Quality of many urban water bodies is impaired because of phosphorus (P) loading from stormwater runoff. Trees near impervious surfaces contribute significantly to this P loading. Mounting evidence indicates that street sweeping, by removing nutrient-rich litterfall from streets, can effectively reduce inputs of pollutants to stormwater and reduce maintenance of downstream BMPs. Yet, street sweeping remains an underdeveloped BMP for P source reduction, as currently there is no easily implementable method for crediting sweeping practices that is approved by the Minnesota Pollution Control Agency (MPCA). Thus, water quality credits for street sweeping practices are typically not applied to permit conditions such as Total Maximum Daily Loads (TMDL) Waste Load Allocations in Minnesota.
Through a new U of M-MPCA-city partnership, we aim to use to improve empirical models to enable the MPCA to develop and disseminate a stormwater P crediting program for street sweeping. In partnership with three cities (Minneapolis, Roseville, Shoreview), we will develop new empirical relationships among sweeper volume, wet mass of solids, dry mass of solids, and P loads removed by different street sweeper types throughout the snow-free season (spring, summer, fall), across the range of tree canopy covers and species composition typical of Minnesota’s cities.
We will use these relationships to develop methods to calculate P load reductions from street sweeping and guidance for applying calculated load reductions as credit toward achieving water quality goals. Methods will be integrated into existing calculators and the Minnesota Stormwater Manual, and disseminated in webinars, workshops, presentations, meetings, and written material.