Site-specific investigations of bedded evaporites began at the Waste Isolation Pilot Plant site in New Mexico (USA) in 1976, and the first waste was accepted in 1999. Here, we describe and discuss some lessons learned from personal experience.

“Fatal flaws” may not be fatal. Features, events, or processes are sometimes useful exclusionary factors, especially during site selection. Solution chimneys discovered northwest of the site in 1975 were possible vertical pathways for radionuclide transport. Intensive field studies since then have indicated no solution chimneys at the Waste Isolation Pilot Plant site. Known chimneys are related to a geologic unit not found at the Waste Isolation Pilot Plant, and chimney fill is not very permeable. Normal fluid flow should be downward if subevaporite formations are connected to near-surface units. If a solution chimney had been found early at the pilot plant, there might have been pressure to relocate it.

Timing is important. Potash resources were assessed in 1976 by drilling 21 boreholes; four were completed as shallow hydrology observation wells. Data from all boreholes would have provided a comprehensive picture of the hydrology early in the project history. Resource conflicts were considered more important at the time than hydraulic parameters.

Critics will always be with you. the Waste Isolation Pilot Plant is recertified every five years, offering multiple opportunities for outside review and comment. Repeated comments about dissolution of some halite beds, for example, rely on conclusions reached before site-specific studies. Intensive studies since 1984 of shafts, cores, and geophysical logs have shown that halite is distributed mainly by depositional processes. Some critics remain well behind the curve of technical work; we still must respond.