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GROUND WATER SAMPLING USING LOW-FLOW TECHNIQUES
Citation:
Paul*, C J. AND R W. Puls*. GROUND WATER SAMPLING USING LOW-FLOW TECHNIQUES. Presented at GWPC Annual Forum, Reno, NV, 09/22-26/2001.
Description:
Obtaining representative ground water samples is important for site assessment and remedial performance monitoring objectives. The sampling device or method used to collect samples from monitoring or compliance well can significantly impact data quality and reliability. Low-flow or minimal draw-down purging and sampling techniques is an alternative method for obtaining representative samples from conventional monitoring or compliance wells or from low permeability formations and fractured rock. Use of low-flow techniques can minimize purge volumes and decrease monitoring costs as well as provide representative and reproducible ground water samples. The use of dedicated sampling devices in conjunction with low-flow purging and sampling can eliminate initial disturbance into the formation caused by pump insertion and further minimize purge time. Periodic monitoring of the water level within the well should be conducted throughout purging and sampling in order to measure draw-down. The flow rate of the pump should be adjusted to match the ground water entrance velocity into the well screen. Water quality indicator parameters (pH, redox, specific conductance, DO, turbidity, temperature) should be monitored during purging to determine when adjacent formation water has entered the well screen and sampling can be initiated. Stabilization criteria for water quality indicators is defined as three successive readings, at three minute intervals, within ? 0.05 for pH, ? 5 mV for redox, ? 3% for specific conductance, ? 10% for DO, and ? 10% for turbidity. However, some parameters are more sensitive than others (e.g., redox, DO) and should be evaluated with time over several sampling events before establishing a sampling protocol.
This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.