Effects of Climate and Ecological Processes on Engineered Uranium Disposal Cell Performance with Respect to Nearby Subsistence-Based Indigenous Communities
Near-surface earthen-engineered disposal covers are used to consolidate uranium mill tailings waste generated from defense-related uranium mines located across the United States. Disposal covers made from compacted soil layers stabilize waste consisting of a mixture of chemical and radiological constituents to limit air, soil, and water contamination above and below ground. However, 20 to 30 years post-construction, vegetative succession, dust deposition, and soil development are changing the as-built engineering design, clearly notwithstanding the longevity standard of 200-1,000 years. Little is known about how natural ecological succession will impact the performance of earthen-engineered covers. Furthermore, there is a dearth of information about how subsistence-dependent Indigenous communities located nearby inactive uranium disposal facilities are impacted by past, present, and future operations of legacy sites. The Department of Energy – Legacy Management (DOE-LM) is evaluating whether natural ecological processes occurring above disposal covers are sustainable and alternate long-term remedies that could reduce maintenance costs and exposures to humans and the environment. Using quantitative and qualitative methodologies, three interdisciplinary studies were completed to address key knowledge gaps for uranium legacy sites. The overall research objectives are: (1) to investigate how natural ecological succession above engineered covers, specifically plant establishment and root intrusion, may be a potential benefit or potential detriment to disposal cover performance; (2) to provide climatological data and future climate trajectories to understand whether engineered cell covers are vulnerable to climate impacts; and (3) to understand community risk perceptions from the unheard voices of indigenous people and the impacts to their livelihoods from uranium legacy sites. In the first study, 144 samples of various vegetation types were analyzed for metal and radiological uptake collected from a broad range of climates and disposal cover designs, where soil development, dust deposition, and moisture provided a favorable habitat for plant growth. The goal was to determine if vegetation was compromising the performance of disposal cell covers by creating an exposure pathway for uranium tailing constituents. It was also important to determine exposure levels because twelve Indigenous tribes living near the study sites have ethnobotanic uses of plants. The results of this research indicate that plant concentrations are not accumulating to toxic levels with the exception of two site locations, where exceedances can be attributed to background soil characteristics. The second study addresses the vulnerability of uranium disposal cell covers to climate change in the U.S. Southwest. We extract monthly precipitation, daily minimum, and daily maximum temperatures to determine climate trends (mean annual temperatures, extreme conditions, and seasonal variation) of the recent past from high-resolution data sets. We also determine future climate by documenting projections from CMIP5 models under two representative concentration pathways (RCP). It was found that there are yearly and seasonal differences in climate outputs compared to historical data. While one site in the southwest experiences a trend towards wet/hot conditions, another site will experience hot/drier conditions under RCP 8.5 projections. From this study, it is hypothesized that allowing plants to grow in regions (Tuba City) that will experience wetter conditions, in normally arid regions, could be an alternative to controlling the water-balance. The third study used indigenous research methodologies to determine the community risk perceptions of two Hopi villages located 7 kilometers (km) downstream from an inactive uranium mill tailings site. Five focus groups were held using the conversational method in which open-ended, broad overview descriptive questions were used as a guide. The results from this study can address broader questions about a needs assessment, exposure and risk assessment, and risk communication, that are unique to the Hopi population but also useful to other tribes. Given the scope of the problem, this dissertation research confirms how natural ecological processes via climate-plant interactions on disposal covers may pose risks to performance, and in other cases it may not. The results will help to prioritize sites that may be good candidates for disposal cell renovations that embraces a sustainable design. Further, the qualitative study provides vital information, not documented in the literature than can be prioritized to bridge partnerships and reduce environmental and health risks.
climate change, ecological processes, indigenous, remediation, soil development, uranium mill tailings
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