Members of the Lakeside Water and Sewer Board voted Aug. 21 to construct a sequence batch reactor in phase two of its wastewater facility treatment project.

The sequence batch reactor is one of three types of sewer treatment plants suggested by an engineering firm, RFA, during the board’s monthly meeting.  

“We need to go forward with something that's going to meet the needs of the district, that meets the needs of this community, with the goal in mind to protect Flathead Lake,” said RFA engineer Brad Koenig.  

In anticipation of population growth, the district is looking not only to replace its nearly 40-year-old wastewater system but also upgrade it to meet capacity needs. The new sewage treatment plant built in phase II of the project will include modern technology that separates nutrients from the water, a key factor in protecting the quality of Flathead Lake, Koenig said. 

Engineers used a 900,000 gallon-per-day estimate — in alignment with the district’s 20-year growth plan — to compare various sewage treatment plants. Estimates also accounted for 53,250 gallons of septage per day, received five days per week.  

This second estimate came from Flathead County, Koenig said, since the Lakeside district entered an interlocal agreement with the county to treat its septic in exchange for federal American Rescue Plan Act funds. 

Based off these numbers, board members were offered three sewage treatment plants to choose from: an oxidation ditch, a sequence batch reactor and a membrane bioreactor. 

All three facilities include a 100,000-gallon septage equalization basin, which allows for consistent dosing of septage into the facility, according to engineers.  

Board members chose the sequence batch reactor with a unanimous vote. This sewage plant has a compact footprint with three 67’ by 67’ basins and is currently used in Whitefish. Plant operations for this facility can easily be adjusted for varying flow and load conditions. 

The capital construction cost for the sequence batch reactor is $18.7 million, a lower price tag than the other two plants. Operational and maintenance costs are estimated to be $314,700, which is cheaper than the membrane bioreactor ($456,300), but more expensive than the oxidation ditch ($288,100). 

Board members voted to construct the plant based on a design flow of 600,000 gallons per day, which was recommended by RFA engineers, with total construction costs at $24.8 million. 

Phase I of the sewer expansion project is expected to be completed by summer of 2026, according to Lakeside Water and Sewer District General Manager Rodney Olsen. Now that a treatment plant has been chosen, engineers, along with the district board and Olsen, will begin designs for the new treatment plant. 

Olsen said the Montana Department of Environmental Quality needs to grant approval of the plant. Engineers will work with department officials on design plans to make sure it meets state standards. 

BEFORE THE vote, board members took public comment on the new sewer treatment plant. Craig Spencer, who spent more than 30 years researching freshwater ecology in the Flathead Basin, said the design of the proposed treatment facilities appears to result in cleaner effluent than the current facility.  

Out of the three options, he believed the membrane bioreactor would result in the greatest reduction of nutrients.  

“However, as I understand the DEQ [groundwater discharge] permit, additional nutrient reductions will be required following groundwater injection in order to meet the permit,” Spencer said, referring to the permit obtained by the district during the first phase of the project. “From my experience, I think this carries some risk.” 

He recalled his experience working on a project in Michigan to test whether an experimental system of ponds and wetlands would effectively reduce phosphorous in wastewater effluent.  

“We saw some phosphorus reduction initially, but after several years, the phosphorus reduction stopped, and the phosphorus just flowed straight through,” Spencer said. “I think similar outcome could happen here, resulting in no long-term phosphorus removal following injection.” 

He suggested the board consider technologies that achieve nutrient reduction without wastewater injection and to find a different effluent discharge location, such as below Curry Dam or outside the Flathead Basin.  

“I think there's risk that the proposed groundwater injection will not achieve the desired results, and I think the risk of failure will increase rapidly as the plant ramps up to treating 900,000 gallons per day along the way,” Spencer said. “We're gambling with water quality and flooded lakes.” 

Reporter Hannah Shields can be reached at 758-4439 or [email protected].