Are Arid Regions Always that Appropriate for Waste Disposal? Examples of Complexity from Yucca Mountain, Nevada

Scott W Tyler

doi:10.3390/geosciences10010030

Abstract

The study of the hydrology of arid regions greatly expanded at the end of the 20th century as humans sought to reduce groundwater pollution from landfills, waste dumps and other forms of land disposal. Historically viewed as wastelands where little or no water percolated to the underlying water table, the discovery of large-scale contamination beneath arid disposal sites such as the Hanford nuclear complex in eastern Washington jumpstarted an industry in studying the hydrology of arid vadose zones and their transport behavior. These studies showed that, in spite of hyper aridity in many areas, precipitation often did infiltrate to deep water. The efforts at Yucca Mountain, Nevada to design a high-level nuclear repository stand out as one of the largest of such studies, and one that fundamentally changed our understanding of not only water flow in fractured rocks, but also of the range of our uncertainty of hydrologic processes in arid regions. In this review and commentary, we present some of the initial concepts of flow at Yucca Mountain, and the evolution in research to quantify the concepts. In light of continued stockpiling of high-level waste, and the renewed interest in opening Yucca Mountain for high-level waste, we then focus on the significant surprises and unanswered questions that remained after the end of the characterization and licensing period; questions that continue to demonstrate the challenges of a geologic repository and our uncertainty about critical processes for long-term, safe storage or disposal of some of our most toxic waste products.

Highlights

The use of arid regions for the disposal of waste is not a new concept; the lack of water, people, agriculture wildlife and general “wasteland” concept of many desert regions suggested that these areas could serve little other purposes
With the development of the field of groundwater hydrology and the ability to pump large quantities groundwater, many arid and semiarid regions have become highly productive in terms of agriculture
Fabryka-Martin et al [24] observed chlorine-36 concentrations in seeps and faults exposed during tunneling operations at Yucca Mountain in the Topopah Springs Tuff indicative of waters that came from the surface (~400 m above the sample depths) after nuclear weapons testing began in the 1940s

Summary

Introduction

The use of arid regions for the disposal of waste is not a new concept; the lack of water, people, agriculture wildlife and general “wasteland” concept of many desert regions suggested that these areas could serve little other purposes. Observations of groundwater contamination at Hanford Washington from disposal well above the water table were initially surprising, yet lysimeter studies quickly showed that disruption and removal of vegetation (a standard practice at most arid region waste sites) led to much-enhanced groundwater recharge (see, for example, Gee et al [2]). These results were confirmed numerous times under very different conditions and environments, and showed that deep infiltration and recharge could occur in arid regions in spite of the lack of precipitation (see, for example, Scanlon et al [3]) and the numerous references cited within). We turn our attention to Yucca Mountain, Nevada, where complexity in the unsaturated zone and its implication for nuclear waste isolation continues today

Enter Yucca Mountain

The Ever-Increasing Rate of Deep Infiltration and Recharge

Whose Infiltration Model is Right?

The Underground Waterfall

Findings

Conclusions and Looking Forward