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Home My WebLink AboutRS_250606_Springbrook Terrace_ECY Final Design Report Final Design Report Springbrook Terrace Water Quality Retrofit CAG-24-081 CITY OF RENTON, WASHINGTON This report was prepared by: William McDonald, EIT And Approved by: Chad Booth, PE David Evans and Associates, Inc June 2025 Final Design Report i Springbrook Terrace Water Quality Retrofit TABLE OF CONTENTS SECTION 1.0 INTRODUCTION ......................................................................................... 1 SECTION 2.0 BASIN DESCRIPTION................................................................................... 2 SECTION 3.0 SITE DESCRIPTION ...................................................................................... 4 SECTION 4.0 MINIMUM REQUIREMENTS ....................................................................... 7 SECTION 5.0 ALTERNATIVES CONSIDERED .................................................................... 14 SECTION 6.0 DESIGN ANALYSIS .................................................................................... 16 SECTION 7.0 QUANTIFY THE WATER QUALITY BENEFIT ................................................. 19 SECTION 8.0 ENGINEER’S OPINION OF PROBABLE COST ............................................... 19 SECTION 9.0 PROPOSED SCHEDULE .............................................................................. 19 SECTION 10.0 REFERENCES ............................................................................................ 20 List of Figures Figure 1. Springbrook Terrace Vicinity Map ................................................................................... 2 Figure 2. Springbrook Terrace Pond Watershed ............................................................................ 3 Figure 3. Plan View of Existing Site with GIS Information .............................................................. 5 Figure 4. SWMMWW Flow Chart for Determining Requirements for New Development ............ 8 List of Tables Table 1. Existing Watershed Land Cover ........................................................................................ 4 Table 2. Proposed Watershed Land Cover ..................................................................................... 4 Table 3. Impervious Surface Classification ..................................................................................... 7 Appendices Appendix A: Maps Appendix B: Preliminary Plan Sheets Appendix C: Engineer’s Opinion of Probable Cost Appendix D: Analysis Program Output Appendix E: Geotechnical Report Appendix F: Proposed Schedule Springbrook Terrace Water Quality Retrofit Page 1 of 20 Final Design Report Section 1.0 Introduction The purpose of the project is to create a stormwater treatment function improving water quality within the system for the existing Springbrook Terrace Pond (the Pond) which drains to Springbrook Creek. The City of Renton (the City) owns the Pond which discharges to a city owned storm sewer system that flows north to South 55th Street and then west along South 192nd Street where the storm sewer discharges to Springbrook Creek approximately 1,600 feet from the Pond (see Figure 1). The Pond was built in 1985 to serve as a detention pond for a small neighborhood of single-family homes and roadways called Springbrook Terrace. The Pond was originally designed and permitted in accordance with the City’s standards at the time for stormwater management based on the requirements of the 1979 King County Storm Drainage Control – Requirements and Guidelines. The stormwater flow control function of the Pond is maintained in the proposed condition with the added benefit of stormwater treatment by using a wetpond best management practice (BMP). The proposed wetpond is designed in accordance with the City of Renton’s 2022 Surface Water Design Manual (SWDM) and the Washington State Department of Ecology’s (DOE) 2019 Stormwater Management Manual for Western Washington (SWMMWW). This project does not update the Pond to comply with current flow control standards, but it does retain all existing flow control performance as originally designed. Adding stormwater treatment capabilities to the Pond may result in improved flow control performance, but the volume and proposed design goal is to meet basic water quality treatment. No issues were identified in the cultural resources review. Springbrook Terrace Water Quality Retrofit Page 2 of 20 Final Design Report Figure 1. Springbrook Terrace Vicinity Map Section 2.0 Basin Description The existing watershed basin of the Pond, shown in Figure 2, is 6.64 acres in area and has approximately 60 percent pervious land cover and approximately 40 percent impervious land cover. A detailed breakdown of the existing land cover types is shown in Table 1, while Table 2 contains the proposed conditions watershed landcover reflecting the approximate 0.04 acres of new impervious surface proposed by the project. The basin was delineated by inspecting LiDAR topographic data and field reconnaissance. The David Evans and Associates, Inc (DEA) team visited the site and surrounding area on August 19, 2024. The DEA team inspected the drainage patterns of the basin from South 55th Street, 98th Ave South, and 98th Place South. The existing storm sewer system contributing to the Pond noted during the site visit matched as-built conditions and the City of Renton’s online geographic information system (GIS) records. Available as-built records, site visit observations, and storm sewer televising records do not indicate that any properties outside of the delineated basin may contribute runoff to the Pond via infrastructure such as tightlined roof draining downspouts. The exclusion of some parcels within the development from the watershed of the Pond is consistent with the previously completed alternatives analysis report discussed in Section 5.0. The historic basin would have been a dense lowland coniferous forest Springbrook Terrace Water Quality Retrofit Page 3 of 20 Final Design Report containing tree species such as Douglas fir creating nearly 100 percent canopy cover for the understory plants species such as salal, salmonberry, and sword fern. According to the City’s online GIS database, the current basin is zoned for quarter-acre residential properties (R-4 per City of Renton municipal code). City of Renton municipal code section 4-2-110A limits R-4 parcels to a maximum impervious surface area of 50 percent, and measurements based upon aerial imagery show that the parcels within the watershed are approximately 45 percent impervious surface. There are no commercial or industrial properties nor waterbodies within the basin. The soil types of the basin are both hydrologic soil type B and are comprised of gravelly sandy loams. A map of soil types within the watershed is contained in Appendix A. Figure 2. Springbrook Terrace Pond Watershed Springbrook Terrace Water Quality Retrofit Page 4 of 20 Final Design Report Table 1. Existing Watershed Land Cover Land Cover Type Area (acres) Percent of Watershed Lawn 3.26 49 Forest 0.70 11 Roadway 1.53 23 Rooftop 1.15 17 Total 6.64 100 Table 2. Proposed Watershed Land Cover Land Cover Type Area (acres) Percent of Watershed Lawn 3.22 48 Forest 0.70 11 Roadway 1.57 24 Rooftop 1.15 17 Total 6.64 100 Section 3.0 Site Description The project site is defined as the city owned parcel (Parcel ID number 79412000230) where the Pond is located and the 37 square feet of the adjacent parcel where gravel will be placed to construct the pond access road and parking area from the existing edge of asphalt. Only one threshold discharge area (TDA) exists for this project because the project is the low point in the basin and has a single outlet. The TDA extents are shown in Appendix A and Figure 2 and match the project site extents. TDA’s as defined do not necessarily encapsulate all areas of contributory flow and therefore should not be used as boundaries for hydrologic and hydraulic analysis. The current land use of the basin, as described in Section 2.0, is quarter-acre residential development while the current land use of the project site is an open space stormwater pond that is proposed to be retrofitted by this project. There are no structures or walls on the site. The Pond is surrounded by an existing chain-link fence that encapsulates about one half of the parcel’s area. Figure 3 shows a plan view of the Pond with publicly available GIS storm sewer and property information displayed. Springbrook Terrace Water Quality Retrofit Page 5 of 20 Final Design Report Figure 3. Plan View of Existing Site with GIS Information According to the City of Renton’s online GIS database, the project site does not contain wetlands nor other critical areas. However, the project parcel’s western boundary is the top of a regulated steep slope. The parcel is predominantly covered in lawn that is periodically maintained. There is typically very little vegetation on the site besides grass and Himalayan blackberries growing along the western edge of the city owned stormwater parcel. The parcel contains 5 trees which are all under 10 inches in diameter. The two existing soil types of the basin belong to hydrologic soil type B and are comprised of gravelly sandy loams. Springbrook Terrace Water Quality Retrofit Page 6 of 20 Final Design Report The existing Pond discharges to a 21-inch corrugated metal pipe (CMP) storm sewer pipe with an oil control separator and flow control restricting orifice located in the existing manhole at the northwest edge of the Pond. The effluent storm sewer pipe flows north to South 55th Street where it converges with an 18-inch reinforced concrete pipe (RCP) storm sewer system that flows west along South 192nd Street and south along Talbot Road South before discharging to Springbrook Creek. The Pond has two influent pipes, a 15-inch CMP in the southeast corner of the Pond and a 12-inch RCP on the north side of the Pond. The influent pipes to the Pond convey runoff from 98th Avenue South and 98th Place South. A small amount of flow contributes to the Pond from the lawns of the adjacent parcels to the east. Access to the site for construction, post construction monitoring, and maintenance is maintained by the approximate 15-foot-wide access easement on the adjacent parcels to the north and east (Parcel ID number 7941200010 and 7941200020) shown on the plan sheets contained in Appendix B. The access easement is located on a paved asphalt driveway, parking lot, and privately owned road which allow for vehicle and foot access to the site. This access easement also includes a portion of 98th Avenue South from South 55th Street to the driveway located in the access easement. Additional easements and land acquisition are not required for this project. No concerns were identified in the DOE cultural resources review (CRR) process initiated by the City of Renton in October 2023. In July 2024 the Washington State Department of Archaeology and Historic Preservation stated in their opinion that “no historic resources will be impacted by the current project as proposed” for the Springbrook Terrace Water Quality Retrofit project, and in August 2024 the comment period for the CRR ended without substantive comments signifying the low probability of encountering cultural resources. This project does not create environmental justice nor population concerns as the project is confined to a single city owned parcel and will improve downstream water quality. The existing and proposed site’s impervious land cover classification, for purposes of assessing applicable Minimum Requirements of the SWMMWW, is contained in Table 3 and shown in Appendix A where PGIS stands for pollution generating impervious surface. The existing project site is almost entirely pervious. The proposed project adds a gravel surface pond access road, quarry spall permanent erosion control, and an internal pond divider wall which are not considered hard surfaces in the impervious surface classification because they are essential to the function of and part of the stormwater BMP. The proposed project disturbs 6,828 square feet of soil as shown in Appendix A on the proposed conditions exhibit which encapsulates the ground disturbing proposed improvements to the site shown on the preliminary plan sheets in Appendix B. All 303 square feet of proposed impervious and PGIS surfaces of the project are due to the new gravel surface parking space added to the site. Springbrook Terrace Water Quality Retrofit Page 7 of 20 Final Design Report Table 3. Impervious Surface Classification Surface Type Area (Square Feet) Project Site/TDA 11,329 Existing Impervious Surface 4 Existing Pervious Surface 11,325 Proposed Impervious Surface 303 Proposed Pervious Surface 11,026 New Impervious Surface 303 Removed Impervious Surface 0 Replaced Impervious Surface 0 New PGIS 303 Replaced PGIS 0 The proposed site and stormwater improvements to the Pond are shown on the plan sheets in Appendix B. The Pond’s volume is increased by grading the interior of the pond to be wider and deeper. The existing storm sewer inlet on the north is reconfigured by connecting to the existing storm with a new manhole and installing a new pond inlet pipe about 4 feet east of the existing inlet pipe to accommodate the proposed wetpond design. An Ecoblock internal pond divider wall with a total height (measured to bottom of wall) of 8 feet and an exposed height (measured to finish grade) of 5.5 feet is proposed for most of the pond’s bottom length to achieve wetpond treatment design criteria. The pond’s storm sewer outlet is reconfigured by adding an additional manhole with a pond water surface elevation controlling effluent pipe invert and overflow capacity. The proposed outlet reconfiguration connects to the existing flow control manhole without altering the flow control properties of the existing structure. Other site improvements include adding a gravel surface pond access road and parking area as well as quarry spall pond inlet pipe protection and emergency spillway. Section 4.0 Minimum Requirements Figure I-3.1 in the SWMMWW, shown in Figure 4 below, was used to determine the minimum requirements (MR) for this project using the impervious surface classification in Table 3 and total project disturbance area stated in Section 3.0. MR 2 is the only minimum requirement that applies to the project per the flow chart in Figure 4. This project does not trigger compliance with or inclusion of MR 6 (Runoff Treatment) or MR 7 (Flow Control) standards due to the scope and size of the development described in Section 3.0 and evaluated in Figure 4. However, a runoff treatment benefit is proposed by this project even though it is not required by DOE and City of Renton development standards. The existing flow control function of the Pond is unaltered by this project and therefore retained and continues to meet the standard for flow control at the time of platting and permitting when the Pond was originally developed. This Springbrook Terrace Water Quality Retrofit Page 8 of 20 Final Design Report project is not required to and does not update the pond to meet current flow control standards. The portion of Minimum Requirement 2 that requires projects to create a Construction Stormwater Pollution Prevention Plan (C-SWPPP) does not apply since this project has less than 7,000 square feet of land disturbance and less than 2,000 square feet of new plus replaced hard surface. However, MR 2 states that all projects consider the 13 elements of a C-SWPPP and develop controls for all 13 elements that pertain to the project. See below for how the project addresses the 13 erosion and sediment control (ESC) elements of a C-SWPPP and Appendix B for the Erosion and Sediment Control plan demonstrating specifically how they are addressed on the project. Figure 4. SWMMWW Flow Chart for Determining Requirements for New Development Springbrook Terrace Water Quality Retrofit Page 9 of 20 Final Design Report ESC Element 1: Preserve Vegetation / Mark Clearing Limits The limits of work will be clearly delineated with silt fence and high visibility construction fence. To prevent and control erosion, as much existing vegetation as possible will be retained on the site. The contractor will be encouraged to complete final landscaping and planting work as early as feasible to aid in erosion prevention and control on the site. The project limits are required to be clearly marked prior to the start of work. BMPs will be installed in appropriate areas to ensure that turbid water does not leave work areas. BMPs Identified: • Preserving natural vegetation • High visibility construction fence • Silt fence ESC Element 2: Establish Construction Access A stabilized construction entrance is shown on the Erosion and Sediment Control (ESC) plan in Appendix B. The standard ESC notes in the plans require the contractor to sweep pavement daily, or more often if required, to remove sediment. If sediment transport becomes a problem, additional BMPs such as wheel washing may be used. BMPs Identified: • Stabilized construction access • Street sweeping • Wheel wash ESC Element 3: Control Flow Rates Risks associated with this element may include runoff volumes and velocities that cause erosive damage within the site or to downstream properties or waterways. The overland contributing slopes are generally moderately sloped and vegetated, and most of the site’s flow comes from two influent existing storm sewer pipes. The ESC plans for the project direct the contractor to stabilize exposed slopes with hydroseed and mulch and use additional BMPs as required per the site conditions to protect exposed soils from erosive flow rates. The ESC plans also contain a temporary sediment trap BMP and a pumping location to accommodate possible sediment laden flow before it is discharged downstream. BMPs Identified: • Sediment Trap • Check Dam • Wattles Springbrook Terrace Water Quality Retrofit Page 10 of 20 Final Design Report ESC Element 4: Install Sediment Controls Sediment controls will be installed prior to land disturbing activities on the site. Existing discharge locations will be maintained throughout the project. Discharge leaving the site is required to meet the turbidity and pH limits listed in the Washington State Construction Stormwater General Permit (CSGP). In the event of wet weather, additional BMPs may be utilized to reduce the transport of sediment. The sediment control BMPs may require regular maintenance to ensure continued functional performance. BMPs Identified: • Silt Fence • Sediment Trap • Check Dam • Wattles ESC Element 5: Stabilize Soils Work may occur during the wet and dry seasons, but it is anticipated that the entire project will be completed during the dry season. About 6,900 square feet of soil will be disturbed by this project. The disturbance will be limited to areas that are actively being worked. Unworked soil will be stabilized if it is to remain unworked for more than two days during the wet season and seven days during the dry season. Although the risk of destabilizing soil is low due to the soil type and limited steep slopes, several BMPs are suggested to the contractor to be used for stabilization including plastic sheeting, mulching, and temporary seeding if the site conditions require. The topography of the site does not create a high risk situation for slope destabilization due to minimizing cuts to steep slopes and since the proposed slopes are 3:1 (H:V) or less. The same conditions that apply to exposed soils and slopes apply to stockpiles of unworked materials on the site. Stockpiles often have steep slopes and can be a point source of pollution. Wattles along the base of the stockpiles should be used to contain sediment in addition to temporarily stabilizing unworked stockpiles with mulch or seed. Temporary seeding may only be effective when weather is conducive to germination and is not stabilizing on its own. If seeding is used, mulch mixed with the seed and fertilizer is considered to temporarily stabilize the soil until the vegetation establishes permanent stabilization. Dust can create water quality problems and health and safety concerns. BMPs such as applying water or mulch to reduce dust emissions may be used. Application of topsoil and hydroseed is the proposed restoration technique for final stabilization of soils and revegetation. BMPs Identified: • Temporary and permanent seeding • Mulching Springbrook Terrace Water Quality Retrofit Page 11 of 20 Final Design Report • Net and blankets • Plastic covering • Topsoiling • Dust control ESC Element 6: Protect Slopes Most of the proposed grading involves excavating the existing ground (cut condition). These slopes will be stabilized with hydroseed and mulch. It is not anticipated that concentrated runoff will flow to or on the existing or proposed slopes. Permanent quarry spall erosion control protection is proposed at each storm sewer pipe inlet to limit erosion near the toe of the slope. The ESC notes in the Appendix B plan set direct the contractor to use additional BMPs such as plastic sheeting, wattles, and temporary mulching to protect slopes as site conditions require. BMPs Identified: • Temporary and permanent seeding • Mulching • Net and blankets • Plastic covering ESC Element 7: Protect Storm Drain Inlets The existing and proposed storm sewer inlets within and adjacent to the project site will be protected with inlet protection BMPs for the duration of the project. BMPs Identified: • Inlet protection ESC Element 8: Stabilize Channels and Outlets Channels and outlet areas are exposed to concentrated flows which increase erosion related risks. Risks may include erosion within the channel or outlet areas and sediment pollution being discharged from the site. A sediment trap will be installed near the pond outlet or where needed during construction to reduce the transport of sediment. The contractor may utilize pumps to convey sediment ladened water (if encountered) to sediment traps or other BMPs to reduce flow rates such as check dams. The Pond’s influent storm sewer pipes’ outlets will be stabilized with permanent quarry spalls. Hydroseed and mulch will be used to stabilize existing and proposed flow paths. Due to the flat bottom of the pond and low anticipated flow rates, mulch and sediment traps will be sufficient to stabilize the soils within the flow paths of the pond. BMPs Identified: • Outlet protection Springbrook Terrace Water Quality Retrofit Page 12 of 20 Final Design Report • Temporary and permanent seeding • Mulching • Check dam • Nets and blankets ESC Element 9: Control Pollutants Risks associated with this element include the discharge of pollutants into stormwater and allowing it to discharge from the site. Pollutants, especially at outfall locations, must be sampled and tested in accordance with the CSGP. Because discharge sample locations are generally not known until construction begins, the sample locations must be added to the ESC plans once construction begins. If discharge locations change during construction, new sample locations will be created and added to the ESC plans. Potential pollutants that could be introduced by this project and how the risk will be mitigated include: • Vehicles, construction equipment, and/or petroleum product storage/dispensing: o All vehicles, equipment, and petroleum product storage/dispensing areas will be inspected regularly to detect any leaks or spills, and to identify maintenance needs to prevent leaks or spills. o On-site fueling tanks and petroleum product storage containers shall include secondary containment, which must be capable of containing 110 percent of the volume in the largest fuel tank. Double-walled tanks do not require additional containment. o Spill prevention measures, such as drip pans, will be used when conducting maintenance and repair of vehicles or equipment. o To perform emergency repairs on site, temporary plastic will be placed beneath and, if raining, over vehicles or equipment being repaired. o Contaminated surfaces shall be cleaned immediately following any discharge or spill incident. • Contamination of stormwater by pH-modifying sources: o Potential contaminated stormwater from pH-modifying sources includes bulk cement, cement kiln dust, fly ash, new concrete and cure water, rubble or waste stockpiles, and aggregate processes that include recycled concrete. Potentially pH affected stormwater must be sampled and potentially neutralized prior to discharge. Stormwater that mixes with cementitious/concrete wastewater is considered cementitious/concrete wastewater and must be managed to prevent discharge to waters of the State and groundwater. o pH affected and conditionally authorized non-stormwater sources must be sampled, and potentially neutralized and dechlorinated in accordance with the CSGP. • Concrete: Springbrook Terrace Water Quality Retrofit Page 13 of 20 Final Design Report o Concrete spillage and cementitious/concrete wastewater are prohibited to discharge to waters of the State. Do not dump excess concrete onsite, except in designated concrete washout facilities. Do not wash out concrete trucks or handling equipment onto ground, streets, into storm drains, or ditches. o Collect concrete slurry generated from cutting or grinding operations on a continual basis immediately and properly dispose of it. BMPs Identified: • Concrete handling • Sawcutting and surfacing pollution prevention • Material delivery, storage, and containment • Concrete washout area • Treatment and disposing of high pH water ESC Element 10: Control Dewatering Dewatering is not anticipated during the project. BMPs Identified: • Not applicable ESC Element 11: Maintain BMPs The ESC plans represent the minimum anticipated BMPs based on known existing and proposed site conditions. Following installation, the contractor is required to maintain, repair, or replace BMPs that are not functioning. In the event the BMPs are insufficient for site conditions, the contractor will install additional BMPs to manage erosion and sediment transport. Although all BMPs will require maintenance, it is anticipated that the proposed silt fence and sediment trap will likely require the most maintenance. BMPs Identified: • Materials on hand • Certified erosion and sediment control lead ESC Element 12: Manage the Project The contractor’s construction project manager will manage the project to comply with all ESC Plan and CSGP requirements. The construction project manager will consider construction phasing, seasonal work limitations, inspection, monitoring, and maintaining an updated ESC plan as described below. • Phasing of Work o The work will be conducted in a manner that reduces the extent of the disturbed areas and considers the weather and seasonal precipitation. Springbrook Terrace Water Quality Retrofit Page 14 of 20 Final Design Report o Following completion of the work, disturbed areas will be stabilized to prevent the transport of sediment from the site during construction. Timely stabilization of exposed areas is an integral part of ESC especially during the wet season. o Offsite work areas related to the project which are not currently known and may not be known to the project owner, must be managed to comply with ESC standards. • Inspection and Monitoring o All BMPs shall be inspected, maintained, and repaired as needed to assure continued performance of their intended function. Site inspections shall be conducted by a person who is knowledgeable in the principles and practices of erosion and sediment control. This person must have the following abilities: ▪ Assess the site conditions and construction activities that could impact stormwater quality. ▪ Assess the effectiveness of ESC measures used to control the quality of stormwater discharges. o A certified erosion and sediment control lead shall always be on-site or on-call. o Whenever inspection or monitoring reveals that the BMPs identified in the ESC plan are inadequate, due to the actual discharge of or potential to discharge a significant amount of any pollutant, appropriate BMPs or design changes will be implemented as soon as possible. o The contractor shall maintain an updated ESC plan throughout the project and always keep a copy of the documents available at the site. BMPs Identified: • Materials on hand • Certified erosion and sediment control lead • Scheduling ESC Element 13: Protect Low-Impact Development BMPs Low-impact BMPs are not anticipated to be used or required on this project. BMPs Identified: • Not applicable Section 5.0 Alternatives Considered In 2021 the City contracted with WSP Global Inc. to conduct an alternatives analysis for adding a runoff treatment benefit to existing flow control stormwater facilities by retrofitting facilities throughout the city. The 2021 WSP stormwater retrofit study developed a preliminary understanding of practical BMP types and sizes for existing city owned stormwater facilities Springbrook Terrace Water Quality Retrofit Page 15 of 20 Final Design Report while considering site-specific conditions such as available space, topography, conveyance capacity, and infiltration potential. The alternatives analysis considered wetpond, wet vaults, sandfilter vault, media filter vault, bioswale, filter strip, bioretention, and media filter drain BMPs to create a water quality benefit in the Pond. The existing Springbrook Terrace detention pond was one of 49 stormwater facilities evaluated by the retrofit study, and one of six stormwater facilities selected by the City in 2022 for conceptual design by WSP following a screening and ranking methodology applied to all 49 sites. The alternatives analysis study conducted by the City and WSP was reviewed and approved by DOE and meets the requirements for grant funding of the Springbrook Terrace water quality retrofit. This design report builds upon the previously completed alternatives analysis to design a practical water quality retrofit for the existing Springbrook Terrace detention pond. Of the BMP alternatives analyzed in the 2021 study, only wetpond and media filter vault were deemed as feasible options to retrofit the site for a water quality benefit as the site lacks generally lacks sufficient space to construct most other BMPs. The existing site lacks sufficient length to implement media filter drain, bioretention, filter strip, bioswale, sandfilter vault, and wet vault BMPs because an existing sanitary sewer service crossing the southern end of the pond and the need for an access road at a suitable grade on the northern end of the pond restricting the maximum BMP length to approximately 110 feet. A wetpond was chosen as the preferred alternative over a media filter vault because of the lower maintenance costs and greater reliability of an open space treatment system like a wetpond which can easily be inspected as compared to a proprietary media filter device in a vault that can have access restrictions due to the likelihood of being classified as a confined space. Although the soils of the project site may be suitable for an infiltration BMP from an infiltration capacity and depth to groundwater perspective and the alternatives analysis study completed in 2021 by WSP stated there was potential to use an infiltration BMP at the Springbrook Terrace site, the site is directly flanked on the west by a steep downward slope away from the project site that is greater than 50 percent grade and 12 feet in relief. According to the SWMMWW, infiltration BMPs are infeasible or inefficient when placed within 50 feet from the top of slopes in excess of 20 percent grade and more than 10 feet of relief. Therefore, infiltration BMPs are ruled out as feasible during final design due to the risk infiltration BMPs pose to steep slopes, and a wetpond was determined to be the most suitable treatment BMP for the site. Infiltration rate, cation exchange capacity, and percent organics of the existing soils were not examined because this project does not propose infiltration treatment nor flow control utilizing the infiltration capacity of the existing soils. Springbrook Terrace Water Quality Retrofit Page 16 of 20 Final Design Report Section 6.0 Design Analysis A basic wetpond BMP was designed per the DOE SWMMWW Section “BMP T10.10: Wetponds – Basic and Large” and the City of Renton’s Surface Water Design Manual (SWDM) Section “6.4.1 Wetponds - Basic and Large.” The basic wetpond design adds a water quality treatment benefit to the existing stormwater detention pond. A wetpond retains a permanent pool of water at least during the wet season to provide stormwater treatment. A low permeability compacted till liner is proposed to aid in the formation of a permanent pool of water within the pond due to the gravelly sandy loam soils of the existing site that would likely allow the ponded water to seep into the ground rendering the wetpond BMP ineffective. Infiltration rate, cation exchange capacity, and percent organics of the existing soils were not examined because a wetpond does not rely on infiltration for stormwater treatment. As described in Section 5.0, an infiltration BMP was deemed infeasible for the site due to the proximity of the project to steep slopes. Drawings of the proposed site improvements, section views of the pond, storm sewer details, and a schematic of flow through the facility are located within the plan sheets contained in Appendix B. The contributing basin to the wetpond is 6.64 acres in area and is shown in Figure 2 and described by Section 2.0. The soil type map in Appendix A shows that all soils of basin are hydrologic soil type B. The geotechnical borings which extend about 40 feet below the ground surface during the dry season did not encounter groundwater. The geotechnical report contained in Appendix E states that mottling of the existing soils about 15 feet below ground surface may provide evidence of seasonally high groundwater levels. A groundwater monitoring well was installed and will be monitored over the wet season to confirm the depth to seasonally high groundwater levels. It is presumed that groundwater levels will not affect the performance of the pond due to preliminary geotechnical recommendations, initial geotechnical observations of soils and groundwater levels at the site, and the position of this pond on a hill which will likely provide a preferred gradient for groundwater to flow rather than mound up near the bottom of the pond. Additional groundwater observation levels will be available in the final geotechnical report preceding 90 percent design to confirm this presumption. The geotechnical report does not examine infiltration capacity of the soil because the proposed BMP does not rely on infiltration. The Western Washington Hydrology Model (WWHM) was used to calculate the required water quality treatment volume and flow rate for on-line facilities. The WWHM output demonstrating the required water quality quantities and flow rates for standard recurrence intervals of the basin is contained in Appendix D. The WWHM model produced an on-line water quality volume of 0.3335 acre-feet (14,257 cubic feet), an on-line water quality (WQ) flow rate of 0.47 cubic feet per second (cfs), a 2-year peak flow rate of 1.15 cfs, a 25-year peak flow rate of 2.10 cfs, Springbrook Terrace Water Quality Retrofit Page 17 of 20 Final Design Report and a 100-year peak flow rate of 2.68 cfs for the proposed conditions land classification shown in Table 2. Only results from the mitigated scenario are relevant to the wetpond design, however the predeveloped scenario was populated with identical mitigated scenario parameters for the model to run. The current flow control capability of the Pond is not diminished by the proposed water quality retrofit because the project does not alter the existing flow control devices in the existing manhole located within the Pond (see Appendix B sheet C4). Additional flow control may be provided by this water quality retrofit project for storm events that occur early in the wet season when the pond’s water surface is below the WQ WSE due to the proposed excavation expanding the pond’s volume and the WQ water surface controlling effluent pipe invert both increasing storage volume of the pond before flow is discharged downstream. Any benefit to the current flow control capability of the Pond has not been quantified. AutoCAD Civil3D was used to evaluate the volume contained within the water quality surface elevation of the pond and the proposed grading. The water quality surface elevation of the pond was set to the maximum feasible elevation for the site at 189 feet. As shown on the plan sheets contained in Appendix B, the bottom elevation of the water quality portion of the wetpond is 184.75 feet, while the bottom of the pond is at an elevation of 184.25 feet with an average width of 2.2 feet. This creates a wetpond BMP 4.25 feet deep with a sediment storage depth of 0.50 feet. The volume between the proposed grading surface and elevation 189 feet exclusive of the proposed Ecoblock internal pond divider wall and sediment storage volumes is 6,846 cubic feet (CF). The pond’s outlet pipe has a water surface controlling invert elevation of 189 feet, as shown on the plans in Appendix B, that creates a ponded surface (dead storage). Water surface elevations (WSE) were calculated for the WQ (0.47 cfs), 2-year (1.15 cfs), and the 100-year (2.68 cfs) flow events to determine the minimum elevations of the overflow opening, top of the Ecoblock internal pond divider wall, and the emergency overflow spillway respectively. The calculated WQ WSE is 189.39 feet and was determined according to the outlined process in the SWDM Sections 6.4.1.1 and 6.4.1.2. Computation output from the Microsoft Excel spreadsheet used to iteratively calculate the WQ WSE is contained in Appendix D. The WQ WSE calculation adds the critical depth and velocity head to the invert of the pond outlet pipe to determine the WQ WSE. The 2-year and 100-year WSE are determined using Autodesk Storm and Sanitary Analysis 2023 (SSA) hydraulic modeling software to analyze the simultaneous flows through the pond’s outlet pipe and overflow weir. The outlet pipe is modeled as a side orifice and the overflow opening is modeled as a sharp-crested contracted rectangular weir. Constant 2-year and 100-year inflows Springbrook Terrace Water Quality Retrofit Page 18 of 20 Final Design Report are applied to the input junctions shown in Appendix D SSA schematic layout. The flow enters two conveyance links; the 12-inch-diameter orifice representing the outlet pipe and a weir representing the overflow inlet in the proposed storm sewer structure SDCB #4. After flow passes through the orifice and weir hydraulic controls in the SSA model, the model features are fabricated to discharge the flow out of the model without affecting the hydraulics of the orifice and weir but do not represent actual project features downstream of the orifice and weir. The SSA model output and supplemental SSA design information are contained in Appendix D and show that the maximum WSE during the 2-year event is 189.48 feet while the 100-year event has a maximum WSE of 189.65 feet. Therefore, the internal pond Ecoblock divider wall must extend at least to an elevation of 189.48 feet and the emergency spillway invert elevation must be 189.65 feet to pass flows greater than the 100-year event. For constructability purposes the Ecoblock divider wall top elevation is 189.75 feet exceeding the minimum calculated elevation. The emergency spillway’s 100-year flow depth assuming all other outlets of the pond are completely blocked is 0.20 feet as calculated in accordance with SWDM Section 5.1.1.2. The iteratively calculating spreadsheet used to determine the emergency spillway flow depth is contained in Appendix D. The water surface elevation of the 100-year event passing through the emergency spillway assuming all other pond outlets are blocked is 189.85 feet. The water quality flowpath length to flowpath width ratio measurements and calculations are documented in a figure within the plan sheets in Appendix B. An Ecoblock wall is proposed within the pond to increase the flowpath length of the influent flow from the northern pond inlet storm sewer pipe. The flowpaths were divided into 5 segments where flowpath length at WQ mid-depth (elevation 186.88 feet), WQ pond average bottom width (elevation 184.75 feet), and WQ pond average top width (elevation 189.00 feet) were measured in accordance with SWDM and SWMMWW guidance. The proposed pond has a WQ flowpath length to width ratio of 5.5 based on the measurements and length-weighting calculations shown in Appendix B. This WQ flowpath length to width ratio exceeds the DOE preferred ratio of 5 and required ratio of 4 for single cell wetponds. The project proposes one storm sewer pipe for conveyance purposes which is a 15-inch- diamater polypropylene (PP) pipe downstream of SDCB #4 shown on the Site Plan in Appendix B. The conveyance capacity of this pipe and the existing downstream 21-inch-diameter CMP were evaluated using Manning’s equation and performing a spreadsheet-based Backwater Analysis in accordance with SWDM Section 4.2.1.2. The uniform flow analysis using Manning’s equation contained in Appendix D shows that the proposed 15-inch-diamater PP pipe and existing 21-inch-diameter CMP have conveyance capacities of 7.85 cfs and 5.90 cfs respectively. The calculated conveyance capacities demonstrate compliance with COR pipe design standards Springbrook Terrace Water Quality Retrofit Page 19 of 20 Final Design Report since the pipes contain the 2.10 cfs 25-year event and prevent the 2.68 cfs 100-year design flow event from surcharging the structure and creating flooding or erosion problems. The surcharging of storm sewer structures was further evaluated using a Backwater Analysis presented in Appendix D to calculate hydraulic grade line elevations. The Backwater Analysis starts by calculating a tailwater elevation of the existing downstream pipe to be used in the existing downstream pipe’s headwater elevation calculation. The greater of downstream pipe’s calculated headwater elevation and the upstream proposed pipe’s calculated tailwater elevation is used as the prevailing tailwater elevation for the upstream proposed pipe. In this case the downstream pipe’s headwater elevation was not hydraulically controlling the upstream proposed pipe during the 25- or 100-year events. The Backwater Analysis shows maximum headwater depths for both pipes during both the 25-year and 100-year events ranges from approximately 0.7 feet to 1 foot demonstrating that the hydraulic grade line is well within the 15-inch-diameter and 21-inch-diameter pipes. The results of the conveyance analysis meet expectations because this project does not meaningfully increase flow rates to the existing storm sewer system. Section 7.0 Quantify the Water Quality Benefit The current level of design provides a water quality wetpond volume for runoff treatment of 6,846 CF. Complete or 100 percent runoff treatment of the Pond’s 6.64-acre watershed according to the WWHM scenario described in Section 6.0 and contained in Appendix D requires 14,527 CF of wetpond volume. Therefore, the proposed project’s current level of design achieves 47 percent of the DOE runoff treatment standard which provides complete runoff treatment for an equivalent developed area of 3.1 acres. Section 8.0 Engineer’s Opinion of Probable Cost The engineer’s opinion of probable cost for the construction project is $392,484. Of the total probable cost, all $392,484 in anticipated project construction costs are deemed eligible for DOE funding. A detailed breakdown of the anticipated project cost by bid item, quantity, and eligibility for DOE funding is contained in Appendix C. Section 9.0 Proposed Schedule The proposed schedule including all design and construction milestones is contained in Appendix F. The design of the project is expected to be completed by November 2025, with construction starting around April 2026 and ending near October 2026. More specifically, 60 percent design is expected to be completed in April 2025, 90 percent design completion is anticipated in September 2025, and 100 percent design will be completed in October 2025. The Springbrook Terrace Water Quality Retrofit Page 20 of 20 Final Design Report creation of final bid documents, announcement of bid documents, and construction contracting are expected to occur from November 2025 to January 2026. Section 10.0 References WSP, 2021. Stormwater Facility Retrofit Study - Identify Stormwater Retrofit Locations (Task 4 Effort). City of Renton, Washington. WSP, 2022. Stormwater Facility Retrofit Study - Retrofit Project Selection and Concept Design (Task 6 Effort). City of Renton, Washington. Springbrook Terrace Water Quality Retrofit Final Design Report Springbrook Terrace Water Quality Retrofit Final Design Report Appendix A - Maps 9 8 t h P l S S 55th St 99 t h P l S 9 8 t h A v e S 100 ft LEGEND Watershed Boundary Parcel Boundary Geologic Unit - AgC Alderwood Gravelly Sandy Loam (Hydrologic Soil Group B) Geologic Unit - AkF Alderwood and Kitsap Soils (Hydrologic Soil Group B) Project Site and TDA Existing and Proposed Flow Direction Watershed and Soil Type Map SS ( R ) SS SS SS SS SS SS SS SS SS SD SD SD SD SD SD SD SD SD SD SD S D S D S D SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD G P P P P P P T T T T T T T T x x x x x x x x x x x x xxxxxxxx x x x x x x x x x x x x x x x x x TV TV TV W W W W W W W W G G G TV T P P P P TV TV TV TV T T T T T T P P P P P P Px x x x x x x x x x x xxx W W S S SD D 187 190 195 200 190 185 205 185 190 185 185 190 195 200 ECOBLOCK WALL Sa v e D a t e : Plo t D a t e : 5/ 2 7 / 2 0 2 5 3 : 5 1 P M 5/ 2 7 / 2 0 2 5 3 : 5 2 P M By : Cg b P:\ R \ R E N T 0 0 0 0 1 9 0 3 \ 0 4 0 0 C A D \ W A \ E X H I B I T S \ P r o p o s e d C o n d i t i o n s E x h i b i t . d w g Ch a d B o o t h By : Fil e : SHEET NO. DATE:REVIEWED BY: DATENO.REVISION CKBY FILE NO. PROJECT NO.QTR: SEC: TWP: RGE: DATUM: HOR: VERT: CHECKED BY: DESIGNED BY: DRAWN BY: ® 14432 SE Eastgate Way Suite 400 Bellevue, WA 98007 Phone: 425.519.6500 Final Design Report Submittal CITY OF RENTON, WASHINGTON Springbrook Terrace Water Quality Retrofit CAG-24-081 RENT00001903 NAD 83 WA S.P. N NAVD 88 NE 06 22N 5E ASR CGB WDM NOT FOR CONSTRUCTION PROPOSED CONDITIONS EXHIBIT EXHIBIT Feet 0 20 40 98TH A V E S 3:1 3: 1 3:1 6:1 SITE PLAN LEGEND PROPOSED CHAIN LINK FENCE POND ACCESS ROAD CHAIN LINK FENCE GATE PROJECT SITE AND TDA BOUNDARY (11,329 SF) EXISTING MAJOR CONTOUR EXISTING MINOR CONTOUR PROPOSED MAJOR CONTOUR PROPOSED MINOR CONTOUR PROPOSED STORM SEWER STRUCTURE PROPOSED STORM SEWER PIPE QUARRY SPALLS FOR PERMANENT EROSION CONTROL GROUNDWATER MONITORING WELL GRAVEL PARKING AREA SURFACE COVER LEGEND PROPOSED IMPERVIOUS SURFACE (303 SF) PROPOSED POLLUTION GENERATING IMPERVIOUS SURFACE [PGIS] (303 SF) EXISTING IMPERVIOUS SURFACE (4 SF) DISTURBANCE LIMITS (6,828 SF) FLOW DIRECTION 4 SF OF EXISTING IMPERVIOUS SURFACE ACCESS EASEMENT NOTE: AREAS NOT HATCHED WITHIN PROJECT SITE ARE PROPOSED PERVIOUS SURFACES OR HARD SURFACES REQUIRED FOR STORMWATER BMP FUNCTION. POND BOTTOM EL. 184.25 Springbrook Terrace Water Quality Retrofit Final Design Report Springbrook Terrace Water Quality Retrofit Final Design Report Appendix B – Preliminary Plan Sheets DEA PROJECT ID RENT00001903 SPRINGBROOK TERRACE WATER QUALITY RETROFIT CAG-24-081 CITY OF RENTON Sa v e D a t e : Plo t D a t e : 3/ 2 8 / 2 0 2 5 1 1 : 3 8 A M 3/ 2 8 / 2 0 2 5 1 1 : 3 9 A M By : Cg b P:\ R \ R E N T 0 0 0 0 1 9 0 3 \ 0 4 0 0 C A D \ W A \ S H E E T S \ E C - G N - R E N T 1 9 0 3 . d w g Ch a d B o o t h By : Fil e : SHEET NO. DATE:REVIEWED BY: DATENO.REVISION CKBY FILE NO. PROJECT NO.SEC: TWP: RGE: DATUM: HOR: VERT: CHECKED BY: DESIGNED BY: DRAWN BY: ® 14432 SE Eastgate Way Suite 400 Bellevue, WA 98007 Phone: 425.519.6500 Ecology Design Report Submittal CITY OF RENTON, WASHINGTON Springbrook Terrace Water Quality Retrofit CAG-24-081 RENT00001903 NAD 83 WA S.P. N NAVD 88 06 22N 5E ASR CGB WDM NOT FOR CONSTRUCTION COVER SHEET INDEX OF SHEETS SHEET NUMBER DESCRIPTION G1 COVER SHEET G2 LEGEND AND ABBREVIATIONS G3 GENERAL NOTES G4 STANDARD ESC NOTES C1 EXISTING CONDITIONS C2 ESC AND DEMOLITION PLAN & DETAILS C3 SITE PLAN C4 DRAINAGE DETAILS AND SECTIONS C5 MISC. CIVIL DETAILS (SHEET 1 OF 2) C6 MISC. CIVIL DETAILS (SHEET 2 OF 2) C7 SURVEY, HORIZONTAL CONTROL, AND SITE ACCESS PLAN G1 APRIL, 2025 Not to Scale PROJECT LOCATION VICINITY MAP Final Design ReSoUt SubPittal Sa v e D a t e : Plo t D a t e : 3/ 2 8 / 2 0 2 5 1 1 : 3 8 A M 3/ 2 8 / 2 0 2 5 1 1 : 3 9 A M By : Cg b P:\ R \ R E N T 0 0 0 0 1 9 0 3 \ 0 4 0 0 C A D \ W A \ S H E E T S \ E C - G N - R E N T 1 9 0 3 . d w g Ch a d B o o t h By : Fil e : SHEET NO. DATE:REVIEWED BY: DATENO.REVISION CKBY FILE NO. PROJECT NO.SEC: TWP: RGE: DATUM: HOR: VERT: CHECKED BY: DESIGNED BY: DRAWN BY: ® 14432 SE Eastgate Way Suite 400 Bellevue, WA 98007 Phone: 425.519.6500 Ecology Design Report Submittal CITY OF RENTON, WASHINGTON Springbrook Terrace Water Quality Retrofit CAG-24-081 RENT00001903 NAD 83 WA S.P. N NAVD 88 06 22N 5E ASR CGB WDM NOT FOR CONSTRUCTION LEGEND AND ABBREVIATIONS G2 EXISTING LEGEND EDGE OF PAVEMENTEP INVERT ELEVATIONIE ASPHALTASPH CURB AND GUTTER CHAIN LINK FENCE CMP CG CLF CONCRETE CULVERT CONCRETE SIDEWALKCW CPP CONC CULV CORRUGATED PLASTIC PIPE CORRUGATED METAL PIPE DRIVEWAY ECC DW EXTRUDED CONCRETE CURB CATCH BASINCB PVC PA RCP TOE TOP WDF WOOD FENCE TOE OF SLOPE TOP OF SLOPE REINFORCED CONCRETE PIPE PLANTED AREA POLYVINYL CHLORIDE PIPE EASEMENT LINE PROPERTY LINE EXISTING RIGHT-OF-WAY LINE FENCE LINE (TYPE AS NOTED) BUILDING OVERHANG BUILDING LINE VEGETATION/BRUSH LINE EXISTING RIGHT-OF-WAY CENTER LINE BUSH TELEPHONE RISERTJR SIGN LIGHT POLE WITH ARM POST OR BOLLARD MAILBOX DECIDUOUS TREE CONIFEROUS TREE WATER VALVE WATER METER STORM DRAIN MANHOLE STORM CATCH BASIN SEWER MANHOLE POWER VAULT POWER CABINET POWER TRANSFORMER GAS VALVE STORM CULVERT END WATER BLOW-OFF S D P P GV WM WV CABLE TV LINETVTV NATURAL GAS PIPEGG POWER LINEPP SANITARY SEWER PIPESSSS STORM SEWER PIPESDSD TELEPHONE LINETT WATER PIPEWW ECB CEDARC ALDERA MAPLEM LAURELLL ROCKERY TAX LOT / PARCEL NUMBER0123456789 MONUMENT (FOUND AS NOTED) CABLE TV RISERTVR CITY OF RENTONCOR STANDARDSTD POINTPT ELEVATIONEL SANITARY SEWER PIPE FROM RECORD DRAWINGSS(R)SS(R) WATER SURFACE ELEVATIONWSE ACCESS EASEMENT x x Final Design ReSoUt SubPittal Sa v e D a t e : Plo t D a t e : 3/ 2 8 / 2 0 2 5 1 1 : 3 8 A M 3/ 2 8 / 2 0 2 5 1 1 : 3 9 A M By : Cg b P:\ R \ R E N T 0 0 0 0 1 9 0 3 \ 0 4 0 0 C A D \ W A \ S H E E T S \ E C - G N - R E N T 1 9 0 3 . d w g Ch a d B o o t h By : Fil e : SHEET NO. DATE:REVIEWED BY: DATENO.REVISION CKBY FILE NO. PROJECT NO.SEC: TWP: RGE: DATUM: HOR: VERT: CHECKED BY: DESIGNED BY: DRAWN BY: ® 14432 SE Eastgate Way Suite 400 Bellevue, WA 98007 Phone: 425.519.6500 Ecology Design Report Submittal CITY OF RENTON, WASHINGTON Springbrook Terrace Water Quality Retrofit CAG-24-081 RENT00001903 NAD 83 WA S.P. N NAVD 88 06 22N 5E ASR CGB WDM NOT FOR CONSTRUCTION GENERAL NOTES G3 GENERAL NOTES: 1.ALL WORK SHALL BE PERFORMED IN ACCORDANCE WITH APPLICABLE LOCAL, STATE, AND FEDERAL LAWS. 2.ALL WORK AND MATERIALS SHALL BE IN ACCORDANCE WITH THE CITY OF RENTON STANDARDS AND SPECIFICATIONS AND WASHINGTON STATE DEPARTMENT OF TRANSPORTATION "STANDARD SPECIFICATIONS FOR ROAD, BRIDGE, AND MUNICIPAL CONSTRUCTION", 2025 AND AS AMENDED BY THE CITY OF RENTON SUPPLEMENTAL SPECIFICATIONS AND THE CONTRACT SPECIAL PROVISIONS. 3.ALL WORK SHALL BE SUBJECT TO THE INSPECTION OF THE CITY ENGINEER OR DESIGNATED REPRESENTATIVE. 4.A COPY OF THESE APPROVED PLANS AND PROJECT SPECIFICATIONS MUST BE ON THE SITE WHENEVER CONSTRUCTION IS IN PROGRESS. 5.THE CONTRACTOR SHALL COMPLY WITH ALL PERMITS AND ALL OTHER REQUIREMENTS BY THE CITY OF RENTON. SEE APPROVED PERMITS AND PERMIT REQUIREMENTS IN THE PROJECT SPECIFICATIONS. 6.CONTRACTOR SHALL BE RESPONSIBLE FOR PREPARATION OF ALL TRAFFIC CONTROL PLANS. CONTRACTOR SHALL SUBMIT PLANS TO THE ENGINEER FOR APPROVAL PRIOR TO THEIR IMPLEMENTATION. SEE TRAFFIC CONTROL REQUIREMENTS IN SECTION 1-10 OF THE SPECIAL PROVISIONS. 7.SEE THE "STANDARD" DETAILS SECTION OF THE PROJECT SPECIFICATIONS FOR REFERENCED CITY OF RENTON (COR) STANDARD DETAILS AND REFERENCE WASHINGTON STATE DEPARTMENT OF TRANSPORTATION (WSDOT) STANDARD DETAILS. 8.NO STAGING AREA IS PROVIDED TO THE CONTRACTOR. ALL STAGING AREAS SHALL BE ON A CONTRACTOR SECURED AREA. ALL ESC REQUIREMENTS SHALL APPLY TO ALL STAGING AREAS. 9.THE LOCATIONS OF ALL EXISTING UTILITIES SHOWN HEREON HAVE BEEN ESTABLISHED BY FIELD SURVEY OR OBTAINED FROM AVAILABLE RECORDS AND SHALL THEREFORE BE CONSIDERED APPROXIMATE ONLY AND NOT NECESSARILY COMPLETE. IT IS THE SOLE RESPONSIBILITY OF THE CONTRACTOR TO INDEPENDENTLY VERIFY THE ACCURACY OF ALL UTILITY LOCATIONS SHOWN, AND TO FURTHER DISCOVER AND AVOID ANY OTHER UTILITIES NOT SHOWN HEREON THAT MAY BE AFFECTED BY THE IMPLEMENTATION OF THIS PLAN. 10.STORM SEWER LENGTHS ARE MEASURED BETWEEN CENTERS OF MANHOLES AND CATCH BASINS UNLESS OTHERWISE NOTED. 11.ALL UTILITY TRENCH BACKFILL AND ROADWAY SUBGRADE SHALL BE COMPACTED TO 95% MAXIMUM DRY DENSITY PER SECTION 2-03.3(14)D - COMPACTION AND MOISTURE CONTROL TESTS OF THE WSDOT STANDARD SPECIFICATIONS. IN PERMEABLE PAVEMENT AND OTHER INFILTRATION AREAS, ALL TRENCH BACKFILL SHALL BE FIRM AND UNYIELDING BUT IN NO CASE SHALL BE COMPACTED TO MORE THAN 92% OF MAXIMUM DRY DENSITY. 12.ALL PIPE AND STRUCTURES SHALL BE STAKED FOR SURVEY LINE AND GRADE PRIOR TO THE START OF CONSTRUCTION. WHERE SHOWN ON THE PLANS OR WHERE DIRECTED BY THE CITY, THE EXISTING MANHOLES, CATCH BASINS, OR INLETS SHALL BE ADJUSTED TO THE GRADE AS STAKED. 13.ALL PIPE AND APPURTENANCES SHALL BE LAID ON A PROPERLY PREPARED FOUNDATION IN ACCORDANCE WITH THE CURRENT STATE OF WASHINGTON STANDARD SPECIFICATION FOR ROAD AND BRIDGE CONSTRUCTION. THIS SHALL INCLUDE NECESSARY LEVELING OF THE TRENCH BOTTOM OR THE TOP OF THE FOUNDATION MATERIAL, AS WELL AS PLACEMENT AND COMPACTION OF REQUIRED BEDDING MATERIAL TO UNIFORM GRADE SO THAT THE ENTIRE LENGTH OF THE PIPE WILL BE SUPPORTED ON A UNIFORMLY DENSE, UNYIELDING BASE. ALL PIPE BEDDING AND BACKFILL SHALL BE AS SHOWN ON THE CITY STANDARD PLAN 220.00, 220.10, AND 220.20. 14.STEEL PIPE SHALL BE ALUMINIZED, OR GALVANIZED WITH ASPHALT TREATMENT 1, 2, OR 5 INSIDE AND OUTSIDE. 15.ALL DRAINAGE STRUCTURES SUCH AS CATCH BASINS AND MANHOLES SHALL BE FITTED WITH DUCTILE IRON, BOLT-LOCKING LIDS PER THE CITY STANDARD PLAN 204.10, 204.20, 204.30, 204.40, AND 204.50. STRUCTURES SHALL HAVE: ·RECTANGULAR OR ROUND, SOLID LIDS WHEN NOT COLLECTING RUNOFF, AND OUTSIDE OF THE ROADWAY. ·ROUND, SOLID LIDS DISPLAYING THE CITY LOGO WHEN WITHIN THE PUBLIC RIGHT-OF-WAY OR IN AN EASEMENT TO THE CITY. 16.THE END OF EACH STORM DRAIN STUB SHALL BE CAPPED. A CLEANOUT TOPPED WITH A BOLT- LOCKING LID MARKED "STORM” OR "DRAIN" SHALL BE LOCATED AT THE PROPERTY LINE OR AT THE POINT OF CONNECTION OF A PRIVATE STORM DRAINAGE CONVEYANCE SYSTEM PER THE CITY STANDARD PLAN 227.00. 17.ALL STORM SYSTEM EXTENSIONS SHALL BE STAKED FOR LINE AND GRADE BY A SURVEYOR LICENSED IN WASHINGTON STATE, AND CUT SHEETS SHALL BE PROVIDED TO THE CITY PRIOR TO CONSTRUCTION. 18.ALL NEWLY-INSTALLED AND NEWLY-REHABILITATED (PUBLIC AND PRIVATE) STORM CONVEYANCE SYSTEMS SHALL BE INSPECTED BY MEANS OF REMOTE CCTV ACCORDING TO THE CITY STANDARD PLAN 266.00. CCTV INSPECTIONS AND REPORTS SHALL BE SUBMITTED TO THE CITY PRIOR TO RECEIVING APPROVAL TO INSTALL PROJECT CURBS, GUTTERS AND/OR PAVEMENT. 19.ALL STORM SYSTEMS AND CONNECTIONS TO EXISTING MAINS SHALL BE TESTED IN ACCORDANCE WITH SECTION 7-04.3(1) OF THE WSDOT STANDARD SPECIFICATIONS AND IN THE PRESENCE OF A REPRESENTATIVE OF THE CITY. STORM DRAIN STUBS SHALL BE TESTED FOR ACCEPTANCE AT THE SAME TIME THE MAIN STORM IS TESTED. 20.FOR ALL DISTURBED PERVIOUS AREAS (COMPACTED, GRADED, LANDSCAPED, ETC.) OF THE DEVELOPMENT SITE, TO MAINTAIN THE MOISTURE CAPACITY OF THE SOIL EITHER STOCKPILE AND REDISTRIBUTE THE EXISTING DUFF LAYER AND NATIVE TOPSOIL OR AMEND THE SOIL WITH COMPOST IN ACCORDANCE WITH STANDARD PLAN 264.00. 21.ADEQUATE SAFEGUARDS, SAFETY DEVICES, PROTECTIVE EQUIPMENT, FLAGGERS, AND ANY OTHER ACTIONS NEEDED TO PROTECT THE LIFE, HEALTH, AND SAFETY OF THE PUBLIC, AND TO PROTECT PROPERTY IN CONNECTION WITH THE PERFORMANCE OF WORK SHALL BE PROVIDED. ANY WORK WITHIN THE TRAVELED RIGHT-OF-WAY THAT MAY INTERRUPT NORMAL TRAFFIC FLOW SHALL REQUIRE A TRAFFIC CONTROL PLAN APPROVED BY THE CITY. ALL SECTIONS OF THE WSDOT STANDARD SPECIFICATIONS 1-10 TEMPORARY TRAFFIC CONTROL SHALL APPLY. 22.MINIMUM COVER OVER STORM DRAINAGE PIPE SHALL CONFORM TO TABLE 4.2.1.A2 OF THE RENTON SWDM. 23.CONTRACTOR SHALL PROVIDE CONTINUOUS ACCESS WITHIN THE ACCESS EASEMENT SHOWN ON SHEET C1 IN ACCORDANCE WITH TEMPORARY TRAFFIC CONTROL SPECIAL PROVISION 1-10.2(1). Final Design ReSoUt SubPittal Sa v e D a t e : Plo t D a t e : 3/ 2 8 / 2 0 2 5 1 1 : 3 8 A M 3/ 2 8 / 2 0 2 5 1 1 : 3 9 A M By : Cg b P:\ R \ R E N T 0 0 0 0 1 9 0 3 \ 0 4 0 0 C A D \ W A \ S H E E T S \ E C - G N - R E N T 1 9 0 3 . d w g Ch a d B o o t h By : Fil e : SHEET NO. DATE:REVIEWED BY: DATENO.REVISION CKBY FILE NO. PROJECT NO.SEC: TWP: RGE: DATUM: HOR: VERT: CHECKED BY: DESIGNED BY: DRAWN BY: ® 14432 SE Eastgate Way Suite 400 Bellevue, WA 98007 Phone: 425.519.6500 Ecology Design Report Submittal CITY OF RENTON, WASHINGTON Springbrook Terrace Water Quality Retrofit CAG-24-081 RENT00001903 NAD 83 WA S.P. N NAVD 88 06 22N 5E ASR CGB WDM NOT FOR CONSTRUCTION STANDARD ESC NOTES G4 STANDARD EROSION AND SEDIMENT CONTROL (ESC) NOTES: 1.THE BOUNDARIES OF THE CLEARING LIMITS, SENSITIVE AREAS AND THEIR BUFFERS, AND AREAS OF VEGETATION PRESERVATION AND TREE RETENTION AS PRESCRIBED ON THE PLAN(S) SHALL BE CLEARLY DELINEATED BY FENCING AND PROTECTED IN THE FIELD IN ACCORDANCE WITH APPENDIX D OF THE CITY OF RENTON SURFACE WATER DESIGN MANUAL (RENTON SWDM) PRIOR TO THE START OF CONSTRUCTION. DURING THE CONSTRUCTION PERIOD, NO DISTURBANCE BEYOND THE CLEARING LIMITS SHALL BE PERMITTED. THE CLEARING LIMITS SHALL BE MAINTAINED BY THE APPLICANT/ ESC SUPERVISOR FOR THE DURATION OF CONSTRUCTION. 2.STABILIZED CONSTRUCTION ENTRANCES SHALL BE INSTALLED AT THE BEGINNING OF CONSTRUCTION AND MAINTAINED FOR THE DURATION OF THE PROJECT. ADDITIONAL MEASURES, SUCH AS CONSTRUCTED WHEEL WASH SYSTEMS OR WASH PADS, MAY BE REQUIRED TO ENSURE THAT ALL PAVED AREAS ARE KEPT CLEAN AND TRACK-OUT TO PAVED AREAS DOES NOT OCCUR FOR THE DURATION OF THE PROJECT. IF SEDIMENT IS TRACKED OFFSITE, PAVED AREAS SHALL BE CLEANED THOROUGHLY AT THE END OF EACH DAY, OR MORE FREQUENTLY DURING WET WEATHER, AS NECESSARY TO PREVENT SEDIMENT FROM ENTERING WATERS OF THE STATE. 3.WASHOUT OF CONCRETE TRUCKS SHALL BE PERFORMED OFF-SITE OR IN DESIGNATED CONCRETE WASHOUT AREAS ONLY. DO NOT WASH OUT CONCRETE TRUCKS ONTO THE GROUND, INTO STORM DRAINS, OR OPEN DITCHES. ON- SITE DUMPING OF EXCESS CONCRETE SHALL ONLY OCCUR IN DESIGNATED CONCRETE WASHOUT AREAS. 4.ALL REQUIRED ESC BMPS SHALL BE CONSTRUCTED AND IN OPERATION PRIOR TO LAND CLEARING AND/OR CONSTRUCTION TO PREVENT TRANSPORTATION OF SEDIMENT TO SURFACE WATER, DRAINAGE SYSTEMS AND ADJACENT PROPERTIES. ALL ESC BMPS SHALL BE MAINTAINED IN A SATISFACTORY CONDITION UNTIL SUCH TIME THAT CLEARING AND/OR CONSTRUCTION IS COMPLETE AND POTENTIAL FOR ON-SITE EROSION HAS PASSED. ALL ESC BMPS SHALL BE REMOVED AFTER CONSTRUCTION IS COMPLETED AND THE SITE HAS BEEN STABILIZED TO ENSURE POTENTIAL FOR ON-SITE EROSION DOES NOT EXIST. THE IMPLEMENTATION, MAINTENANCE, REPLACEMENT, ENHANCEMENT, AND REMOVAL OF ESC BMPS SHALL BE THE RESPONSIBILITY OF THE APPLICANT. 5.ANY HAZARDOUS MATERIALS OR LIQUID PRODUCTS THAT HAVE THE POTENTIAL TO POLLUTE RUNOFF SHALL BE DISPOSED OF PROPERLY. 6.THE ESC BMPS DEPICTED ON THIS DRAWING ARE INTENDED TO BE MINIMUM REQUIREMENTS TO MEET ANTICIPATED SITE CONDITIONS. AS CONSTRUCTION PROGRESSES AND UNEXPECTED OR SEASONAL CONDITIONS DICTATE, THE CONTRACTOR SHALL ANTICIPATE THAT MORE ESC BMPS WILL BE NECESSARY TO ENSURE COMPLETE SILTATION CONTROL ON THE PROPOSED SITE. DURING THE COURSE OF CONSTRUCTION, IT SHALL BE THE OBLIGATION AND RESPONSIBILITY OF THE CONTRACTOR TO ADDRESS ANY NEW CONDITIONS THAT MAY BE CREATED BY THE ACTIVITIES AND TO PROVIDE ADDITIONAL ESC BMPS, OVER AND ABOVE MINIMUM REQUIREMENTS, AS MAY BE NEEDED, TO PROTECT ADJACENT PROPERTIES AND WATER QUALITY OF THE RECEIVING DRAINAGE SYSTEM. 7.ANY AREAS OF EXPOSED SOILS, INCLUDING ROADWAY EMBANKMENTS, THAT WILL NOT BE DISTURBED FOR TWO DAYS DURING THE WET SEASON (OCTOBER 1ST THROUGH APRIL 30TH) OR SEVEN DAYS DURING THE DRY SEASON ( MAY 1ST THROUGH SEPTEMBER 30TH) SHALL BE IMMEDIATELY STABILIZED WITH THE APPROVED ESC COVER METHODS (E.G., SEEDING, MULCHING, PLASTIC COVERING, ETC.) IN CONFORMANCE WITH APPENDIX D OF THE RENTON SWDM. 8.WET SEASON ESC REQUIREMENTS APPLY TO ALL CONSTRUCTION SITES BETWEEN OCTOBER 1ST AND APRIL 30TH, UNLESS OTHERWISE APPROVED BY THE CITY. 9.ANY AREA NEEDING ADDITIONAL ESC MEASURES, NOT REQUIRING IMMEDIATE ATTENTION, SHALL BE ADDRESSED WITHIN SEVEN (7) DAYS. 10.THE ESC BMPS ON INACTIVE SITES SHALL BE INSPECTED AND MAINTAINED AT A MINIMUM OF ONCE A MONTH OR WITHIN 24 HOURS FOLLOWING A STORM EVENT. INSPECTION AND MAINTENANCE SHALL OCCUR MORE FREQUENTLY AS REQUIRED BY THE CITY. 11.BEFORE COMMENCEMENT OF ANY CONSTRUCTION ACTIVITY, CATCH BASIN INSERTS PER THE CITY STANDARD PLAN 216.30 SHALL BE PROVIDED FOR ALL STORM DRAIN INLETS DOWNSLOPE AND WITHIN 500 FEET OF A DISTURBED OR CONSTRUCTION AREA, UNLESS THE RUNOFF THAT ENTERS THE INLET WILL BE CONVEYED TO A SEDIMENT POND OR TRAP. ALL CATCH BASIN INSERTS SHALL BE PERIODICALLY INSPECTED AND REPLACED AS NECESSARY TO ENSURE FULLY FUNCTIONING CONDITION. 12.AT NO TIME SHALL SEDIMENT ACCUMULATION EXCEED 2/3 OF THE CAPACITY OF THE CATCH BASIN SUMP. ALL CATCH BASINS AND CONVEYANCE LINES SHALL BE CLEANED PRIOR TO PAVING. THE CLEANING OPERATION SHALL NOT FLUSH SEDIMENT-LADEN WATER INTO THE DOWNSTREAM SYSTEM. 13.ANY PERMANENT STORMWATER FACILITY LOCATION USED AS A TEMPORARY SETTLING BASIN SHALL BE MODIFIED WITH THE NECESSARY ESC BMPS AND SHALL PROVIDE ADEQUATE STORAGE CAPACITY. IF THE TEMPORARY FACILITY IS TO ULTIMATELY FUNCTION AS AN INFILTRATION SYSTEM IN ITS PERMANENT STATE, THE TEMPORARY FACILITY SHALL BE ROUGH GRADED SO THAT THE BOTTOM AND SIDES ARE AT LEAST THREE FEET ABOVE THE FINAL GRADE OF THE PERMANENT FACILITY. 14.PRIOR TO FINAL CONSTRUCTION ACCEPTANCE, THE PROJECT SITE SHALL BE STABILIZED TO PREVENT SEDIMENT-LADEN WATER FROM LEAVING THE PROJECT SITE, ALL ESC BMPS SHALL BE REMOVED, AND STORMWATER CONVEYANCE SYSTEMS, FACILITIES, AND ON-SITE BMPS SHALL BE RESTORED TO THEIR FULLY FUNCTIONING CONDITION. ALL DISTURBED AREAS OF THE PROJECT SITE SHALL BE VEGETATED OR OTHERWISE PERMANENTLY STABILIZED. AT A MINIMUM, DISTURBED AREAS SHALL BE SODDED OR SEEDED AND MULCHED TO ENSURE THAT SUFFICIENT COVER WILL DEVELOP SHORTLY AFTER FINAL APPROVAL. MULCH WITHOUT SEEDING IS ADEQUATE FOR AREAS TO BE LANDSCAPED BEFORE OCTOBER 1ST. Final Design ReSoUt SubPittal 210 SS ( R ) SS SS SS SS SS SS SS SS SS SD SD SD SD SD SD SD SD SD SD SD S D S D S D SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD G P P P P P P T T T T T T T T x x x x x x x x x x x x xxxxxxxx x x x x x x x x x x x x x x x x x TV TV TV W W W W W W W W G G G TV T P P P P TV TV TV TV T T T T T T P P P P P P Px x x x x x x x x x x xxx W W S S SD D 8557200190 7941200010 7941200020 7941200030 7941200230 794120TRCT 195190 185 190 200 HVAC DECK 2 STORY BUILDING CW CW CW CG CW CW CG CONC DW ASPH DWASPH P A R K I N G L O T GRA S S SHED CG CG CWASPH ASPH PA GRASS EP EP EC C E C C ECC EP PA PA CONC WALL S42 ° 1 2 ' 0 7 " E 22.1 7 ' S00°23'08"W 126.99' S00°23'08"W 29.56' S30°20'10"E 40.05' S05°28'09"E 16.10' S89°36'52"E 22.90' N00°09'56"E 223.32' N89°36'52"W 59.15' 190 195 185 205 215 Sa v e D a t e : Plo t D a t e : 3/ 3 / 2 0 2 5 1 : 3 8 P M 3/ 2 8 / 2 0 2 5 1 1 : 3 9 A M By : Cg b P:\ R \ R E N T 0 0 0 0 1 9 0 3 \ 0 4 0 0 C A D \ W A \ S H E E T S \ E C - E X - R E N T 1 9 0 3 . d w g Ch a d B o o t h By : Fil e : SHEET NO. DATE:REVIEWED BY: DATENO.REVISION CKBY FILE NO. PROJECT NO.SEC: TWP: RGE: DATUM: HOR: VERT: CHECKED BY: DESIGNED BY: DRAWN BY: ® 14432 SE Eastgate Way Suite 400 Bellevue, WA 98007 Phone: 425.519.6500 Ecology Design Report Submittal CITY OF RENTON, WASHINGTON Springbrook Terrace Water Quality Retrofit CAG-24-081 RENT00001903 NAD 83 WA S.P. N NAVD 88 06 22N 5E ASR CGB WDM NOT FOR CONSTRUCTION EXISTING CONDITIONS C1 98TH A V E S 10' DRAINAGE EASEMENT PER AFN 198507020780 SANITARY SEWER EASEMENT PER AFN 8412140947 10' D R A I N A G E E A S E M E N T PER A F N 1 9 8 5 0 7 0 2 0 7 8 0 ACC E S S E A S E M E N T PER A F N 1 9 8 5 0 7 0 2 0 7 8 0 PROJECT SITE PARCEL BOUNDARY CB TYPE 2 RIM=210.78 12" CMP SE IE=203.2 12" CMP N IE=203.2 12" CMP W IE-203.1 CB TYPE 1 RIM=200.17 12" CMP E IE=197.0 12" CMP SW IE=196.9 CB TYPE 1 RIM=200.41 8" CMP NW IE=198.1 BLIND TIE TO NW PER RECORDS CB TYPE 2 RIM=190.90 21" CMP SE IE=185.7 21" CMP N IE=185.7 CULVERT 12" RCP N IE=187.44 CULVERT 21" CMP NW IE=186.66 CULVERT 15" CMP E IE=191.84 CB TYPE 2 RIM=212.55 6" PVC E IE=208.8 15" CMP S IE=197.8 15" CMP W IE=197.7 SSMH RIM=190.49 6" PVC NE IE=182.4 8" PVC S IE=183.1 BUILDING CORNER TRANSFORMER BOX CHAIN LINK FENCE EX. PIPE SLOPE 0.51% Feet 0 20 40 10' DRAINAGE EASEMENT PER AFN 198507020780 Final Design ReSoUt SubPittal SS ( R ) SS SS SS SS SS SS SS SS SS SD SD SD SD SD SD SD SD SD SD SD S D S D S D SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD G P P P P P P T T T T T T T T x x x x x x x x x x x x xxxxxxxx x x x x x x x x x x x x x x x x x TV TV TV W W W W W W W W G G G TV T P P P P TV TV TV TV T T T T T T P P P P P P Px x x x x x x x x x x xxx W W S S SD D185 190 190 190 195 187 195 20 0 205 210 21 5 P Sa v e D a t e : Plo t D a t e : 3/ 3 / 2 0 2 5 1 : 4 3 P M 3/ 2 8 / 2 0 2 5 1 1 : 4 0 A M By : Cg b P:\ R \ R E N T 0 0 0 0 1 9 0 3 \ 0 4 0 0 C A D \ W A \ S H E E T S \ E C - D M - R E N T 1 9 0 3 . d w g Ch a d B o o t h By : Fil e : SHEET NO. DATE:REVIEWED BY: DATENO.REVISION CKBY FILE NO. PROJECT NO.SEC: TWP: RGE: DATUM: HOR: VERT: CHECKED BY: DESIGNED BY: DRAWN BY: ® 14432 SE Eastgate Way Suite 400 Bellevue, WA 98007 Phone: 425.519.6500 Ecology Design Report Submittal CITY OF RENTON, WASHINGTON Springbrook Terrace Water Quality Retrofit CAG-24-081 RENT00001903 NAD 83 WA S.P. N NAVD 88 06 22N 5E ASR CGB WDM NOT FOR CONSTRUCTION ESC AND DEMOLITION PLAN & DETAILS C2 Feet 0 20 40 98TH A V E S LEGEND INLET PROTECTION SILT FENCE 1.CONSTRUCT SILT FENCE PER COR STD DETAIL 214.00. SILT FENCE SHALL BE INSTALLED PRIOR TO ANY EARTH DISTURBING ACTIVITIES. 2.INSTALL INLET PROTECTION PER COR STD DETAIL 216.30. INLET PROTECTION SHALL BE INSTALLED PRIOR TO ANY EARTHE DISTURBING ACTIVITIES. 3.THE ESC FACILITIES SHOWN ON THIS PLAN ARE THE MINIMUM REQUIREMENTS FOR ANTICIPATED SITE CONDITIONS. DURING THE CONSTRUCTION PERIOD THE CONTRACTOR SHALL MODIFY THIS TESC PLAN TO ACCOMMODATE CHANGES TO THE PROJECT SITE AND STORM EVENTS. 4.CONSTRUCT STABILIZED CONSTRUCTION ENTRANCE PER COR STD DETAIL 215.10. 5.CONSTRUCT SEDIMENT TRAP PER COR STD DETAIL 211.00 TO THE MAXIMUM EXTENT THE SITE ALLOWS. 6.PROVIDE TEMPORARY PUMPING AS NEEDED TO CONVEY POND INFLOWS TO EXISTING POND OUTLET DRAINAGE STRUCTURE. TEMPORARY EROSION CONTROL CONSTRUCTION NOTES REMOVE 15 FEET OF EXISTING STORM SEWER PIPE REMOVE 38 FEET OF EXISTING WOODEN FENCE REMOVE 203 FEET OF EXISTING CHAIN LINK FENCE (INCLUDING GATES) REMOVE 22 FEET OF EXISTING STORM SEWER PIPE SALVAGE EXISTING SIGN 1.ALL ITEMS CALLED OUT FOR REMOVAL SHALL BECOME THE PROPERTY OF THE CONTRACTOR AND MUST BE DISPOSED OF OFFSITE. 2.APPROXIMATE MEASUREMENTS OF ITEMS TO BE REMOVED ARE PROVIDED FOR CONVENIENCE. THE REMOVAL OF ALL ITEMS SHALL BE PAID FOR UNDER THE LUMP SUM BID ITEM REMOVAL OF STRUCTURES AND OBSTRUCTIONS AND NOT PAID FOR ON AN INDIVIDUAL MEASURABLE BID ITEM BASIS. DEMOLITION CONSTRUCTION NOTES STABILIZED CONSTRUCTION ENTRANCE HIGH-VISIBILITY FENCE DECOMISSION EXISTING GROUNDWATER MONITORING WELL CLEAR AND GRUB TREE TEMPORARY PUMPING SEDIMENT TRAP Final Design ReSoUt SubPittal SS ( R ) SS SS SS SS SS SS SS SS SS SD SD SD SD SD SD SD SD SD SD SD S D S D S D SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD SD G P P P P P P T T T T T T T T x x x x x x x x x x x x xxxxxxxx x x x x x x x x x x x x x x x x x TV TV TV W W W W W W W W G G G TV T P P P P TV TV TV TV T T T T T T P P P P P P Px x x x x x x x x x x xxx W W S S SD D 187 190 195 200 190 185 205 185 SDMH #1, 48" TYPE 1 N: 159732.23 E: 1299560.05 RIM: 191.75 IE: 188.90 (12" N) IE: 188.30 (12" S) CONNECT TO EXISTING CMP DRAINAGE PIPE 19 LF 12" PP SDCB #4, 54" N: 159723.77 E: 1299540.22 RIM: 190.80 IE: 189.00 (12" SE) IE: 185.90 (8" SE) IE: 185.80 (15" N) 8 LF 15" PP 15 LF 8" PP VALVE AT D/S END 15 LF 12" RCP 190 185 185 190 195 200 Sa v e D a t e : Plo t D a t e : 3/ 2 8 / 2 0 2 5 1 1 : 2 9 A M 3/ 2 8 / 2 0 2 5 1 1 : 4 0 A M By : Cg b P:\ R \ R E N T 0 0 0 0 1 9 0 3 \ 0 4 0 0 C A D \ W A \ S H E E T S \ E C - S T - R E N T 1 9 0 3 . d w g Ch a d B o o t h By : Fil e : SHEET NO. DATE:REVIEWED BY: DATENO.REVISION CKBY FILE NO. PROJECT NO.SEC: TWP: RGE: DATUM: HOR: VERT: CHECKED BY: DESIGNED BY: DRAWN BY: ® 14432 SE Eastgate Way Suite 400 Bellevue, WA 98007 Phone: 425.519.6500 Ecology Design Report Submittal CITY OF RENTON, WASHINGTON Springbrook Terrace Water Quality Retrofit CAG-24-081 RENT00001903 NAD 83 WA S.P. N NAVD 88 06 22N 5E ASR CGB WDM NOT FOR CONSTRUCTION SITE PLAN C3 Feet 0 20 40 98TH A V E S INSTALL PERMANENT PUBLIC STORMWATER SIGN 3:1 3: 1 3:1 6:1 BOTTOM OF POND, EL 184.25 ACCESS ROAD AT 20% MAX SLOPE TOP OF POND, EL 190.0 C4 2BEGIN EMERGENCY SPILLWAY IE = 189.65 GRADE SPILLWAY EDGES TO ADJACENT FINISH GRADE END EMERGENCY SPILLWAY TIE INTO EXISTING AT ELEV 189.00 POND INLET PROTECTION IE 186.75 IE 186.00 CONNECT TO EXISTING DRAINAGE STRUCTURE IE: 185.70 (15" E) PLUG EXISTING PIPE CONNECTION IN EXISTING STRUCTURE AFTER EXISTING PIPE IS REMOVED IN ACCORDANCE WITH STANDARD SPECIFICATION 7-08.3(4). LEGEND PROPOSED CHAIN LINK FENCE 1.CONSTRUCT GRAVEL POND ACCESS ROAD PER COR STD DETAIL 234.50 AT THE GRADE, ELEVATION, AND WIDTHS SHOWN ON THIS PLAN SHEET. 2.CONSTRUCT 6-FOOT TALL CHAIN LINK FENCE AND 6-FOOT TALL CHAIN LINK FENCE GATE PER COR STD DETAIL 234.60 AND COR STD DETAIL 234.70. 3.CONSTRUCT 18-INCH THICK LAYER OF LOW PERMEABILITY COMPACTED TILL LINER TO EXTENTS SHOWN ON THIS SHEET PER SPECIAL PROVISIONS AND DETAIL ON SHEET C4. 4.RESTORE ALL DISTURBED AREAS OF PROJECT NOT PROPOSED TO BE IMPERVIOUS SURFACE WITH A 4-INCH THICK LAYER OF TOPSOIL TYPE A AND ACHIEVE REVEGETATION WITH HYDROSEED. 5.SALVAGE AND REINSTALL PERMANENT PUBLIC STORMWATER SIGN PER COR STD DETAIL 234.30. SIGN SHALL BE INSTALLED ON THE PROPOSED CHAIN LINK FENCE. 6.STORM SEWER LENGTHS ARE MEASURED BETWEEN CENTERS OF MANHOLES AND CATCH BASINS UNLESS OTHERWISE NOTED. 7.CONSTRUCT SDCB #4 PER OUTLET STRUCTURE DETAIL ON SHEET C4. 8.POND INLET SPILLWAY AND POND EMERGENCY SPILLWAY SHALL BE CONSTRUCTED PER DETAILS ON SHEET C4. 9.QUARRY SPALLS FOR PERMANENT EROSION CONTROL SHALL BE PLACED IN A LAYER 12 INCHES THICK. CONSTRUCTION GEOTEXTILE FOR PERMANENT EROSION CONTROL PER WSDOT STD SPECIFICATION 9-33 SHALL BE PLACED UNDER THE QUARRY SPALLS. 10.ALL PROPOSED STORM SEWER PIPE SHALL BE POLYPROPYLENE PIPE (PP), REINFORCED CONRETE PIPE (RCP), OR APPROVED EQUAL. 11.EXISTING 6" PVC SANITARY SEWER ELEVATIONS ARE PER RECORD DRAWINGS. THE CONTRACTOR SHALL VERIFY THE ACTUAL ELEVATION AND NOTIFY THE ENGINEER BEFORE CONSTRUCTING PROPOSED STORM SEWER. CONSTRUCTION NOTES POND ACCESS ROAD ECOBLOCK WALL CHAIN LINK FENCE GATE LOW PERMEABILITY COMPACTED TILL LINER EXTENTS EXISTING MAJOR CONTOUR EXISTING MINOR CONTOUR PROPOSED MAJOR CONTOUR PROPOSED MINOR CONTOUR C4 3 PROPOSED STORM SEWER STRUCTURE PROPOSED STORM SEWER PIPE QUARRY SPALLS FOR PERMANENT EROSION CONTROL EX. CB TYPE 2 RIM=190.90 21" CMP SE IE=185.7 21" CMP N IE=185.7 PROTECT EXISTING FLOW CONTROL FEATURES GROUNDWATER MONITORING WELL POND INLET PROTECTION IE 187.00 GRAVEL PARKING AREA PROTECT EXISTING INLET TOP OF ECOBLOCK WALL, EL 189.75 GRAVEL PARKING AREA PROTECT EXISTING SEWER PIPES R10 ' 10 . 5 ' (T Y P . ) Final Design ReSoUt SubPittal 180 190 200 180 190 200 0+00 0+50 0+50 180 190 200 180 190 200 0+00 0+50 1+00 1+50 0+50 1+00 1+50 Sa v e D a t e : Plo t D a t e : 3/ 2 8 / 2 0 2 5 1 1 : 3 5 A M 3/ 2 8 / 2 0 2 5 1 1 : 4 0 A M By : Cg b P:\ R \ R E N T 0 0 0 0 1 9 0 3 \ 0 4 0 0 C A D \ W A \ S H E E T S \ E C - D R - D T - R E N T 1 9 0 3 . d w g Ch a d B o o t h By : Fil e : SHEET NO. DATE:REVIEWED BY: DATENO.REVISION CKBY FILE NO. PROJECT NO.SEC: TWP: RGE: DATUM: HOR: VERT: CHECKED BY: DESIGNED BY: DRAWN BY: ® 14432 SE Eastgate Way Suite 400 Bellevue, WA 98007 Phone: 425.519.6500 Ecology Design Report Submittal CITY OF RENTON, WASHINGTON Springbrook Terrace Water Quality Retrofit CAG-24-081 RENT00001903 NAD 83 WA S.P. N NAVD 88 06 22N 5E ASR CGB WDM NOT FOR CONSTRUCTION DRAINAGE DETAILS AND SECTIONS C4 2-YEAR WSE = 189.48 SDCB #4 54" DIA. TYPE 2 CB W/ SOLID LID VALVE 8" GRAVITY DRAIN 18" 3.5'x0.5' (LxH) STRUCTURE OPENING W/ 3/4" BARS SPACED 4" O.C. IE = 189.39 SCALE: OUTLET STRUCTURE SECTION N.T.S. 1 C4 WQ DESIGN VOLUME = 6,846 CF 100-YEAR WSE AND EMERGENCY SPILLWAY = 189.65 OVERFLOW WSE = 189.39 WQ DESIGN WSE = 189.00 12" OUTLET PIPE IE 185.90 IE 186.00 IE 185.80 RIM EL 190.80 IE 186.75 IE 189.00 SCALE: WEST-EAST POND SECTION N.T.S. 2 C4 SEDIMENT STORAGE TOP ELEVATION = 184.75 LOW PERMEABILITY COMPACTED TILL LINER 18" EXISTING GROUND FINISH GROUND WQ DESIGN WSE = 189.00 SCALE: SOUTH-NORTH POND SECTION N.T.S. 3 C4 TOP OF SEDIMENT STORAGE ELEVATION = 184.75 LOW PERMEABILITY COMPACTED TILL LINER 18" EXISTING GROUND FINISH GROUND WQ DESIGN WSE = 189.00 SCALE: POND EMERGENCY SPILLWAY N.T.S. 5 C4SCALE: POND INLET PROTECTION N.T.S. 4 C4 12" QUARRY SPALLS SUBGRADE PREPARED PER WSDOT STD. SPEC. 2-12 SUBGRADE PREPARED PER WSDOT STD. SPEC. 2-12 FINISH GRADE PER SHEET C3 - SITE PLAN 12" QUARRY SPALLS 9' 4' CONSTRUCTION GEOTEXTILE FOR PERMANENT EROSION CONTROL PER WSDOT STD SPEC. 9-33 CONSTRUCTION GEOTEXTILE FOR PERMANENT EROSION CONTROL PER WSDOT STD SPEC. 9-33 4" 3:1 (TY P . ) 15" OUTLET PIPE SUMP EL. 183.80 IE 185.70 EX. FLOW CONTROL STRUCTURE EX. OUTLET PIPE TOP OF ECOBLOCK WALL ELEVATION = 189.75 TOP OF ECOBLOCK WALL ELEVATION = 189.75 EX. OVERFLOW ORIFICE EX. TEE SECTION SHEAR GATE IE 185.70 2-YEAR WSE = 189.48 POND BOTTOM ELEVATION = 184.25 BOTTOM OF ECOBLOCK WALL ELEVATION = 181.75 POND BOTTOM ELEVATION = 184.25WALL AND AGGREGATE FOUNDATION NOT SHOWN BELOW GRADE FOR CLARITY FINISH GRADE PER SHEET C3 - SITE PLAN EX. 6" PVC SANITARY SEWER SERVICE 18" LOW PERMEABILITY COMPACTED TILL LINER Final Design ReSoUt SubPittal x x x x x x x x x x x x x x x xxxxxxxxxxxxxxx x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x xx Sa v e D a t e : Plo t D a t e : 3/ 3 / 2 0 2 5 2 : 2 5 P M 3/ 2 8 / 2 0 2 5 1 1 : 4 1 A M By : Cg b P:\ R \ R E N T 0 0 0 0 1 9 0 3 \ 0 4 0 0 C A D \ W A \ S H E E T S \ E C - D T - R E N T 1 9 0 3 . d w g Ch a d B o o t h By : Fil e : SHEET NO. DATE:REVIEWED BY: DATENO.REVISION CKBY FILE NO. PROJECT NO.SEC: TWP: RGE: DATUM: HOR: VERT: CHECKED BY: DESIGNED BY: DRAWN BY: ® 14432 SE Eastgate Way Suite 400 Bellevue, WA 98007 Phone: 425.519.6500 Ecology Design Report Submittal CITY OF RENTON, WASHINGTON Springbrook Terrace Water Quality Retrofit CAG-24-081 RENT00001903 NAD 83 WA S.P. N NAVD 88 06 22N 5E ASR CGB WDM NOT FOR CONSTRUCTION MISC. CIVIL DETAILS (SHEET 1 OF 2) C5 A B C E 67.1' 56.1' 13.8' 29.9' D 2. 9 ' 14 . 8 ' 37.3' 6. 0 ' 15 . 4 ' 2. 7 ' 1 5 . 8 ' 22 . 6 ' TOP OF WATER QUALITY POND EL 189.00 BOTTOM OF WATER QUALITY POND EL 184.75 BOTTOM OF POND EL 184.25WATER QUALITY POND MID-DEPTH EL 186.88 Feet 0 20 40 WATER QUALITY FLOWPATH LENGTH TO WIDTH FIGURE NOTE: THIS FIGURE IS TO DEMONSTRATE COMPLIANCE WITH WA DEPARTMENT OF ECOLOGY WATER QUALITY STANDARDS AND NOT FOR CONSTRUCTION PURPOSES. FLOW PATH (TYP.) Final Design ReSoUt SubPittal Sa v e D a t e : Plo t D a t e : 3/ 3 / 2 0 2 5 2 : 2 5 P M 3/ 2 8 / 2 0 2 5 1 1 : 4 1 A M By : Cg b P:\ R \ R E N T 0 0 0 0 1 9 0 3 \ 0 4 0 0 C A D \ W A \ S H E E T S \ E C - D T - R E N T 1 9 0 3 . d w g Ch a d B o o t h By : Fil e : SHEET NO. DATE:REVIEWED BY: DATENO.REVISION CKBY FILE NO. PROJECT NO.SEC: TWP: RGE: DATUM: HOR: VERT: CHECKED BY: DESIGNED BY: DRAWN BY: ® 14432 SE Eastgate Way Suite 400 Bellevue, WA 98007 Phone: 425.519.6500 Ecology Design Report Submittal CITY OF RENTON, WASHINGTON Springbrook Terrace Water Quality Retrofit CAG-24-081 RENT00001903 NAD 83 WA S.P. N NAVD 88 06 22N 5E ASR CGB WDM NOT FOR CONSTRUCTION MISC. CIVIL DETAILS (SHEET 2 OF 2) C6 TO BE COMPLETED AT 90% Final Design ReSoUt SubPittal SS SS SS SS SD SD SD SD SD SD SD SD S D SD SD SD SD SD SD SD SD SD P TT x x x x x xxxx x x x x x x x x TV W P P PT TP P x x x x x x x S S D D 8557200190 7941200010 7941200020 7941200030 7941200230 794120TRCT 7941200040 7941200160 7931000153 7941200170 7941200150 7941200140 7941200050 7941200060 Sa v e D a t e : Plo t D a t e : 3/ 3 / 2 0 2 5 2 : 3 2 P M 3/ 2 8 / 2 0 2 5 1 1 : 4 1 A M By : Cg b P:\ R \ R E N T 0 0 0 0 1 9 0 3 \ 0 4 0 0 C A D \ W A \ S H E E T S \ E C - H Z - R E N T 1 9 0 3 . d w g Ch a d B o o t h By : Fil e : SHEET NO. DATE:REVIEWED BY: DATENO.REVISION CKBY FILE NO. PROJECT NO.SEC: TWP: RGE: DATUM: HOR: VERT: CHECKED BY: DESIGNED BY: DRAWN BY: ® 14432 SE Eastgate Way Suite 400 Bellevue, WA 98007 Phone: 425.519.6500 Ecology Design Report Submittal CITY OF RENTON, WASHINGTON Springbrook Terrace Water Quality Retrofit CAG-24-081 RENT00001903 NAD 83 WA S.P. N NAVD 88 06 22N 5E ASR CGB WDM NOT FOR CONSTRUCTION SURVEY, HORIZONTAL CONTROL, AND SITE ACCESS PLAN C7 Feet 0 40 80 98TH A V E S SURVEY NOTES UTILITIES MAPPING: ALL EXISTING UTILITIES SHOWN HEREIN ARE TO BE VERIFIED HORIZONTALLY AND VERTICALLY PRIOR TO ANY CONSTRUCTION. ALL EXISTING FEATURES INCLUDING BURIED UTILITIES ARE SHOWN AS INDICATED BY RECORD LOCATION OR FIELD TIED AS A RESULT OF A UTILITY PAINT-OUT DURING THE COURSE OF THE FIELD SURVEY. DAVID EVANS & ASSOCIATES, INC. (DEA) ASSUMES NO LIABILITY FOR THE ACCURACY OF THE RECORD INFORMATION. FOR THE FINAL LOCATION OF THE EXISTING UTILITIES IN AREAS CRITICAL TO CONSTRUCTION, CONTACT THE UTILITY OWNER/AGENCY AND UTILITIES UNDERGROUND CENTER. TOPOGRAPHIC MAPPING: THE MAP SHOWN HEREON IS THE RESULT OF A TOPOGRAPHIC SURVEY BY DAVID EVANS & ASSOCIATES, INC. (DEA) COMPLETED IN AUGUST 2024. DEA ASSUMES NO LIABILITY, BEYOND SAID DATE, FOR ANY FUTURE SURFACE FEATURE MODIFICATIONS OR CONSTRUCTION ACTIVITIES THAT MAY OCCUR WITHIN OR ADJOINING THE PERIMETER OF THIS SURVEY. CONTACT DEA FOR SITE UPDATES AND VERIFICATIONS. HORIZONTAL DATUM: WASHINGTON STATE COORDINATE SYSTEM, NORTH ZONE NAD83, US FEET. VERTICAL DATUM: NORTH AMERICAN VERTICAL DATUM 1988 (NAVD88), US FEET. NOTES: THIS EXISTING BASE MAP WAS PREPARED FROM A SURVEY DRAWING PREPARED BY DAVID EVANS AND ASSOCIATES INC., SURVEYED IN AUGUST 2024, WITH MODIFICATIONS BASED ON FIELD OBSERVATIONS BY DEA STAFF. SURVEY CONTROL PT #DESCRIPTION NORTHING EASTING ELEVATION 1-3/4" BRASS DISC IN CONC MONUMENT 159588.78 1299689.07 211.75 1-3/4" BRASS DISC IN CONC MONUMENT 159824.90 1299660.90 212.79 MONUMENT (CENTER OF LID)159939.00 1299628.73 NOT AVAILABLE 1-3/4" BRASS DISC IN CONC MONUMENT 159969.08 1299629.60 210.68 1 2 3 4 1 2 3 4 S 5 5 T H S T ACCESS EASEMENT FROM CITY RIGHT-OF-WAY TO PROJECT SITE 98TH PL S CENTERLINE 98TH AVE S CENTERLINE Final Design ReSoUt SubPittal Springbrook Terrace Water Quality Retrofit Final Design Report Springbrook Terrace Water Quality Retrofit Final Design Report Appendix C – Engineer’s Opinion of Probable Cost No. Standard Item Description Unit of Measure Quantity Unit Price Item Cost Amount Eligible for DOE Grant Funding 1 MOBILIZATION LS 1 23,300.00$ 23,300.00$ 23,300.00$ 2 MINOR CHANGES FA EST 14,000.00$ $ 14,000.00 14,000.00$ 3 PROJECT TEMPORARY TRAFFIC CONTROL LS 1 4,500.00$ 4,500.00$ 4,500.00$ 4 CONSTRUCTION SURVEYING, STAKING, AND AS-BUILTS LS 1 8,100.00$ 8,100.00$ 8,100.00$ 5 TEMPORARY WATER POLLUTION PREVENTION AND IMPLEMENTATION LS 1 16,200.00$ 16,200.00$ 16,200.00$ 6 DECOMMISSION EXISTING GROUNDWATER MONITORING WELL EA 1 4,800.00$ 4,800.00$ 4,800.00$ 7 REMOVAL OF STRUCTURES AND OBSTRUCTIONS LS 1 5,000.00$ 5,000.00$ 5,000.00$ 8 CONTROL OF WATER (INCLUDES STORM SEWER BYPASSES) LS 1 4,050.00$ 4,050.00$ 4,050.00$ 9 STORM SEWER PIPE 8-INCH DIAMETER - PP LF 15 60.00$ 900.00$ 900.00$ 10 STORM SEWER PIPE 12-INCH DIAMETER - PP LF 19 90.00$ 1,710.00$ 1,710.00$ 11 STORM SEWER PIPE 12-INCH DIAMETER - RCP LF 15 100.00$ 1,500.00$ 1,500.00$ 12 STORM SEWER PIPE 15-INCH DIAMETER - PP LF 8 110.00$ 880.00$ 880.00$ 13 TYPE 1 MANHOLE 48-INCH DIAMETER EA 1 6,500.00$ 6,500.00$ 6,500.00$ 14 TYPE 2 CATCH BASIN 54-INCH DIAMETER OVERFLOW STRUCTURE EA 1 10,500.00$ 10,500.00$ 10,500.00$ 15 CONNECT TO EXISTING STORM SEWER PIPE EA 1 1,620.00$ 1,620.00$ 1,620.00$ 16 CONNECT TO EXISTING DRAINAGE STRUCTURE EA 1 1,800.00$ 1,800.00$ 1,800.00$ 17 POND EXCAVATION INCL. HAUL AND DISPOSAL LS 1 51,000.00$ 51,000.00$ 51,000.00$ 18 6-FOOT TALL CHAIN LINK FENCE LF 231 70.00$ 16,170.00$ 16,170.00$ 19 6-FOOT TALL CHAIN LINK FENCE GATE EA 2 2,500.00$ 5,000.00$ 5,000.00$ 20 REVEGETATION WITH HYDROSEED LS 1 3,600.00$ 3,600.00$ 3,600.00$ 21 POND ACCESS ROAD SY 90 90.00$ 8,100.00$ 8,100.00$ 22 LOW PERMEABILITY COMPACTED TILL LINER MATERIAL CY 184 50.00$ 9,200.00$ 9,200.00$ 23 SALVAGE AND REINSTALL PERMANENT PUBLIC STORMWATER POND SIGN EA 1 800.00$ 800.00$ 800.00$ 24 CCTV NEW STORM SEWER PIPE LF 57 11.00$ 627.00$ 627.00$ 25 SILT FENCE LF 231 11.00$ 2,541.00$ 2,541.00$ 26 INLET PROTECTION EA 3 180.00$ 540.00$ 540.00$ 27 STABILIZED CONSTRUCTION ENTRANCE SY 67 50.00$ 3,350.00$ 3,350.00$ 28 HIGH VISIBILITY FENCE LF 270 9.00$ 2,430.00$ 2,430.00$ 29 CLEAR AND GRUB TREE EA 2 500.00$ 1,000.00$ 1,000.00$ 30 QUARRY SPALLS FOR PERMANENT EROSION CONTROL CY 17 210.00$ 3,570.00$ 3,570.00$ 31 CONSTRUCTION GEOTEXTILE FOR PERMANENT EROSION CONTROL SY 51 19.00$ 969.00$ 969.00$ 32 TOPSOIL TYPE A SY 980 53.00$ 51,940.00$ 51,940.00$ 33 ECOBLOCK WALL SF 576 80.00$ 46,080.00$ 46,080.00$ 34 CRUSHED SURFACING TOP COURSE CY 9 190.00$ 1,710.00$ 1,710.00$ 313,987.00$ 313,987.00$ 78,497.00$ 78,497.00$ 392,484.00$ 392,484.00$ Total Subtotal CONTINGENCY (25%) June 2025 Final Design Report Engineer's Opinion of Probable Cost Springbrook Terrace Water Quality Retrofit / CAG-24-081 City of Renton Appendix C Springbrook Terrace Water Quality Retrofit Final Design Report Springbrook Terrace Water Quality Retrofit Final Design Report Appendix D – Analysis Program Output WWHM2012 PROJECT REPORT Springbrook Terrace WQ Volume 3/14/2025 8:53:36 AM Page 2 General Model Information Project Name:Springbrook Terrace WQ Volume Site Name:Springbrook Terrace Site Address:19203 98th Ave S City:Renton Report Date:3/14/2025 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2021/08/18 Version:4.2.18 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year Springbrook Terrace WQ Volume 3/14/2025 8:53:36 AM Page 3 Landuse Basin Data Predeveloped Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre A B, Forest, Steep 0.703568 A B, Lawn, Mod 3.260065 Pervious Total 3.963633 Impervious Land Use acre ROADS MOD 1.527833 ROOF TOPS FLAT 1.148548 Impervious Total 2.676381 Basin Total 6.640014 Element Flows To: Surface Interflow Groundwater Springbrook Terrace WQ Volume 3/14/2025 8:53:36 AM Page 4 Mitigated Land Use Basin 2 Bypass:No GroundWater:No Pervious Land Use acre A B, Forest, Steep 0.703568 A B, Lawn, Mod 3.220065 Pervious Total 3.923633 Impervious Land Use acre ROADS MOD 1.567833 ROOF TOPS FLAT 1.148548 Impervious Total 2.716381 Basin Total 6.640014 Element Flows To: Surface Interflow Groundwater Springbrook Terrace WQ Volume 3/14/2025 8:53:36 AM Page 5 Routing Elements Predeveloped Routing Springbrook Terrace WQ Volume 3/14/2025 8:53:36 AM Page 6 Mitigated Routing Springbrook Terrace WQ Volume 3/14/2025 8:53:36 AM Page 7 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:3.963633 Total Impervious Area:2.676381 Mitigated Landuse Totals for POC #1 Total Pervious Area:3.923633 Total Impervious Area:2.716381 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 1.132243 5 year 1.480056 10 year 1.732764 25 year 2.078465 50 year 2.355823 100 year 2.650754 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 1.149125 5 year 1.500599 10 year 1.755764 25 year 2.104601 50 year 2.384314 100 year 2.681611 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 1.448 1.470 1950 1.516 1.532 1951 0.995 1.007 1952 0.737 0.747 1953 0.871 0.885 1954 0.942 0.955 1955 1.054 1.071 1956 0.950 0.965 1957 1.088 1.104 1958 0.916 0.931 Springbrook Terrace WQ Volume 3/14/2025 8:55:37 AM Page 8 1959 0.982 0.998 1960 0.956 0.969 1961 0.925 0.939 1962 0.823 0.836 1963 0.984 0.999 1964 0.953 0.968 1965 1.143 1.159 1966 0.782 0.795 1967 1.537 1.554 1968 1.651 1.678 1969 1.018 1.034 1970 1.027 1.043 1971 1.238 1.258 1972 1.438 1.453 1973 0.796 0.809 1974 1.145 1.163 1975 1.258 1.277 1976 0.917 0.932 1977 0.936 0.950 1978 1.288 1.310 1979 1.626 1.653 1980 1.582 1.609 1981 1.107 1.124 1982 1.575 1.600 1983 1.297 1.317 1984 0.808 0.821 1985 1.075 1.091 1986 0.954 0.969 1987 1.486 1.509 1988 0.913 0.927 1989 1.380 1.404 1990 2.611 2.630 1991 1.808 1.831 1992 0.795 0.808 1993 0.904 0.921 1994 0.841 0.856 1995 0.995 1.011 1996 1.469 1.483 1997 1.122 1.137 1998 1.059 1.076 1999 2.226 2.261 2000 1.065 1.081 2001 1.259 1.279 2002 1.303 1.323 2003 1.263 1.284 2004 2.132 2.167 2005 0.880 0.893 2006 0.899 0.911 2007 2.596 2.611 2008 1.720 1.738 2009 1.518 1.543 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 2.6112 2.6300 2 2.5962 2.6111 3 2.2259 2.2614 Springbrook Terrace WQ Volume 3/14/2025 8:55:37 AM Page 9 4 2.1323 2.1668 5 1.8085 1.8305 6 1.7198 1.7383 7 1.6511 1.6783 8 1.6263 1.6525 9 1.5820 1.6091 10 1.5753 1.5996 11 1.5373 1.5536 12 1.5176 1.5428 13 1.5163 1.5321 14 1.4860 1.5090 15 1.4689 1.4826 16 1.4475 1.4697 17 1.4383 1.4532 18 1.3803 1.4043 19 1.3032 1.3228 20 1.2970 1.3172 21 1.2879 1.3097 22 1.2635 1.2842 23 1.2587 1.2792 24 1.2578 1.2774 25 1.2384 1.2581 26 1.1447 1.1631 27 1.1429 1.1594 28 1.1225 1.1367 29 1.1071 1.1240 30 1.0878 1.1045 31 1.0746 1.0907 32 1.0649 1.0812 33 1.0592 1.0758 34 1.0538 1.0708 35 1.0267 1.0428 36 1.0180 1.0336 37 0.9955 1.0108 38 0.9954 1.0073 39 0.9844 0.9994 40 0.9824 0.9985 41 0.9563 0.9688 42 0.9541 0.9688 43 0.9530 0.9684 44 0.9504 0.9649 45 0.9419 0.9552 46 0.9355 0.9503 47 0.9245 0.9393 48 0.9173 0.9319 49 0.9160 0.9305 50 0.9126 0.9267 51 0.9042 0.9207 52 0.8994 0.9107 53 0.8800 0.8932 54 0.8707 0.8846 55 0.8413 0.8558 56 0.8232 0.8360 57 0.8081 0.8209 58 0.7961 0.8089 59 0.7947 0.8078 60 0.7821 0.7946 61 0.7365 0.7475 Springbrook Terrace WQ Volume 3/14/2025 8:55:37 AM Page 10 Springbrook Terrace WQ Volume 3/14/2025 8:55:37 AM Page 11 Duration Flows The Development Failed :duration increase for more than 50% of the flows. Flow(cfs)Predev Mit Percentage Pass/Fail 0.5661 1496 1565 104 Fail 0.5842 1336 1411 105 Fail 0.6023 1208 1275 105 Fail 0.6204 1085 1145 105 Fail 0.6384 980 1038 105 Fail 0.6565 890 940 105 Fail 0.6746 801 851 106 Fail 0.6927 721 764 105 Fail 0.7107 651 691 106 Fail 0.7288 587 622 105 Fail 0.7469 529 564 106 Fail 0.7650 496 512 103 Fail 0.7831 467 483 103 Fail 0.8011 432 458 106 Fail 0.8192 404 425 105 Fail 0.8373 363 390 107 Fail 0.8554 337 356 105 Fail 0.8734 311 329 105 Fail 0.8915 295 310 105 Fail 0.9096 270 286 105 Fail 0.9277 247 267 108 Fail 0.9458 226 240 106 Fail 0.9638 205 220 107 Fail 0.9819 192 202 105 Fail 1.0000 173 188 108 Fail 1.0181 161 170 105 Fail 1.0361 154 161 104 Fail 1.0542 145 154 106 Fail 1.0723 130 144 110 Fail 1.0904 121 129 106 Fail 1.1085 116 121 104 Fail 1.1265 111 116 104 Fail 1.1446 106 111 104 Pass 1.1627 97 106 109 Pass 1.1808 92 96 104 Pass 1.1988 88 90 102 Pass 1.2169 84 88 104 Pass 1.2350 80 84 104 Pass 1.2531 75 80 106 Pass 1.2712 68 75 110 Pass 1.2892 62 68 109 Pass 1.3073 57 63 110 Pass 1.3254 53 58 109 Pass 1.3435 52 52 100 Pass 1.3615 51 52 101 Pass 1.3796 47 51 108 Pass 1.3977 44 47 106 Pass 1.4158 41 45 109 Pass 1.4339 37 41 110 Pass 1.4519 35 38 108 Pass 1.4700 33 35 106 Pass 1.4881 27 33 122 Fail 1.5062 27 28 103 Pass Springbrook Terrace WQ Volume 3/14/2025 8:55:37 AM Page 12 1.5242 23 27 117 Fail 1.5423 22 24 109 Pass 1.5604 22 22 100 Pass 1.5785 21 22 104 Pass 1.5966 20 22 110 Pass 1.6146 19 20 105 Pass 1.6327 18 19 105 Pass 1.6508 17 19 111 Fail 1.6689 16 17 106 Pass 1.6869 16 16 100 Pass 1.7050 14 15 107 Pass 1.7231 13 14 107 Pass 1.7412 13 13 100 Pass 1.7593 13 13 100 Pass 1.7773 11 13 118 Fail 1.7954 11 12 109 Pass 1.8135 10 11 110 Pass 1.8316 9 10 111 Fail 1.8496 8 9 112 Fail 1.8677 8 8 100 Pass 1.8858 7 8 114 Fail 1.9039 7 7 100 Pass 1.9220 7 7 100 Pass 1.9400 7 7 100 Pass 1.9581 7 7 100 Pass 1.9762 7 7 100 Pass 1.9943 7 7 100 Pass 2.0123 6 7 116 Fail 2.0304 6 7 116 Fail 2.0485 6 6 100 Pass 2.0666 6 6 100 Pass 2.0847 6 6 100 Pass 2.1027 6 6 100 Pass 2.1208 6 6 100 Pass 2.1389 5 6 120 Fail 2.1570 4 6 150 Fail 2.1750 4 4 100 Pass 2.1931 4 4 100 Pass 2.2112 4 4 100 Pass 2.2293 3 4 133 Fail 2.2474 3 4 133 Fail 2.2654 2 3 150 Fail 2.2835 2 2 100 Pass 2.3016 2 2 100 Pass 2.3197 2 2 100 Pass 2.3377 2 2 100 Pass 2.3558 2 2 100 Pass The development has an increase in flow durations from 1/2 Predeveloped 2 year flow to the 2 year flow or more than a 10% increase from the 2 year to the 50 year flow. The development has an increase in flow durations for more than 50% of the flows for the range of the duration analysis. Springbrook Terrace WQ Volume 3/14/2025 8:55:37 AM Page 13 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume:0.3335 acre-feet On-line facility target flow:0.4722 cfs. Adjusted for 15 min:0.4722 cfs. Off-line facility target flow:0.266 cfs. Adjusted for 15 min:0.266 cfs. Springbrook Terrace WQ Volume 3/14/2025 8:55:37 AM Page 14 LID Report Springbrook Terrace WQ Volume 3/14/2025 8:56:50 AM Page 15 POC 2 POC #2 was not reported because POC must exist in both scenarios and both scenarios must have been run. Springbrook Terrace WQ Volume 3/14/2025 8:56:50 AM Page 16 POC 3 POC #3 was not reported because POC must exist in both scenarios and both scenarios must have been run. Springbrook Terrace WQ Volume 3/14/2025 8:56:50 AM Page 17 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. Springbrook Terrace WQ Volume 3/14/2025 8:56:50 AM Page 18 Appendix Predeveloped Schematic Springbrook Terrace WQ Volume 3/14/2025 8:57:21 AM Page 19 Mitigated Schematic Springbrook Terrace WQ Volume 3/14/2025 8:57:53 AM Page 20 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 Springbrook Terrace WQ Volume.wdm MESSU 25 PreSpringbrook Terrace WQ Volume.MES 27 PreSpringbrook Terrace WQ Volume.L61 28 PreSpringbrook Terrace WQ Volume.L62 30 POCSpringbrook Terrace WQ Volume1.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 3 PERLND 8 IMPLND 2 IMPLND 4 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 *** 3 A/B, Forest, Steep 1 1 1 1 27 0 8 A/B, Lawn, Mod 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 3 0 0 1 0 0 0 0 0 0 0 0 0 8 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO Springbrook Terrace WQ Volume 3/14/2025 8:57:54 AM Page 21 <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 3 0 0 4 0 0 0 0 0 0 0 0 0 1 9 8 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 *** 3 0 0 0 0 0 0 0 0 0 0 0 8 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 3 0 5 2 400 0.15 0.3 0.996 8 0 5 0.8 400 0.1 0.3 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 3 0 0 2 2 0 0 0 8 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 3 0.2 0.5 0.35 0 0.7 0.7 8 0.1 0.5 0.25 0 0.7 0.25 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 3 0 0 0 0 3 1 0 8 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 *** 2 ROADS/MOD 1 1 1 27 0 4 ROOF TOPS/FLAT 1 1 1 27 0 END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** 2 0 0 1 0 0 0 4 0 0 1 0 0 0 END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* 2 0 0 4 0 0 0 1 9 4 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 *** Springbrook Terrace WQ Volume 3/14/2025 8:57:54 AM Page 22 2 0 0 0 0 0 4 0 0 0 0 0 END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC 2 400 0.05 0.1 0.08 4 400 0.01 0.1 0.1 END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN 2 0 0 4 0 0 END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS 2 0 0 4 0 0 END IWAT-STATE1 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Basin 1*** PERLND 3 0.703568 COPY 501 12 PERLND 3 0.703568 COPY 501 13 PERLND 8 3.260065 COPY 501 12 PERLND 8 3.260065 COPY 501 13 IMPLND 2 1.527833 COPY 501 15 IMPLND 4 1.148548 COPY 501 15 ******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 Springbrook Terrace WQ Volume 3/14/2025 8:57:54 AM Page 23 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 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 1 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*** 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 MASS-LINK 15 IMPLND IWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 15 END MASS-LINK END RUN Springbrook Terrace WQ Volume 3/14/2025 8:57:54 AM Page 24 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 Springbrook Terrace WQ Volume.wdm MESSU 25 MitSpringbrook Terrace WQ Volume.MES 27 MitSpringbrook Terrace WQ Volume.L61 28 MitSpringbrook Terrace WQ Volume.L62 30 POCSpringbrook Terrace WQ Volume1.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 3 PERLND 8 IMPLND 2 IMPLND 4 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 Basin 2 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 *** 3 A/B, Forest, Steep 1 1 1 1 27 0 8 A/B, Lawn, Mod 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 3 0 0 1 0 0 0 0 0 0 0 0 0 8 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO Springbrook Terrace WQ Volume 3/14/2025 8:57:55 AM Page 25 <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 3 0 0 4 0 0 0 0 0 0 0 0 0 1 9 8 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 *** 3 0 0 0 0 0 0 0 0 0 0 0 8 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 3 0 5 2 400 0.15 0.3 0.996 8 0 5 0.8 400 0.1 0.3 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 3 0 0 2 2 0 0 0 8 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 3 0.2 0.5 0.35 0 0.7 0.7 8 0.1 0.5 0.25 0 0.7 0.25 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 3 0 0 0 0 3 1 0 8 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 *** 2 ROADS/MOD 1 1 1 27 0 4 ROOF TOPS/FLAT 1 1 1 27 0 END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** 2 0 0 1 0 0 0 4 0 0 1 0 0 0 END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* 2 0 0 4 0 0 0 1 9 4 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 *** Springbrook Terrace WQ Volume 3/14/2025 8:57:55 AM Page 26 2 0 0 0 0 0 4 0 0 0 0 0 END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC 2 400 0.05 0.1 0.08 4 400 0.01 0.1 0.1 END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN 2 0 0 4 0 0 END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS 2 0 0 4 0 0 END IWAT-STATE1 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Basin 2*** PERLND 3 0.703568 COPY 501 12 PERLND 3 0.703568 COPY 501 13 PERLND 8 3.220065 COPY 501 12 PERLND 8 3.220065 COPY 501 13 IMPLND 2 1.567833 COPY 501 15 IMPLND 4 1.148548 COPY 501 15 ******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 Springbrook Terrace WQ Volume 3/14/2025 8:57:55 AM Page 27 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 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 1 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*** COPY 1 OUTPUT MEAN 1 1 48.4 WDM 701 FLOW ENGL REPL COPY 501 OUTPUT MEAN 1 1 48.4 WDM 801 FLOW ENGL REPL END EXT TARGETS MASS-LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS-LINK 12 PERLND PWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 12 MASS-LINK 13 PERLND PWATER IFWO 0.083333 COPY INPUT MEAN END MASS-LINK 13 MASS-LINK 15 IMPLND IWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 15 END MASS-LINK END RUN Springbrook Terrace WQ Volume 3/14/2025 8:57:55 AM Page 28 Predeveloped HSPF Message File Springbrook Terrace WQ Volume 3/14/2025 8:57:55 AM Page 29 Mitigated HSPF Message File Springbrook Terrace WQ Volume 3/14/2025 8:57:56 AM Page 30 Disclaimer Legal Notice This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2025; All Rights Reserved. Clear Creek Solutions, Inc. 6200 Capitol Blvd. Ste F Olympia, WA. 98501 Toll Free 1(866)943-0304 Local (360)943-0304 www.clearcreeksolutions.com Storm Event Q (cfs) Pipe Diameter (in) Radius (ft) Critical Depth (ft) Critical Flow Area (ft2) Top Width (ft) Critical Depth Formula = 1 Velocity (ft/s) Velocity Head (ft) Outlet Invert (ft) Overflow Water Surface (ft) Water Quality 0.47 12 0.5 0.28 0.18 0.90 1.00 2.56 0.10 189.00 189.39 Critical Depth Formula: Area of Circular Segment Given Its Height: Where: Where: Q = flow rate r = radius of circle T = top width h = height of circular segment g = gravitational acceleration A = area of flow City of Renton Surface Water Design Manual Section 6.4.1.1 Step 6: Design pond outlet and determine primary overflow surface 1. Determine critical depth for water quality flow rate 2. Determine area of critical flow depth 3. Calculate critical velocity using continuity equation V=Q/A 4. Calculate velocity head VH=V2/(2g) 5. Determine primary overflow WSE by adding velocity head and critical depth to the outlet invert City of Renton Springbrook Terrace Water Quality Retrofit Appendix D - Hydraulic Calculations Final Design Report Overflow Water Surface Elevation Calculation (Q2T)/gA3= 1 area =r2cos−1[(r−h)/r]− (r−h) x (2rh−h2)^0.5 2 Year Flow Rate = 1.15 cfs 100 Year Flow Rate = 2.68 cfs Element ID From (Inlet) Node To (Outlet) Node From Node Invert Elevation (ft) To Node Invert Elevation (ft) Weir Type Crest Elevation (ft) Crest Length (ft) Weir Height (ft) Discharge Coefficient Peak Flow (cfs) Max HGL Elevation (ft) Max Flow Depth (ft) Weir Overflow-2yr 2-Year_Input 2-Year-Output 189.00 175.00 Rectangular 189.39 2.91 0.50 3.33 0.24 189.48 0.09 Weir Overflow-100yr 100-Year_Input 100-Year-Output 189.00 175.00 Rectangular 189.39 2.91 0.50 3.33 1.25 189.65 0.26 *Weir elements represent the overflow opening in the proposed overflow structure not the emergency overflow spillway *The "To (Outlet) Node" is a dummy feature and does not represent a proposed storm sewer structure. The invert was set sufficiently low as to not affect the calculations. Element ID From (Inlet) Node To (Outlet) Node From Node Invert Elevation (ft) To Node Invert Elevation (ft) Orifice Type Orifice Shape Orifice Diameter (in) Orifice Invert Elevation (ft) Orifice Coefficient Peak Flow (cfs) Max HGL Elevation (ft) Max Flow Depth (ft) Orifice 12-in-Outlet_Pipe_2yr 2-Year_Input 2-Year-Output 189.00 175.00 Side Circular 12.00 189.00 0.6140 0.91 189.48 0.48 Orifice 12-in-Outlet_Pipe_100yr 100-Year_Input 100-Year-Output 189.00 175.00 Side Circular 12.00 189.00 0.6140 1.43 189.65 0.65 *Orifice elements represent the proposed pond outlet pipe *The "To (Outlet) Node" is a dummy feature and does not represent a proposed storm sewer structure. The invert was set sufficiently low as to not affect the calculations. *Orifice elements use weir equations to calculate flow when the headwater height is less than the orifice diameter. Autodesk SSA Schematic Model Layout: *The Output junction, downstream link, and outfall do not represent nor model the actual storm sewer features. These are all dummy features in the model. 42 3.5 7.13 0.59 2.91 Weir Length (ft) 3/4" Bars Spaced 4" O.C Total Width (in) 3/4" Bars Spaced 4" O.C Total Width (ft) Effective Weir Length (ft) Appendix D - Autodesk Storm and Sanitary Analysis Model Output City of Renton Springbrook Terrace Water Quality Retrofit Final Design Report Weir Length (in) Minimum Elevation Calculations: Ecoblock Divider Wall Top and Emergency Overflow Spillway Invert Effective Overflow Structure Weir Length Calculation: Orifice vs. Weir Flow through Orifices (2023 Autodesk SSA User Manual):Orifice Discharge Equation (2023 Autodesk SSA User Manual):Springbrook Terrace Modeled Outlet Pipe as an Orifice Rating Curve: Weir Flow Patterns (2023 Autodesk SSA User Manual):Weir Discharge Equation (2023 Autodesk SSA User Manual):Springbrook Terrace Modeled Overflow Opening as a Weir Rating Curve: Appendix D - Autodesk Storm and Sanitary Analysis Supplemental Information City of Renton Springbrook Terrace Water Quality Retrofit Final Design Report CwLh1.5 CwLh1.67 CwSh2.5 CwLh1.5 + CwsSh2.5 Storm Event Q (cfs) Discharge Coefficient Gravitiational Acceleration (ft/s2) Weir Length (ft) Height of Water over Weir (ft) Spillway Side Slope (H:1) Flow Event Upstream Structure Downstream Structure Pipe Diameter (in) Pipe Length (ft) Upstream Invert Elev. (ft) Downstream Invert Elev. (ft) Pipe Slope (ft/ft) Manning Roughness Coefficient "n" Design Flow (cfs) Flow Velocity at Capacity (ft/s) Pipe Capacity (cfs) Pipe Capacity Check (Pipe Capacity vs. Design Flow) 25-Year SDCB #4 Ex. CB Type 2 15 8 185.80 185.70 0.0125 0.012 2.10 6.39 7.85 ADEQUATE PIPE CAPACITY 25-Year Ex. CB Type 2 S 55th Street 21 216 185.70 184.60 0.0051 0.025 2.10 2.45 5.90 ADEQUATE PIPE CAPACITY 100-Year SDCB #4 Ex. CB Type 2 15 8 185.80 185.70 0.0125 0.012 2.68 6.39 7.85 ADEQUATE PIPE CAPACITY 100-Year Ex. CB Type 2 S 55th Street 21 216 185.70 184.60 0.0051 0.025 2.68 2.45 5.90 ADEQUATE PIPE CAPACITY Proposed and Existing Features Evaluated: 2022 City of Renton Surface Water Design Manual Equation 4-1 and 4-2: Appendix D - Manning's Equation Storm Sewer Conveyance Analysis City of Renton Springbrook Terrace Water Quality Retrofit Final Design Report 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Flow Event US Structure DS Structure Design Flow (cfs) Pipe Length (ft) Pipe Dia. (in) n DS Inv. El. (ft) US Inv. El. (ft) Barrel Area (ft2) Barrel Vel. (ft/s) Barrel Vel. Head (ft) TW El. (ft) Friction Loss (ft) Entr. HGL El. (ft) Entr. Head Loss (ft) Exit Head Loss (ft) Outlet Control El. (ft) Inlet Control El. (ft) Appr. Vel. Head (ft) Bend Head Loss (ft) Junc. Head Loss (Ft) HW El. (ft) Critical Depth (ft) Critical Velocity (ft/s) Hydraulic Radius (ft) Q/AD.5<3.5 Check HW Depth (ft) Normal Depth (ft) 25-Year Ex. CB Type 2 S 55th Street 2.10 216 21 0.025 184.60 185.70 2.41 0.87 0.01 185.74 0.14 185.88 0.00 0.01 185.89 186.41 0.05 0.00 0.00 186.46 0.53 3.46 0.44 0.66 0.76 0.73 25-Year SDCB #4 Ex. CB Type 2 2.10 8 15 0.012 185.70 185.80 1.23 1.71 0.05 186.61 0.01 186.62 0.01 0.05 186.67 186.62 0.00 0.00 0.00 186.67 0.58 3.81 0.31 1.53 0.87 0.44 100-Year Ex. CB Type 2 S 55th Street 2.68 216 21 0.025 184.60 185.70 2.41 1.11 0.02 185.77 0.23 185.99 0.00 0.02 186.02 186.51 0.07 0.00 0.00 186.59 0.59 3.79 0.44 0.84 0.89 0.83 100-Year SDCB #4 Ex. CB Type 2 2.68 8 15 0.012 185.70 185.80 1.23 2.18 0.07 186.65 0.01 186.66 0.01 0.07 186.75 186.75 0.00 0.00 0.00 186.75 0.64 4.21 0.31 1.95 0.95 0.51 Abbreviations: Notes: US: Upstream 1) Critical depth used to find TW El. determined with Figure 4.3.1.F Critical Depth of Flow for Circular Culverts nomograph contained in the 2022 City of Renton SWDM [columns 10 and 21] DS: Downstream 2) Critical velocity solved for with continuity equation and solving for flow area at critical depth (area of circular segment based on height) [column 22] Dia: Diameter 3) Entrance Loss Coefficient (0.2) used in Entrance Head Loss determined with Table 4.3.1.B Entrance Loss Coefficients contained in the 2022 City of Renton SWDM [column 13] El: Elevation 4) Inlet control headwater depth determined with unsubmerged inlet control equation 4-3 contained in the 2022 COR SWDM [column 16] after validating applicability of equation 4-3 [column 24] n: Mannings Roughness Coefficient 5) Normal depth was solved for using FlowMaster a Bentley software [column 26]. FlowMaster program outputs are contained on the next page. Inv: Invert Vel: Velocity Proposed and Existing Features Evaluated: Equation 4-3 2022 COR SWDM: TW: Tailwater Entr: Entrance HGL: Hydraulic Grade Line Appr: Approach Junc: Junction HW: Headwater COR: City of Renton SWDM: Surface Water Design Manual Column Number: Final Design Report Springbrook Terrace Water Quality Retrofit City of Renton Appendix D - Storm Sewer Backwater Analysis City of Renton SWDM Backwater Analysis Calculation Directions: Appendix D - Storm Sewer Backwater Analysis Springbrook Terrace Water Quality Retrofit Final Design Report City of Renton FlowMaster Steady Uniform Flow Normal Depth Calculation: Property/Result Unit 15" 25-Year 15" 100-Year 21" 25-Year 21" 100-Year Roughness Coefficient 0.012 0.012 0.025 0.025 Channel Slope ft/ft 0.0125 0.0125 0.0051 0.0051 Normal Depth in 5.3 6.1 8.7 9.9 Diameter in 15 15 21 21 Discharge cfs 2.1 2.68 2.1 2.68 Flow Area ft² 0.4 0.5 0.9 1.1 Wetted Perimeter ft 1.6 1.7 2.4 2.7 Hydraulic Radius in 2.9 3.2 4.6 5.1 Top Width ft 1.2 1.23 1.72 1.75 Critical Depth in 6.9 7.9 6.3 7.1 Percent Full % 35.4 40.4 41.3 47.4 Critical Slope ft/ft 0.0047 0.0047 0.0172 0.0172 Velocity ft/s 5.41 5.78 2.24 2.39 Velocity Head ft 0.45 0.52 0.08 0.09 Specific Energy ft 0.9 1.02 0.8 0.92 Froude Number 1.672 1.656 0.536 0.526 Maximum Discharge cfs 8.42 8.42 6.33 6.33 Discharge Full cfs 7.82 7.82 5.88 5.88 Flow Type Supercritical Supercritical Subcritical Subcritical Normal Depth in 5.3 6.1 8.7 9.9 Critical Depth in 6.9 7.9 6.3 7.1 Final Design Report Springbrook Terrace Water Quality Retrofit City of Renton Appendix D - Storm Sewer Backwater Analysis Appendix D - Storm Sewer Backwater Analysis City of Renton Springbrook Terrace Water Quality Retrofit Final Design Report Springbrook Terrace Water Quality Retrofit Final Design Report Springbrook Terrace Water Quality Retrofit Final Design Report Appendix E – Geotechnical Report FINAL GEOTECHNICAL REPORT SPRINGBROOK TERRACE POND RETROFIT PROJECT RENTON, WASHINGTON HWA Project No. 2024-062-21 Prepared for David Evans and Associates, Inc. May 2, 2025 Geotechnical Engineering Pavement Engineering Geoenvironmental Hydrogeology Inspection & Testing 21312 30th Dr. SE, STE. 110, Bothell, WA 98021 | 425.774.0106 | hwageo.com May 2, 2025 HWA Project No. 2024-062-21 David Evans and Associates, Inc. 724 Columbia St NW, Suite 320 Olympia, Washington 98501 Attention: Chad Booth, P.E. Subject:Final Geotechnical Engineering Report Springbrook Terrace Pond Retrofit Project Renton, Washington Dear Mr. Booth: As requested, HWA GeoSciences Inc. (HWA) has performed geotechnical engineering evaluations for the Springbrook Terrace Pond Retrofit project in Renton, Washington. This report presents the results of our geotechnical study and geotechnical engineering recommendations to support the evaluation of design alternatives. We appreciate the opportunity to provide geotechnical engineering services for this project. If you have any questions regarding this report or require additional information or services, please contact us at your convenience. Sincerely, HWA GEOSCIENCES INC. Steven R Wright, P.E. Ahmed Mahmoud, P.E, PMP Geotechnical Engineer, Vice President Geotechnical Engineer Springbrook Terrace Pond Retrofit i HWA GEOSCIENCES INC. TABLE OF CONTENTS Page 1.0 INTRODUCTION..........................................................................................................1 1.1 GENERAL.......................................................................................................1 1.2 PROJECT DESCRIPTION ..................................................................................1 2.0 FIELD INVESTIGATION AND LABORATORY TESTING ..................................................2 2.1 GENERAL.......................................................................................................2 2.2 GEOTECHNICAL BORINGS..............................................................................2 2.3 LABORATORY TESTING .................................................................................3 3.0 SITE CONDITIONS......................................................................................................3 3.1 SITE GEOLOGY..............................................................................................3 3.2 SITE SOIL CONDITIONS..................................................................................3 3.3 GROUNDWATER.............................................................................................4 4.0 CONCLUSIONS AND RECOMMENDATIONS..................................................................4 4.1 GENERAL.......................................................................................................4 4.2 SEISMIC DESIGN CONSIDERATIONS ...............................................................5 4.2.1 Liquefaction Susceptibility..........................................................6 4.3 ALTERNATIVE 1 - GRAVITY BLOCK WALLS ..................................................7 4.3.1 Alternative 1 Design Considerations...........................................7 4.3.2 Wall Design Parameters...............................................................7 4.3.3 Subgrade Preparation...................................................................8 4.3.4 Wall Backfill................................................................................9 4.3.5 Wall Drainage..............................................................................9 4.3.6 Global Stability............................................................................9 4.3.7 Retaining Wall Backfill and Compaction....................................10 4.4 ALTERNATIVE 2 – MODIFIED POND SIDE SLOPES..........................................10 4.4.1 Alternative 2 Design Considerations...........................................10 4.4.2 Divider Wall Within Pond...........................................................10 4.5 GENERAL EARTHWORK.................................................................................11 4.5.1 Temporary Excavations...............................................................11 4.5.2 Subgrade Preparation...................................................................12 4.5.3 Structural Fill...............................................................................12 4.5.4 Compaction..................................................................................13 4.5.5 Wet Weather Earthwork ..............................................................13 5.0 CONDITIONS AND LIMITATIONS .................................................................................14 6.0 REFERENCES..............................................................................................................16 Springbrook Terrace Pond Retrofit ii HWA GEOSCIENCES INC. LIST OF FIGURES (FOLLOWING TEXT) Figure 1 Site and Vicinity Map Figure 2 Site and Exploration Plan Figure 3 BH-1 Water Level Data APPENDIX A: LOGS OF HWA EXPLORATIONS Figure A-1 Legend of Terms and Symbols Used on Exploration Logs Figures A-2 and A-3 Boring Logs APPENDIX B: LABORATORY TEST RESULTS Figures B-1 Summary of Material Properties Figures B-2 to B-5 Particle-Size Analysis of Soils Springbrook Terrace Pond Retrofit 1 HWA GEOSCIENCES INC. FINAL GEOTECHNICAL ENGINEERING REPORT SPRINGBROOK TERRACE POND RETROFIT PROJECT RENTON, WASHINGTON 1.0 INTRODUCTION 1.1 GENERAL This report summarizes the results of the geotechnical engineering study completed by HWA GeoSciences Inc. (HWA) for the Springbrook Terrace Pond Retrofit Project in Renton, Washington. The approximate location of the project site is shown on the Site and Vicinity Map, Figure 1 and on the Site and Exploration Plan, Figure 2. Services provided for this project by HWA included a site reconnaissance, a subsurface investigation, a laboratory testing program, geotechnical engineering analyses, the development of geotechnical recommendations to support the evaluation of design alternatives, and preparation of this report. 1.2 PROJECT DESCRIPTION It is our understanding that the City of Renton plans to evaluate and design modifications to the existing Springbrook Terrace Pond. The purpose of the alternative design modifications being considered is to improve the water quality treatment performance of the existing pond. The following pond retrofit alternatives are currently being considered: Alternative 1: Lower the base of the existing Springbrook Terrace Pond by about 5 ft and use relatively short (up to about 5 ft in exposed height) gravity block walls along portions of the side slopes of the pond to allow the current top of pond slope to remain unchanged. Where needed, the proposed retaining walls will be located approximately midway between the top and bottom of the pond side slopes. Alternative 2: Lower the base of the existing pond by about 5 ft and regrade the pond side slopes (starting at the current top of pond slope) at an inclination of either 3H:1V or 2H:1V. This alternative does not include retaining walls within the pond. Alternative 1 (gravity block walls) was not selected for construction; however, the geotechnical recommendations for this alternative are retained in this report for documentation purposes. In addition to the grading modifications described above, the final design also includes construction of a divider wall within the pond. This wall will increase the stormwater flow path length, thereby enhancing sedimentation and improving overall treatment performance. May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 2 HWA GEOSCIENCES INC. 2.0 FIELD INVESTIGATION AND LABORATORY TESTING 2.1 GENERAL HWA conducted a field investigation in October 2024 that included two (2) geotechnical borings. Approximate boring locations are shown on the Site and Exploration Plan, Figure 2. Laboratory testing was conducted on select soil samples obtained from the borings at HWA’s geotechnical and materials testing laboratory in Bothell, Washington. These tasks are summarized in the following sections. 2.2 GEOTECHNICAL BORINGS HWA advanced two (2) geotechnical borings, designated BH-1 and BH-2, at the site on October 4, 2024. The borings were advanced to depths ranging between approximately 39.5 and 41.5 ft below the existing ground surface (bgs) using a limited access, track-mounted drill rig and hollow stem auger drilling methods. A groundwater monitoring well was installed in boring BH-1 in accordance with Department of Ecology (DOE) requirements to monitor fluctuations in groundwater levels over time. Drilling was performed by Holocene Drilling, Inc., whose services were provided under subcontract to HWA. An HWA representative was on-site full-time during drilling to oversee boring operations and to observe and document subsurface soil and groundwater conditions. Soil samples were collected at 2½-foot intervals to a depth of 10 feet followed by 5-foot intervals to the termination depth of the borings. Split-spoon soil samples were obtained using Standard Penetration Test (SPT) sampling methods in general accordance with ASTM International (ASTM) D 1586. Soil samples were placed in sealed containers and transported to HWA’s geotechnical laboratory for further classification and testing. Borehole BH-2 was backfilled with bentonite chips upon completion of the exploration per DOE decommissioning requirements. A legend explaining the terms and symbols displayed on the logs as well as logs of the borings are presented in Appendix A, Figures A-1 through A-3. The attached boring logs include pertinent information related to the explorations, including subsurface stratigraphy, soil classification, sample depths, SPT blow counts, and select laboratory test results. The stratigraphic contacts shown on the logs represent the approximate boundaries between soil types; actual transitions may be more gradual. Groundwater levels indicated on the logs are valid only for the specific date and locations reported and, therefore, are not necessarily representative of the conditions at other locations and times. The latitude/longitude coordinates shown on the logs were obtained in the field using handheld GPS equipment and should be considered approximate. May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 3 HWA GEOSCIENCES INC. 2.3 LABORATORY TESTING HWA conducted laboratory testing on select soil samples to characterize relevant physical and engineering properties of the soils encountered during the field investigation. Testing included visual classification and determination of natural moisture content and grain size distribution. The tests were conducted in general accordance with appropriate ASTM standards and are discussed in further detail in Appendix B. The test results are presented in Appendix B, and/or displayed on the exploration logs in Appendix A, as appropriate. 3.0 SITE CONDITIONS 3.1 SITE GEOLOGY The project site is located in the Puget Lowland, a region shaped by repeated glacial advances and retreats during the Quaternary period. This glaciation created a complex sequence of depositional and erosional features, including glacial till, outwash, and lacustrine deposits. Each glacial cycle contributed to the layering of sediments, with the most recent advance of the Puget lobe of the Cordilleran ice sheet depositing substantial materials during the Vashon Stade. According to the Geologic Map of the Renton Quadrangle, King County, Washington (D.R. Mullineaux, 1965), the site is underlain primarily by recessional outwash deposits, overlying advance outwash deposits. Recessional outwash consists of stratified sands and gravels deposited by meltwater streams during the retreat of the ice sheet. These materials are typically well-sorted and permeable, reflecting deposition in high-energy environments. The advance outwash beneath the recessional deposits comprises dense to very dense sands with varying amounts of gravel and occasional silt. These deposits formed during the initial advance of the ice sheet as meltwater streams deposited materials ahead of the glacier. The advance outwash was subsequently compacted by the overlying glacier, resulting in high density and reduced permeability. 3.2 SITE SOIL CONDITIONS Our interpretation of the subsurface conditions at the site is based on the results of the geotechnical borings conducted during our field investigation and review of available geologic and geotechnical information for the area in the project vicinity. The soil observed in our borings generally consisted of fill soils overlying native recessional and advanced outwash deposits. A brief description of the soil units observed at the site is provided below in order of deposition, beginning with the most recently deposited unit. Fill/Reworked Native: The uppermost unit, ranging from approximately 7.5 to 10 ft in thickness, consists of loose to dense silty sand with variable gravel content. Organic material, including roots, was noted throughout the unit. This fill likely represents a mix of reworked native soils and imported materials associated with prior construction activities at the site of Springbrook Terrace Pond. May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 4 HWA GEOSCIENCES INC. Recessional Outwash: Underlying the fill, recessional outwash deposits were encountered extending to a depth of approximately 15 ft bgs. These deposits generally consist of loose to medium dense, silty sand with varying gravel content. Mottling observed within this unit suggests periodic saturation, potentially related to seasonal fluctuations in groundwater levels. Advance Outwash: Below the recessional outwash, advance outwash deposits were observed, extending to the borehole termination depths. This unit is characterized by dense to very dense, silty sand with gravel that is occasionally interbedded with lenses of sandy gravel. 3.3 GROUNDWATER At the time of drilling in early October 2024, groundwater was not observed in borings BH-1 and BH-2. However, rust mottling observed in samples of the recessional outwash soils in both borings suggests that groundwater levels may elevate seasonally to depths of 7.5 to 10 ft bgs. Alternatively, water that infiltrates through the bottom of the pond could be the cause of the observed mottling. We installed a 2-inch diameter PVC standpipe well in boring BH-1 to monitor fluctuations in groundwater level over time. The monitoring well was screened from approximately 15 to 35 ft bgs. A pressure transducer was installed to monitor groundwater fluctuations in the well and is set to record the hydrostatic pressure every hour for up to one year. Groundwater elevations from October 2024 through March 18, 2025, obtained from the pressure transducer are included in Figure 3. During this time period, the highest groundwater level has generally been observed to be within about 33 ft of the ground surface (about elevation 162 ft). 4.0 CONCLUSIONS AND RECOMMENDATIONS 4.1 GENERAL The soil conditions and site topography are such that design and construction of the proposed improvements is feasible provided the recommendations presented in this geotechnical report are followed. A general geotechnical summary of our recommendations is provided below, and additional details are provided in the following sections. The proposed pond retrofit will involve either lowering the base of the existing pond by about 5 ft and using gravity block walls along portions of the side slopes of the pond to allow the current top of pond slope to remain unchanged (Alternative 1) or lowering the base of the existing pond by about 5 ft and regrading the pond side slopes at an inclination of either 3H:1V or 2H:1V (Alternative 2). May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 5 HWA GEOSCIENCES INC. For Alternative 2, we evaluated the stability of regraded pond side slopes at inclinations of 3H:1V and 2H:1V. The results of the global stability analysis indicated that 2H:1V pond side slopes are not feasible; however, slopes constructed at 3H:1V are suitable for the proposed pond retrofit. Detailed recommendations for Alternatives 1 and 2 are provided in the following report sections. While both alternatives were considered, the gravity block wall option (Alternative 1) will not be implemented. The geotechnical recommendations for this option are retained in this report for documentation purposes. The final design also includes construction of a divider wall within the pond to increase the stormwater flow path length and enhance treatment efficiency. Geotechnical recommendations for the divider wall are provided in Section 4.5 of this report. 4.2 SEISMIC DESIGN CONSIDERATIONS Earthquake loading for the project site was developed in accordance with the General Procedure provided in Section 3.4 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design, 2nd Edition, 2011 with 2022 Interim Revisions, and the Washington State Department of Transportation (WSDOT) amendments to the AASHTO Guide Specifications provided in the Bridge Design Manual (LRFD) (WSDOT, 2023). For seismic analysis, the Site Class is required to be established and is determined based on the average soil properties in the upper 100 ft below the ground surface. Based on our subsurface explorations and understanding of site geology, it is our opinion that the site is underlain by soils that are consistent with Site Class D. The design parameters for the design level event with a 7 percent probability of exceedance in 75 years (equal to a return period of 1,033 years) were obtained from the United States Geological Survey (USGS) Unified Hazard Tool website using the U.S. 2014 Dynamic Conterminous edition (v4.2.0), which provides the probabilistic seismic hazard parameters from the 2014 Updates to the National Hazard Maps (Peterson, et al., 2014). Site coefficients were developed following the WSDOT BDM that adopts the site coefficients provided in American Society of Civil Engineers 7-16 (ASCE, 2016). The recommended seismic coefficients for the design event at the project site are provided in Table 1. The spectral acceleration coefficient at 1-second period (SD1) is between 0.3 and 0.5; therefore, Seismic Design Category D, as given by AASHTO Table 3.5-1 (AASHTO, 2011), should be used. May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 6 HWA GEOSCIENCES INC. Table 1. Seismic Coefficients Using AASHTO Guide Specifications Calculated by USGS Seismic Unified Hazard Tool Location: Lat. 47.429499; Long. -122.210551 Site CoefficientsSite Class Peak Horizontal Bedrock AccelerationPBA, (g) Spectral Bedrock Acceleration at 0.2 sec Ss, (g) Spectral Bedrock Acceleration at 1.0 sec S1, (g)Fpga Fa Fv Peak Horizontal Acceleration PGA (As), (g) D 0.4465 1.032 0.272 1.154 2.057 1.857 0.515 4.2.1 Liquefaction Susceptibility Liquefaction is a temporary loss of soil shear strength that occurs in response to ground motions during a strong earthquake. Loose, saturated cohesionless soils are most susceptible to earthquake-induced liquefaction; however, research has shown that certain silts and low- plasticity clays are also susceptible. Primary factors controlling the development of liquefaction include the intensity and duration of ground motions, the characteristics of subsurface soils, in-situ stress conditions, and the depth to groundwater. Liquefaction susceptibility of the soils at the project site was determined using the simplified procedure originally developed by Seed and Idriss (1971) and updated by Youd et al. (2001) and Idriss and Boulanger (2004, 2006). The procedure utilizes a semi-empirical approach that compares the cyclic resistance ratio (CRR) required to initiate liquefaction of the material to the cyclic shear stress ratio (CSR) induced by the design earthquake. The factor of safety relative to liquefaction is the ratio of the CRR to the CSR; where this ratio is computed to be less than one, the analysis would indicate that liquefaction is likely to occur during the design earthquake. The CRR is primarily dependent on soil density, with the current practice being based on the Standard Penetration Test (SPT) N-value corrected for hammer efficiency, fines content, and earthquake magnitude. CSR is generally determined by the formulation developed by Seed and Idriss (1971) and relates equivalent shear stress caused in the soil at any depth to the effective stress at that depth and the peak ground acceleration at the surface. The soils encountered at each of the two (2) geotechnical borings completed for this study were analyzed to evaluate liquefaction susceptibility using the methodology described above. The results of our analysis indicate that the soil profiles at BH-1 and BH-2 are not susceptible to liquefaction. May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 7 HWA GEOSCIENCES INC. 4.3 ALTERNATIVE 1 - GRAVITY BLOCK WALLS Alternative 1 includes the use of gravity block walls to accommodate grade changes associated with the proposed pond retrofit. Recommendations for gravity block walls are provided below. 4.3.1 Alternative 1 Design Considerations The following key points should be reviewed when evaluating Alternative 1: To satisfy global wall stability requirements for gravity block walls constructed on the pond slopes, we recommend that walls be embedded at least 2 ft below existing grade but in no case should the embedment depth be less than the exposed height of the gravity block wall (see Section 4.3.2 for additional details). Temporary excavation slopes should be sloped no steeper than 1.5H:1V (see Section 4.5.1 for additional details). This inclination should be considered when evaluating if there is adequate room on the site to achieve the recommended minimum depth of wall embedment and accommodate both the width of the gravity block wall (which could be up to 5 ft for the taller portions of the walls) and the recommended wall drainage system behind the wall (see Section 4.3.5). On the west side of the pond, existing soil that currently prevents water from the pond flowing downslope to the west will need to be removed in order to construct a gravity block wall. Because gravity block walls are not watertight structures, water from the pond could leak through the wall and result in downslope erosion and slope instability. As a result, if Alternative 1 is selected as the preferred alternative, consideration should be given to placing a geosynthetic liner in front of (not under) the western gravity block wall. 4.3.2 Wall Design Parameters We assume that gravity block walls will consist of a proprietary wall system that the wall supplier will design for internal stability. The walls should be designed in accordance with the most current version of the AASHTO LRFD Bridge Design Manual and Section 6.13 of the WSDOT Standard Specifications (WSDOT, 2024). We recommend that the walls be designed using the parameters presented in Table 2. If the design of gravity walls is performed using the Load and Resistance Factor Design (LRFD) method, appropriate resistance factors should be used. For the Extreme Event I Limit State, the walls should be designed for a horizontal seismic acceleration coefficient (Kh) of one-half the peak ground acceleration, or 0.258g, and vertical seismic coefficient (Kv) of 0.0g (assuming the wall is free to move during a seismic event). Extreme Event I Limit State is defined in the AASHTO Standard Specifications as a May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 8 HWA GEOSCIENCES INC. safety check involving an extreme load event resulting from an earthquake in combination with the dead load and a fraction of the live loads. Table 2. Recommended Gravity Block Wall Design Parameters Soil Properties Wall Backfill Retained Soil Foundation Soil Unit Weight (pcf) 125 125 135 Friction Angle (deg) 34 34 38 Cohesion (psf) 10 10 0 Strength Limit State (EP+LL) Extreme Limit State (EP+EQ) Ultimate Bearing Resistance (ksf) 3.5 3.5 Horizontal Seismic Acceleration Coefficient (kh) (g) N/A 0.258 Notes: EP = Earth Pressure LL = Live Load EQ = Earthquake An unfactored coefficient of friction of 0.5 times the effective stress at the base of the wall can be used to estimate sliding resistance. To satisfy global wall stability requirements for gravity block walls constructed on the pond slopes, we recommend that walls be embedded at least 2 ft below existing grade but in no case should the embedment depth be less than the exposed height of the gravity block wall. 4.3.3 Subgrade Preparation Subgrade preparation is important to limit differential settlement of the walls and maintain global stability. Subgrade preparation should begin with the removal of all topsoil, deleterious material, and vegetation to expose competent native soils or adequately compacted fill. A smooth bucket should be used to limit disturbance, and the soils should be thoroughly compacted prior to placement of structural fill for wall bases. We recommend that an HWA geotechnical engineer, or their representative, evaluate the exposed subgrade to identify areas of loose/soft, pumping or otherwise unsuitable soils. If such soils are encountered, they should be over-excavated as directed by the geotechnical engineer or their representative and replaced with properly compacted material. We recommend the retaining walls be constructed on a 1-foot-thick leveling pad consisting of crushed surfacing base course (CSBC) compacted to at least 95 percent of the maximum dry density, as determined by ASTM D 1557 (Modified Proctor). The leveling pad should be graded to establish the proper wall batter. Additional subgrade preparation recommendations are provided in Section 4.5.2 of this report. May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 9 HWA GEOSCIENCES INC. 4.3.4 Wall Backfill Wall backfill materials should consist of Gravel Backfill for Walls, as described in Section 9-03.12(2) of the WSDOT Standard Specifications (WSDOT, 2024) and should be compacted to at least 95 percent of the maximum dry density as determined by ASTM D 1557 (Modified Proctor). The wall backfill should be placed and compacted in layers as each row of blocks is placed. The contractor should consider the weight of construction equipment operating within the fill zone behind the wall. For compaction, materials within about 3 ft of the wall face should be compacted with lighter equipment to limit the loading on the back of the wall. 4.3.5 Wall Drainage Drainage should be provided behind all walls and should consist of a 4- to 6-inch diameter, perforated, rigid, plastic pipe, bedded and backfilled with Gravel Backfill for Drains, as specified in Section 9-03.12(4) of the WSDOT Standard Specifications (WSDOT, 2024). The drain rock should surround the drainpipe by at least 12 inches. The pipes should slope to drain to a suitable outlet. 4.3.6 Global Stability HWA performed global stability analyses of the proposed gravity block walls using limit equilibrium methods and the software SLIDE 8.032 (Rocscience, 2020). Limit equilibrium methods consider force (or moment) equilibrium along potential failure surfaces. The analysis computes results in terms of a factor of safety, which is computed as the ratio of the summation of the resisting forces to the summation of the driving forces. Global stability for gravity block walls was evaluated for static and pseudo-static conditions. For static conditions, the WSDOT Geotechnical Design Manual (WSDOT, 2022) requires a minimum factor of safety of 1.3 for walls not directly supporting structures to be considered sufficiently stable. Our analyses yield a factor of safety of 1.3 or greater for walls embedded as recommended herein, indicating that a gravity wall that is properly designed for internal stability will be sufficiently stable to support static loading. Seismic global stability was performed to evaluate pseudo-static (where applicable) conditions for the proposed gravity walls. For seismic conditions, the WSDOT Geotechnical Design Manual (WSDOT, 2024) requires a minimum factor of safety of 1.1 for a wall to be considered stable. The results of our analysis yield a factor of safety of 1.1 for gravity walls embedded as recommended herein, which indicates sufficient stability during a design level earthquake. In addition, our analysis demonstrates that the proposed retaining walls will provide a slight increase in the overall stability of the existing pond slopes for both static and seismic cases. As a result, we conclude that the proposed retaining walls would not have an adverse impact on nearby private property. May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 10 HWA GEOSCIENCES INC. 4.3.7 Retaining Wall Backfill and Compaction Backfill materials for retaining walls should meet the specifications for Gravel Borrow in Section 9-03.14(1) of the Standard Specifications (WSDOT, 2024) or an approved alternative. Backfill should be compacted to no less than 95 percent of the Maximum Dry Density as determined by ASTM D 1557 (Modified Proctor). Achieving proper density of compacted fills depends on the size and type of compaction equipment, the number of passes, lift thickness, subgrade conditions, and soil moisture-density properties. We recommend a maximum lift thickness of 12 inches in a loose condition to facilitate compaction. In areas where limited space and/or loading considerations restrict the use of heavy equipment, smaller equipment can be used, but the soil must be placed in sufficiently thin lifts to achieve the required density. 4.4 ALTERNATIVE 2 – MODIFIED POND SIDE SLOPES Alternative 2 includes re-grading the pond slopes (starting at the current top of pond slope) at an inclination of either 3H:1V or 2H:1V. This alternative does not include retaining walls within the pond, but it does include construction of a divider wall within the pond. 4.4.1 Alternative 2 Design Considerations The following key points should be reviewed when evaluating Alternative 2: We evaluated the stability of the proposed 3H:1V and 2H:1V pond slopes under both static and seismic cases. Based on the results of this evaluation, we do not recommend re-grading the slopes at an inclination of 2H:1V. Instead, we recommend that permanent pond and adjacent slopes be constructed no steeper than 3H:1V. Furthermore, for pond slopes inclined at 3H:1V or flatter, we anticipate that adequate factors of safety against global failure will be maintained under both static and seismic cases. If the re-grading of pond slopes under Alternative 2 involves the need to place fill to establish all or a portion of the pond side slopes, measures should be taken to prevent surficial instability and/or erosion of the slopes. This could be accomplished by conscientious compaction of the fill material in level lifts, benched cuts into the slope face from undisturbed existing soil, maintaining adequate drainage, and planting the re-graded slope face with vegetation as soon as possible after construction. To achieve the specified compaction at the slope face when placing fill to establish the pond side slopes, it may be necessary to overbuild the slopes several feet, and then trim back to finish grade. 4.4.2 Divider Wall Within Pond A divider wall is planned within the pond to enhance stormwater treatment performance. The wall will act as a physical partition that increases the flow path length of the influent stormwater, May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 11 HWA GEOSCIENCES INC. thereby improving overall treatment efficiency. Recommended geotechnical parameters for the structural design of the divider wall are presented below in Table 3. Table 3. Recommended Divider Wall Design Parameters Parameter Recommended Value Saturated Unit Weight 120 pcf Effective Unit Weight (Submerged)57.6 pcf Soil Internal Friction Angle (φ)32° Ultimate Bearing Capacity 4 ksf Minimum Embedment Depth 18 inches Horizontal Seismic Acceleration Coefficient 0.258g Ultimate Equivalent Fluid Pressure (Passive Resistance) 187 psf/ft Ultimate Friction Coefficient – Soil to Precast Concrete¹ 0.40 Ultimate Friction Coefficient – Soil to Cast-in-Place Concrete¹ 0.50 ¹ Assumes concrete is underlain by at least 6 inches of crushed surfacing base course. The structural engineer should evaluate the stability of the wall under the critical loading condition in which water is present on one side and dry conditions exist on the other. The actual embedment depth required to maintain equilibrium may exceed the minimum value noted above, depending on final design loads. While WSDOT permits waiving seismic design for non-essential, non-life-safety structures, AASHTO recommends including seismic loading for retaining-type structures unless the seismic hazard is negligible. We defer the final seismic design decision to the City and the structural engineer of record. 4.5 GENERAL EARTHWORK The following sections of this report provide general earthwork recommendations. 4.5.1 Temporary Excavations Maintenance of safe working conditions, including temporary excavation stability, is the responsibility of the contractor. In accordance with Part N of Washington Administrative Code (WAC) 296-155, latest revisions, all temporary cuts more than 4 ft in height must be either sloped or shored. May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 12 HWA GEOSCIENCES INC. Based on the WAC guidelines and the results of our geotechnical explorations, the on-site existing fill/disturbed native and native soils classify as Type C soils. These materials should be sloped no steeper than 1.5H:1V. It is possible that seepage could be encountered at shallow depths particularly during periods of wet weather. The recommended maximum slope presented above is applicable to temporary excavations above the water table only; flatter side slopes would be required for excavations where groundwater seepage is encountered. The contractor should monitor the stability of temporary cut slopes and adjust the construction schedule and slope inclination accordingly. The contractor should be responsible for control of groundwater and surface water and should employ sloping, slope protection, ditching, sumps, dewatering, and other measures, as necessary, to prevent sloughing of soils. 4.5.2 Subgrade Preparation Proper subgrade preparation is critical to the performance of new walls and new fill placed to modify the geometry of the pond side slopes. Based on the planned elevations of the proposed improvements, we anticipate that subgrade soils will consist of existing structural fill soils comprised primarily of sand and gravel with variable amounts of silt. In general, these soils are considered suitable subgrade material. Any organic, soft, disturbed, or otherwise unsuitable subgrade material should be removed from the footprint of all walls and new fills. A geotechnical engineer or their representative should inspect subgrade conditions below the footprint of all walls and new fills. Suitability of subgrade soils underlying retaining walls and new fill material is typically determined by visual inspection and T-probe assessment. For project improvements that occupy large areas, subgrade inspection is typically accomplished by performing a proof roll over the footprint of the improvements using heavy construction equipment, such as a fully loaded dump truck or large roller. Areas of limited access can be evaluated with a steel T-probe. If unsuitable subgrade soils are present, the soils should be removed and replaced with structural fill as directed on-site by a geotechnical engineer. Depending on nature of the subgrade materials, HWA may recommend scarifying and recompacting the subgrade in lieu of removal and replacement. The depth and extent of subgrade repair will be directed by the on-site geotechnical engineer. 4.5.3 Structural Fill All materials used as backfill for retaining walls and to construct new pond slopes are to be considered structural fill. The on-site soils are highly variable in composition and will have varying degrees of moisture sensitivity. The existing fill soils may potentially be reused as structural fill provided the material is granular, free-draining, and devoid of organic matter or other deleterious materials. Structural fill should have a maximum particle size of 4 inches in any dimension and should contain less than 10 percent fines (portion passing the U.S. Standard No. 200 sieve) by weight. If any on-site soil is proposed for reuse as structural fill, a May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 13 HWA GEOSCIENCES INC. representative sample should be provided to HWA so that appropriate laboratory testing can be performed to determine the suitability of the material. Imported structural fill should meet the criteria provided in the Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT, 2024) for one of the following materials: Gravel Borrow, Section 9-03.14(1) Crushed Surfacing Base Course (CSBC), Section 9-03.9(3) Crushed Surfacing Top Course (CSTC), Section 9-03.9(3) Aggregate for Gravel Base, Section 9-03.10 4.5.4 Compaction Structural fill should be moisture conditioned and compacted to the requirements specified in Section 2-03.3(14), Method C, of the WSDOT Standard Specifications (WSDOT, 2023), except that maximum dry densities should be obtained using ASTM D 1557 (Modified Proctor). All fills should be placed in lifts and compacted to at least 95 percent of its maximum dry density, as determined using test method ASTM D 1557 (Modified Proctor). In general, the thickness of loose lifts should not exceed 12 inches for heavy duty compactors and 4 inches for hand-operated equipment (such as jumping jacks and small plate compactors). The procedure to achieve proper density of compacted fill depends on the size and type of compaction equipment, the number of passes, thickness of the layer being compacted, and soil moisture-density properties. Achievement of proper density of a compacted fill depends on the size and type of compaction equipment, the number of passes, thickness of the layer being compacted, and soil moisture- density properties. In areas where limited space restricts the use of heavy equipment, smaller equipment can be used, but the soil must be placed in thin enough layers to achieve the required compaction. 4.5.5 Wet Weather Earthwork During periods of wet weather, even the most permeable soil can become difficult to work and compact. We anticipate considerable variability in the fines content of the in-situ soils. Soils with higher fines contents will be difficult to work and compact when wet. If fill is to be placed or earthwork is to be performed in wet weather or under wet conditions, the following recommendations apply: Earthwork should be performed in small areas to minimize exposure to wet weather. Excavation of unsuitable and/or softened soil should be followed promptly by placement and compaction of clean structural fill. The size and type of construction May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 14 HWA GEOSCIENCES INC. equipment used may need to be limited to prevent soil disturbance. Under some circumstances, it may be necessary to excavate soils with a backhoe to minimize subgrade disturbance caused by equipment traffic. Material used as excavation backfill in wet weather should consist of clean granular soil with less than 5 percent passing the U.S. Standard No. 200 sieve, based on wet sieving the fraction passing the ¾-inch sieve. The fines should be non-plastic. It should be noted this is an additional restriction on the structural fill materials specified herein. The ground surface within the construction area should be graded to promote surface water run-off and to prevent ponding. Within the construction area, the ground surface should be sealed on completion of each shift by a smooth drum vibratory roller, or equivalent, and under no circumstances should soil be left uncompacted and exposed to moisture infiltration. Excavation and placement of backfill materials should be monitored by a geotechnical engineer experienced in wet weather earthwork to determine that the work is being accomplished in accordance with the project specifications and the recommendations contained herein. 5.0 CONDITIONS AND LIMITATIONS We have prepared this geotechnical report solely for the City of Renton and David Evans and Associates, Inc. to support the design and construction of the proposed Springbrook Terrace Pond Retrofit project in Renton, Washington. The conclusions and interpretations presented in this report should not be construed as our warranty of subsurface conditions at the site. Experience has shown that soil and groundwater conditions can vary significantly over small distances and with time. Inconsistent conditions can occur between explorations that may not be detected by a geotechnical study of this scope and nature. If, during future site operations, subsurface conditions are encountered which vary appreciably from those described herein, HWA should be notified for review of the recommendations of this report, and revision of such if necessary. Within the limitations of scope, schedule and budget, HWA provided these services in accordance with generally accepted professional principles and practices in the fields of geotechnical engineering and engineering geology in the area at the time the report was prepared. No warranty, express or implied, is made. HWA does not practice or consult in the field of safety engineering. We do not direct the contractor’s operations and cannot be responsible for the safety of personnel other than our own on the site. As such, the safety of others is the responsibility of the contractor. The contractor May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 16 HWA GEOSCIENCES INC. 6.0 REFERENCES American Association of State Highway and Transportation Officials, 2020, LRFD Bridge Design Specifications, 9th Edition, Washington D.C. American Society of Civil Engineers (ASCE) 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures. D.R. Mullineaux, 1965. Geologic Map of the Renton Quadrangle, King County, Washington, Department of the Interior United States Geological Survey, Washington Geologic Quadrangle Map GQ-405, Scale 1:24,000. Idriss, I.M, and Boulanger, RW, 2004, Semi-Empirical Procedures for Evaluating Liquefaction Potential During Earthquakes, presented at the Joint 11th ISCDEE & 3rd ICEGE, January 2004. Idriss, I.M., and Boulanger, R.W., 2006, “Semi-empirical procedures for evaluating liquefaction potential during earthquakes”, Soil Dynamics and Earthquake Engineering, 11th International Conference on Soil Dynamics and Earthquake Engineering (ICSDEE): Part II, Volume 26, Issues 2–4, February–April 2006, Pages 115–130. Petersen, M.D., Moschetti, M.P., Powers, P.M., Mueller, C.S., Haller, K.M., Frankel, A.D., Zeng, Yuehua, Rezaeian, Sanaz, Harmsen, S.C., Boyd, O.S., Field, Ned, Chen, Rui, Rukstales, K.S., Luco, Nico, Wheeler, R.L., Williams, R.A., and Olsen, A.H., 2014, Documentation for the 2014 update of the United States national seismic hazard maps, U.S. Geological Survey Open-File Report 2014–1091, 243 p. Seed, H.B. and Idriss, I.M., 1971, Simplified Procedure for Evaluating Soil Liquefaction Potential. Journal of Soil Mechanics Foundation Division, ASCE, Vol. 97, No. SM9, pp. 1249-1273. WSDOT, 2024, Geotechnical Design Manual, Washington State Department of Transportation. WSDOT, 2024, Bridge Design Manual (LRFD), Washington State Department of Transportation. WSDOT, 2024, Standard Specifications for Road, Bridge, and Municipal Construction, Washington State Department of Transportation. Youd, T.L., et al., 2001, Liquefaction Resistance of Soils: Summary Report from the 1996 NCEER and 1998 NCEER/NSF Workshops on Evaluation of Liquefaction Resistance of May 2, 2025 HWA Project No. 2024-062-21 Springbrook Terrace Pond Retrofit 17 HWA GEOSCIENCES INC. Soils, Journal of Geotechnical and Geoenvironmental Engineering, Geo-Institute of the American Society of Civil Engineers (ASCE), Vol. 127, No. 10, October 2001. © 2024 Microsoft Corporation © 2024 Maxar ©CNES (2024) Distribution Airbus DS © 2024 TomTom © 2024 Microsoft Corporation © 2024 TomTom CF 2024-062-21 SITE AND VICINITY MAP SPRINGBROOK TERRACE POND RETROFIT RENTON, WASHINGTON 0 200'400'600'800' SCALE: 1" = 400' VICINITY MAP SITE MAP 0 1000'2000'3000'4000' SCALE: 1" = 2000' SITE SC 1 DRAWN BY: PROJECT # C:\USERS\CFRY\DESKTOP\2024-062-21 SPRINGBROOK TERRACE POND RETROFIT\2024-062-21 SPRINGBROOK TERRACE POND RETROFIT.DWG <1> Plotted: 10/23/2024 7:30 AM CHECK BY: FIGURE NO.: DBE/MWBE © 2024 Microsoft Corporation © 2024 Maxar ©CNES (2024) Distribution Airbus DS SITE AND EXPLORATION PLAN 2024-062-21 SPRINGBROOK TERRACE POND RETROFIT RENTON, WASHINGTON BASE MAP PROVIDED BY: BING 0 10 20 30 40 SCALE: 1" = 20' SPRINGBROOK TERRACE Scale: 1" = 20'-0"EXPLORATION LEGEND BH-1 BOREHOLE DESIGNATION AND APPROXIMATE LOCATION (HWA, 2024) SC/JLG CF FIGURE NO.: PROJECT NO.: DRAWN BY: CHECK BY: C:\USERS\CFRY\DESKTOP\2024-062-21 SPRINGBROOK TERRACE POND RETROFIT\2024-062-21 SPRINGBROOK TERRACE POND RETROFIT.DWG <2> Plotted: 10/23/2024 7:30 AM 2 DBE/MWBE AERIAL IMAGERY REFERENCE IS APPROXIMATE AND MAY APPEAR OFFSET FROM SURVEYED DATA AND BASEMAPS. BH-1 BH-2 150 152 154 156 158 160 162 164 166 168 170 Gr o u n d W a t e r E l e v a t i o n ( f t ) Date and Time BH-1 Ground Water Elevation BH-1 WATER LEVEL DATA 2024-062-21 FIGURE NO. PROJECT NO.SPRINGBROOK TERRACE POND RETROFIT PROJECT Renton, Washington 3 APPENDIX A LOGS OF HWA EXPLORATIONS A-12024-062-21 Springbrook Terrace Pond Retrofit Renton, Washington SYMBOLS USED ON EXPLORATION LOGS LEGEND OF TERMS AND Clean Gravel (little or no fines) More than 50% of Coarse Fraction Retained on No. 4 Sieve Gravel with SM SC ML MH CH OH RELATIVE DENSITY OR CONSISTENCY VERSUS SPT N-VALUE Very Loose Loose Medium Dense Very Dense Dense N (blows/ft) 0 to 4 4 to 10 10 to 30 30 to 50 over 50 Approximate Relative Density(%) 0 - 15 15 - 35 35 - 65 65 - 85 85 - 100 COHESIVE SOILS Consistency Very Soft Soft Medium Stiff Stiff Very Stiff Hard N (blows/ft) 0 to 2 2 to 4 4 to 8 8 to 15 15 to 30 over 30 Approximate Undrained Shear Strength (psf) <250 250 - No. 4 Sieve Sand with Fines (appreciable amount of fines) amount of fines) More than 50% Retained on No. 200 Sieve Size Sand and Sandy Soils Clean Sand (little or no fines) 50% or More of Coarse Fraction Passing Fine Grained Soils Silt and Clay Liquid Limit Less than 50% 50% or More Passing No. 200 Sieve Size Silt and Clay Liquid Limit 50% or More 500 500 - 1000 1000 - 2000 2000 - 4000 >4000 DensityDensity USCS SOIL CLASSIFICATION SYSTEM Coarse Grained Soils Gravel and Gravelly Soils Highly Organic Soils GROUP DESCRIPTIONS Well-graded GRAVEL Poorly-graded GRAVEL Silty GRAVEL Clayey GRAVEL Well-graded SAND Poorly-graded SAND Silty SAND Clayey SAND SILT Lean CLAY Organic SILT/Organic CLAY Elastic SILT Fat CLAY Organic SILT/Organic CLAY PEAT MAJOR DIVISIONS GW SP CL OL PT GP GM GC SW COHESIONLESS SOILS Fines (appreciable LEGEND 2024-062.GPJ 10/8/24 PROJECT NO.:FIGURE: Coarse sand Medium sand SIZE RANGE Larger than 12 in Smaller than No. 200 (0.074mm) Gravel 3 in to 12 in 3 in to No 4 (4.5mm) No. 4 (4.5 mm) to No. 200 (0.074 mm) COMPONENT DRY Absence of moisture, dusty, dry to the touch. MOIST COMPONENT DEFINITIONS time of drilling) Groundwater Level (measured in well or open hole after water level stabilized) Groundwater Level (measured at TEST SYMBOLS GROUNDWATER SYMBOLS AL Atterberg Limits: California Bearing Ratio CN Consolidation DD OC Organic Content pH pH of Soils 12 - 30% Clayey, Silty, Sandy, Gravelly 3 in to 3/4 in 3/4 in to No 4 (4.5mm) No. 4 (4.5 mm) to No. 10 (2.0 mm) No. 10 (2.0 mm) to No. 40 (0.42 mm) No. 40 (0.42 mm) to No. 200 (0.074 mm) NOTES: Soil classifications presented on exploration logs are based on visual and laboratory observation. Density/consistency, color, modifier (if any) GROUP NAME, additions to group name (if any), moisture content. Proportion, gradation, and angularity of constituents, additional comments. (GEOLOGIC INTERPRETATION) Please refer to the discussion in the report text as well as the exploration logs for a more complete description of subsurface conditions. Soil descriptions are presented in the following general order: < 5% Damp but no visible water. WET Visible free water, usually soil is below water table. Boulders Cobbles Coarse gravel Fine gravel Sand MOISTURE CONTENT COMPONENT PROPORTIONS Fine sand Silt and Clay 5 - 12% PROPORTION RANGE DESCRIPTIVE TERMS Clean Slightly (Clayey, Silty, Sandy) 30 - 50% Components are arranged in order of increasing quantities. Very (Clayey, Silty, Sandy, Gravelly) PID PP CBR DS Direct Shear GS Grain Size Distribution K Permeability Moisture/Density Relationship (Proctor) Resilient Modulus Photoionization Device Reading Res. Resistivity SG Percent Fines%F MD MR Specific Gravity CD Consolidated Drained Triaxial Torvane (Approx. Shear Strength, tsf) Dry Density (pcf) CU Consolidated Undrained Triaxial TV UU Unconsolidated Undrained Triaxial UC Unconfined Compression SAMPLE TYPE SYMBOLS Non-standard Penetration Test(3.0" OD Split Spoon with Brass Rings) (140 lb. hammer with 30 in. drop) Shelby Tube Small Bag Sample Large Bag (Bulk) Sample Core Run 2.0" OD Split Spoon (SPT) PL = Plastic Limit, LL = Liquid Limit Pocket Penetrometer (Approx. Comp. Strength, tsf) 3-1/4" OD Split Spoon S-1 S-2 S-3 S-4 S-5A S-5B S-6 S-7 S-8 S-9 GS GS GS GS %F GS %F SM SM GM SM 7-8-6 6-11-8 4-3-5 6-7-11 17-50/4" 12-36-50/5" 18-50/6" 13-45-47 50/5" Medium dense, light brown, slightly gravelly, silty, fine to coarse SAND, moist. Wood/roots observed. (FILL) Becomes brown-gray and very silty. Wood/roots observed. Loose, brown, gravelly, silty, fine to medium SAND, moist. Roots and trace charcoal observed. Medium dense, brown, slightly gravelly, silty, fine to medium SAND, moist. Roots and trace rust mottling observed. (RECESSIONAL OUTWASH) Becomes very dense. Wood/roots and trace gravel observed. Very dense, brown with rust-mottling, silty, sandy GRAVEL, moist. Low sample recovery, broken gravel. (ADVANCE OUTWASH) Very dense, brown-gray, slightly gravelly, very silty, fine SAND, moist. Wood chips observed at top of sample. 1 inch of mottling observed at 20.3 ft. Becomes dark brown-gray. Roots observed. Rust-mottling and roots observed. Becomes moist to wet. 0 20 40 60 80 100 Water Content (%) Plastic Limit (140 lb. weight, 30" drop) Blows per foot (b l o w s / 6 i n c h e s ) US C S S O I L C L A S S DESCRIPTION SA M P L E T Y P E PE N . R E S I S T A N C E OT H E R T E S T S PI E Z O M E T E R Standard Penetration Test SY M B O L SC H E M A T I C 0 10 20 30 40 50 Liquid Limit BORING: BH-1 Water Content (%) Natural Water ContentNOTE: This log of subsurface conditions applies only at the specified location and on the date indicatedand therefore may not necessarily be indicative of other times and/or locations. PAGE: 1 of 2 SA M P L E N U M B E R A-2FIGURE:PROJECT NO.:2024-062-21 Renton, Washington Springbrook Terrace Pond Retrofit PZO-DSM 2024-062.GPJ 12/1/24Library: Q:\LIBRARY\LIBRARY - BOTHELL BACKUP BACKUP.GLB DE P T H (f e e t ) 0 5 10 15 20 25 30 35 40 190 185 180 175 170 165 160 155 EL E V A T I O N (f e e t ) DATE COMPLETED: 10/4/2024 DRILLING COMPANY: Holocene Drilling DRILLING METHOD: HSA w/ 4.24" ID, Diedrich D-50 Tracked Rig LOCATION: Lat: 47.429558 Long: -122.210406, Datum: WGS 84 DATE STARTED: 10/4/2024 SAMPLING METHOD: SPT, Autohammer LOGGED BY: S. CORTEZ >> >> SURFACE ELEVATION: 193.6 feet Borehole terminated at 39.5 feet below ground surface (bgs) due to broken sample tube. Bottom sample could not be recovered. Groundwater not observed during the exploration. 2-inch PVC standpipe piezometer installed in a 35 foot well with 20 feet of screen. DOE well tag: BQB 720. 0 20 40 60 80 100 Water Content (%) Plastic Limit (140 lb. weight, 30" drop) Blows per foot (b l o w s / 6 i n c h e s ) US C S S O I L C L A S S DESCRIPTION SA M P L E T Y P E PE N . R E S I S T A N C E OT H E R T E S T S PI E Z O M E T E R Standard Penetration Test SY M B O L SC H E M A T I C 0 10 20 30 40 50 Liquid Limit BORING: BH-1 Water Content (%) Natural Water ContentNOTE: This log of subsurface conditions applies only at the specified location and on the date indicatedand therefore may not necessarily be indicative of other times and/or locations. PAGE: 2 of 2 SA M P L E N U M B E R A-2FIGURE:PROJECT NO.:2024-062-21 Renton, Washington Springbrook Terrace Pond Retrofit PZO-DSM 2024-062.GPJ 12/1/24Library: Q:\LIBRARY\LIBRARY - BOTHELL BACKUP BACKUP.GLB DE P T H (f e e t ) 40 45 50 55 60 65 70 75 80 150 145 140 135 130 125 120 115 EL E V A T I O N (f e e t ) DATE COMPLETED: 10/4/2024 DRILLING COMPANY: Holocene Drilling DRILLING METHOD: HSA w/ 4.24" ID, Diedrich D-50 Tracked Rig LOCATION: Lat: 47.429558 Long: -122.210406, Datum: WGS 84 DATE STARTED: 10/4/2024 SAMPLING METHOD: SPT, Autohammer LOGGED BY: S. CORTEZ SURFACE ELEVATION: 193.6 feet GS GS GS %F S-1 S-2 S-3 S-4 S-5 S-6 S-7 S-8 S-9A S-9B Dense, brown, slightly gravelly, silty, fine to medium SAND, moist. Wood/roots observed. (FILL/REWORKED NATIVE) Becomes medium dense, dark gray, very gravelly. Minor mottling. Loose, brown-gray with mottling, slightly gravelly, silty, fine to medium SAND, moist. Roots observed. (RECESSIONAL OUTWASH) Becomes medium dense and gravelly. Very dense, brown-gray with mottling, silty, fine to coarse SAND, moist. Low sample recovery. (ADVANCE OUTWASH) Becomes dense, gravelly, and very silty. Becomes very dense and slightly gravelly. Blowcounts overstated due to gravel in sample tip. Becomes silty with minor mottling. Blowcounts overstated due to gravel in sample tip. Becomes dark brown-gray and without mottling. Roots observed. Very dense, brown-gray, slightly silty, gravelly, poorly graded SAND, moist. 11-19-14 3-4-6 1-3-3 2-8-11 10-50/6" 3-13-22 11-50/5" 9-28-50/6" 24-50/3" SM SM SM SP SM FIGURE:PROJECT NO.:2024-062-21 Renton, Washington Springbrook Terrace Pond Retrofit BORING-DSM 2024-062.GPJ 12/1/24Library: Q:\LIBRARY\LIBRARY - BOTHELL BACKUP BACKUP.GLB Natural Water Content US C S S O I L C L A S S Water Content (%) NOTE: This log of subsurface conditions applies only at the specified location and on the date indicated DESCRIPTION BH-2 PAGE: 1 of 2 (b l o w s / 6 i n c h e s ) GR O U N D W A T E R PE N . R E S I S T A N C E Liquid Limit SY M B O L 0 10 20 30 40 50 0 20 40 60 80 100 SA M P L E T Y P E SA M P L E N U M B E R OT H E R T E S T S Plastic Limit BORING: and therefore may not necessarily be indicative of other times and/or locations. (140 lb. weight, 30" drop) Blows per foot Standard Penetration Test A-3 DE P T H (f e e t ) 0 5 10 15 20 25 30 35 40 185 180 175 170 165 160 155 EL E V A T I O N (f e e t ) DATE COMPLETED: 10/4/2024 DRILLING COMPANY: Holocene Drilling DRILLING METHOD: HSA w/ 4.24" ID, Diedrich D-50 Tracked Rig LOCATION: Lat: 47.429503 Long: -122.210550, Datum: WGS 84 DATE STARTED: 10/4/2024 SAMPLING METHOD: SPT, Autohammer LOGGED BY: S. CORTEZ >> >> SURFACE ELEVATION: 189.9 feet S-10Very dense, grayish-brown, slightly gravelly, silty SAND, moist. Borehole terminated at 41.5 feet below ground surface (bgs). Groundwater not observed during the exploration. Boring abandoned with 3/8" bentonite chips. 26-44-50/5"SM FIGURE:PROJECT NO.:2024-062-21 Renton, Washington Springbrook Terrace Pond Retrofit BORING-DSM 2024-062.GPJ 12/1/24Library: Q:\LIBRARY\LIBRARY - BOTHELL BACKUP BACKUP.GLB Natural Water Content US C S S O I L C L A S S Water Content (%) NOTE: This log of subsurface conditions applies only at the specified location and on the date indicated DESCRIPTION BH-2 PAGE: 2 of 2 (b l o w s / 6 i n c h e s ) GR O U N D W A T E R PE N . R E S I S T A N C E Liquid Limit SY M B O L 0 10 20 30 40 50 0 20 40 60 80 100 SA M P L E T Y P E SA M P L E N U M B E R OT H E R T E S T S Plastic Limit BORING: and therefore may not necessarily be indicative of other times and/or locations. (140 lb. weight, 30" drop) Blows per foot Standard Penetration Test A-3 DE P T H (f e e t ) 40 45 50 55 60 65 70 75 80 145 140 135 130 125 120 115 EL E V A T I O N (f e e t ) DATE COMPLETED: 10/4/2024 DRILLING COMPANY: Holocene Drilling DRILLING METHOD: HSA w/ 4.24" ID, Diedrich D-50 Tracked Rig LOCATION: Lat: 47.429503 Long: -122.210550, Datum: WGS 84 DATE STARTED: 10/4/2024 SAMPLING METHOD: SPT, Autohammer LOGGED BY: S. CORTEZ SURFACE ELEVATION: 189.9 feet APPENDIX B LABORATORY TEST RESULTS Representative soil samples obtained from the explorations were placed in moisture sealed containers and transported to our Bothell, Washington laboratory for further examination and testing. Laboratory tests were conducted on selected soil samples to characterize relevant engineering and index properties of the site soils. The laboratory testing program was conducted in general accordance with the following test methods: MOISTURE CONTENT OF SOIL: Laboratory tests were conducted to determine the natural moisture content of selected soil samples, in general accordance with ASTM D 2216. Test results are indicated on Figure B-1, the Summary of Material Properties, and at the sampled intervals on the appropriate exploration logs in Appendix A. PARTICLE SIZE ANALYSIS OF SOILS: Selected samples were tested to determine the particle size distribution of material in general accordance with ASTM D 6913. The results are summarized on the attached Grain Size Distribution reports, Figures B-2 through B-5, which provide information regarding the classification of the sample. PERCENTAGE FINER THAN #200 SIEVE: The percentage of material finer than the #200 sieve was determined for select samples in general accordance with ASTM D 1140. The soil was oven dried and washed over a #200 sieve to determine the percentage of fines. The results are shown on that attached Grain Size Distribution reports, Figures B-2 through B-5. BH-1,S-1 2.5 4.0 7.4 SM Yellowish-brown, silty SAND with organics BH-1,S-2 5.0 6.5 22.5 0.3 60.1 39.6 SM Dark brown, silty SAND with organics BH-1,S-3 7.5 9.0 12.6 13.5 64.0 22.5 SM Brown, silty SAND with organics BH-1,S-4 10.0 11.5 12.9 8.5 67.0 24.4 SM Brown, silty SAND BH-1,S-5A 15.0 16.5 16.1 SM Dark brown, silty SAND with organics BH-1,S-6 20.0 21.5 11.7 5.3 54.9 39.8 SM Olive-brown, silty SAND BH-1,S-7 25.0 26.5 18.5 33.9 SM Dark olive-brown, silty SAND with organics BH-1,S-8 30.0 31.5 12.9 5.1 49.2 45.7 SM Brown, silty SAND with organics BH-1,S-9 35.0 36.5 19.9 39.8 SM Grayish-brown, silty SAND BH-2,S-1 2.5 4.0 8.6 SM Yellowish-brown, silty SAND BH-2,S-2 5.0 6.5 11.7 30.6 49.3 20.1 SM Very dark grayish-brown, silty SAND with gravel BH-2,S-3 7.5 9.0 15.8 11.1 59.2 29.8 SM Dark yellowish-brown, silty SAND with organics BH-2,S-4 10.0 11.5 13.2 SM Brown, silty SAND with gravel BH-2,S-6 20.0 21.5 11.1 19.3 42.5 38.2 SM Brown, silty SAND with gravel BH-2,S-7 25.0 26.5 13.1 37.3 SM Brown, silty SAND BH-2,S-8 30.0 31.5 11.9 SM Brown, silty SAND BH-2,S-9A 35.0 35.4 13.2 SM Brown, silty SAND with organics BH-2,S-9B 35.4 36.5 6.2 SP-SM Yellowish-brown, poorly graded SAND with silt and gravel BH-2,S-10 40.0 41.5 11.6 SM Yellowish-brown, silty SAND (f e e t ) SUMMARY OF LIMITS (%) ATTERBERG BO T T O M D E P T H CO N T E N T ( % ) LL PL PI(f e e t ) Notes: TO P D E P T H MO I S T U R E CO N T E N T ( % ) OR G A N I C AS T M S O I L % F I N E S SP E C I F I C G R A V I T Y EX P L O R A T I O N DE S I G N A T I O N 1. This table summarizes information presented elsewhere in the report and should be used in conjunction with the report test, other graphs and tables, and the exploration logs. 2. The soil classifications in this table are based on ASTM D2487 and D2488 as applicable. MATERIAL PROPERTIES B-1 PAGE: 1 of 1 % S A N D % G R A V E L CL A S S I F I C A T I O N SAMPLE DESCRIPTION 2024-062-21PROJECT NO.: INDEX MATSUM 3 (LONG DESCRIPTIONS) 2024-062.GPJ 11/5/24 FIGURE: Springbrook Terrace Pond Retrofit Renton, Washington 0 10 20 30 40 50 60 70 80 90 100 0.0010.010.1110 B-2 Coarse #60#40#20 Fine Coarse SYMBOL Gravel% 3"1-1/2" PE R C E N T F I N E R B Y W E I G H T #4 #200 0.3 13.5 8.5 Sand% (SM) Dark brown, silty SAND with organics (SM) Brown, silty SAND with organics (SM) Brown, silty SAND Fines% 0.00050.005 GRAIN SIZE IN MILLIMETERS 50 SAMPLE S-2 S-3 S-4 5.0 - 6.5 7.5 - 9.0 10.0 - 11.5 #10 60.1 64.0 67.0 30 CLASSIFICATION OF SOIL- ASTM D2487 Group Symbol and Name U.S. STANDARD SIEVE SIZES SAND CLAY BH-1 BH-1 BH-1 SILT 3/4" GRAVEL 0.05 5/8" 70 #100 0.5 23 13 13 50 Medium Fine 3/8" 5 PI 90 10 % MC LL PLDEPTH ( ft.) 39.6 22.5 24.4 PARTICLE-SIZE ANALYSIS OF SOILS METHODS ASTM D6913/D1140 2024-062-21PROJECT NO.: HWAGRSZ WITH D1140 2024-062.GPJ 11/5/24 FIGURE: Springbrook Terrace Pond Retrofit Renton, Washington 0 10 20 30 40 50 60 70 80 90 100 0.0010.010.1110 B-3 Coarse #60#40#20 Fine Coarse SYMBOL Gravel% 3"1-1/2" PE R C E N T F I N E R B Y W E I G H T #4 #200 5.3 5.1 Sand% (SM) Olive-brown, silty SAND (SM) Dark olive-brown, silty SAND with organics (SM) Brown, silty SAND with organics Fines% 0.00050.005 GRAIN SIZE IN MILLIMETERS 50 SAMPLE S-6 S-7 S-8 20.0 - 21.5 25.0 - 26.5 30.0 - 31.5 #10 54.9 49.2 30 CLASSIFICATION OF SOIL- ASTM D2487 Group Symbol and Name U.S. STANDARD SIEVE SIZES SAND CLAY BH-1 BH-1 BH-1 SILT 3/4" GRAVEL 0.05 5/8" 70 #100 0.5 12 18 13 50 Medium Fine 3/8" 5 PI 90 10 % MC LL PLDEPTH ( ft.) 39.8 33.9 45.7 PARTICLE-SIZE ANALYSIS OF SOILS METHODS ASTM D6913/D1140 2024-062-21PROJECT NO.: HWAGRSZ WITH D1140 2024-062.GPJ 11/5/24 FIGURE: Springbrook Terrace Pond Retrofit Renton, Washington 0 10 20 30 40 50 60 70 80 90 100 0.0010.010.1110 B-4 Coarse #60#40#20 Fine Coarse SYMBOL Gravel% 3"1-1/2" PE R C E N T F I N E R B Y W E I G H T #4 #200 30.6 11.1 Sand% (SM) Grayish-brown, silty SAND (SM) Very dark grayish-brown, silty SAND with gravel (SM) Dark yellowish-brown, silty SAND with organics Fines% 0.00050.005 GRAIN SIZE IN MILLIMETERS 50 SAMPLE S-9 S-2 S-3 35.0 - 36.5 5.0 - 6.5 7.5 - 9.0 #10 49.3 59.2 30 CLASSIFICATION OF SOIL- ASTM D2487 Group Symbol and Name U.S. STANDARD SIEVE SIZES SAND CLAY BH-1 BH-2 BH-2 SILT 3/4" GRAVEL 0.05 5/8" 70 #100 0.5 20 12 16 50 Medium Fine 3/8" 5 PI 90 10 % MC LL PLDEPTH ( ft.) 39.8 20.1 29.8 PARTICLE-SIZE ANALYSIS OF SOILS METHODS ASTM D6913/D1140 2024-062-21PROJECT NO.: HWAGRSZ WITH D1140 2024-062.GPJ 11/5/24 FIGURE: Springbrook Terrace Pond Retrofit Renton, Washington 0 10 20 30 40 50 60 70 80 90 100 0.0010.010.1110 B-5 Coarse #60#40#20 Fine Coarse SYMBOL Gravel% 3"1-1/2" PE R C E N T F I N E R B Y W E I G H T #4 #200 19.3 Sand% (SM) Brown, silty SAND with gravel (SM) Brown, silty SAND Fines% 0.00050.005 GRAIN SIZE IN MILLIMETERS 50 SAMPLE S-6 S-7 20.0 - 21.5 25.0 - 26.5 #10 42.5 30 CLASSIFICATION OF SOIL- ASTM D2487 Group Symbol and Name U.S. STANDARD SIEVE SIZES SAND CLAY BH-2 BH-2 SILT 3/4" GRAVEL 0.05 5/8" 70 #100 0.5 11 13 50 Medium Fine 3/8" 5 PI 90 10 % MC LL PLDEPTH ( ft.) 38.2 37.3 PARTICLE-SIZE ANALYSIS OF SOILS METHODS ASTM D6913/D1140 2024-062-21PROJECT NO.: HWAGRSZ WITH D1140 2024-062.GPJ 11/5/24 FIGURE: Springbrook Terrace Pond Retrofit Renton, Washington Springbrook Terrace Water Quality Retrofit Final Design Report Springbrook Terrace Water Quality Retrofit Final Design Report Appendix F – Proposed Schedule 60% Design Documents Dept. of Ecology Design Report Approval 90% Design Documents 100% Design Documents Finalize Design Documents Bid Documents Announcement Award Construction Contract Construction Notice to Proceed Begin Construction/Mobilization Construction End Construction/Demobilization Dec Springbrook Terrace Water Quality Retrofit Proposed Schedule AugJulyJuneMayApril 2025 Final Design Report Appendix F 2026 Jan Feb Mar Apr May Jun Jul Aug Sep OctSept NovOct