A Measurement Based Approach to Crediting Street Sweeping

Recent research indicates that targeted street sweeping in urban areas that experience annual leaf drop can be a cost-effective method for reducing phosphorus loads to receiving waters (Bratt et al., 2017; Hixon and Dymond, 2018; Selbig, 2016). Targeted sweeping focuses on one or more of the following practices:

  • Increasing sweeping frequency during fall leaf drop and during flower, seed, and fruit drop in spring.
  • Timing sweeping with predicted rainfall and runoff events.
  • Targeting areas with greater inputs of organic debris during fall leaf drop (i.e., greater tree canopy cover).
  • Using appropriate configurations of sweepers, such as broom sweeping followed by vacuum sweeping.
  • Implementing ordinances that improve sweeping efficiency, such as parking restrictions and raking leaves from boulevards into streets, just prior to sweeping.
  • Targeting sweeping in watersheds having impaired or vulnerable receiving waters.

In an attempt to encourage targeted sweeping, Minnesota developed a phosphorus credit based on direct measurement of material collected. Working with University of Minnesota researchers, the credit is based on relationships between dry or wet mass collected and resulting phosphorus reductions (Hobbie et al., 2020). Stormwater practitioners, including permittees with Total Maximum Daily Load (TMDL) requirements, may apply these phosphorus reductions toward water quality goals and requirements. To further encourage application of the credit, we built a simple phosphorus reduction calculator along with supporting material (Minnesota Stormwater Manual, accessed September 27, 2022).

The next phase of this work involves training and outreach. The University of Minnesota hosted an initial Clean Sweep Training for sweeping practitioners in September, 2022. There will be additional training in spring of 2023. These informational programs incorporate lessons learned from the latest research, including how targeted street cleaning may influence the performance of downstream stormwater control practices such as wet ponds.

In addition to the Minnesota effort, an expert panel recently completed a memo recommending New Hampshire adopt a direct measurement approach to crediting phosphorus (and nitrogen) associated with street sweeping. Both Minnesota and the New Hampshire recommendations allow for crediting using models, but credits for modeled approaches are currently much lower than direct measurement approaches. We anticipate that eventually models will be enhanced with recent research results and our credit will include volume-based measurements, thus providing stormwater practitioners an even wider range of methods that encourage targeted street sweeping in urban areas.

References

Bratt, A. R., J. C. Finlay, S. E. Hobbie, B. D. Janke, A. C. Worm, and K. L. Kemmitt. 2017. Contributions of leaf litter to nutrient export during winter months in an urban residential watershed. Environmental Science & Technology 51:3138‐3147.

Hixon, L. F., and R. L. Dymond. 2018. State the practice: assessing water quality benefits from street sweeping. Journal of Sustainable Water in the Built Environment 4(3):04018007.

Hobbie, S. E., R. A. King, T. Belo, L. A. Baker, and J. C. Finlay. 2020. Developing a Street Sweeping Credit for Stormwater Phosphorus Source Reduction ‐ Final Report. Minnesota Stormwater Research Council Project. University of Minnesota, St. Paul, Minnesota., St. Paul, Minnesota.

Houle, J., E. Buschert, A. Lyon, D. Leonard, and L. Jalbert. 2022. Clean Sweep: Recommendations for New and Updated Credits for Street Cleaning in New Hampshire.

Selbig, W. R. 2016. Evaluation of leaf removal as a means to reduce nutrient concentrations and loads in urban stormwater. Science of The Total Environment 571:124‐133.