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REVIEWED_BLD2021-0503+Storm_Drainage_Report+4.8.2021_9.19.51_AM+2134361�C JACOBSON BLD2O21-0503 ENGINEERING REPORT Storm Drainage Report RECEIVED Apr 08 2021 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT Edmonds School District Woodway Elementary School Portable Placement 9521 240t" ST SW Edmonds, WA 98020 April 7, 2021 Prepared for Edmonds School District 20420 68t" 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@'acobsonen.gineers.com 255 S. King Street, Suite 800, Seattle, WA 98104 1 206.426.2600 1 JACOBSONENGINEERS.COM Storm Drainage Report for WOODWAY ELEMENTARY SCHOOL PORTABLE PLACEMENT DECEIVED Apr 08 2021 CITY OF EDMONDS JACOBSON DEVELOPMENT SERVICES DEPARTMENT mi rm CONSULTING ENGINEERS Project No. C210008-0097 April 7, 2021 TABLE OF CONTENTS I. PROJECT OVERVIEW.................................................................................................................. 2 GENERAL DESCRIPTION......................................................................................................................2 EXISTINGCONDITIONS.........................................................................................................................2 PROPOSEDCONDITIONS.....................................................................................................................2 II. DRAINAGE ANALYSIS................................................................................................................ 3 EXISTINGSITE HYDROLOGY...............................................................................................................3 DEVELOPED SITE HYDROLOGY.........................................................................................................3 UPSTREAM ANALYSIS..........................................................................................................................3 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..................................................................... 5 APPENDICES Appendix A Figures WOODWAY ELEMENTARY SCHOOL PORTABLE PLACEMENT I. PROJECT OVERVIEW RECEIVED Apr 08 2021 CITY OF EDMONDS GDEVELOPMENT SERVICES GENERAL DESCRIPTION DEPARTMENT The following Drainage Report provides the design analysis for the Woodway Elementary School Portable Placement project. The stormwater design for the project was based on the requirements set forth in the 2012 DOE Stormwater Management Manual for Western Washington (Amended 2014) as adopted and amended by the City of Edmonds. The Woodway Elementary School Portable Placement project is located at 9521 240" 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 240th 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 work area within the property boundary is approximately 4,150 square feet (0.10 acres) with approximately 814 square feet of the work area being disturbed. The project proposes to relocate (3) three existing portable buildings currently located on the school district's Spruce Elementary School campus, to Woodway Elementary School. Work will consist of installing new concrete foundations for the portables, asphalt pads/landings for stairs and accessible ramps as required, and metal grated landings, ramps, and stairs. Storm drainage for the new portables will consist of building downspouts that will discharge stormwater onto splash blocks, which will then sheet flow across the existing asphalt play surfacing and be collected in existing catch basins located on the south side of the asphalt play area. *4EdIII fiNtViel►1D7kIII [s] ZR The existing Woodway Elementary School property (Parcel #27033600404600) is currently developed with 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 in the NE corner of the existing asphalt play surfacing area. 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. PROPOSED CONDITIONS The project proposes to relocate (3) three existing portable buildings, currently located on the school district's Spruce Elementary School property, to Woodway Elementary School. Work will consist of installing new concrete foundations for the portables, asphalt pads/landings for stairs and accessible ramps as required, and metal grated landings, ramps, and stairs. Storm drainage for the new portables will consist of building downspouts that will discharge stormwater from the roof onto splash blocks. No additional drainage collection structures are proposed to be installed for this project. Any stormwater runoff will continue to sheet flow across the existing asphalt play surfacing and mimic the existing drainage path and flow into the existing catch basin and piped conveyance system located on the south side of the asphalt play area. =iC JACOBSORN WOODWAY ELEMENTARY SCHOOL PORTABLE PLACEMENT II. DRAINAGE ANALYSIS RECEIVED EXISTING SITE HYDROLOGY Apr 08 2021 CITY OF EDMONDS The existingproject limits area is approximately 4,150 square feet or 0.10 acres, with roughly 814 s ua��eo ENT SERVICES p 1 pp Y q g Y q ARTMSENT ER being actual disturbed area to install concrete portable foundations and asphalt pads for stair and accessible ramp landings. Most of the site is impervious, but approximately 51 square feet of existing grass pervious area will be disturbed and replaced with asphalt or have a portion of the portable building roof overhang over the existing grass area. 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 and TESC Plan, which indicates the land cover characteristics of the existing project site. DEVELOPED SITE HYDROLOGY Proposed site redevelopment will consist of relocating (3) three existing portable buildings, currently located on the school district's Spruce Elementary School property, to Woodway Elementary School. Work will consist of installing new concrete foundations for the portables, asphalt pads/landings for stairs and accessible ramps as required, and metal grated landings, ramps, and stairs. Stormwater runoff from the proposed portable building roof will be discharged onto splash blocks. The stormwater runoff will then continue to sheet flow across the existing asphalt play surfacing and mimic the existing drainage path and flow into the existing catch basin and piped conveyance system located on the south side of the asphalt play area. Table 1 below summarizes the land cover characteristics of the proposed redevelopment (see Appendix A Figure 3, New + Replaced Impervious Areas). TABLE 1 — DEVELOPED SITE CONDITIONS Land Cover Impervious Area (sf) Pervious Area (sf) Total (sf) New Hard Surface 51 0 Replaced Hard Surface 763 0 Total New & Replaced Hard Surface 814 0 Landscaping 0 0 Total Site 814 0 814 % of Site 100.0% 0.0% 100% From Table 1 above, the 51 square feet of new hard surface represents new asphalt landings for stairs and accessible ramps surfaces, and the 651 square feet of replaced hard surface represents replacement of asphalt to install new concrete foundations for the portable buildings. Since the project will add less than 2,000 square feet of new plus replaced hard surface and is therefore required to only evaluate minimum requirements (MR) 1 & 2 per Volume 1 Figure 2.4.2 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. UPSTREAM ANALYSIS Stormwater runoff for the project site will continue to sheet flow across the site from approximately east to west and runoff across the existing asphalt play surfacing. Any upstream flows from the adjacent grass hillside located to the east of the site, will also continue to sheet flow down the hillside and onto the asphalt pavement unimpeded and maintain it's current drainage course. =iC JACOBSORN WOODWAY ELEMENTARY SCHOOL PORTABLE PLACEMENT DOWNSTREAM ANALYSIS RECEIVED The project will maintain existing threshold points of discharge with stormwater runoff continuing to mimjCRQ08 2021 existing drainage path and sheet flow stormwater across the project site where it will be collected and core EDMONDS D L ENT SERVICES in a series of catch basins located on the south side of the asphalt play surfacing area south of project site. D I�TMENT project will only create 51 square feet of new hard 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 2012 DOE Stormwater Management Manual for Western Washington (Amended 2014) references Figure 2.4.2 (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 Woodway Elementary 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 2.5.2 of Volume 1 of the Stormwater Management Manual, the project is "not required to prepare a Construction SWPPP, but must consider all 13 Elements of CSWPP and develop controls for all 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. Civil plans have been prepared for the project. MR 2: STORWMATER POLLUTION PREVENTION PLAN (SWPPP) The project is not required prepare a Construction SWPPP, but must address all 13 Elements of the CSWPP. A breakdown of each element of the SWPPP is provided below: a. 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 parking lot area to the north of the project site shall be utilized to mitigate sediment laden stormwater or sediment and debris from leaving the site. 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, where appropriate, and Catch Basin Protection. d. Element 4: Install Sediment Controls Sediment removal BMPs shall be implemented, and is 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. �C JACOBSON WOODWAY ELEMENTARY SCHOOL PORTABLE PLACEMENT f. Element 6: Protect Slopes RECEIVED All slopes will incorporate the applicable BMPs per the plans and as required during constrUAW08 2021 as field conditions dictate. BMPs such as plastic sheeting, slope roughening, and compost CITY OF EDMONDS blanket, could be utilized where appropriate and as applicable. DEVELOPMENT SERVICES g. Element 7: Protect Permanent Drain Inlets DEPARTMENT 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 stabilized. 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). �C JACOBSON WOODWAY ELEMENTARY SCHOOL PORTABLE PLACEMENT RECEIVED Apr 08 2021 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT Appendix A - Figures min JACOBSORN �C JACOBSON CONSU LTI NO ENGINEERS \\ PCC Community Markets - Edmonds v 4 Sherwood Elementary School o a 104 SHERWOOD FOREST W ay Elementary q FIRDALE VILLAr;, Project Site RECEIVED Apr 08 2021 Project Site a � IJf �5aova j Y Nile Shrine Gt Mth St SW W I 99 %\\ d N xaam St sw Petco Dag'Groaming v — H — --d sa 9 Catholic C aQmn m a ZE IF z vCostcoWhoIesale z H I L L W OO D Ballinger Commons Ir FIGURE 1: VICINITY MAP SCALE: NTS r - -t- 255 S. King Street, Suite 800, Seattle, WA 98104 1 206.426.2600 1 JACOBSONENGINEERS.COM RECEIVED Apr 08 2021 SERVICES 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 Minimum Requirements #1 through #5 apply to Minimum Requirements #2 applies. the new and replaced hard surfaces and the land disturbed. Next Question Does the project add 5,000 square feet or more of new hard surfaces? OR Convert 3/4 acres or more of vegetation to lawn or landscaped areas? OR Convert 2.5 acres or more of native vegetation to pasture? Yes No Next Question All Minimum Requirements apply to the 10 Is this a road new hard surfaces and the converted related project? vegetation areas. Yes No Does the project add 5,000 square feet or more of new hard surfaces? Yes No Do new hard surfaces add 50% or Is the total of new plus replaced hard surfaces more to the existing hard surfaces 5,000 square feet or more, AND does the value within the project limits? of the proposed improvements — including interior improvements — exceed 50% of the assessed value (or replacement value) of the No Yes existing site improvements? No additional requirements Yes All Minimum Requirements apply to the new and replaced hard surfaces and converted vegetation areas. No No additional requirements Figure 2.4.2 — Flow Chart for Determining Requirements for Redevelopment Volume I Minimum Technical Requirements — December 2014 2-6 FIGURE 2: PROJECT MINIMUM REQUIREMENTS FLOW CHART New/Replaced Impervious Areas: Description Quantity Unit I ] I�ERVIOUS) 30 sf ASPA��� ACED IMPERVIOUS) 173 sf CON§2ACED IMPERVIOUS) 590 sf I\ \\ METAL RAMP/STAIRS I�k� EPLACED IMPERVIOUS/PERVIOUS) *549 sf MODULAR CLASSROOPVT�N?@MdNN/ IMPERVIOUS OVER EX PERVIOUS) 21 sf ` MODULAR CLASSROOM BUILDING (RAISED ABOVE OVER EX/REPLACED IMPERVIOUS) *3,506 sf \\ Total 814 sf SURFACE EXCLUDED FROM TOTAL IMPERVIOUS AREA CALCULATION -_ " \ \ EX UTILITY POLE W/ EXTRANSFORMER 6' HIGH CHAINLINK EXISTING BASEBALL/I FENCE W/3'WIDE GATE PER ARCH'L PLANS CONCRETE FOUNDATI - STRUCTURAL PLANSI - , 362.47(IX) 362.51(U) 362.16EE11 F"2.8'WNW \ / I \ / I \ � I PLAYGROUND AREA it WOOD CHIPS DN ASPHALT \ II CONCRETE SPLASHBLOCK� fl (CUT TO FIT) AT EACH I DOWNSPOUT LOCATION (TYP) SEE DETAIL �I 10 it 36114(E \J6 36L(NI (6) METAL STAIR RISERS 0 5.4' EA a 360.861EX) ' EXISTING ASPHALT PLAY \ CONCRETE OR ASPHALT RAMP LANDING COMPLYING WITH SECTION 1012.6. �359 WIDTH EQUAL TO WIDTH OF RAMP OR STAIR$$ AND 5-FT LONG (MEASURED IN THE �IRECTION OF TRAVEL). CROSS SLOPE AT LANDING NOT TO EXCEED 2% \ ILL ANY DIRECTION (TYP). SEE DETAILS 11 12 3.0 3. JS9 \ RN 6'JE CAPPED E 61IRON 5 `� \ M1H INVERTED IC \ POC i f l 4BUILDING RICAL PORTABLE =-�: ORT'363.67 63.67ANDII_361.50(IX) I i AYFIELD IS PER / P) 36262(IXI / 7t NOTE: SET PORTABLE FFE +12.5" ABOVE HIGHEST EXISTING GRADE ELEVATION i . I J, I L - � (4) METAL STAIR M 361.39(t) u) y- - RISERS 0 4.9' EA _362..001IXw, 36103(EX) 36L28(IX) "'� �� 361.981IX) M1'� 360 96 381.26IIXI 361.90IIX) S " ASPHALT OR 361.58(EXI 36o.911E)0 CONCRETE- 361.i81IX) / 362.00 LANDING 361z6J 18 „z6`1' ASPHALT OR KEYNOTES-,35i\361.26(EX) 3U.70 CONCRETE LANDING, ® RAMP €€ SAWCUTAND'R MOVE ASPHALT N 361.69(D) AS NEEDED TO FLAFSEN LANDING 10 m © LANDING AT BOTTOM OF, RAMP AND ROOF OVERHANG (TYP) OS STAIRS FEATHER ASPHALT TO\EX GRADE 360.82(D0 8 \ 360.6\3(EX) w (4)METAL STAIR �80.90(Ex) RISERS @ 5.4' EA \\ I 360.72(EX) - ASPHALT OR 360.73 F. �.F.«y._. yy I CONCRETE _ _ 360 SA(EX) 36147(EX) LANDING 360.66(IX) I 361 362.52 360.62 -. 360.77(IX) 1 PROPOSED P3 PORTABLE BUILDING FFE 362.52 61 S= 1 EXISTING GRASS HILLSIDE I 362.52 sv -s0 6" SD s 1 360.41(EX) IE 12 I 360.6E PROTECT EX CONCRETE \ SIDEWALK TO "AIN ° a4 -L d ) % I PROTECT EX 6" SSsORM'DRAIN PIPE TO \ 4 -. a REMAIN. CONTRACTOR SHALL POTHOLE a AND VERIFY LOCATION AND DEPTH PRIOR TO STARTING -CONSTRUCT-- - - 4 I / I \ I \ j / CONTRACTOR SHALL PROTECT EX SCHOOL BUILDING DURING I / / CONTRACTOR SHALL PROTECT EX SCHOOL BUILDING DURING ��/ CONSTRUCTION j I / CONSTRUCTION ° 4 Call before you. Dig.8-I-I UNDEAGR U 0 5 10 20 SERVICE (USA,SPi SCALE 1"=10' 4 Leaend PROPERTY LINE x 797305 E - 4,81' ASPHALT PAVEMENT STORM DRAINAGE PIPE 8' 6Ryp xx96 YD/CO/CB/CB 2/MH .. ■ ��O GRAVEL DISPERSION TRENCH r1 GRATED STAIRS/RAMPS ,'. . . . . . . . . . . . . ... . GRAVEL r-----_-----� L--___------A NOTE: SHEET HAS BEEN PRINTED TO BE 11 X1 7 AND NOT TO SCALE HUTTEBRLL' +OREMUS II orchRodun 4010 LAKE WASHINGTON BLVD NE SUITE 320 KIRKLAND, WA 98033 425.828.8948 HOARCH.COM ARCHITECT STAMP JC JACOBSON CONSULTANT STAMP v n. JA�cA �v �F 1VAgH "OO W .66 pFCISTt1a�� ss70NAL ECG 4/OL/10TI PROJECT INFORMATION Woodway Elementary School Portable Placement 9521 240th St SW Edmonds, WA 98020 EDMONDS SCHOOL DISTRICT #15 SCHOOL DISTRICT LOGO�\O F Edmonds SCHOOL DISTRICT EaeM1 tWtlen� learning, every tlryl PERMIT SET 04/07/2021 PROJECTNUMBEIN 2101 SHEET NAME CIVIL SITE PLAN FIGURE 3: DISTURBED AREA MAP