Data from a previous MBRS study indicate that most rural ground-water sources (wells and springs) in the vicinity of abandoned uranium mines in the Shiprock Mining District, northeast Navajo Nation, contain elevated levels of Ph, Hg, Fe, As, and Se. Contamination by these toxic metallic species is indicative of mine drainage, as they become mobile under redox conditions introduced by mining operations. Some water sources have contaminant levels that exceed published U.S. EPA standards for potable water, and their use has been proscribed by the Navajo government. However, the majority of sources have concentrations which, when measured at the aquifer, are elevated but do not exceed the legal maxima. The threat to public health posed by these sources, which are freely used by rural Navajos and their livestock, may have been underestimated owing to surface environmental effects. Surface environmental effects are here defined as processes which act to increase trace-metal concentrations in water after it has been drawn from an aquifer. These effects include, but are not limited to: (a) evaporative concentration of solutes; (b) leaching of metals from cisterns, tanks, and pipes; and (c) contamination by windborne materials. The processes may act synergistically and may depend on climatic conditions and patterns of water use. In order to assess this potential public-health threat, a series of time- and climate-integrated chemical analyses will be carried out, at surface storage facilities fed by ground water known to have elevated trace-metal levels. Sampling of stored water, salted scrapings from troughs, and fine sediments from adjacent areas will be carried out at regular intervals. Trace-elements, radionuclide, and anion concentrations will be measured using atomic-absorption spectrophotometry, gross alpha-beta counting, and ion chromatography. Titration and electrode measurements will be used to determine alkalinity, pH, and redox potential of each sample. The data will delineate potential above-ground effects of contaminant levels. When evaluated in the context of local weather patterns and surface geology, the data will also indicate which sources and which times of year may pose the greatest threat to rural water users.
