GEOCHEMICAL AND ISOTOPIC CONSTRAINTS ON GROUND-WATER FLOW DIRECTIONS, MIXING AND RECHARGE AT YUCCA MOUNTAIN, NEVADA
This analysis is governed by the Office of Civilian Radioactive Waste Management (OCRWM) Analysis and Modeling Report Development Plan entitled ''Geochemical and Isotopic Constraints on Groundwater Flow Directions, Mixing and Recharge at Yucca Mountain'' (CRWMS M&O 1999a). As stated in this Development Plan, the purpose of the work is to provide an analysis of groundwater recharge rates, flow directions and velocities, and mixing proportions of water from different source areas based on groundwater geochemical and isotopic data. The analysis of hydrochemical and isotopic data is intended to provide a basis for evaluating the hydrologic system at Yucca Mountain independently of analyses based purely on hydraulic arguments. Where more than one conceptual model for flow is possible, based on existing hydraulic data, hydrochemical and isotopic data may be useful in eliminating some of these conceptual models. This report documents the use of geochemical and isotopic data to constrain rates and directions of groundwater flow near Yucca Mountain and the timing and magnitude of recharge in the Yucca Mountain vicinity. The geochemical and isotopic data are also examined with regard to the possible dilution of groundwater recharge from Yucca Mountain by mixing with groundwater downgradient from the potential repository site. Specifically, the primary tasks of this report, as listed in the AMR Development Plan (CRWMS M&O 1999a), consist of the following: (1) Compare geochemical and isotopic data for perched and pore water in the unsaturated zone with similar data from the saturated zone to determine if local recharge is present in the regional groundwater system; (2) Determine the timing of the recharge from stable isotopes such as deuterium ({sup 2}H) and oxygen-18 ({sup 18}O), which are known to vary over time as a function of climate, and from radioisotopes such as carbon-14 ({sup 14}C) and chlorine-36 ({sup 36}Cl); (3) Determine the magnitude of recharge from relatively conservative tracers such as chloride and/or groundwater age and unsaturated-zone thickness; (4) Correct {sup 14}C ages for possible dilution of radiocarbon by calcite fracture coatings using geochemical reaction models; and (5) Establish mixing relations between waters from different source areas using relatively conservative species such as {sup 2}H and {sup 18}O or chloride and sulfate, and evaluate if inferred flow paths and mixing relations are reasonable based on chemical reactions required to reproduce the observed water chemistry. The analysis presented in this report is appropriate for the intended use described above. This analysis is not directly related to the principal factors, or other factors, for the post-closure safety case, nor is it used directly in calculations or analyses that provide estimates of the effects of potentially disruptive processes and events, as described in AP-3.15Q, Managing Technical Product Inputs.
- Research Organization:
- Yucca Mountain Project, Las Vegas, NV (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- NA
- OSTI ID:
- 883407
- Report Number(s):
- ANL-NBS-HS-000021 REV 00; MOL.20000918.0287 DC#22264; TRN: US0603446
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CALCITE
CARBON 14
CHEMICAL REACTIONS
CHLORIDES
CHLORINE 36
COATINGS
DEUTERIUM
DILUTION
FRACTURES
GROUND WATER
GROUNDWATER RECHARGE
HYDRAULICS
OXYGEN 18
RADIOACTIVE WASTE MANAGEMENT
RADIOISOTOPES
SAFETY
STABLE ISOTOPES
WATER CHEMISTRY
YUCCA MOUNTAIN