A Multiple Tracer Approach to Characterizing Water and Contaminant Movement Through Abandoned Mine Workings Near Rico, Colorado

The Rico Argentine mine is a long-term acid mine drainage (AMD) site where current management of contaminant discharge consists of a series of passive treatment settling ponds.  The settling ponds have a limited lifespan and do not provide a permanent solution to controlling the AMD.  A relatively new but challenging approach to AMD management is using tracers to actively identify the sources and flow paths of contaminants, thereby creating an opportunity for targeted remediation.  At the Rico Argentine mine a suite of inorganic salt and organic dye tracers were used to track the interactions and flows of surface and ground waters.  At several sites the organic and inorganic tracers were applied simultaneously to account for potential problems associated with chemical and physical interactions between organic dyes and AMD geochemistry.  The first objective was to use constant injection and slug injection tracer techniques to determine if water from Silver creek was lost in the vicinity of the mine workings and the Blackhawk fault.  Tracers were also injected at discrete locations within the mine to better understand the interior connections of the mine system.  Additionally, isotopic and geochemical analyses were performed to further identify source waters, flow paths, and residence times of waters moving throughout the mine and discharging to the settling ponds.  Initial results indicate that Silver creek losses are small (<5%) and are potentially moving through near surface pathways, but not directly into underground workings associated with the Blackhawk fault.  Results also indicate significant connectivity of the inner mine workings with arrival times of 17 hours and 10 hours for tracers traveling approximately 5000 feet and 1000 feet respectfully.  The rapid arrival times indicate significant structural integrity of the abandoned mine system and may aid in the development of more localized remediation strategies at the historic Rico Argentine mine system.