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Underwater divers are beginning major construction work on one of Denver Water’s oldest dams.

The 105-year-old Cheesman Dam, located on the South Platte River near Deckers, needs important upgrades to maintain dam safety, provide a viable water supply and ensure smooth operations. During the next year, crews will upgrade the dam’s valve system — which was installed when the dam was built in 1905 — and will install underwater trash racks to prevent debris from clogging the valves.

Crews also will install new control systems and a control building and will update the dam’s electrical systems. Most of the construction at the site will take place underwater using specialized divers. A large working barge will be set up on the reservoir while the divers do their work.

Because of the dangerous nature of the work, the divers have to live within a compression chamber mounted to the working barge for 30 days at a time.

Denver Water is keeping the reservoir full and using underwater divers, instead of emptying the reservoir, because we will need the water stored in Cheesman for the summer irrigation season. Cheesman Reservoir is closed to recreation during the project and will reopen next summer.

The two-year $18.3 million project is part of Denver Water’s 10-year capital plan to replace and rehabilitate aging infrastructure, much of which dates back to the World War II era.

There’s one sure thing about working in Corrosion Control.

Rust never sleeps.

Every day, pipes get a bit older, a tad rustier — a little more likely to break. And it’s the job of Denver Water’s Corrosion Control department to find the pipes in the worst condition and put them on the replacement list before they break.

The employees in Corrosion Control visit almost every main break and leak to study the pipe and figure out why it broke. How fast was it rusting? What was the soil like? Had the pipe been damaged? Did freezing temperatures damage the pipe?

They track more than 4,000 testing sites to measure a pipe’s DC voltage. Those measurements then help Corrosion Control calculate the rates of corrosion and decide which pipes need to be replaced before they cause major damage. Corrosion Control also works with Denver Water’s Hydraulics department to decide which pipes need to be rehabilitated with cement-mortar lining.

Denver Water leads water utilities of its size in the corrosion control department. Many other utilities don’t have a corrosion control plan — they see main breaks as a cost of doing business and make little effort to prevent them. But ignoring that maintenance can get expensive and dangerous, which is why Denver Water strives to prevent breaks from happening before it’s too late.

Crews are beginning a two-year, $17 million project to install a new hydro turbine and expand and repair the outlet works at Williams Fork Dam.

The dam’s outlet works, where operators control the amount of water flowing from the reservoir into the river, was installed during the dam’s original construction in the 1930s. Making repairs to the building’s aging electrical and mechanical systems, as well as to the 50-year-old valves, will bring the outlet works up to current state standards and help it run more efficiently.

Crews also will install a new 0.5 megawatt hydro turbine, which will increase the power plant’s generating capacity to 3.6 megawatts — enough electricity to power more than 3,000 homes. The new turbine also will allow Denver Water to generate electricity during reduced winter flows, when the water level is too low to generate power with the current largesize turbine.

The original dam at Williams Fork Reservoir, located about 20 miles west of Granby, was built in the 1930s. In the mid-1950s, Denver Water doubled the size of the dam, building it up to its current height of 217 feet, and installed a hydropower plant at Williams Fork — making it the first power plant in Denver Water’s system. The construction work began in December 2009 and should be finished in 2012.

Denver Water is working to prevent another “sinkzilla” by replacing a section of the conduit that earned the nickname.

In February 2008, Conduit 94 erupted under Interstate 25 near 56th Avenue, blasting about 2 million gallons of water onto the highway. Denver Water replaced the portion of damaged pipe under the interstate immediately. Now, Denver Water is replacing the rest of the 34-year-old-conduit in sections to prevent further problems.

That replacement project continues this winter as a Henderson-based contractor installs a new six-foot-diameter conduit east of the interstate. The new pipe will stretch almost 2,300 feet, from Interstate 25 and 56th Avenue to Washington and 56th Avenue. Denver Water is replacing the pre-stressed concrete conduit with a steel conduit bought from a Denver-based pipe manufacturing company. This portion of the multi-year replacement project will cost $1.5 million.

Marston Treatment Plant is getting an upgrade.

In 2010, contractors will work on a $12 million project to upgrade the 42-year-old filter beds in Filter Plant No. 2 at Marston Treatment Plant. In 2003, Denver Water completed a similar project in Marston’s Filter Plant No. 1 — which was originally built in 1924 — by building a new structure and plant control room.

To complete the work in Filter Plant No. 2, crews have to demolish some of the building’s interior walls, take out the filters’ anthracite coal and sand, replace the filter underdrain systems, remove most of the piping and valves located in the filter gallery, strip old paint, and replace an outdated valve-operating system with a modern electronic system.

The Marston project is just one way that Denver Water is ramping up efforts to make needed improvements associated with an aging infrastructure. Denver Water owns and maintains more than 3,000 miles of pipe — enough to stretch from Los Angeles to New York — as well as 12 raw water reservoirs, 22 pump stations and four treatment plants.

Denver Water’s 10-year, $1.3 billion capital plan details more than 300 projects, including the Marston project, which will help ensure Denver Water continues serving high-quality water well into the future.

Four parks in the Lowry and Montclair neighborhoods were converted to recycled water in summer 2009, part of Denver Water’s growing effort to free up more water for drinking purposes by using recycled water for irrigation needs.

Crescent, Denison, McNichols and Verbena parks were added to Denver Water’s recycled water system last summer. Recycled water is wastewater treated to Colorado Department of Public Health and Environment standards for irrigation, commercial and industrial purposes. Once the system’s build-out is complete, the project will supply more than 5 billion gallons of recycled water every year for irrigation, industrial and commercial uses, freeing up enough drinking water to serve about 42,500 households a year.

Parks and golf courses that use recycled water are clearly marked with signs. In addition, some valve boxes and sprinkler heads are purple, which is the same color as the pipes used to transport recycled water. Though recycled water is highly treated, people should not drink it because it does not meet drinking water standards. These four parks will add to the 13 Denver parks already being irrigated with recycled water, making a total of 552 acres of parks on recycled water.

A significant portion of Denver Water’s pipes (more than 3,000 miles) were installed during the post-World War II boom years. As many of those pipes near the end of their useful lives, Denver Water replaces them, or, in many cases, rehabilitates them.

Rehabilitation allows Denver Water to reuse pipe rather than replace it — saving time and money while cutting down on traffic disruptions. To rehabilitate a pipe, crews scrape the inside of the pipe down to bare metal. Then they line the inside of the pipe with a layer of cement mortar. They finish by flushing and disinfecting the pipe before reconnecting the rehabilitated pipe to the system.

Depending on the situation, rehabilitation costs are 10 to 40 percent less than open-trench replacement. In 2009, Denver Water spent approximately $6.6 million on main rehabilitation and replacement, and plans to double that annual amount in the next 10 years to keep up with the maintenance required for its aging infrastructure.

Denver Water currently rehabilitates about 30,000 feet of pipe per year. Since 1963, Denver Water has cleaned and lined approximately 110 miles of main, helping the utility save money while continuing to provide high-quality water to its customers.