Accounting for phosphorus load reductions with street sweeping
Many stormwater models do not directly calculate reductions in phosphorus loading associated with street sweeping. P8 and Winslamm are exceptions, though P8 bases reductions on TSS reductions, which likely underestimates reductions because most of the phosphorus loading is likely associated with organic debris. When reporting on phosphorus reductions, stormwater practitioners and permittees need to translate collection of street sweeping debris with a reduction in phosphorus loading.
This page provides some methods for accounting for phosphorus reductions associated with street sweeping.
Mass reduced
The simplest method for tracking reductions associated with sweeping is to estimate or measure the mass of phosphorus reduced. If tracking on a per acre basis is needed, the mass reduced must be determined per unit land area (e.g. per acre).
For example, using the MPCA Street Sweeping tool, assume the following data is collected. The resulting load reduction is 0.64 pounds of phosphorus, or 0.128 lb/ac/yr.
| Area swept (acres) | 5 |
| Dry mass collected (non-fall) | 500 |
| P reduction (non-fall) | 0.21 |
| Dry mass collected (fall) | 500 |
| P reduction (fall) | 0.43 |
| Total P reduced (lbs) | 0.64 |
| Loading rate reduction (lb/ac/yr) | 0.128 |