What is stormwater runoff?

Stormwater runoff is water from rain or melting snow that “runs off” across the land instead of seeping into the ground. This runoff usually flows into the nearest stream, creek, river, lake or ocean. The runoff is not treated in any way.


What causes polluted stormwater runoff?

Polluted stormwater runoff generally happens anywhere people use or alter the land. People going about their daily lives are the number one source of stormwater pollutants. Most people are unaware of how they impact water quality. Some common examples include over fertilizing lawns, excessive pesticide use, not picking up pet waste, using salt or fertilizer to de-ice driveways, letting oil drip out of their vehicles and littering. Developed areas in general, with their increased runoff, concentrated numbers of people and animals, construction and other activities, are a major contributor to pollution, as are agricultural activities. Other contributors include forest harvesting activities, roadways, and malfunctioning septic systems.

Why all the recent fuss about stormwater?

 The federal Clean Water Act requires entities across the United States to take steps to reduce polluted stormwater runoff. These laws require six things: 


Conduct outreach and education about polluted stormwater runoff.


Provide opportunities for residents to participate and be involved in conversations and activities related to reducing polluted stormwater runoff.


Detect illicit discharges (e.g. straight piping or dumping).


Control construction site runoff.


Control post-construction runoff.


Perform municipal housekeeping (e.g. take steps to prevent runoff from city buildings and activities.)

If it only affects streams and creeks, why should I care?

Streams and creeks feed into rivers, lakes and the ocean. We all drink water, so we are all affected when our water is polluted. When water treatment costs rise, the price of drinking water goes up. If you like to fish, swim or boat, you may have heard or been affected by advisories warning you not to swim, fish or boat in a certain area because of unhealthy water or too much algae. When we pollute our water, everyone is affected!



What can I do to reduce the amount of stormwater pollution I contribute?

If you own a car, maintain it so it does not leak oil or other fluids. Be sure to wash it on the grass or at a car wash so the dirt and soap do not flow down the driveway and into the nearest storm drain.

If you own a yard, do not over fertilize your grass. Never apply fertilizers or pesticides before a heavy rain. If fertilizer falls onto driveways or sidewalks, sweep it up instead of hosing it away. Mulch leaves and grass clippings and place leaves in the yard at the curb, not in the street. Doing this keeps leaves out of the gutter, where they can wash into the nearest storm drain. Turn your gutter downspouts away from hard surfaces, seed bare spots in your yard to avoid erosion and consider building a rain garden in low-lying areas of your lawn

If you have a septic system, maintain it properly by having it pumped every three to five years. If it is an older system, be sure it can still handle the volume placed on it today. Never put chemicals down septic systems, they can harm the system and seep into the groundwater.

Pet owners should pick up after their pets and dispose of pet waste in the garbage.

Keep lawn and household chemicals tightly sealed and in a place where rain cannot reach them. Dispose of old or unwanted chemicals at household hazardous waste collections sites or events.

Never put anything in a storm drain.

Don’t litter.

Why are we stenciling the curbs and gutters with a message?

Storm drain stenciling is a great way to remind people that storm drains are for clean rain water only. It’s a visual reminder that pollution prevention is important.

What's the difference between putting water down the storm drain and putting water down the toilet or sink?

The sanitary sewer (toilets and sinks) and storm drain system are two completely different systems. The water that goes down sinks or toilets in homes or businesses flows to the Water Pollution Control Plant, where it is treated before its release. Water that flows down driveways and streets into a gutter goes into a storm drain that flows directly into a water source. This water picks up pollutants along the way and does not receive any treatment to remove pollutants.

What do I do if I see someone dumping something other than rain water down a storm drain?

Call the Environmental Compliance Branch immediately at 303-367-3000 x28682 or after-hours call security at 303-367-3060.

What is an MS4?

MS4 stands for "municipal separate storm sewer system." It is a drainage system owned by a municipality intended to carry only surface runoff i.e. storm water. A separate sewer is not intended to, nor should it, carry storm water combined with sanitary sewage or with any other pollutant.