Opportunities and barriers
Our study showed that targeted street sweeping is a highly cost-efficient approach for removing P from streets, and presumably, from stormwater.
In all scenarios, sweeping costs less than $70/pound removed. In areas with little or no tree canopy cover, it’s about $190/pound.
Both figures are much less expensive than building structural best management practices (BMPs). For example, the Capital Region Watershed District in St. Paul, Minn., calculated that BMP O&M alone, not including design and construction, costs $400 to $1,100/pound.
Thus, where P removal is a primary concern — in areas such as in watersheds with TMDL-specified P limits — enhanced sweeping may be valuable. Sweeping is suited for built-up areas and is relatively adaptable; if a certain level of P removal doesn’t improve water quality, sweeping more often might accomplish the load reduction goal.
There are a couple of caveats about the tool:
- It only represents cities in northern temperate climates and thus reflects the species composition and tree productivity of that region.
- The study upon which it’s based used a regenerative air sweeper, which may remove vegetative debris more efficiently than other sweeper types.
- Many cities would have to buy new equipment to accomplish more and more efficient sweeping. This may be a constraint for smaller cities.
- Some cities lack disposal sites for sweepings.
- Residents may object to more frequent sweeping if there’s on-street parking. There may also be a perception of inequity; the most efficient streets to sweep are those with the most trees, which tend to be in wealthier neighborhoods. The apparent inequity can be offset by explaining that sweeping improves water quality in lakes that all residents use.
Even so, we suggest you take a new look at street sweeping, especially if your community is in a watershed with nutrient-impaired waters and relatively high tree canopy cover. Our free tool enables you to estimate load reductions and costs in a planning mode, before making a budget request.
Lawrence Baker (baker127@umn.edu) is research professor in the University of Minnesota’s Department of Bioproducts and Biosystems Engineering; Sarah Hobbie (shobbie@umn.edu) is a professor in the department; Paula Kalinosky (pkalinosky@eorinc.com) is water resources engineer for Emmons and Olivier Resources Inc.; and Randy Neprash (randy.neprash@stantec.com) is project manager, Stormwater Regulatory Specialist at Stantec.
Next page: Using the free spreadsheet
