Constraints on the hydrology of the unsaturated zone at Yucca Mountain, NV from three-dimensional models of chloride and strontium geochemistry

Saved in:
Authors:Sonnenthal, Eric L.; Bodvarsson, Gudmundur S.
Author Affiliations:Primary:
Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, CA, United States
Volume Title:Yucca Mountain project
Volume Authors:Bodvarsson, Gudmundur S., editor; Tsang, Yvonne W.
Source:Yucca Mountain project, edited by Gudmundur S. Bodvarsson and Yvonne W. Tsang. Journal of Contaminant Hydrology, 38(1-3), p.107-156. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0169-7722
Publication Date:1999
Note:In English. 58 refs.; illus., incl. 5 tables, sketch map
Summary:Three-dimensional (3-D) simulations of the spatial and temporal variations in chloride and strontium concentrations in porewaters were performed to constrain infiltration rates, flow paths, and mixing processes in the unsaturated zone (UZ) at Yucca Mountain, NV. Chloride concentrations in infiltrating water were calculated from aerial distributions of precipitation and infiltration rates for the current climatic conditions and for the last glacial maximum, combined with effective chloride concentrations in precipitation. Modeled concentrations are roughly similar to measured porewater chloride concentrations from the Paintbrush nonwelded tuffs in the Exploratory Studies Facility (ESF) tunnel and in boreholes suggesting that the mean infiltration rate over the site is unlikely to be higher than the calculated mean infiltration rate for the modern climate (∼5 mm/year; [Flint, A. L., Hevesi, J. A., Flint, L. E., 1996. Conceptual and Numerical Model of Infiltration for the Yucca Mountain Area, Nevada. Milestone 3GU1623M. U. S. Geol. Surv. Water Res. Invest. Rep. U. S. Geological Survey, Denver, CO]). Porewaters from the late Pleistocene (>10 ka) could be present in the Paintbrush bedded tuffs and in the underlying Topopah Spring welded tuffs (TSw), predominately under regions of thick alluvium having little infiltration. However, porewaters at the potential repository level may have a higher proportion of Holocene recharge due to the higher calculated infiltration rate in this region. Dual-permeability simulations show that in low infiltration regions chemical disequilibrium can exist between fracture and matrix porewaters, as a result of the climate change 10,000 years ago. Below the potential repository level, simulations show significant mixing due to lateral flow on top of the low permeability basal vitrophyre in the Topopah Spring unit and on zeolitized tuffs in the Calico Hills unit. Perched water chloride concentrations are closely matched using the calculated conditions for the last glacial maximum climate, with some component of Holocene recharge. Measured strontium concentrations in the UZ and in the perched water bodies can be roughly matched by assuming conservative behavior in nonzeolitic units and strong ion exchange in zeolitic units, and indicate that the perched water bodies are poorly mixed. Differences in the Cl contents of samples having a bomb-pulse Cl-36 signature and those with a modern ratio indicate that waters of intermediate 36Cl/Cl ratios may be mixtures, that without other isotopic data could be inferred as either Pleistocene or Holocene age waters. Abstract Copyright (1999) Elsevier, B.V.
Subjects:Alkaline earth metals; Aquifers; Atmospheric precipitation; Boundary conditions; Cenozoic; Chloride ion; Chlorine; Climate change; Concentration; Controls; Ground water; Halogens; High-level waste; Infiltration; Lithostratigraphy; Mathematical models; Metals; Migration of elements; Miocene; Neogene; Nuclear facilities; Paintbrush Tuff; Permeability; Pollution; Pore water; Porous materials; Preferential flow; Preventive measures; Radioactive waste; Safety; Semi-arid environment; Simulation; Site exploration; Soils; Strontium; Terrestrial environment; Tertiary; Theoretical models; Three-dimensional models; Underground disposal; Unsaturated zone; Waste disposal; Waste management; Nevada; Nye County Nevada; United States; Yucca Mountain; Repository
Coordinates:N364400 N370000 W1162500 W1163500
Record ID:1999053606
Copyright Information:GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
Tags: Add Tag
No Tags, Be the first to tag this record!