Down Deep in Durango

Breaks Rock In Southern Colorado To Complete Reservoir Project
May 2009 Vol. 64 No. 5
The Animas La Plata project, more than 50 years in the making, will provide water to the Ute tribe and areas of CO and NM.

After decades of debate and hard work, completion of the Animas La Plata main reservoir in Colorado was down to just two intake lines.

Project deadlines stipulated that crews would begin filling the man-made lake bed by the end of April 2009. Contractor BTrenchless needed an effective and swift construction method for the rock tunnels through mudstone. The contractor decided on a hard rock trenchless boring machine, called the Robbins Motorized Small Boring Unit, to complete the job within the tight schedule.

“Not only is there a tight deadline, but the rock tunnels are connected to an intake structure. We’re making two mid air breakthroughs into a vertical shaft that require crane lifts,” said Tina Connett, project manager for BTrenchless. The design will minimize the time required to construct the intake lines.

Dating back to a 1968 decree, the Animas La Plata project is no short term fix. The $570 million project is being built to fulfill 1868 water rights obtained by the Ute Indian tribe, located on lands near Durango, CO.

“This project is a major milestone highlighting 50 years of work to get water into this area, which is very dry. Once complete, it will distribute water through 45 miles of pipelines down to the New Mexico border,” said Reid Tanner, project manager for EPC Construction (general contractor for the Animas La Plata Intake Structures).

Water stored in the Ridges Basin Dam on the Animas River will form a reservoir, called Lake Nighthorse, which will store 120,000 acre feet of water for use in surrounding areas, and will also serve as a recreational and fishing area. Filling of Lake Nighthorse began in spring 2009 and is expected to take up to two years to complete. The system is scheduled to go online by 2012.

The Bureau of Reclamation (BOR) first contracted the La Plata West Water Authority (LPWWA) to create a distribution system from the new lake to arid areas of La Plata County. Initial site work began in 2002, including construction of an inlet conduit, pumping plant and a dam in Ridges Basin.

Work begins

In 2008, work began on an intake structure consisting of a 118-foot deep intake shaft and two intake tunnels which would allow for dispersal of water from the reservoir. The shaft was completed by Anderson Drilling of Denver, CO, using a down drill auger. Corrugated steel was then set into the shaft and grouted in place, forming a 15-foot diameter wet well.