An update to the city’s wastewater collection master plan in 2020 indicates about 8% of Longmont’s sewer lines are under capacity and that replacements and upgrades will cost the city over $46 million.
The master plan update was presented to the city council earlier this month.
Land use and water use changes, as well as the city’s aging assets, triggered the master plan update which set a criterion for pipe capacity in Longmont’s waste management system. The master plan pinpointed sewer pipe segments anticipated to be under capacity at buildout conditions, according to a city staff report to the council.
In all, the city owns and maintains a wastewater collection system consisting of more than 300 miles of underground pipelines, at least 8,000 manholes, and two pumping stations. “This critical asset requires thoughtful planning to ensure existing infrastructure protects public health and that pipe conveyance capacities will meet current and future needs,” the staff report states.
Longmont made three recent improvements to its sewer system, according to the master plan:
- A new 18-inch polyvinyl chloride (PVC) sanitary sewer line was added from Main Street to the upstream side of Dickens Farm Park.
- Crews removed the 12-inch pipe crossing of the St. Vrain Creek — currently located south of Boston Avenue — and relocated it north of Boston Avenue, where it was connected to an existing pipe. Both lines will then cross under St. Vrain Creek through two parallel 20-inch pipes.
- The pipes under the railroad crossing at the Wastewater Treatment Plant were updated from a single 54-inch in the model to two 20-inch lines.
The master plan identified 27,249 feet of pipe ranging in size from 8-to-27-inches that need upsizing to meet the estimated flow of sewer water from future development. A large portion of that total — 11,450 feet — is from the 27-inch Trunk 9 segment from just east of County Line Road to the manhole upstream of the railroad crossing near the WasteWater Treatment Plant at 501 First Avenue.
Overall, Longmont’s wastewater collection system has about 31,071 feet, or eight percent of pipe, that is undersized for existing growth conditions and estimated buildout flow conditions, the master plan states.
The document puts the total capital improvement cost of upgrading the system at $46,440,000. The master plan recommends the city update its master plan to incorporate the needed pipe upgrades and replacements.
