The rain was heavy, the flooding serious, and the damage to wastewater ponds was the first of its kind in Minnesota.
The city of Willow River, with MPCA assistance, is working to repair its wastewater ponds damaged by flooding in mid-July. 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.
Willow River, a city of 400 people in Pine County in northeastern Minnesota, received 10 inches of rain in less than 48 hours July 11-12, flooding the town and breaching the DNR dam on the river.
“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,” said Wendy Turri, MPCA municipal wastewater section manager.
City and MPCA inspectors found a tear near the top of the primary pond liner. Earthen dikes surrounding both ponds were also 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.