A significant milestone in the construction of the outlet works for Ridges Basin Dam was reached on April 7, 2005 with the excavation of the 1,400 foot tunnel through the solid rock base of Carbon Mountain . The contract for the outlet works construction was awarded to Weeminuche Construction Authority in September 2004. The 1,400 foot excavation effort spans six month (November 2004 to April 2005).

Excavation of the tunnel progressed in a double heading, two-shift undertaking. The upstream half of the tunnel, through shale material, was advanced using a tunneling machine equipped with a hydraulic arm and rotating excavation head (roadheader). The roadheader machine used dual rotating cutter heads equipped with carbide cutting teeth for shaving the rock. Simultaneously, the downstream section of the tunnel was excavated from the opposite direction, using a conventional drill, blast and muck operation.

With the completion of this milestone, construction efforts are now being directed to excavating the 31-feet in diameter by 44-feet in height Gate Chamber structure located at the midpoint of the tunnel. The remaining outlet works features of the dam, include placement of the permanent concrete tunnel lining, installation of mechanical/electrical components and steel piping, construction of the intake structure on the tunnel inlet side from the reservoir, and construction of a control house building downstream of the tunnel for the control of water releases from the dam.

For more information on the Animas-La Plata Project, please visit the Animas-La Plata Project web site.