2631 WALNUT ST JACKSONS 2025-07-28

5.0 PERMANENT STORMWATER CONTROL PLAN A. Existing Site Hydrology To determine if detention was required for this project site, the entire area draining to the ' existing catch basin at the southeast corner was considered in the pre-developed existing condition. This is consistent with the City of Everett Public Works Policy No. 2-11 and WWHM modeling requirements. ' B. Developed Site Hydrology ' Under developed conditions, the vast majority of the site is impervious surface with minor landscaping; however, the amount of impervious surface was not increased. Therefore, detention is not required. Please refer to the flow control sizing criteria on the following pages of this report for the amount and type of land cover used in to model the site basin ' for this project site. C. Performance Standards and Goals ' The performance standard for flow control and water quality is to utilize the WWHM methodology as allowed by the City of Everett Stormwater Management Manual. However, because of City of Everett Public Works Policy No, 2-11, both flow control and water quality are not required for this project. The performance standard utilized for conveyance sizing was the City of Everett Rational Method and all pipes conveyed the 25-year storm event. ' D. Flow Control System As mentioned previously,the flow control is not required. E. Water Quality System ' This project falls within a combined storm sewer system service area. Therefore water quality is not required for this project based on the current City stormwater requirements. F. Conveyance System Analysis and Design As mentioned previously,the conveyance system is based on the City of Everett Rational Method for a 25-year storm event. This is a conservative methodology and creates larger pipes than would actually be required. The conveyance system has been sized and is included on the following pages of this report. 1 1 1 1 ' 16580.007.doc