2202 100TH ST SW 2023-02-07 - Laserfiche WebLink

Pa e2of Sabrina Fandler City of Everett Permit Services September 21, 2020 4. Minimum Requirement #8 a. Explain the project components used to comply with the General Protection Requirements. Additional information has been provided as requested, starting on page 2-5 of the enclosed Storm Drainage Report. b. List Source Control BMPs from Minimum Requirement #3 as part of the Protection from Pollutants requirements in MR #8. Explain how on -site stormwater management and runoff treatment BMPs meet the Protection from Pollutants requirements. Additional information has been provided as requested, starting on page 2-5 of the enclosed Storm Drainage Report. 5. Include the Operation and Maintenance Manual as a separate document. Include the specific O&M requirements for the modular wetland. Revised/provided as requested. This information is also presented in Section 10 of the enclosed Storm Drainage Report. 6. Flow Control / Treatment Trade c. The flow control trade of Basin D for Basin B appears to be inadequate as Basin D has less total and impervious area. Please provide a POC analysis for all basins to show that the duration standard is being met. A POC analysis has been provided in Section 4 of the enclosed Storm Drainage Report. Adding Basin 'B' resulted in the detention vault length increasing by 20 feet (includes factor of safety). See the end of Section 4 for WWHM documentation. d. Basin D collects less impervious area than Basin B. Please address whether the Basin D for Basin B trade provides equivalent treatment. Basin 'D' collects less impervious area than Basin 'B' but the impervious surfaces in Basin 'B-'are primarily curb, gutter and sidewalk which are not subject to vehicular travel and are classified as non -pollution generating impervious surfaces (Non-PGIS). The Basin 'D' impervious surfaces consist mostly of pavement subject to vehicular traffic (PGIS) and will now receive runoff treatment with this proposed treatment trade, in addition to flow control. 7. Provide a printout of the diagrams used for the WWHM model as well as the graphs. Included as requested, see the end of Section 4 of the enclosed Storm Drainage Report for WWHM documentation. 8. Verify the impervious area for Basin C in the Rational Method calculations. Based on Everett mapping and the Basin Map figure, there appears to be more than 4.2 acres of impervious surface in Basin C. The 2018 Snohomish County Aerial was used to estimate the land coverages for Basin 'C'. This aerial differs from the 2015 City of Everett Aerial, when there was a large parking lot on the large vacant parcel (construction parking?) south of 100th St SW. See the image clips below and on the following page for reference.