11500 SILVER LAKE RD 2025-04-21 - Laserfiche WebLink

BMP and Infeasibility description applicable lisp Infeasibility criteria and rationale for each BMP not selected T515 The fallowing criteria can the cited as reasons for infeasibility without No existing hard Permeable furtherjustification(though some require professional services to Pavement make the observation): Surfaces are (continuer) ❑ Where the site cannot reasonably be designed to have: proposed to be impacted and • Porous asphalt surface < 5% slope infiltration BMPs • Pervious concrete surfaces 10%slope • Permeable interlocking concrete pavement surface<12% are not slope recommended, • Grid systems <6-12% slope (check with manufacturer see previous and local supplier to confirm maximum slope) comments. ❑ Where the subgrade soils below a pollution-genemting 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 national 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 0.3Inches 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 lowtruck 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 "me 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 cracks, 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 aNerial). City of Everett Public Works Small Project Stormwater Site Plan Report Dan 2019