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3.4.2 Monitoring Well Construction Groundwater monitoring wells will be constructed using 2 -inch nominal inner diameter, Schedule 80 PVC blank casing and 20 feet of screen to the approximate depths indicated above. Well screens will be formed using machine cut 0.020 -inch slots. A one -inch nominal inner diameter sounding tube constructed of similar PVC casing and screen will also be installed to avoid future conflict between tubes and wires associated with the pump. All well materials, including blank and factory -slotted casing, will be virgin, decontaminated and factory sealed. All well materials will be covered in plastic or similar protective materials when delivered to the site and will remain so until used in construction. All.well casing will be flush -threaded, including the bottom cap at the base of the wells. No glue or solvents will be used to join the sections. Because wells will be constructed through the hollow -stem of the auger, centralizers are not needed. The drillers will suspend the casing from the drill wire during construction to ensure that the casing remains centralized within the augers. Based on the grain size distribution of the shallow, perched aquifer encountered in past site investigations, the proposed filter pack material will consist of commercially available inert, washed and graded number 2/12 Monterey sand (or equivalent). Well filter packing will be accomplished by slowly pouring the sand down the auger flights, which act as a tremie pipe. As sand is introduced, the augers will be withdrawn to allow the sand to fill the annular spaced between the auger and borehole wall. The elevation of the sand will be measured periodically using a decontaminated weight to ensure that no bridging occurs. The filter pack installation will be deemed complete when the sand extends at least three feet above the top of the screen. Following filter pack sand placement, the filter pack will be surged and allowed to settle with additional sand being added as necessary to bring the filter pack up to design depth. A minimum 5 .foot thick granular bentonite seal (chips or pellets) will be placed on top of the well filter pack. The bentonite will be hydrated after placement using a minimum 5 gallons of distilled or GLA -approved water for each 2.5 vertical feet of seal. After the seal has been hydrated, it will be allowed to cure for at least 30 minutes prior further well sampling or construction activities. The remainder of the borehole will be sealed with an expansive neat cement grout. The grout seal will consist of Portland Type II/V cement (or equivalent) and bentonite mixture with a water -to -cement ratio that includes no more than 8 gallons of water per sack of cement and 5 percent bentonite by weight. The grout will be delivered to the borehole via tremie pipe and positive displacement techniques. During their placement, depth soundings will be utilized to evaluate the thickness and uniformity of the sand pack and bentonite seal, and to assure that no bridging occurs. Well 10 2011-0115 CHSL EMP Workplan Geo -Logic Associates Revision 2 — January 11, 2012