack will surround and extend,l�foWabove andt Ww 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% bentonite) via a tremie tube. The tops of the wells will be provided with a T- shaped joint. See Figure 8 for a schematic of AS well construction. _ 6.1.4. Soil Sampling Select soil samples will be collected in 6.0-inch brass liners using a 2.0-inch modified California split spoon sampler. All soil samples will be sealed with Teflon, capped with plastic end caps, labeled and placed in a cooler at 4° Celsius for transport to a California certified laboratory under Chain of Custody procedures. It is proposed that continuous coring be utilized to confirm the soil tithology. These soil samples will be analyzed for TPH-g& BTEX constituents by EPA method 8260B. n,{ cw�v" � Geological reckxics inc. 16 4252 RAP.docx