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Equipment Cleaning Before the sampling event was begun, equipment that was to be placed in P 9 g q the well or would come in contact with groundwater was disassembled and cleaned thoroughly with detergent water, and then steam cleaned with deionized water. Any parts that could have absorbed contaminants, such as plastic pump valves, bladders, etc., were cleaned as described above, ' or replaced. ' During field sampling, equipment surfaces that were placed in the well or contacted groundwater were steam cleaned with deionized water before the next well was purged or sampled. Water-level, Floating Hydrocarbon, and Total Weil-depth ' Measurements Before purging and sampling occurred, the depth to water, floating hydrocarbon thickness, and the total well depth were measured using an interface measuring system. The oil/water interface measuring system consisted of a sonic probe that emitted a continuous audible tone when immersed in a nonconductive fluid, such as oil 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 sonic 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 deionized water or steam cleaned after each use. Alternatively, an electric sounder and a bottom-filling Teflon ' bailer may have been used to record floating hydrocarbon thickness and depth to water. iThe 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 deionized water after each use. The bailer was lowered to a point just below the liquid level, retrieved, and observed for floating hydrocarbon. Liquid measurements were recorded to the nearest 0.01 foot in the field logbook. The groundwater elevation at each monitoring well was calculated pjO\Of901of900020.3az A - 2 Rev. 0 January 27, 1993