Iron Enhanced Sand Filter

Sand and steel keep phosphorous out of Kohlman Lake.

When we began looking for ways to improve the water quality of Kohlman Lake in 2007, it was a challenging task. Traditional projects weren’t able to remove dissolved phosphorus from the stormwater that was polluting the lake. One new and promising management practice was the iron enhanced sand filter.

Sand filters have been used for years to remove solids and some pollutants from stormwater, but it was found that adding steel fibers to the sand removed dissolved phosphorus efficiently and cost-effectively. We had the opportunity to install this filter during construction of the new Country View Lane in Maplewood.

Research through the University of Minnesota and District monitoring indicate this practice is effectively removing about 90 percent of dissolved phosphorus in the tributary stormwater and could last up to 30 years before needing reconstruction. We continue to monitor the iron enhanced sand filter to determine its effectiveness over time.