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1 <br /> Drainage Report <br /> Boeing Everett-E-6 Parking Lot Expansion July 16,2013 <br /> 3.1 Minimum Requirement#1—Preparation of Stormwater Site Plans <br /> The Stormwater Site Plan was prepared in accordance with Volume 1, Chapter 3 of the <br /> Stormwater Manual and includes the minimum requirements applicable to the site based on <br /> thresholds of new impervious surface coverage. <br /> 3.2 Minimum Requirement#2—Construction Stormwater Pollution Prevention <br /> A Construction Stormwater Pollution Prevention Plan (CSWPPP) was prepared in accordance <br /> with Volume 2, Chapter 2 of the Stormwater Manual. The Temporary Erosion and Sediment <br /> Control Plan (TESC Plan) is attached in APPENDIX C and serves as a guide for the contractor <br /> to implement a final TESC Plan. A Stormwater Permit is required since the site disturbs greater <br /> than one acre and has been prepared by others and submitted under separate cover. <br /> 3.3 Minimum Requirement#3—Source Control of Pollution <br /> A Source Control Plan was developed for the site in accordance with Volume IV of the <br /> Stormwater Manual. See Section 5 for additional source control information and APPENDIX G <br /> for the Source Control Activity Worksheet. The catch basins serve as a source control of <br /> pollution on the project site as their outlet pipes are fitted with a 90-degree downturned elbow to <br /> prevent floating oil and debris from entering the drainage facilities. In order to control pollutants, <br /> proper maintenance and cleaning of debris, sediments, and oil from stormwater collection and <br /> conveyance system is required per the operation and maintenance recommendations found in <br /> APPENDIX B. <br /> 3.4 Minimum Requirement#4—Preservation of Natural Drainage Systems and Outfalls <br /> The proposed collection and conveyance system will direct stormwater runoff to the Powder Mill <br /> Gulch detention/water quality pond north of the Boeing campus. The outlet of the detention pond <br /> is Powder Mill Gulch, which, under the original 1991 Boeing Master Plan prepared for the <br /> Boeing facility, is the receiving water body for the basin encompassing the project site. <br /> 3.5 Minimum Requirement#5—On-Site Stormwater Management <br /> The project analyzed the feasibility of onsite stormwater management BMPs and no feasible <br /> options were available given the physical limitations of the site (i.e., soils). See Section 8.6 for a <br /> conveyance design summary and APPENDIX E for conveyance calculations. <br /> 3.6 Minimum Requirement#6—Runoff Treatment ���� <br /> Per Volume 1, Chapter 2, Section 2.2.6 of the Sto ater Manual, the project requires basic <br /> treatment because the site discharge : : ouna wa er . 1. • 1 be used for parking of employees' <br /> private vehicles. However, since the si e • • • I .er the 1991 Boeing Master Plan as a <br /> tributary area to the existing Powder Mill Gulch detention/water quality pond, the project is not <br /> required to provide treatment prior to discharging to the downstream conveyance system. Basic <br /> treatment requirements will be met by the existing detention/water quality pond to the north of <br /> the Boeing campus. See Section 8.5 for additional water quality exemption information. <br /> 3.7 Minimum Requirement#7—Flow Control <br /> As mentioned in Minimum Requirement #6, the project site is exempt from the flow control <br /> requirements as it was included in the 1991 Boeing Master Plan as tributary area to the Powder <br /> 20130715_Drainage Report Boeing Everett Gate E-6 Parking Lot.doc Page 8 <br /> 1 <br />