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BMP and Infeasibility description applicable lists Infeasibility criteria and rationale for each BMP not selected T5.15 The following criteria can be cited as reasons for infeasibility without Permeable further justification(though some require professional services to Pavement make the observation): (continued) ❑ Where the site cannot reasonably be designed to have: • Porous asphalt surface<5%slope • Pervious concrete surface<10°%o slope • Permeable interlocking concrete pavement surface<12% slope ■ Grid systems< 6-12%slope(check with manufacturer and local supplier to confirm maximum slope) ❑ Where the subgrade soils below a pollution-generating permeable pavement(e.g.,road or parking lot)do not meet the soil suitability criteria for providing treatment.See soil suitability criteria for treatment in the SWMMWW,Section V-5. Note:In these instances, a 6 inch sand filter layer meeting city specifications for treatment may be used to provide treatment. ❑ Where underlying soils are unsuitable for supporting traffic loads when saturated.Soils meeting a California Bearing Ratio of 5 percent are considered suitable for residential access roads. ❑ Where replacing existing impervious surfaces unless the existing surface is a non-pollution generating surface over an outwash soil with a saturated hydraulic conductivity of 4 inches per hour or greater. ❑ Where appropriate field testing indicates soils have a measured (a.k.a.,initial)subgrade soil saturated hydraulic conductivity less than 0.3 inches per hour.Only small-scale PIT or large-scale PIT methods in accordance with SWMMWW Section V-5.4 shall be used to evaluate infeasibility of permeable pavement areas. (Note: In these instances,unless other infeasibility restrictions apply, roads and parking lots may be built with an underdrain,preferably elevated within the base course,if flow control benefits are desired.) ❑ Roads that receive more than very low traffic volumes,and areas having more than very low truck traffic. Roads with a projected average daily traffic volume of 400 vehicles or less are very low volume roads(AASHTO 2001)(U.S. Department of Transportation, 2013).Areas with very low truck traffic volumes are roads and other areas not subject to through truck traffic but may receive up to weekly use by utility trucks(e.g.,garbage,recycling),daily school bus use,and multiple daily use by pick-up trucks, mail/parcel delivery trucks,and maintenance vehicles. (Note:This infeasibility criterion does not extend to sidewalks and other non- traffic bearing surfaces associated with the collector or arterial). City of Everett Public Works Small Project Stormwater Site Plan Report-Dec 2019 32