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Groundwater Sampling Techniques

By: Steve Iorio, Project Manager

Groundwater Sampling
Confusion at times arises when considering what technique is preferable in groundwater sampling, the use of low-flow peristaltic pump systems or hand bailers.  The choice of technique in purging a groundwater monitoring well is generally a function of the well diameter, the depth to the water table, the depth of the well itself, the amount of sediment in the well, and the amount of water that is to be removed during purging.  Bailers are generally an attractive option for sampling, as they are relatively inexpensive and can be dedicated to a single well, which reduces the chance for cross-contamination.  In addition, bailers do not require a power source and are generally much faster than peristaltic pumps, allowing them to be used in remote sampling environments.  In contrast, peristaltic pumps are considered useful as they are adaptable to wells with varying diameters, well depths, and volumes of water that are required to be purged.  One of the main benefits of using a peristaltic pump is their ability to remove large volumes of water, with minimal turbidity

 

According to the EPA’s Science and Ecosystem Support Division (SESD) Operating Procedure for Groundwater Sampling, updated to March 6, 2013, portable hand bailers may be used for purging, but only in “appropriate situations” and their use is oftentimes “discouraged because the correct technique is highly operator dependent and improper use may result in an unrepresentative sample”.  Specifically, it is critical that bailers are lowered in the well slowly, allowed to fill, and then removed gently, so as not to disturb sediment or volatile organic constituents.  Further, bailers should generally be composed of stainless steel or Teflon.  In summary, the EPA does not currently have any groundwater sampling regulations to restrict the use of hand bailers vs. peristaltic pumps.  It is therefore up to the project manager or geologist to assess site conditions and decide which purging technique is most beneficial.

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