Willow Pond filtration system to clean up stormwater headed for Bennett Lake

We are currently working on the final design for a spent lime filter at Willow Pond designed to improve the water quality of nearby Bennett Lake.

The City of Roseville will conduct final review and assist with community outreach before the project is put out to bid. A community open house was held at the Roseville City Hall council chambers on June 27 to share information with the public, and the project was well-received by those in attendance.

Filtering stormwater with spent lime

Willow Pond is located off Hamline Ave. and County Road B2 West in Roseville, just west of Bennett Lake. We are proposing to install a low-flow outlet on the north side of the pond, which would route stormwater coming out of the pond into a spent lime filter to remove phosphorus before it flows downstream to Bennett Lake.

This filtration system will remove roughly 16 pounds of total phosphorus each year and is one of several proposed projects to help improve water quality of Bennett Lake, which is impaired for excess phosphorus.

The use of spent lime is a relatively new technology and is used in two systems near Wakefield Lake in Maplewood. Spent lime is a byproduct of municipal drinking water treatment, and it effectively removes phosphorus from stormwater. In this design, polluted stormwater would flow out of Willow Pond, enter the filtration system and interact with spent lime. Phosphorus binds to the spent lime, so the water leaving the chamber is expected to contain about 70 percent less phosphorus than when it entered.

Willow Pond project map
The Willow Pond spent lime filter will remove phosphorus from stormwater that flows east to Bennett Lake (see blue arrows). Locations of other property improvements are noted on the map, each designed to benefit water quality within the Bennett Lake subwatershed.

Next steps

Final plans are expected to be complete in July, and a contract awarded in early August. Construction of the filtration system will happen late summer or early fall 2018. As part of the construction, some invasive plants and scrub trees will be removed, and native trees and shrubs will be planted around the spent lime basin. When construction is complete, the system will be barely visible from the walking path along Willow Pond.

As part of this project, we will work with the City of Roseville on continued restoration along the publically owned portions of Willow Pond shoreline. Private homeowners with shoreline property are eligible for stewardship grants as well and should contact Paige Ahlborg at (651) 792-7964 or paige.ahlborg@rwmwd.org for more information.