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.