6522 WETMORE AVE 2025-08-19 - Laserfiche WebLink

SECTION III: SITE DEVELOPMENT PLAN W/ON-SITE STORMWATER MANAGEMENT The site for Maverick 2 contains 0.39 Acres. The site is currently developed with a home with a detached garage, shed and a gravel driveway from Wetmore Ave. The remainder of the site exists as lawn and native vegetation. The site contains one drainage basin that that slopes slightly to the east. Please refer to the downstream analysis map for more details. Per NRCS survey of Snohomish County, the project site contains Alderwood soils that have a hydrologic classification of Type "C". Please refer to the soils map and descriptions attached in this report for more details. The proposal for the project is to subdivide the site into two lots and build a new garage on Lot I and a new single-family residence on Lot 2 with associated utilities. The access to this site will be from Wetmore Ave. The proposal also includes frontage improvements along Wetmore Ave. Per Figure I-3.1, (flow chart for new development requirements) Volume I SWMMWW, Minimum requirements #1 through 9 shall apply for this project. See Minimum Requirements Summary included later in this report. Flow control requirements are exempt for this project because it will not convert 3/4 acres of native vegetation to lawn, the new effective impervious area is only 3,823 SF, which is less than the threshold of 5,000 SF, and the 100-year flow frequency increase is 0.02 cfs, which is less than the threshold of 0.15 cfs. Water quality is exempt for the project because the proposed PGIS is only 2,175 SF, which is less than the threshold of 5,000 SF. Per Minimum Requirement #5 (Section I-3.4.5 of the SWMMWW), the following NPGIS BMPs shall be applied to provide onsite stormwater management and must be considered in the following order per List #2: Full Dispersion, Infiltration, Bioretention, Basic Dispersion, and then Perforated Stub -Out Connections. Full Dispersion is infeasible because the required native vegetation preservation could not be achieved for the LDMR zoned project. Full Infiltration is also not feasible as the design infiltration rate is only 0.21 in/hr which is less than the recommended 0.3 in/hr. Also, Glacial Till was observed at 1.5- Insight Engineering Co. — Stormwater Site Plan 05/31/2022 -12-