For the past few years, Spokane County has hired an inspection crew to assess the status of stormwater structures in the Stormwater Utility Service Area (“SWSA”). This includes a measurement of how much sediment and debris is in the structure, if there is standing water, and other data related to current conditions. Data collected has provided crucial information about structures throughout the County. Based on the estimated percentage of sediment and debris located in drywells and catch basins, specific structures were identified as needing maintenance. Structures were then assigned to a priority list and the ones requiring immediate maintenance were cleaned first. Work was completed in late September. Over 800 stormwater structures were cleaned out during this season.
During the summer of 2018, 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 stormwater structures. Over time, the debris can accumulate and inhibit the structures from performing the function they were designed to. One type of stormwater structure is a drywell. Drywells are concrete structures, installed in the ground, that allow stormwater to infiltrate 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 reduce the ability of the water to infiltrate into the ground. This can lead to localized flooding while also reducing the volume of recharge to groundwater, which is vital to our aquifer.
The material vacuumed from stormwater structures 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 located at the intersection of Ruby and Farwell. 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 stormwater drainage systems (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 removed 476.48 tons of solids from county-owned drywells and catch basins.