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Frontier Transportation B23502.OIA January 2, 1996 Page A-3 slotted or wire-wrapped. Casing and well screen specifications will depend upon project objectives, site conditions, and project budgets. The well screen and casing sections will be joined by factory-made flush-threaded connections. The well filter pack material will consist of appropriately-sized pre-washed sand. The filter material will be placed in the annulus between the boring wall, from the bottom of the boring to approximately 2 feet above the top of the screen. Subsequent to filter pack emplacement, preliminary development may be performed to provide a uniform filter pack about the casing. Above the filter pack, a 3- to 4-foot thick bentonite seal will be installed. The bentonite may consist of 1/4- or 1/2-inch pellets, or may be in the form of a slurry. If pellets are used, they will be hydrated prior to grouting the well, by adding at least one gallon of water for every bucket of pellets. The thickness of the bentonite seal will depend _ upon local regulatory requirements. The remainder of the well annulus is sealed with a 6-sack sand-cement, or cement grout slurry in one continuous operation from the bottom of the interval to be filled to the top. The remainder of the well annulus will be sealed with a sand-cement slurry, or neat cement grout. For wells more than 15 feet deep, the seal will be emplaced through the hollow augers, which will extend to within 15 feet of the bentonite seal. If required by the local regulatory agency, the seal will be emplaced by pumping through a tremie pipe which extends to within 15 feet of the bottom of the boring. The tremie pipe or augers are withdrawn from the boring in 5-foot increments as the boring fills with grout. A watertight well cap will be placed on top of each groundwater monitoring well, and a 3400t steel standpipe with locking cover or a traffic-rated box will be installed around the wellhead. Monitoring wells will be locked to restrict access to authorized personnel. Monitoring well construction details will be recorded on the field well construction form. Construction information will be transferred to Monitoring Well construction schematics for presentation in final reports. A-3 Standard Operating Procedures for Groundwater Monitoring Well Development Standard operating procedures (SOPS) used by The Twining Laboratories, Inc. (Twining) when developing groundwater monitoring wells are presented below. Twining observes these procedures in order to obtain consistent, reliable data. When possible, initial well development will be performed during installation of the sand pack. A minimum of 48 hours following installation, groundwater monitoring wells will be developed in order to remove sediment that may accumulate in the well during installation, and to settle the filter pack. Groundwater monitoring well development will be performed using a combination of bailing, pumping, and surging. The development of each groundwater monitoring well will continue until a minimum of five well casing volumes of water have been removed, and the displaced water is relatively clear,