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

Thad Newport May 6,2019 2180406.10 .. ge3of6 treatment.The facility is sized to treat 91%of the influent runoff from the pollution generating surfaces. 6. 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 facility.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 check 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. Response: Based on a conversation between StormTech and the City, it has been determined that pretreatment is not required upstream of the chamber facility. Therefore, pretreatment is not provided. Regarding the close proximity to an existing rockery and neighboring structure, the chamber system will be lined with an impermeable liner to prevent significant infiltration. Regarding the "old" drainage system, chambers have been moved to provide more clearance to the existing system. Notes have been added to field verify the existing system and to protect as necessary. 7. 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 operations manual shall be retained on-site or within reasonable access to the site and shall be transferred with the property to any new owner. A log of maintenance activities that indicate what actions were taken shall be kept and available for inspection by the City of Everett upon request.