Iron-Enhanced Sand Filter

• Stormwater filter

• Birch Lake
• Wetlands

Iron-enhanced sand filters are designed to improve water quality by filtering water runoff to remove pollution. Water runoff will collect and soak into the filter basin, which contains sand and iron filings. The iron then binds with the pollutant phosphorus and removes it from water runoff before it enters Birch Lake.

This 1,037 square foot iron-enhanced sand filter captures water runoff from over 52.26 acres of hard surfaces of a largely residential area including streets, roofs, driveways, and sidewalks.

The filter has some of the following features:

• Riprap to slow runoff and settle sediment before it enters the filter
• Weir to hold back and slow runoff before it enters the filter
• 73.5 tons of filtration media consisting of sand and iron filings
• Drain tile to help the filter to dry out between storms 
• New overflow outlet structure to allow water to exit the filter during high volume storms and prevent flooding

This project was a partnership between the City of White Bear Lake, the Birch Lake Improvement District (BLID), Ramsey County, and VLAWMO. The City and County provided funding through local cash match and VLAWMO provided funding through the MN Board of Water and Soil Resources Clean Water Fund grant program. The City, BLID, Ramsey County, and VLAWMO also partner on the maintenance for the iron-enhanced filter.

Data collection and a follow-up study found that an existing wetland at the intersection of 4th Street and Otter Lake Road was a hotspot for collecting excess nutrients, sediment, and other stormwater contaminants due to historical agricultural ditching of wetlands and increased stormwater runoff. The wetland was getting overloaded and releasing these pollutants into Birch Lake during large storms, contributing to algae blooms.

The completed study found that an iron-enhanced sand filter was the most cost effective and space efficient project to treat the runoff before it could enter the wetland and Birch Lake.

The iron-enhanced sand filter is estimated to annually capture 1,419,083 gallons of water runoff, which is equivalent to 4.36 football fields covered with 1 foot of water. The filter also annual removes 8.1 pounds of total phosphorus. Just one pound of phosphorus can create up to 500 pounds of algae. 

Since the iron-enhanced sand filter project, restoration work has been completed of the 1.34-acre woodland area adjacent to the project site and wetland that has enhanced the native plant community, providing habitat and promoting long-term function of the project filter. This restoration has been a partnership between VLAWMO and the City of White Bear Lake. Funding for this restoration was supported by a Conservation Partners Legacy (CPL) grant from the Minnesota DNR  for restoration/reseeding and enhancement of the ongoing restoration.