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BMP and Infeasibility description <br /> applicable lists Infeasibility criteria and rationale for each <br /> BMP not selected <br /> T5.14A The following criteria can be cited as reasons for infeasibility without <br /> Bioretention further justification(though some require professional services to <br /> or Rain Gardens make the observation): <br /> (continued) ❑ Within 100 feet of an underground storage tank and connecting <br /> underground pipes when the capacity of the tank and pipe system <br /> is greater than 1,100 gallons. <br /> E Where field testing indicates potential bioretention/rain garden <br /> sites have a measured(a.k.a.,initial)native soil saturated <br /> hydraulic conductivity less than 0.30 inches per hour.A small-scale <br /> or largescale PIT in accordance with SWMMWW,Section V-5.4 <br /> shall be used to demonstrate infeasibility of bioretention areas. If <br /> the measured native soil infiltration rate is less than 0.30 in/hour, <br /> bioretention/rain garden BMPs are not required to be evaluated as <br /> an option in List#1 or List#2. <br /> E Where the minimum vertical separation of 3 feet to the seasonal <br /> high groundwater elevation or other impermeable layer would not <br /> be achieved below bioretention that would serve a drainage area <br /> that exceeds the following thresholds(and cannot reasonably be <br /> broken down into amounts smaller than indicated): <br /> • 5,000 square feet of pollution-generating impervious <br /> surface(PGIS) <br /> • 10,000 square feet of impervious area <br /> • 0.75 acres of lawn and landscape. <br /> ❑ Where the minimum vertical separation of 1 foot to the seasonal <br /> high groundwater,Hardpan layer,or other impermeable layer would <br /> not be achieved below bioretention that would serve a drainage <br /> area less than the above thresholds. <br /> ❑ Within 100 feet of a drinking water well,or a spring used for <br /> drinking water supply. <br /> ❑ Within 10 feet of small on-site sewage disposal drainfield, <br /> including reserve areas,and grey water reuse systems. For <br /> setbacks from a"large on-site sewage disposal system,"see <br /> Chapter 246-272B WAC. <br /> City of Everett Public Works <br /> Small Project Stormwater Site Plan Report-Dec 2019 35 <br />