Rachel Henderson and Dr. Alan Mayo, Geology
The proposal, by Private Fuel Storage, a Limited Liability Company representing several utilities, to store solid, spent nuclear fuel in Skull Valley requires that many variables be taken into consideration, one of which is groundwater. Groundwater contamination is not anticipated in the proposed short term storage of the waste. However, it is uncertain how long the waste will be stored in Skull Valley. The purpose of this research is to conduct a reconnaissance investigation to evaluate the nature and interaction of various surface and groundwater systems in Skull Valley, and consequently, the likelihood of groundwater contamination from nuclear waste storage.
Four groundwater systems have been identified in the Skull Valley. They include large springs associated with mountain front faulting, an alluvial fan system in valley fill, a playa system in the northern part of the valley, and a low elevation bedrock system. Thirteen samples were collected from springs in a variety of locations along the eastern part of the valley. These samples came from the mountain front fault and alluvial fan systems. Solute and isotopic analysis of these samples show the mountain front fault and alluvial fan systems are two chemically distinct systems. As seen in Figure 1, the mountain fault springs lie in the sodium chloride facies and have high conductivities, whereas the alluvial fan springs lie in the calcium bicarbonate facies, have low conductivities, and have a higher quality of water. Analysis of hydrogen (ä2H) and oxygen (ä18O), isotopes (Table 1) reveal that both systems are recharged by the high elevation snow on the Stanbury Mountains located east of the valley. Carbon (ä13C) isotope analysis (Table 1) reveals that the groundwater in the mountain front fault system moves by fracture flow through carbonates and evaporites that were anciently deposited by a lake. It also indicates that the alluvial fan system groundwater flows through interfingering beds in the soil zone which are rich in calcium and bicarbonate. The two systems both discharge by evapotransporation and as springs, along a fault or at the break in slope between the alluvial fans and the valley. Unfortunately, radiometric ä 14C and Tridium dating of the samples has not been completed.
This reconnaissance evaluation has revealed much about the mountain front fault and alluvial fan groundwater systems. They are separate and chemically distinct systems that are related only through recharge from high elevation snow. Analysis shows that these two systems are not mixing and therefore would not contaminate each other if nuclear waste were to leak into one of them. However, further research of these systems, along with the playa and low elevation bedrock systems, is needed to fully understand the risks that nuclear waste storage in Skull Valley places on the groundwater in the valley.
Figure 1: Piper Diagram of spring solute chemistry. The Mountain Front Fault System is clustered in the sodium chloride facies, on the right side of the diamond graph. The Alluvial Fan System is clustered in the calcium bicarbonate facies, on the left side.
Table 1: Isotope analysis data for several Skull Valley samples. Hydrogen (ä2H) and oxygen (ä18O) isotope data are closer to the HES standard (high elevation snow) than to the South Pole standard. Carbon (ä13C) isotope values increase as a result of groundwater contact with soil.
