The CID i-5 Underpass.
GreenDeck proposed this initiative circa 2014. InterImCDA hosted the board of directors. SiteWorkshop purchased a design-build package with grant money. GreenDeck holds all records reflecting Little Saigon's work for (7) years. The legend continues…
Utilities
Limited utilities are anticipated for both project sites, under I-5, with the implementation of EV charging stations planned in the parking lot adjacent to the underpass parks. The team is exploring options for hand-washing stations and irrigation needs. If water services are required, water mains are located on both Jackson Street and King Street and could provide service to the parks. Further coordination with Seattle Public Utilities will be needed to determine water availability for the sites. Coordination with the plumbing and/or landscape designers will also be needed to determine meter sizes. Please find more information on UHUB and the exciting and innovative new project @ https://www.uhub.ngo/projects-7
Stormwater Management
Stormwater drainage has been evaluated to meet the 2016 COS Stormwater Code. Per the 2017 COS Stormwater Manual, SDCI Director’s Rule 17-2017, both sites must meet onsite stormwater management (OSM), and flow control requirements. Both sites discharge to combined sewers; therefore, no water quality treatment is required. For conservative purposes, both sites were evaluated as parcel-based projects. However, with further discussions with the City of Seattle, the projects may be categorized as a sidewalk project, therefore not requiring flow control.
Handwashing stations are provided at both sites in the current plan. In that case, a proposed 6” sanitary sewer service will be provided where needed and discharged to the 12” combined sewer in Jackson Street and/or the 12” combined sewer located in King Street, depending on the location of the stations.
For both sites, stormwater will sheet flow to trench drains, which will convey runoff to OSM facilities. Non-infiltrating bioretention facilities will be provided throughout both sites to meet the OSM requirement. The bioretention facilities’ overflow drains and underdrains will be tight-lined to discharge into flow control facilities, if needed, which will then discharge to the combined sewers located in Jackson Street and King Street, respectively. For flow control, bioretention facilities or flow control risers will be provided and sized to meet the peak flow requirements for the 2-yr and 25-yr stormwater events.
Infiltration is assumed to be infeasible due to existing soil conditions and site constraints. A geotechnical report is needed to confirm this assumption.
