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LBG 38, LLC ES-4011.05 <br /> February 9, 2017 Page 2 <br /> SCDM On-site Stormwater Management <br /> Pursuant to City of Everett stormwater management requirements, implementation of on-site <br /> stormwater BMPs are required for proposed developments in accordance with specified <br /> thresholds, standards, and lists. The intent of BMP implementation is to infiltrate, disperse, and <br /> retain stormwater runoff on site to the extent feasible. We understand the proposed <br /> development intends to add over 5,000 square feet of new hard surface and therefore must <br /> comply with Minimum Requirements (MRs) 1 through 9, as outlined on Pages 42 through 70 of <br /> Volume I of the referenced stormwater manual. MR 5 concerns on-site stormwater <br /> management, and the viability of specific BMPs are to be evaluated for each type of proposed <br /> surface. The table below summarizes our evaluation of the required BMPs for MR 5, as <br /> outlined in the referenced stormwater manual, from a geotechnical standpoint. It is instructed in <br /> the referenced stormwater manual that BMPs are to be considered in the order listed (from top <br /> to bottom) for each surface type, and the first BMP that is determined to be viable should be <br /> used. For completeness, however, we have evaluated each listed BMP for the proposed <br /> surface types. <br /> BMP — - ---— Viable? Limitations or <br /> Infeasibility Criteria <br /> Lawns and Landscaped Areas <br /> This BMP is considered infeasible on <br /> T5.13: Post-construction soil quality and depth till slopes greater than 33 percent. <br /> (Volume V, Chapter 5) Yes However, it is considered feasible <br /> elsewhere on-site. <br /> Roofs <br /> Existing sloped topography and <br /> existing stormwater runoff flooding and <br /> T5.30: Full dispersion (Volume V, Chapter 5) No erosion concerns noted by neighbors <br /> of the subject site indicate infeasibility <br /> of full dispersion. <br /> The unweathered glacial till soil <br /> deposits observed at relatively shallow <br /> T5.10A: Downspout full infiltration systems depths generally exhibit very poor soil <br /> (Volume III, Chapter 3) No infiltration characteristics; the <br /> presence of the unweathered glacial <br /> till soil deposits and sloped topography <br /> indicate infeasibility of full infiltration. <br /> The unweathered glacial till soil <br /> deposits observed at relatively shallow <br /> depths generally exhibit very poor soil <br /> Bioretention (Volume V, Chapter 7) No infiltration characteristics; the <br /> presence of the unweathered glacial <br /> till soil deposits and sloped topography <br /> indicate infeasibility for bioretention. <br /> Earth Solutions NW, LLC <br />