Underground Stormwater Facilities: Hydrodynamic Separators
Hydrodynamic separators remove oil, grease, trash, and sediment from stormwater runoff. These underground structures include oil and grit separators and proprietary hydrodynamic separators, such as Baysaver,® Aqua-Swirl,® and Stormceptor.® Please visit the manufacturers’ websites for more information about these devices.
Underground hydrodynamic separators are commonly located under parking lots at commercial sites or multi-family residential sites (condominium, apartments, etc.).
How Do They Work?
During a storm, rainwater collects pollutants as it flows across impervious surfaces, such as rooftops, sidewalks, and roads. Flow splitters are often used to send a certain quantity of untreated water, known as the “first flush,” to a hydrodynamic separator. The oil and grit separator captures and treats stormwater by separating oil, grease, trash, and sediment from the captured stormwater through three chambers. The clean water is then returned to the local stream or to the storm drain system.
Proprietary systems such as Baysaver,® Aqua-Swirl,® and Stormceptor,® follow similar processes to remove oil, grease, trash, and sediment from stormwater. The designs of these systems vary.
Why are Hydrodynamic Separators Important?
Maintaining Hydrodynamic Separator
As the property owner, you are responsible for all maintenance unless your hydrodynamic separator has been transferred to the Stormwater Facilities Maintenance Program. Learn more about how you can transfer your hydrodynamic separator into this program.
Why Maintain My Hydrodynamic Separator?
An unmaintained hydrodynamic separator may:
Performing preventive maintenance regularly will prevent long-term damage and help avoid potential violations. These actions will keep your facility looking good and working correctly, which will save you money in the long term. The preventive maintenance actions shown below can be thought of as similar to preventive car maintenance (like changing the oil in your car every 3 months).
Structural maintenance is work done on the components of the filter that allow it to control rainwater and remove pollutants. Structural maintenance problems in the table below are things you should be looking out for. When they happen, call DEP for help (like calling your mechanic when the engine light comes on).
How Will I Know What Maintenance is Required?
DEP recommends owners use a certified contractor to pump-out, power wash, and clean their stormwater facility annually to ensure the facility is properly functioning and passes inspection. If DEP inspects the facility and finds maintenance issues, you will receive a notice of violation with a work order showing the list of required maintenance and repairs. You will have 45 days from the date of the notice to hire a certified contractor to complete the maintenance and repairs. A civil citation may be issued if you have not complied with the maintenance and repair requirements.
DEP can answer your questions and provide additional guidance about maintaining your stormwater facility. Please email firstname.lastname@example.org or call the Montgomery County Customer Service Center at 3-1-1.
Hydrodynamic Separator in the Stormwater Facilities Maintenance Program
The Stormwater Facilities Maintenance Program is responsible for maintaining all public stormwater facilities as well as all private facilities that transferred their maintenance to the County.
Can I remove my hydrodynamic separator after installation?
No, you cannot remove any facilities that were part of your building installation - these are permitted structures and DEP maintains a database of these facility locations as part of the Stormwater Facility Maintenance Program. DEP may perform a maintenance inspection of your practice if it is a permitted structure. Property owners must contact DEP before any major changes can be performed to the structure.
Resources and Financial Incentives
Have a hydrodynamic separator on your property? Financial incentives are available for you.
The Water Quality Protection Charge Credit Program
If your property has a hydrodynamic separator that is maintained in accordance with the Department of Environmental Protection maintenance requirements, then you are now eligible to receive a credit off your annual Water Quality Protection Charge (found on your yearly property tax bill). The credit provides an incentive for maintaining your flow splitter and other stormwater management practices.
You must apply for the WQPC credit separately – the credit will not be provided to you automatically.
Residential property owners can receive up to 50% off their WQPC depending on the type and size of stormwater management practices on the property.
Non-residential and multi-family properties can receive up to 50-60% off their WQPC depending on the type and size of the stormwater management practices on the property.