Each summer, Spokane County hires a field inspection crew to assess the status of storm drains in the Stormwater Service Area (SWSA). Crews record a measurement of how much sediment and debris is in the structure, if there is standing water, and other information related to current conditions. Data collected has provided crucial information about storm drains throughout the County. Based on the estimated percentage of sediment and debris located in storm drains, specific structures were identified as needing maintenance. Storm drains were then assigned to a priority status and the ones requiring immediate maintenance were cleaned first.
During the 2018 and 2019 vactoring seasons, Spokane County Stormwater Utility rented two vactor eductor (“vactor”) trucks to clean storm drains throughout the SWSA. These trucks essentially act as high-powered, large vacuums that remove sediment, pine needles, water and other debris from storm drains. Over time, the debris can accumulate and inhibit the storm drains from performing the function they were designed to. One type of storm drain is a drywell. Drywells are concrete structures, installed in the ground, that allow stormwater to drain into the ground through porous walls in the structure. When sediment and debris build up in drywells, the material can block the porous holes in the walls and prevent water from draining into the ground. This can lead to flooding and will decrease the amount of water entering back into the ground, which is one way our aquifer is refilled. In addition to preventing stormwater from draining, this material may also contain pollutants that are harmful to the aquifer. Removing this material reduces the possibility of contamination from stormwater entering the aquifer.
The material vacuumed from storm drains is stored in the vactor truck tank. When the tank is full, crews remove the materials from the tanks at the Spokane County Decant Facility. The Spokane County Decant Facility was a construction project that was completed in 2014 and was funded in part by a Stormwater Financial Assistance Program Grant through the Department of Ecology. The facility provides an environmentally sound system for handling, treating, and disposing of liquids and solids generated from the cleaning of storm drains (e.g. drywells and catch basins). The material is deposited at the facility and water is separated from the solids. Oils are removed from the water via an oil/water separator before being conveyed to a swale for treatment using biofiltration.
In 2018, Spokane County focused on cleaning storm drains with the highest sediment loads. Work was completed in late September of 2018.Over 800 storm drains were cleaned out during this season and approximately 476tons of solids were removed from county-owned storm drains.
Work is currently being performed for the 2019 vactor season. Crews are focusing on cleaning storm drains located on arterials, which have high traffic counts and therefore usually see more material and pollutants.