Evaluation of Recharge Potential at Subsidence Crater U19b, Central Pahute Mesa, Nevada Test Site
- Desert Research Inst. (DRI), Las Vegas, NV (United States). Division of Hydrologic Sciences
Radionuclides are present both below and above the water table at the Nevada Test Site (NTS) as a result of underground nuclear testing. Mobilization and transport of radionuclides from the vadose zone is a complex process that is influenced by the solubility and sorption characteristics of the individual radionuclides, as well as the soil water flux rate. On the NTS, subsidence craters resulting from testing underground nuclear weapons are numerous and many intercept surface water flows. Craters collect surface water above the subsurface point of device detonation, potentially providing a mechanism for surface water to recharge the groundwater aquifer underlying the NTS. Given this situation, there is a potential for the captured water to introduce contaminants into the groundwater system. The objective of this study was to evaluate the potential for recharge in nuclear subsidence craters formed in the Central Pahute Mesa Corrective Action Unit. Subsidence crater U19b was selected for study because it had the largest drainage area of all the subsidence craters in this region. Two boreholes were augered to determine the soil properties and moisture conditions both inside and outside the crater environment. Surface and vadose zone modeling indicated that recharge is occurring at a higher rate within the crater environment than at other areas studied on Pahute Mesa. This is likely due to the enhanced water collection that has occurred as a result of the detonation crater. However, both the chloride mass-balance approach and analysis of water potential gradients suggest that episodic recharge may have also occurred in the borehole located just outside the crater environment, though at a much lower rate. Vadose zone modeling was conducted using two different sets of vadose zone modeling parameters to bracket the range of probable materials at depth. With material properties similar to the soils encountered during drilling ( coarse sand texture), infiltration to near 200 min approximately 25 years was obtained. Significant drainage beyond 200 m occurred between simulation years 25 and 32. Modeling simulations with finer-grained properties resulted in wetting front advancements to approximately 100 min 32 years. While depths of infiltration were greater in the coarser material simulations, a recharge rate of 32 cm/yr was calculated for both simulations based on the vadose zone modeling.
- Research Organization:
- Desert Research Inst. (DRI), Las Vegas, NV (United States); Nevada Univ., Reno, NV (United States)
- Sponsoring Organization:
- USDOE Office of Environmental Management (EM)
- DOE Contract Number:
- AC08-95NV11508
- OSTI ID:
- 1466727
- Report Number(s):
- DOE/NV/-11508-33; 45161
- Country of Publication:
- United States
- Language:
- English
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