July flooding caused damage to city of Willow River wastewater ponds, repairs to be made

Contact: Steve Mikkelson, 218-316-3887

Brainerd, Minn. — The mid-July heavy rains and flooding throughout Pine County, Minn., caused major damage to the city of Willow River’s wastewater treatment ponds. The city is working with its consultant and the Minnesota Pollution Control Agency to repair the ponds as quickly as possible. Ten inches of rain in less than 48 hours flooded the city and breached a Dept. of Natural Resources-operated dam along the Willow River. This rain event caused damage to both Willow River’s primary and secondary wastewater ponds, confirmed during subsequent MPCA staff inspections.

MPCA staff suspect flood waters caused a rapid rise in groundwater surrounding the secondary pond, and created a buoyancy force strong enough to push the pond liner up in large bubbles which tore the liner in several places. According to MPCA Municipal Wastewater Section Manager Wendy Turri, “this is something we’ve never seen before in Minnesota. The bubbles and tears in the pond liner allowed the wastewater to leak into the groundwater, which flows toward the Kettle River, but away from area drinking water wells.”

A tear was also found near the top of the primary pond liner, and earthen dikes surrounding both ponds were damaged and parts of the interior slopes slid into the ponds. The current water level in the primary pond seems to be holding where the tear was found. This indicates that as wastewater continues to enter the pond, it is leaking into the ground through the visible tear.

As a result, repairs will be made to the primary pond in the coming weeks, with help from State disaster relief funding. To do this, the wastewater in the primary pond will be discharged into the secondary pond so the primary pond can be repaired and operational before winter arrives. The secondary pond will be repaired next summer. Throughout the process, the city and its consultant will monitor ground and surface water to ensure that wastewater is not impacting nearby residential wells and other water bodies.

More information about minimizing flood-related pollution and health risks is available on the MPCA’s Minimizing pollution and health risks from flooding webpage.  The page includes assistance for managing household hazardous materials, preparing heating oil tanks for flooding, drinking water well contamination and what to do after a flood.