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Approved_RESUB2_BLD2023-0275+STORM DRAINAGE REPORT+7.5.2023_4.46.45_PM+3649035
=JC JACOBSON RESU B BLD2023-0275 Jul 06 2023 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT ENGINEERING REPORT For Storm Water Management Edmonds School District Sherwood Elementary School — New Walking Path 22901 106t" Ave W Edmonds, WA 98020 COMPLIES WITH APPLICABLE July 5, 2023 CITY STORM CODE �07/06/2023 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@jacobsonengi neers.com 255 S. King Street, Suite 800, Seattle, WA 98104 1 206.426.2600 1 JACOBSONENGINEERS.COM Storm Drainage Report for SHERWOOD ELEMENTARY SCHOOL — NEW WALKING PATH JACOBSON mi Im CONSU LTING ENGINEERS Project No. C230008-0173 July 5, 2023 TABLE OF CONTENTS I. PROJECT OVERVIEW.................................................................................................................. 2 GENERAL DESCRIPTION......................................................................................................................2 EXISTING CONDITIONS.........................................................................................................................2 PROPOSED CONDITIONS.....................................................................................................................2 II. DRAINAGE ANALYSIS................................................................................................................ 4 EXISTING SITE HYDROLOGY...............................................................................................................4 DEVELOPED SITE HYDROLOGY.........................................................................................................4 RUNOFF TREATMENT...........................................................................................................................5 UPSTREAM ANALYSIS..........................................................................................................................5 DOWNSTREAM ANALYSIS....................................................................................................................5 III. DISCUSSION OF MINIMUM REQUIREMENTS.............................................................................. 6 MR 1: PREPARATION OF STORMWATER SITE PLANS....................................................................6 MR 2: CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN (SWPPP) ..................6 MR 3: SOURCE CONTROL OF POLLUTION........................................................................................7 MR 4: PRESERVATION OF NATURAL DRAINAGE SYSTEMS AND OUTFALLS .............................7 MR 5: ON -SITE STORMWATER MANAGEMENT.................................................................................7 MR 6: RUNOFF TREATMENT................................................................................................................7 MR 7: FLOW CONTROL.........................................................................................................................8 MR 8: WETLANDS PROTECTION.........................................................................................................8 MR 9: OPERATION AND MAINTENANCE............................................................................................8 IV. TEMPORARY EROSION AND SEDIMENT CONTROL..................................................................... 9 V. LOW IMPACT DEVELOPMENT- MR 5....................................................................................... 10 APPENDIXA.................................................................................................................................... 11 APPENDIXB.................................................................................................................................... 12 APPENDIXC.................................................................................................................................... 13 APPENDIXD.................................................................................................................................... 14 SHERWOOD ELEMENTARY SCHOOL — NEW WALKING PATH PROJECT OVERVIEW GENERAL DESCRIPTION The following Drainage Report provides the design analysis for the Edmonds School District's Sherwood Elementary School - New Walking Path 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 (the 2019 WSDOE SWMMWW) as adopted by the City of Edmonds. The Sherwood Elementary School - New Walking Path project is located within the Edmonds city limits at 22901 106th Ave W, Edmonds, WA 98020. The project is located on the north side of the Sherwood Elementary School campus north of the asphalt play surface and parking lot on the existing grass playfield (Parcel #00554600000600) — See Civil Site Plan Sheet C2.00. The site is bounded by 106th Ave W to the west and single-family residential properties to the north, east, and south of the school's campus, as well as a forested area just east of the field (see Appendix A Figure 1 - Vicinity Map). The site is in the northwest quarter of Section 36, Township 27 North, Range 3 East, Willamette Meridian. The project (disturbed) area within the school district property boundary is approximately 12,104 square feet (0.28 acres) with approximately 9,784 square feet (0.22 acres) of the disturbed area being new plus replaced hard surface. The Edmonds School District desires to redevelop the existing project area with the construction of a new porous asphalt walking path around the perimeter of the existing playfield and a portion of porous asphalt pavement to connect the field with the existing asphalt play surface area on the south side of the site. Existing lawn area and soil will be removed as required to construct the improvements. Any disturbed lawn areas will be amended per BMP T5.13 and hydroseeded at a minimum. EXISTING CONDITIONS The existing Sherwood Elementary School campus property (Parcel #00554600000600) is currently developed with the Sherwood Elementary School building, a covered play structure, parking lots to the west and north of existing school building, a playfield on the north side of the campus, and a parking lot west of the playfield. The location of the proposed walking path is on the approximate perimeter of the existing playfield. There is an existing storm system with catch basins that will be protected north, south, and west of the existing playfield and is not anticipated to be impacted by new construction activity. The site currently sheet flows stormwater from the approximate southeast corner of the playfield to northwest corner via overland flow across the playfield. PROPOSED CONDITIONS The proposed site redevelopment will consist of the construction of a new porous asphalt walking path around the approximate perimeter of the existing playfield on the north side of the school campus. Additionally, a portion of porous asphalt will be installed between the field and existing asphalt play surface area south of the field, which will serve as additional play surfacing for the students as well as provide access to the field for school maintenance staff (see Civil Site Plan Sheet C2.00). The existing subgrade soils were reviewed by the project's Geotechnical Engineer and found to be advanced outwash, which is a good receptor for stormwater, and with the anticipated depth to groundwater being in the range of 20-feet to 25-feet below existing grade as well, the installation of porous pavement for this project appears to be achievable and meet City requirements (see Appendix D, Geotechnical Assessment). That said, all new plus replaced hard surfaces for this project will be porous asphalt pavement, which will drain stormwater runoff through the proposed porous asphalt pavement section and allowed to percolate into the surrounding ground around the field. �C JACOBSORN SHERWOOD ELEMENTARY SCHOOL — NEW WALKING PATH The amount of new + plus replaced hard surface constructed for the porous asphalt walking path and additional porous asphalt play/access will be approximately 9,784 square feet (0.22 acres), which is below the 10,000 square feet threshold requirement for flow control (MR #7); however, due to existing storm system capacity constraints in the area, flow control of stormwater runoff will be required. All stormwater runoff for the new + replaced impervious surfaces will be mitigated with the installation of porous asphalt pavement, which will serve as the flow control stormwater BMP for this project, therefore, a traditional stormwater detention system is not required to be installed for the project. Furthermore, since the porous asphalt pavement will not be accessible and used by vehicle traffic, except for occasional school district maintenance vehicles or lawn mowing equipment, that will gain access to the grass playfield via the porous pavement surfacing, it is not considered pollution generating hard surface (PGHS) and therefore not subjected to the requirements for runoff treatment (MR #6). miC JACOBSON SHERWOOD ELEMENTARY SCHOOL — NEW WALKING PATH II. DRAINAGE ANALYSIS EXISTING SITE HYDROLOGY The existing project site disturbed area totals approximately 12,104 square feet or 0.28 acres and consists of existing lawn/grass for playfield on the north side of the school campus. Stormwater runoff is generally conveyed via sheet flow from the southeast to the northwest direction and collected in catch basins located at the north and west sides of the playfield where the stormwater is then conveyed through a series of storm pipes on -site in northwest corner of site before it is conveyed off -site to the existing storm system in 228" ST SW. Table 1 below summarizes the land cover characteristics of the Threshold Discharge Areas of the existing project site (see Appendix A Figure 3, Existing Conditions). TABLE 1 —EXISTING PROJECT SITE CONDITIONS Land Cover Impervious Area (sf) Pervious Area (sf) Total (sf) Asphalt 0 0 Concrete 0 0 Gravel 0 0 Lawn 0 12,104 Total Site 0 12,104 12,104 % of Site 0% DEVELOPED SITE HYDROLOGY FLOW CONTROL 100% 100% The proposed site redevelopment will consist of the construction of a new porous asphalt walking path around the approximate perimeter of the existing playfield on the north side of the school campus. Additionally, a portion of porous asphalt will be installed between the field and existing asphalt play surface area south of the field, which will serve as additional play surfacing for the students as well as provide access to the field for school maintenance staff (see Civil Site Plan Sheet C2.00). The existing subgrade soils were reviewed by the project's Geotechnical Engineer and found to be advanced outwash, which is a good receptor for stormwater, and with the anticipated depth to groundwater being in the range of 20-feet to 25-feet below existing grade as well, the installation of porous pavement for this project appears to be achievable and meet City requirements (see Appendix D, Geotechnical Assessment). That said, all new plus replaced hard surfaces for this project will be porous asphalt pavement, which will drain stormwater runoff through the proposed porous asphalt pavement section and allowed to percolate into the surrounding ground around the field. Table 2 below summarizes the land cover characteristics of the proposed project site redevelopment (see Appendix A Figure 4, New plus Replaced Impervious Areas). TABLE 2 — REDEVELOPED PROJECT SITE CONDITIONS Land Cover Impervious Area (sf) Pervious Area (sf) Total (sf) Asphalt (Porous Asphalt) 9,784 0 Concrete 0 0 Gravel 0 0 Total New & Replaced Hard Surface 9,784 0 Lawn 0 2,320 Total Site 9,784 2,320 12,104 % of Site 80.8% 19.2% 100% =iC JACOBSORN SHERWOOD ELEMENTARY SCHOOL — NEW WALKING PATH The amount of new + plus replaced hard surface constructed for the porous asphalt walking path and additional porous asphalt play/access will be approximately 9,784 square feet (0.22 acres), which is below the 10,000 square feet threshold requirement for flow control (MR #7); however, due to existing storm system capacity constraints in the area, flow control of stormwater runoff will be required. All stormwater runoff for the new + replaced impervious surfaces will be mitigated with the installation of porous asphalt pavement, which will serve as the flow control stormwater BMP for this project, therefore, a traditional stormwater detention system is not required to be installed for the project per MR #7. Additional stormwater mitigation efforts are discussed in Section V below but will consist of amended soils in all disturbed lawn areas and porous asphalt pavement for the new + replaced hard surfaces. RUNOFF TREATMENT The proposed site redevelopment will not be creating more than 5,000 square feet of pollution -generating hard surface (PGHS) and is therefore exempt from providing water quality measures to treat the stormwater runoff for the project per the Snohomish County Drainage Manual Volume 1, Section 2.5.6, Minimum Requirement 6. UPSTREAM ANALYSIS Due to the topography of the site, with the existing field generally being higher than the adjacent parking lot and street to the west and north, and with the asphalt play surfacing and parking lot to the south draining stormwater to the west and away from the field, along with grading conditions to the north and west of project site, upstream runoff onto the site is anticipated to be negligible, with upstream stormwater runoff being diverted around the project site areas. DOWNSTREAM ANALYSIS The amount of new + plus replaced hard surface constructed for the porous asphalt walking path and additional porous asphalt play/access will be approximately 9,784 square feet (0.22 acres), which is below the 10,000 square feet threshold requirement for flow control (MR #7); however, due to existing storm system capacity constraints in the area, flow control of stormwater runoff will be required. The project proposes to construct the new + replaced hard surfaces with porous asphalt pavement material with any stormwater runoff draining through the porous asphalt material and allowed to percolate into the surrounding ground around the field; therefore the project does not anticipate any adverse effects to the existing downstream storm system. The project will maintain any existing threshold points of discharge outside the limits of project disturbance. Additionally, according to both Snohomish County and City of Edmonds GIS data, there are no other known drainage concerns downstream of the proposed project site. See Section I I I for further discussion of the proposed site conditions, including hard surfaces and stormwater mitigation efforts for the project. =iC JACOBSON SHERWOOD ELEMENTARY SCHOOL — NEW WALKING PATH III. DISCUSSION OF MINIMUM REQUIREMENTS The 2019 Washington State Department of Ecology Stormwater Management Manual for Western Washington (2019 WSDOE SWMMWW) references Figure 1-3.1 as the flow chart to follow when determining which Minimum Requirements (MRs) are required to be addressed with the proposed project being a New Development (see appendix A, Figure 2 — Project Minimum Requirements Flow Chart). The proposed Sherwood Elementary School — New Walking Paths project will create 5,000 square feet or more of new plus replaced hard surface, therefore according to the flow chart in Figure 1-3.1, the project will be subject to Minimum Requirements 1-9 for the new and replaced hard surfaces and all disturbed land. See Section 2 above and Appendix A for figures and flow chart from the SWMMWW. 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: CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN (SWPPP) A completed SWPPP has been prepared for the project and is included in Appendix B of this report. A breakdown of each element of the SWPPP has also been 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 fire lane / play surfacing located west and north of the project disturbed areas shall be utilized as construction conditions and schedule allows 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, Catch Basin Protection, and Silt Fencing. d. Element 4: Install Sediment Controls Sediment removal BMPs shall be implemented, and is anticipated per plans, to include, but not limited to, Silt Fencing and Straw Wattles. 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. Element 6: Protect Slopes No grading activity on slopes or hillsides is anticipated as part of this project. =iC JACOBSORN SHERWOOD ELEMENTARY SCHOOL — NEW WALKING PATH Element 7: Protect Permanent Drain Inlets Existing drains shall be protected where applicable throughout the project site by installing filter fabric catch basin inserts to mitigate for any sediment laden construction stormwater from entering the existing storm system. 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. 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 listed in the SWPPP shall be maintained 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 any and all Stormwater BMPs proposed for the project site until the site is stab I ized. MR 3: SOURCE CONTROL OF POLLUTION Stormwater will be prevented from coming into contact with pollutants through a series of BMPs listed within the SWPPP. MR 4: PRESERVATION OF NATURAL DRAINAGE SYSTEMS AND OUTFALLS Downstream receiving waters will not be adversely affected by the construction or completion of this project. No new drainage patterns offsite are expected. All existing drainage outfalls will be protected and maintained as part of the proposed development, including existing catch basins located north, west, and downslope of the playfield. MR 5: ON -SITE STORMWATER MANAGEMENT Projects shall employ On -Site Stormwater Management BMPs to infiltrate, disperse, and retain stormwater runoff onsite to the maximum extent feasible without causing flooding or erosion impacts during construction Stormwater will be drained through the porous asphalt pavement material and allowed to percolate into the surrounding ground around the field. See Section 5 for further discussion on MR5 for this project. MR 6: RUNOFF TREATMENT The proposed site redevelopment will not be creating more than 5,000 square feet of pollution -generating hard surface (PGHS) and is therefore exempt from providing water quality measures to treat the stormwater runoff for the project per the 2019 WSDOE SWMMWW Volume 1, Section 1-3.4.6. =iC JACOBSORN SHERWOOD ELEMENTARY SCHOOL — NEW WALKING PATH MR 7: FLOW CONTROL The amount of new + plus replaced hard surface constructed for the porous asphalt walking path and additional porous asphalt play/access will be approximately 9,784 square feet (0.22 acres), which is below the 10,000 square feet threshold requirement for flow control (MR #7) per the 2019 WSDOE SWMMWW Volume 1, Section 1-3.4.7; however, due to existing storm system capacity constraints in the area, flow control of stormwater runoff will be required. All stormwater runoff for the new + replaced impervious surfaces will be mitigated with the installation of porous asphalt pavement, which will serve as the flow control stormwater BMP for this project, therefore, a traditional stormwater detention system is not required to be installed for the project per MR #7. MR 8: WETLANDS PROTECTION There are no wetlands on the project site and any stormwater from this site does not discharge into a downstream wetland and therefore wetlands protection is not required. MR 9: OPERATION AND MAINTENANCE An operation and maintenance manual for all the proposed stormwater items proposed in this project will be provided as a separate document. See Appendix C, 0&M Manual. =iC JACOBSORN SHERWOOD ELEMENTARY SCHOOL — NEW WALKING PATH 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 both the on -site and off -site public storm systems. Additional information of the BMPs implemented for the project and locations on -site can be found on the civil engineering plans and in the project construction Stormwater Pollution Prevention Plan (SWPPP). See Sheets C1.00 TESC PLAN and C300 SITE DETAILS, and Appendix B SWPPP. miC JACOBSON SHERWOOD ELEMENTARY SCHOOL — NEW WALKING PATH V. LOW IMPACT DEVELOPMENT - MR 5 According to WSDOE SWMMWW Table 1-3.2 of Section 1-3.4.5 MR5 and per City of Edmonds Stormwater Review, the project will utilize the List Approach compliance method for MR5, and will be using List #1. We will address the LID BMPs from List #1 as follows: BMPs for Lawn and landscaped areas: 1. Post -Construction Soil Quality and Depth in accordance with BMP T5.13: Post -Construction Soil Quality and Depth. o The project will amend all soils in disturbed lawn and landscaping areas in accordance with the code requirement. BMPs for Roofs: N/A; the project does not have any new or replaced roofs. BMPs for Other Hard Surfaces: 1. Full Dispersion in accordance with BMP T5.30 in Volume V, Chapter 5 of this manual. o Project site cannot accommodate full dispersion as adequate space is not available to provide a vegetated flow path. 2. Permeable pavement in accordance with BMP T5.15 in Volume V, Chapter 5 of this manual. NOTE: this is not a requirement to pave these surfaces. Where pavement is proposed, it must be permeable to the extent feasible unless full dispersion is employed. o Porous asphalt pavement is proposed to be constructed for the new walking paths and asphalt access/play surfacing on the south side of existing playfield. =iC JACOBSORN 10 SHERWOOD ELEMENTARY SCHOOL - NEW WALKING PATH ►D . FIGURES �C JACOBSON m �C JACOBSOpN -r f ll� THE BOWL OF EDMONDS R e � Edmonds"Kingston Ferry Q D D erwood zElementary School 0 Edmonds n St sw Marina • Beach Park Edmonds City Park in o 0o s E 0 Westgate Elementary School 2zom St SW DO Woodway s 99 Ranch Market® n Esperance 0 E 228th St SW d herw w ntary-School a� s Mountlake ? Terrace WhirlyBall Q T toa / n Project Site � � 236th 0 Woodway Elementary I 99 QRegal Cinebarr toa - Mountlake �205th sr -JE20bth Costco Wholesale N 200th St ECHO L FIGURE 1: VICINITY MAP SCALE: NTS 255 S. King Street, Suite 800, Seattle, WA 98104 1 206.426.2600 1 JACOBSONENGINEERS.COM Figure 1-3.1: Flow Chart for Determining Requirements for New Development Start Here See Redevelopment Project Does the Site have 35% Yes Thresholds and the Figure Flow or more of existing hard No Chart for Determining surface coverage? Requirements for Redevelopment". No Does the Project convert 3/4 IF acres or more of vegetation to Does the Project result in lawn or landscaped areas, or 5,000 square feet, or No convert 2.5 acres or more of greater, of new plus native vegetation to pasture? replaced hard surface area? I \ No Yes Yes Does the Project result in 2,000 IF square feet, or greater, of new plus All Minimum Requirements replaced hard surface area? apply to the new and replaced hard surfaces and converted Yes NO vegetation areas. Does the Project have land Minimum Requirements #1 disturbing activities of 7,000 through #5 apply to the new Yes square feet or greater? and replaced hard surfaces and the land disturbed. No Minimum Requirement #2 applies. Flow Chart for Determining Requirements for New Development DEPARTMENT OF Revised March 2019 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 I �pp - ;w �� Q a �xee ,too maoo c O+ oo r) oE1 — 228TH STREET SW - - - x L NR n u� _—___—_—__— EX CAINDNN FENCE N887644'W 61).97 C (BIJ.90 P) solos /- _ / I iFORIN TIBEE PROTECTION VEG FOII EX TRIBES REMAIN - -- ANDNOT BE D E DISTURBED sEEDEruI(N IP ,�`Y _- LF '� L � I ixV RI•I l SW �W ,s az I I IR T \a CCD I I I I II I —GAS I r 1 \ I 9'12 INSTALL'ONSTHIICTION FLNCI NG fTYPI JLIAL ,I M 1\ I I ,_4 I 20 MPH 1 \111 11 I INSTALLSILT FENCE (DP) SEE DETAIL 10 PROPOSED LIMITS OF WALKING PATH SEE SHEET =.00 (TYR) I I � EXISTING PLAYFlELD PROTECT EX FIELD TO REMAIN UNLESS NOTED OTHERWISE FOR GRADING AND INSTALLATION OF PERVIOUS ASPHALT WALKING PATH (TYP) IT INSTALL CB PROTECTION (T(P) SEE DETAIL ®q F � I / , ->_ IIII II III IIII IIII III III III IIII \\ 1\11 I II \� y I I III Ito"'C1116,111 - 1 / .�- r>rc s 1a� m ,. ' \ \\\1\IIII IIII ) 1 1 IXPLAYGROUND EN�E MP83.Oa E.TGRtlII�D IvA v v v _ a < P� N/ 2817( .I11) ml TEX�SEATI AREA / 1 aR PVC 5 aa21 a'NFVCT:tl[ s ,n ART E1��OS, x �t aBe cnA /� x l-F C AF iIRE _ \vv/ti / STOP GAs V�NM— ss s I I / / \ \ \ V, p y' / R/P v a� AF�ao' III / I 1 J II l l IF '\ PARKING LOT 1 \ IIII I I — Call before Dig.88. D 10 20 4D ® SCALE 1"=20' Sheet Index CI.DO TEED PLAN C2DO CIVIL L SITE PL C3.00 SITE DETAILS LEGEND PROPERTY LINE M1rIT06'F-IST� LIMITS OF CONSTRUCTION un FF FILTER FABRIC FENCING CF TEMPCONSTRUCTION FENCING STRAW WATTLE CG TEMP CONSTRUCTION GATE INLET PROTECTION IP VEG TREE PROTECTION SEE ARCHITECTURAL PLAN SHEET G0.00 FOR ADDITIONAL SITE INFORMATION (PLAYGROUND AREAS, GOAL POSTS, FIELD LAYOUT, ETC) COORDINATE WITH SCHOOL DISTRICT FOR ACCESS TO AND FROM PROJECT SITE GENERAL DEMOLITION AND TESC NOTES 1. NO SEDIMENT SHALL BE TRACKED INTO THE STREET OR ONTO PAVED SURFACES. 2. TESC INFORMATION SHOWN ON PLANS IS FOR PERMITTING INSTALL STRAW PURPOSES ONLY. CONTRACTOR SHALL REVISE OR INSTALL WATTLE (TYP) SEE DETAIL ADDITIONAL TESC MEASURES AS CONSTRUCTIONS CONDITIONS CHANGE. 3. CONTRACTOR SHALL INSTALL TEMPORARY CONSTRUCTION FENCING AROUND JOB SITE TO PROTECT PUSUC AND MAINTAIN PROJECT SITE. INSTALL CONSTRUCTION FENCING (TYP) SEE DETAIL aS PROTT ANDPIMArv7— a,r (e937 _ STOMPN REMAIN (TYP) / / CF \ PROTECT EX PLAYGROUNDAREATO REMAIN BAR— ff //1 m DCHAINUNK FENCE ` PROTECT EX GATE AND INCLUDING FROSTS AND CHNI FENCE TO 7 AON N oay� FENCING MATERIAL REMAIN — PARK[NG LOT � xRen =I �nINT o �_ PLAY SURFACING moo IIIIIIoII Py '� cTs$ EuIsh /\ / Existing Impervious / Pervious Areas: Description Quantity Unit GRASS (PERVIOUS) 9,784 sf NOTE: SHEET HAS BEEN PRINTED TO BE 11 X1 7 AND NOT TO SCALE HUTTEBALL' +OREMUS II neAR•cluro 4010 LAKE WASHINGTON BLVD NE SUITE 320 KIRKIAND, WA 98033 425828.8948 HOARCH COM Sherwood Elementary Walking Path & Playground Improvements E0.mo WA.— EDMONDS SCHOOL DISTRICT #15 A� Edmonds �7 School District a11U9 DWIHP1R1IafiRWOM 1 oltT9 ImmNLmllFllms 2 LIIlf N1'16NRAI®IlClol 3 alav �� PERMIT TESC PLAN FIGURE 3: EXISTING CONDITIONS I /N-11 228TH STREET SW NR n o� EXCHNNUNR� n8876'44'w 6n.9J c (ensD P) FENCE ! Hasa z27-1 1 iqj0, ST4.1'7" x>acs rtn \ 1 I I I I � I Sp � —GAS I �! I I IEr I �a I I IX ASPHALT PARIONG LOT / xa I I I I i I L I1 \ I I R11'- 1 1 \ 1 1 3—R -INET / t9lExt /n L CHAINLINH FENCE TOO FILL IN GAP IN FENCE IPER ARCH PLANS / MATCH EX ASPHALTGRADE Illlillll � �� � 7j/, END sh A L d — i ND •}— rveaas�a�w Blau c (sac (aisle rl — In LEE / INSTALL NEW POROUS ASPHALT PAVEMENT TO SERVE AS PLAY AND _ -_ ACCESS TO FIELD Call before Dig.88. 0 >0 20 40 ® SCALE 1"=20' LEGEND PROPERTY LINE •%=IY4'L-MA_ CONTOUR (INDEX) —s12R" CONTOUR ___109 SPOT ELEVATION 3sflsc xos.as GRADE BREAK aNrz - POROUS ASPHALT SEE DETAIL 19 � i New / Replaced Impervious Areas: NEW DHN"°"X FENCE / Description Quantity Unit TO FILL IN GAP IN FENCE PO'A'FC `PLAINS PROTECT EX —]POROUS ASPHALT WALKING PATH 9,784 sf LAYGROUND AREATO REMAIN `PIII EXGATEas �xea sa lcil // AND CHAINLINH FENCE TO REMAIN NOTE: SHEET HAS BEEN PRINTED TO BE 11 X1 7 AND NOT TO SCALE HUTTEBALL' +OREMUS II neARMun 4010 LANE WASHINGTON BLVD NE SUITE 320 KIAMLAND. WA 90099 42B020.09/0 HOAACH COM Sherwood Elementary Walking Path & Playground Improvements —11DEIN w EDMONDS SCHOOL DISTRICT #15 BLD20230275 190l Edmonds 7 School District OE'.'4� DYXHPARI1081wmx 1 mamFRlMAuallts 2 tJEA MYAL A1611ElLTOI 3 PERMIT CFT CIVIL SITE PLAN I FIGURE 4: NEW + REPLACED IMPERVIOUS AREAS SHERWOOD ELEMENTARY SCHOOL - NEW WALKING PATH �C JACOBSON 12 AhCITY OF Stormwater Pollution Prevention Plan (SWPPP) Short Form SHORELINE For Small and Medium Construction Projects Introduction A Stormwater Pollution Prevention Plan (SWPPP) is a document that explains the potential for stormwater pollution caused by construction activities and the methods required to control those problems. With properly planned, installed and maintained Best Management Practices (BMPs), stormwater impacts such as heavy stormwater flows, soil erosion, and degradation of water quality can be minimized. All projects of any size must manage the stormwater runoff from construction sites, demolition, clearing and grading projects, or other activity that exposes soils. This guide page describes the main parts of a SWPPP for Small and Medium Impact projects, which include: • The SWPPP Short Form (this form), and • The applicable BMP details (located at the end of this form), and • An Erosion and Sediment Control (ESC) plan. The purpose of the SWPPP is to outline the actions that will be implemented on construction sites to reduce or eliminate discharge of sediment and other pollutants into receiving waters. Completing this checklist will ensure a well -prepared plan that meets City of Shoreline standards. Managing construction stormwater runoff and pollution on project sites is required by the Western Washington Phase II Municipal Stormwater Permit issued to the City of Shoreline by the Washington State Department of Ecology. Eligibility and Requirements The SWPPP Short Form is required for all Small and Medium Impact Projects. This includes any project that: • Disturbs up to 7,000 square feet of land, or • Creates less than 5,000 square feet of hard surface, or • Grades/fills less than 500 cubic yards. Any project that exceeds any of these thresholds is required to prepare a formal Department of Ecology SWPPP template. The requirements to complete the SWPPP Short Form are: 1. Complete all sections of the SWPPP Short Form narrative in Section 1: Background Information. 2. Select all appropriate construction stormwater and erosion control BMPs in Section 2: Required Elements Checklist. Attach a copy of the BMP specifications for each selected BMP. 3. Provide an Erosion and Sediment Control (ESC) Plan. The ESC plan should include the information in Section 3: ESC (Erosion and Sediment Control) Plan. 4. Complete the Construction Contact Sheet and attach it, along with the Site Inspection Form, to the Short Form SWPPP. 2/2019 Aik MY OF Stormwater Pollution Prevention Plan (SWPPP) Short Form SHORELINE For Small and Medium Construction Projects Site Inspections Projects that disturb one or more acres must have site inspections conducted by a Certified Erosion and Sediment Control Lead (CESCL). Project sites less than one -acre (not part of a larger common plan of development or sale) may have a person without Certified Erosion and Sediment Control Lead (CESCL) certification conduct the site inspections. The CESCL or inspector must have the skills to assess the: • Site conditions and construction activities that could impact the quality of stormwater. • Effectiveness of erosion and sediment control measures used to control the quality of stormwater discharges. The CESCL or inspector must inspect all areas disturbed by construction activities, all BMPs, and all stormwater discharges at least once every calendar week and within 24 hours of any discharge from the site. The CESCL or inspector must examine stormwater visually for the presence of suspended sediment, turbidity, discoloration, and oil sheen. The CESCL or inspector must complete the Site Inspection Form and attach all completed SWPPP Site Inspection Forms to the SWPPP for reporting and recordkeeping. 2/2019 AhCITY OF Stormwater Pollution Prevention Plan (SWPPP) Short Form SHORELINE For Small and Medium Construction Projects Section 1: Background Information Project Title: Sherwood Elementary School - New Walking Path Site Address: 22901 106th Ave W, Edmonds, WA 98020 Parcel Number(s): 00554600000600 Property Owner: Edmonds School District Contact Person (If different than the property owner): Nick Chou Address of Contact Person: 20420 68th Ave W, Lynnwood, WA 98036 Phone Number: 425.431.7162 1. Give an accurate, brief description of the proposed project's scope and nature: The existing Elementary School campus is already developed with asphalt play, existing building, and an existing grass playfield at the north end of the property. The proposed project will construct a new pervious asphalt walking path around a nnrtinn of tho ovic4inri nlnxifinIA 2. Area of site (square feet or acres): 12,104 sf 3. Area of land disturbance (square feet or acres): 12,104 sf 4. Area of existing impervious surfaces (square feet or acres): 0 sf 5. Area of new hard surfaces (including impervious surfaces, permeable pavement, and gravel in square feet or acres): 6. Area of existing native vegetation to be converted to landscaping or pasture (square feet or acres): 2,320 sf Proposed quantity of excavation (cubic yards): 330 Proposed quantity of fill (cubic yards): 12 Will there be construction stormwater discharges to adjoining properties or waters of the state? No 10. Describe critical areas that are on or adjacent to the site: Erosion Hazard Steep Slope located to the east of the proposed improvements on the school district's property. 11. Describe potential erosion problems on -site: Soils deemed moisture sensitive and shall be protected during inclement weather to mitigate for any sediment laden construction stormwater from leaving the construction site. 1 2/2019 Aik MY OF Stormwater Pollution Prevention Plan (SWPPP) Short Form SHORELINE For Small and Medium Construction Projects Section 2: Required Elements Checklist Part 1: 13 Elements Indicate the BMPs used for each element. If site conditions render an element unnecessary, check "other" and briefly describe why it is not needed. 1. Mark Clearing Limits — Prior to beginning land disturbing activities, all projects must visibly mark clearing limits, critical areas and their buffers, and any trees to be preserved. Clearly mark limits both in the field and on the plans. Do not staple or wire fences to trees. Applicable BMPs include: *Preserve existing vegetation — BMP C101 *High Visibility Plastic or Metal Fence — BMP C103 ❑Tree Protection During Construction — BMP T101 ❑Other: 2. Establish Construction Access — All construction projects subject to vehicular traffic shall provide a means of preventing vehicle tracking of soil from the site onto City streets. At a minimum, access to the site shall be stabilized with a quarry spall pad, or other equivalent BMP, to minimize tracking sediment into the roadway. If the existing paved access to the site is used as the construction access, it must be clearly labeled on the plans. If sediment is tracked off -site, sweep or shovel the affected roadway thoroughly. Street washing is not permitted. After sediment is recovered, transport it to a controlled sediment disposal area. Applicable BMPs include: ❑ Stabilized Construction Entrance — BMP C105 ❑ Wheel Wash — BMP C106 ❑ Construction Road/Parking Area Stabilization — BMP C107 ❑ Other: Existing Asphalt Play to the South and Parking Lot to the SW and West will I 3. Control Flow Rates — Flow control BMPs must be used to protect properties and waterways downstream of construction sites from erosion and discharge of turbid waters. A combination of drainage swales and possibly a sediment trap may be used to control runoff and trap associated sediment before it leaves the construction site. Applicable BMPs include: ❑ Interceptor Dike and Swale — BMP C200 M Straw Wattles — BMP C235 ❑ Sediment Trap — BMP C240 ❑ Other: 4. Install Sediment Controls — Sediment barriers should be used downslope of disturbed areas. Sediment barriers are intended to create a barrier to slow the sheet flow of stormwater and allow the sediment to settle out behind the barrier. Do not used sediment 2 2/2019 AhCITY OF Stormwater Pollution Prevention Plan (SWPPP) Short Form SHORELINE For Small and Medium Construction Projects barriers in streams, channels, ditches, or around inlets/outlets of culverts. Sediment barriers shall be clearly identified on the plan. Design, install, and maintain effective erosion and sediment control BMPs to minimize the discharge of pollutants from the site. BMPs must address factors such as the amount, frequency, intensity, and duration of precipitation. Applicable BMPs include: 0 Silt Fence — BMP C233 ❑ Vegetated Strip — BMP C234 0 Straw Wattles — BMP C235 0 Other: Storm Drain Inlet Protection - BMP C220 5. Stabilize Soils — Protect exposed and unworked soils to reduce erosion from rainfall and wind. Between October 1 and April 30, no soil shall remain uncovered for more than 2 days. From May 1 to September 30, no soil shall remain exposed for more than 7 days. Mulch can be applied to any site where soil has been disturbed and the protective vegetation has been removed. Erosion control blankets may be suitable for post - construction site stabilization or for temporary stabilization of highly erosive soils, such as on steep slopes and areas where vegetation is slow to establish. Applicable BMPs include: 0 Temporary and Permanent Seeding — BMP C120 0 Mulching — BMP C121 ❑ Nets and Blankets — BMP C122 0 Plastic Covering — BMP C123 ❑ Sodding — BMP C124 ❑ Topsoiling — BMP C125 ❑ Other: 6. Protect Slopes — Design, construct, and phase projects in a manner to minimize erosion. Protect slopes by diverting water at the top of slopes. Reduce runoff velocity by minimizing the length of the slope. This can be done by terracing and roughening slope sides. Seeding and establishing vegetation can also help protect slopes. Applicable BMPs include: ❑ Temporary and Permanent Seeding — BMP C120 ❑ Nets and Blankets — BMP C122 ❑ Plastic Covering — BMP C123 ❑ Interceptor Dike and Swale — BMP C200 0 Other: N/A; there are no slopes in the vicinity of the project work scope that will be i 3 2/2019 Aik MY OF Stormwater Pollution Prevention Plan (SWPPP) Short Form SHORELINE For Small and Medium Construction Projects 7. Protect Drain Inlets — Prevent sediment from entering the drainage system both on -site and downstream by installing inlet protection devices. Inlet protection shall be installed on all drains within 500' of the project site, including those that become operable during construction. Maintain 2/3 of the available storage in inlet protection devices at all times. Inlet protection shall be removed after final stabilization of the site. Applicable BMPs include: M Storm Drain Inlet Protection — BMP C220 ❑ Other: 8. Stabilize Channels and Outlets — Design, construct, and stabilize all on -site drainage channels to prevent erosion from a 10-year 24-hour frequency storm for the developed conditions. Provide stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes and downstream reaches at the outlets of all conveyance systems. The best method of stabilizing channels is to line the channel completely with a blanket product and then add check dams as necessary to function as an anchor and slow the flow of water. Applicable BMPs include: ❑ Channel Lining — BMP C202 ❑ Outlet Protection — BMP C209 ❑ Other: N/A; no construction stormwater runoff is anticipated for this project. 9. Control Pollutants — Handle and dispose of all pollutants, including waste materials and demolition debris that occur on -site in a manner that does not contaminate surface water. Do not maintain heavy equipment or vehicles on -site. Clean any spills immediately. Handle concrete waste appropriately. Applicable BMPs include: ❑ Concrete Handling — BMP C151 ❑ Sawcutting and Surfacing Pollution Prevention — BMP C152 M Material Delivery, Storage and Containment — BMP C153 ❑ Other: 10. Control Dewatering —All dewatering from excavation, trenching, etc. shall be discharged into a controlled conveyance system prior to discharge to a sediment trap or sediment pond. At a minimum, geotextile fabric socks/bags/cells will be used to filter sediment and reduce turbidity. All discharge to sanitary sewer requires King County and Ronald Wastewater approval. Applicable BMPs include: ❑ Level Spreader — BMP C206 ❑ Infiltration (Provide details) 4 2/2019 Aik MY OF Stormwater Pollution Prevention Plan (SWPPP) Short Form SHORELINE For Small and Medium Construction Projects ❑ Discharge to sanitary sewer (King County and Ronald Wastewater approval is required) ❑ Other: N/A; no dewatering is anticipated for this project. 11. Maintain BMPs — All BMPs shall be maintained and repaired as needed to ensure continued function and performance. Visual monitoring shall occur at least once per calendar week and within 24 hours of any discharge from the site. All BMPs shall be removed within 30 days of final stabilization of the site or until the BMPs are no longer necessary. Applicable BMPs include: M Maintain and repair in accordance with BMP specifications. Refer to Chapter 4 of Volume II of the 2014 Department of Ecology Stormwater Manual for Western Washington. ❑ Other: 12. Manage the Project — Projects shall be phased to the maximum degree practicable and take into account seasonal work limits. Projects that disturb one or more acres must have site inspections conducted by a Certified Erosion and Sediment Control Lead (CESCL). Project sites less than one -acre (not part of a larger common plan of development or sale) may have an inspector without Certified Erosion and Sediment Control Lead (CESCL) certification conduct the site inspections. The SWPPP must identify the CESCL/inspector who shall be present on -site or on -call at all times. 0 Phase construction activities to account for seasonal work limitations. 0 Maintain SWPPP documentation on -site at all times. 0 Update SWPPP documentation as necessary. 0 Attach the Construction Emergency Contact Sheets to the SWPPP. 0 Inspect and monitor all BMPs. 0 Attach all completed SWPPP Site Inspection Forms to the SWPPP for reporting and recordkeeping. 13. Protect Low Impact Development (LID) BMPs — All LID BMPs, including infiltration facilities, bioretention, rain gardens, and permeable pavement facilities, shall be clearly marked and protected from compaction during construction. Any facilities that have accumulated sediment during construction must be restored to their fully functioning condition. Sediment -laden runoff is not permitted onto permeable pavement. Applicable BMPs include: ❑ Buffer Zones — BMP C102 0 High Visibility Fence — BMP C103 0 Silt Fence — BMP C233 ❑ Vegetated Strip — BMP C234 ❑ Other: 5 2/2019 AhCITY OF Stormwater Pollution Prevention Plan (SWPPP) Short Form SHORELINE For Small and Medium Construction Projects Part 2: BMP Details For each BMP selected in the checklist, attach a copy of the BMP detail to the SWPPP Short Form. The details referenced in the checklist are provided at the end of this document for reference. Additional BMP details and specifications can be found in Chapter 4 of Volume II of the 2014 Department of Ecology Stormwater Manual for Western Washington. 6 2/2019 BMP C101: Preserving Natural Vegetation Purpose The purpose of preserving natural vegetation is to reduce erosion wherever practicable. Limiting site disturbance is the single most effective method for reducing erosion. For example, conifers can hold up to about 50 percent of all rain that falls during a storm. Up to 20-30 percent of this rain may never reach the ground but is taken up by the tree or evaporates. Another benefit is that the rain held in the tree can be released slowly to the ground after the storm. Conditions of Use Natural vegetation should be preserved on steep slopes, near perennial and intermittent water- courses or swales, and on building sites in wooded areas. . As required by local governments. Phase construction to preserve natural vegetation on the project site for as long as possible during the construction period. Design and Installation Specifications Natural vegetation can be preserved in natural clumps or as individual trees, shrubs and vines. The preservation of individual plants is more difficult because heavy equipment is generally used to remove unwanted vegetation. The points to remember when attempting to save individual plants are: . Is the plant worth saving? Consider the location, species, size, age, vigor, and the work involved. Local governments may also have ordinances to save natural vegetation and trees. Fence or clearly mark areas around trees that are to be saved. It is preferable to keep ground disturbance away from the trees at least as far out as the dripline. Plants need protection from three kinds of injuries: Construction Equipment- This injury can be above or below the ground level. Damage results from scarring, cutting of roots, and compaction of the soil. Placing a fenced buffer zone around plants to be saved prior to construction can prevent construction equipment injuries. Grade Changes- Changing the natural ground level will alter grades, which affects the plant's ability to obtain the necessary air, water, and minerals. Minor fills usually do not cause prob- lems although sensitivity between species does vary and should be checked. Trees can typ- ically tolerate fill of 6 inches or less. For shrubs and other plants, the fill should be less. When there are major changes in grade, it may become necessary to supply air to the roots of plants. This can be done by placing a layer of gravel and a tile system over the roots before the fill is made. The tile system should be laid out on the original grade leading from a dry well 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 271 around the tree trunk. The system should then be covered with small stones to allow air to cir- culate over the root area. Lowering the natural ground level can seriously damage trees and shrubs. The highest per- centage of the plant roots are in the upper 12 inches of the soil and cuts of only 2-3 inches can cause serious injury. To protect the roots it may be necessary to terrace the immediate area around the plants to be saved. If roots are exposed, construction of retaining walls may be needed to keep the soil in place. Plants can also be preserved by leaving them on an undis- turbed, gently sloping mound. To increase the chances for survival, it is best to limit grade changes and other soil disturbances to areas outside the dripline of the plant. Excavations - Protect trees and other plants when excavating for drainfields, power, water, and sewer lines. Where possible, the trenches should be routed around trees and large shrubs. When this is not possible, it is best to tunnel under them. This can be done with hand tools or with power augers. If it is not possible to route the trench around plants to be saved, then the following should be observed: Cut as few roots as possible. When you have to cut, cut clean. Paint cut root ends with a wood dressing like asphalt base paint if roots will be exposed for more than 24-hours. Backfill the trench as soon as possible. Tunnel beneath root systems as close to the center of the main trunk to preserve most of the important feeder roots. Some problems that can be encountered with a few specific trees are: • Maple, Dogwood, Red alder, Western hemlock, Western red cedar, and Douglas fir do not readily adjust to changes in environment and special care should be taken to protect these trees. . The windthrow hazard of Pacific silver fir and madrona is high, while that of Western hemlock is moderate. The danger of windthrow increases where dense stands have been thinned. Other species (unless they are on shallow, wet soils less than 20 inches deep) have a low windthrow hazard. . Cottonwoods, maples, and willows have water -seeking roots. These can cause trouble in sewer lines and infiltration fields. On the other hand, they thrive in high moisture conditions that other trees would not. . Thinning operations in pure or mixed stands of Grand fir, Pacific silver fir, Noble fir, Sitka spruce, Western red cedar, Western hemlock, Pacific dogwood, and Red alder can cause ser- ious disease problems. Disease can become established through damaged limbs, trunks, roots, and freshly cut stumps. Diseased and weakened trees are also susceptible to insect attack. Maintenance Standards Inspect flagged and/or fenced areas regularly to make sure flagging or fencing has not been removed or damaged. If the flagging or fencing has been damaged or visibility reduced, it shall be repaired or replaced immediately and visibility restored. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 272 If tree roots have been exposed or injured, "prune" cleanly with an appropriate pruning saw or top- pers directly above the damaged roots and recover with native soils. Treatment of sap flowing trees (fir, hemlock, pine, soft maples) is not advised as sap forms a natural healing barrier. BMP C102: Buffer Zones N/A Purpose Creation of an undisturbed area or strip of natural vegetation or an established suitable planting that will provide a living filter to reduce soil erosion and stormwater runoff velocities. Conditions of Use Buffer zones are used along streams, wetlands and other bodies of water that need protection from erosion and sedimentation. Contractors can use vegetative buffer zone BMPs to protect natural swales and they can incorporate them into the natural landscaping of an area. Do not use critical -areas buffer zones as sediment treatment areas. These areas shall remain com- pletely undisturbed. The local permitting authority may expand the buffer widths temporarily to allow the use of the expanded area for removal of sediment. The types of buffer zones can change the level of protection required as shown below: Designated Critical Area Buffers - buffers that protect Critical Areas, as defined by the Washington State Growth Management Act, and are established and managed by the local permitting authority. These should not be disturbed and must protected with sediment control BMPs to prevent impacts. The local permitting authority may expand the buffer widths temporarily to allow the use of the expan ded area for removal of sediment. Vegetative Buffer Zones - areas that may be identified in undisturbed vegetation areas or managed vegetation areas that are outside any Designated Critical Area Buffer. They may be utilized to provide an additional sediment control area and/or reduce runoff velocities. If being used for pre- servation of natural vegetation, they should be arranged in clumps or strips. They can be used to pro- tect natural swales and incorporated into the natural landscaping area. Design and Installation Specifications • Preserving natural vegetation or plantings in clumps, blocks, or strips is generally the easiest and most successful method. • Leave all unstable steep slopes in natural vegetation. • Mark clearing limits and keep all equipment and construction debris out of the natural areas and buffer zones. Steel construction fencing is the most effective method to protect sensitive areas and buffers. Alternatively, wire -backed silt fence on steel posts is marginally effective. Flagging alone is typically not effective. • Keep all excavations outside the dripline of trees and shrubs. • Do not push debris or extra soil into the buffer zone area because it will cause damage by 2019 Stormwater Management Manual for Western Washington Volume ll - Chapter 3 - Page 273 burying and smothering vegetation. . Vegetative buffer zones for streams, lakes or other waterways shall be established by the local permitting authority or other state or federal permits or approvals. Maintenance Standards Inspect the area frequently to make sure flagging remains in place and the area remains undis- turbed. Replace all damaged flagging immediately. Remove all materials located in the buffer area that may impede the ability of the vegetation to act as a filter. BMP C103: High -Visibility Fence Purpose High -visibility fencing is intended to: • Restrict clearing to approved limits. • Prevent disturbance of sensitive areas, their buffers, and other areas required to be left undis- turbed. . Limit construction traffic to designated construction entrances, exits, or internal roads. • Protect areas where marking with survey tape may not provide adequate protection. Conditions of Use To establish clearing limits plastic, fabric, or metal fence may be used: . At the boundary of sensitive areas, their buffers, and other areas required to be left uncleared. . As necessary to control vehicle access to and on the site. Design and Installation Specifications High -visibility plastic fence shall be composed of a high -density polyethylene material and shall be at least four feet in height. Posts for the fencing shall be steel or wood and placed every 6 feet on center (maximum) or as needed to ensure rigidity. The fencing shall be fastened to the post every six inches with a polyethylene tie. On long continuous lengths of fencing, a tension wire or rope shall be used as a top stringer to prevent sagging between posts. The fence color shall be high -visibility orange. The fence tensile strength shall be 360 Ibs/ft using the ASTM D4595 testing method. If appropriate install fabric silt fence in accordance with BMP C233: Silt Fence to act as high -visibility fence. Silt fence shall be at least 3 feet high and must be highly visible to meet the requirements of this BMP. Metal fences shall be designed and installed according to the manufacturer's specifications. Metal fences shall be at least 3 feet high and must be highly visible. Fences shall not be wired or stapled to trees. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 274 Maintenance Standards If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately and visibility restored. BMP C105: Stabilized Construction Access N/A Purpose Stabilized construction accesses are established to reduce the amount of sediment transported onto paved roads outside the project site by vehicles or equipment. This is done by constructing a sta- bilized pad of quarry spalls at entrances and exits for project sites. Conditions of Use Construction accesses shall be stabilized wherever traffic will be entering or leaving a construction site if paved roads or other paved areas are within 1,000 feet of the site. For residential subdivision construction sites, provide a stabilized construction access for each res- idence, rather than only at the main subdivision entrance. Stabilized surfaces shall be of sufficient length/width to provide vehicle access/parking, based on lot size and configuration. On large commercial, highway, and road projects, the designer should include enough extra mater- ials in the contract to allow for additional stabilized accesses not shown in the initial Construction SWPPP. It is difficult to determine exactly where access to these projects will take place; additional materials will enable the contractor to install them where needed. Design and Installation Specifications See Figure II-3.1: Stabilized Construction Access for details. Note: the 1 00'minimum length of the access shall be reduced to the maximum practicable size when the size or configuration of the site does not allow the full length (100'). Construct stabilized construction accesses with a 12-inch thick pad of 4-inch to 8-inch quarry spalls, a 4-inch course of asphalt treated base (ATB), or use existing pavement. Do not use crushed con- crete, cement, or calcium chloride for construction access stabilization because these products raise pH levels in stormwater and concrete discharge to waters of the State is prohibited. A separation geotextile shall be placed under the spalls to prevent fine sediment from pumping up into the rock pad. The geotextile shall meet the standards listed in Table 11-3.2: Stabilized Con- struction Access Geotextile Standards. Table 11-3.2: Stabilized Construction Access Geotextile Standards Geotextile Property I Required Value Grab Tensile Strength (ASTM D4751) 1 200 psi min. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 275 Crushed roc , base, etc., shall be added as required to maintain a stable urface and to stabilize any areas that ed. Following construction, these areas shall re -construction condition or better to pre- vent future erosion. Per eet cleaning at the end of each day or more often if necessary. BMP C120: Temporary and Permanent Seeding Purpose Seeding reduces erosion by stabilizing exposed soils. A well -established vegetative cover is one of the most effective methods of reducing erosion. Conditions of Use Use seeding throughout the project on disturbed areas that have reached final grade or that will remain unworked for more than 30 days. The optimum seeding windows for western Washington are April 1 through June 30 and September 1 through October 1. Between July 1 and August 30 seeding requires irrigation until 75 percent grass cover is established. Between October 1 and March 30 seeding requires a cover of mulch or an erosion control blanket until 75 percent grass cover is established. Review all disturbed areas in late August to early September and complete all seeding by the end of September. Otherwise, vegetation will not establish itself enough to provide more than average pro- tection. Mulch is required at all times for seeding because it protects seeds from heat, moisture loss, and transport due to runoff. Mulch can be applied on top of the seed or simultaneously by hydroseeding See BMP C121: Mulching for specifications. Seed and mulch all disturbed areas not otherwise vegetated at final site stabilization. Final sta- bilization means the completion of all soil disturbing activities at the site and the establishment of a permanent vegetative cover, or equivalent permanent stabilization measures (such as pavement, riprap, gabions, or geotextiles) which will prevent erosion. See BMP T5.13: Post -Construction Soil Qualitv and Depth. Design and Installation Specifications General Install channels intended for vegetation before starting major earthwork and hydroseed with a Bonded Fiber Matrix. For vegetated channels that will have high flows, install erosion control blankets over the top of hydroseed. Before allowing water to flow in vegetated channels, establish 75 percent vegetation cover. If vegetated channels cannot be established by seed 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 284 before water flow; install sod in the channel bottom — over top of hydromulch and erosion con- trol blankets. • Confirm the installation of all required surface water control measures to prevent seed from washing away. • Hydroseed applications shall include a minimum of 1,500 pounds per acre of mulch with 3 per- cent tackifier. See BMP C121: Mulching for specifications. . Areas that will have seeding only and not landscaping may need compost or meal -based mulch included in the hydroseed in order to establish vegetation. Re -install native topsoil on the disturbed soil surface before application. See BMP T5.13: Post -Construction Soil Quality and Depth. • When installing seed via hydroseeding operations, only about 1/3 of the seed actually ends up in contact with the soil surface. This reduces the ability to establish a good stand of grass quickly. To overcome this, consider increasing seed quantities by up to 50 percent. • Enhance vegetation establishment by dividing the hydromulch operation into two phases: Phase 1- Install all seed and fertilizer with 25-30 percent mulch and tackifier onto soil in the first lift. Phase 2- Install the rest of the mulch and tackifier over the first lift. Or, enhance vegetation by: o Installing the mulch, seed, fertilizer, and tackifier in one lift. o Spread or blow straw over the top of the hydromulch at a rate of 800-1000 pounds per acre. Hold straw in place with a standard tackifier. Both of these approaches will increase cost moderately but will greatly improve and enhance vegetative establishment. The increased cost may be offset by the reduced need for: o Irrigation. Reapplication of mulch. Repair of failed slope surfaces. This technique works with standard hydromulch (1,500 pounds per acre minimum) and Bon- ded Fiber Matrix/ Mechanically Bonded Fiber Matrix (BFM/MBFMs) (3,000 pounds per acre minimum). . Seed may be installed by hand if: o Temporary and covered by straw, mulch, or topsoil. Permanent in small areas (usually less than 1 acre) and covered with mulch, topsoil, or erosion blankets. The seed mixes listed in Table II-3.4: Temporary and Permanent Seed Mixes include 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 285 recommended mixes for both temporary and permanent seeding. . Apply these mixes, with the exception of the wet area seed mix, at a rate of 120 pounds per acre. This rate can be reduced if soil amendments or slow -release fertilizers are used. Apply the wet area seed mix at a rate of 60 pounds per acre. Consult the local suppliers or the local conservation district for their recommendations. The appropriate mix depends on a variety of factors, including location, exposure, soil type, slope, and expected foot traffic. Alternative seed mixes approved by the local authority may be used, depending on the soil type and hydrology of the area. Table 11-3.4: Temporary and Permanent Seed Mixes Common Name Latin Name % Weight % Purity % Germination Temporary Erosion Control Seed Mix A standard mix for areas requiring a temporary vegetative cover. Chewings or Festuca rubra var. annual bluegrass commutata or Poa 40 98 90 anna Perennial rye Lolium perenne 50 98 90 Redtop or colonial Agrostis alba or 5 92 85 bentgrass Agrostis tenuis White dutch clover Trifolium repens 5 98 90 Landscaping Seed Mix A recommended mix for landscaping seed. Perennial rye blend Lolium perenne 70 98 90 Chewings and red Festuca rubra var. fescue blend commutata or Fes- 30 98 90 tuca rubra Low -Growing Turf Seed Mix A turf seed mix for dry situations where there is no need for watering. This mix requires very little main- tenance. Dwarf tall fescue Festuca arundin- 45 98 90 (several varieties) acea var. Dwarf perennial Lolium perenne 30 98 90 rye (Barclay) var. barclay Red fescue Festuca rubra 20 98 90 Colonial bentgrass Agrostis tenuis 5 98 90 Bioswale Seed Mix A seed mix for bioswales and other intermittently wet areas. Tall or meadow fes- Festuca arundin- 75-80 98 90 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 286 Table II-3.4: Temporary and Permanent Seed Mixes (continued) Common Name Latin Name % Weight % Purity % Germination acea or Festuca cue elatior Seaside/Creeping Agrostis palustris 10-15 92 85 bentgrass Redtop bentgrass Agrostis alba or 5-10 90 80 Agrostis gigantea Wet Area Seed Mix A low -growing, relatively non-invasive seed mix appropriate forvery wet areas that are not regulated wet- lands. Consult Hydraulic Permit Authority (HPA) for seed mixes if applicable. Tall or meadow fes- Festuca arundin- acea or Festuca 60-70 98 90 cue elatior Seaside/Creeping Agrostis palustris 10-15 98 85 bentgrass Meadow foxtail Alepocurus praten- 10-15 90 80 sis Alsike clover Trifolium hybridum 1-6 98 90 Redtop bentgrass Agrostis alba 1-6 92 85 Meadow Seed Mix A recommended meadow seed mix for infrequently maintained areas or non -maintained areas where col- onization by native plants is desirable. Likely applications include rural road and utility right-of-way. Seed- ing should take place in September or very early October in order to obtain adequate establishment prior to the winter months. Consider the appropriateness of clover, a fairly invasive species, in the mix. Amending the soil can reduce the need for clover. Redtop or Oregon Agrostis alba or bentgrass Agrostis ore- 20 92 85 gonensis Red fescue Festuca rubra 70 98 90 White dutch clover Trifolium repens 10 98 90 Roughening and Rototilling The seedbed should be firm and rough. Roughen all soil no matter what the slope. Track walk slopes before seeding if engineering purposes require compaction. Backblading or smoothing of slopes greater than 4H:1 V is not allowed if they are to be seeded. Restoration -based landscape practices require deeper incorporation than that provided by a simple single -pass rototilling treatment. Wherever practical, initially rip the subgrade to improve long-term permeability, infiltration, and water inflow qualities. At a minimum, 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 287 permanent areas shall use soil amendments to achieve organic matter and permeability per- formance defined in engineered soil/landscape systems. For systems that are deeper than 8 inches complete the rototilling process in multiple lifts, or prepare the engineered soil system per specifications and place to achieve the specified depth. Fertilizers • Conducting soil tests to determine the exact type and quantity of fertilizer is recommended. This will prevent the over -application of fertilizer. . Organic matter is the most appropriate form of fertilizer because it provides nutrients (includ- ing nitrogen, phosphorus, and potassium) in the least water-soluble form. . In general, use 10-4-6 N-P-K (nitrogen -phosphorus -potassium) fertilizer at a rate of 90 pounds per acre. Always use slow -release fertilizers because they are more efficient and have fewer environmental impacts. Do not add fertilizer to the hydromulch machine, or agit- ate, more than 20 minutes before use. Too much agitation destroys the slow -release coating. . There are numerous products available that take the place of chemical fertilizers. These include several with seaweed extracts that are beneficial to soil microbes and organisms. If 100 percent cottonseed meal is used as the mulch in hydroseed, chemical fertilizer may not be necessary. Cottonseed meal provides a good source of long-term, slow -release, available nitrogen. Bonded Fiber Matrix and Mechanically Bonded Fiber Matrix . On steep slopes use Bonded Fiber Matrix (BFM) or Mechanically Bonded Fiber Matrix (MBFM) products. Apply BFM/MBFM products at a minimum rate of 3,000 pounds per acre with approximately 10 percent tackifier. Achieve a minimum of 95 percent soil coverage during application. Numerous products are available commercially. Most products require 24-36 hours to cure before rainfall and cannot be installed on wet or saturated soils. Generally, products come in 40-50 pound bags and include all necessary ingredients except for seed and fertilizer. . Install products per manufacturer's instructions. • BFMs and MBFMs provide good alternatives to blankets in most areas requiring vegetation establishment. Advantages over blankets include: • BFM and MBFMs do not require surface preparation. • Helicopters can assist in installing BFM and MBFMs in remote areas. • On slopes steeper than 2.5H:1 V, blanket installers may require ropes and harnesses for safety. • Installing BFM and MBFMs can save at least $1,000 per acre compared to blankets. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 288 Maintenance Standards Reseed any seeded areas that fail to establish at least 75 percent cover (100 percent cover for areas that receive sheet or concentrated flows). If reseeding is ineffective, use an alternate method such as sodding, mulching, nets, or blankets. Reseed and protect by mulch any areas that experience erosion after achieving adequate cover. Reseed and protect by mulch any eroded area. Supply seeded areas with adequate moisture, but do not water to the extent that it causes run- off. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology's website at: https:Hecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies BMP C121: Mulching Purpose Mulching soils provides immediate temporary protection from erosion. Mulch also enhances plant establishment by conserving moisture, holding fertilizer, seed, and topsoil in place, and moderating soil temperatures. There are a variety of mulches that can be used. This section discusses only the most common types of mulch. Conditions of Use As a temporary cover measure, mulch should be used: . For less than 30 days on disturbed areas that require cover. At all times for seeded areas, especially during the wet season and during the hot summer months. During the wet season on slopes steeper than 3H:1 V with more than 10 feet of vertical relief. Mulch may be applied at anytime of the year and must be refreshed periodically. For seeded areas, mulch may be made up of 100 percent: cottonseed meal; . fibers made of wood, recycled cellulose, hemp, or kenaf; 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 289 . compost; or blends of these. Tackifier shall be plant -based, such as guar or alpha plantago, or chemical -based such as poly- acrylamide or polymers. Generally, mulches come in 40-50 pound bags. Seed and fertilizer are added at time of application. Recycled cellulose may contain polychlorinated biphenyl (PCBs). Ecology recommends that products should be evaluated for PCBs prior to use. Refer to BMP C 126: Polyacrylamide (PAM) for Soil Erosion Protection for conditions of use. PAM shall not be directly applied to water or allowed to enter a water body. Any mulch or tackifier product used shall be installed per the manufacturer's instructions. Design and Installation Specifications For mulch materials, application rates, and specifications, see Table II-3.6: Mulch Standards and Guidelines. Consult with the local supplier or the local conservation district for their recom- mendations. Increase the application rate until the ground is 95% covered (i.e. not visible under the mulch layer). Note: Thickness may be increased for disturbed areas in or near sensitive areas or other areas highly susceptible to erosion. Where the option of "Compost" is selected, it should be a coarse compost that meets the size grad- ations listed in Table 11-3.5: Size Gradations of Compost as Mulch Material when tested in accord- ance with Test Method 02.02-13 found in Test Methods for the Examination of Composting and Compost (Thompson, 2001). Table 11-3.5: Size Gradations of Compost as Mulch Material Sieve Size Percent Passing 3" 100% 1" 90% -100% 3/4" 70% -100% 1/4" 40% - 100% Mulch used within the ordinary high-water mark of surface waters should be selected to minimize potential flotation of organic matter. Composted organic materials have higher specific gravities (densities) than straw, wood, or chipped material. Consult the Hydraulic Permit Authority (H PA) for mulch mixes if applicable. Maintenance Standards The thickness of the mulch cover must be maintained. Any areas that experience erosion shall be remulched and/or protected with a net or blanket. If the erosion problem is drainage related, then the problem shall be fixed and the eroded area remulched. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 290 Table II-3.6: Mulch Standards and Guidelines Mulch Mater- Guideline Description ial Quality Standards Air-dried; free from undesirable seed and coarse material. Application 2"-3" thick; 5 bales per 1,000 sf or 2-3 tons per acre Rates Cost-effective protection when applied with adequate thickness. Hand - application generally requires greater thickness than blown straw. The Straw thickness of straw may be reduced by half when used in conjunction with seeding. In windy areas straw must be held in place by crimping, using a tackifier, or covering with netting. Blown straw always has to be held in Remarks place with a tackifier as even light winds will blow it away. Straw, however, has several deficiencies that should be considered when selecting mulch materials. It often introduces and/or encourages the propagation of weed species and it has no significant long-term benefits It should also not be used within the ordinary high-water elevation of surface waters (due to flot- ation). Quality No growth inhibiting factors. Standards Application Approx. 35-45 Ibs per 1,000 sf or 1,500 -2,000 Ibs per acre Hydromulch Rates Shall be applied with hydromulcher. Shall not be used without seed and Remarks tackifier unless the application rate is at least doubled. Fibers longer than about 3/4 -1 inch clog hydromulch equipment. Fibers should be kept to less than 3/4 inch. Quality No visible water or dust during handling. Must be produced per WAC 173- Standards 350, Solid Waste Handling Standards, but may have up to 35% biosolids. Application 2 thick min.; approx. 100 tons per acre (approx. 750 Ibs per cubic yard) Rates More effective control can be obtained by increasing thickness to 3". Excel - Compost lent mulch for protecting final grades until landscaping because it can be dir- ectly seeded or tilled into soil as an amendment. Compost used for mulch Remarks has a coarser size gradation than compost used for BMP C 125: Topsoiling / Composting or BMP T5.13: Post -Construction Soil Quality and Depth. It is more stable and practical to use in wet areas and during rainy weather conditions. Do not use near wetlands or near phosphorous impaired water bodies. Quality Gradations from fines to 6 inches in length for texture, variation, and inter - Chipped Standards locking properties. Include a mix of various sizes so that the average size Site Veget- is between 2- and 4- inches. ation Application Rates 2" thick min.; 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 291 Table 11-3.6: Mulch Standards and Guidelines (continued) Mulch Mater- Guideline Description ial This is a cost-effective way to dispose of debris from clearing and grub- bing, and it eliminates the problems associated with burning. Generally, it should not be used on slopes above approx. 10% because of its tendency to be transported by runoff. It is not recommended within 200 feet of sur- Remarks face waters. If permanent seeding or planting is expected shortly after mulch, the decomposition of the chipped vegetation may tie up nutrients important to grass establishment. Note: thick application of this material over existing grass, herbaceous spe- cies, and some groundcovers could smother and kill vegetation. Quality No visible water or dust during handling. Must be purchased from a supplier Standards `^iith a Solid Waste Handling Permit or one exempt from solid waste reg- ulations. Application 2" thick min.; approx. 100 tons per acre (approx. 750 lbs. per cubic yard) Wood- Rates Based This material is often called "wood straw" or "hog fuel". The use of mulch Mulch ultimately improves the organic matter in the soil. Special caution is Remarks advised regarding the source and composition of wood -based mulches. Its preparation typically does not provide any weed seed control, so evidence of residual vegetation in its composition or known inclusion of weed plants or seeds should be monitored and prevented (or minimized). Quality A blend of loose, long, thin wood pieces derived from native conifer or Standards deciduous trees with high length -to -width ratio. Application 2" thick min. Rates Wood Cost-effective protection when applied with adequate thickness. A min - Strand imum of 95-percent of the wood strand shall have lengths between 2 and Mulch 10-inches, with a width and thickness between 1/16 and 1/2-inches. The Remarks mulch shall not contain resin, tannin, or other compounds in quantities that would be detrimental to plant life. Sawdust orwood shavings shall not be used as mulch. [Specification 9-14.4(4) from the Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT, 2019 BMP C122: Nets and Blankets N/A Purpose Erosion control nets and blankets are intended to prevent erosion and hold seed and mulch in place on steep slopes and in channels so that vegetation can become well established. In addition, some nets and blankets can be used to permanently reinforce turf to protect drainage ways during high flows. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 292 BMP C123: Plastic Covering Purpose Plastic covering provides immediate, short-term erosion protection to slopes and disturbed areas. Conditions of Use Plastic covering may be used on disturbed areas that require cover measures for less than 30 days, except as stated below. • Plastic is particularly useful for protecting cut and fill slopes and stockpiles. However, the rel- atively rapid breakdown of most polyethylene sheeting makes it unsuitable for applications greater than six months. • Due to rapid runoff caused by plastic covering, do not use this method upslope of areas that might be adversely impacted by concentrated runoff. Such areas include steep and/or unstable slopes. • Plastic sheeting may result in increased runoff volumes and velocities, requiring additional on - site measures to counteract the increases. Creating a trough with wattles or other material can convey clean water away from these areas. . To prevent undercutting, trench and backfill rolled plastic covering products. . Although the plastic material is inexpensive to purchase, the cost of installation, maintenance, removal, and disposal add to the total costs of this BMP. • Whenever plastic is used to protect slopes, install water collection measures at the base of the slope. These measures include plastic -covered berms, channels, and pipes used to convey clean rainwater away from bare soil and disturbed areas. Do not mix clean runoff from a plastic covered slope with dirty runoff from a project. . Other uses for plastic include: • Temporary ditch liner. • Pond liner in temporary sediment pond. • Liner for bermed temporary fuel storage area if plastic is not reactive to the type of fuel being stored. • Emergency slope protection during heavy rains. • Temporary drainpipe ("elephant trunk") used to direct water. Design and Installation Specifications Plastic slope cover must be installed as follows: 1. Run plastic up and down the slope, not across the slope. 2. Plastic maybe installed perpendicular to a slope if the slope length is less than 10 feet. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 298 3. Provide a minimum of 8-inch overlap at the seams. 4. On long or wide slopes, or slopes subject to wind, tape all seams. 5. Place plastic into a small (12-inch wide by 6-inch deep) slot trench at the top of the slope and backfill with soil to keep water from flowing underneath. 6. Place sand filled burlap or geotextile bags every 3 to 6 feet along seams and tie them together with twine to hold them in place. 7. Inspect plastic for rips, tears, and open seams regularly and repair immediately. This prevents high velocity runoff from contacting bare soil, which causes extreme erosion. 8. Sandbags may be lowered into place tied to ropes. However, all sandbags must be staked in place. • Plastic sheeting shall have a minimum thickness of 0.06 millimeters. . If erosion at the toe of a slope is likely, a gravel berm, riprap, or other suitable protection shall be installed at the toe of the slope in order to reduce the velocity of runoff. Maintenance Standards . Torn sheets must be replaced and open seams repaired. • Completely remove and replace the plastic if it begins to deteriorate due to ultraviolet radi- ation. • Completely remove plastic when no longer needed. • Dispose of old tires used to weight down plastic sheeting appropriately. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology's website at: httos://ecoloay.wa.aov/Reaulations-Permits/Guidance-technical-assistance/Stormwater-Der- mittee-auidance-resources/Emeraina-stormwater-treatment-technoloaies BMP C124: Sodding N/A Purpose The purpose of sodding is to establish turf for immediate erosion protection and to stabilize drainage paths where concentrated overland flow will occur. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 299 BMP C140: Dust Control Purpose Dust control prevents wind transport of dust from disturbed soil surfaces onto roadways, drainage ways, and surface waters. Conditions of Use Use dust control in areas (including roadways) subject to surface and air movement of dust where on -site or off -site impacts to roadways, drainage ways, or surface waters are likely. Design and Installation Specifications . Vegetate or mulch areas that will not receive vehicle traffic. In areas where planting, mulching, or paving is impractical, apply gravel or landscaping rock. • Limit dust generation by clearing only those areas where immediate activity will take place, leaving the remaining area(s) in the original condition. Maintain the original ground cover as long as practical. . Construct natural or artificial windbreaks or windscreens. These may be designed as enclos- ures for small dust sources. • Sprinkle the site with water until the surface is wet. Repeat as needed. To prevent carryout of mud onto the street, refer to BMP C105: Stabilized Construction Access and BMP C106: Wheel Wash. . Irrigation water can be used for dust control. Irrigation systems should be installed as a first step on sites where dust control is a concern. • Spray exposed soil areas with a dust palliative, following the manufacturer's instructions and cautions regarding handling and application. Used oil is prohibited from use as a dust sup- pressant. Local governments may approve other dust palliatives such as calcium chloride or PAM. • PAM (BMP C 126: Polyacrylamide (PAM) for Soil Erosion Protection) added to water at a rate of 0.5 pounds per 1,000 gallons of water per acre and applied from a water truck is more effect- ive than water alone. This is due to increased infiltration of water into the soil and reduced evaporation. In addition, small soil particles are bonded together and are not as easily trans- ported by wind. Adding PAM may reduce the quantity of water needed for dust control. Note that the application rate specified here applies to this BMP, and is not the same application rate that is specified in BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection, but the downstream protections still apply. Refer to BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection for conditions of use. PAM shall not be directly applied to water or allowed to enter a water body. • Contact your local Air Pollution Control Authority for guidance and training on other dust con- trol measures. Compliance with the local Air Pollution Control Authority constitutes 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 313 compliance with this BMP. • Use vacuum street sweepers. • Remove mud and other dirt promptly so it does not dry and then turn into dust. • Techniques that can be used for unpaved roads and lots include: • Lower speed limits. High vehicle speed increases the amount of dust stirred up from unpaved roads and lots. • Upgrade the road surface strength by improving particle size, shape, and mineral types that make up the surface and base materials. • Add surface gravel to reduce the source of dust emission. Limit the amount of fine particles (those smaller than .075 mm) to 10 to 20 percent. • Use geotextile fabrics to increase the strength of new roads or roads undergoing recon- struction. • Encourage the use of alternate, paved routes, if available. • Apply chemical dust suppressants using the admix method, blending the product with the top few inches of surface material. Suppressants may also be applied as surface treatments. • Limit dust -causing work on windy days. • Pave unpaved permanent roads and other trafficked areas. Maintenance Standards Respray area as necessary to keep dust to a minimum. BMP C150: Materials on Hand Purpose Keep quantities of erosion prevention and sediment control materials on the project site at all times to be used for regular maintenance and emergency situations such as unexpected heavy rains. Hav- ing these materials on -site reduces the time needed to replace existing or implement new BMPs when inspections indicate that existing BMPs are not meeting the Construction SWPPP require- ments. In addition, contractors can save money by buying some materials in bulk and storing them at their office or yard. Conditions of Use . Construction projects of any size or type can benefit from having materials on hand. A small commercial development project could have a roll of plastic and some gravel available for immediate protection of bare soil and temporary berm construction. A large earthwork project, such as highway construction, might have several tons of straw, several rolls of plastic, flexible 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 314 pipe, sandbags, geotextile fabric and steel "T" posts. • Materials should be stockpiled and readily available before any site clearing, grubbing, or earthwork begins. A large contractor or project proponent could keep a stockpile of materials that are available for use on several projects. . If storage space at the project site is at a premium, the contractor could maintain the materials at their office or yard. The office or yard must be less than an hour from the project site. Design and Installation Specifications Depending on project type, size, complexity, and length, materials and quantities will vary. A good minimum list of items that will cover numerous situations includes: • Clear Plastic, 6 mil • Drainpipe, 6 or 8 inch diameter . Sandbags, filled . Straw Bales for mulching • Quarry Spalls • Washed Gravel • Geotextile Fabric • Catch Basin Inserts . Steel "T" Posts . Silt fence material . Straw Wattles Maintenance Standards . All materials with the exception of the quarry spalls, steel "T" posts, and gravel should be kept covered and out of both sun and rain. • Re -stock materials as needed. BMP C151: Concrete Handling N/A Purpose Concrete work can generate process water and slurry that contain fine particles and high pH, both of which can violate water quality standards in the receiving water. Concrete spillage or concrete dis- charge to waters of the State is prohibited. Use this BMP to minimize and eliminate concrete, con- crete process water, and concrete slurry from entering waters of the State. 2019 Stormwater Management Manual for Western Washington Volume ll - Chapter 3 - Page 315 sign and Installation Specifications • uum slurry and cuttings during cutting and surfacing operations. . Slurry a cuttings shall not remain on permanent concrete or asphalt pave t overnight. . Slurry and cutti s shall not drain to any natural or constructed draina conveyance includ- ing stormwater sys s. This may require temporarily blocking cat basins. • Dispose of collected slurr nd cuttings in a manner that do of violate ground water or sur- face water quality standards. • Do not allow process water generat during by -demolition, surface roughening or similar operations to drain to any natural or cons c drainage conveyance including stormwater systems. Dispose of process water in a that does not violate ground water or surface water quality standards. • Handle and dispose of cleanin aste material and de ition debris in a manner that does not cause contamination o ater. Dispose of sweeping ma ial from a pick-up sweeper at an appropriate disposal s' . Maintenance ndards Continually itor operations to determine whether slurry, cuttings, or process wate ould enter waters of estate. If inspections show that a violation of water quality standards could oc stop oper ns and immediately implement preventive measures such as berms, barriers, secon c ainment, and/or vacuum trucks. BMP C153: Material Delivery, Storage, and Containment Purpose Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses from material delivery and storage. Minimize the storage of hazardous materials on -site, store mater- ials in a designated area, and install secondary containment. Conditions of Use Use at construction sites with delivery and storage of the following materials: • Petroleum products such as fuel, oil and grease • Soil stabilizers and binders (e.g., Polyacrylamide) • Fertilizers, pesticides and herbicides • Detergents . Asphalt and concrete compounds 2019 Stormwater Management Manual for Western Washington Volume // - Chapter 3 - Page 318 • Hazardous chemicals such as acids, lime, adhesives, paints, solvents, and curing compounds . Any other material that maybe detrimental if released to the environment Design and Installation Specifications . The temporary storage area should be located away from vehicular traffic, near the con- struction entrance(s), and away from waterways or storm drains. . Safety Data Sheets (SDS) should be supplied for all materials stored. Chemicals should be kept in their original labeled containers. • Hazardous material storage on -site should be minimized. • Hazardous materials should be handled as infrequently as possible. • During the wet weather season (Oct 1 — April 30), consider storing materials in a covered area. • Materials should be stored in secondary containments, such as an earthen dike, horse trough, or even a children's wading pool for non -reactive materials such as detergents, oil, grease, and paints. Small amounts of material may be secondarily contained in "bus boy" trays or con- crete mixing trays. • Do not store chemicals, drums, or bagged materials directly on the ground. Place these items on a pallet and, when possible, within secondary containment. . If drums must be kept uncovered, store them at a slight angle to reduce ponding of rainwater on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of drums, preventing water from collecting. • Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall be stored in approved containers and drums and shall not be overfilled. Containers and drums shall be stored in temporary secondary containment facilities. . Temporary secondary containment facilities shall provide for a spill containment volume able to contain 10% of the total enclosed container volume of all containers, or 110% of the capa- city of the largest container within its boundary, whichever is greater. • Secondary containment facilities shall be impervious to the materials stored therein for a min- imum contact time of 72 hours. • Sufficient separation should be provided between stored containers to allow for spill cleanup and emergency response access. • During the wet weather season (Oct 1 — April 30), each secondary containment facility shall be covered during non -working days, prior to and during rain events. . Keep material storage areas clean, organized and equipped with an ample supply of appro- priate spill clean-up material (spill kit). . The spill kit should include, at a minimum: 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 319 1-Water Resistant Nylon Bag 3-Oil Absorbent Socks Yx 4' 2-Oil Absorbent Socks 3" x 10' O 12-Oil Absorbent Pads 17"xl9" 1-Pair Splash Resistant Goggles o 3-Pair Nitrile Gloves 10-Disposable Bags with Ties Instructions Maintenance Standards • Secondary containment facilities shall be maintained free of accumulated rainwater and spills. In the event of spills or leaks, accumulated rainwater and spills shall be collected and placed into drums. These liquids shall be handled as hazardous waste unless testing determines them to be non -hazardous. • Re -stock spill kit materials as needed. BMP C154: Concrete Washout Area N/A Purpose Prevent or reduce the discharge of pollutants from concrete waste to stormwater by conducting washout off -site, or performing on -site washout in a designated area. Conditions of Use Concrete washout areas are implemented on construction projects where: • Concrete is used as a construction material . It is not possible to dispose of all concrete wastewater and washout off -site (ready mix plant, etc.). • Concrete truck drums are washed on -site. Note that auxiliary concrete truck components (e.g. chutes and hoses) and small concrete handling equipment (e.g. hand tools, screeds, shovels, rakes, floats, trowels, and wheel- barrows) may be washed into formed areas awaiting concrete pour. At no time shall concrete be washed off into the footprint of an area where an infiltration feature will be installed. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 320 BMP C160: Certified Erosion and Sediment Control Lead Purpose The project proponent designates at least one person as the responsible representative in charge of erosion and sediment control (ESC), and water quality protection. The designated person shall be responsible for ensuring compliance with all local, state, and federal erosion and sediment control and water quality requirements. Construction sites one acre or larger that discharge to waters of the State must designate a Certified Erosion and Sediment Control Lead (CESCL) as the responsible representative. Conditions of Use A CESCL shall be made available on projects one acre or larger that discharge stormwater to sur- face waters of the state. Sites less than one acre may have a person without CESCL certification conduct inspections. The CESCL shall: Have a current certificate proving attendance in an erosion and sediment control training course that meets the minimum ESC training and certification requirements established by Ecology. Ecology has provided the minimum requirements for CESCL course training, as well as a list of ESC training and certification providers at: https:Hecology.wa.gov/Regulations-Permits/Permits-certifications/Certified-erosion-sed- iment-control K7 Be a Certified Professional in Erosion and Sediment Control (CPESC). For additional inform- ation go to: http://www.envirocertintl.org/cpesc/ Specifications . CESCL certification shall remain valid for three years. . The CESCL shall have authority to act on behalf of the contractor or project proponent and shall be available, or on -call, 24 hours per day throughout the period of construction. . The Construction SWPPP shall include the name, telephone number, fax number, and address of the designated CESCL. See II-2 Construction Stormwater Pollution Prevention Plans (Construction SWPPPs . A CESCL may provide inspection and compliance services for multiple construction projects in the same geographic region, but must be on site whenever earthwork activities are 2019 Stormwater Management Manual for Western Washington Volume // - Chapter 3 - Page 327 occurring that could generate release of turbid water. Duties and responsibilities of the CESCL shall include, but are not limited to the following: • Maintaining a permit file on site at all times which includes the Construction SWPPP and any associated permits and plans. • Directing BMP installation, inspection, maintenance, modification, and removal. • Updating all project drawings and the Construction SWPPP with changes made. • Completing any sampling requirements including reporting results using electronic Dis- charge Monitoring Reports (WebDMR). • Facilitate, participate in, and take corrective actions resulting from inspections per- formed by outside agencies or the owner. • Keeping daily logs, and inspection reports. Inspection reports should include: ■ Inspection date/time. ■ Weather information; general conditions during inspection and approximate amount of precipitation since the last inspection. ■ Visual monitoring results, including a description of discharged stormwater. The presence of suspended sediment, turbid water, discoloration, and oil sheen shall be noted, as applicable. ■ Any water quality monitoring performed during inspection. ■ General comments and notes, including a brief description of any BMP repairs, maintenance or installations made as a result of the inspection. ■ A summary or list of all BMPs implemented, including observations of all erosion/sediment control structures or practices. The following shall be noted: 1. Locations of BMPs inspected. 2. Locations of BMPs that need maintenance. 3. Locations of BMPs that failed to operate as designed or intended. 4. Locations of where additional or different BMPs are required. BMP C162: Scheduling Purpose Sequencing a construction project reduces the amount and duration of soil exposed to erosion by wind, rain, runoff, and vehicle tracking. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 328 Conditions of Use The construction sequence schedule is an orderly listing of all major land -disturbing activities together with the necessary erosion and sedimentation control measures planned for the project. This type of schedule guides the contractor on work to be done before other work is started so that serious erosion and sedimentation problems can be avoided. Following a specified work schedule that coordinates the timing of land -disturbing activities and the installation of control measures is perhaps the most cost-effective way of controlling erosion during construction. The removal of ground cover leaves a site vulnerable to erosion. Construction sequen- cing that limits land clearing, provides timely installation of erosion and sedimentation controls, and restores protective cover quickly can significantly reduce the erosion potential of a site. Design Considerations . Minimize construction during rainy periods. Schedule projects to disturb only small portions of the site at any one time. Complete grading as soon as possible. Immediately stabilize the disturbed portion before grading the next por- tion. Practice staged seeding in order to revegetate cut and fill slopes as the work progresses. II-3.3 Construction Runoff BMPs BMP C200: Interceptor Dike and Swale N/A Purpose Provide a dike of compacted soil or a swale at the top or base of a disturbed slope or along the peri- meter of a disturbed construction area to convey stormwater. Use the dike and/or swale to intercept the runoff from unprotected areas and direct it to areas where erosion can be controlled. This can prevent storm runoff from entering the work area or sediment -laden runoff from leaving the con- struction site. Conditions of Use Use an interceptor dike or swale where runoff from an exposed site or disturbed slope must be con- veyed to an erosion control BMP which can safely convey the stormwater. Locate upslope of a construction site to prevent runoff from entering the disturbed area. When placed horizontally across a disturbed slope, it reduces the amount and velocity of run- off flowing down the slope. Locate downslope to collect runoff from a disturbed area and direct it to a sediment BMP (e.g. BMP C240: Sediment Trap or BMP C241: Sediment Pond (Temporary)). 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 329 thickness is 2 feet. utlets at the base of steep slope pipes (pipe slope greater than ercent), use an engine d energy dissipator. Filter fabric or e 'on control blankets should alI'd ays sed under riprap to prevent scour and channel er n. See BMP C122: Net Blankets. Bank stabilization, bioengineering, a abitat ures may be required for disturbed areas. This work may require a Hydraulic Projec roval (HPA) from the Washington State Depart- ment of Fish and Wildlife. See 1-2.1 draulic ct Approvals. Maintenance Standa . Inspect and re as needed. . Add ro as needed to maintain the intended function. energy dissipator if sediment builds up. BMP C220: Inlet Protection Purpose Inlet protection prevents coarse sediment from entering drainage systems prior to permanent sta- bilization of the disturbed area. Conditions of Use Use inlet protection at inlets that are operational before permanent stabilization of the disturbed areas that contribute runoff to the inlet. Provide protection for all storm drain inlets downslope and within 500 feet of a disturbed or construction area, unless those inlets are preceded by a sediment trapping BMP. Also consider inlet protection for lawn and yard drains on new home construction. These small and numerous drains coupled with lack of gutters can add significant amounts of sediment into the roof drain system. If possible, delay installing lawn and yard drains until just before landscaping, or cap these drains to prevent sediment from entering the system until completion of landscaping. Provide 18-inches of sod around each finished lawn and yard drain. Table II-3.10: Storm Drain Inlet Protection lists several options for inlet protection. All of the methods for inlet protection tend to plug and require a high frequency of maintenance. Limit contributing drain- age areas for an individual inlet to one acre or less. If possible, provide emergency overflows with additional end -of -pipe treatment where stormwater ponding would cause a hazard. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 356 Table 11-3.10: Storm Drain Inlet Protection Type of Inlet Pro- Emergency Applicable for tection Overflow Paved/ Earthen Sur- Conditions of Use faces Drop Inlet Protection Yes, temporary Applicable for heavy flows. Easy Excavated drop flooding may Earthen to maintain. Large area requirement: inlet protection occur 30'x30'/acre Block and gravel Applicable for heavy concentrated flows. drop inlet pro- Yes Paved or Earthen Will not pond. tection Gravel and wire Applicable for heavy concentrated flows. drop inlet pro- No Paved or Earthen Will pond. Can withstand traffic. tection Catch basin filters Yes Paved or Earthen Frequent maintenance required. Curb Inlet Protection Curb inlet pro- Small capacity Used for sturdy, more compact install- tection with overflow Paved ation. wooden weir Block and gravel curb inlet pro- Yes Paved Sturdy, but limited filtration. tection Culvert Inlet Protection Culvert inlet sed- N/A N/A 18 month expected life. iment trap Design and Installation Specifications Excavated Drop Inlet Protection Excavated drop inlet protection consists of an excavated impoundment around the storm drain inlet. Sediment settles out of the stormwater prior to entering the storm drain. Design and installation spe- cifications for excavated drop inlet protection include: . Provide a depth of 1-2 ft as measured from the crest of the inlet structure. . Slope sides of excavation should be no steeper than 2H:1 V. . Minimum volume of excavation is 35 cubic yards. Shape the excavation to fit the site, with the longest dimension oriented toward the longest inflow area. . Install provisions for draining to prevent standing water. . Clear the area of all debris. 2019 Stormwater Management Manual for Western Washington Volume 11- Chapter 3 - Page 357 • Grade the approach to the inlet uniformly. • Drill weep holes into the side of the inlet. • Protect weep holes with screen wire and washed aggregate. • Seal weep holes when removing structure and stabilizing area. • Build a temporary dike, if necessary, to the down slope side of the structure to prevent bypass flow. Block and Gravel Filter A block and gravel filter is a barrier formed around the inlet with standard concrete blocks and gravel. See Figure II-3.17: Block and Gravel Filter. Design and installation specifications for block gravel fil- ters include: • Provide a height of 1 to 2 feet above the inlet. • Recess the first row of blocks 2-inches into the ground for stability. • Support subsequent courses by placing a pressure treated wood 2x4 through the block open- ing. • Do not use mortar. • Lay some blocks in the bottom row on their side to allow for dewatering the pool. • Place hardware cloth or comparable wire mesh with'/2-inch openings over all block openings. • Place gravel to just below the top of blocks on slopes of 2H:1 V or flatter. . An alternative design is a gravel berm surrounding the inlet, as follows: • Provide a slope of 3H:1 V on the upstream side of the berm. • Provide a slope of 2H:1 V on the downstream side of the berm. • Provide a 1-foot wide level stone area between the gravel berm and the inlet. Use stones 3 inches in diameter or larger on the upstream slope of the berm. Use gravel'/2- to 3/4-inch at a minimum thickness of 1-foot on the downstream slope of the berm. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 358 Figure II-3.17: Block and Gravel Filter Drain grate a �595 CPC In, Plan View crete block Gravel backfill Concrete block Wire screen or filter fabric Gravel backfill Overflow waterer —I��� (�Ponding height on o9'� II Water I II I I I I n ^� fino Drop inlet Section A -A Notes: 1. Drop inlet sediment barriers are to be used for small, nearly level drainage areas. (less than 5%) 2. Excavate a basin of sufficient size adjacent to the drop inlet. 3. The top of the structure (ponding height) must be well below the ground elevation downslope to prevent runoff from bypassing the inlet. A temporary dike may be necessary on the downslope side of the structure. NOT TO SCALE Block and Gravel Filter Revised June 2016 DEPARTMENT OF ECOLOGYPlease see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, State of Washington limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 359 Gravel and Wire Mesh Filter Gravel and wire mesh filters are gravel barriers placed over the top of the inlet. This method does not provide an overflow. Design and installation specifications for gravel and wire mesh filters include: • Use a hardware cloth or comparable wire mesh with'/2-inch openings. Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot bey- ond each side of the inlet structure. Overlap the strips if more than one strip of mesh is necessary. • Place coarse aggregate over the wire mesh. Provide at least a 12-inch depth of aggregate over the entire inlet opening and extend at least 18-inches on all sides. Catch Basin Filters Catch basin filters are designed by manufacturers for construction sites. The limited sediment stor- age capacity increases the amount of inspection and maintenance required, which may be daily for heavy sediment loads. To reduce maintenance requirements, combine a catch basin filter with another type of inlet protection. This type of inlet protection provides flow bypass without overflow and therefore may be a better method for inlets located along active rights -of -way. Design and install- ation specifications for catch basin filters include: • Provides 5 cubic feet of storage. • Requires dewatering provisions. • Provides a high -flow bypass that will not clog under normal use at a construction site. . Insert the catch basin filter in the catch basin just below the grating. Curb Inlet Protection with Wooden Weir Curb inlet protection with wooden weir is an option that consists of a barrier formed around a curb inlet with a wooden frame and gravel. Design and installation specifications for curb inlet protection with wooden weirs include: • Use wire mesh with'/2-inch openings. • Use extra strength filter cloth. • Construct a frame. . Attach the wire and filter fabric to the frame. • Pile coarse washed aggregate against the wire and fabric. • Place weight on the frame anchors. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 360 Block and Gravel Curb Inlet Protection Block and gravel curb inlet protection is a barrier formed around a curb inlet with concrete blocks and gravel. See Figure 11-3.18: Block and Gravel Curb Inlet Protection. Design and installation spe- cifications for block and gravel curb inlet protection include: • Use wire mesh with'/2-inch openings. • Place two concrete blocks on their sides abutting the curb at either side of the inlet opening. These are spacer blocks. • Place a 2A stud through the outer holes of each spacer block to align the front blocks. • Place blocks on their sides across the front of the inlet and abutting the spacer blocks. • Place wire mesh over the outside vertical face. • Pile coarse aggregate against the wire to the top of the barrier. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 361 Figure II-3.18: Block and Gravel Curb Inlet Protection n Back of sidewalk Back of curb Wire scre filter %a << . Drain gravel Plan View 3/4 inch (20 mm) Drain gravel Wire screen or filter fabric 2x4 Wood stud (100x50 Timber stud) Ponding height Overflow ANNow Catch basin Concrete block ud block Section A -A Notes: 1. Use block and gravel type sediment barrier when curb inlet is located in gently sloping street segment, where water can pond and allow sediment to separate from runoff. 2. Barrier shall allow for overflow from severe storm event. 3. Inspect barriers and remove sediment after each storm event. Sediment and gravel must be removed from the traveled way immediately. NOT TO SCALE Block and Gravel Curb Inlet Protection Revised June 2016 DEPARTMENT OF ECOLOGYPlease see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, State of Washington limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 362 Curb and Gutter Sediment Barrier Curb and gutter sediment barrier is a sandbag or rock berm (riprap and aggregate) 3 feet high and 3 feet wide in a horseshoe shape. See Figure II-3.19: Curb and Gutter Barrier. Design and installation specifications for curb and gutter sediment barrier include: Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 feet high and 3 feet wide, at least 2 feet from the inlet. . Construct a horseshoe shaped sedimentation trap on the upstream side of the berm. Size the trap to sediment trap standards for protecting a culvert inlet. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 363 Figure II-3.19: Curb and Gutter Barrier Back of sidewalk Burlap sacks to overlap onto curb Back of curb Runoff � " I��1-- Curb inlet Runoff Spillway Catch basin Plan View Gravel filled sandbags stacked tightly Notes: 1. Place curb type sediment barriers on gently sloping street segments, where water can pond and allow sediment to separate from runoff. 2. Sandbags of either burlap or woven 'geotextile' fabric, are filled with gravel, layered and packed tightly. 3. Leave a one sandbag gap in the top row to provide a spillway for overflow. 4. Inspect barriers and remove sediment after each storm event. Sediment and gravel must be removed from the traveled way immediately. NOT TO SCALE DEPARTMENT OF ECOLOGY State of Washington Curb and Gutter Barrier Revised June 2016 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 364 Maintenance Standards Inspect all forms of inlet protection frequently, especially after storm events. Clean and replace clogged catch basin filters. For rock and gravel filters, pull away the rocks from the inlet and clean or replace. An alternative approach would be to use the clogged rock as fill and put fresh rock around the inlet. Do not wash sediment into storm drains while cleaning. Spread all excavated material evenly over the surrounding land area or stockpile and stabilize as appropriate. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology's website at: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies BMP C231: Brush Barrier N/A Purpose The purpose of brush barriers is to reduce the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use Brush barriers maybe used downslope of disturbed areas that are less than one -quarter acre. Brush barriers are not intended to treat concentrated flows, nor are they intended to treat sub- stantial amounts of overland flow. Any concentrated flows must be directed to a sediment trap- ping BMP. The only circumstance in which overland flow can be treated solely by a brush barrier, rather than by a sediment trapping BMP, is when the area draining to the barrier is small. . Brush barriers should only be installed on contours. Design and Installation Specifications Height: 2 feet (minimum) to 5 feet (maximum). Width: 5 feet at base (minimum) to 15 feet (maximum). Filter fabric (geotextile) maybe anchored over the brush berm to enhance the filtration ability of the barrier. Ten -ounce burlap is an adequate alternative to filter fabric. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 365 BMP C233: Silt Fence Purpose Silt fence reduces the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use Silt fence may be used downslope of all disturbed areas. Silt fence shall prevent sediment carried by runoff from going beneath, through, or over the top of the silt fence, but shall allow the water to pass through the fence. Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial amounts of overland flow. Convey any concentrated flows through the drainage system to a sediment trapping BMP. Do not construct silt fences in streams or use in V-shaped ditches. Silt fences do not provide an adequate method of silt control for anything deeper than sheet or overland flow. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 370 Figure 11-3.22: Silt Fence Joints in geotextile fabric shall be spliced at posts. Use staples, wire rings or equivalent to attach fabric to posts 2"x2" by 14 Ga. wire or equivalent, if standard strength fabric used —:\—\i\—�i1�\LLB%`\\/.��i�\/\\!`\ Minimum I I 6' max I I 4"x4" trench u Post spacing may be increased to 8' if wire backing is used 2"x2" wood posts, steel fence posts, or equivalent DEPARTMENT OF ECOLOGY State of Washington 2"x2" by 14 Ga. wire or equivalent, if standard strength fabric used Geotextile fabric 2' min Backfill trench with native soil or 4" - /\� 1.5" washed gravel �j12' min Minimum 47x4" trench 27x2" wood posts, steel fence posts, or equivalent Silt Fence NOT TO SCALE Revised July 2017 Please see http://www.ecy.wa.gov/cop3aVht.html for copyright notice including permissions, limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 371 Design and Installation Specifications . Use in combination with other construction stormwater BMPs. Maximum slope steepness (perpendicular to the silt fence line) 1 H:1 V. Maximum sheet or overland flow path length to the silt fence of 100 feet. Do not allow flows greater than 0.5 cfs. Use geotextile fabric that meets the following standards. All geotextile properties listed below are minimum average roll values (i.e., the test result for any sampled roll in a lot shall meet or exceed the values shown in Table 11-3.11: Geotextile Fabric Standards for Silt Fence): Table II-3.11: Geotextile Fabric Standards for Silt Fence Geotextile Property Minimum Average Roll Value 0.60 mm maximum for slit film woven (#30 sieve). Polymeric Mesh AOS 0.30 mm maximum for all other geotextile types (#50 sieve). (ASTM D4751) 0.15 mm minimum for all fabric types (#100 sieve). Water Permittivity 0.02 sec-1 minimum (ASTM D4491) Grab Tensile Strength 180 lbs. Minimum for extra strength fabric. (ASTM D4632) 100 Ibs minimum for standard strength fabric. Grab Tensile Strength 30% maximum (ASTM D4632) Ultraviolet Resistance 70% minimum (ASTM D4355) Support standard strength geotextiles with wire mesh, chicken wire, 2-inch x 2-inch wire, safety fence, or jute mesh to increase the strength of the geotextile. Silt fence materials are available that have synthetic mesh backing attached. . Silt fence material shall contain ultraviolet ray inhibitors and stabilizers to provide a minimum of six months of expected usable construction life at a temperature range of 0°F to 120°F. One -hundred percent biodegradable silt fence is available that is strong, long lasting, and can be left in place after the project is completed, if permitted by the local jurisdiction. Refer to Figure 11-3.22: Silt Fence for standard silt fence details. Include the following Stand- ard Notes for silt fence on construction plans and specifications: The Contractor shall install and maintain temporary silt fences at the locations shown in the Plans. 2. Construct silt fences in areas of clearing, grading, or drainage prior to starting those activities. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 372 3. The silt fence shall have a 2-feet min. and a 2'/2-feet max. height above the original ground surface. 4. The geotextile fabric shall be sewn together at the point of manufacture to form fabric lengths as required. Locate all sewn seams at support posts. Alternatively, two sections of silt fence can be overlapped, provided that the overlap is long enough and that the adjacent silt fence sections are close enough together to prevent silt laden water from escaping through the fence at the overlap. 5. Attach the geotextile fabric on the up -slope side of the posts and secure with staples, wire, or in accordance with the manufacturer's recommendations. Attach the geotextile fabric to the posts in a manner that reduces the potential for tearing. 6. Support the geotextile fabric with wire or plastic mesh, dependent on the properties of the geotextile selected for use. If wire or plastic mesh is used, fasten the mesh securely to the up -slope side of the posts with the geotextile fabric up -slope of the mesh. 7. Mesh support, if used, shall consist of steel wire with a maximum mesh spacing of 2- inches, or a prefabricated polymeric mesh. The strength of the wire or polymeric mesh shall be equivalent to or greater than 180 lbs. grab tensile strength. The polymeric mesh must be as resistant to the same level of ultraviolet radiation as the geotextile fabric it supports. 8. Bury the bottom of the geotextile fabric 4-inches min. below the ground surface. Backfill and tamp soil in place over the buried portion of the geotextile fabric, so that no flow can pass beneath the silt fence and scouring cannot occur. When wire or polymeric back-up support mesh is used, the wire or polymeric mesh shall extend into the ground 3-inches min. 9. Drive or place the silt fence posts into the ground 18-inches min. A 12—inch min. depth is allowed if topsoil or other soft subgrade soil is not present and 18-inches cannot be reached. Increase fence post min. depths by 6 inches if the fence is located on slopes of 3H :1 V or steeper and the slope is perpendicular to the fence. If required post depths cannot be obtained, the posts shall be adequately secured by bracing or guying to pre- vent overturning of the fence due to sediment loading. 10. Use wood, steel or equivalent posts. The spacing of the support posts shall be a max- imum of 6-feet. Posts shall consist of either: • Wood with minimum dimensions of 2 inches by 2 inches by 3 feet. Wood shall be free of defects such as knots, splits, or gouges. . No. 6 steel rebar or larger. . ASTM A 120 steel pipe with a minimum diameter of 1-inch. • U, T, L, or C shape steel posts with a minimum weight of 1.35 lbs./ft. • Other steel posts having equivalent strength and bending resistance to the post sizes listed above. 11. Locate silt fences on contour as much as possible, except at the ends of the fence, 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 373 where the fence shall be turned uphill such that the silt fence captures the runoff water and prevents water from flowing around the end of the fence. 12. If the fence must cross contours, with the exception of the ends of the fence, place check dams perpendicular to the back of the fence to minimize concentrated flow and erosion. The slope of the fence line where contours must be crossed shall not be steeper than 3H:1 V. . Check dams shall be approximately 1-foot deep at the back of the fence. Check dams shall be continued perpendicular to the fence at the same elevation until the top of the check dam intercepts the ground surface behind the fence. . Check dams shall consist of crushed surfacing base course, gravel backfill for walls, or shoulder ballast. Check dams shall be located every 10 feet along the fence where the fence must cross contours. Refer to Figure II-3.23: Silt Fence Installation by Slicing Method for slicing method details. The following are specifications for silt fence installation using the slicing method: 1. The base of both end posts must be at least 2- to 4-inches above the top of the geo- textile fabric on the middle posts for ditch checks to drain properly. Use a hand level or string level, if necessary, to mark base points before installation. 2. Install posts 3- to 4-feet apart in critical retention areas and 6- to 7-feet apart in standard applications. 3. Install posts 24-inches deep on the downstream side of the silt fence, and as close as possible to the geotextile fabric, enabling posts to support the geotextile fabric from upstream water pressure. 4. Install posts with the nipples facing away from the geotextile fabric. 5. Attach the geotextile fabric to each post with three ties, all spaced within the top 8- inches of the fabric. Attach each tie diagonally 45 degrees through the fabric, with each puncture at least 1-inch vertically apart. Each tie should be positioned to hang on a post nipple when tightening to prevent sagging. 6. Wrap approximately 6-inches of the geotextile fabric around the end posts and secure with 3 ties. 7. No more than 24-inches of a 36-inch geotextile fabric is allowed above ground level. 8. Compact the soil immediately next to the geotextile fabric with the front wheel of the tractor, skid steer, or roller exerting at least 60 pounds per square inch. Compact the upstream side first and then each side twice for a total of four trips. Check and correct the silt fence installation for any deviation before compaction. Use a flat -bladed shovel to tuck the fabric deeper into the ground if necessary. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 374 Figure 11-3.23: Silt Fence Installation by Slicing Method Ponding height max. 24" Attach fabric to upstream side of post FLOW - Drive over each side of silt fence 2 to 4 times with device exerting 60 p.s.i. or greater POST SPACING: 7' max. on open runs 4' max. on pooling areas POST DEPTH: As much below ground as fabric above ground 100% compaction 11 1 100% com N No more than 24" of a 36" fabric is allowed above ground Operation Horizontal chisel point (76 mm width) Top of Fabric ` Belt I# topy 8" f Diagonal attachment doubles strength Attachment Details: • Gather fabric at posts, if needed. • Utilize three ties per post, all within top 8" of fabric. • Position each tie diagonally, puncturing holes vertically a minimum of 1" apart. • Hang each tie on a post nipple and tighten securely. Use cable ties (50 Ibs) or soft wire. Roll of silt fence Slicing blade (18 mm width) Vibratory plow is not acceptable because of horizontal compaction DEPARTMENT OF ECOLOGY State of Washington Fabric above ground 200 - 300mm F Post installed after compaction Silt Fence Completed Installation NOT TO SCALE Silt Fence Installation by Slicing Method Revised June 2016 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 375 Maintenance Standards . Repair any damage immediately. . Intercept and convey all evident concentrated flows uphill of the silt fence to a sediment trap- ping BMP. . Check the uphill side of the silt fence for signs of the fence clogging and acting as a barrier to flow and then causing channelization of flows parallel to the fence. If this occurs, replace the fence and remove the trapped sediment. Remove sediment deposits when the deposit reaches approximately one-third the height of the silt fence, or install a second silt fence. Replace geotextile fabric that has deteriorated due to ultraviolet breakdown. BMP C234: Vegetated Strip N/A Purpose Vegetated strips reduce the transport of coarse sediment from a construction site by providing a physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use . Vegetated strips may be used downslope of all disturbed areas. Vegetated strips are not intended to treat concentrated flows, nor are they intended to treat substantial amounts of overland flow. Any concentrated flows must be conveyed through the drainage system to BMP C241: Sediment Pond (Temporary) or other sediment trapping BMP. The only circumstance in which overland flow can be treated solely by a vegetated strip, rather than by a sediment trapping BMP, is when the following criteria are met (see Table 11- 3.12: Contributing Drainage Area for Vegetated Strips): Table II-3.12: Contributing Drainage Area for Vegetated Strips Average Contributing Area Slope Average Contributing Area Per- cent Slope Max Contributing area Flowpath Length 1.5H : 1 V or flatter 67% or flatter 100 feet 2H : 1 V or flatter 50% or flatter 115 feet 4H : 1 V or flatter 25% or flatter 150 feet 6H : 1 V or flatter 16.7% or flatter 200 feet 1 OH : 1 V or flatter 10% or flatter 250 feet 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 376 n and Installation Specifications . The ve tated strip shall consist of a continuous strip of dense vegetation with to it for a min- imum of a 254pot length along the flowpath. Grass -covered, landscaped are are generally not adequate be se the volume of sediment overwhelms the grass. I Ily, vegetated strips shall consist of undis ed native growth with swell -developed so' at allows for infiltration of runoff. . The slope within the vegetated stri hall not exceed 4 . V. . The uphill boundary of the vegetated strip I delineated with clearing limits. Maintenance Standards . Any areas damaged by eros' or construction activity shall b eeded immediately and pro- tected by mulch. . If more than �fe of theoriginal vegetated strip width has had vegetation oved or is being eroded, so be installed. . If t e are indications that concentrated flows are traveling across the vegetated strip,3tc ater runoff controls must be installed to reduce the flows entering the vegetated strip, or tional perimeter protection must be installed. BMP C235: Wattles Purpose Wattles are temporary erosion and sediment control barriers consisting of straw, compost, or other material that is wrapped in netting made of natural plant fiber or similar encasing material. They reduce the velocity and can spread the flow of rill and sheet runoff, and can capture and retain sed- iment. Conditions of Use Wattles shall consist of cylinders of plant material such as weed -free straw, coir, wood chips, excelsior, or wood fiber or shavings encased within netting made of natural plant fibers unaltered by synthetic materials. . Use wattles: In disturbed areas that require immediate erosion protection. On exposed soils during the period of short construction delays, or over winter months. o On slopes requiring stabilization until permanent vegetation can be established. . The material used dictates the effectiveness period of the wattle. Generally, wattles are effect- ive for one to two seasons. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 377 Prevent rilling beneath wattles by entrenching and overlapping wattles to prevent water from passing between them. Design Criteria . See Figure 11-3.24: Wattles for typical construction details. • Wattles are typically 8 to 10 inches in diameter and 25 to 30 feet in length. . Install wattles perpendicular to the flow direction and parallel to the slope contour. • Place wattles in shallow trenches, staked along the contour of disturbed or newly constructed slopes. Dig narrow trenches across the slope (on contour) to a depth of 3- to 5-inches on clay soils and soils with gradual slopes. On loose soils, steep slopes, and areas with high rainfall, the trenches should be dug to a depth of 5- to 7- inches, or 1 /2 to 2/3 of the thickness of the wattle. . Start building trenches and installing wattles from the base of the slope and work up. Spread excavated material evenly along the uphill slope and compact it using hand tamping or other methods. . Construct trenches at intervals of 10- to 25-feet depending on the steepness of the slope, soil type, and rainfall. The steeper the slope the closer together the trenches. . Install the wattles snugly into the trenches and overlap the ends of adjacent wattles 12 inches behind one another. . Install stakes at each end of the wattle, and at 4-foot centers along entire length of wattle. . If required, install pilot holes for the stakes using a straight bar to drive holes through the wattle and into the soil. • Wooden stakes should be approximately 0.75 x 0.75 x 24 inches min. Willow cuttings or 3/8- inch rebar can also be used for stakes. • Stakes should be driven through the middle of the wattle, leaving 2 to 3 inches of the stake pro- truding above the wattle. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 378 Figure II-3.24: Wattles Straw rolls must be placed along slope contours 10' - 25' (3-8m) Spacing depends on soil type and slope steepness Live Stake 7— 3' - 4' � f (1.2m) /// Sediment, organic matter, and native seeds are captured behind the rolls. 3" - 5" (75-125mm) V x 1" Stake l/ (25 x 25mm) Overlap adjacent rolls 12" behind one another 8" - 10" Dia. (200-250mm) wt NOTE: r 1. Straw roll installation requires the placement and secure staking of the roll in a trench, 3" - 5" (75-125mm) deep, dug on contour. Runoff must not be allowed to run under or around roll. NOT TO SCALE Wattles Revised December 2016 DEPARTMENT OF ECOLOGYplease see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, State of Washington limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 379 Maintenance Standards Wattles may require maintenance to ensure they are in contact with soil and thoroughly entrenched, especially after significant rainfall on steep sandy soils. . Inspect the slope after significant storms and repair any areas where wattles are not tightly abutted or water has scoured beneath the wattles. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology's website at: https:Hecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies BMP C236: Vegetative Filtration N/A Purpose Vegetative filtration as a BMP is used in conjunction with detention storage in the form of portable tanks or BMP C241: Sediment Pond (Temporary), BMP C206: Level Spreader, and a pumping sys- tem with surface intake. Vegetative filtration improves turbidity levels of stormwater discharges by fil- tering runoff through existing vegetation where undisturbed forest floor duff layer or established lawn with thatch layer are present. Vegetative filtration can also be used to infiltrate dewatering waste from foundations, vaults, and trenches as long as runoff does not occur. Conditions of Use • For every five acres of disturbed soil use one acre of grass field, farm pasture, or wooded area. Reduce or increase this area depending on project size, ground water table height, and other site conditions. • Wetlands shall not be used for vegetative filtration. • Do not use this BMP in areas with a high ground water table, or in areas that will have a high seasonal ground water table during the use of this BMP. . This BMP may be less effective on soils that prevent the infiltration of the water, such as hard till. • Using other effective source control measures throughout a construction site will prevent the generation of additional highly turbid water and may reduce the time period or area need for this BMP. . Stop distributing water into the vegetated filtration area if standing water or erosion results. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 380 Maintenance Standards • Remove sediment from the pond when it reaches 1 foot in depth. • Repair any damage to the pond embankments or slopes. BMP C250: Construction Stormwater Chemical Treatment Purpose This BMP applies when using chemicals to treat turbidity in stormwater by either batch or flow - through chemical treatment. Turbidity is difficult to control once fine particles are suspended in stormwater runoff from a con- struction site. BMP C241: Sediment Pond (Temporary) is effective at removing larger particulate matter by gravity settling, but is ineffective at removing smaller particulates such as clay and fine silt. Traditional Construction Stormwater BMPs may not be adequate to ensure compliance with the water quality standards for turbidity in the receiving water. Chemical treatment can reliably provide exceptional reductions of turbidity and associated pol- lutants. Chemical treatment may be required to meet turbidity stormwater discharge requirements, especially when construction proceeds through the wet season. Conditions of Use Formal written approval from Ecology is required for the use of chemical treatment, regardless of site size. See https://fortress.wa.gov/ecy/publications/SummaryPages/ecy070258.html for a copy of the Request for Chemical Treatment form. The Local Permitting Authority may also require review and approval. When authorized, the chemical treatment systems must be included in the Con- struction Stormwater Pollution Prevention Plan (SWPPP). Chemically treated stormwater discharged from construction sites must be nontoxic to aquatic organ- isms. The Chemical Technology Assessment Protocol - Ecology (CTAPE) must be used to evaluate chemicals proposed for stormwater treatment. Only chemicals approved by Ecology under the CTAPE may be used for stormwater treatment. The approved chemicals, their allowable application techniques (batch treatment or flow -through treatment), allowable application rates, and conditions of use can be found at the Department of Ecology Emerging Technologies website: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-permittee- guidance-resources/E merging-stormwater-treatment-technologies Background on Chemical Treatment Systems Coagulation and flocculation have been used for over a century to treat water. The use of coagu- lation and flocculation to treat stormwater is a very recent application. Experience with the treatment of water and wastewater has resulted in a basic understanding of the process, in particular factors 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 396 that affect performance. This experience can provide insights as to how to most effectively design and operate similar systems in the treatment of stormwater. Fine particles suspended in water give it a milky appearance, measured as turbidity. Their small size, often much less than 1 pm in diameter, give them a very large surface area relative to their volume. These fine particles typically carry a negative surface charge. Largely because of these two factors (small size and negative charge), these particles tend to stay in suspension for extended periods of time. Thus, removal is not practical by gravity settling. These are called stable suspensions. Chem- icals like polymers, as well as inorganic chemicals such as alum, speed the settling process. The added chemical destabilizes the suspension and causes the smaller particles to flocculate. The pro- cess consists of three primary steps: coagulation, flocculation, and settling or clarification. Ecology requires a fourth step, filtration, on all stormwater chemical treatment systems to reduce floc dis- charge and to provide monitoring prior to discharge. General Design and Installation Specifications • Chemicals approved for use in Washington State are listed on Ecology's TAPE website, http://www.ecy.wa.gov/programs/wq/stormwater/newtech/technologies.html, under the "Con- struction" tab. . Care must be taken in the design of the withdrawal system to minimize outflow velocities and to prevent floc discharge. Stormwater that has been chemically treated must be filtered through BMP C251: Construction Stormwater Filtration for filtration and monitoring prior to dis- charge. . System discharge rates must take into account downstream conveyance integrity. . The following equipment should be located on site in a lockable shed: • The chemical injector. • Secondary containment for acid, caustic, buffering compound, and treatment chemical. • Emergency shower and eyewash. • Monitoring equipment which consists of a pH meter and a turbidimeter. There are two types of systems for applying the chemical treatment process to stormwater: the batch chemical treatment system and the flow -through chemical treatment system. See below for further details for both types of systems. Batch Chemical Treatment Systems A batch chemical treatment system consists of four steps: coagulation, flocculation, clarification, and polishing and monitoring via filtration. Step 1: Coagulation Coagulation is the process by which negative charges on the fine particles are disrupted. By dis- rupting the negative charges, the fine particles are able to flocculate. Chemical addition is one method of destabilizing the suspension, and polymers are one class of chemicals that are generally effective. Chemicals that are used for this purpose are called coagulants. Coagulation is complete 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 397 when the suspension is destabilized by the neutralization of the negative charges. Coagulants per- form best when they are thoroughly and evenly dispersed under relatively intense mixing. This rapid mixing involves adding the coagulant in a manner that promotes rapid dispersion, followed by a short time period for destabilization of the particle suspension. The particles are still very small and are not readily separated by clarification until flocculation occurs. Step 2: Flocculation Flocculation is the process by which fine particles that have been destabilized bind together to form larger particles that settle rapidly. Flocculation begins naturally following coagulation, but is enhanced by gentle mixing of the destabilized suspension. Gentle mixing helps to bring particles in contact with one another such that they bind and continually grow to form "flocs." As the size of the flocs increase, they become heavier and settle. Step 3: Clarification The final step is the settling of the particles, or clarification. Particle density, size and shape are important during settling. Dense, compact flocs settle more readily than less dense, fluffy flocs. Because of this, flocculation to form dense, compact flocs is particularly important during chemical treatment. Water temperature is important during settling. Both the density and viscosity of water are affected by temperature; these in turn affect settling. Cold temperatures increase viscosity and dens- ity, thus slowing down the rate at which the particles settle. The conditions under which clarification is achieved can affect performance. Currents can affect set- tling. Currents can be produced by wind, by differences between the temperature of the incoming water and the water in the clarifier, and by flow conditions near the inlets and outlets. Quiescent water, such as that which occurs during batch clarification, provides a good environment for settling. One source of currents in batch chemical treatment systems is movement of the water leaving the clarifier unit. Because flocs are relatively small and light, the velocity of the water must be as low as possible. Settled flocs can be resuspended and removed by fairly modest currents. Step 4: Filtration After clarification, Ecology requires stormwater that has been chemically treated to be filtered and monitored prior to discharge. The sand filtration system continually monitors the stormwater effluent for turbidity and pH. If the discharge water is ever out of an acceptable range for turbidity or pH, the water is returned to the untreated stormwater pond where it will begin the treatment process again. Design and Installation of Batch Chemical Treatment Systems A batch chemical treatment system consists of a stormwater collection system (either a temporary diversion or the permanent site drainage system), an untreated stormwater storage pond, pumps, a chemical feed system, treatment cells, a filtering and monitoring system, and interconnecting piping. The batch treatment system uses a storage pond for untreated stormwater, followed by a minimum of two lined treatment cells. Multiple treatment cells allow for clarification of chemically treated water in one cell, while other cells are being filled or emptied. Treatment cells may be ponds or tanks. Ponds with constructed earthen embankments greater than six feet high or which impound more than 10 acre-feet are subject to the Washington Dam Safety Regulations (Chapter 173-175 WAC). 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 398 See BMP D.1: Detention Ponds for more information regarding dam safety considerations for ponds. Stormwater is collected at interception point(s) on the site and is diverted by gravity or by pumping to an untreated stormwater storage pond or other untreated stormwater holding area. The stormwater is stored until treatment occurs. It is important that the storage pond is large enough to provide adequate storage. The first step in the treatment sequence is to check the pH of the stormwater in the untreated storm - water storage pond. The pH is adjusted by the application of carbon dioxide or a base until the storm water in the untreated storage pond is within the desired pH range, 6.5 to 8.5. When used, carbon dioxide is added immediately downstream of the transfer pump. Typically sodium bicarbonate (bak- ing soda) is used as a base, although other bases may be used. When needed, base is added dir- ectly to the untreated stormwater storage pond. The stormwater is recirculated with the treatment pump to provide mixing in the storage pond. Initial pH adjustments should be based on daily bench tests. Further pH adjustments can be made at any point in the process. See BMP C252: Treating and Disposing of High pH Water for more information on pH adjustments as a part of chemical treat- ment. Once the stormwater is within the desired pH range (which is dependant on the coagulant being used), the stormwater is pumped from the untreated stormwater storage pond to a lined treatment cell as a coagulant is added. The coagulant is added upstream of the pump to facilitate rapid mixing The water is kept in the lined treatment cell for clarification. In a batch mode process, clarification typ ically takes from 30 minutes to several hours. Prior to discharge, samples are withdrawn for analysis of pH, coagulant concentration, and turbidity. If these levels are acceptable, the treated water is with drawn, filtered, and discharged. Several configurations have been developed to withdraw treated water from the treatment cell. The original configuration is a device that withdraws the treated water from just beneath the water sur- face using a float with adjustable struts that prevent the float from settling on the cell bottom. This reduces the possibility of picking up floc from the bottom of the cell. The struts are usually set at a min imum clearance of about 12 inches; that is, the float will come within 12 inches of the bottom of the cell. Other systems have used vertical guides or cables which constrain the float, allowing it to drift up and down with the water level. More recent designs have an H-shaped array of pipes, set on the hori- zontal.This scheme provides for withdrawal from four points rather than one. This configuration reduces the likelihood of sucking settled solids from the bottom. It also reduces the tendency for a vor tex to form. Inlet diffusers, a long floating or fixed pipe with many small holes in it, are also an option. Safety is a primary concern. Design should consider the hazards associated with operations, such as sampling. Facilities should be designed to reduce slip hazards and drowning. Tanks and ponds should have life rings, ladders, or steps extending from the bottom to the top. Sizing Batch Chemical Treatment Systems Chemical treatment systems must be designed to control the velocity and peak volumetric flow rate that is discharged from the system and consequently the project site. See Element 3: Control Flow Rates for further details on this requirement. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 399 The total volume of the untreated stormwater storage pond and treatment cells must be large enough to treat stormwater that is produced during multiple day storm events. It is recommended that at a minimum the untreated stormwater storage pond be sized to hold 1.5 times the volume of runoff generated from the site during the 10-year, 24-hour storm event. Bypass should be provided around the chemical treatment system to accommodate extreme storm events. Runoff volume shall be calculated using the methods presented in III-2.3 Single Event Hydrograph Method. Worst -case land cover conditions (i.e., producing the most runoff) should be used for analyses (in most cases, this would be the land cover conditionsjust prior to final landscaping). Primary settling should be encouraged in the untreated stormwater storage pond. A forebay with access for maintenance may be beneficial. There are two opposing considerations in sizing the treatment cells. A larger cell is able to treat a lar- ger volume of water each time a batch is processed. However, the larger the cell, the longer the time required to empty the cell. A larger cell may also be less effective at flocculation and therefore require a longer settling time. The simplest approach to sizing the treatment cell is to multiply the allowable discharge flow rate (as determined by the guidance in Element 3: Control Flow Rates) times the desired drawdown time. A 4-hour drawdown time allows one batch per cell per 8-hour work period, given 1 hour of flocculation followed by two hours of settling. See BMP C251: Construction Stormwater Filtration for details on sizing the filtration system at the end of the batch chemical treatment system. If the chemical treatment system design does not allow you to discharge at the rates as required by Element 3: Control Flow Rates, and if the site has a permanent Flow Control BMP that will serve the planned development, the discharge from the chemical treatment system may be directed to the per- manent Flow Control BMP to comply with Element 3: Control Flow Rates. In this case, all discharge (including water passing through the treatment system and stormwater bypassing the treatment sys- tem) will be directed into the permanent Flow Control BMP. If site constraints make locating the untreated stormwater storage pond difficult, the permanent Flow Control BMP may be divided to serve as the untreated stormwater storage pond and the post -treatment temporary flow control pond. A berm or barrier must be used in this case so the untreated water does not mix with the treated water. Both untreated stormwater storage requirements, and adequate post -treatment flow control must be achieved. The designer must document in the Construction SWPPP how the per- manent Flow Control BMP is able to attenuate the discharge from the site to meet the requirements of Element 3: Control Flow Rates. If the design of the permanent Flow Control BMP was modified for temporary construction flow control purposes, the construction of the permanent Flow Control BMP must be finalized, as designed for its permanent function, at project completion. Flow -Through Chemical Treatment Systems Background on Flow -Through Chemical Treatment Systems A flow -through chemical treatment system adds a sand filtration component to the batch chemical treatment system's treatment train following flocculation. The coagulant is added to the stormwater upstream of the sand filter so that the coagulation and flocculation step occur immediately prior to the filter. The advantage of a flow -through chemical treatment system is the time saved by immediately filtering the water, as opposed to waiting for the clarification process necessary in a batch chemical 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 400 treatment system. See BMP C251: Construction Stormwater Filtration for more information on fil- tration. Desian and Installation of Flow-Throuah Chemical Treatment Svstems At a minimum, a flow -through chemical treatment system consists of a stormwater collection system (either a temporary diversion or the permanent site drainage system), an untreated stormwater stor- age pond, and a chemically enhanced sand filtration system. As with a batch treatment system, stormwater is collected at interception point(s) on the site and is diverted by gravity or by pumping to an untreated stormwater storage pond or other untreated storm. water holding area. The stormwater is stored until treatment occurs. It is important that the holding pond be large enough to provide adequate storage. Stormwater is then pumped from the untreated stormwater storage pond to the chemically enhanced sand filtration system where a coagulant is added. Adjustments to pH may be necessary before coagulant addition. The sand filtration system continually monitors the stormwater effluent for turbidity and pH. If the discharge water is ever out of an acceptable range for turbidity or pH, the water is returned to the untreated stormwater pond where it will begin the treatment process again. Sizing Flow -Through Chemical Treatment Systems Refer to BMP C251: Construction Stormwater Filtration for sizing requirements of flow -through chemical treatment systems. Factors Affecting the Chemical Treatment Process Coagulants Cationic polymers can be used as coagulants to destabilize negatively charged turbidity particles present in natural waters, wastewater and stormwater. Polymers are large organic molecules that are made up of subunits linked together in a chain -like structure. Attached to these chain -like struc- tures are other groups that carry positive or negative charges, or have no charge. Polymers that carry groups with positive charges are called cationic, those with negative charges are called anionic, and those with no charge (neutral) are called nonionic. In practice, the only way to determ- ine whether a polymer is effective for a specific application is to perform preliminary or on -site test- ing. Aluminum sulfate (alum) can also be used as a coagulant, as this chemical becomes positively charged when dispersed in water. Polymers are available as powders, concentrated liquids, and emulsions (which appear as milky liquids). The latter are petroleum based, which are not allowed for construction stormwater treat- ment. Polymer effectiveness can degrade with time and also from other influences. Thus, man- ufacturers' recommendations for storage should be followed. Manufacturer's recommendations usually do not provide assurance of water quality protection or safety to aquatic organisms. Con- sideration of water quality protection is necessary in the selection and use of all polymers. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 401 Application Application of coagulants at the appropriate concentration or dosage rate for optimum turbidity removal is important for management of chemical cost, for effective performance, and to avoid aquatic toxicity. The optimum dose in a given application depends on several site -specific features. Turbidity of untreated water can be important with turbidities greater than 5,000 NTU. The surface charge of particles to be removed is also important. Environmental factors that can influence dosage rate are water temperature, pH, and the presence of constituents that consume or otherwise affect coagulant effectiveness. Laboratory experiments indicate that mixing previously settled sediment (floc sludge) with the untreated stormwater significantly improves clarification, therefore reducing the effective dosage rate. Preparation of working solutions and thorough dispersal of coagulants in water to be treated is also important to establish the appropriate dosage rate. For a given water sample, there is generally an optimum dosage rate that yields the lowest residual turbidity after settling. When dosage rates below this optimum value (underdosing) are applied, there is an insufficient quantity of coagulant to react with, and therefore destabilize, all of the turbidity present. The result is residual turbidity (after flocculation and settling) that is higher than with the optimum dose. Overdosing, application of dosage rates greater than the optimum value, can also negatively impact performance. Like underdosing, the result of overdosing is higher residual turbidity than that with the optimum dose. Mixing The G-value, or just "G", is often used as a measure of the mixing intensity applied during coagu- lation and flocculation. The symbol G stands for "velocity gradient", which is related in part to the degree of turbulence generated during mixing. High G-values mean high turbulence, and vice versa. High G-values provide the best conditions for coagulant addition. With high G's, turbulence is high and coagulants are rapidly dispersed to their appropriate concentrations for effective destabilization of particle suspensions. Low G-values provide the best conditions for flocculation. Here, the goal is to promote formation of dense, compact flocs that will settle readily. Low G's provide low turbulence to promote particle col- lisions so that flocs can form. Low G's generate sufficient turbulence such that collisions are effective in floc formation, but do not break up flocs that have already formed. pH Adjustment The pH must be in the proper range for the coagulants to be effective, which is typically 6.5 to 8.5. As polymers tend to lower the pH, it is important that the stormwater have sufficient buffering capacity. Buffering capacity is a function of alkalinity. Without sufficient alkalinity, the application of the polymer may lower the pH to below 6.5. A pH below 6.5 not only reduces the effectiveness of the polymer as a coagulant, but it may also create a toxic condition for aquatic organisms. Stormwater may not be discharged without readjustment of the pH to above 6.5. The target pH should be within 0.2 stand- ard units of the receiving water's pH. Experience gained at several projects in the City of Redmond has shown that the alkalinity needs to be at least 50 mg/L to prevent a drop in pH to below 6.5 when the polymer is added. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 402 Maintenance Standards Monitoring At a minimum, the following monitoring shall be conducted. Test results shall be recorded on a daily log kept on site. Additional testing may be required by the N PDES permit based on site conditions. Operational Monitoring • Total volume treated and discharged. • Flow must be continuously monitored and recorded at not greater than 15-minute inter- vals. • Type and amount of chemical used for pH adjustment. • Type and amount of coagulant used for treatment. • Settling time. Compliance Monitoring Influent and effluent pH, flocculent chemical concentration, and turbidity must be con- tinuously monitored and recorded at not greater than 15-minute intervals. o pH and turbidity of the receiving water. . Biomonitoring Treated stormwater must be non -toxic to aquatic organisms. Treated stormwater must be tested for aquatic toxicity or residual chemicals. Frequency of biomonitoring will be determined by Ecology. Residual chemical tests must be approved by Ecology prior to their use. If testing treated stormwater for aquatic toxicity, you must test for acute (lethal) toxicity. Bioassays shall be conducted by a laboratory accredited by Ecology, unless otherwise approved by Ecology. Acute toxicity tests shall be conducted per the CTAPE protocol and Appendix G of Whole Effluent Toxicity Testing Guidance and Test Review Criteria (Marshall, 2016). Discharge Compliance Prior to discharge, treated stormwater must be sampled and tested for compliance with pH, floc- culent chemical concentration, and turbidity limits. These limits may be established by the Con- struction Stormwater General Permit or a site -specific discharge permit. Sampling and testing for other pollutants may also be necessary at some sites. pH must be within the range of 6.5 to 8.5 stand- ard units and not cause a change in the pH of the receiving water by more than 0.2 standard units. Treated stormwater samples and measurements shall be taken from the discharge pipe or another location representative of the nature of the treated stormwater discharge. Samples used for determ- ining compliance with the water quality standards in the receiving water shall not be taken from the 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 403 treatment pond prior to decanting. Compliance with the water quality standards is determined in the receiving water. Operator Training Each project site using chemical treatment must have a trained operator who is certified for oper- ation of an Enhanced Chemical Treatment system. The operator must be trained and certified by an organization approved by Ecology. Organizations approved for operator training are found at the fol- lowing website: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-permittee- auidance-resources/Contaminated-water-on-construction-sites Sediment Removal and Disposal Sediment shall be removed from the untreated stormwater storage pond and treatment cells as necessary. Typically, sediment removal is required at least once during a wet season and at the decommissioning of the chemical treatment system. Sediment remaining in the cells between batches may enhance the settling process and reduce the required chemical dosage. . Sediment that is known to be non -toxic maybe incorporated into the site away from drain- ages. BMP C251: Construction Stormwater Filtration Purpose Filtration removes sediment from runoff originating from disturbed areas of the site. Conditions of Use Traditional Construction Stormwater BMPs used to control soil erosion and sediment loss from con- struction sites may not be adequate to ensure compliance with the water quality standard for tur- bidity in the receiving water. Filtration may be used in conjunction with gravity settling to remove sediment as small as fine silt (0.5 pm). The reduction in turbidity will be dependent on the particle size distribution of the sediment in the stormwater. In some circumstances, sedimentation and fil- tration may achieve compliance with the water quality standard for turbidity. The use of construction stormwater filtration does not require approval from Ecology as long as treat- ment chemicals are not used. Filtration in conjunction with BMP C250: Construction Stormwater Chemical Treatment requires testing under the Chemical Technology Assessment Protocol — Eco- logy (CTAPE) before it can be initiated. Approval from Ecology must be obtained at each site where chemical use is proposed prior to use. See https://- fortress.wa.gov/ecy/publications/SummaryPages/ecy070258.html for a copy of the Request for Chemical Treatment form. 2019 Stormwater Management Manual for Western Washington Volume // - Chapter 3 - Page 404 Design and Installation Specifications Two types of filtration systems may be applied to construction stormwater treatment: rapid and slow. Rapid filtration systems are the typical system used for water and wastewater treatment. They can achieve relatively high hydraulic flow rates, on the order of 2 to 20 gpm/sf, because they have auto- matic backwash systems to remove accumulated solids. Slow filtration systems have very low hydraulic rates, on the order of 0.02 gpm/sf, because they do not have backwash systems. Slow filtration systems have generally been used as post construction BMPs to treat stormwater (see V-6 Filtration BMPs). Slow filtration is mechanically simple in com- parison to rapid filtration, but requires a much larger filter area. Filter Twes and Efficiencies Sand media filters are available with automatic backwashing features that can filter to 50 pm particle size. Screen or bag filters can filter down to 5 pm. Fiber wound filters can remove particles down to 0.5 pm. Filters should be sequenced from the largest to the smallest pore opening. Sediment removal efficiency will be related to particle size distribution in the stormwater. Treatment Process and Descri Stormwater is collected at interception point(s) on the site and diverted to an untreated stormwater sediment pond or tank for removal of large sediment, and storage of the stormwater before it is treated by the filtration system. In a rapid filtration system, the untreated stormwater is pumped from the pond or tank through the filtration media. Slow filtration systems are designed using gravity to convey water from the pond or tank to and through the filtration media. Sizing Filtration treatment systems must be designed to control the velocity and peak volumetric flow rate that is discharged from the system and consequently the project site. See Element 3: Control Flow Rates for further details on this requirement. The untreated stormwater storage pond or tank should be sized to hold 1.5 times the volume of run- off generated from the site during the 10-year, 24-hour storm event, minus the filtration treatment system flowrate for an 8-hour period. For a chitosan-enhanced sand filtration system, the filtration treatment system flowrate should be sized using a hydraulic loading rate between 6-8 gpm/ft2.Other hydraulic loading rates may be more appropriate for other systems. Bypass should be provided around the filtration treatment system to accommodate extreme storm events. Runoff volume shall be calculated using the methods presented in III-2.3 Single Event Hydrograph Method. Worst -case land cover conditions (i.e., producing the most runoff) should be used for analyses (in most cases, this would be the land cover conditionsjust prior to final landscaping). If the filtration treatment system design does not allow you to discharge at the rates as required by Element 3: Control Flow Rates, and if the site has a permanent Flow Control BMP that will serve the planned development, the discharge from the filtration treatment system may be directed to the per- manent Flow Control BMP to comply with Element 3: Control Flow Rates. In this case, all discharge (including water passing through the treatment system and stormwater bypassing the treatment 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 405 system) will be directed into the permanent Flow Control BMP. If site constraints make locating the untreated stormwater storage pond difficult, the permanent Flow Control BMP may be divided to serve as the untreated stormwater storage pond and the post -treatment temporary flow control pond. A berm or barrier must be used in this case so the untreated water does not mix with the treated water. Both untreated stormwater storage requirements, and adequate post -treatment flow control must be achieved. The designer must document in the Construction SWPPP how the per- manent Flow Control BMP is able to attenuate the discharge from the site to meet the requirements of Element 3: Control Flow Rates. If the design of the permanent Flow Control BMP was modified for temporary construction flow control purposes, the construction of the permanent Flow Control BMP must be finalized, as designed for its permanent function, at project completion. Maintenance Standards • Rapid sand filters typically have automatic backwash systems that are triggered by a pre-set pressure drop across the filter. If the backwash water volume is not large or substantially more turbid than the untreated stormwater stored in the holding pond or tank, backwash return to the untreated stormwater pond or tank may be appropriate. However, other means of treat- ment and disposal may be necessary. . Screen, bag, and fiber filters must be cleaned and/or replaced when they become clogged. . Sediment shall be removed from the storage and/or treatment ponds as necessary. Typically, sediment removal is required once or twice during a wet season and at the decommissioning of the ponds. • Disposal of filtration equipment must comply with applicable local, state, and federal reg- ulations. BMP C252: Treating and Disposing of High pH Water Purpose When pH levels in stormwater rise above 8.5, it is necessary to lower the pH levels to the acceptable range of 6.5 to 8.5 prior to discharge to surface or ground water. A pH level range of 6.5 to 8.5 is typ- ical for most natural watercourses, and this neutral pH range is required for the survival of aquatic organisms. Should the pH rise or drop out of this range, fish and other aquatic organisms may become stressed and may die. Conditions of Use . The water quality standard for pH in Washington State is in the range of 6.5 to 8.5. Storm - water with pH levels exceeding water quality standards may be either neutralized on site or disposed of to a sanitary sewer or concrete batch plant with pH neutralization capabilities. Neutralized stormwater may be discharged to surface waters under the Construction Storm - water General permit. Neutralized process water such as concrete truck wash -out, hydro -demolition, or saw -cutting slurry must be managed to prevent discharge to surface waters. Any stormwater 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 406 contaminated during concrete work is considered process wastewater and must not be dis- charged to waters of the State or stormwater collection systems. . The process used for neutralizing and/or disposing of high pH stormwater from the site must be documented in the Construction Stormwater Pollution Prevention Plan. Causes of High pH High pH at construction sites is most commonly caused by the contact of stormwater with poured or recycled concrete, cement, mortars, and other Portland cement or lime containing construction materials. (See BMP C151: Concrete Handling for more information on concrete handling pro- cedures). The principal caustic agent in cement is calcium hydroxide (free lime). Calcium hardness can contribute to high pH values and cause toxicity that is associated with high pH conditions. A high level of calcium hardness in waters of the state is not allowed. Ground water stand- ard for calcium and other dissolved solids in Washington State is less than 500 mg/l. Treating High pH Stormwater by Carbon Dioxide Sparging Advantages of Carbon Dioxide Sparging • Rapidly neutralizes high pH water. • Cost effective and safer to handle than acid compounds. • CO2 is self -buffering. It is difficult to overdose and create harmfully low pH levels. • Material is readily available. The Chemical Process of Carbon Dioxide Sparging When carbon dioxide (CO2) is added to water (H2O), carbonic acid (H2CO3) is formed which can further dissociate into a proton (H+) and a bicarbonate anion (HCO3-) as shown below: CO2 + H2O H H2CO3 H H+ + HCO3- The free proton is a weak acid that can lower the pH. Water temperature has an effect on the reac- tion as well. The colder the water temperature is, the slower the reaction occurs. The warmer the water temperature is, the quicker the reaction occurs. Most construction applications in Washington State have water temperatures in the 50°F or higher range so the reaction is almost simultaneous. The Treatment Process of Carbon Dioxide Sparqinq High pH water may be treated using continuous treatment, continuous discharge systems. These manufactured systems continuously monitor influent and effluent pH to ensure that pH values are within an acceptable range before being discharged. All systems must have fail safe automatic shut off switches in the event that pH is not within the acceptable discharge range. Only trained operators may operate manufactured systems. System manufacturers often provide trained operators or train- ing on their devices. The following procedure may be used when not using a continuous discharge system: 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 407 1. Prior to treatment, the appropriate jurisdiction should be notified in accordance with the reg- ulations set by the jurisdiction. 2. Every effort should be made to isolate the potential high pH water in order to treat it separately from other stormwater on -site. 3. Water should be stored in an acceptable storage facility, detention pond, or containment cell prior to pH treatment. 4. Transfer water to be treated for pH to the pH treatment structure. Ensure that the pH treat- ment structure size is sufficient to hold the amount of water that is to be treated. Do not fill the pH treatment structure completely, allow at least 2 feet of freeboard. 5. The operator samples the water within the pH treatment structure for pH and notes the clarity of the water. As a rule of thumb, less CO2 is necessary for clearer water. The results of the samples and water clarity observations should be recorded. 6. In the pH treatment structure, add CO2 until the pH falls into the range of 6.9-7.1. Adjusting pH to within 0.2 pH units of receiving water (background pH) is recommended. It is unlikely that pH can be adjusted to within 0.2 pH units using dry ice. Compressed carbon dioxide gas should be introduced to the water using a carbon dioxide diffuser located near the bottom of the pH treatment structure, this will allow carbon dioxide to bubble up through the water and diffuse more evenly. 7. Slowly discharge the water, making sure water does not get stirred up in the process. Release about 80% of the water from the pH treatment structure leaving any sludge behind. If turbidity remains above the maximum allowable, consider adding filtration to the treatment train. See BMP C251: Construction Stormwater Filtration. 8. Discharge treated water through a pond or drainage system. 9. Excess sludge needs to be disposed of properly as concrete waste. If several batches of water are undergoing pH treatment, sludge can be left in the treatment structure for the next batch treatment. Dispose of sludge when it fills 50% of the treatment structure volume. 10. Disposal must comply with applicable local, state, and federal regulations. Treating High pH Stormwater by Food Grade Vinegar Food grade vinegar that meets FDA standards may be used to neutralize high pH water. Food grade vinegar is only 4% to 18% acetic acid with the remainder being water. Food grade vinegar may be used if dosed just enough to lower pH sufficiently. Use a treatment process as described above for CO2 sparging, but add food grade vinegar instead of CO2. This treatment option for high pH stormwater does not apply to anything but food grade vinegar. Acetic acid does not equal vinegar. Any other product or waste containing acetic acid must go through the evaluation process in Appendix G of Whole Effluent Toxicity Testing Guidance and Test Review Criteria (Marshall, 2016). 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 408 Disposal of High pH Stormwater Sanitary Sewer Disposal Local sewer authority approval is required prior to disposal via the sanitary sewer. Concrete Batch Plant Disposal . Only permitted facilities may accept high pH water. • Contact the facility to ensure they can accept the high pH water. Maintenance Standards Safety and materials handling: . All equipment should be handled in accordance with OSHA rules and regulations. • Follow manufacturer guidelines for materials handling. Each operator should provide: . A diagram of the monitoring and treatment equipment. . A description of the pumping rates and capacity the treatment equipment is capable of treat- ing. Each operator should keep a written record of the following: • Client name and phone number. • Date of treatment. • Weather conditions. • Project name and location. . Volume of water treated. • pH of untreated water. . Amount of CO2 or food grade vinegar needed to adjust water to a pH range of 6.9-7.1. • pH of treated water. • Discharge point location and description. A copy of this record should be given to the client/contractor who should retain the record for three years. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 409 Aik CITY OF Stormwater Pollution Prevention Plan (SWPPP) Short Form SHORELINE For Small and Medium Construction Projects Section 3: ESC (Erosion and Sediment Control) Plan Attach a site plan (minimum 11" x 17") that includes the following: 1. Legal description of the property. 2. North Arrow 3. Property boundaries 4. Boundaries of existing vegetation (tree lines, pasture areas, etc.) 5. Identify and label areas of potential erosion problems. 6. Identify any on -site or adjacent surface waters or critical areas and associated buffers. 7. Identify FEMA base flood boundaries and Shoreline Management boundaries (if applicable). 8. Show existing and proposed contours. 9. Delineate limits of clearing and grading. 10. Indicate BMPs. 11. Name and phone number of the person responsible for preparing and maintaining the SWPPP. NOTE: The ESC Plan can be included on the project site plan, if the plan is legible. 7 2/2019 �C JACOBSOpN r Project Site , -r f ll� I THE BOWL OF EDMONDS R e � Edmonds "Kingston Ferry Q a n oo zElementary School 0 Edmonds n St sw Marina • Beach Park © Edmonds City Park in o 0o s E 0 Westgate Elementary School 2zom St SW DO Woodway s 99 Ranch Market® n Esperance 0 E 228th St SW d herw w ntary-School a� s Mountlake ? Terrace WhirlyBall Q T toa / n Project Site � � 236th 0 Woodway Elementary I 99 Regal Cinebarr o �� oa © Mountlake O �t �t�tE-205th-st_ = rrEzosth sr Costco Wholesale N 200th St ECHO LAKE VICINITY MAP n � 1 SCALE: NTS 255 S. King Street, Suite 800, Seattle, WA 98104 1 206.426.2600 1 JACOBSONENGINEERS.COM ADD Aw 0 = S� -------—-- -- P/D c ry 29125 r Ervos� t— Bs D P - - - . - - D/w 228TH STREET SW ----- -� ----------- x d - •MAP / a iADo Ess I \ \ I \ ; ---_ RI A A AV A A AV A A AV kUC EXCHAINIJNK FENCE 'T0 7 — — — — — — \ NSTNOTIBE aN f VEG �dEMAIR'- Ili t � —SEE-DETAIL � sD— -- AND ISTLiRBED •v-ty. / / VEG- --_ -- - _ DIN_ - _- LA Ivy / {III r✓..... attPE I aNCS ID ]6 ,/'6 —SW eMfArvcww eta /rv� / 21�55 I i I E / CF / 2A�cNPI w 2RBst0/ / IN ARE PVC E/2R96 / P N 2]0.Z] / INSTALLSILT N lull,/ / V /I I { 111 / I FENCE (TYP) I ' Pvc NE 2'a / SEE DETAIL fc/ / /DEBRIS flACN W / s / ; ' POINT OF DISCHARGE T T r IP / AR I �BBD 0,fi ��OWfiNG I j \ PROPOSED LIMITS OF / LAYFlELD 7 I IL ICENSERUCTIO / WALKING PATH SEE � \�✓ /I _ FENCING(TV SHEET C2.00(T1'P) / / SEE DETAIL 15 , N L/C i I �wryvc Nq/s2/sse PROTECT E% FIELD TO REMAIN UNLESS NOTED IP OTHERWISE FOR GRADING AND INSTALLATION OF PERVIOUS ASPHALT WALKING PATH (TYP) \ y \ �EAII ExO I AIGI DINNN LG APDRIS'ELT DRANACE STtEM // ND BBAuow "'AL' 3 %1 stP �.,B �fi02 UNABLE TO DDNDRN GANDECNDrv2 I I DEI'AEEN STRUCTURES NOS AND TO / ' / BEEN O STDRM sY5rtM5 FROM I I �..� A ASPHALT I � � I I // BEEN oNSERvnnorvs / YII�I I / II I ARMING LOT V / rr I I I A / 1 F v) I I v ' , I LIT RLM CB / BW I N,RROTEGTIONmP) / Call before YOE Djg. S-Iw-! 0 10 20 40 METANC SCALE ® Sheet Index CLOD TESCPLAN C200 CMLSREPLAN C3.DO SREDETAILS LEGEND PROPERTY LINE N)r170R'F-MwIK_ LIMITS OF CONSTRUCTION W FF FILTER FABRIC FENCING CF TEMPCONSTRUCTION FENCING STRAW WATTLE CG TEMP CONSTRUCTION GATE INLET PROTECTION IP _ VEG TREEPROTEGTION SEE ARCHITECTURAL PLAN SHEET 130.00 FOR ADDITIONAL SITE INFORMATION (PLAYGROUND AREAS, GOAL POSTS, FIELD LAYOUT, ETC) COORDINATE WITH SCHOOL DISTRICT FOR ACCESS TO AND FROM PROJECT SITE GENERAL DEMOLITION AND TESC NOTES 1. NO SEDIMENT SHALL BE TRACKED INTO THE STREET OR ONTO PAVED SURFACES. 2. TESC INFORMATION SHOWN ON PLANS IS FOR PERMITTING INSTALL STRAW PURPOSES ONLY. CONTRACTOR SHALL REVISE OR INSTALL WATTLE (TYPI SEE DETAIL ADDITIONAL TESC MEASURES AS CONSTRUCTIONS CONDITIONS CHANGE. 3. CONTRACTOR SHALL INSTALL TEMPORARY CONSTRUCTION FENCING AROUND JOB SITE TO PROTECT PUBLIC AND MAINTAIN PROJECT SITE. INSTALL CONSTRUCTION FENCING (TYP) SEE DETAIL @ SEE DETAIL E mEYE//O/oe � / wDelc RSnsEn+E rvvAFU DYETEM NrvASI PEINVERT wom IP a Ns °\ / �. \ / BONN \ �� PROTECT EX AREA OAR IIR Tl� �� Nu 2e2.BI \ AND ASSOCIATED rvee'Jfi'4Yw fitfl25 C (st&3e Pj 11I 'a I B' RDN NW 3I285 \ / / / STORM PIPING TO BB B' flCN B 2T NO ) � / �mucruRE�xGT cxuRNBfD / \ / / REMAIN (TYP) uv s N BEwADE FEE,AGEA U av 1 \` q REAeRA_ :iM 201.28 GA— PC IP x B' FK w/E 2)>9.t3 / \ s' V2vc 9 21111 I II I i II 11\ \I IP \\ b D vsD (� IP i a sip BID 12 aT /� A sD I — — — y Pu,aaUND AN — T — m bl III IIII x 17111 I, I' pM BE\10O 2w II o / / / 0 Gaup MEry s) / w- PC s BIT Da 1.1 BIT M zBN.Da BErvaE / a P Wrv-sM PLAYGROUND / \ \ \(I I II 1 \ �ROU D EaCIPNErvT CF VC3.n/s zeTn (wooD ales) \ EA NNAIN SIT m b\ y\ \\ `\\` \\ �221 a R CABINET \ \ \\\\\\ =��S,A BR 5FVC528218 /// �PRQTECT EX DORDER PLAYGROUNDAREATO 1i0 \ \�\ \\\ \� ztCx ' / — \? REMAIN P �P PEOU PMCNND E1��„ X .�tBaB9 B <'4r — \I (WOOD CHIPS) /4 CUP \ \\II x M LINE �RAiPE \\\\ \ GAS STOP IT I aI II % mr P AE� _ASPHALT I IR/ PARIONG LOT SW S g \ - NI ` PROTECT EX GATE AND DEMO THIS PIECE OF `SD D N N CHAINLINK CFENCE, J D e CONC5 28219 H INC POFENCE TO FRUITS AND CHAIN LINK ( - P R12IM IRD1P t9W 2 CB�� FENCING MATERIAL REMAIN S S� SD IX ASPHALT RIM 28 D F j— PARIONG LOT \ \ m =D V �1 �IBNT ooD j PLAY SURFACING \ / P NO uinui ` \ II ��\ I OOOO�O�OO O / \ I //\\ m A \ >n GAS cTs� ENDS /d\ / NOTE: SHEET HAS BEEN PRINTED TO BE 11 X1 7 AND NOT TO SCALE HUTTEBRLL IN *OREMUS II .Nrchttdun 4010 LAKE WASHINGTON BLVD NE S JITE 320 KIRKIAND. WA 98033 425828.8948 HOARCH COM O A.JgC as/zt/»e� JC JACOBSON Sherwood Elementary Walking Path & Playground Improvements EDMONDS SCHOOL DISTRICT #15 1901 Edmonds == School District of 1010 OWIGf PHN,CBV,MRIN 1 MEARDINAL.AUTUALL, 2 PARINEIGUwMnO PLnHn�ARTDUGULA 3 PERMIT SET 03.03.2023 PROAMBIANBTR: 2BC11 INRI NAME TESC PLAN NIETEIIEEI C 1.00 STRAW ROLLS MUST BE PLACED `f/ ALONG SLOPE CONTOUR$ YY ADJACENT ROLLS SHALLTIGHTLYAB UE ,3e �l zs. �' ` YG ADAPEER RETRIEVAL STRAP SKIRT SEDIMENT ORGANIC , AND NATIVE SEDSARE CAPTURED SEEDS �48 .. 48 BEHIND THE ROLLS ROLL SPACING DEPENDS ON SOIL \ TYPE AND SLOPE STEEPNESS 3"3'(]5-125mm) CIA. _ (200-250mm) OVERFLOW ITO BYPASS PEAK STORM GEOTE RLE FABRIC VOLUMES) FABRIC WIRE FENCE X 10,E ENSAR GSI SAFETY TO STEEL POST FENCE OR EQUAL GALVANIZED WIRE OR OTHER APPROVED MATERIAL LIVESTAKE SEDIMENT CLIP FENCE TO WIRE ACCUMULATION STEEL FENCE POST 1'xl'STAKE INLET PROTECTION NOTE: NOlE3: FILTERS SHALL BE INSPECTED AFTER EACH STORM EVENT AND 1. MAWROLL INSTALLATION REQUIRES THE PLACEMENT AND SECURE STAKING CLEANED OR REPLACES WHEN I/3 FULL OFTHE ROLL IN A TRENCH, 3- x 5- (75-125mm) DEEP, DUG ON CONTOUR. 2. RUNOFF MUST NOT BE ALLOWED TO RUN UNDER OR AROUND ROLL. 3. FOR ASPHALT OR CONCRETE APPLICATIONS, STRAW WATTLE SHALL BE LAID ON TOP OF PAVEMENT AND HELD IN PLACE AS NEEDED WITH SAND BAGS AND NTS Not Used 1 NTS Not Used Z ADIUSTEDASNECESSAIR AS PHASING OR FIELD CONDITIONS CHANGE. NTS Straw Wattle 3 NTS Inlet Protection 4 NTS Clearing Limits Fearing 5 12'(MIN) STRUCTURAL FILL AS REQUIRED 3' CLASS'B'ASPHALT OR EXISTING SU6GRADE COMPACTEDTO CONCRETE PAVEMENT 95% MAX DENSITY PER ASTM D 155] SAWCUT TACK AND 4" CRUSHED SURFACING MATCH E%ASPHALT EASE%MAX EOMPACT FULL DEPTH 12" T095%MAX DENSITY �ST L,�.... I z zl; --'a "�I - CE METALS UPPORT al POST 6- VON CENER SPACING MIN 5'HEIGHT 5'POST HEIGHT BARRICADE FENCING (ORANGE 2'x4-WOOD POSTS, NOTE: FILTER FABRIC FENCES STEEL FENCE POSTS, SHALL BE INSTALLEDALONG REAR, OR EQUIVALENT CONTOUR WHENEVER POSSIBLE JOINTS IN FILTER FARIC SHALL BE SPLICED AT POSTS. USE STAPLES, 2'x2"BY 14 GE. WIRE OR WIRERINGS, OREQUIVALENTTO EQUIVALENT, IF STANDARD ATTACH FABRIC TO POSTS. STRENGTH FABRIC USED f - �Jq�y' ` CONSTRUCTION FENCE) MIN 4' FILTER FABRIC �IJI- II-I�- Ill i-IF-ITl �I II -4�m II- L_�qIIJ�L�-I J.IJIIJ.LIII l l ExIsrlNcasPHaLr vNOTES:EXUNDISTURBED PAVEMill \�\\�\\�\\�\\�\ HEIGHT SURROUND TREE OR 2'POST BURIAL DEPTH GROUP OF TREES AT DRIP LINE�'r� OR AS SHOWN ON PLANS 1. A MINIMUM 4 FOOT HIGH TEMPORARY FENCE MUST BE PLACED AT THE DRIP LINE OF TREES PRIOR TO THECOMMENCEMENTOFCLEARING R EARTHWORK. NOTIFYTHE GLARING AND GRADING MINIMUM 4'x4' TRENCH SUB_ SE MUST BE WM ACTE 1111\\�\\\�\\j AND APPROVAL OF FLAGGED CLEARING TO GETTIIONTENCINGEAROUND (TEMP 95% LAAXXD EN PER AST.D155O �r OR PRO ECTNSPEC70 TRECTION ES TOANDE BE SAVED PER THE APPROVED AND GRADING PLAN. T� _I��III�II�I�III�II�I�III�II�I�III�II�I�III�F 2. NO STOCKPILING OF MATERIAL AND NO VEHICULAR TRAFFIC ARE ALLOWED WITHIN THE LIMITS OF THE TEMPORARY FENCING.FILLING,EXCAVATION, AND CLEARING MUST BE ACCOMPLISHED BY HAND METHODS ONLY. 3. ROOTSOTH OWING TO :FORD DAMAGED ER1- DURING CONSTRUCTION MUST BETRATGHT CU IN OOTSOVER TOREMOVETHE DAMAGED PORTION OF ONE ROOT. ALL NEXPOSED EROOTS WILL BE TEMPORARILY T 1 BACNFILL TRENCH WRH IR pOST$PACING GMAXMAY BE INCREASED r NATIVE SOIL OR 3/A'1.EL WASHED GRAVEL Li TO IF WIRE BACKING IS USED 2"x4"WOOD POSTS, NOES: COVERED WITH DAMP BURLAP OR WOOD SHAVINGS TO PREVENT DRYING AND COVERED WITH EARTH STEEL FENCE POSTS, AS SOON AS POSSIBLE. REBAR, OR EQUIVALENT 1. ASP HALT PAVEMENT SHALL BE PLACED IN (2) LIFTS. FINAL LIFT SHALL BE CONSTRUCTED WITH THE OVERLAY OF THE EXISTING 4. SEE TREE PROTECTION AND TESC PLAINS FOR LOCATION OF EXISTING TREES TO RECEIVE TEMPORARY ASPHALT ONLY AFTER BUILDING IMPROVEMENTS ARE COMPLETE FENCING. 5. SEESPECIFICATIONSS FOR PRUNING, WATERING, AND OTHER MAINTENANCE REQUIREMENTS NTS Not Used 6 NTS Not Used % NTS Standard Asphalt Pavement $ NTS Tree Protection 9 NIS Sik Fence 1 FINISHED GRADE PER PLAN 5/8' WIRE ROPE PROVIDE SECURE END ATTACHMENTAT CORNER AND GATE POSTS AND PROVIDE RUNNING ATTACHMENT AT LINE POSTS AND PEDESTRIAN SURFACE WIDTH PER PLAN NEAR CENTER OF EACH FENCE PANEL TRUSS ROD 3/8' DIA TOP RAIL W/ TENSION DEVICE 5.6661NCH O.D. STRETCHER LINE POST (TYR) AR 2.375 INCH O.D. _ / r) I °o 3" COMPACTED DEPTH OF POROUS HOT MIX ASPHALT SIDEWALK PER WSDOT SPEC SECTION 9-03.8/5-04.2 2' DEPTH CHOKER/LEVELING COURSE (5/9" CLAN ROCK) ENSIGN WIRE BRACE RAIL 9MIN DEPTH BASE COURSE OF PERMEABLE AND CABLE CONCRETE BLOCK 1.666INCH O.D. BALLAST PER MOOT SPEC SECTION 9-03.9I2) STD WGT GALVANIZED CORNER POST NON -WOVEN GEOTEXTILE ON BOTTOM AND SIDES. NT$ 11 Not Used NTS 1 Not Used NT$ 1 Not Used PER WSDOT SPEC SECTION 933.2(1) NTS 14 Porous Asphalt Sidewalk NTS 15 Construction Fence NOTE: SHEET HAS BEEN PRINTED TO BE 11 X1 7 AND NOT TO SCALE NTS 1 C Not Used V NTS 1 Not Used NTS 1 p Not Used V NTS 1 Not Used NTS �O Not Used HUTTEBRLL IN *OREMUS I/ erchhadure 4010 LAKE WASHINGTON BLVD NE S JITE 320 KIRKIAND. WA 98033 :Y}�:YI:AEFf:I HOARCH COM =in JACOBSON Pr01[Ci NCELIRIp Sherwood Elementary Walking Path & Playground Improvements EDMONDS SCHOOL DISTRICT #15 1901 Edmonds == School District 011013 OuxGf PRix 106f1 WIOM t 2 20RZ1 P,nM4.UTA AFOOLNON 3 oOL 1®EfSB PERMIT SET 03.03.2023 I'MICTNNBER: P9112 SNFfI NAME SITE DETAILS SHIES-BER C3.00 Ah CITY OF SHORELINE Stormwater Pollution Prevention Plan (SWPPP) Short Form For Small and Medium Construction Projects Page intentionally left blank. 2/2019 CONSTRUCTION EMERGENCY CONTACT SHEET Date: 7/5/2023 Project Name: Sherwood Elementary School - New Walking Path Project Address: 22901 106th Ave W, Edmonds, WA 98020 Type of work: Construction of a New Pervious Asphalt Walking Path - - - - - - - - - - - - - - - Developer: Nick Chou c/o Edmonds School District Office Phone: 425.431.7162 24-hour Phone: 425.431.7162 Owner: Nick Chou c/o Edmonds School District Office Phone: 425.431.7162 24-hour Phone: 425.431.7162 General Contractor: Wyser Construction Office Phone: 425.742.0898 Project Manager: Office Phone: Superintendent: Office Phone: Foreman: Office Phone: CESCL/Inspector: Office Phone: 24-hour Phone: 206.510.0672 24-hour Phone: 24-hour Phone: 24-hour Phone: 24-hour Phone: City of Shoreline Customer Response Team: 206-801-2700 1 of 2 2/2019 CONSTRUCTION EMERGENCY CONTACT SHEET INJURY or FIRE— Call 911 Provide project location or address (If no address, describe the location of the construction access so that it can be relayed to emergency responders) SPILL (Any hazardous materials including diesel fuel, gasoline, hydraulic fluid that enters the storm drain system or receiving waters) OR WATER QUALITY IMPACTS (Site stormwater runoff turbidity exceeds 250 ntu) • Call City of Shoreline Customer Response Team: 206-801-2700 • Call Washington State Department of Ecology within 24 hrs: 425-649-7000 FISH KILL OR DISTRESS • Call City of Shoreline Customer Response Team: 206-801-2700 • Call Washington Department of Fish and Wildlife Area Habitat Biologist: 425-313-5683 ARCHAEOLOGICAL FINDS • Call City of Shoreline Customer Response Team: 206-801-2700 • Call Army Corps of Engineers, Seattle office: 206-764-3634 2 of 2 2/2019 Project: CESCL/Inspector: Inspection Type: ❑ After a rain event ❑ Other —explain: Weather: Precipitation: Since last inspection: Description of General Site Conditions: SWPPP SITE INSPECTION FORM ❑ Weekly Permit No.: _ Date: Time: ❑ Turbidity benchmark exceedance inches In last 24 hours: inches Will existing BMPs need to be modified or removed, or otherBMPs installed? ❑YES ❑NO If YES, list the action items to be completed on the following table: Actions to be Completed Date Completed/ Initials 1. 2. 3. 4. 5. Was water quality sampling (turbidity and pH) part of this inspection? ❑YES ❑NO • If yes, attach Turbidity & pH Monitoring Data Sheet. Is the site in compliance with the SWPPP and the permit requirements? ❑YES ❑ NO • If no, indicate the tasks necessary to bring the site into compliance on the "Actions to be Completed" table above and include dates each job will be completed. • If no, has the non-compliance been reported to the City of Shoreline? ❑YES ❑ NO • If no, should the SWPPP be modified? ❑YES ❑ NO I certify that this report is true, accurate, and complete, to the best of my knowledge and belief. Name of Inspector (Print) Title/Qualification Signature Date 1 of 3 2/2019 Project: CESCL/Inspector: SWPPP SITE INSPECTION FORM Permit No.: Date: Time: Overall Need Site BMPs Condition Repair? Comments/Observations Element 1: Clearing Limits • Preserve existing vegetation P F Y N • High Visibility Plastic or Metal Fence P F Y N • Tree Protection During Construction P F Y N • Other P F Y N Element 2: Construction Access • Stabilized Construction Entrance P F Y N • Wheel Wash P F Y N • Const. Road/Parking Area Stable P F Y N • Other P F Y N Element 3: Control Flow Rates • Interceptor Dike and Swale P F Y N • Straw Wattles P F Y N • Sediment Trap P F Y N • Other P F Y N Element 4: Sediment Controls • Silt Fence P F Y N • Vegetated Strip P F Y N • Straw wattles P F Y N • Other P F Y N Element 5: Stabilize Soils • Seeding P F Y N • Mulch P F Y N • Nets and Blankets P F Y N • Plastic Covering P F Y N • Sodding P F Y N • Topsoil P F Y N • Other P F Y N Element 6: Protect Slopes • Seeding P F Y N • Nets and Blankets P F Y N • Plastic Covering P F Y N • Interceptor Dike and Swale P F Y N • Other P F Y N Element 7: Protect Drain Inlets • Storm drain inlet protection P F Y N • Other P F Y N Element 8: Stabilize Channels & Outlets • Channel Lining P F Y N • Outlet Protection P F Y N • Other P F Y N P=Pass, F=Fail, Y=Yes, N=No 2of3 2/2019 Overall Need Site BMPs Condition Repair? Comments/Observation Element 9: Control Pollutants • Concrete Handling P F Y N • Sawcutting and Surfacing Pollution P F Y N Prevention • Material Delivery, Storage and P F Y N Containment P F Y N • Other P F Y N Element 10: Control Dewatering • Level Spreader P F Y N • Infiltration P F Y N • Discharge to sanitary sewer P F Y N • Other P F Y N Element 11: Maintenance • Weekly BMP maintenance P F Y N • Other P F Y N Element 12: Manage the Project • Phase construction activities P F Y N • SWPPP on -site P F Y N • Update SWPPP P F Y N • Emergency contacts on SWPPP P F Y N • Inspect and monitor all BMPs P F Y N • Attach all completed SWPPP forms P F Y N to the SWPPP for recordkeeping Element 13: Protect Low Impact Development BMPs • Buffer Zones P F Y N • High Visibility Fence P F Y N • Silt Fence P F Y N • Vegetated Strip P F Y N • Other P F Y N P=Pass, F=Fail, Y=Yes, N=No 3of3 2/2019 SHERWOOD ELEMENTARY SCHOOL - NEW WALKING PATH APPENDIX C 0&M MANUAL �C JACOBSON 13 July 2021 Maintenance Standards Permeable ComponentPotential Condition When Maintenance Maintenance Action and Defect is Needed Expected Results All pavement Unstable soil • Runoff from adjacent areas • Remove deposited material types: on adjacent deposits soil, mulch, or from pavement, and stabilize • Porous area sediment on permeable adjacent areas so that further asphalt pavement deposition of material on Pervious pavement will not occur. concrete • Permeable Adjacent • Vegetation impedes • Trim or remove vegetation so pavers vegetation is infiltration in permeable that infiltration is not impeded • Open -celled covering pavement paving grid permeable pavement Unwanted • Unwanted vegetation • Remove unwanted vegetation, vegetation or impedes infiltration in repair permeable pavement as moss is permeable pavement or needed, replace desired growing in or displaced desired vegetation vegetation as needed on permeable pavement None • N/A • Vacuum or sweep according to (routine equipment manufacturer's maintenance) specifications so that infiltration is not impeded Debris or • Sediment or debris deposits • Remove sediment or debris sediment on are visible on pavement and vacuum or sweep pavement according to equipment manufacturer's specifications so that infiltration is not impeded Infiltration • Water ponds on pavement • Vacuum or sweep according to capacity is or runs off pavement during equipment manufacturer's reduced rain events specifications so that infiltration is not impeded Settlement • Settlement of pavement • Restore pavement to design impedes infiltration grade .... .om........................................................... Snohomish County Drainage Manual Volume VI - Stormwater Facility Maintenance 110 July 2021 • 20 Permeable Pavement ComponentPotential il M Defect is Needed I Expected Porous asphalt Cracks in • Pavement spalls or ravels at • Patch or cut and replace the and pervious pavement crack edges affected area with paving concrete material similar to the original pavement. Replace in -kind where feasible. Porous asphalt may be replaced with conventional asphalt if it is a small percentage of the total permeable pavement area and does not impact the overall permeable pavement function. Permeable Paving block • Paving block missing or • Repair or replace missing or pavers missing or damaged damaged pavers according to damaged manufacturer's specifications Paving grid . Three or more adjacent rings • Repair or replace missing or Open -celled missing or in paving grid missing or damaged paving grid according paving grid damaged damaged to manufacturer's specifications Loss of • Loss of aggregate in paving • Replenish aggregate material aggregate in grid in grid to manufacturer's paving grid specifications Poor / • Poor / missing grass in • Replace growing medium in missing grass vegetated paving grid grid, replant or reseed with in vegetated grass paving grid Pipe inlet/ Pipe system • Flow does not pass as • Clean or repair pipe system to outlet/ is blocked or designed through pipe restore design flow capacity underdrain damaged system system .... .om........................................................... Snohomish County Drainage Manual Volume VI - Stormwater Facility Maintenance 111 SHERWOOD ELEMENTARY SCHOOL - NEW WALKING PATH APPENDIX D GEOTECH N ICAL ASSESSMENT �C JACOBSON 14 0U0 May 18, 2023 Project No. 20170214EO03 Edmonds School District 15 20420 68th Avenue West Lynnwood, Washington 98036 Attention: Mr. Nick Chou a s s o c i a t e d earth sciences i n c o r p o r a t e d Subject: Updated Limited Permeable Pavement Feasibility Assessment/ Permit Comment Response New Walking Path Sherwood Elementary School 22901 106th Avenue West Edmonds, Washington References: City of Edmonds Stormwater Review Comments April 4, 2023 Application #: BLD2023-0275 Project: Sherwood Elementary Walking Path Address: 22901 106th Avenue West Plan Check BLD2023-0275 22901 - 106th Ave W, Edmonds Sherwood Elementary - Walking Path at New Playground City of Edmonds May 12, 2023 Sherwood Elementary Walking Path & Playground Improvements Civil Engineering Plan Set (3 Pages) Jacobson Consulting Engineers March 3, 2023 Dear Mr. Chou: As requested, this updated letter presents data from subsurface explorations onsite and provides responses to review comments related to groundwater separation below planned permeable paving, and Landslide Hazard Areas(LHAs). Our work was authorized by a District Purchase Order and was completed in accordance with our scope and cost proposal dated April 14, 2023. Our work was completed in accordance with local standards of practice in the field of geotechnical engineering at the time it was completed. No other warranty, express or implied, is made. Kirkland I Tacoma I Mount Vernon 425-827-7701 1 www.aesgeo.com Sherwood Elementary School - New Walking Path Edmonds, Washington PROJECT DESCRIPTION Updated Limited Permeable Pavement Feasibility Assessment/Permit Comment Response The project will include construction of a permeable asphalt paving walking path around the perimeter of the existing natural turf field on the north part of the school campus. A small area of permeable asphalt paving is also proposed to provide accessto the walking path and to serve as a play area. The project will be constructed close to existing grade without substantial earthwork cuts or fills. The new permeable paving is expected to be used primarily by pedestrians, with occasional incidental crossing by landscape maintenance equipment. The permeable paving will be constructed using Edmonds Standard Detail SD-621. That standard detail includes a treatment layer, permeable ballast, a choker course, and 4 inches of surficial permeable asphalt paving. The total section thickness is 18 to 19 inches depending on the choker course option that is selected. The detail specifies that the base of the permeable paving section must be at least one foot above seasonal high groundwater or any hydraulically restrictive layer. A copy of SD-621 is included with this letter for reference. The existing grass playfield where the walking path will be built is adjacent to a slope that rises from the east side of the field approximately 50 feet to meet a neighborhood of existing houses. The slope meets geometric criteria for treatment as a LHA in accordance with Edmonds Community Development Code (ECDC). The east slope is outside the proposed project limits. Geotechnical critical areas are discussed in detail later in this letter. The project location is shown on the "Vicinity Map," Figure 1, approximate locations of explorations completed for this study are depicted on the Site and Exploration Plan, Figure 2, and logs of hand -auger borings completed for the current task and results of laboratory grain -size testing are attached. SUBSURFACE EXPLORATIONS Subsurface explorations completed for the current task included two shallow hand -auger borings. The hand -auger borings were completed at the approximate locations depicted on Figure 2 using a posthole digger and a hand auger with depth extensions. HA-6 was completed to a depth of approximately 9 feet below the existing ground surface and HA-7 was completed to a depth of approximately 7 feet. Soil samples were collected at approximately 1-foot-depth intervals. Each sample was visually described in the field and placed in a sealed plastic bag for transport to our geotechnical laboratory. Interpretive logs of the explorations are attached with this letter. It should be noted that the hand -auger borings completed for the current task were labeled HA-6 and HA-7, following five hand -auger borings we completed onsite in 2017 in support of portable classroom placement on the south part of the site. Logs of earlier explorations are available on request but are not included with this letter. May 18, 2023 ASSOCIATED EARTH SCIENCES, INC. BWG11d - 20170214EO03-003 Page 2 Sherwood Elementary School - New Walking Path Edmonds, Washington Subsurface Conditions Existing Topsoil and Fill Updated Limited Permeable Pavement Feasibility Assessment/Permit Comment Response The hand -auger borings completed for the current task encountered surficial grass and topsoil approximately 8 inches thick, underlain by brown silty sand interpreted as existing fill to depths of approximately 1 to 1.5 feet below the existing ground surface. Vashon Advance Outwash Below the existing fill, both hand -auger borings completed for the current task encountered medium dense to dense, moist, brownish grayand gray, fine sand, trace silt, trace fine to coarse gravel, interpreted as Vashon advance outwash sediments. Advance outwash was deposited by proglacial meltwater streams and was subsequently glacially overridden and compacted by the advancing glacial ice. Hydrology Free groundwater was not observed in either of the hand -auger borings completed for this study, or in the five hand -auger explorations completed in 2017 on the south part of this site for a previous project. A previous Associated Earth Sciences, Inc. (AESI) study for a different project approximately one -quarter mile to the north of Sherwood Elementary School suggests that the regional water level in the Vashon advance outwash aquifer is deeper than elevation 260 feet (approximately 20 to 25 feet below the existing ground surface) in the current project area. Published Geologic Ma We reviewed a published geologic map for the project area: Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangles, Washington, J.P. Minard, U.S. Geological Survey Miscellaneous Field Studies Map MF-1541, 1983, 1:24,000. The published geologic map indicates that the site is expected to be underlain by Vashon advance outwash sediments. Our observations and interpretations of subsurface conditions are consistent with the referenced map, in our opinion. CONCLUSIONS AND RECOMMENDATIONS Permeable Paving Based on subsurface data from HA-6 and HA-7, it appears that construction of permeable paving in accordance with Edmonds Standard Detail SD-621 to a surface elevation that matches existing grade will result in removal of existing fill to reach paving subgrade elevation. The subgrade for the permeable paving section is expected to consist of Vashon advance outwash. HA-6 and HA-7 were completed in April 2023 when groundwater levels are typically elevated. Soil samples May 18, 2023 ASSOCIATED EARTH SCIENCES, INC. BWG/Id-20170214EO03-003 Page 3 Sherwood Elementary School - New Walking Path Updated Limited Permeable Pavement Edmonds, Washington Feasibility Assessment/Permit Comment Response recovered from the explorations did not exhibit mottling or other indications of intermittent saturation in the advance outwash sediments. In our opinion seasonal high groundwater below the project area is likely deeper than the maximum depths explored in HA-6 and HA-7 of 9 and 7 feet, respectively. In our opinion the subsurface explorations completed for the current task demonstrate that the minimum separation between the base of the permeable paving section and winter high groundwater meets the 1-foot minimum required by SD-621. The permeable paving section depicted in SD-621 is adequate, in our opinion, to support regular pedestrian use and incidental landscape maintenance equipment traffic. In order to achieve the intended infiltration performance of the permeable paving section, we recommend: • Permeable pavement subgrade conditions should be verified at the time of construction to be consistent with conditions observed in HA-6 and HA-7. • The aggregate gradation for Choker Course, Permeable Ballast, and Runoff Treatment Layer materials should be confirmed to be in accordance with gradation requirements in SD-621. • The native soil subgrade at the base of the paving layer should be exposed by excavating as needed, then should be lightly scarified prior to placement of the first layer of the paving section. • Compaction of the paving section layers should use light -duty equipment such as a vibratory sled or small smooth drum roller. Compactive effort should be adequate to meet compaction standards below paving, but over -compaction should be avoided. • Optional geotextile separation fabric discussed in SD-621 note 4 is not recommended for this project. Permeable Paving Comment Response Summary This letter is intended to respond to Comments #1 and #2 in the referenced Stormwater Review Comments: 1. The location of the seasonal high ground water or an underlying impermeable/low permeable layer need to be investigated for permeable pavement to work. If either the seasonal high ground water or an underlying impermeable/low permeable layer conditions exist within one foot of the bottom of the lowest layer that has been designed to be part of the BMP, such as the lowest gravel base course, it is considered an infeasible BMP. 2. If permeable asphalt is deemed feasible. a. Please use city standard detail SD-621. b. The engineer needs to certify that SD-621 is adequate for the loads expected for the permeable pavement. May 18, 2023 ASSOCIATED EARTH SCIENCES, INC. BWG11d - 20170214EO03-003 Page 4 Sherwood Elementary School - New Walking Path Edmonds, Washington Geotechnical Critical Areas Updated Limited Permeable Pavement Feasibility Assessment/Permit Comment Response Slopes east of the current project meet geometric criteria for treatment as LHAs in accordance with ECDC Section 23.80. The slopes that meet the criteria for treatment as LHAs are outside the limits of the proposed project, with the distance from the proposed new walking path to the base of the LHAs ranging from approximately 19 to 30 feet. ECDC Section 23.80 does not specify a minimum LHA buffer, but defersto a site -specific critical areas geotechnical studyto establish an appropriate buffer width. The following paragraphs summarize geotechnical considerations relevant to adjacent LHAs and are intended to support the current proposal without further slope stability analyses which in our opinion are not warranted based on the limited scope of the proposed project. Mapped Geology - As previously discussed, the site is expected to be underlain at shallow depths by Vashon advance outwash sediments. Advance outwash consists typically of very dense sand and gravel that was glacially overridden and compacted. Advance outwash typically performs adequately from a slope stability standpoint when exposed at slope inclinations such as those adjacent to the east of the current project. Observed Subsurface Conditions - Hand -auger explorations completed for the current project and previous hand explorations completed on the south part of the site by AESI in support of a previous portable classrooms placement project encountered dense sandy sediments interpreted as advance outwash, consistent with published mapping. Slope Reconnaissance -The existing slope east of the current project is densely vegetated and undeveloped. We completed a visual reconnaissance of the slope and observed no visual indications of substantial erosion or slope instability. The existing slope is assumed to have existed in approximately its current configuration since at least 1985 based on historical air photographs, and likely since the existing school was established in 1966. Based on our reconnaissance and review of available historical photographs the slope east of the project has performed adequately from a stability and erosion standpoint since at least 1985 and likely since 1966. Project Separation -The proposed walking path will be located at least 19 feet and typically 25 or more feet from the limits of the LHAs. Limited Scope -The project will not include any workthat isexpected to changethe slope stability or erosion potential of the LHA adjacent to the east. Ground surface elevations will not change. The existing natural turf surface likely infiltrates surface water in a manner similar to the proposed new permeable paving. Conclusion -The LHA adjacent to the east of the project area is anticipated to be composed of dense granular native sediments and appears to have performed adequately from a slope stability and erosion standpoint since at least 1985 and likely since 1966. The current project will May 18, 2023 ASSOCIATED EARTH SCIENCES, INC. BWG/Id-20170214EO03-003 Page 5 Sherwood Elementary School - New Walking Path Updated Limited Permeable Pavement Edmonds, Washington Feasibility Assessment/Permit Comment Response not include any work that is anticipated to change the stability or erosion potential of the existing slope. In our opinion the project will not adversely affect slope stability and will not result in increased risks of slope -related damage to the site or adjacent properties. Geotechnical Critical Areas Comment Response Summa The section of this letter above is intended to respond to the Geotechnical Report comment in the City of Edmonds review comments dated May 12, 2023 cited above. The review comment is complex and lengthy and not easily incorporated into this letter in its entirety. AESI can provide a copy of the review comment on request. CLOSURE We appreciate the opportunity to be of service. If you have any questions, please do not hesitate to call. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Kirkland, Washington Er"Ce 6"ellz*l- Bruce W. Guenzler, L.E.G. Principal Engineering Geologist Kurt D. Merriman, P.E. Senior Principal Engineer Attachments: Figure 1 - Vicinity Map Figure 2 - Site and Exploration Plan Subsurface Exploration Logs - HA-6 and HA-7 Laboratory Test Data Copy of Permeable Paving Standard Detail SD-621 May 18, 2023 BWG/Id - 20170214EO03-003 ASSOCIATED EARTH SCIENCES, INC. Page 6 FT '�•; �� v. �:� —.• . � . ___.ate ' `�?�F .i.F'': _,. U EDMOND. F' - ------------------ r` f 'b2 it 41 -.1;� ,� _ SITE I i 7-7 I , 104 I 7A I Snohomish County 'V { • r 11 I i' , • • _- _________—_ . ��' 1 • '�'.. v ''1 •fy ti + -� yr, +.;' a_ a s s o c i a t e d N earth sciences i n c o r p o rat e d 0 2000 VICINITY MAP FEET DATA SOURCES / REFERENCES: SHERWOOD ELEMENTARY SCHOOL WALKING PATH USGS: 7.5' SERIES TOPOGRAPHIC MAPS, ESRIII-CUBED/NATIONAL NOTE: BLACK AND WHITE GEOGRAPHIC SOCIETY2013 REPRODUCTION OF THIS COLOR EDMONDS, WASHINGTON ORIGINAL MAY REDUCE ITS SNOHOMISH CO: STREETS, CITY LIMITS, PARCELS, 7122 EFFECTIVENESS AND LEAD TO PROJ NO. DATE: FIGURE: LOCATIONS AND DISTANCES SHOWN ARE APPROXIMATE INCORRECT INTERPRETATION 20170214EO03 5/23 1 22H STREEfi SW R ,s,--',�-''-'---------- = -- �------IssC I\�t\XISN. \\ �T� IN , vv .}..rya / / �'�;•`'• V s'v ! \ . ! v %-A � 1 ExcHAINunIK a — t� _ ` �__ \--------\• _ ���`; vs.rs,rEx) 11� �� c91 ,ge/ IIIr a� �y� v / aza.aa° l A.J 1 \� §,. RN 2F590 i 19 " ➢ 74 Y( ) / C C C \r I ��,�\ I. 11 e' For,c's aa.4o / s i vs.ra) / asas4 .l >' 296 I e reed 1 raor �1 r / �1 1'PYC ( 2.P (- / I / ?8314(EX) a e cL 1 i N CMPN 270.27All j E JM-�O lil t �? I V/ F \ I / ISTING / I zso. 17S79• / IAYFIELD A\! W zre 04 j / 4 / s4 NEX) PROTECT EX ELDTO REMAIN UNLESY NOTED / -� \ v ) I��• _ / OTHERWISUFOR GRADING AND INSTALLATION 1 OFPERVI S ASPHALT WALKING PATH(TYP( 'IIJSTALLT NEW POROUS / p3PHALWALKING PAT 1 SEE DETAIL qa e E 0 eONEa C3NNEeT / I Iwys vest I nLI weEN ewuewrcm-nvu Io / I A1ZNT —` V srs7uS raCM �- -_ • ' \ I , l 1 �I ' � / E__¢ I Wc �A\ I sazev= \� 2I- 1 NOT N LCc_ 0' l I 1 �p rP I i um II,'; 1 /, p .r+i / f PROTECTIXAREA DRAIN3eD ' 'J' —/ 1 f 1 ASSOCIATED STORM PIPIN TO \ / z (eREMAIN CT P) / IN,-j{yII� R1O 2.45fEx1 REPLACE EAAREA DRAIN FRAME N99'A'7 5 7 9 ;EI4.3B 7 „ I �'� al I' ��\ p v(L /` AND GRATE WITH NEW FRAME AND a 11 AEI Ixov s1 2a 210' ¢sago , SOLID LOCKING COVER WITH A 'I s r cTua •. NON-SLWMETHYLMETHACRYLATE (MM ALL BE RX-DPER MANUFACTURERS RE)bMMENDATONS N212 E 29 Pl' NEw PNGRDUND C 1/1 ,( zees' �k \ y�✓ /y\\ - AREf}PERAA.,R�CHH%- k/ \ u� _zsz N 3 III IIII\ \��J - -�� INSTALL NEW STANDARD ASPHALT 1I cxr PAVEMENTTOSEP.VEASPLAYAND 1ur7c Szel kl. - to {sp -62. AD MSTORELD \; b SEEDETAIL g A* II 1. IIII / 9 H E / aaanm nnI A I - _ _ _ e i v �.FXPIA ROAN❑ a L - ruvcaaunp w ( d yVI I �_ �l / ilam)r��'. 2� )I Eny N I I I I I �� NEWCHAINUNK FENCE \ \ / / TO FILL IN GAP IN FENCE 1� \ \ 1 lT(l. ) Pf 02 _ PER ARCH'L PUNS \` "\,283.cEN d E 9 \ (I II C y� ��V �_ ,� \ 71 1y'1 E PRDII k(GROUx _ - \. _ r Ex ®EAI IH NL+ a - r' I / / ALAYGRDREM I ` ' 1li(�VAV�AA\ -�� - x � � - Fes" I - I I � N3F1�T0 REMAIN T rw _ — ELAN°I°Nr° / Ea aae r. �/ z A�,C M'o00 aErsl /� ALE r Lk �% zsA 1 Ex_ P a za i(ul �zs4so(tx) I.I —� A�- NEILINK FENCE s4(Ex} TO F LNI rtAP IN FENCE PROTECT EX SATE n AND CHAIN LINK / rr or / f;Eg RCH'L PLAIJS \ I FENCE TD REMAIN (2' n rry l�,s s�a�/ \ MATCH EX _ _ _ s9D9,9 ` •'M, �9 / \ \\ \ D +D �I"r ' ASPHALT Gf}�DE / EXASPHALT I L,--Nn--�. LEGEND SITE O HAND BORING DATA SOURCES / REFERENCES: SNOHOMISH CO: STREETS 3/22, PARCELS 7/22 HUTTERBALL+OREMUS ARCHITECTURE, JACOBSON CONSULTING ENGINEERS, CIVIL SITE PLAN, SHERWOOD ELEMENTARY WALKING PATH & PLAYGROUND IMPROVEMENTS, SHEET C2.00, 02/27/2023 LOCATIONS AND DISTANCES SHOWN ARE APPROXIMATE N A 0 50 FEET BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY REDUCE ITS EFFECTIVENESS AND LEAD TO INCORRECT INTERPRETATION a s s o c i a t e d earth sciences i n c o r p o rat e d SITE AND EXPLORATION PLAN SHERWOOD ELEMENTARY SCHOOL WALKING PATH EDMONDS, WASHINGTON PROJ NO. DATE: I FIGURE: 20170214EO03 1 5/23 2 > D U) o o N zo c o :° LO 2 a) o CD U cn o ° o z cD 0 @ 0 o �, g > @ = i_ V1� v o N NI o o 0 �� O 0 0 0 00o o 0 o O 0 O 0 0 O 0 b 0 0� O GW GP GM GC Well -graded gravel and gravel with sand, little to no fines Poorly -graded ravel g and gravel with sand, little to no fines Silty gravel and silty gravel with sand Clayey gravel and clayey gravel with sand Terms Describing Relative Density and Consistency tst Density SPT blows/foot Coarse Very Loose 0 to 4 Loose 4to10 Test Symbols Grained Soils Medium Dense 10 to 30 G = Grain Size Dense 30 to 50 M = Moisture Content Very Dense >50 A = Atterberg Limits tat C =Chemical Consistency SPT blows/foot Very Soft 0 to 2 DD =Dry Density Fine- Soft 2 to 4 K = Permeability Grained Soils Medium Stiff 4 to 8 Stiff 8 to 15 VeryStiff 15 to 30 Hard >30 ` w o ° ° ° 0 0 Component Definitions Well graded sand p V o 0 ° 0 SW and sand with gravel, Descriptive Term Size Range and Sieve Number N 2 L 0 0 0 little to no fines Boulders Larger than 12" .T to o m > �. �I :-._....;. ". :..; . Cobbles 3" to 12" Poorly -graded sand rp U U) Sp and sand with gravel, Gravel 3" to No. 4 (4.75 mm) — m ° little to no fines Coarse Gravel 3" to 3/4" o d Fine Gravel 3/4" to No. 4 (4.75 mm) q Silty sand and Sand No. 4 (4.75 mm) to No. 200 (0.075 mm) .: SM Coarse Sand No. 4 4.75 mm to No. 10 2.00 mm silty sand with ( ) ( ) 0 o a �,; ..':: gravel Medium Sand No. 10 (2.00 mm) to No. 40 (0.425 mm) v Fine Sand No. 40 (0.425 mm) to No. 200 (0.075 mm) � Clayey sand and Silt and Clay Smaller than No. 200 (0.075 mm) NI ...,: SC clayey sand with (4) U) gravel Estimated Percentage Moisture Content Component Percentage by Weight Dry - Absence of moisture, Silt, sandy silt, gravelly Trace <5 dusty, dry to the touch � ML silt, silt with sand or Slightly Moist - Perceptible > a? c gravel Some 5 to <12 moisture ; ' = Moist - Damp but no visible N U n Clay of low to medium Modifier 12 to <30 water Z CL plasticity; silty, sandy, or (silty, sandy, gravelly) Very Moist - Water visible but Cn w E gravelly clay, lean clay not free draining Very modifier 30 to <50 Wet - Visible free water, usually a(silty, sandy, gravelly) from below water table - ---- OL Organic clay or silt m o -=�== of low plasticity Symbols 2 ----- Cement Cement grout ° Elastic silt, clayey silt, Sampler Type and Description Groundwater surface seal o o MH silt with micaceous 10 depth 15 Blows/6" or of 6" Bentonite seal a� Ln o portion or diatomaceous fine p ATD 1 T 2 sand or silt Split -Spoon Sampler (SPT) At time Filter pack with 0 v oo Clay of high California Sampler of drilling blank casing (D CH plasticity, sandy or Ring Sampler section : m E Static water Q : gravelly clay, fat clay - Screened casing Continuous Sampling m u, � level (date) with sand or gravel or Hydrotip with 6 to : m ° Grab Sample filter pack c `� J // Organic clay or silt of Portion not recovered ' End cap OH medium to high plasticity Classifications of soils in this report are based on visual field and/or laboratory observations, U which include density/consistency, moisture condition, grain size, and plasticity estimates r Peat, muck and other and should not be construed to imply field or laboratory testing unless presented herein. °' a U) T PT hi hl Or aniC Soils Visual -manual and/or laboratory classification methods of ASTM D-2487 and D-2488 were g y g O used as an identification guide for the Unified Soil Classification System. (1) Percentage by dry weight a s s o c i a t e d (2) Combined USCS symbols used for fines between 5% and 12% (3) (SPT) Standard Penetration earth S C i e n C e S Test (ASTM D-1586) (4) In General Accordance with Standard Practice for Description i n c o r p o r a t e d and Identification of Soils (ASTM D-2488) Exploration Boring HA-6 a s s o c i a t e d Sherwood Elementary School Walking Path Sheet: 1 of 1 e a r t h s c 1 e n c e s Edmonds, WA Start Date: 04/29/23 Logged By: BG i n c o r p o r a t e d 20170214EO03 Ending Date: 04/29/23 Approved By: JHS Driller/Equipment: Hand Auger Total Depth (ft): 9 Hammer Weight/Drop: N/A Ground Surface Elevation (ft): z285 Hole Diameter (in): 4 Datum: NAVD 88 ZGroundwater Depth ATD (ft): N/A 2L Groundwater Depth Post Drilling (ft) (Date): () a) � N L V Blows/Foot v Q °1 Q E Q- E Description 3 L E N (0 Ln o T N ate+ O CO 0 O 0 0 0 0 0 \' Grass / Topsoil - 0.6 feet 1 - Fill 2 Loose to medium dense, moist, brown with oxidized stringers, some silt, _-___ some fine gravel (SP-SM). Vashon Advance Outwash 2.5 `-- = - Medium dense to dense, moist, gray, fine SAND; few silt; trace fine to =rE coarse gravel (SP). 5 r' 7.5 No groundwater encountered. 10 12.5 15 17.5 Occnriitprl Farth Cripnrpc inr Exploration Boring HA-7 a s s o c i a t e d Sherwood Elementary School Walking Path Sheet: 1 of 1 e a r t h s c 1 e n c e s Edmonds, WA Start Date: 04/29/23 Logged By: BG i n c o r p o r a t e d 20170214EO03 Ending Date: 04/29/23 Approved By: JHS Driller/Equipment: Hand Auger Total Depth (ft): 7 Hammer Weight/Drop: N/A Ground Surface Elevation (ft): z281 Hole Diameter (in): 4 Datum: NAVD 88 ZGroundwater Depth ATD (ft): 2L Groundwater Depth Post Drilling (ft) (Date): () a) � N L V Blows/Foot v °1 E Q- E Description 3 L Q Q E (0 Ln T N aa+ O CO N o 0 0 0 0 0 O 0 \" Grass / Topsoil - 0.6 feet 1 = Fine =, ,,,--,-_ E 2 Loose to medium dense, moist, brown, fine SAND, some silt, some fine '=== gravel (SP-SM). Vashon Advance Outwash 2.5_'- Medium dense to dense, moist, brownish gray, fine SAND; trace silt; trace -= fine to coarse gravel (SP). 5 s-E� No groundwater encountered. 7.5 10 12.5 15 17.5 Occnriitprl Farth Cripnrpc inr 0 LLJ Z LL H Z W U 0-1 0_ 100 90 80 70 60 50 40 30 20 10 0 Particle Size Distribution Report C C O O O C C C\ C C C t N M y�y M N co M cV � „�' \ M 3k 3k 3k �k ik 3k 3k 3k ik 100 10 1 0.1 0.01 0.001 GRAIN SIZE - mm. % +3" % Gravel % Sand % Fines Coarse Fine Coarse Medium Fine Silt Clay 0.0 1.4 2.9 1.0 20.3 69.5 4.9 TEST RESULTS Opening Percent Spec." Pass? Size Finer (Percent) (X=Fail) 1" 100.0 3/4" 98.6 5/8" 97.9 1/2" 97.4 3/8" 97.1 #4 95.7 #8 94.9 #10 94.7 #20 93.4 #40 74.4 #60 25.2 #100 8.3 #200 4.9 Material Description SAND, trace gravel, trace silt Atterberg Limits (ASTM D 4318) PL= NP LL= NV PI= Classification USCS (D 2487)= SP AASHTO (M 145)= A-3 Coefficients D90= 0.5945 D85= 0.5092 D60= 0.3613 D50= 0.3273 D30= 0.2658 D15= 0.2070 D10= 0.1710 Cu= 2.11 Cc= 1.14 Remarks Date Received: 5/3/2023 Date Tested: 5/8/2023 Tested By: Cl Checked By: BG Title: (no specification provided) Location: Onsite Date Sampled: 4/29/2023 Sample Number: HA-6 Depth: 3' a s s o C i a t e d Client: Edmonds School District e a r t h sciences Project: Sherwood Elementary Portables i n c o r p o rated Project No: 20170214 E003 Figure 0-1 LLJ Z LL H Z W U 0-1 0_ 100 90 80 70 60 50 40 30 20 10 0 Particle Size Distribution Report C C O O O co M cV � � \` \ M it Sk 3k Xk ik 3k 3k 3k ik 100 10 1 0.1 0.01 0.001 GRAIN SIZE - mm. % +3" % Gravel % Sand % Fines Coarse Fine Coarse Medium Fine Silt Clay 0.0 0.0 1.3 0.5 38.4 56.4 3.4 TEST RESULTS Opening Percent Spec." Pass? Size Finer (Percent) (X=Fail) 3/4" 100.0 5/8" 99.4 1/2" 99.4 3/8" 99.1 #4 98.7 #8 98.4 #10 98.2 #20 93.4 #40 59.8 #60 20.5 #100 6.7 #200 3.4 Material Description SAND, trace gravel, trace silt Atterberg Limits (ASTM D 4318) PL= NP LL= NV PI= Classification USCS (D 2487)= SP AASHTO (M 145)= A-3 Coefficients D90= 0.7513 D85= 0.6568 D60= 0.4263 D50= 0.3747 D30= 0.2901 D95= 0.2218 D10= 0.1870 Cu= 2.28 Cc= 1.06 Remarks Date Received: 5/3/2023 Date Tested: 5/8/2023 Tested By: Cl Checked By: BG Title: (no specification provided) Location: Onsite Date Sampled: 4/29/2023 Sample Number: HA-6 Depth: 6' a s s o C i a t e d Client: Edmonds School District e a r t h sciences Project: Sherwood Elementary Portables i n c o r p o rated Project No: 20170214 E003 Figure 4" (MIN) PAVEMENT BASE COURSE, SEE NOTE 2 6" PATB: 2" (MIN) (MIN) OR CSCC: 3" (MIN) OR PER MANUFACTURER RECOMMENDATION 6" (MIN) 1' (MIN) ABOVE SEASONAL HIGH GROUNDWATER TABLE OR HYDRAULICALLY RESTRICTIVE LAYER GENERAL NOTES: POROUS HMA/WMA, SEE NOTE 1 PERMEABLE ASPHALT TREATED BASE COURSE OR CRUSHED SURFACING CHOKER COURSE, SEE NOTE 3 PERMEABLE BALLAST, SEE NOTE 4 RUNOFF TREATMENT LAYER (IF REQUIRED PER EDMONDS STORMWATER CODE), SEE NOTE 5 SUBGRADE, SEE NOTE 6 1. REFER TO THE 2022 CITY OF EDMONDS STORMWATER ADDENDUM FOR SETBACK (CHECKLIST 11) AND INFEASIBILITY REQUIREMENTS. 2. THE MINIMUM THICKNESS SHOWN ABOVE MAY NOT BE SUFFICIENT FOR ALL APPLICATIONS. A PROJECT SPECIFIC PAVEMENT DESIGN SHALL BE PREPARED BY A PROFESSIONAL ENGINEER LICENSED IN THE STATE OF WASHINGTON IN CIVIL ENGINEERING TO: 2.1. SUPPORT THE ANTICIPATED LOADING (E.G. PAVEMENT DESIGN LIFE, INITIAL AND TERMINAL SERVICEABILITY, RELIABILITY, ETC.) AND 2.2. TO SATISFY THE HYDROLOGIC REQUIREMENTS OF THE CITY OF EDMONDS STORMWATER CODE (I.E., CODE MAY WARRANT A THICKER PAVEMENT SECTION THAN THE MINIMUM STRUCTURAL SECTION REQUIRED). 3. FOR SUBGRADE SLOPES 3% OR GREATER, SUBSURFACE CHECK DAMS OR OTHER METHODS TO PROMOTE SUBSURFACE PONDING ARE REQUIRED (SEE SD-627). 4. GEOTEXTILE SHALL NOT BE USED IN PAVEMENT SECTION UNLESS REQUIRED BY GEOTECHNICAL ENGINEER. IF REQUIRED, GEOTEXTILE SHALL CONFORM TO WSDOT 9.33.2(1) GEOTEXTILE FOR SEPARATION, WOVEN TYPE. 5. REFER TO WSDOT LOCAL AGENCY GSPs DIVISIONS 2-9 FOR APWA GSPs. NOTES: 1. POROUS HMA SHALL CONFORM TO REQUIREMENTS OF APWA GSP 5-04. 2. SURFACE SLOPE SHALL BE BETWEEN 0.5% AND 6%. 3. PAVEMENT BASE SHALL BE INSTALLED PER APWA GSP 4-04.3(5) SHAPING AND COMPACTION. 4. PERMEABLE ASPHALT TREATED BASE (PATB) SHALL CONFORM TO THE REQUIREMENTS OF APWA GSP 4—SA2. CRUSHED SURFACING CHOKER COURSE (CSCC) SHALL CONFORM TO THE REQUIREMENTS OF APWA GSP 4-04.2(9-03.9(2)).OPT2. 5. PERMEABLE BALLAST SHALL CONFORM TO THE REQUIREMENTS OF APWA GSP 4-04.2(9-03.9(2)).OPT1. 6. RUNOFF TREATMENT LAYER SHALL MEET THE REQUIREMENTS OF 2022 CITY OF EDMONDS STORMWATER ADDENDUM. 7. PREPARE AND PROTECT SUBGRADE PER APWA GSP 2-06.3(3) SUBGRADE FOR PERMEABLE PAVEMENTS. `St. IB9— REVISION DATE CITY OF EDMONDS TYPICAL POROUS APRIL 2023 ASPHALT PAVEMENT PUBLIC WORKS STANDARD DEPARTMENT DETAIL APPROVED BY: R. ENGLISH S D - 6 21