Grounded in Groundwater Statistics

摘要

In 2017, many power agencies implemented various statistical methods to help them comply with the Environmental Protection Agency’s Hazardous and Solid Waste Management System; Disposal of Coal Combustion Residuals from Electric Utilities; Final Rule. With the passing of the January 30, 2018 deadline for active impoundments to submit results from the detection monitoring rounds and issuing of public notices of Statistically Significant Increases (SSI) of Appendix III constituents over background concentration levels, many CCR Unit facilities with noted SSI’s have completed or are in the process of completing the statistical evaluation of Appendix IV and III constituents for assessment monitoring and possibly corrective actions or closure. The groundwater sampling and analysis requirements of Parts 257.95, 297.98, and 257.102 form critical steps in the compliance process; however, the implementation is challenging since the language in subsections 257.95 (e),(f),(g),(h), 257.98 (1),(2), and 257.102(c) does not clearly spell out what statistical tests to use for determining SSIs over background and statistically significant levels (SSL) over groundwater protection standards (GWPS). The purpose of this paper is to breakdown the language in these parts in understandable terms and demonstrate correct structures for hypothesis testing for SSIs over background and SSLs over GWPS. The paper will use examples to help practitioners apply the correct hypothesis framework using well- established test statistics such as the upper prediction limits, upper and lower confidence limits, and upper tolerance limits. In doing so, they will have confidence that their statistical test results appropriately determine whether the CCR unit can remain in assessment monitoring, return to detection monitoring or be required to assess corrective measures to remedy the identified releases.