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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5089

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Introduction

The Idaho National Laboratory (INL), operated by the U.S. Department of Energy (DOE), encompasses about 890 mi² of the eastern Snake River Plain in southeastern Idaho (fig. 1). Names formerly used for this site, from earliest to most recent, were National Reactor Testing Station (NRTS, 1949–1974), Idaho National Engineering Laboratory (INEL, 1974–1997), and Idaho National Engineering and Environmental Laboratory (INEEL, 1997–2005). The INL facilities are used in the development of peacetime atomic-energy applications, nuclear safety research, defense programs, environmental research, and advanced energy concepts. Radiochemical and chemical wastewater generated at these facilities has been discharged to either onsite infiltration ponds, evaporation ponds, disposal wells, or a combination thereof, since 1952. Wastewater disposal has resulted in detectable concentrations of several waste constituents in water from the Snake River Plain aquifer underlying the INL. Disposal of wastewater to infiltration ponds and infiltration of surface water at waste-burial sites resulted in formation of perched ground water in basalts and in sedimentary interbeds that overlie the Snake River Plain aquifer. Perched ground water is an integral part of the pathway for waste-constituent migration to the aquifer.

The DOE requires information about the mobility of dilute radiochemical- and chemical-waste constituents in the Snake River Plain aquifer and in perched ground water above the aquifer. Waste-constituent mobility is determined, in part, by (1) the rate and direction of ground-water flow; (2) the locations, quantities, and methods of waste disposal; (3) waste-constituent chemistry; and (4) the geochemical processes taking place in the aquifer. This study was conducted by the U.S. Geological Survey (USGS) in cooperation with the DOE Idaho Operations Office.

Purpose and Scope

In 1949, the U.S. Atomic Energy Commission, which later became the DOE, requested that the USGS describe the water resources of the area now known as the INL. The purpose of the resulting study was to characterize these resources before the development of nuclear-reactor testing facilities. Since that time, the USGS has maintained water-level and water-quality monitoring networks at the INL to determine hydrologic trends and to delineate the movement of radiochemical and chemical wastes in the Snake River Plain aquifer and in perched ground water.

This report presents an analysis of water-level and water-quality data collected from wells in the USGS ground-water monitoring networks during 2002–05 as part of the continuing hydrogeologic investigations conducted by the USGS at the INL. The report describes the distribution and concentration of selected radiochemical and chemical constituents in ground water and perched ground water at the INL, and changes in the water-level regime since 2001. The report also summarizes the history of waste disposal at the Reactor Technology Complex (RTC) (formerly known as the Test Reactor Area [TRA]), Idaho Nuclear Technology and Engineering Center (INTEC) (formerly known as the Idaho Chemical Processing Plant [ICPP]) , Radioactive Waste Management Complex (RWMC), Test Area North (TAN), and the Central Facilities Area (CFA). Perched ground water has been detected beneath infiltration ponds and ditches at other facilities at the INL, but is not discussed in this report because of the relatively small quantity of wastewater and associated radiochemical and chemical constituents discharged.

Previous Investigations

A list of references and copies of published reports are available from the USGS INL Project Office or the USGS Publications Warehouse Web site at http://infotrek.er.usgs.gov/pubs/.

Hydrologic conditions and distribution of selected wastewater constituents in ground water and perched ground water are discussed in a series of reports describing the NRTS. Table 1 summarizes selected previous investigations on the hydrology, geology, and characteristics of water at and near the INL, and periods included in those investigations.

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