The earthquake that woke Missoula residents in the early hours of 2016 and again in the evening of 2020 opened new springs in the South Hills, which are now seeping into city streets and causing a variety of problems.
But members of the Missoula City Council this week approved a nearly $400,000 service agreement with WGM Group to capture the water and convert it to the city's stormwater system.
The project is one of three stormwater schemes for the South Hills to deal with runoff and changing conditions resulting from growth and development – and sedimentation and earthquakes.
"There was an earthquake a few years ago, and there were several springs on private property. Those springs have caused a lot of issues," said Adam Marsh utility engineer with the city. "Springs constantly flow into public paths. During the winter months, they freeze, causing public safety problems and roadway damage."
To deal with the springs, Marsh said the city would expand its stormwater system and install additional storm inlets to collect the water. This should keep it off the road and divert it to the natural contours of the South Hills drainage system.
Based in the South Hills, the city also plans to improve retention and biodiversity at Cattell Corner, a 3-acre wetland near Russell and 39th Streets. The property is part of the city's park system and is home to red-winged blackbirds, waterfowl and raccoons.
But it also plays a role in the stormwater system for the South Hills, capturing and storing runoff from the sloping terrain. Marsh said the pond is not functioning properly and efforts will be made to improve it this summer.
"The biology of the wetland isn't particularly good right now. It's a mono-culture of cattail and it's not a very good habitat," Marsh said. “It has also experienced well sedimentation over the past 20 years. The pond basically lacks much of the holding capacity.”
Marsh said the city plans to install new dry wells around the perimeter of the pond to offset flow from the South Hills, particularly near 55th Street. The work will also remove some of the sediment and cattail from the pond to diversify the habitat and increase retention.
The city-sanctioned major stormwater project also includes work on 55th Street, which also has runoff issues.
"They are all interrelated," Marsh said of the challenges. "The goal is to design and build them in 2022."
Funding will come primarily from American Rescue Plan, with a 10% match thought to come from the city's Stormwater Enterprise Fund. For now, at least, it will eliminate the need to create a special corrections district to cover the cost, Marsh said.