The Choteau City Council at its Sept. 1 meeting took public comment on a proposed $1.3 million wastewater collection system project that could break ground next spring.
Engineer Collette Anderson with Great West Engineering presented her preliminary engineering report (PER) for the project which is designed to reduce the amount of groundwater infiltration into the city’s wastewater collection system.
The city requested Anderson to develop a PER for this project because infiltration is at times so great in volume that it exceeds the daily capacity of the wastewater treatment plant and forces the city to use the old facultative lagoon as a holding pond for excess flows. Also, when the sewer lines are running at or above capacity, sewage can back up and flow into people’s basements. This happened to more than a dozen homes on the northeast side of town last year, creating a public health and safety issue.
Anderson said her PER looked at the city’s overall wastewater collection and treatment project, came up with options to address the deficiencies, produced cost estimates for the options and did an environmental assessment on any proposed improvements.
She said the analysis included looking at Choteau’s population today (estimated at 1,713 as of 2018) and designed for 1.4% annual growth to the year 2040. She noted that the city’s relatively new wastewater treatment plant was designed to accommodate a city population of 2,292.
In Choteau’s wastewater system, sewer lines convey wastewater through a gravity fed collection system to a lift station, where the sewage is then pumped into the new treatment plant.
The collection system includes 260 manholes and around 8,100 feet of sewer mains. The mains include 22,000 linear feet of cured in place plastic pipe in six-inch to 15-inch diameters; 2,100 linear feet of concrete pipe in six-inch to 10-inch diameter; 30,000 linear feet of PVC pipe in six-inch to 15-inch diameter; 8,000 linear feet of pipe of unknown type (which may be vitrified clay pipe installed in 1914); and 18,000 feet of thermoplastic high-pressure pipe that takes wastewater from the lift station to the treatment plant.
Anderson said a study of the wastewater flowing into the plant and water flowing out of the plant show a disparity between inflow and outflow, particularly in the spring when groundwater is high. Choteau’s average daily inflow is 787,000 gallons per day while the average outflow is 651,000 gpd. In the winter, when the water table is ow and people aren’t irrigating their yards or gardens, the average daily inflow is 174,000 gpd.
While infiltration is highest during the spring, Anderson said, her research shows that infiltration is happening throughout the year. Groundwater is coming into the system through leaking pipe joints, damaged manholes, cracked or broken pipes, leaking joints where the individual user’s service line joins a main line, Anderson said. Surface water may also be entering the system through manholes or roof drains, storm drains and through basement sump pumps in homes that are emptying into the wastewater system (though city code doesn’t present this practice).
The federal Environmental Protection Agency says that people use on average 120 gallons of water a day per capita, but Choteau’s per capita inflow is 450 gpd per person — indicating that 70% of the water flowing into the system is coming from infiltration.
Anderson said she divided the city into six basins and put a flow meter in one manhole in each basin to study flows. She determined that two basins, one on the north east side of the city and one on the southeast side, contribute the most infiltration into the system.
Basin one had 0 gallons per day average, basin 2’s minimum daily flow was 104,675 gpd; basin three’s was 16,651 gpd, basin four was 54,854 gpd, basin five was 101,724 gpd and basin six was 0 gpd.
In addition to looking at the collection system, she also analyzed the new treatment plant and found it is working well with no major deficiencies except that the city has not been able to fully abandon use of the old lagoon and reclaim the lagoon site.
Anderson said she then developed alternatives to address the deficiencies in the collection system and the old lagoon cell. The options were:
•No action (zero cost).
•Open cut replacement of leaking sewer mains ($1,305,000 cost). This would entail digging up and replacing 5,400 linear feet of pipes and manholes between Third and Eighth avenues northeast.
•Open cut and Cured In Place rehabilitation of leaking mains ($965,000 cost). This would include 2,150 feet of Cured in Place relining of existing pipes and digging up and replacing 3,250 linear feet of line between Third and Eighth avenues northeast. One of the downsides to this option is that the city cannot change the grade of sewer lines and lining the existing lines with the CIP plastic will reduce their diameter (though the slick plastic versus vitrified clay will help sustain flow rates).
•Abandoning and reclaiming the old lagoon cell ($937,000 cost). This would entail removing all the existing sludge, filling in the lagoon and planting new vegetation over the site.
•Rehabilitating the old lagoon cell to reclaim most of the lagoon but to create an overflow pond for use as needed ($1,519,000 cost). This would give the city an overflow pond that meets EPA regulations while still getting rid of the existing old lagoon and reclaiming that land.
Anderson recommended that the city break the work into two phases. The first phase would be the open-cut replacement of sewer mains at an estimated cost of $1,305,000.
Once that project was done, she said, the city would then roll into the second phase, which would be to rehabilitate the old lagoon cell and to create a new holding pond that complies with all state and federal rules at an estimated cost of $1,519,000.
Anderson said she then developed funding packages for the preferred alternatives. She started by looking at the city’s existing wastewater treatment plant to see whether they fall above or below the Montana Department of Commerce’s target rate. Choteau’s combined water and sewer rate is $86.77 per ratepayer per month. The state’s target rate is $73.85 so Choteau is already above that rate and eligible for grant and loan funding.
Since the city is already applying for state funding through the Department of Natural Resources and Conservation and the Treasure State Endowment Program for its water system improvements, Anderson said, its funding options for the sewer project are limited the State Revolving Loan Fund and the U.S. Department of Agriculture’s Rural Development Fund.
She designed a funding package for the first phase of a $168,000 SRF loan, a $460,350 loan from RD, a $376,650 grant from RD and a city budget contribution of $300,000. With this package, she said, city sewer ratepayers would need to pay $2 to $3 a month for debt service, and that amount of debt could likely be covered without a rate increase, according to the city finance officer.
Anderson also said that the environmental assessment on the preferred alternative has been deemed sufficient and a more in-depth Environmental Impact Study won’t be needed, but the city has yet to hear back from the Little Shell Tribe on whether a cultural resource inventory will be needed to make sure that none of the digging in Choteau’s alleys disrupts any Native American artifacts. RD is considering the Little Shell Tribe’s request for a cultural resource inventory to determine whether it will be needed.
The timeline for the first phase of the project, Anderson said, is to submit funding applications in September, to complete design work in October, to obtain DEQ approval in January 2021, to put the project out to bid in February 2021 and to start construction in the spring of 2021.
Answering questions about the PER, Anderson said the work includes 70 service lines to be reconnected to new or rehabilitated sewer mains, and agreed with Councilman Steve Howard that putting in all new pipe, while more expensive than CIP plastic lining, would give the city more flexibility to fix the system.
City Public Works Director Mike Maples said the first phase of this project would really reduce the big spikes in infiltration that affect the wastewater treatment plant each spring.
Anderson said she could not say for sure how much infiltration the project would reduce and said the city is unlikely to ever get rid of all infiltration.
Because of that, she said, the second phase of the project, to reclaim most of the old lagoon and create and EPA-compliant holding pond is necessary.
In other business at the meeting, the council:
•Closed the public hearing on the 2020-21 budget and adopted the final budget with only minor changes from the preliminary draft.
•Approved the 2020-21 fiscal year special assessments for the city at the same levels as last year.
•Approved the Choteau Tourism Business Improvement District’s 2020-21 business plan and reappointed Barb Bouma with the Stage Stop Inn and Maggie Carr with Dropstone Outfitting to the TBID board for three-year terms.
•Approved requesting the city’s share of special gas tax revenue to use for street maintenance.
•Heard public comment from Nate White on COVID-19 and the Common Core curriculum among other topics.
The meeting was held in person and online via Zoom. The council’s next meeting will be Sept. 15 at 6:30 p.m. at the Choteau Pavilion and via Zoom. Contact the city office for Zoom registration information before the meeting.