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

At Project Area C, 1,850 square feet of asphalt sidewalk will be constructed to improve pedestrian and ADA access along Millwright Loop North/ 13th Street. This sidewalk is considered temporary until parcels B1 and B10 are developed, and the final concrete hardscaping is constructed. 4. CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN A construction stormwater pollution prevention plan (SWPPP) has been prepared for this project and is included in Appendix B. The SWPPP is prepared following the guidelines in the SWMMWW Volume II. Execution of the SWPPP during construction will be the responsibility of the Contractor. 5. HYDROLOGY Currently, the site is covered with mostly impervious surfaces (gravel and asphalt). The total area within the project limits is 7.57 acres and the total disturbed area is 5.7 acres. The WPC project is considered to have 1 TDA. Project Area A drains to the North Marina and project Areas B and C drain to the Central Marina. Proposed conditions at the end of this MWL- PH1 reduce the total amount of impervious surface, thus reducing the amount of runoff draining to these conveyance systems. No new permanent stormwater conveyance systems are proposed as part of this project, therefore hydrologic analysis is not required. 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 calculations for the trench drain and the bioswale are included in Appendix E. 6. PERMANENT STORMWATER CONTROL PLAN The permanent stormwater control plan for this area is a part of the WPC development project, which includes new conveyance and stormwater treatment systems covering the entire area of MWL-PH1. In the interim, Project Area A will be graded as follows: • Temp Roadway portions of Project Area A will be sheet flow to a new bioswale prior to being conveyed to the existing stormwater conveyance system located at the western of the project area. • All remaining surface water within project Area A will follow the existing drainage patterns and discharge directly to the North Marina via sheet flow. Project areas B and C will be graded to maintain existing site drainage patterns which are then conveyed to a series of existing catch basins, underground conveyance systems, that are routed through either an existing oil water separator or modular wetland treatment vault before discharging south into the Central Marina (Snohomish River). 7. OFFSITE ANALYSIS The proposed project will reduce the amount of stormwater runoff to the existing conveyance systems. There are no noted conveyance capacity issues for either existing conveyance. By inspection, no offsite analysis is required. 8. MINIMUM REQUIREMENTS The minimum requirements for the project are determined per Volume I of the SWMMVWV. Per Figure I- 3.2: Flow Chart for Determining Requirements for Redevelopment, all minimum requirements shall apply for this project. See Figure 7-1. 7IF117