From The Denver Post (Bruce Finley):
The divers’ environment — 200 feet beneath the surface of Denver’s mainstay reservoir and under 70 pounds per square inch of pressure — resembles “a space shuttle in reverse,” said Spencer Dell, 36, a member of Seattle-based contractor Global Diving & Salvage Inc.’s underwater team. A phone-booth-size diving bell will carry two team members out from a six-bunk main chamber, connected by hoses and wires, for 12-hour construction shifts. They’ll wear rubber suits heated with warm water and hard yellow helmets fitted with earpieces and microphones. Because the helium-oxygen mix they will breathe distorts voices, their words must be unscrambled by a support crew listening from a floating steel barge. The overhaul of rusty, leaking cast- iron fixtures — scheduled to begin Monday at dawn — marks Denver’s first major effort to upgrade the dam, a 221-foot-high granite-brick structure that, when the reservoir opened in 1905, was the tallest in the world…
Tunnels blasted and chiseled through granite a century ago, but currently closed off and never inspected, eventually must be cleaned to prevent clogging. The overhaul also includes major electrical upgrades. If all goes well, Denver will be set for another century…
After blasting, cutting and prying out corroded iron fixtures, the divers must bolt in three rectangular stainless-steel sleeves designed to carry reservoir water into tunnels — each gate worth $500,000 — and then inject grout and seal them in place. They also must install a grate with 2-inch holes — coated with enamel designed to prevent invasive mussels from attaching — to keep debris from clogging Denver’s supply system. Project engineers, who planned this overhaul for five years, relied on century-old blueprints. They’re bracing for surprises divers probably will encounter.
Here’s the Cheesman Dam history page from Denver Water. From the website:
Cheesman Dam, which was named for Walter Scott Cheesman, was the world’s tallest at 221 feet when it was completed in 1905. Cheesman was the first reservoir of Denver’s mountain storage facilities – a small, but visionary, beginning that helped expand Denver Water’s system. In 1973, the dam was designated a National Historic Civil Engineering Landmark. It remains, after more than 100 years, the workhorse of the storage system and jewel among the system’s dams, a monument to thoughtful planning and wise water use.
More Denver Water coverage here.