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NOT NEEDED BLD2024-0519+Storm_Drainage_Report+4.17.2024_3.49.32_PM+4203417=JC JACOBSON ENGINEERING REPORT Storm Drainage Report Edmonds School District Woodway Center Campus Portable Placement 9521 240t" ST SW Edmonds, WA 98020 March 26, 2024 Prepared for Edmonds School District 20420 68' Ave W Lynnwood, WA 98036 Prepared through Hutteball + Oremus Architecture 4010 Lake Washington Blvd NE #320 Kirkland, WA 98033 Prepared by Jacobson Consulting Engineers Sascha Eastman 206.426.2600 sascha@jacobsonengineers.com 255 S. King Street, Suite 800, Seattle, WA 98104 1 206.426.2600 1 JACOBSONENGINEERS.COM Storm Drainage Report for WOODWAY CENTER CAMPUS PORTABLE PLACEMENT JACOBSON mi Im CO NSU LTIN G ENGINEERS Project No. C230008-0180 March 26, 2024 TABLE OF CONTENTS I. PROJECT OVERVIEW............................................................................................................. 2 GENERAL DESCRIPTION.. EXISTING CONDITIONS..... PROPOSED CONDITIONS. 2 2 2 II. DRAINAGE ANALYSIS............................................................................................................ 3 EXISTING SITE HYDROLOGY...............................................................................................................3 DEVELOPED SITE HYDROLOGY.........................................................................................................3 UPSTREAMANALYSIS..........................................................................................................................4 DOWNSTREAM ANALYSIS....................................................................................................................4 III. DISCUSSION OF MINIMUM REQUIREMENTS.......................................................................... 4 MR 1: PREPARATION OF STORMWATER SITE PLANS....................................................................4 MR 2: STORWMATER POLLUTION PREVENTION PLAN (SWPPP).................................................4 IV. TEMPORARY EROSION AND SEDIMENT CONTROL.................................................................. 6 APPENDICES Appendix A Figures WOODWAY CENTER CAMPUS PORTABLE PLACEMENT PROJECT OVERVIEW GENERAL DESCRIPTION The following Drainage Report provides the design analysis for the Woodway Center Campus Portable Placement project. The stormwater design for the project was based on the requirements set forth in the 2019 Washington State Department of Ecology Stormwater Management Manual for Western Washington (2019 WSDOE SWMMWW) as adopted by the City of Edmonds. The Woodway Elementary School Portable Placement project is located at 9521 2401h ST SW, Edmonds, WA 98020 (see Appendix A Figure 1, Vicinity Map). The project site area is located in the NE corner of the existing asphalt play surfacing and north side of the existing classroom buildings (Parcel #27033600404600) on the north side of the school campus (see civil plan sheet C2.00, CIVIL SITE PLAN). The property is bounded by 240" ST SW to the south, and residential properties to the west, east, and north. The site is in the southeast quarter of Section 36, Township 27 North, Range 3 East, Willamette Meridian. The project's limits of disturbed area within the property boundary is approximately 1,996 square feet (-0.05 acres). See Developed Site Hydrology in Section II below. The project proposes to relocate (1) one existing portable building currently located at the school district's Oak Heights Elementary School campus, to Woodway Center Campus, north of the existing (3) three portables on the north side of the campus in the southeast corner of the existing playfield. Work will consist of installing new concrete foundations for the portables, gravel pads/landings for stairs and accessible ramps as required, and metal grated landings, ramps, and stairs. Storm drainage for the proposed portables will consist of a building downspout that will discharge stormwater onto a splash block, which will then sheet flow across the grass on the south side of portable building and onto the existing asphalt play surfacing and will eventually drain to a catch basin located approximately 150-ft to the south, maintaining the natural drainage course for this area (see civil plan sheet C2.00, CIVIL SITE PLAN). EXISTING CONDITIONS The existing Woodway Center Campus property (Parcel #27033600404600) is currently developed with a school building in the middle of the campus, asphalt and soft surface play surfacing on the west and north sides of the school building, asphalt parking lots to the south and southeast sides of the campus, concrete sidewalks, and playfield to the north. There is native vegetation and forested areas along the west and east sides of the property. The location of the proposed portable placement project is located north of the existing school building and north of the existing (3) three portables in the SE corner of the existing playfield. The project site currently sheet flows stormwater from the northeast to southwest direction across the asphalt play surfacing and collects the stormwater in existing catch basins located along the south side of the asphalt play area and conveys the stormwater to the west via a 6-inch piped storm drain system. See Proposed Conditions discussion below. PROPOSED CONDITIONS The project proposes to relocate (1) one existing portable building currently located at the school district's Oak Heights Elementary School campus, to the Woodway Center Campus, north of the existing (3) three portables on the north side of the campus in the southeast corner of the existing playfield. Work will consist of installing new concrete foundations for the portables, gravel pads/landings for stairs and accessible ramps as required, and metal grated landings, ramps, and stairs. Storm drainage for the proposed portables will consist of a building downspout that will discharge stormwater onto a splash block that will that will discharge stormwater onto a splash block, which will then sheet flow across the grass on the south side of portable building and onto the existing asphalt play surfacing and will eventually drain to a catch basin located approximately 150-ft to the south, maintaining the natural drainage course for this area. =iC JACOBSORN WOODWAY CENTER CAMPUS PORTABLE PLACEMENT II. DRAINAGE ANALYSIS EXISTING SITE HYDROLOGY The existing project limits area is approximately 1,996 square feet or —0.05 acres, with roughly 1,635 square feet of area being disturbed for the portable to install the concrete foundation, gravel pads/landings for stair and accessible ramps, as well as proposed downspout and splashblock. Power and communications, including fire alarm for proposed portable, will be fed aerial from the existing utility pole located near the SE corner of the portable building. The downspout and splashblock will be installed on the south side of building at the SW corner. Most of the project site where the proposed classroom portable will be installed is grass (pervious). Stormwater runoff is generally conveyed via sheet flow from the northeast to the southwest direction and collected in existing catch basins located along the south side of the asphalt play area. See civil plan sheet C1.00, DEMOLITION AD TESC PLAN, which indicates the land cover characteristics of the existing project site. DEVELOPED SITE HYDROLOGY The project proposes to relocate (1) one existing portable building currently located at the school district's Oak Heights Elementary School campus, to the Woodway Center Campus, north of the existing (3) three portables on the north side of the campus in the southeast corner of the existing playfield. Work will consist of installing new concrete foundations for the portables, gravel pads/landings for stairs and accessible ramps as required, and metal grated landings, ramps, and stairs. Storm drainage for the proposed portables will consist of a building downspout that will discharge stormwater onto a splash block that will that will discharge stormwater onto a splash block, which will then sheet flow across the grass on the south side of portable building and onto the existing asphalt play surfacing and will eventually drain to a catch basin located approximately 150-ft to the south, maintaining the natural drainage course for this area. See civil plan sheet C2.00, CIVIL SITE PLAN. Table 1 below summarizes the land cover characteristics of the proposed redevelopment (see Appendix A Figure 3, New + Replaced Impervious Areas). TABLE 1 — DEVELOPED PROJECT SITE CONDITIONS Land Cover Impervious Area (sf) Pervious Area (sf) Total (sf) New + Replaced Roof 1,635 0 New + Replaced Gravel 32 0 Metal Ramps/Stairs/Landings *329 Total New & Replaced Hard Surface *1,996 0 Landscaping (Grass Restoration) 0 0 Total Site *1,996 0 1,996 % of Site 100% 0.0% 100% From Table 1 above, 1,996 square feet of new + replaced impervious surface represents new gravel pads/landings for stairs and accessible ramps, as well as proposed portable building roof. The metal ramps, stairs, and landings, per drainage code, can be considered 50% impervious and 50% pervious. This results in a revised new hard + replaced impervious surface area of 1,832 square feet. Since the project will add less than 2,000 square feet of new plus replaced hard surface, it is therefore required to only evaluate minimum requirements (MR) 1 & 2 per Volume 1 Figure 1-3.2 of the DOE Stormwater Management Manual for Western Washington (see Appendix A Figure 2, Project Minimum Requirements Flow Chart). The project will also not be subject to flow control and runoff treatment requirements. Both MR#1 and MR#2 will be addressed below in Section III of this report. =iC JACOBSORN WOODWAY CENTER CAMPUS PORTABLE PLACEMENT UPSTREAM ANALYSIS Stormwater runoff for the project site will continue to sheet flow across the site from approximately north to south and be drained to the existing catch basin located approximately 150-ft to the south that then conveys the stormwater south through a series of 6-inch storm pipes located on the west side of the existing campus, maintaining its current drainage course. DOWNSTREAM ANALYSIS The project will maintain existing threshold points of discharge with stormwater runoff continuing to mimic the existing drainage path and sheet flow stormwater across the project site where it will be collected and conveyed in a series of catch basins located on the south side of the existing asphalt play surfacing. The project will create 1,831 square feet of new hard + replaced impervious surface and does not anticipate any adverse effects to the existing downstream storm system because of the proposed site improvements. In addition, there are no known drainage concerns downstream of the proposed project site. III. DISCUSSION OF MINIMUM REQUIREMENTS The 2019 DOE Stormwater Management Manual for Western Washington references Figure 1-3.2 (Flow Chart for Determining Requirements for Redevelopment), as the method to determine which Minimum Requirements are required to be addressed for the proposed project redevelopment (see appendix A Figure 2, Project Minimum Requirements Flow Chart). The proposed Edmonds-Woodway High School Portable Placement project will install less than 2,000 square feet of new + replaced hard surface and does not result in land disturbing activity of 7,000 square feet or greater. As a result, the project will therefore only will be subject to Minimum Requirements 1 & 2 for the new and replaced hard surfaces and all disturbed land. In addition, per section 1-3.4.2 of Volume 1 of the Stormwater Management Manual, the project is "not required to prepare a Construction SWPPP, but must consider all of the Construction SWPPP listed below (in MR 2) and develop controls for all Construction SWPPP Elements that pertain to the site". A discussion of these Minimum requirements is discussed in the following sections: MR 1: PREPARATION OF STORMWATER SITE PLANS Project shall provide Concurrence and Coordinated Civil Plans in accordance with all local requirements. A Storm Water Site Plan drainage report has been prepared for this project and conforms to the requirements set forth in the 2019 SWMMWW Section III-3. MR 2: STORWMATER POLLUTION PREVENTION PLAN (SWPPP) The project is not required to prepare a Construction SWPPP, but must address all 13 Elements of the CWWPP. A breakdown of each element of the SWPPP is provided below: Element 1: Preserve Vegetation / Mark Clearing Limits Clearing Limits are noted on plans and will be implemented prior to any offsite impacts or damage due to construction. b. Element 2: Establish Construction Access The Contractor, per the plans, shall implement necessary BMP measures to ensure sediment does not leave site onto streets or adjacent properties. The existing asphalt play surfacing and fire lane to the south-southwest of the project site shall be utilized to mitigate sediment laden stormwater or sediment and debris from leaving the site. JC JACOBSON WOODWAY CENTER CAMPUS PORTABLE PLACEMENT C. Element 3: Control Flow Rates Flow rates from the project site will be controlled through a series of BMPs, including, but not limited to, Straw Wattles and Catch Basin Protection. d. Element 4: Install Sediment Controls Sediment removal BMPs shall be implemented, and are anticipated per plans, to include, but not limited to, Straw Wattles and Catch Basin Protection. e. Element 5: Stabilize Soils Soils shall be stabilized through a series of BMPs. Typical stabilization methods are temporary seeding, mulching, and providing temporary "hog fuel" during wet weather work, and dust control during drier weather conditions. f. Element 6: Protect Slopes All slopes will incorporate the applicable BMPs per the plans and as required during construction, as field conditions dictate. BMPs such as plastic sheeting, slope roughening, and compost blanket, could be utilized where appropriate and as applicable. g. Element 7: Protect Permanent Drain Inlets Existing drains shall be protected with Catch Basin Protection where applicable throughout the project site. h. Element 8: Stabilize Channels and Outlets Channels and outlets shall be protected and stabilized where applicable throughout the project site. i. Element 9: Control Pollutants BMPs shall be implemented to prevent or treat contamination of stormwater runoff by pH modifying sources. In addition, all waste materials from the site will be removed in a manner that does not cause contamination of stormwater runoff. j. Element 10: Control De -Watering No De -Watering is anticipated as part of this project. k. Element 11: Maintain Best Management Practices (BMPs) BMPs indicated on plans shall be maintained and supplemented as needed throughout the project. As portions of the project get completed, portions of the established BMPs shall be adjusted to other areas of the project site until their completion. I. Element 12: Manage the Project The contractor / owner will employ a project CESCL to manage the site and ensure construction BMP's are properly implemented and maintained. M. Element 13: Protect On -Site Stormwater Management BMPs for Runoff from Roofs and Other Hard Surfaces The project will protect the Stormwater BMPs proposed for the project site until the site is stabi I ized. miC JACOBSON WOODWAY CENTER CAMPUS PORTABLE PLACEMENT IV. TEMPORARY EROSION AND SEDIMENT CONTROL Erosion control systems will be implemented throughout the construction process until the site is stabilized. All temporary erosion and sedimentation control requirements will follow the Department of Ecology (DOE) Best Management Practices (BMPs). Best Management Practices are defined as physical, structural, and/or managerial practices, that when used singly or in combination, prevent or reduce pollution of storm water runoff caused by construction activities. The Temporary Erosion and Sedimentation Control plan for the proposed site has been designed to protect off -site properties, as well as to prevent sediment -laden water from entering the public storm system. Additional information of the BMPs implemented for the project and locations on -site can be found on the civil engineering plans (see civil plan sheet C1.00, DEMOLITION AND TESC PLAN). miC JACOBSON WOODWAY CENTER CAMPUS PORTABLE PLACEMENT Appendix A — Figures =iC JACOBSORN �C JACOBSON Project Site PCC Community Markets - Edmonds W E S T G A T E 19 ©Sherwood Elementary School SHERWOOD FOREST 238th St SW Elementary 0 0 F FIROALE VILI Project Site n z F 244th St S. H I L L W 0 0 D P Safeway < F Petco Dog Grooming_ --_ Holyrood Catholic C S `n Q Costco Wholesale = FIGURE 1: VICINITY MAP SCALE: NTS r - -I- 255 S. King Street, Suite 800, Seattle, WA 98104 1 206.426.2600 1 JACOBSONENGINEERS.COM Figure 1-3.2: Flow Chart for Determining Requirements for Redevelopment Does the Project result in 2,000 square feet, or more, of new plus replaced hard surface area? OR Does the land disturbing activity total 7,000 square feet or greater? Yes No Minimum Requirements #1 through #5 apply to the new and replaced hard Minimum Requirement #2 applies. surfaces and the land disturbed. Next Question Does the Project add 5,000 square feet or more of new hard surfaces? OR Convert % acres or more of vegetation to lawn or landscaped areas? OR Convert 2.5 acres or more of native vegetation to pasture? Yes All Minimum Requirements apply to the new hard surfaces and the converted vegetation areas. No Next Question Is this a road related project? Yes LM Does the Project add 5,000 square feet or more of new hard surfaces? Yes No Is the total of new plus replaced hard surfaces 5,000 square feet or more, Do the new hard AND surfaces add 50% or does the value of the proposed improvements - No No additional No including interior improvements - exceed 50% of the more to the existing assessed value or replacement value of the: hard surfaces within requirements. ( P ) the Site? • existing Project Site improvements (for commercial or industrial projects) OR • existing Site improvements (for all other projects) Yes All Minimum Requirements apply to the new and replaced hard surfaces and converted vegetation areas. Yes Flow Chart for Determining Requirements for Redevelopment Revised March 2019 DEPARTMENT OF ECOLOGYPlease see http://www.ecy.wa.go✓%opyright.html for copyright notice including permissions, State of Washington limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington FIGURE 2: PROJECT MINIMUM REQUIREMENTS FLOW CHART SOUTHEAST 1/4 OF SECTION 36, TOWNSHIP 27 NORTH, RANGE 03 EAST, W.M. CB TYPT i� RIM 1I;361.6/' 12"CYP(NL) 17"C', P(S) IT: 357 6' / BTM:356.7' i * i +, c i I NOTE: KEYNOTES' CONTRACTOR SHALL UTILIZE RAMP uNDmc EX ASPHALT PLAY FOR STAGING AND LAVDOWN. COORDINATE WITH OWNER \ PRIOR TO STARTING CONSTRUCTION. \ STAIRS \ r 62.T�IEKI 6 3632<, �i II �� I✓oC� clot PLAY 3.� 10', AGADMLOARTNDBINLaG6a.1 �RM '71T)T/ MANUFACTURER _•.-,- L _ HANDRAIL s3o IEV _ IXPLAYFIELD \ as2.si�crl 36 3-1 g� \ I; -- 7 b b a522a(L� ysa.2<gLW EDGE OFIX b —_ d��`�'/(1VI - -- - - — ASPHALT LIY� —1 �wA2- � ILL 'L PROTECT EX ASPHALT - /y "��� I � IX PLAYGROUND I I New/Replaced Impervious Areas:\ Y Description Quantity Unit \ \ ------------, CB TYPE 6''DI(SW) WIELBOW IE:361 BTM:35e PROPOSED ) / PORTABLE FFE 364.80 -36325(EY� GRATED METAL LANDING AND STAIRS PER PORTABLE ' MANUFACTURER Fiti w (CUTTOFIDATDOWNSPOUF \ SEE DETAIL 13 7I CP' �IrC EX PORTABLE BUILDING ROOF (NEW + REPLACED IMPERVIOUS) GRAVEL (NEW + REPLACED IMPERVIOUS) 1,635 32 sf sf _ METAL RAMP/STAIRS (OVER REPLACED PERVIOUS) *329 Sf PROTECT EX METAL PROTECT RAM PAND LANDING \ PORTABLES / Y _* GRASS EXCLUDED FROM TOTAL IMPERVIOUS Total 1,832 Sf a p METAL KAMP AREA CALCULATION; METAL RAMPS 50% \ /WALKWAY\ A � \ IMPERVIOUS PER DRAINAGE CODE ,PPS j, /a v 7W�d (nI��WAY I APTA �V6N,1 11 � r =\y /r l/ 0 T_Ib /v III`\'% —PLAYCLOUNJ I \/ \ e EXASPHALT PLAY SDMH - � /FIRE LANE '-- ) / / L35770" - RIME . 4"DI W/ELBOW(SJ E35E _-- \ ,_ yN / METAL RAMP 7 -- A,-_- �/ BTM:354.4' `v / WALKWAY �- - (4)RISERS_------ Ar5 ]" EACH L 5X5'GRAVELAND NG PA SEE DEf14LD ---------------- PROTECT IX POWER I POLE AND OVERHEADI II l l l POWER LINES TO REMgI E I I IXPORTABLE RESTORE a I I I I AREA WITH HV MINIMUM FOR I !rI BACKSTOP FEP COORDINATE / 1 STORY WOOD / PORTABLE \ \ \ vI-- -- -- EA VE IX PORTABLE %A 7 STORY WOOD z PORTABLE 3V / IXPLAVGROUND _ / PLAYG OUND � \ s E UIP -'SDC:1 --3�/---� / /------=----_-- --- - --- --- --- -- - - r ----- _ - —_ j WOOD RET VALL P Q�r o 'a SD SDCO PAVE a f : 0o na IXCASSRGOM 6"CRW IP < 6"CRW \ SDCO SG�pE" CO SIXoRLassRGOM EA CONC BLDG BUILDING N NO I I Ao I 6 'I LOCATABLE SGNAL a I ® Call before you D g�B-I-I 0 51- t� u SCALE 1"=10' is Leaend PROPERTY LINE CONCRETE PAVEMENT STORM DRAINAGE PIPE YD/CO/CB/CB 2/MH GRATED STAIRS/RAMPS GRAVEL PAD NOTE: SHEET HAS BEEN PRINTED TO BE 11 X1 7 AND NOT TO SCALE fiWERA IMM 4010IAKE WASHINGTON BLVD NE SUITE320 KIBNNND, WA 98033 425.828.8948 HOARCH.COM e'/./- .JIM JACOBSON Woodway Center Portable Placement 2024 EDMONDS SCHOOL DISTRICT No. 15 Al Edmonds School District PERMIT SET CIVIL SITE PLAN I FIGURE 3: DISTURBED AREA MAP