GROUNDWATER
RESTORATION LONG BEYOND CLOSURE AT THE HOMESTAKE-MILAN AND UNITED NUCLEAR-CHURCH
ROCK URANIUM MILL TAILINGS PILES, NEW MEXICO, USA: FULL-SCALE PROGRAMS REQUIRING
MORE THAN 20 YEARS OF ACTIVE TREATMENT
In:
"Proceedings of Conference on Uranium Mining and Hydrogeology - II", Claudia
Helling, et. al. editors, Technical University -Freiberg, Saxony, Germany,
September, 1998
Wm. Paul Robinson(1)
(1) Wm. Paul Robinson is Research Director, Southwest
Research and Information Center, P. O. Box 4524, Albuquerque, NM
87106
Abstract
Since as early as 1975, groundwater contamination from New Mexico uranium
mill tailings has been investigated with two sites - Homestake-Milan and United
Nuclear- Church Rock - showing severe enough groundwater damage to merit listing
on the US Environmental Protection Agency's (EPA) Superfund National Priority
List - a nationwide list based on severity of pollution and water resource
usefulness. These two sites provide valuable case studies for the first - 1950s
- and second - 1970s - generations of uranium mill tailings facilities
demonstrating the severity of contamination which ineffective control can allow
and the challenge of full scale groundwater restoration. While the groundwater
restoration at these sites began in the 1970s and 1980s, active treatment is
anticipated into the 21st century.
This paper summarizes the groundwater restoration programs at two of these
sites - Homestake Mining Company's (HMC) Milan Mill (now called the "Grants
Project") and United Nuclear Corporation's (UNC) Church Rock Mill. The two sites
are summarized with respect to operations, groundwater impact, tailings disposal
systems, hydrogeological characteristics of the site and affected areas,
applicable standards, and remedial technology applied. This review provides a
basis for initial comparisons with uranium mill tailings groundwater restoration
challenges outside the USA.
These sites provide an important benchmark the complexity of restoration at
for large-scale uranium mill tailings sites. The longevity of the restoration
efforts demonstrate the results of low-intensity responses to contamination upon
detection and delayed enforcement actions. These "witnesses" to the value of
effective pollution prevention in tailings design and full review and monitoring
of tailings operations, have potential to be models of effective groundwater
restoration.
Introduction
Home to 45% of USA uranium production, New Mexico and its resident uranium
producers established seven uranium mills and tailings piles, each with a
extensive pattern of ground water contamination. Two of the site, HMC's Milan
Mill - now called the "Grants Project" - and UNC's - Church Rock Mill, have been
included on the USEPA's Superfund National Priority List - a nationwide list of
sites ranked on the basis of severity of pollution and usefulness of affected
water resources - are the focus of this paper.
Both sites are subject to groundwater restoration requirements of New Mexico
Water Quality Control Commission (NMWQCC) groundwater regulations, (USNRC)
uranium mill tailings reclamation criteria - 10CFR20 Appendix A - and USEPA's
"Superfund" Program. These groundwater restoration programs are in addition to
site-wide surface remediation, including tailings pile regrading, stabilization
and capping programs required by the USNRC under authority of the 1978 US
Uranium Mill Tailings Radiation Control Act (UMTRCA) as active sites - Title II.
As "active sites" in operation when UMTRCA became law, the Grants Project and
Church Rock facility's costs of compliance USNRC, EPA and NMWQCC requirements
are borne by the site owner-operator, rather than USA and State-government
funded reclamation as with "inactive - Title I - sites".
Groundwater investigations at both sites detected groundwater contamination
in the late 1970's. EPA investigations near the Homestake-Grants site
demonstrated dramatically increased levels of uranium, radium, chloride,
molybdenum, nitrate and selenium. These 1975 analyses of ground water in
residential drinking water wells downgradient of the mill showed selenium
concentrations up to 3.42 mg/l - more than 300 times the maximum recommended for
drinking water. Extensive groundwater contamination at the UNC-Church Rock
tailings was first detected in 1979, soon after the mill reopened following
repair of 10 meter breach in the tailings dam. Significant levels of chloride,
sulfate, nitrate, radium and thorium were among the many elevated constituents
detected in either alluvial or bedrock aquifer systems.
Both sites continue to undergo groundwater restoration long after demolition
of the mill facilities and closure of surface reclamation of the tailings piles.
Progress to date indicates a requirements for further groundwater treatment into
the 21st century.
Site Overviews
The HMC-Grants operation processed 3,500 ton of uranium ore per day in an
alkaline leach mill from 1958 - 1990, producing two tailings piles, a 1,200,000
ton "inactive pile" and a 21,000,000 ton active pile, both which were unlined.
The large tailings pile was constructed using a "ring-dike" system, with a small
starter "ring" raised with cyclone-separated tailings continuously over the 32
year life of the operation to create a 30 meter tall, 100 hectare pile.
The
tailings liquids were confined within the rectangular "ring dike" of tailings on
top of the pile, substantially increasing the hydrostatic force carrying seepage
through the unlined pile into the underlying alluvial aquifer. Restoration at
this third largest uranium mill tailing sites in the USA has included extraction
of contaminated fluid at the downgradient end of the plume and injection of
clean water between the pile and the plume margin to create an artificial ground
water mound. Alternative water supplies have been provided to residents of the
affected downgradient residential communities for more than 15 years.
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