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Facilities - Sand filter

Sand filter

A sand filter functions by filtering stormwater through a sand bed.  A typical sand filtration system consists of a pretreatment system for removing large sediment and debris from the runoff, a flow spreader, sand bed, and system of underdrain piping.  The sand filter bed typically includes a woven (geotextile) fabric between the sand bed and the underdrain system. Sand filters may also be above ground or in a subsurface vault.  


Maintenance is needed if you see these signs

Trash, debris or sediment accumulation on sand bed

Standing water on sand filter for more than 24 hours after a rainfall event

Trash or debris accumulation on flow spreader

Flow spreader uneven or clogged so that flows are not uniformly distibuted across sand filter (above ground)

Baffles, inlet/outlet pipes or slab show signs of damage


Tips for fixing problems and general maintenance

Inspect sand filter regularly.  Remove trash or debris that accumulates on surface of filter or flow spreader.

Remove sediment from surface or sand bed.

If filter becomes clogged, remove top several inches of sand and replace with clean sand.


Confined space warning for underground facilities

Due to potential dangers, only trained and certified persons should enter confined spaces.  Confined spaces are defined as:

  • Large enough that an individual could fully enter the space and work.
  • Having limited or restricted entry or exit.
  • Not primarily designed for human occupancy.

For more information visit Washington State Department of Labor & Industries.  

Report Spills

Chemical spills such as oil, gasoline, paint or herbicides/pesticides may cause harm to surface or groundwater.  Spills MUST be reported to the Washington State Department of Ecology and your local city or county.  DO NOT attempt to rinse away the spill until it's been checked.  

Washington Department of Ecology 24-hour Spill Response Number: (360) 407-6300