Page 123
Appendix B
Human Intrusion Scenarios
Oil, gas and other mineral resources are frequently found in association with salt beds, such as the Salado, where the WIPP is situated. The region around the WIPP has known a high rate of drilling activities in the past and future energy trends indicate that there will be incentives to explore the region again, once institutional controls are removed (starting 100 years after the closure of the repository). The risk of drilling directly into the repository and thus creating pathways for the release of radionuclides into the environment will then increase. Drilling through the repository could transport radioactive materials from the repository to the surface or bring water in contact with substances stored in the repository. The following two scenarios are possible sources of concern about the performance of the repository and have been taken into account in the performance assessment of the WIPP.
1. If there were an oilfield water-flooding operation in the vicinity of WIPP, a large amount of brine could flow from a leaky injection well and induce a hydraulic fracture in the anhydrite (or marker bed) directly above or below the WIPP repository (Box B.1). If, at some later time, another well were drilled through the repository and into this brine-filled fracture, the high-pressure brine in the fracture could flow through the borehole and flood the repository causing a release of radioactive materials. The scenario is known as the Hartman scenario.
2. Direct drilling into the WIPP repository could allow circulating drilling fluid to bring radioactive materials to the surface through a borehole as cuttings or spallings. The situation could be serious if the repository were flooded with high-pressure brines. The Sandia National Laboratories examined three possible flooding scenarios, designated as E1, E2, and E1E2, in their performance assessment. These scenarios are briefly explained in Box B.2, Box B.3, and Box B.4 and they are described in detail in the Compliance Certification Application (DOE, 1996).