INVESTIGATION OF GROUNDWATER INFLOWS INTO THE COMMODORE MINE COMPLEX

The Commodore mine complex is located just north of the town of Creede in southern Colorado, and was developed along the Amethyst Vein in the early 1890’s in search of silver ore. Discoveries of rich silver ore and associated base metals enabled periodic mining throughout the early 20^th century until 1976 when mining officially ended. Now, over 250 gallons per minute of metal laden waters flow from the mine workings through the Nelson Tunnel polluting over three miles of Willow Creek and eventually spilling into the Rio Grande River. Recent designation of the Nelson Tunnel as a Superfund site by the EPA has accelerated ongoing investigations by local stakeholders, state and federal agencies into groundwater hydrology within the mine complex in hopes of implementing source control as a remedy. Various hypotheses regarding recharge and pathways for groundwater flow within the mine have been proposed and are currently being verified through tracer studies, geochemical and isotopic water analysis and underground investigations including pump tests. Understanding water movement within the mine complex has been compounded due to extensive flooding and difficult access, but work to this point has identified at least three major mine pools, and has identified the likeliest point for groundwater entry into the mine. Effective source control depends on a full hydrologic understanding of groundwater movement within the mine complex and surrounding region. Detailed historic records regarding groundwater inflow during periods of mining are helping to complete a hydrologic understanding of water movement within the mine historically, while more recent observations made during mining at the adjacent Bulldog Mine have provided a regional context for understanding the current groundwater flow regime.