Rapid growth in Olympia, WA, has lead to an increase in stormwater pollution. With nine streams, four lakes, four large wetlands and six miles of shoreline within the city’s 24 square mile limits, it’s no surprise that protecting water quality is of utmost importance. Managing runoff in accordance with the Western Washington Phase II Municipal Stormwater Permit, issued by the Washington State Department of Ecology (WDOE) in January of 2007, is the city’s responsibility.
Runoff from two blocks of Decatur Street and much of the surrounding neighborhood was piped north to the Schneider Creek Watershed, and ultimately Puget Sound, without treatment. With no land available to build large stormwater ponds, the conventional option for stormwater treatment, the city turned to an innovative Low Impact Development (LID) approach. The project was funded as a demonstration project through a WDOE grant to test and monitor new LID methods.
LID design seeks to minimize runoff by treating and infiltrating it on-site. “We installed geogrids on the entire 600-foot project” said Craig Anderson, from the City of Olympia’s Public Works Water Resources department. “Then we incorporated three different LID stormwater treatment systems every 200-ft”
Two of the systems use regular asphalt pavement combined with a treatment system where treated flow is discharged into a perforated pipe and then released into the subsoil beneath the road surface. The first treatment system uses the CatchBasin StormFilter system, and the second, a rain garden. The third system is porous asphalt pavement.
According to Anderson, “We chose the filter systems because we had experience with most of them. Personally, I like the Contech StormFilter method because during the construction phase it was the most straightforward method and easiest to construct”
Following construction, 100% of the stormwater runoff from these two blocks will be treated on-site. Each system will be measured for amount of water soaking, amount of pollutants removed, amount of runoff receiving water quality treatment and durability and maintenance.