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MR 3- Water Pollution Source Control for New Development <br /> This is a typical residential site which typically does not have source control <br /> BMP's that apply to it. None are proposed. <br /> MR 4— Preservation of Natural Drainage Systems and Outfalls, and Provisions <br /> of Off-Site Mitigation <br /> Discharges to the site will continue to,occur as sheetflow. Energy dissipation <br /> is provided in accordance with the DOE SMMWW through BMP T5.12 <br /> (sheetflow dispersal) and BMP T5.10C(Perforated Stub-out. No mitigation for <br /> off-site drainage impacts is required. <br /> MR 5 — On-Site Stormwater Management <br /> The LID BMP selection process included List 1 from the Drainage Manual as <br /> MR6 and MR7 did not apply as noted above. Volume 1 Section 2.5.5. <br /> Applicability states that projects that are flow control exempt from MR7 as set <br /> forth in 2.5.7 do not have to achieve the LID performance standard, nor <br /> consider bioretention, rain gardens, permeable pavement and full dispersion if <br /> using List 1 or 2. They do have to implement BMP T5.13, BMP T5.10 and <br /> BMP T5.12. All of these are being used. <br /> Roof Areas: The site was evaluated for infiltration. The soil is Alderwood- <br /> Urban which can be suited to infiltration. A soil log was dug in the northwest <br /> corner of the site where infiltration could be placed. The soil log showed gravel <br /> in the top 6" and then 8" of hard, brown gravelly sandy silt. Below 14" the soil <br /> remained hard and became moist with iron staining. The soil became very <br /> hard at 30" and I could not dig deeper than 36" with a post hole digger. Thus <br /> the soil is not suitable for infiltration. <br /> Next full dispersion was evaluated. The site has no native vegetation or flow <br /> paths 100' log so the site is not suitable for full dispersion. <br /> Rain gardens and Bioretention also require suitable soils. The soils are not <br /> suitable and per the exemption form MR7 these do not need to be considered. <br /> The requirements for dispersion were investigated but with the available flow <br /> paths and existing slopes to off-site, there are not any areas that can meet the <br /> required flow paths of 50' or 25'. This BMP is not suitable. <br /> The roof areas are being piped through a perforated stub-out to the street <br /> drainage system with BMP T5.10C. <br /> Kravchuk Targeted Drainage Plan Page 8 <br />