Frost and Kennard Spent Lime Filter

An underground stormwater filter keeps phosphorus out of Wakefield Lake.

This innovative stormwater filter is located on a plot of city-owned land at the corner of Frost Avenue and Kennard Street in Maplewood, a few blocks upstream from Wakefield Lake. It is designed to capture and filter stormwater runoff from a large portion of the lake’s 944-acre subwatershed.

The filter intercepts water from the storm sewer and routes it into a 20- by 36-foot underground chamber. There, the water interacts with spent lime, a chalky clay-like material repurposed from municipal drinking water treatment. Phosphorus binds to calcium in the spent lime material, and water leaving the chamber is expected to contain significantly less phosphorus (we will measure reduction rates over the coming months).

Water quality sampling equipment is installed at three points to monitor phosphorus levels and other properties as water moves through the system on its way to Wakefield Lake.