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HERRIGSTAD ENGINEERING PS <br /> Civil Engineer <br /> 4320 Whistle Lake Road Dale Herrigstad, P.E. <br /> Anacortes, WA 98221 (360)299-8804 <br /> May 17, 2018 <br /> fl <br /> 1111 <br /> City of Anacortes s <br /> Department of Planning, Community&Economic Development MAY 8 20 <br /> Steven Lange �� <br /> 5th Street. C17°Y OAF�lv/�i.:C3TES <br /> Anacortes, WA 98221 <br /> Subject: High School Accessory Building Drainage Review response <br /> The following is the response to the review by Gray&Osborn, Inc. dated February 12, 2018. <br /> SITE PLAN(EXHIBIT A) COMMENTS <br /> 1. I clarified that the roof drainage is connected to the downstream system in the northeast corner of <br /> the building. • <br /> DRAINAGE ANALYSIS COMMENTS <br /> 2. Clarified that the soils report is"ATTACHMENT D". <br /> Minimum Requirement 1 <br /> 3. Added addition information including referencing the City of Anacortes Stormwater <br /> Management Plan of 2007. <br /> Minimum Requirement 4 <br /> 4. Added flow arrows to the developed site plan as to the flow direction for the new impervious <br /> areas, <br /> Minimum Requirement 5 <br /> 5. Corrected some inadvertent references to previous report and clarified the impracticality of <br /> allowing infiltration above the Middle School Gym. <br /> SWPPP <br /> 6. Agree the silt fence along North side of building would better be served as a construction fence. <br /> 7. I believe the sediment trap is in the best location especially if dewatering is necessary. <br /> 8. I have added a note to consider an interceptor trench but I believe it is likely there is adequate <br /> drainage along the retaining wall for the gym. <br /> 9. Added a note on sheet Cl as to the location of a temporary concrete washout area. <br /> 10. Dewater would be directed to the temporary sediment pond. <br /> 11. The sediment trap is to be sized for the peak 2 year event of.04 cfs. Or 2080 square feet for cfs <br /> inflow. Pond size should be 83 square feet or 9ft x 9ft. This has been added to the drainage <br /> report under Minimum requirement#2 and to the ECS plan. <br /> Please let us know if you need any more information. <br /> Sincerely, <br /> ale Herrigstad PE <br /> dale@herrigstad.com <br />