Comments on an evaluation of the 1992 performance assessment for the Waste Isolation Pilot Plant

The following topics are discussed in a review of the 1992 performance assessment (PA) for the Waste Isolation Pilot Plant (WIPP): (1) inclusion of potash mining and other disruptions in the definition of possible futures at the WIPP, (2) definition of future drilling rates in the vicinity of the WIPP, (3) possible non-conservatisms in analysis assumptions, (4) characterization of uncertainty in solubilities, and (5) characterization of uncertainty in distribution coefficients. With respect to (1) and (2), the 1992 WIPP PA attempted to follow guidance in the US Environmental Protection Agencyʹs (EPAʹs) standard for the geological disposal of radioactive waste, 40 CFR 191. Many of the reviewerʹs comments relate to the EPAʹs recent guidance in 40 CFR 194 on assessing compliance with 40 CFR 191, which was not published until early 1996 and which makes many changes from the guidance given in 40 CFR 191. The 1996 WIPP PA, which will support a compliance certification application to the EPA, will follow the guidance in 40 CFR 194. With respect to (3), (4) and (5), the WIPP PA tries to avoid both deliberate conservatism and deliberate non-conservatism. The 1992 WIPP PA attempted to use all the information available to it consistent with the requirements to incorporate uncertainty in PA results and to use ‘reasonable expectation’ as the criterion for assessing compliance with 40 CFR 191. Since 1992, many additional results related to solubilities and distribution coefficients have become available. The 1996 WIPP PA will incorporate these new results.