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Sand Filters

A sand filter is a type of stormwater management facility designed to filter rainwater through sand to remove pollutants. Filters are typically a depression in the ground filled with sand that helps to manage polluted or excess rainwater. To the untrained eye, it may look like a sand box or volleyball court. You can find sand filters in residential neighborhoods and around commercial businesses. 

 

Image of a sand filter.How Does a Sand Filter Work?

During a storm, rainwater collects pollutants as it flows across hard 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 surface sand filter. The sand filter captures the rain water, directs it through layers of sand and gravel that filter and remove the pollutants, and returns the clean water back to the local stream or into the storm drain system.

Sand filters are often found with infiltration trenches.

 

Why are Sand Filters Important?

Sand filters are important stormwater management tools, because they:

  • Remove pollutants

  • Improve health of streams and rivers

  • Help to make our waters fishable and swimmable

  • Improve the quality of the Chesapeake Bay

As rainwater flows over hard surfaces and lawns it picks up pollutants such as sediment, trash, pesticides from lawns, nutrients from fertilizer or pet waste, and oil and grease from cars. Sand filters reduce this pollution and stormwater runoff entering our waterways.

 

Graphical representation of a sand filter.
How a sand filter works.

 

Maintaining Sand Filters

As the property owner, you are responsible for all maintenance of your sand filter unless a shared maintenance agreement has been made with the DEP Stormwater Facility Maintenance Program.  Sand filters at County facilities and schools are the maintenance responsibility of the Department of Environmental Protection. 

Image of the front of the Non-structural Sand Filter and Infiltration Trench Maintenance Fact Sheet.
Need Help with Sand Filter Maintenance?
Download the Fact Sheet
(PDF, 371KB)

Sand filters require regular maintenance similar to other landscaped areas, including grass cutting, trash removal and vegetation management. Please visit the stormwater facilities maintenance page for a list of approved contractors. DEP-approved contractors are recommended but not required for non-structural maintenance like weeding or trash pick-up. 

Un-maintained sand filters may:

  • Not remove pollutants as intended, sending polluted water to streams and rivers

  • Become an eyesore for your community

  • Over time, allow unwanted vegetation to grow over it, reducing its effectiveness

  • Allow water to pool long enough for insects to breed (longer than 3 days)

  • Cost more to fix if problems are left unchecked

By maintaining your sand filter, you are doing your part to help the environment and protect your local streams and the Chesapeake Bay.

Image of a sand filter before cleaning. The site needs to be raked and sand replaced. Image of a sand filter after cleaning. Vegetation was removed.
Sand filter before maintenance.
After maintenance, including vegetation removal.

 

How Will I Know What Maintenance is Required?

Montgomery County regulations require that you perform ongoing routine grass cutting, trash removal, and vegetation management of your stormwater facility. If the work described below is not done regularly, you could receive a notice of violation.

Grass Cutting

✔ Mow grass at least twice a year

  • Around sand filter
  • Prevent cut grass from blowing into the filter 

 

Vegetation Management

✔ At least twice a year

  • Remove all trees and woody vegetation from the sand filter
  • Remove all grass and weeds growing in the facility
  • Prevent trees and woody vegetation from growing in the facility
  • Rake the surface of the sand filter
  • Seed and cover adjacent areas of bare soil to prevent erosion

 Do not apply herbicides or pesticides within the facility. Vegetation removal should be performed manually.

 

Trash Removal

✔ Remove trash and debris from all areas in and around the filter monthly

 

Image of the front of the Structural Sand Filter Maintenance Fact Sheet.
Need Help with Sand Filter Structural Maintenance?
Download the Fact Sheet
(PDF, 365KB)

Preventive Maintenance

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 listed above can be thought of as similar to preventive car maintenance (like changing the oil in your car every 3 months).

As needed:

✔ Know the pollutant sources on your property and try to reduce or eliminate the pollutants at the source

✔ Notify DEP if beaver activity or animal burrowing is observed

✔ Keep children from playing in the sand or stones

✔ Inform contractors working on your property of the location of the sand filter to prevent accidental damage and the placement of snow over the sand filter

✔ Inspect the facility after every major storm and contact DEP if you are concerned

 

Structural Maintenance

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).
 

Structural Maintenance Actions for a Sand Filter 
(Only by a Contractor)
Problem: Possible Fix
Water standing in filter for more than 3 days Filter media and other components may need to be replaced
Erosion along flow paths Erosion should be corrected and flow paths possibly re-graded
Vegetation absent or not growing around the filter, which could cause erosion Re-establish the vegetation on side slopes and adjacent areas 
Damage to structural components (i.e., pipes, swales and ditches, and overflow structures) Specific maintenance for these components to be determined by DEP
Animals burrows Fill burrow and establish vegetation

 

The DEP performs inspections of all sand filters in Montgomery County every 3 years. If DEP finds maintenance issues during its inspection, you will receive a notice of violation with a work order showing a list of items that need to be performed to restore your facility to proper working condition. You will have 60 days from the date of the notice to make the noted repairs. A civil citation may be issued if you have not complied with the maintenance requirements. 

View the list of DEP-approved contractors who can perform the structural maintenance on stormwater facilities.

DEP can answer your questions and provide additional guidance about maintaining your stormwater facility. Please email askdep@montgomerycountymd.gov or call the Montgomery County Customer Service Center at 3-1-1.

 

Sand Filters in the Stormwater Facilities Maintenance Program

Image of a man mowing around a stormwater pond.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. .

Not sure if your sand filter is part of the Stormwater Facilities Maintenance Program?  Check out online Facilities Map or email askdep@montgomerycountymd.gov.

 

Can I remove my sand filter 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 sand filter on your property? Financial incentives are available for you.

 

The Water Quality Protection Charge Credit Program

After you have installed your sand filter, 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 sand filter 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.

Learn more on the WQPC Credit webpage.

Image of a sand filter.