320 S CABOT RD 2023-01-26 - Laserfiche WebLink

9. FLOW CONTROL Projects shall be exempt from flow control if the following thresholds are met: • Total effective impervious area less 5,000 sf, • Conversion of less than 3/ acre of native vegetation to landscaping, or • Conversion of less than 2.5 acres of native vegetation to pasture, • Improvements that cause less than or equal to 0.15 cfs between the existing and developed 100-year peak discharge from the site. As detailed in Section 7 of this report, the new roof surfaces of the garage and SFR will be infiltrated via infiltration trenches. Also, since permeable pavement is being utilized for a portion of the driveway surfaces, the effective impervious area will be less than 5,000 sf. This project is shown to construct less than 5,000 sf of effective impervious surfaces (EIS) and less than 3/acre of land conversion. By fully infiltrating the site runoff generated by the proposed roof surfaces and half of the driveway surfaces, this project is shown to decrease the peak flows in the downstream system (See Appendix A for WWHM2012 printout). Therefore, flow control is not required for this project. 10. WETLAND PROTECTION By designing the on-site improvements to decrease the peak flow rates from the site and by maintaining the sheet flow condition, this will provide the necessary protection to any downstream NGPA. 11. OPERATION AND MAINTENANCE MANUAL The Property Owner will be responsible for maintaining the stormwater and landscaping facilities within this development. Routine inspections and maintenance will improve the long-term performance of the stormwater facilities. If at any time you are unsure if a problem exists or how to address a specific problem, contact a Professional Engineer. A copy of the maintenance and operations manual shall be retained on-site or within reasonable access to the site and shall be transferred with the property to any new owner. . A log of maintenance activities that indicate what actions were taken shall be kept and be available for inspection by the City of Everett upon request. 12. SUMMARY This project proposes to construct less than 5,000 sf of new effective hard surfaces. As a result, the use and land cover for less than 5,000 sf of the site will be converted pervious to impervious surfaces. Stormwater management techniques have been incorporated into the design. Therefore, the stormwater design for this project has met or exceeded all of the applicable Minimum Requirements 1-5. Fogg-LEXAR SLDS 19-0506 July 2019 Revised:September 2019 Page 11