Surface Water Topics

Catch Basin Inspections & Cleaning

What are those metal grates in my neighborhood?

The City of Mill Creek has approximately 5,000 public and private stormwater structures across 4.7 square miles designed to collect runoff from the entire surface of Mill Creek and route it to outfalls into our natural receiving waters. The image below is an example map that illustrates the city's catch basin locations (with dark purple representing basins locating in public streets).

The City is required by our municipal stormwater permit from the Department Ecology to inspect each publicly-owned catch basin once every two years.  The current two-year period is August 2021 to July 2023, with a new two-year period starting August 2023.

As these inspections are very time-intensive, the City contracted with The Watershed Company, a local environmental firm, to inspect our public street catch basins.  This work began in January 2023.  

Each catch basin inspection verifies whether the catch basin is working as intended, and also whether maintenance or, less frequently, repair or replacement will be required.  Follow-up maintenance, repairs, and/or replacement activities are scheduled when City staff time and resources allow, and generally comply with the Ecology-approved maintenance standards the City has adopted. 

The information from each catch basin inspection includes the following:

1.  The physical condition of the underground concrete basin structure, the pipe connections, and the grate/lid and frame at street level;
2.  The presence of garbage or debris that need to be removed;

3.  Evidence of pollutants, by sight or smell;
4.  The level of sediment accumulated in the bottom of the concrete basin (often in a sump specifically intended to catch this sediment).

Watch this video from the City of Bellingham to learn more information about the catch basin inspection process and why it is an important part of our overall surface water utility program!

What Can I Do For My Community?

To learn more about surface and stormwater runoff in Mill Creek, more information can be found here:  What is Surface Water Runoff?

When it starts raining, even a small city of Mill Creek's size can produce and accumulate a lot of runoff water quickly.  The city is about 4.7 square miles in area (nearly 3,000 acres or nearly 130 million square feet!).  Even the grassy and other vegetated areas in Mill Creek do not absorb all the rain right where it lands. 

All that runoff that needs to be controlled and helped to flow down to North Creek.  Our combination of public and private stormwater pipes and facilities help with that, along with our natural streams like Penny Creek.

Even with nearly 5,000 street storm drains in the city to collect runoff, and nearly that same number of additional drains located in parking lots similar areas, it is common for water to pond up and not drain away quickly.  Hard surfaces like streets and driveways are particularly prone to this ponding.

Keep drains and gutters clear
Leaves, grass and bush clippings, and other debris from trees and plants tend to accumulate, sometimes very quickly, at drain grates and similar structures.  Even a small accumulation can either partially block water flow or deflect it in an unwelcome fashion.

Use rakes and remove any debris that accumulates.

Keep leaves, grass and bush clippings, and other yard debris out of the street
Do not blow leaves from yards into the street, even if you think the City street sweeper will pick up the debris.  Sweepers are not designed for that work, and City staff cannot sweep all city streets fast or frequent enough to remove excess leaves and other debris in the street.  Whenever it rains, the streets are designed to move the runoff to the catch basin grates, which also moves any other debris on the street. 

Instead, dispose of all leaves, grass and bush clippings, and other yard debris from your yard and property as yard waste.

Do not release car wash water into our stormwater system
Car washes generate multiple sources of pollution, including both the soap and all the dirt, oil, grease, and grim washed off the vehicle.  This polluted water must not be flushed into our storm drain system, either by directly flowing into a street drain or by flowing into a private property drain or surface channel (ditch) that is connected to our City stormwater system.  

Using biodegradable soap does not work as an alternative.  Any soap, biodegradable or now, works by lifting the dirt, oil, metal dust, grease, and other chemical pollutants off the car and washing those away with the water.

Remember, all water drains somewhere away from your property.  Water in your yard, even in grassy areas, can run off into the street or to a yard drain.  Driveways, in particular, are designed to drain runoff water off the driveway (often into the street or a channel next to the street, which moves that water to catch basins). 

Keeping wash water out of all drains in your yard or driveway is usually very difficult.  If you have a large, grassy area that you can park your car on while washing it, that may work.  You might also be able to direct all the wash water to such an area, so long as none of it escapes to a drain.  However, in both cases, please recognize that washing a vehicle typically requires a lot more water than many grassy areas can absorb, resulting in the excess running off into drains.

The best overall option for car washing is to do it at a commercial car wash.  Commercial car washes collect wash and rinse water for re-use, recycling/treatment, or discharge into sanitary sewer connections.

An image saying Contact Us
Angela Bolton
Surface Water Program Coordinator
Phone: 425-921-5752
Email: [email protected]
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