3003 W CASINO RD BLDG 40-YD 2019-11-27

Drainage Report—Revision 1 Boeing Everett— Rail Spur Parking Lot September 26,2013 3.1.10 Minimum Requirement#10: Operation and Maintenance The Boeing Company will be responsible for the maintenance of the proposed on-site storm systems. An operation and maintenance schedule for all proposed stormwater facilities and BMPs is included in APPENDIX B of this report. 3.1.11 Minimum Requirement#11:Financial Liability The Boeing Company will be the financially responsible party during the course of the project. A performance bond will not be submitted as part of this project unless it becomes a requirement from the City of Everett. 4. OFF-SITE ANALYSIS Stormwater runoff from the developed site will be conveyed to an existing stormwater detention pond west of Perimeter Road by a series of culverts and drainage swales. As stipulated in Volume I, Chapter I-2, Section I-2.12 of the Stormwater Manual, the downstream drainage system from the site must be inspected for one-quarter mile. Located southwest of the existing site,just outside the security fence, there is an existing Type 1 catch basin with a 12" outlet pipe that runs under Perimeter Road in a westerly direction to the existing water quality swale. The existing Type I catch basin with outlet to the swale is the connection point for the developed site. The outlet pipe spans for approximately 100 feet before it discharges into an existing water quality swale (N-1). N-1 is 8 feet wide and stretches for 230' before a culvert connects N-1 to another drainage swale (N-2). N-2 is connected to a third drainage swale (N-3). N-2 and N-3 span a combined 95 feet. N-3 discharges into a 35,200 cubic foot detention pond. The outlet of the detention pond discharges to swale W-1 which flows west and makes a 90 degree turn when it connects to the northerly flowing swale W-2. Swales W-1 and W-2 have a combined length of approximately 350 feet before a culvert flowing westerly conveys the stormwater to another existing drainage swale that flows in the northerly direction for the extents of the downstream analysis. See Section 5 and APPENDIX F for additional information on the existing drainage features described above. 5. ANALYSIS AND DESIGN OF PROPOSED STORMWATER RUNOFF TREATMENT AND CONTROL Per the requirements in Volume I, Chapter 1-2, Section I-2.4 of the Stormwater Manual, Minimum Requirements #4 (Runoff Treatment BMPs) and #5 (Streambank Erosion Control) must be addressed for this project. However, a 1992 storm drainage report by CH2M Hill titled Storm Drainage Calculations for Rail Receival Facility (Building 40-55) Site Displacement Package—Stormwater Detention Pond and Water Quality Swale Design, attached in APPENDIX F, explains that the central subbasin is included in the 3.3 acre subbasin from which a nearby water quality swale and detention pond were sized for. The water quality swale and detention pond have the capacity (based on the then-current City of Everett requirements) to include the runoff from the developed conditions of the central basin since the pond and swale were sized assuming the central subbasin was comprised entirely of impervious surface. Therefore, the project is exempt from additional runoff treatment BMPs and streambank erosion control measures for the central subbasin. Water quality facilities, however, will be required for the DCG, Inc. Page 5 of 11