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WELL PURGING STUDY
Citation:
Impact/Purpose:
The eight state underground storage tank programs in EPA Region 4 require the sampling of thousands of groundwater monitoring wells each year. One of the practices utilized in the sampling of wells is purging prior to sample collection. For many years it has been debated as to whether the water in the well that has been standing for some time could be considered stagnant and not representative of the waters in the formation. Conventional purging incurs additional costs when compared to the no purging technique. This study provides guidelines for situations in which purging does not produce any statistically significant benefits.
Description:
Purging of wells with bailers has been a standard practice in the underground storage tank program as well as other groundwater regulatory programs for many years. Several studies in the Northeast and the West have shown that, under certain circumstances, samples collected without prior purging of the well are not statistically different from samples collected with conventional well purging. Results from these studies prompted a limited comparative study of purged wells versus non-purged wells by state underground storage tank programs in EPA Region 4. Monitoring wells sampled during the study were sampled using bailers, screened across the groundwater table, and did not have any free product present. Overall results of this purge versus no-purge study indicates that there is not a significant statistical difference in the no-purge versus purge analytical results for BTEX. For MTBE, the difference is significant but less than 1%. This information suggests that non-purged wells could be utilized at some locations for a cost savings.