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Methods for Minimization and Management of Variability in Long-Term Groundwater Monitoring Results

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Technical Report,01 Sep 2012,01 Dec 2015

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GSI Environmental Houston United States

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High variability in groundwater monitoring results makes it difficult to accurately evaluate remedy effectiveness and to predict remediation timeframes. In order to determine the effect of sample collection method on monitoring variability, five methods for collecting groundwater samples from monitoring wells were compared at two sites in Texas and California with chlorinated VOC plumes. The five sample collection methods evaluated included three variations of low-flow purge sampling low-flow with purge to parameter stability Low-Flow Standard, low-flow with fixed small volume purge 3 Liters, and low-flow with fixed large volume purge 18 Liters, and two no purge methods using commercial devices Active No Purge HydraSleeve and Passive No Purge SNAP samplers. Eight monitoring wells were sampled at each site six times using each sampling method at approximately two month intervals, resulting in a total of 480 groundwater samples. For the dataset as a whole, the five sample methods yielded relatively small differences in VOC concentration -20 , and with the exception of the Active No Purge HydraSleeve method at the California site, only small differences in variability between sample events. For the purge methods tested, results indicate that low flow purge sampling using a fixed purge volume provides results of equal quality compared to standard low flow purge sampling based on field parameter stability. The overall results suggest that for most monitoring well sampling methods tested, data quality was independent of method. In that context, factors such as cost, ease of implementation, and sample volume requirements become prominent deciding factors in sample method selection.

Subject Categories:

  • Hydrology, Limnology and Potamology

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