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above the peagravel to prevent the cement from entering the well pack The remaining annulus is backfilled to grade with a bentonite cement slurry Wells are protected with a traffic-rated, cast-alununum utility box equipped with a PVC skit The box has a watertight seal to protect against surface-water infiltration and must be opened with a special wrench The design of this box discourages vandalism and reduces the possibility of accidental disturbance of the well Well Development EMCON waits a minimum of 24 hours after well installation before developing the monitoring wells to allow the grout to seal Before developing the well, a water sample is collected for subjective analysis from near the water surface in the well with a Teflon bailer cleaned with a laboratory-grade detergent and detonized water The well is developed with a surge block and pump Well development continues until the discharge water is clear of silt and sand Clay-size sediments derived from the screened portion of the formation cannot be entirely eliminated by well development Water Level, Floating Hydrocarbon, and Total Well Depth Measurements Before purging and sampling occurred, the depth to water, floating hydrocarbon thickness, and the total well depth were measured using an oil/water interface measuring system The oil/water interface measuring system consists of a probe that emus a continuous audible tone when immersed in a nonconductive fluid, such as od or gasoline, and an intermittent tone when Immersed in a conductive fluid, such as water The floating hydrocarbon thickness and water level were measured by lowering the probe into the well Liquid levels were recorded relative to the tone emitted at the groundwater surface The sonic probe was decontaminated by being rinsed with denonnzed water or steam cleaned after each use A bottom filling, clear Teflon bailer was used to verify floating hydrocarbon thickness measurements of less than 0 02 foot Alternatively, an electric sounder and a bottom-filling Teflon bailer may have been used to record floating hydrocarbon thickness and depth to water The electric sounder is a transistorized instrument that uses a reel-mounted, two- conductor, coaxial cable that connects the control panel to the sensor Cable markings are stamped at 1-foot intervals The water level was measured by lowering the sensor into the monitoring well A low-current circuit was completed when the sensor contacted the water, which served as an electrolyte The current was amplified and fed into an indicator light and audible buzzer, signaling when water had been contacted A sensitivity control compensated for highly saline or conductive water The electric sounder was decontaminated by being rinsed with detocuzed water after each use The bailer was S AON 1P7010805108051470 i AN-94\dms 1 A-3