August 23rd, 2023 was the first day for crews to be on-site for a spent lime application. Three loads have been delivered as of September 5th. The project is now on a break as the City of WBL Water Treatment Plant is serviced. The project will resume when the facility is back online.
Related to this project, trucks may be parked on Oak Knoll Drive, Birch Street, or White Bear Avenue to access the pond.
Funding for this effort is provided by VLAWMO and the City of White Bear Lake.
Stormwater ponds are a valuable tool for collecting pollutants, such as phosphorus and sediment, before these pollutants flow into a larger waterbody. Stormwater ponds require maintenance over time to remove pollutants that have accumulated and keep the ponds functioning. Dredging is a common technique for improving pond performance, removing pollutants, and increasing storage capacity. Dredging, transporting, and disposing of the sediment can be costly and disrupts the environment.
The research team at Barr Engineering has been looking at practical alternatives to pond dredging, such as the application of spent lime. Spent lime is available as a byproduct of drinking water treatment. Lime is applied to drinking water to soften the water by removing calcium and magnesium ions. The resulting spent lime still has the capacity to bind to phosphorus. Excess phosphorus in waterbodies stimulates algae blooms and reduces water quality. As a readily available material, Barr Engineering, wondered if spent lime could be used to improve water quality in our ponds, streams, and lakes. Specifically, spent lime would be used to bind phosphorus and keep it in the sediment of a waterbody, where it can’t stimulate algae growth. Barr worked with VLAWMO and Ramsey Washington Metro Watershed District to conduct small pond experiments by treating them with spent lime as part of a research study funded by the University of Minnesota during 2021. Those experiments showed promise. The next step is to test spent lime in larger waterbodies to see if similar positive results can be produces and assess how long they will last.
The overarching goal of the demonstration project in Oak Knoll Pond/Wood Lake is to address the effectiveness of spent lime in a larger waterbody and determine the longevity of the treatment.
Spent lime slurry will be sprayed into the pond during the summer and fall of 2023. Oak Knoll Pond/Wood Lake was selected for the study because of its size, depth, and location. Lab analyses were conducted to determine the buffering capacity of the pond/lake because pH is a sensitive issue when applying spent lime. Buffering capacity means that the pond water and sediment tends to resist changes in pH because of the chemical compositions and interactions. A high buffering capacity means a tendency to resist changes in pH. This work expands upon a 2021 study conducted in Ash Street Pond in Lino Lakes and a separate small pond in Ramsey Washington Metro Watershed District.
Spent lime is sprayed into a waterbody with a hose and quickly sinks to the bottom to treat the sediment. Achieving even coverage of the sediment is important, with a focus on deeper water areas where oxygen is reduced at key times during the year (often late summer and during the winter). During and following the application, monitoring is conducted for possible changes in pH and to analyze how phosphorus levels respond to the spent lime.
The City of White Bear Lake is providing the spent lime for the project.
Find results from the small pond experimental work, including a presentation at the Minnesota Stormwater Seminar Series, at:
Visit the MPCA website for more information on spent lime as a stormwater management tool.
For questions, contact firstname.lastname@example.org