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at the sample site. When plastic bottles and caps are used, they will be constructed of linear polyethylene. All sampling containers will be used only once and discarded after analysis is complete. Water-Level and Total Well Measuremgntt Immediately prior to well purging, the water level and total depth of the wells will be measured using an electric sounder. (The electric sounder should be a transistorized instrument that uses a reel - mounted, two-conductor, coaxial cable which connects the control panel to the sensor. A low-current circuit is completed when the sensor makes contact with the water, which serves as an electrolyte. The current is amplified and fed into an indicator light and audible buzzer, thus signaling when water has been contacted. ) Water levels will be recorded to the nearest 0.01 foot in the field logbook. When possible, the total depth will be measured by lowering the sensor to the bottom of the well . Well total depth will be recorded to the nearest 0.5 foot in the field logbook for use in purge volume calcula- tions. The electric sounder will be decontaminated with deionized water after each use. Well Purging Prior to sampling, standing water in the casing and sand pack will be purged from the well using either a dedicated positive displacement bladder pump or a dedicated pneumatic displacement pump. The amount of water purged prior to sampling will be greater than or equal to four casing volumes so that water representative of the in situ ground water is obtained. During the purging operation, purged water will be monitored for tem- perature, pH, and specific conductance at an approximate frequency of one measurement per casing volume removed. Prior to collecting sam- ples for laboratory analysis, these parameters must be stabilized to verify that stagnant water has been evacuated from the well ; that PJ9 9390207.00D -2