5900 36TH AVE W PRE APP 015 - 032 - SOUNDVIEW BUSINESS CAMPUS - VERITAS Drainage Report 2025-04-22

SOUNDVIEW TECHNOLOGY CENTER EVERETT, WA Response: A stormwater site plan has been prepared for the development. The stormwater site plan includes the design drawings and this report. Minimum Requirement #2: Construction Stormwater Pollution Prevention (SWPP) All new development and redevelopment projects are responsible for preventing erosion and discharge sediment and other pollutants into the receiving waters. Projects in which the new, replaced, or new plus replaced impervious surfaces total 2,000 square feet or more, or disturb 7,000 square feet or more of land must prepare a Construction SWPP Plan (SWPPP) as part of the Stormwater Site Plan. Each of the twelve elements must be considered and included in the Construction SWPPP unless site conditions render the element unnecessary and the exemption from that element is clearly justified in the narrative of the SWPPP. Response: The 72 elements of a SWPP are addressed in the Construction SWPP section of this report. A full Construction SWPP will be prepared for the site before construction begins. Minimum Requirement #3: Pollution Source Control All known, available and reasonable source control BMPs shall be applied to all projects. Source control BMPs shall be selected, designed, and maintained according to Volume IV of the manual. Response: All available and reasonable source control BMPs have been applied to this project. These include, but are not limited to, Dust Control at Disturbed Land Areas, Landscaping and Lawn/Vegetation Management, and Maintenance of Stormwater Drainage and Treatment Systems. Minimum Requirement #4: Natural Drainage Systems and Outfalls Preservation Natural drainage patterns shall be maintained, and discharges from the project site shall occur at the natural location, to the maximum extent practicable. The manner by which runoff is discharged from the project site must not cause a significant adverse impact to downstream receiving waters and downgradient properties. All outfalls require energy dissipation. Response: Runoff from the proposed project will discharge to a new on -site conveyance systems that will outlet into 4 separate basins (Vault #2 discharging to basin A, Vault #3&5 discharging to basin B, Vault #4 discharging to basin C, and Storm Chamber System #7 to basin D). Stormwater will be dispersed at outlets A, B, and C through a level spreader, outlet D will be directed into an existing drainage channel through a rock pad. The upstream basins tributary to the site will be collected in a swale and concrete channel that is connected to the same basin outfalls (A & D). Minimum Requirement #5: On -site Stormwater Management Projects shall employ On -site Stormwater Management BMPs to infiltrate, disperse, and retain stormwater runoff onsite to the maximum extent feasible without causing flooding or erosion impacts. Roof Downspout Control BMPs, functionally equivalent to those described in Chapter 3 of Volume III, and Dispersion and Soil Quality BMPs, functionally equivalent to those in Chapter 5 of Volume V, shall be required to reduce the hydrologic disruption of developed sites. Projects shall use Ecology's 2014 Stormwater Management Manual for Western Washington: Volume I of Section 2.5.5, Chapter 3 of Volume III, and Chapter 5 of Volume V to determine which on -site stormwater management BMPs shall be employed on a particular project site, and document that determination in the drainage report. Response: On -site stormwater runoff will be collected and transported via a system of catch basins and underground storm pipes to one of five detention vaults. All of the stormwater is being collected, detained, treated, and released. The detained stormwater will be control -released from the vaults at the historical discharge rate. See below for the Flow Chart for Determining LID MR #5 Requirements. MAY 23, 2017 STORMWATER DRAINAGE REPORT PAGE 4 1