The WIPP Facility
The WIPP facility is limited by the Land Withdrawal Act to receiving up to 168,520 cubic meters of contact-handled transuranic (CH-TRU) waste (equivalent to approximately 810,000 55-gallon drums) and up to 7080 cubic meters of remote-handled (RH-TRU) waste (equivalent to about 7500 canisters.) The facility itself consists of above ground construction, the underground panels, rooms and corridors where the waste will be emplaced and shafts connecting the two.
The above ground facility includes the Waste Handling Building where the waste is received, stored, and sent below ground in the waist hoist. Support structures as well as the intake and exhaust points for the repository air system, the Exhaust Filter Building and a surface salt storage area are also above ground as is an outside storage area for waste stored in transportation containers.
There are 4 shafts from the surface into the repository underground. The Construction and Salt Handling Shaft, the Waste Shaft, the Air Intake Shaft and the Exhaust Shaft. Since all the air in the repository exits to the surface through the Exhaust Shaft, this shaft is a major potential pathway for airborn radioactive and hazardous waste to reach the surface.
The underground repository is excavated 2150 feet below the surface in the Salado Formation--a bedded salt formation that is interspersed with relatively thin layers of clay and shale. When fully excavated, the underground repository would consist of 10 panels--8 side panels, each of which would contain 7 rooms, and 2 panel-equivalents in the main drifts or corridors.
The Wet Repository
The Salado salt was supposed to be dry but is, in fact, wet. (DOE calls it "essentially dry".) Water from the ancient sea that covered this area is locked into the salt crystals. This water seeps into the repository fairly quickly after the repository is mined. In addition, water has flowed into the Exhaust Shaft where the excavation makes connections to water-bearing formations. There are also many man-made connections to the clay seams and anhydrite beds above and below the repository which can leak water. It is actually not at all uncommon for salt mines to become inundated with water, and mining experts in both Carlsbad and Germany have said that all salt mines eventually flood. Some leaks are small, but some continue over a long period of time and cause a progressive flooding of the mine.
This water or brine has a huge potential to cause problems in the future since eventually parts of the repository may have large amounts of brine in contact with the waste. (Some parts of the repository are lower than the rest, so some rooms would collect brine sooner than others.) This would corrode the waste containers and the waste, and cause the waste to become mixed into a slurry which would be much more easily transported into the outside environment than dry waste would be. The brine also reacts with components of the waste and the steel waste containers to create gases which could affect the closure rate of the rooms or could push waste into the clay and shale layers.
There are radiation detectors in the Exhaust Shaft and below in the repository, but the detectors (called Continuous Air Monitors or CAMs) can be severely affected by the buildup of salt particles in the repository air—sometimes losing 90% of their plutonium detection efficiency. Water flowing into the Exhaust Shaft from the excavated rock also causes problems for the CAM there.
Exhaust air is not routinely filtered to remove radioactivity. Only if the CAMs detect alpha particles, is the exhaust air diverted through filters. This is what happened on Valentine's Day, 2014. Unfortunately, a significant amount of radiation was released before the filters kicked in. And because the filters are not 100% effective, radiation levels remain elevated above ground well after the initial event.
Interbeds as Pathways
Also of concern, are the connections that have been made to the interbeds above and below the repository. The salt in which WIPP is excavated is not completely pure but is periodically interrupted by layers of clay and anhydrite. These layers, called interbeds or sometimes marker beds, are continuous layers that run across the entire Delaware Basin for tens--or sometimes hundreds--of miles. Fluids can flow through these marker beds about 1000 times more easily than they can through the salt in the Salado Formation. So the flow of fluids into and contamination out of the repository is controlled not by salt but instead by salt mixed with clay, clay layers and fractured anhydrite layers. Marker Bed (MB) 138 is about 20 feet above the waste rooms and MB 139 is 3-5 feet below the floor (except where the floor has been milled virtually all the way down to Marker Bed 139). Both these marker beds are made up of fractured anhydrite and clay. Open fractures in the marker beds and openings along the clay seams where the anhydrite meets the salt can allow the water or brine to flow even faster. (In 1995, water from the Exhaust Shaft had moved through the repository floor to MB 139 and had already moved along this marker bed for several hundred feet.)
Mine maintenance and stabilization, (see the section on Panel 1 below) has created numerous connections to these interbeds above and below the repository. In describing the effects the stabilization system has had on the repository salt, the Environmental Evaluation Group (EEG), the State's former watchdog group, stated that "...the interbeds above the roof have been allowed to be fractured; at least 286 connections have been made between the room and the fractured anhydrite "b" layer through roofbolts; and, the floor of the rooms is thoroughly fractured and connected with the underlying heavily fractured Marker Bed 139 through periodic milling of the floors". (EEG-71: Mine Stability Evaluation of Panel 1 During Waste Emplacement Operations at WIPP) (Anhydrite layer b is between the repository and MB138 and is only 7 feet above the waste room ceilings.) In addition, the original panel closure designs allowed the salt to be excavated up to anhydrite layer b and down to Marker Bed 139 to give the closures more stability. This creates a direct connection to these 2 potential pathways.
All the shafts and boreholes that have been drilled on or near the site are additional potential release pathways after the repository has been closed, especially if the waste has been turned into a slurry. Each of them passes through numbers of marker beds. If a fracture, roof-fall or other event connects the waste rooms to a marker bed, that anydrite layer could become a horizontal pathway. Then a borehole or another fracture could allow contamination to travel higher. The marker beds connect the repository with the WIPP shafts and all other boreholes in the basin that cross them.
Subsidence fracturing could become a serious problem after the whole WIPP repository has been mined. There are 2150 feet of salt, rock and water above WIPP pressing down on the repository roof. As the salt closes in on itself, the roof will sag (subside) more and more. Room closure will become more and more rapid until the salt becomes brittle and the roof collapses causing subsidence and vertical fracturing of the layers above the repository. The effects of fracturing over the area of a single room would not travel up very far, but the effects over the area of the whole repository could be quite serious.
There is usually a thin layer of clay between a marker bed and the salt above and below it. There can be openings in this clay layer so that the salt is not actually tightly attached to the clay or anhydrite layers. When support disappears from underneath the salt and an overlying marker bed, the salt first sags and then breaks away at the clay seam. This causes support to disappear from the marker bed and salt layers above and the process is repeated over and over again.
An example of this is the Esterhazy salt mine in Germany where subsidence over a panel which was about the size of the WIPP repository caused fractures that went through 100 feet of rock salt and clay seams, crossed 18 feet of mudstone and breached an impermeable layer to reach the aquifer. Water from this aquifer eroded the fractures into solution channels and flowed into the mine. Sometimes water would run along a clay seam until it could force its way through the clay and carve through the salt into the mine. The speed of this erosion was spectacular and could excavate an area 4 feet by 100 feet by 1000 feet in weeks. Although the brines which entered the Esterhazy mine were saturated, the increase in temperature in the mine and the velocity of the bine flow allowed this water to dissolve the salt very rapidly.
It is unknown how far above the WIPP repository this subsidence fracturing would go. But even if it didn't reach all the way through the salt to the water in the formation above it, this fracturing would still breach many of the 40-plus marker beds above the repository. These breached interbeds carry a lot of fluid and it would all drain into WIPP. This could increase brine inflow to the repository by a factor of 20. If waterflooding were actively pushing water into any of these interbeds the problem would simply be multiplied enormously.
And the fractures would not necessarily have to go all to way to the Rustler Formation on their own. Above the repository, but still in the Salado Formation is an area of concentrated potash. (The Salado is not just made of one kind of salt but of several. Potash is one kind of salt that is used in agriculture. The halite around the repository is another kind of salt.) Most of the potash reserves in the United States are right around WIPP. So, although potash mining above the WIPP site is prohibited now, after time has passed it is likely that this resource will be mined--perhaps by waterflooding. If the mines are large, they will cause the same kind of subsidence fracturing as the repository does. This will make the connection from WIPP to the aquifers above it much easier.
Of course, if a pathway is created which lets fluid into the repository, that pathway then exists for contamination to be pushed out as well. Further waterflooding or a breach to the pressurized brine below WIPP could do this. Even salt creep could act as this pushing force; as the mine closes in on itself, air, gases and fluids containing contamination will be squeezed out of the repository and into the interbeds and fractures that will exist above and around the repository.
After WIPP has been filled with waste and closed, complex chemical reactions will begin to take place between the organic materials (plastics, cellulose, rubber), the radionuclides and chemicals in the waste, the metal in the containers and repository support structures, brine from the surrounding formations, and the magnesium oxide added to the waste as an engineered barrier. Although some general chemical reactions like methane production and radiolysis can be predicted, the real chemical conditions of the repository over time cannot be predicted with much accuracy be cause there are so many unknowns involved in the calculations. For one thing, so many chemicals mixed together--especially with the addition of radiation--can have unpredictable effects on one another, so what the exact chemical outcome will be becomes uncertain.
In addition, WIPP was originally certified by the Environmental Protection Agency (EPA) as being able to contain the waste before DOE truly understood the effects of their backfill or the solubility of plutonium. Both of these are critical to determining how much plutonium would be dissolved in the brine and therefore available for transport to the outside environment.