2235 LAKE HEIGHTS DR 2020-12-23 - Laserfiche WebLink

• PUBLIC WORKS Compliance with BMP T5.13 is required and must be referenced in the report. MR#6—Runoff Treatment: Enhanced stormwater treatment is required for this project, which StoiiiiFilters do not provide. The City requires a GULD rating from Ecology for the level of stormwater treatment proposed with any proprietary device. Additional information can be found on Ecology's website at the following web address: https://ecology.wa.gov/Regulations-Permits/Guidance-technical- assistance/Stormwater-permittee-guidance-resources/Emerging-stormwater- treatment-technologies The most current GULD approval from Ecology must be included in the Stormwater Site Plan if a proprietary device is used. This inclusion allows the City to go back and find out what Ecology's requirements were at the time of design if issues come up in the future. If the GULD requires the manufacturer to approve each device design or the project's site plan, the City will require a project-specific letter from the manufacturer which acknowledges their review and approval. MR#7—Flow Control: Ecology approved pretreatment is required upstream of the StormTech stormwater chamber detention system. The City's Surface Water Management group has determined that Ecology approved pretreatment for sediment removal must be provided upstream of stormwater detention systems such as StormTech stormwater chamber systems, in order for these facilities to be deemed equivalent to detention vaults or pipes. This pretreatment is required because these alternate systems provide much less access to the system and ability to remove accumulated sediment than vaults or pipes. Given the location of the proposed detention system, and its proximity to the property line, rockery, and building on the adjacent property, this detention system must be lined to prevent significant infiltration—please see Section 9 of the StormTech design manual for more information. A leak test of the system will be required. There is a rockery located along the western property line,just to the west of the storm chamber system. In addition, there is a portion of the "old" drainage system, which includes two footing drains, which may still be connected to the original outlet from this site's original stormwater facilities. This portion of the system is located at the northwest corner of the proposed storm chamber system and is shown on the Area B demolition plan. The original discharge from the site is to a catch basin on the adjacent property to the west,through a private drainage easement. See the attached drawings for reference. This portion of the system needs to be checked to see if it's still a functioning part of the site's drainage system, and its location needs to be considered in the design/placement of the detention system. MR#9—Operation and Maintenance: The maintenance and operation information for the stormwater facilities needs to be provided in a separate document entitled "Maintenance and Operations Manual", and it must include a first page indicating the party responsible for maintenance and operation. In addition, the following language shall also be included in both the M&O manual and the drainage report: A copy of the maintenance and Page 3 of 5