THE WASTE ISOLATION PILOT PLANT AND HUMAN INTRUSION
If undisturbed, performance assessments of the 10,000 year compliance period indicate that the radioactivity at WIPP will remain contained by the Salado Formation, which is primarily halite with some clay and thin inter-bedded anhydrite layers. The only plausible mechanism for release of radioactivity that has been identified is human intrusion by drilling. Thus, the drilling rate is an important factor in calculated potential releases from WIPP, as the expected number of intrusions over 10,000 years is ~5-6.
WIPP is in a sedimentary basin with natural resources and a drilling history, so EPA required DOE to use the past 100 years’ record of drilling as the drilling rate for the 10,000 year compliance period. In contrast, the Yucca Mountain repository, in volcanic tuff, used a deterministic, stylized intrusion scenario. If the Agency develops a new generic standard what criteria should be used in addressing potential future human intrusion? Should there be a difference in assumptions for drilling in different lithologies as in current guidance to 40 CFR 191?