9600 SHARON DR EXPLORER MIDDLE SCHOOL 2022-03-11

0 0 BMP and Infeasibility description applicable lists Infeasibility criteria and rationale for each BMP not selected T5.14A The following criteria can be cited as reasons for infeasibility without Bioretention further justification (though some require professional services to or Rain Gardens make the observation): (continued) ❑ Where field testing indicates potential bioretention/rain garden sites have a measured (a.k.a., initial) native soil saturated hydraulic conductivity less than 0.30 inches per hour. A small-scale or largescale PIT in accordance with SWMMWW Volume III, Section V- 5.4 shall be used to demonstrate infeasibility of bioretention areas. If the measured native soil infiltration rate is less than 0.30 in/hour, bioretention/rain garden BMPs are not required to be evaluated as an option in List #1 or List 42. CI Where the minimum vertical separation of 3 feet to the seasonal high groundwater elevation, hardpan layer, or other impermeable layer would not be achieved below bioretention that would serve a drainage area that exceeds the following thresholds (and cannot reasonably be broken down into amounts smaller than indicated): • 5,000 square feet of pollution -generating impervious surface (PGIS) 10,000 square feet of impervious area • 0.75 acres of lawn and landscape. N Where the minimum vertical separation of 1 foot to the seasonalhigh groundwater or other impermeable layer would not be achieved below bioretention that would serve a drainage area less than the above thresholds. ❑ Within 100 feet of a drinking water well, or a spring used for drinking water supply. ❑ Within 10 feet of small on -site sewage disposal drainfield, including reserve areas, and grey water reuse systems. For setbacks from a 'large on -site sewage disposal system," see Chapter 246-272B WAC. City of Everett Public Works Small Project Stormwater Site Plan Report -Dec 2079 28