Stormwater basin treatment to reduce algae

A project funded with a Yahara WINS grant tested out a method for mitigating phosphorus in urban stormwater retention basins. Many practices in Yahara WINS are focused on preventing phosphorus from entering water bodies, but once phosphorus has already made it into a waterway, it can keep fueling algae growth unless removed or transformed. In this project, a team of water management experts treated a stormwater retention pond at the Verona Technology Park to remove dissolved phosphorus from the water, spurred by a desire of nearby businesses to make the water body more usable and pleasant to be around.

The team added aluminum chlorohydrate, a chemical that binds with phosphorus so it settles out of the water column and can no longer feed algae overgrowth. The treatment reduced an estimated 287 pounds of phosphorus from the pond, and higher water clarity was observed after the treatment. This project occurred outside the Yahara Watershed, but Yahara WINS saw value in funding the project as an opportunity to demonstrate how this treatment could work in the watershed.

Alum treatment helped to significantly clear the water in this pond
Alum treatment of this stormwater basin reduced an estimated 287 pounds of phosphorus and improved the water clarity.