Fall River (now) runs over it
CGRS replaces sewer line compromised in 2013 flood
Without a bridge, crossing a river is tricky but not impossible. Installing a sewer line underneath one near the end of a Colorado winter? Now that’s the kind of challenge Team CGRS is likely to take on.
The Upper Thompson Sanitation District (UTSD), which serves the areas surrounding the Town of Estes Park, Colorado, contracted with CGRS to repair 220 linear feet of an 8-inch sewer main line and 100 feet of a 6 inch sewer line compromised in the 2013 flood. Mott McDonald served as design engineer and partnered with the district in managing the project.
It’s a project not unlike many others CGRS’s Water/Wastewater Construction team has completed; the difference is that this project was just outside of Rocky Mountain National Park and required the sewer line to go under Fall River. Dave Gauld, a CGRS foreman with vast experience in excavation and riprap projects, headed up the project.
“It was not incapacitated … but it was operating in a capacity it was not designed for,” explained Matt Allen, UTSD Collection System Superintendent, of the sewer line. “The damage was to the structure around the sewer line crossing. It had been removed and eroded, and the rip rap reinforcement had disappeared. It had become exposed and undermined.
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“That one kept me up at night sometimes,” he added. “It was basically a concrete bridge going across the river with nothing underneath it. It was not designed to be an aerial crossing.”
This project was one of six river crossings the UTSD had budgeted to repair in 2019 but the only one it could not get done before the river’s high runoff last year. The other projects were completed between February and June 2019.
Although CGRS would have to deal with wintry conditions, work began in February to complete the river crossing portion of the project before high runoff. CGRS maintained service to UTSD customers throughout the project with bypass pumping.
CGRS’s construction crew performed the river crossing in two phases, first forcing the river to the south side of the stream bed using material from the river bed, installing half of the new sewer line and encasing it in concrete. The crew then pushed the river to the north, over the top of the new encased sewer line, and installed and encased the second half of the line under the river.
One of the biggest challenges – literally – was the fact that many of the boulders encountered during the river crossing were too large to move with CGRS’s 70,000-pound excavator. Blasting wasn’t an option because the boulders were submerged in the water. CGRS elected to break up the boulders with a demolition hammer and use them as riprap that would protect the new concrete encased sewer line and provide erosion protection for the river bank.
Allen said CGRS worked well with both UTSD and the owners of the Pine Haven Resort to ensure the post-construction profile of the river channel resembled the pre-construction profile as closely as possible. He believes that, using the 75 tons of riprap, CGRS actually improved the river’s flow as well as the area’s aesthetics.
“I couldn’t speak high enough of Dave’s attention to detail and care given to the small things,” Allen said. “I think that’s a lost art, taking the time to do things right the first time, thinking one step ahead.
“Dave has a good eye for cleanup, what looks nice and what is functional. Putting the river channel back, that can be a can of worms. He always has a good plan and executes it well. That river channel looks great.”
The total length for the sewer line crossing the river was about 100 linear feet and took four weeks to install, with a week to spare before high runoff. Weather delays added six days to the completion date in June.