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Reporting phosphorus and TSS reduction credits from street sweeping
Research conducted by Bill Selbig (USGS) shows that streets, when cleaned of leaf litter prior to a storm, can significantly decrease phosphorus loads in stormwater runoff (Link to study)
At this time, the MPCA has not developed guidance for how to credit reductions in phosphorus or total suspended solid loading associated with enhanced street sweeping. We anticipate developing this guidance in 2022. In developing this guidance, consider the following.
- Baseline: Credits toward permit compliance, such as compliance with total maximum daily loads, can only be applied toward enhanced street sweeping. This is sweeping that results in pollutant reductions above pollutant reductions associated with sweeping that occurred at the baseline year.
- Accounting for seasonality: The image on the right illustrates the seasonal nature of phosphorus loading in areas where leaves and other organic sources are a source of phosphorus. Most models and other methods of estimating annual loads do not consider this seasonality and most likely significantly underestimates annual phosphorus loading. Accurate representation of impacts from enhanced street sweeping will require adjusting initial (baseline) calculations of loading. The MPCA is discussing appropriate methods for accounting for this seasonality.
- Downstream BMPs: Enhanced street sweeping potentially impacts loading to and performance of downstream BMPs. The MPCA is discussing if adjustments in downstream loading and/or adjustments in BMP performance are needed to accurately determine changes in phosphorus loading in areas where enhanced street sweeping is implemented.