MS4 modeling guidance

Download the modeling guidance developed for municipalities permitted under the Municipal Separate Storm Sewer System (MS4) WPDES program. The guidance discusses minimum pollutant loading analyses for total suspended solids and phosphorus, including percent TSS reductions to be assessed and areas required to be included in the calculations. The guidance on grass swales provides additional information on how to model the water quality benefits of this practice to establish water quality credits. The MS4 TMDL Implementation Guidance provides direction to MS4 permittees and their consultants on how Total Maximum Daily Load (TMDL) waste load allocations will be implemented within MS4 permits. This guidance also discusses how an MS4 permittee will be expected to model its MS4 service area and storm water management measures to show compliance with TMDL requirements.

MS4 municipalities must, to the maximum extent practicable, implement a reduction in total suspended solids in runoff that enters waters of the state as compared to no controls. See the Errata notes at the end of the table for updates to the standards.