Dr. David Snow was the first rebuttal witness for
Citizens for Alternatives to Radioactive Dumping (CARD)
Dr. Snow has degrees in geology and engineering science. Dr. Snow's thesis
was on Flow Through Fractured Media. Dr. Snow has worked for 45 years as a
consultant, mostly in the mining industry, on hydrology, geology, and
geotechnical engineering. He has also consulted on nuclear waste disposal,
including 14 months at WIPP where he reviewed WIPP's hydrology. In 1986
Dr. Snow reviewed the No-Migration Petition for the WIPP site. Dr. Snow
did not think WIPP was feasible because when caverns in plastic salt close,
it causes new stresses on the waste as it evolves.
REBUTTAL TESTIMONY OF DR. DAVID T. SNOW; March 25, 1999.
Dr. Snow's work at WIPP emphasized transport in the Rustler, especially in
the Culebra Dolomite. Dr. Snow was critical of the tracer test design for
the Culebra. Dr. Snow believed the tracer test needed a better database of
the physical properties of the Culebra in order to set up the test in a
better way. The Culebra has gypsum filled fractures throughout which are
leached out from east to west. Dr. Snow believes there is a lack of
understanding of the evolution of the Culebra. If glassy gypsum (selenite)
is found, this is proof that it has evolved by dissolution and the flowing
of groundwater. The Culebra in the outcrop along the Pecos River shows
evidence of dissolution of the dolomite and a complicated history of
interfilling of vugs. The primary permeability has been altered so now it
has a secondary permeability. The partially open fractures in the Culebra
are the main reason for the permeability in that unit.
BRINE INFLOW FROM THE SALT, DISTURBED ROCK ZONE (DRZ)
AND ANHYDRITE BEDS
The assumption is that most brine is in the salt and anhydrite, but most
transport will be in the anhydrite beds. The anhydrite beds have measured
properties about one million times that of the salt. Salt has low
permeability in the laboratory, but in the field, salt has six orders of
magnitude more permeability. The Salado, as a whole, has more horizontal
permeability than vertical permeability. Salt does not have perfectly
plastic flow. Salt can also be brittle. If the stress is at a higher
rate, the salt will be brittle and will fracture as it has done in some of
the ceilings in the WIPP site.
Coring at WIPP has suffered because the DOE uses a single tube core barrel
(commonly used for potash mining) and this seldom gives good results with
fractured, weathered rock or discontinuous features. This example
demonstrates DOE's lack of understanding of core. There is little intact
core in the WIPP Core Library. Most of the core is rubble so there is a
lot of debate about the true origin of the claylike features recovered.
The Rustler characterization problem is compounded by the exploration
difficulty. It is easy to miss the largest flow path, but it is possible
to see residues left behind when the path moves elsewhere. There is a thin
interval of clay in the core. If the highest core technology is not used,
the clay will be ground up.
Dr. Powers does not believe the salt beds were present and then dissolved
from the Rustler. Most of the scientific community disagrees with Dr.
Powers because they know the WIPP site is located in a karst region. Dr.
Powers is in error. However, dissenters who believe there is karst at the
WIPP site have left the DOE and Sandia. Dr. Powers is the principle author
of most of the data that relates to karst at the WIPP site.
The logging of the Exhaust Shaft lithology of the Rustler rings true to Dr.
Powers' interpretation that it was formed in alluvial channels on the
surface with cross bedding, laminations, pebbles, etc., which are typical
of streams. But there are similar features at 3,000 feet below ground
surface (bgs) that were formed by open flow in large evaporite channels.
One thing unique to Dr. Powers' logs of the clay members is the presence of
"slickensides." This is especially true, since Dr. Powers' logs are all
The permeability of the Salado is very low, about 10 to 21 meters/second.
The anhydrites are about 3 orders of magnitude more permeable. But what is
important is how fractures propagate above a mined repository. The whole
WIPP repository is not mined now.
Dr. Snow showed a series of slides and viewgraphs of the Kominko Mine near
Saskatoon and the K-2 mine at Esterhazy. The slides and viewgraphs showed
that after a few years there was sagging of the roof and fracturing at a 45
degree angle above the roof with breaches up to the horizontal clay
partings. The typical failure at WIPP and elsewhere in salt mines will be
a sudden collapse of the roof. Dr. Snow was once in a mine where a roof
fall occurred about a mile away from where he was and he was almost bowled
over by the blast of air through the drifts.
None of the packaging at WIPP can absorb the stresses of roof slabs that
weigh hundreds of tons. Drums will be crushed, will leak, and their
contents will spill out. The first line of defense--engineered
barriers--will not be very effective. Fractures through the roof and floor
can carry free liquids away from the repository. After the waste is
crushed and mixed with brine and salt, retrieval is only tongue in cheek.
The slides showed that subsidence fractures reached well above the opening.
WIPP and all mines track subsidence rates at the surface. Typical rates
are about 3 to 6 inches/year. As the rooms close the rate will be about 12
inches per year below. Closure will be more and more rapid until the salt
becomes brittle and the roof collapses. It is unclear what will happen
above Marker Bed 138 or what the extent of the fractures above this marker
bed will be. The best evidence is to go to an analog situation. It would
be nice if the DOE could have explored some of the old potash mines in the
WIPP area. But when the DOE had the opportunity to do this, the DOE
decided against it.
In the K-2 mine slide, it is possible to see the roof deflecting, the beam
bends, and there is shear of the lower member above the upper member. This
slide demonstrates what is shearing the WIPP rock bolts as well. Nothing
can be done about that.
At Esterhazy the roof fractures went through 100 feet of overburden,
breaching the integrity of the rock salt and clay seams. There were
inclined fractures. The sagging roof beams relieved the vertical stress,
but the horizontal stress stayed the same. Salt stress is usually
lithostatic and the failure that happens is a thrust fault (fractures in
one block move up and the other block moves down). The fractures reached
up to the top of the salt, crossed 18 feet of mudstone (the First Redbeds)
and breached the impermeable Redbeds to the dolomite aquifer. Leakage
occurred along the fractures. Because of the tremendous gradient of 3,000
feet of water, eroded solution channels in the roof provided the pathway
and the water drained into the mine. Sometimes water would run along a
clay seam until it could force its way through the clay. Then the water
carved its way through the salt into the mine. First, there was a solution
channel flat along the seam and then the water dug a gorge into the panel.
The subsidence is not just over one room, but over the rooms acting
together as a panel. There was a steep fault from the roof into the
It is impossible to know exactly what will happen over the WIPP repository,
but the situation is sufficiently analogous to the examples shown here.
Every anhydrite bed is bordered by clay. This thin seam of clay is where
the roof breaks away and it will continue to break away at the clay seams.
The most brine that has been estimated to inflow is about 800 liters/meter
of room, which is about 2% saturation. This is fairly insignificant and
the brine is carried away by evaporation. But the Repository has about a
1% dip to the east. The floor will be fractured to the marker bed below and
brine will accumulate in the down dip region while the upper portion will
be drained. Some rooms will be flooded before others.
Fracturing above the roof could go up at least 300 meters so that the
breach would occur in the salt and in all the anhydrite beds. Dr. Snow
could not say if the fracturing would go all the way to the Rustler, but
stated that the fracturing will multiply the amount of brine inflow by a
factor of 20. The fractures would also provide passages of egress for air,
evolved gases, and fluids as the mine opening loses pore space due to
creep. The fractures can let fluids escape from waterflooding, drilling,
or the tapping of Castile brines. Finally, the subsidence fractures in the
roof can facilitate the escape of fluids from the repository and it is
possible the fractures could go all the way to the Rustler.
HIGHLIGHTS OF CROSS EXAMINATION OF DR. SNOW
The Lowenstein report concluded that dissolution does not have to remove
all the primary sedimentary features. There will still be traces of salt,
clay, and other insoluble residues.
The first anhydrite layer is actually Anhydrite B (7 feet above the
repository), which is 6 feet above Anhydrite A. Above those Marker Bed
138. The clays associated with the boundary with any of these anhydrites
are the most important. There are thin clay seams associated with the
anhydrite/salt interfaces of most of the anhydrites. There are also thin
clay seams without anhydrite. Shear strength on clay partings is less than
that of the salt. When friction on the partings is destroyed, the whole
system sags because there is no shear strength on the partings. Failure
implicit in one beam is implicit in all of them. If there are 43 marker
beds up through a thousand feet of salt, failure can propagate all the way
Slickensides are features on a dislocation surface that reveal the relative
movement of the rocks.
The speed of erosion from the water in the examples that Dr. Snow gave
could be spectacular. The biggest leak was up to 8,000 gallons/minute and
could dissolve the salt in days or weeks. It could excavate an area 4' x
100' x 1000' in that time. The brines entering the mine through the cover
rocks was already very saturated. A little change in temperature (which
increases as you go deeper) controls the dissolution rate. Also velocity
controls the rate. Even if the brine is saturated, it is possible to have
dissolution of the salt if the velocity is high enough.
Dr. Snow is aware that the RCRA timeframe is 80 years.
The K-2 was at a horizon that was below 90 to 110 feet of salt. Over this
horizon was mudstone--the First Redbeds--which were about 30 feet thick.
Over that layer was the brine saturated Dawson Bay Limestone, which was
about 250-300 feet thick. The K-2 mine was about 3100 feet below ground
surface (bgs). There is 1,300 feet of salt between WIPP and the Rustler
and no 30-foot thick mudstone layer above the repository. There is also no
250-300 foot thick limestone layer and WIPP is at 2,150 feet bgs. In a
gross sense, there is a difference in the stratigraphy between K-2 and
WIPP. Also, all 10 panels of the whole WIPP repository are about the size
of a single panel at K-2.
The DOE claims that only 40% of the total subsidence will occur during the
80 years of the RCRA timeframe. Dr. Snow stated that that figure is not
necessarily shown in the DOE documents and that the figure would have to be
There are about 40 marker beds above WIPP. WIPP hydrology needs better
delineation even with all the wells that have already been drilled. The
Culebra fractures are also vertical. The fractures will probably not be
found so the frequency, orientation, apertures etc., of the fractures in
the Culebra are not known well enough to do transport modeling. The
willingness of the DOE to find what is necessary to do the characterization
in the zone between the repository and the surface remains incomplete.
Subsidence fractures may transect large parts or all of the Salado.
Shafts, boreholes, etc. will be breached by fractures. The sealing of the
shafts and boreholes is immaterial if fractures compromise them. Brine in
the down dip rooms compromises the panel seals even though it is not
claimed that the panel seals are barriers to movement. The technology of
borehole sealing is debatable and has been researched for many years. An
experiment to verify the ability to seal boreholes is impossible. Salt
causes corrosion of the sealing materials. There is an effect of shear on
the boundary with stiff and compliant sediments. A small leak along the
contact will soon become a solution passage.
In Esterhazy, the German consultant said that every potash mine ultimately
floods. Ralph Crosser in Carlsbad also said they all leak. Clay seams and
anhydrite beds leak water. Some leaks are small, but some continue over a
long period of time and cause a progressive inundation of the workings.
Subsidence from roof-falls would not go to the surface from a single room,
but perhaps subsidence could from an entire panel or the whole repository.
The groundwater in Mexico probably would not be contaminated by WIPP, but
it is the quality of water in the Rio Grande that is at risk.