Constructed Wetlands for Stormwater Treatment in Alaska

Anchorage, Alaska, is situated at 61° latitude, at the very northernmost extension of the Pacific Ocean. Centered on a broad peninsula between the Chugach Mountains and the marine waters of Knik and Turnagain Arms, the city receives 15–20 inches per year of precipitation, roughly half of which falls as snow. Anchorage is home to 260,000 people, with a convenient road network of over 3000 miles. The Municipality of Anchorage and State of Alaska Department of Transportation and Public Facilities expect to receive an NPDES permit for municipal storm water discharge from the USEPA by early 1998. The Municipality has been using wet pond sedimentation basins for BMP treatment of stormwater runoff and snowmelt for over a decade. Suspended solids are the primary contaminant of concern in Anchorage, based on the sensitivity of local salmon-bearing streams to increased sediment loadings and contaminants associated with sediments. Sediments are also particularly relevant in Anchorage storm water and melt water runoff, as a result of sanding of city streets to improve winter traction. These sedimentation basins have been documented as achieving removal of suspended solids as high as 80% during storm events.