Stormwater project protects Lake Bemidji, Mississippi River
Beltrami SWCD’s Clean Water Fund-backed project in Bemidji targets nutrient-impaired Lake Irving, but its benefits extend to Lake Bemidji and beyond. The work will safeguard a source of Twin Cities drinking water, contain the flow in case of an oil spill, beautify a bike trail and increase pollinator habitat.
BEMIDJI ꟷ What’s good for Lake Irving is good for Lake Bemidji, the Mississippi River and the downstream communities that rely on the river as a source of drinking water.
Beltrami Soil & Water Conservation District’s (SWCD) stormwater treatment project under construction this fall is designed to improve the water quality of nutrient-impaired Lake Irving. The Mississippi River, which flows through both lakes, supplies St. Cloud and parts of the Twin Cities with drinking water.
“We’re cleaning up water that goes into the Mississippi River,” said Beltrami SWCD Board Supervisor Sam Christenson. “The impacts can go way downstream.”
The $490,000 project ꟷ a stormwater treatment wetland, iron enhanced sand filter and re-meandered stretch of ditch that collects city stormwater runoff from an 886-acre drainage area including a Bemidji industrial park ꟷ taps a $156,000 Clean Water Fund grant from the Minnesota Board of Water and Soil Resources (BWSR).
“What we’re trying to do here is reduce as much of the negative impact from human use around the lake as possible,” said Zach Gutknecht, Beltrami SWCD clean water specialist. He said water-quality issues arise in lakes with a 50:1 watershed-to-lake surface area ratio. The higher the ratio, the more potential for pollution. “Lake Irving has a 500:1 ratio.”
Project partners include the city of Bemidji, the Mississippi Headwaters Board (MHB) and Enbridge.
At the city’s request, the SWCD expanded the project to re-meander an 800-foot-long stretch of ditch and plant native grasses, forbs and shrubs throughout the site. Those plants will not only improve aesthetics along the Paul Bunyan State Trail but also add pollinator habitat.
Bemidji will draw $300,000 from its stormwater utility fund to cover most of the remaining cost. The city will own the treatment system and maintain the iron enhanced sand filter.
“Bemidji is the first city on the Mississippi, so stormwater treatment is very important,” said Craig Gray, city engineer and public works director. “Our city is on Lake Bemidji and Lake Irving and the Mississippi River. Without those three bodies of water, we really don’t have a city. The water quality of those bodies of water is very, very important to us, so we really try to do whatever we can to reduce any nutrient loading going into those lakes and the river.”
Street sweeping and existing stormwater ponds weren’t enough to cut phosphorus loading to Lake Irving by 268 pounds a year ꟷ the 36% reduction the Minnesota Pollution Control Agency (MPCA) determined necessary to meet water-quality standards.
This project will keep an estimated 233 pounds of phosphorus ꟷ 87% of the reduction goal ꟷ out of Lake Irving each year. Phosphorus feeds the algae that can turn lakes green.
Lake Irving ranked in the Top 5 for phosphorus removal in a Mississippi Headwaters Board study that identified more than 150 potential pollution-reduction projects for 12 cities on the first 400 miles of the Mississippi River. An $81,000 Clean Water Fund grant from BWSR backed the study, which gave cities stormwater planning options that prioritized, targeted and calculated the effectiveness of best management practices.
“When we protect cities and we work on projects like Lake Irving, we’re doing a service not just to the people that live there but everyone downstream,” said Tim Terrill, MHB executive director.
“The Mississippi is used for drinking water in the Twin Cities,” Terrill said, and improving water quality upstream is more cost-effective than treating it downstream. “The Mississippi isn’t just a river that has a recreational value. It has a very important drinking water component to it.”
The MHB developed a public-private partnership with Enbridge, which contributed $50,000 to the Lake Irving project. An Enbridge oil pipeline runs south of the site, which incorporates an outlet structure that can be closed in the event of an oil spill.
Work began in early September.
Shawn Tracy, a lead scientist with HR Green, worked with Bemidji on its stormwater retrofit analysis that led to a Lake Irving feasibility study. He was in Bemidji in early September to monitor construction.
By then, contractors had hauled in topsoil to boost the success of native seeds sown at the sandy site. A skimmer mechanism at the temporary outlet cleaned water before it discharged to the lake. Along with additional de-watering, the skimmer safeguards groundwater that intersects with the ditch. During construction, the ditch was closed off via the outlet structure that Enbridge would close in case of an oil spill.
Tracy described how the Lake Irving project will work:
Water from the re-meandered ditch will enter the stormwater wetland. There, sediment-bound phosphorus will settle out. Dissolved phosphorus will be stripped from runoff as it flows through the iron enhanced sand filter to Lake Irving.
Construction was expected to finish by the first week of November.
“Lake Irving’s impaired. Lake Bemidji is close, and we know Lake Irving has been saving Lake Bemidji since we’ve been here, since the city’s been here. Anything we can do to reduce the impacts either to Irving or Lake Bemidji is going to prolong that,” Gutknecht said.