BELLWOOD DR. STORMWATER RETROFIT PROJECT
(Stormwater Utility Project SWN232)
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The Bellwood Drive Stormwater Retrofit Project will provide new water quality treatment facilities in an area where none currently exists. Polluted stormwater is currently disposed of via direct injection into the subsurface via drywells. This project is located in a Critical Aquifer Recharge Area over the Spokane Valley-Rathdrum Prairie Aquifer which is designated by the Environmental Protection Agency as a Sole Source Aquifer. These improvements are proposed on Bellwood Drive between Mill Road and Hastings Road. The project is located in the growing Fairwood/Wandermere area in north Spokane in S7, T26N, R43, EWM.
Spokane County Stormwater Utility has received preliminary notice of 75/25 match grant funding from Washington State Department of Ecology for the construction and implementation of these new stormwater treatment facilities. Stormwater Utility would like to combine the stormwater improvement project with a future Spokane County Roads Department resurfacing or pavement maintenance project. Project design is anticipated to be completed in 2016-17, with construction occurring by the end of construction season in either 2019 or 2020.
Bellwood Drive is 0.4 miles in length and is designated an Urban Local Access Road per the Spokane County Road system. It serves as a connector to Hastings Road from Mill Road and is frequently used to bypass the stop light at Mill and Hastings. The ADT of 1229, while a seemingly low volume, is deceptive with regard to the number of vehicles parked and accessing the housing and businesses along Bellwood Drive.
Bellwood Drive also serves as back-access to Calvary Chapel Church, which has an occupancy of 1500 and an average attendance of around 1000 for each of the two Sunday services. Bellwood also serves multi-family housing, such as townhouses and apartments, along the entire south side of the street, and provides access to a drive-through bank, an animal hospital, a dentist office, a restaurant/tavern and various small businesses and shops in the adjacent Fairwood Shopping Center.
The method of water quality treatment that is proposed for this project is bio-retention swales. The swales will be constructed within the existing road right-of-way, within the existing road prism (between curb-lines), with very little expected disturbance to the adjacent sidewalk and curbing. Swales will be constructed on both sides of the road, alternating as much as possible from side to side, allowing for existing parking to remain between the swales. When complete, this retrofit project will provide water quality treatment at 100% of today's new / re-development criteria. Existing drywells will be abandoned and replaced with new double-depth (Spokane County Type B) drywells. The drainage area has been re-evaluated and the number of drywells necessary for disposal of stormwater run-off is less than existing, reducing the potential impact to the aquifer due to fewer underground injection control facilities.
All of the drywells within this section of roadway were identified as a priority for retrofit in Spokane County. They are all within the top 600 (of approximately 2000) drywells in the most critical need of retrofit. This prioritization was determined by a recent Ecology funded ranking and prioritization of all underground injection control facilities within Spokane County's inventory.
As previously noted, this project is located over the Spokane Valley-Rathdrum Prairie Aquifer which is designated as a Sole Source Aquifer by the Environmental Protection Agency and is the drinking water source for over 500,000 people. The entire project is situated in an area where the vadose zone treatment capacity (per Underground Injection Control, UIC, Guidelines) is categorized as "NONE." The project is also situated over a "HIGH" Critical Aquifer Recharge Area, indicating that the aquifer is highly susceptible to pollutant contamination in this area, elevating the need to retrofit the existing drywells in this location. The project area is also within 250 feet of a Special Wellhead Protection Zone.
All of the drywells within this section of roadway were identified as a priority for retrofit in Spokane County. Fifteen of the 18 drywells in the project area are within the top 600 (of approximately 2000) in the most critical need of retrofit. This prioritization was determined by a prior Ecology funded “ranking and prioritization” of all UIC facilities within Spokane County's stormwater structure inventory.
Bellwood Drive was constructed in 1974, and most recently received a 2-inch ACP inlay in 2002. Although there are no current plans to improve the roadway surface, Bellwood Drive may be ready for resurfacing during the contract window of 2016-2021, making it more cost efficient to postpone construction a year or two in anticipation that road funding will be available in the near future.
The final design for this project will be in accordance with the Stormwater Management Manual for Eastern Washington, and the Spokane Regional Stormwater Manual which is an Ecology approved equivalent manual to the Stormwater Management Manual for Eastern Washington.
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If you have questions about this project, please contact Project Manager, Colleen Little, P.E., by calling 509.477.3600.