What is Municipal Separate Storm Sewer System (MS4)?

Polluted stormwater runoff is commonly transported through Municipal Separate Storm Sewer Systems (MS4s), from which it is often discharged untreated into local water bodies. To prevent harmful pollutants from being washed or dumped into an MS4, operators must obtain a National Pollutant Discharge Elimination System (NPDES) permit and develop a stormwater management program.

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1. What is Stormwater Runoff?
2. Why is does it matter?
3. What is Municipal Separate Storm Sewer System (MS4)?