The Edgemont Site in South Dakota contains a 145-hectare disposal cell that encapsulates contaminated tailings and waste from a former uranium mill. Long-term stewardship activities at the site include annual inspections of the disposal cell, restricting access, and maintenance. The disposal cell will be monitored and maintained in perpetuity at an estimated average annual cost of $7,800. The site provides long-term isolation of 2.3 million cubic meters of contaminated material beneath an engineered cap designed to last 200-1000 years.

1. Edgemont
South Dakota
Long-Term Stewardship Site Highlights
Edgemont Site (page 3)
Major Activities- disposal cell monitoring; access restrictions; inspections;
maintenance
Site Size -145 hectares (360 acres)
Start/End Years - 1996/in perpetuity
Estimated Average Annual Cost FY 2000-2006- $7,800

3. Table of Contents
Table of Contents
Edgemont Site .......................................................................... 3
South Dakota I

4. National Defense Authorization Act (NDAA) Long-Term Stewardship Repm·t
South Dakota 2

5. Edgemont Site
EDGEMONT SITE
1.0 SITE SUMMARY
1.1 Site Description and Mission
The Edgemont Site (also known as Edgemont Vicinity
Properties) is the location of a disposal cell built by the
Tennessee Valley Authority (TVA) to encapsulate
uranium mill tailings and other contaminated materials
from the former Edgemont Mill, located 3.2 kilometers
(two miles) away. The 145-hectare (360-acre) site is
located in the southwest corner of the State of South
Dakota, approximately five kilometers (three miles)
south ofthe town of Edgemont. The site's disposal cell
occupies 40 hectares (100 acres) of the site.
Uranium ore processing operations at the nearby former
mill created uranium mill tailings and other process-
related wastes. TVA built the disposal cell at the
Edgemont Site as part of the Edgemont Mill's
remediation strategy. TVA encapsulated the tailings
LONG-TERM STEWARDSHIP HIGHLIGHTS
Major Long-Term Stewardship Activities - disposal
cell monitoring; access restrictions; inspections;
maintenance
Total Site Area -145 hectares (360 acres)
Estimated Volume ofResidual Contaminants-
engineered unit 2.3 million cubic meters (3.0 million
cubic yards)
Long-Term Stewardship Start-End Years- 1996-in
perpetuity
Average Annual Long-Term Stewardship Cost FY
2000-2006-$7,800
Landlord- U.S. Department of Energy, Grand
Junction Office
and other contaminated wastes from the former Edgemont Mill materials in the cell in 1989.
The current mission for the site is the long-term monitoring and maintenance of the disposal cell. The disposal
site is subject to Title II of the Uranium Mill Tailings Radiation Control Act of1978 (UMTRCA). As such, the
DOE Grand Junction Office is responsible for long-term stewardship activities at the site. DOE began long-term
stewardship activities in 1996.
The Edgemont Site had no historic mission, otherthan to be the final repository for the contaminated mill tailings
and soils remediated from the former Edgemont Mill. The historic mission ofthe Edgemont Mill was to process
and provide uranium to support the U.S. Government national defense program. Mines Development, Inc. built
the Edgemont Mill in 1956 to process uranium ore and operated it until1974. Almost all the ore processed at
the Edgemont Mill was mined in the Black Hills area of southwestern South Dakota and northeastern Wyoming.
TVA acquired the mill facility in 1974, but decided against processing uranium ore at the mill based on
engineering, economic, and environmental studies. Therefore, TVA never operated the mill.
1.2 Site Cleanup and Accomplishments
In 1986, the U.S. Nuclear Regulatory Commission (NRC) approved the reclamation alternative to relocate the
tailings to an engineered disposal site located 3.2 kilometers (two miles) from the former Edgemont Mill.
Decommissioning activities began at the mill site in 1986, and reclamation was completed by 1989. Remediation
of the Edgemont Mill consisted of demolishing site structures, excavating onsite contamination, and relocating
mill tailings and contaminated structural materials into the Edgemont Site disposal cell. Concurrently,
contaminated materials from vicinity properties in and around the town ofEdgemont were removed and disposed
ofin the Edgemont Site's disposal cell. The disposal cell contains 4,000,000 tons ofcontaminated material, with
an estimated total activity of 527 curies of radium-226.
The base of the disposal cell lies on shale of the Belle Fourche Formation, which has a thickness of 56.4 meters
(185 feet) immediately offthe site. Underlying the Belle Fourche Formation are more than 91 meters (300 feet)
South Dakota 3

6. National Defense Authorization Act (NDAA) Long-Term Stewardship Report
of generally impermeable strata that isolate the uppermost confined aquifer from the surface. Consequently, no
groundwater remediation or monitoring is needed at this site.
Edgemont Site
TVA conducted all remediation at the site under its NRC license. Once reclamation was complete, the site was
eligible for transfer to DOE for custody and long-term care. To enable the site's transfer to DOE, TVA provided
a one-time payment to the U.S. Treasury to cover monitoring and maintenance costs. The Edgemont Site was
transferred to DOE in June 1996 for long-term stewardship activities.
2.0 SITE-WIDE LONG-TERM STEWARDSHIP
2.1 Long-Term Stewardship Activities
The DOE Grand Junction Office is responsible for performing long-term stewardship activities ofthe Edgemont
Site. Access to the site is controlled by a locked stock fence around the perimeter of the site. DOE permits
limited grazing on the land to maintain the health of the vegetation. Signs and markers notify potential intruders
of the final site conditions. A metal sign displaying the international trefoil symbol for radioactive materials is
placed at the site entrance and replaced as necessary. DOE performs sign and fence repairs on an as-needed
basis. No drilling or other intrusive activities are allowed within the property boundary.
Site records are in permanent storage at the DOE Grand Junction Office in Colorado. The types of records
maintained include site characterization data, remedial action design information, the site completion report,
long-term monitoring plans, annual inspection reports, and current and historic monitoring data. DOE develops
South Dakota 4

7. Edgemont Site
and updates records and reports required in the site long-term surveillance plan. These reports are submitted
annually to the NRC to summarize, describe, and evaluate all surveillance and maintenance actions, as required
under Title 10 of the Code ofFederal Regulations, Part 40.
2.2 Specific Long-Term Stewardship Activities
Engineered Units
The Edgemont Site disposal cell is approximately 426
meters (466 yards) wide and 944 meters (1,033 yards)
long and occupies 40 hectares (100 acres) of the 145-
hectare (360-acre) site. The cell contains
approximately 2.3 million cubic meters (3.0 million
cubic yards) of uranium mill tailings, soils, and
construction debris contaminated with radium and
thorium.
STAKEHOWER INTERACTION
Community interaction has been minimal since the
remedial action was completed. Copies of the annual
inspection report for the Edgemont Disposal Site are
distributed to the State of South Dakota and to any
stakeholders requesting them. The report is also
published on the DOE Grand Junction Office website
at www.doe.gjpo.com.
The 2.7-meter (three-yard) thick cover over the tailings consists ofa 0.91-meter (one-yard) thick compacted clay
radon barrier, a 1.52-meter (1.7-yard) thick compacted fill frost protection layer, and a 0.3-meter (0.3-yard) thick
layer of topsoil material. The Edgemont Site disposal cell was designed and constructed to last for 200 to 1,000
years, in accordance with EPA standards. The cell design promotes rapid runoff of precipitation to minimize
leachate. The site location and design were selected to minimize the potential for erosion from onsite runoff or
storm water flow. All surrounding disturbed areas were regraded and reseeded to prevent wind and water
erosion. An existing gully northwest of the cell and the containment dam face were armored with riprap for
erosion protection. Additional riprap and grass-protected diversion ditches were installedto channel runoffwater
away from the disposal cell.
Long-term stewardship activities at the site include annual inspections of the disposal cell and maintenance, as
needed. Grazing is allowed to enhance the success of the revegetation efforts.
Groundwater
Because of the more than 91 meters (300 feet) of generally impermeable strata that isolate the uppermost
confined aquifer from the surface, no groundwater monitoring or remediation is needed.
2.3 Regulatory Regime
In 1996, the Edgemont Site came under a general license issued by NRC for custody and long-term care of
residual radioactive disposal sites (contained at Title 10 ofthe Code ofFederal Regulations, Section 40.28). The
purpose ofthe general license is to ensure that such sites will be cared for in a manner that protects human health
and safety and the environment. The general license went into effect when NRC agreed that the site conformed
to cleanup standards and formally accepted the site-specific long-term surveillance plan.
Long-term stewardship activities at the Edgemont Site are governed by several requirements in the following
acts: the Uranium Mill Tailings Radiation Control Act of1978; the Atomic Energy Actof1954, as amended, and
the National Environmental Policy Act of1969, as amended.
2.4 Assumptions and Uncertainties
Because DOE Grand Junction Office has been performing long-term stewardship activities at the site since 1996,
South Dakota 5

8. National Defense Authm·ization Act (NDAA) Long-Term Stewardship Repm·t
long-term stewardship activities are well known and are not expected to dramatically change.
The cap over the disposal site is not expected to be replaced for a minimum of 200 years. In addition,
groundwater monitoring is not anticipated since there exists immediately offthe site an impermeable strata which
isolates the uppermost confined aquifer from the surface.
3.0 ESTIMATED LONG-TERM STEWARDSHIP COSTS
TVA made a one-time payment of $581,610 to the U.S. Treasury in June 1996, as required under UMTRCA, to
cover the costs associated with long-term stewardship activities of the site.
The cost estimates, identified below, are based on the costs of ongoing long-term stewardship activities at the
site. Contingency costs, such as cap replacement, have not been incorporated in the cost estimates.
Site Long-Term Stewardship Costs (Constant Year 2000 Dollars)
Year(s) Amount Year(s) Amount Year(s) Amount
FY 2000 $10,800 FY 2008 $7,000 FY 2036-2040 $34,100
FY 2001 $8,300 FY 2009 $7,000 FY 2041-2045 $34,100
FY 2002 $7,200 FY 2010 $6,900 FY 2046-2050 $34,100
FY 2003 $7,000 FY 2011-2015 $32,700 FY 2051-2055 $34,100
FY 2004 $7,100 FY 2016-2020 $31,800 FY 2056-2060 $34,100
FY 2005 $7,100 FY 2021-2025 $31,900 FY 2061-2065 $34,100
FY 2006 $7,000 FY 2026-2030 $33,700 FY 2066-2070 $34,100
FY 2007 $7,100 FY 2031-2035 $34,100
4.0 FUTURE USES
The primary future use of the site will be the long-term surveillance and maintenance of the onsite disposal cell.
DOE permits some limited grazing on the land to ensure the health of the vegetation.
For more information about the Edgemont Site, please contact:
Art Kleinrath, Long-Term Surveillance and Maintenance Program Manager
U.S. Department of Energy, Grand Junction Office
2597 B3/4 Road, Grand Junction, CO 81503
Phone:970-248-6037
or visit the Internet website at http://www.doegjpo.com
South Dakota 6