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APPROVED STM BLD2023-0401+Drainage Report+7.19.2023_12.56.59_PM+3675114�23 2 og 1PAS8l��l P � J��s �P6 S $4$� Gti�w sIONAL CIVIL FNGINFFRING MR 1-5 Storm Drainage Summary Shen/Federman Residence L Page 1 of 9 MR1-5 Drainage Report 23310 Humber Lane Edmonds, WA 98020 7/17/2023 CES #2070 23310 Humber Lane Edmonds, WA 98020 Parcel ID: 00571300101000 4,455 sf new & replaced impervious July 17, 2023 updated SOILS ....................glacial till STORM DISCHARGE......... dispersion trench Coauthored by Stephenie Seawall, civil engineer Duffy Ellis, P.E. COMPLIES WITH APPLICABLE CITY STORM CODE '---i'70�.P.�. 7/28/2023 S O L U T I O N S General: This site's proposed impervious area is below 5,000 sf, site is subject to minimum requirements MR1-5 identified below. Reference attached Edmonds Figure 3.1. MR1 = Preparation of Storm Water Site See C2.0 Drainage Plan Plans MR2 = Construction Storm Water Pollution See CSWPPP included with this Prevention Plan submittal. Also see sheet C1.0 TESCP in the civil plan set. MR3 = Source Control of Pollution See C1.0 for Temporary Erosion & Sediment Control. Also see the CSWPPP document prepared for this project. MR4 = Preservation of Natural Drainage This suburban lot and surrounding Systems and Outfalls area have a moderate topographic tilt toward the west. A dispersion trench is proposed which mimics the natural topography and historic drainage pattern of this lot. We discuss MR4 in more depth on page 6. MR5 = On -site Stormwater Management A "Basic" dispersion trench is proposed for the roof and driveway areas. See specific MR5 discussion of each BMP on pages 6 and 7 of this report. See the Infiltration report in the appendix. MR6 = Runoff Treatment N/A, project under 5,000 sf MR7 = Flow Control N/A, project under 5,000 sf MR8 = Wetlands Protection N/A, project under 5,000 sf MR9 = Operations and Maintenance N/A, project under 5,000 sf Page 2of9 MR1-5 Drainage Report 23310 Humber Lane Edmonds, WA 98020 7/17/2023 CES #2070 CIVIL ENGINEERING Street View Vicinity Map i1 �' �• r_-- _ +Southwest County Park ' J iget Sound ��J/ f i� rj ` l 99; �j I - Edmonds L _ 4n Shen/Federman Wood I - r Mountlak �1 S -� Terrace i1 � '�1, • � . � r I I Lake B+Jli.yn Page 3of9 MR1-5 Drainage Report 23310 Humber Lane Edmonds, WA 98020 7/17/2023 CES #2070 S O L U T I O N S Background: A new single-family two-story house is proposed on this lot adjacent to the east border of Woodway. Subject lot slopes down to the west at an average grade of 7%. Soil is glacial till and not great for infiltration. See soil summary below for full explanation. This lot falls within the Deer Creek drainage basin which is tributary to Lake Washington. The total new or replaced impervious area is under 5,000 sf including all roof area and on -site driveway. See exact areas in the appendix. Soils and Infiltration Feasibility: Conclusion sourced from the geotech report (see appendix for report)... Soil is glacial till. During our January 18, 2023 site visit, we assessed the subsurface conditions in two test holes located... Published geologic maps indicate that the site and surrounding area are underlain by glacial till, a glacially -compressed mixture of gravel, silt, and fine-grained sand. The natural soil conditions encountered in the test holes consist of topsoil overlying weathered, slightly gravelly, silty sand. Beneath this thin weathered layer is dense, slightly gravelly, silty sand that has been glacially compressed, and which is referred to as glacial till. This is consistent with the mapped geology for the area. A layer of fill was encountered over the native soils in the western test hole (Test Pit 2). We expect that fill may be encountered elsewhere around the existing house, resulting from the excavation and grading that occurred during the original site development. The test holes were conducted following several months of wet weather. Shallow seepage perched on top of the glacial till, which is relatively impervious, was observed. This is a common occurrence in the Pacific Northwest on properties where glacial till or other impervious soils lie close to the ground surface... Considering the observed soil conditions and the presence of seasonal shallow perched groundwater, it is our professional opinion that infiltration of concentrated storm water runoff is infeasible for this site. Attempting to infiltrate or disperse stormwater on the site would only increase the potential for surface and subsurface drainage problems on neighboring properties. Page 4of9 MR1-5 Drainage Report 23310 Humber Lane Edmonds, WA 98020 7/17/2023 CES #2070 CIVIL ENGINEERING Existing Drainage Pattern narrative: It is unknown what the existing house does with its stormwater. (Normally houses built in this era splash -blocked their water.) See downstream map below, assuming water is not pumped up to the existing city storm (which would also end up in Deer Creek). Lake Washington Existing Impervious area: 3,800 sf Proposed Impervious area: < 5,000 sf See impervious spreadsheet in appendix for breakdown Page 5of9 MR1-5 Drainage Report 23310 Humber Lane Edmonds, WA 98020 7/17/2023 CES #2070 S O L U T I O N S MR 4 Preservation of Natural Drainage Systems and Outfalls MR#4 Definition Natural drainage patterns shall be maintained, and discharges from the project site shall occur at the natural location, to the maximum extent practicable. The manner by which runoff is discharged from the project site must not cause a significant adverse impact to downstream receiving waters and downgradient properties. All outfalls require energy dissipation. (ref. DOE Manual, 1-2.5.4) Response: There are no well-defined natural outfalls based on our review of this lot. We would characterize the dispersion trench solution as exactly meeting MR4 intent. MR#4 Objective To preserve and utilize natural drainage systems to the fullest extent because of the multiple stormwater benefits these systems provide; and to prevent erosion at and downstream of the discharge location. (ref. DOE Manual, 1-2.5.4) Response: See response above. The Dispersion trench fully meets MR4's goal. MR#4 Supplemental Guidelines Creating new drainage patterns results in more site disturbance and more potential for erosion and sedimentation during and after construction. Creating new discharge points can create significant stream channel erosion problems as the receiving water body typically must adjust to the new flows. Diversions can cause greater impacts than would otherwise occur by discharging runoff at the natural location. (ref. DOE Manual, 1-2.5.4) Response: This project should in no way cause adverse problems mentioned above which are more potential issues related to larger projects as opposed to urban single family. MR 5 Proposed On -site Stormwater management: The List Approach (List #1) selection process was applied to site: Lawn and Landscaped Areas: Page 6of9 MR1-5 Drainage Report 23310 Humber Lane Edmonds, WA 98020 7/17/2023 CES #2070 S O L U T I O N S • Post -Construction Soil Quality and Depth in accordance with BMP T5.13 in Chapter 5 of Volume V of the DOE Manual. Compost -Amended Soil is required and proposed. Roofs: Full Dispersion: Not feasible: A minimum native vegetative flowpath length of 100 lineal feet is not achievable. • Downspout Full Infiltration: Full Infiltration is not feasible. Project geotechnical engineer encountered "dense" vashon till at shallow depths along with perched shallow groundwater at 3.5' and 2' below ground surface. Infeasibility Reference o There is not at least 1 foot or more of permeable soil from the proposed bottom of the infiltration system to the seasonal high groundwater table. (Ref.- See Edmonds' Appendix A o The lot does not have outwash or loam soils (Ref. Appendix A) • Bio-retention / Raingarden: Bio-retention/raingarden is not feasible. Project geotech found perched shallow groundwater at 3.5' and 2' below ground surface at each hand auger location. Infeasibility Reference o There is not at least 1 foot or more of permeable soil from the proposed bottom of the infiltration system to the seasonal high groundwater table. (Ref.- See Edmonds' Appendix A) o The lot does not have outwash or loam soils (Ref.- Appendix A) • Downspout Dispersion: Proposed. See plans for sizing. • PTC Project is not proposing a city storm connection where this would be logical choice if so. Other Hard Surfaces (i.e. Driveway): Driveway: • Full Dispersion serving driveway: Not feasible: Page 7of9 MR1-5 Drainage Report 23310 Humber Lane Edmonds, WA 98020 7/17/2023 CES #2070 S O L U T I O N S A minimum native vegetative flowpath length of 100 lineal feet is not achievable. • Permeable Pavement Driveway Permeable Pavement is not feasible. The wearing course slope exceeds 6% after reasonable attempts to grade. (Proposed driveway grade is 8%.) See Edmonds' Appendix A. • Bioretention serving driveway: Bio-retention/raingarden is not feasible. Project geotech found perched shallow groundwater at 2' below ground surface. There is not at least 1 foot or more of vertical separation to the seasonal groundwater. See Edmonds' Appendix A. • Sheet Flow Dispersion serving driveway: Infeasible: Positive drainage for sheet flow runoff cannot be achieved; driveway drains toward the house. See Edmonds' Appendix A. • Concentrated Flow Dispersion serving driveway: Dispersion proposing serving roof and driveway. See plans. Walkway: Sidenote: Narrow strips of impervious like walkways typically do not warrant a standalone formal BMP assessment in our opinion. They inherently disperse runoff to adjacent areas. • Full Dispersion serving walkway: Not feasible and highly impracticle: A minimum native vegetative flowpath length of 100 lineal feet is not achievable. • Permeable Pavement Walkway Permeable Pavement is not proposed for following reason(s). (1) the wearing course slope exceeds 6% after reasonable attempts to grade. (Proposed walkway grade is 7% in places.) • Bioretention serving walkway: Bio-retention/raingarden is not realistic option for serving walking isolated walking surfaces. Besides fact the Project geotech found perched shallow groundwater at 2' below ground surface. It's just not practical to attempt to properly capture ground level walking surfaces like this and pipe to a bio-retention or rain garden. • Sheet Flow Dispersion serving walkway: A full -spec BMP flow path length (25-feet) cannot be achieved. As mentioned above, strip surfaces like walkways inherently have BMP's "baked -in" due to their surrounding soil and landscaping to intake the small runoff they generate and easily disperse. Simple is the best. Page 8of9 MR1-5 Drainage Report 23310 Humber Lane Edmonds, WA 98020 7/17/2023 CES #2070 MR6 Runoff Treatment N/A — Project under 5,000 sf MR7 Flow Control N/A — Project under 5,000 sf CIVIL ENGINEERING APPENDIX • Impervious Area Spreadsheet • Figure 3.1 — Flow Chart for Determining Requirements for Development • Reference: Edmonds Appendix A — Onsite Stormwater Management BMP Infeasibility Criteria • Geotechnical Report, Geotech Consultants, Inc., Marc McGinnis, PE, January 19, 2023 Page 9of9 MR1-5 Drainage Report 23310 Humber Lane Edmonds, WA 98020 7/17/2023 CES #2070 UPDATED JULY 18, 2023 Impervious Area Spreadsheet (Stormwater) Shen/Federman Residence - 23310 Humber Lane, Edmonds, WA 98020 Site Area 12,600 sf 0.289 acres Existing impervious area Ex. impervious area to be demo'ed 3,595 sf Ex. imprevious area to remain sf total existing impervious = 3,595 sf Existing vegetated area 9,005 sf Proposed Impervious Area (on -site) Roof 3,094 sf Exposed driveway 567 sf Exposed front/side walkway 779 sf total new + replaced impervious = 4,440 sf Existing imprevious area to remain 0 sf Total proposed impervious = 4,4401 sf Proposed vegetated area 8,160 sf Does the project result in 2,000 square feet, or greater, of new plus replaced hard surface area? OR Does the land disturbing activity total 7,000 square feet or greater? Yes No Minimum Requirements No. 1 through 5 apply I Minimum Requirement No. 2 applies Next Question Does the project add 5,000 square feet or more of new plus replaced hard surfaces? OR Convert 0.75 acres or more of vegetation to lawn or landscaped areas? OR Convert 2.5 acres or more of native vegetation to pasture? No Yes Is this a road related project? No Yes Does the project add 5,000 square feet or No more of new hard surfaces? Yes All Minimum Requirements apply to the new and replaced Yes Do new hard surfaces add 50% or hard surfaces and converted more to the existing hard surfaces vegetation areas. within the project limits? All Minimum Requirements apply to the new hard surfaces and converted vegetation areas. No Figure 3.1. Flow Chart for Determining Requirements for Development. No additional requirements. 12,600 sf site area 3,800 sf existing impervious area 30% existing impervious area 4,455 sf new/replaced impervious area 8 3. APPLICABILITY OF THE MINIMUM REQUIREMENTS JUNE 2022 APPENDIX A - ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA Appendix A — On -Site Stormwater Management BMP Infeasibility Criteria The following tables summarize infeasibility criteria that can be used to justify not using various on -site stormwater management BMPs for consideration in the List No. 1 or List No. 2 option of Minimum Requirement No. 5. Much of this information is also included under the detailed descriptions of each BMP in the SWMMWW, but is summarized here in this Addendum appendix for additional clarity and efficiency. However, note that this appendix also includes several City -specific infeasibility criteria that are not included in the SWMMWW. Therefore, where any inconsistencies or lack of clarity exists between the SWMMWW and this appendix, the requirements of this appendix shall apply, and project proponents should consult with the City for any clarifications. If a project is limited by one or more of the infeasibility criteria specified below, but still wishes to use the given BMP, they may propose a functionally equivalent design to the City for review and approval. Lawn and Landscaped Areas BMP Infeasibility Criteria — This BMP is INFEASIBLE under the following conditions: Post -Construction • Lawn and landscape area is on till slopes greater than 33 percent. Soil Quality and Depth Roofs BMP Infeasibility Criteria — This BMP is INFEASIBLE under the following conditions: Full Dispersion • Where the dispersion area is within the North Edmonds Earth Subsidence and Landslide Hazard Area (ESLHA). • The flowpath or dispersal area is within the buffer of the ESLHA (minimum buffer equal to the height of the steep slope or 50 feet, whichever is greater) unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system. • The slope of the flowpath or dispersal area is steeper than 15 percent for any 20-foot reach of the flowpath, or steeper than 33 percent if a level spreader is used upstream and vegetation is established. • The flowpath or dispersal area is within 50 feet of the top of slopes greater than 15 percent (unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system). • A 65 to 10 ratio of forested or native vegetation area to impervious area cannot be achieved. • A minimum forested or native vegetation flowpath length of 100 feet (25 feet for sheet flow from a nonnative pervious surface) cannot be achieved. A. ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA 1 APPENDIX A - ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA JUNE 2022 Roofs (continued) BMP Infeasibility Criteria — This BMP is INFEASIBLE under the following conditions: Full Dispersion • The flow path cannot be located on site or in a reserved offsite tract or (continued) easement area. • The flowpath cannot be located between the dispersion device and any downstream drainage feature such as a pipe, ditch, stream, river, pond, lake, or wetland. • Flowpaths for adjacent dispersion devices cannot be sufficiently spaced to prevent overlap of flows in the flowpath areas. • For sites with onsite or adjacent septic systems, the discharge point must be at least 30 feet upgradient, or 10 feet downgradient, of the drainfield primary and reserve areas (per WAC 246-272A-0210). This requirement can be modified by the City if site topography will clearly prohibit flows from intersecting the drainfield or where site conditions (soil permeability, distance between systems, etc.) indicate that this is unnecessary. • The dispersion area is within the buffer of a Category 1 or Category 2 wetland. • The dispersion area is within the buffer of a Category 3 or Category 4 wetland, except for the outer 25 percent of the buffer. • The dispersion of runoff would create flooding or erosion impacts. Downspout Full • Where the infiltration system is within the North Edmonds Earth Subsidence Infiltration Systems and Landslide Hazard Area (ESLHA). • Within the buffer of the ESLHA (minimum buffer equal to the height of the steep slope or 50 feet, whichever is greater) unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system. • Within 50 feet of the top of slopes greater than 15 percent (unless a geotechnical assessment and soils report is prepared addressing the potential im act of the proposed system). • The lot(s) or site does not have outwash or loam soils. • There is not at least 3 feet or more of permeable soil from the proposed final grade to the seasonal high groundwater table or other impermeable layer. • There is not at least 1 foot or more of permeable soil from the proposed bottom of the infiltration system to the seasonal high groundwater table or other impermeable layer. • Within 5 feet from any property lines and easements. • If the contributing area is less than 5,000 square feet, within 5 feet from a structure without a basement and 10 feet for a structure with a basement. • If the contributing area is greater than or equal to 5,000 square feet, within a 1Horizontal: 1Vertical slope line from the bottom edge of the facility to a structure. (Minimum clearance 5 feet from a structure with a basement and 10 feet for a structure with a basement.) 2 A. ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA JUNE 2022 APPENDIX A - ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA Roofs (continued) BMP Infeasibility Criteria — This BMP is INFEASIBLE under the following conditions: Downspout Full • For sites with onsite or adjacent septic systems, the discharge point must be Infiltration Systems at least 30 feet upgradient, or 10 feet downgradient, of the drainfield primary (continued) and reserve areas (per WAC 246-272A-0210). This requirement can be modified by the City if site topography will clearly prohibit flows from intersecting the drainfield or where site conditions (soil permeability, distance between systems, etc.) indicate that this is unnecessary. • If placed in fill material, the measured infiltration rate is less than 8 inches per hour. • If placed under pavement, overflow cannot be sited at least 1 foot below the pavement (i.e., to prevent saturation of the pavement if system fails). • Within the buffer of a Category 1 or Category 2 wetland. • Within the buffer of a Category 3 or Category 4 wetland, except for the outer 25 percent of the buffer. Bioretention or Note: Criteria with setback distances are as measured from the bottom edge of Rain Gardens the bioretention soil mix. Citation of any of the following infeasibility criteria must be based on an evaluation of site -specific conditions and a written recommendation from an appropriate licensed professional (e.g., engineer, geologist, hydrogeologist): • Where professional geotechnical evaluation recommends infiltration not be used due to reasonable concerns about erosion, slope failure, or downgradient flooding. • Where the only area available for siting would threaten the safety or reliability of pre-existing underground utilities, pre-existing underground storage tanks, pre-existing structures, or pre-existing road or parking lot surfaces. • Where the only area available for siting does not allow for a safe overflow pathway to stormwater drainage system or private storm sewer system. • Where there is a lack of usable space for bioretention/rain garden areas at redevelopment sites, or where there is insufficient space within the existing public right-of-way on public road projects. • Where infiltrating water would threaten existing below grade basements. • Where infiltrating water would threaten shoreline structures such as bulkheads. The following infeasibility criteria are based on conditions such as topography and distances to predetermined boundaries. Citation of the following criteria do not need site -specific written recommendations from a licensed professional, although some may require professional services to determine: • Where the system is within the North Edmonds Earth Subsidence and Landslide Hazard Area (ESLHA). A. ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA 3 APPENDIX A - ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA JUNE 2022 Roofs (continued) BMP Infeasibility Criteria — This BMP is INFEASIBLE under the following conditions: Bioretention or • Within the buffer of the ESLHA (minimum buffer equal to the height of the Rain Gardens steep slope or 50 feet, whichever is greater) unless a geotechnical (continued) assessment and soils report is prepared addressing the potential impact of the proposed system. • Within 50 feet of the top of slopes greater than 15 percent (unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system). • Where they are not compatible with surrounding drainage system as determined by the City (e.g., project drains to an existing stormwater collection system whose elevation or location precludes connection to a properly functioning bioretention/rain garden area). • Where the site cannot be reasonably designed to locate bioretention/rain garden areas on slopes less than 8 percent. • Properties with known soil or groundwater contamination (typically federal Superfund sites or state cleanup sites under the Model Toxics Control Act [MTCA]): O Within 100 feet of an area known to have deep soil contamination. O Where groundwater modeling indicates infiltration will likely increase or change the direction of the migration of pollutants in the groundwater. o Wherever surface soils have been found to be contaminated unless those soils are removed within 10 horizontal feet from the infiltration area. o Any area where these facilities are prohibited by an approved cleanup plan under the state Model Toxics Control Act or Federal Superfund Law, or an environmental covenant under Chapter 64.70 RCW. • Within 100 feet of a closed or active landfill. • Within 100 feet of a drinking water well, or a spring used for drinking water supply. • For sites with onsite or adjacent septic systems, the discharge point must be at least 30 feet upgradient, or 10 feet downgradient, of the drainfield primary and reserve areas (per WAC 246-272A-0210). This requirement can be modified by the City if site topography will clearly prohibit flows from intersecting the drainfield or where site conditions (soil permeability, distance between systems, etc.) indicate that this is unnecessary. • Within 10 feet of an underground storage tank and connecting underground pipes when the capacity of the tank and pipe system is 1,100 gallons or less. As used in these criteria, an underground storage tank means any tank used to store petroleum products, chemicals, or liquid hazardous wastes of which 10 percent or more of the storage volume (including volume in the connecting piping system) is beneath the ground surface. • Within 100 feet of an underground storage tank and connecting underground pipes when the capacity of the tank and pipe system is greater than 1,100 gallons. 4 A. ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA JUNE 2022 APPENDIX A - ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA Roofs (continued) BMP Infeasibility Criteria — This BMP is INFEASIBLE under the following conditions: Bioretention or • Where field testing indicates potential bioretention/rain garden sites have a Rain Gardens measured (a.k.a., initial) native soil saturated hydraulic conductivity less (continued) than 0.30 inches per hour. A small-scale or large-scale PIT in accordance with Appendix B shall be used to demonstrate infeasibility. If the measured native soil infiltration rate is less than 0.30 in/hour, bioretention/rain garden BMPs are not required to be evaluated as an option in List No. 1 or List No. 2. In these slow draining soils, a bioretention area with an underdrain may be used to treat pollution -generating surfaces to help meet Minimum Requirement No. 6. If the underdrain is elevated within a base course of gravel, it will also provide some modest flow reduction benefit that will help achieve Minimum Requirement No. 7. • Where the minimum vertical separation of 3 feet to the seasonal high groundwater elevation or other impermeable layer would not be achieved below bioretention that would serve a drainage area that meets or exceeds the following thresholds: 1. 5,000 square feet of pollution -generating impervious surface (PGIS) 2. 10,000 square feet of impervious area 3. 0.75 acres of lawn and landscape. AND cannot reasonably be broken down into amounts smaller than those listed in 1-3 (above). • Where the minimum vertical separation of 1 foot to the seasonal high groundwater or other impermeable layer would not be achieved below bioretention that would serve a drainage area that is less than: 1. 5,000 square feet of pollution -generating impervious surface (PGIS) 2. 10,000 square feet of impervious area 3. 0.75 acres of lawn and landscape. • If the contributing area is less than 5,000 square feet, within 5 feet from a structure without a basement and 10 feet for a structure with a basement. • If the contributing area is greater than or equal to 5,000 square feet, within a I Horizontal: 1 Vertical slope line from the bottom edge of the facility to a structure. (Minimum clearance 5 feet from a structure with a basement and 10 feet for a structure with a basement.) • Within 5 feet from any property lines and easements. • Within the buffer of a Category 1 or Category 2 wetland. • Within the buffer of a Category 3 or Category 4 wetland, except for the outer 25 percent of the buffer. A. ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA 5 APPENDIX A - ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA JUNE 2022 Roofs (continued) BMP Infeasibility Criteria — This BMP is INFEASIBLE under the following conditions: Downspout • Where dispersion area is within the North Edmonds Earth Subsidence and Dispersion Systems Landslide Hazard Area (ESLHA). • Within the buffer of the ESLHA (minimum buffer equal to the height of the steep slope or 50 feet, whichever is greater) unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system. • For splashblocks, a vegetated flowpath at least 50 feet in length from the downspout to the downstream property line, structure, stream, wetland, slope over 15 percent (unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system), or other impervious surface is not feasible. • For trenches, a vegetated flowpath of at least 25 feet in between the outlet of the trench and any property line, structure, stream, wetland, or impervious surface is not feasible. A minimum vegetated flowpath of at least 50 feet between the outlet of the trench and any slope steeper than 15 percent is not feasible (unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system). • For trenches, a trench width of at least 10 feet is not feasible. • Flowpaths for adjacent dispersion devices cannot be sufficiently spaced to prevent overlap of flows in the flowpath areas. • For trenches within 5 feet from any property lines and easements. • For sites with onsite or adjacent septic systems, the discharge point must be at least 30 feet upgradient, or 10 feet downgradient, of the drainfield primary and reserve areas (per WAC 246-272A-0210). This requirement can be modified by the City if site topography will clearly prohibit flows from intersecting the drainfield or where site conditions (soil permeability, distance between systems, etc.) indicate that this is unnecessary. • Within the buffer of a Category 1 or Category 2 wetland. • Within the buffer of a Category 3 or Category 4 wetland, except for the outer 25 percent of the buffer. Perforated Stub- • Where the system is within the North Edmonds Earth Subsidence and Out Connections Landslide Hazard Area (ESLHA). • Within the buffer of the ESLHA (minimum buffer equal to the height of the steep slope or 50 feet, whichever is greater) unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system. • Within 50 feet of the top of slopes greater than 15 percent (unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system). • There is not at least 1 foot of permeable soil from the proposed bottom of the perforated stub -out connection trench to the highest estimated groundwater table or other impermeable layer. 6 A. ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA JUNE 2022 APPENDIX A - ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA Roofs (continued) BMP Infeasibility Criteria — This BMP is INFEASIBLE under the following conditions: Perforated Stub- • The only location available for the perforated stub -out connection is under Out Connections impervious or heavily compacted soils. (continued) • For sites with onsite or adjacent septic systems, the discharge point must be at least 30 feet upgradient, or 10 feet downgradient, of the drainfield primary and reserve areas (per WAC 246-272A-0210). This requirement can be modified by the City if site topography will clearly prohibit flows from intersecting the drainfield or where site conditions (soil permeability, distance between systems, etc.) indicate that this is unnecessary. • Within the buffer of a Category 1 or Category 2 wetland. • Within the buffer of a Category 3 or Category 4 wetland, except for the outer 25 percent of the buffer. Detention Vaults Subject to review and approval by the City; infeasibility may be determined and Pipes when a project meets any of the following infeasibility criteria: • Where the downstream analysis in Minimum Requirement No. 4, or available City data, indicate that peak flow control from the site is not beneficial. • Where there is less than 1,000 square feet of contributing site impervious surfaces that are not proposed to be managed by other On -Site Stormwater Management BMPs. (This includes combining of areas from multiple types of surfaces listed under the list options for Minimum Requirement No. 5, e.g., roofs and other hard surfaces.) • Where there is not a downstream drainage system that allows for connection to the City storm system or an appropriate dispersion and overflow path. Other Hard Surfaces BMP Infeasibility Criteria — This BMP is INFEASIBLE under the following conditions: Full Dispersion • See Full Dispersion under "Roofs" section above. Permeable Citation of any of the following infeasibility criteria must be based on an Pavement evaluation of site -specific conditions and a written recommendation from an appropriate licensed professional (e.g., engineer, geologist, hydrogeologist): • Where professional geotechnical evaluation recommends infiltration not be used due to reasonable concerns about erosion, slope failure, or downgradient flooding. • Where infiltrating and ponded water below the new permeable pavement area would compromise adjacent impervious pavements. • Where infiltrating water below a new permeable pavement area would threaten existing below grade basements. • Where infiltrating water would threaten shoreline structures such as bulkheads. A. ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA 7 APPENDIX A - ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA JUNE 2022 Other Hard Surfaces (continued) BMP Infeasibility Criteria — This BMP is INFEASIBLE under the following conditions: Permeable • Down slope of steep, erosion prone areas that are likely to deliver sediment. Pavement • Where fill soils are used that can become unstable when saturated. (continued) . On excessively steep slopes where water within the aggregate base layer or at the subgrade surface cannot be controlled by detention structures and may cause erosion and structural failure, or where surface runoff velocities may preclude adequate infiltration at the pavement surface. • Where permeable pavements cannot provide sufficient strength to support heavy loads at industrial facilities such as ports. • Where installation of permeable pavement would threaten the safety or reliability of pre-existing underground utilities, pre-existing underground storage tanks, or pre-existing road subgrades. The following infeasibility criteria are based on conditions such as topography and distances to predetermined boundaries. Citation of the following criteria do not need site -specific written recommendations from a licensed professional, although some require professional services to determine: • Where the permeable pavement is within the North Edmonds Earth Subsidence and Landslide Hazard Area (ESLHA). • Within the buffer of the ESLHA (minimum buffer equal to the height of the steep slope or 50 feet, whichever is greater) unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system. • Within 50 feet of the top of slopes greater than 15 percent (unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system). • Properties with known soil or groundwater contamination (typically federal Superfund sites or state cleanup sites under the Model Toxics Control Act [MTCA]): o Within 100 feet of an area known to have deep soil contamination. o Where groundwater modeling indicates infiltration will likely increase or change the direction of the migration of pollutants in the groundwater. o Wherever surface soils have been found to be contaminated unless those soils are removed within 10 horizontal feet from the infiltration area. o Any area where these facilities are prohibited by an approved cleanup plan under the state Model Toxics Control Act or Federal Superfund Law, or an environmental covenant under Chapter 64.70 RCW. • Within 100 feet of a closed or active landfill. • Within 100 feet of a drinking water well, or a spring used for drinking water supply. If permeable pavement is (or has run-on from) a pollution - generating hard surface. 8 A. ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA JUNE 2022 APPENDIX A - ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA Other Hard Surfaces (continued) BMP Infeasibility Criteria — This BMP is INFEASIBLE under the following conditions: Permeable • For sites with onsite or adjacent septic systems, the discharge point must be Pavement at least 30 feet upgradient, or 10 feet downgradient, of the drainfield primary (continued) and reserve areas (per WAC 246-272A-0210). This requirement can be modified by the City if site topography will clearly prohibit flows from intersecting the drainfield or where site conditions (soil permeability, distance between systems, etc.) indicate that this is unnecessary. • Within 10 feet of any underground storage tank and connecting underground pipes, regardless of tank size. As used in these criteria, an underground storage tank means any tank used to store petroleum products, chemicals, or liquid hazardous wastes of which 10 percent or more of the storage volume (including volume in the connecting piping system) is beneath the ground surface. • At multi -level parking garages, and over culverts and bridges. • Where the site design cannot avoid putting pavement in areas likely to have long-term excessive sediment deposition after construction (e.g., construction and landscaping material yards). • Where the subgrade slope exceeds 6 percent after reasonable efforts to grade. Where the permeable pavement wearing course slope exceeds 6 percent after reasonable efforts to design grade. • Where the native soils below a pollution -generating permeable pavement (e.g., road or parking lot) do not meet the soil suitability criteria for providing treatment. See soil suitability criteria for treatment in SWMMWW, Volume V, Section 5.6. Note: In these instances, the City may approve installation of a 6-inch sand filter layer meeting City specifications for treatment as a condition of construction. • Where underlying soils are unsuitable for supporting traffic loads when saturated. Soils meeting a California Bearing Ratio of 5 percent are considered suitable for residential access roads. • Where appropriate field testing indicates soils have a measured (a.k.a., initial) native soil saturated hydraulic conductivity less than 0.30 inches per hour. A small-scale or large-scale PIT in accordance with Appendix B shall be used to demonstrate infeasibility. (Note: In these instances, unless other infeasibility restrictions apply, roads and parking lots may be built with an underdrain, preferably elevated within the base course, if flow control benefits are desired.) A. ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA 9 APPENDIX A - ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA JUNE 2022 Other Hard Surfaces (continued) BMP Infeasibility Criteria — This BMP is INFEASIBLE under the following conditions: Permeable • Roads that receive more than very low traffic volumes, and areas having Pavement more than very low truck traffic. Roads with a projected average daily (continued) traffic volume of 400 vehicles or less are very low volume roads (AASHTO 2001) (U.S. Department of Transportation 2013). Note: This infeasibility criterion does not extend to sidewalks and other non -traffic bearing surfaces. • Areas having more than very low truck traffic. Areas with very low truck traffic volumes are roads and other areas not subject to through truck traffic but may receive up to weekly use by utility trucks (e.g., garbage, recycling), daily school bus use, and multiple daily use by pick-up trucks, mail/parcel delivery trucks, and maintenance vehicles. Note: This infeasibility criterion does not extend to sidewalks and other non -traffic bearing surfaces. • Where replacing existing impervious surfaces unless the existing surface is a non -pollution generating surface over an outwash soil with a saturated hydraulic conductivity of 4 inches per hour or greater. • At sites whose land use required oil control BMPs per SWMMWW, Volume III, Section 1.2. • In areas with "industrial activity" as identified in 40 CFR 122.26(b)(14). • Where the risk of concentrated pollutant spills is more likely such as gas stations, truck stops, and industrial chemical storage sites. • Where routine, heavy applications of sand occur in frequent snow zones to maintain traction during weeks of snow and ice accumulation. • Where the seasonal high groundwater or an underlying impermeable/low permeable layer would create saturated conditions within I foot of the bottom of the lowest gravel base course. • Within the buffer of a Category 1 or Category 2 wetland. • Within the buffer of a Category 3 or Category 4 wetland, except for the outer 25 percent of the buffer. Bioretention or • See Bioretention or Rain Gardens under "Roofs" section above. Rain Gardens Sheet Flow • Where the dispersion area is within the North Edmonds Earth Subsidence Dispersion and Landslide Hazard Area (ESLHA). • Within the buffer of the ESLHA (minimum buffer equal to the height of the steep slope or 50 feet, whichever is greater) unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system. • Where the dispersion area is within 50 feet of the top of slopes greater than 15 percent (unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system). • Positive drainage for sheet flow runoff cannot be achieved. 10 A. ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA JUNE 2022 APPENDIX A - ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA Other Hard Surfaces (continued) BMP Infeasibility Criteria — This BMP is INFEASIBLE under the following conditions: Sheet Flow • Area to be dispersed (e.g., driveway, patio) cannot be graded to have less Dispersion than a 15 percent slope. (continued) • For flat to moderately sloped areas, at least a 10-foot-wide vegetation buffer for dispersion of the adjacent 20 feet of contributing surface cannot be achieved. For variably sloped areas, at least a 25-foot vegetated flowpath between berms cannot be achieved. • The dispersion of runoff would create flooding or erosion impacts. • For sites with onsite or adjacent septic systems, the discharge point must be at least 30 feet upgradient, or 10 feet downgradient, of the drainfield primary and reserve areas (per WAC 246-272A-0210). This requirement can be modified by the City if site topography will clearly prohibit flows from intersecting the drainfield or where site conditions (soil permeability, distance between systems, etc.) indicate that this is unnecessary. • The dispersion area is within the buffer of a Category 1 or Category 2 wetland. • The dispersion area is within the buffer of a Category 3 or Category 4 wetland, except for the outer 25 percent of the buffer. Concentrated Flow • Where the dispersion area is within the North Edmonds Earth Subsidence Dispersion and Landslide Hazard Area (ESLHA). • Within the buffer of the ESLHA (minimum buffer equal to the height of the steep slope or 50 feet, whichever is greater) unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system. • A minimum vegetated flowpath of 50 feet between the discharge point and the top of slopes greater than 15 percent is not feasible (unless a geotechnical assessment and soils report is prepared addressing the potential impact of the proposed system). • A minimum 3-foot length of rock pad and 50-foot flowpath OR a dispersion trench and 25-foot flowpath for every 700 sq. ft. of drainage area (within applicable setbacks) cannot be achieved. • More than 700 square feet drainage area drains to any dispersion device. • The dispersion of runoff would create flooding or erosion impacts. • A minimum vegetated flowpath of 50 feet (if using rock pads) or 25 feet (if using dispersion trenches) between the discharge point and any property line, structure, stream, lake, wetland, or other impervious surface is not feasible. A. ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA 11 APPENDIX A - ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA JUNE 2022 Other Hard Surfaces (continued) BMP Infeasibility Criteria — This BMP is INFEASIBLE under the following conditions: Concentrated Flow • For sites with onsite or adjacent septic systems, the discharge point must be Dispersion at least 30 feet upgradient, or 10 feet downgradient, of the drainfield primary (continued) and reserve areas (per WAC 246-272A-0210). This requirement can be modified by the City if site topography will clearly prohibit flows from intersecting the drainfield or where site conditions (soil permeability, distance between systems, etc.) indicate that this is unnecessary. • The dispersion area is within the buffer of a Category 1 or Category 2 wetland. • The dispersion area is within the buffer of a Category 3 or Category 4 wetland, except for the outer 25 percent of the buffer. Detention Vaults • See Detention Vaults and Pipes under "Roofs" section above. and Pipes 12 A. ON -SITE STORMWATER MANAGEMENT BMP INFEASIBILITY CRITERIA OEOTECH CONSULTANTS, INC_ Bernard Shen & Catherine Federman 417 N.W. 32"d Street Seattle, Washington 98177 via email: bernard8shen(aMotmail.cam & cefer8(a-hotmail.com Subject: Geotechnical Report Proposed New Residence 23310 Humber Lane Edmonds, Washington Greetings: 2401 1 Oth Ave E Seattle, Washington 98102 (425)747-5618 January 19, 2023 J N 23011 This report presents our geotechnical conclusions related to the planned redevelopment of the subject property. On January 18, 2023, the undersigned principal geotechnical engineer visited the subject site to assess both the surface and subsurface conditions. In addition to this work, we have reviewed published geologic maps, as well as the mapping by the Natural Resources Conservation Service (NRCS). Based on the information provided by Patricia Brennan Architects, the existing residence will be demolished and be replaced with a new home having a larger footprint. The west wall of the new house will be close to the western extent of the existing residence, and the new house's footprint will extend eastward from the existing. The new home will be two stories in height. No basement or deep below -grade spaces will be included. SITE CONDITIONS The existing house is one story in height and is centrally located on the lot. A paved driveway extends from Humber Lane through the southern portion of the property to the garage located in the south end of the current residence. The remainder of the property is covered primarily with grass, with some landscape beds. There are two small detached sheds located in the southwestern portion of the lot. There are no steep slopes on, or near, the subject property. Consistent with the neighboring properties, the natural ground surface slopes only gently downward toward the west from the edge of Humber Lane. It appears that a storm sewer and associated catch basins are located along the western edge of paved portion of Humber Lane. The neighboring properties are similarly developed with one-story homes. During our January 18, 2023 site visit, we assessed the subsurface conditions in two test holes located as indicated on the attached Site Exploration Plan. Logs of the test pits are also attached. Published geologic maps indicate that the site and surrounding area are underlain by glacial till, a glacially -compressed mixture of gravel, silt, and fine-grained sand. The natural soil conditions encountered in the test holes consist of topsoil overlying weathered, slightly gravelly, silty sand. GEOTECH CONSULTANTS, INC. Shen & Federman A 23011 January 19, 2023 Page 2 Beneath this thin weathered layer is dense, slightly gravelly, silty sand that has been glacially compressed, and which is referred to as glacial till. This is consistent with the mapped geology for the area. A layer of fill was encountered over the native soils in the western test hole (Test Pit 2). We expect that fill may be encountered elsewhere around the existing house, resulting from the excavation and grading that occurred during the original site development. The test holes were conducted following several months of wet weather. Shallow seepage perched on top of the glacial till, which is relatively impervious, was observed. This is a common occurrence in the Pacific Northwest on properties where glacial till or other impervious soils lie close to the ground surface. CONCLUSIONS AND RECOMMENDATIONS Based on the conditions observed in the test holes, it is our professional opinion that conventional foundations can be utilized for the proposed residence. All footing areas will have to be excavated down to the dense, native, glacially -compressed soil. It is possible that this may require overexcavation below the planned footing grades. We recommend that the footings be excavated using a smooth bucket, in order to prevent the subgrade disturbance that can result from the teeth on an excavator's bucket. Where overexcavation below the planned footing grades is necessary, the additional excavation can be backfilled to the planned footing grade using compacted quarry spalls or railroad ballast rock. In wet conditions, the footing subgrades should be protected with a layer of clean crushed gravel, in order to prevent disturbance and softening of the bearing soils during the placement of foundation forms and rebar. There are no geologically critical areas on, or near, the site. The potential for future slope movement is nonexistent and the glacially -compressed soils do not present a seismic hazard. No significant retaining walls are expected for the new project. The erosion control measures needed during the site development will depend heavily on the weather conditions that are encountered. We anticipate that a silt fence will be needed around the downslope sides of any cleared areas until house excavation is are lowered below the surrounding grades. Cut slopes and soil stockpiles should be covered with plastic during wet weather. Following rough grading, it may be necessary to mulch or hydroseed bare areas that will not be immediately covered with landscaping or an impervious surface. As with most projects, it may be necessary to implement additional erosion control measures to address site and weather conditions during the earthwork and construction. If crawl spaces or interior slab floors are lower than the surrounding grade, footing drains should be provided. A typical footing drain detail is attached. Given the impermeable nature of the dense soils, it is not uncommon for shallow seepage to enter crawl spaces. As a result, it would be prudent to provide a layer of gravel and perforated pipes under the vapor retarder/barrier, in addition to the perimeter footing drains. SEISMIC CONSIDERATIONS In accordance with the International Building Code (IBC), the site class within 100 feet of the ground surface is best represented by Site Class Type D (stiff soil). GEOTECH CONSULTANTS, INC. Shen & Federman JN 23011 January 19, 2023 Page 3 The IBC and ASCE 7 require that the potential for liquefaction (soil strength loss) be evaluated for the peak ground acceleration of the Maximum Considered Earthquake (MCE), which has a probability of occurring once in 2,475 years (2 percent probability of occurring in a 50-year period). The dense, glacially -compressed soil that will support the foundations is not susceptible to seismic liquefaction under the ground motions of the MCE. CONVENTIONAL FOUNDATIONS The proposed residence can be supported on conventional continuous and spread footings bearing on undisturbed, dense soil, or on compacted crushed rock structural fill placed above this competent native soil. Prior to placing structural fill beneath foundations, the excavation should be observed by the geotechnical engineer or building inspector to document that adequate bearing soils have been exposed. We recommend that continuous and individual spread footings have minimum widths of 12 and 16 inches, respectively. Exterior footings should also be bottomed at least 18 inches below the lowest adjacent finish ground surface for protection against frost and erosion. The local building codes should be reviewed to determine if different footing widths or embedment depths are required. Footing subgrades must be cleaned of loose or disturbed soil prior to pouring concrete. Depending upon site and equipment constraints, this may require removing the disturbed soil by hand. Depending on the encountered soil conditions, overexcavation may be required below the footings to expose competent native soil. Unless lean concrete is used to fill an overexcavated hole, the overexcavation must be at least as wide at the bottom as the sum of the depth of the overexcavation and the footing width. For example, an overexcavation extending 2 feet below the bottom of a 2-foot-wide footing must be at least 4 feet wide at the base of the excavation. If lean concrete is used, the overexcavation need only extend 6 inches beyond the edges of the footing. An allowable bearing pressure of 2,500 pounds per square foot (psf) is appropriate for footings supported on competent native soil. A one-third increase in this design bearing pressure can be used when considering short-term wind or seismic loads. For the above design criteria, it is anticipated that the total post -construction settlement of footings founded on competent native soil will be less than one inch, with differential settlements on the order of one -half -inch in a distance of 25 feet along a continuous footing with a uniform load. Lateral loads due to wind or seismic forces may be resisted by friction between the foundation and the bearing soil, or by passive earth pressure acting on the vertical, embedded portions of the foundation. For the latter condition, the foundation must be either poured directly against relatively level, undisturbed soil or be surrounded by level, well -compacted fill. We recommend using the following ultimate values for the foundation's resistance to lateral loading: PARAMETER ULTIMATE VALUE Coefficient of Friction 0.40 Passive Earth Pressure 300 pcf Where: pcf is Pounds per Cubic Foot, and Passive Earth Pressure is computed using the Equivalent Fluid Density. GEOTECH CONSULTANTS, INC. Shen & Federman JN 23011 January 19, 2023 Page 4 If the ground in front of a foundation is loose or sloping, the passive earth pressure given above will not be appropriate. The above ultimate values for passive earth pressure and coefficient of friction do not include a safety factor. EVALUATION OF INFILTRATION FEASIBILITY The dense soil known to underlie this area, and which was observed in the test holes is glacially compressed. Our review of published geologic maps confirms that the near -surface geologic unit in this area is glacial till (aka hardpan), which is consistent with the observed soil conditions. There are no large or continuous pore spaces in the glacial till soils that can transmit water. This soil is essentially impermeable, preventing downward percolation of water, which often causes a perched water table to form following extended heavy rainfall. A 1997 study published by U.S. Geologic Survey (USGS) in cooperation with the Washington Department of Ecology (WDOE) determined the infiltration capacity of various Washington till soils to vary between 0.0005 and 0.005 inches/hour. We have found similar extremely low infiltration rates in Pilot Infiltration Tests (PITS) our firm has conducted in glacial till soils. Often, the impermeable nature of the glacial till causes a shallow seasonal perched water table to form where the ground surface is not covered by an impervious layer. This is a common problem in the wet season throughout the Pacific Northwest, and shallow seepage is evident in the test pits conducted on the site. Our review of the Web Soil Survey website run by the Natural Resources Conservation Service (NRCS) indicates that the soil mapping is Alderwood-Urban land complex. This is consistent with the soil conditions observed in the test pit. The following information is from the Web Soil Survey, and also indicates that the limiting layer has a very low permeability, far below what is allowed for design of infiltration systems. 5—Alderwood-Urban land complex, 2 to 8 percent slopes Map Unit Composition • Alderwood and similar soils: 60 percent • Urban land: 25 percent • Minor components: 15 percent • Estimates are based on observations, descriptions, and transects of the mapunit. Properties and qualities • Slope: 2 to 8 percent • Depth to restrictive feature: 20 to 40 inches to densic material • Drainage class: Moderately well drained • Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) • Depth to water table: About 18 to 36 inches • Frequency of flooding: None • Frequency of ponding: None • Available water supply, 0 to 60 inches: Low (about 3.0 inches) Considering the observed soil conditions and the presence of seasonal shallow perched groundwater, it is our professional opinion that infiltration of concentrated storm water runoff is infeasible for this site. Attempting to infiltrate or disperse stormwater on the site would only increase the potential for surface and subsurface drainage problems on neighboring properties. GEOTECH CONSULTANTS, INC. Shen & Federman January 19, 2023 Please contact us if you have any questions regarding this report. Respectfully submitted, GEOTECH CONSULTANTS, INC. ��-G R- McGI,�, e OF WASy� '1'lcP AL 1 /19/2023 Marc R. McGinnis, P.E. Principal Attachments: Vicinity Map, Site Exploration Plan, Test Pit Logs, Footing Drain Detail cc: Patricia Brennan Architects via email. office(a�.patriciabrennanarchitects.com MRM:kg J N 23011 Page 5 GEOTECH CONSULTANTS, INC. GEOTECH CONSULTANTS, INC. (Source: Microsoft MapPoint, 2013) VICINITY MAP 23310 Humber Lane Edmonds, Washington Job No: Date: Plate: 23011 Jan.2023 I 1 Legend: TP-1 Test Hole Location GEOTECH CONSULTANTS, INC. SITE EXPLORATION PLAN 23310 Humber Lane Edmonds, Washington Job No: Date: Plate: 23011 Jan. 2023 No Scale 1 2 TEST PIT 1 Depth feet Soil Description 0 — 1.0 Crushed Rock over Topsoil 1.0 — 2.0 Orangish-bro.°, n. slightly gravelly. silty SAND. fine-grained, very moist. loose 2.0 — 3.0 Grayish-bro�,,.rn, slightly gravelly, silty SAND, fine-grained, very moist, dense Glacial Till) Test Hole v,as terminated at a depth of 3.0 feet on January 17, 2023. Perched ground ,ater seepage ,%as observed at 2.0 feet. TEST PIT 2 Depth feet Soil Description 0-2.0 Bro-:,,m, slightly gravelly, silty SAND. fine-grained. very moist. loose i FILLI 2.0 — 2.5 Old Topsoil 2.5 — 3.5 Orangish-bro,.,:,n, slightly gravelly, silty SAND, fine-grained, very moist. loose 3.5 Grayish-bro,.^:,n, slightly gravelly, silty SAND, fine-grained, very moist, dense iGlacial Till) Test Hole ✓as terminated at a depth of 3.5 feet on January 18, 2023. Perched ground,• ater seepage was encountered at a depth of 3.5 feet. GEOTECH CONSULTANTS, INC. TEST PIT LOGS 23310 Humber Lane Edmonds, Washington Job No: Date: Plate: 23011 Jan.2023 1 1 3 Slope backfill away from foundation. Provide surface drains where necessary. 4" min. Tightline Roof Drain (Do not connect to footing drain) Backfill (See text for requirements) O c� Nonwoven Geotextile Filter Fabric O LL Possible Slab oo.a�-000.a� 000.a�0 .00a ° o°< 0 0 0 0 0 "Oo� oO oO oO oO oOo oo.00a 0'0� o O ° Q' aQ o 0 O L�IL)00(� �-o o� 000 4" Perforated Hard PVC Pipe (Invert at least 6 inches below slab or crawl space. Slope to drain to appropriate outfall. Place holes downward.) a.o.o 0 o.a.o-a o a.o:o-o 0 o.a:o-o 0 o.a 00° ` oO' 00 ` oO' 0o0 ` 00, 0000°° boa 0'o a�oa 0 0000�00 0 000�00 0 000�c o,00q °o ° Vapor Retarder/Barrier and Capillary Break/Drainage Layer (Refer to Report text) NOTES: (1) In crawl spaces, provide an outlet drain to prevent buildup of water that bypasses the perimeter footing drains. (2) Refer to report text for additional drainage, waterproofing, and slab considerations. GEOTECH CONSULTANTS, INC. TYPICAL FOOTING DRAIN 23310 Humber Lane Edmonds, Washington Job No: Date: Plate. 4 23011 Jan.2023