Water-resources study of Fort Irwin National Training Center

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The U.S. Army at Fort Irwin National Training Center (NTC) obtains all of its potable water supply from Irwin, Langford, and Bicycle Basins within the base boundaries. Groundwater pumping, since as early as 1941, has resulted in water-level declines in all of these basins and the disposal of treated wastewater in the Irwin Basin has resulted in elevated nitrate concentrations in some wells in Irwin Basin. 

Map showing Fort Irwin National Training Center boundary, drainage basin boundaries, and areas of interest.

Map showing Fort Irwin National Training Center boundary, drainage basin boundaries, and areas of interest.

(Public domain.)

Land-surface deformation, consisting of an earth fissure and sink-like depressions, occurred in 2005 on the Bicycle Lake (dry) playa in the southern part of the Bicylce Basin. Earth fissures are a major concern to the NTC because aircraft runways constructed on the playa are used for transporting troops and supplies.

In 1992, the U.S. Geological Survey (USGS) entered into an agreement with the NTC to evaluate the long-term availability and quality of groundwater in the Irwin, Langford, and Bicycle Basins. The objectives of the study were to describe the geohdrologic and geochemical frameworks of these basins; develop groundwater flow models to help refine the understanding of the geohydrology; and evaluate the long-term availability and quality of groundwater at the base. The evaluations of Irwin and Langford Basins have been completed, and the evaluation of Bicycle Basin is scheduled to be completed in 2011. In 2008, the USGS began a study to evaluate the location, extent, and magnitude of land-surface deformation on the Bicylce Lake playa in Bicyle Basin. Monitoring of the Bicycle Lake playa is ongoing.

The NTC is planning to expand the area of the base in the near future. The base expansion will involve training additional troops, which will increase the water demand at the base. In addition, the U.S. Army Corps of Engineers has selected the NTC for the construction of the largest solar power plant proposed to date within the Department of Defense. Treated wastewater will be used as the cooling water for the solar power plant. Currently the treated wastewater is a major source of recharge to the Irwin Basin (Densmore and Londquist, 1997). To effectively plan for the base expansion and the solar plant, there will be a need to update and utilize the groundwater-flow models developed for the Irwin, Langford, and Bicycle Basins to evaluate the effect of future recharge and pumping on the available water resources at the base. In addition, groundwater basins that have not been previously studied on the base need to be evaluated to determine their potential for providing additional water supply.

The objectives of this study are to evaluate the current and long-term availability of groundwater resources at the NTC. The study will involve (1) collecting and compiling existing hydrologic data for the entire NTC; (2) updating the groundwater-flow models for Irwin, Langford, and Bicycle Basins to 2010 conditions; (3) collecting new hydrologic data to improve the understanding of groundwater availability at the base with special emphasis on groundwater basins not previously investigated by the USGS (Superior Basin, Coyote Basin, “Central Corridor” area, Goldstone Basin, Leach Basin, Red Pass Basin, Nelson Basin, and Drinkwater Basin); (4) evaluating the cause of land-surface deformation on the Bicycle Lake playa and its impact on water supply from Bicycle basin; and (5) utilizing the updated Irwin, Langford, and Bicycle Basins models and hydrologic information collected from the groundwater basins not previously studied to evaluate the long-term availability of water at the NTC. The proposed study will be completed in a phased approach depending on the availability of funding. 

The study approach involves evaluating the water resources at each of the major groundwater basins overlain by the NTC. Previous studies have investigated in detail the groundwater resources of the Irwin, Langford, and Bicycle Basins; therefore, work on these basins will involve updating the existing data and models developed for the basins and collecting new data where the previous studies indicated data gaps. Few data are available in the previously unstudied basins; therefore, the investigations of these basins will involve the collection of geophysical data to characterize the size and shape of the basins, well drilling to characterize the aquifer properties and water quality, and preliminary groundwater models to evaluate the long-term availability of groundwater. Work needed to evaluate each of the major groundwater basins at the NTC is described below. The order of investigation will be determined by the NTC.