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• <br /> Option I . Dispersion Design Worksheet <br /> *This BMP can only be used for roof runoff per the SWMMWW* <br /> • Roof area requiring mitigation (ft2): no new roofing area <br /> • Minimum 50 ft flow path provided: Yes x No <br /> Dispersion systems with 25-50 ft flow path must be modeled using a continuous runoff model to <br /> confirm project meets the flow control requirements, attach modeling results to this worksheet. <br /> Dispersion is not allowed where less than 25 ft flow path can be achieved and another BMP shall <br /> be used to meet the flow control requirement. <br /> • Number of splashblock downspout dispersions: 4 and/or Downspout dispersion <br /> trenches 1 (Minimum of two-50 ft long downspout dispersions and one per 350 sf of roof <br /> area, is required to meet the flow control requirement using this worksheet) <br /> Downspout Dispersion areas do not overlap. <br /> One of the following must be met for the dispersion area(s), check one: <br /> The vegetated flow path consists of well-established lawn or pasture, landscaping with <br /> well-established groundcover, native vegetation with natural groundcover, or an area that meets <br /> BMP T5.13: Post-Construction Soil Quality and Depth. The groundcover is dense enough to help <br /> disperse and infiltrate flows and to prevent erosion. <br /> BMP T5.1 3 Post-Construction Soil Quality and Depth is being provided for dispersion areas <br /> (area to be shown on project plans) <br /> The following design criteria shall be met (check each to confirm the requirement has <br /> been met): <br /> I. Maintain a setback of at least 5 feet between any edge of the trench and any structure or property line. <br /> 2. Setback requirements in Section 4-4.1 (3) of the DCSS have been met. <br /> Including: <br /> • 50 feet setback from slopes greater than 15 percent and greater than 10 feet in height. <br /> 3. Maintain a vegetated flow path of at least 50 feet between the discharge point and any property line, <br /> structure, slope steeper than 15%, stream, wetland, lake, or other impervious surface. Sensitive area <br /> buffers may count toward flow path lengths. <br /> 4. A maximum of 350 square feet of roof area may drain to each splashblock or dispersion trench. <br /> 5. Place a splashblock or a pad of crushed rock(2 feet wide by 3 feet long by 6 inches deep) at each <br /> downspout discharge point. <br /> City of Everett Public Works <br /> Small Project Storm water Site Plan Report for Projects in <br /> the Combined Sewer Area-April 2021 /1;_3 <br />