5900 36TH AVE W PRE APP 015 - 032 - SOUNDVIEW BUSINESS CAMPUS - VERITAS O&M Manual 2025-04-17

I 4. Ecology approves the MWS - Linear Modular Wetland Stormwater Treatment System units for Basic, Phosphorus, and Enhanced treatment at the hydraulic loading rate listed above. Designers shall calculate the water quality design flow rates using the following procedures: • Western Washington: For treatment installed upstream of detention or retention, the water quality design flow rate is the peak 15-minute flow rate as calculated using the latest version of the Western Washington Hydrology Model or other Ecology-approved continuous runoff model. • Eastern Washington: For treatment installed upstream of detention or retention, the I water quality design flow rate is the peak 15-minute flow rate as calculated using one of the three methods described in Chapter 2.2.5 of the Stormwater Management Manual for Eastern Washington (SWMMEW) or local manual. I • Entire State: For treatment installed downstream of detention, the water quality design flow rate is the full 2-year release rate of the detention facility. 5. These use level designations have no expiration date but may be revoked or amended by Ecology, and are subject to the conditions specified below. Ecology's Conditions of Use: Applicants shall comply with the following conditions: 1. Design, assemble, install, operate, and maintain the MWS —Linear Modular Wetland I Stormwater Treatment System units, in accordance with Modular Wetland Systems, Inc. applicable manuals and documents and the Ecology Decision. 2. Each site plan must undergo Modular Wetland Systems, Inc. review and approval before site installation. This ensures that site grading and slope are appropriate for use of a MWS —Linear Modular Wetland Stormwater Treatment System unit. 1 3. MWS—Linear Modular Wetland Stormwater Treatment System media shall conform to the specifications submitted to, and approved by, Ecology. 4. The applicant tested the MWS—Linear Modular Wetland Stormwater Treatment System with an external bypass weir. This weir limited the depth of water flowing through the media, and therefore the active treatment area, to below the root zone of the plants. This I GULD applies to MWS — Linear Modular Wetland Stormwater Treatment Systems whether plants are included in the final product or not. 5. Maintenance: The required maintenance interval for stormwater treatment devices is often dependent upon the degree of pollutant loading from a particular drainage basin. Therefore, Ecology does not endorse or recommend a "one size fits all" maintenance cycle for a particular model/size of manufactured filter treatment device. • Typically, Modular Wetland Systems, Inc. designs MWS - Linear Modular Wetland systems for a target prefilter media life of 6 to 12 months. • Indications of the need for maintenance include effluent flow decreasing to below the design flow rate or decrease in treatment below required levels. I • Owners/operators must inspect MWS - Linear Modular Wetland systems for a minimum of twelve months from the start of post-construction operation to determine site-specific I