Stormwater Basics

  • What is Stormwater Runoff?

    Rain or melted snow that flows over land. Stormwater runoff can pick up pollutants before it flows into storm drains and ditches that empty into our waterbodies. Polluted runoff affects water quality, drinking water, human health, wildlife, and property values.

    Learn More

  • Pollution Prevention

    Any pollution that can be kept off the land so the next storm can’t pick it up, keeps our water cleaner and safer.

    By reducing or eliminating our use of fertilizers, pesticides, road salt, and other chemicals, we can keep these pollutants out of our waterways.

    Learn More

  • Stormwater Treatment

    Some stormwater pollutants, like sediment and nutrients, can be removed through treatment infrastructure like rain gardens, bioswales, and tree boxes.

    However, some pollutants, like road salt, are not able to be removed without extremely intensive and expensive desalinization facilities.

    Learn More

Stormwater Pollutants

Stormwater pollutants are everywhere. Since most pollutants are from nonpoint sources, their individual impacts to our local waterways vary. Often it is the cumulative impact of multiple different pollutants or a large volume of one pollutant that causes stress to local waterways.

  • Soil erosion is the #1 water pollutant in Maine. Erosion is a natural process where soil is moved by water or wind. However, human actions, like construction activities, can increase erosion rates.

    Learn more

  • While plants need lots of different types of nutrients to grow, they use nitrogen and phosphorus the most. Fertilizers can contain varying percentages of nitrogen and fertilizer, making it easy to overapply or apply incorrectly. Excess fertilizer can be picked up by stormwater runoff and carried to local waterways, allowing algae to quickly grow.

    Learn more

  • Pesticides (umbrella term for insecticides, herbicides, fungicides, etc.) have numerous unintended consequences, including being carried from yards, businesses, and farm fields by stormwater to local waterbodies. Aquatic plants, insects, crustaceans, and other wildlife can be killed and harmed by the pesticide chemicals.

    Learn more

  • Winter road salt is one of the toughest stormwater pollutants because a only a small amount is needed to make freshwater too salty for its plants and wildlife. For context, the salt concentration in ocean water averages 35 parts per thousand (ppt), while freshwater wants to be below 0.1 ppt. Many waterbodies in Maine are above safe levels due to decades of high road salt use.

    Since it is extremely expensive and time-intensive to remove salt from water, road salt reduction is a more effective solution to keep Maine freshwaters fresh.

    Learn more

  • Dog waste is high in nitrogen, phosphorus, and pathogens. When dog waste isn’t scooped, bagged, and trashed, it becomes a soil and water pollutant and a health hazard to people and other dogs. It only takes a few irresponsible dog owners in an area to cause algal blooms and closed beaches due to high bacteria levels.

    Learn more

  • Litter causes problems throughout the stormwater system. Litter can clog storm drain grates, causing localized flooding; create flow-restricting clogs and complete blocks in the underground pipe network; and add debris to our freshwater and saltwater habitats which can block shelter and be confused for food by wildlife.

    Learn more

  • Illicit discharges enter the stormwater network through direct (e.g., wastewater pipes either mistakenly or deliberately connected to stormwater pipes) or indirect connections (e.g., infiltration into stormwater pipes from nearby damaged or leaking wastewater pipes, spills collected by storm drains, or paint or used motor oil dumped directly into a storm drain). The result is untreated stormwater that contributes high levels of pollutants, including heavy metals; harmful chemicals; fats, oils, and grease; solvents; nutrients; and pathogens to receiving waterbodies.

    These contaminants can be detected during routine outfall sampling but requires expensive and time intensive methods to try to trace back to the source. Oftentimes the cause of the source is long gone, making it difficult to prevent future illicit discharges.

  • The stormwater system can have sewer cross contamination through direct connections (e.g., wastewater pipes either mistakenly or deliberately connected to stormwater pipes) and indirect connections (e.g., infiltration into stormwater pipes from nearby damaged or leaking wastewater pipes). This contamination can add harmful bacteria, household cleaners, and other chemicals to stormwater while it travels underground to nearby waterbodies.

    This contamination can be detected through routine outfall sampling but requires expensive and time intensive methods to try to trace back to the source. Direct connections often happen on private property and indirect connections require the repair, lining, or replacement of wastewater and/or stormwater pipes.

    Combined sewer overflows (CSO) owned by municipalities and sewer districts are required by the USEPA Clean Water Act and Maine state laws to be licensed and have abatement programs. The CSO program is separate from the municipal separate storm sewer system (MS4) permit program.

  • Legacy and emerging pollutants are being researched to learn more about the impacts they may have on human health, wildlife, and the environment. This research is crucial to identify and create appropriate laws, regulations, source mitigation, and monitoring actions.

    Examples include:

    • Heavy metals

    • Banned industrial chemicals

    • BPAs

    • PFAS

    • Microplastics

    • 6PPD-quinone

Federal Stormwater Regulations

Maine Stormwater Regulations

Climate Impacts

  • More frequent storms, increased precipitation, and/or larger volumes in shorter periods of time exacerbated inland and coastal flooding

    • Requires current stormwater infrastructure to be updated and capacity increased

    • Increases need for stormwater storage to prevent overwhelming local waterbodies

  • Rising sea levels can flow back up low-lying stormwater outfalls