City of Madison

City of Madison Engineering | Photo Credit: Archie Nicolette

Stormwater Alum Demonstration Project

The City of Madison Engineering Division is starting a demonstration project to test the effectiveness of Aluminum Sulfate, commonly called alum for urban stormwater treatment. Surrounding municipalities, including the City of Madison, have requirements from the EPA to meet the Rock River TMDL for Total Suspended Solids (TSS) and Phosphorus (P). The City is pursuing the use of alum treatment to evaluate its effectiveness as one potential measure to reduce nutrient concentrations and improve water quality for our lakes and river.

Alum has been used in the treatment of water and wastewater for over 100 years. In addition, Alum has been recognized since the 1970s for control of nutrients in many natural lakes, included several in Wisconsin. Alum treatment of urban stormwater has been an established stormwater quality retrofit option primarily in the southeast part of the country but more recently in the Midwest including projects in Minnesota and Indiana. The potential value of alum treatment for water quality improvements has been identified as one potential measure for control of phosphorus inputs to the Yahara Chain of Lakes in Dane County.

The location for this urban stormwater alum treatment project is Marion-Dunn Pond (aka Glenway Pond), a stormwater detention pond located on property owned by the UW Arboretum which receives runoff from the City of Madison's 230-acre watershed.  Runoff enters the detention pond through a large storm sewer structure located adjacent to Monroe street and discharges through two concrete pipe outlets which then discharge into watercourses that drain to Lake Wingra. Liquid alum will be pumped into the stormwater based on the measured inflow in order to generate the "floc" that binds and removes phosphorus and other nutrients from the water column. A pH control agent is likely to be required due to the low alkalinity of the incoming stormwater. The alum and pH control agent will be stored in tanks located within a temporary shelter. Measurements will be taken for the stormwater at both the inlet and outlet of the pond to monitor nutrient concentrations. Most pollutants including solids, bacteria and heavy metals will be retained within the pond so downstream concentrations, and hence discharge to Lake Wingra of these contaminants will likely decrease. The City of Madison plans to conduct the demonstration of alum treatment for a two year period to investigate the effectiveness of reducing nutrient loads.

For questions please contact Greg Fries, (608)267-1199.


Aerial photo of pond