Scientific Investigations Report 2006–5232

U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5232

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Summary and Conclusions

This report presents qualitative and quantitative comparisons of water-quality data from the Idaho National Laboratory to determine if the change from purging 3 wellbore volumes to 1 wellbore volume has a discernible effect on the comparability of data. Historical water-quality data for 30 wells were visually compared to water-quality data collected after purging only 1 wellbore volume of water from the same 30 wells. Of the 322 qualitatively examined constituent plots, 97.5 percent met one or more of the criteria established for determining data comparability. A simple statistical equation to determine if water-quality data collected from 17 wells with long purge times (after pumping 1 and 3 wellbore volumes of water) were statistically the same at the 95-percent confidence level indicated that 98.2 percent of 337 constituent pairs were equivalent. The same simple statistical equation to determine if water-quality data collected during a previous study from 11 wells at the Idaho National Laboratory with long purge times (after pumping 1, 2, and 3 wellbore volumes) were statistically the same at the 95-percent confidence level indicated that 95.2 percent of 126 constituent pairs were equivalent. When all 1 and 3 wellbore volume constituent pairs were considered together, 371 of 379 pairs (97.9 percent) were statistically equivalent.

Comparability of water-quality data determined from both the qualitative (97.5 percent comparable) and quantitative evaluations (97.9 percent comparable) indicated that the change from purging 3 to 1 wellbore volumes had no discernible effect on comparability of water-quality data at the Idaho National Laboratory. However, the qualitative evaluation was limited by a small data set. Only October-November 2003 data were available for comparison to historical data.

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