This image shows a person document findings while inspecting an outfall
Person document findings while inspecting an outfall


It is generally easier and less expensive to prevent pollution at the source than restore surface waters once they're polluted. Permitted municipal separate storm sewer system (MS4) communities are the first line of defense for many pollutants entering storm sewer systems within their jurisdiction, such as

  • sand and salt for de-icing
  • fertilizers and pesticides on municipal properties
  • vehicle fueling and maintenance chemicals

MS4 General Permit requirements for MCM 6

Minimum Control Measure (MCM) 6 in the MS4 General Permit requires permittees to maintain a operations and maintenance program to prevent or reduce pollutant discharges from municipally owned or operated properties. The program must include:

  1. A Facility Inventory that documents municipally owned/operated facilities that may pollute stormwater.
  2. Best management practices (BMPs) to prevent or reduce the stormwater impacts from the facilities documented on the Facility Inventory.
  3. BMPs to protect Source Water Protection Areas, such as Drinking Water Supply Management Areas and source water protection areas for surface intakes.
  4. Stormwater pond assessment procedures and schedule to evaluate the effectiveness of total suspended solids (TSS) and total phosphorus (TP) removal of municipally owned/operated ponds.
  5. Municipal operation inspections which is inspections of structural stormwater BMPs annually, at least one inspection of ponds and outfalls during the permit term, and quarterly inspections of stockpiles and storage and material handling areas documented in the Facility Inventory.
  6. Maintenance of structural BMPs, outfalls, and ponds based on the results of the Municipal operation inspections.
  7. Employee training as appropriate for the employee's position. Training should address the importance of protecting water quality and describe relevant MS4 General Permit requirements. The training should have a schedule that establishes initial training for new and seasonal employees and recurring training for existing employees.
  8. Documentation detailed here.


Click on the blue links above in the "MS4 General Permit requirements" section to get more information and resources specific to those permit requirements. In addition, all resources related to MCM 6 are below.

Fact sheets and guidance

Training tools

Documentation and tracking templates


Example procedures