by Mary Ann Capehart, Former WRRC Graduate Outreach Assistant
Carrie Nuva Joseph is a Ph.D. student in the Soil, Water, and Environmental Sciences Department of the College of Agriculture and Life Sciences at the University of Arizona. She is the rare researcher whose efforts directly benefit the place she calls home and the people who raised her. Joseph studies inactive uranium mill sites across the country, specifically targeting those located in Native American communities. Her studies are part of a uranium mill site remediation project funded by the Department of Energy (DOE). The DOE manages former mill sites, four of which are located in tribal communities in the Four Corners region, where Arizona, Utah, Colorado, and New Mexico meet. More than five hundred abandoned uranium mines remain within the Four Corners region.
Joseph grew up and remains closely tied to her village community, Moenkopi, on Hopi lands in northeast Arizona. Her personal connection to the area has made her aware of its history. During the Cold War era, in the mid-1900s, acid and mechanical leaching processes left behind uranium tailings and a legacy of contaminated regions located in native communities, Joseph explains. Uranium tailings were left uncovered and unregulated until the early 1990s in many locations. Tailings were not defined as a source of radioactive waste, according to the Atomic Energy Commission. They didnt fall under a legal definition of a source material. The Energy Commission insisted that they didnt have jurisdiction over these tailings.
Josephs village of Moenkopi is seven miles downstream from the Tuba City Arizona Disposal Site. Managed by the DOEs Office of Legacy Management, the engineered 50-acre disposal cell confines low-level radioactive tailings accumulated from uranium milling between 1956 and 1966. Uranium ore extracted at the site was used exclusively for atomic energy defense activities of the United States. Active ground water remediation is also part of the strategy to remove the uranium (the primary site contaminant) and other site-related contaminants in compliance with the Uranium Mill Tailings Radiation Control Act of 1978. Within the contaminated region of the aquifer, 37 extraction wells and a network of monitoring wells operate daily. Surface water seeps, associated with the Tuba City site, are present along the cliffs that border the Moenkopi Wash, about 4,000 feet south of the site. The wash continues southeast from there to where it enters the village of Moenkopi.
The Navajo and Hopi residents residing near the site use water from the Moenkopi wash for stock watering and agricultural diversions. Every year we irrigate corn plots, Joseph said. During the planting season direct precipitation, runoff, and water gained from the subsurface flows contribute to the Moenkopi Wash (an intermittent stream) that runs directly through the village. Pumps and man-made canals take the water from the wash into our corn fields.
As Hopi people everything revolves around corn, Joseph added. To maintain our responsibilities as Hopi, our cornfields should never be neglectedour survival and cultural and religious practices depend on this life way. Hopi people will continue to rely on the resources the natural world provides us, for many generations.
Of most concern in sites of uranium milling waste, is Radon-222, produced from the radioactive decay of radium-226. Disposal sites are required to be operational for the long-termfrom 200 to 1,000 yearsand to limit the flux of radon to below 20 picocuries per meter squared per second. This limit is designed to prevent any kind of environmental or human health effects. Heaps of tailings are confined by a 3-layer cap or cover, two layers of rock riprap to guard the tailings from water and wind erosion and a clayey soil layer that creates a barrier to limit the escape of radon gas into the atmosphere and the seepage of rainwater into the waste below.
Early caps were not designed for vegetation growth. Today, disposal cell covers located in semi-arid regions are integrating vegetation into designs. Desert shrubs, like four-wing salt bush or rubber rabbit brush, help take up rainwater through transpiration, preventing both water seepage into the tailings and the erosion of the top layer of riprap rock.
Josephs research will help answer questions that the DOE has on how disposal cell covers located in the semi-arid regions of the Southwest will adapt to short- and long-term climate change while maintaining long-term performance standards for uranium mill tailings. Environmental impacts to the disposal cell cover, such as wind and water erosion, can mobilize contaminants in the tailings pile, says Joseph. Climate-related changes in temperature and precipitation, and the magnitude of infrequent storm events will impact vegetation cover and how vegetation will change over time. The environment is changing and we need to identify how these projected changes will impact cell cover performance.
Some plants have the potential to send roots deep into the cover system in search of water and to take up contaminants if roots reach the tailings. Plant roots can also leave fine cracks in the clayey soil layer potentially allowing radon gas to escape above regulation limits and water to seep into tailings waste underground. Josephs Master of Science thesis work found evidence of plant uptake of contaminants at some sites with early cover designs.
There is an urgent need to figure out these environmental challenges, Joseph reflects, because we cant relocate to another areathese are our ancestral lands. We are permanently fixed within the reservation boundary areas.
Joseph plans to extend her research further into understanding the perception of risk on the part of her Hopi village community, as regards the tailings waste storage. Many members of Hopi communities naturally fear the effects of contamination and its possible connection to higherthan- average cancer rates in the area. She aims to bridge the communication between community members and DOE, with the goal of protecting human health, water resources, and the surrounding environment.