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New Approach to Purging Monitoring Wells: Lower Flow Rates Reduce Required Purging Volumes and Sample Turbidity
Citation:
Puls*, R W. New Approach to Purging Monitoring Wells: Lower Flow Rates Reduce Required Purging Volumes and Sample Turbidity. GROUND WATER AGE 28(5):18-19, (1994).
Impact/Purpose:
Journal Article
Description:
It is generally accepted that monitoring wells must be purged to access formation water to obtain “representative” ground water quality samples. Historically anywhere from 3 to 5 well casing volumes have been removed prior to sample collection to evacuate the standing well water and access the adjacent formation water. However, a common result of such purging practice is highly turbid samples from excessive down-hole disturbance to the sampling zone. An alternative purging strategy has been proposed using pumps which permit much lower flow rates (< 1 liter/min) and placement within the screened interval of the monitoring well. The advantages of this approach include increased spatial resolution of sampling points, less variability, less purge time (and volume), and low-turbidity samples. The overall objective is a more passive approach to sample extraction with the ideal approach being to match the intake velocity with the natural ground water flow velocity. The volume of water extracted to access formation water is generally independent of well size and capacity and dependant upon well construction, development, hydrogeologic variability and pump flow rate. Copy available at NTIS as PB94146263.