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HomeMy WebLinkAboutRS_Drainage_Technical_Report_C2MY_Engineers_240729_v1.pdf Single-Family Residence 1828 NE 20th Street Renton, WA 98056 TECHNICAL INFORMATION REPORT May 29, 2024 Prepared By: Prepared For: C2MY Engineers, LLC. Yin Yin Leong PO Box 52883 1110 Edmonds Ave NE Bellevue, WA 98015 Renton, WA 98056 PH: (206) 451-7856 Contact: Chaohua Chang, AIA Contact: Choomeng Chin, PE Ph: (425) 785-3992 cmchin.c2my@gmail.com chcarch@gmail.com 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 2 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 3 TABLE OF CONTENTS I. PROJECT OVERVIEW ...................................................................................................................... 7 II. CONDITIONS & REQUIREMENTS SUMMARY ........................................................................ 14 III. OFFSITE ANALYSIS .................................................................................................................... 19 IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ............. 33 Water Quality Treatment Requirements: ........................................................................................ 35 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN ............................................................... 40 VI. SPECIAL REPORT AND STUDIES ............................................................................................. 44 VII. OTHER PERMITS ........................................................................................................................ 48 VIII. EROSION & SEDIMENT CONTROL (ESC) ANALYSIS AND DESIGN .............................. 52 IX. BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION OF COVENANT ... 60 X. MAINTENANCE AND OPERATION MANUAL ....................................................................... 64 APPENDIX ........................................................................................................................................... 70 WWHM REPORT AND SUMMARY FOR FLOW CONTROL EXEMPTION: ............................... 72 WWHM REPORT AND SUMMARY FOR WATER QUALITY TREATMENT: ............................ 77 WWHM REPORT AND SUMMARY FOR PERMEABLE PAVEMENT INFILTRATION: ........... 83 GEOTECHNICAL REPORT: .............................................................................................................. 97 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 4 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 5 SECTION I PROJECT OVERVIEW 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 6 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 7 I. Project Overview This Technical Information Report (TIR)/Drainage Assessment provides the technical information and design analysis required for preparing Drainage Plan for the proposed development of single- family residence and accessory Dwelling Unit (ADU). This project will follow the 2022 City of Renton Surface Water Design Manual (SWDM). The proposed site is located on the north side of NE 20th Street, Renton, WA (see Figure 1 – Vicinity Map). The address is 1828 NE 20th Street, Renton, WA 98056. The total site within the property as surveyed is approximately 51,069 s.f. (1.17 +/- acres). Existing Drainage System Presently, the project site is a vacant panhandle lot with gravel driveway, a concrete pad and open space. The surrounding area consists of single-family residential lots. The majority of existing on- site ground slopes southwesterly to a wetland area approximately 1% -10% (see Figure 2, Existing Site Map). Proposed Drainage System The development of the site will implement on-site storm water management to the maximum extent feasible and keep the existing drainage patterns. All pervious area runoff from the area will continue to sheet flow southwesterly direction to the onsite wetland. The driveways will be constructed of permeable pavement. The runoff from the proposed impervious roof area, driveway turn-around, and sidewalk will be infiltrated on-site using infiltration trenches. All pervious disturbed area with have amended soil. All existing improvements will be demolished. The proposed main residential buildings roof area is approximately 5,515 s.f. and a DADU of 1,005 s.f. The total driveway and parking area is 9,508 s.f. The off-site frontage improvement will be deferred to future development. The drainage design will follow the City of Renton SWDM design guidelines for drainage requirements. According to the soil map of USGS soil survey map, the on-site soil consists of Indianola loamy sand (InC), 5-15% slopes. These soils consist of sandy glacial outwash. It is considered as hydrologic soil group A and/or B, outwash soil classification. Please see geotechnical report prepared by Pioneer Engineers, Inc. in appendix for additional information. Also refer to the Wetland Report for additional information. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 8 FIGURE 1: VICINITY MAP – (SCALE: NTS)  North 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 9 FIGURE 2: SOIL SURVEY MAP - (SCALE: NTS)  North 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 10 FIGURE 3: EXISTING SITE CONDITIONS MAP (NTS) 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 11 FIGURE 4: PROPOSED SITE DEVELOPMENT MAP (NTS)  2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 12 SECTION II CONDITIONS AND REQUIREMENTS 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 13 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 14 II. Conditions & Requirements Summary This site development is required to comply with current 2022 Surface Water Design Manual. The proposed project is a redevelopment of a single-family lot with a new house, and ADU, new driveway, and sidewalk and will add new and/or replaced impervious area of greater than 2,000 s.f., it will require drainage review. The project site is proposed to add a total new plus replaced impervious surface of 13,822 s.f. and does not subject to Simplified Drainage Review or Large Project Drainage review. It falls into the Directed Drainage Review and is required to comply per Section 1.1.2.3 of SWDM and all Core Requirements per Table 1.1.2.A. Core Requirements: 1. Discharge at a natural location (1.2.1): Runoff from the site will be discharged at the natural location. 2. Offsite Analysis (1.2.2): The development site drains to a wetland system that begins on the subject property and extends offsite/downstream and discharges to Kennydale Creek and eventually to Lake Washington, approximately 1 mile away. 3. Flow Control (1.2.3): The site will incorporate flow control BMPs to the satisfy the flow control requirements. 4. Conveyance System (1.2.4): All runoff from the impervious building roof areas, driveway turn-around, and sidewalk will be tightlined to discharge to infiltration trenches with 4” PVC pipes at a minimum slope of 2%. 5. Temporary Erosion and Sediment Control (1.2.5): See Temporary Erosion and Sediment Control Plan per KCSWDM requirements and Section VIII. 6. Maintenance and Operation (1.2.6): On-site storm drainage system is owned and maintained by the owner. See Section X for maintenance guidelines information. 7. Financial Guarantees and Liability (1.2.7): The owner and contractor will obtain all necessary permits and provide financial guarantees required by the City prior to the beginning of construction. 8. Water Quality (1.2.8): The new and replaced PGIS pavement area is greater than 5000 s.f., water quality treatment is required. Permeable pavement will be used for the driveway with underlying permeable soils meeting the criteria for water quality treatment for the driveway. For the impermeable driveway, a Stormfilter will be provided to remove pollutants from stormwater before collection and distribution to an infiltration trench. 9. On-Site BMPs (1.2.9): Implement on-site BMPs to the maximum extend feasible. Special Requirements: 1. Other Adopted Area-Specific Requirements (1.3.1): N/A. 2. Flood Hazard Area Delineation (1.3.2): The project site is not located within a 100-year floodplain. 3. Flood Protection Facilities (1.3.3): The project site does not contain a class 1 or 2 stream and will not be constructing or modifying an existing flood protection facility. 4. Source Control (1.3.4): N/A. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 15 5. Oil Control (1.3.5): N/A. 6. Aquifer Protection Area (1.3.6): N/A 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 16 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 17 SECTION III OFF-SITE ANALYSIS 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 18 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 19 III. Offsite Analysis Upstream Analysis Upstream area consists of established single-family lots that drain from the north side through the subject property to the onsite/offsite wetlands. The offsite drainage path will bypass the proposed development area to continue to the natural location as currently existed. The upstream drainage will not affect the drainage system on site. Downstream drainage Analysis: The outfall from the project site is at the western portion of the subject property to the existing onsite/offsite wetland area that is also part of the Kennydale Creek system that flow northwesterly. Task 1. Study Area Definition and Maps The upstream tributary area to this project consists of established single-family lots with established drainage system that primarily passes through the wetlands on and adjacent to the subject property, away from the area to be developed. There is no likelihood that the proposed project activities could impact the upstream area with backwater conditions as the runoff flow path will be maintained. The discharge point of the project is at the is at the western portion of the subject property to the existing wetland system that discharge to Kennydale Creek. A reduced copy of the existing conditions map is included as Figure 3, an existing site map showing the property lines. Task 2. Resource Review In our effort to determine, if there were any existing or potential problems with this downstream portion of the city drainage system, the following resources recommended by the KCSWDM were reviewed: a) Adopted Basin Plans: Not Applicable (N/A) b) Finalized Drainage Studies: N/A c) Basin Reconnaissance Summary Reports: N/A d) Critical Drainage Area Maps: N/A e) Floodplain/floodway (FEMA) Maps: Not present f) Other Offsite Analysis Reports: N/A g) Sensitive Area Folio: None h) DNR Drainage Problem Maps: N/A i) Road Drainage Problems: None known. j) U.S. Department of Agriculture Soil Survey: Indianola loamy sand (InC), KCRTS Soil Group Outwash k) Wetland Inventory Maps: On and Off site. 1) Migrating River Studies: N/A m) WA Ecology Water Quality Assessment 303(d)/305(b) Integrated Report – None. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 20 FIGURE 5: DRAINAGE SYSTEM MAP (NTS) 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 21 FIGURE 6: FEMA FLOOD MAP (NTS) 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 22 FIGURE 7: KING COUNTY TOPOGRAPHIC MAP (NTS) 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 23 Task 3. Field Inspection A field observation was conducted to gather information including a level 1 Downstream Analysis and off-site conveyance system. Level 1 Field Study 1. No reported or observed problems. 2. No existing or potential constrictions or lack of capacity in the existing drainage system was apparent. 3. No reported flooding areas or sign of flooding were discovered. 4. No existing/potential overtopping, scouring, bank sloughing, or sedimentation is apparent. 5. No known aquatic habitats in the conveyance route. 6. The downstream area consists mainly of established roadway drainage system with pipes, structures and open ditches. The topography is moderate for the drainage route. 7. The pipe sizes encountered are from 18 inches up to 24 inches in diameter. 8. Off-site areas tributary to the project site were consistent with the site map included. 9. No known complaints of flooding. 10. The site visit was conducted at 2:30 pm on February 28, 2024. The weather was cloudy and 45 ºF. Task 4. Drainage System Description and Problem Descriptions Upstream The upstream tributary area to this project consists of established single-family subdivisions. Runoff from these lots have an established flow control drainage system that discharges from the north side through the subject property to the onsite/offsite wetlands. The offsite drainage path will bypass the proposed development area to continue to the natural location as currently existed. The upstream drainage will not affect the drainage system on site. No anticipation of any impact to the upstream drainage system due to this development Down Stream Drainage System Description: Runoff from the proposed site drains to the existing wetland area (A) at the west property line. From this point it continues westerly approximately 130’ to the Kennydale Creek (B). Then it continues northerly and northwesterly through heavily wooded area on private properties for approximately 810 l.f. to east edge of Jones Avenue (C) and enter a 24” CMP culvert to a CB on the street. At this point, it continues westerly in an 18” CMP to the east edge of the street approximately 43’ to an open channel (Kennydale Creek) (D). Then it continues in the open channel through private properties and through a driveway culvert approximately 330 l.f. to a 24” culvert that connect to a CB (E) on the south side of NE 24th Street. Runoff then crossing under NE 24th Street to another CB (F) located on the north side of NE 24th Street approximately 18 l.f. away. From this point it appears to continue northerly in a 24’ pipe approximately 30’(G) and discharges to the creek with designated wetland on the east side of I-405 where the analysis terminated for a total distance of an approximately 1,361 l.f., that is greater than ¼ miles from the project site. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 24 During the downstream drainage field visit no areas of an existing or potential drainage problems were apparent. Problem description: No apparent problem was noticed or observed along the runoff route. Culvert inlet is protected by the riprap of the ditch but no other debris that can restrict flow. All pipe opening in the catch basins are not districted by any sediment in the catch basins. The downstream drainage system as described above is a not prone to stream bank erosion, siltation, and slides and does not threaten destruction of aquatic habitats. Task 5. Mitigation of Existing or Potential Problems No off-site mitigation is necessary as there are no observed problems during the analysis. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 25 OFF-SITE ANALYSIS DRAINAGE SYSTEM TABLE Surface Water Design Manual, Core Requirement #2 Downstream Path to South SEOLA CREEK BASIN Symbol Drainage Component Type, Name, and Size Drainage Component Description Slope Distance from site discharge Existing Problems Potential Problems Observations of field inspector resource reviewer, or resident see map Type: sheet flow, swale stream, channel, pipe, pond; Size: diameter surface area drainage basin, vegetation, cover, depth, type of sensitive area, volume % 1/4 mi=1,320 ft constrictions, under capacity, ponding, overtopping, flooding, habitat or organism destruction, scouring, bank sloughing, sedimentation, incision, other erosion tributary area, likelihood of problem, overflow pathways, potential impacts. A-B SHEET FLOW FORESTED AND SCRUB/SHRUB WETLAND AND BUFFERS FLAT8 0-130’ NONE OBSERVED NONE ANTICIPATED ROADWAY DRAINAGE - NO ISSUE B-C CHANNEL FORESTED AND SCRUB/SCRUB VEGETATION, MAINTAINED RESIDENTIAL LAWN,/PASTURE, CREEK, VEGETATION 0.7% 130-940’ NONE OBSERVED NONE ANTICIPATED WETLAND CREEK - NO ISSUE C-D 18”/24” CMP PIPE FLOW 1% 940-983’ NONE OBSERVED NONE ANTICIPATED ROADWAY DRAINAGE – NO ISSUE D-E CHANNEL/CULVERT CREEK /PIPE FLOW 1% 983-1313’ NONE OBSERVED NONE ANTICIPATED CREEK CHANNEL DRAINAGE - NO ISSUE E-F 24” PIPE (THROUGH STRUCTURES ON STREET) PIPE FLOW 1% 1313-1331’ NONE OBSERVED NONE ANTICIPATED ROADWAY DRAINAGE - NO ISSUE F-G 24” PIPE (THROUGH STRUCTURES ON STREET) PIPE FLOW 1% 1331-1361’ NONE OBSERVED NONE ANTICIPATED ROADWAY DRAINAGE - NO ISSUE 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 26 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 27 Looking down stream west property line Point (A) Upstream culvert inlet at Point (C) Culver entrance at point (C) Culvert discharge to ditch at Point (D) 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 28 Ditch crossing under private driveway between Points D and E Culvert entrance to at Point E Structure Catch Basin at Point E Solid grate catch basin at point G 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 29 Culvert exists from Point G Structure Looking downstream from Culvert discharge Point G 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 30 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 31 SECTION IV FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 32 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 33 IV. Flow Control and Water Quality Facility Analysis and Design This project falls into the Directed Drainage Review. All new proposed runoff from the site will be required to meet all core requirements. Flow control duration standards is to match forested site conditions. Drainage Cover Area Summary PRESENT CONDITION Area (SF) AREA (ac) Pervious: Open space Total Pervious 44,784 1.0281 Impervious: Gravel driveway 3,043 0.0699 Asphalt driveway 2,677 0.0614 Concrete pad 565 0.0130 Total Impervious 6,285 0.1443 Total Area: 51,069 1.1724 PROPOSED CONDITION Pervious Landscaping/grass/wetland 31,774 0.7294 Total Pervious 31,774 0.7294 Impervious Main Building Roof 5,515 0.1266 DADU Roof 1,103 0.0253 Walkway and Patio 235+69+188=492 0.0113 Driveways & turn around 4,294 0.0986 Existing asphalt driveway 2,677 0.0615 Total Impervious 14,081 0.3233 Permeable driveway 5,214 0.1197 Total Area: 51,069 1.1724 Off-site Frontage improvements to be deferred to future improvements. Area summary for WWHM input: Existing: Assumed forested = 1.1724 acs Proposed: Impervious Roofs = 5,515 + 1,103 sf = 6,618 sf = 0.1519 acs (fully infiltrated) = 0 sf Vehicle turn around, parking & paths = 4294 + 235 +69 = 4598 sf = 0.1056 acs (fully infiltrated) = 0 s.f. Permeable Driveway = 5,214 sf = 0.1197 acs. (Model as 50% impervious & 50% grass) = 0.05985 & 0.05985 acs Existing driveway = 2,677 sf (0.0615 acs) Wetland restored area (Wooded) = 19,739 sf = 0.4531 acs Open pervious area = 12,223 sf = 0.2806 acs Total Pervious=0.4531 + 0.2806 + 0.05985 = 0.79355 acs Total Impervious = 0.0615 + 0.05985= 0.12135 acs 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 34 Total proposed area = 0.79355+0.12135 acs = 0.9149 acs WWHM Runoff Summary: The peak runoff as calculated based on the proposed land cover and input into the WWHM modeling program in one basin. As calculated, the pre-developed and developed peak runoffs are as follow: The flow rates result in the Appendix are as follow: Storm Event: 2 –yr 10-yr 50-yr 100-yr Pre-developed 0.0010 cfs 0.0019 cfs 0.0031 cfs 0.0037 cfs Developed 0.0486 cfs 0.0801 cfs 0.0997 cfs 0.1341 cfs Per Core Requirement #3, 2022 SWDM, Section 1.2.3, this site is located in Flow Control Duration Standard Matching Forested Site Conditions area and meets the Exceptions 3 per the peak flow calculation using the historic site conditions as follow, i.e. The facility requirement in Flow Control Duration Standard Matching Forested Site Conditions Areas is waived for any threshold discharge area in which there is no more than a 0.15-cfs difference (when modeled using 15 minute time steps) in the sum of developed 100-year peak flows for those target surfaces subject to this requirement and the sum of forested (historical) site conditions100-year peak flows (modeled using same time step unit (e.g., 15 minute) used to calculate the developed flow) for the same surface areas.. The existing 100-yr peak flow rate as calculated is 0.0037 cfs compared to the developed rate of 0.1341 cfs, increases 0.1304 cfs, that is less than 0.15 cfs and it meets the exception and no flow control facility is proposed. See Appendix page 70 for WWHM calculations. On-Site BMP Selection for Core Requirement #9: Roof Area: BMP On-Site List infeasibility Additional information Full Dispersion • The minimum native vegetation flow path length is less than 100 feet. Full Dispersion is not feasible Full Infiltration • Infiltration is proposed See Geotechnical Report for soil classification Bioretention Facilities • NA Downspout Basic Dispersion •NA Other Hard Surface: Driveway BMP On-Site List infeasibility Additional information 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 35 Full Dispersion • The site has less than a 65 to 10 ratio of the native vegetation area to the impervious area. • The minimum native vegetation flow path length is less than 100 feet. Full Dispersion is not feasible Sheet Flow Dispersion • The minimum vegetated flow path for sheet flow cannot be met. Not feasible Permeable Pavement Surfaces Provide driveway with permeable pavement except turn around area See soil report for soil type. Full Infiltration • Infiltration is proposed for turn around area and walk See Geotechnical Report for soil classification Based on the soil map of USGS, The Geologic Map of Seattle, the soil on site is classified as Indianola (InC) loamy sand soil. See Appendix for soil report for more information. It is classified as hydrologic soil group A/B that is outwash soil. Infiltration Trenches Design Per soil report, the soils are classified as medium sand. Total roof areas = 5,515 s.f. + 1103 s.f. +188 s.f. = 6,806 s.f. Trench required = (6806/1000) x 30 = 198.54 l.f. (408 s.f.) required. Using 8’ wide with 51 l.f. trench (408 s.f.) provided. Turn-around area and walk Area = 4294+235+69= 4598 s.f. Trench required = (4598/1000) x 30 = 137.94 l.f. (275.88 s.f.) required Using 10’ wide with 28 l.f. trench (280 s.f. ) provided Water Quality Treatment Requirements: The site is located within the basic water quality treatment for all new pollution generated pavement area with the treatment goal of 80% removal of total suspended solids from leaving the site. The total PGIS is 9,508 s.f. and hence water quality treatment is required per Core Requirement #8. Drainage from the turn-around area will be treated using Stormfilter catch basin before discharge to a catch basin that drain to the infiltration trench. The permeable driveway area water quality will be provided with native underlying soils that meet the criteria for ground water protection. Water quality flow rate for the turn-around area PGIS of 4294 s.f. is (0.0986 acs) and the water quality off-line BMP flow rate per the WWHM calculation is 0.0133 cfs. See WWHM calculation in Appendix. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 36 At the driveway turn-around area, water quality is proposed to be maintained by a pre-cast Storm filter catch basin unit. This unit will contain one canister that will effectively remove common contaminants such as greases, oils and some metals. Canisters contain media that effectively removes most sediment, oils, greases and soluble metals that might be suspended or dissolved in water. Storm filter containing ZPG media is commonly used when treating runoff derived from parking areas. The Storm Filter unit is sized to treat runoff from a 6-month design storm as calculated. The number of cartridges can be estimated on the basis that each cartridge is reported to operate effectively at 10.2 gpm. It follows that the number of cartridges can be estimated as follows: Number of Cartridges = (0.0133𝑠𝑠) �1728 𝑖𝑖𝑛𝑛3 𝑓𝑓𝑡𝑡3�231 𝑖𝑖𝑛𝑛3 𝑔𝑔𝑔𝑔𝑔𝑔⁄��60 𝑠𝑠𝑠𝑠𝑠𝑠𝑚𝑚𝑖𝑖𝑛𝑛 ÷  1 𝑠𝑠𝑔𝑔𝑛𝑛𝑖𝑖𝑠𝑠𝑡𝑡𝑠𝑠𝑐𝑐10.2𝑔𝑔𝑔𝑔𝑚𝑚� = 0.585 use 1 cartridge A Stormfilter catch basin with 1 canister will be required for the pavement area runoff treatment. Runoff in excess of the design storm will bypass the canister. The Stormfilter unit is designed with a built-in weir overflow bypass so that excess stormwater can be directed over the canisters. Please WWHM Modeling information in Appendix. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 37 FIGURE 7: IMPERVIOUS AREA SUMMARY MAP (NTS) 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 38 SECTION V CONVEYANCE SYSTEM ANALYSIS AND DESIGN 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 39 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 40 V. Conveyance System Analysis and Design CONVEYANCE REQUIREMENTS FOR NEW SYSTEMS (1.2.4.1): The new conveyance system mainly consists of roof drain tightlines. The 4” PVC tightline with minimum slope of 2% has a capacity of 0.27 cfs. It has sufficient capacity to convey the proposed impervious roof area for conveyance design of 25-yr storm and also 100-yr storm. Areas of Contribution Summary Downspout System (4”): Maximum contribution to each section of area = 2758 s.f. = 0.0633 ac. C = 0.9 Concveyance Calculations: Roof Runoff From KCSWDM Figure 3.2.1.A-D aR bR Tc Pr iR IR 2-yr 1.58 0.58 6.30 2.00 0.54 1.09 10-yr 2.44 0.64 6.30 2.90 0.75 2.18 25-yr 2.66 0.65 6.30 3.40 0.80 2.73 100-yr 2.61 0.63 6.30 3.90 0.82 3.19 IR=(Pr) (iR) Peak Rainfall Intensity iR = (aR)*(Tc)^-(bR) Unit peak rainfall intensity factor Downspout System : Peak Runoff C Area (A) IR Q2 = 0.062 cfs 0.9 0.0633 1.09 Q25 = 0.115 cfs 0.9 0.0633 2.01 Q100 = 0.182 cfs 0.9 0.0633 3.19 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 41 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 42 SECTION VI SPECIAL REPORT AND STUDIES 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 43 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 44 VI. Special Report and Studies Geotechnical Report. See appendix. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 45 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 46 SECTION VII OTHER PERMITS 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 47 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 48 VII. Other Permits Water main extension and Wetland Variance 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 49 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 50 SECTION VIII EROSION AND SEDIMENT CONTROL ANALYSIS AND DESIGN 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 51 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 52 VIII. Erosion & Sediment Control (ESC) Analysis and Design Project Description: The project will consist of a single-family residence and ADU with a total lot area of approximately 1.17 acres and a total disturbed area of 0.68 acres will be involved in the development activity. The wetland and buffer area will be enhanced under a wetland variance. Existing Site Conditions: The existing project site is vacant lot with gravel driveway, a small concrete pad, open grass and trees with a forested wetland along the western portion of the property, downslope of the proposed homesite. Existing drainage for the project site is from the east to west of the site to the wetland area and drain to Kennydale Creek drainage system that discharges to Lake Washington. During the proposed construction this drainage pattern will be maintained. The discharge from the project will exit the site to the wetland at the current discharge location. Erosion and Sediment Control Measures: Delineate Clearing and easement limits The development drawings clearly indicate the limits of development activities for this developed site. Prior to any clearing or construction on site, the clearing limits for the project stage shall be clearly marked. The stakes shall be vividly marked with surveyors flagging and located with surveying methods. Cover measures According to the standard ESC notes included all disturbed areas to remain unworked for more than seven days during the dry season (May 1 to September 30) or two days during the wet season (October 1 to April 30), unless otherwise determined by the City of Renton. Any disturbed areas to remain unworked for more than 30 days will be seeded or sodded, unless the City of Renton determines that winter weather makes the vegetation establishment unfeasible. During the wet season any stockpiles to remain unworked for more than 12 hours will remain covered. Perimeter Protection A filter fabric silt fence shall be installed at the downstream end of the disturbed areas of the site. The silt fence/wattles shall be so located that any sediment laden runoff that does not directly enter the protected inlets will be filtered prior to offsite discharge. The perimeter protection will be installed prior to upslope grading. Traffic Area Stabilization Prior to the start of general construction, the construction vehicle entrances to the site shall be stabilized with a rock pad as detailed on the drawings, unless the proposed location of the construction entrance at the existing grave driveway access is acceptable to the County. Sediment retention Due to the forested and heavy underbrush that will be preserved at the perimeter of the lot for this development, the silt fence/wattle will be sufficient to trap sediment on site. However, contractor 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 53 will be required to prevent any sediment laden runoff discharges offsite and will need to implement sediment control measure such as additional silt fence/wattles, diversion dike, straw/mulch application, erosion control matting, or temporary sediment trap if necessary. Surface Water Collection Surface runoff on to the side is not anticipated as the upstream is stabilized large lot single-family with heavily wooded perimeter and the construction site is approximately 3 feet higher than the natural surface drainage upslope and downslope of the subject property. However, at the construction site, if the sediment retention measures are found to be insufficient for management of surface flow, other surface water collection measures (e.g., ditches, berms, etc.) shall be installed to intercept all surface water from disturbed areas, convey it to a temporary sediment pond or trap, and discharge it downstream of any disturbed areas. Dewatering Control Dewatering of the site is not anticipated as the ground water is not encountered during soil exploration per Geotechnical Evaluation Report. Dust Control Dust control will be conducted by watering bare soil areas using a water truck or hoses fed by the water truck, as needed. Mulching of bare soil areas may also be used to prevent dust liberation from the site. Flow Control Surface runoff for flow control is not anticipated as the project will be constructed during the dry season. However, if condition change during construction, surface water from the disturbed area will be routed to a temporary sediment trap and install flow control if necessary. Control Pollutants All pollutants, including waste materials and demolition debris, that occur onsite shall be handled and disposed of in a manner that does not cause contamination of stormwater. Good housekeeping and preventative measures will be taken to ensure that the site will be kept clean, well- organized, and free of debris. If required, BMPs to be implemented to control specific sources of pollutants are discussed below. Vehicles, construction equipment, and/or petroleum product storage/dispensing:  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.  On-site fueling tanks and petroleum product storage containers shall include secondary containment. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 54  Spill prevention measures, such as drip pans, will be used when conducting maintenance and repair of vehicles or equipment.  In order to perform emergency repairs on site, temporary plastic will be placed beneath and, if raining, over the vehicle.  Contaminated surfaces shall be cleaned immediately following any discharge or spill incident. Protect Flow Control BMPs Protect all infiltration trench BMPs from sedimentation through installation and maintenance of erosion and sediment control BMPs on portions of the site that drain into the BMPs. Restore the BMPs to their fully functioning condition if they accumulate sediment during construction. Restoring the BMP must include removal of sediment and any sediment-laden soils.  Prevent compacting infiltration trench BMPs by excluding construction equipment and foot traffic. Protect completed lawn and landscaped areas from compaction due to construction equipment.  Control erosion and avoid introducing sediment from surrounding land uses onto permeable pavements. Do not allow muddy construction equipment on the base material or pavement. Do not allow sediment-laden runoff onto permeable pavements.  Keep all heavy equipment off existing soils under LID facilities that have been excavated to final grade to retain the infiltration rate of the soils. Maintain BMPs All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired as needed to assure continued performance of their intended function. Maintenance and repair shall be conducted in accordance with each particular BMP’s specifications. Visual monitoring of the BMPs will be conducted at least once every calendar week and within 24 hours of any rainfall event that causes a discharge from the site. If the site becomes inactive, and is temporarily stabilized, the inspection frequency will be reduced to once every month. All temporary erosion and sediment control BMPs shall be removed within 30 days after the final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment shall be removed or stabilized on site. Disturbed soil resulting from removal of BMPs or vegetation shall be permanently stabilized. Manage the Project Erosion and sediment control BMPs for this project have been designed based on the following principles:  Design the project to fit the existing topography, soils, and drainage patterns. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 55  Emphasize erosion control rather than sediment control.  Minimize the extent and duration of the area exposed.  Keep runoff velocities low.  Retain sediment on site.  Thoroughly monitor site and maintain all ESC measures.  Schedule major earthwork during the dry season. Phasing of Construction  The construction project is being phased to the extent practicable in order to prevent soil erosion, and, to the maximum extent possible, the transport of sediment from the site during construction.  Revegetation of exposed areas and maintenance of that vegetation shall be an integral part of the clearing activities during each phase of construction. Seasonal Work Limitations  From October 1 through April 30, clearing, grading, and other soil disturbing activities shall only be permitted if shown to the satisfaction of the local permitting authority that silt-laden runoff will be prevented from leaving the site through a combination of the following:  Site conditions including existing vegetative coverage, slope, soil type, and proximity to receiving waters; and  Limitations on activities and the extent of disturbed areas; and  Proposed erosion and sediment control measures.  Based on the information provided and/or local weather conditions, the local permitting authority may expand or restrict the seasonal limitation on site disturbance.  The following activities are exempt from the seasonal clearing and grading limitations:  Routine maintenance and necessary repair of erosion and sediment control BMPs;  Routine maintenance of public facilities or existing utility structures that do not expose the soil or result in the removal of the vegetative cover to soil; and  Activities where there is 100 percent infiltration of surface water runoff within the site in approved and installed erosion and sediment control facilities. Coordination with Utilities and Other Jurisdictions  Care has been taken to coordinate with utilities, other construction projects, and the local jurisdiction in preparing this Construction SWPPS and scheduling the construction work. Inspection and Monitoring  All BMPs shall be inspected, maintained, and repaired as needed to assure continued performance of their intended function. Site inspections shall be 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 56 conducted by a person who is knowledgeable in the principles and practices of erosion and sediment control. This person has the necessary skills to:  Assess the site conditions and construction activities that could impact the quality of stormwater, and  Assess the effectiveness of erosion and sediment control measures used to control the quality of stormwater discharges.  A Certified Erosion and Sediment Control Lead shall be on-site or on-call at all times.  Whenever inspection and/or monitoring reveals that the BMPs identified in this TESC Plan are inadequate, due to the actual discharge of or potential to discharge a significant amount of any pollutant, appropriate BMPs or design changes shall be implemented as soon as possible. Maintaining an Updated Construction SWPPS  This TESC shall be retained on-site or within reasonable access to the site.  The TESC plan shall be modified whenever there is a change in the design, construction, operation, or maintenance at the construction site that has, or could have, a significant effect on the discharge of pollutants to waters of the state.  The TESC plan shall be modified if, during inspections or investigations conducted by the owner/operator, or the applicable local or state regulatory authority, it is determined that the TESC plan is ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. The TESC plan shall be modified as necessary to include additional or modified BMPs designed to correct problems identified. Revisions to the TESC plan shall be completed within seven (7) days following the inspection. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 57 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 58 SECTION IX BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION OF COVENANT 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 59 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 60 IX. Bond Quantities, Facility Summaries and Declaration of Covenant Declaration of Covenant Attached in Appendix 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 61 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 62 SECTION X MAINTENANCE AND OPERATION MANUAL 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 63 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 64 X. MAINTENANCE AND OPERATION MANUAL The project site development proposes on-site flow control BMP systems. The following is brief description of the facilities, their purpose, and their operation. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 65 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 66 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 67 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 68 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 69 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 70 Appendix 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 71 This page intentionally left blank 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 72 WWHM Report and Summary for Flow Control Exemption: Predeveloped Input 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 73 Developed Input 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 74 Flow Frequencies 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 75 WWHM Report Summary: WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: 2343-1828 NE 24th 20th St Renton-Exempt Site Name: 1828 SFR Site Address: 1828 NE 20th Ave St City : Renton, WA Report Date: 5/26/2024 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2023/01/27 Version : 4.2.19 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre A B, Forest, Flat 1.1724 Pervious Total 1.1724 Impervious Land Use acre Impervious Total 0 Basin Total 1.1724 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : 42312119 Bypass: No GroundWater: No Pervious Land Use acre A B, Forest, Flat .4531 A B, Lawn, Flat .34045 Pervious Total 0.79355 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 76 Impervious Land Use acre DRIVEWAYS FLAT 0.12135 Impervious Total 0.12135 Basin Total 0.9149 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:1.1724 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.79355 Total Impervious Area:0.12135 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.000995 5 year 0.001506 10 year 0.001921 25 year 0.002546 50 year 0.00309 100 year 0.003708 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.048568 5 year 0.066409 10 year 0.080107 25 year 0.099707 50 year 0.116077 100 year 0.134055 __________________________________________________________________ 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. 2005-2024; All Rights Reserved. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 77 WWHM Report and Summary for Water Quality Treatment: Predeveloped Input 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 78 Developed Input 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 79 WQ Flow Frequencies 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 80 WQ Flow Rate 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 81 WWHM Report Summary: WQ WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: 2343-1828 NE 24th St Renton-WQ Site Name: 1828 SFR Site Address: 1828 NE 20th St City : Renton, WA Report Date: 5/29/2024 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2023/01/27 Version : 4.2.19 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre A B, Forest, Flat .0986 Pervious Total 0.0986 Impervious Land Use acre Impervious Total 0 Basin Total 0.0986 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre Pervious Total 0 Impervious Land Use acre 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 82 DRIVEWAYS FLAT 0.0986 Impervious Total 0.0986 Basin Total 0.0986 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.0986 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0 Total Impervious Area:0.0986 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.000084 5 year 0.000127 10 year 0.000162 25 year 0.000214 50 year 0.00026 100 year 0.000312 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.059036 5 year 0.075293 10 year 0.086192 25 year 0.100178 50 year 0.110779 100 year 0.121554 ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.0119 acre-feet On-line facility target flow: 0.0237 cfs. Adjusted for 15 min: 0.0237 cfs. Off-line facility target flow: 0.0133 cfs. Adjusted for 15 min: 0.0133 cfs. ___________________________________________________________________ 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. 2005-2024; All Rights Reserved. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 83 WWHM Report and Summary for Permeable Pavement Infiltration: Predeveloped Input 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 84 Developed Input 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 85 Permeable Pavement Infiltration Design 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 86 Permeable Pavement Flow Frequency 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 87 Permeable Pavement POC 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 88 WWHM Report Summary: WQ WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: 2343-1828 NE 24th St Renton-Permeable Pav Site Name: 1828 SFR Site Address: 1828 SE 2oth Street City : Renton, WA 98056 Report Date: 5/29/2024 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2023/01/27 Version : 4.2.19 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre A B, Forest, Flat .1197 Pervious Total 0.1197 Impervious Land Use acre Impervious Total 0 Basin Total 0.1197 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre Pervious Total 0 Impervious Land Use acre ROADS FLAT 0.1197 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 89 Impervious Total 0.1197 Basin Total 0.1197 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ Name : Permeable Pavement 1 Pavement Area: 0.1197 ft. Pavement Length: 260.70 ft. Pavement Width: 20.00 ft. Pavement slope 1: 0.0077 To 1 Pavement thickness: 0.5 Pour Space of Pavement: 0.33 Material thickness of second layer: 0 Pour Space of material for second layer: 0 Material thickness of third layer: 0 Pour Space of material for third layer: 0 Infiltration On Infiltration rate: 1.4 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 17.553 Total Volume Through Riser (ac-ft.): 0 Total Volume Through Facility (ac-ft.): 17.553 Percent Infiltrated: 100 Total Precip Applied to Facility: 0 Total Evap From Facility: 1.172 Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Permeable Pavement Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.119 0.000 0.000 0.000 0.0111 0.119 0.000 0.000 0.169 0.0222 0.119 0.000 0.000 0.169 0.0333 0.119 0.001 0.000 0.169 0.0444 0.120 0.001 0.000 0.169 0.0556 0.120 0.002 0.000 0.169 0.0667 0.120 0.002 0.000 0.169 0.0778 0.120 0.003 0.000 0.169 0.0889 0.120 0.003 0.000 0.169 0.1000 0.120 0.004 0.000 0.169 0.1111 0.120 0.004 0.000 0.169 0.1222 0.120 0.004 0.000 0.169 0.1333 0.120 0.005 0.000 0.169 0.1444 0.120 0.005 0.000 0.169 0.1556 0.120 0.006 0.000 0.169 0.1667 0.120 0.006 0.000 0.169 0.1778 0.120 0.007 0.000 0.169 0.1889 0.120 0.007 0.000 0.169 0.2000 0.120 0.007 0.000 0.169 0.2111 0.121 0.008 0.000 0.169 0.2222 0.121 0.008 0.000 0.169 0.2333 0.121 0.009 0.000 0.169 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 90 0.2444 0.121 0.009 0.000 0.169 0.2556 0.121 0.010 0.000 0.169 0.2667 0.121 0.010 0.000 0.169 0.2778 0.121 0.011 0.000 0.169 0.2889 0.121 0.011 0.000 0.169 0.3000 0.121 0.011 0.000 0.169 0.3111 0.121 0.012 0.000 0.169 0.3222 0.121 0.012 0.000 0.169 0.3333 0.121 0.013 0.000 0.169 0.3444 0.121 0.013 0.000 0.169 0.3556 0.121 0.014 0.000 0.169 0.3667 0.121 0.014 0.000 0.169 0.3778 0.122 0.015 0.000 0.169 0.3889 0.122 0.015 0.000 0.169 0.4000 0.122 0.016 0.000 0.169 0.4111 0.122 0.016 0.000 0.169 0.4222 0.122 0.016 0.000 0.169 0.4333 0.122 0.017 0.000 0.169 0.4444 0.122 0.017 0.000 0.169 0.4556 0.122 0.018 0.000 0.169 0.4667 0.122 0.018 0.000 0.169 0.4778 0.122 0.019 0.000 0.169 0.4889 0.122 0.019 0.000 0.169 0.5000 0.122 0.020 0.000 0.169 0.5111 0.122 0.022 0.019 0.169 0.5222 0.122 0.023 0.055 0.169 0.5333 0.122 0.025 0.101 0.169 0.5444 0.123 0.026 0.156 0.169 0.5556 0.123 0.027 0.218 0.169 0.5667 0.123 0.029 0.286 0.169 0.5778 0.123 0.030 0.361 0.169 0.5889 0.123 0.031 0.441 0.169 0.6000 0.123 0.033 0.526 0.169 0.6111 0.123 0.034 0.616 0.169 0.6222 0.123 0.036 0.711 0.169 0.6333 0.123 0.037 0.810 0.169 0.6444 0.123 0.038 0.914 0.169 0.6556 0.123 0.040 1.021 0.169 0.6667 0.123 0.041 1.132 0.169 0.6778 0.123 0.042 1.248 0.169 0.6889 0.123 0.044 1.366 0.169 0.7000 0.123 0.045 1.489 0.169 0.7111 0.124 0.046 1.615 0.169 0.7222 0.124 0.048 1.744 0.169 0.7333 0.124 0.049 1.876 0.169 0.7444 0.124 0.051 2.012 0.169 0.7556 0.124 0.052 2.151 0.169 0.7667 0.124 0.053 2.292 0.169 0.7778 0.124 0.055 2.437 0.169 0.7889 0.124 0.056 2.585 0.169 0.8000 0.124 0.058 2.735 0.169 0.8111 0.124 0.059 2.889 0.169 0.8222 0.124 0.060 3.045 0.169 0.8333 0.124 0.062 3.204 0.169 0.8444 0.124 0.063 3.365 0.169 0.8556 0.124 0.064 3.530 0.169 0.8667 0.124 0.066 3.696 0.169 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 91 0.8778 0.125 0.067 3.866 0.169 0.8889 0.125 0.069 4.037 0.169 0.9000 0.125 0.070 4.212 0.169 0.9111 0.125 0.071 4.388 0.169 0.9222 0.125 0.073 4.568 0.169 0.9333 0.125 0.074 4.749 0.169 0.9444 0.125 0.076 4.933 0.169 0.9556 0.125 0.077 5.119 0.169 0.9667 0.125 0.078 5.307 0.169 0.9778 0.125 0.080 5.498 0.169 0.9889 0.125 0.081 5.691 0.169 1.0000 0.125 0.083 5.886 0.169 ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.1197 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0 Total Impervious Area:0.119697 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.000102 5 year 0.000154 10 year 0.000196 25 year 0.00026 50 year 0.000315 100 year 0.000379 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0 5 year 0 10 year 0 25 year 0 50 year 0 100 year 0 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.000 0.000 1950 0.000 0.000 1951 0.000 0.000 1952 0.000 0.000 1953 0.000 0.000 1954 0.000 0.000 1955 0.000 0.000 1956 0.000 0.000 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 92 1957 0.000 0.000 1958 0.000 0.000 1959 0.000 0.000 1960 0.000 0.000 1961 0.000 0.000 1962 0.000 0.000 1963 0.000 0.000 1964 0.000 0.000 1965 0.000 0.000 1966 0.000 0.000 1967 0.000 0.000 1968 0.000 0.000 1969 0.000 0.000 1970 0.000 0.000 1971 0.000 0.000 1972 0.000 0.000 1973 0.000 0.000 1974 0.000 0.000 1975 0.000 0.000 1976 0.000 0.000 1977 0.000 0.000 1978 0.000 0.000 1979 0.000 0.000 1980 0.000 0.000 1981 0.000 0.000 1982 0.000 0.000 1983 0.000 0.000 1984 0.000 0.000 1985 0.000 0.000 1986 0.000 0.000 1987 0.000 0.000 1988 0.000 0.000 1989 0.000 0.000 1990 0.000 0.000 1991 0.000 0.000 1992 0.000 0.000 1993 0.000 0.000 1994 0.000 0.000 1995 0.000 0.000 1996 0.001 0.000 1997 0.000 0.000 1998 0.000 0.000 1999 0.000 0.000 2000 0.000 0.000 2001 0.000 0.000 2002 0.000 0.000 2003 0.000 0.000 2004 0.000 0.000 2005 0.000 0.000 2006 0.000 0.000 2007 0.001 0.000 2008 0.000 0.000 2009 0.000 0.000 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 93 Rank Predeveloped Mitigated 1 0.0010 0.0000 2 0.0007 0.0000 3 0.0005 0.0000 4 0.0002 0.0000 5 0.0002 0.0000 6 0.0002 0.0000 7 0.0002 0.0000 8 0.0001 0.0000 9 0.0001 0.0000 10 0.0001 0.0000 11 0.0001 0.0000 12 0.0001 0.0000 13 0.0001 0.0000 14 0.0001 0.0000 15 0.0001 0.0000 16 0.0001 0.0000 17 0.0001 0.0000 18 0.0001 0.0000 19 0.0001 0.0000 20 0.0001 0.0000 21 0.0001 0.0000 22 0.0001 0.0000 23 0.0001 0.0000 24 0.0001 0.0000 25 0.0001 0.0000 26 0.0001 0.0000 27 0.0001 0.0000 28 0.0001 0.0000 29 0.0001 0.0000 30 0.0001 0.0000 31 0.0001 0.0000 32 0.0001 0.0000 33 0.0001 0.0000 34 0.0001 0.0000 35 0.0001 0.0000 36 0.0001 0.0000 37 0.0001 0.0000 38 0.0001 0.0000 39 0.0001 0.0000 40 0.0001 0.0000 41 0.0001 0.0000 42 0.0001 0.0000 43 0.0001 0.0000 44 0.0001 0.0000 45 0.0001 0.0000 46 0.0001 0.0000 47 0.0001 0.0000 48 0.0001 0.0000 49 0.0001 0.0000 50 0.0001 0.0000 51 0.0001 0.0000 52 0.0001 0.0000 53 0.0001 0.0000 54 0.0001 0.0000 55 0.0001 0.0000 56 0.0001 0.0000 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 94 57 0.0001 0.0000 58 0.0001 0.0000 59 0.0001 0.0000 60 0.0001 0.0000 61 0.0001 0.0000 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0001 3005 0 0 Pass 0.0001 2766 0 0 Pass 0.0001 2406 0 0 Pass 0.0001 2128 0 0 Pass 0.0001 1940 0 0 Pass 0.0001 1692 0 0 Pass 0.0001 1464 0 0 Pass 0.0001 1353 0 0 Pass 0.0001 1179 0 0 Pass 0.0001 997 0 0 Pass 0.0001 873 0 0 Pass 0.0001 682 0 0 Pass 0.0001 547 0 0 Pass 0.0001 466 0 0 Pass 0.0001 355 0 0 Pass 0.0001 246 0 0 Pass 0.0001 160 0 0 Pass 0.0001 37 0 0 Pass 0.0001 26 0 0 Pass 0.0001 26 0 0 Pass 0.0001 26 0 0 Pass 0.0001 26 0 0 Pass 0.0001 25 0 0 Pass 0.0001 25 0 0 Pass 0.0001 24 0 0 Pass 0.0001 23 0 0 Pass 0.0001 23 0 0 Pass 0.0001 23 0 0 Pass 0.0001 22 0 0 Pass 0.0001 22 0 0 Pass 0.0001 22 0 0 Pass 0.0001 21 0 0 Pass 0.0001 21 0 0 Pass 0.0001 21 0 0 Pass 0.0001 21 0 0 Pass 0.0001 19 0 0 Pass 0.0001 19 0 0 Pass 0.0001 18 0 0 Pass 0.0002 18 0 0 Pass 0.0002 18 0 0 Pass 0.0002 16 0 0 Pass 0.0002 16 0 0 Pass 0.0002 16 0 0 Pass 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 95 0.0002 16 0 0 Pass 0.0002 16 0 0 Pass 0.0002 15 0 0 Pass 0.0002 15 0 0 Pass 0.0002 15 0 0 Pass 0.0002 14 0 0 Pass 0.0002 13 0 0 Pass 0.0002 13 0 0 Pass 0.0002 13 0 0 Pass 0.0002 13 0 0 Pass 0.0002 13 0 0 Pass 0.0002 13 0 0 Pass 0.0002 12 0 0 Pass 0.0002 12 0 0 Pass 0.0002 12 0 0 Pass 0.0002 11 0 0 Pass 0.0002 11 0 0 Pass 0.0002 11 0 0 Pass 0.0002 11 0 0 Pass 0.0002 10 0 0 Pass 0.0002 10 0 0 Pass 0.0002 10 0 0 Pass 0.0002 9 0 0 Pass 0.0002 9 0 0 Pass 0.0002 9 0 0 Pass 0.0002 9 0 0 Pass 0.0002 8 0 0 Pass 0.0002 8 0 0 Pass 0.0002 8 0 0 Pass 0.0002 8 0 0 Pass 0.0002 8 0 0 Pass 0.0002 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 0.0003 8 0 0 Pass 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 96 _____________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0 acre-feet On-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. Off-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. ___________________________________________________________________ LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Permeable Pavement 1 POC N 15.97 N 100.00 Total Volume Infiltrated 15.97 0.00 0.00 100.00 0.00 0% No Treat. Credit Compliance with LID Standard 8 Duration Analysis Result = Passed ___________________________________________________________________ Perlnd and Implnd Changes No changes have been made. ___________________________________________________________________ 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. 2005-2024; All Rights Reserved. 2343 TIR 1828 NE 20th St - SFR G:\2343\2343tir.doc\Page 97 Geotechnical Report: Attached GEOTECHNICAL EVALUATION REPORT PROPOSED 1828 RESIDENCE 1828 NE 20TH STREET RENTON, WASHINGTON For Yin Yin Leong c/o Ms. Tracy Hung 1828 NE 20th Street Renton, WA 98056 Prepared by Pioneer Engineers, Inc. P. O. Box 33628, Seattle, WA 98133 Phone: (206) 427-9118, Fax: (206) 306-2982 josephwu.pei@gmail.com December 30, 2023 PIONEER ENGINEERS, INC. Geotechnical Engineering Earth Science Water Resources ___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ P. O. Box 33628Seattle, WA 98133 Phone: (206) 427-9118 Fax: (206) 306-2982 josephwu.pei@gmail.com December 30, 2023 Yin Yin Leong c/o Ms. Tracy Hung 1828 NE 20th Street Renton, WA 98056 Subject: Geotechnical Evaluation Proposed 1828 Residence 1828 NE 20th Street Renton, Washington Dear Ms. Hung: Per your request, Pioneer Engineers, Inc. (“PEI”) has explored subsurface conditions with four test pits (“TP-1 through TP-4”) in the area for stormwater infiltration and development at the above subject site in Renton, Washington. The site is located east of the intersection of Northeast 20th Street and Jones Avenue Northeast, as shown in Figure 1. Based on the architectural plans prepared by CHC Architects and the boundary and topographic survey plan by Eastside Consultants, Inc., PEI understands that the development will consist of a one-story wood framed residence with an attached garage, accessible from Northeast 20 th Street. Minor grading is anticipated to establish the foundation and access driveway. An investigation of subsurface soil and groundwater conditions is required for evaluation of on-site stormwater infiltration. SCOPE OF WORK The purpose of this geotechnical evaluation is to characterize the subsurface conditions by four test pits and a pilot infiltration test (“PIT”) at TP-3, and use such information obtained for evaluation of stormwater infiltration. To achieve the purpose, the scope of services specifically comprises the following items: December 30, 2023 Proposed 1828 Residence PEI Project No. G23A20 Page 2 PIONEER ENGINEERS, INC. 1. Explore subsurface conditions with two test pits to a maximum depth of 10 feet. The underlying soils encountered are visually classified; 2. Conduct a PIT at TP-3 and analyze test data; 3. Perform a site reconnaissance to observe and document existing surface features; 4. Review geologic and surficial soil conditions with a geologic or soil publication; 5. Prepare a written report to present the findings and geotechnical recommendations as well as the evaluation of on-site stormwater infiltration. SITE CONDITIONS Surface Conditions The site is a vacant property irregular in shape bounded to the south by Northeast 20 th Street, and adjoins private properties on the other three sides. It is measured 26.01 feet along the street, encompassing an area of 1.15 acres. Topographically, the site is located slightly above the toe of a regional slope ascending mildly toward northeast. The ground surface is covered mostly with berry and grass, dotted with grown trees. Geologic Setting A publication, Geologic Map of Surficial Deposits in the Seattle 30’ x 60’ Quadrangle, Washington, prepared by James C. Yount, James P. Minard and Glenn R. Dembroff in 1993 was referenced for the soil conditions at the site. According to this publication, the site is mapped in Recessional outwash (“Qvr”). Qvr was deposited mostly from the meltwater flowing from the retreating glaciers during the last glaciation period. In general, this soil unit is of high permeability and low shear strength since it had not been overridden and consolidated by thick, heavy glacial ice. It is suitable for use to support a light-weight wooded structure, and also is a competent natural material bolstering stormwater infiltration. December 30, 2023 Proposed 1828 Residence PEI Project No. G23A20 Page 3 PIONEER ENGINEERS, INC. Subsurface Exploration On December 20, 2023, subsurface conditions were explored with four test pits to a maximum depth of 10 feet. Approximate pit locations were determined with reference to existing surface features, as shown in Figure 2. Subsurface exploration was continuously monitored by an engineer from PEI who documented subsurface soil and groundwater conditions, maintained a log of each pit, and observed pertinent site features. The final test pit logs represent PEI’s interpretation of subsurface conditions explored. The stratification lines in the logs indicate approximate boundaries between soil types where actual transitions may be more gradual in the natural geologic setting. The soils encountered are visually classified in general accordance with Unified Soil Classification System (“USCS”) as shown in Figure 3, with reference to USDA Classification System of Soil Texture Triangle. Subsurface Soils All test pits encountered considerably consistent soil conditions: 8 to 10 inches of topsoil underlain by a thin layer of tan brown, silty, fine sand. Underlying this silty sand was medium- dense recessional outwash of light brown, fine to medium sand with a trace of silt and coarse gravel, occasional cobble. Light gray, medium- to coarse-grained sand with a trace of coarse gravel was last encountered, underlying light brown sand to the termination depths. This cleaner, coarser sand was also interpreted as recessional outwash. More information of soil conditions is presented in Figures 4 and 5. Groundwater Conditions Light to moderate groundwater was encountered at depths varying from 7 to 9 feet in 3 of 4 test pits. Groundwater levels generally fluctuate with seasons, depending on the amount of precipitation and surface runoff, denseness of groundcover, purpose of land use, and other factors. Groundwater levels were at or close to their seasonal high following recent persistent precipitation. December 30, 2023 Proposed 1828 Residence PEI Project No. G23A20 Page 4 PIONEER ENGINEERS, INC. CONCLUSIONS AND RECOMMENDATIONS Based on the soil and groundwater conditions encountered in subsurface exploration, it is PEI’s opinion that, from a geotechnical engineering viewpoint, the site is appropriate for the development if recommendations in this report are closely followed. The explored area is able to bolster stormwater infiltration for management of on-site stormwater, due to the prevailing existence of Recessional outwash and relatively low groundwater levels. It is recommended that collective stormwater from a pollution-generating impervious surface (“PGIS”) over threshold criteria be treated prior to entering an infiltration facility. Conventional spread footings bearing on medium-dense Recessional outwash should be able to provide adequate support for the proposed residence. It is advisable that grading work be started and completed in the dry season in order to minimize the impacts from precipitation. GRADING AND SITE PREPARATION Site preparation includes clearing and removal of ground features, and implementations of temporary erosion and sediment control (“TESC”) measures. Clearing of ground includes stripping and grubbing of surface vegetation within the construction limits. Occasional overexcavation may be required when local weak soil pockets encountered. Overexcavation should be backfilled with structural fill and compacted to a stable condition. On- site topsoil is unsuitable for use in any structural areas. This soil should be disposed of at approved locations or used solely for landscaping purposes. Prior to starting construction activities, a silt fence should be installed along the lower boundary of the site. This fence may be implemented with a highly visible grid fence to delineate the clearing limits. A portion of the existing gravel driveway will be preserved to serve as a construction entrance. The silt fence and the preserved driveway serve as TESC measures during construction, and they should remain in place until full establishment of permanent ESC measures. December 30, 2023 Proposed 1828 Residence PEI Project No. G23A20 Page 5 PIONEER ENGINEERS, INC. The following strategies and methods should be implemented in the grading phase for enhancements of TESC measures and site stability during construction:  The bare and disturbed ground outside the clearing limits should be protected with a layer of straw mulch (a minimum thickness of 2 inches; about 2 bales per 1,000 square feet of land) during any period of precipitation, in order to minimize soil erosion by storm runoff. Straw needs to be air-dried and free of any undesirable weed or coarse material.  Cut/fill slopes and stockpiles of soils should be covered with durable plastic sheeting weighed down by securely-anchored sand bags if they are to remain unworked for more than 12 hours; other disturbed areas should be covered with straw mulch as addressed above if they are to remain unworked for more than 2 days.  TESC measures in place should have regular inspection weekly and more frequent inspection immediately before, during and after significant precipitation events. STRUCTURAL FILL AND COMPACTION Structural fill is the material placed under footings, on-grade slabs and pavements where it withstands loading. Structural fill should be free of organic, construction debris and other deleterious substances. It should consist of clean soils with individual particles not greater than 3 inches in size. On-site outwash soils containing a significant quantity of free-draining, granular particles can be compacted to meet the criteria in all weather. Recycled concrete may be used as structural fill provided that the requirements of 9-03.12(2) of the latest Washington State Department of Transportation (“WSDOT”) standard specifications are met. Structural fill should be placed per loose lift not more than 12 inches in thickness, and compacted to meet the required percentage of maximum dry density determined by ASTM D1557 (Modified Proctor Method) as summarized in the following table: December 30, 2023 Proposed 1828 Residence PEI Project No. G23A20 Page 6 PIONEER ENGINEERS, INC. Applicable Area Maximum Dry Soil Density Under Footing 95% Under Driveway and On-Grade Slab 95% for upper 2 feet, 90% below Foundation Wall Backfill 95% for upper 3 feet, 90% below Utility Trench Backfill 95% for upper 4 feet, 90% below Controlled Density Fill (“CDF”) may be used as an alternative for structural fill. CDF (a flowable, self-compacting, rigid-setting and low-density material) is generally used in overexcavation in a foundation or utility trench. Wherever applicable, neither compaction efforts are required to densify this fill, nor density tests needed to ensure the adequacy of compaction efforts. This material’s flowability enables it to access difficult spots and displace standing water in the trench. CDF has a typical slump of 10 inches and a 30-day compressive strength of 200 pounds per square inch (“psi”) or less. Low compressive strength allows CDF for convenient excavation in case of any design alteration during construction. FOUNDATION SUPPORT Foundations are constructed of individual spread footings and/or continuous strip footings bearing on medium-dense Recessional outwash. Individual footings are usually used to support columns, and continuous footings for bearing walls. For footings constructed as stated above, design criteria for these foundations are summarized:  Allowable soil bearing pressure for spread footings poured on medium-dense Recessional outwash should be no more than 1,500 pounds per square foot (“psf”);  Minimum depth to bottom of perimeter footing below adjacent exterior finish grade should be at least 18 inches to reduce the risk of the foundation damage by the frost effect;  Interior footings supporting bearing walls or bracing walls should have a minimum depth of 12 inches from the top of the on-grade floor slab to the bottom of the footing; December 30, 2023 Proposed 1828 Residence PEI Project No. G23A20 Page 7 PIONEER ENGINEERS, INC. WELLHEAD PROTECTION AREA The site is located in a Zone 1 Modified wellhead protection area. Zone 1 Modified is defined as “the land area situated between a well or well field owned by the City and the three hundred sixty-five (365) day groundwater travel time contour but for the purpose of protecting a high- priority well, wellfield, or spring withdrawing from a confined aquifer with partial leakage in the overlying or underlying confining layers” in accordance with Renton Municipal Code (“RMC”) 4- 3-050G.8. In this zone, collective storm runoff from a PGIS exceeding the threshold area should be treated prior to entering the infiltration facility. STORMWATER INFILTRATION In accordance with Surface Water Design Manual released 6/22/2022 by City of Renton, low impact development (“LID”) is “a stormwater and land use management strategy that strives to mimic pre-disturbance hydrologic processes of infiltration, filtration, storage, evaporation and transpiration by emphasizing conservation and use of on-site natural features, site planning and distributed stormwater management practices that are integrated into a project design.” In recent years, this strategy has been applied primarily to prevent potential pollutants from entering natural water bodies and to reduce the amount of stormwater into a public storm drainage system. To achieve the objectives, LID measures consisting of infiltration trenches, drywells, green roofs, bioretention cells, rain gardens, stormwater harvesting devices and pervious pavements have been widely accepted to enhance safety of water environment, street landscape and urban amenities. These measures have higher application priority than conventional (structural) stormwater management practices such as detention vaults or pipes. They are taken into consideration prior to application of conventional practices. PIT Procedures and Results The infiltration test was conducted at a depth of 2.0 feet in TP-3 with a bottom area of 12 square feet. With an effort of minimizing scour, tap water was carefully dispersed into the pit to soak soils in the infiltration zone for about one hour. A hydraulic head of 12 inches was maintained during this period of time. After soaking, the pit was filled up to have a hydraulic head of 12 inches and the drop of water levels measured over elapsed time to obtain measured infiltration December 30, 2023 Proposed 1828 Residence PEI Project No. G23A20 Page 8 PIONEER ENGINEERS, INC. rates. Drops of water levels were taken from the readings at a scaled wood stake accurate to half an inch placed in the middle of the pit. This procedure was repeated to obtain the final field infiltration rate after a steady-state rate was reached. Measured water levels versus elapsed time were logged and shown in the table. Soil Elapsed Water Water Level Infiltration Description Time, min. Level, in. Drop, in. Rate, in/hr Light brown, 0 12.0 0.0 fine to medium 15 10.2 1.8 7.2 sand, trace coarse 30 8.5 1.7 6.8 gravel, trace silt, 45 7.3 1.2 4.8 occasional 60 6.0 1.3 5.2 cobble. 75 5.0 1.0 4.0 165 0.0 5.0 3.3 The lowest measured infiltration rate of 3.3 in/hr is selected from the above values. It reasonably represents the infiltration rate in the upper Recessional outwash in the explored area. The exploration depth was further extended three feet from the bottom after fully drained, and no groundwater mounding observed. Design Infiltration Rate In accordance with the aforementioned design manual, correction was made to account for factors (types of field infiltration tests, Ftesting; the depth from the infiltration facility bottom to the groundwater table, Fgeometry; flow channels plugged by fine particles in soil mass, Fplugging) that may affect long-term performance of on-site stormwater infiltration. The correction for the measured infiltration rate is summarized: Idesign = Imeasured x Ftesting x Fgeometry x Fplugging Ftesting = 0.5 (small- or large-scale PIT) Fgeometry = 4(D/W) + 0.05 = 4(3/3) + 0.05 = 4.05 > 1.0, Use Fgeometry = 1.0 D: depth from the bottom of the proposed facility to the maximum wet season water table or nearest impervious layer, whichever is less = 3.0 feet December 30, 2023 Proposed 1828 Residence PEI Project No. G23A20 Page 9 PIONEER ENGINEERS, INC. W: width of facility = 3.0 feet (assumed) Fplugging = 0.85 (loamy sandy to sand) Idesign = Imeasured x Ftesting x Fgeometry x Fplugging = (3.3 in/hr)(0.5)(1.0)(0.85) = 1.40 in/hr The design infiltration rate is 1.40 in/hr for a storm facility to be constructed at a depth of 2 feet, a maximum ponding depth of 12 inches and a width of 3 feet. PEI recommends that an infiltration trench or multiple be used for on-site stormwater management. Infiltration Trench The trench should consist of a level 6-inch perforated PVC pipe with a (cleanout) stand pipe of same size and material at its end. The level pipe should be surrounded by 0.75- to 1.5-inch washed rock wrapped with non-woven geotextile such as Mirafi 140N, where the bottom area left open to receptor soil. Receptor soil surface should be scarified or grooved prior to placement of washed rock. The trench should be setback a minimum of 5 feet from the residence without a basement or a crawl space; at least 10 feet from the residence with a basement or a crawl space; a minimum clearance of two time the trench width from an additional trench. LIMITATIONS This report has been prepared for the specific application to this project for the exclusive use of Ms. Tracy Hung and her authorized personnel. PEI’s geotechnical recommendations are based on the soil and groundwater conditions encountered in the test pits, PIT results, local experience and engineering judgment. The recommendations are professional opinions derived in a manner consistent with the level of care and skill ordinarily exercised by other members of the profession currently practicing under similar conditions in local areas. No warranty, expressed or implied, is made. December 30, 2023 Proposed 1828 Residence PEI Project No. G23A20 Page 10 PIONEER ENGINEERS, INC. Respectfully submitted, PIONEER ENGINEERS, INC. Joseph Wu, P.E. Engineering Consultant Five figures attached. VICINITY MAP PROPOSED 1828 RESIDENCE 1828 NE 20TH STREET Geotechnical Engineering · Earth Science · Water Resources RENTON, WASHINGTON PROJ. NO. G23A20 DATE 12/30/23 FIGURE 1 PIONEER ENGINEERS, INC. NTS NE 20th StKennewick Pl NEJones Ave NELincoln Pl NEKennewick Pl NEAberdeen Ave NENE 20th St SITE Aberdeen Pl NE 23rd St NE 21st St SITE EXPLORATION PLAN PROPOSED 1828 RESIDENCE 1828 NE 20TH STREET Geotechnical Engineering · Earth Science · Water Resources RENTON, WASHINGTON PROJ. NO. G23A20 DATE 12/30/23 FIGURE 2 PIONEER ENGINEERS, INC. Scale: 1" = 50'± Approx. Test Pit NE 20TH ST TP-1TP-2 TP-3 TP-4 PROPERTY FROM STANDARD PENETRATION TEST SILTY OR CLAYEY SOILS Relative Density Friction Angle %φ 0 - 15 15 - 35 26 - 30 35 - 65 28 - 35 65 - 85 35 - 42 USCS CHART PROPOSED 1828 RESIDENCE 1828 NE 20TH STREET Geotechnical Engineering · Earth Science · Water Resources RENTON, WASHINGTON PROJ. NO. G23A20 DATE 12/30/23 FIGURE 3 Hard > 50 85 - 100 38 - 46 Very Dense > 4.00 15 - 30 > 30 0.50 - 1.00 1.00 - 2.00 2.00 - 4.00 8 - 15 4 - 8 Very Stiff Medium Stiff Stiff Very Soft Description Soft2 - 4 < 0.25 0.25 - 0.50 Unconfined Strength qu, tsf Loose Medium Dense Dense < 2 Blow Count N PIONEER ENGINEERS, INC. SANDY SOILS N Blow Count 0 - 4 4 - 10 10 - 30 Description 30 - 50 Very Loose TEST PIT NO. TP-1 Logged By:JW Date:12/20/23 Depth brown Sample (N) W USCS Soil Description Blows/ Other Test ft.Type No. ft. % 8" Topsoil. SM Tan brown, silty, fine SAND, trace coarse gravel, occasional cobble, loose, moist. (Transitional Soil: Loamy Sand) SP-SM Light brown, fine to medium SAND, trace silt, trace coarse gravel, occasional cobble, medium-dense, moist. (Recessional Outwash; Loamy Sand to Sand) B 5 SP Light gray, medium to coarse SAND, trace coarse B gravel, medium-dense, very moist. (Recessional Outwash; Sand) 10 Test pit terminated @ 9 ft; light groundwater and minor caving encountered @ 9 ft during exploration. TEST PIT NO. TP-2 Logged By:JW Date:12/20/23 Depth Sample (N) W USCS Soil Description Blows/ Other Test ft.Type No. ft. % 9" Topsoil. SM Tan brown, silty, fine SAND, trace coarse gravel, occasional cobble, loose, moist. (Transitional Soil: Loamy Sand) SP-SM Light brown, fine to medium SAND, trace silt, trace coarse gravel, occasional cobble, medium-dense, moist. (Recessional Outwash; Loamy Sand to Sand) B 5 SP Light gray, medium to coarse SAND, trace coarse gravel, medium-dense, very moist. (Recessional Outwash; Sand) B 10 Test pit terminated @ 10 ft; light groundwater and minor caving encountered @ 7 ft during exploration. LEGEND: SS - 2" O.D. Split-Spoon Sample GROUNDWATER: Seal ST - 3" O.D. Shelby-Tube Sample Water Level B - Bulk Sample Observation Well Tip TEST PIT LOGS 1 & 2 PROPOSED 1828 RESIDENCE 1828 NE 20TH STREET Geotechnical Engineering · Earth Science · Water Resources RENTON, WASHINGTON PROJ. NO. G23A20 DATE 12/30/23 FIGURE 4 2 2 PIONEER ENGINEERS, INC. 1 1 TEST PIT NO. TP-3 Logged By:JW Date:12/20/23 Depth brown Sample (N) W USCS Soil Description Blows/ Other Test ft.Type No. ft. % 10" Topsoil. 1 SM Tan brown, silty, fine SAND, trace coarse gravel, occasional cobble, loose, moist. (Transitional Soil)PIT @ 2 ft. SP-SM Light brown, fine to medium SAND, trace silt, trace coarse gravel, occasional cobble, medium-dense, moist. (Recessional Outwash; Loamy Sand to Sand) 5 Pilot infiltration test ("PIT") conducted @ 2 ft; no groundwater mounding occurred within 3 ft extension after testing water fully drained. No occurrence of caving. 10 TEST PIT NO. TP-4 Logged By:JW Date:12/20/23 Depth Sample (N) W USCS Soil Description Blows/ Other Test ft.Type No. ft. % 10" Topsoil. 1 SM Tan brown, silty, fine SAND, trace coarse gravel, occasional cobble, loose, moist. (Transitional Soil) SP-SM Light brown, fine to medium SAND, trace silt, trace coarse gravel, occasional cobble, medium-dense, moist. (Recessional Outwash; Loamy Sand to Sand) B 5 SP Light gray, medium to coarse SAND, trace coarse gravel, medium-dense, very moist. (Recessional Outwash; Sand) B Test pit terminated @ 7 ft; moderate caving @ 5 ft, moderate groundwater encountered @ 7 ft during exploration. 10 LEGEND: SS - 2" O.D. Split-Spoon Sample GROUNDWATER: Seal ST - 3" O.D. Shelby-Tube Sample Water Level B - Bulk Sample Observation Well Tip TEST PIT LOGS 3 & 4 PROPOSED 1828 RESIDENCE 1828 NE 20TH STREET Geotechnical Engineering · Earth Science · Water Resources RENTON, WASHINGTON PROJ. NO. G23A20 DATE 12/30/23 FIGURE 5 1 PIONEER ENGINEERS, INC. 2 SUPPLEMENTAL GEOTECHNICAL REPORT PROPOSED 1828 RESIDENCE 1828 NE 20TH STREET RENTON, WASHINGTON For Yin Yin Leong c/o Ms. Tracy Hung 1828 NE 20th Street Renton, WA 98056 Prepared by Pioneer Engineers, Inc. P. O. Box 33628, Seattle, WA 98133 Phone: (206) 427-9118, Fax: (206) 306-2982 josephwu.pei@gmail.com April 15, 2024 PIONEER ENGINEERS, INC. Geotechnical Engineering Earth Science Water Resources ___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ P. O. Box 33628Seattle, WA 98133 Phone: (206) 427-9118 Fax: (206) 306-2982 josephwu.pei@gmail.com April 15, 2024 Yin Yin Leong c/o Ms. Tracy Hung 1828 NE 20th Street Renton, WA 98056 Subject: Supplemental Geotechnical Report Proposed 1828 Residence 1828 NE 20th Street Renton, Washington Dear Ms. Hung: Per your and the civil engineer’s requests, Pioneer Engineers, Inc. (“PEI”) has conducted soil sampling in the proposed permeable pavement area for the development at the subject site in Renton, Washington. The sample is tested to obtain organic content (“OC”) and cation exchange capacity (“CEC”), where the approximate sampling location shown in Figure 1 - Site Exploration and Sampling Plan. Also presented in this report are geologic hazards and test results. Wellhead protection is addressed in PEI’s 12/30/2023 geotechnical evaluation report. Delineation of wetlands at the site performed by a wetland specialist is not included in this report. GEOLOGIC HAZARDS In accordance with RMC 4-3-050G(5), geologic hazards associated with the site include steep slope hazard, landslide hazard, erosion hazard, seismic hazard and coal mine hazard. Discussions, conclusions and recommendations are addressed in subtitled topics: Steep Slope and Landslide Hazards In accordance with RMC 4-3-050G(5a) and RMC 4-3-050G(5b), the site is located in a flat area with an overall ground slope less than 15 percent; therefore, it pertains to a classified low landslide (“LL”) hazard area. Steep slopes are susceptible to landslide hazards due to April 15, 2024 Proposed 1828 Residence PEI Project No. G23A20S Page 2 PIONEER ENGINEERS, INC. steepness contributing to the mobilization (sliding) of a soil mass on a slope by gravitational force. As stated above, the site’s topographic condition makes it unable to meet the criteria of sensitive slopes or protected slopes, and thus it is not in an area of steep slope hazard. Erosion Hazard In accordance with RMC 4-3-050G(5c), the site is located in an area of low erosion hazard (“EL”) due to its overall site grade less than 15 percent. Based on the custom soil report from the interactive website of Natural Resources Conservation Service (“NRCS”) of USDA, the site is located in InC (Indianola loamy sand). InC is a dominant soil type on 5 to 15 percent slopes. During construction, the potential hazard can be further minimized by closely following the recommendations in Grading and Site Preparation of PEI’s 12/30/2023 geotechnical evaluation report and additional erosion control measures herein:  Construction will keep minimal disturbance to surface vegetation including trees, bushes and groundcover outside the clearing limits;  Standing water is not allowed to preside over the building area during construction;  Concentrated stormwater is forbidden from discharging onto a slope within the site;  Construction debris and yard waste are not dumped onto a slope;  Straw mulch should be placed over the bare ground to guard against erosion by surface runoff, prior to start of grading activities;  Grading activities are scheduled to start and complete in the official dry season;  All disturbed ground and disruption of surface vegetation due to construction activities are restored and re-planted with approved natural vegetation. With prudent implementations of the measures stated above, disturbance of ground can be minimized and related erosion hazard be mitigated to a lower level. April 15, 2024 Proposed 1828 Residence PEI Project No. G23A20S Page 3 PIONEER ENGINEERS, INC. Seismic Hazard Seismic hazard is mostly caused by liquefaction during earthquake events in local areas. Liquefaction is a phenomenon when a loose saturated sand deposit subject to vibration, tends to compact and decrease in volume. If the sand deposit is unable to drain, the pore water pressure will build up in a soil mass to reach the effective overburden earth pressure at some depths. When these two pressures are equal, the sand deposit will completely lose its shear strength and bearing capacity to support structures. Consequently, the sand deposit reaches a "quick" condition, and liquefaction occurs. In accordance with RMC 4-3-050G(5d) and subsurface exploration, the site is underlain by competent native soils and stratified deposits of coarser particles in the lower soil profile, the risk of liquefaction to occur across the site is low. This adverse potential can be further mitigated when design of residential buildings is in compliance with the standards and specifications stated in 2021 International Building Code (“2021 IBC”). Based on the 2021 IBC, the site is located in a classified Site Class D. The 0.2-second and 1-second spectral response accelerations are presented for seismic design: Regional Earthquake Ground Motion for the 0.2-Second Spectral Response Acceleration, SS = 1.440 g Regional Earthquake Ground Motion for the 1-Second Spectral Response Acceleration, S1 = 0.494 g Regional Earthquake Ground Motion for the 0.2-Second Spectral Response Design Parameter, Site Class D SDS = 0.960 g Regional Earthquake Ground Motion for the 1-Second Spectral Response Design Parameter, Site Class D SD1 = 0.593 g Site Coefficient Fa as a Function of Site Class and Mapped Spectral Response Acceleration at a 0.2-second Period (Ss) Fa = 1.000 Site Coefficient Fv as a Function of Site Class and Mapped Spectral Response Acceleration at a 1-Second Period (S1) Fv = 1.800 The development closely following the above design parameters will enhance structural integrity and further lower the risk of foundation distress by liquefaction during major seismic events. April 15, 2024 Proposed 1828 Residence PEI Project No. G23A20S Page 4 PIONEER ENGINEERS, INC. Coal Mine Hazard The site is not located in an area of known coal mine workings and predicted ground subside, and thus the coal mine hazard is low, in accordance with RMC 4-3-050G(5e). OC AND CEC The OC test was performed in general accordance with ASTM D2974, using moisture content method A burnt at 221°F and ash content method C burnt at 824°F. The result was recorded as percentage by weight. The CEC test was performed closely following the test method EPA 9081, where the soil sample is mixed with an excess of sodium acetate solution, resulting in an exchange of the added sodium cations for the matrix cations. Subsequently, the sample is washed with isopropyl alcohol. An ammonium acetate solution is then added to replace the adsorbed sodium with ammonium. The concentration of displaced sodium is determined by atomic absorption, emission spectroscopy, or an equivalent measure. The sampling depth was taken as per the civil engineer’s specification. Please refer to the summary of material properties in Appendix for the sample’s soil information. The results indicate that OC is 3.8 percent greater than the threshold of 1.0 percent, and CEC is 5.9 meg/100g exceeding the threshold of 5.0 meg/100g. Respectfully submitted, PIONEER ENGINEERS, INC. Joseph Wu, P.E. Engineering Consultant One figure and one appendix attached. Scale: 1" = 80' 4/15/24G23A20S SITE EXPLORATION AND SAMPLING PLAN PROPOSED 1828 RESIDENCE 1828 NE 20TH STREET RENTON, WASHINGTON 1 TP-1TP-2 TP-3 TP-4 A-1 APPROX. SAMPLING LOCATION APPROX. TEST PIT LOCATION APPENDIX OC and CEC PIONEER ENGINEERS, INC. A-1-2,2.0 2.0 32.6 3.8 SM Very dark brown, silty SAND A-2-2,2.0 2.0 17.8 1.8 SM Olive-brown, silty SAND A-3-2,4.0 4.0 22.0 1.3 SM Olive-brown, silty SAND A-4-2,4.0 4.0 13.6 1.4 SM Olive-brown, silty SAND(feet)TOP DEPTHSAMPLE DESCRIPTION Notes:ASTM SOILMOISTURECONTENT (%)ORGANIC% FINESEXPLORATIONDESIGNATION1. 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 1 PAGE: 1 of 1 SUMMARY OF LIMITS (%) ATTERBERG BOTTOM DEPTHCONTENT (%)% SAND% GRAVELPIPLLL CLASSIFICATION(feet)SPECIFIC GRAVITY2024-123 T100PROJECT NO.: INDEX MATSUM 2 2024-123 T100.GPJ 4/9/24 FIGURE: 1828 Residence MLT for PEI HWA GEOSCIENCES 21312 30TH DRIVE SE, STE 110 BOTHELL , WA 98021 4/5/2024 Soil PROJ 2024-123 A-1-2 S24-06454 Date Received: Grower: Sampled By: Field: Laboratory #: Test Results Customer Account #: Customer Sample ID: Other Tests: Cation Exchange meq/100gCEC 5.9 pH 1:1 E.C. 1:1 m.mhos/cm Est Sat Paste E.C. m.mhos/cm Effervescence Lbs/Acre Ammonium - N mg/kg %Organic Matter W.B.ENR: $16.00This is your Invoice #: List Cost:K. Bair, PhD, CReviewed by:S24-06454 Account #:188200 We make every effort to provide an accurate analysis of your sample. For reasonable cause we will repeat tests, but because of factors beyond our control in sampling procedures and the inherent variability of soil, our liability is limited to the price of the tests. Recommendations are to be used as general guides and should be modified for specific field conditions and situations. Note: "u" indicates that the element was analyzed for but not detected Figure 2 Page 1 of 12 Return Address: City Clerk’s Office City of Renton 1055 S Grady Way Renton, WA 98057 DECLARATION OF COVENANT FOR INSPECTION AND MAINTENANCE OF DRAINAGE FACILITIES AND ON-SITE BMPS Grantor: Yin Yin Leong Grantee: City of Renton, a Washington municipal corporation Legal Description: Lot 284 C.D. Hillman’s Lake Washinton Garden of Eden no.4, According to the Plat Therefore Recorded in Volume 11 of Plats, Page(s) 82, Record of King County, Washington Except The West 126 Feet Therefore Lying North of the South 234 Feet Thereof, Except the South 234 Feet Thereof Lying West of the East 26 Feet Thereof. Assessor's Tax Parcel ID#: 334390-3201 IN CONSIDERATION of the approved City of Renton (check one of the following)  Residential Building Permit Commercial Building Permit Clearing and Grading Permit Civil Construction or Utility Permit for Permit(s) (Construction/Building/Utility Permit #) relating to the real property ("Property") described above, the Grantor(s), the owner(s) in fee of that Property, hereby covenants (covenant) with the City of Renton (“City of Renton” or “City”), a municipal corporation of the state of Washington, that he/she (they) will observe, consent to, and abide by the conditions and obligations set forth and described in Paragraphs 1 through 9 below with regard to the Property, and hereby grants (grant) an easement as described in Paragraphs 2 and 3. Grantor(s) hereby grants (grant), covenants (covenant), and agrees (agree) as follows: 1. The Grantor(s) or his/her (their) successors in interest and assigns ("Owners ") shall at their own cost, operate, maintain, and keep in good repair, the Property's drainage facilities constructed as required in the approved construction plans and specifications (Project Plan #) on file with the City of Renton and submitted to the City of Renton for the review and approval of permit(s) (Construction/Building/Utility Permit #). The Property's drainage facilities are shown and/or listed on Exhibit A – Site Plan. The Property’s drainage facilities shall be maintained in compliance with the operation and maintenance schedule included and attached herein as Exhibit B – Operations and Maintenance. Drainage facilities include pipes, channels, flow control facilities, water quality facilities, on-site best management practices (BMPs) and other engineered structures designed to manage and/or Page 2 of 12 treat stormwater on the Property. On-site BMPs include dispersion and infiltration devices, bioretention, permeable pavements, rainwater harvesting systems, tree retention credit, reduced impervious surface footprint, vegetated roofs and other measures designed to mimic pre-developed hydrology and minimize stormwater runoff on the Property. 3. City of Renton shall have the right to ingress and egress over those portions of the Property necessary to perform inspections of the stormwater facilities and BMPs and conduct maintenance activities specified in this Declaration of Covenant and in accordance with the Renton Municipal Code. City of Renton shall provide at least thirty (30) days’ written notice to the Owners that entry on the Property is planned for the inspection of drainage facilities. After the thirty (30) days, the Owners shall allow the City of Renton to enter for the sole purpose of inspecting drainage facilities. In lieu of inspection by the City, the Owners may elect to engage a licensed civil engineer registered in the state of Washington who has expertise in drainage to inspect the drainage facilities and provide a written report describing their condition. If the engineer option is chosen, the Owners shall provide written notice to the City of Renton within fifteen (15) days of receiving the City’s notice of inspection. Within thirty (30) days of giving this notice, the Owners, or engineer on behalf of the Owners, shall provide the engineer’s report to the City of Renton. If the report is not provided in a timely manner as specified above, the City of Renton may inspect the drainage facilities without further notice. 4. If City of Renton determines from its inspection, or from an engineer’s report provided in accordance with Paragraph 2, that maintenance, repair, restoration, and/or mitigation work is required to be done to any of the drainage facilities, City of Renton shall notify the Owners of the specific maintenance, repair, restoration, and/or mitigation work (“Work”) required pursuant to the Renton Municipal Code. The City shall also set a reasonable deadline for the Owners to complete the Work, or to provide an engineer’s report that verifies completion of the Work. After the deadline has passed, the Owners shall allow the City access to re-inspect the drainage facilities unless an engineer’s report has been provided verifying completion of the Work. If the Work is not completed within the time frame set by the City, the City may initiate an enforcement action and/or perform the Work and hereby is given access to the Property for such purposes. Written notice will be sent to the Owners stating the City’s intention to perform such Work. This Work will not commence until at least seven (7) days after such notice is mailed. If, within the sole discretion of the City, there exists an imminent or present danger, the seven (7) day notice period will be waived and Work will begin immediately. 5. The Owners shall assume all responsibility for the cost of any Work, or any measures taken by the City to address conditions as described in Paragraph 3. Such responsibility shall include reimbursement to the City within thirty (30) days of the receipt of the invoice for any such Work performed. Overdue payments will require payment of interest at the maximum legal rate allowed by RCW 19.52.020 (currently twelve percent (12%)). If the City initiates legal action to enforce this agreement, the prevailing party in such action is entitled to recover reasonable litigation costs and attorney’s fees. 6. The Owners are required to obtain written approval from City of Renton prior to filling, piping, cutting, or removing vegetation (except in routine landscape maintenance) in open vegetated stormwater facilities (such as swales, channels, ditches, ponds, etc.), or performing any alterations or modifications to the drainage facilities referenced in this Declaration of Covenant. Page 3 of 12 7. Any notice or consent required to be given or otherwise provided for by the provisions of this Agreement shall be effective upon personal delivery, or three (3) days after mailing by Certified Mail, return receipt requested. 8. With regard to the matters addressed herein, this agreement constitutes the entire agreement between the parties, and supersedes all prior discussions, negotiations, and all agreements whatsoever whether oral or written. 9. This Declaration of Covenant is intended to protect the value and desirability and promote efficient and effective management of surface water drainage of the real property described above, and shall inure to the benefit of all the citizens of the City of Renton and its successors and assigns. This Declaration of Covenant shall run with the land and be binding upon Grantor(s), and Grantor's(s') successors in interest, and assigns. 10. This Declaration of Covenant may be terminated by execution of a written agreement by the Owners and the City that is recorded by King County in its real property records. IN WITNESS WHEREOF, this Declaration of Covenant for the Inspection and Maintenance of Drainage Facilities is executed this day of , 20 _. GRANTOR, owner of the Property GRANTOR, owner of the Property STATE OF WASHINGTON ) COUNTY OF KING )ss. On this day personally appeared before me: , to me known to be the individual(s) described in and who executed the within and foregoing instrument and acknowledged that they signed the same as their free and voluntary act and deed, for the uses and purposes therein stated. Given under my hand and official seal this day of , 20 ____. Printed name Notary Public in and for the State of Washington, residing at My appointment expires _______________ Page 4 of 12 Exhibit A – Site Plan Page 5 of 12 Exhibit B – Operations and Maintenance Page 6 of 12 Page 7 of 12 Page 8 of 12 Page 9 of 12 Page 10 of 12 Page 11 of 12 Page 12 of 12 Exhibit C – LEGAL DESCRIPTION Lot 284 C.D. Hillman’s Lake Washinton Garden of Eden no.4, According to the Plat Therefore Recorded in Volume 11 of Plats, Page(s) 82, Record of King County, Washington Except The West 126 Feet Therefore Lying North of the South 234 Feet Thereof, Except the South 234 Feet Thereof Lying West of the East 26 Feet Thereof. 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