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In 2003, DOE implemented the first phase of an interim
action system at the site to address concerns regarding
elevated ammonia levels in ground water while it evaluates
long-term solutions to site contamination. Referred
to as Configuration 1, the first phase consisted of
10 closely spaced extraction wells designed to remove
contaminant mass (ammonia) from the ground water system
before it discharges to critical habitat areas of
the Colorado River. Configuration 1 extraction wells
and the lined evaporation pond became fully operational
in early September 2003. During 2003, ground water
was extracted from the shallow aquifer and pumped
via pipeline to the evaporation pond. The evaporation
pond covers approximately 4 acres and was constructed
outside the 100-year floodplain, on top of the tailings
pile.
Configuration 2 of the interim action was completed
in 2004 with the addition of a series of 10 dual-purpose
extraction and fresh water injection wells to the
north of Configuration 1. Installation of Configuration
3 of the interim action was completed in August 2005
and consists of another series of 10 dual-purpose
extraction and fresh water injection wells to the
north of Configuration 2 along the river bank. Configuration
4, which is located to the south of Configuration
1 and consists of 10 dual-purpose wells, became operational
mid-September 2006. As of June 30, 2008, more than 111,000,000
gallons of ground water had been extracted
through the interim action system.
The entire well field was shut down between mid-May and mid-June 2008 (in accordance with the project Flood Mitigation Plan) in response to the flooding potential associated with the spring runoff. At this time, Configurations 1, 3, and 4 are actively extracting ground water from the well field.
An infiltration trench was added to the interim action
well field north of Configuration 3 and became fully
operational at the end of September 2006. This trench is
designed to inject filtered freshwater into the subsurface
via four injection ports. The infiltration system
was shut down for the winter in October 2007, and is anticipated to be reactivated in July 2008 when the river stage has decreased. Prior to
shutdown, more than 6 million gallons of freshwater
had been injected into the trench.
A 17-acre land-applied spray evaporation system was
installed in spring 2004 to enhance evaporation of
water pumped from the interim action evaporation pond
by using a sprinkler system installed on top of the
Moab tailings pile. The sprinkler system consists
of micro-spray nozzles on 25-foot centers. The system
was expanded to include an additional 11 acres in
March 2005. Forty more sprinklers were added in 2006,
primarily along the northwest crest line of the pile.
The sprinklers currently cover a combined total of
38 acres and operate in conjunction with the existing
evaporation pond to maximize the evaporative capacity
of the interim action system. The system is designed
to evaporate the water before it infiltrates the tailings
pile and to provide dust suppression. This system
was restarted in late March 2008.
This interim action is not intended as a long-term activity; however, the effectiveness of the system is being evaluated and it may eventually become part of the final ground water remedy. See Ground Water Interim Remedial Action for project documents associated with the interim action. |