Uranium Resources and Environmental Issues
Uranium environmental issues
Uranium and its decay products and associated trace elements create human health and environmental hazards wherever they occur in unusually elevated levels. Although uranium mill tailings have beenthe subject of extensive investigation and cleanup at mill sites across the U.S., uranium mine wastes remain at a number of sites throughout the western United States and constitute a significant hazard for casual visitors to the site from gamma exposure and inhalation of windblown dust. Visitors to underground uranium operations, which are common in many recreational areas of the west, have been exposed to extreme levels of radon. These hazards have been recognized by responsible Federal and State agencies and reclamation of many uranium mine sites in the west and closure of undergound mine openings has occurred. However, the extent and success of these programs has been controlled by the availability of funds under such programs as the Surface Mine Reclamation Act. The availability of these funds varies from State to State. Many areas of some western States continue to have exposed unreclaimed uranium mine wastes at former mining sites. The leaching of radionuclides and other elements by precipitation and the erosion of waste piles by wind and runoff are primary mechanisms by which adjacent soils, water, and ecosystems are impacted by uranium mine waste piles, yet very few studies of waste piles have occurred to document whether such processes create hazards beyond the immediate vicinity of the piles.
The USEPA is in the process of releasing guidelines for uranium mine waste cleanup. In 2006 they will publish two volumes on the topic, a background volume and a risk assessment volume. These documents are based on the best available data but detailed studies that could further support the waste assessment and risk assessment are limited.
As recreational uses of older uranium mining areas increase and as residential areas expand into former uranium mine and prospect areas such as those in the Uravan Mineral belt and the Front Range of Colorado human exposures will increase. Evaluating uranium mine waste sites will assist Federal and State land management and environmental officials in assessing hazards and prioritizing needed cleanup.
Related to uranium mining environmental issues is the natural radiochemical and radiometric background for rocks, soils, and waters in the U.S. in general and uranium mining areas in particular. Cleanup standards for uranium mine sites should be based on the local background radiochemical and radiometric setting which is often poorly known. Moreover, environmental and health officials across the U.S. have been surprised when anomalously high levels of radon and uranium in domestic drinking water or indoor radon turn up in areas known by geologists to be uranium-enriched. Oftentimes nearby industrial activities are suspected as sources for contamination. Studies that assist local, state, and Federal health and environment officials in properly understanding these occurrences, assessing natural and anthropogenic sources, and then communicating the hazards associated with these occurrences are needed.
Some data are directly relevant to understanding the natural background for radionuclides in the U.S. Another effort of the National Uranium Resource Evaluation program of the Department of Energy was the national airborne radiometric and aeromagnetic reconnaissance survey which gathered gamma-ray data from almost all of the U.S. and Alaska. The USGS also became the archival agency for these data and much of the data has been published on CD-ROMs in the USGS’ Digital Data Series. This data can be processed to produce such images as this:
This map shows the equivalent uranium (eU) concentrations in surface soils and rocks across the U.S. The term "equivalent uranium" is used because the gamma rays from naturally occurring uranium in surface soils and rocks cannot be detected by airborne instruments, however the gamma rays from one of uranium's major decay products, bismuth-214, can. The uranium concentration at the surface can be calculated from the bismuth-214 gamma-ray signature. There are some situations where the conversion is not exact.
The gamma rays emitted by soil and rock can escape to the surface from depths no greater than about 40 cm (about 1.2 feet). If the soil is water saturated, the gamma rays will also be strongly adsorbed by the water.
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U.S. Department of the Interior |
U.S. Geological Survey
SIR 2007-5246