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'Shutting off a super-sized spigot': Denver Water shuts down key supply system to juggle critical construction projects

Pausing water collection in north system allows for handful of major projects
US agency approves Denver water utility's dam expansion plan
Posted at 2:23 PM, Oct 26, 2021

Denver Water is in the middle of a rare and tricky maneuver — juggling multiple critical infrastructure projects while the entire north region of its water collection system is shut down.

The shutdown of its north collection, delivery and treatment systems, which has already happened, means that all 1.5 million people who rely on Denver Water are getting their water from the southern systems instead.

And it will stay that way until the spring, with an expected end date in March or April.

Denver Water shuts down key supply system to juggle critical construction projects

In the months leading up to this undertaking, Denver Water has had to move mountains of water from its northern region to the systems in its southern region.

“Shifting all that water here and there — it’s a lot to keep straight, a lot to think about, a lot to juggle,” said Nathan Elder, manager of water supply for Denver Water. “And it all comes on top of watching the weather to see what it might, or might not, bring us as far as precipitation.”

The complicated rearrangement is necessary so crews can complete a series of "major maintenance and construction projects," according to Denver Water. It means Denver Water will need to rely almost fully on supplies from the southern collection system, which collects water from the South Platte River and Dillon Reservoir.

“We’ve been setting the stage on this for months,” Elder said. “Taking the north end out of the equation means we have to set up our southern end for all the heavy lifting for nearly an eight-month span. It’s a highly unusual and tricky undertaking.”

Denver Water_north and south split

Shutdown will allow for the competition of multiple Denver Water projects

The biggest project crews are focused on now is constructing a connection between the emerging Northwater Treatment Plant to Denver Water’s distribution system. This is the main reason why the north side flows must be shut down.

The Northwater Treatment Plant is part of Denver Water's $600 million North System Renewal Effort, which includes installing new pipes to move water from the Northwater Treatment Plant, plus upgrades to the old Moffat Treatment Plant. The latter, which was built in 1937 in Lakewood, will continue to operate for at least 20 years but at reduced capacity after the Northwater Treatment Plant opens in 2024.

Connecting the Northwater Treatment Plant to Denver Water requires taking the Moffat Treatment Plant offline. The upgrade to the old plant and creation of the new one will cost approximately $520 million, according to Denver Water. The new plant's pipeline will cost about $80 million.

Moffat tunnel east end construction portal summer 2021.jpeg
Work started in August to replace concrete at the East Portal of the Moffat Tunnel near Rollinsville. Repairs were required on both the inside and outside of the portal area.

Another major project included replacing the massive grate at the bottom of the Gross Dam, which has been lovingly nicknamed a "trashrack." This project began on Aug. 23 and is almost complete.

The old grate prevented anything large, such as logs, from making its way into the infrastructure under the dam. While it works just fine, Denver Water said "it no longer aligns with new regulations associated with the Division of Water Resources and the Federal Energy Regulatory Commission."

Specially trained drivers worked about 300 feet below the surface to deconstruct, remove, and replace it with an upgraded grate, according to Denver Water. The divers spent weeks working underwater and lived in a saturation chamber in a pressurized state.

This technique, called saturation diving, allowed them to "complete the work far faster than if divers had to undergo more frequent preparation and recovery for underwater work shifts," according to Denver Water.

Todd Hartman with Denver Water said this required "really delicate work."

"We had to bring in contractors with expertise in diving because that work actually took place hundreds of feet underwater for weeks," he said. "So, it was quite a project and it's about to be wrapped up. So we're excited about that."

Three other major projects are underway:

  • Replacing concrete at the Moffat Canal near the east portal of the Moffat Tunnel near the James Peak Wilderness. The freeze-thaw cycle at 9,200 feet has taken a toll and allowed for water to seep underneath concrete and create the potential for damaging erosion
  • Repairing deteriorated concrete within the Moffat Tunnel caused by years of scour within the tunnel
  • Replacing key structures at Ralston Reservoir near Golden. The work will replace equipment that regulates the way water moves through the dam, allowing for safer operation of reservoir releases. Replacing that equipment requires draining the reservoir. It will be out of commission until April 2022
ralston reservoir drained construction summer 2021.jpeg
Ralston Reservoir, a key water supply bucket near Golden, has been drained to allow Denver Water to construct a new outlet works to release water from the base of the dam.

The combination of the Moffat Treatment Plant staying offline plus Ralston Reservoir remaining out of commission until the spring means that all water treatment needs fall on the shoulders of the Marston and Foothills plants in the southwest side of the region.

Hartman said some of these projects are already nearing completion.

"The bigger work that really requires holding the water upstream is down here at the Ralston Reservoir at the Northwater treatment plant and at the Moffat treatment plant — that work is really going to take all winter to conduct," he said.

Preparations for turning off a massive 'spigot'

Multiple coincidences lined up to make this project particularly tricky for Denver Water.

In 2020, Denver Water underwent a large shift in how it moved water in its systems due to repair work that forced the closure of Roberts Tunnel, which moves water 23 miles under the Continental Divide, for two months. This temporarily closed off access to water from the Dillon Reservoir.

In addition, Denver Water had to release a large amount of water from the Williams Fork and Wolford Mountain reservoirs on the West Slope to make up for a water debt. This did not impact projects on the north end, but was an added aspect of Denver Water's obligations just ahead of the closure.

Despite the challenges, engineers decided it would be easiest to coordinate all of the aforementioned projects into a single fall-winter cycle.

Jennifer Gelmini, a senior engineer at Denver Water who is coordinating the projects, explained why it made sense to condense the work into a smaller time frame rather than spread them out.

“We realized we were going to have a long outage for the work needed for the Northwater plant connections and Moffat modifications and looked at how we could take advantage of this big shutdown and what other projects could fit into that time frame," she said.

northwater-treatment-plant-constuction-summer-2021-flocsed-100x518.jpeg
Construction continues at the emerging Northwater Treatment Plant below Ralston Reservoir. Work this fall and winter will connect the facility to Denver Water’s distribution system. The plant is expected to be complete in 2024.

Hartman said it made more sense to stack the projects into one period of time and let the southern systems carry the weight.

"And we're confident it can do that," he said. "And it sets us up really well for spring and it sets us up well for the long-term."

Hartman said this mission required all kinds of orchestration among water supply managers.

"It's a very unusual event," he said. "And it's taken a lot of planning and foresight to ensure it goes well... I would add to that — this illustrates the key, the importance, of having a large and flexible system. Because if you don't have that flexibility, it becomes much more difficult to do these already very difficult and challenging maintenance projects. It's harder to shut things down when you're reliant on a single source of supply."

A Denver Water update compared the project as a whole to "shutting off a super-sized spigot."

"You know, turning off a big spigot is kind of a simplified way of saying, 'We're no longer going to be pulling water through that system,'" Hartman said. "We have water coming down, to some extent, over the winter and being held at Gross Reservoir. But we will not be bringing water farther down into Ralston Reservoir and into the... treatment plant. So that's essentially what we mean by turning that system off."

While few people may have noticed the tiny cues that something was underway — such as heavier flows in the North Fork of the South Platte River as utility crews moved more water than usual from the Dillon Reservoir, through Roberts Tunnel and into the North Fork to then be stored in reservoirs — there is no difference to residents' supplies now that they're using water collected in the southern systems.

In short: You shouldn't notice a thing.

Denver Water moved all the water around in the late summer so its southern systems would be prepared for a heavier lift throughout the winter. It also lined up with the season when outdoor irrigation stops. Hartman said most of the water being used in the winter is by residents in their homes.

"So we don't anticipate any supply issues," he said.

By the spring, the projects tied to the north region shutdown will wrap up, which will lend water managers more flexibility to manage water between the north and south systems. Hartman said everything should be completed around March or April, just in time for spring runoff.

Denver Water's collection systems cover about 2.5 million acres in Park, Grand, Jefferson, Summit, Teller, Douglas, Clear Creek and Gilpin Counties. It maintains 3,000 miles of pipes for distribution, which is enough to stretch from Los Angeles to New York City with a couple hundred miles to spare.