Municipal Separate Storm Sewer Systems

In cities, small sewer systems (otherwise known as municipal separate storm sewer systems or MS4s) are regulated according to the Phase II Stormwater Rule per the EPA. This requires MS4s to reduce stormwater pollutants (read more about stormwater pollutants on our stormwater page) by creating a stormwater management program. Under these programs, municipalities tackle stormwater pollution by reducing the amount of impervious surface, investing in green infrastructure projects, and inspecting construction sites - all with the aim to improve the water quality in local streams and ponds. 

Discharges from MS4s in urbanized or additionally designated areas must be authorized in accordance with a permit for stormwater discharges from MS4s. You can read more about the MS4 permit below.