Stormwater runoff occurs when rain or snowmelt flows over developed surfaces such as streets, sidewalks, driveways, rooftops, lawns, and construction sites. Because these impervious surfaces prevent water from soaking into the ground, runoff collects pollutants and carries them untreated into nearby streams, rivers, lakes, wetlands, and other waterbodies.
Stormwater runoff can degrade water quality by increasing stream flows, altering natural drainage patterns, damaging aquatic habitat, and raising pollutant levels. These impacts affect the waterbodies our community relies on for recreation, wildlife habitat, and drinking water.
The purpose of the City of Mandan Storm Water Program is to educate residents, property owners, businesses, and developers about how stormwater systems work, how runoff affects water quality, and how pollution can be reduced to protect local waterways.
What Is Stormwater Runoff?
Stormwater runoff is generated when rainfall or snowmelt flows over land altered by development. Roads, parking lots, sidewalks, and rooftops increase the volume and speed of runoff, allowing pollutants to be transported directly into storm drains and nearby waterbodies.
How Stormwater Affects Water Quality
Stormwater runoff may contain pollutants such as sediment, nutrients like phosphorus and nitrogen, heavy metals, bacteria, chemicals, organic material, and trash. After rain events, these pollutants enter local waters, where they can impair water quality, disrupt beneficial uses, and damage aquatic habitat.
Common Sources of Stormwater Pollution
The most common source of water pollution is runoff from everyday land uses, including lawns, streets, driveways, parking lots, and agricultural areas. Common pollutants include oil and grease, fertilizers and pesticides, lawn clippings, leaves, pet waste, and litter.
Anything that enters a storm drain is discharged untreated into local waterbodies used for swimming, fishing, and drinking water.
How Residents Can Help Prevent Stormwater Pollution
Residents and property owners can reduce stormwater pollution by following these best practices:
- Compost or mulch yard waste; do not sweep it into streets or storm drains
- Pick up and properly dispose of pet waste
- Use commercial car washes
- Check vehicles and equipment for leaks
- Clean up spills using absorbent materials
- Recycle used motor oil and automotive fluids
- Use fertilizers and pesticides sparingly
- Avoid overwatering lawns
Small actions at home can make a meaningful difference in protecting water quality.
Illicit Discharges into Stormwater Systems
Illicit discharges are non-stormwater materials that enter the storm sewer system, such as wastewater, chemicals, oil, paint, or septic effluent. Because stormwater systems are not designed to treat these materials, illicit discharges introduce pollutants directly into rivers and lakes.
The City of Mandan conducts regular inspections of the stormwater system. Residents and businesses can help prevent illicit discharges by never dumping materials into storm drains and by maintaining plumbing and septic systems.
Construction Site Stormwater Runoff Control
Construction and redevelopment can significantly increase runoff and sediment if not properly managed. Construction sites of one acre or larger must obtain stormwater permit coverage and implement erosion and sediment controls through a Storm Water Pollution Prevention Plan (SWPPP).
The City of Mandan requires stormwater plans to be submitted and approved prior to qualifying building permits or plat approvals. These requirements apply during construction and after construction to reduce runoff volume and pollutant loading and to meet federal MS4 requirements.
Stormwater Protection and City Operations
Pollution prevention and good housekeeping practices are key components of the City’s stormwater program. Mandan reduces pollution from municipal activities through employee training, proper vehicle maintenance, reuse of street sanding materials, and regular inspection and maintenance of storm sewer systems.
These efforts help reduce pollutants that collect on streets, parking lots, and public facilities before they enter local waterways.
Additional Stormwater Resources
- North Dakota Department of Environmental Quality – Water Quality
- U.S. Environmental Protection Agency – Stormwater Information
- Stormwater Pollution Prevention for Small Residential Construction Sites
- Development Application Information
- Inert Waste Landfill and Waste Disposal (Public Works)
- Education Outreach Program (Environmental Protection Agency)