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sample analyses. The screen interval for all wells will be determined in the field and will be based on the lithologic logs. All monitoring wells will be installed using the procedures described below. Drill core material will be disposed of as described in Section 3.4. A typical well construction diagram is presented in Figure 3. All monitoring wells will be flush mounted with 2-inch outside-diameter(O.D.)casings and screens. Each well will have a 2 feet of blank casing on the bottom, 10 feet of Schedule 40 PVC flush threaded 0.020 slot screen,and 2-inch OD Schedule 40 PVC casing to the ground surface. The wells will be completed with flush-mounted heavy traffic-rated well boxes. The well installation procedures for the four 100-foot deep wells are as follows: • Drill 6-inch diameter boring to approximately 100 feet bgs using mud-rotary drilling methods. • Soil samples for lithologic description shall be taken at 5-foot intervals from ground surface to, approximately 80 feet bgs and continuously from 80 to 100 feet bgs using a 94 mm core system. • Install Schedule 40,2-inch OD PVC casing and 10 feet of 0.020-inch slot well screen in the borehole. A 2-foot sediment trap (blank casing)with a threaded PVC bottom cap will be placed below the screen. • Centralizers will be placed on the casing every 40 feet,with additional centralizers at the top and bottom of the screen. r • Sand pack will be installed through a 1-inch tremie pipe. A sand size will be chosen such that no more than 10 percent of the sand passes through the screen slots (such as Lone Star No. 2/12). The sand pack depth will be sounded at regular intervals to ensure a solid pack with no bridging. The sand pack will extend approximately 2 feet above the top of the screen. • Two feet of bentonite pellets will be placed above the sand pack and hydrated. • Cement-bentonite grout containing approximately 2 percent non-beneficiated bentonite will be in- stalled from the top of the bentonite seal to the ground surface. Grout mixture will not exceed 7-1/2 gallons of water for each 94-pound bag of cement. The grout will be pumped through a tremie pipe from the bottom of the remaining annulus to the surface. The grout will be allowed to set for 24 hours before well development. • Wells will be developed by air surging,pumping,and/or bailing until the pumped water is free of sand. If necessary,air lifting may be used. At a minimum, 10 casing volumes of water will be pumped from the well. The well depths will be measured before completion of development. Accumulated fine-sized materials will be removed from the well. Wells will be completed below grade with a locking cover and any other protection necessary to protect the well from vandalism and surface traffic. Typical well head completions include traffic-rated flush mounted Wheaton boxes. • The top elevation of the well casing and ground surface will be surveyed to the nearest 0.01 foot. The well installation procedures for the deep monitoring well are the same as above with the following exceptions: • Drill 6-inch diameter pilot boring to approximately 120 feet bgs using mud-rotary drilling methods ( • Soil samples for lithologic description shall be taken continuously from 100 feet until a competent confining layer with a minimum thickness of 5 feet is encountered using a 94 mm core system. CATEMMWORKPLAN-DCk1.DOC 6