Quick Facts:

Spent lime is a byproduct from the drinking water treatment process. It has been shown to be safe for the environment and the project is approved by the Minnesota Pollution Control Agency (MPCA).  

Spent lime is commonly used as an agricultural additive.

A research project looking at alternative ways to improve the health of storm ponds and potentially larger waterbodies such as lakes.  

Funding:

Funding for this effort is provided by the University of Minnesota Water Resources Center, through the Clean Water Land and Legacy Amendment. The project is facilitated by Barr Engineering in partnership with VLAWMO.

Reason for project:

Stormwater ponds are a valuable tool for settling pollutants such as sediment before they get to a larger waterbody. However, they can face challenges, and require maintenance over time. When stormwater ponds have gathered sediment and nutrients from the surrounding landscape, they can leak these pollutants into downstream lakes, wetlands, or streams. Dredging is a common technique for improving pond performance and increasing storage capacity, but this can be very expensive.

The research team at Barr Engineering and the U of M will be looking for practical alternatives to pond dredging that also trap and bind phosphorus in place. Due to the large abundance of spent lime from drinking water treatment, new uses for it beyond agriculture would be an efficient and useful resource for the greater Twin Cities Metro and beyond.

Implementation:

Spent lime slurry was sprayed into a pond located near Ash Street in Lino Lakes (see map above). The pond was selected according to its size and depth, striving for a small pond for this stage in the research. Targeted doses took place between June and July, 2021. 

When applied, the spent lime sinks to the bottom and treats the sediment. Following the dosing, the research team collected water and sediment samples to analyze how phosphorus responds to the spent lime. The Cities of Maplewood and White Bear Lake are providing the spent lime for the project.

Results:

The research study helped inform possible new uses for spent lime for stormwater ponds and lakes across the State of Minnesota and beyond. 

Study summary: 2021

U of M Water Resources Center Spent Lime web page

Visit the MPCA website for more information on spent lime as a stormwater management tool. This site also contains information about other forms of lime, some of which are chemicals not approved for application or testing in ways that relate to this study, and thus were not used in any way in this study. 

View the research spotlight presentation below, recorded on November 17th, 2021 for the Minnesota Stormwater Seminar Series.

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