9600 SHARON DR EXPLORER MIDDLE SCHOOL 2022-03-11

Worksheet 2 Infeasibility Criteria MINIMUM REQUIREMENT #5 On -Site Stormwater Management The following tables summarize infeasibility criteria that can be used to justify not using various on -site stormwater management best management practices (BMPs) for consideration for Minimum Requirement 45. This information is also included under the detailed descriptions of each BMP in the 2019 SWMM but is provided here in this worksheet for additional clarity and efficiency. Where any inconsistencies or lack of clarity exists, the requirements in the main text of the Stormwater Manual shall be applied. Evaluate the feasibility of the BMPs in priority order based on List #1 or #3. Select the first BMP that is considered feasible for each surface type. Document the infeasibility (narrative description and rationale) for each BMP that was not selected. Only one infeasibility criterion needs to be selected for a BMP before evaluating the next BMP on the list. Attach additional pages for supporting information if necessary. BMP and Infeasibility description applicable lists Infeasibility criteria and rationale for each BMP not selected T5.13 ❑ Siting and design criteria provided in BMP T5.13 Postconstruction (Stormwater Manual Volume V, Section 5.3) cannot be achieved. Soil Quality and ❑ Lawn and landscape area is on till slopes greater than 33 percent. Depth BMP and Infeasibility description applicable lists Infeasibility criteria and rationale for each BMP not selected T5.30 ❑ Site setbacks and design criteria provided in BMP T5.30 Full Dispersion (Stormwater Manual Volume V, Section 5.3) cannot be achieved. 0 A 65 to 10 ratio of forested or native vegetation area to impervious area cannot be achieved. ❑ A minimum forested or native vegetation flowpath length of 100 feet (25 feet for sheet flow from a non-native pervious surface) cannot be achieved. T5.10A ❑ Evaluation of infiltration is not required per the Infiltration Downspout Infeasibility Map due to steep slopes, erosion hazards, or Full Infiltration landslide hazards. ❑ Site setbacks and design criteria provided in BMP T5.10A (Stormwater Manual Volume III, Section 3.1.1) cannot be achieved. ❑ The lot(s) or site does not have out -wash or loam soils. * There is not at least 3 feet or more of permeable soil from the proposed final grade to the seasonal high groundwater table, hardpan layer, or other impermeable layer. ❑ There is not at least 1 foot or more of permeable soil from the proposed bottom of the infiltration system to the seasonal high groundwater table, hardpan layer, or other impermeable layer. City of Everett Public Works Small Project Stormwater Site Plan Report -Dec 2079 25