Cowenhoven Tunnel: Aspen’s greatest mining undertaking | AspenTimes.com

Cowenhoven Tunnel: Aspen’s greatest mining undertaking

Tim Willoughby
Aspen Times Weekly

Willoughby CollectionFour-fifths of a mile from its entrance, the Cowenhoven Tunnel (red) bisected the Park Reagent Mine ore bodies (blue), easing transportation of ore out of Aspen's Smuggler Mountain.

Adolph Sutro, one-time mayor of San Francisco, conceived the idea of a transportation and drainage tunnel for the Comstock mines in Virginia City, Nev. After securing property rights and funding from Congress he began his miles-long tunnel, intending to come in below existing workings. The 10-year project was completed in 1878 just before Aspen was founded, and after the Comstock reached its peak and had devised other methods for water drainage. A decade later, Aspen’s famous mining engineer, D. W. Brunton, proposed a similar tunnel for the Smuggler Mountain mines.

Brunton’s scheme was similar to Sutro’s: Run a tunnel below existing workings that would drain the ever-present water, provide ventilation, and create a more efficient way to transport ore from the depths. His two-mile long tunnel would thread through nine different mining properties, each of which featured downward-following veins. The tunnel company would make money by charging each mine a rate for their traffic through the tunnel, plus drainage fees.

The idea attracted backers immediately and the The Cowenhoven Mining Transportation and Drainage Tunnel Company was formed. D.R.C. Brown and H. P. Cowenhoven subscribed as major investors, and claimed naming rights. New York investor Jerome Wheeler contributed, along with Elmer Butler, who held interest in several of the mines. Brunton was the engineer, project manager and partner.

The length proposed far exceeded anything conceived to date for Aspen. In addition, it was to be wide enough for two tracks, one for cars going out and one for cars coming in, sufficient to handle the expected high volume of traffic. The tunnel was a nearly 10-foot bore, large enough to accommodate an 18-inch-wide and two-foot-deep drainage ditch, more than twice the size of other Aspen tunnels.

Ground was broken in 1889 and work continued for three arduous years at a rate of 3 to 8 feet a day. Miners were paid an above average miner’s wage, $115 to $132 a month with a bonus for feet driven. Work was dangerous and unpleasant, since water was encountered the whole distance, usually 650 to 1,000 gallons a minute flowing out of the tunnel. Visitors to the tunnel described the working conditions as constant rain.

Several sections challenged Brunton’s engineering skills. The tunnel passed through unstable wet sand and silt that was similar to quicksand. Brunton had to invent a method to push timbering into the muck, holding tons of material in place while men excavated; then they permanently timbered to prevent more material from filling up the tunnel.

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Soft sections of ground were under great pressure from above, necessitating massive timbering. The timber sets were made of 12-by-14-inch side timbers and 16-inch-thick roof pieces (caps) set every two feet. Outside of the mine, each timber was cut and numbered, and then transported to the location for assembly. They cut all the large trees anywhere near Aspen. The tunnel passed through carboniferous shale that absorbed oxygen. Before connecting to the other mines to create air circulation, air had to be continuously pumped into the tunnel or miners would perish.

For a long time there was a debate about whether Hunter Creek, because the tunnel passed below it, was the source of tunnel water. Whenever water flow increased in the tunnel, Hunter Creek’s volume decreased. However, tunnel water was 15 degrees warmer than that of the creek, suggesting they were not connected.

Some sections of the tunnel were easy to construct, requiring no timbering. The record for one month’s work was 379 feet bored through dolomite with no timbering.

As the tunnel passed under a mine, connections were made from above for hauling ore, making the tunnel profitable from the very beginning. As designed, it passed 500 to 1,000 feet below the lowest levels of the mines it crossed. Years passed before mines worked below tunnel level. Even when mining below the tunnel level, it was easier to raise ore and pump water to the tunnel level rather than all the way to the surface via a vertical shaft. As it turned out, many Smuggler Mountain mines reached only half way to their ultimate depth when they intersected the Cowenhoven Tunnel level.

The Cowenhoven Tunnel was one of D.W. Brunton’s greatest triumphs, and one of Aspen’s most successful enterprises.