920 MILLWRIGHT LOOP S BASE FILE 2023-12-29

WATERFRONT PLACE CENTRAL A17 PROJECT SITE —HH SUMMARY PORT OF EVERETT—PSA 1-2015-0OS PND No. 154016-021.02 INTRODUCTION The document is intended to provide a supplemental summary of the proposed A17 project site drainage as it applies to the Warctfiiwt Pare Cmerat (WPCJ Phase 2 and 3—Hydrologm cod Hydraulic Report (2017—POE HH Report), as prepared by END Engineers in December ton. 1. PROJECT DESCRIPTION The A17 project site is pan of the greater WPC development and includes construction of a public restroom and commercial space along the Pon of EvetetPs (Pott) Central Manna Waterfront. Site features will include two public access plaza areas, picnic tables, bike racks, and Flagpoles for the USA, Coast Guard, and Navy. 2. STORMWATER MANAGEMENT The A17 site has progressed in detail significantly from the 2017 - POE HH Report, with the site consisting of five sub -drainage basins. A detailed basin summary map is provided in Attachment 1. • Sub -Basin 1— Consists of 5,700 SF of new hardscape/landsnping and is non -pollution Scanning surfaces (Non PGIS). Drainage from this sub basin will drain to the landscaping on the eastern edge of the A17 parcel where it will be infiltrated into the landscaping or released to directly to the Genteel Marina Basm. • Sub -Basin 2—Consists of 3,072 SF of new hardscapingand is non -pollution generating(Non-PGIS). Drainage from this sub -basin will drain south and discharge directly to the Central Machin Basin. • Sub -Basin 3 — Consists of 2,6W SF of new building roof and is to be collected and discharged to the existing private summoner system Millwright Loop South (MIS). • Sub -Basin 4 — Consists of 1,430 SF of new hardscape/landscaping and is non -pollution generating surfaces (Non-PGIS). Drainage from this sub basin will discharge to the west into the existing Central Marra parking lot where it is collected within an existing perch drain, where it is conveyed and Heated withing the existing MIS stocmwater system. • Sub -Basin 5— Consists of 6" SF of temporary asphalt hadscaping and gavel surfacing. Drainage from this basin generally drains Northwest to South East Millwright Lop where it is conveyed and created within the existing MLS drainage srormwater system. 3. IMPACTS ON THE MLS STORMWATER SYSTEM The 2017 - POE HIT Report delineated 21 separate sub -basins that contribute surface runoff to the MLS stomrwater system totaling 7.76 acres of tributary area. Sub -basin F16 from the 2017 analysis accounted for 0.11 acres of the A17 project site which is to be tributary to the MLS system. • Sub -Basins 3 and 4 equal a roW of 4,070 SF oc approximately 0.093 Acres of area from the A17 site that discharge to the MIS system. • Sub -Basin 5 is accounted for in Sub -Basin Fib from the 2017 analysis. The proposed developed area of A17 that is contributing the MLS system is less than the 2017 area allotted in MLS SubBasinF16 and therefore the prayed site is in compliance with the 2017 conveyance, treatment and backwater analysis for the MLS system. MlEI® 1