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1 <br /> ' Water-level, Floating Hydrocarbon, and Total Well-depth Measurements <br /> ' Before purging and sampling occurs, the depth to water, floating hydrocarbon <br /> thickness, and the total well depth will be measured using an oil/water interface <br /> measuring system The oil/water interface measuring system consists of a sonic <br /> ' probe that emits a continuous audible tone when immersed in a nonconductive <br /> fluid, such as oil or gasoline, and an intermittent tone when immersed in a <br /> conductive fluid, such as water The floating hydrocarbon thickness and water <br /> level will be measured by lowering the sonic probe into the well Liquid levels will <br /> be recorded relative to the tone emitted at the groundwater surface The sonic <br /> probe will be decontaminated by being rinsed with deionized water after each use <br /> ' Alternately, an electric sounder and a bottom-filling, clear Teflon® bailer may be <br /> used to record floating hydrocarbon thickness and depth to water <br /> ' The electric sounder is a transistorized instrument that uses a reel-mounted, two- <br /> conductor, coaxial cable that connects the control panel to the sensor Cable <br /> ' markings are stamped at 1-foot intervals The water level will be measured by <br /> lowering the sensor into the monitoring well A low-current circuit is completed <br /> when the sensor contacts the water, which serves as an electrolyte The current is <br /> amplified and fed into an indicator light and audible buzzer, signaling when water <br /> has been contacted A sensitivity control compensates for highly saline or <br /> conductive water The electric sounder will be decontaminated by being nnsed <br /> with deionized water after each use The bailer will be lowered to a point just <br /> below the liquid level, retrieved, and observed for floating hydrocarbon <br /> ' Liquid measurements will be recorded to the nearest 0 01 foot in the field logbook <br /> The groundwater elevation at each monitoring well will be calculated by subtracting <br /> the measured depth to water from the surveyed elevation of the top of the well <br /> casing (Every attempt will be made to measure depth to water for all wells on the <br /> same day ) Total well depth will then be measured by lowering the sensor to the <br /> bottom of the well Total well depth, used to calculate purge volumes and to <br /> ' determine whether the well screen is partially obstructed by silt, will be recorded to <br /> the nearest 0 5 foot in the field logbook <br /> ' In the event of shallow wells where water surface is visible, direct measurement <br /> using a clean tape measure may be employed Well purging will be carried out <br /> prior to sampling for contamination <br /> ' C-3 <br /> 1 <br />