3721 OAKES AVE EVERETT MEMORIAL STADIUM 2018-12-21

iiengine Minimum Requirement#8—Wetlands Protection(MR#8) The project site does not discharge directly to a wetland;therefore,this minimum requirement does not apply. Minimum Requirement#9—Operation and Maintenance(MR#9) An operations and maintenance manual for the proposed drainage systems has been provided in Appendix D of this report. This manual will be kept onsite at the school front office. OFFSITE ANALYSIS The following Offsite Analysis was based on the City of Everett's"MapEverett"interactive mapping tool and the site survey. Stormwater falling upon the existing natural grass baseball field is collected by an existing 4-inch perforated underdrain pipes running northwest-southeast within the outfield footprint.The infield surface is not underdrained. The perforated laterals flow towards 8-inch collector lines running in the center of the field.The collector lines converge at a type-1 catch basin beneath the field surface in centerfield.An outlet conveys flow southeast,connecting to the existing 48-inch combined sewer system.There is a sewer manhole,also located beneath the centerfield surfacing,but based on field investigation,it does not appear that the storm outlet connects to this manhole. The 48-inch combined sewer line takes flow off the site near the northeast corner of the property, eventually a 60-inch system as the sewer system travels west and north.Per City of Everett mapping,this is noted as the Summit Ave Interceptor combined sewer. The northbound sewer system,eventually conveys flow to the Water Pollution Control Facility(WPCF)approximately 3 miles from the site. Refer to Figure 6—Site Discharge Map for layout of existing drainage and sewer system in the proximity of the project disturbance area. PERMANENT STORMWATER CONTROL PLAN As noted above,the project is required to address Minimum Requirements#1 through#9 for the new and replaced hard surfaces and the converted vegetation areas for the project area. Per Policy #2-11,and as described earlier,Minimum Requirement#6 Runoff Treatment is not required. Also as described earlier in the Minimum Requirements Section of this report shown above,the project will not increase the 100-year flow by 0.15 cfs,therefore minimum Requirement#7 is also not required. Pre-developed Site Hydrology Refer to Figure 4—Existing Conditions for a layout of the existing surfacing of the field. See the Offsite Analysis section of this report for more on the existing drainage system. LPD Engineering, PLLC Page 1 Everett Memorial Stadium Baseball Field Replacement Storm Drainage Report, September 15, 2011