This page provides a summary of methods that can be used to quantify pollutant reductions from street sweeping.
TP Credits for Street Sweeping
These methods are approved for calculating pollutant reductions for total phosphorus. Guidance for calculating pollutant reduction is contained in this manual.
- Dry mass measurement. This method involves weighing the total (wet) mass of street sweepings and collecting samples for calculating the dry mass as a percent of total (wet) mass. The dry mass represents total solids collected. To calculate total phosphorus, dry mass is multiplied by a conversion factor.
- Wet mass measurement. This method involves weighing the total (wet) mass of street sweepings and multiplying by conversion factors to calculate total solids or total phosphorus.
- Organic matter measurement. This method is applicable for calculating phosphorus reductions and is similar to the procedure for dry mass measurement.
- Modeling. WINSLAMM and P8 are acceptable models for calculating pollutant reductions from street sweeping.
- Empirical methods. Empirical methods may be based on factors such as miles swept, number of times swept in a year, and type of sweeper equipment. Some empirical methods are summarized in Survey of street sweeping crediting approaches. Empirical methods are acceptable but typically provide small reductions in pollutant loading.
Methods that are not approved but may be acceptable for calculating pollutant reductions from street sweeping
The following methods may be acceptable if appropriate protocol are followed. This manual does not provide guidance for applying these methods. Pollutant reductions calculated with these methods must be approved by the MPCA if used for permit compliance.
- Direct measurement of phosphorus. This method applies to phosphorus measurement and will typically involve sending samples to approved laboratories to determine phosphorus content of sweeping material.
- Volume. Calculating pollutant reduction based on volume of material collected requires establishing relationships between volume and dry mass. The methods and procedures for establishing these relationships must be fully documented for permit compliance.
- Modeling. Models other than WINSLAMM and P8 may be acceptable, but MPCA must be contacted if the model results are used for permit compliance.
- Empirical methods. Empirical methods other than those summarized in Survey of street sweeping crediting approaches may be acceptable. MPCA must be contacted for permit compliance.
TSS Credits for Street Sweeping
The Minnesota Pollution Control Agency (MPCA) has not developed total suspended solids (TSS) credits (stormwater credit) associated with street sweeping. On this page we discuss ways that a practitioner or permittee can calculate TSS credits for street sweeping.
Relationships have not been established between street sweeping and TSS. This is due to the large variability in the composition of street sweepings. For example, sweepings collected during summer may consist primarily of sediment, while sweepings collected during fall may consist largely of organic material which does not contribute to TSS. Thus, dry mass of street sweepings is not a consistently good indicator for TSS.
To determine TSS reductions associated with street sweeping, models or empirical methods may be used. Two widely used models for street sweeping are P8 and WINSLAMM. Guidance for using these models is provided at the following links.
Empirical methods are based on some characteristic of sweeping practices, such as frequency, miles swept, season, type of sweeper, or a combination of these. Several entities have developed empirical relationships for calculating credits for TSS reductions from street sweeping. The MPCA accepts the following methods. The credits can be found at the associated links.
The MPCA will accept credits developed using empirical methods if they have general application. Credits developed for a specific set of sweeping conditions at a local level may not be applicable. See this table for a list of some methods and this page for more information on other methods.
Credits may also be determined directly by measuring the mass of sediment in street sweepings. To do this, the water and organic content of sweepings must be determined. Standard operating procedures for determining phosphorus can be used. For example assume 100 pounds of sweepings were collected. Subsampling following standard procedures reveals the sweepings have a water content of 50 percent by weight, and the dry material has an organic matter content of 50 percent by weight. The solid content is thus 100 pounds X 0.50 X 0.50 = 25 pounds.