2005 EPA WIPP RECERTIFICATION FACT SHEET No. 6
Karst in the Area of WIPP
Some stakeholders believe that the geologic characteriza-
tion of the subsurface surrounding the WIPP repository
does not adequately identify the presence of karst. As a
result of these concerns, EPA agreed to re-evaluate the po-
tential for the presence of karst at WIPP and the possible
impacts of the long-term containment of waste for WIPP
Recertification.
While the EPA has not seen any indicators of karst within
the Land Withdrawal Boundary to date, additional data can
improve the details of our understanding of the geology
around the WIPP site. EPA is continuing to review informa-
tion related to karst at WIPP and the Agency will provide
its findings at the time of the final recertification decision.
During the time of certification, EPA reviewed existing
information to understand the issue of karst around the
WIPP site. As a result of that review, EPA agreed that there
are karst features in the vicinity of the WIPP site, but that
karst feature development will not impact the contain-
ment capabilities of the WIPP for at least the 10,000-year
regulatory period.
EPA based its decision on multiple lines of evidence
including:
• Hydrologic testing. Pump tests on wells drilled into the
Culebra Dolomite within the Land Withdrawal Boundary
show evidence of flow through the rock matrix, fracture
flow or both, however, they do not indicate any con-
nection to cavernous flow zones. EPA's analysis of all
available data supports the conclusion that karst fea-
tures have not been found within the Land Withdrawal
Boundary.
• Geologic information. The widespread evidence of the
Mesacalero caliche (a desert soil formed by the near
surface crystallization of calcite and/or other soluble
minerals by upward-moving solutions) indicates that
infiltration around the WIPP site is minimal and has
What is Karst?
Karst is a type of topography in which there are
numerous sinkholes and large voids, such as caves.
Karst is caused when soluble rocks dissolve. Karst
may form when rainwater, reacting with carbon dioxide
from the air and forming carbonic acid, seeps through
the soil into the rock. Soluble rock includes limestone
and evaporite rocks, such as halite (salt) and gypsum.
If substantial and abundant karst features were pres-
ent at WIPP, this could increase the speed at which
releases of radionuclides travel away from the reposi-
tory through the subsurface.
been so for the past 500,000 years. EPA's conclusions
are also supported by recent research in the desert
southwest. This research affirms DOE's expectation
of minimal infiltration at the WIPP site over the last
10,000 to 15,000 years.
Karst is present west of the WIPP site in Nash Draw. Nash
Draw formed around 600,000 years ago from dissolution
and erosion of rock and is still being modified by these
processes.
The Rustler Formation, which includes the Culebra and
Magenta Dolomites, is near the surface where it intersects
with Nash Draw and appears susceptible to infiltration of
water from the surface. DOE studies indicate that the sub-
surface dissolution of the Rustler Formation extends east
under Livingston Ridge, but does not approach the WIPP
Land Withdrawal Boundary (LWB). The LWB is the point at
which DOE must demonstrate compliance with regulatory
release limits.
United States Environmental Protection Agency I Office of Air and Radiation (6608J) I EPA402-F-05-007 I June 2005
www.epa.gov/radiation/wipp
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Legend
Easternmost wells
with evidence of
possible Karst
Roads
WIPPtacility
Lew Elevations {Nash Draw)
are yellow (lighter) color. Higher
Elevations are brown to blue.
Miles
I
0
i i I i
12
i ' I
4
This surface map shows a selection of natural and
man-made features in the vicinity of WIPP. Nash
Draw has the lowest elevation in the area, around
3000-3200 feet above sea level. The center of
the WIPP site is about 3400 feet above sea level.
Shown also are the three easternmost wells found
to have evidence of possible karst features. No test
wells from inside the Land Withdrawal Boundary
have yielded data indicative of karst.
In contrast, the ground surface at the
WIPP site is located several hundred
feet above and to the east of Nash
Draw and Livingston Ridge. Because
the Rustler Formation dips, or tilts,
to the southeast and is topographi-
cally lower than the plateau on which
WIPP is located, the Rustler is more
than 500 feet below the ground at the
WIPP site itself and over 1,000 feet
above the repository.
Ongoing EPA Activities
To ensure we have a complete under-
standing, the EPA continues to con-
duct a number of activities to further
investigate any potential for karst near
the WIPP site.
• EPA is examining the geophysical
methods suggested by stakehold-
ers to locate karst and will prepare
a report on the efficacy of using
these methods at the WIPP site. A
final report will be released in con-
junction with the Recertification
Decision, but preliminary findings
can be found in Issue Paper #5,
Stakeholder Karst Proposal.
• EPA is conducting a thorough re-
view of geologic and hydrologic in-
formation related to karst. As part
of this effort, EPA made a field trip
to re-examine the evidence of karst
around the WIPP site.
• EPA is looking for karst indicators
such as sinkholes, evidence of
large-scale water exchange under-
ground, or rapidly flowing springs
in the vicinity of WIPP. EPA will
release a report documenting our
findings in conjunction with the
Recertification Decision.
• EPA is considering all pertinent
information, including the 1999
draft report by Carol A. Hill, Letter
Report: Intrastratal Karst at the
WIPP Site.
• EPA requested that DOE/Sandia
National Laboratory (SNL) conduct
a separate analysis of the potential
for karst. This work will be com-
plete in Summer 2005.
• EPA also requested DOE/SNL to re-
view the hydrologic data and better
explain why it believes that the data
does not reflect karst development.
• EPA is also investigating an allega-
tion that the draft Mercer and Orr
(1979) report, Interim Data Report
on the Geohydrology of the pro-
posed Waste Isolation Pilot Plant
Site Southeast New Mexico (USGS
WRI 79-98), was modified. This
work is ongoing.
• EPA has identified the need for
DOE/SNL to perform additional
testing of the Magenta and other
units in order to verify that their
present understanding of these
units has not changed.
Fact Sheets in this Series:
Recertification Overview Fact Sheet No. 1
Public Involvement Fact Sheet No. 2
Performance Assessment Fact Sheet No. 3
TRU Waste Inventory Fact Sheet No. 4
Groundwater Fact Sheet No. 5
Karst
Fact Sheet No. 6
United States Environmental Protection Agency I Office of Air and Radiation (6608J) I EPA402-F-05-007 I June 2005
www.epa.gov/radiation/wipp
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