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RS_Drainage_Technical_Information_Report_250509_v1
Civil Engineers ● Structural Engineers ● Landscape Architects ● Community Planners ● Land Surveyors Preliminary Technical Information Report PREPARED FOR: Ravenshouse, LLC Mark Raabe 22222 SE 42nd Ln Issaquah, WA 98029 PROJECT: 8225 South 132nd Street 5 Townhouses Renton, WA 2250007.10 PREPARED BY: Jeremy DeRuiter Project Engineer REVIEWED BY: Scott T. Kaul, PE, LEED AP Associate Principal DATE: March 2025 Preliminary Technical Information Report PREPARED FOR: Ravenshouse, LLC Mark Raabe 22222 SE 42nd Ln Issaquah, WA 98029 PROJECT: 8225 South 132nd Street 5 Townhouses Renton, WA 2250007.10 PREPARED BY: Jeremy DeRuiter Project Engineer REVIEWED BY: Scott T. Kaul, PE, LEED AP Associate Principal DATE: March 2025 I hereby state that this Technical Information Report for 8225 South 132nd Street 5 Townhouses has been prepared by me or under my supervision and meets the standard of care and expertise that is usual and customary in this community for professional engineers. I understand that City of Renton does not and will not assume liability for the sufficiency, suitability, or performance of drainage facilities prepared by me. Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 2250007.10 Table of Contents Section Page 1.0 Project Overview ............................................................................................................................ 1 1.1 Purpose and Scope............................................................................................................. 1 1.2 Predeveloped Conditions .................................................................................................... 1 1.3 Development Conditions ..................................................................................................... 2 2.0 Conditions and Requirements Summary .................................................................................... 2 2.1 Core Requirements ............................................................................................................. 2 2.1.1 CR 1 – Discharge at the Natural Location ............................................................. 2 2.1.2 CR 2 – Off-Site Analysis ........................................................................................ 2 2.1.3 CR 3 – Flow Control Facilities ................................................................................ 3 2.1.4 CR 4 – Conveyance System .................................................................................. 3 2.1.5 CR 5 – Construction Stormwater Pollution Prevention .......................................... 3 2.1.6 CR 6 – Maintenance and Operations .................................................................... 3 2.1.7 CR 7 – Financial Guarantees and Liability ............................................................ 3 2.1.8 CR 8 – Water Quality Facilities .............................................................................. 3 2.1.9 CR 9 – Onsite Best Management Practices (BMPs) ............................................. 3 2.2 Special Requirements ......................................................................................................... 5 2.2.1 SR 1 – Critical Drainage Areas .............................................................................. 5 2.2.2 SR 2 – Flood Hazard Area Delineation .................................................................. 5 2.2.3 SR 3 – Flood Protection Facilities .......................................................................... 5 2.2.4 SR 4 – Source Controls ......................................................................................... 5 2.2.5 SR 5 – Oil Control .................................................................................................. 5 2.2.6 SR 6 – Aquifer Protection Area .............................................................................. 6 3.0 Offsite Analysis .............................................................................................................................. 6 3.1 Downstream Analysis.......................................................................................................... 6 3.2 Upstream Analysis .............................................................................................................. 6 4.0 Flow Control, Low Impact Development (LID), and Water Quality Facility Analysis and Design ............................................................................................................................................. 6 4.1 Existing Site Hydrology ....................................................................................................... 6 4.2 Developed Site Hydrology .................................................................................................. 6 4.3 Performance Standards ...................................................................................................... 7 4.4 Flow Control System ........................................................................................................... 7 4.5 Water Quality System ......................................................................................................... 7 Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 2250007.10 5.0 Conveyance System Analysis and Design .................................................................................. 7 6.0 Special Reports and Studies ........................................................................................................ 7 7.0 Other Permits ................................................................................................................................. 7 8.0 Construction Stormwater Pollution Prevention Analysis and Design ..................................... 7 8.1 ESC Plan Analysis and Design ........................................................................................... 7 8.2 SWPPS Plan Design ........................................................................................................... 8 9.0 Bond Quantities, Facility Summaries, and Declaration of Covenant ....................................... 8 10.0 Operation and Maintenance Manual ............................................................................................ 8 11.0 Conclusion ...................................................................................................................................... 8 Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 2250007.10 Appendices Appendix A Figures A-1 .......... Vicinity Map A-2 .......... Soils Map A-3 .......... Existing Conditions Map A-4 .......... Developed Conditions Map A-5 .......... Downstream Drainage Map A-6 .......... FEMA Flood Map A-7 .......... Aquifer Protection Map Appendix B Hydrologic Analysis B-1 .......... Drainage Basin Map B-2 .......... Preliminary WWHM Report Appendix C Geotechnical Engineering Report Nelson Geotechnical Associates, Inc., March 28, 2025 Appendix D Non-Structural BMPs Appendix E Critical Areas Report Eastside Environmental Pros, Inc., November 26, 2024 Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 1 2250007.10 1.0 Project Overview 1.1 Purpose and Scope This report accompanies the Site Plan Review (SPR) application for the 8225 South 132nd Street 5 Townhouses Project. The project site is in the Northeast Quarter of Section 13, Township 23 North, Range 4 East, Willamette Meridian, in the city of Renton, King County, Washington. This site is located at 8225 South 132nd Street (see Appendix A-1 for the Vicinity Map). The project is located on Parcel 2144800535, totaling approximately 0.61 acre, with the proposed onsite disturbed area totaling approximately 0.32 acre. Proposed offsite disturbed area within the right-of-way totals to 0.03 acre. The proposed project is for a five-unit townhouse building of approximately 4,250 square feet. An asphalt driveway is proposed on the west side of the building with garage access. A pedestrian access is proposed along the east side of the units. The project also includes stormwater improvements, water, sanitary sewer, and dry utilities. The design for this project meets or exceeds the requirements of the 2022 City of Renton Surface Water Design Manual (Storm Manual), which establishes the methodology and design criteria used for this project. 1.2 Predeveloped Conditions Nelson Geotechnical Associates evaluated the existing soils (see Appendix C). The onsite soils were evaluated to be approximately 1 foot of loose to medium dense fill, followed by interbedded sands and silts. The fill layer was observed to be up to 6 feet in the southeast portion of the site. Perched groundwater was observed in all test pits at depths of 0.5 to 2 feet below the surface. The geotechnical engineer determined infiltration is infeasible onsite due to the high silt content of the soil and the presence of shallow groundwater. Existing Vegetation/Cover: The northern half of the existing site has been cleared in the past and the southern half is forested. The northern half of the site consists primarily of light brush and grasses and the southern half consists of an unnamed (Ns) stream and surrounding trees. An existing sanitary 8-inch sewer main runs north to south through the project site. Two existing manholes are located near the center of the parcel. There is an existing 8-inch water main north of the site on the north side of South 132nd Street. Power and other utilities are located adjacent to the north end of the project site. There are existing fences on the northern, eastern, and western boundaries of the north half of the site. The remainder of the site remains undeveloped. The site slopes to the south from the road at approximately 7 percent. The site sheet flows stormwater to the existing unnamed stream in the southern half of the site. Refer to Appendix A-5 for the Downstream Drainage Map beyond the property boundaries. An evaluation of wetlands, streams, and buffers was conducted by Eastside Environmental Pros, Inc. (see Appendix E). The stream is an unnamed stream, determined as a Type Ns, non-fish- bearing stream. The stream has a 50-foot degraded and denuded natural buffer. Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 2 2250007.10 1.3 Development Conditions Approximately 0.32 acre of the 0.61-acre plot will be disturbed. The proposed improvements are for a new five-unit townhouse building and associated parking. The project also includes stormwater improvements, water, sanitary sewer , and dry utilities. The existing stream will be provided with a 40-foot stream buffer. A stormwater detention system with an outfall control structure is proposed to mitigate the stormwater impact associated with the new development. 2.0 Conditions and Requirements Summary 2.1 Core Requirements 2.1.1 CR 1 – Discharge at the Natural Location Currently, runoff from the project site flows south to an unnamed stream, which flows through the southern portion of the site and continues east. This flow regime is mimicked by the proposed storm discharge to the unnamed stream. 2.1.2 CR 2 – Off-Site Analysis AHBL staff performed a Level 1 offsite drainage analysis in March 2025. The analysis included: • Defining and mapping the study area. • Reviewing available information on the study area, including the project geotechnical report and critical area report, as well as City and County GIS • Analyzing the existing drainage system, including its existing and predicted problems, if any. Field inspection of the study area will be performed during final engineering. The project discharges to an unnamed stream, where it runs across the southern portion of the project site. The stream continues to flow to the east through several adjacent properties and through a culvert under 84th Avenue South. The stream continues east and through a culvert under Renton Avenue South, and then continues northeast until it enters underground manmade conveyance that takes it under Taylor Avenue NW, Hardie Avenue NW, and Rainier Avenue North. It then flows underground north along the western perimeter of the Renton Municipal Airport and then discharges to Lake Washington. GIS contours indicate the stream decreases in elevation from around 205 on the project site to around 65 at the start of the underground conveyance, around 0.4 mile away from the project site. To our knowledge, there are no existing downstream restrictions and the project will maintain the discharge to pre-developed rates. Therefore, the downstream conveyance system should have adequate capacity to convey the proposed flows from this project. Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 3 2250007.10 2.1.3 CR 3 – Flow Control Facilities Per the Storm Manual, the project requires Flow Control Duration Standard – Matching Forested Conditions. An underground stormwater detention system is proposed to meet flow control requirements. Proposed mitigation will meet the predeveloped conditions, as evaluated using the Western Washington Hydrology Model (WWHM) program from 50 percent of the 2-year up to the full 50-year flow and matching peaks for the 2- and 10-year return periods. 2.1.4 CR 4 – Conveyance System The project includes the construction of a new conveyance system to direct surface stormwater to an onsite detention system and then to the unnamed stream. Closed-pipe conveyance is provided from the detention system to a stabilized discharge into the unnamed stream. Roof drains discharge directly to the storm detention system. Conveyance calculations will be provided with the final site development plans. 2.1.5 CR 5 – Construction Stormwater Pollution Prevention An erosion and sediment control plan will be included with the site development submittal package. A Construction Stormwater Pollution Prevention Plan will be included with the site development submittal package. 2.1.6 CR 6 – Maintenance and Operations A maintenance plan for the stormwater management system will be provided with the site development permit. 2.1.7 CR 7 – Financial Guarantees and Liability A bond, assignment of funds, or certified check will be provided, as required, prior to construction. 2.1.8 CR 8 – Water Quality Facilities Water quality is not required per the surface area exemption detailed in the Storm Manual. To meet this exemption, the project must create less than 5,000 square feet of new plus replaced pollution generating impervious surfaces (PGIS) and create less than 0.75 acre of new pollution generating pervious surfaces (PGPS). The project proposes approximately 3,393 square feet of PGIS and 0.02 acre of PGPS, satisfying the criteria for water quality exemption . 2.1.9 CR 9 – Onsite Best Management Practices (BMPs) The project falls under the Large Lot BMP requirements because the size of the property is greater than 22,000 square feet. Core Requirement 9 BMPs have been evaluated in the order described per the Storm Manual, with infeasibility justification provided. 1. Full Dispersion Infeasibility Justification: Full dispersion requires that a 100-foot minimum vegetated flow path be provided. The small area and site plan do not allow for the required flow path. Full dispersion also requires that a maximum 15 percent of the site be impervious surfaces. The project will convert approximately 30 percent of the site to impervious surfaces. Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 4 2250007.10 2. Full Infiltration of Roof Runoff Infeasibility Justification: Full infiltration of Roof Runoff has been determined infeasible by the geotechnical analysis performed by Nelson Geotechnical Associates. Site soils and shallow groundwater presence indicate infiltration is infeasible. 3. Option 1 - Full Infiltration Infeasibility Justification: Full infiltration has been determined infeasible by the geotechnical analysis performed by Nelson Geotechnical Associates. 3. Option 2 - Limited Infiltration Infeasibility Justification: Limited infiltration BMPs, per the Storm Manual, are the same as full infiltration systems but located in poor infiltrative soils that are likely to clog and work less effectively over time. Infiltration has been determined infeasible by the geotechnical analysis performed by Nelson Geotechnical Associates. Limited infiltration facilities would not adequately provide infiltration. 3. Option 3 - Bioretention Infeasibility Justification: Bioretention is infeasible due to the lack of usable area on the project site. 3. Option 4 - Permeable Pavement Infeasibility Justification: Infiltration has been determined infeasible by the geotechnical analysis performed by Nelson Geotechnical Associates . Permeable paving is proposed west of the center of the site, south of the parking area, to reduce onsite hard surfaces. 4. Basic Dispersion Infeasibility Justification: The small area and site plan do not allow for the required vegetated flow paths for basic dispersion devices and our site discharges toward slopes that exceed maximums established for dispersion BMPs 5. Onsite BMPs Underground detention chambers are proposed to manage flows from all impervious areas onsite. The detention outfall will be through a stabilized riprap pad to the Type Ns stream. Soil Amendment: All disturbed areas will be amended per the Soil Amendment BMP. The pollution generating impervious surfaces will be provided with flow control. Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 5 2250007.10 2.2 Special Requirements 2.2.1 SR 1 – Critical Drainage Areas The project does not lie within a critical drainage area. 1. Master Drainage Plans (MDPs) The project does not lie within an area covered by an approved Master Drainage Plan. 2. Basin Plans (BPs) The project does not lie within an area with an adopted Basin Plan. 3. Salmon Conservation Plans (SCPs) The project does not lie within an area with an adopted Salmon Conservation Plan. 4. Lake Management Plans The project does not lie within an area with an adopted Lake Management Plan. 5. Hazard Mitigation Plan The project does not lie within a flood hazard area and is not tributary to any identified flooding per the City of Renton Hazard Mitigation Plan, February 2025. 6. Shared Facility Drainage Plans (SFDPs) The project does not propose a Shared Facility Drainage Plan. 2.2.2 SR 2 – Flood Hazard Area Delineation The proposed project is not within or adjacent to a flood hazard area, as identified by City of Renton in the Hazard Plan per FEMA study. 2.2.3 SR 3 – Flood Protection Facilities The project does not meet any of the conditions requiring flood protection facilities. 2.2.4 SR 4 – Source Controls Source control BMPs, as identified in the King County Stormwater Pollution Prevention Manual and Renton Municipal Code, Title IV, have been incorporated into the layout and design of the proposed stormwater management system. The site use will require non-structural BMPs to maintain source control. BMPs R-1, R-2, R-3, R-4, R-5, R-6, and R-8 from the King County Stormwater Pollution Prevention Manual shall be adhered to. Refer to Appendix D for non- structural BMPs. 2.2.5 SR 5 – Oil Control The proposed site is not expected to meet the high-use site criteria. No oil control is proposed. Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 6 2250007.10 2.2.6 SR 6 – Aquifer Protection Area The project site is not within an Aquifer Protection Area. Refer to Appendix A-7 for the Aquifer Protection Map. 3.0 Offsite Analysis 3.1 Downstream Analysis Refer to CR 2 above for AHBL’s downstream analysis of the site. 3.2 Upstream Analysis The project site does not receive any substantive runoff from offsite properties , except for the flows through the unnamed stream, which flows through the southern portion of the project site. The current flow pattern will not be modified by this project. 4.0 Flow Control, Low Impact Development (LID), and Water Quality Facility Analysis and Design An underground detention system and control structure are proposed to meet flow control requirements. Preliminary design is based on the Appendix B-1 Drainage Basin Map and the basin characteristics below. The Flow Control Basin is characterized as follows: Total Area: 0.270 acre Building Area: 0.098 acre Asphalt Pavement Area: 0.077 acre Sidewalk Area: 0.010 acre Landscape Area: 0.085 acre 4.1 Existing Site Hydrology The existing site has been previously cleared. To meet the area-specific flow control facility requirements, the existing conditions will be modeled as forest. The threshold discharge area currently directs site runoff to an unnamed stream, a degraded but stable stream showing no impacts of high flows and no known drainage problems. The existing basin for modeling is determined as the same footprint as the developed conditions to provide stormwater management replicating existing conditions. To best mimic the site conditions, the predeveloped hydrology will be evaluated as Type C soils with moderate slopes. 4.2 Developed Site Hydrology All onsite improvements will be provided with flow control management. A storm chamber detention system will provide flow control to match predevelopment and post-development flow duration curves for all flows from 50 percent of the 2-year flow up to the full 50-year flow. All onsite impervious surfaces will be conveyed to the detention system to effectively mitigate runoff. The Geotechnical Engineering Study discovered 0.5 to 3 feet of fill material above native glacial till soils in test pits terminating at 10 feet below existing ground surface. Therefore, the landscape areas are modeled as Type C soils. Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 7 2250007.10 4.3 Performance Standards The Area-Specific Flow Control Facility requirement for this project will be the Flow Control Duration Standard – Matching Forested Conditions. The City has identified the required flow control standards per the City of Renton Flow Control Application Map. This project falls under the Large Lot BMP Requirements. Underground detention is proposed to meet onsite BMP requirements. Stormwater from the site will discharge close to the unnamed stream, with a rock outfall pad to prevent erosion. To meet conveyance requirements, all new pipe systems will be sized to sufficiently convey and contain the 25-year peak flow. 4.4 Flow Control System The flow control system schematic layout can be found on the civil plan sheets. Refer to Appendix B-2 for supporting documentation on the preliminary sizing of the detention system and flow control structure. 4.5 Water Quality System Water Quality is not required for this project (see Section 2.1.8 above). 5.0 Conveyance System Analysis and Design Closed-pipe conveyance is provided from the detention system to the discharge at the unnamed stream. Roof drains are conveyed to the detention system. A conveyance analysis will be provided with final site development plans . 6.0 Special Reports and Studies A geotechnical engineering report has been prepared by Nelson Geotechnical Associates (see Appendix C). A Critical Areas Report has been prepared by Eastside Environmental Pros, Inc. (see Appendix E). 7.0 Other Permits This project will require a Building Permit and a Civil Construction Permit. A Buffer Enhancement Plan will be required for the existing stream buffer. 8.0 Construction Stormwater Pollution Prevention Analysis and Design 8.1 ESC Plan Analysis and Design A Construction Stormwater Pollution Prevention Plan will be provided for final site development plans. Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 8 2250007.10 8.2 SWPPS Plan Design A Temporary Erosion and Sediment Control Plan (TESC Plan) will be provided for the final site development plans. A Construction Stormwater Pollution Prevention (CSWPP) supervisor will be appointed by the Contractor at the time of construction to implement and update TESC plans , as required. The CSWPP supervisor shall be a Certified Professional in Erosion and Sediment Control or a Certified Erosion and Sediment Control Lead. The CSWPP supervisor will be responsible for compliance with all City of Renton construction stormwater requirements . 9.0 Bond Quantities, Facility Summaries, and Declaration of Covenant A bond quantities worksheet will be provided for final site development permit. All easement requests will be submitted to the City of Renton Community and Economic Development (CED) Department. 10.0 Operation and Maintenance Manual An Operation and Maintenance Manual will be provided for final site development. 11.0 Conclusion This project is designed to meet the 2022 City of Renton Surface Water Design Manual guidelines for stormwater management. This analysis is based on data and records either supplied to or obtained by AHBL, Inc . These documents are referenced within the text of the analysis. The analysis has been prepared using procedures and practices within the standard accepted practices of the industry. We conclude that this project, as proposed, will not create any new problems within the existing downstream drainage system. AHBL, Inc. Jeremy DeRuiter Project Engineer JD/lsk March 2025 Q:\2025\2250007\WORDPROC\Reports\20250326 Rpt (Storm TIR) 2250007.10.docx Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 2250007.10 Appendix A Figures A-1 .................... Vicinity Map A-2 .................... Soils Map A-3 .................... Existing Conditions Map A-4 .................... Developed Conditions Map A-5 .................... Downstream Drainage Map A-6 .................... FEMA Flood Map A-7 .................... Aquifer Protection Map 1200 6th Avenue, Suite 1620, Seattle, WA 98101 206.267.2425 TEL 206.267.2429 FAX RAABE TOWNHOMES 2250007.10 VICINITY MAP A-1 Q:\2025\2250007\10_CIV\CAD\EXHIBITS\Vicinity Map.dwg RENTON AVE S S 132ND ST NVICINITY MAP NOT TO SCALE SITE S 130TH ST S 134T H S T S 128TH ST 84 T H A V E S 80 T H A V E S Soil Map—City of Seattle, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 3/10/2025 Page 1 of 3 52 5 9 2 1 0 52 5 9 2 2 0 52 5 9 2 3 0 52 5 9 2 4 0 52 5 9 2 5 0 52 5 9 2 6 0 52 5 9 2 7 0 52 5 9 2 8 0 52 5 9 2 9 0 52 5 9 3 0 0 52 5 9 2 1 0 52 5 9 2 2 0 52 5 9 2 3 0 52 5 9 2 4 0 52 5 9 2 5 0 52 5 9 2 6 0 52 5 9 2 7 0 52 5 9 2 8 0 52 5 9 2 9 0 52 5 9 3 0 0 558010 558020 558030 558040 558050 558060 558070 558080 558010 558020 558030 558040 558050 558060 558070 558080 47° 29' 4'' N 12 2 ° 1 3 ' 4 8 ' ' W 47° 29' 4'' N 12 2 ° 1 3 ' 4 4 ' ' W 47° 29' 1'' N 12 2 ° 1 3 ' 4 8 ' ' W 47° 29' 1'' N 12 2 ° 1 3 ' 4 4 ' ' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84 0 20 40 80 120 Feet 0 5 10 20 30 Meters Map Scale: 1:513 if printed on A portrait (8.5" x 11") sheet. Soil Map may not be valid at this scale. A-2 MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:12,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: City of Seattle, Washington Survey Area Data: Version 8, Aug 28, 2024 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jul 31, 2022—Aug 8, 2022 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Soil Map—City of Seattle, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 3/10/2025 Page 2 of 3 Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 3056 Urban land-Alderwood complex, 5 to 12 percent slopes 0.5 100.0% Totals for Area of Interest 0.5 100.0% Soil Map—City of Seattle, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 3/10/2025 Page 3 of 3 City of Seattle, Washington 3056—Urban land-Alderwood complex, 5 to 12 percent slopes Map Unit Setting National map unit symbol: 2xtbd Elevation: 20 to 540 feet Mean annual precipitation: 30 to 40 inches Mean annual air temperature: 48 to 52 degrees F Frost-free period: 180 to 240 days Farmland classification: Not prime farmland Map Unit Composition Urban land:60 percent Alderwood and similar soils:15 percent Minor components:25 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Urban Land Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 8 Hydric soil rating: No Description of Alderwood Setting Landform:Hills Landform position (two-dimensional):Summit, shoulder, backslope Landform position (three-dimensional):Nose slope, side slope, crest Down-slope shape:Linear Across-slope shape:Convex Parent material:Glacial drift and/or glacial outwash over dense glaciomarine deposits Typical profile A - 0 to 7 inches: gravelly sandy loam Bw1 - 7 to 21 inches: very gravelly sandy loam Bw2 - 21 to 30 inches: very gravelly sandy loam Bg - 30 to 35 inches: very gravelly sandy loam 2Cd1 - 35 to 43 inches: very gravelly sandy loam 2Cd2 - 43 to 59 inches: very gravelly sandy loam Properties and qualities Slope:5 to 12 percent Depth to restrictive feature:20 to 39 inches to densic material Drainage class:Moderately well drained Map Unit Description: Urban land-Alderwood complex, 5 to 12 percent slopes---City of Seattle, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 3/10/2025 Page 1 of 2 Capacity of the most limiting layer to transmit water (Ksat):Very low to moderately low (0.00 to 0.01 in/hr) Depth to water table:About 18 to 35 inches Frequency of flooding:None Frequency of ponding:None Available water supply, 0 to 60 inches: Very low (about 2.7 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4s Hydrologic Soil Group: A Ecological site: F002XA004WA - Puget Lowlands Forest Hydric soil rating: No Minor Components Everett Percent of map unit:10 percent Landform:Hills Landform position (two-dimensional):Shoulder, backslope Landform position (three-dimensional):Side slope, crest Down-slope shape:Linear Across-slope shape:Convex Ecological site:F002XA004WA - Puget Lowlands Forest Hydric soil rating: No Mckenna Percent of map unit:10 percent Landform:Drainageways Landform position (three-dimensional):Tread Down-slope shape:Concave Across-slope shape:Concave Ecological site:F002XA007WA - Puget Lowlands Wet Forest Hydric soil rating: Yes Kitsap Percent of map unit:5 percent Landform:Terraces Landform position (three-dimensional):Tread Down-slope shape:Linear Across-slope shape:Linear Ecological site:F002XA004WA - Puget Lowlands Forest Hydric soil rating: No Data Source Information Soil Survey Area: City of Seattle, Washington Survey Area Data: Version 8, Aug 28, 2024 Map Unit Description: Urban land-Alderwood complex, 5 to 12 percent slopes---City of Seattle, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 3/10/2025 Page 2 of 2 2215 North 30th Street Suite 300 Tacoma, WA 98403 253.383.2422 TEL 253.383.2572 FAX SUNSET HIGHLANDS MIXED USE 2190210.10 EXISTING CONDITIONS MAP A-3 SUNSET HIGHLANDS - 2230621.10 N 0 1 ° 1 7 ' 5 4 " E 30 . 0 1 ' N 87°29'01" W 90.05' (90' PLAT) N 0 1 ° 1 6 ' 5 4 " E 2 9 4 . 5 3 ' ( 2 9 4 . 2 5 ' P L A T ) N 87°29'40" W 89.96' (90' PLAT) N 0 1 ° 1 7 ' 5 4 " E 2 9 4 . 5 1 ' 29 4 . 2 5 ' P L A T ) SSMH RIM=222.24' IE 8"PVC(N.)=212.44'(C.C.) IE 15"PVC(E./W.)=212.44'(C.C.) CB (TYPE 1) RIM=238.29' IE 12"CPEP(S.)=234.39' CB (TYPE 1) SOLID RIM=238.30' IE 12"CPEP(N.)=234.45' IE 12"CPEP(E.)=234.40' IE 12"CPEP(W.)=234.30' CB (TYPE 1) SOLID RIM=236.59' IE 12"CPEP(N.)=232.94' IE 12"CPEP(E.)=232.89' IE 12"CPEP(W.)=232.84' CB (TYPE 1) RIM=236.50' IE 8"CONC(NE.)=233.25' IE 12"CPEP(S.)=233.05' SDMH RIM=237.27' IE 12"CPEP(E./W.) =233.42' SSMH RIM=238.09' IE 8"PVC(N./S./E./W.)=225.29'(C.C.) SET REBAR/CAP AT PROP COR CB (TYPE 1) SOLID RIM=234.78' IE 12"CPEP(E.)=230.98' IE 12"CPEP(W.)=230.93' SSMH RIM=222.29' IE 8"PVC(N./SE.)=214.83'(C.C.) SSMH RIM=220.71' IE 8"CONC(NW./S.) =213.65'(C.C.) CONC WALL WOOD WALL ASPH ROADFOUND REBAR/CAP LS# 28101 0.08'E FROM PROP COR FOUND REBAR/CAP LS# 37540 0.28'N OF LINE & 0.75'E FROM PROP COR FOUND REBAR/CAP LS# 37540 0.28'N OF LINE & 0.48'E FROM PROP COR GRA D E B R E A K GRA D E B R E A K GRADE BREAK GATE FENCE COR 2.5'E OF LINE & 0.4'S FROM PROP COR FENCE COR 3.7' W FENCE COR 0.6' W FENCE COR 0.6'S OF LINE & 0.3'W FROM PROP COR SSCO 14" DEC G R A D E B R E A K APPROX. LOCATION OF GAS PER PSE MAP NO. Q208079 SEWER EASEMENT PER REC. NO. 20131219000501 PO W E R E A S E M E N T P E R R E C . NO . 2 0 1 6 1 0 2 1 0 0 0 5 6 1 SITE TBM PK W/ WASHER ELEV=237.30' N 01°17'54" E 30.01' N 01°16'54" E 294.53' (294.25' PLAT) N 8 7 ° 2 9 ' 4 0 " W 8 9 . 9 6 ' ( 9 0 ' P L A T ) N 01°17'54" E 294.51' IE 1 2 " C P E P ( S . ) = 2 3 4 . 3 9 ' CB ( T Y P E 1 ) SO L I D R I M = 2 3 6 . 5 9 ' IE 1 2 " C P E P ( N . ) = 2 3 2 . 9 4 ' IE 1 2 " C P E P ( E . ) = 2 3 2 . 8 9 ' IE 1 2 " C P E P ( W . ) = 2 3 2 . 8 4 ' SD M H RI M = 2 3 7 . 2 7 ' IE 1 2 " C P E P ( E . / W . ) =2 3 3 . 4 2 ' SS M H RI M = 2 3 8 . 0 9 ' IE 8 " P V C ( N . / S . / E . / W . ) = 2 2 5 . 2 9 ' ( C . C . ) SE T RE B A R / C A P AT P R O P C O R SS M H RI M = 2 2 2 . 2 9 ' IE 8 " P V C ( N . / S E . ) = 2 1 4 . 8 3 ' ( C . C . ) SS M H RI M = 2 2 0 . 7 1 ' IE 8 " C O N C ( N W . / S . ) =2 1 3 . 6 5 ' ( C . C . ) CO N C WA L L WO O D WA L L AS P H RO A D FOUN D R E B A R / C A P LS # 2 8 1 0 1 0.08'E FR O M P R O P C O R G R A D E B R E A K GR A D E B R E A K GA T E FE N C E C O R 2. 5 ' E O F L I N E & 0 . 4 ' S FR O M P R O P C O R FE N C E C O R 3. 7 ' W FE N C E C O R 0. 6 ' W FE N C E C O R 0.6'S OF L I N E & 0 . 3 ' W FROM P R O P C O R SS C O 14 " D E C GR A D E B R E A K AP P R O X . L O C A T I O N OF G A S P E R P S E MA P N O . Q 2 0 8 0 7 9 SE W E R E A S E M E N T P E R R E C . NO . 2 0 1 3 1 2 1 9 0 0 0 5 0 1 POWER EASEMENT PER REC. NO. 20161021000561 EL E V = 2 3 7 . 3 0 ' 23 0 22 4 22 6 22 8 2 3 2 2 3 4 2 3 6 2 3 8 238 226 228 224 226 230 228 232 2 3 4 2 3 6 CITY OF RENTON IN COMPLIANCE WITH CITY OF RENTON STANDARDS T A C O M A 2215 North 30th Street, Suite 300 Tacoma, WA 98403 253.383.2422TEL 253.383.2572FAX www.ahbl.comWEB S E A T T L E S P O K A N E T R I - C I T I E S 132ND ST TOWNHOMES AHBL JOB #2250007.10 3 Know what's below. before you dig.Call R R-____ CONCEPTUAL DRAINAGE AND UTILITY PLAN C0.1 C0.1 1 N GRAPHIC SCALE 0 10 20 1" = 10 FEET 5 2215 North 30th Street Suite 300 Tacoma, WA 98403 253.383.2422 TEL 253.383.2572 FAX SUNSET HIGHLANDS MIXED USE 2190210.10 DOWNSTREAM DRAINAGE MAP A-5 SUNSET HIGHLANDS - 2230621.10RAABE TOWNHOMES - 2250007.10 King C ou n ty King C ounty iMap Dat e : 3/10 /2025 Not e s:±Th e in fo rmatio n in clude d o n th is map h a s be e n comp iled by K ing C o unt y s ta ff from a va rie ty o f so u rc es a n d is su bject tochange w itho ut no tic e. Kin g C ounty mak es n o re p res ent a tion s o r w arra n tie s, e xpre ss o r imp lied , as to ac cu ra cy,co mp let e ne s s, time lin e ss, or rig hts to t he use o f su ch inf o rma tion . This do cumen t is n ot int end ed f or use a s a surve yproduct. K ing Co u n ty sha ll n ot be liab le f or a ny gen era l, spe cia l, indire ct , in cide n ta l, o r co n se q uent ial d am age s in cludin g ,bu t no t limit e d to , lo st reve nu e s o r lost prof its re sultin g from th e u se or misu se of t he inf o rma tion co ntained o n this map .An y sale of this map or in formatio n o n t h is m ap is p roh ib it ed excep t by writ te n permission o f K in g Coun ty. Leg end Pa rcels St rea m t ype S - Sh ore line o f thestate F - F ishhabitat,Bio lo gical F - F ishhabitat,Ph ysical F - F ishhabitat,Pr esume d N - Non-fish b ea ring Un cla ss ified Ca tch ba sin or in let Mainte nan ce hole Pu mp Co ntro l struc tur e Pr op rieta ry tr eatme ntstructure Dispe rsion o rinfiltration s truc tur e Weir Un define d str ucturetype Un kn ow n co nn ec tio ntype (bu ried or p aved -ov er) Cul ve rts and pipes cu lve rt pipe roo f d rain , u nde rd ra in,or y ar d dr ain Ditch Line ar d ra in Curb s and flowspreaders cu rb flo w s pre ad er Bio filtration s wa le Line ar biore te ntion,dis per sion, a nd in filt rationdevices bior eten tio n s wa le disper sio n orinfiltration d ev ice Filte r str ip Ta nk Bi-dire ct ion al f low arr ow cu lve rt ditch ope n conv ey a nce pipe other bi-d ire ction alflow ar ro w Po nd Va ult Co ntro l o r trea tm entsystem Pr op rieta ry c on trol o rtreatment sys te m Na tu ra l w ater co ur sestructure Na tu ra l w ater co ur seconveyance Na tu ra l w ater co ur sepolygon Stream St ormwa te r fac i lity PROJECT SITE STREAM FLOWS TO LAKE WASHINGTON National Flood Hazard Layer FIRMette 0 500 1,000 1,500 2,000250 Feet Ü SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT SPECIAL FLOOD HAZARD AREAS Without Base Flood Elevation (BFE) Zone A, V, A99 With BFE or Depth Zone AE, AO, AH, VE, AR Regulatory Floodway 0.2% Annual Chance Flood Hazard, Areas of 1% annual chance flood with average depth less than one foot or with drainage areas of less than one square mile Zone X Future Conditions 1% Annual Chance Flood Hazard Zone X Area with Reduced Flood Risk due to Levee. See Notes.Zone X Area with Flood Risk due to Levee Zone D NO SCREEN Area of Minimal Flood Hazard Zone X Area of Undetermined Flood Hazard Zone D Channel, Culvert, or Storm Sewer Levee, Dike, or Floodwall Cross Sections with 1% Annual Chance 17.5 Water Surface Elevation Coastal Transect Coastal Transect Baseline Profile Baseline Hydrographic Feature Base Flood Elevation Line (BFE) Effective LOMRs Limit of Study Jurisdiction Boundary Digital Data Available No Digital Data Available Unmapped This map complies with FEMA's standards for the use of digital flood maps if it is not void as described below. The basemap shown complies with FEMA's basemap accuracy standards The flood hazard information is derived directly from the authoritative NFHL web services provided by FEMA. This map was exported on 3/10/2025 at 8:40 PM and does not reflect changes or amendments subsequent to this date and time. The NFHL and effective information may change or become superseded by new data over time. This map image is void if the one or more of the following map elements do not appear: basemap imagery, flood zone labels, legend, scale bar, map creation date, community identifiers, FIRM panel number, and FIRM effective date. Map images for unmapped and unmodernized areas cannot be used for regulatory purposes. Legend OTHER AREAS OF FLOOD HAZARD OTHER AREAS GENERAL STRUCTURES OTHER FEATURES MAP PANELS 8 B 20.2 The pin displayed on the map is an approximate point selected by the user and does not represent an authoritative property location. 1:6,000 122°14'5"W 47°29'16"N 122°13'28"W 47°28'52"N Basemap Imagery Source: USGS National Map 2023 A-6 144,448 12, 037 Groundwater Protection Areas Legend 8,18504,093 Feet Notes 8,185 WGS_1984_Web_Mercator_Auxiliary_Sphere All data, information, and maps are provided "as is" without warranty or any representation of accuracy, timeliness of completeness. The burden for determining accuracy, completeness, timeliness, merchantability and fitness for or the appropriateness for use rests solely on the user. City and County Labels City and County Boundary Renton <all other values> Wellhead Protection Area Zones Zone 1 Zone 1 Modified Zone 2 Floodway Special Flood Hazard Areas (100 year flood) Environment Designations Natural Shoreline High Intensity Shoreline Isolated High Intensity Shoreline Residential Urban Conservancy Jurisdictions Streams (Classified) S - Shoreline F - Fish Np - Non-Fish Ns - Non-Fish Seasonal Unclassfied Wetlands Citations PROJECT SITE A-7 Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 2250007.10 Appendix B Hydrologic Analysis B-1 .................... Drainage Basin Map B-2 .................... Preliminary WWHM Report N 01°17'54" E 30.01' N 8 7 ° 2 9 ' 0 1 " W 9 0 . 0 5 ' ( 9 0 ' P L A T ) N 01°16'54" E 294.53' (294.25' PLAT) N 8 7 ° 2 9 ' 4 0 " W 8 9 . 9 6 ' ( 9 0 ' P L A T ) N 01°17'54" E 294.51' 294.25' PLAT) CB ( T Y P E 1 ) RI M = 2 3 8 . 2 9 ' IE 1 2 " C P E P ( S . ) = 2 3 4 . 3 9 ' CB ( T Y P E 1 ) SO L I D R I M = 2 3 6 . 5 9 ' IE 1 2 " C P E P ( N . ) = 2 3 2 . 9 4 ' IE 1 2 " C P E P ( E . ) = 2 3 2 . 8 9 ' IE 1 2 " C P E P ( W . ) = 2 3 2 . 8 4 ' CB ( T Y P E 1 ) RI M = 2 3 6 . 5 0 ' IE 8 " C O N C ( N E . ) = 2 3 3 . 2 5 ' IE 1 2 " C P E P ( S . ) = 2 3 3 . 0 5 ' SD M H RI M = 2 3 7 . 2 7 ' IE 1 2 " C P E P ( E . / W . ) =2 3 3 . 4 2 ' SS M H RI M = 2 3 8 . 0 9 ' IE 8 " P V C ( N . / S . / E . / W . ) = 2 2 5 . 2 9 ' ( C . C . ) SE T RE B A R / C A P AT P R O P C O R SS M H RI M = 2 2 2 . 2 9 ' IE 8 " P V C ( N . / S E . ) = 2 1 4 . 8 3 ' ( C . C . ) SS M H RI M = 2 2 0 . 7 1 ' IE 8 " C O N C ( N W . / S . ) =2 1 3 . 6 5 ' ( C . C . ) CO N C WA L L WO O D WA L L FO U N D R E B A R / C A P LS # 2 8 1 0 1 0. 0 8 ' E F R O M P R O P C O R FO U N D R E B A R / C A P LS # 3 7 5 4 0 0. 2 8 ' N O F L I N E & 0 . 7 5 ' E GR A D E B R E A K G R A D E B R E A K GR A D E B R E A K GA T E FE N C E C O R 2. 5 ' E O F L I N E & 0 . 4 ' S FR O M P R O P C O R FE N C E C O R 3. 7 ' W FE N C E C O R 0. 6 ' W FE N C E C O R 0. 6 ' S O F L I N E & 0 . 3 ' W FR O M P R O P C O R SS C O 14 " D E C GR A D E B R E A K AP P R O X . L O C A T I O N OF G A S P E R P S E MA P N O . Q 2 0 8 0 7 9 SE W E R E A S E M E N T P E R R E C . NO . 2 0 1 3 1 2 1 9 0 0 0 5 0 1 POWER EASEMENT PER REC. NO. 20161021000561 SI T E T B M PK W / W A S H E R EL E V = 2 3 7 . 3 0 ' N GRAPHIC SCALE 0 30 60 1" = 30 FEET 15 Civil Engineers Structural Engineers Landscape Architects Community Planners Land Surveyors Neighbors RAABE TOWNHOUSES 2250007.10 Q:\2025\2250007\10_CIV\CAD\EXHIBITS\Developed Basin Map.dwg BASIN 1 AREA ROAD 0.077 ACRES SIDEWALK 0.010 ACRES ROOF 0.098 ACRES LAWN 0.085 ACRES BASIN 1 BYPASS BASIN BYPASS BASIN AREA LAWN 0.040 ACRES WWHM2012 PROJECT REPORT B-2 Prelim Detain 3/10/2025 1:54:10 PM Page 2 General Model Information WWHM2012 Project Name:Prelim Detain Site Name:Raabe Townhomes Site Address: City:Renton Report Date:3/10/2025 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.167 Version Date:2024/06/28 Version:4.3.1 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year Prelim Detain 3/10/2025 1:54:10 PM Page 3 Landuse Basin Data Predeveloped Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Mod 0.31 Pervious Total 0.31 Impervious Land Use acre Impervious Total 0 Basin Total 0.31 Element Flow Componants: Surface Interflow Groundwater Componant Flows To: POC 1 POC 1 Prelim Detain 3/10/2025 1:54:10 PM Page 4 Mitigated Land Use SITE Bypass:No GroundWater:No Pervious Land Use acre A B, Lawn, Flat 0.085 Pervious Total 0.085 Impervious Land Use acre ROADS FLAT 0.077 ROOF TOPS FLAT 0.098 SIDEWALKS FLAT 0.01 Impervious Total 0.185 Basin Total 0.27 Element Flow Componants: Surface Interflow Groundwater Componant Flows To: Tank 1 Tank 1 Prelim Detain 3/10/2025 1:54:10 PM Page 5 BYPASS Bypass:No GroundWater:No Pervious Land Use acre A B, Pasture, Flat 0.04 Pervious Total 0.04 Impervious Land Use acre Impervious Total 0 Basin Total 0.04 Element Flow Componants: Surface Interflow Groundwater Componant Flows To: Tank 1 Tank 1 Prelim Detain 3/10/2025 1:54:10 PM Page 6 Routing Elements Predeveloped Routing Prelim Detain 3/10/2025 1:54:10 PM Page 7 Mitigated Routing Tank 1 Dimensions Depth:3.5 ft. Tank Type:Circular Diameter:3.5 ft. Length:424 ft. Discharge Structure Riser Height:2.5 ft. Riser Diameter:18 in. Notch Type:Rectangular Notch Width:0.023 ft. Notch Height:0.428 ft. Orifice 1 Diameter:0.488 in.Elevation:0 ft. Element Outlets: Outlet 1 Outlet 2 Outlet Flows To: Tank Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.0000 0.000 0.000 0.000 0.000 0.0389 0.007 0.000 0.001 0.000 0.0778 0.010 0.000 0.001 0.000 0.1167 0.012 0.001 0.002 0.000 0.1556 0.014 0.001 0.002 0.000 0.1944 0.015 0.002 0.002 0.000 0.2333 0.017 0.002 0.003 0.000 0.2722 0.018 0.003 0.003 0.000 0.3111 0.019 0.004 0.003 0.000 0.3500 0.020 0.004 0.003 0.000 0.3889 0.021 0.005 0.004 0.000 0.4278 0.022 0.006 0.004 0.000 0.4667 0.023 0.007 0.004 0.000 0.5056 0.024 0.008 0.004 0.000 0.5444 0.024 0.009 0.004 0.000 0.5833 0.025 0.010 0.004 0.000 0.6222 0.026 0.011 0.005 0.000 0.6611 0.026 0.012 0.005 0.000 0.7000 0.027 0.013 0.005 0.000 0.7389 0.027 0.014 0.005 0.000 0.7778 0.028 0.015 0.005 0.000 0.8167 0.028 0.016 0.005 0.000 0.8556 0.029 0.017 0.006 0.000 0.8944 0.029 0.018 0.006 0.000 0.9333 0.030 0.020 0.006 0.000 0.9722 0.030 0.021 0.006 0.000 1.0111 0.030 0.022 0.006 0.000 1.0500 0.031 0.023 0.006 0.000 1.0889 0.031 0.024 0.006 0.000 1.1278 0.031 0.026 0.006 0.000 1.1667 0.032 0.027 0.007 0.000 1.2056 0.032 0.028 0.007 0.000 1.2444 0.032 0.029 0.007 0.000 1.2833 0.032 0.031 0.007 0.000 Prelim Detain 3/10/2025 1:54:10 PM Page 8 1.3222 0.033 0.032 0.007 0.000 1.3611 0.033 0.033 0.007 0.000 1.4000 0.033 0.035 0.007 0.000 1.4389 0.033 0.036 0.007 0.000 1.4778 0.033 0.037 0.007 0.000 1.5167 0.033 0.038 0.007 0.000 1.5556 0.033 0.040 0.008 0.000 1.5944 0.033 0.041 0.008 0.000 1.6333 0.034 0.042 0.008 0.000 1.6722 0.034 0.044 0.008 0.000 1.7111 0.034 0.045 0.008 0.000 1.7500 0.034 0.046 0.008 0.000 1.7889 0.034 0.048 0.008 0.000 1.8278 0.034 0.049 0.008 0.000 1.8667 0.034 0.050 0.008 0.000 1.9056 0.033 0.052 0.008 0.000 1.9444 0.033 0.053 0.009 0.000 1.9833 0.033 0.054 0.009 0.000 2.0222 0.033 0.056 0.009 0.000 2.0611 0.033 0.057 0.009 0.000 2.1000 0.033 0.058 0.009 0.000 2.1389 0.033 0.060 0.010 0.000 2.1778 0.033 0.061 0.012 0.000 2.2167 0.032 0.062 0.013 0.000 2.2556 0.032 0.063 0.015 0.000 2.2944 0.032 0.065 0.017 0.000 2.3333 0.032 0.066 0.019 0.000 2.3722 0.031 0.067 0.021 0.000 2.4111 0.031 0.068 0.024 0.000 2.4500 0.031 0.070 0.026 0.000 2.4889 0.030 0.071 0.029 0.000 2.5278 0.030 0.072 0.103 0.000 2.5667 0.030 0.073 0.303 0.000 2.6056 0.029 0.074 0.574 0.000 2.6444 0.029 0.075 0.899 0.000 2.6833 0.028 0.077 1.266 0.000 2.7222 0.028 0.078 1.667 0.000 2.7611 0.027 0.079 2.092 0.000 2.8000 0.027 0.080 2.531 0.000 2.8389 0.026 0.081 2.976 0.000 2.8778 0.026 0.082 3.417 0.000 2.9167 0.025 0.083 3.843 0.000 2.9556 0.024 0.084 4.247 0.000 2.9944 0.024 0.085 4.619 0.000 3.0333 0.023 0.086 4.955 0.000 3.0722 0.022 0.087 5.249 0.000 3.1111 0.021 0.088 5.499 0.000 3.1500 0.020 0.088 5.708 0.000 3.1889 0.019 0.089 5.880 0.000 3.2278 0.018 0.090 6.025 0.000 3.2667 0.017 0.091 6.236 0.000 3.3056 0.015 0.091 6.392 0.000 3.3444 0.014 0.092 6.543 0.000 3.3833 0.012 0.092 6.692 0.000 3.4222 0.010 0.093 6.837 0.000 3.4611 0.007 0.093 6.979 0.000 3.5000 0.000 0.093 7.118 0.000 3.5389 0.000 0.000 7.255 0.000 Prelim Detain 3/10/2025 1:54:10 PM Page 9 Prelim Detain 3/10/2025 1:54:10 PM Page 10 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.31 Total Impervious Area:0 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.125 Total Impervious Area:0.185 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.012777 5 year 0.021715 10 year 0.028823 25 year 0.039159 50 year 0.04785 100 year 0.057399 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.007613 5 year 0.010712 10 year 0.013194 25 year 0.016874 50 year 0.020046 100 year 0.02362 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.019 0.007 1950 0.020 0.007 1951 0.025 0.014 1952 0.008 0.006 1953 0.007 0.007 1954 0.010 0.007 1955 0.016 0.008 1956 0.014 0.008 1957 0.013 0.007 1958 0.012 0.007 Prelim Detain 3/10/2025 1:54:40 PM Page 11 1959 0.010 0.007 1960 0.020 0.009 1961 0.010 0.007 1962 0.007 0.006 1963 0.009 0.007 1964 0.013 0.007 1965 0.010 0.007 1966 0.008 0.006 1967 0.022 0.008 1968 0.012 0.007 1969 0.011 0.007 1970 0.009 0.007 1971 0.012 0.007 1972 0.020 0.008 1973 0.009 0.006 1974 0.012 0.007 1975 0.015 0.008 1976 0.011 0.007 1977 0.005 0.006 1978 0.009 0.007 1979 0.005 0.006 1980 0.035 0.009 1981 0.008 0.006 1982 0.020 0.009 1983 0.013 0.007 1984 0.008 0.006 1985 0.005 0.007 1986 0.020 0.009 1987 0.019 0.009 1988 0.008 0.006 1989 0.005 0.006 1990 0.059 0.009 1991 0.027 0.011 1992 0.011 0.007 1993 0.009 0.007 1994 0.004 0.006 1995 0.013 0.007 1996 0.033 0.013 1997 0.024 0.014 1998 0.009 0.007 1999 0.038 0.008 2000 0.009 0.007 2001 0.002 0.006 2002 0.013 0.009 2003 0.022 0.006 2004 0.020 0.028 2005 0.014 0.007 2006 0.014 0.007 2007 0.045 0.041 2008 0.046 0.029 2009 0.020 0.008 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.0590 0.0408 2 0.0459 0.0287 3 0.0452 0.0283 Prelim Detain 3/10/2025 1:54:40 PM Page 12 4 0.0379 0.0141 5 0.0349 0.0141 6 0.0332 0.0132 7 0.0270 0.0113 8 0.0251 0.0093 9 0.0238 0.0091 10 0.0218 0.0091 11 0.0217 0.0090 12 0.0205 0.0089 13 0.0204 0.0088 14 0.0203 0.0086 15 0.0200 0.0084 16 0.0199 0.0084 17 0.0196 0.0084 18 0.0195 0.0078 19 0.0189 0.0076 20 0.0186 0.0076 21 0.0157 0.0076 22 0.0154 0.0075 23 0.0145 0.0075 24 0.0141 0.0074 25 0.0138 0.0074 26 0.0133 0.0074 27 0.0130 0.0073 28 0.0127 0.0072 29 0.0127 0.0072 30 0.0126 0.0072 31 0.0121 0.0072 32 0.0120 0.0071 33 0.0119 0.0071 34 0.0117 0.0071 35 0.0113 0.0070 36 0.0112 0.0070 37 0.0106 0.0069 38 0.0102 0.0069 39 0.0100 0.0069 40 0.0099 0.0068 41 0.0097 0.0068 42 0.0095 0.0068 43 0.0094 0.0068 44 0.0092 0.0067 45 0.0091 0.0067 46 0.0091 0.0066 47 0.0090 0.0066 48 0.0090 0.0066 49 0.0083 0.0065 50 0.0082 0.0064 51 0.0080 0.0064 52 0.0079 0.0064 53 0.0078 0.0063 54 0.0070 0.0063 55 0.0066 0.0062 56 0.0054 0.0062 57 0.0052 0.0061 58 0.0048 0.0061 59 0.0047 0.0059 60 0.0040 0.0059 61 0.0023 0.0056 Prelim Detain 3/10/2025 1:54:40 PM Page 13 Prelim Detain 3/10/2025 1:54:40 PM Page 14 Duration Flows The Facility PASSED Flow(cfs)Predev Mit Percentage Pass/Fail 0.0064 16206 15832 97 Pass 0.0068 14117 10327 73 Pass 0.0072 12192 6943 56 Pass 0.0076 10506 4577 43 Pass 0.0081 9161 3275 35 Pass 0.0085 7961 1987 24 Pass 0.0089 6949 1172 16 Pass 0.0093 6141 548 8 Pass 0.0097 5450 440 8 Pass 0.0102 4868 380 7 Pass 0.0106 4368 332 7 Pass 0.0110 3921 302 7 Pass 0.0114 3486 270 7 Pass 0.0118 3089 248 8 Pass 0.0123 2731 225 8 Pass 0.0127 2415 201 8 Pass 0.0131 2165 182 8 Pass 0.0135 1935 161 8 Pass 0.0139 1761 143 8 Pass 0.0143 1598 131 8 Pass 0.0148 1395 126 9 Pass 0.0152 1246 120 9 Pass 0.0156 1118 117 10 Pass 0.0160 1035 114 11 Pass 0.0164 944 111 11 Pass 0.0169 876 107 12 Pass 0.0173 789 103 13 Pass 0.0177 715 100 13 Pass 0.0181 633 95 15 Pass 0.0185 546 94 17 Pass 0.0190 465 89 19 Pass 0.0194 391 82 20 Pass 0.0198 349 80 22 Pass 0.0202 310 77 24 Pass 0.0206 265 72 27 Pass 0.0210 218 71 32 Pass 0.0215 184 68 36 Pass 0.0219 152 66 43 Pass 0.0223 126 63 50 Pass 0.0227 113 59 52 Pass 0.0231 93 57 61 Pass 0.0236 80 54 67 Pass 0.0240 67 52 77 Pass 0.0244 60 47 78 Pass 0.0248 49 44 89 Pass 0.0252 44 40 90 Pass 0.0257 41 36 87 Pass 0.0261 34 33 97 Pass 0.0265 30 31 103 Pass 0.0269 25 26 104 Pass 0.0273 20 21 104 Pass 0.0277 18 18 100 Pass 0.0282 12 12 100 Pass Prelim Detain 3/10/2025 1:54:40 PM Page 15 0.0286 12 7 58 Pass 0.0290 11 5 45 Pass 0.0294 11 5 45 Pass 0.0298 10 5 50 Pass 0.0303 9 5 55 Pass 0.0307 9 4 44 Pass 0.0311 9 4 44 Pass 0.0315 9 3 33 Pass 0.0319 9 3 33 Pass 0.0324 9 3 33 Pass 0.0328 9 3 33 Pass 0.0332 9 3 33 Pass 0.0336 8 3 37 Pass 0.0340 8 2 25 Pass 0.0344 8 2 25 Pass 0.0349 7 2 28 Pass 0.0353 6 2 33 Pass 0.0357 6 2 33 Pass 0.0361 6 2 33 Pass 0.0365 6 2 33 Pass 0.0370 6 2 33 Pass 0.0374 6 2 33 Pass 0.0378 6 2 33 Pass 0.0382 5 2 40 Pass 0.0386 5 2 40 Pass 0.0391 5 2 40 Pass 0.0395 5 2 40 Pass 0.0399 5 1 20 Pass 0.0403 5 1 20 Pass 0.0407 5 1 20 Pass 0.0411 5 0 0 Pass 0.0416 4 0 0 Pass 0.0420 4 0 0 Pass 0.0424 4 0 0 Pass 0.0428 4 0 0 Pass 0.0432 4 0 0 Pass 0.0437 4 0 0 Pass 0.0441 4 0 0 Pass 0.0445 4 0 0 Pass 0.0449 4 0 0 Pass 0.0453 3 0 0 Pass 0.0458 3 0 0 Pass 0.0462 1 0 0 Pass 0.0466 1 0 0 Pass 0.0470 1 0 0 Pass 0.0474 1 0 0 Pass 0.0479 1 0 0 Pass Prelim Detain 3/10/2025 1:54:40 PM Page 16 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume:0 acre-feet On-line facility target flow:0 cfs. Adjusted for 15 min:0 cfs. Off-line facility target flow:0 cfs. Adjusted for 15 min:0 cfs. Prelim Detain 3/10/2025 1:54:40 PM Page 17 LID Report Prelim Detain 3/10/2025 1:55:11 PM Page 18 Model Default Modifications Total of 0 changes have been made. PERLND Changes No PERLND changes have been made. IMPLND Changes No IMPLND changes have been made. Prelim Detain 3/10/2025 1:55:11 PM Page 19 Appendix Predeveloped Schematic Prelim Detain 3/10/2025 1:55:13 PM Page 20 Mitigated Schematic Prelim Detain 3/10/2025 1:55:14 PM Page 21 Predeveloped UCI File RUN GLOBAL WWHM4 model simulation START 1948 10 01 END 2009 09 30 RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 UNIT SYSTEM 1 END GLOBAL FILES <File> <Un#> <-----------File Name------------------------------>*** <-ID-> *** WDM 26 Prelim Detain.wdm MESSU 25 PrePrelim Detain.MES 27 PrePrelim Detain.L61 28 PrePrelim Detain.L62 30 POCPrelim Detain1.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 11 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 Basin 1 MAX 1 2 30 9 END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** END OPCODE PARM # # K *** END PARM END GENER PERLND GEN-INFO <PLS ><-------Name------->NBLKS Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 11 C, Forest, Mod 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 11 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 11 0 0 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO Prelim Detain 3/10/2025 1:55:14 PM Page 22 PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 11 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC 11 0 4.5 0.08 400 0.1 0.5 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 11 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 11 0.2 0.5 0.35 6 0.5 0.7 END PWAT-PARM4 PWAT-STATE1 <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS GWVS 11 0 0 0 0 2.5 1 0 END PWAT-STATE1 END PERLND IMPLND GEN-INFO <PLS ><-------Name-------> Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* END PRINT-INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS END IWAT-STATE1 Prelim Detain 3/10/2025 1:55:14 PM Page 23 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Basin 1*** PERLND 11 0.31 COPY 501 12 PERLND 11 0.31 COPY 501 13 ******Routing****** END SCHEMATIC NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems Printer *** # - #<------------------><---> User T-series Engl Metr LKFG *** in out *** END GEN-INFO *** Section RCHRES*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* END PRINT-INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC A1 A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------><--------><--------><--------><--------><--------><--------> *** END HYDR-PARM2 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><--------> <---><---><---><---><---> *** <---><---><---><---><---> END HYDR-INIT END RCHRES SPEC-ACTIONS END SPEC-ACTIONS FTABLES END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 1.167 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 1.167 IMPLND 1 999 EXTNL PREC Prelim Detain 3/10/2025 1:55:14 PM Page 24 WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** COPY 501 OUTPUT MEAN 1 1 48.4 WDM 501 FLOW ENGL REPL END EXT TARGETS MASS-LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS-LINK 12 PERLND PWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 12 MASS-LINK 13 PERLND PWATER IFWO 0.083333 COPY INPUT MEAN END MASS-LINK 13 END MASS-LINK END RUN Prelim Detain 3/10/2025 1:55:14 PM Page 25 Mitigated UCI File RUN GLOBAL WWHM4 model simulation START 1948 10 01 END 2009 09 30 RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 UNIT SYSTEM 1 END GLOBAL FILES <File> <Un#> <-----------File Name------------------------------>*** <-ID-> *** WDM 26 Prelim Detain.wdm MESSU 25 MitPrelim Detain.MES 27 MitPrelim Detain.L61 28 MitPrelim Detain.L62 30 POCPrelim Detain1.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 7 IMPLND 1 IMPLND 4 IMPLND 8 PERLND 4 RCHRES 1 COPY 1 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 Tank 1 MAX 1 2 30 9 END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** END OPCODE PARM # # K *** END PARM END GENER PERLND GEN-INFO <PLS ><-------Name------->NBLKS Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 7 A/B, Lawn, Flat 1 1 1 1 27 0 4 A/B, Pasture, Flat 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 7 0 0 1 0 0 0 0 0 0 0 0 0 4 0 0 1 0 0 0 0 0 0 0 0 0 Prelim Detain 3/10/2025 1:55:14 PM Page 26 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 7 0 0 4 0 0 0 0 0 0 0 0 0 1 9 4 0 0 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 7 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC 7 0 5 0.8 400 0.05 0.3 0.996 4 0 5 1.5 400 0.05 0.3 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 7 0 0 2 2 0 0 0 4 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 7 0.1 0.5 0.25 0 0.7 0.25 4 0.15 0.5 0.3 0 0.7 0.4 END PWAT-PARM4 PWAT-STATE1 <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS GWVS 7 0 0 0 0 3 1 0 4 0 0 0 0 3 1 0 END PWAT-STATE1 END PERLND IMPLND GEN-INFO <PLS ><-------Name-------> Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 1 ROADS/FLAT 1 1 1 27 0 4 ROOF TOPS/FLAT 1 1 1 27 0 8 SIDEWALKS/FLAT 1 1 1 27 0 END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** 1 0 0 1 0 0 0 4 0 0 1 0 0 0 8 0 0 1 0 0 0 END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* 1 0 0 4 0 0 4 1 9 4 0 0 4 0 0 0 1 9 Prelim Detain 3/10/2025 1:55:14 PM Page 27 8 0 0 4 0 0 0 1 9 END PRINT-INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** 1 0 0 0 0 0 4 0 0 0 0 0 8 0 0 0 0 0 END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC 1 400 0.01 0.1 0.1 4 400 0.01 0.1 0.1 8 400 0.01 0.1 0.1 END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN 1 0 0 4 0 0 8 0 0 END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS 1 0 0 4 0 0 8 0 0 END IWAT-STATE1 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** SITE*** PERLND 7 0.085 RCHRES 1 2 PERLND 7 0.085 RCHRES 1 3 IMPLND 1 0.077 RCHRES 1 5 IMPLND 4 0.098 RCHRES 1 5 IMPLND 8 0.01 RCHRES 1 5 BYPASS*** PERLND 4 0.04 RCHRES 1 2 PERLND 4 0.04 RCHRES 1 3 ******Routing****** PERLND 7 0.085 COPY 1 12 IMPLND 1 0.077 COPY 1 15 IMPLND 4 0.098 COPY 1 15 IMPLND 8 0.01 COPY 1 15 PERLND 7 0.085 COPY 1 13 PERLND 4 0.04 COPY 1 12 PERLND 4 0.04 COPY 1 13 RCHRES 1 1 COPY 501 16 END SCHEMATIC NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** Prelim Detain 3/10/2025 1:55:14 PM Page 28 END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems Printer *** # - #<------------------><---> User T-series Engl Metr LKFG *** in out *** 1 Tank 1 1 1 1 1 28 0 1 END GEN-INFO *** Section RCHRES*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** 1 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* 1 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC A1 A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** 1 0 1 0 0 4 0 0 0 0 0 0 0 0 0 2 2 2 2 2 END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------><--------><--------><--------><--------><--------><--------> *** 1 1 0.08 0.0 0.0 0.5 0.0 END HYDR-PARM2 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><--------> <---><---><---><---><---> *** <---><---><---><---><---> 1 0 4.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 END HYDR-INIT END RCHRES SPEC-ACTIONS END SPEC-ACTIONS FTABLES FTABLE 1 91 4 Depth Area Volume Outflow1 Velocity Travel Time*** (ft) (acres) (acre-ft) (cfs) (ft/sec) (Minutes)*** 0.000000 0.000000 0.000000 0.000000 0.038889 0.007142 0.000186 0.001273 0.077778 0.010043 0.000523 0.001800 0.116667 0.012231 0.000958 0.002204 0.155556 0.014041 0.001470 0.002545 0.194444 0.015607 0.002047 0.002846 0.233333 0.016996 0.002681 0.003117 0.272222 0.018248 0.003367 0.003367 0.311111 0.019390 0.004099 0.003599 0.350000 0.020440 0.004874 0.003818 0.388889 0.021413 0.005688 0.004024 0.427778 0.022317 0.006538 0.004221 0.466667 0.023161 0.007423 0.004408 0.505556 0.023952 0.008339 0.004588 0.544444 0.024694 0.009285 0.004762 0.583333 0.025392 0.010259 0.004929 0.622222 0.026050 0.011260 0.005090 0.661111 0.026669 0.012285 0.005247 Prelim Detain 3/10/2025 1:55:14 PM Page 29 0.700000 0.027254 0.013333 0.005399 0.738889 0.027806 0.014404 0.005547 0.777778 0.028326 0.015496 0.005691 0.816667 0.028818 0.016607 0.005832 0.855556 0.029281 0.017737 0.005969 0.894444 0.029718 0.018884 0.006103 0.933333 0.030130 0.020048 0.006234 0.972222 0.030518 0.021227 0.006363 1.011111 0.030882 0.022421 0.006489 1.050000 0.031223 0.023629 0.006613 1.088889 0.031543 0.024849 0.006734 1.127778 0.031841 0.026082 0.006853 1.166667 0.032119 0.027326 0.006970 1.205556 0.032377 0.028580 0.007086 1.244444 0.032615 0.029843 0.007199 1.283333 0.032834 0.031116 0.007310 1.322222 0.033034 0.032397 0.007420 1.361111 0.033215 0.033685 0.007529 1.400000 0.033379 0.034980 0.007636 1.438889 0.033525 0.036281 0.007741 1.477778 0.033653 0.037587 0.007845 1.516667 0.033763 0.038898 0.007947 1.555556 0.033856 0.040213 0.008049 1.594444 0.033932 0.041531 0.008149 1.633333 0.033992 0.042852 0.008247 1.672222 0.034034 0.044175 0.008345 1.711111 0.034059 0.045499 0.008441 1.750000 0.034067 0.046824 0.008537 1.788889 0.034059 0.048148 0.008631 1.827778 0.034034 0.049473 0.008724 1.866667 0.033992 0.050795 0.008817 1.905556 0.033932 0.052116 0.008908 1.944444 0.033856 0.053434 0.008999 1.983333 0.033763 0.054749 0.009088 2.022222 0.033653 0.056060 0.009177 2.061111 0.033525 0.057366 0.009265 2.100000 0.033379 0.058667 0.009704 2.138889 0.033215 0.059962 0.010746 2.177778 0.033034 0.061250 0.012113 2.216667 0.032834 0.062531 0.013723 2.255556 0.032615 0.063804 0.015531 2.294444 0.032377 0.065068 0.017507 2.333333 0.032119 0.066322 0.019627 2.372222 0.031841 0.067566 0.021874 2.411111 0.031543 0.068798 0.024232 2.450000 0.031223 0.070019 0.026690 2.488889 0.030882 0.071226 0.029236 2.527778 0.030518 0.072420 0.103725 2.566667 0.030130 0.073600 0.303809 2.605556 0.029718 0.074763 0.574638 2.644444 0.029281 0.075911 0.899260 2.683333 0.028818 0.077041 1.266654 2.722222 0.028326 0.078152 1.667367 2.761111 0.027806 0.079243 2.092212 2.800000 0.027254 0.080314 2.531835 2.838889 0.026669 0.081363 2.976653 2.877778 0.026050 0.082388 3.417005 2.916667 0.025392 0.083388 3.843415 2.955556 0.024694 0.084362 4.246960 2.994444 0.023952 0.085308 4.619707 3.033333 0.023161 0.086225 4.955211 3.072222 0.022317 0.087109 5.249065 3.111111 0.021413 0.087960 5.499499 3.150000 0.020440 0.088774 5.708020 3.188889 0.019390 0.089548 5.880093 3.227778 0.018248 0.090281 6.025858 3.266667 0.016996 0.090966 6.236489 3.305556 0.015607 0.091601 6.391986 3.344444 0.014041 0.092178 6.543774 3.383333 0.012231 0.092690 6.692107 Prelim Detain 3/10/2025 1:55:14 PM Page 30 3.422222 0.010043 0.093124 6.837210 3.461111 0.007142 0.093462 6.979285 3.500000 0.001000 0.093647 7.118515 END FTABLE 1 END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 1.167 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 1.167 IMPLND 1 999 EXTNL PREC WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** RCHRES 1 HYDR RO 1 1 1 WDM 1000 FLOW ENGL REPL RCHRES 1 HYDR STAGE 1 1 1 WDM 1001 STAG ENGL REPL COPY 1 OUTPUT MEAN 1 1 48.4 WDM 701 FLOW ENGL REPL COPY 501 OUTPUT MEAN 1 1 48.4 WDM 801 FLOW ENGL REPL END EXT TARGETS MASS-LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS-LINK 2 PERLND PWATER SURO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 2 MASS-LINK 3 PERLND PWATER IFWO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 3 MASS-LINK 5 IMPLND IWATER SURO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 5 MASS-LINK 12 PERLND PWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 12 MASS-LINK 13 PERLND PWATER IFWO 0.083333 COPY INPUT MEAN END MASS-LINK 13 MASS-LINK 15 IMPLND IWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 15 MASS-LINK 16 RCHRES ROFLOW COPY INPUT MEAN END MASS-LINK 16 END MASS-LINK END RUN Prelim Detain 3/10/2025 1:55:14 PM Page 31 Predeveloped HSPF Message File Prelim Detain 3/10/2025 1:55:14 PM Page 32 Mitigated HSPF Message File Prelim Detain 3/10/2025 1:55:14 PM Page 33 Disclaimer Legal Notice This program and accompanying documentation are provided 'as-is' without warranty of any kind. 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Clear Creek Solutions, Inc. 6200 Capitol Blvd. Ste F Olympia, WA. 98501 Toll Free 1(866)943-0304 Local (360)943-0304 www.clearcreeksolutions.com Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 2250007.10 Appendix C Geotechnical Engineering Report Nelson Geotechnical Associates, Inc., March 28, 2025 NELSON GEOTECHNICAL ASSOCIATES, INC. March 28, 2025 Mark Raabe VIA Email: markdraabe@comcast.net Geotechnical Engineering Evaluation South 132nd Street Townhomes 8225 South 132nd Street Renton, Washington NGA File No. 11444C24 Dear Mark: We are pleased to submit the attached report titled “Geotechnical Engineering Evaluation – South 132nd Street Townhomes– 8225 South 132nd Street – Renton, Washington.” This report summarizes our observations of the existing surface and subsurface conditions within the site and provides general recommendations for the proposed site development. Our services were completed in general accordance with the proposal signed by you on January 31, 2025. We previously provided a geotechnical evaluation report in 2019 for a large piece of property that included the subject site. The current study includes additional and more specific explorations within the subject site, as well as updated recommendations in line with current codes. We visited the site to observe the existing surface and subsurface conditions of the property on February 26, 2025. The property is rectangular in shape and covers approximately 0.61 acres in area. It is currently vacant and undeveloped. Topographically, the northern portion of the site is relatively level to gently sloping, while the southern portion of the site is moderately sloping down towards the south. Vegetation within the site consists of grass yard areas and sparse deciduous and evergreen trees. We understand that plans for development include the construction of multiple townhome structures. It is our opinion from a geotechnical standpoint that the planned site development is feasible, provided that our recommendations are incorporated into the design and construction of this project. We recommend that the residence foundations be designed to utilize conventional spread footings extending down to the underlying competent native bearing glacial soils for bearing capacity and settlement considerations. We also recommend the minimum setback allowed by the City of Renton of 15 feet from the toe of the steep slope located in the northeast and an effective setback of 25 feet from the top of the slope in the southeast corner of the properties. Competent, glacial, bearing deposits should generally be encountered approximately 1.5 to 6.0 feet below the existing ground surface, based on our explorations. This is further discussed in the attached report. We have also provided general recommendations for foundations, structure setbacks, slab-on-grade, retaining walls, site grading, subgrade preparation, drainage, and erosion control. Geotechnical Engineering Evaluation NGA File No. 11444C24 South 132nd Street Townhomes March 28, 2025 Renton, Washington Summary - Page 2 __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ NELSON GEOTECHNICAL ASSOCIATES, INC. We recommend that NGA be retained to review the geotechnical aspects of the project plans prior to construction. We recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications. We appreciate the opportunity to provide service to you on this project. Please contact us if you have any questions regarding this report or require further information. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Khaled M. Shawish, PE Principal NELSON GEOTECHNICAL ASSOCIATES, INC. TABLE OF CONTENTS INTRODUCTION .......................................................................................................... 1 SCOPE ........................................................................................................................ 1 SITE CONDITIONS ....................................................................................................... 2 Surface Conditions ....................................................................................................... 2 Subsurface Conditions .................................................................................................. 2 Hydrogeologic Conditions ............................................................................................ 3 SENSITIVE AREA EVALUATION .................................................................................... 3 Seismic Hazard ............................................................................................................. 3 Erosion Hazard ............................................................................................................. 4 Landslide Hazard/Slope Stability .................................................................................. 4 CONCLUSIONS AND RECOMMENDATIONS .................................................................. 5 General ......................................................................................................................... 5 Erosion Control and Slope Protection Measures ......................................................... 6 Structure Setbacks….. ................................................................................................... 6 Site Preparation and Grading ....................................................................................... 6 Temporary Slopes ......................................................................................................... 7 Foundation Support ..................................................................................................... 7 Retaining Walls ............................................................................................................. 9 Structural Fill .............................................................................................................. 10 Slab-on-Grade and Pavements ................................................................................... 10 Utilities ....................................................................................................................... 11 Site Drainage .............................................................................................................. 11 CONSTRUCTION MONITORING ................................................................................. 12 USE OF THIS REPORT ................................................................................................ 12 LIST OF FIGURES Figure 1 – Vicinity Map Figure 2 – Site Plan Figure 3 – Soil Classification Chart Figure 4 – Exploration Logs NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation South 132nd Street Townhomes 8225 South 132nd Street Renton, Washington INTRODUCTION This report presents the results of our geotechnical engineering investigation and evaluation of the proposed South 132nd Street Townhome Development project in Renton, Washington. The project site is located at 8225 South 132nd Street as shown on the Vicinity Map in Figure 1. The parcel number for the property is 2144800535. The purpose of this study is to explore and characterize the site’s surface and subsurface conditions and to provide geotechnical recommendations for the proposed site development. We previously provided a geotechnical evaluation report in 2019 for a large piece of property that included the subject site. The current study includes additional and more specific explorations within the subject site, as well as updated recommendations in line with current codes. The property is rectangular in shape and covers approximately 0.61 acres in area. It is currently vacant and undeveloped. The property is bordered by South 132nd Street to the north and by neighboring residential properties on all other sides. Topographically, the northern portion of the site is relatively level to gently sloping, while the southern portion of the site is moderately sloping down towards the south. Vegetation within the site consists of grass yard areas and sparse deciduous and evergreen trees. We understand that plans for development include the construction of multiple townhomes. SCOPE The purpose of this study is to explore and characterize the site surface and subsurface conditions and provide general recommendations for site development. Specifically, our scope of services included the following: 1. Reviewing available soil and geologic maps of the area as well as other relevant geotechnical information, as provided. 2. Exploring the subsurface soil and groundwater conditions within the site using trackhoe- excavated test pits. Excavation services were subcontracted by NGA. 3. Mapping the conditions on the site slopes using shallow, hand-tool explorations where necessary to construct geological cross sections and qualitatively evaluate slope stability. 4. Providing long-term design infiltration rates based on on-site Small Pilot Infiltration Testing (PIT) per the 2022 RSWDM, if feasible. 5. Providing our opinion on stormwater infiltration feasibility. Geotechnical Engineering Evaluation NGA File No. 11444C24 South 132nd Street Townhomes March 28, 2025 Renton, Washington Page 2 NELSON GEOTECHNICAL ASSOCIATES, INC. 6. Providing recommendations for site drainage and erosion control. 7. Providing recommendations for earthwork, foundation support, retaining walls, and slabs-on-grade. 8. Documenting the results of our findings, conclusions, and recommendations in a written geotechnical report. SITE CONDITIONS Surface Conditions The property is rectangular in shape and covers approximately 0.61 acres in area. It is currently vacant and undeveloped. Vegetation within the site consists of grass yard areas and sparse deciduous and evergreen trees. The topography within the entire site generally slopes gently from the upper northern portion of the site, with moderate south facing slopes to the northeast and south. A localized moderate slope is located along the western property line as well as a moderate slope leading down to the creek bed in the southern portion of the lot. We encountered slight to moderate groundwater in all of our explorations during our visit on February 26, 2025. The moderate slopes encountered within the south and west of the site are mapped as a regulated steep slope per the City of Renton (COR) map. The slopes on the northern flank of the creek and in the western portion of the site are mapped as sensitive slopes while a relatively localized area in the southeast corner of the lot is mapped as a protected slope. Subsurface Conditions Geology: The geologic units for this area are shown on the Geologic Map of the Renton Quadrangle, King County, Washington, by Mullineaux, D.R. (USGS, 1965). The site is mapped as glacial till (Qgt). Glacial till is described as a compact non-sorted, diamict of silt, sand and sub-rounded to well-rounded gravel. In our explorations, we encountered silty sand interbedded with silty fine to medium sand which we interpreted as native glacial till soils at depth. Explorations: The subsurface conditions within the site were explored on February 26, 2025 with four trackhoe-excavated test pits throughout the site. The approximate locations of our most recent explorations are shown on the Site Plan in Figure 2. A geologist from NGA was present during the explorations, examined the soils and geologic conditions encountered, obtained samples of the different soil types, and maintained logs of the explorations. The soils were visually classified in general accordance with the Unified Soil Classification System, presented in Figure 3. Exploration logs are attached as Figure 4. A brief summary of subsurface conditions is presented below. For a detailed description of the subsurface conditions, the exploration logs should be reviewed. Geotechnical Engineering Evaluation NGA File No. 11444C24 South 132nd Street Townhomes March 28, 2025 Renton, Washington Page 3 NELSON GEOTECHNICAL ASSOCIATES, INC. At the surface of Test Pits One through Four, we generally encountered approximately 0.5 to 3.0 feet of dark brown, silty, fine to medium sand with roots, gravel, and organics which we interpreted as undocumented fill or topsoil material. Underlying the surficial soils, we encountered gray-brown to gray silty fine sand with interbedded silty fine to medium sand which we interpreted as native advance outwash soils. All our test pit explorations were terminated within the native glacial till deposits at 10.0 feet below the existing ground surface. Hydrogeologic Conditions Groundwater seepage was encountered between 0.5 to 2.0 feet within our explorations which we interpreted as perched groundwater. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of relatively low permeability materials. Perched water does not represent a regional groundwater "table" within the upper soil horizons. Perched water tends to vary spatially and is dependent upon the amount of rainfall. We would expect the amount of perched groundwater to decrease during drier times of the year and increase during wetter periods. SENSITIVE AREA EVALUATION Seismic Hazard We reviewed the 2021 International Building Code (IBC) for seismic site classification for this project. Since strength data or shear wave velocity measurements were not collected for the site, the IBC site classification of Default D was used. Table 1 below provides seismic design parameters for the site obtained from the ASCE7 Hazard Tool that are in conformance with the 2021 IBC, which specifies consideration of a design earthquake having a 2% probability of occurrence in 50 years (return interval of 2,474 years), and the 2014 USGS seismic hazard maps. Table 1 – 2021 IBC Seismic Design Parameters Site Class Spectral Acceleration at 0.2 sec. (g) Ss Spectral Acceleration at 1.0 sec. (g) S1 Site Coefficients Design Spectral Response Parameters Fa Fv SDS SD1 D 1.461 0.498 1.200 N/A 1.169 N/A The spectral response accelerations were obtained from the USGS Earthquake Hazards Program Interpolated Probabilistic Ground Motion website (2014 data) for the project latitude and longitude. Geotechnical Engineering Evaluation NGA File No. 11444C24 South 132nd Street Townhomes March 28, 2025 Renton, Washington Page 4 NELSON GEOTECHNICAL ASSOCIATES, INC. Hazards associated with seismic activity include liquefaction potential and amplification of ground motion. Liquefaction is caused by a rise in pore pressures in a loose, fine sand deposit beneath the groundwater table. It is our opinion that the dense outwash deposits interpreted to underlie the site have a low potential for liquefaction or amplification of ground motion. Erosion Hazard The criteria used for determination of the erosion hazard for affected areas include soil type, slope gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related to vegetative cover and the specific surface soil types, which are related to the underlying geologic soil units. The Soil Survey of King County Area, Washington and City of Seattle, Washington by the Natural Resources Conservation Service (NRCS) classifies the site as Urban land-Alderwood complex, 5 to 12 percent slopes. The erosion hazard rating is not listed within the site; however, based on our experience in the area and our observations in the field, it is our opinion that the site would have a moderate erosion hazard for areas where the soils are exposed. It is our opinion that the erosion hazard for soils should be low in areas where vegetation is not disturbed. Recommendations in the Erosion Control section of this report will reduce the risk for the erosion hazard to impact site slopes. Landslide Hazard/Slope Stability The criteria used for evaluation of landslide hazards include soil type, slope gradient, and groundwater conditions. The topography within the site is generally gently sloping to the south with moderate slopes within the south and western portions of the property. The steepest slopes are in the southern portion of the property but are generally under 10 feet in vertical relief. The COR has mapped a localized area in the west and the southern portion of the site as steep slopes. All the slopes near the development area are considered sensitive or less, according to COR map. A small area in the southeast corner of the site is mapped as a protected steep slope. However, it is across the creek from the proposed development and is situated more than 100 feet away from the development area. Relatively shallow sloughing failures as well as surficial erosion are natural processes and should be expected on the steep slopes, especially during extreme environmental conditions. It is our opinion that while there is potential for erosion, soil creep, and shallow failures within the loose surficial soils on the steep slopes within the site, there is not a significant potential for deep-seated slope failures under current conditions. Proper slope management measures, retaining wall construction, site grading, and drainage as recommended in this report should help maintain and enhance current stability. Geotechnical Engineering Evaluation NGA File No. 11444C24 South 132nd Street Townhomes March 28, 2025 Renton, Washington Page 5 NELSON GEOTECHNICAL ASSOCIATES, INC. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the planned site development is feasible from a geotechnical standpoint. Our explorations indicated that the site was generally underlain by competent native bearing soils at relatively shallow depths with some deeper areas of unsuitable soils. We recommend that the planned structures be designed utilizing shallow foundations. Footings should extend through any loose soil or undocumented fill soils and be founded on the underlying medium dense or better native glacial bearing soils, or structural fill extending to these soils. Competent native soils should be encountered approximately between 0.5 and 6.0 feet below the existing ground surface. We should note that localized areas of deeper unsuitable soils and/or undocumented fill could be encountered at this site. This condition would require additional excavations in foundation, slab, and pavement areas to remove the unsuitable soils. Over-excavation may be needed within areas where the native, bearing material is found as deep as 6.0 feet from the existing ground surface. The surficial soils encountered on this site are considered moisture-sensitive and may disturb easily when wet. We recommend that construction take place during the drier summer months, if possible. If construction is to take place during wet weather, the soils may disturb and additional expenses and delays may be expected due to the wet conditions. Additional expenses could include the need for placing a blanket of rock spalls to protect exposed subgrades and construction traffic areas. The native on-site soils are not suitable for use as structural fill due to the amount of fines and deleterious organic matter they contain. Erosion Control and Slope Protection Measures The erosion hazard for the on-site soils is interpreted to be moderate to severe for exposed soils, but actual erosion potential will be dependent on how the site is graded and how water is allowed to concentrate. Best Management Practices (BMPs) should be used to control erosion. Areas disturbed during construction should be protected from erosion. Erosion control measures may include diverting surface water away from the stripped or disturbed areas. Silt fences and/or straw bales should be erected to prevent muddy water from leaving the site. Disturbed areas should be planted as soon as practical and the vegetation should be maintained until it is established. The erosion potential of areas not stripped of vegetation should be low to moderate. Geotechnical Engineering Evaluation NGA File No. 11444C24 South 132nd Street Townhomes March 28, 2025 Renton, Washington Page 6 NELSON GEOTECHNICAL ASSOCIATES, INC. Structure Setbacks Uncertainties related to building along steep slopes are typically addressed by the use of building setbacks. The purpose of the setback is to establish a “buffer zone” between the structure and the top of the slope so that ample room is allowed for normal slope recession during a reasonable life span of the structure. In a general sense, the greater the setback distance, the lower the risk of slope failures impacting the structure. From a geological standpoint, the setback dimension is based on the slope’s physical characteristics, such as slope height, surface angle, material composition, and hydrology. Other factors such as historical slope activity, rate of regression, and the type and desired life span of the development are important considerations as well. The slopes within the southern and western portions of the site are less than 40 percent in inclination do not require a setback per COR regulation. It is our opinion that no further setback is required along the slopes that are less than 40 percent grade. We recommend, however, that all foundation elements be keyed into the underlying native soil. Site Preparation and Grading After erosion control measures are implemented, site preparation should consist of removing loose soils, topsoil, and any undocumented fill from foundation, slab, and pavement areas down to expose firm native soils. Stripping depths will vary between 0.5 and 6.0 feet based on our explorations. The stripped soil should be removed from the site or stockpiled for later use as a landscaping fill. If significant surface water flow is encountered during construction, this flow should be diverted around subgrade areas and the exposed subgrade maintained in a semi-dry condition. If wet conditions are encountered, alternative site grading techniques might be necessary. These could include using large excavators equipped with wide tracks and a smooth bucket to complete site grading, and covering exposed subgrade with a layer of crushed rock for protection. If wet conditions are encountered or construction is attempted in wet weather, the subgrade should not be compacted, as this could cause further subgrade disturbance. In wet conditions, it may be necessary to cover the exposed subgrade with a layer of crushed rock as soon as it is exposed to protect the extremely moisture sensitive soils from disturbance by machine or foot traffic during construction. The prepared subgrade should be protected from construction traffic and surface water should be diverted around areas of prepared subgrade. Geotechnical Engineering Evaluation NGA File No. 11444C24 South 132nd Street Townhomes March 28, 2025 Renton, Washington Page 7 NELSON GEOTECHNICAL ASSOCIATES, INC. Temporary Slopes Temporary cut slope stability is a function of many factors, including the type and consistency of soils, depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains open, and the presence of surface or groundwater. It is exceedingly difficult under these variable conditions to estimate a stable, temporary, cut slope angle. Therefore, it should be the responsibility of the contractor to maintain safe slope configurations at all times as indicated in OSHA guidelines for cut slopes. The following information is provided solely for the benefit of the owner and other design consultants and should not be construed to imply that Nelson Geotechnical Associates, Inc. assumes responsibility for job site safety. Job site safety is the sole responsibility of the project contractor. For planning purposes, we recommend that temporary cuts in the upper surficial and/or undocumented fill soils should be no steeper than 1.5 Horizontal to 1 Vertical (1.5H:1V). The lower competent glacial till soils could be cut at 0.5H:1V inclination. If significant groundwater seepage or surface water flow were encountered, we would expect that temporary shoring will be needed. We recommend that cut slopes be protected from erosion. The slope protection measures may include covering cut slopes with plastic sheeting and diverting surface runoff away from the top of cut slopes. We do not recommend vertical slopes for cuts deeper than three feet, if worker access is necessary. We recommend that cut slope heights and inclinations conform to appropriate OSHA/WISHA regulations. Permanent cut and fill slopes should be no steeper than 2H:1V. However, flatter inclinations may be required in areas where loose soils are encountered. Permanent slopes should be vegetated and the vegetative cover maintained until established. Foundation Support Conventional shallow spread foundations should be placed on medium dense or better native bearing soils or be supported on structural fill or rock spalls extending to those soils. Medium dense or better bearing soils should be encountered approximately 0.5 to 6.0 feet below ground surface based on our explorations. Where undocumented fill or less dense soils are encountered at footing bearing elevation, the subgrade should be over-excavated to expose suitable bearing soil. The over-excavation may be filled with structural fill, or the footing may be extended down to the competent native bearing soils. If footings are supported on structural fill, the fill zone should extend outside the edges of the footing a distance equal to half of the depth of the over-excavation below the bottom of the footing. Geotechnical Engineering Evaluation NGA File No. 11444C24 South 132nd Street Townhomes March 28, 2025 Renton, Washington Page 8 NELSON GEOTECHNICAL ASSOCIATES, INC. Footings should extend at least 18 inches below the lowest adjacent finished ground surface for frost protection and bearing capacity considerations. Foundations should be designed in accordance with the 2021 IBC. Footing widths should be based on the anticipated loads and allowable soil bearing pressure. Water should not be allowed to accumulate in footing trenches. All loose or disturbed soil should be removed from the foundation excavation prior to placing concrete. For foundations constructed as outlined above, we recommend an allowable bearing pressure of not more than 2,000 pounds per square foot (psf) be used for the design of footings founded on the medium dense or better native bearing soils or structural fill extending to the competent native bearing material. The foundation bearing soil should be evaluated by a representative of NGA. We should be consulted if higher bearing pressures are needed. Current IBC guidelines should be used when considering increased allowable bearing pressure for short-term transitory wind or seismic loads. Potential foundation settlement using the recommended allowable bearing pressure is estimated to be less than 1-inch total and ½-inch differential between adjacent footings or across a distance of about 20 feet, based on our experience with similar projects. Lateral loads may be resisted by friction on the base of the footing and passive resistance against the subsurface portions of the foundation. A coefficient of friction of 0.35 may be used to calculate the base friction and should be applied to the vertical dead load only. Passive resistance may be calculated as a triangular equivalent fluid pressure distribution. An equivalent fluid density of 200 pounds per cubic foot (pcf) should be used for passive resistance design for a level ground surface adjacent to the footing. This level surface should extend a distance equal to at least three times the footing depth. These recommended values incorporate safety factors of 1.5 and 2.0 applied to the estimated ultimate values for frictional and passive resistance, respectively. To achieve this value of passive resistance, the foundations should be poured “neat” against the native medium dense soils or compacted fill should be used as backfill against the front of the footing. We recommend that the upper one foot of soil be neglected when calculating the passive resistance. Geotechnical Engineering Evaluation NGA File No. 11444C24 South 132nd Street Townhomes March 28, 2025 Renton, Washington Page 9 NELSON GEOTECHNICAL ASSOCIATES, INC. Retaining Walls Final plans were not available when this report was prepared, but retaining walls may be incorporated into the final project plans. In general, the lateral pressure acting on retaining walls is dependent on the nature and density of the soil behind the wall, the amount of lateral wall movement which can occur as backfill is placed, wall drainage conditions, and the inclination of the backfill. For walls that are free to yield at the top at least one thousandth of the height of the wall (active condition), soil pressures will be less than if movement is limited by such factors as wall stiffness or bracing (at-rest condition). We recommend that walls supporting horizontal backfill and not subjected to hydrostatic forces, be designed using a triangular earth pressure distribution equivalent to that exerted by a fluid with a density of 40 pcf for yielding (active condition) walls, and 60 pcf for non-yielding (at-rest condition) walls. A seismic design loading of 8H in psf should also be included in the wall design where “H” is the total height of the wall. These recommended lateral earth pressures are for a drained granular backfill and are based on the assumption of a horizontal ground surface behind the wall for a distance of at least the height of the wall, and do not account for surcharge loads except as provided above. Additional lateral earth pressures should be considered for surcharge loads acting adjacent to walls and within a distance equal to the height of the wall. This would include the effects of surcharges such as special traffic loads, floor slab loads, slopes, or other surface loads. We could consult with the structural engineer regarding additional loads on retaining walls during final design, if needed. The lateral pressures on walls may be resisted as described in the Foundation Support section of this report. All wall backfill should be well compacted as outlined in the Structural Fill subsection of this report. Care should be taken to prevent the buildup of excess lateral soil pressures due to over-compaction of the wall backfill. This can be accomplished by placing wall backfill in 8-inch loose lifts and compacting the backfill with small, hand-operated compactors within a distance behind the wall equal to at least half the height of the wall. The thickness of the loose lifts should be reduced to accommodate the lower compactive energy of the hand-operated equipment. The recommended level of compaction should still be maintained. Permanent drainage systems should be installed for retaining walls. Recommendations for these systems are found in the Subsurface Drainage subsection of this report. We recommend that we be retained to evaluate the proposed wall drain backfill material and observe installation of the drainage systems. Geotechnical Engineering Evaluation NGA File No. 11444C24 South 132nd Street Townhomes March 28, 2025 Renton, Washington Page 10 NELSON GEOTECHNICAL ASSOCIATES, INC. Structural Fill General: Fill placed beneath foundations, pavement, or other settlement-sensitive structures should be placed as structural fill. Structural fill, by definition, is placed in accordance with prescribed methods and standards, and is monitored by an experienced geotechnical professional or soils technician. Field monitoring procedures would include the performance of a representative number of in-place density tests to document the attainment of the desired degree of relative compaction. The area to receive the fill should be suitably prepared as described in the Site Preparation and Grading subsection prior to beginning fill placement. Sloping areas to receive fill should be benched using a minimum 8-foot-wide horizontal benches into competent soils. Materials: Structural fill should consist of a good quality, granular soil, free of organics and other deleterious material, and be well graded to a maximum size of about three inches. All-weather fill should contain no more than five-percent fines (soil finer than U.S. No. 200 sieve, based on that fraction passing the U.S. 3/4-inch sieve). The onsite soils are generally considered unsuitable for use as structural fill. Structural fill below groundwater should consist of quarry spalls. We should be retained to evaluate all proposed structural fill material prior to placement. Fill Placement: Following subgrade preparation, placement of structural fill may proceed. All filling should be accomplished in uniform lifts up to eight inches thick. Each lift should be spread evenly and be thoroughly compacted prior to placement of subsequent lifts. All structural fill underlying building areas and pavement subgrade should be compacted to a minimum of 95 percent of its maximum dry density. Maximum dry density, in this report, refers to that density as determined by the ASTM D-1557 Compaction Test procedure. The moisture content of the soils to be compacted should be within about two percent of optimum so that a readily compactable condition exists. It may be necessary to over-excavate and remove wet soils in cases where drying to a compactable condition is not feasible. All compaction should be accomplished by equipment of a type and size sufficient to attain the desired degree of compaction and should be tested. Slab-on-Grade and Pavements Slabs-on-grade should be supported on subgrade soils prepared as described in the Site Preparation and Grading subsection of this report. Specifically, where slabs or pavements are not supported on native competent soil, we recommend that the subgrade be prepared by over excavating three feet of material below finished grade and replacement with 2- to 4-inch quarry spalls. The top six inches of improved subgrade may be filled with compacted, crushed rock to provide a surface for pavement or concrete sections. Geotechnical Engineering Evaluation NGA File No. 11444C24 South 132nd Street Townhomes March 28, 2025 Renton, Washington Page 11 NELSON GEOTECHNICAL ASSOCIATES, INC. We recommend that all floor slabs be underlain by at least six inches of free-draining gravel with less than three percent by weight of the material passing Sieve #200 for use as a capillary break. We recommend that the capillary break be hydraulically connected to the footing drain system to allow free drainage from under the slab. A suitable vapor barrier, such as heavy plastic sheeting (6-mil, minimum), should be placed over the capillary break material. An additional 2-inch-thick moist sand layer may be used to cover the vapor barrier. This sand layer is optional, and is intended to be used to protect the vapor barrier membrane and to aid in curing the concrete. Utilities We recommend that underground utilities be bedded with a minimum six inches of pea gravel prior to backfilling the trench with on-site or imported material. Existing stormwater lines will likely need to be realigned to avoid areas to be developed. Trenches within settlement sensitive areas should be compacted to 95 percent of the modified proctor as described in the Structural Fill subsection of this report. Trenches located in non-structural areas should be compacted to a minimum 90 percent of the maximum dry density. Trench backfill compaction should be tested. Site Drainage infiltration: During our explorations, we encountered slight to heavy perched groundwater conditions at depths in the range of 0.5 to 2.0 feet below the existing ground surface. Based on the presence of perched groundwater at shallow depths within all our explorations, and the relatively compact nature of the native glacial soils that underly the site at depth, it is our opinion that the onsite native glacial till soils are not conducive for stormwater infiltration systems. We recommend that all stormwater generated from proposed structures and other hard surfaces within the site be directed to on-site detention systems and ultimately into an approved point of discharge likely found within the adjacent roadways Surface Drainage: The finished ground surface should be graded such that stormwater is directed to an appropriate stormwater collection system. Water should not be allowed to stand in any areas where footings, slabs, or pavements are to be constructed. Final site grades should allow for drainage away from the structures. We suggest that the finished ground be sloped at a minimum downward gradient of three percent, for a distance of at least 10 feet away from the residence. Surface water should be collected by permanent catch basins and drain lines, and be discharged into an approved discharge system. The overflow water should be directed to discharge into an approved location. Geotechnical Engineering Evaluation NGA File No. 11444C24 South 132nd Street Townhomes March 28, 2025 Renton, Washington Page 12 NELSON GEOTECHNICAL ASSOCIATES, INC. Subsurface Drainage: If groundwater is encountered during construction, we recommend that the contractor slope the bottom of the excavation and collect the water into ditches and small sump pits where the water can be pumped out and routed into a permanent storm drain. We recommend the use of footing drains around the structure to control moisture. Footing drains should be installed at least one foot below planned finished floor elevation. The drains should consist of a minimum 4-inch-diameter, rigid, slotted or perforated, PVC pipe surrounded by free-draining material wrapped in a filter fabric. We recommend that the free-draining material consist of an 18-inch-wide zone of clean (less than three-percent fines), granular material placed along the back of walls. Pea gravel is an acceptable drain material. The free-draining material should extend behind any retaining walls to one foot below the finished ground surface. The top foot of soil should consist of low permeability soil placed over plastic sheeting or building paper to minimize the migration of surface water or silt into the footing drain. Footing drains should discharge into tightlines leading to an approved collection and discharge point with convenient cleanouts to prolong the useful life of the drains. Roof drains should not be connected to wall or footing drains. Due to shallow perched groundwater across the site, and depending on final grades, we recommend that an under-slab drainage system be incorporated into the design. This system typically consists of a series of 4-inch perforated PVC pipes placed within the capillary break layer no more than 10 feet apart. The perforated pipes typically drain into a solid manifold pipe that in turn, drains any collected water into the permanent drainage system. CONSTRUCTION MONITORING We should be retained to provide construction monitoring services during the earthwork phase of the project to evaluate structure setbacks, subgrade conditions, temporary cut conditions, fill compaction, and drainage system installation. USE OF THIS REPORT NGA has prepared this report for Mark Raabe, and his agents, for use in the planning and design of the development on this site only. The scope of our work does not include services related to construction safety precautions and our recommendations are not intended to direct the contractors’ methods, techniques, sequences, or procedures, except as specifically described in our report for consideration in design. There are possible variations in subsurface conditions between the explorations and also with time. Our report, conclusions, and interpretations should not be construed as a warranty of subsurface conditions. A contingency for unanticipated conditions should be included in the budget and schedule. Geotechnical Engineering Evaluation NGA File No. 11444C24 South 132nd Street Townhomes March 28, 2025 Renton, Washington Page 13 NELSON GEOTECHNICAL ASSOCIATES, INC. All people who own or occupy homes on or near hillsides should realize that landslide movements are always a possibility. The landowner should periodically inspect the slope, especially after a winter storm. If distress is evident, a geotechnical engineer should be contacted for advice on remedial/preventative measures. The probability that landsliding will occur is substantially reduced by the proper maintenance of drainage control measures at the site (the runoff from the roofs should be led to an approved discharge point). Therefore, the homeowner should take responsibility for performing such maintenance. Consequently, we recommend that a copy of our report be provided to any future homeowners of the property if the home is sold. We recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications. We should be contacted a minimum of one week prior to construction activities and could attend pre-construction meetings if requested. Within the limitations of scope, schedule, and budget, our services have been performed in accordance with generally accepted geotechnical engineering practices in effect in this area at the time this report was prepared. No other warranty, expressed or implied, is made. Our observations, findings, and opinions are a means to identify and reduce the inherent risks to the owner. o-o-o Geotechnical Engineering Evaluation NGA File No. 11444C24 South 132nd Street Townhomes March 28, 2025 Renton, Washington Page 14 NELSON GEOTECHNICAL ASSOCIATES, INC. It has been a pleasure to provide service to you on this project. If you have any questions or require further information, please call. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Daniel J. O’Dell Project Geologist Khaled M. Shawish, PE Principal DJO:RJB:KMS:dy Four Figures Attached 3.28.2025 Not to Scale VICINITY MAP 8225 S 132nd Street Townhome Development Vicinity Map 1 No.Project Number Date By CKRevision Woodinville Office 17311-135th Ave. NE, A-500 Woodinville, WA 98072 (425) 486-1669 / Fax: 481-2510 Wenatchee Office 105 Palouse St. Wenatchee, WA 98801 (509) 665-7696 / Fax: 665-7692www.nelsongeotech.com C: \ U s e r s \ A n n a S c h l u n e g e r \ N G A \ N e l s o n G e o t e c h n i c a l A s s o c i a t e s , I n c - C o m p a n y \ 2 0 2 4 N G A W E S T \ 1 1 4 4 4 C - 2 4 8 2 2 5 S o u t h 1 3 2 n d S t R e n t o n T o w n h o m e s \ D r a f t i n g \ S P - V M . d w g 3/19/25 AMS DJOOriginal Figure 1 11444C24 King County, WA Project Site 8225 S 132nd Street Townhome Development Site Plan 1 No.Project Number Date By CKRevision Woodinville Office 17311-135th Ave. NE, A-500 Woodinville, WA 98072 (425) 486-1669 / Fax: 481-2510 Wenatchee Office 105 Palouse St. Wenatchee, WA 98801 (509) 665-7696 / Fax: 665-7692www.nelsongeotech.com C: \ U s e r s \ A l e x a n d e r ( A l e x ) B a u c c \ O n e D r i v e - N e l s o n G e o t e c h n i c a l A s s o c i a t e s , I n c \ 2 0 2 4 N G A P r o j e c t \ 1 1 4 4 4 C - 2 4 8 2 2 5 S o u t h 1 3 2 n d S t R e n t o n T o w n h o m e s \ D r a f t i n g \ S P - V M . d w g 3/19/25 AMS DJOOriginal Figure 2 11444C24 Site Plan Reference: Site Plan based on field measurements, observations, and aerial imagery. LEGEND Number and approximate location of test pits Property line TP-1 TP-1 TP-3 TP-4 TP-2 S 132nd St 0 35 70 Approximate Scale: 1 inch = 35 feet Proposed Driveway Proposed Townhomes GW GP GM GC SW SP SM SC ML CL OL MH CH OH PT PEAT ORGANIC CLAY, ORGANIC SILT CLAY OF HIGH PLASTICITY, FAT CLAY SILT OF HIGH PLASTICITY, ELASTIC SILT SILTY SAND SILT ORGANIC SILT, ORGANIC CLAY CLAY CLAYEY SAND POORLY GRADED SAND WELL-GRADED SAND, FINE TO COARSE SAND CLAYEY GRAVEL SILTY GRAVEL POORLY-GRADED GRAVEL WELL-GRADED, FINE TO COARSE GRAVELCLEAN GRAVEL GRAVEL WITH FINES CLEAN SAND SAND WITH FINES INORGANIC ORGANIC INORGANIC ORGANIC HIGHLY ORGANIC SOILS GRAVEL SAND SILT AND CLAY SILT AND CLAY MORE THAN 50 % OF COARSE FRACTION RETAINED ON NO. 4 SIEVE PASSES NO. 4 SIEVE LIQUID LIMIT LESS THAN 50 % 50 % OR MORE LIQUID LIMIT MORE THAN 50 % OF COARSE FRACTION COARSE - GRAINED SOILS FINE - GRAINED SOILS MORE THAN 50 % RETAINED ON NO. 200 SIEVE PASSES NO. 200 SIEVE MORE THAN 50 % MAJOR DIVISIONS GROUP SYMBOL GROUP NAME UNIFIED SOIL CLASSIFICATION SYSTEM NOTES: 1) Field classification is based on visual examination of soil in general accordance with ASTM D 2488-93. 2) Soil classification using laboratory tests is based on ASTM D 2488-93. 3) Descriptions of soil density or consistency are based on interpretation of blowcount data, visual appearance of soils, and/or test data. SOIL MOISTURE MODIFIERS: Dry - Absence of moisture, dusty, dry to the touch Moist - Damp, but no visible water. Wet - Visible free water or saturated, usually soil is obtained from below water table 1 No.Project Number Date By CKRevision Woodinville Office 17311-135th Ave. NE, A-500 Woodinville, WA 98072 (425) 486-1669 / Fax: 481-2510 Wenatchee Office 105 Palouse St. Wenatchee, WA 98801 (509) 665-7696 / Fax: 665-7692www.nelsongeotech.com C: \ U s e r s \ A n n a S c h l u n e g e r \ N G A \ N e l s o n G e o t e c h n i c a l A s s o c i a t e s , I n c - C o m p a n y \ 2 0 2 4 N G A W E S T \ 1 1 4 4 4 C - 2 4 8 2 2 5 S o u t h 1 3 2 n d S t R e n t o n T o w n h o m e s \ D r a f t i n g \ S C . d w g Figure 3 11444C24 3/19/25 AMS DJOOriginal 8225 S 132nd Street Townhome Development Soil Classification Chart LOG OF EXPLORATION DEPTH (FEET) USCS SOIL DESCRIPTION SAM NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 1144C24 FIGURE 4 TEST PIT TP-1 0.0 – 3.0 Dark brown, silty fine to medium SAND with gravel, cobbles, roots, and iron-oxide weathering (loose to medium dense, moist to wet) (undocumented fill/topsoil) 3.0 – 6.0 Gray to gray-brown, silty fine to medium SAND with gravel and iron-oxide staining (medium dense, moist to wet) (undocumented fill) 6.0 – 10.0 SM Gray to orange-brown interbedded silty fine SAND and silty fine to medium SAND with iron-oxide staining (medium dense to dense, moist) Samples were not collected Moderate to severe groundwater seepage was encountered at 2.0 feet Test pit caving was not encountered Test Pit TP-1 was completed at 10.0 feet on 2/26/2025 TEST PIT TP-2 0.0 – 1.0 Dark brown, silty fine to medium SAND with gravel, cobbles, roots, and iron-oxide weathering (loose, moist to wet) (undocumented fill/topsoil) 1.0 – 10.0 SM Gray to gray-brown interbedded silty fine SAND and silty fine to medium SAND with iron-oxide staining (medium dense to dense, moist to wet) Samples were not collected Slight to moderate groundwater seepage was encountered at 2.0 feet Test pit caving was encountered at 7.0 feet to 8.0 feet Test Pit TP-2 was completed at 10.0 feet on 2/26/2025 TEST PIT TP-3 0.0 – 1.0 Dark brown, silty fine to medium SAND with gravel, cobbles, roots, and iron-oxide weathering (loose, moist to wet) (topsoil) 1.0 – 10.0 SM Gray to orange-brown interbedded silty fine to medium SAND and silt with fine SAND and iron- oxide staining (medium dense to dense, moist to wet) Samples were not collected Slight groundwater seepage was encountered at 1.0 feet Test pit caving was not encountered Test Pit TP-3 was completed at 10.0 feet on 2/26/2025 TEST PIT TP-4 0 – 0.5 Dark brown, silty fine to medium SAND with roots, organics, iron-oxide weathering, and gravel (loose, dry to moist) (undocumented fill/topsoil) 0.5 – 10.0 SM Gray to orange-brown interbedded silty fine to medium SAND and silt with fine SAND and iron- oxide staining (medium dense to dense, moist to wet) Samples were not collected Slight to moderate groundwater seepage was encountered at 0.5 feet Test pit caving was not encountered Test Pit TP-4was completed at 10.0 feet on 2/26/2025 Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 2250007.10 Appendix D Non-Structural BMPs Stormwater Pollution Prevention Manual King County Stormwater Services 123 July 2021 R-1: Residential Automobile and Boat Washing The following best management practices (BMPs) apply to washing vehicles and boats at your house. Vehicle washing is one of the most common residential activities that pollute streams, creeks, lakes, and Puget Sound. Even soaps that are labeled "biodegradable," "environmentally friendly", or "nontoxic" are harmful to aquatic life and water quality. The “nontoxic” label simply means the soap is less toxic to humans. The most environmentally responsible thing to do is to take your vehicle to a commercial car wash where wash water is properly recycled and discharged to the sanitary sewer. Potential pollutants can include but are not limited to hydrocarbons, metals, nutrients, oil and grease, oxygen demanding substances, PCBs, pH, sediment, and other pollutants. BMPs are required by King County Water Quality Code (KCC 9.12). If the BMPs included here are not enough to prevent contamination of stormwater, you will be required to take additional measures. Required BMPs • Washing may only be done in an area that allows for infiltration of the wash water, such as gravel, grass, or loose soil. • When washing vehicles or boats, use a mild detergent or soap that is pH neutral. • Never clean or pressure wash the engine or undercarriage of your vehicle at home. The pollutants from this activity can contaminate your property or well water. • Dispose of any remaining soapy water in your wash bucket down the toilet or sink. • Do not wash or rinse vehicles on permeable pavement or pavers. • If you wash on an impermeable (conventional) paved area such as your driveway and use soaps or detergents, you must do one of the following: o Redirect the wash water to vegetated areas such as the lawn using temporary measures such as a berm, boom/socks, or other solid materials like a piece of lumber placed at the low point of where your vehicle is parked. This will redirect the flow of water to the vegetated area where it can infiltrate into the ground; or. o Use a wet vacuum or pump to collect the wash water and then dispose of the water in your sink or toilet for treatment at your local sewage treatment plant. Tips • Use a hose nozzle with a trigger and shut it off when you’re not using it to conserve water. • There are several waterless car wash products on the market. Cloths, rags, etc. used with these products should be disposed of as solid waste. Stormwater Pollution Prevention Manual King County Stormwater Services 124 July 2021 • Do not take your car to a “charity car wash” unless you can see that the wash water is being collected and discharged to the sewer system. When in doubt, ask the event organizers where the car wash water is being disposed of. For more information or assistance contact the King County Stormwater Services at 206–477–4811 and visit kingcounty.gov/stormwater. Stormwater Pollution Prevention Manual King County Stormwater Services 125 July 2021 R-2: Residential Storage of Solid Waste and Food Wastes (Garbage) Leaking garbage cans, waste containers without lids, and scrap piles can cause polluted runoff, which can harm surface waters and groundwater. Accumulated garbage can attract rodents, rats, mosquitoes, and other pests that are also health hazards. Potential pollutants include but are not limited to fecal coliform bacteria, hydrocarbons, metals, nutrients, oil and grease, oxygen demanding substances, PCBs, pH, sediment, and other pollutants. Best Management Practices (BMPs) are required by King County Water Quality Code (KCC 9.12). If the BMPs included here are not enough to prevent contamination of stormwater, you will be required to take additional measures. Required BMPs • Keep garbage, recyclables, and food wastes in covered or lidded containers. • Dispose of waste, using a curbside pick-up service or take it to a solid waste transfer station. • Do not let garbage accumulate to the point that it spills out of the container or prevents people from using the container. Tips • Recycle as much as possible. Use the King County “What do I do with…?” website to find businesses that accept materials for recycling, donations and disposal https://info.kingcounty.gov/services/recycling-garbage/solid-waste/what-do-i-do-with/ • King County Solid Waste Division waste disposal information http://your.kingcounty.gov/solidwaste/index.asp • Household hazardous waste disposal: www.hazwastehelp.org, or contact the Household Hazards Line at 206-296-4692. See activity sheet R-4: Residential Hazardous Waste Use, Storage, and Disposal for more information. • Composting yard and food waste http://your.kingcounty.gov/solidwaste/composting/index.asp • Yard waste collection http://your.kingcounty.gov/solidwaste/garbage-recycling/yardwaste.asp • Dispose of pet waste in your garbage, see activity sheet R-8: Residential Animal Waste For more information or assistance contact the King County Stormwater Services at 206–477–4811 and visit kingcounty.gov/stormwater. Stormwater Pollution Prevention Manual King County Stormwater Services 126 July 2021 R-3: Residential Vehicle Repair and Maintenance Many people repair and maintain their vehicles at home. Keeping your vehicle from leaking oil or other fluids is an important pollution prevention measure. These activities cannot pollute streams, rivers, and lakes. Potential pollutants include but are not limited to hydrocarbons, metals, oil and grease, oxygen demanding substances, pH, sediment, and other pollutants. Best Management Practices (BMPs) are required by King County Water Quality Code (KCC 9.12). If the BMPs included here are not enough to prevent contamination of stormwater, you will be required to take additional measures. Required BMPs • Collect all used oil, antifreeze, and other vehicle fluids in containers with tight fitting lids. Do not mix these fluids in the same container. • Recycle oil at an auto parts store or service station. Oil and other fluids can be disposed of at a household hazardous waste collection site. Call the household hazardous waste line at 206-296-4692 or see https://www.hazwastehelp.org/HHW/disposal-locations.aspx for recycling and disposal information and locations. Never dispose of any fluids or waste materials into the stormwater drainage system, surface waters, or onto the ground. • Never clean the engine or undercarriage of your vehicle at home. For this type of cleaning, take the vehicle to a commercial car wash facility. • Use drip pans, tarps, or even cardboard and newspaper under the vehicle to capture leaks or spills that may occur during maintenance and repair activities. This ensures spilled fluids won't be washed to the stormwater drainage system. • Clean up spills with rags or absorbent material, such as sand, dirt, or cat litter. Do not wash down spills. Sweep up absorbents and dispose of them as garbage. • Store used batteries under cover and off the ground or inside until they can be recycled. Tips • Take your vehicle to a commercial car repair facility where fluids are handled, recycled, and disposed of properly. For more information or assistance contact the King County Stormwater Services at 206–477–4811 and visit kingcounty.gov/stormwater. Stormwater Pollution Prevention Manual King County Stormwater Services 127 July 2021 R-4: Residential Hazardous Waste Use, Storage and Disposal A variety of hazardous materials are routinely used in and around our homes including chemical cleaners, pesticides, paints, solvents, lighter fluid, gasoline, antifreeze, brake fluid and other automotive products, wood preservatives and even batteries from our electronic equipment. Improper disposal and failure to keep hazardous products from rainwater contact may cause surface water and groundwater pollution. With so many hazardous materials present in thousands of households in King County, the cumulative adverse effects of poor usage, storage and disposal practices are potentially severe to human and environmental health. Potential pollutants can include but are not limited to fecal coliform bacteria, hydrocarbons, metals, nutrients, oil and grease, oxygen demanding substances, PCBs, pH, sediment, and other pollutants. Best Management Practices (BMPs) are required by King County Water Quality Code (KCC 9.12). If the BMPs included here are not enough to prevent contamination of stormwater, you will be required to take additional measures. Required BMPs • Store all hazardous materials inside a building, shed or under cover. Do not expose hazardous materials to rainwater. • Use products only as specified on labeling directions. • Carefully follow disposal directions on containers of chemicals. • Never discharge or dump hazardous chemicals into storm drainage systems or on to the ground. Disposal Options Dispose of and recycle hazardous wastes through the Household Hazardous Waste Program or other recycling programs or businesses. There are three fixed hazardous waste collection sites for household hazardous waste in Seattle and King County. See www.hazwastehelp.org/ or call the Household Hazards Line at 206-296-4692 for more information. Tips • Use the least toxic product available. See https://kingcountyhazwastewa.gov/en/households-disposal/households-safer-home-products for information on finding alternatives to hazardous household products. For more information or assistance contact the King County Stormwater Services at 206–477–4811 and visit kingcounty.gov/stormwater. Stormwater Pollution Prevention Manual King County Stormwater Services 128 July 2021 R-5: Residential Gardening, Lawn Care, Irrigation and Fertilizer Application Many pollutants can enter stormwater systems, groundwater, and water bodies as a result of typical lawn and gardening work. Runoff contaminated by pesticides and fertilizers can severely degrade streams and lakes and adversely affect fish and other aquatic life. Disposal of grass clippings and other vegetation into water bodies leads to decreased oxygen levels that can be lethal to fish and other aquatic life. In addition, disposal of leaf litter and other debris to the storm drain system can clog drainage pipes, leading to street flooding and increased maintenance costs. Some gardening chemicals are also harmful to children and pets. Potential pollutants can include but are not limited to fecal coliform bacteria, metals, nutrients, oil and grease, oxygen demanding substances, PCBs, and sediment. Best Management Practices (BMPs) are required by King County Water Quality Code (KCC 9.12). If the BMPs included here are not enough to prevent contamination of stormwater, you will be required to take additional measures. Required BMPs • Never apply herbicides, insecticides, rodenticides, or fungicides near water or when it is raining. • Manually or mechanically remove weeds and other pests rather than using pesticides near water. • Store all bags, piles, and containers of fertilizers and pesticides in a covered location such as a garden shed. • Do not sweep, blow, or dump grass clippings, leaves, or twigs into any street, drainage ditch, storm drain, or surface waters. Instead, collect and either compost it or dispose as yard waste. • Store piles of erodible materials, such as topsoil, on lawns or other pervious areas. If these materials are stored on impervious areas such as driveways, cover them with a tarp so they are not washed into storm drains or ditches. • Control lawn and garden watering so that no runoff leaves your property. Check automatic sprinkler systems to ensure there is no overspray to driveways and sidewalks that drain to storm drainage systems. Tips • Compost your yard waste, or use it as mulch in your yard or garden. Contact your local solid waste utility to see if yard waste pickup service is available. See http://your.kingcounty.gov/solidwaste/garbage-recycling/yardwaste.asp. • Use as little pesticide as possible and always follow the label directions for application. Try pest control measures that do not require chemicals first. Stormwater Pollution Prevention Manual King County Stormwater Services 129 July 2021 • Learn about alternatives to chemical pesticides and fertilizers. Contact the King County Hazardous Waste Management Program at 206-296-4692, or visit http://www.hazwastehelp.org and the Garden Hotline at https://gardenhotline.org/ • Avoid planting species on the Noxious Weeds list. For assistance or questions contact King County’s Noxious Weed Program at 206-296-1900 or visit https://www.kingcounty.gov/services/environment/animals-and-plants/noxious-weeds.aspx. • For additional information on pesticides and fertilizers see activity sheet A-5: Storage and Use of Pesticides and Fertilizers. • For additional information on vegetation management and irrigation see activity sheet A-26: Landscaping Activities, Vegetation Management, and Irrigation. For more information or assistance contact the King County Stormwater Services at 206–477–4811 and visit kingcounty.gov/stormwater. Stormwater Pollution Prevention Manual King County Stormwater Services 130 July 2021 R-6: Residential Home Maintenance and Repair There are a variety of home maintenance and repair activities that have the potential to adversely affect our streams, rivers, and lakes. Pollutants generated from these activities can affect whether a water body is swimmable or fishable. Potential pollutants can include but are not limited to hydrocarbons, metals, nutrients, pH, sediment, and other pollutants. Best Management Practices (BMPs) are required by King County Code 9.12. If the BMPs included here are not enough to prevent contamination of stormwater, you will be required to take additional measures. Required BMPs • Do not dispose of wastewater into the street, gutter, storm drain, drainage ditch, or surface water (e.g., stream, creek, or any other body of water). Painting • Do not dispose of wash water from cleaning brushes, paint rollers, paint buckets, or containers to surface water, storm drains, or ditches. • Wash water from latex paints can be disposed of to the sanitary sewer (down a sink or toilet). • Empty containers of latex paint can be left open to dry out any residual paint, and then, once a solid, can be disposed of in your normal garbage or taken to a transfer station for disposal. • Residual oil-based paint, paint thinners, and solvents must be disposed of as hazardous waste. Washing • Water from washing decks, driveways, roofs, or other hard surfaces may contain suspended solids and other pollutants that should not be directly discharged to stormwater drainage systems. • Redirect wash water to vegetated areas or areas such as gravel, lawns, landscaping, or bare soil where the water will infiltrate slowly into the ground. If this cannot be accomplished, then filter the wash water through filter fabric, or other filtering media to collect the suspended solids before discharging the water to a stormwater drainage system. • If any chemicals, soaps or detergents are used the wash water must be collected and disposed of in a sanitary sewer system (i.e., a sink or toilet) or infiltrated on-site. Do not dispose of this wash water to the stormwater drainage system or surface waters. • If moss control or another chemical treatment is used during the washing of roofs, then disconnect the downspouts so the chemicals do not discharge to the Stormwater Pollution Prevention Manual King County Stormwater Services 131 July 2021 stormwater drainage system. Disperse this wash water onto adjacent lawns and landscaping to infiltrate. Carpet Cleaning • Most commercial carpet cleaners have onboard wastewater recycling systems. If you do your own carpet cleaning, then the wash water must be discharged to the sanitary sewer or your septic system. • Filter the water if it contains lint or other particles to avoid clogging the drains. • If you prefer not to discharge the water to your septic system, you may also discharge the water to your lawn or a landscaped area to allow the wash water to infiltrate slowly into the ground. • Be aware that detergents and other cleaning chemicals such as solvents can be harmful to vegetation and septic systems. • Discharging wash water to the ground may not be allowed if you live in a critical aquifer recharge area. For additional information on critical aquifer recharge areas in King County, refer to King County Code 21A.24.311-316. • Never dispose of carpet cleaning wash water to a storm drain, drainage ditch, or surface water. Carpet cleaning wastewater contains chemicals, detergents, and suspended solids that adversely impact the quality of surface and ground waters. Cement/Concrete Work • Concrete/cement wash water has a pH level that is toxic to aquatic life. • Do not allow wash water from concrete work to discharge into stormwater drainage systems, including small yard drains or adjacent roadways. • This is especially important when installing washed aggregate driveways or patios. Direct the wash water to vegetated areas or dig a hole where the wash water can settle and infiltrate slowly into the ground. The cement residue can be mixed into the soil where the wash water is infiltrated with no detrimental effects, and the pH will be neutralized. Tips • Hire a professional home maintenance and repair company that follows the approved BMPs for home repair and maintenance. If you have questions about which BMPs a business must comply with contact King County Stormwater Services at 206-477-4811 or visit www.kingcounty.gov/stormwater. • Remember, as a homeowner, you have a responsibility to ensure your contractors follow these required BMPs and all King County codes and regulations. For more information or assistance contact the King County Stormwater Services at 206–477–4811 and visit kingcounty.gov/stormwater. Stormwater Pollution Prevention Manual King County Stormwater Services 134 July 2021 R-8: Residential Animal Waste Animal feces that enters lakes, streams or Puget Sound begins to decay, using up oxygen and releasing ammonia (nutrients). Low oxygen levels and ammonia combined with warm water can kill fish. Nutrients encourage weed and algae growth, and contribute to low oxygen and high pH in waters we use for swimming, boating, and fishing. Most importantly, feces and fecal contaminated wash water can carry viruses and bacteria that could cause disease and lead to beach or shellfish harvesting closures. Potential pollutants can include but are not limited to fecal coliform bacteria, nutrients, oxygen demanding substances, PCBs, and sediment. Best Management Practices (BMPs) are required by King County Water Quality Code (KCC 9.12). If the BMPs included here are not enough to prevent contamination of surface water and stormwater, you will be required to take additional measures. Supplemental BMPs – Pet Waste • Promptly pick up and dispose of your pet waste when away from home. • Regularly pick up pet waste deposited on your property. • Put pet waste in a securely closed bag and deposit it in the trash. Do not place pet waste in yard waste containers because pet waste may carry diseases, and composting may not kill disease-causing organisms. • Do not compost or use pet waste as fertilizer. Harmful bacteria, worms, and parasites that can transmit disease can live in the soil for years even after the solid portion of the pet waste has dissolved. • When cleaning out cages and kennels, dispose of wash water down the toilet or a mop sink. Otherwise, wash directly over lawn areas or make sure the wash water drains to a vegetated area. • Bathe pets indoors or in a manner that wash water won’t be discharged to storm drain systems, ditches, or surface waters. Required BMPs – Goose Waste • If possible, pick up goose waste using shovels, brooms, rakes, power sweepers, and trash cans. Properly dispose of goose waste in the garbage. • Do not blow, sweep, or wash goose waste into surface waters or stormwater drainage systems. • Regularly clean goose waste from areas of chronic deposition. Supplemental BMPs – Pet Pharmaceuticals and Pesticides • Do not dispose of unused pet pharmaceuticals in a toilet or down a sink. • Pet pharmaceuticals can be disposed of at several medicine return drop-boxes located throughout the county. Refer to www.kingcountysecuremedicinereturn.org for guidelines and to locate a drop-box near you. Stormwater Pollution Prevention Manual King County Stormwater Services 135 July 2021 • Pet pesticides, such as flea prevention, cannot be disposed of at a medicine return drop-box. Pesticides should be taken to at a local hazardous waste drop-off location. Refer to www.hazwastehelp.org for guidelines and to find a drop-off location near you. Supplemental BMPs – Goose Waste • Do not feed wild geese or other waterfowl. • Change areas of chronic accumulation of goose waste from goose friendly to goose resistant. Reduce lawn areas and increase the height of shoreline vegetation (tall grass, shrubs) as geese are reluctant to walk through tall vegetation. • Geese’s favorite food is new shoots of grass. Let grass grow to six inches or taller. Stop fertilizing and watering lawn in areas of geese accumulation to reduce the palatability of the lawn. • Create a natural geese barrier of 20 to 100 feet of herbaceous vegetation at least 3 feet in height to discourage geese. A narrow, winding path through the plantings will allow for beach access, while preventing geese from having a direct line of sight through the planted area. Minimize open sight lines for geese to less than 30 feet. • Where space is limited, use one or two rows of shrub plantings combined with a fence to construct a geese barrier. Fences can be made from woven wire, poultry netting, plastic netting, plastic snow fencing, mono-filament line, or electrified wire. Fences should be at least 24 inches tall (3 feet may be better), firmly constructed, and installed to prevent the geese from walking around the ends. Lower openings should be no larger than 4 inches from the ground to prevent goslings from walking under or through the fence. • Construct bank slopes steeper than 4:1 to discourage geese by preventing a clear view of the bank top and potential predators. Or, separate the beach from the grass with a few steep steps, which makes the ascent too difficult for most geese. • Plant shrubs or trees along ponds to limit takeoff and landing opportunities. • Scare geese away when they are around. Geese often learn quickly to ignore scare devices that are not a real physical danger. Vary the use, timing, and location of tactics. Take advantage of geese being fearful of new objects. Examples of harassment and scare tactics include: o Dog patrols: Dogs are the method of choice for large open areas. Results are often immediate. After an aggressive initial use (several times a day for one or two weeks), geese get tired of being harassed and will use adjacent areas instead. A dog can be tethered to a long lead (which may require relocating the dog and tether frequently to cover more area), be allowed to chase and retrieve a decoy thrown over a large flock of geese, or be periodically released to chase the birds (if this is not against leash laws). o Eyespot Balloons: Large, helium-filled balloons with large eye-like images. Tether balloons on a 20 to 40-foot monofilament line attached to a stake or heavy object. Locate balloons where they will not tangle with trees or utility lines. Stormwater Pollution Prevention Manual King County Stormwater Services 136 July 2021 o Flags and Streamers: Simple flags from plastic mounted on tall poles or mylar tape to make 6-foot streamers attached to the top of 8-foot-long poles. Flags and streamers work best in areas where there is steady wind. o Scarecrows: Effective in areas where geese view humans as dangerous predators. For maximum effect, the arms and legs should move in the wind, use bright colors, and large eyes. Large, blow-up toy snakes are reported to work as a type of scarecrow. • Canada geese are protected under federal and state law and a hunting license and open season are required to hunt them. Where lethal control of Canada geese is necessary outside of hunting seasons, it should be carried out only after the above nonlethal control techniques have proven unsuccessful and only under permits issued by the U.S. Fish and Wildlife Service. Currently, the only agency permitted for lethal removal is the U.S. Department of Agriculture’s Wildlife Services. Lethal control techniques include legal hunting, shooting out of season by permit, egg destruction by permit, and euthanasia of adults by government officials. • The Humane Society of the United States’ Solving Problems with Canada Geese: A Management Plan and Information Guide http://www.humanesociety.org/assets/pdfs/wild_neighbors/canada_goose_guide.pdf For more information or assistance contact the King County Stormwater Services at 206–477–4811 and visit kingcounty.gov/stormwater. Preliminary Technical Information Report 8225 South 132nd Street 5 Townhouses 2250007.10 Appendix E Critical Areas Report Eastside Environmental Pros, Inc., November 26, 2024 Eastside Environmental Pros 26 November 2024 EE-532 Mark Raabe Via email: markdraabe@comcast.net REFERENCE: 8225 S 132nd St Renton, WA 98178 King County Parcel 214480-0535 SUBJECT: Critical Areas Feasibility Letter Dear Mark, At your request, Eastside Environmental Pros has investigated the property located 8225 S 132nd Street, in Renton (hereinafter referred to as “Site”) and areas within 300 feet of the property for the presence of critical areas (i.e. wetlands and streams). The Site and 300 feet surrounding the Site are referred to jointly as the “Study Area”. Critical Areas discussed in this report are based on approximations only. This report is not suitable for permit applications. PROPERTY LOCATION The Site is composed of one (1) King County parcel (TPN: 214480-0535) located at 8225 S 132nd Street in Renton, Washington. The Public Land Survey System location of the Site is the northeastern quarter of Section 13, Township 23 North, Range 04 East, of the Willamette Meridian. METHODOLOGY The Study Area was evaluated for the presence of critical areas on 13 November 2024 using the routine approach described in the Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Western Mountains, Valleys, and Coast Region (U.S. Army Corps of Engineers, 2010) and the Washington State Department of Ecology’s publication, Determining the Ordinary High Water Mark for Shoreline Management Compliance in Washington State (2016). Offsite areas were evaluated from what could be observed visually from the boundary of the Site, public rights-of-way, and via agency databases. Waterbodies were classified based on the water classification system according to WAC §222-16-30 per RMC §4-3-050G.7 and their buffers per RMC §4-3-050G.2. Wetlands were rated according to RMC §4-3-050G.9 and their buffers established per RMC §4-3-050G.9.d. ONSITE INVESTIGATION RESULTS One (1) intermittent waterbody (Stream 1) and one (1) wetland (Wetland A) were identified onsite, and one (1) wetland (Wetland B) was identified offsite during the 13 November 2024 Site visit. No other critical areas were found within the Study Area. This feature is described below in Table 1. Table 1. Critical Areas Summary Table. Critical Area Category / Type HGM / Cowardin Class Standard Buffer* Stream 1 Type Ns N/A 50 feet Wetland A (17-sf, 0.0004-ac) Category IV Slope/ Scrub-shrub 50 feet Wetland B (2,626-sf, 0.06-ac) Category III Riverine/ Emergent, Scrub-shrub 100 feet *Buildings and other structures shall be set back 15-feet from the edges of all critical area buffers per RMC §4-3-050G.2. STREAM 1 Stream 1 flows eastward through the southern portion of the Site. This watercourse’s banks can generally be described as degraded based on the amount of debris along its northern bank and invasive species prevalence. The northern bank of Stream 1 is stabilized by a retaining wall of used car tires and removal of this debris with the addition of slope stabilizing vegetation could be an option for enhancement. This watercourse is mapped by the City of Renton as a Type Ns watercourse. Additionally, the Washington Department of Fish and Wildlife (WDFW) identifies upstream and downstream fish barriers. Therefore, this watercourse qualifies as a Type Ns watercourse per the Interim Water Typing System (WAC 222-16-031) and requires a 50-foot buffer plus a 15-foot building setback per RMC §4-3-050G.2. WETLAND A Wetland A is approximately 17-sf and is located on the northern bank of Stream 1. Wetland A has slope hydrogeomorphic (HGM) classification (Brinson, 1993), with Palustrine scrub-shrub Cowardin classification (Cowardin et al., 1979). Wetland A scored 6 points for improving water quality functions, 5 points for hydrologic functions, and 4 points for habitat functions through the 2014 Wetland Rating Form. These scores total 15 points and qualify Wetland A as a Category IV wetland. Category IV wetlands with a habitat score of 4 require a standard 50-foot buffer, plus a 15-foot building setback measured from the edge of the critical area buffer per RMC §4-3-050G.2. WETLAND B Wetland B is approximately 2,626-sf (0.06-acres) and is located entirely offsite to the east of Stream 1. Wetland B has riverine hydrogeomorphic (HGM) classification (Brinson, 1993), with Palustrine emergent and scrub-shrub Cowardin classifications (Cowardin et al., 1979). Wetland B scored 8 points for improving water quality functions, 6 points for hydrologic functions, and 5 points for habitat functions through the 2014 Wetland Rating Form. These scores total 19 points and qualify Wetland B as a Category III wetland. Category III wetlands with a habitat score of 5 require a standard 100-foot buffer, plus a 15-foot building setback measured from the edge of the critical area buffer per RMC §4-3-050G.2. BUILDABLE AREA DISCUSSION The northern portion of the Site is unencumbered with critical areas buffers, as depicted in green on the Buildable Area Map. In total, the Site contains 10,193 (0.23-acres) of unencumbered area. The City may allow buffer modification methods described in the following sections for redevelopment. ALLOWED BUFFER MODIFICATIONS Reduction of Degraded Critical Area Buffer Widths with Enhancement The City of Renton allows for reductions to degraded critical area buffer widths provided that buffers are enhanced and meet the criteria listed in RMC §4-3-00I-2 and RMC §4-3-050I-3. The extent to which these buffers may be reduced are determined by the City planning director. Maximum reduction widths are not explicitly stated within the City of Renton’s Critical Areas Code. Stream Buffer Width Reduction with Enhancement In order to gain approval for stream buffer width reduction with enhancement, the applicant must demonstrate that the buffer reduction will result in an overall improvement in water quality, enhance fish and wildlife habitats, improve drainage or stormwater detention capabilities, and must not have a detrimental effect on surrounding properties or the City as a whole. A Critical Areas Report would need to be prepared and evaluate current buffer functions, including habitat quality, water quality, stormwater detention, groundwater recharge, shoreline protection, and erosion control, and assess how the proposed modification will maintain, or increase these functions. A Critical Areas Report must be prepared to evaluate site-specific buffer adequacy. This report should reference recognized resources, such as Wetlands in Washington State, Volume 1: A Synthesis of the Science and Volume 2: Managing and Protecting Wetlands, or similar methods, to document how the proposed buffer enhancement will achieve or exceed current functional levels. The proposed buffer standards must also align with the best available science as described in WAC §365-195-905. Approval may be granted upon submittal of a Critical Areas Report and Buffer Enhancement Plan that meet these requirements. The City requires a third-party review by the City’s consultant, to be funded by the applicant, to ensure compliance with the criteria. Wetland Buffers Width Reduction with Enhancement For your proposed development, reducing the wetland buffer width with enhancement would be an option, provided the reduced buffer demonstrates a higher level of ecological function than the standard buffer. However, the enhanced buffer must be situated on slopes less than 15%. The City of Renton interactive map records the presence of adjacent regulated slopes (equal to or greater than 15%) within the wetland and surrounding areas, which disqualifies this property from meeting the criteria for buffer width reduction. Additional evaluation of slope conditions would be necessary to determine eligibility. Stream and Wetland Buffer Width Averaging Buffer width averaging allows for the reduction of buffer width in one area, provided that an equivalent buffer area is replaced elsewhere on the site. However, this pathway has strict limitations, including restrictions on how much the buffer can be reduced and requirements for the location and ecological suitability of replacement buffer areas. Unfortunately, buffer width averaging requires the presence of existing physical improvements, such as structures, within or near the water body or buffer. Since the site currently lacks development, this option is not applicable for your project. With this information, we recommend further exploration of the Stream Buffer Width Reduction with Enhancement pathway for your future development considering that these alternative approaches do not appear to be an option for this Site. Summary The Site contains areas of degraded stream channel and buffer, and the ecological functions of Stream 1 and its buffer are impaired. This property appears to be a suitable candidate for the Stream Buffer Reduction with Enhancement provision available through the Renton Municipal Code. This code provision would allow for some flexibility to the overall buffer width and given its degraded condition, Stream 1 a good candidate for this pathway. The level of buffer reduction possible is decided by the planning director based on mitigation plan prepared by a qualified consultant. The mitigation plan must demonstrate an overall improvement in water quality, fish and wildlife habitat, and drainage or stormwater detention capabilities. To meet these requirements, the director would have to deem enhancement sufficient, likely through the removal of debris and invasive species, and replanting with native plantings throughout the stream buffer areas. We trust that the information presented here sufficiently describes and documents critical areas, unencumbered areas, and buffer modification allowances for your property. Please note that this report is not sufficient for permitting and is for planning purposes only. Should you have questions or wish to discuss any of the information in this report, please contact me via email at EmilyNW@wetland-consulting.com. Sincerely, Eastside Environmental Pros, Inc. Emily Newton-Weideman, Ecologist 220 22 0 230 220 230 220 220 A-1 A-0 A-2 SP-1 SP-2 S1-1A S1-1B S1-2A S1-2B S1-3B S1-3B S1-3B S1-6B S1-7B S1-8B S1-9B S1-3A S1-4A S1-5A S1-7A S1-8A S1-9A SP-3 SP-4 S1-6A 2 1 0 210 240 PLAN LEGEND PROPERTY LINE EXISTING WETLAND WETLAND BUFFER WETLAND FLAG LOCATION SOIL TEST PIT LOCATION STREAM ORDINARY HIGH WATER MARK (OHWM) STREAM BUFFER STREAM OHWM FLAG LOCATION 15-FT BUILDING SETBACK (BSBL) EXISTING CONTOURS (2-FT) PROTECTED SLOPE (>40% & <90%) SENSITIVE SLOPE (>25% & <40% SLOPE (>15% & <25%) UNENCUMBERED AREA (10,193 SF - 0.23 AC) 0HWM-# A-# SP-# 100 DRAWN BY: AS DATE SCALE RAABE FEASIBILITY RENTON, WASHINGTON FIGURE FIGURE 11-27-2024 18500 156th Ave NE, Suite 203 Woodinville, Washington 98072 Bus (425) 949-6659 EASTSIDE ENVIRONMENTAL PROS, INC. #1 EXISTING CONDITIONS MAP AS SHOWN#1 0 ( IN FEET ) GRAPHIC SCALE 20'40'80' GRAPHIC SCALE: 1"=40' PARCEL DATA EXTRACTED FROM KING COUNTY GIS. ELEVATION DATA EXTRACTED FROM 2021 LiDAR DATA. WETLAND BOUNDARIES LOCATED WITH EOS ARROW 100 SUB-METER GPS DEVICE. PROJECT SITE ADDRESS 22222 SE 42ND LANE, ISSAQUAH, WA 98029 PARCEL 2144800535 UNENCUMBERED AREA 10,193 SF (0.23 AC) STREAM 1 TYPE Ns 50' STD BUFFER WETLAND B CATEGORY III 2,626 SF (0.06 AC) 100' STD BUFFER WETLAND A CATEGORY IV 17 SF (0.0004 AC) 50' STD BUFFER S 132ND ST 1 0 0 ' 50 ' 50 ' 15 '