Glenwood Springs water system relatively safe, but water treatment costs could reach $4M
Glenwood Springs’ water supply is safer than expected from the effects of the Grizzly Creek Fire, and steps are underway to mitigate risks.
Yet more sobering news is the estimated $2.4-$4 million expense to mitigate increased sediment load during water treatment.
Those were the messages from a two-pronged City Council work session Thursday afternoon.
Eric Petterson of SGM engineering in Glenwood said that about 2.9% of the Grizzly Creek watershed above the diversion over to No Name was in the burn area, and that was mostly low to moderate intensity — not the type usually associated with debris flows.
There was little burn above the Grizzly Creek pipeline, so there is little concern of damage there.
The fire burned much more intensely below the diversion, and while that is not a concern for the water supply, there is potential for big debris flows there, Petterson said.
No Name was a little worse off, with 9.2% of its watershed in the burn area. It was also mostly low-to-moderate-intensity burn, but there was some high-intensity burn on the ridge between the two drainages.
Petterson said there is a moderate to high risk of ash and mud flows in No Name and low to moderate risk of a major debris flow in either drainage.
He outlined a few recommendations at the water facilities in those drainages such as stabilization and installation of jersey barriers.
Glenwood Public Works director Matt Langhorst said the city is trying to get all of that work done before spring runoff.
“We’ll be No Name residents for the next 45-90 days,” he said.
Councilor Paula Stepp asked about costs to do the work. Langhorst said the city has a Natural Resources Conservation Services Emergency Watershed Protection Program 80/20 matching grant and that as much of this work as possible will be paid through this grant.
Leanne Miller of Carollo Engineers first provided council with a primer on water treatment.
She said that impacts from fires don’t follow a pattern, and each fire has to be evaluated separately in terms of impact on water quality.
Her list of good news included: the risks can be mitigated; the long conveyance to the treatment plant can allow for some sediment to drop out before reaching the treatment plant; Glenwood has an alternative water source; and water demands are half of the design capacity, giving the plant higher treatment capacity.
She next outlined seven solutions: water quality sampling and remote monitoring; the construction of the Roaring Fork pipeline; increasing sediment removal before the plant; providing tools for staff to target the correct water chemistry to remove sediment; providing diagnostic tools for decision making; increasing solids removal and storage capabilities; and having mobile treatment units as a backup plan.
Of these, the Roaring Fork pipeline work is under way — with Langhorst saying he was working on a $1 million DOLA grant during the meeting — and remote turbidity monitoring has been installed at No Name.
Sediment removal will take place in the No Name Cave, which Miller said was the city’s water treatment plant in 1975. It would take some retrofitting at a cost of between $200,000 and $450,000.
Additional solids removal would be performed in a blending facility — previously referred to in Post Independent stories as a settling pond — near the plant. This is the big ticket item among the water treatment expenses at $2 million to $3 million, with Miller emphasizing the these are preliminary cost estimates.
Councilor Charlie Willman was concerned about the ability of the soils in that area to handle such a facility based on studies in the ’80s. Miller responded that her structural engineer also has similar concerns.
City manager Debra Figueroa said staff will work on a cost and use summary to give council a best guess at how these items will be paid for.
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