And about 50 miles (80 km) of tunnels at that!
Last Sunday, while at Utah's Snowbird Resort for the AWRA 2011 Summer Specialty Conference, eleven of us went for a walking field trip to see the resort's drinking and snow-making water supply. Our host was Keith Hanson, General Manager for Salt Lake County Service Area #3, which provides Snowbird's drinking water and sewage services and manages the Town of Alta's water system.
The water is obtained from Wasatch Drain Tunnel, constructed in 1912-1916 to drain water from and improve access to the lead, copper, zinc, and silver mines within the Little Cottonwood (Canyon) Mining District (read the Service Area's history). Hanson noted that there are about 100 miles of tunnels in the district, with about 1000 miles (1610 km) on the other side of the mountains in the Summit County area.
The tunnels act as drains -- massive horizontal (or nearly so) wells - that harvest the infiltrating snowmelt and rain. The Snowbird Resort averages about 500 inches (almost 13 meters) of snowfall per year; this year the figure exceeeded 780 inches (20 m). Even when you account for the snow-water equivalent, that's a lot of water seeping into the cracks and fissures in the rock (granite, quartzite, and limestone).
I had heard about these tunnel water sources before. Colleague and friend Todd Jarvis, who used to work in private industry in Salt Lake City, designed tunnel water-supply systems in Summit County. And of course there are the ancient qanats still in use, especially in the Middle East.
Hanson escorted us about 1000 feet (305 meters) into the tunnel. There is a treatment plant in the tunnel, because a number of metals (lead, others) must be removed from the water before it can be consumed by humans. There is radon in the finished water but there is no drinking- waterstandard for it. Here is the 2009 drinking water quality report.
The picture shows our group listening to Hanson explain the treatment system.
At the end of the tunnel was a unique feature - a mssive steel and concrete bulkhead sealing the tunnel. Hanson explained that they wanted to store water, so in 1985 they sealed the end of the tunnel so that they could trap the water behind it and keep it from draining until they wanted it to. There are about 35,000,000 gallons (c. 133,ooo cubic meters or about 107 acre-feet) behind and above (330 feet or 100 meters) the main tunnel. The water is stored in the other tunnels plus the cracks and fissures in the rocks.
Hanson said that at one point there were about 360 feet (110 meters) of water above the bulkhead but that was causing seepage problems in the overlying Town of Alta so theynow keep the water level no higher than its current elevation.
Here is Hanson at the bulkhead explaining the operation. That's a pressure gage on the bulkhead.
Hanson, a veritable fountain of knowledge on the region, told us the story of five miners (right after World War II, I think) who drilled into a high fluid pressure zone 4.5 miles (7 km) into one the tunnels. A huge torrent of water burst through the rock wall and swept them the length of the tunnel and deposited them outside. All five survived, and three even came back to work.
If I am not mistaken I believe Hanson said the system can produce up to 450 gallons per minute (about 1 cfs or 1.7 cubic meters per minute). The tunnel also provides flow to Little Cottonwood Creek.
Another interesting tidbit: the Service Area has to pay $2 per 1000 gallons to Salt Lake City for the raw water. That is expensive.
Our visit took about two hours and we all enjoyed it.
"I've searched all the parks in all the cities and found no statues of committees." - G.K. Chesterton