Shingle Creek, like all streams in Minneapolis and the Upper Mississippi River, is designated as an Impaired Water for periodically exceeding the state water quality standard for bacteria. In agricultural areas, bacteria sources may be readily apparent – concentrations of livestock or other animals, application of manure to fields or septic systems – but in urban areas bacteria sources are scattered and options for reducing loads are limited.
In lab experiments, researchers from the University of Minnesota’s St. Anthony Falls Lab and Stanford University successfully removed phosphorus and bacteria from water by using an iron-enhanced sand filter and a specially engineered type of charcoal called biochar. Now the Shingle Creek and West Mississippi Watershed Management Commissions and the Minneapolis Park and Recreation Board are using an Environmental Protection Agency grant from the Minnesota Pollution Control Agency to test these promising methods in real-world conditions.
Webber Park BioBox
Here’s how the project works: A steel box, called the BioBox, sits on the viewing platform at Shingle Creek Falls. Water is redirected from the top of Shingle Creek Falls into a pipe leading to the BioBox. Inside the BioBox, water percolates through a biochar filter to remove bacteria and an iron-enhanced sand filter to remove phosphorus. After traveling through the filters inside the Biobox, water flows back into Shingle Creek. Water is tested before and after the BioBox to measure the filters’ effectiveness.
Testing will continue through October 2018. Researchers are studying whether this type of direct treatment can be scaled up to make a significant impact on bacteria concentrations in the Shingle Creek and other urban waterways.
Webber Park was chosen for this experiment because it is the only place on Shingle Creek where gravity can be used to move water through the BioBox. At other sites along the creek, electric pumps would be needed to operate the BioBox, which would make the project more expensive and more complicated.
Minnesota Filters and Catch Basin Inserts
There are two other ways this project tests the new technology. Three existing stormwater treatment ponds across the Shingle Creek Watershed are being retrofitted with enhanced ‘Minnesota Filter’ benches that surround the pond, including one at Creekview Park in North Minneapolis. When pond elevation rises, water percolates through the Minnesota Filter benches, which are designed to absorb dissolved phosphorus and reduce bacteria using the same iron- and biochar-enhanced filters used in the BioBox.
The second application modifies standard catch basin sediment-control inserts to incorporate an iron- and biochar-enhanced sand filter. The top layer of the insert catches sediment, debris and organic material. This layer can be easily lifted out and cleaned off. The bottom layer contains the enhanced sand filter, which will filter out smaller particles, dissolved phosphorus, and bacteria.
Data collected from these experiments will be used to create and improve designs for stormwater best management practices (BMPs) for watersheds that have bacteria impairments. Eventually, new BMPs installed throughout Shingle Creek Watershed aim to lower bacteria levels in the creek and improve water quality so that it’s fishable and swimmable.
Check out the Shingle Creek Watershed District website, shinglecreek.org/studies.html to learn more about these exciting new water quality experiments.