GROUNDWATER AT WIPP
2006 EPA WIPP FACT SHEET No. 5
Wh
at is Groundwater?
Groundwater is water that exists under the Earth's surface. Depending on the types of rock present, groundwater can be stored in
different quantities, and move at different speeds. In general, groundwater travels through dense rock exceptionally slowly, as slow
as a few feet over hundreds and even thousands of years. Groundwater moves more quickly through porous rocks where cracks, or
fractures, exist. Such rocks are said to be permeable to groundwater.
How Does Groundwater Affect the WIPP?
For over 25 years, DOE scientists have studied
groundwater flow and conditions at the WIPP site
to determine potential pathways for radioactive
releases. DOE's certification application identi-
fied two geologic units that are potential ground-
water pathways for radioactive releases to the
environment:
1. The Culebra Dolomite
unit in the Rustler
Formation
2. The Salado Anhydrite
units within the salt bed
and close to the waste.
Although none of the geologic
units above the repository are highly permeable,
the most permeable unit is the Culebra Dolo-
mite. Because the Culebra is located over 1,000
feet above the WIPP repository, radioactive re-
leases into this rock unit would only be possible
if a borehole was drilled through the repository.
The Salado Formation contains thick layers of
salt, thin layers of anhydrites, and some clay.
The Salado Anhydrite units are located above
and below the zone where waste is being placed.
(You may see them referred to as marker beds
138 and 139.) Even though the Salado has very
low permeability to groundwater, it is still mod-
eled (via the marker beds) as a potential pathway
for radioactive releases.
Dockum
Group
Ground
Surface
Feet
500 —
1000-
1500.
2000.
2500-
3000-
3500-
4000-
4500-
Meters
-200
-400
-600
-800
-1000
-1200
-1400
Cross-section showing major geologic units
above and below the WIPP repository.
United States Environmental Protection Agency I Office of Air and Radiation (6608J) I EPA402-F-06-010
www.epa.gov/radiation/wipp
March 2006
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Both groundwater units were included in DOE's calcula-
tions for the certification performance assessment. Both
units were found to have only very minor contributions
to releases from the WIPP repository. This is due to the
large amount of time it would take radionuclides to travel
through them, and the limited amount of radionuclides
expected to reach them.
Monitoring of Groundwater at WIPP
• As part of the overall monitoring plan for WIPP, DOE
maintains an extensive groundwater monitoring program.
• EPA conducts annual inspections of the DOE's ground-
water monitoring program and receives and analyzes
periodic reports on groundwater data from DOE.
• Since 1998, DOE has reported overall increases in water
levels in the wells that monitor the Culebra Dolomite
unit.
• DOE is drilling new wells to enhance monitoring of the
Culebra Dolomite unit.
• EPA has identified the need for DOE to increase under-
standing of the hydrologic characteristics of the geologic
units above the repository, such as the Magenta.
EPA's Technical Evaluation of Groundwater in the
2004 Recertification Application
The 2004 recertification application appropriately docu-
mented changes in the water levels of the Culebra Dolomite
wells. The changes were incorporated into the groundwater
modeling of the performance assessment. These changes
resulted in longer times for projected radionuclide releases
than were last estimated in the certification application.
EPA determined that DOE adequately incorporated ground-
water changes into the recertification application, including
the performance assessment.
For more information on EPA's evaluation of groundwater
for recertification, go to EPA's website or docket to the
Compliance Application Review Documents for Section 15.
Fact Sheets in this Series:
Recertification 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
Fact Sheet No. 6
United States Environmental Protection Agency I Office of Air and Radiation (6608J) I EPA402-F-06-010 I March 2006
www.epa.gov/radiation/wipp
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