Vault Filter
Good: Well-maintained interior of a 
stormwater filter vault facility.

Stormwater filter

A stormwater filter is a passive, flow-through filtration system. It is comprised of a vault that houses rechargeable filter cartridges. It works by passing stormwater through the filters, which traps particulates and/or absorbs pollutants such as dissolved metals and oils.

The filter material is housed in cartridges enclosed in concrete vaults or manholes. Various filter materials are available from private companies.

Vortex sedimentation vault

A vortex-enhanced sedimentation vault consists of a cylindrical vessel in which incoming water spirals like a whirlpool, causing the heavier particles to settle out.  It uses a vortex-enhanced settling mechanism (swirl-concentration) to capture solids, floatables, oil, and grease.

Vault Closed Detention
Good: Lid and entrance to an underground
detention facility.

Closed detention system

A closed detention system is an underground structure, typically a concrete vault or series of large diameter pipes or plastic modular chambers, which temporarily stores stormwater and releases it slowly. They typically are used on sites that do not have space for a pond and are placed under paved surfaces. These underground detention systems are enclosed spaces where harmful chemicals and vapors can accumulate. Therefore, the inspection and maintenance of these facilities can only be done by individuals trained and certified to work in hazardous, confined spaces.

Finding a maintenance contractor to service vault systems

The majority of vault systems used in Clark County are manufactured by three companies, Contech, Oldcastle, and Baysaver Technologies.  The manufacturer name is usually found on the vaults.  Find a list of local contractors here (take note of company location as some are out of state).

Confined space warning for underground facilities

WarningConfinedSpace.gifDue 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.  

Maintenance sheets

Closed detention system vault (tank)
Wet vault

Maintenance is needed if you see these signs  

Problem sediment buildup in Vault Filter
Problem: This stormwater filter vault has
sediment buildup, indicating the filter needs
to be replaced by a professional.

Leaves, trash and other debris accumulated in vault, pipe or inlet/outlet

Accumulated sediment depth exceeds 10% of the diameter of the storage area for 1/2 length of storage vault or any point
depth exceeds 15% of diameter (closed detention system)

Sediment in vault bottom exceeds the depth of sediment zone plus 6 inches (wet vault)

Cracks wider than 1/2 inch at joint of inlet/outlet pipe or wider than 1/4 inch in slab

Ventilation area blocked or plugged

Inlet/outlet pipes or access cover damaged


Tips for fixing problems and general maintenance

Remove any vegetation covering the lid.

Inspection or maintenance that requires entering the underground facility can only be done by individuals trained and certified to work in hazardous confined spaces.

  • Remove trash and debris regularly.
  • Identify sources of leaks or spills and contain them as quickly as possible.
  • Remove sediment.

Check inlets and any open or confined standing water for mosquito larvae (see photos below).  If mosquitoes are a concern, contact Clark County Mosquito Control District for information. The 24-hour service request line is (360) 397-8430.

mosquito larve.jpg     mosquito larve1.jpg

Additional elements to vault facilities

Flow control structure / flow restrictorFlow control structure

Underground flow control structures and flow restrictors direct or restrict flow in or out of facilities. They slowly release stormwater at a specific rate. It is important to make sure they do not become plugged or damaged because the facility could release water too quickly or too slowly and overflow. They are usually found in manholes.

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