What is Stormwater?

Stormwater runoff is generated when precipitation from rain and snowmelt flows over land or impervious surfaces and does not percolate into the ground. As the runoff flows over the land or impervious surfaces (paved streets, parking lots, and building rooftops), it accumulates debris, chemicals, sediment or other pollutants that can adversely affect water quality in our local rivers, ponds, and wetlands if the runoff is discharged untreated.

Typical pollutants that occur in stormwater are oil, grease, and heavy metals from local roadways, road salt and sand from winter operations, plastic wrappers and trash, and cigarette butts.

 How is it Stormwater Managed?

"Grey" Infrastructure

Past methods for dealing with stormwater consisted of capturing and discharging stormwater through "hard" or "grey" infrastructure. These methods typically involve the use of capturing the stormwater in catch basins, conveying the stormwater through drain pipes, and discharging it directly to local water ways, untreated.

In addition to conveying pollutants directly to waterways, the discharged water from "grey" infrastructure in the summer months tends to be much warmer than the receiving waters. Impervious surfaces act as a heat-sink, and the runoff from these surfaces absorbs this heat. This warmer water is lethal to aquatic life, and creates intolerable conditions for many native species, such as brook trout.

"Green" Infrastructure

Recently, more environmentally friendly, or "green", methods for dealing with stormwater have been encouraged. These methods consist of capturing the stormwater, then retaining and the treating the stormwater through "Best Management Practices" (BMPs) such as rain gardens, detention ponds, or grass swales. Using these methods, stormwater is allowed to infiltrate into the ground as it would prior to urban development. By infiltrating stormwater into the ground, we help replenish our aquifers, and maintain even streamflows during periods of dry weather.

The best, and least costly, method for treating stormwater is to reduce the amount of impervious area during new construction or redevelopment. Impervious area can be reduced through the use of porous ashpalt pavements, or using brick pavers .

Due to the age of our infrastructure in the Northeast United States, much of our stormwater infrastructure consists of "grey" infrastructure.

A diagram describing the transition of water to stormwater runoff

How Can I Help!

For things you can do (even on your own property!) to help the City meet it's stormwater goals, please visit the following the websites or contact the Engineering Department.

EPA's Stormwater Home Page - Provides general stormwater information, and also contains information regarding Municipality Stormwater Permitting Requirements administered by the EPA.

EPA's Region 1 - "Soak up the Rain" Campaign - Information for Homeowners in New England on how they can help reduce negative stormwater impacts

Nashua River Watershed Association - Local advocacy group for our main local waterway

Massachusetts Watershed Coalition - Based in Leominster, advocacy group for all our rivers and streams across the Commonwealth