1001 14TH ST 2024-03-01 - Laserfiche WebLink

The site is part of a highly developed basin. The current discharge locations and drainage patterns will be maintained. 8.5. MR #5 — On -Site Stormwater Management The project will use List #3 located in Table 1-3.2 of the SWMMWW manual provide compliance with minimum requirement #5. No landscape areas are proposed with this project. Future project phases will include the construction of new landscape areas using BMP T5.13 Post -Construction Soil Quality and Depth. For other hard surfaces on site, the proposed finished ground will be graded such that stormwater runoff is not concentrated but is as evenly dispersed as practicable. Full infiltration is deemed to be infeasible due to high groundwater elevations and inadequate separation between any infiltration facility and the groundwater table. The groundwater elevation at the site mirrors tidal elevations. Anticipated sea level rise over the next 100 years ranges between +1' to +5'. The current Mean Higher -High Water elevation is 11.11' (NOAA Tides and Currents) and with an estimated 1'-5' due to sea level rise, future groundwater elevations are predicted to be within 3' of the ground surface. 8.6. MR #6 — Runoff Treatment A continuous inflow biofiltration swale is planned for the Temporary Access Road within Project Area A to account for this new pollution generating impervious surface (PGIS). This biofiltration Swale will provide basic treatment for the temp access road and is planned to be removed when Millwright Loop North is constructed. The biofiltration Swale is designed per the requirements of BMP T9.10 of the 2019 SWMMWW. Calculations for the biofiltration can be found in Appendix E. Runoff from the existing asphalt pavement south of the surcharge fill pile between the 14f street bulkhead and the edge of surcharge will be collected and conveyed via a temporary trench drain to a existing Modular Wetland Treatment vault. The vault was installed in the Southeast Millwright Loop project and was sized to treat runoff from this area. The trench drain will be removed when Millwright Loop South is constructed in its final condition and runoff from all hardscape surfaces in this area will be conveyed to the Modular Wetland Vault. The future WPC project will construct new stormwater treatment vaults that collect and treat stormwater from Location A and Location B in accordance with the 2019 SWMMWW. 8.7. MR #7 — Flow Control The proposed project is Flow Control exempt, as it drains through an existing conveyance system to the Puget Sound, a water body listed as Flow Control exempt in Appendix I -A of the SWMMWW manual. 8.8. MR #8 — Wetlands Protection No wetlands are located on or downstream of the project site, therefore minimum requirement 8 does not apply. 8.9. MR #9 — Operation and Maintenance A continuous inflow bioswale is proposed along the temporary access road. The bioswale is intended to be in service during the construction of the final Waterfront Place Central development and will be 7IF117