Joseph P. Rousseau

Hydrogeology of the unsaturated zone, North Ramp area of the Exploratory Studies Facility, Yucca Mountain, Nevada

Yucca Mountain, in southern Nevada, is being investigated by the US Department of Energy as a potential site for a repository for high-level radioactive waste. This report documents the results of surface-based geologic, pneumatic, hydrologic, and geochemical studies conducted during 1992 to 1996 by the US Geological Survey in the vicinity of the North Ramp of the Exploratory Studies Facility (ESF) that are pertinent to understanding multiphase fluid flow within the deep unsaturated zone. Detailed stratigraphic and structural characteristics of the study area provided the hydrogeologic framework for these investigations. Shallow infiltration is not discussed in detail in this report because the focus in on three major aspects of the deep unsaturated-zone system: geologic framework, the gaseous-phase system, and the aqueous-phase system. However, because the relation between shallow infiltration and deep percolation is important to an overall understanding of the unsaturated-zone flow system, a summary of infiltration studies conducted to date at Yucca Mountain is provided in the section titled Shallow Infiltration. This report describes results of several Site Characterization Plan studies that were ongoing at the time excavation of the ESF North Ramp began and that continued as excavation proceeded.

Kilometer-Scale Rapid Transport of Naphthalene Sulfonate Tracer in the Unsaturated Zone at the Idaho National Engineering and Environmental Laboratory

To investigate possible long-range flow paths through the interbedded basalts and sediments of a 200-m-thick unsaturated zone, we applied a chemical tracer to seasonally filled infiltration ponds on the Snake River Plain in Idaho. This site is near the Subsurface Disposal Area for radioactive and other hazardous waste at the Idaho National Engineering and Environmental Laboratory. Within 4 mo, we detected tracer in one of 13 sampled aquifer wells, and in eight of 11 sampled perched-water wells as far as 1.3 km away. These detections show that (i) low-permeability layers in the unsaturated zone divert some flow horizontally, but do not prevent rapid transport to the aquifer; (ii) horizontal convective transport rates within the unsaturated zone may exceed 14 m d−1, perhaps through essentially saturated basalt fractures, tension cracks, lava tubes, or rubble zones; and (iii) some perched water beneath the Subsurface Disposal Area derives from episodic surface water more than 1 km away. Such rapid and far-reaching flow may be common throughout the Snake River Plain, and possibly occurs in other locations that have a geologically complex unsaturated zone and comparable sources of infiltrating water.

Steady-state and transient models of groundwater flow and advective transport, Eastern Snake River Plain aquifer, Idaho National Laboratory and vicinity, Idaho

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Hydraulic Characteristics of Bedrock Constrictions and Evaluation of One- and Two-Dimensional Models of Flood Flow on the Big Lost River at the Idaho National Engineering and Environmental Laboratory, Idaho

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The Use of Chemical and Physical Properties for Characterization of Strontium Distribution Coefficients at the Idaho National Engineering and Environmental Laboratory, Idaho

The U.S. Geological Survey and Idaho State University, in cooperation with the U.S. Department of Energy, conducted a study to determine strontium distribution coefficients (Kds) of surficial sediments at the Idaho National Engineering and Environmental Laboratory (INEEL). Batch experimental techniques were used to determine experimental Kds of 20 surficial-sediment samples from the INEEL. The Kds describe the distribution of a solute between the solution and solid phase. A best-fit model was obtained using a four-variable data set consisting of surface area, manganese oxide concentration, specific conductance, and pH. Application of the model to an independent split of the data resulted in an average relative error of prediction of 20 percent and a correlation coefficient of 0.921 between predicted and observed strontium Kds. Chemical and physical characteristics of the solution and sediment that could successfully predict the Kd values were identified. Prediction variable select ion was limited to variables which are either easily determined or have available tabulated characteristics. The selection criterion could circumvent the need for time- and labor-intensive laboratory experiments and provide an alternate faster method for estimating strontium Kds.

Multimode reverse time VSP imaging over complex structures at Yucca Mountain, Nye County, Nevada

Structural interpretation of vertical seismic profiles (VSP’s) is always a challenge because conventional plots of the reflected wavefield itself, observed along a borehole, do not bear much resemblance to the reflectors responsible for the reflected events. Wyatt and Wyatt (1981) and Dillon and Thomson (1983) pioneered this problem by mapping or migrating the reflected events from space-time into spacespace domains. A more elaborate migration of an extensive multiple offset VSP was demostrated by Mons, et al (1985).