Conclusions after eleven years of studying brine at the Waste Isolation Pilot Plant

The Waste Isolation Pilot Plant (WIPP) was established to demonstrate the safe disposal of defense-generated transuranic waste in the United States. When excavations began at the WIPP in 1982, small brine seepages (weeps) were observed on the walls. WIPP performance assessment activities raised the concern that the brine could cause anoxic corrosion of metal in the waste storage drums and waste inventory, potentially producing large quantities of hydrogen gas, which would affect the long-term performance of Thee repository. Th WIPP Brine Sampling and Evaluation Program was developed to investigate the origins, hydraulic characteristics, extent, and composition of brine occurrences. The WIPP is excavated in the Salado Formation, which is bedded salt of Permian age. The sediments exposed in the excavations consist of clear halite and polyhalitic halite, halite containing clay, thin clay seams, and interbedded anhydrite layers. The clear halite beds contain little brine and are effectively impermeable. The clay within the salt and in the clay seams contains brine that is released to the excavations, although virtually all of the brine release occurs within the first few years of mining. Consequently, by the time the waste storage rooms at the WIPP are filled and sealed, most of the brine that can be derived from the clay will have evaporated. These is no observed evidence from the WIPP excavations that brine will seep into the working from the anhydrite beds. It has been postulated, however, that brine could seep through the underlying anhydrite Marker Bed 139 (MB139). Recently acquired data on the hydrologic properties of MB139 show that, even if flow through the anhydrite occurs, the brine released to the storage rooms could only corrode a small percentage of the susceptible metal in the repository