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Approved_BLD2023-0623+Storm_Drainage_Report+8.30.2023_1.56.34_PM+3756318RESUB Aug 30 2023 BLD2023-0623 Drainage Report Landsverk SFR For OWNER/APPLICANT: Duane & Deanne Landsverk 24113 56th Ave W Mountlake Terrace, WA 98043 duane@lqh-inc.com 425.754.2069 CIVIL ENGINEER: Omega Engineering, Inc. Joseph Smeby, P.E. joe@oemega-eng.com 425.903.4852 SITE LOCATION: 19515 94th PI W Edmonds, WA 98020 Tax Parcel: 00434600005801 Legal Description: Lot A of City of Edmonds Short Plat S-9-89 Zoning: RS-12 COMPLIES WITH APPLICABLE CITY STORM CODE P ie�. 08/31 /2023 Prepared by: Elias J. Troutman, E.I.T. Checked by: Joseph M. Smeby, P.E. Job No: 23-0404 May 2023 Revised: August 2023 TABLE OF CONTENTS TABLE OF CONTENTS...........................................................................................................................1 LISTOF FIGURES..................................................................................................................................2 1. INTRODUCTION & SITE CLASSIFICATION.....................................................................................3 2. EXISTING SITE HYDROLOGY.........................................................................................................3 3. STORMWATER SITE PLAN............................................................................................................4 4. SWPPP NARRATIVE......................................................................................................................5 A. SITE GRADING/EROSION CONTROL RISK ASSESSMENT...............................................................6 B. SWPPP MINIMUM ELEMENTS.....................................................................................................6 5. WATER POLLUTION SOURCE CONTROL.......................................................................................8 6. PRESERVATION OF NATURAL DRAINAGE SYSTEM......................................................................8 7. ON -SITE STORMWATER MANAGEMENT (MR #5).......................................................................9 8. RUN-OFF TREATMENT (MR #6).................................................................................................10 9. FLOW CONTROL (MR#7)...........................................................................................................10 10. WETLANDS PROTECTION (MR#8).........................................................................................12 11. OPERATIONS AND MAINTENANCE MANUAL (MR#9)..........................................................12 APPENDIX C Landsverk SFR 23-0404 May 2023 Revised: August 2023 Page 1 LIST OF FIGURES ITEM PAGE FIGURE 1 VICINITY MAP.......................................................................................10 FIGURE 2 EXISTING DRAINAGE BASIN MAP.......................................................11 FIGURE 3 DEVELOPED DRAINAGE BASIN MAP.................................................12 Landsverk SFR May 2023 Revised: August 2023 23-0404 Page 2 1. INTRODUCTION & SITE CLASSIFICATION This document is intended to provide engineering information necessary to support the building permit application submittal to the City of Edmonds for the new single family residence proposed on this parcel. The property is approximately 1.19 acres. Access to the existing home on this site is from 94th PL W that wraps around the west and north sides of the lot. The existing driveway access is from the north near the northeastern property corner and will be maintained for this project. The total proposed area of disturbance including clearing and grading is approximately 32,800 sf and the new total new plus replaced impervious surfaces proposed is 14,309 sf. Therefore, this project is classified as Category 2 and shall comply with Minimum Requirements No. 1 through No. 9. This classification was completed using figure 3.1 of the 2022 Edmonds Stormwater Addendum. The geotechnical engineer found that infiltration is feasible in the outwash sands located about 4 feet below grade, so all new impervious surface runoff will be infiltrated for this project. Refer to Section 6 of this report for a detailed feasibility analysis. This proposed project will create approximately 14,309 sf of new and replaced impervious surfaces including the proposed SFR roof, driveway and walkways. The existing home on site will be demolished and removed along with some of the existing gravel driveway surfaces. All of the new impervious and pervious surfaces will be mitigated through infiltration and amended soils, respectively. The site is located at 19515 94th PI W, Edmonds, WA 98020, and in Section 13, Township 27N, Range 3E, Willamette Meridian. See Figure 1 - Vicinity Map. 2. EXISTING SITE HYDROLOGY The existing site consists of an existing single family residence and patios (that have recently been demolished and removed from the site) and a gravel driveway. Vegetation consists of scattered trees and lawn within the project site, with some thick brush existing on the steep slope areas. During the site visit, there appeared to be a small of -site area to the east that drains toward the project area. This project will not affect any off -site flows from flowing onto and through the site as in the existing conditions. Currently no drains, channels, swales or other stormwater management facilities exist within the project site. Immediately adjacent to the west within 94th PI W exists a stormwater conveyance system consisting of catch basins and underground pipes that pick up and convey surface water. The project site is located atop a high point, so runoff from the project site currently drains in a northwestern, western and southwestern direction away from the project site and toward the steep slopes that surround this property. Runoff flows down these slopes and onto 94th PI W where it is collected by the existing conveyance system. A geotechnical report was prepared by Cobalt Geosciences. Soils were found to be approximately 3.5 feet of silty -fine to medium grained sand underlain by fine to medium grained sand with gravel to 12 feet below grade. Groundwater was not encountered to this depth, and a design infiltration rate of 1.3 inches per hour was found for this site. Landsverk SFR 23-0404 May 2023 Revised: August 2023 Page 3 3. STORMWATER SITE PLAN As noted in Section 1 of this report this project is classified as a Category 2 Project. Therefore, this drainage design has been prepared to address the requirements contained in the 2022 Edmonds Stormwater Addendum along with the 2019 Stormwater Management Manual for Western Washington (SWMMWW). This document is intended to provide the supporting information to justify the BMPs used and to detail how the design of the selected BMPs meet the required standards. For this project, the geotechnical engineer found stormwater infiltration to be feasible, so all new impervious surface runoff will be infiltrated via permeable pavers and dry wells. This site proposes to construct approximately 14,309 sf of new and replaced hard surfaces. The following table summarizes the PGHS and NPGHS proposed. PGHS (sf) NPGHS (sf) Total (sf) Existing 6,611 4,350 10,961 Removed 4,411 3,050 7,461 Replaced 2,200 1,300 3,500 New 996 9,813 10,809 New + Replaced 3,196 11,113 14,309 Total On -site Hard Surfaces 3,196 11,113 14,309 Total Effective Hard Surfaces 0 0 0 The following table summarizes the project pervious surfaces. Total (sf) Disturbed Pervious Areas 21,839 Converted Vegetation Areas 6,000 Undisturbed Areas 19,000 Landsverk SFR May 2023 Revised: August 2023 23-0404 Page 4 4. SWPPP NARRATIVE Clearing, grading, and temporary erosion and sediment control plans will be prepared as part of the final engineering drawings. However, since a construction site is dynamic it will be necessary to reassess the erosion control BMP's during construction and install additional measures when necessary. Proposed temporary measures possible for this project will include the following BMP's: • Installation of stabilized construction entrance. • Retention of Existing Vegetation • Straw mulch, hydroseed or other mulching and planting method to stabilized unworked areas. • Silt fencing if necessary Permanent measures to reduce or eliminate erosion or water quality degradation will include the following BMP's: • Paving all traffic areas (concrete/asphalt) • Permanent landscaping in pervious areas. • Limiting cut and fill slopes to 2:1 maximum and 3:1 maximum where exposed to standing water. • Routine maintenance and inspection of the grounds and response to developing problems. The listed erosion control BMP's will be engineered for anticipated conditions in compliance with City and DOE guidelines. With proper installation, maintenance and inspection the proposed BMP's should result in minimal impact to the surrounding environment. The City retains the authority by code to require additional measures should the existing BMPs prove insufficient. Landsverk SFR 23-0404 May 2023 Revised: August 2023 Page 5 A. SITE GRADING/EROSION CONTROL RISK ASSESSMENT Area proposed to be cleared/worked: 32,800 sf = 0.76 acres Average slope for the site (w/in the area of disturbance): 8% Erosion Hazard of Soil Moderate Critical Areas downslope Yes (Steep Slopes) Site is upstream of an ESA Stream No Based on the above information and the fact that the site will retain some existing vegetation and construction site runoff will filter through the soil and silt fence prior to reaching the steep slopes, and that if site conditions warrant, additional BMP's can be implemented as corrective measures the Risk Category for this site is Moderate Risk. B. SWPPP MINIMUM ELEMENTS 1: Mark Clearing Limits The first step in the "Construction Sequence" included on the clearing and grading plan sheets is for the limits of clearing to be flagged and to have construction fencing placed along the limits prior to any other construction activity. 2: Establish Construction Access The SWPPP calls for the existing gravel driveway to be used as the construction entrance. 3: Control Flow Rates This project is below the thresholds requiring flow control for the project. During construction, surface flows will be controlled with straw wattles per plan & details. Shallow depressions will be added to ea. wattle to capture & infiltrate runoff. Depressions will be dug prior to final soil amendments. Once roofed, flow will be directed to the drywells via temporary or permanent downspouts. 4: Install Sediment Controls This site and SWPPP proposes to construct/maintain a construction entrance, retained vegetation and silt fencing. These features are intended to minimize the opportunity for sediment to leave the site via stormwater or on vehicles. The construction of these features is one of the first items required in the "Construction Sequence". Mulch will also be used on the exposed soil as necessary to limit erosion. 5: Stabilize Soils The "Construction Sequence" calls for the stabilization of soils that remain unworked for certain lengths of time based on the time of year. Stabilization techniques may include but not limited to mulching, plastic sheeting or hydroseeding, notes have been added to the plan regarding protection for the stockpile area if necessary. A stockpile area has been identified on the SWPPP. 6: Protect Slopes All disturbed slopes on site during construction are required to be protected with mulch or other means as specified in the construction sequence. No concentrated runoff or significant amounts of sheet flow will be directed to new cut or fill slopes during construction. Landsverk SFR 23-0404 May 2023 Revised: August 2023 Page 6 7: Protect Drain Inlets Existing and proposed drain inlets shall be protected with silt sock or other approved City method. 8: Stabilize Channels and Outlets No new channels or outlets are proposed for this site. 9: Control Pollutants No outside chemicals are expected to be necessary for the construction of this project. All vehicles working on and around the site would need to meet the State requirements for emissions. 10: Control DeWatering DeWatering will not be necessary for this project as the geotechnical engineer did not encounter water table to at least 10 feet below grade. 11: Maintain BMPs The construction supervisor will be responsible for maintaining all BMPs during construction and working with the City to relocate or add BMPs as necessary as site conditions change. 12: Manage the Project It will be the responsibility of the Contractor and Developer to manage this project and coordinate with the City Inspector and Engineer. Inspection and Monitoring: Site inspections shall be done by a person who is knowledgeable in the principles and practices of erosion and sediment control. The person must have skills to first assess the site conditions and construction activities that could impact the quality of stormwater, and second assess the effectiveness of erosion and sediment control measures used to control the quality of stormwater discharges. Whenever inspection and/or monitoring reveals that the BMPs identified in the Construction SWPPP are inadequate, due to the actual discharge of or potential to discharge a significant amount of any pollutant, appropriate BMPs or design changes shall be implemented as soon as possible. Maintaining an Updated Construction SWPPP: The construction 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 Landsverk SFR 23-0404 May 2023 Revised: August 2023 Page 7 additional or modified BMPs designed to correct problems identified. Revisions to the SWPPP shall be completed within seven days following inspection. 13: Protect Low Impact Development BMPs The use of infiltration BMPs will allow for the construction of the permeable pavers and dry wells at the end of the project to protect those areas from compaction. 5. WATER POLLUTION SOURCE CONTROL The City of Edmonds Stormwater Supplement and DOE Drainage manual was reviewed to determine if the proposed land -use for this project required any site -specific source control BMPs to be constructed. All single-family residential projects shall, at a minimum, incorporate BMPs from DOE SWMMWW Volume IV, S411 — BMPs for Landscaping and Lawn/Vegetation Management. The BMPS from this section that shall be utilized for this project area: • Select the right plants for the planting location based on proposed use, available maintenance, soil conditions, sun exposure, water availability, height, sight factors, and space available • Ensure the plants selected for planting are not on the noxious weed list. • Do not dispose of collected vegetation into waterways or storm sewer systems. • Do not blow vegetation or other debris into the drainage system. • Dispose of collected vegetation by composting or recycling. 6. PRESERVATION OF NATURAL DRAINAGE SYSTEM The runoff from the project site in the existing condition drains in multiple directions. Runoff from the eastern half of the site flows to a low pothole area within the area of the existing gravel driveway. Runoff from the western portion of the site flows west, down the steep slopes and onto the private properties to the west where it is collected by a series of catch basins within 94th PI W. All of the new impervious surface runoff will be collected and infiltrated via permeable pavers and dry wells within the front yard of the new house within the existing low pothole area, matching the existing drainage path. This will allow the maximum amount of runoff to be treated and naturally absorb into the on -site soils while not concentrating any of the flows. Runoff from the western portion of the site will continue to flow west and onto 94th PI W as it does in the existing conditions. Runoff is collected within several catch basins and is routed southeast down 94th place where it flows into the stormwater conveyance system within Puget Drive. Runoff flows approximately 500 feet west in this conveyance system where it outfalls into Northstream Creek on private property. Runoff flows approximately % mile in Northstream Creek and through multiple large culverts on its way to discharging into the Puget Sound. During the site visit, no erosion or capacity issues were noted throughout the downstream system. Landsverk SFR 23-0404 May 2023 Revised: August 2023 Page 8 This project will result in a reduced amount of runoff draining in a western direction toward the steep slopes, further protecting those slopes. By not grading or compacting some of the pervious surfaces to remain after construction in the area of disturbance, a maximum amount of site runoff from the developed project will be absorbed into the existing on -site soils and remain as sheet flow. During the downstream analysis, no erosion or capacity issues were observed. A small portion of the adjacent property to the east appears to drain toward the project site. However, the large vegetative buffer to be maintained between the project site and the eastern property line will work to attenuate any off -site flows from the east and allow them to naturally infiltrate before reaching the project site. This project will not affect any off -site flows from flowing onto and through the site as in the existing conditions. 7. ON -SITE STORMWATER MANAGEMENT (MR #5) The on -site soils for this project have been studied and described in a Geotechnical Evaluation Report prepared by Cobalt Geosciences. Test pits generally found approximately 6 inches of topsoil underlain by 3.5 feet of silty -fine to medium grained sand with gravel (Weathered Advance Outwash) underlain by fine to medium grained sand (Vashon Advance Outwash) to a depth of 12 feet. Refer to Appendix A for the Geotechnical report. This project proposes to construct approximately 10,248 sf of new roof surfaces. Because this project proposes to construct over 5,000 square feet of hard surfaces, Minimum Requirements 1 through 9 are required. Projects of this size within the UGA are either required to use LID BMPs from List #2 for all surfaces within each surface type, or achieve the LID Performance Standard. This project is selecting List #2. Lawn and Landscaped Areas: Post -Construction Soil Quality and Depth: This option was selected, and the specifications will be provided on the future construction engineering plans. The total area of disturbed soils to be amended is 15,500 square feet. The total area of native vegetation retained for this project is approximately 19,000 square feet of the site. The rest of the site will consist of impervious surfaces and lawn/landscaping. Rnnfc Full Dispersion: Full dispersion was found to be infeasible due to not having the required 100-foot flow paths. Downspout Full Infiltration: Full infiltration was found to be feasible, as the geotechnical report states that "infiltration is feasible in the outwash sands below about 4 feet". Downspout infiltration will be achieved using dry wells. The geotechnical report states that "all (infiltration) systems must penetrate into the sands at least 6 inches. The soils are consistent with Medium Sand per the USDA textural triangle if prescriptive sizing is used". Per the SWMMWW, dry wells shall be sized with a storage rock volume of 90 cubic feet per 1,000 sf of contributing roof Landsverk SFR 23-0404 May 2023 Revised: August 2023 Page 9 area. For a total roof area of 10,248 sf, the required storage rock volume is 923 cubic feet. Therefore, two 9' x 9' x 6' deep drywells shall be used with approximately half of the total roof area flowing to each for a total storage volume of 972 cubic feet. Bioretention or Rain Gardens: Higher priority BMP selected. Downspout Dispersion Systems: Higher priority BMP selected. Perforated Stubout Connections: Higher priority BMP selected. Other Hard Surfaces: Permeable Pavement: Feasible and selected for this project. The geotechnical engineer provided a design infiltration rate of 1.3 inches per hour for the site. Even at a very conservative infiltration rate of 0.1 inches per hour, permeable pavers with a 4-inch thick top course layer (porosity = 0.25) and 6-inch thick storage course layer (porosity = 0.35) are shown to infiltrate 100 percent of accumulated runoff up to the 100 year storm. See Appendix A for "permeable pavement" WWHM printout. Bio-Retention/Rain Gardens/Infiltration: Higher Priority BMP selected. Sheet Flow Dispersion: Higher priority BMP selected. Concentrated Flow Dispersion: Higher priority BMP selected. Detention Vaults and Pipes: Higher priority BMP selected. 8. RUN-OFF TREATMENT (MR #6) This project proposes to construct 3,196 sf of new PGIS which is below the 5,000 sf threshold that requires runoff treatment. Therefore, runoff treatment is not required for this project. 9. FLOW CONTROL (MR #7) The site design for the improvements is for 14,309 sf of new impervious surfaces. As detailed in Section 7 of this report, runoff from the proposed NPGHS (0.25 acres) will be infiltrated via dry wells and has been left out of the developed conditions in the model because it will be a non- effective impervious surface. Runoff from the new driveway (0.07 acres) will be infiltrated via permeable pavers and has also been left out of the developed conditions in the model because it will be a non -effective impervious surface. Runoff from the walkways and patios (0.02 acres will also be constructed of permeable pavers and those areas have been left out of the developed conditions as well. The predeveloped pervious areas have been conservatively modeled as forest on moderate slopes, even though most of the project area is currently developed with an existing house and gravel driveway. The final pervious areas (0.43 acres) have been modeled as lawn. The Western Washington Hydrology Model (WWHM12) was used to analyze the change in the 100-year peak flow rates for the existing and developed conditions. Per the Department of Ecology Stormwater Management Manual for Western Washington (SWMMWW), the 100-year flow frequency may be analyzed using the 1-hour timestep or 15-minute timestep. The 15-minute Landsverk SFR 23-0404 May 2023 Revised:August 2023 Page 10 timestep was used in this analysis. Therefore, the difference in the 100-year flow frequency from the threshold discharge area must not exceed 0.15 cfs. The following summarizes the calculations for the peak runoff rates from the developed portion of the site: The inputs to WWHM12 are as follows. PreDeveloped Conditions: C, Forest, Mod: 0.76 acres Developed conditions: C, Lawn, Mod: 0.43 acres Peak 100-year flow rate for Existing Condition: 0.027 cfs Peak 100-year flow rate for Developed Condition: 0.13 cfs Change in 100-year flow rate: 0.10 cfs The thresholds for flow control are as follows: • Total effective impervious area over 10,000 sf, • Conversion of % acre or more of native vegetation to landscaping, • Conversion of 2.5 acres or more of native vegetation to pasture, A combination of hard surfaces and converted pervious surfaces cause a 0.1 cubic feet per second (cfs) or greater increase in the 100-year flow frequency from a threshold discharge area as estimated using the Western Washington Hydrology Model or other model approved by the Washington State Department of Ecology and Snohomish County, and one -hour time steps (or a 0.15 cfs increase or greater using 15-minute time steps). The 0.10 cfs (one -hour time steps) or 0.15 cfs (15-minute time steps) increase should be a comparison of the post -project runoff to the existing condition runoff. NOTE: For the purpose of applying the 0.10 cfs or 0.15 cfs thresholds, the existing condition shall be the pre -project land cover, with the condition that Snohomish County may require the use of land cover documented for the site at an earlier date in accordance with the requirements of SCC 30.63A.845. This project is shown to construct less than 10,000 sf of effective hard surfaces (EHS), with all new impervious surface runoff being infiltrated and therefore deemed non -effective. This project also proposes to convert less than % acres of native vegetation to landscaping and less than 2.5 acres of native vegetation to pasture. Finally, the site has been analyzed for the existing conditions and developed conditions to determine the increase for the 100-year peak runoff rate of 0.10 cfs which is below the 0.15 cfs threshold (15-minute time steps). Landsverk SFR 23-0404 May 2023 Revised:August2023 Page 11 10. WETLANDS PROTECTION (MR #8) This project will not impact any wetland on -site or downstream of the project site, as all impervious surface runoff will be infiltrated on -site and the runoff in the developed conditions is shown to increase by less than 0.15 cfs as compared to the existing condition. 11. OPERATIONS AND MAINTENANCE MANUAL (MR #9) The Property Owner will be responsible for maintaining the stormwater and landscaping facilities within this development. Included in Appendix C of this manual are checklists for each feature specific to this project. Copies should be made of the checklists as necessary during routine inspections and required maintenance. Specific problems can be recorded along with the appropriate action taken. These checklists are a guide for inspections and maintenance. The frequency of the inspections/maintenance is identified in the left-hand column with the following abbreviations: A = Annual (March or April preferred) M = Monthly S = After Major Storms (Use 1-inch in 24 hours as a guideline) Routine inspections and maintenance will improve the long-term performance of the stormwater facilities. If at any time you are unsure if a problem exists or how to address a specific problem, contact a Professional Engineer. Refer to Appendix A for a list of each facility to be maintained and the appropriate maintenance checklist (To be provided with final engineering report). Landsverk SFR 23-0404 May 2023 Revised: August 2023 Page 12 APPENDIX C OPERATIONS & MAINTENANCE MANUAL APPENDIX C The following specified structures and/or BMP's are provided herein for the single-family development at: 19515 94" Place West Edmonds, WA 98020 (see attached Map 1 for Lot Description and Details): Permeable Pavement Infiltration Trench/Gallery/Drywell O Detention Pipe/Tank/Vault O Concentrated Flow Dispersion O Other: O Infiltration Tank/Vault O Sheet Flow Dispersion O Reduced Impervious Footprint O Rain Garden / Bioretention Cell Stormwater system consists of infiltration pits with tightline downspout drains to yard drains and driveways/walkways of permeable materials for direction infiltration. For design details please reference Drainage Report dated May 2023. No maintenance requirements are provided for newly planted or retained landscaping as they are not a BMP pursued in this project. Operations and Maintenance Standards 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. The Owners shall maintain the size, placement, and design ofthe 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 ofmaintenance and repair shall be the sole responsibility of the Owners. 3. 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. Refer to Table 1 for frequency and description of maintenance required for BMP's applicable to the property herein. Final engineering report to be provided to Owners in conjunction with descriptions below for best maintenance practices: Table 1— Maintenance Checklist STRUCTURE OR BMP FREQUENCY OF MAINTENANCE DESCRIPTION DESCRIPTION MAINTENANCE Permeable Pavers Annual Check pop-up drains to monitor infiltration rates. Dry Wells Annual Ensure CB's are clear of all debris and maintain cleanouts er City of Edmonds SD-638. Map 1— Site Plan & Description DRIVEWAY: PERMEABLE PAVERS � o PROPOSED 1 STORY 1 RESIDENCE 1 I u !1 1 L- - - - - - - - -- I (2) 9'x9'x6' i DRYWELLS. j 4" PVC ROOF 1 DRAINS PER ; CIVIL PLANS I 1 I 1 I I I Dated: 8/23/23 DECLARANT(S): (Signature) Duane Landsverk me) ue) Deanne Landsverk (Print Name) State of Washington ss. County of Snohomish APPROVED: CITY OF EDMONDS (Signature) (Print Name) (Title) On this day personally appeared before me Duane & Deanne Landsverk {Declarant(s)} to me known to be the individual, or individuals described in and who executed the within and foregoing instrument, and acknowledged that he/she/they/it signed the same as his/her/their/its free and voluntary act and deed, for the uses and purposes therein mentioned. SUBSCRIBED AND SWORN before me this 23rd day of August , 2023. e)/ e NOTAgy ��ij► (Name legibly printed or stamped) poet Ic Notary Public in and for the State of Washington. �e •' Residing at_ ���''q;;riW AQQ-'�� My commission expires 8142 .23 cn Z N W 0 Z N m - SITE 2TH VICINITY MAP SCALE 1 " = 2000' 13 FIG. 1 OMEGA VICINITY MAP ENGINEERING, INC. LANDSVERK SFR 2707 WETMORE AVE. DATE JOB NO. SCALE SHEET Everett, WA 98201 (o)425.387.3820 (f) 425.259.1958 5/9/23 23-0404 1 " = 2000' 1 OF 1 ce mu=za3.� INV. arx(F) SSMH PoM=259.13 \ INY. 874C(E)=25T.88 � ' Q0 co ram' J 26 I I 2l8 — I I A 0• F . X EX. SFR s — /A, 6 i T �„ 4• I II �` \\ /_�/a 0/ 59.95 6 ANK--, 2�� ,p ��' \ IN✓. IT�CNP(SW)=TJT.9T N FIG. 2 OMEGA EXISTING BASIN MAP ENGINEERING, INC. LANDSVERK SFR 2707 WETMORE AVE. DATE JOB NO. SCALE SHEET Everett, WA 98201 (o)425.387.3820 (f) 425.259.1958 5/9/23 23-0404 1 = 50 1 OF 1 C8 RIM-283.44 INV. j f7=18f.55 IN✓. P s.]e OtR BLS I 3: / I (o(g) N I III l / I(I r PROP! SFR co\ 111111111\ \ R;—�76 �`--2t,8 9'x9' DR � (� 11 \\\ 1 c9 6 \ �\\ _C _ \ 2d'cp 0 M24 / INV. 14"CMP(SW)=PJ204 N FIG. 3 OMEGA DEVELOPED BASIN MAP ENGINEERING, INC. LANDSVERK SFR 2707 WETMORE AVE. DATE JOB NO. SCALE SHEET Everett, WA 98201 (o)425.387.3820 (f) 425.259.1958 7/28/23 23-0404 1 = 50 1 OF 1 -xi WWHM2012 PROJECT REPORT PERMEABLE PAVEMENT General Model Information Project Name: PERMEABLE PAVEMENT Site Name: LANDSVERK SFR Site Address: City: EDMONDS Report Date: 7/27/2023 Gage: Everett Data Start: 1948/10/01 Data End: 2009/09/30 Timestep: 15 Minute Precip Scale: 0.800 Version Date: 2021 /08/18 Version: 4.2.18 POC Thresholds Low Flow Threshold for POC1: 50 Percent of the 2 Year High Flow Threshold for POC1: 50 Year PERMEABLE PAVEMENT 7/27/2023 4:00:18 PM Page 2 Landuse Basin Data Predeveloped Land Use Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod 0.09 Pervious Total 0.09 Impervious Land Use acre Impervious Total 0 Basin Total 0.09 Element Flows To: Surface Interflow Groundwater PERMEABLE PAVEMENT 7/27/2023 4:00:18 PM Page 3 Mitigated Land Use PERMEABLE PAVEMENT 7/27/2023 4:00:18 PM Page 4 Routing Elements Predeveloped Routing PERMEABLE PAVEMENT 7/27/2023 4:00:18 PM Page 5 Mitigated Routing Permeable Pavement 1 Pavement Area:0.0895 acre. Pavement Length:195.00 ft. Pavement Width: 20.00 ft. Pavement slope 1:0.02 To 1 Pavement thickness: 0.25 Pour Space of Pavement: 0.05 Material thickness of second layer: 0.33 Pour Space of material for second layer: 0.25 Material thickness of third layer: 0.5 Pour Space of material for third layer: 0.35 Infiltration On Infiltration rate: 0.1 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 9.557 Total Volume Through Riser (ac-ft.): 0 Total Volume Through Facility (ac-ft.): 9.557 Percent Infiltrated: 100 Total Precip Applied to Facility: 0 Total Evap From Facility: 1.004 Element Flows To: Outlet 1 Outlet 2 Permeable Pavement Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.089 0.000 0.000 0.000 0.0231 0.089 0.000 0.000 0.009 0.0462 0.089 0.001 0.000 0.009 0.0693 0.089 0.002 0.000 0.009 0.0924 0.089 0.002 0.000 0.009 0.1156 0.089 0.003 0.000 0.009 0.1387 0.089 0.004 0.000 0.009 0.1618 0.089 0.005 0.000 0.009 0.1849 0.089 0.005 0.000 0.009 0.2080 0.089 0.006 0.000 0.009 0.2311 0.089 0.007 0.000 0.009 0.2542 0.089 0.008 0.000 0.009 0.2773 0.089 0.008 0.000 0.009 0.3004 0.089 0.009 0.000 0.009 0.3236 0.089 0.010 0.000 0.009 0.3467 0.089 0.010 0.000 0.009 0.3698 0.089 0.011 0.000 0.009 0.3929 0.089 0.012 0.000 0.009 0.4160 0.089 0.013 0.000 0.009 0.4391 0.089 0.013 0.000 0.009 0.4622 0.089 0.014 0.000 0.009 0.4853 0.089 0.015 0.000 0.009 0.5084 0.089 0.015 0.000 0.009 0.5316 0.089 0.016 0.000 0.009 0.5547 0.089 0.016 0.000 0.009 0.5778 0.089 0.017 0.000 0.009 0.6009 0.089 0.017 0.000 0.009 0.6240 0.089 0.018 0.000 0.009 0.6471 0.089 0.018 0.000 0.009 PERMEABLE PAVEMENT 7/27/2023 4:00:18 PM Page 6 0.6702 0.089 0.019 0.000 0.009 0.6933 0.089 0.019 0.000 0.009 0.7164 0.089 0.020 0.000 0.009 0.7396 0.089 0.020 0.000 0.009 0.7627 0.089 0.021 0.000 0.009 0.7858 0.089 0.021 0.000 0.009 0.8089 0.089 0.022 0.000 0.009 0.8320 0.089 0.022 0.000 0.009 0.8551 0.089 0.022 0.000 0.009 0.8782 0.089 0.022 0.000 0.009 0.9013 0.089 0.022 0.000 0.009 0.9244 0.089 0.023 0.000 0.009 0.9476 0.089 0.023 0.000 0.009 0.9707 0.089 0.023 0.000 0.009 0.9938 0.089 0.023 0.000 0.009 1.0169 0.089 0.023 0.000 0.009 1.0400 0.089 0.023 0.000 0.009 1.0631 0.089 0.023 0.000 0.009 1.0862 0.089 0.025 0.008 0.009 1.1093 0.089 0.027 0.083 0.009 1.1324 0.089 0.029 0.200 0.009 1.1556 0.089 0.031 0.345 0.009 1.1787 0.089 0.033 0.516 0.009 1.2018 0.089 0.036 0.707 0.009 1.2249 0.089 0.038 0.918 0.009 1.2480 0.089 0.040 1.146 0.009 1.2711 0.089 0.042 1.391 0.009 1.2942 0.089 0.044 1.650 0.009 1.3173 0.089 0.046 1.925 0.009 1.3404 0.089 0.048 2.213 0.009 1.3636 0.089 0.050 2.514 0.009 1.3867 0.089 0.052 2.827 0.009 1.4098 0.089 0.054 3.153 0.009 1.4329 0.089 0.056 3.490 0.009 1.4560 0.089 0.058 3.838 0.009 1.4791 0.089 0.060 4.198 0.009 1.5022 0.089 0.062 4.568 0.009 1.5253 0.089 0.065 4.948 0.009 1.5484 0.089 0.067 5.338 0.009 1.5716 0.089 0.069 5.738 0.009 1.5947 0.089 0.071 6.147 0.009 1.6178 0.089 0.073 6.566 0.009 1.6409 0.089 0.075 6.994 0.009 1.6640 0.089 0.077 7.430 0.009 1.6871 0.089 0.079 7.876 0.009 1.7102 0.089 0.081 8.330 0.009 1.7333 0.089 0.083 8.792 0.009 1.7564 0.089 0.085 9.263 0.009 1.7796 0.089 0.087 9.742 0.009 1.8027 0.089 0.089 10.22 0.009 PERMEABLE PAVEMENT 7/27/2023 4:00:18 PM Page 7 2.0107 0.089 0.108 14.94 0.009 2.0338 0.089 0.110 15.50 0.009 2.0569 0.089 0.112 16.07 0.009 2.0800 0.089 0.114 16.65 0.009 PERMEABLE PAVEMENT 7/27/2023 4:00:18 PM Page 8 Analysis Results POC 1 If, 1pii Percent Time Exceetlir�g + Predeveloped Predeveloped Landuse Totals for POC #1 Total Pervious Area: 0.09 Total Impervious Area: 0 Mitigated Landuse Totals for POC #1 Total Pervious Area: 0 Total Impervious Area: 0.089532 omi x Mitigated Flow Frequency Method: Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.001108 5 year 0.001733 10 year 0.002122 25 year 0.002576 50 year 0.002885 100 year 0.00317 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0 5 year 0 10 year 0 25 year 0 50 year 0 100 year 0 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.000 0.000 1950 0.001 0.000 1951 0.001 0.000 1952 0.001 0.000 1953 0.001 0.000 1954 0.002 0.000 1955 0.002 0.000 1956 0.002 0.000 1957 0.002 0.000 1958 0.001 0.000 PERMEABLE PAVEMENT 7/27/2023 4:00:18 PM Page 9 1959 0.001 0.000 1960 0.001 0.000 1961 0.001 0.000 1962 0.001 0.000 1963 0.001 0.000 1964 0.001 0.000 1965 0.001 0.000 1966 0.001 0.000 1967 0.002 0.000 1968 0.002 0.000 1969 0.001 0.000 1970 0.001 0.000 1971 0.001 0.000 1972 0.001 0.000 1973 0.001 0.000 1974 0.001 0.000 1975 0.001 0.000 1976 0.001 0.000 1977 0.000 0.000 1978 0.001 0.000 1979 0.002 0.000 1980 0.001 0.000 1981 0.001 0.000 1982 0.001 0.000 1983 0.001 0.000 1984 0.001 0.000 1985 0.002 0.000 1986 0.004 0.000 1987 0.001 0.000 1988 0.001 0.000 1989 0.001 0.000 1990 0.001 0.000 1991 0.001 0.000 1992 0.001 0.000 1993 0.001 0.000 1994 0.000 0.000 1995 0.001 0.000 1996 0.003 0.000 1997 0.005 0.000 1998 0.001 0.000 1999 0.001 0.000 2000 0.001 0.000 2001 0.000 0.000 2002 0.001 0.000 2003 0.001 0.000 2004 0.001 0.000 2005 0.001 0.000 2006 0.003 0.000 2007 0.002 0.000 2008 0.002 0.000 2009 0.001 0.000 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.0046 0.0000 2 0.0042 0.0000 3 0.0025 0.0000 PERMEABLE PAVEMENT 7/27/2023 4:08:56 PM Page 10 4 0.0025 0.0000 5 0.0025 0.0000 6 0.0019 0.0000 7 0.0019 0.0000 8 0.0019 0.0000 9 0.0018 0.0000 10 0.0016 0.0000 11 0.0016 0.0000 12 0.0016 0.0000 13 0.0015 0.0000 14 0.0015 0.0000 15 0.0014 0.0000 16 0.0014 0.0000 17 0.0013 0.0000 18 0.0013 0.0000 19 0.0013 0.0000 20 0.0012 0.0000 21 0.0012 0.0000 22 0.0012 0.0000 23 0.0012 0.0000 24 0.0012 0.0000 25 0.0012 0.0000 26 0.0012 0.0000 27 0.0012 0.0000 28 0.0011 0.0000 29 0.0011 0.0000 30 0.0011 0.0000 31 0.0011 0.0000 32 0.0011 0.0000 33 0.0011 0.0000 34 0.0010 0.0000 35 0.0010 0.0000 36 0.0009 0.0000 37 0.0009 0.0000 38 0.0009 0.0000 39 0.0009 0.0000 40 0.0009 0.0000 41 0.0009 0.0000 42 0.0009 0.0000 43 0.0009 0.0000 44 0.0009 0.0000 45 0.0008 0.0000 46 0.0008 0.0000 47 0.0008 0.0000 48 0.0008 0.0000 49 0.0007 0.0000 50 0.0007 0.0000 51 0.0007 0.0000 52 0.0007 0.0000 53 0.0007 0.0000 54 0.0006 0.0000 55 0.0006 0.0000 56 0.0006 0.0000 57 0.0006 0.0000 58 0.0004 0.0000 59 0.0004 0.0000 60 0.0002 0.0000 61 0.0001 0.0000 PERMEABLE PAVEMENT 7/27/2023 4:08:56 PM Page 11 PERMEABLE PAVEMENT 7/27/2023 4:08:56 PM Page 12 Duration Flows The Facility PASSED Flow(cfs) Predev Mit Percentage Pass/Fail 0.0006 21079 0 0 Pass 0.0006 19276 0 0 Pass 0.0006 17528 0 0 Pass 0.0006 15999 0 0 Pass 0.0006 14510 0 0 Pass 0.0007 13297 0 0 Pass 0.0007 12157 0 0 Pass 0.0007 11135 0 0 Pass 0.0007 10187 0 0 Pass 0.0008 9370 0 0 Pass 0.0008 8620 0 0 Pass 0.0008 7931 0 0 Pass 0.0008 7341 0 0 Pass 0.0009 6727 0 0 Pass 0.0009 6226 0 0 Pass 0.0009 5704 0 0 Pass 0.0009 5238 0 0 Pass 0.0010 4795 0 0 Pass 0.0010 4404 0 0 Pass 0.0010 4062 0 0 Pass 0.0010 3760 0 0 Pass 0.0010 3480 0 0 Pass 0.0011 3204 0 0 Pass 0.0011 2954 0 0 Pass 0.0011 2723 0 0 Pass 0.0011 2547 0 0 Pass 0.0012 2385 0 0 Pass 0.0012 2252 0 0 Pass 0.0012 2120 0 0 Pass 0.0012 2007 0 0 Pass 0.0013 1904 0 0 Pass 0.0013 1791 0 0 Pass 0.0013 1685 0 0 Pass 0.0013 1590 0 0 Pass 0.0014 1487 0 0 Pass 0.0014 1384 0 0 Pass 0.0014 1322 0 0 Pass 0.0014 1251 0 0 Pass 0.0014 1204 0 0 Pass 0.0015 1158 0 0 Pass 0.0015 1120 0 0 Pass 0.0015 1077 0 0 Pass 0.0015 1033 0 0 Pass 0.0016 993 0 0 Pass 0.0016 964 0 0 Pass 0.0016 930 0 0 Pass 0.0016 895 0 0 Pass 0.0017 858 0 0 Pass 0.0017 822 0 0 Pass PERMEABLE PAVEMENT 7/27/2023 4:08:56 PM Page 13 0.0018 683 0 0 Pass 0.0018 664 0 0 Pass 0.0018 645 0 0 Pass 0.0019 626 0 0 Pass 0.0019 607 0 0 Pass 0.0019 584 0 0 Pass 0.0019 567 0 0 Pass 0.0020 556 0 0 Pass 0.0020 541 0 0 Pass 0.0020 527 0 0 Pass 0.0020 515 0 0 Pass 0.0021 505 0 0 Pass 0.0021 495 0 0 Pass 0.0021 483 0 0 Pass 0.0021 471 0 0 Pass 0.0022 459 0 0 Pass 0.0022 443 0 0 Pass 0.0022 428 0 0 Pass 0.0022 417 0 0 Pass 0.0022 405 0 0 Pass 0.0023 388 0 0 Pass 0.0023 371 0 0 Pass 0.0023 356 0 0 Pass 0.0023 339 0 0 Pass 0.0024 325 0 0 Pass 0.0024 318 0 0 Pass 0.0024 307 0 0 Pass 0.0024 302 0 0 Pass 0.0025 291 0 0 Pass 0.0025 287 0 0 Pass 0.0025 279 0 0 Pass 0.0025 274 0 0 Pass 0.0026 268 0 0 Pass 0.0026 265 0 0 Pass 0.0026 262 0 0 Pass 0.0026 257 0 0 Pass 0.0026 253 0 0 Pass 0.0027 245 0 0 Pass 0.0027 242 0 0 Pass 0.0027 236 0 0 Pass 0.0027 231 0 0 Pass 0.0028 226 0 0 Pass 0.0028 224 0 0 Pass 0.0028 222 0 0 Pass 0.0028 220 0 0 Pass 0.0029 217 0 0 Pass 0.0029 211 0 0 Pass PERMEABLE PAVEMENT 7/27/2023 4:08:56 PM Page 14 Water Quality 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. PERMEABLE PAVEMENT 7/27/2023 4:08:56 PM Page 15 LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Permeable Pavement 1 POC ❑ 8.70 ❑ 100.00 Total Volume Infiltrated 8.70 n I 1 1 00 100.00 0.00 0% No Treat. Credit Duration Compliance with LID Analysis Standard 8% of 2-yr to 50% of Result= 2 yr Passed PERMEABLE PAVEMENT 7/27/2023 4:08:56 PM Page 16 Model Default Modifications Total of 0 changes have been made. PERLND Changes No PERLND changes have been made. IMPLND Changes No IMPLND changes have been made. PERMEABLE PAVEMENT 7/27/2023 4:09:24 PM Page 17 Appendix Predeveloped Schematic L. -j Basin 1 .. Li 0.09ac PERMEABLE PAVEMENT 7/27/2023 4:09:24 PM Page 18 Mitigated Schematic Perme ble Pave ent 1 PERMEABLE PAVEMENT 7/27/2023 4:09:26 PM Page 19 Predeveloped UCI File RUN GLOBAL WWHM4 model simulation START 1948 10 01 END RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 END GLOBAL 2009 09 30 FILES <File> <Un#> END FILES OPN SEQUENCE UNIT SYSTEM 1 <----------- File Name----- ------------------------->*** *** INGRP INDELT 00:15 PERLND 11 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<---------- Title ----------- >***TRAN PIVL DIG1 FIL1 1 Basin 1 MAX END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** END OPCODE PARM # # K *** END PARM END GENER PERLND GEN-INFO PYR DIG2 FIL2 YRND 1 2 30 9 <PLS ><------- Name ------- >NBLKS Unit -systems Printer *** # - # User t-series Engl Metr *** in out *** 11 C, Forest, Mod 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 11 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT -INFO <PLS > ***************** Print -flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 11 0 0 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT -INFO PERMEABLE PAVEMENT 7/27/2023 4:09:28 PM Page 20 PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 11 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY 11 0 4.5 0.08 400 0.1 0.5 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 # - # ***PETMAX PETMIN INFEXP 11 0 0 2 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 # - # CEPSC UZSN NSUR 11 0.2 0.5 0.35 END PWAT-PARM4 AGWRC 0.996 *** INFILD DEEPFR BASETP AGWETP 2 0 0 0 *** INTFW IRC LZETP *** 6 0.5 0.7 PWAT-STATEI <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS 11 0 0 0 0 2.5 1 END PWAT-STATEI END PERLND IMPLND GEN-INFO <PLS ><------- Name ------- > END GEN-INFO *** Section IWATER*** Unit -systems Printer *** User t-series Engl Metr *** in out *** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** END ACTIVITY PRINT -INFO <ILS > ******** Print -flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* END PRINT -INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN END IWAT-PARM3 IWAT-STATEI <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS END IWAT-STATEI GWVS 0 PERMEABLE PAVEMENT 7/27/2023 4:09:28 PM Page 21 END IMPLND SCHEMATIC <-Source-> <Name> # Basin 1*** PERLND 11 PERLND 11 ******Routing****** END SCHEMATIC <--Area--> <-Target-> MBLK <-factor-> <Name> # Tbl# 0.09 COPY 501 12 0.09 COPY 501 13 NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems Printer *** # - #<------------------ >< --- > User T-series Engl Metr LKFG *** in out *** END GEN-INFO *** Section RCHRES*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** END ACTIVITY PRINT -INFO <PLS > ***************** Print -flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* END PRINT -INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC Al A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------ ><-------- ><--------><--------><--------><--------><--------> *** END HYDR-PARM2 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><-------- > <---><---><---><---><---> *** <---><---><---><---><---> END HYDR-INIT END RCHRES SPEC -ACTIONS END SPEC -ACTIONS FTABLES END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 0.8 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 0.8 IMPLND 1 999 EXTNL PREC PERMEABLE PAVEMENT 7/27/2023 4:09:28 PM Page 22 WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** COPY 501 OUTPUT MEAN 1 1 48.4 WDM 501 FLOW ENGL REPL END EXT TARGETS MASS -LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS -LINK 12 PERLND PWATER SURD 0.083333 COPY INPUT MEAN END MASS -LINK 12 MASS -LINK 13 PERLND PWATER IFWO 0.083333 COPY INPUT MEAN END MASS -LINK 13 END MASS -LINK END RUN PERMEABLE PAVEMENT 7/27/2023 4:09:28 PM Page 23 Mitigated UC/ File RUN GLOBAL WWHM4 model simulation START 1948 10 01 END RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 END GLOBAL 2009 09 30 FILES <File> <Un#> END FILES OPN SEQUENCE UNIT SYSTEM 1 <----------- File Name----- ------------------------->*** *** INGRP INDELT 00:15 IMPLND 16 RCHRES 1 COPY 1 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<---------- Title ----------- >***TRAN PIVL DIG1 FIL1 1 Permeable Pavement 1 MAX END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** END OPCODE PARM # # K *** END PARM END GENER PERLND GEN-INFO PYR DIG2 FIL2 YRND 1 2 30 9 <PLS ><------- Name ------- >NBLKS Unit -systems Printer *** # - # User t-series Engl Metr *** in out *** END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** END ACTIVITY PRINT -INFO <PLS > ***************** Print -flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* END PRINT -INFO PWAT-PARM1 PERMEABLE PAVEMENT 7/27/2023 4:09:28 PM Page 24 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 # - # ***PETMAX PETMIN INFEXP END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 # - # CEPSC UZSN NSUR END PWAT-PARM4 AGWRC *** INFILD DEEPFR BASETP AGWETP *** INTFW IRC LZETP *** PWAT-STATEI <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS END PWAT-STATEI END PERLND IMPLND GEN-INFO <PLS ><------- Name ------- > 16 Porous Pavement END GEN-INFO *** Section IWATER*** Unit -systems Printer *** User t-series Engl Metr *** in out *** 1 1 1 27 0 ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** 16 0 0 1 0 0 0 END ACTIVITY PRINT -INFO <ILS > ******** Print -flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* 16 0 0 4 0 0 0 1 9 END PRINT -INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** 16 0 0 0 0 0 END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC 16 400 0.01 0.1 0.1 END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN 16 0 0 END IWAT-PARM3 IWAT-STATEI <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS 16 0 0 END IWAT-STATEI GWVS PERMEABLE PAVEMENT 7/27/2023 4:09:29 PM Page 25 END IMPLND SCHEMATIC <-Source-> <--Area--> <Name> # <-factor-> IMPLND 16 0.0895 ******Routing****** RCHRES 1 1 END SCHEMATIC <-Target-> MBLK *** <Name> # Tbl# *** RCHRES 1 5 COPY 501 17 NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems # - #<------------------ >< --- > User T-series in out 1 Permeable Paveme-008 2 1 1 1 END GEN-INFO *** Section RCHRES*** Printer *** Engl Metr LKFG *** *** 28 0 1 ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** 1 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT -INFO <PLS > ***************** Print -flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* 1 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT -INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC Al A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** 1 0 1 0 0 4 5 0 0 0 0 0 0 0 0 2 2 2 2 2 END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------ ><-------->< -------- ><-------- >< -------- ><-------- ><-------- > *** 1 1 0.04 0.0 0.0 0.5 0.0 END HYDR-PARM2 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><-------- > <--- ><--- ><--- >< --- ><---> *** <--- ><--- ><--- ><--- ><---> 1 0 4.0 5.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 END HYDR-INIT END RCHRES SPEC -ACTIONS END SPEC -ACTIONS FTABLES FTABLE 1 PERMEABLE PAVEMENT 7/27/2023 4:09:29 PM Page 26 91 5 Depth Area Volume Outflowl Outflow2 (ft) (acres) (acre-ft) (cfs) (cfs) 0.000000 0.089532 0.000000 0.000000 0.000000 0.023111 0.089532 0.000724 0.000000 0.009028 0.046222 0.089532 0.001448 0.000000 0.009028 0.069333 0.089532 0.002173 0.000000 0.009028 0.092444 0.089532 0.002897 0.000000 0.009028 0.115556 0.089532 0.003621 0.000000 0.009028 0.138667 0.089532 0.004345 0.000000 0.009028 0.161778 0.089532 0.005069 0.000000 0.009028 0.184889 0.089532 0.005794 0.000000 0.009028 0.208000 0.089532 0.006518 0.000000 0.009028 0.231111 0.089532 0.007242 0.000000 0.009028 0.254222 0.089532 0.007966 0.000000 0.009028 0.277333 0.089532 0.008691 0.000000 0.009028 0.300444 0.089532 0.009415 0.000000 0.009028 0.323556 0.089532 0.010139 0.000000 0.009028 0.346667 0.089532 0.010863 0.000000 0.009028 0.369778 0.089532 0.011587 0.000000 0.009028 0.392889 0.089532 0.012312 0.000000 0.009028 0.416000 0.089532 0.013036 0.000000 0.009028 0.439111 0.089532 0.013760 0.000000 0.009028 0.462222 0.089532 0.014484 0.000000 0.009028 0.485333 0.089532 0.015208 0.000000 0.009028 0.508444 0.089532 0.015726 0.000000 0.009028 0.531556 0.089532 0.016243 0.000000 0.009028 0.554667 0.089532 0.016760 0.000000 0.009028 0.577778 0.089532 0.017278 0.000000 0.009028 0.600889 0.089532 0.017795 0.000000 0.009028 0.624000 0.089532 0.018312 0.000000 0.009028 0.647111 0.089532 0.018830 0.000000 0.009028 0.670222 0.089532 0.019347 0.000000 0.009028 0.693333 0.089532 0.019864 0.000000 0.009028 0.716444 0.089532 0.020381 0.000000 0.009028 0.739556 0.089532 0.020899 0.000000 0.009028 0.762667 0.089532 0.021416 0.000000 0.009028 0.785778 0.089532 0.021933 0.000000 0.009028 0.808889 0.089532 0.022451 0.000000 0.009028 0.832000 0.089532 0.022554 0.000000 0.009028 0.855111 0.089532 0.022657 0.000000 0.009028 0.878222 0.089532 0.022761 0.000000 0.009028 0.901333 0.089532 0.022864 0.000000 0.009028 0.924444 0.089532 0.022968 0.000000 0.009028 0.947556 0.089532 0.023071 0.000000 0.009028 0.970667 0.089532 0.023175 0.000000 0.009028 0.993778 0.089532 0.023278 0.000000 0.009028 1.016889 0.089532 0.023382 0.000000 0.009028 1.040000 0.089532 0.023485 0.000000 0.009028 1.063111 0.089532 0.023589 0.000000 0.009028 1.086222 0.089532 0.025658 0.008172 0.009028 1.109333 0.089532 0.027727 0.083648 0.009028 1.132444 0.089532 0.029796 0.199969 0.009028 1.155556 0.089532 0.031865 0.345791 0.009028 1.178667 0.089532 0.033934 0.516024 0.009028 1.201778 0.089532 0.036004 0.707565 0.009028 1.224889 0.089532 0.038073 0.918263 0.009028 1.248000 0.089532 0.040142 1.146511 0.009028 1.271111 0.089532 0.042211 1.391051 0.009028 1.294222 0.089532 0.044280 1.650863 0.009028 1.317333 0.089532 0.046350 1.925096 0.009028 1.340444 0.089532 0.048419 2.213028 0.009028 1.363556 0.089532 0.050488 2.514036 0.009028 1.386667 0.089532 0.052557 2.827575 0.009028 1.409778 0.089532 0.054626 3.153162 0.009028 1.432889 0.089532 0.056695 3.490368 0.009028 1.456000 0.089532 0.058765 3.838805 0.009028 1.479111 0.089532 0.060834 4.198121 0.009028 1.502222 0.089532 0.062903 4.567998 0.009028 1.525333 0.089532 0.064972 4.948141 0.009028 Velocity Travel Time*** (ft/sec) (Minutes)*** PERMEABLE PAVEMENT 7/27/2023 4:09:29 PM Page 27 1.548444 0.089532 0.067041 5.338280 0.009028 1.571556 0.089532 0.069110 5.738167 0.009028 1.594667 0.089532 0.071180 6.147567 0.009028 1.617778 0.089532 0.073249 6.566267 0.009028 1.640889 0.089532 0.075318 6.994062 0.009028 1.664000 0.089532 0.077387 7.430765 0.009028 1.687111 0.089532 0.079456 7.876196 0.009028 1.710222 0.089532 0.081526 8.330188 0.009028 1.733333 0.089532 0.083595 8.792583 0.009028 1.756444 0.089532 0.085664 9.263230 0.009028 1.779556 0.089532 0.087733 9.741987 0.009028 1.802667 0.089532 0.089802 10.22872 0.009028 1.825778 0.089532 0.091871 10.72330 0.009028 1.848889 0.089532 0.093941 11.22560 0.009028 1.872000 0.089532 0.096010 11.73551 0.009028 1.895111 0.089532 0.098079 12.25292 0.009028 1.918222 0.089532 0.100148 12.77771 0.009028 1.941333 0.089532 0.102217 13.30979 0.009028 1.964444 0.089532 0.104287 13.84905 0.009028 1.987556 0.089532 0.106356 14.39541 0.009028 2.010667 0.089532 0.108425 14.94877 0.009028 2.033778 0.089532 0.110494 15.50904 0.009028 2.056889 0.089532 0.112563 16.07615 0.009028 2.080000 0.089532 0.114632 16.65000 0.009028 END FTABLE 1 END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 0.8 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 0.8 IMPLND 1 999 EXTNL PREC WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 RCHRES 1 EXTNL POTEV END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** COPY 1 OUTPUT MEAN 1 1 48.4 WDM 701 FLOW ENGL REPL COPY 501 OUTPUT MEAN 1 1 48.4 WDM 801 FLOW ENGL REPL END EXT TARGETS MASS -LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS -LINK 5 IMPLND IWATER SURO 0.083333 RCHRES INFLOW IVOL END MASS -LINK 5 MASS -LINK 17 RCHRES OFLOW OVOL 1 COPY INPUT MEAN END MASS -LINK 17 END MASS -LINK END RUN PERMEABLE PAVEMENT 7/27/2023 4:09:29 PM Page 28 Predeveloped HSPF Message File PERMEABLE PAVEMENT 7/27/2023 4:09:29 PM Page 29 Mitigated HSPF Message File PERMEABLE PAVEMENT 7/27/2023 4:09:29 PM Page 30 Disclaimer Legal Notice This program and accompanying documentation are provided 'as -is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim 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. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by: Clear Creek Solutions, Inc. 2005-2023; All Rights Reserved. Clear Creek Solutions, Inc. 6200 Capitol Blvd. Ste F Olympia, WA. 98501 Toll Free 1(866)943-0304 Local (360)943-0304 www.clearcreeksolutions.com PERMEABLE PAVEMENT 7/27/2023 4:09:29 PM Page 31 WWHM2012 PROJECT REPORT FLOW CONTROL CHECK General Model Information Project Name: Landsverk SFR WWHM Site Name: LANDSVERK SFR Site Address: City: EDMONDS Report Date: 6/29/2023 Gage: Everett Data Start: 1948/10/01 Data End: 2009/09/30 Timestep: 15 Minute Precip Scale: 0.800 Version Date: 2021 /08/18 Version: 4.2.18 POC Thresholds Low Flow Threshold for POC1: 50 Percent of the 2 Year High Flow Threshold for POC1: 50 Year Landsverk SFR WWHM 6/29/2023 4:37:14 PM Page 2 Landuse Basin Data Predeveloped Land Use Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod 0.76 Pervious Total 0.76 Impervious Land Use acre Impervious Total 0 Basin Total 0.76 Element Flows To: Surface Interflow Groundwater Landsverk SFR WWHM 6/29/2023 4:37:14 PM Page 3 Mitigated Land Use Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Mod 0.43 Pervious Total 0.43 Impervious Land Use acre Impervious Total 0 Basin Total 0.43 Element Flows To: Surface Interflow Groundwater Landsverk SFR WWHM 6/29/2023 4:37:14 PM Page 4 Routing Elements Predeveloped Routing Landsverk SFR WWHM 6/29/2023 4:37:14 PM Page 5 Mitigated Routing Landsverk SFR WWHM 6/29/2023 4:37:14 PM Page 6 Analysis Results POC 1 n F 0.02 )U 0.01 Q iL 0.01 0.00 1.0 Cumulative Probability TIO on — o+ + + + w ++ oo1 s x x x ���x��% 001 -- - -- _ -- 1n lnri omi �aoi Percent Time Exceetlir�g 05 7 2 5 70 20 30 50 70 W 90 95 95 99 99.5 7 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area- 0.76 Total Impervious Area- 0 Mitigated Landuse Totals for POC #1 Total Pervious Area- 0.43 Total Impervious Area- 0 Flow Frequency Method- Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.009358 5 year 0.014636 10 year 0.017921 25 year 0.021749 50 year 0.02436 100 year 0.026772 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.018291 5 year 0.035025 10 year 0.050257 25 year 0.075096 50 year 0.098242 100 year 0.125881 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.001 0.024 1950 0.012 0.030 1951 0.009 0.017 1952 0.007 0.018 1953 0.005 0.016 1954 0.016 0.080 1955 0.016 0.033 1956 0.013 0.016 1957 0.015 0.034 1958 0.010 0.052 Landsverk SFR WWHM 6/29/2023 4:37:14 PM Page 7 1959 0.010 0.015 1960 0.009 0.017 1961 0.010 0.131 1962 0.006 0.019 1963 0.008 0.047 1964 0.009 0.026 1965 0.009 0.009 1966 0.005 0.006 1967 0.013 0.018 1968 0.013 0.019 1969 0.007 0.120 1970 0.007 0.013 1971 0.011 0.025 1972 0.010 0.033 1973 0.006 0.017 1974 0.011 0.042 1975 0.008 0.026 1976 0.007 0.013 1977 0.003 0.008 1978 0.007 0.009 1979 0.014 0.057 1980 0.008 0.022 1981 0.007 0.010 1982 0.010 0.015 1983 0.010 0.033 1984 0.009 0.011 1985 0.014 0.021 1986 0.036 0.048 1987 0.012 0.015 1988 0.008 0.010 1989 0.006 0.023 1990 0.010 0.010 1991 0.011 0.010 1992 0.008 0.018 1993 0.005 0.009 1994 0.003 0.010 1995 0.010 0.011 1996 0.021 0.032 1997 0.039 0.066 1998 0.005 0.009 1999 0.010 0.008 2000 0.006 0.014 2001 0.001 0.003 2002 0.009 0.010 2003 0.006 0.008 2004 0.009 0.017 2005 0.008 0.009 2006 0.021 0.045 2007 0.016 0.035 2008 0.021 0.026 2009 0.008 0.008 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.0386 0.1305 2 0.0355 0.1195 3 0.0213 0.0804 Landsverk SFR WWHM 6/29/2023 4:37:52 PM Page 8 4 0.0212 0.0664 5 0.0208 0.0569 6 0.0162 0.0518 7 0.0160 0.0480 8 0.0160 0.0471 9 0.0148 0.0452 10 0.0137 0.0417 11 0.0136 0.0348 12 0.0133 0.0344 13 0.0130 0.0335 14 0.0129 0.0334 15 0.0119 0.0330 16 0.0118 0.0317 17 0.0111 0.0296 18 0.0109 0.0264 19 0.0107 0.0261 20 0.0103 0.0259 21 0.0102 0.0246 22 0.0102 0.0243 23 0.0102 0.0227 24 0.0099 0.0223 25 0.0099 0.0208 26 0.0098 0.0193 27 0.0098 0.0191 28 0.0095 0.0185 29 0.0093 0.0177 30 0.0093 0.0177 31 0.0091 0.0172 32 0.0090 0.0170 33 0.0089 0.0168 34 0.0088 0.0167 35 0.0088 0.0164 36 0.0080 0.0156 37 0.0079 0.0155 38 0.0079 0.0151 39 0.0079 0.0146 40 0.0078 0.0143 41 0.0077 0.0134 42 0.0075 0.0125 43 0.0074 0.0112 44 0.0072 0.0106 45 0.0070 0.0105 46 0.0069 0.0103 47 0.0068 0.0102 48 0.0065 0.0101 49 0.0061 0.0099 50 0.0060 0.0096 51 0.0057 0.0094 52 0.0056 0.0094 53 0.0055 0.0093 54 0.0054 0.0092 55 0.0053 0.0088 56 0.0051 0.0084 57 0.0049 0.0083 58 0.0034 0.0078 59 0.0034 0.0077 60 0.0014 0.0060 61 0.0012 0.0026 Landsverk SFR WWHM 6/29/2023 4:37:52 PM Page 9 Landsverk SFR WWHM 6/29/2023 4:37:52 PM Page 10 Duration Flows Flow(cfs) Predev Mit Percentage Pass/Fail 0.0047 21068 29388 139 Fail 0.0049 19222 26565 138 Fail 0.0051 17522 23955 136 Fail 0.0053 15954 21581 135 Fail 0.0055 14495 19408 133 Fail 0.0057 13267 17436 131 Fail 0.0059 12147 15588 128 Fail 0.0061 11103 13873 124 Fail 0.0063 10173 12448 122 Fail 0.0065 9332 11111 119 Fail 0.0067 8609 9948 115 Fail 0.0069 7931 8898 112 Fail 0.0071 7328 8031 109 Fail 0.0073 6727 7244 107 Fail 0.0075 6205 6481 104 Fail 0.0077 5702 5839 102 Fail 0.0079 5230 5193 99 Pass 0.0081 4789 4665 97 Pass 0.0083 4389 4235 96 Pass 0.0085 4057 3874 95 Pass 0.0087 3752 3574 95 Pass 0.0089 3474 3320 95 Pass 0.0091 3206 3037 94 Pass 0.0093 2945 2719 92 Pass 0.0095 2723 2494 91 Pass 0.0096 2541 2293 90 Pass 0.0098 2383 2108 88 Pass 0.0100 2252 1948 86 Pass 0.0102 2122 1795 84 Pass 0.0104 2006 1679 83 Pass 0.0106 1904 1577 82 Pass 0.0108 1789 1476 82 Pass 0.0110 1684 1383 82 Pass 0.0112 1593 1316 82 Pass 0.0114 1489 1243 83 Pass 0.0116 1386 1179 85 Pass 0.0118 1322 1122 84 Pass 0.0120 1252 1071 85 Pass 0.0122 1202 1028 85 Pass 0.0124 1158 977 84 Pass 0.0126 1119 921 82 Pass 0.0128 1079 878 81 Pass 0.0130 1033 836 80 Pass 0.0132 994 810 81 Pass 0.0134 965 784 81 Pass 0.0136 930 756 81 Pass 0.0138 895 739 82 Pass 0.0140 857 711 82 Pass 0.0142 822 679 82 Pass Landsverk SFR WWHM 6/29/2023 4:37:52 PM Page 11 0.0154 664 578 87 Pass 0.0156 645 563 87 Pass 0.0158 626 547 87 Pass 0.0160 607 534 87 Pass 0.0162 584 520 89 Pass 0.0164 568 510 89 Pass 0.0166 556 496 89 Pass 0.0168 541 476 87 Pass 0.0170 527 458 86 Pass 0.0172 515 446 86 Pass 0.0174 505 437 86 Pass 0.0176 495 425 85 Pass 0.0178 483 415 85 Pass 0.0180 472 408 86 Pass 0.0182 459 402 87 Pass 0.0184 443 394 88 Pass 0.0186 428 387 90 Pass 0.0188 417 377 90 Pass 0.0190 405 366 90 Pass 0.0192 388 358 92 Pass 0.0194 371 352 94 Pass 0.0196 356 346 97 Pass 0.0198 339 338 99 Pass 0.0200 325 328 100 Pass 0.0202 318 320 100 Pass 0.0204 307 314 102 Pass 0.0206 302 303 100 Pass 0.0208 292 295 101 Pass 0.0210 287 285 99 Pass 0.0212 279 277 99 Pass 0.0214 274 271 98 Pass 0.0216 268 263 98 Pass 0.0218 265 259 97 Pass 0.0220 262 247 94 Pass 0.0222 257 243 94 Pass 0.0224 253 235 92 Pass 0.0226 245 225 91 Pass 0.0228 242 216 89 Pass 0.0230 236 203 86 Pass 0.0232 231 198 85 Pass 0.0234 226 192 84 Pass 0.0236 224 185 82 Pass 0.0238 222 175 78 Pass 0.0240 220 168 76 Pass 0.0242 217 161 74 Pass 0.0244 211 148 70 Pass 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. Landsverk SFR WWHM 6/29/2023 4:37:52 PM Page 12 Water Quality 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. Landsverk SFR WWHM 6/29/2023 4:37:52 PM Page 13 LID Report LILTesYinique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Total Volume Infiltrated 0.00 0.00 0.00 0.00 0.00 0% No Treat. Credit Duration Compliance with LID Analysis Standard 8% of 2-yr to 50% of Result = 2 yr Failed Landsverk SFR WWHM 6/29/2023 4:37:52 PM Page 14 Model Default Modifications Total of 0 changes have been made. PERLND Changes No PERLND changes have been made. IMPLND Changes No IMPLND changes have been made. Landsverk SFR WWHM 6/29/2023 4:38:19 PM Page 15 Appendix Predeveloped Schematic L. -j Basin .. Li 0.76ac Landsverk SFR WWHM 6/29/2023 4:38:19 PM Page 16 Mitigated Schematic Basin 1 0.43ac Landsverk SFR WWHM 6/29/2023 4:38:21 PM Page 17 Predeveloped UCI File Landsverk SFR WWHM 6/29/2023 4:38:23 PM Page 18 Mitigated UC/ File RUN GLOBAL WWHM4 model simulation START 1948 10 01 END RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 END GLOBAL 2009 09 30 FILES <File> <Un#> END FILES OPN SEQUENCE UNIT SYSTEM 1 <----------- File Name----- ------------------------->*** *** INGRP INDELT 00:15 PERLND 17 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<---------- Title ----------- >***TRAN PIVL DIG1 FIL1 1 Basin 1 MAX END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** END OPCODE PARM # # K *** END PARM END GENER PERLND GEN-INFO PYR DIG2 FIL2 YRND 1 2 30 9 <PLS ><------- Name ------- >NBLKS Unit -systems Printer *** # - # User t-series Engl Metr *** in out *** 17 C, Lawn, Mod 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 17 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT -INFO <PLS > ***************** Print -flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 17 0 0 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT -INFO Landsverk SFR WWHM 6/29/2023 4:38:23 PM Page 19 PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 17 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY 17 0 4.5 0.03 400 0.1 0.5 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 # - # ***PETMAX PETMIN INFEXP 17 0 0 2 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 # - # CEPSC UZSN NSUR 17 0.1 0.25 0.25 END PWAT-PARM4 AGWRC 0.996 *** INFILD DEEPFR BASETP AGWETP 2 0 0 0 *** INTFW IRC LZETP *** 6 0.5 0.25 PWAT-STATEI <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS 17 0 0 0 0 2.5 1 END PWAT-STATEI END PERLND IMPLND GEN-INFO <PLS ><------- Name ------- > END GEN-INFO *** Section IWATER*** Unit -systems Printer *** User t-series Engl Metr *** in out *** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** END ACTIVITY PRINT -INFO <ILS > ******** Print -flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* END PRINT -INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN END IWAT-PARM3 IWAT-STATEI <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS END IWAT-STATEI GWVS 0 Landsverk SFR WWHM 6/29/2023 4:38:23 PM Page 20 END IMPLND SCHEMATIC <-Source-> <Name> # Basin 1*** PERLND 17 PERLND 17 ******Routing****** END SCHEMATIC <--Area--> <-Target-> MBLK <-factor-> <Name> # Tbl# 0.43 COPY 501 12 0.43 COPY 501 13 NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems Printer *** # - #<------------------ >< --- > User T-series Engl Metr LKFG *** in out *** END GEN-INFO *** Section RCHRES*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** END ACTIVITY PRINT -INFO <PLS > ***************** Print -flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* END PRINT -INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC Al A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------ ><-------- ><--------><--------><--------><--------><--------> *** END HYDR-PARM2 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><-------- > <---><---><---><---><---> *** <---><---><---><---><---> END HYDR-INIT END RCHRES SPEC -ACTIONS END SPEC -ACTIONS FTABLES END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 0.8 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 0.8 IMPLND 1 999 EXTNL PREC Landsverk SFR WWHM 6/29/2023 4:38:23 PM Page 21 WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** COPY 1 OUTPUT MEAN 1 1 48.4 WDM 701 FLOW ENGL REPL COPY 501 OUTPUT MEAN 1 1 48.4 WDM 801 FLOW ENGL REPL END EXT TARGETS MASS -LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS -LINK 12 PERLND PWATER SURO 0.083333 COPY INPUT MEAN END MASS -LINK 12 MASS -LINK 13 PERLND PWATER IFWO 0.083333 COPY INPUT MEAN END MASS -LINK 13 END MASS -LINK END RUN Landsverk SFR WWHM 6/29/2023 4:38:23 PM Page 22 Predeveloped HSPF Message File Landsverk SFR WWHM 6/29/2023 4:38:23 PM Page 23 Mitigated HSPF Message File Landsverk SFR WWHM 6/29/2023 4:38:23 PM Page 24 Disclaimer Legal Notice This program and accompanying documentation are provided 'as -is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim 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. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by: Clear Creek Solutions, Inc. 2005-2023; All Rights Reserved. Clear Creek Solutions, Inc. 6200 Capitol Blvd. Ste F Olympia, WA. 98501 Toll Free 1(866)943-0304 Local (360)943-0304 www.clearcreeksolutions.com Landsverk SFR WWHM 6/29/2023 4:38:23 PM Page 25 COBALT G E 0 S C I E N C E S January 14, 2023 Landsverk Quality Homes Attn: Duane Landsverk & Joseph Rowett 24113 56th Avenue West Mountlake Terrace, Washington RE: Geotechnical Evaluation Proposed Development 19515 94th Place West Edmonds, Washington Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, Washington 98028 In accordance with your authorization, Cobalt Geosciences, LLC has prepared this letter to discuss the results of our geotechnical evaluation at the referenced site. The purpose of our evaluation was to provide recommendations for foundation design, stormwater management, grading, and earthwork. Site Description The site is located at 19515 94th Place West in Edmonds, Washington. The site consists of one irregularly shaped parcel (No. 004346o00058o1) with a total area of about 1.19 acres. We understand that the project will likely include boundary line adjustments with the parcel to the east and south (No. 00434600005805), with the new parcel including steep slope areas to the south. The western portion of the site is developed with a residence. There is a driveway extending north of the residence providing access for the subject property and property to the east (same owner). The remainder of the site is undeveloped and vegetated with grasses, ferns, ivy, blackberry vines, bushes, and variable diameter trees. The site and developed portions of the property to the east are situated on a west -trending ridge with low slope magnitudes (5 to 12 percent). There are locally steep and very steep natural and partially graded slopes extending downward from the ridge to the north, west, and south. We describe these areas as follows: The steep slopes near the west property line are mostly the result of prior grading associated with the access roadway. This slope is 15 to 20 feet tall and has magnitudes of 50 to 8o percent. The slope is locally faced with rockery walls. The steep slopes near the southern portion of the site and adjacent parcel have magnitudes of up to vertical to overturned as a result of sloughing. Overall, the slope magnitudes range from 6o to 150 percent where vegetation is present. There are rockery walls at the toe of this slope near the area roadways. The areas near the top of the slope have exposed outwash sands in sloughs. These areas are 3 to 7 feet in height with the height increasing to the east. There are trees and other understory hanging over the sloughed zones. The total height of these slopes is 40 to 6o feet. www.cobaltgeo.com (2o6) 331-1097 January 14, 2023 Page 2 of 14 Geotechnical Evaluation The steep slope areas to the north of the site have magnitudes of 40 to 90 percent and relief of 40 to 50 feet from west to east. These slopes continue to the north at lower magnitudes. There are apparent wetland areas and standing water further north in the low lying areas. The site is bordered to the north and east by residential properties, to the west by an access road and residences, and to the south by right of way and Puget Drive. As noted, the proposed development includes boundary line adjustments between the subject parcel and property to the east followed by construction of a new residence, driveway, and garage in the east -central portion of the site. The existing residence will removed. Stormwater will include infiltration or other systems depending on feasibility. Site grading may include cuts and fills of 3 feet or less, and foundation loads are expected to be light. We should be provided with the final plans to verify if our recommendations remain valid or require updating. Area Geology The Geologic Map of the Edmonds East and West Quadrangles, indicates that the site is underlain by Vashon Glacial Till and near the contacts with Vashon Advance Outwash. Vashon Glacial Till includes mixtures of silt, sand, clay, and gravel. These materials are usually impermeable and are typically dense to very dense below a weathered zone. These deposits are often underlain by Vashon Advance Outwash. The outwash includes fine to medium grained sand with minor gravel and silt. These deposits are typically permeable. Soil & Groundwater Conditions As part of our evaluation, we excavated a test pit within the property areas, where accessible. We also traversed steeper slope areas and advanced shallow hand borings/probes to determine the approximate depth to medium dense soils and general soil composition. The test pit encountered approximately 6 inches of grass and topsoil underlain by approximately 3.5 feet of loose to medium dense, silty -fine to medium grained sand with gravel (Weathered Advance Outwash). These materials were underlain by medium dense to dense, fine to medium grained sand trace to with gravel (Vashon Advance Outwash), which continued to the termination depths of the exploration. Groundwater was not encountered during the exploration work. There is a very slight chance that interflow could develop in some areas of the site on finer grained soils. In general, outwash sands are well draining. Groundwater is most often found at the base of the advance outwash, likely 50 or more feet below site elevations. Based on our review of nearby explorations and slope reconnaissance, regional groundwater is likely present at an elevation of about 210 to 215 feet above sea level. This is about 8o feet below site elevations. Water table elevations often fluctuate over time. The groundwater level will depend on a variety of factors that may include seasonal precipitation, irrigation, land use, climatic conditions and soil permeability. Water levels at the time of the field investigation may be different from those encountered during the construction phase of the project. www.cobaltgeo.com (206) 331-1097 January 14, 2023 Page 3 of 14 Geotechnical Evaluation Steep Slope and Landslide Hazard Areas Most municipal codes designate slope areas with magnitudes greater than 40 percent and relief of at least io feet as potentially geologically hazardous. The site contains steep slope and erosion hazard areas due to the combination of steeper topography and presence of coarser outwash sands. The site and developed portions of the property to the east are situated on a west -trending ridge with low slope magnitudes (5 to 12 percent). There are locally steep and very steep natural and partially graded slopes extending downward from the ridge to the north, west, and south. We describe these areas as follows: The steep slopes near the west property line are mostly the result of prior grading associated with the access roadway. This slope is 15 to 20 feet tall and has magnitudes of 50 to 8o percent. The slope is locally faced with rockery walls. The steep slopes near the southern portion of the site and adjacent parcel have magnitudes of up to vertical to overturned as a result of sloughing. Overall, the slope magnitudes range from 6o to 150 percent where vegetation is present. There are rockery walls at the toe of this slope near the area roadways. The areas near the top of the slope have exposed outwash sands in sloughs. These areas are 3 to 7 feet in height with the height increasing to the east. There are trees and other understory hanging over the sloughed zones. The total height of these slopes is 40 to 6o feet. The steep slope areas to the north of the site have magnitudes of 40 to 90 percent and relief of 40 to 50 feet from west to east. These slopes continue to the north at lower magnitudes. There are apparent wetland areas and standing water further north in the low lying areas. During our site visit, we observed the overall surface condition of the steep slope areas within and near the site. There is evidence of surface sloughing of outwash sands in the upper portions of the south slope. These areas are consistent with peel off associated with oversteepened slopes through prior grading and erosion. The toe of this slope has been cut as part of area grading for roadways. There is a rockery at the toe of this slope. We discussed historic slide activity on a west -facing steep slope located several hundred feet northwest of the site on an adjacent parcel. We understand that there were drain pipes allowing surface water to saturate the near surface weathered outwash sands. This sloughing resulted in deposition below the slope. We note no similar sloughing on the west or north slopes near the site. We did observe evidence of minor soil creep as indicated by curved trunks of some of the trees on the north and south slope areas. Soil creep is a natural process in which soil very slowly migrates downward and result in local curvature of trees and other vegetation. Soil creep occurs in most slope areas of magnitudes greater than about 50 percent. Code Information 23.80.o6o Development standards — General requirements. A. Alterations of geologically hazardous areas or associated buffers may only occur for activities that: 1. Will not increase the threat of the geological hazard to adjacent properties beyond predevelopment conditions; 2. Will not adversely impact other critical areas; www.cobaltgeo.com (2o6) 331-1097 January 14, 2023 Page 4 of 14 Geotechnical Evaluation 3. Are designed so that the hazard to the project is eliminated or mitigated to a level equal to or less than predevelopment conditions; and 4. Are certified as safe as designed and under anticipated conditions by a qualified engineer or geologist, licensed in the state of Washington. The currently proposed project includes minimal excavation work associated with new foundation areas only. The work will not occur in or near steep slope or significant erosion hazard areas and as such, can be completed without adversely affecting these areas and any geologic hazards. This report provides recommendations to facilitate safe construction, including temporary excavation recommendations, fill compaction and placement, drainage and foundation design. It is our opinion that this work will not affect global or local stabilily provided work is monitored by the geotechnical engineer and erosion control measures are in place during construction. The proposed construction will not increase the threat of geologic hazards on adjacent pro even rties, will not impact other critical areas, and are safe as designed under anticipated conditions. 23.80.07o Development standards — Specific hazards. A. Erosion and Landslide Hazard Areas. Activities on sites containing erosion or landslide hazards shall meet the requirements of ECDC 22.80.o6o, Development standards — General requirements, and the specific following requirements: 1. Minimum Building Setback. The minimum setback shall be the distance required to ensure the proposed structure will not be at risk from landslides for the life of the structure, considered to be 120 years, and will not cause an increased risk of landslides taking place on or off the site. A setback shall be established from all edges of landslide hazard areas. The size of the setback shall be determined by the director consistent with recommendations provided in the geotechnical report to eliminate or minimize the risk of property damage, death, or injury resulting from landslides caused in whole or part by the development, based upon review of and concurrence with a critical areas report prepared by a qualified professional; We recommend a minimum building setback of 25 feet from the steep slopes near the south margin of the site: a minimum building setback of 15 feet from the steep slope near the west property line: and a minimum building setback of 25 feet from the steep slope near the north property line. Infiltration systems should be located at least 40 feet from the top of the south steep slope, �o feet from the west steep slope, and 40 feet from the north property line. 2. Buffer Requirements. A buffer may be established with specific requirements and limitations, including but not limited to, drainage, grading, irrigation, and vegetation. Buffer requirements shall be determined by the director consistent with recommendations provided in the geotechnical report to eliminate or minimize the risk of property damage, death, or injury resulting from landslides caused in whole or part by activities within the buffer area, based upon review of and concurrence with a critical areas report prepared by a qualified professional; We recommend that the areas within io feet of the top of the steep slope areas remain fu11X vegetated. This io foot buffer is included within the building setback and is not additive. 3. Alterations. Alterations of an erosion or landslide hazard area, minimum building setback and/or buffer may only occur for activities for which a hazards analysis is submitted and certifies that: a. The alteration will not increase surface water discharge or sedimentation to adjacent properties beyond predevelopment conditions; www.cobaltgeo.com (2o6) 331-1097 January 14, 2023 Page 5 of 14 Geotechnical Evaluation b. The alteration will not decrease slope stability on adjacent properties; and c. Such alterations will not adversely impact other critical areas; Provided earthwork activities are performed in accordance with the approved plans, all runoff is fully controlled, and periodic geotechnical oversight is performed, the development will not decrease slope stability on adjacent properties, will not increase surface water discharge or sedimentation beyond current levels, and will not impact other critical areas. Temporary and permanent erosion and sediment control devices should be in at all times during construction. 4. Design Standards within Erosion and Landslide Hazard Areas. Development within an erosion or landslide hazard area and/or buffer shall be designed to meet the following basic requirements unless it can be demonstrated that an alternative design that deviates from one or more of these standards provides greater long-term slope stability while meeting all other provisions of this title. The requirement for long-term slope stability shall exclude designs that require regular and periodic maintenance to maintain their level of function. The basic development design standards are: a. The proposed development shall not decrease the factor of safety for landslide occurrences below the limits of 1.5 for static conditions and 1.2 for dynamic conditions. If stability at the proposed development site is below these limits, the proposed development shall provide practicable approaches to reduce risk to human safety and improve the factor of safety for landsliding. In no case shall the existing factor of safety be reduced for the subject property or adjacent properties; b. Structures and improvements shall be clustered to avoid geologically hazardous areas and other critical areas; c. Structures and improvements shall minimize alterations to the natural contour of the slope, and foundations shall be tiered where possible to conform to existing topography; d. Structures and improvements shall be located to preserve the most critical portion of the site and its natural landforms and vegetation; e. The proposed development shall not result in greater risk or a need for increased buffers on neighboring properties; f. The use of retaining walls that allow the maintenance of existing natural slope area is preferred over graded artificial slopes; and g. Development shall be designed to minimize impervious lot coverage; The project scope does not pose a risk to critical areas or the need to increase buffers on adjacent properties. The residence will be located well away from steep slope areas. Factors of safety against landslide movements are well above minimum values based on the soil Wes, topography, and locations of the development relative to the slope systems. 5. Vegetation Retention. Unless otherwise provided or as part of an approved alteration, removal of vegetation from an erosion or landslide hazard area or related buffer shall be prohibited; 6. Seasonal Restriction. Clearing shall be allowed only from May 1st to October 1st of each year; provided, that the director may extend or shorten the dry season on a case -by -case basis depending on actual weather conditions, except that timber harvest, not including brush clearing or stump removal, may be allowed pursuant to an approved forest practice permit issued by the city of Edmonds or the Washington State Department of Natural Resources; www.cobaltgeo.com (2o6) 331-1097 January 14, 2023 Page 6 of 14 Geotechnical Evaluation 7. Point Discharges. Point discharges from surface water facilities and roof drains onto or upstream from an erosion or landslide hazard area shall be prohibited except as follows: a. Conveyed via continuous storm pipe downslope to a point where there are no erosion hazard areas downstream from the discharge; b. Discharged at flow durations matching predeveloped conditions, with adequate energy dissipation, into existing channels that previously conveyed storm water runoff in the predeveloped state; or c. Dispersed discharge upslope of the steep slope onto a low -gradient, undisturbed buffer demonstrated to be adequate to infiltrate all surface and storm water runoff, and where it can be demonstrated that such discharge will not increase the saturation of the slope; and We concur with the above code items and have no additional comments at this time. Erosion Hazard The Natural Resources Conservation Services (NRCS) maps for Snohomish County indicate that the site is underlain by Alderwood Everett gravelly sandy loams (25 to 70 percent slopes). These soils would have a moderate to very severe erosion potential in a disturbed state depending on the slope magnitude. It is our opinion that soil erosion potential at this project site can be reduced through landscaping and surface water runoff control. Typically, erosion of exposed soils will be most noticeable during periods of rainfall and may be controlled by the use of normal temporary erosion control measures, such as silt fences, hay bales, mulching, control ditches and diversion trenches. The typical wet weather season, with regard to site grading, is from October 31st to April ist. Erosion control measures should be in place before the onset of wet weather. Seismic Hazard The overall subsurface profile below the fill corresponds to a Site Class D as defined by Table 1613.5.2 of the International Building Code (IBC). A Site Class D applies to an overall profile consisting of medium dense to very dense soils within the upper too feet. We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to obtain values for Ss, Sl, FQ, and F,,. The USGS website includes the most updated published data on seismic conditions. The following tables provide seismic parameters from the USGS web site with referenced parameters from ASCE 7-16. Seismic Design Parameters (ASCE 7-16) Site Spectral Spectral Site Design Spectral Design Class Acceleration Acceleration Coefficients Response Parameters PGA at 0.2 sec. (g) at 1.o sec. (g) Fa F„ SDS SDl D 1.294 0.456 1.0 Null 0.862 Null 0.552 www.cobaltgeo.com (206) 331-1097 January 14, 2023 Page 7 of 14 Geotechnical Evaluation Additional seismic considerations include liquefaction potential and amplification of ground motions by soft/loose soil deposits. The liquefaction potential is highest for loose sand with a high groundwater table. The site has a low likelihood of liquefaction. For items listed as "Null" see Section 11.4.8 of the ASCE. Conclusions and Recommendations General The site is underlain by primarily Vashon Advance Outwash. There appear to be areas of Vashon Glacial Till near the western margin and on adjacent parcels to the west. The outwash becomes denser with depth. The proposed residential structure may be supported on a shallow foundation system bearing on medium dense or firmer native soils or on structural fill placed on the native soils. Infiltration appears to be feasible in the outwash sands that underlie the site at variable depths. The depth to outwash will vary with location and drywells will likely be the most suitable type of infiltration system. We can provide additional recommendations upon request. We should review the plans to verify suitability of the system locations and elevations. We recommend a minimum building setback of 25 feet from the steep slopes near the south margin of the site; a minimum building setback of 15 feet from the steep slope near the west property line; and a minimum building setback of 25 feet from the steep slope near the north property line. Infiltration systems should be located at least 40 feet from the top of the south steep slope, 30 feet from the west steep slope, and 40 feet from the north property line. Site Preparation Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic -rich soil and fill. Based on observations from the site investigation program, it is anticipated that the stripping depth will be 6 to 18 inches. Deeper excavations will be necessary below larger trees, foundation systems, and in any areas underlain by undocumented fill. The native soils consist of silty -sand with gravel and poorly graded sand. The poorly graded sands and native soils are likely suitable for use as fill provided all debris and organic materials are removed. These soils may be used as structural fill provided they achieve compaction requirements and are within 3 percent of the optimum moisture. Some of these soils may only be suitable for use as fill during the summer months, as they will be above the optimum moisture levels in their current state. These soils are variably moisture sensitive and may degrade during periods of wet weather and under equipment traffic. Imported structural fill should consist of a sand and gravel mixture with a maximum grain size of 3 inches and less than 5 percent fines (material passing the U.S. Standard No. 200 Sieve). Structural fill should be placed in maximum lift thicknesses of 12 inches and should be compacted to a minimum of 95 percent of the modified proctor maximum dry density, as determined by the ASTM D 1557 test method. www.cobaltgeo.com (2o6) 331-1097 January 14, 2023 Page 8 of 14 Geotechnical Evaluation Temporary Excavations Based on our understanding of the project, we anticipate that the grading could include local cuts on the order of approximately 3 feet or less for foundation and most of the utility placement. Any deeper temporary excavations should be sloped no steeper than 1.511:1V (Horizontal:Vertical) in loose native soils and fill, 111:1V in medium dense native soils and 3/41-1:1V in dense to very dense native soils. If an excavation is subject to heavy vibration or surcharge loads, we recommend that the excavations be sloped no steeper than 2H:1V, where room permits. Temporary cuts should be in accordance with the Washington Administrative Code (WAC) Part N, Excavation, Trenching, and Shoring. Temporary slopes should be visually inspected daily by a qualified person during construction activities and the inspections should be documented in daily reports. The contractor is responsible for maintaining the stability of the temporary cut slopes and reducing slope erosion during construction. Temporary cut slopes should be covered with visqueen to help reduce erosion during wet weather, and the slopes should be closely monitored until the permanent retaining systems or slope configurations are complete. Materials should not be stored or equipment operated within 10 feet of the top of any temporary cut slope. Soil conditions may not be completely known from the geotechnical investigation. In the case of temporary cuts, the existing soil conditions may not be completely revealed until the excavation work exposes the soil. Typically, as excavation work progresses the maximum inclination of temporary slopes will need to be re-evaluated by the geotechnical engineer so that supplemental recommendations can be made. Soil and groundwater conditions can be highly variable. Scheduling for soil work will need to be adjustable, to deal with unanticipated conditions, so that the project can proceed and required deadlines can be met. If any variations or undesirable conditions are encountered during construction, we should be notified so that supplemental recommendations can be made. If room constraints or groundwater conditions do not permit temporary slopes to be cut to the maximum angles allowed by the WAC, temporary shoring systems may be required. The contractor should be responsible for developing temporary shoring systems, if needed. We recommend that Cobalt Geosciences and the project structural engineer review temporary shoring designs prior to installation, to verify the suitability of the proposed systems. Foundation Design The proposed structure may be supported on a shallow spread footing foundation system bearing on undisturbed medium dense or firmer native soils or on properly compacted structural fill placed on the suitable native soils. Any undocumented fill and/or loose native soils should be removed and replaced with structural fill below foundation elements. It may be feasible to recompact outwash to a firm and unyielding condition depending on the moisture content. For shallow foundation support, we recommend widths of at least 16 and 24 inches, respectively, for continuous wall and isolated column footings supporting the proposed structure. Provided that the footings are supported as recommended above, a net allowable bearing pressure of 2,500 pounds per square foot (psf) may be used for design. A 1/3 increase in the above value may be used for short duration loads, such as those imposed by wind and seismic events. Structural fill placed on bearing, native subgrade should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Footing excavations should be inspected to verify that the foundations will bear on suitable material. www.cobaltgeo.com (2o6) 331-1097 January 14, 2023 Page 9 of 14 Geotechnical Evaluation Exterior footings should have a minimum depth of 18 inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower. Interior footings should have a minimum depth of 12 inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower. If constructed as recommended, the total foundation settlement is not expected to exceed 1 inch. Differential settlement, along a 25-foot exterior wall footing, or between adjoining column footings, should be less than 1/2 inch. This translates to an angular distortion of 0.002. Most settlement is expected to occur during construction, as the loads are applied. However, additional post -construction settlement may occur if the foundation soils are flooded or saturated. All footing excavations should be observed by a qualified geotechnical consultant. Resistance to lateral footing displacement can be determined using an allowable friction factor of 0.4o acting between the base of foundations and the supporting subgrades. Lateral resistance for footings can also be developed using an allowable equivalent fluid passive pressure of 225 pounds per cubic foot (pcf) acting against the appropriate vertical footing faces (neglect the upper 12 inches below grade in exterior areas). The frictional and passive resistance of the soil may be combined without reduction in determining the total lateral resistance. Care should be taken to prevent wetting or drying of the bearing materials during construction. Any extremely wet or dry materials, or any loose or disturbed materials at the bottom of the footing excavations, should be removed prior to placing concrete. The potential for wetting or drying of the bearing materials can be reduced by pouring concrete as soon as possible after completing the footing excavation and evaluating the bearing surface by the geotechnical engineer or his representative. Concrete Retaining Walls The following table, titled Wall Design Criteria, presents the recommended soil related design parameters for retaining walls with a level backslope. Contact Cobalt if an alternate retaining wall system is used. This has been included for new cast in place walls. Wall Design Criteria "At -rest" Conditions (Lateral Earth Pressure — EFD+) 55 pcf (Equivalent Fluid Density) "Active" Conditions (Lateral Earth Pressure — EFD+) 35 pcf (Equivalent Fluid Density) Seismic Increase for "At -rest" Conditions (Lateral Earth Pressure) 14H* (Uniform Distribution) Seismic Increase for "Active" Conditions (Lateral Earth Pressure) 7H* (Uniform Distribution) Passive Earth Pressure on Low Side of Wall (Allowable, includes F.S. = 1.5) Neglect upper 2 feet, then 250 pcf EFD+ Soil -Footing Coefficient of Sliding Friction (Allowable; includes F.S. = 1.5) 0.40 'H is the height of the wall; Increase based on one in 500 year seismic event (10 percent probability of being exceeded in 50 years), ,EFD — Equivalent Fluid Density www.cobaltgeo.com (2o6) 331-1097 January 14, 2023 Page io of 14 Geotechnical Evaluation The stated lateral earth pressures do not include the effects of hydrostatic pressure generated by water accumulation behind the retaining walls. Uniform horizontal lateral active and at -rest pressures on the retaining walls from vertical surcharges behind the wall may be calculated using active and at -rest lateral earth pressure coefficients of 0.3 and 0.5, respectively. A soil unit weight Of 125 pcf may be used to calculate vertical earth surcharges. To reduce the potential for the buildup of water pressure against the walls, continuous footing drains (with cleanouts) should be provided at the bases of the walls. The footing drains should consist of a minimum 4-inch diameter perforated pipe, sloped to drain, with perforations placed down and enveloped by a minimum 6 inches of pea gravel in all directions. The backfill adjacent to and extending a lateral distance behind the walls at least 2 feet should consist of free -draining granular material. All free draining backfill should contain less than 3 percent fines (passing the U.S. Standard No. 200 Sieve) based upon the fraction passing the U.S. Standard No. 4 Sieve with at least 30 percent of the material being retained on the U.S. Standard No. 4 Sieve. The primary purpose of the free -draining material is the reduction of hydrostatic pressure. Some potential for the moisture to contact the back face of the wall may exist, even with treatment, which may require that more extensive waterproofing be specified for walls, which require interior moisture sensitive finishes. We recommend that the backfill be compacted to at least go percent of the maximum dry density based on ASTM Test Method D1557. In place density tests should be performed to verify adequate compaction. Soil compactors place transient surcharges on the backfill. Consequently, only light hand operated equipment is recommended within 3 feet of walls so that excessive stress is not imposed on the walls. Stormwater Management Feasibility The site is underlain by Vashon Advance Outwash. Infiltration is generally feasible in the outwash sands. Infiltration is not typically feasible or recommended in glacial till soils, if encountered in some locations. The design infiltration rate was determined by applying correction factors to the observed infiltration rate as prescribed in Volume III, Section 3.3.6 of the DOE. The observed rate must be reduced through appropriate correction factors for site variability (CFv), uncertainty of test method (CFT), and degree of influent control (CFM) to prevent siltation and bio-buildup. It should be noted that construction traffic or other disturbance to the target infiltration area could compact the soil, which may decrease the effective infiltration rates. The correction factors and resulting design infiltration rate are also shown in the table below. Test Pit Sample Observed Correction Factors Design Number Depth (ft) Infiltration Infiltration Rate (in/hr) Rate CFv CFT CFM (in/hr) TP-1 5 3.6 0.8 0.5 0.9 1.3 Widespread infiltration is feasible in the outwash sands below about 4 feet (in the test pit location areas). This soil consists of coarser outwash sands. Drywells will likely be most suitable option for stormwater management. www.cobaltgeo.com (206) 331-1097 January 14, 2023 Page 11 of 14 Geotechnical Evaluation We must be on site to verify soil conditions in the drywells during construction. All systems must penetrate into the sands at least 6 inches. The soils are consistent with Medium Sand per the USDA textural triangle if a prescriptive sizing is used. The depth to suitable outwash will vary across the site and overexcavation of till or silty -sands will be required to achieve the outwash soils at depth. We must be on site to confirm soil conditions. We should be provided with final plans for review to determine if the intent of our recommendations has been incorporated or if additional modifications are needed. Slab -on -Grade We recommend that the upper 12 inches of the native soils within slab areas below the fill be re - compacted to at least 95 percent of the modified proctor (ASTM D1557 Test Method). Often, a vapor barrier is considered below concrete slab areas. However, the usage of a vapor barrier could result in curling of the concrete slab at joints. Floor covers sensitive to moisture typically requires the usage of a vapor barrier. A materials or structural engineer should be consulted regarding the detailing of the vapor barrier below concrete slabs. Exterior slabs typically do not utilize vapor barriers. The American Concrete Institutes ACI 36oR-o6 Design of Slabs on Grade and ACI 302.1R-04 Guide for Concrete Floor and Slab Construction are recommended references for vapor barrier selection and floor slab detailing. Slabs on grade may be designed using a coefficient of subgrade reaction of 18o pounds per cubic inch (pci) assuming the slab -on -grade base course is underlain by structural fill placed and compacted as outlined above. A 4- to 6-inch-thick capillary break layer should be placed over the prepared subgrade. This material should consist of pea gravel or 5/8 inch clean angular rock. A perimeter drainage system is recommended unless interior slab areas are elevated a minimum Of 12 inches above adjacent exterior grades. If installed, a perimeter drainage system should consist of a 4-inch diameter perforated drain pipe surrounded by a minimum 6 inches of drain rock wrapped in a non -woven geosynthetic filter fabric to reduce migration of soil particles into the drainage system. The perimeter drainage system should discharge by gravity flow to a suitable stormwater system. Exterior grades surrounding buildings should be sloped at a minimum of one percent to facilitate surface water flow away from the building and preferably with a relatively impermeable surface cover immediately adjacent to the building. Erosion and Sediment Control Erosion and sediment control (ESC) is used to reduce the transportation of eroded sediment to wetlands, streams, lakes, drainage systems, and adjacent properties. Erosion and sediment control measures should be implemented, and these measures should be in general accordance with local regulations. At a minimum, the following basic recommendations should be incorporated into the design of the erosion and sediment control features for the site: • Schedule the soil, foundation, utility, and other work requiring excavation or the disturbance of the site soils, to take place during the dry season (generally May through September). However, provided precautions are taken using Best Management Practices (BMP's), grading activities can be completed during the wet season (generally October through April). All site work should be completed and stabilized as quickly as possible. www.cobaltgeo.com (2o6) 331-1097 January 14, 2023 Page 12 of 14 Geotechnical Evaluation Additional perimeter erosion and sediment control features may be required to reduce the possibility of sediment entering the surface water. This may include additional silt fences, silt fences with a higher Apparent Opening Size (AOS), construction of a berm, or other filtration systems. • Any runoff generated by dewatering discharge should be treated through construction of a sediment trap if there is sufficient space. If space is limited other filtration methods will need to be incorporated. Utilities Utility trenches should be excavated according to accepted engineering practices following OSHA (Occupational Safety and Health Administration) standards, by a contractor experienced in such work. The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent to trench walls should be reduced; cyclic wetting and drying of excavation side slopes should be avoided. Depending upon the location and depth of some utility trenches, groundwater flow into open excavations could be experienced, especially during or shortly following periods of precipitation. In general, sandy soils were encountered at shallow depths in the explorations at this site. These soils have low cohesion and density and will have a tendency to cave or slough in excavations. Shoring or sloping back trench sidewalls is required within these soils in excavations greater than 4 feet deep. All utility trench backfill should consist of imported structural fill or suitable on site soils. Utility trench backfill placed in or adjacent to buildings and exterior slabs should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. The upper 5 feet of utility trench backfill placed in pavement areas should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Below 5 feet, utility trench backfill in pavement areas should be compacted to at least 90 percent of the maximum dry density based on ASTM Test Method D1557. Pipe bedding should be in accordance with the pipe manufacturer's recommendations. The contractor is responsible for removing all water -sensitive soils from the trenches regardless of the backfill location and compaction requirements. Depending on the depth and location of the proposed utilities, we anticipate the need to re -compact existing fill soils below the utility structures and pipes. The contractor should use appropriate equipment and methods to avoid damage to the utilities and/or structures during fill placement and compaction procedures. CONSTRUCTION FIELD REVIEWS Cobalt Geosciences should be retained to provide part time field review during construction in order to verify that the soil conditions encountered are consistent with our design assumptions and that the intent of our recommendations is being met. This will require field and engineering review to: ■ Monitor and test structural fill placement and soil compaction ■ Observe bearing capacity at foundation locations ■ Observe slab -on -grade preparation ■ Verify soil conditions in infiltration systems if utilized ■ Monitor foundation drainage placement ■ Observe excavation stability www.cobaltgeo.com (2o6) 331-1097 January 14, 2023 Page 13 of 14 Geotechnical Evaluation Geotechnical design services should also be anticipated during the subsequent final design phase to support the structural design and address specific issues arising during this phase. Field and engineering review services will also be required during the construction phase in order to provide a Final Letter for the project. CLOSURE This report was prepared for the exclusive use of Landsverk Quality Homes and their appointed consultants. Any use of this report or the material contained herein by third parties, or for other than the intended purpose, should first be approved in writing by Cobalt Geosciences, LLC. The recommendations contained in this report are based on assumed continuity of soils with those of our test holes and assumed structural loads. Cobalt Geosciences should be provided with final architectural and civil drawings when they become available in order that we may review our design recommendations and advise of any revisions, if necessary. Use of this report is subject to the Statement of General Conditions provided in Appendix A. It is the responsibility of Landsverk Quality Homes who is identified as "the Client" within the Statement of General Conditions, and its agents to review the conditions and to notify Cobalt Geosciences should any of these not be satisfied. Sincerely, Cobalt Geosciences, LLC r H0Nr� P �F WAs�.q �Q ✓ •1 �t 54896 <� 0�FssLIST ZONAL�- 1/14/2023 Phil Haberman, PE, LG, LEG Principal www.cobaltgeo.com (2o6) 331-1097 January 14, 2023 Page 14 of 14 Geotechnical Evaluation Statement of General Conditions USE OF THIS REPORT: This report has been prepared for the sole benefit of the Client or its agent and may not be used by any third party without the express written consent of Cobalt Geosciences and the Client. Any use which a third party makes of this report is the responsibility of such third parry. BASIS OF THE REPORT: The information, opinions, and/or recommendations made in this report are in accordance with Cobalt Geosciences present understanding of the site specific project as described by the Client. The applicability of these is restricted to the site conditions encountered at the time of the investigation or study. If the proposed site specific project differs or is modified from what is described in this report or if the site conditions are altered, this report is no longer valid unless Cobalt Geosciences is requested by the Client to review and revise the report to reflect the differing or modified project specifics and/or the altered site conditions. STANDARD OF CARE: Preparation of this report, and all associated work, was carried out in accordance with the normally accepted standard of care in the state of execution for the specific professional service provided to the Client. No other warranty is made. INTERPRETATION OF SITE CONDITIONS: Soil, rock, or other material descriptions, and statements regarding their condition, made in this report are based on site conditions encountered by Cobalt Geosciences at the time of the work and at the specific testing and/or sampling locations. Classifications and statements of condition have been made in accordance with normally accepted practices which are judgmental in nature; no specific description should be considered exact, but rather reflective of the anticipated material behavior. Extrapolation of in situ conditions can only be made to some limited extent beyond the sampling or test points. The extent depends on variability of the soil, rock and groundwater conditions as influenced by geological processes, construction activity, and site use. VARYING OR UNEXPECTED CONDITIONS: Should any site or subsurface conditions be encountered that are different from those described in this report or encountered at the test locations, Cobalt Geosciences must be notified immediately to assess if the varying or unexpected conditions are substantial and if reassessments of the report conclusions or recommendations are required. Cobalt Geosciences will not be responsible to any parry for damages incurred as a result of failing to notify Cobalt Geosciences that differing site or sub -surface conditions are present upon becoming aware of such conditions. PLANNING, DESIGN, OR CONSTRUCTION: Development or design plans and specifications should be reviewed by Cobalt Geosciences, sufficiently ahead of initiating the next project stage (property acquisition, tender, construction, etc), to confirm that this report completely addresses the elaborated project specifics and that the contents of this report have been properly interpreted. Specialty quality assurance services (field observations and testing) during construction are a necessary part of the evaluation of sub -subsurface conditions and site preparation works. Site work relating to the recommendations included in this report should only be carried out in the presence of a qualified geotechnical engineer; Cobalt Geosciences cannot be responsible for site work carried out without being present. www.cobaltgeo.com (2o6) 331-1097 19516 ' d All 111111 AA 19511 19518 t9 51 1 52WIN 19524 �� 52 PUGE'T DR Sno. Co. Gis Map TP-i N Approximate Test Pit Location Not to Scale Cobalt Geosciences, LLC Proposed Residence SITE MAP P.O. Box 82243 _ . 19515 94th Place West Ken 3 e, 0978028 = — Edmonds, Washington FIGURE 1 www.cobaltgeo.com cobaltgeo(&gmail.com Slab on Grade Basement or Shallow Foundation Wall 12" Free Draining Backfill and/or Drainage Mat Attached to Wall Backfill Soils Compacted per Geotechnical Report 4" Diameter Perforated Pipe -- --�H H Native Soils Benched as Required Filter Fabric Over Rock (Mirafi 14oN) 3//4" Washed Rock or Clean Angular Rock Not to Scale Cobalt Geosciences, LLC PO Box 1792 Typical Foundation Drain Detail Attachment North Bend, WA 98045 • _ (2o6) 331-1097 GEOSCIENCES www.cobaltgeo.com Philpcobaltgeo.com Unified Soil Classification System (USCS) MAJOR DIVISIONS SYMBOL TYPICAL DESCRIPTION Clean Gravels Gw Well -graded gravels, gravels, gravel -sand mixtures, little or no fines Gravels (more than 50% (less than 5% fines) GP Poorly graded gravels, gravel -sand mixtures, little or no fines COARSE GRAINED SOILS of coarse fraction retained on No. 4 sieve) Gravels with Fines (more than 12% fines) GM Silty gravels, gravel -sand -silt mixtures GC Clayey gravels, gravel -sand -clay mixtures (more than 50% retained on Clean Sands :•: sw Well -graded sands, gravelly sands, little or no fines No. 200 sieve) Sands (50% or more of coarse fraction (less than 5% fines) sP Poorly graded sand, gravelly sands, little or no fines passes the No. 4 sieve) Sands with Fines sM Silty sands, sand -silt mixtures (more than 12% fines) sc Clayey sands, sand -clay mixtures ML Inorganic silts of low to medium plasticity, sandy silts, gravelly silts, FINE GRAINED (50% or more Silts and Clays (liquid limit less than 50) Inorganic cL or clayey silts with slight plasticity Inorganic clays of low to medium plasticity, gravelly clays, sandy clays silty clays, lean clays Organic rganic oL Organic silts and organic silty clays of low plasticity passes the MH Inorganic silts, micaceous or diatomaceous fine sands or silty soils, No. 200 sieve) Silts and Clays (liquid limit 50 or more) Inorganic elastic silt CH Inorganic clays of medium to high plasticity, sandy fat clay, or gravelly fat clay Organic OHOrganic clays of medium to high plasticity, organic silts HIGHLY ORGANIC SOILS Primarily organic matter, dark in color, and organic odor PT Peat, humus, swamp soils with high organic content (ASTM D4427) Classification of Soil Constituents MAJOR constituents compose more than 50 percent, by weight, of the soil. Major constituents are capitalized (i.e., SAND). Minor constituents compose 12 to 50 percent of the soil and precede the major constituents (i.e., silty SAND). Minor constituents preceded by "slightly" compose 5 to 12 percent of the soil (i.e., slightly silty SAND). Trace constituents compose o to 5 percent of the soil (i.e., slightly silty SAND, trace gravel). Relative Density (Coarse Grained Soils) Consistency (Fine Grained Soils) N, SPT, Relative N, SPT, Relative Blows/FT Density Blows/FT Consistency 0-4 Very loose Under 2 Very soft 4 -10 Loose 2-4 Soft 10 - 30 Medium dense 4-8 Medium stiff 30 - 50 Dense 8 -15 Stiff Over 50 Very dense 15 - 30 Very stiff Over 3o Hard Grain Size Definitions Description Sieve Number and/or Size Fines <#200 (o.o8 mm) Sand -Fine #200 to #40 (o.o8 to 0.4 mm) -Medium #40 to #10 (0.4 to 2 mm) -Coarse #10 to #4 (2 to 5 mm) Gravel -Fine #4 to 3/4 inch (5 to 19 mm) -Coarse 3/4 to 3 inches (19 to 76 mm) Cobbles 3 to 12 inches (75 to 305 mm) Boulders >12 inches (305 mm) 1 Moisture Content Definitions 1 Dry Absence of moisture, dusty, dry to the touch Moist Damp but no visible water Wet Visible free water, from below water table Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 Soil Classification Chart Figure Ci (2o6) 331-1097 _ www.cobaltgeo.com cobaltgeo(&gmail.com Test Pit TP-1 Date: December 2022 Depth: 12' Groundwater: None Contractor: Client provided Elevation: N/A Logged By: PH Checked By: SC N 0) o Moisture Content (%) u Q E Plastic I Limit I Liquid Limit � � L Material Description DCP Equivalent N-Value o C ? o O 0 10 20 30 40 50SP Cobalt Geosciences, LLC Proposed Residence P.O. Box 82243 COBALT 19515 94th Place West Test Pit Kenmore, WA 98028 (2o6) 331-1097 GEOSCIENCES Edmonds, Washington Logs www.cobaltgeo.com cobaltgeopgmail.com _______Topsoil and Grass 1 • ' ' : • SP/ Loose to medium dense, silty -fine to medium grained sand trace - • • SM gravel yellowish brown to grayish brown, moist. 2 ;l;-:� � • (Weathered Advance Outwash) 3 • tif . • • ; •• Medium dense to dense, fine to medium grained sand trace gravel 5 grayish brown, moist. ;1,-••'.;:' (Advance Outwash) 10 End of Test Pit 12' COBALT G E 0 S C I E N C E S August 3, 2023 Landsverk Quality Homes Attn: Duane Landsverk & Joseph Rowett 24113 56th Avenue West Mountlake Terrace, Washington RE: Plan Review and Response to Comments Proposed Development 19515 94th Place West Edmonds, Washington Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, Washington 98028 In accordance with your authorization, Cobalt Geosciences, LLC has prepared a plan review with comment responses for the proposed development at the referenced location. Infiltration trenches or drywell systems should be located at least 40 feet from the top of the slope located north of the property, not from the property line. The discussion of the setback from the property line in the geotechnical report was in error. We have reviewed the provided civil plans by Omega Engineering Inc dated May 26, 2023 and updated July 27, 2023 and are in general agreement with the information therein. We note that a small permeable paver patio will be situated about 23 feet from the top of the slope to the north of the property. This is acceptable as the volumes will be minimal and the near -surface soils are generally coarse outwash. Larger scale infiltration trenches should be located 4o feet from the top of the slope as noted above. CONSTRUCTION FIELD REVIEWS Cobalt Geosciences should be retained to provide part time field review during construction in order to verify that the soil conditions encountered are consistent with our design assumptions and that the intent of our recommendations is being met. This will require field and engineering review to: ■ Monitor and test structural fill placement and soil compaction ■ Observe bearing capacity at foundation locations ■ Observe slab -on -grade preparation ■ Verify soil conditions in infiltration systems ■ Monitor foundation drainage placement ■ Observe excavation stability Geotechnical design services should also be anticipated during the subsequent final design phase to support the structural design and address specific issues arising during this phase. Field and engineering review services will also be required during the construction phase in order to provide a Final Letter for the project. www.cobaltgeo.com (206) 331-1097 August 3, 2023 Page 2 of 2 Geotechnical Evaluation Sincerely, Cobalt Geosciences, LLC NONry9 �tik• OF WAsy/y �<^ c P IL k 54= ' cols FSSfONAL 8/3/2023 Phil Haberman, PE, LG, LEG Principal 0 �Ii PHILUP MASEMAN www.cobaltgeo.com (2o6) 331-1097