In 2019, the U.S. Geological Survey (USGS), in cooperation with the U.S. Department of Energy, drilled and constructed boreholes USGS 148A and USGS 149 for stratigraphic framework analyses and long-term groundwater monitoring of the eastern Snake River Plain aquifer at the Idaho National Laboratory (INL) in southeastern Idaho. Initially, boreholes USGS 148A and USGS 149 were continuously cored to allow the USGS and INL subcontractor to collect select geophysical and seismic data and evaluate properties of recovered core material. The USGS geophysical data and descriptions of core material are described in this report; however, data collected by the INL contractor, including seismic data, are not included as part of the report.

The unsaturated zone at both borehole locations is relatively thick, depth to water was measured at approximately 663.6 feet (ft) below land surface (BLS) in USGS 148A, and at approximately 654.1 ft BLS at USGS 149. On completion of coring and data collection, both boreholes (USGS 148A and USGS 149) were repurposed as monitoring wells. Well USGS 148A was constructed to a depth of 759 ft BLS and instrumented with a dedicated submersible pump and measurement line; well USGS 149 was constructed to a depth of 974 ft BLS and instrumented with a multilevel monitoring system (Westbay^TM).

Geophysical data, collected by the USGS, were used to characterize the subsurface geology and aquifer conditions. Natural gamma log measurements were used to assess sediment-layer thickness and location. Neutron and gamma-gamma source logs were used to confirm fractured and vesicular basalt identified for aquifer testing and multilevel monitoring well zone testing. Acoustic televiewer logs, collected for well USGS 149, were used to identify fractures and assess groundwater movement when compared with neutron measurements. Furthermore, gyroscopic deviation measurements were used to measure horizontal and vertical displacement for the constructed boreholes USGS 148A and USGS 149.

A single-well aquifer test was done in well USGS 148A during November 6–7, 2019, to provide estimates of transmissivity and hydraulic conductivity. Estimates for transmissivity and hydraulic conductivity were 6.34×10³ feet squared per day and 3.17 feet per day, respectively. The aquifer test was run overnight (21.3 hours) and measured drawdown was relatively small (0.09 ft) at sustained pumping rates ranging from 15.7 to 16.1 gallons per minute. The transmissivity estimates for well USGS 148A were slightly lower than those determined from previous aquifer tests for wells near the Materials and Fuels Complex, but well within range of other aquifer tests done at the INL.

Water-quality samples, collected from well USGS 148A and from four zones in well USGS 149, were analyzed for cations, anions, metals, nutrients, volatile organic compounds, stable isotopes, and radionuclides. Water samples for most of the inorganic constituents showed similar chemistry in USGS 148A and all four zones in USGS 149. Water samples for stable isotopes of oxygen and hydrogen indicated some possible influence of irrigation on the water quality. Nitrate plus nitrite concentrations indicated influence from anthropogenic sources. The volatile organic compound and radiochemical data indicated that wastewater disposal practices at the Materials and Fuels Complex or from drilling had no detectable influence on these wells.