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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