FAQs

What is stormwater?

Stormwater is rain and snow melt that runs off of impervious surfaces such as rooftops, paved streets, highways, and parking lots. Stormwater runoff collects pollutants and transports pollutants to surface water bodies such as Lake Ballinger and Lake Washington. Cities like Mountlake Terrace that have high level of development produce more stormwater runoff unless Low Impact Development practices are implemented.

Is stormwater treated?

In Mountlake Terrace, stormwater is not treated when it goes into a storm drain. The stormwater system is not connected to the sanitary sewer system nor is it treated in any way to remove pollutants before being released into the environment. Therefore, the quality of stormwater going into the drainage system is what determines the level of pollution in surface water.

What are stormwater pollutants and what do they do?

Any substance that is not naturally in rain can be considered a pollutant. Typical stormwater pollutants include:

Sediment in excess turns the water cloudy, making it less suitable for recreation, aquatic life, and plant growth. When the sediment settles in the receiving water, it can smother trout and salmon eggs, destroy insect habitat (a food source for fish), and cover prime spawning areas. Many other pollutants (oils, metals, toxic chemicals, bacteria) attach to the sediment. This pollutant-laden sediment can settle and contaminate the receiving water body. Exposed earth, construction, and dirt from equipment, vehicles and parking lots are sources for sediment.

Nutrients such as phosphorus and nitrogen are needed by plants to grow, but high levels can be harmful to water quality. Excess nutrient levels can over-stimulate the growth of algae and other aquatic plants, resulting in unpleasant odors, unsightly surface scums, and lowered dissolved oxygen levels from plant decay. Lower dissolved oxygen levels kill fish. Some forms of algae are also toxic to fish and other aquatic organisms, pets, and humans. Fertilizers, animal wastes, detergents, road deicing salts, automobile emissions, and organic matter are all contributors to excessive nutrient levels in stormwater runoff.

Metals, including lead, copper, zinc and cadmium, are commonly found in urban runoff. Dissolved metals in very low concentrations can be toxic to aquatic organisms, interfere with their ability to respond to predators, and interfere with reproduction. Metals can adhere to and contaminate sediments in water bodies. Sources of metals in stormwater include vehicle use (copper from brakes and zinc from tires), galvanized metal (zinc from roofs, fences), pesticides, and paints.

Oils and greases are known to be toxic to aquatic organisms at relatively low concentrations; they can coat fish gills and prevent oxygen from entering the water. Sources of oils and grease include vehicle use, streets and highways, parking lots, fueling areas, and equipment and machinery storage areas.

Chemical and hazardous substances such as pesticides, cleaners, and paints are particularly dangerous in the aquatic environment and can be lethal to aquatic organisms. Excessive application of insecticides, herbicides, fungicides, and rodenticides shortly before a storm, or application on impervious surfaces, can result in the pesticide being carried to receiving waters. Cleaners, even those marked non-toxic and biodegradable, are toxic to aquatic organisms in very small quantities. Many other toxic organic compounds can affect receiving waters, including phenols, glycol ethers, esters, nitrosamines, and other nitrogen compounds. Common sources of these compounds include wood preservatives, antifreeze, and cleaners.

Bacteria and other pathogens, such as fecal coliform bacteria, may indicate the presence of pathogenic (disease-causing) bacteria and viruses. Pet wastes, wildlife wastes, leaking dumpsters, and improperly connected sanitation systems can all contribute fecal coliform bacteria. Bacteria contamination can cause human illness, limit recreational use of a water body, and lead to closures of shellfish harvesting areas and public swimming beaches.

pH is a measure of water and can be neutral, very high (basic), or very low (acidic). High or low pH in water can release metals or other contaminants into the environment and cause biological problems for aquatic organisms and fish. Several sources can contribute to change of pH in runoff, including acidic chemicals, cement used in concrete products and concrete pavement, and chemical cleaners.

Information from the Port of Seattle.

What is the primary source of pollutants?

The primary cause of pollution in stormwater runoff is individual human activity, not industrial dumping. Success in reducing environmental pollution depends upon everyone’s participation.

What can I do to improve stormwater in Mountlake Terrace?

Check out our page on how to get involved here.

What do I do if I see something other than stormwater going into a drain or stream?

To report a pollutant spill to the stormwater system call the Public Works Department at 425-670-8264 between 8 a.m. and 5 p.m. weekdays. Call 911 after hours, on weekends, or during holidays.