Information: We recently updated this page and will continue to work on information about MS4 stormwater management. If you have suggestions, we welcome comments using the comment box at the bottom of most pages in the manual.
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The municipal separate storm sewer systems (MS4s) stormwater program is designed to reduce the amount of sediment and pollution that enters surface and ground water from storm sewer systems. Public entities that own or operate an MS4 play a key role in preventing or reducing the negative impacts stormwater runoff has on our valuable water resources.

Proper stormwater runoff management in urbanized areas is especially important for restoring and protecting surface waters. Urbanized areas are more likely to have activities that contribute pollutants to stormwater runoff, like applying anti/deicing mixtures to roads; fueling vehicles; grease, oil, and other spills; landscaping; and using pesticides and fertilizers. Urbanized areas have a large amount of impervious surfaces, or surfaces that rain and snowmelt cannot pass through, such as streets, driveways, rooftops, parking lots and sidewalks. Stormwater runoff from these surfaces travels faster and in higher amounts, damaging rivers, streams, and wetlands; destroying aquatic habitats; increasing the amount of pollutants that enter surface waters; and limiting groundwater recharge.

MS4 stormwater program overview

MS4 stormwater permit

MS4 Permit Minimum Control Measure (MCM) overview and guidance

Guidance document to help local MS4 staff meet the requirements of the six MCMs in the MS4 General Permit and assist with overall stormwater management

Other technical assistance and guidance

Phase II MS4 audit process

Total Maximum Daily Loads (TMDLs)

Other links

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