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23-101052-SU Technical Information Report 2-28-23 February 14, 2023 Koval Short Plat Technical Information Report Applicant Mr. Roman Koval 23118 126th Avenue Southeast Kent, WA 98031 (206) 531-9287 romanrk@hotmail.com Engineer Valor Civil Engineering, PLLC 1009 North 9th Street Tacoma, WA 98403 (253) 861-7741 valorcivilengineering@hotmail.com Contact: Frank Marescalco, PE February 2023 Koval Short Plat Page i https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx Project Engineer’s Certification I hereby state that this technical information report has been prepared by me or under my supervision and meets the standard of care and expertise which is usual and customary in this community for professional engineers. This report has been prepared for review by the City of Federal Way Department of Community Development (City) in accordance with the 2016 King County Surface Water Design Manual as amended by the City of Federal Way Addendum to the King County Surface Water Design Manual, published January 8, 2017. This document is hereinafter referred to simply as the “Manual.” February 2023 Koval Short Plat Page ii https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx Table of Contents Technical Information Report Section 1: Project Overview ......................................................................................................................................... 1 Project Proposal ........................................................................................................................................................ 1 Project Threshold Summary ................................................................................................................................ 1 Existing Conditions .................................................................................................................................................. 1 Critical Areas .............................................................................................................................................................. 2 Soils ................................................................................................................................................................................ 3 Section 2: Conditions and Requirements Summary ........................................................................................... 3 Drainage Review Required ................................................................................................................................... 3 Core Requirements .................................................................................................................................................. 4 Special Requirements ............................................................................................................................................. 8 Other Conditions or Requirements ................................................................................................................... 8 Section 3: Offsite Analysis ............................................................................................................................................. 8 Section 4: Flow Control, LID, and Water Quality Facility Analysis and Design ....................................... 9 Performance Standards .......................................................................................................................................... 9 Flow Control System ............................................................................................................................................ 10 Water Quality System .......................................................................................................................................... 10 Section 5: Conveyance System Analysis and Design ....................................................................................... 10 Section 6: Special Reports and Studies ................................................................................................................. 11 Section 7: Other Permits ............................................................................................................................................. 11 Section 8: CSWPPP Analysis and Design .............................................................................................................. 11 Erosion and Sediment Control Plan Analysis and Design ..................................................................... 11 Stormwater Pollution Prevention and Spill Control Plan Design ...................................................... 11 Section 9: Bond Quantities, Facility Summaries, and Declaration of Covenant ................................... 11 Section 10: Operations and Maintenance Manual ............................................................................................ 11 List of Tables Table 1: Project Threshold Summary ....................................................................................................................... 2 List of Figures Figure A-1: FEMA Map ............................................................................................................................................... A-2 Figure A-2: Downstream Flow Path ..................................................................................................................... A-3 Figure A-3: Existing Project Site Conditions ..................................................................................................... A-4 Figure A-4: Proposed Project Site Conditions ................................................................................................. A-5 Appendixes Appendix A: Figures and Maps ............................................................................................................................... A-1 Appendix B: Project Plans ........................................................................................................................................ B-1 Appendix C: Construction SWPPP ........................................................................................................................ C-1 Appendix D: Geotechnical Report ......................................................................................................................... D-1 February 2023 Koval Short Plat Page 1 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx Section 1: Project Overview This technical information report has been prepared to support an application for the subdivision of an existing single-family residential property into two new single-family properties. The address of the subject property is 27634 25th Drive South, Federal Way, WA 98003. The current tax parcel number for this lot is 7575600130. The property is about 16,900 square feet in area and is zoned RS5.0 according to the City’s records. Project Proposal The project proposal will subdivide the existing lot into two new building lots. The lot is generally rectangular with its longest dimension in the north-south direction. Two new lots will be created by the subdivision. The existing home will be retained on what will be the new Lot 1, while an empty single-family building lot will be created on the new Lot 2. Both lots have direct access to 25th Drive South. Private roads or “public purpose” tracts are not required for the proposed short plat action. Project Threshold Summary All of the project’s new impervious surfaces will be created on-site. Off-site improvements are not anticipated at this time, except for a minimal amount of impervious surface in the right-of- way for the driveway approach onto 25th Drive South for the new home. For the purposes of analyzing the project thresholds, the small areas of disturbance within the right-of-way are considered together with on-site impacts as a single project. The project area is defined as the sum of the total area of the property and the area of the right- of-way disturbed by construction. The project site area is defined as the portion of the project area that is actually affected by construction. All impacts are within a single threshold discharge area. Table 1 summarizes the project thresholds. Figures A-3 and A-4 show the existing and proposed conditions for the project site area. Because this is engineering requested with a two-lot short plat, the thresholds in Table 1 are a combination of known quantities associated with plat improvements and unknown quantities which are associated with speculative future development of an undefined nature. In other words, we don’t know the shape and size of the home, driveway, or any other appurtenance impervious surfaces that might be associated with a future building permit application. Therefore, we must put a maximum allowable limit on the development potential of the lot such that our proposal remains valid in the future. Existing Conditions The property is currently developed and in use as a single-family residence. The lot is surrounded on all sides by developed single-family lots similar in character and developed around the same time as the subject property. The property is generally rectangular with its longest dimension in the north-south direction. Improvements on the property consist of a February 2023 Koval Short Plat Page 2 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx home generally built on the north side of the lot, a driveway accessing the home’s attached garage, and a large yard. Table 1: Project Threshold Summary Description Total (ft2) Existing Hard Surface (Roof) 0 Hard Surface (Driveway and Sidewalk) 458 Lawn and Landscape 5,020 Vegetated Area (Cleared and forested) 0 Total Project/Lot Area 17,308 Total Project Site Area 5,478 Proposed New Hard Surface 3,520 New PGHS1 244 Replaced Hard Surface 458 Replaced PGHS 458 New + Replaced Hard Surface 3,978 New + Replaced PGHS 702 Existing Hard Surface Converted to Vegetation 0 Land Disturbed 5,478 New Lawn/Landscape 02 Native Vegetation to Pasture 0 Existing Hard Surface to Remain Unaltered 0 1. Pollution-generating hard surface All pervious surfaces within project area are already lawn/landscape Land cover at the site is primarily urban lawn and landscape around the home and in the area of interest for the new building lot. The east half of the property, speaking approximately, is a steeply sloped area with established, mature vegetation and trees. Topography at the site varies from moderate to steep slopes. The west half of the property can be said to be moderately sloped from west to east. This portion of the property has a total relief on the order of about 20 feet and an average slope of approximately 20 to 25 percent. The east part of the site is more steeply sloped with a total relief of about 20 feet in 34 feet horizontally, producing an inclination of about 50-60 percent. The area is generally well developed and adequately supported by utilities and infrastructure. Natural gas, power, water, sewer, and storm drainage are all available to the site directly from 25th Drive South. Critical Areas As mentioned previously, steep slopes are located on the eastern half of the site. The slope has a total height of about 20 feet and an inclination averaging 50 to 60 percent. The slope is densely vegetated with understory and large trees. February 2023 Koval Short Plat Page 3 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx The site is also considered by definition to be an erosion hazard area. Because of the rather liberal definition of what constitutes an erosion hazard area, the entire property is considered to be one. If the property is located within an aquifer recharge area, our review of records did not reveal that. The property is not located within an area of flood hazard, regulated or otherwise. See Figure A-1 for a map from the FEMA service. The site is not known to be host or adjacent to any other kinds of critical areas (e.g., wetlands, streams, etc.). Soils Soil analysis of the site was conducted by a qualified geotechnical professional in September 2022. The soil analysis consisted of a review of geologic literature, observations of the surface and general condition of the site, and limited excavation at the site. In general, the geologic literature available for the site and general project vicinity suggest that one expects to find Vashon till in the area. On-site excavation and soil characterization confirmed that soils at the site are generally characteristic of glacial till. Observations also noted the presence of undocumented fill material, presumably a result of mass earth-moving activities associated with the original development of the site. No groundwater was encountered to a depth of 10 feet. The presence of a nearby slope downward and a review of nearby public well logs both suggest that perched groundwater is unlikely to form at the site, having ample vertical relief away from the area. In general, with respect to on-site stormwater management, it was determined that any attempt to infiltrate runoff on the site would be a mistake. This is due in part to the nature of the soils themselves, as glacial till tends to be a relatively impermeable barrier to the movement of groundwater. However, even shallow interflow should be minimized because water in the soil would tend to move toward the steep slope and become a destabilizing factor for the slope over time. Runoff should be collected and sent away from the site in the interest of public safety and the protection of life and property. Section 2: Conditions and Requirements Summary Drainage Review Required Figure 1.1.2.A was consulted to determine that a directed drainage review is required for this project. The development is a single-family project that meets all the criteria for simplified drainage review. However, the presence of steep slopes on the site is germane to the analysis of stormwater code as it relates to the site and project. Therefore, target drainage review is appropriate. According to Section 1.1.2.2 of the Manual, the proposed project would be subject to TDR Project Category #1. The principle of targeted drainage review is to limit the review of core and special requirements to those that impact the project. February 2023 Koval Short Plat Page 4 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx In an effort to minimize regulatory interference with the project, we will evaluate all nine of the core requirements and all five of the special requirements. Core Requirements The following sections summarize how each of the core requirements apply to this project. Core Requirement #1: Discharge at the Natural Location The natural discharge location for the part of the site being considered for development is the steep slope on the east side of the property. This is where natural drainage would exit the property following prevailing topographic trends. However, the project proposes to re-route the drainage from the developed site to the public drainage system within 25th Drive South. This is primarily for the purposes of avoiding any drainage traversing on or under the steep slope. It is secondarily to avoid any adverse impacts to the adjacent developed private property to the east of the site. This may seem at first to require an adjustment to Core Requirement #1. However, it does not violate the requirement for the following reasons: · The current “natural” flow path of the drainage and the proposed re-routed flow path intersect with one another approximately 700 feet downstream of the site, less than ¼ mile · Re-routing the drainage does not have any adverse impacts to the drainage system in 25th Drive South · Re-routing the drainage does not have any negative impact to the drainage system in 26th Avenue South, which is the current receiving branch of the drainage system · No natural freshwater bodies are affected by the revision to the flow path. Therefore, we conclude that the project meets Core Requirement #1. Core Requirement #2: Offsite Analysis A level 1 offsite analysis was performed for this project. The analysis did not identify any downstream drainage problems that require special attention. See Section 3 for the detailed analysis. Core Requirement #3: Flow Control This project is exempt from Core Requirement #3 because the total new and replaced impervious surface area is less than 5,000 square feet and less than ¾ acre of vegetation is converted for the project. February 2023 Koval Short Plat Page 5 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx Core Requirement #4: Conveyance System This project proposes no formal on-site conveyance systems requiring quantitative engineering analysis. The site’s drainage improvements consist of small-diameter roof and footing drain systems typically associated with single-family development. According to Section 1.2.4.2 of the Manual, existing off-site conveyance systems only need to be analyzed to the extent required by Core Requirement #2 unless the project is subject to Core Requirement #3 and flows will be released from the site without flow control mitigation. Since this project is not subject to Core Requirement #3, no quantitative analysis of the off-site conveyance system has been completed. Core Requirement #5: Erosion and Sediment Control All projects are subject to Core Requirement #5 if they clear, grade, or otherwise disturb land. The application of Core Requirement #5 to this proposal is not exactly straightforward because the proposed action is a land division. The drainage analysis being completed is for a hypothetical development, not an actual development proposal for a building permit. The only construction activities associated with this proposal are minor disturbances in the street and on-site needed to install utility stubs for a new home on what will become the new lot. A more site-specific, useful proposal with respect to the control of construction runoff can be developed once a specific building permit proposal is made after the new lot is created. The review and approval of individual lot TESC BMPs would be completed at that time. To satisfy Core Requirement #5 with respect to the contemplated, minimal scope of work needed to create the new lot, a very simple CSWPPP document has been prepared as a separate document. A general TESC plan is included with the engineering plans. Core Requirement #6: Maintenance and Operations A maintenance and operation manual has not been prepared for this project because there are no private BMPs or facilities that require maintenance. Core Requirement #7: Financial Guarantees and Liability The applicant is aware that financial guarantees may be required and is prepared to post such guarantees as required by the City. Core Requirement #8: Water Quality According to Step 3 of the City’s addendum to the King County Manual, Section 1.1.1.A, any project generating 2,000 square feet or more of new and replaced hard surface is subject to water quality review. Paragraph 2 of Section 1.2.8 of the addendum refers the King County Manual for impervious and pervious surface requirements. February 2023 Koval Short Plat Page 6 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx According to the King County Manual, this project is exempt from providing a water quality facility. This is on the basis of exception 1, the surface area exception, which states that the project does not need to provide a facility as long as it generates less than 5,000 square feet of new and replaced impervious surface and less than ¾ of an acre of new pollution- generating pervious surface. Since this project does not reach either of those thresholds, a water quality facility is not required. Core Requirement #9: Flow Control BMPs According to Section 1.2.9.1, this project can be categorized as a subdivision project on a property less than 5 acres in size within the urban growth area. This is covered by Paragraph D.3 of the same section. Paragraph D.3 specifies that the evaluation of flow control BMPs for plat infrastructure must be done per Section 1.2.9.3 and must occur concurrently with the subdivision proposal and associated infrastructure build-out. The implementation of BMPs on individual lots may be deferred to the time of lot build-out if desired. For the purposes of this project, individual lot BMPs are governed by Section 1.2.9.2.1 and plat infrastructure BMPs are governed by Section 1.2.9.3.1. As it turns out, this project proposal does not have any target surfaces that would be classified as plat improvements. No improvements are needed to support the proposed new lot. The new lot has direct frontage along 25th Drive South which is already fully stabilized and improved. Therefore, the analysis of Core Requirement #9 is limited to target surfaces on-site. The target surfaces on-site consist of the future home and driveway with any associated minor appurtenant surfaces like decks, patios, and walkways. Given the importance of the steep slope to the engineering at this point in the process, the applicant will not defer the analysis of individual lot BMPs. The following narrative demonstrates the analysis of Section 1.2.9.2.1 for small lot BMPs related to the future build-out of the new lot. This list is organized in the priority order that it appears in the Manual. 1. Full dispersion: Full dispersion is not feasible for any of the target hard surfaces because a suitable flow path is not available on the site and the site’s ratio of existing or restorable vegetation will not be sufficient relative to the impervious surfaces created. 2. Full infiltration of roof runoff: this BMP is not feasible for two reasons. The first reason is that the site’s soils are generally not supportive of infiltration of stormwater. The second reason is that infiltration of any runoff on the site could reduce the stability of the steep slope on the site. February 2023 Koval Short Plat Page 7 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx 3. Full infiltration of runoff from any surface: This BMP is infeasible for the same reason that full infiltration of roof runoff is not feasible. 4. Limited infiltration: this BMP is infeasible for the same reason that full infiltration is not feasible. 5. Bioretention: Bioretention is not feasible as a means of on-site stormwater management for the same reason that full and limited infiltration are infeasible. 6. Permeable pavement: Permeable pavement should not be used on the site because it would tend to introduce runoff into the soil which would cause problems for the existing home to the north, the steep slope, and existing improvements on the adjacent property to the east of the site. 7. Basic dispersion: Basic dispersion is not feasible at the site for the roof surface because dispersion BMPs would direct runoff to the steep slope and neighboring, developed private property. Furthermore, the steep inclination of the slope would render any attempt to disperse stormwater a failure because runoff would tend to travel down the slope rather than spread out, as is the intent for dispersion. Basic dispersion for the driveway is most likely feasible. The feasibility of this BMP will ultimately depend on the placement of the driveway. Due to access management policies and topography at the site, it is likely that the driveway to the new home will be located far enough away from the new north property line that basic dispersion can be achieved. 8. Reduced impervious surface credits and native growth retention credits: These BMPs are not feasible at the site due to the small size of the lot and the lack of sufficient native vegetation on the site. 9. Post-construction soil amendment: This BMP is feasible for all target surfaces, which include any soil disturbed by construction and not covered by an impervious surface. 10. Perforated stub-out: A perforated stub-out should not be used because it would introduce subsurface water on the site that would become a problem for existing improved adjacent private property and the steep slope on the site. In summary, the only flow control BMPs that can safely be implemented at the site are: · Post-construction soil amendments for all disturbed soils · Sheet flow dispersion for the driveway area, if the driveway is built in a location which allows for the BMP to be sited on the lot. February 2023 Koval Short Plat Page 8 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx Special Requirements The following sections address each of the special requirements applicable to this project. Special Requirement #1: Other Adopted Area-Specific Requirements No area-specific requirements are known to exist for this project beyond those in the Manual. Special Requirement #2: Flood Hazard Area Delineation Since this project is not located near a flood hazard area, this requirement does not apply to the project. Special Requirement #3: Flood Protection Facilities Special requirement #3 does not apply to this project because this project does not rely on any existing flood protection facilities for protection against flood hazards. This project does not propose to construct a new flood protection facility or modify an existing one. Special Requirement #4: Source Control Special requirement #4 does not apply to the project because it is not a commercial building or a commercial site development. Special Requirement #5: Oil Control Special requirement #5 does not apply to this project because the project does not propose to create or redevelop a site with high-use characteristics. Other Conditions or Requirements No other conditions or requirements beyond those discussed above are known to exist at this time. The applicant is aware that the County may impose other conditions or requirements as a result of the information presented in the technical information report. Section 3: Offsite Analysis A level 1 offsite analysis is provided for this project. Drainage from the project area generally travels north. In the current condition, drainage travels north and east as unconcentrated overland sheet flow. It traverses the steep slope and adjacent private property before collecting in 26th Avenue South and entering the City’s public storm drainage system. In the developed condition, the drainage will be re-routed to the public storm drainage system in 25th Drive South. The system in 26th Drive South ultimately connects February 2023 Koval Short Plat Page 9 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx to the system in 25th Drive South about 700 feet downstream of the site, at the intersection of the two streets. The remainder of the downstream analysis is based on field observation of surface features of the City’s underground drainage system and topographic maps of the downstream area. Information about the sizes and exact locations of pipes was not available to us. From the intersection of 25th Drive South and 26th Avenue South, drainage flows within the City’s storm drainage system to the northeast to South Star Lake Road. The drainage system within South Star Lake Road is most likely a robust regional drainage system owing to the nature of the street and the surrounding topography. Drainage within this part of the system travels northwest, following the road to South 272nd Street. From there, the drainage is most likely released to a natural drainageway mapped as the South Fork McSorley Creek. This appears to be a regional natural drainage course that flows north and then east on its way to Saltwater State Park and ultimately to Puget Sound. Figure A-2 shows a map of the downstream flow path. To identify potential water quality concerns, the Department of Ecology’s Water Quality Atlas was used. The atlas did not identify any water quality concerns within a mile downstream of the site. Much farther downstream, there are 303(D) listings for temperature, dissolved oxygen, and bacteria. There is also a Category 2 listing for copper (category 2 is not as severe as a 303(D) listing). Section 1.2.2.3 of the Manual specifies what mitigation, if any, is required for these conditions. Since none of these conditions occur within ¼ mile downstream of the site (i.e., they are farther downstream), technically no mitigation is required at the site. But even ignoring the distance factor, no mitigation is required. That is because the project does not propose any land use or drainage features that would affect the relevant water quality factors. Section 4: Flow Control, LID, and Water Quality Facility Analysis and Design Performance Standards The following performance standards apply to the project: · Area-specific flow control facility standard: Flood control · Conveyance system capacity standards: none apply (see Section 2) · Area-specific water quality standard: Basic/Enhanced (City’s map is not clear) · Flow control BMPs o Plat infrastructure: Section 1.2.9.3.1 o Individual lot: Section 1.2.9.2.1 February 2023 Koval Short Plat Page 10 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx Flow Control System The project is exempt from Core Requirement #3. Construction of a flow control facility is not required. Water Quality System This project is exempt from providing a water quality facility on the basis of its minimal impervious surface impacts. The City of Federal Way has assured us through pre-design correspondence that some measure of water quality improvement is required for any project over 2,000 square feet, regardless of whether the project includes actual impacts from pollution-generating impervious surface or meets the thresholds identified in the King County Manual. Due the partially speculative nature of this permit application, we cannot be certain as to the exact locations and types of impervious surfaces that will be ultimately constructed. We can be reasonably sure that the proposal will include a driveway and a roof, and know somewhat the general vicinity of these eventual improvements. Water quality for the future driveway can be met by employing sheet flow dispersion for the driveway surface. This is a good choice for the property because the location of the driveway and the topography of the property are such that sheet flow dispersion is feasible at virtually no cost. Runoff leaving the driveway surface can be evenly distributed over the area that will become the front lawn of the new home, effectively settling out particulate matter and filtering the runoff through vegetation. This also meets the intent of on-site management. No version of any city or county code or even Ecology’s version of the stormwater code considers runoff from a roof to be contaminated or polluted. Typical organic materials from trees and particulate matter that might be loosened by rain impacts from roofs (e.g., sand from a composition roof) are not considered to be pollutants in the stormwater code. Nonetheless, we will propose an improvement as a show of good faith to the City. Both of these kinds of materials can be settled out of the runoff from the future roof surface by passing the runoff through a typical catch in a typical stormwater structure. Therefore, a catch basin is proposed to serve as the private point of connection on the subject lot. Any runoff from roof drains or footing drains passing through the structure would be slowed enough to settle out larger materials, provided the system is maintained in good condition. Section 5: Conveyance System Analysis and Design The project proposes a 6-inch diameter connection to the public drainage system to collect runoff from the future home to be built on the lot. The pipe is sized based on the minimum allowed by the City. Ample vertical relief and limited contributing surface area ensure that the prescriptive minimum is sufficient for any reasonable development proposal. February 2023 Koval Short Plat Page 11 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx Section 6: Special Reports and Studies A geotechnical study was completed for the property. The geotechnical study was completed for purposes of addressing the geologic hazard areas present on the site and for making recommendations for management of stormwater and other aspects of construction. The soils report is discussed in greater detail in Section 1 of the report. No other reports or studies associated with the property were made available to us. Section 7: Other Permits A building permit is required for the build-out of the new lot in the future. No other permits are known to be needed for the project. Section 8: CSWPPP Analysis and Design Erosion and Sediment Control Plan Analysis and Design The attached, separate CSWPPP document provides in-depth narrative for the elements of erosion and sediment control. This project does not require any engineered erosion and sediment control measures. Typical single-family prescriptive BMPs will be sufficient. Stormwater Pollution Prevention and Spill Control Plan Design The attached, separate SWPPS document provides in-depth narrative for the elements of the pollution prevention plan applicable to this project. The project does not require any engineered measures. Typical single-family prescriptive BMPs will be sufficient. The project does not propose any deviations or alternatives to the standard BMPs. Section 9: Bond Quantities, Facility Summaries, and Declaration of Covenant Drainage facilities for single-family residential building permits are not normally bonded. Therefore, no bond quantities worksheet has been included with the report. Because the project does not propose any formal facilities for flow control or water quality, there is no summary sheet, sketch, or declaration of covenant included with the report. Section 10: Operation and Maintenance Manual A separate operation and maintenance manual has not been prepared for this project because there are no private BMPs or facilities that would trigger a need for such a document. February 2023 Koval Short Plat Page A-1 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx Appendix A: Figures and Maps Attached 25TH DRIVE SOUTH LOT 1LOT 2 25TH DRIVE SOUTH LOT 1LOT 2 February 2023 Koval Short Plat Page B-1 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx Appendix B: Project Plans Project plans are provided as a separate, attached document. February 2023 Koval Short Plat Page C-1 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx Appendix C: Construction SWPPP The Construction Stormwater Pollution Prevention Plan is provided as a separate, attached document. Temporary erosion and sediment control drawings are part of the project plans. February 2023 Koval Short Plat Page D-1 https://d.docs.live.net/dd3d702c0b79cef1/valor civil engineering^j pllc/projects/2022/2022-102 - koval short plat/drainage reports/2022-102 technical information report.docx Appendix D: Geotechnical Report Attached 1 10/26/2022 Roman Koval 23118 126th Ave SE Kent, WA Subject: Geotechnical Services Report Koval Short Plat Geotechnical Consultation TPN: 7575600130; 27634 25th Dr. S, Federal Way, WA Project Number: QG22-173 Dear Mr. Koval, At your request, Quality Geo NW, PLLC (QG) has completed a soils investigation of the above referenced project. The investigation was performed in accordance with our proposal for professional services. We would be pleased to continue our role as your geotechnical consultant of record during the project planning and construction phases, as local inspection firms have not been found to be as familiar or reliably experienced with geotechnical design. This may include soil subgrade inspections, periodic review of special inspection reports, or supplemental recommendations if changes occur during construction. We will happily meet with you at your convenience to discuss these and other additional Time & Materials services. We thank you for the opportunity to be of service on this project and trust this report satisfies your project needs currently. QG wishes you the best while completing the project. Respectfully Submitted, Quality Geo NW, PLLC Alexander Barnes Staff Geologist Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 2 SOILS REPORT KOVAL SHORT PLAT TPN: 7575600130, 27634 25th DRIVE SOUTH FEDERAL WAY, WA Roman Koval 23118 126th Ave SE Kent, WA Prepared by: Approved by: Alexander Barnes Luke Preston McCann, L.E.G. Staff Geologist Principal Licensed Engineering Geologist Quality Geo NW, PLLC Geotechnical Investigation & Engineering Consultation Phone: 360-878-9750| Web: qualitygeonw.com Mail: 4631 Whitman Ln SE, Ste D, Lacey, WA 98513 10/26/2022 QG Project # QG22-173 Copyright © 2022 Quality Geo NW, PLLC All Rights Reserved 10/26/2022 Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 3 TABLE OF CONTENTS 1.0 INTRODUCTION ...............................................................................................................4 1.1 PROJECT DESCRIPTION ............................................................................................................................. 4 1.2 FIELD WORK ................................................................................................................................................ 4 2.0 EXISTING SITE CONDITIONS ........................................................................................5 2.1 AREA GEOLOGY .......................................................................................................................................... 5 2.2 SITE & SURFACE CONDITIONS ................................................................................................................ 5 2.3 SOIL LOG ....................................................................................................................................................... 6 2.4 SURFACE WATER AND GROUNDWATER CONDITIONS ..................................................................... 6 3.0 GEOTECHNICAL RECOMMENDATIONS .....................................................................7 3.1 SETBACK RECOMMENDATIONS ............................................................................................................. 7 3.2 SHALLOW FOUNDATION RECOMMENDATIONS ................................................................................. 7 3.2.1 BUILDING SLAB ON GRADE FLOOR ............................................................................................. 9 3.3 INFILTRATION RATE DETERMINATION .............................................................................................. 10 3.3.1 INFILTRATION FEASIBILITY ....................................................................................................... 10 3.3.2 DRAINAGE RECOMMENDATIONS ............................................................................................... 10 4.0 CONSTRUCTION RECOMMENDATIONS ...................................................................11 4.1 EARTHWORK ............................................................................................................................................. 11 4.1.1 GRADING & EXCAVATION ............................................................................................................ 11 4.1.2 SUBGRADE EVALUATION & PREPARATION ............................................................................ 11 4.1.3 SITE PREPARATION, EROSION CONTROLL, WET WEATHER............................................... 11 4.2 STRUCTURAL FILL MATERIALS AND COMPACTION ....................................................................... 12 4.2.1 MATERIALS ...................................................................................................................................... 12 4.2.2 FILL PLACEMENT AND COMPACTION ...................................................................................... 13 4.3 TEMPORARY EXCAVATIONS AND TRENCHES .................................................................................. 13 5.0 SPECIAL INSPECTION ...................................................................................................15 6.0 LIMITATIONS ..................................................................................................................16 Region & Vicinity Maps ................................................................................................................ 17 Exploration Map ............................................................................................................................. 18 Slope Profile A-A’.......................................................................................................................... 19 Exploration Logs ............................................................................................................................ 20 Laboratory Results .......................................................................................................................... 22 Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 4 1.0 INTRODUCTION This report presents the findings and recommendations of Quality Geo NW’s (QG) soil investigation conducted in support of new site surface improvements. 1.1 PROJECT DESCRIPTION QG understands the project entails new construction within a presently developed parcel. QG has been contracted to evaluate soil, foundation, infiltration conditions, and necessary slope setbacks. 1.2 FIELD WORK Site exploration activities were performed on 9/19/2022. Exploration locations were marked in the field by a QG Staff Geologist with respect to the provided map and cleared for private and public conductible utilities. Our exploration locations were selected by an QG Staff Geologist prior to field work to provide safest access to relevant soil conditions. The geologist directed the advancement of 1 excavated test pit (TP). The test pit was advanced within the vicinity of the anticipated development footprint area, to a maximum depth of 10.0 feet below present grade (BPG) in general accordance with the specified contract depth. During explorations QG logged each soil horizon encountered, and field classified them in accordance with the Unified Soil Classification System (USCS). Representative soil samples were collected from each unit, identified according to boring location and depth, placed in plastic bags to protect against moisture loss, and were transported to the soil laboratory for supplemental classification and other tests. QG advanced 1 Wildcat Dynamic Cone Penetrometer (DCP) tests at a representative location within the vicinity of a proposed structure location and as slope conditions permitted. The penetrometer test was terminated upon reaching the equipment’s maximum practical extent. During penetrometer advancement, blow counts were recorded in 10-centimeter increments as a thirty-five-pound weight was dropped a distance of 15 inches. Blow counts were then converted to resistance (kg/cm2), standard penetration blow counts (N-values), and corresponding soil consistency, with complete results shown on the attached logs. An aerial site plan with relevant features is presented in Appendix B. Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 5 2.0 EXISTING SITE CONDITIONS 2.1 AREA GEOLOGY QG reviewed available map publications to assess known geologic conditions and hazards present at the site location. The Washington Geologic Information Portal (WGIP), maintained by the Department of Natural Resources Division of Geology and Earth Resources, provides 1:24,000- scale geologic mapping of the region. Geology of the site location and vicinity consists of Vashon till (Qvt). The deposits on site are described as “Compact diamict containing subrounded to well- rounded clasts in massive, silt- or sand-rich matrix. Glacially transported and deposited. Generally, a few meters to a few tens of meters thick, forming undulatory surface. Also found sporadically within areas mapped as unit Qvi.” The WGIP Map also offers layers of mapped geohazard conditions within the state. According to the regional-scale interactive map, there are no mapped landslide deposits to exist within the extent or vicinity of the parcel. Available LiDAR imagery of the site did not reveal any obvious or prominent geologic hazards within the site or immediate vicinity. The United States Department of Agriculture portal (USDA) provides a soil mapping of the region. The soils in the southern vicinity are mapped as Alderwood gravelly sandy loam (AgD) formed as ridges and hills. The parent material for the soils on site is glacial drift and/or glacial outwash over dense glaciomarine deposits. The soils are described as gravelly sandy loam from 0 to 7 inches, and very gravelly sandy loam from 7 to 59 inches. Depth to restrictive feature is 20 to 39 inches to densic material. Capacity of most limiting layer to transmit water (ksat), is listed as very low to moderately low (0.00 to 0.06 in/hr). Depth to water table is 18 to 37 inches. 2.2 SITE & SURFACE CONDITIONS The parcel is divided in half north to south and contains an existing residential home north of the build site. When QG arrived on site, the project area had been graded with a generally level platform cut into the gentle north-south trending slope, with loose cuttings and fill covering an over-steepened slope facing west and grading downward to the boundary of the parcel. The build site it undeveloped and has no vegetation, with the exception of remaining young and mature maple trees on the western slope. Native soils and intact vegetation north of the fill material consist of bushes and dense brambles, making the slope inaccessible. No surface water features were observed on site. The natural slope west of the house displayed tension cracks at the crest of the slope, within 5-10 feet of the foundation. Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 6 2.3 SOIL LOG Representative lab samples were taken from TP-1 from an estimated 3 feet below native grade within the graded project area. Soil conditions on site were as follows: • 0’ to 10.0’ – Silty Sand with Gravel (SM): A dominant soil unit characterized as brown, moist, and presenting few organics. Cobbles were present and observed up to 5-inches in diameter. Layer was dense to very dense condition, common with till soils and glacial drift. 2.4 SURFACE WATER AND GROUNDWATER CONDITIONS No active surface water features are present on site. In the near vicinity, Star Lake is ~2400 feet east of the parcel. During our test pit explorations, no groundwater table was encountered. Available groundwater data does not exist based on well logs made publicly available by the WA Department of Ecology. QG’s scope of work did not include determination or monitoring of seasonal groundwater elevation variations, formal documentation of wet season site conditions, or conclusive measurement of groundwater elevations at depths past the extent feasible for explorations at the time of the field explorations. Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 7 3.0 GEOTECHNICAL RECOMMENDATIONS 3.1 SETBACK RECOMMENDATIONS Considering the inclination and conditions of the adjacent slope, specific setback requirements must be followed for successful construction at this location. The local critical area ordinance delineates minimum slope toe setbacks for slopes inclined greater than 40% (~22°), which may be further reduced upon review by a licensed geotechnical professional. QG’s reviewed existing topographic data and general site observations made during our visit to infer general slope face and slope toe setbacks based on height and inclination of the typical slopes present on the site in proximity to the proposed structure. Horizontal setbacks were determined based on standard International Building Code (IBC) requirements as accepted by the State of Washington. The IBC details required setback delineations for slopes with an overall inclination less than or equal to 45 degrees. Structures in the vicinity of descending slopes shall maintain a minimum horizontal slope crest setback, the lesser of H/3 or 40 feet. Structures shall also maintain a minimum slope toe setback, H/2 or 15 feet from ascending slopes. These setbacks can commonly be achieved through a combination of increasing footing embedment depths, in combination with expanding the building fill pad, and/or partially adjusting the footprint location. QG made limited inclination measurements in the field and reviewed existing topographic and LIDAR data, in comparison to our general site observations made during our visit, to evaluate the adjusted setback requirements. QG recommends a minimum 9-foot horizontal crest setback for any new foundation (see Appendix C). This does not apply to lightweight surface improvements such as uncovered decks, patios, walkways, landscaping, pathways, septic drainfields, etc. QG does not recommend reducing the setback unless further site-specific foundation design efforts are undertaken to ensure building and slope stability is maintained. 3.2 SHALLOW FOUNDATION RECOMMENDATIONS QG recommends excavating loose or organic cover soils down to firm bearing conditions expected within 2.0 feet from the surface. As the variability in subgrade support between consolidated glacial deposits and weathered medium dense cover soils may result in differential settlement, QG recommends that foundations be placed on compacted native soils wherever, or on firm structural fill installed over these compacted soils to achieve footing grade. Assuming site preparation is completed as described above, we recommend the following: Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 8 • Subgrade Preparation QG recommends excavating and clearing any loose or organic cover soils, including overriding topsoil where necessary, from areas of proposed construction, down to firm bearing conditions and benching the final bottom of subgrade elevation flat. Excavations should be performed with a smooth blade bucket to limit disturbance of subgrade soils. Vibratory compaction methods are suitable for densification of the non-organic native soils. After excavations have been completed to the planned subgrade elevations, but before placing fill or structural elements, the exposed subgrade should be evaluated under the periodic guidance of a QG representative. Any areas that are identified as being soft or yielding during subgrade evaluation should be brought to the attention of the geotechnical engineer. Where over excavation is performed below a structure, the over excavation area should extend beyond the outside of the footing a distance equal to the depth of the over excavation below the footing. The over excavated areas should be backfilled with properly compacted structural fill. The proposed buildings may utilize either stepped or continuous footings with slab-on-grade elements. For continuous footing elements, upon reaching bearing strata, we recommend benching foundation lines flat. Continuous perimeter and strip foundations may be stepped as needed to accommodate variations in final subgrade level. We also recommend maximum steps of 18 inches with spacing of at least 5 feet be constructed unless specified otherwise by the design engineer. Structural fill may then be placed as needed to reestablish final foundation grade. • Allowable Bearing Capacity: Up to 1,500 pounds per square foot (psf) for foundations placed on compacted native soil or on approved structural fill soils placed in accordance with the recommendations of Section 4.2. Bearing capacities, at or below 1,500 psf may eliminate the need for additional inspection requirements if approved by the county. The allowable bearing capacity may be increased by 1/3 for transient loading due to wind and seismic events. • Minimum Footing Depth: For a shallow perimeter and spread footing system, all exterior footings shall be embedded a minimum of 18 inches and all interior footings shall be embedded a minimum of 12 inches below the lowest adjacent finished grade, but not less than the depth required by design. However, all footings must also penetrate to the prescribed bearing stratum cited above. Minimum depths are referenced per IBC requirements for frost protection; other design concerns may dictate greater values be applied. Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 9 • Minimum Footing Width: Footings should be proportioned to meet the stated bearing capacity and/or the IBC 2012 (or current) minimum requirements. For a shallow perimeter and spread footing system, continuous strip footings should be a minimum of 16 inches wide and interior or isolated column footings should be a minimum of 24 inches wide. • Estimated Settlements: All concrete settles after placement. We estimate that the maximum settlements will be on the order of 0.5 inch, or less, with a differential settlement of ½ inch, or less, over 50 linear feet. Settlement is anticipated to occur soon after the load is applied during construction. 3.2.1 BUILDING SLAB ON GRADE FLOOR QG anticipates that slab-on-grade floors are planned for the interior of the proposed building. Based on typical construction practices, we assume finished slab grade will be similar to or marginally above present grade for the below recommendations. If floor grades are planned to be substantially raised or lowered from existing grade, QG should be contacted to provide revised or alternative recommendations. • Capillary Break: A capillary break will be helpful to maintain a dry slab floor and reduce the potential for floor damage resulting from shallow perched water inundation. To provide a capillary moisture break, a 6-inch thick, properly compacted granular mat consisting of open-graded, free- draining angular aggregate is recommended below floor slabs. To provide additional slab structural support, or to substitute for a structural fill base pad where specified, QG recommends the capillary break should consist of crushed rock all passing the 1-inch sieve and no more than 3 percent (by weight) passing the U.S. No. #4 sieve, compacted in accordance with Section 5.2.2 of this report. • Vapor Barrier: A vapor retarding membrane such as 10 mil polyethylene film should be placed beneath all floor slabs to prevent transmission of moisture where floor coverings may be affected. Care should be taken during construction not to puncture or damage the membrane. To protect the membrane, a layer of sand no more than 2 inches thick may be placed over the membrane if desired. If excessive relict organic fill material is discovered at any location, additional sealant or more industrial gas barriers may be required to prevent off-gassing of decaying material from infiltrating the new structure. These measures shall be determined by the structural engineer to meet local code requirements as necessary. Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 10 • Structural Design Considerations: QG assumes design and specifications of slabs will be assessed by the project design engineer. We suggest a minimum unreinforced concrete structural section of 4.0 inches be considered to help protect against cracking and localized settlement, especially where larger equipment or localized loads are anticipated. It is generally recommended that any floor slabs and annular exterior concrete paving subject to vehicular loading be designed to incorporate reinforcing. Additionally, some level of reinforcing, such as a wire mesh may be desirable to prolong slab life due to the overwhelming presence of such poor underlying soils. It should be noted that QG does not express any guarantee or warranty for proposed slab sections. 3.3 INFILTRATION RATE DETERMINATION QG understands design of on-site stormwater controls are pending the results of this study to confirm design parameters and interpreted depths to perched seasonal groundwater and restrictive soil features. 3.3.1 INFILTRATION FEASIBILITY Qg does not recommend dispersion or infiltration of collected stormwater on slopes, as increased runoff or localized stormwater inundation can negatively impact long-term erosional and global slope stability. Stormwater management measures will be the responsibility of the clients retained site designer. 3.3.2 DRAINAGE RECOMMENDATIONS QG recommends proper drainage controls for stormwater runoff during and after site development to protect the site. The ground surface adjacent to structures should be sloped to drain away at a 5% minimum to prevent ponding of water adjacent to them. QG recommends all stormwater catchments (new or existing) be tightlined (piped) away from structures to an existing catch basin, stormwater system, established channel, or approved outfall to be released using appropriate energy-dissipating features at the outfall to minimize point erosion. Roof and footing drains should be tightlined separately or should be gathered in an appropriately sized catch basin structure and redistributed collectively. If storm drains are incorporated for impervious flatworks (driveways, sidewalks, etc.) collected waters should also be discharged according to the above recommendations. Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 11 4.0 CONSTRUCTION RECOMMENDATIONS 4.1 EARTHWORK 4.1.1 GRADING & EXCAVATION A grading plan was not available to QG at the time of this report. However, based on provided conceptual plans, this study assumes finished site grade will approximate current grade. Therefore, depths referred to in this report are considered roughly equivalent to final depths. Excavations can generally be performed with conventional earthmoving equipment such as bulldozers, scrapers, and excavators. 4.1.2 SUBGRADE EVALUATION & PREPARATION After excavations have been completed to the planned subgrade elevations, but before placing fill or structural elements, the exposed subgrade should be evaluated under the part-time observation and guidance of an QG representative. The special inspection firm should continuously evaluate all backfilling. Any areas that are identified as being soft or yielding during subgrade evaluation should be over excavated to a firm and unyielding condition or to the depth determined by the geotechnical engineer. Where over excavation is performed below a structure, the over excavation area should extend beyond the outside of the footing a distance equal to the depth of the over excavation below the footing. The over excavated areas should be backfilled with properly compacted structural fill. 4.1.3 SITE PREPARATION, EROSION CONTROLL, WET WEATHER Any silty or organic rich native soils may be moisture-sensitive and become soft and difficult to traverse with construction equipment when wet. During wet weather, the contractor should take measures to protect any exposed soil subgrades, limit construction traffic during earthwork activities, and limit machine use only to areas undergoing active preparation. Once the geotechnical engineer has approved subgrade, further measures should be implemented to prevent degradation or disturbance of the subgrade. These measures could include, but are not limited to, placing a layer of crushed rock or lean concrete on the exposed subgrade, or covering the exposed subgrade with a plastic tarp and keeping construction traffic off the subgrade. Once subgrade has been approved, any disturbance because the subgrade was not protected should be repaired by the contractor at no cost to the owner. During wet weather, earthen berms or other methods should be used to prevent runoff from draining into excavations. All runoffs should be collected and disposed of properly. Measures may Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 12 also be required to reduce the moisture content of on-site soils in the event of wet weather. These measures can include, but are not limited to, air drying and soil amendment, etc. QG recommends earthwork activities take place during the summer dry season. 4.2 STRUCTURAL FILL MATERIALS AND COMPACTION 4.2.1 MATERIALS All material placed below structures or pavement areas should be considered structural fill. Excavated native soils may be considered suitable for reuse as structural fill on a case-by-case basis. Imported material can also be used as structural fill. Care should be taken by the earthwork contractor during grading to avoid contaminating stockpiled soils that are planned for reuse as structural fill with native organic materials. Frozen soil is not suitable for use as structural fill. Fill material may not be placed on frozen soil. Structural fill material shall be free of deleterious materials, have a maximum particle size of 4 inches, and be compactable to the required compaction level. Imported structural fill material should conform to the WSDOT manual Section 9-03.14(1) Gravel Borrow, or an approved alternative import material. Controlled-density fill (CDF) or lean mix concrete can be used as an alternative to structural fill materials, except in areas where free-draining materials are required or specified. Imported materials utilized for trench back fill shall conform to Section 9-03.19, Trench Backfill, of the most recent edition (at the time of construction) of the State of Washington Department of Transportation Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT Standard Specifications). Imported materials utilize as grade fill beneath roads shall conform to WSDOT Section 9-03.10, Gravel Base. Pipe bedding material should conform to the manufacturer’s recommendations and be worked around the pipe to provide uniform support. Cobbles exposed in the bottom of utility excavations should be covered with pipe bedding or removed to avoid inducing concentrated stresses on the pipe. Soils with fines content near or greater than 10% fines content may likely be moisture sensitive and become difficult to use during wet weather. Care should be taken by the earthwork contractor during grading to avoid contaminating stockpiled soils that are planned for reuse as structural fill with native organic materials. The contractor should submit samples of each of the required earthwork materials to the materials testing lab for evaluation and approval prior to delivery to the site. The samples should be Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 13 submitted at least 5 days prior to their delivery and sufficiently in advance of the work to allow the contractor to identify alternative sources if the material proves unsatisfactory. 4.2.2 FILL PLACEMENT AND COMPACTION For lateral and bearing support, structural fill placement below footings shall extend at minimum a distance past each edge of the base of the footing equal to the depth of structural fill placed below the footing [i.e. extending at least a 1H:1V past both the interior and the exterior of the concrete footing]. Prior to placement and compaction, structural fill should be moisture conditioned to within 3 percent of its optimum moisture content. Loose lifts of structural fill shall not exceed 12 inches in thickness. All structural fill shall be compacted to a firm and unyielding condition and to a minimum percent compaction based on its modified Proctor maximum dry density as determined per ASTM D1557. Structural fill placed beneath each of the following shall be compacted to the indicated percent compaction: • Foundation and Floor Slab Subgrades: 95 Percent • Pavement Subgrades & wall backfill (upper 2 feet): 95 Percent • Pavement Subgrades & wall backfill (below 2 feet): 90 Percent • Utility Trenches (upper 4 feet): 95 Percent • Utility Trenches (below 4 feet): 90 Percent A sufficient number of tests should be performed to verify compaction of each lift. The number of tests required will vary depending on the fill material, its moisture condition and the equipment being used. Initially, more frequent tests will be required while the contractor establishes the means and methods required to achieve proper compaction. Jetting or flooding is not a substitute for mechanical compaction and should not be allowed. 4.3 TEMPORARY EXCAVATIONS AND TRENCHES All excavations and trenches must comply with applicable local, state, and federal safety regulations. Construction site safety is the sole responsibility of the Contractor, who shall also be solely responsible for the means, methods, and sequencing of construction operations. We are providing soil type information solely as a service to our client for planning purposes. Under no circumstances should the information be interpreted to mean that QG is assuming responsibility for construction site safety or the Contractor’s activities; such responsibility is not being implied and should not be inferred. The contractor shall be responsible for the safety of personnel working in utility trenches. Given that steep excavations in native soils may be prone to caving, we recommend all utility trenches, but particularly those greater than 4 feet in depth, be supported in Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 14 accordance with state and federal safety regulations. Heavy construction equipment, building materials, excavated soil, and vehicular traffic should not be allowed near the top of any excavation. Temporary excavations and trenches should be protected from the elements by covering with plastic sheeting or some other similar impermeable material. Sheeting sections should overlap by at least 12 inches and be tightly secured with sandbags, tires, staking, or other means to prevent wind from exposing the soils under the sheeting. Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 15 5.0 SPECIAL INSPECTION The recommendations made in this report assume that an adequate program of tests and observations will be made throughout construction to verify compliance with these recommendations. Testing and observations performed during construction should include, but not necessarily be limited to, the following: • Geotechnical plan review and engineering consultation as needed prior to construction phase, • Observations and testing during site preparation, earthwork, structural fill, and pavement section placement, • Consultation on temporary excavation cutslopes and shoring if needed, • Consultation as necessary during construction. QG recommends that a local and reputable materials testing & inspection firm be retained for construction phase testing and observation in accordance with the local code requirements. We also strongly recommend that QG be retained as the project Geotechnical Engineering Firm of Record (GER) during the construction of this project to perform periodic supplementary geotechnical observations and review the special inspectors reports during construction. Our knowledge of the project site and the design recommendations contained herein will be of great benefit in the event that difficulties arise and either modifications or additional geotechnical engineering recommendations are required or desired. We can also, in a timely fashion observe the actual soil conditions encountered during construction, evaluate the applicability of the recommendations presented in this report to the soil conditions encountered, and recommend appropriate changes in design or construction procedures if conditions differ from those described herein. We would be pleased to meet with you at your convenience to discuss the Time & Materials scope and cost for these services. Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 16 6.0 LIMITATIONS Upon acceptance and use of this report, and its interpretations and recommendations, the user shall agree to indemnify and hold harmless QG, including its owners, employees and subcontractors, from any adverse effects resulting from development and occupation of the subject site. Ultimately, it is the owner’s choice to develop and live in such an area of possible geohazards (which exist in perpetuity across the earth in one form or another), and therefore the future consequences, both anticipated and unknown, are solely the responsibility of the owner. By using this report for development of the subject property, the owner must accept and understand that it is not possible to fully anticipate all inherent risks of development. The recommendations provided above are intended to reduce (but may not eliminate) such risks. This report does not represent a construction specification or engineered plan and shall not be used or referenced as such. The information included in this report should be considered supplemental to the requirements contained in the project plans & specifications and should be read in conjunction with the above referenced information. The selected recommendations presented in this report are intended to inform only the specific corresponding subjects. All other requirements of the above-mentioned items remain valid, unless otherwise specified. Recommendations contained in this report are based on our understanding of the proposed development and construction activities, field observations and explorations, and laboratory test results. It is possible that soil and groundwater conditions could vary and differ between or beyond the points explored. If soil or groundwater conditions are encountered during construction that differ from those described herein, or if the scope of the proposed construction changes from that described in this report, QG should be notified immediately in order to review and provide supplemental recommendations. The findings of this study are limited by the level of scope applied. We have prepared this report in substantial accordance with the generally accepted geotechnical engineering practice as it exists in the subject region. No warranty, expressed or implied, is made. The recommendations provided in this report assume that an adequate program of tests and observations will be conducted by a WABO approved special inspection firm during the construction phase in order to evaluate compliance with our recommendations. This report may be used only by the Client and their design consultants and only for the purposes stated within a reasonable time from its issuance, but in no event later than 18 months from the date of the report. It is the Client's responsibility to ensure that the Designer, Contractor, Subcontractors, etc. are made aware of this report in its entirety. Note that if another firm assumes Geotechnical Engineer of Record responsibilities, they need to review this report and either concur with the findings, conclusions, and recommendations or provide alternate findings, conclusions and recommendation. Land or facility use, on- and off-site conditions, regulations, or other factors may change over time, and additional work may be required. Based on the intended use of the report, QG may recommend that additional work be performed and that an updated report be issued. Non-compliance with any of these requirements by the Client or anyone else will release QG from any liability resulting from the use of this report. The Client, the design consultants, and any unauthorized party, agree to defend, indemnify, and hold harmless QG from any claim or liability associated with such unauthorized use or non-compliance. We recommend that QG be given the opportunity to review the final project plans and specifications to evaluate if our recommendations have been properly interpreted. We assume no responsibility for misinterpretation of our recommendations. Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 17 Region & Vicinity Maps REGION VICINITY Quality Geo NW, PLLC Site Region Koval Short Plat Geo Figure 1 Source: Google Imagery, 2022 Scale & Locations are approx. Not for Construction Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 18 Exploration Map Figure 2 Source: King Co. GIS, 2022 Scale & Locations are approx. Not for Construction 30 0 SCALE (FEET) Quality Geo NW, PLLC Site Map Koval Short Plat Geo A A’ Toe TP-1 DCP-1 Build site Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 19 Slope Profile A-A’ Quality Geo NW, PLLC Slope Profile A-A’ Koval Short Plat Geo Figure 3 Source: WA LIDAR 2021 & Hand Measurements Scale & Locations are approx. Not for Construction 15° 45° H ≈ 26ft Minimum 9 ft horizontal crest setback Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 20 Exploration Logs Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 21 Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 22 Laboratory Results Koval Short Plat Geo - Soils Report Quality Geo NW, PLLC 10/26/2022 Project # QG22-173 23