3535 RIVERFRONT BLVD 2023-02-21 - Laserfiche WebLink

lI • Minimum Requirement 6:Runoff Treatment According to Section 2.5.6 in Volume 1 of the SWMMWW, runoff treatment is required if the total pollution-generating hard surface within a threshold discharge area(TDA)is 5,000 square feet or more. The total pollution-generating hard surface area within the project site is 36,539.77 square feet(0.84 I acres),thereby triggering runoff treatment. The water quality runoff volume will be collected and treated on site before draining to the nearby Snohomish River. Refer to Section 5 for more information regarding water quality treatment. I • Minimum Requirement 7: Flow Control Flow Control is not required on this project as the entire project area discharges to the Snohomish River, which is a flow control exempt water body according to Section 2.5.7 and Appendix I-E in Volume 1 of Ithe SWMMWW. • Minimum Requirement 8: Wetland Protection IWetland protection is not required as the project does not impact any wetlands. • Minimum Requirement 9: Operation and Maintenance I The proposed public drainage facilities will be maintained by the City of Everett per their maintenance standards and schedule. 4. DEVELOPED CONDITIONS The final built-out, developed condition for the project site will consist of access roads, a trail, concrete I pavement, lawn areas, asphalt parking lot, a building for restrooms, and a picnic shelter. The west side of the parking lot,the restrooms building, and picnic shelter are to be constructed by the City of Everett in a future phase. The drainage infrastructure and storm systems have been designed to accommodate the future 1 improvements to avoid replacing and cutting into new improvements wherever possible. Runoff from the access road, parking lot, and a portion of the concrete pad sheet flows into four bioretention cells placed along the west side of the driveway as well as two catch basins located at low points along the driveway. Flow from • the bioretention cells, underdrains, and catch basins is conveyed by a storm drain system that is routed to SDMH#10008 and discharged via the city's storm outfall. Runoff from the trail, playground, and landscape • areas situated at the east of the site sheet flows into the trench system and catch basins placed at low points 1 across the site and connects to the storm drain conveyance system. Because of the instability of the existing soils and possible settlement issues with site development, a I settlement analysis for the site was performed by the project geotechnical team. Based on this analysis, it was concluded that the area under fill (preload area)could experience a total of 3 to 5 inches of settlement and the area outside the fill could experience up to 10 inches of settlement over 50 years. It was further concluded I that the differential settlement between the preload and non-preload areas could be as much as 5 to 8 inches over a length of 30 feet. Therefore, the storm drain conveyance system and utilities such as water and sanitary sewer include flexible joints to accommodate this settlement. Storm and sanitary sewer includes Kor- N-Seal boots at the connecting structures. I Everett Riverfront Development 3 Acre Park—Riverfront Commercial Investment LLC 3