It’s not often that wastewater treatment gets a lot of press attention, but in recent weeks this has been the case in the Flathead Valley. And for good reason, as stringent wastewater treatment is crucial to protect our community’s most valuable asset – the crystal-clear blue waters of Flathead Lake and its watershed.
Some of the headlines reported the opening of the new membrane bioreactor plant at the Flathead Lake Biological Station. Indeed, we were proud to bring this unit online, replacing our stalwart sequencing batch reactor unit that was installed in the mid 1970s. It was the first advanced wastewater treatment plant in the Flathead to include tertiary treatment to reduce phosphorus emissions to low levels. Phosphorus is the nutrient that at higher levels could turn Flathead Lake from clear blue to cloudy green from algae.
To the very end of its lifespan, our original plant could reduce phosphorus concentrations from 2 mg/L to about 0.2 mg/L, and in the 1980s it helped motivate the implementation of tertiary treatment throughout the watershed. Our new plant can do even better, reducing effluent phosphorus to concentrations as low as 0.01 mg/L, concentrations similar to those in the lake itself. Bringing our new plant online took years of planning, fundraising and engineering but we are proud to take responsibility for our own waste and to go above and beyond to assure that the lake is protected from nutrient pollution.
Also, in the headlines these days have been the hearings and recent approval of an expansion and upgrade of the wastewater treatment plant near Lakeside. While the Bio Station has not been involved in this process, we did try to learn about the plans and to share information with the community about different aspects of wastewater treatment.
Expanded capacity at Lakeside is certainly needed in light of increasing population and the decision to accept regional septage. We also note that the proposed new sequencing batch reactor plant is designed to perform better than the existing plant. According to information from Lakeside County Water and Sewer District, phosphorus concentrations in effluent are targeted to be four times lower than currently achieved (5.4 mg/L vs 1.2 mg/L). Since flows are projected to increase two- or three-fold in the approved plan, the four-fold improvement in phosphorus removal at the facility, if achieved, may be able to keep phosphorus inputs to the lake in check, but important concerns remain.
These issues surround the planned discharge of treated effluent into groundwater through the use of rapid infiltration basins in order to keep up with the increased volume of treated water.
Reasonable concerns about the potential for subsurface phosphorus movement to the lake have been raised by a number of experts and other community members, highlighting uncertainties about groundwater flow rates and pathways, as well as the possibility of rapid saturation of the phosphorus binding capacity of soils and sediments in that part of the valley.
These worries are especially relevant if indeed the upgraded plant only reduces phosphorus concentrations to roughly 1.2 mg/L. We note that, in our communications with Lakeside County Water and Sewer and indeed in the public hearings, the district indicated that the current plan includes capacity for tertiary treatment of effluent through the use of alum, a chemical process commonly used to remove phosphorus to low levels. However, it is not clear from available information if and how tertiary treatment to remove phosphorus will actually be engineered into the planned upgrade.
In light of these important concerns about the suitability of the effluent disposal site and uncertainty about whether alum will be used to increase phosphorus removal, we call on the district to use all available technologies to remove nutrients to the lowest possible levels before discharging effluent in order to protect our world-renowned clean waters.
If possible, within financial and operational limits, we also suggest reconsidering the decision to choose a sequencing batch reactor over a membrane bioreactor plant, as a membrane bioreactor plant is a more modern technology that, as we have seen at the Bio Station, is markedly more effective in removing phosphorus.
In sum, we encourage the district to develop, implement and communicate with the public, explicit construction and operational plans for tertiary treatment of effluent (preferably via membrane bioreactor plant, but minimally via sequencing batch reactor using alum or similar), especially the effluent entering rapid infiltration basins.
Doing so will greatly decrease the risk to water quality in Flathead Lake, build goodwill and assure our community that those who have responsibility for protecting our most precious resource are indeed doing all they can to keep Flathead Lake blue.
Jim Elser is director, and Tom Bansak is associate director of Flathead Lake Biological Station.