Stormwater management - Southwest Washington

- Pervious pavement

- Oil/water separator

- Sand filter

Video: Cover - an ounce of prevention is worth a pound of cure. The most effective and least costly way to deal with polluted runoff is to keep stormwater from picking up pollution in the first place.

Video: Contain - be prepared. When accidents happen, lessen the impact to your business and your water resources by being prepared to contain and clean up spills.

Video: Clean - use a broom, not a hose. Storm runoff that enters a storm drain doesn't go to a wastewater treatment plant, it ends up in our streams, rivers, lakes and the groundwater that supplies our faucets. Spills of any kind or size should never be washed into a storm drain.

Video: Maintain - stormwater management systems need tune-ups, too. Catch basins, oil water separators, and swales all need regular maintenance to function properly.

Pervious pavers

Pervious pavers, note the spaces between the pavers.

Pervious asphalt

Pervious asphalt, note the coarse appearance.

Oil/water separator

Problem: Some oil/water separators include coalescing plates (wavy-edged sheets shown above) that separate oil from water, so it can then be skimmed off. Plates should be white when clean.



Information for businesses

Commercial properties could have unique stormwater features in addition to those typically found in residential areas. These features include pervious pavement, which allows rain on parking lots and walkways to soak into the ground rather than run off; oil/water separators, underground structures typically located in parking lots and at automotive businesses; and sand filters which can be located above or below ground.

Because these features often are out of sight or blend into their surroundings, maintenance can easily be forgotten or overlooked. Regular inspection and cleaning are important to keep these structures functioning properly and avoid potentially costly repairs. Maintenance is a requirement of state stormwater rules and local stormwater ordinances.

Pervious pavement

Pervious pavement allows water to pass through it and soak into the ground, reducing runoff and mimicking the natural hydraulic cycle. Pervious pavement typically is a layer of specially formulated concrete, asphalt or pavers on top of a thick layer of gravel (8 – 24 inches). As water passes through the pavement and gravel, contaminants are filtered out. The water is stored in the gravel layer until it can soak into the ground. Pervious pavement requires regular maintenance to allow water to pass freely.

Maintenance is needed if you see these signs:
• Standing water during or after a rainfall event
• Visible debris or sediment on pavement surface
• Height of gravel between pavers depleted by more than ½-inch (permeable pavers only)

Oil/water separator

An oil/water separator treats stormwater by trapping oil at the surface of the water and sediment at the bottom, allowing treated water to pass through. It is most commonly used as the first pre-treatment facility in a series of stormwater management facilities and is usually found in parking lots, service and fuel stations. A unit should be inspected monthly and after a major storm. Make sure to keep records of your inspections and maintenance activities.

Maintenance is needed if you see these signs:
• Discharge water shows obvious signs of oil or other contaminants
• Thick layer of oil (thicker than 1 inch) on surface of water in vault
• Sediment accumulation of more than 6 inches on the bottom of the vault
• Accumulation of trash or debris

Checklist for maintenance and fixing problems (PDF).

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 be above ground or in a subsurface vault.

Maintenance is needed if you see these signs:
• 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

Checklist for maintenance and fixing problems (PDF).