Stormwater Basics

  • A lake surrounded by green trees, with a fence in the foreground and a church steeple in the background.

    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.

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  • A woman in a red tank top and black pants emptying a trash can in a park while a German Shepherd dog sits beside her.

    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.

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  • A landscaped garden with small trees and shrubs, a stone pathway, and a modern building with large windows in the background.

    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.

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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.

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  • 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.

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  • 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.

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  • 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.

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  • 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.

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  • 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.

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  • 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

  • USEPA Clean Water Act National Pollutant Discharge Elimination System (NPDES) Stormwater Rules and Final Notices:

    • USEPA MS4 Phase I stormwater permitting process began in 1990

    • USEPA MS4 Phase II stormwater permitting process began in 1999

  • USEPA Clean Water Act NPDES Combined Sewer Overflow (CSO) Control Policy began in 1994

  • These regulations separated stormwater into its own utility, in addition to drinking water and wastewater

  • USEPA authorized the State of Maine to implement NPDES regulations in 2001

    • The Maine Department of Environmental Protection (DEP) sets up the Maine Pollutant Discharge Elimination System (MEPDES) program to implement EPA delegated responsibilities.

Maine Stormwater Regulations

Climate Impacts

  • More frequent storms and increased precipitation exacerbate inland and coastal flooding

    • Requires current stormwater infrastructure to be updated and capacity increased

    • Increases need for stormwater infiltration and storage to prevent overwhelming local waterbodies

  • Greater variety in winter storms requires creative designs and tools

    • Requires more strategic drainage design and capacity for winter rain and freeze-thaw periods to prevent localized flooding and increased chloride applications

    • Increases need for regional weather stations, condition cameras, and vehicle sensors

    • Increases need for range of municipal and state snow removal and chloride application equipment to work all types of storms and temperatures

    • Requires coordinated landscaping decisions for impervious cover summer shade and winter sun

  • Hotter and drier summers increase waterbody stressors

    • Requires additional funding and resources to maintain plant health in green infrastructure

    • Decreases the soil’s ability to infiltrate

    • Reduces the waterbody’s ability to dilute or buffer inputs from lower water levels and flow

    • Increases need for stormwater infiltration to recharge groundwater and maintain waterbody baseflow levels

  • Invasive species increasing complexities related to natural resource management

    • Development-related construction and maintenance increases the likelihood of invasive species introduction to a site through equipment and materials

    • Development-related disturbances increased the likelihood of invasive species spread around the site

    • Some invasive plants can reduce the soil’s ability to infiltrate, increase erosion rates, and reduce stormwater BMP pollutant treatment capacity

    • Invasive pests and diseases can weaken or shrink vegetative buffers protecting natural resources and stabilizing slopes and shorelines

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

    • Requires elevating infrastructure or installing smart technology pumps or gates to control outfall flows

Limited Liability Legislation

A snowplow clearing snow from a road during a snowstorm.

The application of winter road salt is a common solution to melting ice on roadways, walkways and parking lots to keep drivers and pedestrians safe. However, the improper and over-application of salt has detrimental impacts on the environment and infrastructure, creating hidden and permanent ecological costs in this seemingly affordable deicing material. 

Chloride is not significantly removed by chemical reactions, evaporation or vegetation. Therefore, nearly all of the chloride applied to the land surface as road salt will eventually end up in the nearby surface waters or groundwater. Preventing chloride contamination through implementation of best management practices is the most cost-effective and environmentally sound option.

Road salt is bad for fresh water. We can further reduce chlorides in Maine (while still keeping people safe) by passing Limited Liability Insurance Legislation, similar to the New Hampshire Green SnowPro program, so snow removal contractors can limit salt application without legal risk and preserve the quality of our water.