Spokane County Stormwater Utility (SWU) is exploring a potential stormwater project along Wall Street, between Francis Avenue and Monroe Street, in north Spokane. The project would retrofit the stormwater structures along Wall Street to bring them closer to current water quality treatment standards. This retrofit project may include work that extends into the surrounding neighborhood streets around Wall Street, depending upon the need and resources available.
Currently, polluted stormwater runoff is captured by drywells and then discharged – untreated – directly into the ground. These pollutants can include oils, heavy metals, and suspended solids, which originate from vehicles, equipment, and heavy machinery. Nitrates and phosphorus are also pollutants of concern and are found in runoff from fertilized lawns and landscaping. Current design standards are in agreement with the Environmental Protection Agency’s Clean Water Act, intended to protect our drinking water, as well as lakes, rivers, and streams, from stormwater pollutant contamination.
The subsurface soils beneath this section of County road have been designated as susceptible for contamination with respect to connectivity to our sole-source of drinking water, the Spokane Valley-Rathdrum Prairie aquifer. Therefore, since there is currently no stormwater treatment in this area, this proposed project is desirable as a stormwater retrofit. The types of stormwater treatment improvement being considered for the Wall Street area are as follows: roadside bioinfiltration swales, sand filters, and possibly porous pavement.
Roadside Bioinfiltration Swale
Sand Filter - Closed Lid
Sand Filter - Open Lid
Bioinfiltration swales are depressed areas, commonly referred to as swales. These facilities are either planted with grasses, shrubs, and trees, or are sodded and irrigated, or seeded with drought tolerant native grasses. Sand filters are used in areas where space constraints render typical roadside swales not feasible. Sand filters are either placed under the sidewalk or in the curbline, intercepting the stormwater and filtering it through a special media that captures pollutants. Porous pavement is only proposed in areas where vehicle travel does not occur, such as parking areas or, again, in areas where space or utility conflicts make swales or sand filter construction difficult. All of these treatment facilities are effective practices for stormwater pollutant removal.
Spokane County SWU tries to combine our stormwater retrofit projects with current or projected future road restoration projects in order to economize the cost associated with such work. Combining projects also means less disruption to the surrounding area as both the road and stormwater structures are improved at the same time versus in separate construction seasons.
Spokane County Stormwater Utility would like your input on this proposed project. Please take a moment to complete a survey to provide us with valuable feedback with regard to this proposed project.