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.