Progress Ridge, a 110-acre mixed-use development, is designed around a reclaimed rock quarry on the border between the cities of Beaverton and Tigard, Ore. The quarry is now an 11-acre lake surrounded by 746 high-density residential units, a commercial town center and 43 acres of parkland.
Beaverton requires on-site detention of stormwater runoff to control the volume of runoff sent to downstream channels. This protects channels from scouring and reduces potential flooding. Under EPA permit regulations, a specific level of water quality is required before discharging runoff into downstream waterways.
In a development like Progress Ridge, engineers typically meet stormwater requirements with large above ground detention ponds. Because of the development’s size, a detention pond would displace 200 to 300 residential units.
Site engineers considered detention facilities at different locations, or installing individual water quality manholes to provide settling before directing runoff to a larger on-site collection facility. While both offered flow control and water quality improvement, each would reduce the amount of developable land.
Polygon Northwest, a Vancouver, Washington, engineering firm, proposed installing underground filtration systems manufactured by Contech to meet detention and water quality requirements and maximize land use.
“We decided that this development might not happen if we didn’t find a way to accommodate some form of stormwater management that didn’t include above-ground detention using valuable land on the site,” said Gary Brentano, operations director for the City of Beaverton. “You hit a point where a developer can’t generate enough return on investment to make the investment to begin with. That’s in part what led us to consider the StormFilter.”
The Stormwater Management StormFilter® is a passive filtration system with an underground concrete vault housing rechargeable, media-filled filter cartridges. The system filters polluted stormwater runoff through cartridges that are customized to remove site-specific pollutants such as sediments, nutrients, organic compounds and metals. Each filter cartridge’s integrated surface-cleaning function helps to maintain the permeability of the filter surface and enhances the overall performance and longevity of the system.
Available with H-20 load-rated manhole lids, the system can be installed in traffic areas or under a parking space. Manhole lids provide easy access for inspections and maintenance.
The plan included installation of five StormFilter systems containing a total of 144 cartridges, and two highflow bypass structures for directing any runoff that exceeds the design water-quality flow rate away from the treatment structures. The high-flow bypass structures prevent potential re-suspension of collected pollutants. The Panel Vault StormFilter from Contech was the largest of the five systems, holding 111 cartridges. The 36.5--ft. by 11.5--ft. Panel Vault StormFilter and a 6--ft. by 12--ft. StormFilter containing 14 cartridges were installed next to the lake to treat runoff between the development and SW Barrows Road. The three additional filtration units are being installed in the residential development area to treat roadway runoff.
Runoff from the site and Barrows Road flows into an underground vault that collects trash and debris before flowing to the panel vault for treatment. Whenever the flow exceeds the vault’s design, excess water flows into the 6--ft. by 12--ft. precast vault.
Treated runoff is discharged directly to the lake. The 80-million-gallon lake fills a quarry gravel pit and is stocked with fish from the US Fish and Wildlife Service. The lake is fed by winter stormwater runoff that is supplemented in the summer by the city’s domestic water supply.
Three of the five filtration system units have been installed, including the panel vault, the 6--ft. by 12--ft. unit and an 8--ft. by 16--ft. unit that treats runoff from the residential section that is currently under construction. Construction of the remaining two units are in progress, with installation expected in 2005. The development is scheduled for completion in 2007.
“I think from a development perspective, this solution offers a whole host of benefits, including unifying the outfall to the lake in one location and doing so with some fairly high water quality,” said Brentano.
From a cost and space standpoint, the StormFilter has proven to be the right solution for the Progress Ridge development. From a performance standpoint, it has proven in similar installations that it is able to meet and surpass the water quality requirements for the site and address pollutant concerns.
“We were trying to make sure the developer got a fair opportunity to develop as much of the land as possible while otherwise ensuring that the city was able to maintain as high a water quality at the outfall as possible,” says Brentano. “A lot of this project was about how to make the process of development as cost effective for the developer as it could be, recognizing that our needs had to be addressed in the course of that.”