Driven between 1893 and 1910, the 10-foot wide by 12-foot high tunnel runs four miles, serving as a drainage tunnel for several mines in the Central City-Idaho Springs mining district. It currently discharges acidic metals-laden mine water at a rate of 200 to 600 gallons per minute. Since 1998, discharge has been treated at the Argo Tunnel Water Treatment Facility, which was constructed as part of remedial actions associated with the Central City/Clear Creek Superfund Site.

The flow-through bulkhead inside the tunnel provides a long term means of controlling the rate of discharge from the tunnel, and mitigates the hazard of future surge events (or seasonal high flow periods) from overwhelming the treatment facility. The project included constructing a concrete bulkhead approximately 200 feet inside the tunnel, installing piping from the bulkhead to the portal, and installing instrumentation and controls to allow flow control operations to be performed from within the treatment facility. Shannon & Wilson evaluated ground conditions within the tunnel, designed ground support measures, and lead the bulkhead design team. We also provided full-time construction observation.