6101 23RD DR W NORPRO 2025-07-29

Response: Runoff treatment will be provided for the main site portion of the Powdermill Gulch Creek drainage basin by a Stormfilter downstream of a pre-settling structure. The small parking lot area in the southern portion of the existing development that is also tributary to Powdermill Gulch Creek will receive runoff treatment via a single cartridge Storm Filter Catchbasin. The Narbeck Creek basin will receive runoff from roof drainage and non-pollution generating landscape area only. Therefore there will be no pollution generating surface within the threshold discharge area that requires water quality treatment. Minimum Requirement#7: Flow Control Projects must provide flow control to reduce the impacts of stormwater runoff from impervious surfaces and land cover conversions. The requirement applies to projects that discharge stormwater directly or indirectly through a conveyance system, into a fresh water. Response: Powdermill Gulch Creek basin —As discussed in the Basin Summary section of the Project Overview, no onsite flow control is required. Narbeck Creek basin — Per correspondence with the City of Everett on July 14, 2011, if the impervious area within the Narbeck Creek basin is limited to less than 10,000'square feet, the flow control facility may be sized utilizing a single-event model such as SBUH. Flow control for the Narbeck Creek basin will be provided in a detention tank designed utilizing SBUH methodology. ' Minimum Requirement#8: Wetlands Protection These requirements apply only to projects whose stormwater discharges into a wetland, either directly or indirectly through a conveyance system. These requirements must be met in addition to meeting Minimum Requirement#6, Runoff Treatment. Response: There are no wetlands within the limits of disturbance onsite. Narbeck Creek is located ' in the eastern portion of the site; however, neither the creek nor the slopes above the creek will be disturbed as part of this project. Runoff tributary to Narbeck Creek will be routed to an existing outfall to the creek to the north of the site; therefore, no construction is proposed within the creek's buffer. Minimum Requirement Operation nd Maintenance u #9: a A Maintenance Plan that is consistent with the provisions in the manual shall be provided for all proposed stormwater facilities and BMPs for projects that exceed the thresholds in Chapter 2.1. The party (or parties) responsible for operation and maintenance shall be identified in the Maintenance Plan. At private facilities, a copy of the Maintenance Plan shall be retained on-site or ' within reasonable access to the site, and shall be transferred with the property to subsequent owners. For public facilities, a copy of the Maintenance Plan shall be retained in the appropriate department. A tracking system (e.g., log) of maintenance activity that indicates what actions were taken shall be kept and be available for inspection by the City. Response:See the Operation and Maintenance Manual provided in this report. 1 1 6/16/2011 Stormwater Site Plan Page 9