SOURCE IDENTIFICATION FOR PARTICLE-BOUND METALS IN THE SAN JUAN RIVER SYSTEM

The accidental release of 3 million gallons of contaminated water into the Animas River on August 5^th, 2015 turned national and state attention towards mining sourced metal loading in the Animas and San Juan River systems. Whereas extensive sampling was completed during and after the spill to understand the mass, fate, and transport of metals released from the Gold King Mine (GKM), little is known about the ongoing and historical metal loading from combined anthropogenic and natural sources present in the tributaries of the San Juan Watershed. Particle-associated metals from the San Juan Watershed have accumulated in Lake Powell since its construction in 1963. However, mining-contaminated bed sediments are distributed throughout the reach of the San Juan River, and several geologic units in the watershed are known to release trace elements naturally. Determination of signatures to differentiate particle-associated metals derived from mining versus natural sources is a goal of our work. Measuring contaminant loads in mined (Animas and San Juan upstream of Farmington, NM) versus unmined (Mancos, McElmo, and Chinle washes) tributaries will help distinguish impacts from mining versus natural sources. Raw (unfiltered) and dissolved (filtered) metals present in the surface water of the San Juan tributaries were measured via ICP-MS along with the total suspended solids concentration and particle size. Ratios of particle-bound metal concentration per mass of sediment were calculated from surface water samples collected by the University of Utah as well as by various state and federal agencies during and following the GKM spill. Additionally, all surface water measurements were converted into loads using discharge data from United States Geological Survey stream gauges. Historically, lead isotopes have been shown to differentiate mineralized rock (ore that is mined) from non-mineralized rock. Samples were collected for lead isotopic analysis post-spill. Each of these techniques (elemental ratios, loads, and lead isotopes) will be used to fingerprint the metal input of mined and unmined tributaries. Ultimately, the knowledge gained from source identification in the particle bound metals of the San Juan Watershed will be used to understand current and historical loading in Lake Powell (via sediment collected by USGS).