What Is Stormwater?

Stormwater runoff is water from rain or melting snow that does not soak into the ground. In a natural environment, stormwater will be filtered by the soil and not pose a threat to the quality of nearby waters. In a developed environment, stormwater can become polluted when it runs over streets, lawns, farms, and construction sites as it picks up pollutants such as dirt, oil, nutrients, sediments, pesticides, and bacteria. If untreated, stormwater can cause water quality impairments when it flows into our lakes and rivers.

Stormwater and the pollutants it may carry can have negative impacts on Boxborough’s receiving water bodies, threatening the quality of their use for shellfishing, swimming, fishing, boating, and drinking water. Proper management of stormwater runoff will help ensure these water resources can be enjoyed by future generations.

Pollutant Sources

Pollutant sources related to stormwater runoff are discussed as follows.

Impervious Surfaces

Impervious surfaces such as roads, driveways, decks, and even compacted soils, change the way the water flows over and through the land. They prevent stormwater from soaking into the ground, which increases the volume of stormwater runoff that needs to be managed by the Town. Unmanaged stormwater runoff contributes to flooding, stream bank erosion, and reduced groundwater recharge.


Erosion is the gradual wearing away of land by water, wind, or ice. During construction, land can be disturbed by excavation, filling, and paving. This can increase erosion by exposing the soil to stormwater. Nutrients such as phosphorus have the ability to "stick" to soil and can be transported to lakes and rivers.

Fertilizer, Pet Waste & Septic Systems

Fertilizer, pet waste, and septic systems can contribute excess nutrients that speed up plant and algae growth, including cyanobacteria, which can harm humans and animals and can be a nuisance for swimming and boating. They can also contribute bacteria that can make swimmers sick and lead to beach closures.


Other pollutant sources that may contaminate stormwater runoff include salt and deicing materials, lawn and agricultural pesticides, and automobile chemicals among others. Many of the chemicals in these products may be toxic to aquatic organisms, humans, and other animals.