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APPROVED STM RESUB2 BLD2022-0527+DRAINAGE REPORT+10.2.2023_11.19.35_AM+3815420C � ENGINEERING 250 4th Ave S Ste 200 Edmonds, WA 98020 Phone: (425) 778-8500 Fax: (425) 778-5536 civil & structural engineering & planning BLD2022-0527 RES U B Oct 02 2023 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT DRAINAGE REPORT Westgate Station 9601 Edmonds Way Edmonds, WA 98020 0312212023 CG Project No.: 19440.20 Report Date: March 22, 2023 COMPLIES WITH APPLICABLE CITY STORMWATER CODE 10/18/2023 Table of Contents Section I — Project Overview Section II — Off -Site Analysis Section III — Permanent Stormwater Control Plan Section IV — Construction Stormwater Pollution Prevention Plan Section V — Special Reports and/or Studies Section VI — Other Permits Section VII — Bond Quantities, Declaration of Covenant, & Operation and Maintenance Manual Appendix A — WWHM Report 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 March 22, 2023 Drainage Report Section I, Page 1 Section I — Project Overview Section I Summa Overview Existing Condition Developed Condition Minimum Requirements Overview This drainage report has been written for the development of a new three-story mixed -use building with a parking garage, walkways, patio space, and two driveways with uncovered parking. The lot is 1.10 ac, and it is located at 9601 Edmonds Way in Edmonds, WA (Tax Parcel Number: 00937900001000). The site is currently undeveloped, and site topography descends northeast to southwest. The total new/replaced impervious area, including work in the right-of-way, proposed is approximately 31,347 sf (0.720 ac). The project will meet minimum requirements 1 through 9 of the 2014 Department of Ecology Stormwater Management Manual for Western Washington (herein referred to as the SWMMWW) and comply with those requirements as modified in the Edmonds Community Development Code Chapter 18.30 (herein referred to as ECDC 18.30) and the June 2017 Addendum to ECDC 18.30 (herein referred to as the Edmonds Stormwater Addendum). The site is within the Edmonds Way Watershed. As such, BMPs were designed using the Edmonds Way direct discharge requirement per the ECDC. Existing Condition The site is currently undeveloped. Vegetation on -site generally consists of grass, shrubs, and small trees. A portion of the site has been previously graded, and a gravel surfaced parking area already exists. Site topography descends northeast to southwest. Along the south property line, it is flatter with slopes at 4%, near the east property line slopes average at 16%, and along the north property lines it is very steep with slopes ranging from 40% to 80%. There is about 10 ft of grade change between the east and west property lines, and about 30 ft of grade change between the north and south property lines. According to the site survey and City of Edmonds GIS map, the site contains Severe Erosion Hazards and Landslide Hazard Areas near the north property line, with steep slopes containing grades above 40%. Site soils consist of gravel surfacing underlain by glacial till, advanced outwash, or a combination of the two. Two infiltration pits were dug near the southern property line. The western pit gave a design infiltration rate of 0.63 in/hr, and the eastern pit gave a design infiltration rate of 2.88 in/hr. Both infiltration rates are used in designing the BMPs. See Section V for more details. On the project site there is a rain garden from an upstream property to the north. Most of the northern site is mitigated using a detention vault, however, 4,223 sf (0.097 acres) of impervious area was not able 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 March 22, 2023 Drainage Report Section I, Page 2 to be mitigated due to gravity concerns. The rain garden mitigating this area is on the east side of the site but is generally not visible due to vegetation growth in the area. The area from these upstream hard surfaces is to be controlled in the new on -site stormwater management system discussed in Section III. Single-family residences border the site on the north and east sides, Edmonds Way borders the south side, and there is a gas station on the west side. Utilities are generally located in Edmonds Way (see Figure I- 2). There is an 8" sewer main that runs north to south on the east side of the site and an 8" storm pipe which is an overflow from the detention vault which controls the drainage off the eight single family residences north of the property. This storm pipe connects to an on -site catch basin within a 15' x 87' utility easement running along Edmonds Way. This catch basin conveys stormwater west through catch basins and a shallow swale and then flows south and connects to the city MS4 system in Edmonds Way. Developed Condition The project is classified as New Development and will occur on an undeveloped lot. The proposed development is the construction of a 3-story mixed use building with commercial and residential space, a driveway, underground parking, walkways, and patio areas. The total new impervious area, including work in the ROW, is 31,347 sf (0.720 ac). Areas from an upstream property are proposed to be mitigated on - site, which will contribute an additional 4,223 sf (0.097 acres). Land disturbance will be to the extents of the clearing limits and will be approximately 40,695 sf (see civil plans). The site will utilize infiltrating rain gardens and infiltration trenches to address Minimum Requirement #5. The rain gardens and infiltration trenches were designed using WWHM 2012 to meet the Edmonds Way direct discharge requirement, see Section III for details. The overflow from the rain gardens does not exceed 0.25 and 0.45 cfs/acre of impervious surface in the post developed condition. Three rain gardens with a total surface area of 1,137 sf are shown broken up between the replaced sidewalk along Edmonds Way and the proposed building. Two infiltration trenches with a total surface area of 1,331 sf are shown in the western and eastern driveways. All runoff from impervious areas will be tied and conveyed to the on -site BMPs. The overflow is tied to an existing catch basin at the southwest corner of the site directing stormwater to the system in Edmonds Way. See the civil plans and Section III for details. The proposed impervious areas were considered as follows: Impervious Areas Roof: 16,818 sf (0.386 ac) Driveway/Parking: 8,750 sf (0.201 ac) *includes driveway on property to west Walkways: 3,610 sf (0.083 ac) Walkways (ROW): 1,524 sf (0.035 ac) Driveway (ROW): 645 sf (0.015 ad Total: 31,347 sf (0.720 ac) 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Section I, Page 3 The new and replaced pollution -generating impervious areas were considered as follows: Pollution -generating Impervious Areas Driveway (on -site): 8,750 sf (0.201 ac) *includes driveway on property to west Driveway (ROW): 645 sf (0.015 ad Total: 9,395 sf (0.216 ac) Total Lot Area: 1.10 ac Total New Impervious Area: 0.720 ac PGHS/PGIS: 0.216 ac Parent Material: Glacial Outwash and Glacial Till Hydro. Soil Group: B/C 228th PI ar t4 o m 5 A a5 o� 04, 769 Wells Fargo Bank© qAay �d�o�as Project Site oa Edmonds Way 936 QCity Kids Quality Consignments Mailbox HaConstructs Figure 1-1. Vicinity map (Google Maps). 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Section I, Page 4 nn�I�N50 vl PRIVATE'9 q"I 22809 / Ln o a 228040 PRIVATE 34 N o o M ON 9>06 / ' CP- dR ON PROJECT SITE 0 6' �O 9� C ill jel� l r�r--`" I N EXISTING SEWER EXISTING WATER PRNA N ON PRIVATE \ EXISTING STORM 59620 A� ,5-79 7� Figure 1-2. Map showing existing utilities near site (City of Edmonds GIS map). -9 S s 0 wo 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 March 22, 2023 Drainage Report Section I, Page 5 OW ..r► 3 � ` LAL�c� Wpm' 1. PROJECT SITE'�a / Figure 1-3. Aerial image of site (City of Edmonds GIS map). 0y Minimum Requirements Stormwater requirements were determined per the Edmonds Stormwater Addendum, the ECDC, and Ecology's 2014 Stormwater Management Manual for Western Washington (herein referred to as the SWMMWW). This report is based on the steps outlined in Chapter 3 of Volume I of the SWMMWW and the Edmonds Stormwater Addendum. The project is classified as a Category 2 project per the ECDC and the Edmonds Stormwater Addendum, and will comply with Minimum Requirements #1-9 per Figure 1-4. Minimum Requirement #1: Preparation of Stormwater Site Plans: The stormwater site plan consists of this report and the civil drawings, and is prepared in accordance with Chapter 3 of Volume 1 of the SWMMWW and the requirements in the Edmonds Stormwater Addendum. Minimum Requirement #2: Construction Stormwater Pollution Prevention Plan (SWPPP): The SWPPP shall include a narrative and drawings. The SWPPP narrative shall include documentation that addresses the 13 elements of Construction Stormwater Pollution Prevention. See Section IV and the civil drawings. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 March 22, 2023 Drainage Report Section I, Page 6 Minimum Requirement #3: Source Control of Pollution: All known, available and reasonable source control BMPs must be required for all projects approved by the City. At a minimum, incorporate required BMPs from SWMMWW Volume IV, S411— BMPs for Landscaping and Lawn/Vegetation Management. The Operation & Maintenance Manual found in Section VII addresses Lawn/Vegetation management. Minimum Requirement #4: Preservation of Natural Drainage Systems and Outfalls: Natural drainage patterns shall be maintained, and discharges from the project site shall occur at the natural location, to the maximum extent practicable. The manner by which runoff is discharged from the project site must not cause a significant adverse impact to downstream receiving waters and down gradient properties. All projects shall submit an off -site qualitative analysis. A qualitative analysis of the upstream and downstream system entering the site is presented in Section II. Minimum Requirement #5: On -Site Stormwater Management: The proposed project is classified as a Category 2 project per the Edmonds Stormwater Addendum. Per Chapter 5.5.2 of the Edmonds Stormwater Addendum, the project shall either use On -Site Stormwater Management BMPs from List No. 2 for all new plus replaced hard surfaces and land disturbed, or demonstrate compliance with the LID Performance Standard. However, this project direct discharges into Edmonds Way and is not required to evaluate the LID Performance Standard. This project will demonstrate compliance with the LID Performance Standard via the infiltrating rain garden and infiltration trenches on site (see Section III for more). It will also meet the specific flow requirements for the Edmonds Way Basin, per ECDC 18.30.060. D.5. b. iv. b. Minimum Requirement #6: Runoff Treatment: This requirement applies to the new plus replaced hard surfaces and the converted vegetation areas. The following require construction of stormwater treatment facilities: i.) Projects in which the total of pollution -generating hard surface (PGHS) is 5,000 square feet or more in a threshold discharge area of the project, or ii.) projects in which the total of pollution -generating pervious surfaces (PGPS), not including permeable pavements, is 0.75 acres or more in a threshold discharge area, and from which there will be a surface discharge in a natural or man-made conveyance system from the site. The project's total amount of PGHS is more than 5,000 square feet therefore runoff treatment is required. See Section III for details. Minimum Requirement #7: Flow Control: This requirement applies to projects that discharge stormwater directly, or indirectly through a conveyance system, into a receiving waterbody. This project enters the City's MS4 within Edmonds Way and directly drains to the Puget Sound, therefore flow control is required. Per ECDC 18.30.060.D.7.a, projects discharging into the Edmonds Way MS4 must meet the Edmonds Way standard for flow control, detailed in Section IV of this report. Minimum Requirement #8: Wetlands Protection: This requirement applies only to projects whose stormwater discharges into a wetland, either directly or indirectly through a conveyance system. This project site's stormwater does not discharge into a wetland and does not require wetland protection. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Section I, Page 7 Minimum Requirement #9: Operation and Maintenance: An operation and maintenance manual that is consistent with the provisions in Volume I and Volume V of the SWMMWW is required for proposed Stormwater Treatment and Flow Control BMPs/facilities. The party (or parties) responsible for maintenance and operation shall be identified in the operation and maintenance manual. For private facilities approved by the City, a copy of the operation and maintenance manual shall be retained on -site or within reasonable access to the site and shall be transferred with the property to the new owner. For public facilities, a copy of the operation and maintenance manual shall be retained in the appropriate department. A log of maintenance activity that indicates what actions were taken shall be kept and be available for inspection. See Section VIII. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Section I, Page 8 Does the project result in 2,000 square feet, or greater, of new plus replaced hard surface area? OR Does the land disturbing activity total 7,000 square feet or greater? No Minimum Requirements No. 1 through 5 apply Iiiiimum Requirement No. 2 applies Next Question Does the project add 5,000 square feet or more of new plus replaced hard surfaces'' OR Convert 0.75 acres or more of vegetation to lawn or landscaped areas? OR Convert 2.5 acres or more of native vegetation to pasture? Yes Is this a road related project? All Minimum Requirements Yes apply to the new and replaced hard surfaces and converted vegetation areas. All Minimum Requirements apply to the new hard surfaces and converted vegetation areas. No Yes Does the project add 5,000 square feet or No more of new hard surfaces? Yes Do new hard surfaces add 50% or more to the existing hard surfaces within the project limits? No INo additional requirements. Figure 1-4. Flow Chart for Determining Minimum Requirements for Development (Edmonds Stormwater Addendum). 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Section II, Page 1 Section II — Off -Site Analysis Section II Summary Task 1 — Define and map the study area Task 2 — Review all available information of the study area Task 3 — Field inspect the area Task 4 - Describe the drainage system, and its existing and predicted problems Task 1— Define and map the study area An initial qualitative analysis shall document potential off -site impacts of stormwater discharges for each upstream drainage system entering a site, and each downstream drainage system leaving a site according to Section 6.2.1 of the Edmonds Stormwater Addendum. The downstream analysis shall extend from the project site to the receiving water, or up to one -quarter mile, whichever is less. Runoff from the site will enter the City's MS4 within one -quarter mile since the project proposes to connect into an existing catch basin at the southwest corner of the site. The catch basin conveys runoff to the public storm main within Edmonds Way that continues west along Edmonds Way until it outfalls into the Puget Sound. Although this flow path crosses other streams and other watersheds the Edmonds Way watershed directly outfalls into the Puget Sound 1.93 miles downstream of the site. i LU _I 0LU C Q � � 1 Puget, \ u - �Watershed —D.hii y r= 4 Willow 4' Creek , P W atersh, dd�P IQ 00 S' IV LNlJ1 ST Edn �MOIItpS W ZZUTH ST 5W PROJECT SITE Figure II-1. Map showing Edmonds Watersheds (from City of Edmonds GIS map). 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Section II, Page 2 Task 2 — Review all available information on the study area Existing stormwater improvements were determined from the survey and the city GIS map. The proposed point of connection for the site's stormwater will be through an overflow pipe to an existing catch basin near the southwest corner of the site where the system ties into the storm main within Edmonds Way. The catch basin conveys runoff through an 8" DIP pipe to a catch basin along the curb of Edmonds Way. From here the stormwater is conveyed west by a 36" concrete pipe, upsizes to a 42", up to a 48" pipe which outfalls into the Puget Sound 1.93 miles west of the project site. Per the City GIS map, the site contains erosion and landslide hazard areas (see Figure II-2 below). This area will be limitedly disturbed during the project construction. City of Edmonds _ 9/Ub 1105 �' 22727 22731 q1 Z Map Title N N N N 8�S — 72721 h 9511 Legend 8 of n Creeks ❑i Seismic Hazard Areas q� PL"yr. - Earth Subsidence and Landslide I O� q3 22809 96Z Cl T 1 i Minimum Buffer Adjacent to Hal 72804 ° Welands 9�06 � � � WMlartds Boundary k p vnu.ne I��naan., vm can aeml 00 // Fbodplains tT P tiry 10` \ I—. nE F 1 Landslide Hazard Area ao% Severe Erosion Hazard IS%-00% ❑ Erosion Hazard Areas 15% 40% V N ArcSDE.GIS.STREET CENTERLINE — -II ntR.�rRlwa+ (T -4 1 9715 i .: A 0 �' W AY4, 9620 EDM0NDS ;- �i - — F fir'A' 23001, ^i 23003 1:2,257 O Notes 9w 01 1111 FM Thn mD0 is ewer Fene,ated stela oO1Dv1 IrOm an Inerrct rt.yldnF yle and it Id ,elererte uNy. D.. I—, In.,.lare , an this —m nut be e¢urele, WGS_1981eb M WelcatorAuedwry_Sphe a--l. m Otherwise re4 * V City of Edmonds THIS MAD IS NOT 10 BE VSED TOR DESIGN OR CONSIRUC PION Figure II-2. Landslide and Erosion Hazard area map (from City of Edmonds GIS map). Task 3 — Field inspect the study area From evaluating surrounding conditions, the site does not appear to take on significant upstream runoff. The project proposes to tie infiltrate all impervious surfaces. Any overflow from the infiltrating BMPs is to be routed to a 36" concrete main in the Edmonds Way ROW. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Section II, Page 3 Task 4 — Describe the drainage system, and its existing and predicted problems Existing stormwater improvements were determined from the survey and the city GIS map. The proposed point of connection for the site's stormwater will be through an overflow pipe to an existing catch basin near the southwest corner of the site where the system ties into the storm main within Edmonds Way. The catch basin conveys runoff through an 8" DIP pipe to a catch basin along the curb of Edmonds Way. From here the stormwater is conveyed west by a 36" concrete pipe, upsizes to a 42", up to a 48" pipe which outfalls into the Puget Sound 1.93 miles west of the project site. The project proposes to route all runoff from impervious surfaces of the site to infiltrating rain gardens and infiltration trenches on site. The rain gardens are situated between the south side of the building and Edmonds Way, and the infiltration trenches are located in the western and eastern parking lots. Designed per the specific requirements for Edmonds Way, the overflow of the system will be tied to the existing catch basin near the southwest corner of the site. There are no anticipated problems associated with the development from this project. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 March 22, 2023 Drainage Report Section III, Page 1 Section III — Permanent Stormwater Control Plan Section III Summary Narrative IVnrrntivo The project is classified as a Category 2 project and will comply with Minimum Requirements #1-9 because the project proposes more than 5,000 sf of new impervious surfaces. The project discharges directly to the Puget Sound through the City's MS4, and thus it is not required to meet the LID Performance Standard, nor consider bioretention, rain gardens, permeable pavement, or full dispersion. Although the LID Performance consideration is waived, the infiltrating rain garden and infiltration trenches designed for this project will demonstrate compliance with the LID Performance Standard. It will also meet the specific Edmonds Way flow control requirements. For the remaining project runoff either not managed by the rain gardens or infiltration trenches, the post -development 10- and 100-year recurrence interval peak flows shall not exceed 0.25 and 0.45 cfs per acre of impervious surface, respectively. See ECDC 18.30.060. D.S. b. iv. b. Three infiltrating rain gardens and two infiltration trenches have been chosen to demonstrate compliance with the LID Performance Standard for this site. All BMPs were sized using WWHM 2012. An infiltration rate of 0.63 in/hr was used for the design of all BMPs except one, noted as Bioretention 1 in the model, which used a higher rate of 2.88 in/hr due to its location. The proposed location of Bioretention 1, or the northernmost rain garden, is in the same location as Infiltration Pit 2 in the geotechnical report. This pit had a measured rate of 8 in/hr, and thus infiltrating BMPs in the immediate surrounding area of the pit could use the design rate of 2.88 in/hr. Otherwise, infiltrating BMPs were to use a rate of 0.63 in/hr. The BMPs were additionally required to meet the Edmonds Way direct discharge requirement outlined above. On site, the design rain garden is broken up into three parts with 1.5' of bioretention mix. The overflow meets the requirement as the 10 — year and the 100 — year peak flow are less than 0.25/acre and 0.45/acre of contributing impervious, respectively. (See WWHM output in Appendix A). There is 0.767 acres of contributing impervious area, the majority of which (0.670 ac) is coming from the proposed development. The off -site existing 0.097 ac is also included in the calculation. 10 Year target flow 0.767 x 0.25 cfs = 0.192 cfs 100 Year target flow 0.767 x 0.45 cfs = 0.345 cfs Per the Edmonds Stormwater Addendum, Appendix C, a treatment facility must infiltrate more than 91% of the influent runoff in order to meet water quality requirements. The runoff must be infiltrated through soils with a cation exchange capacity (CEC) of 5 meq/100 g or greater. Per Checklist 10 of the Edmonds Stormwater Addendum, the default bioretention soil media (BSM) has a minimum CEC of 5 meq/100 g. A 1.5' deep layer of sand blend with a CEC of greater than 5 meq/100 g will 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Section III, Page 2 be installed below the infiltration trench to provide sufficient water quality treatment. The eastern infiltration trench will only infiltrate roof runoff, and native soils will remain below the trench. Both the rain garden system and west infiltration trench are proposed to infiltration more than 91% of the influent runoff, and the treatment facility requirements are being met. Refer to Appendix A for a complete WWHM output and explanation. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 March 22, 2023 Drainage Report Section IV, Page 1 Section IV— Construction Stormwater Pollution Prevention Plan Section IV Summary: Narrative Construction SWPPP Elements Erosion control details are provided consistent with the City of Edmonds guidelines. Erosion control plan sheets are provided in full size as a part of the civil drawing set. A full Construction SWPPP is not required by the Department of Ecology because land -disturbing activity will be under one acre. The remainder of this section is a discussion of the Construction SWPPP Elements per Section 2.5.2 of Volume I of the SWMMWW and the requirements in the Edmonds Stormwater Addendum. See the civil plans for reference. Construction SWPPP Elements The elements for construction pollution prevention are discussed as follows: Element 1: Mark Clearing Limits To protect adjacent properties and to reduce the area of soil exposed to construction, the limits of construction will be clearly marked before land -disturbing activities begin. Clearing limits will be to the extents of necessary land disturbance for the new building and associated driveway and walkways. The BMPs relevant to marking the clearing limits that will be applied for this project include: High Visibility Plastic or Metal Fence (BMP C103) Element 2: Establish Construction Access Construction access or activities occurring on unpaved areas shall be minimized, yet where necessary, access points shall be stabilized to minimize the tracking of sediment onto public roads. The location of the existing southwest driveway area should be used for a stabilized construction entrance to the site. The BMPs relevant to establishing construction access are: Stabilized Construction Entrance (BMP C105) Element 3: Control Flow Rates The site is small enough that a silt fence used for Element 4 may be used to control flow rates. Element 4: Install Sediment Controls All stormwater runoff from disturbed areas shall pass through an appropriate sediment removal BMP before leaving the construction site or prior to being discharged. Silt fence will be installed on the western, 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 March 22, 2023 Drainage Report Section IV, Page 2 eastern, and southern borders of the site, and can be seen on the Temporary Erosion Control Plan, C2.1. Pollution prevention facilities on the erosion control plan must be constructed prior to or in conjunction with all clearing and grading to ensure that the transport of sediment to surface waters and adjacent properties is minimized. The specific BMPs to be used for controlling sediment on this project include: Silt Fence (BMP C233) Element 5: Stabilize Soils Exposed and unworked soils shall be stabilized with the application of effective BMPs to prevent erosion throughout the life of the project. The specific BMPs for soil stabilization that shall be used on this project include: Temporary and Permanent Seeding (BMP C120) Mulching (BMP C121) Nets and Blankets (BMP C122) Plastic Covering (BMP C123) Sodding (BMP C124) Topsoiling/Composting (BMP C125) Surface Roughening (BMP C130) Dust Control (BMP C140) Element 6: Protect Slopes Exposed slopes shall be stabilized with BMPs found in Element 5. Element 7: Protect Drain Inlets Drain inlets along Edmonds Way and as made operable on -site will be protected from sedimentation. Stormwater shall not enter the conveyance system without first being filtered or treated to remove sediment. Inlet protection devices shall be cleaned or removed and replaced when sediment has filled one-third of the available storage (or as specified by the manufacturer). The specific BMPs to be used for protecting drain inlets are: Storm Drain Inlet Protection (BMP C220) Element 8: Stabilize Channels and Outlets Conveyance channels are not located on or in the immediate vicinity of the site. Element 9: Control Pollutants Design, install, implement, and maintain effective pollution prevention measures to minimize the discharge of pollutants. The suggested BMPs are: Concrete Handling (BMP C151) Sawcutting and Surfacing Pollution Prevention (BMP C152) 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Section IV, Page 3 Material Delivery, Storage and Containment (BMP C153) Element 10: Control De -Watering De -watering is not anticipated. Element 11: Maintain BMPs All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired as needed to assure continued performance of their intended function. Element 12: Manage the Project • Phase development projects to the maximum degree practicable and take into account seasonal work limits. • Inspection and monitoring— Inspect, maintain, and repair all BMPs as needed to assure continued performance of their intended function. Conduct site inspections and monitoring in accordance with the Construction Stormwater General Permit or local plan approval authority. • Maintain an Updated Construction SWPPP - This SWPPP shall be retained on -site or within reasonable access to the site. The SWPPP shall be modified whenever there is a change in the design, construction, operation, or maintenance at the construction site that has, or could have, a significant effect on the discharge of pollutants to waters of the state. The SWPPP shall be modified if, during inspections or investigations conducted by the owner/operator, or the applicable local or state regulatory authority, it is determined that the SWPPP is ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. The SWPPP shall be modified as necessary to include additional or modified BMPs designed to correct problems identified. Revisions to the SWPPP shall be completed within seven (7) days following the inspection. Element 13: Protect Low Impact Development BMPs High visibility fence shall be placed around the proposed rain gardens and infiltration trenches to protect them from compaction during construction activities. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Section V, Page 1 Section V — Special Reports and/or Studies Section V Summary: Narrative The following reports are included in this section: 1. Natural Resources Conservation Service Soil Resource Report dated December 07, 2018. 2. Geotechnical Engineering Evaluation by Nelson Geotechnical Associates, Inc., dated April 14, 2020. 3. Environmental Soil Testing Summary by Nelson Geotechnical Associates, Inc., dated May 9, 2022. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 3 547480 47' 47 34" N I 8 47' 47 21" N 547480 547540 547600 547660 547720 547780 Map Scale: 1:2,750 if printed on A landscape (11" x 8.5") sheet. Meters N 0 40 80 160 240 Feet 0 100 200 400 600 Map projection: Web Mercator Comer coordinates: WGS84 Edge dcs: UTM Zone 1ON WGS84 USDA Natural Resources Web Soil Survey Conservation Service National Cooperative Soil Survey Soil Map —Snohomish County Area, Washington 547540 5476M 547660 547720 5477M 547840 547900 547960 547W 547900 547%0 3 54WX 47' 4734" N I 8 47' 47 21" N 548020 a 12/7/2018 Page 1 of 3 MAP LEGEND Area of Interest (AOI) Area of Interest (AOI) Soils 0 Soil Map Unit Polygons 0,0 Soil Map Unit Lines C Soil Map Unit Points Special Point Features V Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot O Landfill ALava Flow Marsh or swamp j* Mine or Quarry OMiscellaneous Water OPerennial Water V Rock Outcrop + Saline Spot Sandy Spot _ Severely Eroded Spot Q Sinkhole Slide or Slip 0o Sodic Spot Soil Map —Snohomish County Area, Washington MAP INFORMATION ® Spoil Area The soil surveys that comprise your AOI were mapped at 1:24,000. Q Stony Spot Very Stony Spot Warning: Soil Map may not be valid at this scale. Wet Spot Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil Other line placement. The maps do not show the small areas of Special Line Features contrasting soils that could have been shown at a more detailed scale. Water Features Streams and Canals Please rely on the bar scale on each map sheet for map measurements. Transportation .+. Rails Source of Map: Natural Resources Conservation Service Web Soil Survey URL: ..� Interstate Highways Coordinate System: Web Mercator (EPSG:3857) US Routes Maps from the Web Soil Survey are based on the Web Mercator Major Roads projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Local Roads Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. Background Aerial Photography This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Snohomish County Area, Washington Survey Area Data: Version 20, Sep 10, 2018 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jul 7, 2014—Jul 8, 2014 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. uSDA Natural Resources Web Soil Survey 12/7/2018 Conservation Service National Cooperative Soil Survey Page 2 of 3 Soil Map —Snohomish County Area, Washington Map Unit Legend Mit Symbol Map Unit Name Acres in AOI Percent of AOI 3 Alderwood gravelly sandy 5.3 16.4% loam, 15 to 30 percent slopes 5 Alderwood-Urban land 8.1 24.6% complex, 2 to 8 percent slopes 6 Alderwood-Urban land 6.9 21.0% complex, 8 to 15 percent slopes 17 Everett very gravelly sandy 5.5 16.7% loam, 0 to 8 percent slopes 51 Pits 2.0 6.2% 78 Urban land 4.9 15.1% Totals for Area of Interest 32.7 100.0% USDA Natural Resources Web Soil Survey 12/7/2018 Conservation Service National Cooperative Soil Survey Page 3 of 3 Map Unit Description: Alderwood gravelly sandy loam, 15 to 30 percent slopes ---Snohomish County Area, Washington Snohomish County Area, Washington 3—Alderwood gravelly sandy loam, 15 to 30 percent slopes Map Unit Setting National map unit symbol: 2t627 Elevation: 0 to 1,000 feet Mean annual precipitation: 25 to 60 inches Mean annual air temperature: 46 to 52 degrees F Frost -free period: 160 to 240 days Farmland classification: Farmland of statewide importance Map Unit Composition Alderwood and similar soils: 85 percent Minor components: 15 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Alderwood Setting Landform: Ridges, hills Landform position (two-dimensional): Backslope Landform position (three-dimensional): Side slope, nose slope, talf Down -slope shape: Linear, convex Across -slope shape: Convex Parent material: Glacial drift and/or glacial outwash over dense glaciomarine deposits Typical profile A - 0 to 7 inches: gravelly sandy loam Bw1 - 7 to 21 inches: very gravelly sandy loam Bw2 - 21 to 30 inches: very gravelly sandy loam Bg - 30 to 35 inches: very gravelly sandy loam 2Cd1 - 35 to 43 inches: very gravelly sandy loam 2Cd2 - 43 to 59 inches: very gravelly sandy loam Properties and qualities Slope: 15 to 30 percent Depth to restrictive feature: 20 to 39 inches to densic material Natural drainage class: Moderately well drained Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) Depth to water table: About 18 to 37 inches Frequency of flooding: None Frequency of ponding: None Available water storage in profile: Very low (about 2.7 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4e Hydrologic Soil Group: B USDA Natural Resources Web Soil Survey 12/7/2018 Conservation Service National Cooperative Soil Survey Page 1 of 2 Map Unit Description: Alderwood gravelly sandy loam, 15 to 30 percent slopes ---Snohomish County Area, Washington Forage suitability group: Limited Depth Soils (G002XS301 WA), Limited Depth Soils (G002XF303WA), Limited Depth Soils (G002XN302WA) Hydric soil rating: No Minor Components Indianola Percent of map unit: 5 percent Landform: Eskers, kames, terraces Landform position (three-dimensional): Tread Down -slope shape: Linear Across -slope shape: Linear Hydric soil rating: No Everett Percent of map unit: 5 percent Landform: Karnes, eskers, moraines Landform position (two-dimensional): Backslope Landform position (three-dimensional): Side slope Down -slope shape: Convex Across -slope shape: Convex Hydric soil rating: No Shalcar Percent of map unit: 3 percent Landform: Depressions Landform position (three-dimensional): Dip Down -slope shape: Concave Across -slope shape: Concave Hydric soil rating: Yes Norma Percent of map unit: 2 percent Landform: Depressions, drainageways Landform position (three-dimensional): Dip Down -slope shape: Concave, linear Across -slope shape: Concave Hydric soil rating: Yes Data Source Information Soil Survey Area: Snohomish County Area, Washington Survey Area Data: Version 20, Sep 10, 2018 USDA Natural Resources Web Soil Survey 12/7/2018 Conservation Service National Cooperative Soil Survey Page 2 of 2 Map Unit Description: Alderwood-Urban land complex, 2 to 8 percent slopes ---Snohomish County Area, Washington Snohomish County Area, Washington 5—Alderwood-Urban land complex, 2 to 8 percent slopes Map Unit Setting National map unit symbol: 2hz9 Elevation: 50 to 800 feet Mean annual precipitation: 25 to 60 inches Mean annual air temperature: 48 to 52 degrees F Frost -free period. 180 to 220 days Farmland classification: Not prime farmland Map Unit Composition Alderwood and similar soils: 60 percent Urban land: 25 percent Minor components: 15 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Alderwood Setting Landform: Till plains Parent material: Basal till Typical profile H1 - 0 to 7 inches: gravelly ashy sandy loam H2 - 7 to 35 inches: very gravelly ashy sandy loam H3 - 35 to 60 inches: gravelly sandy loam Properties and qualities Slope: 2 to 8 percent Depth to restrictive feature: 20 to 40 inches to densic material Natural drainage class: Moderately well drained Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) Depth to water table: About 18 to 36 inches Frequency of flooding: None Frequency of ponding: None Available water storage in profile: Low (about 3.0 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4s Hydrologic Soil Group: B Forage suitability group: Limited Depth Soils (G002XN302WA) Hydric soil rating: No Minor Components Mckenna Percent of map unit: 5 percent Landform: Depressions USDA Natural Resources Web Soil Survey 12/7/2018 Conservation Service National Cooperative Soil Survey Page 1 of 2 Map Unit Description: Alderwood-Urban land complex, 2 to 8 percent slopes ---Snohomish County Area, Washington Hydric soil rating: Yes Norma, undrained Percent of map unit: 5 percent Landform: Depressions Hydric soil rating: Yes Terric medisaprists, undrained Percent of map unit: 5 percent Landform: Depressions Hydric soil rating: Yes Data Source Information Soil Survey Area: Snohomish County Area, Washington Survey Area Data: Version 20, Sep 10, 2018 USDA Natural Resources Web Soil Survey 12/7/2018 Conservation Service National Cooperative Soil Survey Page 2 of 2 Map Unit Description: Alderwood-Urban land complex, 8 to 15 percent slopes ---Snohomish County Area, Washington Snohomish County Area, Washington 6—Alderwood-Urban land complex, 8 to 15 percent slopes Map Unit Setting National map unit symbol: 2hzn Elevation: 50 to 800 feet Mean annual precipitation: 25 to 60 inches Mean annual air temperature: 48 to 52 degrees F Frost -free period. 180 to 220 days Farmland classification: Not prime farmland Map Unit Composition Alderwood and similar soils: 60 percent Urban land: 25 percent Minor components: 5 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Alderwood Setting Landform: Till plains Parent material: Basal till Typical profile H1 - 0 to 7 inches: gravelly ashy sandy loam H2 - 7 to 35 inches: very gravelly ashy sandy loam H3 - 35 to 60 inches: gravelly sandy loam Properties and qualities Slope: 8 to 15 percent Depth to restrictive feature: 20 to 40 inches to densic material Natural drainage class: Moderately well drained Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) Depth to water table: About 18 to 36 inches Frequency of flooding: None Frequency of ponding: None Available water storage in profile: Low (about 3.0 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4s Hydrologic Soil Group: B Forage suitability group: Limited Depth Soils (G002XN302WA) Hydric soil rating: No Minor Components Norma, undrained Percent of map unit: 5 percent Landform: Drainageways USDA Natural Resources Web Soil Survey 12/7/2018 Conservation Service National Cooperative Soil Survey Page 1 of 2 Map Unit Description: Alderwood-Urban land complex, 8 to 15 percent slopes ---Snohomish County Area, Washington Hydric soil rating: Yes Data Source Information Soil Survey Area: Snohomish County Area, Washington Survey Area Data: Version 20, Sep 10, 2018 USDA Natural Resources Web Soil Survey 12/7/2018 Conservation Service National Cooperative Soil Survey Page 2 of 2 Map Unit Description: Everett very gravelly sandy loam, 0 to 8 percent slopes ---Snohomish County Area, Washington Snohomish County Area, Washington 17—Everett very gravelly sandy loam, 0 to 8 percent slopes Map Unit Setting National map unit symbol: 2t629 Elevation: 30 to 900 feet Mean annual precipitation: 35 to 91 inches Mean annual air temperature: 48 to 52 degrees F Frost -free period: 180 to 240 days Farmland classification: Farmland of statewide importance Map Unit Composition Everett and similar soils: 80 percent Minor components: 20 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Everett Setting Landform: Eskers, moraines, kames Landform position (two-dimensional): Summit, shoulder Landform position (three-dimensional): Crest, interfluve Down -slope shape: Convex Across -slope shape: Convex Parent material: Sandy and gravelly glacial outwash Typical profile Oi - 0 to 1 inches: slightly decomposed plant material A - 1 to 3 inches: very gravelly sandy loam Bw - 3 to 24 inches: very gravelly sandy loam C1 - 24 to 35 inches: very gravelly loamy sand C2 - 35 to 60 inches: extremely cobbly coarse sand Properties and qualities Slope: 0 to 8 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Somewhat excessively drained Capacity of the most limiting layer to transmit water (Ksat): High (1.98 to 5.95 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Available water storage in profile: Low (about 3.2 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4s Hydrologic Soil Group: A USDA Natural Resources Web Soil Survey 12/7/2018 Conservation Service National Cooperative Soil Survey Page 1 of 2 Map Unit Description: Everett very gravelly sandy loam, 0 to 8 percent slopes ---Snohomish County Area, Washington Forage suitability group: Droughty Soils (G002XS401 WA), Droughty Soils (G002XF403WA), Droughty Soils (G002XN402WA) Hydric soil rating: No Minor Components Alderwood Percent of map unit: 10 percent Landform: Ridges, hills Landform position (two-dimensional): Summit Landform position (three-dimensional): Crest, talf Down -slope shape: Linear, convex Across -slope shape: Convex Hydric soil rating: No Indianola Percent of map unit: 10 percent Landform: Eskers, kames, terraces Landform position (three-dimensional): Tread Down -slope shape: Linear Across -slope shape: Linear Hydric soil rating: No Data Source Information Soil Survey Area: Snohomish County Area, Washington Survey Area Data: Version 20, Sep 10, 2018 USDA Natural Resources Web Soil Survey 12/7/2018 Conservation Service National Cooperative Soil Survey Page 2 of 2 Map Unit Description: Pits ---Snohomish County Area, Washington Snohomish County Area, Washington 51—Pits Map Unit Composition Pits: 100 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Pits Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 8 Hydric soil rating: No Data Source Information Soil Survey Area: Snohomish County Area, Washington Survey Area Data: Version 20, Sep 10, 2018 USDA Natural Resources Web Soil Survey 12/7/2018 Conservation Service National Cooperative Soil Survey Page 1 of 1 Map Unit Description: Urban land ---Snohomish County Area, Washington Snohomish County Area, Washington 78—Urban land Map Unit Composition Urban land: 100 percent Estimates are based on observations, descriptions, and transects of the mapunit. Data Source Information Soil Survey Area: Snohomish County Area, Washington Survey Area Data: Version 20, Sep 10, 2018 USDA Natural Resources Web Soil Survey 12/7/2018 Conservation Service National Cooperative Soil Survey Page 1 of 1 NELSON GEOTECHNICAL ASSOCIATES. INC. April 14, 2020 Mr. Marc Wislen 4412 Russell Road, Unit A Mukilteo, Washington 98275 Via email: marc@platers. net Geotechnical Engineering Evaluation Westgate Station Commercial Development 9601 Edmonds Way Edmonds, Washington NGA File No. 1156720 Dear Mr. Wislen: 17311-13511 Ave. N.E. Suite A-500 Woodinville, WA 98072 (425) 486-1669 www.nelsongeotech.com We are pleased to submit this report titled "Geotechnical Engineering Evaluation — Westgate Station Commercial Development — 9601 Edmonds Way — Edmonds, Washington." This report documents our surface and subsurface explorations within the site, and provides general recommendations for future site development. Our services were completed in general accordance with the agreement which was authorized by you on February 5, 2020. The site is currently vacant and generally consists of a relatively level gravel parking area within the southern and central portion of the site. A moderate to steep south -facing slope is located above the lower parking area within the northern portion of the property. We understand that the proposed development will include construction of a new multi -level commercial structure within the lower relatively level area and extending into the lower portion of the moderate to steep slope within the northern portion of the property. We performed three geotechnical borings using a track -mounted drill rig along within seven backhoe-excavated test pits in the areas of potential development and within the steeply sloping areas. Our explorations generally encountered surficial undocumented fill soils underlain by competent native glacial till and advance outwash soils at relatively shallow depths within the proposed development areas. It is our opinion that the proposed site development is feasible from a geotechnical engineering standpoint, provided that our recommendations for site development are incorporated into project plans. In general, the native glacial soils underlying the site should adequately support the planned structure. Foundations should be advanced through any loose soils down to the competent glacial bearing soils interpreted to underlie the site, for bearing capacity and settlement considerations. These soils should generally be encountered approximately two to three feet below the existing ground surface, based on our explorations. If loose soils or undocumented fill are encountered in unexplored areas of the site, they should be removed and replaced with structural fill for foundation and pavement support. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Summary - Page 2 It is also our opinion that the soils that underlie the site and form the core of the site slopes within the vicinity of the site should be stable with respect to deep-seated earth movements, due to their inherent strength and slope geometry. However, there is a potential for shallow sloughing and erosion events to occur on the steeper site slopes within the property especially within the loose surficial and fill soils mantling some of the slope areas. We understand that the majority of the proposed structure will be located along the toe of the steep slope areas. In our opinion, this should be feasible, provided the upslope side of the proposed structure is designed to retain the slope and extends a minimum of three feet above finished ground surface, to protect the structure against debris impact generated from potential failures on this slope. This is intended to provide a catchment measure should any sloughing debris travel towards the proposed structures during extreme weather or as a result of an earthquake. Specific grading plans were not available at the time this report was prepared. However, we anticipate that tall cuts and retaining walls will likely be needed for the planned structure especially along the northern side of the proposed structure along the toe of the steep slope. Due to the proposed depth of the anticipated cuts, tight site constraints and to limit significant temporary excavations extending into the steep slope areas, we recommend that temporary/permanent soldier pile shoring walls be utilized to support cut excavations for the structure construction. We recommend that any temporary cuts that are greater than four feet and not able to be sloped back to a safe inclination should be supported with soldier pile shoring wall. These walls can ultimately be incorporated into the building as permanent retaining walls, if feasible. The City of Edmonds utilizes the 2014 WSDOE Stormwater Management Manual for Western Washington to determine long- term design infiltration rates for the site. In accordance with the manual, long-term design infiltration rates for this site were determined by performing on -site infiltration testing consisting of the Small Pilot Infiltration Test (PIT). We performed two small- scale PIT tests within the site in accordance with the manual to determine the infiltration capabilities of the site soils. It is our opinion that the more granular native advance outwash soils encountered at depth within our explorations are suitable for stormwater infiltration. In the attached report, we have also provided general recommendations for site grading, slabs -on -grade, structural fill placement, foundations, retaining walls, soldier pile wall installation, erosion control, and drainage. We should be retained to review and comment on final development plans and observe the earthwork phase of construction. We also recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications. It has been a pleasure to provide service to you on this project. Please contact us if you have any questions regarding this report or require further information. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. rZOMM, Khaled M. Shawish, PE Principal NELSON GEOTECHNICAL ASSOCIATES, INC. TABLE OF CONTENTS INTRODUCTION............................................................................................................................................1 SCOPE..........................................................................................................................................................1 SITECONDITIONS.........................................................................................................................................2 SurfaceConditions......................................................................................................................................... 2 SubsurfaceConditions................................................................................................................................... 3 Explorations................................................................................................................................................... 3 HydrogeologicConditions.............................................................................................................................. 4 SENSITIVE AREA EVALUATION......................................................................................................................4 SeismicHazard............................................................................................................................................... 4 ErosionHazard............................................................................................................................................... 5 Landslide Hazard/Slope Stability................................................................................................................... 5 CONCLUSIONS AND RECOMMENDATIONS...................................................................................................6 General.......................................................................................................................................................... 6 Erosion Control and Slope Protection Measures........................................................................................... 8 SitePreparation and Grading........................................................................................................................ 9 Temporaryand Permanent Slopes.............................................................................................................. 10 Foundations................................................................................................................................................. 10 ShoringWall................................................................................................................................................. 11 Tie-Backs...................................................................................................................................................... 13 OtherRetaining Walls.................................................................................................................................. 14 StructuralFill................................................................................................................................................ 15 Slabson Grade............................................................................................................................................. 16 Pavements................................................................................................................................................... 16 Utilities......................................................................................................................................................... 16 SiteDrainage................................................................................................................................................ 16 CONSTRUCTION MONITORING...................................................................................................................18 SLOPEMONITORING..................................................................................................................................18 USEOF THIS REPORT..................................................................................................................................19 LIST OF FIGURES Figure 1— Vicinity Map Figure 2 —Site Plan Figure 3 — Cross Section A -A' Figure 4 —Cross Section B-B' Figure 5 — Cross Section C-C' Figure 6—Soil Classification Chart Figures 7 through 9 — Boring Logs Figure 10 —Test Pit Logs Figure 11— Schematic Soldier Pile Wall Detail NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Westgate Station Commercial Development 9601 Edmonds Way Edmonds, Washington INTRODUCTION This report presents the results of our geotechnical engineering evaluation of the proposed Westgate Station Commercial Development project located at 9601 Edmonds Way in Edmonds, Washington, as shown on the Vicinity Map in Figure 1. The purpose of this study is to explore and characterize the surface and subsurface conditions within the site and to provide general opinions and recommendations for the future site development. The site is currently vacant and generally consists of a relatively level gravel parking area within the southern and central portion of the site. A moderate to steep south -facing slope is located above the lower parking area within the northern portion of the property. We understand that the proposed development will include construction of a new multi -level commercial structure within the lower relatively level area and extending into the lower portion of the moderate to steep slope within the northern portion of the property. Specific grading and stormwater handling plans were not available at the time this report was prepared. However, we do understand that stormwater generated within the property may be directed to onsite infiltrations systems, if feasible. The existing site layout and proposed building location are shown on the Site Plan in Figure 2. SCOPE The purpose of this study is to explore and characterize the site surface and subsurface conditions, to provide an assessment of the site's geologic hazards, and to provide our geotechnical opinions and preliminary recommendations regarding potential site development. Specifically, our scope of services includes the following: 1. Review available soil and geologic maps of the area, available plans, and any available geotechnical reports for the property. 2. Explore the subsurface soil and groundwater conditions within the site with three geotechnical borings using a track -mounted drill rig. Drilling was subcontracted by NGA. 3. Provide long-term design infiltration rates based on on -site Small Scale Pilot Infiltration Test (PIT) per the 2014 DOE Stormwater Manual. Provide our opinion on the feasibility of infiltration for the onsite soils. 4. Perform laboratory classification and analyses on soil samples obtained from the explorations, as necessary. 5. Qualitatively map conditions on site slopes by constructing a geological cross section using hand-augered explorations where necessary, and evaluate current slope stability conditions. 6. Provide recommendations for site grading and earthwork, including structural fill materials and construction standards. 7. Provide recommendations for steep slope setbacks. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 2 8. Provide recommendations for temporary and permanent slopes. 9. Provide recommendations for temporary and permanent shoring, as needed. 10. Provide recommendations for permanent retaining walls, as well as shoring walls. 11. Provide recommendations for pavement subgrade. 12. Provide recommendations for drainage and erosion control. 13. Document the results of our conclusions and recommendations in a written geotechnical engineering report. SITE CONDITIONS Surface Conditions The site consists of an irregular -shaped parcel covering approximately 1.1 acres. The property is currently undeveloped. The property is bordered to the north and east by existing residential properties, to the south by Edmonds Way and to the east by a gas station. The ground surface within the southern and central portion of the site is relatively level to gently sloping down from the northeast to the southwest. Steep to very steep southeast -facing slopes are located within the northern portion of the property. The steep to very steep southeast -facing slopes descend from the northern property line to the lower relatively level parking area within the central portion of the site at gradients in the range of approximately 24 to 45 degrees (45 to 100 percent). Near vertical exposures of glacial till were also observed within portions of the upper slope areas along the very northern portion of the site. The overall height of the steep slopes within the site range from approximately 30 to 40 feet. The existing site topography and interpreted subsurface conditions are presented as Cross Sections A -A', B-B', and C-C' in Figures 3 through 5, respectively. The slopes are generally vegetated with sparse trees and underbrush. We did not observe significant signs of recent slope movement within the site such as deep-seated landsliding. However, we did observe some indications of past surficial sloughing and erosion that appears to have occurred on the upper steeper site slopes in the past. We did not observe any ponding water or groundwater seepage emitting from the site slopes during our site visits. Subsurface Conditions Geology: The Geologic map of the Edmonds East and part of the Edmonds West quadrangles, Washington (MF-1541), by James P. Minard, (USGS, 1983) was reviewed for this site. This geologic map indicates the location of the subject property is underlain by Vashon till (Qvt) and advance outwash deposits (Qva). Vashon till typically consists of a concrete -like mixture of relatively equal parts of silt, sand, and gravel, while advance outwash is generally comprised of mostly clean, gray, pebbly sand. Our explorations generally encountered silty fine to medium sand with gravel and fine to medium sand with silt and gravel that we interpreted as native glacial till and advance outwash soils, respectively. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 3 Explorations We visited the site on February 28 and March 3, 2020 to explore the subsurface soil and groundwater conditions by drilling three exploratory borings and seven test pit explorations using a track -mounted drill rig and excavator, respectively. The approximate locations of our explorations are indicated on the Site Plan in Figure 2. A geologist from Nelson Geotechnical Associates, Inc. (NGA) was present during the explorations, examined the soils and geologic conditions encountered, obtained samples of the different soil types, and maintained logs of the explorations. A Standard Penetration Test (SPT) was performed on each of the samples during drilling to document soil density at depth. The SPT consists of driving a 2- inch outer -diameter, split -spoon sampler 18 inches using a 140-pound hammer falling 30 inches. The number of blows required to drive the sampler the final 12 inches is referred to as the "N" value and is presented on the boring logs. The N value is used to evaluate the strength and density of the deposit. The soils were visually classified in general accordance with the Unified Soil Classification System, presented in Figure 6. The logs of our borings are presented as Figures 7 through 9, and the log of the test pits are presented as Figure 10. The following paragraphs contain a general description of the subsurface conditions encountered in the explorations. For a detailed description of the subsurface conditions, the boring and test pit logs should be reviewed. Borings B-1 through B-3 were performed within the lower relatively level to gently sloping portion of the property. Borings B-2 and B-3 encountered surficial gravel surfacing underlain by approximately 7.0 feet of dense to very dense, gray silty fine to medium sand soils that we interpreted as native glacial till soils. Underlying the ground surface in Boring B-1 and the glacial till soils in Borings B-2 and B-3, we encountered medium dense to very dense, fine to coarse sand with varying amounts of silt and gravel that we interpreted as native advance outwash soils. Borings B-1 through B-3 were terminated within the native advance outwash soils at depths in the range of approximately 30.0 and 30.5 feet below the existing ground surface. All of our test pit explorations encountered approximately 0.5 to 6.0 feet of surficial gravel surfacing or undocumented fill soils. Underlying the undocumented fill in Test Pits 2 through 5 and Infiltration Pit 2, we encountered approximately 1.0 to 8.0 feet of medium dense to very dense, gray silty fine to medium sand and gravel that we interpreted as native glacial till soils. Below the undocumented fill in Test Pits Test Pits 1, 6 and Infiltration Pit 1, and the glacial till soils in Test Pits 2 through 5 and Infiltration Pit 2, we encountered medium dense to very dense fine to coarse sand with gravel that we interpreted as native advance outwash soils. Test Pit 3 was terminated within the native glacial till soils at a depth of approximately 6.0 feet below the existing ground surface while Test Pits 1, 2, 4, 5, 6 and Infiltration Pits 1 and 2 were terminated within the native advance outwash deposits at depths in the range of approximately 5.0 to 10.0 feet. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 4 Hydrogeologic Conditions We did not encounter groundwater within our explorations to the depths explored. If groundwater is encountered during construction we would interpret this as perched water. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of a relatively low permeability material. Perched water does not represent a regional groundwater "table" within the upper soil horizons. Perched water tends to vary spatially and is dependent upon the amount of rainfall. We would expect the amount of perched groundwater to decrease during drier times of the year and increase during wetter periods. SENSITIVE AREA EVALUATION Seismic Hazard The 2018 International Building Code (IBC) seismic design section provides a basis for seismic design of structures. Since medium dense or better native glacial soils were generally encountered underlying the site at relatively shallow depths throughout the site, the site conditions best fit the IBC description for Site Class D. Table 1 below provides seismic design parameters for the site that are in conformance with the 2018 IBC, which specifies a design earthquake having a 2% probability of occurrence in 50 years (return interval of 2,475 years), and the 2008 USGS seismic hazard maps. Table 1— 2018 IBC Seismic Design Parameters Site Class Spectral Acceleration Spectral Acceleration Site Coefficients Design Spectral at 0.2 sec. (g) at 1.0 sec. (g) Response Ss S1 Parameters Fa Fv SDs SD1 D 1.263 0.494 1.061 1.506 0.842 0.496 The spectral response accelerations were obtained from the USGS Earthquake Hazards Program Interpolated Probabilistic Ground Motion website (2008 data) for the project latitude and longitude. Hazards associated with seismic activity include liquefaction potential and amplification of ground motion. Liquefaction is caused by a rise in pore pressures in a loose, fine sand deposit beneath the groundwater table. It is our opinion that the competent native glacial soils interpreted to underlie the site have a low potential for liquefaction or amplification of ground motion. The competent native glacial soils interpreted to form the core of the site slopes are considered stable with respect to deep-seated slope failures. However, the overlying loose surficial and fill soils mantling the portions of the steep slopes have the potential for shallow sloughing failures during seismic events. Such events should not affect the planned structure provided the foundations, retaining walls along with the slope stabilization measures are designed as described in this report NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 5 Erosion Hazard The criteria used for determination of the erosion hazard for affected areas include soil type, slope gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related to vegetative cover and the specific surface soil types, which are related to the underlying geologic soil units. The Soil Survey of Snohomish County Area, Washington, by the Natural Resources Conservation Service (NRCS) was reviewed to determine the erosion hazard of the on -site soils. The surface soils for this site were mapped as Alderwood-Urban land complex, 8 to 15 percent slopes and Everett very gravelly sandy loam, 0 to 8 percent slopes. The erosion hazard for these materials is listed as slight. It is our opinion that the erosion hazard for site soils should be low in areas where the site is not disturbed. Landslide Hazard/Slope Stability The criteria used for evaluation of landslide hazards include soil type, slope gradient, and groundwater conditions. The ground surface within the central and southern portions of the property is generally relatively level to gently sloping down from the northeast to the southwest. Steep to very steep southeast -facing slope areas are located within the northern portion of the property. The steep to very steep southeast -facing slopes descend from the northern property line to the lower relatively level parking area within the central portion of the site at gradients in the range of approximately 24 to 45 degrees (45 to 100 percent). Near vertical exposures of glacial till were also observed within portions of the upper slope areas along the very northern portion of the site. The overall height of the steep slopes within the site range from approximately 30 to 40 feet. We did not observe evidence of significant slope instability within or in the immediate vicinity of the property during our investigation, such as deep-seated landsliding. However, we did observe some indications of past surficial sloughing and erosion that appears to have occurred on the upper steeper site slopes in the past. We did not observe any groundwater seepage emitting from the site slopes during our site visits. We reviewed the City of Edmonds GIS Website and portions of the site are mapped as a landslide hazard area. It is our opinion that the steep to very steep southeast -facing slopes within the northern portion of the property meet the classification as a landslide hazard area in accordance with Edmonds Community Development Code 23.80.020.B.4. This is due to the overall height of the sloping areas being greater than 10 feet and slope inclinations within the steep slope areas being greater than 40 percent. The core of the site slopes within the site and within the near vicinity of the site are inferred to consist primarily of dense or better native glacial soils. Relatively shallow sloughing failures as well as surficial erosion are natural processes and should be expected on the steeper site slopes during extreme weather conditions. This is especially true within the loose surficial and undocumented fill soils on the slopes. It is our opinion that while there is potential for erosion, soil creep, and shallow failures within the loose surficial soils on the steep slope, there is not a significant potential for deep-seated slope failures under current site conditions. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 6 We understand that the proposed structure will be located along the toe of the steep slope area. We anticipate that temporary cut excavations along the lower portion of the slope will be reduced by installing a soldier pile shoring wall where temporary cut excavations cannot be sloped back safely or are greater than four feet in overall height. As a result, we anticipate that the proposed development will have minimal impact on the existing steep slope stability conditions. The stability conditions of the steep slope area will ultimately be improved as the proposed structure will be designed to support the steep slope areas above. It is our opinion that the proposed commercial development should not adversely impact or decrease the existing stability of the steep slope areas, neighboring properties, or critical areas; and is in compliance with the City of Edmonds Codes 23.80.060 and 23.80.070, provided our recommendations are incorporated into the proposed plans and followed during construction. We should be retained to review the proposed development and grading plan to analyze the slope stability of the proposed conditions once finalized. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the proposed commercial development within the site is feasible from a geotechnical standpoint. Our explorations indicated that the site is generally underlain by competent native glacial soils at relatively shallow depths throughout the site. The native glacial deposits encountered at depth should provide adequate support for foundation, slab, and pavement loads. We recommend that the planned structures be designed utilizing shallow foundations. Footings should extend through any loose soil or undocumented fill soils and be founded on the underlying medium dense or better native glacial bearing soils, or structural fill extending to these soils. The competent native glacial bearing soils should typically be encountered approximately two to three feet below the existing surface, based on our explorations. We should note that localized areas of deeper unsuitable soils and/or undocumented fill could be encountered at this site. This condition would require additional excavations in foundation, slab, and pavement areas to remove the unsuitable soils. It is also our opinion that the soils that underlie the site and form the core of the steep slopes within the northern portion of the subject site should be stable with respect to deep-seated earth movements, due to their inherent strength and slope geometry. However, shallow failures could occur on the slopes in the loose surficial and undocumented fill soils, especially during adverse weather or a significant seismic event. We understand that the proposed structure will be located along the toe of the steep slope area within the northern portion of the property. In our opinion, this should be feasible, provided the upslope side of the proposed structure is designed to retain the slope and extends a minimum of three feet above finished ground surface, to protect the structure against debris impact generated from potential failures on this slope. This is intended to provide a catchment measure should any sloughing debris travel towards the proposed structures during extreme weather or as a result of an earthquake. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 7 We anticipate that tall cuts and retaining walls will likely be needed for the planned structure especially along the northern side of the proposed structure along the toe of the steep slope area. Due to the proposed depth of the anticipated cuts, tight site constraints and to limit significant temporary excavations extending into the steep slope areas, we recommend that temporary/permanent soldier pile shoring walls be utilized to support temporary cut excavations for the structure construction. We recommend that any temporary cuts that are greater than four feet in height that are not able to be sloped back to a safe inclination should be supported with soldier pile shoring wall. The soldier pile shoring wall can ultimately be incorporated into the building as permanent retaining walls, if feasible. We provided recommendations for temporary and permanent cut slopes in the Temporary and Permanent Slopes section of this report. We also provide recommendations for the soldier pile shoring walls in the Soldier Pile Shoring Wall subsections of this report. We should be retained to review grading and retaining wall plans once development plans are finalized. Under no circumstances should fill be placed on any slopes without engineering analysis and specific recommendations by NGA. The City of Edmonds utilizes the 2014 WSDOE Stormwater Management Manual for Western Washington to determine long-term design infiltration rates for the site. In accordance with the manual, long-term design infiltration rates for this site were determined by performing on -site infiltration testing consisting of the Small Pilot Infiltration Test (PIT). We performed two small-scale PIT tests within the site in accordance with the manual to determine the infiltration capabilities of the site soils. It is our opinion that the more granular native glacial advance outwash soils encountered at depth within our explorations are suitable for stormwater infiltration. We have included details of our on -site infiltration testing in the Infiltration Testing subsection of this report. All grading operations and drainage improvements planned as part of this development should be planned and completed in a matter that enhances the stability of the steep slopes, not reduces it. Excavation spoils associated with the structure excavations should not be stockpiled near the site slopes or be allowed to encroach on the slopes. Also, all runoff generated within the site should be collected and routed into a permanent discharge system and not be allowed to flow over the slopes. Future vegetation management on the slopes should be the subject of a specific evaluation and a plan approved by the City of Edmonds. The site slopes should be monitored on an ongoing basis, especially during the wet season, for any signs of instability, and corrective actions promptly taken should any signs of instability be observed. Lawn clipping and any other trash or debris should never be allowed to reach the slopes. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 8 The soils encountered on this site are considered moisture -sensitive and will disturb easily when wet. To lessen the potential impacts of construction on the slopes and to reduce cost overruns and delays, we recommend that construction take place during the drier summer months. If construction takes place during the rainy months, additional expenses and delays should be expected. Additional expenses could include the need for placing erosion control and temporary drainage measures to protect the slopes, the need for placing a blanket of rock spalls on exposed subgrades, and construction traffic areas prior to placing structural fill, and the need for importing all-weather material for structural fill. We recommend that NGA be retained to review final project plans and provide consultation regarding structure placement, site grading, drainage plans, and foundation support. We also recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications. Erosion Control and Slope Protection Measures The erosion hazard for the on -site soils is interpreted as low to moderate but the actual hazard will be dependent on how the site is graded and how water is allowed to concentrate. Best Management Practices (BMPs) should be used to control erosion. Areas disturbed during construction should be protected from erosion. Erosion control measures may include diverting surface water away from the stripped or disturbed areas. Silt fences and/or straw bales should be erected to prevent muddy water from leaving the site or flowing over the slopes. Stockpiles should be covered with plastic sheeting during wet weather and stockpiled material should be kept away from the steep slope on the southern property line. Disturbed areas should be planted as soon as practical and the vegetation should be maintained until it is established. The erosion potential for areas not stripped of vegetation should be low to moderate. Protection of the steep slope areas should be performed as required by the City of Edmonds. Specifically, we recommend that the site slopes not be disturbed or modified through placement of any fill or removal of the existing vegetation. No additional material of any kind should be placed on either slope or be allowed to reach the slopes, such as excavation spoils, lawn clippings, and other yard waste, trash, and soil stockpiles. Vegetation should not be removed from the slopes. Replacement of vegetation should be performed in accordance with City of Edmonds code. Under no circumstances should water be allowed to concentrate on the slopes. The clearing of vegetation within the area of the proposed development area should not affect slope stability, provided the temporary cut slopes are supported as recommended in this report and disturbed areas outside the building are revegetated as soon as practical and protected from erosion. In areas that are disturbed during or after construction, planting, hydro seeding, and/or straw mulching are effective ways to minimize erosion and allow vegetation to be re- established rapidly. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 9 Site Preparation and Grading After erosion control measures are implemented, site preparation should consist of stripping any loose soils and undocumented fill to expose medium dense or better native soil in foundation, slab -on -grade, and pavement areas. The stripped materials should be removed from the site or stockpiled for later use as landscaping fill. Based on our observations, we anticipate stripping depths of two to three feet, depending on the specific locations. However, additional stripping may be required if areas of deeper undocumented fill and/or loose soil are encountered in unexplored areas of the site. If the ground surface, after site stripping, should appear to be loose, it should be compacted to a non -yielding condition. Areas observed to pump or weave during compaction should be over -excavated and replaced with properly compacted structural fill or rock spalls. If loose soils are encountered in any slab areas, the loose soils should be removed and replaced with rock spalls or granular structural fill. If significant surface water flow is encountered during construction, this flow should be diverted around areas to be developed, and the exposed subgrades should be maintained in a semi -dry condition. This site is underlain by moisture -sensitive soils. Due to these conditions, special site stripping and grading techniques might be necessary, especially if grading is attempted in wet weather. These could include using large excavators equipped with wide tracks and a smooth bucket to complete site grading and promptly covering exposed subgrades with a layer of crushed rock for protection. If wet conditions are encountered or construction is attempted in wet weather, the subgrade should not be compacted as this could cause further subgrade disturbance. In wet conditions, it may be necessary to cover the exposed subgrade with a layer of crushed rock as soon as it is exposed to protect the moisture sensitive soils from disturbance by machine or foot traffic during construction. The prepared subgrade should be protected from construction traffic and surface water should be diverted around prepared subgrade. Shallow groundwater, if encountered, should be intercepted with cut-off drains and routed around the planned grading area, or the groundwater should be controlled with sump -pumps or dewatering systems. Failure to follow these recommendations could cause erosion and failures on the slopes, as well as result in inadequate subgrades. The site soils are considered to be moisture -sensitive and will disturb easily when wet. We recommend that construction take place during the drier summer months if possible. However, if construction takes place during the wet season, additional expenses and delays should be expected due to the wet conditions. Additional expenses could include the need for placing a blanket of rock spalls on exposed subgrades, construction traffic areas, and paved areas prior to placing structural fill. Wet weather grading will also require additional erosion control and site drainage measures. Some of the on -site soils may be suitable for use as structural fill, depending on the moisture content of the soil at the time of construction. NGA should be retained to evaluate the suitability of all on -site and imported structural fill material during construction. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 10 Temporary and Permanent Slopes In general, cut -slope stability is a function of many factors, including the type and consistency of soils, depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains open, and the presence of surface or groundwater. It is exceedingly difficult under these variable conditions to estimate a stable, temporary, cut slope angle. Therefore, it should be the responsibility of the contractor to maintain safe slope configurations since they are continuously at the job site, able to observe the nature and condition of the cut slopes, and able to monitor the subsurface materials and groundwater conditions encountered. The following information is provided solely for the benefit of the owner and other design consultants and should not be construed to imply that Nelson Geotechnical Associates, Inc. assumes responsibility for job site safety. Job site safety is the sole responsibility of the project contractor. For planning purposes, we recommend that temporary cuts in the surficial fill soils and native glacial soils near the steep slope area of the site be no steeper than 2.0 Horizontal to 1.0 Vertical (2H:1V). Temporary cuts in the competent native glacial soils within the relatively level southern portion of the property away from the steep slopes should be no steeper than 1H:1V. If temporary cut excavations are not able to achieve the recommended inclinations or are greater than four feet in overall height along the toe of the steep slope area, we recommend that the cuts be shored with a soldier pile shoring wall as discussed in the Soldier Pile Shoring Wall subsection of this report. If perched groundwater or loose soils are encountered, we would expect that flatter inclinations would be necessary. We recommend that cut slopes be protected from erosion. Measures taken may include covering cut slopes with plastic sheeting and diverting surface runoff away from the top of cut slopes. We do not recommend vertical slopes for cuts deeper than four feet, if worker access is necessary. We recommend that cut slope heights and inclinations conform to appropriate OSHA/WISHA regulations. We recommend that the final slope inclinations for structural fill and the native soils be no steeper than 2HAV. However, flatter inclinations may be necessary in areas where loose soils are encountered. Final slopes should be vegetated and covered with jute netting. The vegetation should be maintained until it is established. Foundations Conventional shallow spread foundations should be placed on medium dense or better native glacial bearing soils, or be supported on structural fill or rock spalls extending to those soils. Medium dense soils should be encountered approximately two to three feet below ground surface within the proposed development area based on our explorations. Where undocumented fill or less dense soils are encountered at footing bearing elevation, the subgrade should be over - excavated to expose suitable bearing soil. The over -excavation may be filled with structural fill, or the footing may be extended down to the competent native bearing soils. If footings are supported on structural fill, the fill zone should extend outside the edges of the footing a distance equal to one half of the depth of the over -excavation below the bottom of the footing. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 11 Footings should extend at least 18 inches below the lowest adjacent finished ground surface for frost protection and bearing capacity considerations. Foundations should be designed in accordance with the 2018 IBC. Footing widths should be based on the anticipated loads and allowable soil bearing pressure. Water should not be allowed to accumulate in footing trenches. All loose or disturbed soil should be removed from the foundation excavation prior to placing concrete. For foundations constructed as outlined above, we recommend an allowable design bearing pressure of not more than 3,000 pounds per square foot (psf) be used for the design of footings founded on the medium dense or better native bearing glacial soils or structural fill extending to the competent native material. The foundation bearing soil should be evaluated by a representative of NGA. We should be consulted if higher bearing pressures are needed. Current IBC guidelines should be used when considering increased allowable bearing pressure for short-term transitory wind or seismic loads. Potential foundation settlement using the recommended allowable bearing pressure is estimated to be less than 1-inch total and %-inch differential between adjacent footings or across a distance of about 20 feet, based on our experience with similar projects. Lateral loads may be resisted by friction on the base of the footing and passive resistance against the subsurface portions of the foundation. A coefficient of friction of 0.35 may be used to calculate the base friction and should be applied to the vertical dead load only. Passive resistance may be calculated as a triangular equivalent fluid pressure distribution. An equivalent fluid density of 200 pounds per cubic foot (pcf) should be used for passive resistance design for a level ground surface adjacent to the footing. This level surface should extend a distance equal to at least three times the footing depth. These recommended values incorporate safety factors of 1.5 and 2.0 applied to the estimated ultimate values for frictional and passive resistance, respectively. To achieve this value of passive resistance, the foundations should be poured "neat" against the native medium dense soils or compacted fill should be used as backfill against the front of the footing. We recommend that the upper one foot of soil be neglected when calculating the passive resistance. Shoring Wall General: We understand that tall cuts will be necessary along the northern side of the building along the toe of the steep slopes. These temporary cuts will require shoring systems to complete the earthwork and foundation installation. We would recommend that the proposed shoring system consist of a soldier pile shoring wall. A solider pile wall typically consists of a series of steel H-beams placed vertically at a certain spacing from one another (typically six to ten feet). The beams are usually placed in drilled shafts that are filled with structural concrete or a lean mix. The concrete shafts are typically embedded below the bottom of the planned excavation a distance equals one to two times the exposed height of the wall. The steel beams are extended above finished ground surface to provide shoring capabilities for the area to be NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 12 retained. The beams are typically spanned by pressure treated timber lagging or concrete panels. The H-beam size, shaft diameter, shaft embedment, and pile spacing are dependent on the nature of the soils anticipated to be retained by the wall and the soils at depth, wall height, drainage conditions, and the final geometry. A schematic detail of the wall is shown on the Conceptual Soldier Pile Wall Detail in Figure 11. Wall Design: The shoring wall should be designed by an experienced structural engineer licensed in the State of Washington. The lateral earth pressure acting on the shoring wall will be dependent on the nature and density of the soil behind the wall, structure and traffic loads on the wall, and the amount of lateral wall movement that may occur as material is excavated from the front of the wall. If the shoring wall is free to yield at least one -thousandth of the retained height, an "active" loading condition develops. If the wall is restrained from movement by stiffness or bracing, the wall is considered in an "at -rest" loading condition. Active and at -rest earth pressure can be calculated based on equivalent fluid densities. The shoring wall should be designed to resist a lateral load resulting from a fluid with a unit weight of 45 and 65 pounds per cubic foot (pcf) for the active and at -rest loading conditions, respectively. A uniform surcharge 8H (in psf) should be applied to the wall design to account for seismic loading, respectively if the shoring walls are intended to provide permanent support. H in this case is the exposed height of the wall. These loads should be applied across the pile spacing above the excavation line. These loads can be resisted by a passive pressure of 200 pcf on the below grade medium dense or better soils. The passive pressure should be applied on two -pile diameters under the excavation line. These values of the passive pressure incorporate a factor of safety of 2.0. The upper two feet of pile embedment should be neglected when calculating the passive resistance for the permanent condition. Also, for the permanent condition, the below -grade portion of the wall should be no less than 1.5 times the wall stick-up height. The above loads should be applied on the full center -to -center pile spacing above the base of the exposed portion of the wall. A 50 percent reduction of the active pressure could be applied for the purpose of designing the wall lagging. The above pressures assume that the on -site soils retained by the shoring wall are not significantly disturbed and that hydrostatic forces are not allowed to build up behind the wall. These values do not include the effects of surcharges other than what is described above. The retained soils should be readily drained and collected water should be routed into a permanent storm system. Adequate gaps should be maintained between the lagging elements to allow for any potential water seepage buildup to flow through the wall. If a concrete wall is proposed to be cast on the face of the shoring wall, we recommend that a drainage composite such as a Miradrain mat be placed between the face of the shoring wall and the concrete wall. The drainage composite should be directed to flow into a drainage collector at the base of the shoring wall and ultimately to an approved discharge point. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 13 The wall designer should calculate the predicted wall deflection, including deflection resulting from the below -grade movement of the piles. The predicted deflection values should be confirmed in the field through a survey monitoring program. Also, surrounding structures should be monitored for any adverse effects resulting from shoring wall installation. Shoring Wall Installation: The shoring wall should be installed by a shoring contractor experienced with this type of system. We anticipate that an open -hole drilling method may prove difficult to achieve for installing the soldier piles in the on -site soils, and therefore we recommend that the shoring contractor should have the capability of casing the holes as sloughing and/or water seepage if encountered. It might be prudent to perform one or more "test" holes to confirm installation conditions prior to finalizing budget and work plans. Any sloughing or water that may collect in the drilled holes should be removed prior to pumping grout. Grout should be readily available on site at the time the holes are drilled. If groundwater seepage is encountered, we recommend that water be pumped out of the holes and the concrete be tremied from the bottom of the excavations to displace the groundwater to the surface. Extra Portland Cement, or other additives, may also be placed in the excavations to reduce the effects of seepage. The spoils from the soldier pile excavations are expected to be moisture -sensitive materials and should be removed from the site. We should be retained to monitor on site activities during the shoring wall installation on a full-time basis. Tiebacks General: If tiebacks are needed to support lateral loads, we recommend that these systems consist of drilled, grouted tieback anchors. All nearby existing utilities and structures should also be fully understood prior to finalizing the tieback design. We recommend that at least two of the anchors be performance tested to a minimum of 200 percent of the design loads to confirm design values. We recommend that measurements be made by the contractor in the field at the time of tieback installation to verify that tiebacks do not encounter any existing structures or underground utilities. No -Load Zone: The anchor portion of all tiebacks must be located a sufficient distance behind the wall face to develop resistance within a stable soil mass. We recommend the anchorage be obtained behind an assumed no-load zone. The no- load zone is defined by a line extending horizontally from the base of the shoring wall back towards the cut a distance of six feet. This line should then extend up from the base elevation at an angle from the horizontal of 60 degrees. We recommend that we monitor soil conditions during anchor installation in order to evaluate adequate penetration into competent soils. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 14 Soil Design Values: The tiebacks must terminate in native, competent soil interpreted to exist below the fill. For use in design of the anchors, we estimate an allowable grout to soil adhesion of 1,500 pounds per square foot (psf) be utilized for anchors terminated within the competent native glacial soils. This value should be verified through two performance tests prior to ordering the production anchors. Tieback Installation and Testing: The contractor should be responsible for using equipment suited for the site conditions. We do not recommend the use of an open -hole method for the purpose of installing the tiebacks due to the potential for soil caving. Secondary grouting to increase soil adhesion may be used; however, if secondary grouting is used, the anchors should be tested using the methods outlined for the performance testing. All anchors should be installed at an approximate inclination of 15 to 20 degrees below horizontal. Two anchors should be performance -tested to 200 percent of the anchor design capacity. The performance test should consist of cyclic loading in increments of 25 percent of the design load, as outlined in the Federal Highways Administration (FHA) report No. FHWA/RD-82/047. The test locations should be determined in the field by NGA, based on soil conditions observed during anchor installation. All other tiebacks should be proof -tested to at least 130 percent of design capacity. Other Retaining Walls The lateral pressure acting on subsurface retaining walls is dependent on the nature and density of the soil behind the wall, the amount of lateral wall movement which can occur as backfill is placed, wall drainage conditions, and the inclination of the backfill. For walls that are free to yield at the top at least one thousandth of the height of the wall (active condition), soil pressures will be less than if movement is limited by such factors as wall stiffness or bracing (at -rest condition). We recommend that walls supporting horizontal backfill and not subjected to hydrostatic forces be designed using a triangular earth pressure distribution equivalent to that exerted by a fluid with a density of 45 pounds per cubic foot (pcf) for yielding (active condition) walls, and 65 pcf for non -yielding (at -rest condition) walls. To account for seismic loading, a uniform surcharge of 8H should also be included in the wall design where "H" is the total height of the wall. These recommended lateral earth pressures are for a drained backfill and are based on the assumption of a maximum 2H:1V slope above the wall for a distance of at least the subsurface height of the wall, and do not account for additional surcharge loads. Additional lateral earth pressures should be considered for surcharge loads acting adjacent to subsurface walls and within a distance equal to the subsurface height of the wall. This would include the effects of surcharges such as traffic loads, floor slab loads, or other surface loads. We could consult with you and your structural engineer regarding additional loads on retaining walls during final design, if needed. The lateral pressures on walls may be resisted by friction between the foundation and subgrade soil, and by passive resistance acting on the below -grade portion of the foundation. Recommendations for frictional and passive resistance to lateral loads are presented in the Foundations subsection of this report. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 15 All wall backfill should be well compacted as outlined in the Structural Fill subsection of this report. Care should be taken to prevent the buildup of excess lateral soil pressures due to over -compaction of the wall backfill. This can be accomplished by placing wall backfill in 8-inch loose lifts and compacting the backfill with small, hand -operated compactors within a distance behind the wall equal to at least one-half the height of the wall. The thickness of the loose lifts should be reduced to accommodate the lower compactive energy of the hand -operated equipment. The recommended level of compaction should still be maintained and should be tested. Permanent drainage systems should be installed for retaining walls. Recommendations for these systems are found in the Subsurface Drainage subsection of this report. We recommend that we be retained to evaluate the proposed wall drain backfill material and observe installation of the drainage systems. Structural Fill General: Fill placed beneath foundations, pavement, or other settlement -sensitive structures should be placed as structural fill. Structural fill, by definition, is placed in accordance with prescribed methods and standards, and is monitored by an experienced geotechnical professional or soils technician. Field monitoring procedures would include the performance of a representative number of in -place density tests to document the attainment of the desired degree of relative compaction. The area to receive the fill should be suitably prepared as described in the Site Preparation and Grading subsection prior to beginning fill placement. Materials: Structural fill should consist of a good quality, granular soil, free of organics and other deleterious material, and be well graded to a maximum size of about three inches. All-weather fill should contain no more than five -percent fines (soil finer than U.S. No. 200 sieve, based on that fraction passing the U.S. 3/4-inch sieve). Some of the more granular on - site soils may be suitable for use as structural fill, but this will be highly dependent on the moisture content of these soils at the time of construction. We should be retained to evaluate all proposed structural fill material prior to placement. Fill Placement: Following subgrade preparation, placement of structural fill may proceed. All filling should be accomplished in uniform lifts up to eight inches thick. Each lift should be spread evenly and be thoroughly compacted prior to placement of subsequent lifts. All structural fill underlying building areas and pavement subgrade should be compacted to a minimum of 95 percent of its maximum dry density. Maximum dry density, in this report, refers to that density as determined by the ASTM D-1557 Compaction Test procedure. The moisture content of the soils to be compacted should be within about two percent of optimum so that a readily compactable condition exists. It may be necessary to over -excavate and remove wet soils in cases where drying to a compactable condition is not feasible. All compaction should be accomplished by equipment of a type and size sufficient to attain the desired degree of compaction and should be tested. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 16 Slab -on -Grade Slabs -on -grade should be supported on subgrade soils prepared as described in the Site Preparation and Grading subsection of this report. We recommend that all floor slabs be underlain by at least six inches of free -draining gravel with less than three percent by weight of the material passing Sieve #200 for use as a capillary break. A suitable vapor barrier, such as heavy plastic sheeting (6-mil, minimum), should be placed over the capillary break material. An additional 2-inch- thick moist sand layer may be used to cover the vapor barrier. This sand layer may be used to protect the vapor barrier membrane and to aid in curing the concrete. Pavements Pavement subgrade preparation and structural filling where required, should be completed as recommended in the Site Preparation and Grading and Structural Fill subsections of this report. The pavement subgrade should be proof -rolled with a heavy, rubber -tired piece of equipment, to identify soft or yielding areas that require repair. The pavement section should be underlain by a minimum of six inches of clean granular pit run or crushed rock. We should be retained to observe the proof -rolling and recommend subgrade repairs prior to placement of the asphalt or hard surfaces. Utilities We recommend that underground utilities be bedded with a minimum six inches of pea gravel prior to backfilling the trench with on -site or imported material. Trenches within settlement sensitive areas should be compacted to 95% of the modified proctor as described in the Structural Fill subsection of this report. Trench backfill should be compacted to a minimum of 95% of the modified proctor maximum dry density. Trenches located in non-structural areas and five feet below roadway subgrade should be compacted to a minimum 90% of the maximum dry density. The trench backfill compaction should be tested. Site Drainage Infiltration: The subsurface soils within our explorations generally consisted of granular glacial advance outwash soils to the depths explored. In accordance with the 2016 King County Surface Water Design Manual, we conducted a Small PITS within Infiltration Pit 1 and 2, as shown on the attached Schematic Site Plan in Figure 2. Infiltration Pit 1 measured 4.0- feet long by 3.0-feet wide by 5.0-feet deep. Infiltration Pit 2 measured 4.0-feet long by 3.0-feet wide by 8.5-feet deep. The pits were filled with 12-inches of water at the beginning of the day and we began the soaking period of the PIT for approximately 6 hours. At this time, the water flow rate into the holes was monitored with a Great Plains Industries (GPI) TM 075 water flow meter for the pre-soak period. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 17 Infiltration Pit 1 (Western): After the 6-hour soaking period was completed, the water level was maintained at approximately 12-inches for one hour for the steady-state period. The flow rate for Infiltration Pit 1 stabilized at 0.285 gallons per minute (17.10 gallons per hour), which equates to an approximate infiltration rate of 2.3 inches per hour. The water was shut off after the steady-state period and monitored every 15 minutes for one hour. After one hour, the water level within the pit had dropped 1.75 inches, resulting in an infiltration rate of 1.75 inches per hour. Infiltration Pit 2 (Eastern): After the 6-hour soaking period was completed, the water level was maintained at approximately 12-inches for one hour for the steady-state period. The flow rate for Infiltration Pit 2 stabilized at 1.90 gallons per minute (114 gallons per hour), which equates to an approximate infiltration rate of 15.2 inches per hour. The water was shut off after the steady-state period and monitored every 15 minutes for one hour. After one hour, the water level within the pit had dropped 8.0 inches, resulting in an infiltration rate of 8.0 inches per hour. It is our opinion that the more granular advance outwash soils within the site are suitable for traditional stormwater infiltration. The subsurface soils within the proposed development area generally consisted of surficial fill underlain by silty fine to medium sand that we interpreted as native glacial till soils with fine to medium sand and gravel soils that we interpreted as native advance outwash soils at depth. These granular advance outwash sand and gravel soils were generally encountered at approximately 3.0 and up to 9.0 feet below the existing ground surface within the southwestern and southeastern portions of the property, respectively. We have selected the overall measured field rates of 1.75 in/hr obtained from the falling head portion of the test within Infiltration Pits 1 be utilized in determining the long-term design infiltration rate for the infiltration systems within the southern portion of the property. This rate is conservative compared to the rate obtained from the more eastern infiltration test and should be utilized in the initial design of the infiltrations systems within the site. In accordance with the Table 3.5 of the Department of Ecology 2014 Stormwater Management Manual for Western Washington, correction factors of 0.8, 0.5, and 0.9 for site variability and number of locations tested (CF ), testing method (CFt), and degree of influent control to prevent siltation and bio-buildup (CFm), respectively were applied to the field measured infiltration rate of 1.75 inches per hour, selected from the falling -head portion of the testing. A total correction factor of 0.36 was applied to the measured field infiltration rate obtained from the falling head portion of the test to determine the long-term design infiltration rate. Using this correction factor, we calculated a long-term design infiltration rate of 0.63 inches per hour to be utilized in designing the proposed infiltration systems founded within the native granular advance outwash soils. We recommend that the base of the on -site infiltration systems be terminated in the native advance outwash deposits. We did not encounter groundwater or indications of groundwater within the site to the depths explored. It is our opinion that proposed infiltration systems should be able to maintain the minimum separation from the base of the infiltration systems to any impermeable surfaces and/or groundwater table. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 18 We recommend that any additional infiltration systems be placed as to not negatively impact any proposed or existing nearby structures and also meet all required setbacks from existing property lines, structures, and sensitive areas as discussed in the drainage manual. In general, infiltration systems should not be located within proposed fill areas within the site associated with site grading or retaining wall backfill as such condition could lead to failures of the placed fills and/or retaining structures. We should be retained to evaluate the infiltration system design and installation during construction, if necessary. Surface Drainage: The finished ground surface should be graded such that stormwater is directed to an approved stormwater collection system. Water should not be allowed to stand in any areas where footings, slabs, or pavements are to be constructed. Final site grades should allow for drainage away from the structures. We suggest that the finished ground be sloped at a minimum downward gradient of three percent, for a distance of at least 10 feet away from the structures. Surface water should be collected by permanent catch basins and drain lines, and be discharged into an approved discharge system. Subsurface Drainage: If groundwater is encountered during construction, we recommend that the contractor slope the bottom of the excavation and collect the water into ditches and small sump pits where the water can be pumped out and routed into a permanent storm drain. We recommend the use of footing drains around the structures. Footing drains should be installed at least one foot below planned finished floor elevation. The drains should consist of a minimum 4-inch-diameter, rigid, slotted or perforated, PVC pipe surrounded by free -draining material wrapped in a filter fabric. We recommend that the free -draining material consist of an 18-inch-wide zone of clean (less than three -percent fines), granular material placed along the back of walls. Pea gravel is an acceptable drain material. The free -draining material should extend up the wall to one foot below the finished surface. The top foot of backfill should consist of impermeable soil placed over plastic sheeting or building paper to minimize surface water or fines migration into the footing drain. Footing drains should discharge into tightlines leading to an approved collection and discharge point with convenient cleanouts to prolong the useful life of the drains. Roof drains should not be connected to wall or footing drains. 'AfI► I111:11111I411111910VA191►1111t9]C11►1:0 We should be retained to provide construction monitoring services during the earthwork phase of the project to evaluate subgrade conditions, temporary cut conditions, fill compaction, and drainage system installation. SLOPE MONITORING We also recommend that we be retained to periodically observe the steep slopes and evaluate the existing stability conditions, especially after a significant storm event. If any distress is observed, we can then provide recommendations for mitigation measures at that time. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 19 USE OF THIS RERORT This preliminary report has been prepared for Mr. Marc Wislen, and his agents, for use in the planning and design of the proposed development on this site only. The scope of our work does not include services related to construction safety precautions and our recommendations are not intended to direct the contractors' methods, techniques, sequences, or procedures, except as specifically described in our letter. There are possible variations in subsurface conditions between the explorations and also with time. Our report, conclusions, and interpretations should not be construed as a warranty of subsurface conditions. A contingency for unanticipated conditions should be included in the budget and schedule. We recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not retaining wall and foundation support installation complies with our recommendations. We should be contacted a minimum of one week prior to construction activities. All people who own or occupy strucrtures on or near hillsides should realize that landslide movements are always a possibility. The landowner should periodically inspect the slope, especially after a winter storm. If distress is evident, a geotechnical engineer should be contacted for advice on remedial/preventative measures. The probability that landsliding will occur is substantially reduced by the proper maintenance of drainage control measures at the site (the runoff from the roofs and all other hard surfaces should be led to an approved discharge point). Therefore, the homeowner should take responsibility for performing such maintenance. Consequently, we recommend that a copy of our report be provided to any future homeowners of the property if the home is sold. Within the limitations of scope, schedule and budget, our services have been performed in accordance with generally accepted geotechnical engineering practices in effect in this area at the time this report was prepared. No other warranty, expressed or implied, is made. Our observations, findings, and opinions are a means to identify and reduce the inherent risks to the owner. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Westgate Station Commercial Development Edmonds, Washington NGA File No. 1156720 April 14, 2020 Page 20 We appreciate the opportunity to provide service to you on this project. If you have any questions or require further information, please call. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Lee S. Bellah, LG Project Geologist Khaled Shawish, PE Principal LSB:KMS:sw Eleven Figures Attached NELSON GEOTECHNICAL ASSOCIATES, INC. VICINITY MAP Not to Scale U Birch St A� 9 N 9� Q P IAA Way SW 104 14th St SW 224th St SW 0 s < > FIVE 15tt151 S{y 226th St SW P ro a ct © Edmonds Memorial s s Cemetery Site = D D WEST - 22Bth s1 SW Goodwill Edmonds Q 228th St SW ` PCC CornnwnitY' �amonds Wdy Q Westgate Chapel QFC Markets - Edmond Sherwood 0 itary School 1O0 - o a o � - � S D D 231sP 231ary} f _ h f z 2J2nc S( SW RoW Hood © Scriber Lake High School Former Woodway ® g High School ➢ > 234th St SW Nottingharn Rd M f w 235th Pt SVt S n 9 D D Robb —Rohs: Re � f Z 2361h St SW 236th St SW 236th Pt SW 3 Hickman Park o Madrona K-8 School 0 s r - y S o a 23M St SW a. 3 Woodway Elementary 0 Edmonds, WA N 222nd St SW 224th St SW 224th St SW 5 F E s p e r a n, 228th St SW �y c QLocal Roots Marijuana 236th �N Project Number NELSON GEOTECHNICAL No. Date Revision By CK o Westgate Station � ASSOCIATES INC. N 1156720 Commercial Development �+A 1 3/16/20 Original DPN DJO etL GEOTECHNICAL ENGINEERS & GEOLOGISTS E Figure 1 Vicinity Map W°35th Av.. NE, East Wenatchee Office 17311-135[h Ave. NE, A-500 552fi Industry Lane, it2 a J Woodinville, WA 98072 East Wenatchee, WA 98802 (425) 486-16691 Fax:481-2510 ww—lsongeotech.com (509) 665-76961 Fax: 665-7692 = D I D I D o -oa �§ CD (n 3 m v A cu m 0 o a0 oC o� r 3 v 3 0, C m o 07 m o v In� o v � D � � Z: �- -0 o x 5.o 3 3 cn CD CD �1 v o Z 0 C .4 y 3 '• ,'.. —0 3 CD \ •� \ .;. � E \ - E -. E E \ E e Fes, I � Fs y F s Map ^ ¢ I Qz v_ i *1i II111111� \ G Z a Project Number 1156720 Westgate Station NELSON GEOTECHNICAL NGA ASSOCIATES, INC. No. Date Revision By CK 0 s 1 3/16/20 Original DPN DJO Commercial Development GEOTECHNICAL ENGINEERS & GEOLOGISTS Site Plan Figure 2 Woodinville Office East Wenatchee Office U 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 ? Woodinville, WA98072 East Wenatchee, WA 98802 (425) 486-1669 / Fax: 481-2510-nelsongeotech.com (509) 665-7696 / Fax: 665-7692 A A' T ,o ,C CrI� CD -4C rQ CD m Northwest Southeast 420 420 0 0 o 3 C,mm Ta a Cn v 0 p m 390 390 0 0 D a v D-0 0 0 -CD o 0 360 w 360 � na m Dn m 4 45' o x TP-4 x'm Z y 0 INF-1 B-3 n � Z Q 330 54 50-6 330 m m Z r 50-4 _ N (n o O 50-6 m O Z 50-5 m 0 � 50-4 3 N M Q 0-5 m W m 300 300 n z I I I I I I I I I I I I I I I TS Z - ^^- 0 30 60 90 120 150 180 210 a "N r Distance (feet) Exploration z ° d Boring Designation B-1 23 Test Pit Designation TP-1 T. 23 Groundwater Level ---> 1 <-- SPT N-value Groundwater Level � 1 NOTES: 3 23 During Exploration 23 During Exploration 1) Stratigraphic conditions are interpolated between 23 Geologic Contact --> ? _ —? Geologic Contact --> the explorations. Actual conditions 2) Elevations are approximate. may vary. W (approximate) Reference: Cross Section is based (approximate) on field measurements using a hand-held clinometer and 100-ft tape measure. o `o 0 X \\HILL\company\2020 NGA Project Folders\11567-20 Westgate Station Edmonds Way Commercial Development\Drafting\CS.dwg o B B, T , ,C CrI� CD -4C rQ cD m Northwest Southeast 420 420 0 0 o 3 C,mm Ta a Cn v 0 p m 390 390 0 0 00 o v p0 -0 = c -CD o 0 360 w 360 a�� m ° ° o Z c6 24° Dpi� X TP-3 B-2 Z > Q 62 n r19 Z Q 330 72 50-6 330 m zy r 50-4 N in Z N o 50-6 m 0 z 50-6 m 00 3 N 06 a m -1 0 m in m 300 300 n z Z I I I I I I I I I I I I I I I TS - ^^- 0 30 60 90 120 150 180 210 a "N r Distance (feet) Exploration z ° d m Boring Designation ---> B-1 23 Test Pit Designation ---> TP-1 y z3 Groundwater Level 1 SPT N-value Groundwater Level � 1 NOTES: 3 23 During Exploration z3 During Exploration 1) Stratigraphic conditions are interpolated between 23 Geologic Contact ? _ —? Geologic Contact --> 2) the explorations. Actual conditions may vary. Elevations are approximate. W (approximate) Reference: Cross Section is based (approximate) on field measurements using a hand-held clinometer and 100-ft tape measure. o `o 0 X \\HILL\company\2020 NGA Project Folders\11567-20 Westgate Station Edmonds Way Commercial Development\Drafting\CS.dwg C C' C CD __4C rQ CD m Northwest Southeast 420 420 0 0 0 3 in 0 CD v v &CD p m 390 390 0 0 < cn C� o v n-0 0 c -� 0 0 360 w 360 m 0 o Z 35° D � M� x X B-1 x'm Z y 0 INF-2 54 �nm o n � Z 0- Q 330 �TP ao 50-4 330 m Z> r 50-6 Z N o 50-5 M 0 Z 50-4 m n C) 3 00 N a m 0 m m 300 300 n z Z I I I I I I I I I I I I I I I TS - ^^- 0 30 60 90 120 150 180 210 a "N r Distance (feet) Exploration z ° d Boring Designation B-1 23 Test Pit Designation TP-1 T. 23 Groundwater Level ---> 1 <-- SPT N-value Groundwater Level � 1 NOTES: 3 23 During Exploration 23 During Exploration 1) Stratigraphic conditions are interpolated between 23 Geologic Contact ---> ? _ —? Geologic Contact --> 2) the explorations. Actual conditions may vary. Elevations are approximate. W (approximate) Reference: Cross Section is based (approximate) on field measurements using a hand-held clinometer and 100-ft tape measure. o `o 0 X \\HILL\company\2020 NGA Project Folders\11567-20 Westgate Station Edmonds Way Commercial Development\Drafting\CS.dwg UNIFIED SOIL CLASSIFICATION SYSTEM GROUP MAJOR DIVISIONS GROUP NAME SYMBOL CLEAN GW WELL -GRADED, FINE TO COARSE GRAVEL COARSE- GRAVEL GRAVEL GP POORLY -GRADED GRAVEL GRAINED MORE THAN 50 % GRAVEL GM SILTY GRAVEL OF COARSE FRACTION RETAINED ON SOILS NO.4 SIEVE WITH FINES GC CLAYEY GRAVEL SAND CLEAN SW WELL -GRADED SAND, FINE TO COARSE SAND SAND SP POORLY GRADED SAND MORE THAN 50 % RETAINED ON MORE THAN 50 % NO. 200 SIEVE OF COARSE FRACTION SAND SM SILTY SAND PASSES NO. 4 SIEVE WITH FINES SC CLAYEY SAND FINE - SILT AND CLAY ML SILT INORGANIC GRAINED LIQUID LIMIT CL CLAY LESS THAN 50 % SOILS ORGANIC OL ORGANIC SILT, ORGANIC CLAY SILT AND CLAY MH SILT OF HIGH PLASTICITY, ELASTIC SILT INORGANIC MORE THAN 50 % PASSES LIQUID LIMIT CH CLAY OF HIGH PLASTICITY, FAT CLAY NO. 200 SIEVE 50 % OR MORE ORGANIC OH ORGANIC CLAY, ORGANIC SILT HIGHLY ORGANIC SOILS PT PEAT NOTES: 1) Field classification is based on visual SOIL MOISTURE MODIFIERS: examination of soil in general accordance with ASTM D 2488-93. Dry - Absence of moisture, dusty, dry to the touch 2) Soil classification using laboratory tests is based on ASTM D 2488-93. Moist - Damp, but no visible water. 3) Descriptions of soil density or Wet - Visible free water or saturated, consistency are based on usually soil is obtained from interpretation of blowcount data, below water table visual appearance of soils, and/or test data. Project Number NELSON GEOTECHNICAL No. Date Revision By CK 1156720 Westgate Station NGA ASSOCIATES, INC. Commercial Development GEOTECHNICAL ENGINEERS & GEOLOGISTS 1 3/16/20 Original DPN DJO Figure 6 Soil Classification Chart W°35thAv..NE,°e Ea=1We"at°yLanehee 2 311-1%[h Ave.NE,A-500 Industry Lane,88 Woodinville, WA 98072 East Wenatchee, WA 98802 East W (425) 486-1669 / F_ 481-2510 www. nelsongeotech.com (509) 665-7696 1 Fax: 665-7692 BORING LOG B-1 Approximate Ground Surface Elevation: ?? Soil Profile Sample Data Penetration Resistance 0) (Blows/foot -) 10 20 30 40 50 50+ I I I I N Piezometer Installation - `—' ` Ground Water Description a Q o 0 Q ° � Moisture Content o Data o f o CO v E la L 0 (Percent - �) O (Depth in Feet) (D fn cn 10 20 30 40 50 50+ p J Gray, fine to medium sand with silt and gravel (medium dense, moist) 30 -becomes medium dense :... •.. 23 5 ................................................... 5 SP-SM -becomes dense 32 -becomes very dense 94-11 '10 .......................................... ........ 10 -----------------:• Gray, fine to coarse sand with gravel and trace silt (very dense, moist) .. 15 .................................................... 15 50-4 Sp 50-6 20 .................................................... 41 20 50-5 25 .................................................... 41 25 No recovery LEGEND ❑ Solid PVC Pipe Concrete M Moisture Content Limits 0 Slotted PVC Pipe Bentonite A AtterbergGrain-size Depth Driven and Amount Recovered P G Grain -size Analysis with 2-inch O.D. Split -Spoon Sampler Monument/ Cap Native Soil DS Direct Shear to Piezometer PP Pocket Penetrometer Readings, tons/ft Depth Driven and Amount Recovered ❑ Silica Sand P �k Liquid Limit P Sample Pushed with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log. Project Number NGEOTECHNICAL No. Date Revision By CK Westgate Station ASSOCIATES,NELSON ATINC. NGA 1156720 Commercial Development Boring Log GEOTECHNICAL ENGINEERS & GEOLOGISTS � 3�,s�zo Original DPN DJO Figure 7 Woodinville Office East Wenatchee office 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 Page 1 2 of (425)486-1669/Fax: 4812510-nelsongeutech.corn (509)6 5-7696/ Fax: 6657692 BORING LOG B-1 (cont.) Soil Profile Sample Data Penetration Resistance (Blows/foot - 10 20 30 40 50 50+ Piezometer Installation - �, Ground Water Description a 0- �° 3 Q Moisture Content m Data J o o m v m L (Percent - �) o (Depth in Feet) c� fn cn 0 CL 10 20 30 40 50 50+ -p J 50-0 Boring terminated below existing grade at 30.0 feet on 3/3/20. Groundwater seepage was not encountered during drilling. 35 .................................................... 35 40 .................................................... 40 45 .................................................... 45 50 .................................................... 50 55 .................................................... 55 LEGEND ❑ Solid PVC Pipe Concrete M Moisture Content 0 Slotted PVC Pipe Bentonite A Atterberg Limits Depth Driven and Amount Recovered G Grain -size Analysis with 2-inch O.D. Split -Spoon Sampler Monument/ Cap Native Soil DS Direct Shear to Piezometer PP Pocket Penetrometer Readings, tons/ft Depth Driven and Amount Recovered ❑ Silica Sand P * Liquid Limit P Sample Pushed with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log. Project Number NGEOTECHNICAL No. Date Revision By CK Westgate Station ASSOCIATES,NELSON ATINC. NGA 1156720 Commercial Development Boring Log GEOTECHNICAL ENGINEERS & GEOLOGISTS � 3�,s�zo Original DPN DJO Figure 7 Woodinville Office East Wenatchee office 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 Page 2 2 of (425)486-1669/Fax: 4812510-nelsongeutech.corn (509)6 5-7696/ Fax: 6657692 BORING LOG B-2 Approximate Ground Surface Elevation: ?? Soil Profile Sample Data Penetration Resistance (Blows/foot -) 10 20 30 40 50 50+ 0) N Piezometer Installation - �, ` Ground Water Description a rn Q o = - a) a ° � Moisture Content o Data o f o m v E m L 0 (Percent - 0) o (Depth in Feet) C7 fn cn 10 20 30 40 50 50+ m p J Gray, silty fine to medium sand with gravel (very dense, moist) SM 62 'Ilk 72 5 ................................................... 5 Gray, fine to coarse sand with gravel and trace silt (medium dense, moist) 19 ' becomes very dense 50-6 ' .. 50-4 ' 15 .................................................... 15 SP ' ~ 50-6 20 1 ............... ..... .... ..... 20 50-6 ' 25 .................................................... 25 LEGEND ❑ Solid PVC Pipe Concrete M Moisture Content Limits ❑ Slotted PVC Pipe Bentonite A AtterbergGrain-size Depth Driven and Amount Recovered P G Grain -size Analysis with 2-inch O.D. Split -Spoon Sampler Monument/ Cap `" Native Soil DS Direct Shear to Piezometer PP Pocket Penetrometer Readings, tons/ft Depth Driven and Amount Recovered ❑ Silica Sand P �k Liquid Limit P Sample Pushed with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log. Project Number NGEOTECHNICAL No. Date Revision By CK Westgate Station ASSOCIATES,NELSON ATINC. NGA 1156720 Commercial Development Boring Log GEOTECHNICAL ENGINEERS & GEOLOGISTS � 3�,s�zo Original DPN DJO Figure 8 Woodinville Office East Wenatchee office 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 Page 1 2 of (425)486-1669/Fax: 4812510-nelsongeutech.corn (509)6 5-7696/ Fax: 6657692 BORING LOG B-2 (cont.) Soil Profile Sample Data Penetration Resistance (Blows/foot - 10 20 30 40 50 50+ Piezometer Installation - �, Ground Water Description a 0- �° 3 Q Moisture Content m Data J o o m v m L (Percent - �) o (Depth in Feet) c� fn cn 0 CL 10 20 30 40 50 50+ -p J 50-6 Boring terminated below existing grade at 30.5 feet on 3/3/20. Groundwater seepage was not encountered during drilling. 35 .................................................... 35 40 .................................................... 40 45 .................................................... 45 50 .................................................... 50 55 .................................................... 55 LEGEND ❑ Solid PVC Pipe Concrete M Moisture Content 0 Slotted PVC Pipe Bentonite A Atterberg Limits Depth Driven and Amount Recovered G Grain -size Analysis with 2-inch O.D. Split -Spoon Sampler Monument/ Cap Native Soil DS Direct Shear to Piezometer PP Pocket Penetrometer Readings, tons/ft Depth Driven and Amount Recovered ❑ Silica Sand P * Liquid Limit P Sample Pushed with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log. Project Number NGEOTECHNICAL No. Date Revision By CK Westgate Station ASSOCIATES,NELSON ATINC. NGA 1156720 Commercial Development Boring Log GEOTECHNICAL ENGINEERS & GEOLOGISTS � 3�,s�zo Original DPN DJO Figure 8 Woodinville Office East Wenatchee office 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 Page 2 2 of (425)486-1669/Fax: 4812510-nelsongeutech.corn (509)6 5-7696/ Fax: 6657692 BORING LOG B-3 Approximate Ground Surface Elevation: ?? Soil Profile Sample Data Penetration Resistance 0) (Blows/foot -) 10 20 30 40 50 50+ N Piezometer Installation - �, ` Ground Water Description a rn Q o = - a) a ° � Moisture Content o Data o f o m v E m L 0 (Percent - 0) o (Depth in Feet) C7 fn cn 10 20 30 40 50 50+ m p J Gray, silty fine to medium sand with gravel (very dense, moist) SM 54 ' -becomes dense, less silt _ 40 5 ...................................... ............ 5 Gray, fine to medium sand with silt and trace gravel (very dense, moist) 50-6 ' SP-SM 10 .................................................... 10 50-4 ' ---------------:• Gray, fine to coarse sand with gravel and trace silt (very dense, moist) .. 50-6 ' 15 .................................................... 15 SP 20 .................................................... 20 50-5 ' 50-4 ' 25 .................................................... 25 No recovery LEGEND ❑ Solid PVC Pipe Concrete M Moisture Content Limits 0 Slotted PVC Pipe Bentonite A AtterbergGrain-size Depth Driven and Amount Recovered P G Grain -size Analysis with 2-inch O.D. Split -Spoon Sampler Monument/ Cap Native Soil DS Direct Shear to Piezometer PP Pocket Penetrometer Readings, tons/ft Depth Driven and Amount Recovered ❑ Silica Sand P �k Liquid Limit P Sample Pushed with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log. Project Number NGEOTECHNICAL No. Date Revision By CK Westgate Station ASSOCIATES,NELSON ATINC. NGA 1156720 Commercial Development Boring Log GEOTECHNICAL ENGINEERS & GEOLOGISTS � 3�,s�zo Original DPN DJO Figure 9 Woodinville Office East Wenatchee office 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 Page 1 2 of (425)486-1669/Fax: 4812510-nelsongeutech.corn (509)6 5-7696/ Fax: 6657692 BORING LOG B-3 (cont.) Soil Profile Sample Data Penetration Resistance (Blows/foot - 10 20 30 40 50 50+ Piezometer Installation - �, Ground Water Description a 0- �° 3 Q Moisture Content m Data J o o m v m L (Percent - �) o (Depth in Feet) c� fn cn 0 CL 10 20 30 40 50 50+ -p J 50-5 Boring terminated below existing grade at 30.5 feet on 3/3/20. Groundwater seepage was not encountered during drilling. 35 .................................................... 35 40 .................................................... 40 45 .................................................... 45 50 .................................................... 50 55 .................................................... 55 LEGEND ❑ Solid PVC Pipe Concrete M Moisture Content 0 Slotted PVC Pipe Bentonite A Atterberg Limits Depth Driven and Amount Recovered G Grain -size Analysis with 2-inch O.D. Split -Spoon Sampler Monument/ Cap Native Soil DS Direct Shear to Piezometer PP Pocket Penetrometer Readings, tons/ft Depth Driven and Amount Recovered ❑ Silica Sand P * Liquid Limit P Sample Pushed with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log. Project Number NGEOTECHNICAL No. Date Revision By CK Westgate Station ASSOCIATES,NELSON ATINC. NGA 1156720 Commercial Development Boring Log GEOTECHNICAL ENGINEERS & GEOLOGISTS � 3�,s�zo Original DPN DJO Figure 9 Woodinville Office East Wenatchee office 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 Page 2 2 of (425)486-1669/Fax: 4812510-nelsongeutech.corn (509)6 5-7696/ Fax: 6657692 LOG OF EXPLORATION DEPTH (FEET) TEST PIT ONE 0.0 - 0.5 0.5 - 1.0 1.0 - 10.0 TEST PIT TWO 0.0 - 0.5 0.5 - 3.0 3.0 - 8.5 8.5 - 10.0 TEST PIT THREE USC SOIL DESCRIPTION GRAVEL SURFACING (UNDOCUMENTED FILL) GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ORGANICS (MEDIUM DENSE, MOIST) (UNDOCUMENTED FILL) SP GRAY, FINE TO COARSE SAND WITH GRAVEL AND TRACE SILT (DENSE TO VERY DENSE, MOIST) (ADVANCE OUTWASH) SAMPLES WERE COLLECTED AT 2.0, 4.0, 8.0 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 10.0 FEET ON 2/27/2020 GRAVEL SURFACING (UNDOCUMENTED FILL) SM BROWN -GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL (MEDIUM DENSE TO DENSE, MOIST) (WEATHERED GLACIAL TILL) SM GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL (DENSE TO VERY DENSE, MOIST) (GLACIAL TILL) SP BROWN, FINE TO COARSE SAND WITH GRAVEL AND TRACE SILT (DENSE, MOIST) (ADVANCE OUTWASH) SAMPLES WERE COLLECTED AT 2.0, 5.0, AND 9.0 GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 10.0 FEET ON 2/27/2020 0.0 - 6.0 DARK BROWN, SILTY FINE TO MEDIUM SAND WITH ROOTS, ORGANICS, AND GRAVEL (LOOSE TO MEDIUM DENSE, MOIST) (UNDOCUMENTED FILL) 6.0 - 8.0 SM GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL (DENSE TO VERY DENSE, MOIST) (GLACIAL TILL) SAMPLES WERE COLLECTED AT 3.0 AND 6.5 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 8.0 FEET ON 2/27/2020 TEST PIT FOUR 0.0-2.0 DARK BROWN, SILTY FINE TO MEDIUM SAND WITH ROOTS, ORGANICS, AND GRAVEL (LOOSE TO MEDIUM DENSE, MOIST) (UNDOCUMENTED FILL) 2.0 - 3.0 SM BROWN -GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL (MEDIUM DENSE TO DENSE, MOIST) (GLACIAL TILL) 3.0 - 7.5 SP GRAY, FINE TO MEDIUM SAND WITH TRACE GRAVEL AND TRACE SILT (DENSE, MOIST) (ADVANCE OUTWASH) SAMPLE WAS COLLECTED AT 6.0 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 7.5 FEET ON 2/27/2020 DJO NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 1156720 FIGURE 10 LOG OF EXPLORATION DEPTH (FEET) USC SOIL DESCRIPTION TEST PIT FIVE 0.0 - 2.0 DARK BROWN TO BLACK, SILTY FINE TO MEDIUM SAND WITH ROOTS, ORGANICS, AND GRAVEL (LOOSE TO MEDIUM DENSE, MOIST) (UNDOCUMENTED FILL) 2.0-4.0 SM BROWN -GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL (MEDIUM DENSE TO DENSE, MOIST) (GLACIAL TILL) 4.0 - 7.5 SP GRAY, FINE TO MEDIUM SAND WITH TRACE GRAVEL AND TRACE SILT (DENSE, MOIST) (ADVANCE OUTWASH) SAMPLE WAS COLLECTED AT 4.5 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 7.5 FEET ON 2/27/2020 INFILTRATION PIT ONE 0.0 - 0.5 GRAVEL SURFACING (UNDOCUMENTED FILL) 0.5 - 1.0 GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ORGANICS (MEDIUM DENSE, MOIST) (UNDOCUMENTED FILL) 1.0 - 5.0 SP GRAY, FINE TO COARSE SAND WITH GRAVEL AND SILT (DENSE TO VERY DENSE, MOIST) (ADVANCE OUTWASH) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 5.0 FEET ON 2/27/20 INFILTRATION PIT TWO 0.0 - 0.5 GRAVEL SURFACING (UNDOCUMENTED FILL) 0.5 - 7.5 SM GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL (DENSE TO VERY DENSE, MOIST) (GLACIAL TILL) 7.5 - 8.5 SP GRAY, FINE TO COARSE SAND WITH GRAVEL AND TRACE SILT (DENSE, MOIST) (ADVANCE OUTWASH) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 8.5 FEET ON 2/27/20 DJO NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 1156720 FIGURE 10 Conceptual Soldier Pile Wall Detail NOT FOR CONSTRUCTION USE -, Lean concrete above UO excavation line 0 Iz x w Concrete wall Miradrain drainage matting full height & width centered between piles, installed with fabric to lagging Waterproofing membrane along length of wall Pressure treated timber lagging with 1/4-inch gap between boards Multiflow drainage collector 4-inch diameter weep holes Project Number NELSON GEOTECHNICAL 1156720 Westgate Station Commercial NGA ASSOCIATES, INC. Development Conceptual Soldier Pile Wall Detail GEOTECHNICAL ENGINEERS & GEOLOGISTS Figure 11 "Wo dine pe WA 8 7200 Weoetohee Che en (509 6377666 (425)486-16691 Fax 481-2510-nelsongeolech.com 4-inch diameter PVC pipe tightlined to storm drainage system NOT TO SCALE No. I Date I Revision I By I CK 1 1 3/29/20 1 Original I LSB I KMS r City of Edmonds Map Title 22727 JLynnwood .�j 22721 c/,moods q,�0 N 22731 N , 1 :- . 1 -fl,ke �TMxe � I �• . 0> 60S ^� � _ 9511 Legend = Creeks � O� OI �� hC1 Seismic Hazard Areas 01 i 22809 , - �, O� � Earth Subsidence and Landslide I L! Minimum Buffer Adjacent to Haz 1 ") 22804 N Wetlands 9 ,06 r-) �� M C� u7)� Wetlands Boundary � -- Wetland Boundaries Not Complete) 9' � I _ Wetland Known Extents p co �� RD Floodplains ON �. �O V ■ ❑ A ® AE 01 C) ■ J I ® VE X Landslide Hazard Area 40% .O jO ❑ Severe Erosion Hazard 15%-40% ❑ Erosion Hazard Areas 15%-40% 9727 N . / ArcSDE.GIS.STREET_CENTERLINE: — <all other values, 9715 O 10 0 ,�� ' h 1 Z _ 9;71;7;8 ---------- 9620 y ED - ----- • 23003 — 23001 1: 2,257 O Notes 0 94.04 188.1 Feet This map is a user generated static output from an Internet mapping site and is for WGS_1984_Web-Mercator _Auxiliary -Sphere reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. © City of Edmonds THIS MAP IS NOT TO BE USED FOR DESIGN OR CONSTRUCTION NELSON GEOTECHNICAL ASSOCIATES. INC. MEMORANDUM 17311-13511 Ave. N.E. Suite A-500 Woodinville, WA 98072 (425) 486-1669 www.nelsongeotech.com DATE: May 9, 2022 TO: Mr. Robert Gregg —Gregg Property Associates, LLC CC: Mr. Greg Guillen — CG Engineering FROM: Khal M. Shawish, PE IV o°A Lee S. Bellah, LG ; ct� a /w RE: Environmental Soil Testing Summary �^ Westgate Station Commercial Development 4 35215 Jw 9601 Edmonds Way fir'/STES'�i9C> SszoNAL Edmonds, Washington E� NGA File No. 1156720 5.09.2022 This memo summarizes the results of our recent environmental testing services for the Westgate Station Commercial Development project located at 9601 Edmonds, Washington. Introduction We previously prepared a geotechnical evaluation for the site dated April 14, 2022. We understand that runoff from the proposed development will be directed into on -site infiltration systems and that the site soils may be utilized for water quality treatment purposes. We have been requested to conduct laboratory testing on site soils samples to determine if the site soils are suitable for water quality treatment. In accordance with the 2019 Department of Ecology Stormwater Management Manual for Western Washington, infiltration facilities that double as treatment facilities will need to be tested for Cation Exchange Capacity (USEPA method 9081) and Organic Content (ASTM D 2974) to determine if the soil is adequate for removing the target pollutants. Sampling and Results Cation Exchange Capacity (CEC) and Organic Content tests were conducted by AMTest Laboratories on soil samples obtained from the site as shown on Tables 1 and 2 below, respectively. Please refer to the previous geotechnical evaluation for sample locations. The 2019 Department of EcologV Stormwater Management Manual for Western Washington requires soil to be used for treatment to have a CEC greater or equal to 5 milliequivalents (meq) CEC per 100 grams (CEC/100g). The manual also specifies that filtration soils must have a minimum of 1.0 percent organic content. Environmental Soil Testing Summary Westgate Station Commercial Development Edmonds, Washington NGA File No. 1156720 May 9, 2022 Page 2 Based on the test results, the lower granular outwash soils meet the minimum organic content requirements but do not meet the minimum CEC requirements for use as filtration soils. As a result, if the proposed infiltration facilities are to be utilized for water quality treatment purposes, we recommend that soils at the base of the infiltration facilities be amended with imported soils meeting the CEC and organic content requirements per the stormwater manual and civil engineer. Once amended, an infiltration test should be conducted at the bottom of the facility to confirm design infiltration rates. The test results are attached to this memo as Appendix A. Table 1. Cation Test Results Test Pit Number/Sample Number Depth (Feet) Cation Test Results (CEC/100g) Suitable for Filtration (Yes/No) Test Pit 1 4.0 2.9 No Test Pit 9 9.0 4.1 No Table 2. Organic Content Results Test Pit Number Depth (Feet) Organic Content Results (Percent) Suitable for Filtration (Yes/No) Test Pit 1 4.0 1.0 Yes Test Pit 2 9.0 1.1 Yes We trust this memorandum should satisfy your needs at this time. Please contact us if you have any questions. .•. Attachment: Appendix A - Laboratory Test Results NELSON GEOTECHNICAL ASSOCIATES, INC. 7 111-11 1 Cation Exchange Capacity (CEC) and Organic Content Laboratory Test Results Am Test Inc. 13600 NE 126TH PL Suite C Kirkland, WA 98034 (425) 885-1664 www.amtestlab.com /ia11RMT L A 6 O R A T O R I E S ANALYSIS REPORT NELSON GEOTECH 17311 135TH AVE NE WOODINVILLE, WA 98072 Attention: LEE BIELLAH Project Name: W ESTGATE STATION Project #: 1156720 All results reported on an as received basis. AMTEST Identification Number Client Identification Sampling Date Conventionals 22-AO04952 TEST PIT 1 @ 4.01FT 04/01 /22, 09:00 Professional Analytical Services Date Received: 04/01/22 Date Reported: 4/19/22 PARAMETER IRESULT UNITS Q D.L. METHOD ANALYST I DATE Cation Exchange Capacity 12.9 meq/100g 1 10.5 SW-846 9081 JKF 04/11/22 Miscellaneous PARAMETER RESULT JUNITS Q D.L. IMETHOD JANLST DATE Organic Matter 11.0 % 1 1 ISM 2540G JMD 04/11/22 NELSON GEOTECH Project Name: WESTGATE STATION AmTest ID: 22-AO04953 AMTEST Identification Number Client Identification Sampling Date Conventionals 22-AO04953 TEST PIT 2 @ 9.OFT 04/01/22, 09:00 IPARAMETER IRESULT JUNITS IQ D.L. IMETHOD 1ANALYST I DATE ICation Exchange Capacity 14.1 Imeq/100g 1 10.5 ISW-846 9081 JKF 104/11/22_ Miscellaneous IPARAMETER IRESULT JUNITS IQ ID.L. IMETHOD JANLST I DATE JOrganic Matter 11.1 1% 1 1 ISM 2540G JMD 104/11/22 Ka1hy �:ugiel President Westgate Station - CG #19440 Drainage Report March 22, 2023 Section VI, Page 1 Section VI — Other Permits Section VI Summary: Narrative Other permits are not anticipated beyond those required by the City of Edmonds. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Section VII, Page 1 Section VII — Bond Quantities, Declaration of Covenant, & Operation and Maintenance Manual Section VII Summ Narrative The Bond Quantity Worksheet is a standalone document that can also be submitted to the City of Edmonds separately from this document. A Declaration of Covenant is provided for the proposed on -site BMPs. The Operation and Maintenance Manual is a standalone document that will be given to the property owner following the construction of the project. The maintenance manual contained herein is for the Westgate Station building project. The contractor will be responsible for the maintenance and operation of all stormwater structures and BMPs requiring maintenance during construction, and after construction, responsibility will pass to the property owner(s). The project contractor will be responsible for passing along the information in this maintenance manual to the owner(s). Upon request by the City, it shall be made available for their inspection. It is generally expected that few to none of these defects will be present upon the yearly inspection of each facility. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Site Improvement Bond Quantity Worksheet S15 Webdate: 04/03/201E LQ King County Department of Permitting & Environmental Review 35030 SE Douglas Street, Suite 210 Snoqualmie, Washington 98065-9266 206-296-6600 TTY Relay 711 Project Name: Westgate Station Location: 9601 Edmonds Way, Edmonds, WA 98026 Clearing greater than or equal to 5,000 board feet of timber? yes If yes, Forest Practice Permit Number: (RCW 76.09) Page 1 of 9 Bond Quantities .xIs X no For alternate formats, call 206-296-6600. Date: 3/22/2023 Project No.: Activity No.: BLD2022-0527 Note: All prices include labor, equipment, materials, overhead and profit. Prices are from IRS Means data adjusted for the Seattle area or from local sources if not included in the IRS Means database. Unit prices updated: 3/2/2015 Version: 3/2/2015 Report Date: 3/22/2023 Site Improvement Bond Quantity Worksheet S15 Webdate: 04/03/201� Reference # Unit Price Unit Quantity # of Applications Cost EROSION/SEDIMENT CONTROL Number Backfill & compaction -embankment ESCA $ 6.00 CY Check dams, 4" minus rock ESC-2 SWDM 5.4.6.3 $ 80.00 Each Crushed surfacing 1 1/4" minus ESC-3 WSDOT 9-03.9(3) $ 95.00 CY Ditching ESC-4 $ 9.00 CY Excavation -bulk ESC-5 $ 2.00 CY Fence, silt ESC-6 SWDM 5.4.3.1 $ 1.50 LF 423 1 635 Fence, Temporary (NGPE) ESC-7 $ 1.50 LF Hydroseeding ESC-8 SWDM 5.4.2.4 $ 0.80 SY Jute Mesh ESC-9 SWDM 5.4.2.2 $ 3.50 SY Mulch, by hand, straw, 3" deep ESCA0 SWDM 5.4.2.1 $ 2.50 SY Mulch, by machine, straw, 2" deep ESCA1 SWDM 5.4.2.1 $ 2.00 SY Piping, temporary, CPP, 6" ESC-12 $ 12.00 LF Piping, temporary, CPP, 8" ESCA3 $ 14.00 LF Piping, temporary, CPP, 12" ESC-14 $ 18.00 LF Plastic covering, 6mm thick, sandbagged ESCA5 SWDM 5.4.2.3 $ 4.00 SY 67 1 268 Rip Rap, machine placed; slopes ESCA6 WSDOT 9-13.1(2) $ 45.00 CY Rock Construction Entrance, 50'x15'x1' ESCA7 SWDM 5.4.4.1 $ 1,800.00 Each Rock Construction Entrance, 100'x15'x1' ESCA8 SWDM 5.4.4.1 $ 3,200.00 Each 1 1 3200 Sediment pond riser assembly ESC-19 SWDM 5.4.5.2 $ 2,200.00 Each Sediment trap, 5' high berm ESC-20 SWDM 5.4.5.1 $ 19.00 LF Sed. trap, 5' high, riprapped spillway berm section ESC-21 SWDM 5.4.5.1 $ 70.00 LF Seeding, by hand Sodding, 1" deep, level ground ESC-22 SWDM 5.4.2.4 $ 1.00 SY ESC-23 SWDM 5.4.2.5 $ 8.00 SY Sodding, 1" deep, sloped ground ESC-24 SWDM 5.4.2.5 $ 10.00 SY TESC Supervisor ESC-25 $ 110.00 HR 40 1 4400 Water truck, dust control ESC-26 SWDM 5.4.7 $ 140.00 HR 40 1 5600 WRITE -IN -ITEMS **** (see page 9) 4,000 Gallon Storage Tank $ 5,000.00 Each 1 1 5000 Temporaary CB Inserts $ 150.00 Each 6 1 900 High Visibility Fence $ 3.00 LF 1 2958 11 8874 ESC SUBTOTAL: 30% CONTINGENCY & MOBILIZATION: ESC TOTAL: COLUMN: Page 2 of 9 Bond Quantities .xIs $ 28,876.50 $ 8,662.95 $ 37,539.45 A Unit prices updated: 3/2/2015 Version: 3/2/2015 Report Date: 3/22/2023 Site Improvement Bond Quantity Worksheet Web date: 04/03/2015 Existing Right -of -Way Future Public Right of Way & Drainage Facilities Private Improvements Unit Price Unit Quant. Cost Quant. Cost Quant. Cost GENERAL ITEMS No. Backfill & Compaction- embankment GI - 1 $ 6.00 CY 410 2,460.00 Backfill & Compaction- trench GI - 2 $ 9.00 CY Clear/Remove Brush, by hand GI - 3 $ 1.00 SY Clearing/Grubbing/Tree Removal GI - 4 $10,000.00 Acre Excavation - bulk GI - 5 $ 2.00 CY 950 1,900.00 Excavation - Trench GI - 6 $ 5.00 CY Fencing, cedar, 6' high GI - 7 $ 20.00 LF Fencing, chain link, vinyl coated, 6' high GI - 8 $ 20.00 LF Fencing, chain link, gate, vinyl coated, 20' GI - 9 $ 1,400.00 Each Fencing, split rail, 3' high GI - 10 $ 15.00 LF Fill & compact - common barrow GI - 11 $ 25.00 CY Fill & compact - gravel base GI - 12 $ 27.00 CY Fill & compact - screened topsoil GI - 13 $ 39.00 CY Gabion, 12" deep, stone filled mesh GI - 14 $ 65.00 SY Gabion, 18" deep, stone filled mesh GI - 15 $ 90.00 SY Gabion, 36" deep, stone filled mesh GI - 16 $ 150.00 SY Grading, fine, by hand GI - 17 $ 2.50 SY 241 602.50 401 1,002.50 Grading, fine, with grader GI - 18 $ 2.00 SY 972 1,944.00 Monuments, 3' long GI - 19 $ 250.00 Each Sensitive Areas Sign GI - 20 $ 7.00 Each Sodding, 1" deep, sloped ground GI - 21 $ 8.00 SY Surveying, line & grade GI - 22 $ 850.00 Day Surveying, lot location/lines GI - 23 $ 1,800.00 Acre Traffic control crew ( 2 flaggers) GI - 24 $ 120.00 HR 40.00 Trail, 4" chipped wood GI - 25 $ 8.00 SY Trail, 4" crushed cinder GI - 26 $ 9.00 SY Trail, 4" top course GI - 27 $ 12.00 SY Wall, retaining, concrete GI - 28 $ 55.00 SF 1260 69,300.00 Wall, rockery GI - 29 $ 15.00 SF Page 3of9 SUBTOTAL 642.50 606.50 Unit prices updated: 03/02/2015 "KCC 27A authorizes only one bond reduction. Version: 03/02/2015 Bond Quantities .xls Report Date: 3/22/2023 Site Improvement Bond Quantity Worksheet Web date: 04/03/2015 Existing Right-of-way Future Public Right of Way & Drainage Facilities Private Improvements Unit Price Unit Quant. Cost Quant. Cost Quant. Cost ROAD IMPROVEMENT No. AC Grinding, 4' wide machine < 1000sy RI - 1 $ 30.00 SY AC Grinding, 4' wide machine 1000-2000 RI - 2 $ 16.00 SY AC Grinding, 4' wide machine > 2000sy RI - 3 $ 10.00 SY AC Removal/Disposal RI - 4 $ 35.00 SY 114 3,990.00 Barricade, type III ( Permanent) RI - 6 $ 56.00 LF Curb & Gutter, rolled RI - 7 $ 17.00 LF Curb & Gutter, vertical RI - 8 $ 12.50 LF 337 Curb and Gutter, demolition and disposal RI - 9 $ 18.00 LF 337 6,066.00 Curb, extruded asphalt RI - 10 $ 5.50 LF Curb, extruded concrete RI - 11 $ 7.00 LF 698 4,886.00 Sawcut, asphalt, 3" depth RI - 12 $ 1.85 LF 377 697.45 Sawcut, concrete, per 1" depth RI - 13 $ 3.00 LF 72 216.00 Sealant, asphalt RI - 14 $ 2.00 LF Shoulder, AC, ( see AC road unit price ) RI - 15 $ - SY Shoulder, gravel, 4" thick RI - 16 $ 15.00 SY Sidewalk, 4" thick RI - 17 $ 38.00 SY 169 6,422.00 401 15,238.00 Sidewalk, 4" thick, demolition and disposal RI - 18 $ 32.00 SY 169 5,408.00 Sidewalk, 5" thick RI - 19 $ 41.00 SY Sidewalk, 5" thick, demolition and disposal RI - 20 $ 40.00 SY Sign, handicap RI - 21 $ 85.00 Each 1 85.00 Striping, per stall RI - 22 $ 7.00 Each 13 91.00 Striping, thermoplastic, ( for crosswalk) I RI - 23 $ 3.00 SF Striping, 4" reflectorized line I RI - 24 $ 0.50 LF Page 4 of 9 22,102.00 20,997.45 Unit prices updated: 03/02/2015 "KCC 27A authorizes only one bond reduction. Version: 03/02/2015 Bond Quantities As Report Date: 3/22/2023 Site Improvement Bond Quantity Worksheet Web date: 04/03/2015 Existing Right-of-way Future Public Right of Way & Drainage Facilities Private Improvements Unit Price Unit Quant. Cost Quant. Cost QuantT Cost ROAD SURFACING No. 4" Rock = 2.5 base & 1.5" top course 9 1/2" Rock= 8" base & 1.5" top course Additional 2.5" Crushed Surfacing RS - 1 $ 3.60 SY HMA 1/2" Overlay, 1.5" RS - 2 $ 14.00 SY HMA 1/2" Overlay 2" RS - 3 $ 18.00 SY HMA Road, 2", 4" rock, First 2500 SY RS - 4 $ 28.00 SY HMA Road, 2", 4" rock, Qty. over 2500 SY RS - 5 $ 21.00 SY HMA Road, 3", 9 1/2" Rock, First 2500 S RS - 6 $ 42.00 SY HMA Road, 3", 9 1/2" Rock, Qty Over 250 RS - 7 $ 35.00 SY Not Used RS - 8 Not Used RS - 9 HMA Road, 6" Depth, First 2500 SY RS - 10 $ 33.10 SY 117 3,872.70 HMA Road, 6" Depth, Qty. Over 2500 SY RS - 11 $ 30.00 SY HMA 3/4" or 1 ", 4" Depth RS - 12 $ 20.00 SY Gravel Road, 4" rock, First 2500 SY RS - 13 $ 15.00 SY Gravel Road, 4" rock, Qty. over 2500 SY RS - 14 $ 10.00 SY PCC Road (Add Under Write -Ins w/Desig RS - 15 Thickened Edge IRS - 17 $ 8.60 LF Page 5 of 9 SUBTOTAL 3,872.70 Unit prices updated: 03/02/2015 "KCC 27A authorizes only one bond reduction. Version: 03/02/2015 Bond Quantities .xls Report Date: 3/22/2023 Site Improvement Bond Quantity Worksheet Web date: 04/03/2015 Existing Right-of-way Future Public Right of Way & Drainage Facilities Private Improvements Unit Price Unit Quant. Cost Quant. Cost Quant. Cost DRAINAGE (CPP = Corrugated Plastic Pipe, N12 or Equivalent) For Culvert prices, Average of 4' cover was assumed. Assume perforated PVC is same price as solid pipe. Access Road, R/D D - 1 $ 21.00 SY Bollards - fixed D - 2 $ 240.74 Each Bollards - removable D - 3 $ 452.34 Each " (CBs include frame and lid) CB Type I D - 4 $ 1,500.00 Each 7 10,500.00 CB Type IL D - 5 $ 1,750.00 Each CB Type II, 48" diameter D - 6 $ 2,300.00 Each 1 2,300.00 for additional depth over 4' D - 7 $ 480.00 FT 2 960.00 CB Type II, 54" diameter D - 8 $ 2,500.00 Each for additional depth over 4' D - 9 $ 495.00 FT CB Type II, 60" diameter D - 10 $ 2,800.00 Each for additional depth over 4' D - 11 $ 600.00 FT CB Type II, 72" diameter D - 12 $ 3,600.00 Each for additional depth over 4' D - 13 $ 850.00 FT Through -curb Inlet Framework (Add) D - 14 $ 400.00 Each Cleanout, PVC, 4" D - 15 $ 150.00 Each Cleanout, PVC, 6" D - 16 $ 170.00 Each 20 3,400.00 Cleanout, PVC, 8" D - 17 $ 200.00 Each Culvert, PVC, 4" D - 18 $ 10.00 LF 604 6,040.00 Culvert, PVC, 6" D - 19 $ 13.00 LF 692 8,996.00 Culvert, PVC, 8" D - 20 $ 15.00 LF 194 2,910.00 Culvert, PVC, 12" D - 21 $ 23.00 LF Culvert, CMP, 8" D - 22 $ 19.00 LF Culvert, CMP, 12" D - 23 $ 29.00 LF Culvert, CMP, 15" D - 24 $ 35.00 LF Culvert, CMP, 18" D - 25 $ 41.00 LF Culvert, CMP, 24" D - 26 $ 56.00 LF Culvert, CMP, 30" D - 27 $ 78.00 LF Culvert, CMP, 36" D - 28 $ 130.00 LF Culvert, CMP, 48" D - 29 $ 190.00 LF Culvert, CMP, 60" D - 30 $ 270.00 LF Culvert, CMP, 72" D - 31 $ 350.00 LF Page 6 of 9 SUBTOTAL 35,106.00 Unit prices updated: 03/02/2015 "KCC 27A authorizes only one bond reduction. Version: 03/02/2015 Bond Quantities .xls Report Date: 3/22/2023 Site Improvement Bond Quantity Worksheet Web date: 04/03/2015 DRAINAGE CONTINUED Existing Right-of-way Future Public Right of Way & Drainage Facilities Private Improvements No. Unit Price Unit Quant. Cost Quant. Cost Quant. Cost Culvert, Concrete, 8" D - 32 $ 25.00 LF Culvert, Concrete, 12" D - 33 $ 36.00 LF Culvert, Concrete, 15" D - 34 $ 42.00 LF Culvert, Concrete, 18" D - 35 $ 48.00 LF Culvert, Concrete, 24" D - 36 $ 78.00 LF Culvert, Concrete, 30" D - 37 $ 125.00 LF Culvert, Concrete, 36" D - 38 $ 150.00 LF Culvert, Concrete, 42" D - 39 $ 175.00 LF Culvert, Concrete, 48" D - 40 $ 205.00 LF Culvert, CPP, 6" D - 41 $ 14.00 LF Culvert, CPP, 8" D - 42 $ 16.00 LF Culvert, CPP, 12" D - 43 $ 24.00 LF Culvert, CPP, 15" D - 44 $ 35.00 LF Culvert, CPP, 18" D - 45 $ 41.00 LF Culvert, CPP, 24" D - 46 $ 56.00 LF Culvert, CPP, 30" D - 47 $ 78.00 LF Culvert, CPP, 36" D - 48 $ 130.00 LF Ditching D - 49 $ 9.50 CY Flow Dispersal Trench (1,436 base+) D - 50 $ 28.00 LF French Drain (3' depth) D - 51 $ 26.00 LF Geotextile, laid in trench, polypropylene D - 52 $ 3.00 SY Mid -tank Access Riser, 48" dia, 6' deep D - 54 $ 2,000.00 Each Pond Overflow Spillway D - 55 $ 16.00 SY Restrictor/Oil Separator, 12" D - 56 $ 1,150.00 Each Restrictor/Oil Separator, 15" D - 57 $ 1,350.00 Each Restrictor/Oil Separator, 18" D - 58 $ 1,700.00 Each Riprap, placed D - 59 $ 42.00 CY Tank End Reducer (36" diameter) D - 60 $ 1,200.00 Each Trash Rack, 12" D - 61 $ 350.00 Each Trash Rack, 15" D - 62 $ 410.00 Each Trash Rack, 18" D - 63 $ 480.00 Each Trash Rack, 21" D - 64 $ 550.00 Each Page 7of9 SUBTOTAL Unit prices updated: 03/02/2015 "KCC 27A authorizes only one bond reduction. Version: 03/02/2015 Bond Quantities .xls Report Date: 3/22/2023 Site Improvement Bond Quantity Worksheet Web date: 04/03/2015 Existing Right-of-way Future Public Right of Way & Drainage Facilities Private Improvements Unit Price Unit Quant. Price Quant. Cost Quant. Cost PARKING LOT SURFACING Not To Be Used For Roads Or Shoulders No. 2" AC, 2" top course rock & 4" borrow PL - 1 $ 21.00 SY NA NA 2" AC, 1.5" top course & 2.5" base cours PL - 2 $ 28.00 SY NA NA 972 27216 4" select borrow PL - 3 $ 5.00 SY NA NA 1.5" top course rock & 2.5" base course PL - 4 $ 14.00 SY NA NA UTILITY POLES & STREET LIGHTING Utility pole relocation costs must be accompanied by Franchise Utility's Cost Estimate Utility Pole(s) Relocation UP-1 Lump Sum Street Light Poles w/Luminaires UP-2 $ 7,500.00 Each WRITE -IN -ITEMS (Such as detention/water quality vaults.) No. Yard Drain WI-1 $ 400.00 Each 3 1,200.00 6" DIP Culvert WI-2 $ 26.00 LF 9 234.00 8" DIP Culvert WI-3 $ 30.00 LF 98 2,940.00 2"-3" Washed Rock WI-4 $ 10.00 CY 633 6,330.00 Lenz 50-50 Sand Blend WI-5 $ 40.00 CY 58 2,320.00 Bioretention Soil Mix W I - 6 $ 40.00 CY 190 7,600.00 48" SSMH W I - 7 $ 3,500.00 Each 3 10,500.00 DCDA Vault W I - 8 $10,000.00 Each 1 10,000.00 FDC WI-9 $ 1,000.00 Each 1 1,000.00 FH Assembly W I - 10 $ 1,500.00 Each 21 3,000.00 8" GV WI - 11 $ 1,500.00 Each 41 6,000.00 1 "-2" Water Meter W I - 12 $ 300.00 Each 21 600.00 SUBTOTAL SUBTOTAL (SUM ALL PAGES): 30%CONTINGENCY & MOBILIZATION: GRANDTOTAL: COLUMN: Page 8 of 9 "KCC 27A authorizes only one bond reduction. Bond Quantities As 26,617.20 7,985.16 34,602.36 B C D 211,649.95 63,494.99 275,144.94 Unit prices updated: 03/02/2015 Version: 03/02/2015 Report Date: 3/22/2023 Site Improvement Bond Quantity Worksheet Original bond computations prepared by: Name: Greg Guillen, PE, SE Date: PE Registration Number: 25385 Tel. #: Firm Name: CG Engineering Address: 250 4th Ave S #200, Edmonds, WA 98020 Project No: Stabilization/Erosion Sediment Control (ESC) Existing Right -of -Way Improvements Future Public Right of Way & Drainage Facilities Private Improvements Calculated Quantity Completed Total Right -of Way and/or Site Restoration Bond*/** (First $7,500 of bond* shall be cash.) Performance Bond* Amount (A+B+C+D) = TOTAL Maintenance/Defect Bond* Total NAME OF PERSON PREPARING BOND* REDUCTION: (A) (B) (C) (D) Web date: 04/03/2015 3/22/2023 425.778.8500 BLD2022-0527 FINANCIAL GUARANTEE REQUIREMENTS PERFORMANCE BOND* MINIMUM BOND* AMOUNT PUBLIC ROAD & DRAINAGE AMOUNT REQUIRED FOR RECORDING OR MAINTENANCE/DEFECT BOND* TEMPORARY OCCUPANCY AT 37,539.5 SUBSTANTIAL COMPLETION *** 34,602.4 $ 275,144.9 (A+B) $ 72,141.8 (T) $ 347,286.7 Minimum is $2000. x 0.30 $ 104,186.0 Minimum is $2000. Date: (B+C) x 0.25 = $ 8,650.6 Minimum is $2000. * NOTE: The word "bond" as used in this document means a financial guarantee acceptable to King County. ** NOTE: KCC 27A authorizes right of way and site restoration bonds to be combined when both are required. The restoration requirement shall include the total cost for all TESC as a minimum, not a maximum. In addition, corrective work, both on- and off -site needs to be included. Quantities shall reflect worse case scenarios not just minimum requirements. For example, if a salmonid stream may be damaged, some estimated costs for restoration needs to be reflected in this amount. The 30% contingency and mobilization costs are computed in this quantity. *** NOTE: Per KCC 27A, total bond amounts remaining after reduction shall not be less than 30% of the original amount (T) or as revised by major design changes. REQUIRED BOND* AMOUNTS ARE SUBJECT TO REVIEW AND MODIFICATION BY KING COUNTY Page 9 of 9 Unit prices updated: 03/02/2015 Check out the DDES Web site at www.kin_gcounty-goy/permits Version: 03/02/2015 Bond Quantities .xIs Report Date: 3/22/2023 After recording return to: City Clerk City of Edmonds 121 Fifth Avenue North Edmonds, WA 98020 Document Title(s) Declaration of Covenant - Private Stormwater BMP Reference Number(s) of Related Documents City of Edmonds (permit number) BLD2022-0527 Grantor(s) (Last, First and Middle Initial) Marc Wilsen Grantee: City of Edmonds Legal Description (abbreviated form; i.e., lot, plat or section, township, range, quarter/quarter) SECTION 36 TOWNSHIP 27 NORTH, RANGE 3 EAST, W.M. Assessor's Property Tax Parcel/Account Number at the Time of Recording: 00937900001000 The Auditor/Recorder will rely on the information provided on this form. The staff will not read the document to verify the accuracy or completeness of the indexing information provided herein. DECLARATION OF COVENANT Private Stormwater BMP WHEREAS, the undersigned Declarant(s) have installed one or more stormwater facilities under Edmonds Community Development Code (ECDC) Chapter 18.30 known as "stormwater best management practices (BMP)" as selected below: ❑ Permeable Pavement L Infiltration Trench/Gallery/Drywell ❑ Detention Pipe/Tank/Vault ❑ Concentrated Flow Dispersion ❑ Other: ❑ Infiltration Tank/Vault ❑ Sheet Flow Dispersion ❑ Reduced Impervious Footprint X Rain Garden / Bioretention Cell WHEREAS, the City of Edmonds has allowed installation of the BMP, subject to the execution and recording of this Declaration of Covenant; NOW, THEREFORE, THE UNDERSIGNED DECLARANT(S), being the owners of the real property ("the Property") located at the following address: 9601 Edmonds Way in the City of Edmonds, Washington, and legally described on Exhibit A attached hereto and incorporated herein by this reference as if set forth in full, hereby covenants and agrees, on behalf of himself/herself/themselves/itself and his/her/their/its successors and assigns, as follows: Declarant(s) warrant that he/she/they/it is/are the owner(s) of the property described on Exhibit A and have the authority to impose this covenant on the property and bind all future owners, successors, and assigns of the Declarant(s). The Declarant(s), future owners, successors, and assigns of the Declarant(s) shall be referred to collectively as "Owners." 2. The Owners of the Property agree that the Property contains one or more stormwater management facilities referred to as a 'BMP," which was installed to mitigate the stormwater quantity and quality impacts of some or all of the impervious or non-native pervious surfaces on the property. a. For infiltration -based BMPs, the BMP shall include all pretreatment devices upstream, the infiltration facility, and a minimum of 3-feet of soil beneath the infiltration contact layer, defined as the elevation at which runoff enters native soils. b. For bio-retention or rain garden BMPs, the BMP shall include all pretreatment devices upstream, the retention facility, the vegetation within the retention facility, and a minimum of 3-feet of soil beneath the infiltration contact layer, defined as the elevation at which runoff enters native soils. While specific plants are not necessarily required, a quantitative amount of vegetation coverage is required and may be subject to maintenance requests per Section 5. c. For dispersion based BMPs, the BMP shall include all pretreatment devices upstream, the dispersion mechanism/device, and all elements of the downstream vegetated flow path, including restrictions on slopes and surface materials, as required by ECDC 18.30. d. For detention BMPs, the BMP shall include all pretreatment devices upstream, the detention device, and the control structure device. e. For reduced impervious footprints, the BMP shall include all areas which are used as mitigation credits, including a full ten foot (10') driveway width when using wheel strip driveways. 3. The Owners shall maintain the size, placement, and design of the BMP as depicted on the approved site plan, Exhibit B, attached hereto and incorporated herein by this reference as if set forth in full, and design details shall be maintained and may not be changed without written approval either from the Engineering Division of the City of Edmonds or through a future development permit from the City of Edmonds. Chemical fertilizers and pesticides shall not be used where a BMP is located. All costs of maintenance and repair shall be the sole responsibility of the Owners. 4. The Owners shall inspect BMPs annually for physical defects. After major storm events, the system shall also be checked to ensure that the overflow system is working properly. The Owners also shall maintain all BMPs so they function as designed on a year-round basis. 5. The City of Edmonds is hereby granted by the Owners the right, but not the obligation, to enter upon the Property described on Exhibit A at all reasonable times for the purpose of inspecting the private stormwater BMP facility. If, as the result of any such inspection, the City of Edmonds determines that the BMP is in disrepair, requires maintenance or repair, or is otherwise not functioning as provided in the site plan, the City Engineer or his designee shall have the right, but not the obligation, to order the Owners to maintain or repair the same. The Owners agree to maintain reasonable one-man access to all portions of the BMP and shall avoid permanent or lockable obstructions from blocking a reasonable path of access by City inspectors. Such obstruction may be the sole cause for the City to request maintenance as noted above. 6. If the City of Edmonds determines that the BMP requires maintenance or repair pursuant to Section 5, the City of Edmonds shall provide notice to the Owners of the deadline within which such maintenance or repair must be completed. Said notice may further advise that, should the Owners fail to perform required maintenance or make repairs within the established deadline, the work may be done by the City or a contractor designated by the City Engineer and the expense thereof shall be charged to the Owners. The City's officers, agents, employees, and contractors shall have the right, which is hereby granted by the Owners, to enter upon the Property described on Exhibit A in order to perform such work. The Owners shall bear the cost of all work performed. 7. The Owners shall indemnify, defend and hold harmless the City of Edmonds, its officers, officials, employees and agents from any and all claims, demands, suits, penalties, losses, damages, judgments, attorneys' fees and/or costs of any kind whatsoever, arising out of or in any way resulting from the approval of the BMP(s), the installation and presence of the BMP(s), and the acts or omissions of the Owners, their officers, employees, contractors, and agents relating to the construction, operation and maintenance of the BMP(s) on the Property, except for the City's intentional and willful tortious acts, and waive and release the City of Edmonds from any and all claims for damages and injunctive relief which the Owners may themselves have now or in the future, by reason of the construction, maintenance and operation of said BMP(s). 8. This covenant shall run with the land and be binding upon the Owners. Dated: DECLARANT(S): APPROVED: CITY OF EDMONDS (Signature) (Title) (Signature) (Print Name) (Print Name) (Title) Corporation STATE OF WASHINGTON ) ss. COUNTY OF ) On this day of , 20, before me, the under -signed, a Notary Public in and for the State of Washington, duly commissioned and sworn, personally appeared to me known to be the of , the corporation that executed the foregoing instrument, and acknowledged the said instrument to be the free and voluntary act and deed of said corporation, for the uses and purposes therein mentioned, and on oath stated that was authorized to execute said instrument and that the seal affixed is the corporate seal of said corporation. WITNESS my hand and official seal hereto affixed the day and year first above written. NOTARY PUBLIC in and for the State of Washington, residing at My commission expires Exhibit A Legal description SECTION 36 TOWNSHIP 27 RANGE 3 QUARTER NE K. ELISE BLK 000 D-00 LOT 10 LESS S/HWY PER SCC 108154 Exhibit B Site Plan Westgate Station - CG #19440 Drainage Report March 22, 2023 Section VI I, Page 2 Westgate Station 9601 Edmonds Way Edmonds, WA 98020 OPERATION AND MAINTENANCE MANUAL Date: March 2023 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 March 22, 2023 Drainage Report Section VII, Page 3 Operation and Maintenance Manual This Operation and Maintenance Manual has been created for the Westgate Station a mixed -use project on a 1.10-acre lot. The proposed storm system consists of infiltrating rain gardens and infiltration trenches that collect runoff from all new impervious areas on -site via roof drains and catch basins. Included in this Operation and Maintenance Manual is an 11" x 17" grading and drainage plan sheet showing the location of the rain garden system and infiltration trenches. Please note that this map is generated during the design phase and may not reflect all changes made in permitting and construction. CG Engineering may be contacted for an updated copy of this map once the as -built drawings are completed for the site. The contractor will be responsible for the maintenance and operation of all stormwater structures and BMPs requiring maintenance during construction, and after construction, responsibility will pass to the property owner(s). An aerial image of the project area can be seen on the following page in Figure VII-1. Included in this manual are maintenance sheets taken from the 2014 Stormwater Management Manual for Western Washington for the following facilities/activities: Infiltration: The downward movement of water from the surface to the subsoil. The rain gardens and infiltration trenches fall under this category. See "No. 2" for maintenance. Typical Biofiltration Swale: The rain gardens along the south property line fall under this category. The rain gardens will have an overflow structure and be open bottom to allow for infiltration into the subsoil. Specifically chosen Bioretention Soil and specific plants will work together to slow down the runoff. Catch Basins: Concrete structures with steel grates that collect stormwater runoff from the site and act as junctions for storm conveyance pipes. See "No. 5" for maintenance. Vegetation Management: Landscaping can include grading, soil transfer, vegetation removal, pesticide and fertilizer applications, and watering. Stormwater contaminants include toxic organic compounds, heavy metals, oils, total suspended solids, coliform bacteria, fertilizers, and pesticides. Facilities shall be inspected for defects listed in the following facility sheets. Most maintenance tasks are generally reactionary to a defect being found, rather than a matter of constant upkeep. It is generally expected that few to none of these defects will be present upon the yearly inspection of each facility. The facility sheets list the potential conditions warranting maintenance and the expected result following any maintenance. Several engineer's notes for specific tasks are provided within the facility sheets. Unless otherwise noted on the facility sheets the maintenance tasks should be performed on an "as needed" basis: (a) when the described defect is visible to whomever performs the yearly inspection, or (b) should any defect become apparent between inspections. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Section VI I, Page 4 Figure VII-1. Aerial image of project area (City of Edmonds GIS Map). GM 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com NE 1/ 95�0 SIB 6 1 5 / 2 O O 009379000.0 21 I 00937900000500 O CITY BANN ' / PHILIP Y. JANG / ( P, G 0011711 0010101 I AREA DRAIN (TIE / CITY BANK INTO ROOF ID IN) RIM: 336.70 SHORING WALL PER STRUCT R ofRAILPLANSc �/ ,TOW:3 TOP: 3 TOE:, 5nTo"°i OW: 353.0, g'4 TOP: 350.0 TOE: 337.25 0 TW334/ OE337.Z5 /T /�@�//� /OP: 341 / TOP:344.0: 3�37.23. J/ `TOW: 344. TOP: 341.24- AREA DRAIN (TIE 'TOW: 42'3F INTO ROOF DRAOF _fT 33 ': TQE: 3337.25� RIM: 336.70 _ - - / S / PIPE XING 6"PVC TOP: 333.16 ` 'IPE�r' --- --� /./i --- 6"PVC IE: 332.66 _ - - _ _ GAS SERVICE IE: 334.7± N PIN ROCK i' W-0.09' 2 C3. 27'x13'x3' INFILTRATION TRENCH A33.5 PIPE XING 0.9 STORM TOP: 335 STORM IE: 330.45 WATER TOP: 329.45 WATER IE: 329.28 DISTANCE BETWEEN STORM IE AND WATER TOP: V 333.4 9 LF ^'6"DIP @1.1% le x 5 : ace is-� 4, SECTION 36, TOWNSHIP 27 00y.�790JD000 00 CITY/BAN/ 38 LF^6 PVC @25.0%±,/ // / ( PICK UP EXIST PIPE TO / / / Ek/I STING EXIST RAIN GAIfDEfy YARD DRAIN �I TOW: 351.0 TOP: 348.- TOE:348,0 / v / 00 TOW: 354. "/ TOP: 351.44//\ 34L, 5 e�p�ZCE: oeE TOW: 353.84 %/ k TOP: 350.84�/ 0a ' TOE: 34a,)I9�7\ N. / NORTH, RANGE 3 EAST, W.M. EXISTING DETENTION VAULT OUTFALLTO BE ADJUSTED FOR NEW GRADES D 32 LF - 8" PVC @ 32.0%� P o�p \\ Q PIPE ANCHOR REQUIRED M.H. FORPIPEWITH32% SLOPE. TO BE DESIGNED BYGEOTECHNICALOR ,J CIVIL ENGINEER A- 49'x20'x3' INFILTRATION TRENCH 1 2 EXISTING TRANSMISSIONS rv�oiazo nozia POLE TO BE EX. M.H. ✓ A PE XING zasx PIPE DIP TOP: 334.66 1. 6" DIP IE: 334.16 8" PVC TOP: 330.76 8" PVC IE: 330,21 DISTANCE BETWEEN 6"DIP / IE AND 8" PVC TOP: 3.4' JP 3 V ciN g1ANN. / / / DISTRIBUTION LINES / CATCH BASIN SCHEDULE MARK TYPE RIM ELEV INV ELEV NOTES SOLID LID PER WSDOT TYPE II 354.0 IN): 348.51 STANDARDS 48„� (8" S): 348.0 2 4 C3.3 C3.3 SOLID LID PER WSDOT (8" N): 337.50 STANDARDS Q TYPEI 340.50 IS" S):337.40 1 2 3 C3.3 C3.3 C3.3 SOLID LID PER WSDOT Q TYPEI 341.0 (8" N): 338.0 STANDARDS IS" S):337.90 1 2 C3.3 C3. ® TYPEI 337.80 (N): 335.7 (E): 335.3 1 2 3 (S): 335.2 C3.3 C3.3 C3.3 Q TYPEI 337.50 (N): 335.0 (E). 334.0 1 2 3 (W): 3339 C3.3 C3.3 C3.3 © TYPEI 336.70 IN): 334.2 1 2 3 C3.3 C3.3 C3.3 Q AREA 337.50 (S): 335.0 MAX TIE INTO RAIN GARDEN p1 DRAIN 332.9 MIN ® AREA 337.50 (S): 335.0 MAX TIE INTO RAIN GARDEN N2 DRAIN 332.8 MIN O AREA 337.50 (S): 335.0 MAX TIE INTO RAIN GARDEN #3 DRAIN 332.6 MIN INCLUDE REMOVEABLE ® TYPEI 332.75 IS" E): 330.5 PUSH -ON PVC TEE ON OUTLET PIPE 1 2 3 C3.3 C3. C3.3 INCLUDE REMOVEABLE (6" W): 335.7 PUSH ON PVC TEE ON OUTLET © TYPEI 338.5 (6" E): 335.6 PIPE, SOLID U 1 2 3 C3.3 C3.3 C3. GRADING QUANTITIES TOTAL EXCAVATION (CUT) - 950 CU YDS TOTAL EMBANKMENT (FILL) 410 CU YDS TOTAL 1360 CU YDS THE QUANTITIES SHOWN ABOVE ARE FOR THE PERMIT PROCESS ONLY. THESE VALUES ARE APPROXIMATE. DO NOT USE FOR BIDDING, PAYMENT, OR ESTIMATING PURPOSES. INFILTRATION BMP TABLE INFILTRATING BMP LENGTH (FT) WIDTH FT DEPTH FT IEIN IE OUT OUTLET STRUCTURE INFILTRATION RATE(IN/HR) TRENCH 1 (WEST) 23 15 3 330.4 330.9 DOWNTURNED ELBOW 0.68 TRENCH 2 (EAST) 49 20 3 (W, N) 335.5 336.0 DOWNTURNED ELBOW 0.68 RAIN GARDEN Rl 50 11 4.5 (E, NW): 3323327 .8 MIN 2.88 332.9 MAX C3.3 RAIN GARDEN#2 37 11 4.5 (E, NW): 332.7 332. MIN 0.68 MAX C3. RAIN GARDEN#3 20 9 4.5 (E, NW): 332.5 MIN 0.68 330. MAX C3, ram' `..4.. i�&GRADINGAND DRAI AGE PLAN .DRAI AGE PLAN . i • SCALE: 1 20' GRADING AND DRAINAGE NOTES: 20 0 10 20 40© 6. A MINIMUM OF 2' OF COVER IS REQUIRED FOR ALL PIPES LOCATED UNDER DRIVEABLE SURFACES AND V OF COVER UNDER LANDSCAPE SURFACES. 1. SOILS REPORT REPORT NUMBER: 115670 7. PRIOR TO PLACING ANY SURFACING MATERIAL ON THE ROADWAY, IT WILL BE THE RESPONSIBILITY OF THE DEVELOPER/CONTRACTOR TO PROVIDE PREPARED BY: NELSON GEOTECHNICAL ASSOCIATES DENSITY TEST REPORT CERTIFIED BYA PROFESSIONAL ENGINEER REGISTERED IN THE STATE OF WASHINGTON. DATED: APRIL 14, 2020 8. NEW/REPLACED IMPERVIOUS SURFACE (INCLUDING OFF -SITE): 35,438 SF 2. THIS SITE IS DESIGNATED AS A STEEP SLOPE CRITICAL AREA. -- NEW BUILDING:16,818 SF ROOF AREA (INCLUDES OVERHANGS). RUNOFF ROUTED TO EASTERN INFILTRATION TRENCH THROUGH ROOF DRAINS. 3. TOP AND TOE REFER TO FINISHED GRADE AT THE TOP AND BOTTOM OF THE WALLS,RESPECTIVELY. TOW REFERS TO THE TOP OF THE WALL. -- NEW SIDEWALK:3,864 SF. RUNOFF ROUTED TO RAIN GARDENS THROUGH AREA DRAINS AND CONVEYANCE PIPES. -- NEW ASPHALT: 7,899 SF. RUNOFF ROUTED TO INFILTRATION TRENCHES THROUGH CATCH BASINS AND CONVEYANCE PIPES. 4. A MINIMUM OF T HORIZONTAL SEPARATION AND V VERTICAL SEPARATION IS REQUIRED BETWEEN DRY UTILITIES (POWER, GAS, PHONE, CABLE, ETC) -- NEW SIDEWALK (ROW): 1,464 SF. RUNOFF WILL FLOW INTO THE GUTTER AND PUBLIC STORM SYSTEM. AND SEWER, WATER AND STORM, AND A MINIMUM OF 5' HORIZONTAL SEPARATION AND I' VERTICAL SEPARATION FROM ANY CITY -OWNED LINES. -- NEW ASPHALT (OFF -SITE) : 1,170 SF. RUNOFF ROUTED TO WESTERN INFILTRATION TRENCH THROUGH CATCH BASINS AND CONVEYANCE PIPES. 5. ATYPE II CATCH BASIN IS REQUIRED WHENEVER RIM TO INVERT EXCEEDS 51. -- EXISTING ROOF (OFF -SITE): 4,223 SF. RUNOFF ROUTED TO EASTERN INFILTRATION TRENCH THROUGH CATCH BASINS AND CONVEYANCE PIPES. B L DXXXX-XXXX APPROVED FOR CONSTRUCTION CITY OF EDMONDS DATE. BY: CITY ENGINEERING DIVISION C 4m ENGINEERING 250 4TH AVE. S., SUITE 200 EDMONDS, WASHINGTON 98020 PHONE (425) 778-8500 FAX (425) 778-5536 P w XK/NK I O O N N X Q ti O N N X N C) V\1 X O 0 O O X DESIGN: SBG DRAWN: ATD CHECK: JPU JOB NO: 19440.20 DATE: 02/14/2020 v / J_ Q I-- (..1..( LO Z � I Q Lo < cv Q Z p 00 Q 0 J F- 0 � o a Z [L Q (n o 3: w Lu M 0 Qoo 0 Z za Z mo Q Q ?irnLu CD SHEET C3.1 No. 2 — Infiltration Maintenance Defect Conditions When Maintenance Is Results Expected When Component Needed Maintenance Is Performed General Trash & Debris See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). Poisonous/Noxious See "Detention Ponds" (No. 1). See "Detention Ponds" Vegetation (No. 1). Contaminants and See "Detention Ponds" (No. 1). See "Detention Ponds" Pollution (No. 1). Rodent Holes See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1) Storage Area Sediment Water ponding in infiltration pond after Sediment is removed rainfall ceases and appropriate time and/or facility is cleaned allowed for infiltration. Treatment basins so that infiltration system should infiltrate Water Quality Design Storm works according to Volume within 48 hours, and empty within design. 24 hours after cessation of most rain events. (A percolation test pit or test of facility indicates facility is only working at 90% of its designed capabilities. Test every 2 to 5 years. If two inches or more sediment is present, remove). Filter Bags (if Filled with Sediment and debris fill bag more than 1/2 Filter bag is replaced or applicable) Sediment and full. system is redesigned. Debris Rock Filters Sediment and By visual inspection, little or no water flows Gravel in rock filter is Debris through filter during heavy rain storms. replaced. Side Slopes of Erosion See "Detention Ponds" (No. 1). See "Detention Ponds" Pond (No. 1). Emergency Tree Growth See "Detention Ponds" (No. 1). See "Detention Ponds" Overflow Spillway (No. 1). and Berms over 4 feet in height. Piping See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). Emergency Rock Missing See "Detention Ponds" (No. 1). See "Detention Ponds" Overflow Spillway (No. 1). Erosion See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). Pre -settling Facility or sump 6" or designed sediment trap depth of Sediment is removed. Ponds and Vaults filled with Sediment sediment. and/or debris Volume V — Runoff Treatment BMPs — December 2014 4-35 No. 5 — Catch Basins Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed General Trash & Trash or debris which is located immediately No Trash or debris located Debris in front of the catch basin opening or is immediately in front of blocking inletting capacity of the basin by catch basin or on grate more than 10%. opening. Trash or debris (in the basin) that exceeds 60 No trash or debris in the percent of the sump depth as measured from catch basin. the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than a minimum of six inches clearance from the debris surface to the invert of the lowest pipe. Trash or debris in any inlet or outlet pipe Inlet and outlet pipes free blocking more than 1 /3 of its height. of trash or debris. Dead animals or vegetation that could No dead animals or generate odors that could cause complaints vegetation present within or dangerous gases (e.g., methane). the catch basin. Sediment Sediment (in the basin) that exceeds 60 No sediment in the catch percent of the sump depth as measured from basin the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than a minimum of 6 inches clearance from the sediment surface to the invert of the lowest pipe. Structure Top slab has holes larger than 2 square Top slab is free of holes Damage to inches or cracks wider than 1/4 inch and cracks. Frame and/or Top Slab (Intent is to make sure no material is running into basin). Frame not sitting flush on top slab, i.e., Frame is sitting flush on separation of more than 3/4 inch of the frame the riser rings or top slab from the top slab. Frame not securely and firmly attached. attached Fractures or Maintenance person judges that structure is Basin replaced or repaired Cracks in unsound. to design standards. Basin Walls/ Bottom Grout fillet has separated or cracked wider Pipe is regrouted and than 1/2 inch and longer than 1 foot at the secure at basin wall. joint of any inlet/outlet pipe or any evidence of soil particles entering catch basin through cracks. Settlement/ If failure of basin has created a safety, Basin replaced or repaired Misalignment function, or design problem. to design standards. Vegetation Vegetation growing across and blocking more No vegetation blocking than 10% of the basin opening. opening to basin. Vegetation growing in inlet/outlet pipe joints No vegetation or root that is more than six inches tall and less than growth present. six inches apart. Contamination See "Detention Ponds" (No. 1). No pollution present. and Pollution Volume V — Runoff Treatment BMPs — December 2014 4-38 No. 5 — Catch Basins Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed Catch Basin Cover Not in Cover is missing or only partially in place. Catch basin cover is Cover Place Any open catch basin requires maintenance. closed Locking Mechanism cannot be opened by one Mechanism opens with Mechanism maintenance person with proper tools. Bolts proper tools. Not Working into frame have less than 1/2 inch of thread. Cover Difficult One maintenance person cannot remove lid Cover can be removed by to Remove after applying normal lifting pressure. one maintenance person. (Intent is keep cover from sealing off access to maintenance.) Ladder Ladder Rungs Ladder is unsafe due to missing rungs, not Ladder meets design Unsafe securely attached to basin wall, standards and allows misalignment, rust, cracks, or sharp edges. maintenance person safe access. Metal Grates Grate opening Grate with opening wider than 7/8 inch. Grate opening meets (If Applicable) Unsafe design standards. Trash and Trash and debris that is blocking more than Grate free of trash and Debris 20% of grate surface inletting capacity. debris. Damaged or Grate missing or broken member(s) of the Grate is in place and Missing. grate. meets design standards. No. 6 �—is Barriers (e.g., Trash Racks) Maintenance fect Condition When Maintenance is Results Expec hen Components Needed Maintena s Performed General Trash and$Trash or debris that is plugging more B r cleared to design flow Debris 20% of the openings in the barrier. apacity. Metal Damaged/ Bars a ent out of shape more n 3 Bars in place with no bends more Missing inches. than 3/4 inch. Bars. Bars are! miss" mier Bars in place according to design. missing. 0,0 are loose and rust is causing % Barrier replaced or repaired to deterioration to any part of barrier. design standards. InI utlet Debris barrier missing or not attached to er firmly attached to pipe pe pipe Volume V — Runoff Treatment BMPs — December 2014 4-39 No. 8 — Typical Biofiltration Swale Maintenance Defect or Condition When Recommended Maintenance to Correct Component Problem Maintenance is Needed Problem General Sediment Sediment depth exceeds 2 Remove sediment deposits on grass Accumulation on inches. treatment area of the bio-Swale. When Grass finished, swale should be level from side to side and drain freely toward outlet. There should be no areas of standing water once inflow has ceased. Standing Water When water stands in the Any of the following may apply: remove swale between storms and sediment or trash blockages, improve does not drain freely. grade from head to foot of swale, remove clogged check dams, add underdrains or convert to a wet biofiltration swale. Flow spreader Flow spreader uneven or Level the spreader and clean so that flows clogged so that flows are not are spread evenly over entire swale width. uniformly distributed through entire swale width. Constant When small quantities of Add a low -flow pea -gravel drain the length Baseflow water continually flow through of the swale or by-pass the baseflow the swale, even when it has around the swale. been dry for weeks, and an eroded, muddy channel has formed in the swale bottom. Poor Vegetation When grass is sparse or bare Determine why grass growth is poor and Coverage or eroded patches occur in correct that condition. Re -plant with plugs more than 10% of the swale of grass from the upper slope: plant in the bottom. swale bottom at 8-inch intervals. Or re- seed into loosened, fertile soil. Vegetation When the grass becomes Mow vegetation or remove nuisance excessively tall (greater than vegetation so that flow not impeded. 10-inches); when nuisance Grass should be mowed to a height of 3 to weeds and other vegetation 4 inches. Remove grass clippings. starts to take over. Excessive Grass growth is poor because If possible, trim back over -hanging limbs Shading sunlight does not reach and remove brushy vegetation on swale. adjacent slopes. Inlet/Outlet Inlet/outlet areas clogged with Remove material so that there is no sediment and/or debris. clogging or blockage in the inlet and outlet area. Trash and Trash and debris Remove trash and debris from bioswale. Debris accumulated in the bio-swale. Accumulation Erosion/Scouring Eroded or scoured swale For ruts or bare areas less than 12 inches bottom due to flow wide, repair the damaged area by filling channelization, or higher with crushed gravel. If bare areas are flows. large, generally greater than 12 inches wide, the swale should be re -graded and re -seeded. For smaller bare areas, overseed when bare spots are evident, or take plugs of grass from the upper slope and plant in the swale bottom at 8-inch intervals. Volume V — Runoff Treatment BMPs — December 2014 4-41 Applicable Operational BMPs: • Eliminate unpermitted wastewater discharges to water, or surface water. , • Convey unpermitted discharges to a local sewer authority, or to other ap] Obtain appropriate state and local RecXnmended Additional Operati indus ' 1 facilities, conduct a survey to storm Zkains and to surface water/ sewer, ground if allowed by the for these discharges. BMPs: At commercial and wastewater discharge connections follows: • Conduct Xleld survey of bu' dings, particularly older buildings, and other Indust ' 1 areas to to to storm drains from buildings and paved surfaces. Note here thgAe join the public storm drain(s). • During non -storm r conditions inspect each storm drain for non- 0 dischar�allitted rd the locations of all non -stormwater discharges. Incl e discharges. • If useful, pre re a map of Nkch location of orm sewers, sani unpermit d discharges. Aerial such a iping schematics to fide and ow these on the map. Co an ysis tests to detect connecti .g., process water and stormw inspections of the storm drains area. Show on the map the known sewers, and permitted and p tos may be useful. Check records nti own side sewer connections Compare the observed locations of connections 'th the information on the map and revise the map accordingly. Note s ect connections that are inconsistent with the field survey. • Identify all connections to storm sewers or to surface wai'$f and take the actions specified above as applicable BMPs. S411 BMPs for Landscaping and Lawn/ Vegetation Management Description of Pollutant Sources: Landscaping can include grading, soil transfer, vegetation removal, pesticide and fertilizer applications, and watering. Stormwater contaminants include toxic organic compounds, heavy metals, oils, total suspended solids, coliform bacteria, fertilizers, and pesticides. Lawn and vegetation management can include control of objectionable weeds, insects, mold, bacteria, and other pests with pesticides. Examples include weed control on golf course lawns, access roads, and utility corridors and during landscaping; sap stain and insect control on lumber and logs; rooftop moss removal; killing nuisance rodents; fungicide application to patio decks, and residential lawn/plant care. It is possible to Volume IV - Source Control BMPs — December 2014 2-21 release toxic pesticides such as pentachlorophenol, carbamates, and organometallics to the environment by leaching and dripping from treated parts, container leaks, product misuse, and outside storage of pesticide contaminated materials and equipment. Poor management of the vegetation and poor application of pesticides or fertilizers can cause appreciable stormwater contamination. Pollutant Control Approach: Control of fertilizer and pesticide applications, soil erosion, and site debris to prevent contamination of stormwater. Develop and implement an Integrated Pest Management Plan (IPM) and use pesticides only as a last resort. Carefully apply pesticides/ herbicides, in accordance with label instructions. Maintain appropriate vegetation, with proper fertilizer application where practicable, to control erosion and the discharge of stormwater pollutants. Where practicable grow plant species appropriate for the site, or adjust the soil properties of the subject site to grow desired plant species. Applicable Operational BMPs for Landscaping: • Install engineered soil/landscape systems to improve the infiltration and regulation of stormwater in landscaped areas. Do not dispose of collected vegetation into waterways or storm sewer systems. Recommended Additional Operational BMPs for Landscaping: • Conduct mulch -mowing whenever practicable • Dispose of grass clippings, leaves, sticks, or other collected vegetation, by composting, if feasible. • Use mulch or other erosion control measures on soils exposed for more than one week during the dry season or two days during the rainy season. • Store and maintain appropriate oil and chemical spill cleanup materials in readily accessible locations when using oil or other chemicals. Ensure that employees are familiar with proper spill cleanup procedures. • Till fertilizers into the soil rather than dumping or broadcasting onto the surface. Determine the proper fertilizer application rate for the types of soil and vegetation encountered. • Till a topsoil mix or composted organic material into the soil to create a well -mixed transition layer that encourages deeper root systems and drought -resistant plants. • Use manual and/or mechanical methods of vegetation removal rather than applying herbicides, where practical. Volume IV - Source Control BMPs — December 2014 2-22 Applicable Operational BMPs for the Use of Pesticides: • Develop and implement an IPM (See section on IPM in Applicable Operational BMPs for Vegetation Many ems) and use pesticides only as a last resort. • Implement a pesticide -use plan and include at a minimum: a list of selected pesticides and their specific uses; brands, formulations, application methods and quantities to be used; equipment use and maintenance procedures; safety, storage, and disposal methods; and monitoring, record keeping, and public notice procedures. All procedures shall conform to the requirements of Chapter 17.21 RCW and Chapter 16-228 WAC (Appendix IV-D R.7). • Choose the least toxic pesticide available that is capable of reducing the infestation to acceptable levels. The pesticide should readily degrade in the environment and/or have properties that strongly bind it to the soil. Conduct any pest control activity at the life stage when the pest is most vulnerable. For example, if it is necessary to use a Bacillus thurin ig'ens application to control tent caterpillars, apply it to the material before the caterpillars cocoon or it will be ineffective. Any method used should be site -specific and not used wholesale over a wide area. • Apply the pesticide according to label directions. Do not apply pesticides in quantities that exceed manufacturer's instructions. • Mix the pesticides and clean the application equipment in an area where accidental spills will not enter surface or ground waters, and will not contaminate the soil. • Store pesticides in enclosed areas or in covered impervious containment. Do not discharge pesticide contaminated stormwater or spills/leaks of pesticides to storm sewers. Do not hose down the paved areas to a storm sewer or conveyance ditch. Store and maintain appropriate spill cleanup materials in a location known to all near the storage area. • Clean up any spilled pesticides. Keep pesticide contaminated waste materials in designated covered and contained areas. • The pesticide application equipment must be capable of immediate shutoff in the event of an emergency. • Spraying pesticides within 100 feet of open waters including wetlands, ponds, and rivers, streams, creeks, sloughs and any drainage ditch or channel that leads to open water may have additional regulatory requirements beyond just following the pesticide product label. Additional requirements may include: Obtaining a discharge permit from Ecology. Obtaining a permit from the local jurisdiction. Using an aquatic labeled pesticide. Volume IV - Source Control BMPs — December 2014 2-23 obtain a publication entitled "Suspended, Canceled, and Restricted Pesticides" which lists all restricted pesticides and the specific uses that are allowed. Applicable Operational BMPs for Vegetation Management: Use at least an eight -inch "topsoil' layer with at least 8 percent organic matter to provide a sufficient vegetation -growing medium. Amending existing landscapes and turf systems by increasing the percent organic matter and depth of topsoil can substantially improve the permeability of the soil, the disease and drought resistance of the vegetation, and reduce fertilizer demand. This reduces the demand for fertilizers, herbicides, and pesticides. Organic matter is the least water-soluble form of nutrients that can be added to the soil. Composted organic matter generally releases only between 2 and 10 percent of its total nitrogen annually, and this release corresponds closely to the plant growth cycle. Return natural plant debris and mulch to the soil, to continue recycling nutrients indefinitely. Select the appropriate turfgrass mixture for the climate and soil type. Certain tall fescues and rye grasses resist insect attack because the symbiotic endophytic fungi found naturally in their tissues repel or kill common leaf and stem -eating lawn insects. However, they do not, repel root -feeding lawn pests such as Crane Fly larvae, and are toxic to ruminants such as cattle and sheep. The fungus causes no known adverse effects to the host plant or to humans. Endophytic grasses are commercially available; use them in areas such as parks or golf courses where grazing does not occur. Local agricultural or gardening resources such as Washington State University Extension office can offer advice on which types of grass are best suited to the area and soil type. • Use the following seeding and planting BMPs, or equivalent BMPs to obtain information on grass mixtures, temporary and permanent seeding procedures, maintenance of a recently planted area, and fertilizer application rates: Temporary and Permanent Seeding, Mulching, Plastic Covering, and Sodding as described in Volume II. Adjusting the soil properties of the subject site can assist in selection of desired plant species. For example, design a constructed wetland to resist the invasion of reed canary grass by layering specific strata of organic matters (e.g., composted forest product residuals) and creating a mildly acidic pH and carbon -rich soil medium. Consult a soil restoration specialist for site -specific conditions. • Aerate lawns regularly in areas of heavy use where the soil tends to become compacted. Conduct aeration while the grasses in the lawn are growing most vigorously. Remove layers of thatch greater than 3/4-inch deep. Volume IV - Source Control BMPs — December 2014 2-25 Mowing is a stress -creating activity for turfgrass. Grass decreases its productivity when mown too short and there is less growth of roots and rhizomes. The turf becomes less tolerant of environmental stresses, more disease prone and more reliant on outside means such as pesticides, fertilizers, and irrigation to remain healthy. Set the mowing height at the highest acceptable level and mow at times and intervals designed to minimize stress on the turf. Generally mowing only 1/3 of the grass blade height will prevent stressing the turf. Irrigation: The depth from which a plant normally extracts water depends on the rooting depth of the plant. Appropriately irrigated lawn grasses normally root in the top 6 to 12 inches of soil; lawns irrigated on a daily basis often root only in the top 1 inch of soil. Improper irrigation can encourage pest problems, leach nutrients, and make a lawn completely dependent on artificial watering. The amount of water applied depends on the normal rooting depth of the turfgrass species used, the available water holding capacity of the soil, and the efficiency of the irrigation system. Consult with the local water utility, Conservation District, or Cooperative Extension office to help determine optimum irrigation practices. Fertilizer Management: Turfgrass is most responsive to nitrogen fertilization, followed by potassium and phosphorus. Fertilization needs vary by site depending on plant, soil, and climatic conditions. Evaluation of soil nutrient levels through regular testing ensures the best possible efficiency and economy of fertilization. For details on soils testing, contact the local Conservation District, a soils testing professional, or a Washington State University Extension office. Apply fertilizers in amounts appropriate for the target vegetation and at the time of year that minimizes losses to surface and ground waters. Do not fertilize when the soil is dry. Alternatively, do not apply fertilizers within three days prior to predicted rainfall. The longer the period between fertilizer application and either rainfall or irrigation, the less fertilizer runoff occurs. Use slow release fertilizers such as methylene urea, IDBU, or resin coated fertilizers when appropriate, generally in the spring. Use of slow release fertilizers is especially important in areas with sandy or gravelly soils. • Time the fertilizer application to periods of maximum plant uptake. Ecology generally recommends application in the fall and spring, although Washington State University turf specialists recommend four fertilizer applications per year. Volume IV - Source Control BMPs — December 2014 2-26 Westgate Station - CG #19440 Drainage Report March 22, 2023 Section VII, Page 5 SAMPLE ACTIVITY LOG DATE FACILITY MAINTENANCE PERFORMED RESULTS/ NOTES 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 March 22, 2023 Drainage Report Appendix A, Page 1 Appendix A — WWHM Report Appendix A Summary: A-1 Narrative A-1 Basin Delineation A-2 Edmonds Way Direct Discharge Requirement A-3 Edmonds Stormwater Addendum Water Quality Requirement A-4 WWHM Model Output Narrative Calculations in this section verify compliance with the Edmonds Way direct discharge requirement, the Edmonds Stormwater Addendum water quality requirements, and the Low Impact Development (LID) Standard. The majority of developed areas on the site are fully infiltrated, and any overflow is to be routed to the storm main located in Edmonds Way. The WWHM model depicts five infiltrating BMPs: two infiltration trenches and three rain gardens. Basin Delineation In the predeveloped condition, three basins represent the total on and off -site area contributing to the BMPs. The first, labeled "Off -site (West)" represents the off -site areas of the proposed western driveway. The second, labeled "On -site" represents the areas on the property. The third, labeled "Off -site (North)" represents the areas of a building to the north of the site (see Section I for details on this off -site portion). See WWHM Model Output for details. In the developed condition, the basins are delineated slightly differently. The "Off -site (West)" basin includes the entire western driveway. This is so the model can route all flows from the western driveway to one infiltrating BMP, called "West Infiltration Trench". The "On -site" basin is now both smaller, and split into two separate basins. The first basin, labeled "Roof", contains only the roof of the proposed building on site. The second basin, labeled "On -site w/o roof' accounts for the remaining impervious and pervious surfaces on site. The "Off -site (North)" basin remains the same. The "Off -site (West)" basin flows to the "West Infiltration Trench". The "Roof' and "Off -site (North)" basins flow to the "East Infiltration Trench". The overflow from "East Infiltration Trench" is routed to "Bioretention 1". "Bioretention 1" also receives runoff from the remaining on -site areas, from "On -site w/o roof'. Any remaining overflow is subsequently routed to rain gardens "Bioretention 2" and "Bioretention 3", after which it is routed to the Edmonds Way storm main. See Figure A-1 for a visual representation. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 2 OFF -SITE ( EST) ROOF O F-SITE (NORTH) O ( -SITE /O ROOF) EAST INFILTRATION . . TRENCH WEST INFILTRATION TRENCH BIORETE TION #1 BIORETENTION #2 1 BIORETE TION #3 Figure A-1: Developed basin to BMP flow chart Edmonds Way Direct Discharge Requirement As discussed in Section III, project runoff not managed by the rain gardens or infiltration trenches must meet the Edmonds Way direct discharge requirement. This requires that the post -development 10- and 100-year recurrence interval peak flows do not exceed 0.25 and 0.45 cfs per acre of impervious surface, respectively. See calculations for the target values below. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 3 10 Year target flow 0.767 x 0.25 cfs = 0.192 cfs 100 Year target flow 0.767 x 0.45 cfs = 0.345 cfs The WWHM output indicates that the values for the 10- and 100-year flows are both 0.000. This is below the target values calculated, and therefore the requirement is met. See page A-19 and A-20 for model outputs. Edmonds Stormwater Addendum Water Quality Requirement As discussed in Section III, an infiltration system must infiltrate more than 91% of the influent runoff to meet water quality requirements. The runoff must also be infiltrated through soils with a cation exchange capacity (CEC) of 5 meq/100 g or greater. The bioretention soil media, used the rain gardens, will meet this requirement. A 1.5' thick treatment layer of sand with a CEC greater than 5 meq/100 g will be placed under the proposed west infiltration trench to meet the treatment requirement. A portion of the proposed pollution generating surfaces are routed to Bioretention #1, which infiltrates 97.8% of flow routed to it. The remaining PHGS is routed to the west infiltration trench which infiltrates 100% of the inflow. The following table illustrates the calculations for amount of runoff infiltrated by the on -site BMPs Table A-1: Runoff infiltrated by on -site BMPs. BMP Name Runoff Received (% of original) Runoff Infiltrated (% of incoming) Runoff Remaining (% of original) West Infiltration Trench 100 100 0 East Infiltration Trench 100 95.6 4.4 Bioretention #1 100 97.8 2.2 Bioretention #2 2.2 53.6 1.0 Bioretention #3 1.0 26.7 0.7 The West Infiltration Trench fully infiltrates (100%). Bioretention #1, infiltrates 97.8% of runoff routed to it. This value is greater than 91% and thus the water quality treatment requirement is met. The following model outputs were calculated by WWHM. Included is the LID standard. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 4 WWHM2012 PROJECT REPORT Project Name: Westgate Trenches + RGs 12.8.22 Site Name: Westgate Station Site Address: 9601 Edmonds Way City : Edmonds Report Date: 12/8/2022 MGS Regoin Puget East Data Start 1901/10/1 Data End : 2058/09/30 DOT Data Number: 03 Version Date: 2019/09/13 Version : 4.2.17 Low Flow Threshold for POC 1 : 50 Percent of the 2 Year High Flow Threshold for POC 1: 50 year PREDEVELOPED LAND USE Name : Off -site (West) Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Flat .019 Pervious Total 0.019 Impervious Land Use acre Impervious Total 0 Basin Total 0.019 Element Flows To: Surface Interflow Name : On -site Bypass: No GroundWater: No Pervious Land Use C, Forest, Flat acre .579 Groundwater 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 5 C, Forest, Mod .214 C, Forest, Steep .307 Pervious Total 1.1 Impervious Land Use acre Impervious Total 0 Basin Total 1.1 Element Flows To: Surface Interflow Name : Off -site (North) Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod .097 Pervious Total 0.097 Impervious Land Use acre Impervious Total 0 Basin Total 0.097 Element Flows To: Surface Interflow MITIGATED LAND USE Name : Off -site (West) Bypass: No GroundWater: No Pervious Land Use Pervious Total Impervious Land Use C �M ENGINEERING acre 0 acre Groundwater Groundwater 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 6 ROADS FLAT 0.05 Impervious Total 0.05 Basin Total 0.05 Element Flows To: Surface Interflow Groundwater West Infiltration TrenWest Infiltration Tren Name : Roof Bypass: No GroundWater: No Pervious Land Use Pervious Total Impervious Land Use ROOF TOPS FLAT Impervious Total Basin Total acre 0 acre 0.386 0.386 0.386 Element Flows To: Surface Interflow Groundwater East Infiltration TrenEast Infiltration Tren Name : Off -site (North) Bypass: No GroundWater: No Pervious Land Use acre Pervious Total 0 Impervious Land Use acre ROOF TOPS FLAT 0.097 Impervious Total 0.097 Basin Total 0.097 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 7 Element Flows To: Surface Interflow Groundwater East Infiltration TrenEast Infiltration Tren Name : On -site (w/o roof) Bypass: No Groundwater: No Pervious Land Use acre C, Forest, Steep .25 C, Lawn, Flat .152 C, Lawn, Steep .046 Pervious Total 0.448 Impervious Land Use acre ROADS FLAT 0.151 SIDEWALKS FLAT 0.083 Impervious Total 0.234 Basin Total 0.682 Element Flows To: Surface Interflow Groundwater Surface retention 1 Surface retention 1 Name : West Infiltration Trench Bottom Length: 27.00 ft. Bottom Width: 13.00 ft. Trench bottom slope 1: 0 To 1 Trench Left side slope 0: 0 To 1 Trench right side slope 2: 0 To 1 Material thickness of first layer: 3 Pour Space of material for first layer: 0.3 Material thickness of second layer: 0 Pour Space of material for second layer: 0 Material thickness of third layer: 0 Pour Space of material for third layer: 0 Infiltration On Infiltration rate: 0.63 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 18.271 Total Volume Through Riser (ac-ft.): 0 Total Volume Through Facility (ac-ft.): 18.271 Percent Infiltrated: 100 Total Precip Applied to Facility: 0 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 8 Total Evap From Facility: 0 Discharge Structure Riser Height: 2.95 ft. Riser Diameter: 12 in. Element Flows To: Outlet 1 Outlet 2 Gravel Trench Bed Hydraulic Table Stage(feet) Area(ac.) Volume(ac-£t.) Discharge(c£s) In£ilt(c£s) 0.0000 0.008 0.000 0.000 0.000 0.0333 0.008 0.000 0.000 0.005 0.0667 0.008 0.000 0.000 0.005 0.1000 0.008 0.000 0.000 0.005 0.1333 0.008 0.000 0.000 0.005 0.1667 0.008 0.000 0.000 0.005 0.2000 0.008 0.000 0.000 0.005 0.2333 0.008 0.000 0.000 0.005 0.2667 0.008 0.000 0.000 0.005 0.3000 0.008 0.000 0.000 0.005 0.3333 0.008 0.000 0.000 0.005 0.3667 0.008 0.000 0.000 0.005 0.4000 0.008 0.001 0.000 0.005 0.4333 0.008 0.001 0.000 0.005 0.4667 0.008 0.001 0.000 0.005 0.5000 0.008 0.001 0.000 0.005 0.5333 0.008 0.001 0.000 0.005 0.5667 0.008 0.001 0.000 0.005 0.6000 0.008 0.001 0.000 0.005 0.6333 0.008 0.001 0.000 0.005 0.6667 0.008 0.001 0.000 0.005 0.7000 0.008 0.001 0.000 0.005 0.7333 0.008 0.001 0.000 0.005 0.7667 0.008 0.001 0.000 0.005 0.8000 0.008 0.001 0.000 0.005 0.8333 0.008 0.002 0.000 0.005 0.8667 0.008 0.002 0.000 0.005 0.9000 0.008 0.002 0.000 0.005 0.9333 0.008 0.002 0.000 0.005 0.9667 0.008 0.002 0.000 0.005 1.0000 0.008 0.002 0.000 0.005 1.0333 0.008 0.002 0.000 0.005 1.0667 0.008 0.002 0.000 0.005 1.1000 0.008 0.002 0.000 0.005 1.1333 0.008 0.002 0.000 0.005 1.1667 0.008 0.002 0.000 0.005 1.2000 0.008 0.002 0.000 0.005 1.2333 0.008 0.003 0.000 0.005 1.2667 0.008 0.003 0.000 0.005 1.3000 0.008 0.003 0.000 0.005 1.3333 0.008 0.003 0.000 0.005 1.3667 0.008 0.003 0.000 0.005 1.4000 0.008 0.003 0.000 0.005 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 9 1.4333 0.008 0.003 0.000 0.005 1.4667 0.008 0.003 0.000 0.005 1.5000 0.008 0.003 0.000 0.005 1.5333 0.008 0.003 0.000 0.005 1.5667 0.008 0.003 0.000 0.005 1.6000 0.008 0.003 0.000 0.005 1.6333 0.008 0.003 0.000 0.005 1.6667 0.008 0.004 0.000 0.005 1.7000 0.008 0.004 0.000 0.005 1.7333 0.008 0.004 0.000 0.005 1.7667 0.008 0.004 0.000 0.005 1.8000 0.008 0.004 0.000 0.005 1.8333 0.008 0.004 0.000 0.005 1.8667 0.008 0.004 0.000 0.005 1.9000 0.008 0.004 0.000 0.005 1.9333 0.008 0.004 0.000 0.005 1.9667 0.008 0.004 0.000 0.005 2.0000 0.008 0.004 0.000 0.005 2.0333 0.008 0.004 0.000 0.005 2.0667 0.008 0.005 0.000 0.005 2.1000 0.008 0.005 0.000 0.005 2.1333 0.008 0.005 0.000 0.005 2.1667 0.008 0.005 0.000 0.005 2.2000 0.008 0.005 0.000 0.005 2.2333 0.008 0.005 0.000 0.005 2.2667 0.008 0.005 0.000 0.005 2.3000 0.008 0.005 0.000 0.005 2.3333 0.008 0.005 0.000 0.005 2.3667 0.008 0.005 0.000 0.005 2.4000 0.008 0.005 0.000 0.005 2.4333 0.008 0.005 0.000 0.005 2.4667 0.008 0.006 0.000 0.005 2.5000 0.008 0.006 0.000 0.005 2.5333 0.008 0.006 0.000 0.005 2.5667 0.008 0.006 0.000 0.005 2.6000 0.008 0.006 0.000 0.005 2.6333 0.008 0.006 0.000 0.005 2.6667 0.008 0.006 0.000 0.005 2.7000 0.008 0.006 0.000 0.005 2.7333 0.008 0.006 0.000 0.005 2.7667 0.008 0.006 0.000 0.005 2.8000 0.008 0.006 0.000 0.005 2.8333 0.008 0.006 0.000 0.005 2.8667 0.008 0.006 0.000 0.005 2.9000 0.008 0.007 0.000 0.005 2.9333 0.008 0.007 0.000 0.005 2.9667 0.008 0.007 0.022 0.005 3.0000 0.008 0.007 0.118 0.005 Name : East Infiltration Trench Bottom Length: 49.00 ft. Bottom Width: 20.00 ft. Trench bottom slope 1: 0 To 1 Trench Left side slope 0: 0 To 1 Trench right side slope 2: 0 To 1 Material thickness of first layer: 3 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 10 Pour Space of material for first layer: 0.3 Material thickness of second layer: 0 Pour Space of material for second layer: 0 Material thickness of third layer: 0 Pour Space of material for third layer: 0 Infiltration On Infiltration rate: 0.63 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 169.501 Total Volume Through Riser (ac-ft.): 7.811 Total Volume Through Facility (ac-ft.): 177.312 Percent Infiltrated: 95.59 Total Precip Applied to Facility: 0 Total Evap From Facility: 0 Discharge Structure Riser Height: 2.95 ft. Riser Diameter: 18 in. Element Flows To: Outlet 1 Outlet 2 Surface retention 1 Gravel Trench Bed Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.022 0.000 0.000 0.000 0.0333 0.022 0.000 0.000 0.014 0.0667 0.022 0.000 0.000 0.014 0.1000 0.022 0.000 0.000 0.014 0.1333 0.022 0.000 0.000 0.014 0.1667 0.022 0.001 0.000 0.014 0.2000 0.022 0.001 0.000 0.014 0.2333 0.022 0.001 0.000 0.014 0.2667 0.022 0.001 0.000 0.014 0.3000 0.022 0.002 0.000 0.014 0.3333 0.022 0.002 0.000 0.014 0.3667 0.022 0.002 0.000 0.014 0.4000 0.022 0.002 0.000 0.014 0.4333 0.022 0.002 0.000 0.014 0.4667 0.022 0.003 0.000 0.014 0.5000 0.022 0.003 0.000 0.014 0.5333 0.022 0.003 0.000 0.014 0.5667 0.022 0.003 0.000 0.014 0.6000 0.022 0.004 0.000 0.014 0.6333 0.022 0.004 0.000 0.014 0.6667 0.022 0.004 0.000 0.014 0.7000 0.022 0.004 0.000 0.014 0.7333 0.022 0.004 0.000 0.014 0.7667 0.022 0.005 0.000 0.014 0.8000 0.022 0.005 0.000 0.014 0.8333 0.022 0.005 0.000 0.014 0.8667 0.022 0.005 0.000 0.014 0.9000 0.022 0.006 0.000 0.014 0.9333 0.022 0.006 0.000 0.014 0.9667 0.022 0.006 0.000 0.014 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 11 1.0000 0.022 0.006 0.000 0.014 1.0333 0.022 0.007 0.000 0.014 1.0667 0.022 0.007 0.000 0.014 1.1000 0.022 0.007 0.000 0.014 1.1333 0.022 0.007 0.000 0.014 1.1667 0.022 0.007 0.000 0.014 1.2000 0.022 0.008 0.000 0.014 1.2333 0.022 0.008 0.000 0.014 1.2667 0.022 0.008 0.000 0.014 1.3000 0.022 0.008 0.000 0.014 1.3333 0.022 0.009 0.000 0.014 1.3667 0.022 0.009 0.000 0.014 1.4000 0.022 0.009 0.000 0.014 1.4333 0.022 0.009 0.000 0.014 1.4667 0.022 0.009 0.000 0.014 1.5000 0.022 0.010 0.000 0.014 1.5333 0.022 0.010 0.000 0.014 1.5667 0.022 0.010 0.000 0.014 1.6000 0.022 0.010 0.000 0.014 1.6333 0.022 0.011 0.000 0.014 1.6667 0.022 0.011 0.000 0.014 1.7000 0.022 0.011 0.000 0.014 1.7333 0.022 0.011 0.000 0.014 1.7667 0.022 0.011 0.000 0.014 1.8000 0.022 0.012 0.000 0.014 1.8333 0.022 0.012 0.000 0.014 1.8667 0.022 0.012 0.000 0.014 1.9000 0.022 0.012 0.000 0.014 1.9333 0.022 0.013 0.000 0.014 1.9667 0.022 0.013 0.000 0.014 2.0000 0.022 0.013 0.000 0.014 2.0333 0.022 0.013 0.000 0.014 2.0667 0.022 0.013 0.000 0.014 2.1000 0.022 0.014 0.000 0.014 2.1333 0.022 0.014 0.000 0.014 2.1667 0.022 0.014 0.000 0.014 2.2000 0.022 0.014 0.000 0.014 2.2333 0.022 0.015 0.000 0.014 2.2667 0.022 0.015 0.000 0.014 2.3000 0.022 0.015 0.000 0.014 2.3333 0.022 0.015 0.000 0.014 2.3667 0.022 0.016 0.000 0.014 2.4000 0.022 0.016 0.000 0.014 2.4333 0.022 0.016 0.000 0.014 2.4667 0.022 0.016 0.000 0.014 2.5000 0.022 0.016 0.000 0.014 2.5333 0.022 0.017 0.000 0.014 2.5667 0.022 0.017 0.000 0.014 2.6000 0.022 0.017 0.000 0.014 2.6333 0.022 0.017 0.000 0.014 2.6667 0.022 0.018 0.000 0.014 2.7000 0.022 0.018 0.000 0.014 2.7333 0.022 0.018 0.000 0.014 2.7667 0.022 0.018 0.000 0.014 2.8000 0.022 0.018 0.000 0.014 2.8333 0.022 0.019 0.000 0.014 2.8667 0.022 0.019 0.000 0.014 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 12 2.9000 0.022 0.019 0.000 0.014 2.9333 0.022 0.019 0.000 0.014 2.9667 0.022 0.020 0.034 0.014 3.0000 0.022 0.020 0.177 0.014 Name : Bioretention 1 Bottom Length: 50.00 ft. Bottom Width: 11.00 ft. Material thickness of first layer: 1.5 Material type for first layer: SMMWW 12 in/hr Material thickness of second layer: 1.5 Material type for second layer: GRAVEL Material thickness of third layer: 0 Material type for third layer: GRAVEL Infiltration On Infiltration rate: 2.88 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 133.188 Total Volume Through Riser (ac-ft.): 3.05 Total Volume Through Facility (ac-ft.): 136.238 Percent Infiltrated: 97.76 Total Precip Applied to Facility: 5.511 Total Evap From Facility: 3.697 Underdrain not used Discharge Structure Riser Height: 0.5 ft. Riser Diameter: 18 in. Element Flows To: Outlet 1 Outlet 2 Surface retention 2 Bioretention 1 Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.0126 0.0000 0.0000 0.0000 0.0495 0.0126 0.0003 0.0000 0.0000 0.0989 0.0126 0.0006 0.0000 0.0000 0.1484 0.0126 0.0009 0.0000 0.0000 0.1978 0.0126 0.0011 0.0000 0.0009 0.2473 0.0126 0.0014 0.0000 0.0015 0.2967 0.0126 0.0017 0.0000 0.0023 0.3462 0.0126 0.0020 0.0000 0.0025 0.3956 0.0126 0.0023 0.0000 0.0034 0.4451 0.0126 0.0026 0.0000 0.0047 0.4945 0.0126 0.0029 0.0000 0.0064 0.5440 0.0126 0.0031 0.0000 0.0083 0.5934 0.0126 0.0034 0.0000 0.0102 0.6429 0.0126 0.0037 0.0000 0.0106 0.6923 0.0126 0.0040 0.0000 0.0133 0.7418 0.0126 0.0043 0.0000 0.0163 0.7912 0.0126 0.0046 0.0000 0.0197 0.8407 0.0126 0.0049 0.0000 0.0235 0.8901 0.0126 0.0051 0.0000 0.0249 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 13 0.9396 0.0126 0.0054 0.0000 0.0278 0.9890 0.0126 0.0057 0.0000 0.0324 1.0385 0.0126 0.0060 0.0000 0.0367 1.0879 0.0126 0.0063 0.0000 0.0367 1.1374 0.0126 0.0066 0.0000 0.0367 1.1868 0.0126 0.0069 0.0000 0.0367 1.2363 0.0126 0.0071 0.0000 0.0367 1.2857 0.0126 0.0074 0.0000 0.0367 1.3352 0.0126 0.0077 0.0000 0.0367 1.3846 0.0126 0.0080 0.0000 0.0367 1.4341 0.0126 0.0083 0.0000 0.0367 1.4835 0.0126 0.0086 0.0000 0.0367 1.5330 0.0126 0.0088 0.0000 0.0367 1.5824 0.0126 0.0091 0.0000 0.0367 1.6319 0.0126 0.0093 0.0000 0.0367 1.6813 0.0126 0.0096 0.0000 0.0367 1.7308 0.0126 0.0099 0.0000 0.0367 1.7802 0.0126 0.0101 0.0000 0.0367 1.8297 0.0126 0.0104 0.0000 0.0367 1.8791 0.0126 0.0106 0.0000 0.0367 1.9286 0.0126 0.0109 0.0000 0.0367 1.9780 0.0126 0.0112 0.0000 0.0367 2.0275 0.0126 0.0114 0.0000 0.0367 2.0769 0.0126 0.0117 0.0000 0.0367 2.1264 0.0126 0.0119 0.0000 0.0367 2.1758 0.0126 0.0122 0.0000 0.0367 2.2253 0.0126 0.0125 0.0000 0.0367 2.2747 0.0126 0.0127 0.0000 0.0367 2.3242 0.0126 0.0130 0.0000 0.0367 2.3736 0.0126 0.0132 0.0000 0.0367 2.4231 0.0126 0.0135 0.0000 0.0367 2.4725 0.0126 0.0137 0.0000 0.0367 2.5220 0.0126 0.0140 0.0000 0.0367 2.5714 0.0126 0.0143 0.0000 0.0367 2.6209 0.0126 0.0145 0.0000 0.0367 2.6703 0.0126 0.0148 0.0000 0.0367 2.7198 0.0126 0.0150 0.0000 0.0367 2.7692 0.0126 0.0153 0.0000 0.0367 2.8187 0.0126 0.0156 0.0000 0.0367 2.8681 0.0126 0.0158 0.0000 0.0367 2.9176 0.0126 0.0161 0.0000 0.0367 2.9670 0.0126 0.0163 0.0000 0.0367 3.0000 0.0126 0.0165 0.0000 0.0367 Surface retention 1 Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) To Amended(cfs) Wetted Surface 3.0000 0.0126 0.0165 0.0000 0.1528 0.0000 3.0495 0.0126 0.0171 0.0000 0.1528 0.0000 3.0989 0.0126 0.0178 0.0000 0.1629 0.0000 3.1484 0.0126 0.0184 0.0000 0.1679 0.0000 3.1978 0.0126 0.0190 0.0000 0.1729 0.0000 3.2473 0.0126 0.0196 0.0000 0.1780 0.0000 3.2967 0.0126 0.0203 0.0000 0.1830 0.0000 3.3462 0.0126 0.0209 0.0000 0.1880 0.0000 3.3956 0.0126 0.0215 0.0000 0.1931 0.0000 3.4451 0.0126 0.0221 0.0000 0.1981 0.0000 3.4945 0.0126 0.0228 0.0000 0.2031 0.0000 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 14 3.5440 0.0126 0.0234 0.1466 0.2082 0.0000 3.5934 0.0126 0.0240 0.4535 0.2132 0.0000 3.6429 0.0126 0.0246 0.8548 0.2183 0.0000 3.6923 0.0126 0.0253 1.3261 0.2233 0.0000 3.7418 0.0126 0.0259 1.8479 0.2283 0.0000 3.7912 0.0126 0.0265 2.4011 0.2334 0.0000 3.8407 0.0126 0.0271 2.9662 0.2384 0.0000 3.8901 0.0126 0.0278 3.5234 0.2434 0.0000 3.9396 0.0126 0.0284 4.0534 0.2485 0.0000 3.9890 0.0126 0.0290 4.5388 0.2535 0.0000 4.0385 0.0126 0.0296 4.9654 0.2585 0.0000 4.0879 0.0126 0.0302 5.3242 0.2636 0.0000 4.1374 0.0126 0.0309 5.6134 0.2686 0.0000 4.1868 0.0126 0.0315 5.8404 0.2737 0.0000 4.2363 0.0126 0.0321 6.0242 0.2787 0.0000 4.2857 0.0126 0.0327 6.2817 0.2837 0.0000 4.3352 0.0126 0.0334 6.4763 0.2888 0.0000 4.3846 0.0126 0.0340 6.6653 0.2938 0.0000 4.4341 0.0126 0.0346 6.8491 0.2988 0.0000 4.4835 0.0126 0.0352 7.0280 0.3039 0.0000 4.5000 0.0126 0.0355 7.2025 0.3056 0.0000 Name : Surface retention 1 Element Flows To: Outlet 1 Outlet 2 Surface retention 2 Bioretention 1 Name : Bioretention 2 Bottom Length: 37.00 ft. Bottom Width: 11.00 ft. Material thickness of first layer: 1.5 Material type for first layer: SMMWW 12 in/hr Material thickness of second layer: 1.5 Material type for second layer: GRAVEL Material thickness of third layer: 0 Material type for third layer: GRAVEL Infiltration On Infiltration rate: 0.63 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 1.626 Total Volume Through Riser (ac-ft.): 1.407 Total Volume Through Facility (ac-ft.): 3.033 Percent Infiltrated: 53.61 Total Precip Applied to Facility: 0.067 Total Evap From Facility: 0.084 Underdrain not used Discharge Structure Riser Height: 0.5 ft. Riser Diameter: 18 in. Element Flows To: Outlet 1 Outlet 2 Surface retention 3 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 15 Bioretention 2 Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.0093 0.0000 0.0000 0.0000 0.0495 0.0093 0.0002 0.0000 0.0000 0.0989 0.0093 0.0004 0.0000 0.0000 0.1484 0.0093 0.0006 0.0000 0.0000 0.1978 0.0093 0.0008 0.0000 0.0006 0.2473 0.0093 0.0011 0.0000 0.0011 0.2967 0.0093 0.0013 0.0000 0.0017 0.3462 0.0093 0.0015 0.0000 0.0018 0.3956 0.0093 0.0017 0.0000 0.0025 0.4451 0.0093 0.0019 0.0000 0.0035 0.4945 0.0093 0.0021 0.0000 0.0047 0.5440 0.0093 0.0023 0.0000 0.0059 0.5934 0.0093 0.0025 0.0000 0.0059 0.6429 0.0093 0.0027 0.0000 0.0059 0.6923 0.0093 0.0030 0.0000 0.0059 0.7418 0.0093 0.0032 0.0000 0.0059 0.7912 0.0093 0.0034 0.0000 0.0059 0.8407 0.0093 0.0036 0.0000 0.0059 0.8901 0.0093 0.0038 0.0000 0.0059 0.9396 0.0093 0.0040 0.0000 0.0059 0.9890 0.0093 0.0042 0.0000 0.0059 1.0385 0.0093 0.0044 0.0000 0.0059 1.0879 0.0093 0.0046 0.0000 0.0059 1.1374 0.0093 0.0049 0.0000 0.0059 1.1868 0.0093 0.0051 0.0000 0.0059 1.2363 0.0093 0.0053 0.0000 0.0059 1.2857 0.0093 0.0055 0.0000 0.0059 1.3352 0.0093 0.0057 0.0000 0.0059 1.3846 0.0093 0.0059 0.0000 0.0059 1.4341 0.0093 0.0061 0.0000 0.0059 1.4835 0.0093 0.0063 0.0000 0.0059 1.5330 0.0093 0.0065 0.0000 0.0059 1.5824 0.0093 0.0067 0.0000 0.0059 1.6319 0.0093 0.0069 0.0000 0.0059 1.6813 0.0093 0.0071 0.0000 0.0059 1.7308 0.0093 0.0073 0.0000 0.0059 1.7802 0.0093 0.0075 0.0000 0.0059 1.8297 0.0093 0.0077 0.0000 0.0059 1.8791 0.0093 0.0079 0.0000 0.0059 1.9286 0.0093 0.0081 0.0000 0.0059 1.9780 0.0093 0.0083 0.0000 0.0059 2.0275 0.0093 0.0084 0.0000 0.0059 2.0769 0.0093 0.0086 0.0000 0.0059 2.1264 0.0093 0.0088 0.0000 0.0059 2.1758 0.0093 0.0090 0.0000 0.0059 2.2253 0.0093 0.0092 0.0000 0.0059 2.2747 0.0093 0.0094 0.0000 0.0059 2.3242 0.0093 0.0096 0.0000 0.0059 2.3736 0.0093 0.0098 0.0000 0.0059 2.4231 0.0093 0.0100 0.0000 0.0059 2.4725 0.0093 0.0102 0.0000 0.0059 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 16 2.5220 0.0093 0.0104 0.0000 0.0059 2.5714 0.0093 0.0106 0.0000 0.0059 2.6209 0.0093 0.0107 0.0000 0.0059 2.6703 0.0093 0.0109 0.0000 0.0059 2.7198 0.0093 0.0111 0.0000 0.0059 2.7692 0.0093 0.0113 0.0000 0.0059 2.8187 0.0093 0.0115 0.0000 0.0059 2.8681 0.0093 0.0117 0.0000 0.0059 2.9176 0.0093 0.0119 0.0000 0.0059 2.9670 0.0093 0.0121 0.0000 0.0059 3.0000 0.0093 0.0122 0.0000 0.0059 Surface retention 2 Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) To Amended(cfs) Wetted Surface 3.0000 0.0093 0.0122 0.0000 0.1131 0.0000 3.0495 0.0093 0.0127 0.0000 0.1131 0.0000 3.0989 0.0093 0.0131 0.0000 0.1205 0.0000 3.1484 0.0093 0.0136 0.0000 0.1242 0.0000 3.1978 0.0093 0.0141 0.0000 0.1280 0.0000 3.2473 0.0093 0.0145 0.0000 0.1317 0.0000 3.2967 0.0093 0.0150 0.0000 0.1354 0.0000 3.3462 0.0093 0.0155 0.0000 0.1391 0.0000 3.3956 0.0093 0.0159 0.0000 0.1429 0.0000 3.4451 0.0093 0.0164 0.0000 0.1466 0.0000 3.4945 0.0093 0.0168 0.0000 0.1503 0.0000 3.5440 0.0093 0.0173 0.1466 0.1541 0.0000 3.5934 0.0093 0.0178 0.4535 0.1578 0.0000 3.6429 0.0093 0.0182 0.8548 0.1615 0.0000 3.6923 0.0093 0.0187 1.3261 0.1652 0.0000 3.7418 0.0093 0.0191 1.8479 0.1690 0.0000 3.7912 0.0093 0.0196 2.4011 0.1727 0.0000 3.8407 0.0093 0.0201 2.9662 0.1764 0.0000 3.8901 0.0093 0.0205 3.5234 0.1801 0.0000 3.9396 0.0093 0.0210 4.0534 0.1839 0.0000 3.9890 0.0093 0.0215 4.5388 0.1876 0.0000 4.0385 0.0093 0.0219 4.9654 0.1913 0.0000 4.0879 0.0093 0.0224 5.3242 0.1951 0.0000 4.1374 0.0093 0.0228 5.6134 0.1988 0.0000 4.1868 0.0093 0.0233 5.8404 0.2025 0.0000 4.2363 0.0093 0.0238 6.0242 0.2062 0.0000 4.2857 0.0093 0.0242 6.2817 0.2100 0.0000 4.3352 0.0093 0.0247 6.4763 0.2137 0.0000 4.3846 0.0093 0.0252 6.6653 0.2174 0.0000 4.4341 0.0093 0.0256 6.8491 0.2211 0.0000 4.4835 0.0093 0.0261 7.0280 0.2249 0.0000 4.5000 0.0093 0.0262 7.2025 0.2261 0.0000 Name : Surface retention 2 Element Flows To: Outlet 1 Outlet 2 Surface retention 3 Bioretention 2 Name : Bioretention 3 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 17 Bottom Length: 20.00 ft. Bottom Width: 9.00 ft. Material thickness of first layer: 1.5 Material type for first layer: SMMWW 12 in/hr Material thickness of second layer: 1.5 Material type for second layer: GRAVEL Material thickness of third layer: 0 Material type for third layer: GRAVEL Infiltration On Infiltration rate: 0.63 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 0.376 Total Volume Through Riser (ac-ft.): 1.033 Total Volume Through Facility (ac-ft.): 1.409 Percent Infiltrated: 26.69 Total Precip Applied to Facility: 0.014 Total Evap From Facility: 0.013 Underdrain not used Discharge Structure Riser Height: 0.5 ft. Riser Diameter: 18 in. Element Flows To: Outlet 1 Outlet 2 Bioretention 3 Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.0041 0.0000 0.0000 0.0000 0.0495 0.0041 0.0001 0.0000 0.0000 0.0989 0.0041 0.0002 0.0000 0.0000 0.1484 0.0041 0.0003 0.0000 0.0000 0.1978 0.0041 0.0004 0.0000 0.0003 0.2473 0.0041 0.0005 0.0000 0.0005 0.2967 0.0041 0.0006 0.0000 0.0008 0.3462 0.0041 0.0007 0.0000 0.0008 0.3956 0.0041 0.0007 0.0000 0.0011 0.4451 0.0041 0.0008 0.0000 0.0015 0.4945 0.0041 0.0009 0.0000 0.0021 0.5440 0.0041 0.0010 0.0000 0.0026 0.5934 0.0041 0.0011 0.0000 0.0026 0.6429 0.0041 0.0012 0.0000 0.0026 0.6923 0.0041 0.0013 0.0000 0.0026 0.7418 0.0041 0.0014 0.0000 0.0026 0.7912 0.0041 0.0015 0.0000 0.0026 0.8407 0.0041 0.0016 0.0000 0.0026 0.8901 0.0041 0.0017 0.0000 0.0026 0.9396 0.0041 0.0018 0.0000 0.0026 0.9890 0.0041 0.0019 0.0000 0.0026 1.0385 0.0041 0.0020 0.0000 0.0026 1.0879 0.0041 0.0021 0.0000 0.0026 1.1374 0.0041 0.0021 0.0000 0.0026 1.1868 0.0041 0.0022 0.0000 0.0026 1.2363 0.0041 0.0023 0.0000 0.0026 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 18 1.2857 0.0041 0.0024 0.0000 0.0026 1.3352 0.0041 0.0025 0.0000 0.0026 1.3846 0.0041 0.0026 0.0000 0.0026 1.4341 0.0041 0.0027 0.0000 0.0026 1.4835 0.0041 0.0028 0.0000 0.0026 1.5330 0.0041 0.0029 0.0000 0.0026 1.5824 0.0041 0.0030 0.0000 0.0026 1.6319 0.0041 0.0031 0.0000 0.0026 1.6813 0.0041 0.0031 0.0000 0.0026 1.7308 0.0041 0.0032 0.0000 0.0026 1.7802 0.0041 0.0033 0.0000 0.0026 1.8297 0.0041 0.0034 0.0000 0.0026 1.8791 0.0041 0.0035 0.0000 0.0026 1.9286 0.0041 0.0036 0.0000 0.0026 1.9780 0.0041 0.0037 0.0000 0.0026 2.0275 0.0041 0.0037 0.0000 0.0026 2.0769 0.0041 0.0038 0.0000 0.0026 2.1264 0.0041 0.0039 0.0000 0.0026 2.1758 0.0041 0.0040 0.0000 0.0026 2.2253 0.0041 0.0041 0.0000 0.0026 2.2747 0.0041 0.0042 0.0000 0.0026 2.3242 0.0041 0.0042 0.0000 0.0026 2.3736 0.0041 0.0043 0.0000 0.0026 2.4231 0.0041 0.0044 0.0000 0.0026 2.4725 0.0041 0.0045 0.0000 0.0026 2.5220 0.0041 0.0046 0.0000 0.0026 2.5714 0.0041 0.0047 0.0000 0.0026 2.6209 0.0041 0.0048 0.0000 0.0026 2.6703 0.0041 0.0048 0.0000 0.0026 2.7198 0.0041 0.0049 0.0000 0.0026 2.7692 0.0041 0.0050 0.0000 0.0026 2.8187 0.0041 0.0051 0.0000 0.0026 2.8681 0.0041 0.0052 0.0000 0.0026 2.9176 0.0041 0.0053 0.0000 0.0026 2.9670 0.0041 0.0053 0.0000 0.0026 3.0000 0.0041 0.0054 0.0000 0.0026 Surface retention 3 Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) To Amended(cfs) Wetted Surface 3.0000 0.0041 0.0054 0.0000 0.0500 0.0000 3.0495 0.0041 0.0056 0.0000 0.0500 0.0000 3.0989 0.0041 0.0058 0.0000 0.0533 0.0000 3.1484 0.0041 0.0060 0.0000 0.0549 0.0000 3.1978 0.0041 0.0062 0.0000 0.0566 0.0000 3.2473 0.0041 0.0064 0.0000 0.0582 0.0000 3.2967 0.0041 0.0066 0.0000 0.0599 0.0000 3.3462 0.0041 0.0068 0.0000 0.0615 0.0000 3.3956 0.0041 0.0070 0.0000 0.0632 0.0000 3.4451 0.0041 0.0072 0.0000 0.0648 0.0000 3.4945 0.0041 0.0074 0.0000 0.0665 0.0000 3.5440 0.0041 0.0077 0.1466 0.0681 0.0000 3.5934 0.0041 0.0079 0.4535 0.0698 0.0000 3.6429 0.0041 0.0081 0.8548 0.0714 0.0000 3.6923 0.0041 0.0083 1.3261 0.0731 0.0000 3.7418 0.0041 0.0085 1.8479 0.0747 0.0000 3.7912 0.0041 0.0087 2.4011 0.0764 0.0000 3.8407 0.0041 0.0089 2.9662 0.0780 0.0000 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 19 3.8901 0.0041 0.0091 3.5234 0.0797 0.0000 3.9396 0.0041 0.0093 4.0534 0.0813 0.0000 3.9890 0.0041 0.0095 4.5388 0.0830 0.0000 4.0385 0.0041 0.0097 4.9654 0.0846 0.0000 4.0879 0.0041 0.0099 5.3242 0.0863 0.0000 4.1374 0.0041 0.0101 5.6134 0.0879 0.0000 4.1868 0.0041 0.0103 5.8404 0.0896 0.0000 4.2363 0.0041 0.0105 6.0242 0.0912 0.0000 4.2857 0.0041 0.0107 6.2817 0.0929 0.0000 4.3352 0.0041 0.0109 6.4763 0.0945 0.0000 4.3846 0.0041 0.0111 6.6653 0.0962 0.0000 4.4341 0.0041 0.0113 6.8491 0.0978 0.0000 4.4835 0.0041 0.0115 7.0280 0.0995 0.0000 4.5000 0.0041 0.0116 7.2025 0.1000 0.0000 Name : Surface retention 3 Element Flows To: Outlet 1 Outlet 2 Bioretention 3 ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC #1 Total Pervious Area:1.216 Total Impervious Area:O Mitigated Landuse Totals for POC #1 Total Pervious Area:0.448 Total Impervious Area:0.767 Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.020811 5 year 0.036994 10 year 0.046602 25 year 0.056879 50 year 0.063204 100 year 0.068518 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0 5 year 0 10 year 0 < 0.192 Target Flow, PASSES 25 year 0 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 20 50 year 0 100 year 0 < 0.345 Target Flow, PASSES Stream Protection Duration Annual Peaks for Predeveloped and Mitigated Year Predeveloped Mitigated 1902 0.030 0.000 1903 0.009 0.000 1904 0.022 0.000 1905 0.012 0.000 1906 0.004 0.000 1907 0.035 0.059 1908 0.022 0.000 1909 0.024 0.000 1910 0.039 0.000 1911 0.019 0.000 1912 0.079 0.119 1913 0.032 0.000 1914 0.007 0.000 1915 0.010 0.000 1916 0.018 0.000 1917 0.005 0.000 1918 0.021 0.000 1919 0.014 0.000 1920 0.021 0.000 1921 0.021 0.000 1922 0.024 0.000 1923 0.019 0.000 1924 0.009 0.000 1925 0.009 0.000 1926 0.018 0.000 1927 0.024 0.000 1928 0.016 0.000 1929 0.039 0.000 1930 0.020 0.000 1931 0.020 0.000 1932 0.014 0.000 1933 0.017 0.000 1934 0.051 0.070 1935 0.017 0.000 1936 0.029 0.000 1937 0.027 0.000 1938 0.023 0.000 1939 0.000 0.000 1940 0.018 0.000 1941 0.019 0.000 1942 0.027 0.024 1943 0.009 0.000 1944 0.028 0.253 1945 0.020 0.000 1946 0.017 0.000 1947 0.012 0.000 1948 0.045 0.107 1949 0.037 0.136 1950 0.017 0.000 1951 0.023 0.000 C 4m ENGINEERING POC #1 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 21 1952 0.074 0.235 1953 0.059 0.232 1954 0.018 0.000 1955 0.010 0.000 1956 0.007 0.000 1957 0.024 0.000 1958 0.061 0.167 1959 0.036 0.000 1960 0.012 0.000 1961 0.038 0.075 1962 0.019 0.000 1963 0.005 0.000 1964 0.005 0.000 1965 0.044 0.066 1966 0.007 0.000 1967 0.017 0.000 1968 0.022 0.000 1969 0.016 0.000 1970 0.027 0.000 1971 0.048 0.118 1972 0.031 0.053 1973 0.034 0.019 1974 0.022 0.000 1975 0.053 0.134 1976 0.021 0.000 1977 0.011 0.000 1978 0.045 0.069 1979 0.011 0.000 1980 0.021 0.000 1981 0.021 0.000 1982 0.012 0.000 1983 0.035 0.016 1984 0.008 0.000 1985 0.017 0.000 1986 0.016 0.000 1987 0.036 0.115 1988 0.026 0.000 1989 0.021 0.000 1990 0.024 0.000 1991 0.019 0.000 1992 0.031 0.000 1993 0.026 0.000 1994 0.046 0.092 1995 0.009 0.000 1996 0.050 0.067 1997 0.024 0.000 1998 0.021 0.000 1999 0.000 0.000 2000 0.015 0.000 2001 0.011 0.000 2002 0.039 0.000 2003 0.023 0.000 2004 0.026 0.000 2005 0.033 0.000 2006 0.014 0.000 2007 0.016 0.000 2008 0.022 0.000 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 22 2009 0.013 0.000 2010 0.010 0.000 2011 0.014 0.000 2012 0.022 0.134 2013 0.015 0.000 2014 0.008 0.000 2015 0.018 0.000 2016 0.003 0.000 2017 0.037 0.146 2018 0.067 0.176 2019 0.071 0.234 2020 0.023 0.000 2021 0.030 0.000 2022 0.010 0.000 2023 0.024 0.000 2024 0.081 0.113 2025 0.018 0.000 2026 0.034 0.000 2027 0.010 0.000 2028 0.007 0.000 2029 0.025 0.000 2030 0.051 0.094 2031 0.012 0.000 2032 0.009 0.000 2033 0.011 0.000 2034 0.012 0.000 2035 0.054 0.158 2036 0.027 0.000 2037 0.004 0.000 2038 0.028 0.000 2039 0.001 0.000 2040 0.008 0.000 2041 0.013 0.000 2042 0.058 0.169 2043 0.024 0.000 2044 0.032 0.000 2045 0.020 0.000 2046 0.023 0.000 2047 0.015 0.000 2048 0.021 0.000 2049 0.021 0.000 2050 0.013 0.000 2051 0.023 0.062 2052 0.011 0.000 2053 0.022 0.000 2054 0.024 0.025 2055 0.007 0.000 2056 0.008 0.000 2057 0.013 0.000 2058 0.017 0.000 Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC ##1 Rank Predeveloped Mitigated 1 0.0814 0.2534 2 0.0790 0.2352 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 23 3 0.0742 0.2338 4 0.0709 0.2322 5 0.0672 0.1761 6 0.0614 0.1692 7 0.0589 0.1674 8 0.0580 0.1583 9 0.0536 0.1463 10 0.0534 0.1363 11 0.0514 0.1343 12 0.0510 0.1339 13 0.0501 0.1192 14 0.0483 0.1176 15 0.0456 0.1152 16 0.0452 0.1130 17 0.0446 0.1074 18 0.0440 0.0944 19 0.0392 0.0923 20 0.0392 0.0746 21 0.0390 0.0696 22 0.0380 0.0691 23 0.0372 0.0670 24 0.0370 0.0657 25 0.0364 0.0622 26 0.0355 0.0589 27 0.0353 0.0533 28 0.0349 0.0250 29 0.0344 0.0240 30 0.0342 0.0191 31 0.0330 0.0157 32 0.0323 0.0000 33 0.0316 0.0000 34 0.0313 0.0000 35 0.0310 0.0000 36 0.0303 0.0000 37 0.0297 0.0000 38 0.0288 0.0000 39 0.0283 0.0000 40 0.0279 0.0000 41 0.0275 0.0000 42 0.0274 0.0000 43 0.0270 0.0000 44 0.0265 0.0000 45 0.0264 0.0000 46 0.0261 0.0000 47 0.0256 0.0000 48 0.0249 0.0000 49 0.0244 0.0000 50 0.0242 0.0000 51 0.0240 0.0000 52 0.0240 0.0000 53 0.0240 0.0000 54 0.0239 0.0000 55 0.0238 0.0000 56 0.0238 0.0000 57 0.0237 0.0000 58 0.0235 0.0000 59 0.0234 0.0000 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 24 60 0.0232 0.0000 61 0.0232 0.0000 62 0.0227 0.0000 63 0.0225 0.0000 64 0.0222 0.0000 65 0.0222 0.0000 66 0.0220 0.0000 67 0.0220 0.0000 68 0.0219 0.0000 69 0.0218 0.0000 70 0.0216 0.0000 71 0.0210 0.0000 72 0.0210 0.0000 73 0.0209 0.0000 74 0.0208 0.0000 75 0.0207 0.0000 76 0.0207 0.0000 77 0.0206 0.0000 78 0.0206 0.0000 79 0.0206 0.0000 80 0.0205 0.0000 81 0.0205 0.0000 82 0.0203 0.0000 83 0.0203 0.0000 84 0.0199 0.0000 85 0.0193 0.0000 86 0.0193 0.0000 87 0.0189 0.0000 88 0.0188 0.0000 89 0.0185 0.0000 90 0.0184 0.0000 91 0.0180 0.0000 92 0.0180 0.0000 93 0.0178 0.0000 94 0.0176 0.0000 95 0.0175 0.0000 96 0.0174 0.0000 97 0.0174 0.0000 98 0.0174 0.0000 99 0.0173 0.0000 100 0.0168 0.0000 101 0.0168 0.0000 102 0.0167 0.0000 103 0.0162 0.0000 104 0.0162 0.0000 105 0.0161 0.0000 106 0.0160 0.0000 107 0.0154 0.0000 108 0.0153 0.0000 109 0.0148 0.0000 110 0.0141 0.0000 111 0.0141 0.0000 112 0.0139 0.0000 113 0.0138 0.0000 114 0.0135 0.0000 115 0.0133 0.0000 116 0.0133 0.0000 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 25 117 0.0132 0.0000 118 0.0125 0.0000 119 0.0124 0.0000 120 0.0121 0.0000 121 0.0119 0.0000 122 0.0118 0.0000 123 0.0117 0.0000 124 0.0112 0.0000 125 0.0109 0.0000 126 0.0108 0.0000 127 0.0108 0.0000 128 0.0105 0.0000 129 0.0103 0.0000 130 0.0103 0.0000 131 0.0097 0.0000 132 0.0097 0.0000 133 0.0096 0.0000 134 0.0095 0.0000 135 0.0092 0.0000 136 0.0092 0.0000 137 0.0091 0.0000 138 0.0087 0.0000 139 0.0086 0.0000 140 0.0079 0.0000 141 0.0078 0.0000 142 0.0076 0.0000 143 0.0076 0.0000 144 0.0074 0.0000 145 0.0074 0.0000 146 0.0069 0.0000 147 0.0069 0.0000 148 0.0068 0.0000 149 0.0054 0.0000 150 0.0048 0.0000 151 0.0045 0.0000 152 0.0043 0.0000 153 0.0036 0.0000 154 0.0035 0.0000 155 0.0010 0.0000 156 0.0002 0.0000 157 0.0002 0.0000 Stream Protection Duration POC #1 The Facility FAILED Facility FAILED duration standard for 1+ flows. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0104 11558 184 1 Pass 0.0109 10444 184 1 Pass 0.0115 9455 182 1 Pass 0.0120 8602 182 2 Pass 0.0125 7856 181 2 Pass 0.0131 7173 180 2 Pass 0.0136 6539 176 2 Pass 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 26 0.0141 5958 174 2 Pass 0.0147 5462 171 3 Pass 0.0152 5004 171 3 Pass 0.0157 4588 169 3 Pass 0.0163 4226 166 3 Pass 0.0168 3865 161 4 Pass 0.0173 3537 157 4 Pass 0.0179 3264 154 4 Pass 0.0184 2996 152 5 Pass 0.0189 2758 149 5 Pass 0.0195 2554 148 5 Pass 0.0200 2384 148 6 Pass 0.0205 2202 147 6 Pass 0.0211 2037 145 7 Pass 0.0216 1906 143 7 Pass 0.0221 1791 141 7 Pass 0.0227 1664 137 8 Pass 0.0232 1557 137 8 Pass 0.0237 1462 135 9 Pass 0.0243 1362 133 9 Pass 0.0248 1275 133 10 Pass 0.0253 1213 131 10 Pass 0.0259 1147 131 11 Pass 0.0264 1074 130 12 Pass 0.0269 1015 129 12 Pass 0.0275 950 129 13 Pass 0.0280 899 129 14 Pass 0.0285 856 127 14 Pass 0.0291 814 125 15 Pass 0.0296 777 123 15 Pass 0.0301 741 123 16 Pass 0.0307 706 122 17 Pass 0.0312 677 120 17 Pass 0.0317 646 119 18 Pass 0.0323 617 119 19 Pass 0.0328 588 119 20 Pass 0.0333 563 117 20 Pass 0.0339 544 116 21 Pass 0.0344 512 115 22 Pass 0.0349 486 113 23 Pass 0.0355 461 111 24 Pass 0.0360 444 111 25 Pass 0.0365 428 109 25 Pass 0.0371 403 109 27 Pass 0.0376 385 108 28 Pass 0.0381 367 108 29 Pass 0.0387 346 108 31 Pass 0.0392 331 108 32 Pass 0.0397 313 108 34 Pass 0.0403 301 108 35 Pass 0.0408 288 107 37 Pass 0.0413 271 107 39 Pass 0.0419 254 106 41 Pass 0.0424 241 105 43 Pass 0.0429 225 103 45 Pass 0.0435 214 103 48 Pass 0.0440 192 103 53 Pass 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 27 0.0445 186 102 54 Pass 0.0451 172 101 58 Pass 0.0456 159 100 62 Pass 0.0461 153 100 65 Pass 0.0467 139 100 71 Pass 0.0472 130 99 76 Pass 0.0477 120 99 82 Pass 0.0483 110 98 89 Pass 0.0488 96 98 102 Pass 0.0493 91 98 107 Pass 0.0499 85 98 115 Fail 0.0504 77 97 125 Fail 0.0509 71 96 135 Fail 0.0515 65 95 146 Fail 0.0520 62 95 153 Fail 0.0525 56 94 167 Fail 0.0531 51 91 178 Fail 0.0536 45 90 200 Fail 0.0541 42 89 211 Fail 0.0547 38 89 234 Fail 0.0552 35 89 254 Fail 0.0557 32 89 278 Fail 0.0563 30 88 293 Fail 0.0568 29 88 303 Fail 0.0573 25 88 352 Fail 0.0579 23 87 378 Fail 0.0584 21 86 409 Fail 0.0589 17 84 494 Fail 0.0595 16 84 525 Fail 0.0600 15 83 553 Fail 0.0605 13 83 638 Fail 0.0611 13 82 630 Fail 0.0616 11 81 736 Fail 0.0621 11 79 718 Fail 0.0627 10 77 770 Fail 0.0632 10 76 760 Fail The development has an increase in flow durations from 1/2 Predeveloped 2 year flow to the 2 year flow or more than a 10% increase from the 2 year to the 50 year flow. Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0 acre-feet On-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. Off-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. LID Report LID Technique Used for Total Volume Percent Water Quality Percent Comment Treatment? Needs Volume Water Quality Treatment Infiltrated Treated C 4m ENGINEERING Volume Infiltration Cumulative Through Volume Volume Facility (ac-ft.) Infiltration 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Westgate Station - CG #19440 Drainage Report March 22, 2023 Appendix A, Page 28 retention 3 POC 26.67 retention 2 53.62 retention 1 97.76 Total Volume Infiltrated 96.10 0.00 0% Compliance with LID Standard 8 Duration Analysis Result = Passed Perind and Impind Changes No changes have been made. (ac-ft) (ac-ft N 1.28 N 2.76 N 123.98 128.02 0.00 No Treat. Credit 0.00 Credit N N N This program and accompanying documentation is provided 'as -is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by the user. Clear Creek Solutions, Inc. disclaims all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions, Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions, Inc. has been advised of the possibility of such damages. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com