Use of chlorine-36 and other geochemical data to test a groundwater flow model for Yucca Mountain, Nevada
Defining the spatial distribution and timing of subsurface fluid percolation is one of the most important factors determining long term performance of the potential high-level radioactive waste repository at Yucca Mountain, Nevada. The nonwelded interval of the Paintbrush Group (PTn), which overlies most of the potential repository, has high matrix porosities and permeabilities and is mostly unfractured. The Exploratory Studies Facility (ESF) is a 8-km long, 7.6-m diameter, tunnel excavated beneath Yucca Mountain to the level of the potential repository horizon in order to provide access for characterization of these rocks. Several samples collected within the ESF have measured {sup 36}Cl/Cl ratios that record anthropogenic {sup 36}Cl (bomb-pulse {sup 36}Cl), indicating that at least some fraction of the water has traversed the overlying PTn in 40 years or less and that flow is not confined to the matrix of that unit. The presence of a fast path transmitting bomb-pulse {sup 36}Cl to depth appears to require the simultaneous presence of a structure (such as a fault) cutting the PTn and sufficiently high magnitude to surface infiltration to initiate and sustain at least a small component of fracture flow along the connected fracture path associated with the structure. The {sup 36}Cl data have been simulated using the flow and transport model FEHM in order to establish bounds on infiltration rates at the site and to provide greater confidence in the understanding of unsaturated flow processes at the site by showing consistency between the observed and simulated data sets. An analogous effort simulating the distribution of porewater chloride concentrations is providing an independent means for confirming the conceptual model.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE Office of Civilian Radioactive Waste Management, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 674563
- Report Number(s):
- LA-UR-98-1043; CONF-9709276-; ON: DE98006317; TRN: 99:000539
- Resource Relation:
- Conference: Use of hydrogeochemical information in testing groundwater flow models, Borgholm (Sweden), 1-3 Sep 1997; Other Information: PBD: [1998]
- Country of Publication:
- United States
- Language:
- English
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USING CHLORIDE TO TRACE WATER MOVEMENT IN THE UNSATURATED ZONE AT YUCCA MOUNTAIN
Chlorine-36 investigations of groundwater infiltration in the Exploratory Studies Facility at Yucca Mountain, Nevada