IDENTIFYING THE SOURCES OF METALS TO THE SAN JUAN RIVER THROUGH THE NAVAJO NATION, FOUR CORNERS REGION, USA

The San Juan River is a major water source for communities in the Four Corners Region of the United States (Colorado, Arizona, New Mexico, Utah), a vital source of water for the Navajo Nation, and is a major tributary of the Colorado River. Surface water sampling of the San Juan River by the Navajo Nation Environmental Protection Agency (NNEPA) has revealed lead, arsenic, and aluminum at concentrations that exceed NNEPA surface water standards under certain hydrologic regimes. This project aims to identify where metals at concentrations above surface water standards may be entering the river by evaluating the chemistry of water and sediment in the major tributaries of the San Juan River. Sources of metals include legacy hard rock mining, natural mineralized deposits, oil and gas development, coal mining, coal-fired power plants, urban areas, illegal trash dumping, abandoned uranium mines and mills, overgrazed areas, natural geology, and subsurface agricultural return flows. One natural source of metals is from the Animas River, which flows past legacy hard rock mining and mineralized areas. This source became especially evident during the Gold King Mine spill in August 2015. However, the Animas River is not the only source of metals to the San Juan River. Single-stage syphon samplers, sediment traps, and pressure transducers were deployed in 33 primarily ephemeral tributaries to the San Juan River, which collected post-monsoonal water and sediment samples. Preliminary results of general chemistry and metal isotopes will be presented. Determining the relative contribution and effect of each source on the San Juan River will help the Navajo Nation, public drinking-water managers, irrigation districts, scientists, and the public in their efforts to protect the environment and human health.