Intra-Well Comparisons

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With intra-well comparisons, data from a single well are compared to historical data from the same well. Typically four to twelve samples are required from the well to establish a baseline concentration. For the analysis to be valid, the baseline samples must not be impacted by the facility. Some regulators have recommended that intra-well comparisons be made only for wells that existed prior to waste disposal at the facility.

The advantage of intra-well comparisons is that they eliminate the spatial variability of natural ground water quality. The disadvantage of intra-well comparisons is the large number of historical samples required and known not to be impacted from waste disposal activities. Sufficient samples may not be available at many facilities.

The following methods can be implemented as intra-well comparisons: