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BMP and <br />Infeasibility description <br />applicable lists <br />Infeasibility criteria <br />and rationale for each <br />BMP not selected <br />T5.30 <br />❑ Site setbacks and design criteria provided in BMP T5.30 <br />Full Dispersion <br />(SWMMWW, Section V-4.1) cannot be achieved. <br />0 A 65 to 10 ratio of forested or native vegetation area to impervious <br />area cannot be achieved. <br />❑ A minimum forested or native vegetation flowpath length of 100 <br />feet (25 feet for sheet flow from a non-native pervious surface) <br />cannot be achieved. <br />T5.15 <br />Citation of any of the following infeasibility criteria must be based on <br />Permeable <br />an evaluation of site -specific conditions and a written <br />Pavement <br />recommendation from an appropriate licensed professional (e.g., <br />engineer, geologist, hydrogeologist): <br />❑ Where professional geotechnical evaluation recommends <br />infiltration not be used due to reasonable concerns about erosion, <br />slope failure, or downgradient flooding. <br />❑ Within an area whose ground water drains into an erosion hazard, <br />or landslide hazard area. <br />❑ Where infiltrating and ponded water below the new permeable <br />pavement area would compromise adjacent impervious <br />pavements. <br />❑ Where infiltrating water below a new permeable pavement area <br />would threaten existing below grade basements. <br />❑ Where infiltrating water would threaten shoreline structures such <br />as bulkheads. <br />❑ Down slope of steep, erosion prone areas that are likely to deliver <br />sediment. <br />❑ Where fill soils are used that can become unstable when saturated. <br />❑ Excessively steep slopes where water within the aggregate base <br />layer or at the subgrade surface cannot be controlled by detention <br />structures and may cause erosion and structural failure, or where <br />surface runoff velocities may preclude adequate infiltration at the <br />pavement surface. <br />❑ Where permeable pavements cannot provide sufficient strength to <br />support heavy loads at industrial facilities such as ports. <br />❑ Where installation of permeable pavement would threaten the <br />safety or reliability of pre-existing underground utilities, pre- <br />existing underground storage tanks, or pre-existing road <br />subgrades. <br />City of Everett Public Works <br />Small Project Stormwater Site Plan Report -Dec 2019 30 <br />