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4 September 11, 2008 <br /> HWA Project No. 2008 094 <br /> assembly mounted on a pickup truck or tractor. Steel pipe(1.25-2 inch diameter) <br /> is driven into the ground using a hydraulic impact driver. Soil samples can then <br /> be retrieved through the pipe, and ground water sampled via temporary well <br /> points. We anticipate completing 10 to 14 probe locations in two days. <br /> Maximum probe depth will be 20 feet,or probe refusal. We will collect <br /> continuous soil core samples. We will submit soil samples and ground water <br /> samples to a laboratory for analysis. <br /> • Boring abandonment. After all direct push probes reach their maximum depth <br /> and are sampled, the steel pipe will be withdrawn from the ground and the hole <br /> grouted to the ground surface using hydrated granular or powdered bentonite. <br /> The drillers will also use concrete or asphalt to patch any boreholes installed <br /> through paved surfaces. <br /> • Ground water monitoring welts. The drillers will advance borings with a truck- <br /> mounted hollow-stem auger drilling rig, using 8-inch outside diameter continuous <br /> flight augers. Maximum boring depth will be 25 feet(at least 10 feet below the <br /> ground water surface). HWA field staff will collect soil samples at a minimum of <br /> 5 foot intervals, starting at or above five feet below grade. They will collect soil <br /> samples through the hollow stem of the auger using a standard split spoon <br /> sampler,shelby tube, or modified split barrel sampler driven or pushed ahead of <br /> the auger bit, depending on soil conditions. <br /> The monitoring wells will be constructed using 2-inch-diameter, schedule 40, <br /> PVC casing,with ten feet of 0.010-inch, mill slotted well screen. Well screens <br /> will be installed to intersect the ground water surface,as determined during <br /> drilling. Flush mount, road rated wellheads with watertight gaskets and locking <br /> caps will be installed. HWA will survey the relative elevation of each wellhead. <br /> • Well Development. After the wells are installed, they will be developed to <br /> improve hydraulic connection and water clarity. Wells with ground water in them <br /> will be developed by surging with a surge block and pumping or bailing. <br /> • Decontamination. To prevent potential cross-contamination of samples, [TWA <br /> will maintain appropriate decontamination procedures. Between sampling <br /> intervals in each boring,field staff will wash all sampling devices in a detergent <br /> solution, rinse with tap water and then rinse again with deionized water_ To <br /> prevent potential cross-contamination of boring sites, we will use only previously <br /> decontaminated probe rods at each location. Drillers will steam clean all augers, <br /> rods,and other downhole tooling between boring locations. <br /> • <br /> • Sampling. At each sampling interval, EIWA will log the soil samples and obtain <br /> and record pertinent information including soil sample depths, stratigraphy, <br /> ground water occurrence, and any visual or olfactory observations regarding the <br /> presence of contamination. HWA will log the sample for Ethology and field <br /> screen the samples for organic vapors by headspace analysis using a 3 <br /> Drywall GTS HWA SOW Exhibit A 9 17 08.doc 4 HWA GEOSCIENCES INC. . <br /> 1 <br />