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HomeMy WebLinkAboutMiscWilson Park & Wilson Park #2 1 LUA09-140 &1 13 720 South 55th Streetr Renton, Washington 98055 DRAINAGE REPORT November 5, 2013 Updated May 13, 2014 Prepared for: Robert Wilson, Owner 21703 60th Street East Lake Tapps, Washington D9ravin0comcast.net Prepared by: 98391 Offe Engineers, PLLC Darrell Offe, P.E. 13932 SE 159th Place Renton, Washington 98058-7832 (425) 260-3412 office (425) 227-9460 fax darrell Offe@comcast.net 5 o� GeNf'v aUN. ',I 201 11 rq' Table of Contents • Technical Information Worksheet • Section 1: Project Overview • Section 2: Conditions and Requirements Summary • Section 3: Offsite Analysis • Section 4: Flow Control and Water Quality Facility Analysis and Design • Section 5: Conveyance System Analysis and Design • Section 6: Special Reports and Studies • Section 7: Other Permits • Section S: CSWPPP Analysis and Design • Section 9: Bond Quantities, Facility Summaries, and Declaration of Covenant • Section 10: Operations and Maintenance Manual City of Renton TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Project Owner: Robert Wilson Address: 21703 60"' Street East Lake Tapps, WA 98391 Phone: (253) 205-3263 Project Engineer: Darrell Offe, P.E. Company: Offe Engineers, PLLC Address/Phone: 13932 SE 159th Place Renton, WA 98058 (425) 260-3412 Part 3 TYPE OF PERMIT APPLICATION Subdivision X 2 plats/PUD ❑ Grading ❑ Commercial ❑ Other Part 2 PROJECT LOCATION AND DESCRIPTION Project Name: Wilson Park & Wilson Park 2 Location Township: 23 North Range: 5 East Section: 31 Part4 OTHER REVIEWS AND PERMITS ❑ DFW HPA ❑ COE 404 ❑ DOE Dam Safety ❑ FEMA Floodplain ❑ COE Wetlands Part5 SITE COMMUNITY AND DRAINAGE BASIN Community South Renton Drainage Basin Springbrook Creek / Green River / Puget Sound Part 6 SITE CHARACTERISTICS ❑ River ❑ Stream ❑ Critical Stream Reach ❑ Depressions/Swales ❑ Lake X Steep Slopes ❑ Shoreline Management X Rockery X Structural Vaults X Other NPDES ❑ Floodplain ❑ Seeps/Springs ❑ High Groundwater Table ❑ Groundwater Recharge X Other _Steep Terrain_ Part 7 SOILS Soil Type Slopes Erosion Potential Erosive Velocities SM 15-40% moderate ❑ Additional Sheets Attached Part 8 DEVELOPMENT LIMITATIONS REFERENCE ❑ Ch. 4 — Downstream Analysis ❑ Additional Sheets Attached Part 9 ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION Sedimentation Facilities Stabilized Construction Entrance Perimeter Runoff Control Clearing and Grading Restrictions Cover Practices Construction Sequence ❑ Other LIMITATION/SIT CONSTRAINT _ MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION ❑ Stabilize Exposed Surface Remove and Restore Temporary ESC Facilities Clean and Remove All Silt and Debris Ensure Operation of Permanent Facilities Flag Limits of SAO and open space preservation areas ❑ Other Part 10 SURFACE WATER SYSTEM Method of Analysis ❑ Grass Lined DispersiongDepression Channel Energy Dissipater 2009 City of Renton L Pipe System ❑ Wetland Ll Flow Dispersal Manual Compensation/Mitigati Open Channel ❑ Stream r_ Waiver on of Eliminated Site ❑ Dry Pond ❑ Regional Storage Detention Brief Description of System Operation: Catch basins within curb line of street, conveyance to a new storm water facility discharging into an existing storm system located at Talbot and South 55'' Street. Facility Related Site Limitations Reference Facility Limitation Part 11 STRUCTURAL ANALYSIS Cast in Place Vault ! Retaining Wall Rockery > 4' High Structural on Steep Slope ❑ Other Part 12 EASEMENTSITRACTS Tract Other Part 13 SIGNATURE OF PROFESSIONAL ENGINEER I or a civil engineer under my supervision my supervision have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attachments. To the best of my knowledge the information provided here is accurate. Section 1: Project Overview The proposal is to create twenty-two lots from these two parcels located at the south end of the City of Renton on 4.61 acres. Two parcels received separate preliminary plats known as: Wilson Park LUA 09-140 (KC Tax #312305-9125) and Wilson Park #2 LUA 12-013 (KC Tax #312305- 9119). Baima & Holmberg, Inc. was the engineers for the preliminary plat of Wilson Park. Offe Engineers, PLLC was the engineer for Wilson Park #2. For construction permit approval, Offe Engineers, PLLC was chosen to prepare the utility and roadway plans for both projects. The two projects are combined in one utility permit, U13005662. As a condition of Wilson Park #2 only, a walkway along the north side of South 55th Street is required. This widening improvement off site was submitted as a separate permit, U13005791. The two projects will be constructed from these plans. Section 2, Conditions and Requirements Summary • Preliminary Report to the Hearing Examiner, Wilson Park Preliminary Plat (LUA09-140) • Report to the Hearing Examiner, Wilson Park II (LUA12-013) An overview of the Core Requirements is outlined below, further discussion of these requirements can be found within the remainder of this report. Core Requirement No. i -Discharge at Natural Location The current property has no single point of discharge; the runoff leaves the property along the west side and flows south and west into a roadside ditch along South 55th Street. The proposed developed property is to collect the runoff from the new road section within a stormwater facility located at the entry of the property off of South 55th Street. This system will then discharge into a new conveyance system on South 55th following the natural discharge point for the property. Core Requirement No. 2 - Offsite Analysis There is 27.5 acres of upstream area that contributes to the new storm system within South 55th Street. This area currently flows within a conveyance system on the north side of S. 55t" Street and enters the property on the west side of lot 10, Wilson Park 2. This flow will be conveyed around the project within a new storm system. The downstream system was reviewed and documented during the Wilson Park preliminary plat process. Offe Engineers has reviewed this previous work and concurs with the study. Additional information on the upstream area can be found within Section 5. The downstream system study can be found within Section 3. Core Requirement No. 3 - Flow Control The property is located within the City of Renton, Flow Control Duration Standard, Forested Conditions. The storm water runoff from the proposed development will be to: mitigate on the lots br u5ing infiltration ry wells or trenches at time of buiidin ermits; collection of the roadway section into catch basins and a stormwater facility to treat for detention and water quaRty, This new vault will be located at the entry of the probe an connect into the existing downstream, system at the intersection of Talbot Road South and South 55h Street. Core Requirement No. 4 - Conveyance System The proposed on-site conveyance improvements will include curb, catch basins and a pipe network for collection of surface runoff from landscape, roadway and sidewalks. The review and analysis of this proposed conveyance system includes calculations that are provided as part of this report within Section 5. The proposed runoff was analyzed using the 25 year event. Core Requirement No. 5 - Erosion and Sediment Control A Temporary Erosion and Sediment Control Plan implementing the Best Management Practices have been included within the civil plans. The project exceeds the State requirements of clearing over 1 acre in size. Therefore the developer will be required to obtain a NPDES permit form the Washington State Dept. of Ecology. The temporary pond facility has been sized using the 2 year - 15 minute interval storm event. The calculations for the temp, pond is included within this report. Core Requirement No. 6 - Maintenance and Operations The Maintenance and Operations for the Wilson Park projects include both a public and private system. Within this report are the maintenance requirements for the facilities being installed as part of the plat and the facilities to be installed as part of the residential building permits. Core Requirement No. 7 - Financial Guarantees and Liability The Financial Guarantees and Liabilities will be required prior to the project being finalized by the City of Renton. Bond Quantity worksheets are provided within this report. Core Requirement No. 8 — Water Quality The project is required to provide water quality (WQ) treatment. The WQ has been provided within the storm water treatment pond. Sizing for this portion of the pond are included within section 4. WILSON PARK LUA 09-140 PUBLIC City of Renton HEARINGDepartment of Community and Economic Development PRELIMINARY REPORT TO THE HEARING EXAMINER A. SUMMARY AND PURPOSE OF REQUEST: PUBLIC HEARING DATE: March 16, 2010 Project Name: Wilson Park Preliminary Plat Applicant/owner: Robert Wilson; 21703 601h Street East; Lake Tapps, WA 98391 Contact: Shupe Holmberg; Baima & Holmberg Inc., 100 Front Street; Issaquah, WA 98027 File !Number: LUA09-140, PP, ECF Project Manager: Gerald Wasser, Associate Planner Project Summary: The applicant is requesting approval of a Preliminary Plat for the subdivision of a 108,884 square foot (2.5 acre) parcel in the R-1, R-8 and R-14 zones and in the Urban Separator Overlay. The original proposal encompassed 13 -lots and 4 -tracts (for open space and storm detention). The revised proposal encompasses 12 -lots and 3 -tracts (for open space). A portion of proposed Lot 12 would also contain an open space easement. A proposed stormwater vault would be located under the proposed access road. Proposed lots range in size from 4,500 to 13,006 square feet with a density of 7.99 dwelling units per acre. The proposed lots are intended for the future construction of single family residences. Slopes generally range from 13% to 39% and the southwestern portion of the site contains a small area of protected slopes (over 40%). Access to the proposed lots would be via a new street off of South 55th Street; a secondary access for emergency vehicles is also proposed. Grading would involve approximately 17,000 cubic yards of cut with approximately 6,000 cubic yards used as structural fill. Approximately 500 cubic yards of crushed rock fill would be used for road construction. Project Location: 720 South 55th Street Project Location Mop LUA09-140, ECF, PP City of Renton Community and Economic Development Department Preliminary Report to the Hearing Examiner WILSON PARK PRELIMINARY PLAT LUA09-140, PP, ECF PUBLIC HEARING DATE March 16, 2010 Page 1 of 13 S. HEARING EXHIBITS: Exhibit 1: Project file ("yellow file") containing the application, reports, staff comments, and other material pertinent to the review of the project. Exhibit 2: Vicinity Map (date stamped 10/16/09) Exhibit 3: Preliminary Plat Map (Baima & Holmberg Inc., Sheet 1/1, revised 01/11/10) Exhibit 4: Boundary/Topography Map, (Baima & Holmberg Inc., Sheet 1/5, revised 01/11/10) Exhibit 5: Generalized Utilities/Drainage/Control/Conceptual Grading/Landscaping Plant (Sheet 2/5, revised 01/11/10) Exhibit 6: Road Profile (Baima & Holmberg Inc., Sheet 3/5, revised 01/11/10) Exhibit 7: Wall Profiles & Cross Sections, (Baima & Holmberg Inc., Sheet 4/5, revised 01/11/10) Exhibit 8: Tree Inventory, (Baima & Holmberg Inc., Sheet 5/5, revised 01/11/10) Exhibit 9: Zoning Map (Sheet 13, East %) Exhibit 10: Administrative Policy/Code Interpretation affecting Urban Separator Overlay Regulations, effective January 14, 2010 Exhibit 11: Street Modification letter, dated November 10, 2009 C. GENERAL INFORMATION: 1. Owner of Record: Richard Wilson 21703 60th Street East Lake Tapps, WA 98391 2. Zoning Designation: 3. Comprehensive Plan Designation: 4. Existing Site Use: S. Neighborhood Characteristics: North: East: South: West: 6. Site Area: D. HISTORICAL/BACKGROUND; Residential —1 du/ac (R-1); Residential -- 8 du/ac.- Residential u/ac;Residential —14 du/ac (R-14); Urban Separator Overlay Residential Low Density (RLD); Residential Single Family (RSF); and, Residential Medium Density (RMD) Single-family home Vacant (R-1, R-8, and R-14 Vacant (R-4) Vacant and Single Family Home (R-1, R-8, and R-14) Single Family Residential Plat (Geneva Court, R-14) 2.49 acres (108,884 gross square feet) Action Land Use File No. Ordinance No. Date Annexation N/A 3268 12/13/78 Comprehensive Plan N/A 5099 11/01/2004 Zoning Code N/A 5100 11/01/2004 E PUBLIC SERVICES: 1. Utilities: Water: Water service is provided by Soos Creek Water and Sewer District. LUA09-140, ECF, PP City of Renton Community and Economic Development Department Preliminary Report to the Hearing Examiner WILSON PARK PRELIMINARY PLAT LUA09-140, PP, ECF PUBLIC HEARING DATE March 16, 2010 Page 3 of 13 Sewer: Sewer service is provided by City of Renton. An 8 -inch diameter sanitary sewer is required to be extended to serve the site. Surface Water/Storm Water: Storm conveyance is City of Renton. 2. Streets: All streets are within the City of Renton. 3. Fire Protection: City of Renton Fire Department F. APPLICABLE SECTIONS OF THE RENTON MUNICIPAL CODE: 1. Chapter 2 Land Use Districts a. Section 4-2-020: Purpose and Intent of Zoning Districts b. Section 4-2-070: Zoning Use Tables c. Section 4-2-110: Residential Development Standards d. Section 4-2-115: Residential Design and Open Space Standards 2. Chapter 4 Property Development Standards a. Section 4-2-030: Development Guidelines and Regulations 3. Chapter 6 Streets and Utility Standards a. Section 4-6-060: Street Standards 4. Chapter 7 Subdivision Regulations a. Section 4-7-080: Detailed Procedures for Subdivision b. Section 4-7-120: Compatibility with existing Land Use and Plan — General Requirements and Minimum Standards c. Section 4-7-150: Streets — General Requirements and Minimum Standards d. Section 4-7-170: Residential Lots — General Requirements and Minimum Standards e. Section 4-7-220: Hillside Subdivisions 5. Chapter 9 Procedures and Review Criteria 6. Chapter 11 Definitions G. APPLICABLE SECTIONS OF THE COMPREHENSIVE PLAN.- 1. LAN. 1. Land Use Element: Residential Low Density; Residential Single Family; Residential Medium Density 2. Community Design Element: Natural Areas; Urban Separators; New and Infill Development: Site Planning; 3. Environmental Element: Storm Water; Steep Slopes, Landslide, and Erosion Hazards H. DEPARTMENT ANALYSIS. 1. Proiec# Description/Background The applicant proposes subdividing an existing 2.49 acre parcel (APN 312305-9125) into 12 lots suitable for the eventual development of detached single family homes and 3 tracts for open space. The resulting parcels would range in size from 4,500 to 13,006 square feet. In addition, the applicant is also LUA09 140, ECF, PP City of Renton Community and Economic Development Department Preliminary Report to the Hearing Examiner WILSON PARK PRELIMINARY PLAT LUA09-I40, PP, ECF PUBLIC HEARING DATE March 16, 2010 Page 4 of 13 proposing that 4,884 square feet of proposed Lot 12 (which is within the Talbot Urban Separator) be designated as a Native Growth Protection Easement. The site is comprised of three zoning classifications: 27,156 square feet in the Residential -1 dwelling units per acre zone (R-1) ; 79,343 square feet in the Residential — 8 dwelling units per acre (R-8) zone; and, 2,384 square feet in the Residential —14 dwelling units per acre (R-14) zone. In addition, the Talbot Urban Separator Overlay is present and corresponds to the R-1 zoning in the western portion of the site. Overall density of the 12 -lot proposal on the site would be 7.99 dwelling units per acre. Primary access to the site would be via a 50 -foot wide access easement from South 55th Street. This access easement is approximately 300 -feet in length and accesses the westerly portion of the site and is identified as "Road A" on the revised site plan. A secondary emergency access on the easterly side of the property is also proposed via a 30 -foot wide access easement and continues to the northerly property line. This access is identified as "Road 8" on the Preliminary Plat plan. A stormwater detention vault is proposed off-site and to be located under proposed Road A. The applicant is proposing grading involving 17,000 cubic yards of cut with approximately 6,000 cubic yards of it being used as structural fill material with the remainder to be exported. In addition, approximately 500 cubic yards of crushed rock fill would be imported to the project site for road construction. An existing single family residence (3,520 square feet) would be demolished to accommodate the proposed development. Because average slopes are in excess of 20 percent this project is considered a hillside subdivision. 2. Environmental Review Pursuant to the City of Renton's Environmental Ordinance and SEPA (RCW 43.21C, 1971 as amended), on Feb 22, 2010, the Environmental Review Committee issued a Determination of Non -Significance Mitigated (DNS -M) for the Wilson Park Preliminary Plat. A 14 -day appeal period commenced on February 26, 2010 and ended on March 12, 2010. No appeals of the threshold determination were filed as of the writing of this staff report. 3. Compliance with ERC Conditions Based on an analysis of probable impacts from the proposal, the Environmental Review Committee (ERC) issued the following mitigation measure with the Determination of Non -Significance — Mitigated: L The applicant shall place a note on the face of the plat which requires a 15 -foot building setback line from the top of slopes which are 40% or greater. 2. The applicant will be required to comply with the recommendations contained in the Geotechnical Engineering Study, prepared by Liu & Associates, Inc. dated February 20, 2009. 3. The applicant shall clearly mark and fence trees outside the construction area and replant exposed ground as soon as possible after construction activities. 4. That the applicant shall provide a Temporary Erosion and Sedimentation Plan designed pursuant to the 2005 Department of Ecology's Erosion and Sediment Control Requirements and provide staff with a Construction Mitigation Plan prior to issuance of construction permits. LUA09-140, FGF, PP Co of Renton Community and Economic Development Department Preliminary Report to the Nearing Examiner WILSON PARK PRELIMINARY PLAT LUA09-140, PP, ECF PUBLIC NEARING DATE March 16, 2010 Page 5 of 13 5. Weekly reports on the status and condition of the erosion control plan with any recommendations of change or revision to maintenance schedules or installation shall be submitted by the Project Engineer of record to the Public Works inspector. 6. Grading and foundation activities shall be conducted during the dryer months of the year from April Z through October 31 unless otherwise approved by the Development Services Division. 7. The final drainage report and design shall be subject to the 2009 King County Surface Water Design Manual. S. The applicant shall be required to pay a Parks Mitigation Fee based on $530.76 per each new single family lot prior to recording the final plat (with credit given for the existing house). The fee is estimated to be $5,838.36. 9. The applicant shall be required to pay a Traffic Mitigation Fee based on $75.00 per each new average daily vehicle trip_ associated with the proposed project prior to recording of the final plat (with credit given for the existing house). The fee is estimated to be $7,895.25. 10. The applicant shall be required to pay a Fire Mitigation Fee based on $488.00 per each new single family lot prior to recording the final plat (with credit given for the existing house). The fee is estimated at $5,368.00. 11_ The applicant shall submit a sample board indicating the texture and tinting to be used on all visible surfaces of retaining walls for the review and approval of the Planning Division project manager prior to the issuance of construction permits. 4. Staff Review Comments Representatives from various departments have reviewed the application materials to identify and address issues raised by the proposed development. These comments are contained in the official file, and the essence of the comments has been incorporated into the appropriate sections of this report and the Departmental Recommendation at the end of the report. 5. Consistency with Preliminary Plat Criteria Approval of a plat is based upon several factors. The following preliminary plat criteria have been established to assist decision -makers in the review of the plat: a) Compliance with the Comprehensive Plan Designation The site is designated Residential Low Density (RLD), Residential Single Family (RSF), and Residential Medium Density (RMD) on the City's Comprehensive Pian Land Use Map. The proposal is consistent with all of the following Comprehensive Plan Land Use policies: Policy CD -1. Integrate development into natural areas by clustering development and/or adjusting site plans to preserve wetlands, steep slopes, and notable stands of trees or other vegetation. Natural features should function as site amenities. Use incentives such as flexible lot size and configuration to encourage preservation and add amenity value. ✓ Policy Objective Met ❑ Not Met Polity CD -22. During land division, all lots should front streets or parks. Discourage single tier lots with rear yards backing onto a street. Where a single -tier plat is the only LUll09-140, ECF, PP City of Renton Community and Economic Development Department Preliminary Report to the Hearing Examiner WIL50N PARK PRELIMINARY PLAT LUA09-140, PP, ECF PUBLIC HEARING DATE March 16, 2010 Page 6 of 13 viable alternative due to land configuration, significant environmental constraints, or location on a principal arterial, additional design features such as larger setbacks, additional landscaping, or review of fencings should be required. a. Evaluation of land configuration should consider whether a different layout of streets or provision of alleys is physically possible and could eliminate the need for a single -tier plat. b. Evaluation of environmental constraints should consider whether the location and extent of critical areas prevents a standard plat design. c. Review of fencing should ensure that the development does not "turn its back" to public areas. ✓ Policy Objective Met ❑ Not Met Policy CD -25. Streets, sidewalks, and pedestrian or bike paths should be arranged an interconnecting network. Dead-end streets and cul-de-sacs should be discouraged. A grid or "flexible grid" pattern of streets and pathways, with a hierarchy of widths and corresponding traffic volumes, should be used. ✓ Policy Objective Met ❑ Not Met Policy CD -26. Interpret development standards to support plats designed to incorporate vehicular and pedestrian connections between plats and neighborhoods. Small projects composed of single parcels and/or multiple parcels of insufficient size to provide such connections, should include future street stubs. Future street connections should be clearly identified to notify residents of future roadway connections. ✓ Policy Objective Met ❑ Not Met Policy EN -28. Minimize on-site erosion and sedimentation during and after construction. ✓ Policy Objective Met ❑ Not Met Policy EN -71. Allow land alteration only for approved development proposals or approved mitigation efforts that will not create unnecessary erosion, undermine the support of nearby land, or unnecessarily scar the landscape. ✓ Policy Objective Met ❑ Not Met Policy LU -156. Residential Low Density areas may be incorporated into Urban Separators. ✓ Policy Objective Met ❑ Not Met Policy EN -28. Minimize on-site erosion and sedimentation during and after construction. ✓ Policy Objective Met ❑ Not Met b) Compliance with the Underlying Zoning Designation The subject site is designated R-1, R-8, and R-14 on the City of Renton Zoning Map. The proposed development would allow for the future construction of 12 new single-family dwelling units. Density: The density permitted in the R-1 zone is a maximum of 1 dwelling per net acre (du/ac). The density range in the R-8 zone is a minimum oOf 4.0 up to a maximum of 8.0 du/ac. The density range in the R-14 zone is a minimum of 10.0 and a maximum of 14.0 du/ac. Net density is calculated after public rights -of way, private access easements, and LUAo9-140, EGF, PP City of Renton Community and Economic Development Department Preliminary Report to the Hearing Examiner WILSON PARK PRELIMINARY PLAT LUA09-14a PP, ECF PUBLIC HEARING DATE March 16, 2010 Page 7 of 13 critical areas are deducted from the gross acreage of the site. The net acreage of the R-1 area of the property is 0.3882 acre (23,795 sf — 5,927 sf of road area and 958 sf of steep slope area = 16,910 sf or 0.3882 ac); the net acreage of the R-8 portion of the property is 63,277 sf or 1.4526 ac (80,632 sf —17,355 sf of road area = 63,277 sf or 1,4526 ac); and the net acreage of the R-14 area of the property is 2,094 sf or 0.0481 acre (2,384 sf — 290 sf of road area = 2,094 sf or 0.0481 acre). The overall net density for the project is 7.99 du/ac. Lot Dimensions: Twelve lots and three tracts are proposed. The minimum lot size required in the R-1 zone is 1 acre or 10,000 sf for cluster developments; minimum lot width in the R- 1 zone is 75 -feet for interior lots and 85 -feet for corner lots and the minimum depth is 85 - feet. The minimum lot size in the R-8 zone is 4,500 sf for parcels greater than one acre in size; the minimum lot width in the R-8 zone is 50 -feet for interior lots and 60 -feet for corner lots. No lots are proposed in the R-14 portion of the property. As proposed and demonstrated in the table below, all lots meet the requirement for minimum width. Lnt Area (sq- ft� Width/Depth ft. Notes 1 4,594 63/75 R-8 Zone; abuts open space Tracts B &D 2 4,500 60/75 R-8 Zo n e 3 5,896 80/75 R-8 Zone; corner lot 4 5,993 50/120 R-8 Zone 5 5,979 50/120 R-8 Zone 6 5,964 50/120 R-8 Zone 7 5,782 57/120 R-8 Zone; future road connection to north 8 6,269, 70/90 R-8 Zone; corner lot 9 5,400 60/90 R-8 Zone 10 5,400 60/90 R-8 Zone 11 5,404 60/90 R-8 and R-1 Zones 12 13,006 (net lot area 8,122) 108/90 Ft. R-1 Zone; includes 4,884 sq. ft. of open space B 958 N/A Steep Slope Open Space Tract C 4,195 N/A Open Space Tract D 2,900 N/A Open Space Tract Setbacks: Proposed Lots 1-11 are subject to the setback requirements of the R-8 Zone. Lot 12 is entirely within the R-1 Zone, and is, therefore, subject to R-1 setbacks. None of the proposed lots are subject to the requirements of the R-14 zone. R-1 zone setback requirements are a minimum of 30 -feet front yard, 15 -feet side yard and 25 -feet rearyard. R-8 setback requirements are a minimum of 15 -feet for the primary LUA09-140, ECF, PP City of Renton Community and Economic Development Department Preliminary Report to the Nearing Examiner WILSON PARK PRELIMINARY PLAT LUA09-140, PP, ECF PUBLIC NEARING DATE March 16, 2030 Page 8 of 13 structure and 20 -feet for attached garages in the front yard, 5 -feet side yard and 20 -feet rear yard. As proposed, all lots appear to contain adequate area to provide all required setback areas. Compliance with building setback requirements would be reviewed at the time of building permit review. The applicant has indicated that the existing residence on portions of proposed Lots 2, 3, 8, and 9 would be removed- Since the existing house is within the area of several proposed lots and the Road B, the house will need to be removed prior to recording. Staff recommends as a condition of approval, that the applicant apply for and obtain a demolition permit, remove the existing residence, and complete final inspections of the demolition prior to plat recording. Building Standards: The R-1 and R-8 zones permit one residential structure per lot. Each of the proposed lots would support the construction of one detached single family home/ Building height in the R-1 (Lot 12) and R-8 zones (Lots I - 11) is limited to 30 feet. The maximum lot coverage in the R-1 Zone (Lot 12) is 35% percent; while the maximum impervious lot coverage in the R-8 Zone is dependent on the lot size. For lots greater than 5,000 square feet (Lots 3 - 11) 35% lot coverage or 2,500 sq. ft. is permitted, whichever is greater; for lots less than 5,000 sq. ft. (Lots 1 and 2) 50% lot coverage is permitted. It appears that all of the proposed parcels contain enough area to accommodate single family residential homes that comply with the lot coverage requirements. The building standards for proposed lots would be verified at the time of building permit review. Proposed Lot 12 contains an open space easement which would be recorded as a part of the Native Growth Protection Easement (NGPE) recommended in this report. d) Community Assets Landscapin The applicant will be required to provide landscape strips along the internal roads where street trees shall be planted. Proposed Road A within the plat would require an 8 -foot landscape strip between the street and the sidewalk along the north side of the street. The off-site portion of Road A will also require an 8 -foot planter strip between the street and the sidewalk. Proposed Road B is required to have a 5 -foot planter strip landscaped with street trees. The applicant has submitted a tree inventory and tree retention worksheet which indicates that there are 101 trees on the site. A total of 25 trees must be retained and the applicant is proposing to retain 15 of these trees. The replacement ratio is six, 2 -inch caliper trees per tree removed. The applicant is proposing to provide 60 replacement trees. The majority of these replacement trees are proposed to be planted within the Urban Separator Area (R-1 zoning) which encompasses the eastern portion of proposed Lot 12, and Tracts B, C, and D. Staff recommends as a condition of approval that a Native Growth Protection Easement (NGPE) be recorded over the eastern portion of Lot 12 and Tracts B, C, and D. The edge of the NGPE shall be delineated with a split rail fence and identified with signage as approved by the Planning Division project manager. A fencing and signage detail shall be submitted to the Planning Division project manager for review and approval at the time of construction permit application. The fencing and signage shall be installed prior to recording the final plat. In order to ensure that the proposed open space area would be provided with vegetation enhancement, staff recommends as a condition of approval that the applicant be required to plant replacement trees as indicated on Exhibit 8. Staff further recommends as a condition of approval that the applicant establish a Homeowners LUA09-140, ECF, PP City of Renton Community and Economic Development Department Preliminary Report to the Nearing Examiner WILSON PARK PRELIMINARY PLAT LUA09-140, PP, ECF PUBLIC HEARING DATE March 16, 2010 Page 9 of 13 Association which would be responsible for maintenance of the open space areas within the plat - Open Space: lat_ Open_Space: The R-1 zoned portion of the property coincides with the Talbot Road Urban Separator Overlay. RMC 4-3-110 identifies two Urban Separator Overlay areas in the City: the May Valley Urban Separator and the Talbot Road Urban Separator. In the May Valley Urban Separator, entire properties are included in the Urban Separator designation. However, in the Talbot Road Urban Separator only portions of properties are within the Urban Separator. Urban Separators are intended to create contiguous open space corridors within and between urban communities, which provide environmental, visual, recreational and wildlife benefits. The purpose of the Urban Separator is also to protect resources and environmentally sensitive areas. Properties located within Urban Separators are required to dedicate 50 percent of the designated gross area of the property as open space. For properties in May Valley, where entire properties are within the Urban Separator, this is appropriate. However, for properties in the Talbot Road area, where only portions of the sites are within the designated Urban Separator, the requirement for dedicating 50 percent -of the area as open space is a hardship. By requiring 50 percent of the area designated as Urban Separator to be dedicated as open space, there is uniformity and fairness between the Talbot Road and May Valley Urban Separator areas. An Administrative Policy/Code Interpretation which became effective on. January 14, 2010 states that properties in the Talbot Urban Separator will be required to dedicate 50 percent of the gross land area in the Urban Separator as open space, rather than 50 percent of the gross site area. The area to be dedicated may also include portions of the site abutting the Urban Separator. The area of the project site within the Talbot Road Urban Separator (R-1 zone) is 23,795 sf. Using the Administrative Policy/Code Interpretation cited, above, the applicant would be required to dedicate 11,898 sf of open space. The applicant proposes to provide 12,937 sf of open space (958 sf in Tract B, 4,1.95 sf in Tract C, 2,900 sf in Tract D, and 4,884 sf in the open space easement as part of proposed Lot 12). e) Compliance with the Subdivision Regulations Streets: Access to the site would require the dedication of a new public street across an abutting property. This street would 26 -feet of paving, an 8 -foot planter strip and a 5 -foot sidewalk. A secondary emergency access across the abutting property to the southeast is required. This emergency access would be gated and is required to have 20 -feet of paving. Residential Blocks: RMC 4-7-160A states that blocks shall be wide enough to accommodate two tiers of lots, except where the location and extent of environmental constraints prevent a standard plat land configurations including size and shape of the parcel. In addition, prior the approval of a single tier of lots, the applicant must demonstrate that a different layout or provision of an alley system is not feasible. The site contains environmental constraints including limited access, steep slopes, and narrow underlying lot width which preclude a double tier of lots or an alley configuration. Furthermore, the applicant initially proposed a different lot layout, with more parcels, and redesigned the plat to conform to the multiple underlying zone classifications and the Urban Separator Overlay. Staff supports the current lot layout. The parcels are uniform in size and shape. Lots: The proposed lots are generally rectangular in shape and conform to Code requirements in terms of minimum size and width. Proposed Lots 3 and 8 would be corner lots and frontage has been determined to be on proposed Road A. Staff recommends as a LUA09-140, ECF, PP City of Renton Community and Economic Development Department Preliminary Report to the Hearing Examiner WIL50N PARK PRELIMINARY PLAT LUA09-140, PP, ECF PUBLIC HEARING DATE March 16, 2010 Page 10 of 13 condition of approval that proposed Lots 3 and 8 front on proposed Road A and, therefore, a note shall be placed on the face of the plat prior to recording. D Reasonableness of Proposed Boundaries: Access: Each of the proposed lots and tracts would have access to a public street. The applicant has proposed to extend a new 42 -foot wide public street from South 55£h Street. This street would have 26 -feet of paving, an 8 -foot planter strip, a five-foot sidewalk, curb and gutter along the westerly side of the street. This street would require off-site dedication. Within the plat, Road A would be a 42 -foot wide right-of-way consisting of 26 feet of paving, with and 8 -foot wide landscape strip and 5 -foot wide sidewalk fronting proposed Lots 8 —12. The sidewalk and planting strip would be located on only on the north side of the street fronting Road A. Improvements proposed on proposed Road B fronting Lots 4 — 7 consist of a 5 -foot wide sidewalk and a 5 -foot wide sidewalk and a 5 -foot wide planting strip along the east side of proposed Lot 8. Improvements for proposed Road B would end at the northern property line. Staff recommends as a condition of approval that the applicant place a sign at the northern terminus of proposed Road B that alerts future property owners that this road may be extended to the north should future development warrant such an extension. Emergency secondary access would be provided via an emergency vehicle access extending from the southeast terminus of Road 'B' (near Lots 3 and 4) to South 55th Street. This emergency access would require 20 -feet of pavement. Property owners to the west have expressed concern about the installation of new roads to the proposed project. They are concerned about appropriate setbacks, easements and fences along property lines. Additionally, these property owners are concerned about safety on these roads in inclement weather. The surrounding property owners also suggest a concrete barrier wall for cars travelling southbound (downhill) on proposed Road A. The applicant must address all appropriate City of Renton road safety issues at the time of construction. The property owners to the west are also concerned about traffic on S 55th Street which is serpentine and slopes downward from east to west in the vicinity of the proposed project. While it is acknowledged that vehicle accidents have occurred in this area on S 55th Street, the Traffic Study submitted with the application materials indicates that sight distances at the proposed access point for the proposed project are adequate. This has been verified by City staff. Togo rag AhY: The site contains areas of protected slopes (greater than 40 percent) in the southwestern portion of the property. The Environmental Review Committee imposed a mitigation measure which requires the applicant to place a note on the face of the plat that requires a 15 -foot building setback line from the top of slopes which are 40 percent or greater. The applicant has indicated proposed retaining walls along the westerly side of proposed Lot 12 (within the R-14 portion of the property) and through proposed Lots 5, 6, and 7. These walls range in height from 12 to.20-feet in height. The retaining wall on the easterly side of the property would be poured concrete or soil nail composition. The retaining wall on the westerly side of the property would be poured concrete or reinforced earth. Because the height of these proposed walls may cause visual impacts to adjoining property owners to the west and northeast, the Environmental Review Committee imposed a mitigation measure to require a combination of texturing and tinting on all visible surfaces LUA09-1411, ECF, PP City of Renton Community and Economic Development Department Preliminary Report to the Nearing Examiner WILSON PARK PRELIMINARY PLAT LUA09-140, PP, ECF PUBLIC NEARING DATE March 16, 1010 Page 11 of 13 of the proposed retaining walls. Because proposed retaining walls would be in close proximity to property lines, staff recommends as a condition of approval that the applicant obtain any necessary construction and maintenance easements for the retaining walls and the stormwater vault. Property owners to the west of the project site have expressed concern about appropriate engineering of the proposed project so that the properties below the site are not compromised by increased danger of landslides or run-off. The Geotechnical Engineering Study prepared by Liu & Associates, Inc., dated February 20, 2009 and the Technical Information Report prepared by Baima & Holmberg, Inc., dated May 5, 2009 address these issues and present recommendations to avoid such consequences. Relationshi to Existin Uses: Single-family residences abut the project site to the west and south with vacant land to the north and east. The detached single-family residences would be compatible with the surrounding development. 9) Availability and Impact on Public Services (Timeliness) Police and Fire: Police and Fire Prevention staff indicated that sufficient resources exist to furnish services to the proposed development. flue to limited access staff recommends, as a condition of approval, any future residence constructed within the plat shall be sprinkled unless the requirement is removed by the City of Renton Fire Marshal or his/her designee. A note shall be recorded on the face of the short plat to this effect. The proposal would add new residential units to the City that would potentially impact the City's Police and Fire Emergency Services. Staff recommended through SETA Environmental Review as a condition of approval to mitigate for these impacts that requires the applicant to pay a Fire Mitigation Fee, based on $488.00 per new single-family residence payable prior to recoding of the final plat. The fire mitigation fee is estimated to be $5,386 (11 new units x $488.00 = $5,386.00) Schools: The project site is served by schools in the Renton School District. It is anticipated that the Renton School District can accommodate any additional students generated by this proposal at the following schools: Benson Hill Elementary, Nelsen Middle School and Lindbergh High School. School impact fees are regulated under RMC 4-1-160 and are in effect at the time of permit application or final plat approval. Currently, the Renton School District required fee is $6,310.00 per each new single-family residence; however, school mitigation and impact fees are updated annually and are subject to change. Surface Water: The applicant submitted a Technical Information Report for Wilson Park, prepared by Baima & Holmberg, Inc. dated May 5, 2009. That report includes an analysis of upstream tributary drainage which states that the parcel to the east drains onto the site. The Level 1 Downstream Drainage Analysis in the report states that runoff from the site flows west into lots in the adjacent Geneva Court development. The majorities of these flows collect in a drain constructed along the back yards of the western -most lots of the Geneva Court development and then flow into the storm system in South 53rd Place. This flow collects in a stormwater pond/bioswale facility located at the intersection of Talbot Road S and South 53rd Place approximately 750 -feet downstream from the site. This facility outfalls through an 18 -inch pipe to the west side of Talbot Road S into a poorly defined channel flowing into the woods. The flows then pass through a 12 -inch culvert under a walking path and continue to flow west to a wooded wetland area more than a quarter LUA09-140, ECF, PP City of Renton Community and Economic Development Deportment Preliminary Report to the Hearing Examiner WILSON PARK PRELIMINARY PLAT LUA09-140, PP, ECF PUBLIC HEARING DATE March 16, 2010 Page 12 of 13 .mile downstream from the site. Flows into the ditch along S 55th Street continue west in a rock lined channel along the north side of the street to the intersection of Talbot Road S and S 55th Street. The channel is eroded and shows signs of flowing into the street. Flows from the ditch along Talbot Road S collect in the storm system about 850 -feet downstream from the site eventually flowing into Springbrook Creek at about 1,800 -feet downstream from the site. Springbrook Creek continues flowing west to about one-half mile downstream of the site where it enters a box culvert crossing SR 167. The Technical Information Report indicates that there are no apparent drainage problems. The plans submitted by the applicant indicate that a proposed storm water detention vault would be located off-site in the easterly proposed access road to control downstream stormwater impacts. The Environmental Review Committee imposed a mitigation measure that requires the final drainage report shall be subject to the 2009 King County Surface Water Design Manual. Property owners to the west have expressed concern about changes in drainage due to impervious surfaces created by the proposed project. The applicant proposes to install a stormwater vault within the off-site portion of proposed Road A. Additionally, the applicant would be required to use the 2009 King County Surface Water Design Manual in the final drainage report. Water: The applicant proposes to serve the subject subdivision with a public water supply and distribution system managed by the Soos Creek Water and Sewer District. A Certificate of Water Availability, dated November 7, 2008, has been issued by the Soos Creek Water & Sewer District. The applicant will show, during engineering review, the location and distance of all existing fire hydrants within 300 feet of the site. Existing and new hydrants will be required to be retrofitted with Storz "quick disconnect" fittings, if not already in place. Furthermore, the Fire Department requires that all new houses be sprinklered. Sewer: The site is within the City of Renton sewer service area. A minimum 8 -inch diameter sanitary sewer extension is required to serve the site. Streets: The streets within the proposed project would be dedicated public streets and would become part of the City's street system. Improvements required on these streets are described ion the Access section, above. As indicated in that section, the neighboring property owners are concerned about how street safety issues would affect them. The Traffic Study prepared by Traffex, dated June 23, 2009 cites accident history in the project vicinity on South 55th Street between 98th Avenue S and 9e Place S. A total of four accidents occurred between January 1, 2004 and December 31, 2008. Two of the accidents were injury accidents with one of them being fatal. None of the accidents occurred at the curve on South 55th Street where the site access is proposed. The Traffic Study indicates that sight distances are adequate for the curves in the vicinity of the proposed project. The adequacy of sight distances has been verified by City staff and has been found to be appropriate for the proposed plat LUA09-140, ECF, PP City of Renton Community and Economic Development Deportment Preliminary Report to the Hearing Examiner WILSON PARK PRELIMINARY PLAT LUA09-140, PP, ECF PUBLIC HF_4RING DATE March 15, 2010 Page 13 of 13 G. RECOMMENDATIONS. Staff recommends approval of the Wilson Park Preliminary Plat, Project File No. LUA09-140, PP. ECF) subject to the following conditions: 1. The applicant shall comply with all requirements of the Determination of Non -Significance — Mitigated that was issued by the Environmental Review Committee on February 22, 2010 for Project File No. LUA09-140, ECF, PP. 2. The applicant shall apply for a demolition permit, remove the existing residence and complete final inspections of the demolition prior to plat recording. 3. A Dative Growth Protection Easement (NGPE) shallbe recorded over the eastern portion of Lot 12 and Tracts B, C, and D. The edge of the NGPE shall be delineated with a split rail fence and identified with signage as approved by the Planning Division project manager. A fencing and signage detail shall be submitted to the Planning Division project -manager for review and approval at the time of construction permit application. The fencing and signage shall be installed prior to recording the final plat. 4. The applicant shall be required to plant replacement trees as indicated on Exhibit 8 prior to recording of the final plat. 5. The applicant shall establish a Homeowners Association for the maintenance of the NGPE, the stormwater vault and the retaining walls and provide the appropriate documents for the review and approval of the Planning Division project manager prior to recording of the final plat. 6. A note shall be placed on the face of the plat which indicates that Lots 3 and 8 shall be oriented to take access from proposed Road A. 7. The applicant shall place signs at the northerly terminus of proposed Road B which alert future property owners that this road may be extended to the north should future development warrant such an extension. These signs shall be installed prior to recording of the final plat. 8. The applicant shall obtain any necessary construction and maintenance easements for the retaining walls and the stormwater vault subject to review and approval by the City Attorney. EXPIRATION PERIODS: The Preliminary Plat approval will expire 5 years from the date of approval. An extension may be requested pursuant to RMC Section 4-7-0801. LUA09-140 ECF PP tp6 E t J D EXHIBIT 2 E d qp p `4. % 0. W e M 6 •7d '• I N '7' m HAtd i r oj r �l8 M _ Cll — is - .w . � • z C a - dy i H twcazas ?� y® Y® rL■J•, •'a 3AY: ■ 9. r NZ l C ■ ar tl Y� I [ 9' N 33,,,; ~ \,s 1p .� v..I . 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MUNICIPAL CODE SECTIONS: RMC 4-3-110, Urban Separator Overlay Regulations. REFERENCE: Wilson Park Preliminary Plat (LUA09-140, PP, ECF) SUBJECT: Determination regarding dedication of open space requirements for properties within the Talbot Urban Separator. BACKGROUND: The City received an application for a development proposal on a 2.5 acre site in the R-14, R-1, and R-8 zones. The site includes a portion of the Talbot Urban Separator, which is an overlay intended to create contiguous open space corridors within and between urban communities, which provide environmental, visual, recreational and wildlife benefits. The purpose of the Urban Separator is also to protect resources and environmentally sensitive areas. There are two Urban Separator areas: May Valley and Talbot Road. In the May Valley Urban Separator, entire properties are included in the Urban Separator designation. However, in the Talbot area, only portions of properties are within the Urban Separator, and these are generally portions of the property containing steep slopes. Properties located within the Urban Separator are required per RMC 4-3-110.E.2.a to dedicate 50% of the gross land area of the parcel or parcels as a non - revocable open space tract. In May Valley, since the entire property is designated Urban Separator, the dedication of 50% of the gross site area is appropriate. However, in the Talbot Urban Separator where only a very small portion of the site is designated Urban Separator, it is inequitable to require that 50% of the gross site area be retained. JUSTIFICATION: Urban Separator regulations require dedication of 50% of designated properties gross area as open space. For properties in May Valley, where the entire site is within the Urban Separator, this is appropriate. However, for properties in the Talbot area, where only a portion of the site is designated Urban Separator, the requirement for dedication of H.\CED\Planning\Title W\Docket�Administrative Policy Code lnterpretation\Cl-06\Code Interpretation.doc Page 1 of 2 50% of the area as open space is a hardship. By requiring 50% of the area designated as Urban Separator to be dedicated as open space, there is uniformity and fairness between the Talbot and May Valley areas. DECISION: Properties in the Talbot Urban Separator will be required to dedicate 50% of the gross land area in the Urban Separator as open space, rather than 50% of the gross site area. The area to be dedicated may also include portions of the site abutting the Urban Separator, in order to create a contiguous open space corridor. PLANNING DIRECTOR APPROVAL. - C. E. "Chip„ Vincent...-... DATE: January 14, 2010 APPEAL PROCESS: To appeal this determination, a written appeal --accompanied by the required filing fee --must be filed with the City's Hearing Examiner (1055 S. Grady Way, Renton, WA 98057) no more than 14 days from the date of this decision. Your submittal should explain the basis for the appeal. Section 4-8-110 of the Renton Municipal Code provides further information on the appeal process. CODE AMENDMENTS NEEDED TO IMPLEMENT DETERMINATIONS: RMC 4-3-110.E.2 should be amended to read as shown on Attachment A. 0.05 Page 2 of 2 Attachment A RMC 4-3-110.E. 2. Dedication of Open Space Required. a. Approval of a plat, and/or building permit on an undeveloped legal lot in the .May Valley Urban Separator Overlay shall require dedication of fifty percent (50%) of the gross land area of the parcel or parcels as a non -revocable open space tract retained by property owner, or dedicated to a homeowners association or other suitable organization as determined by the reviewing official. Approval of a plat, and/or building permit on an undeveloped legal lot in the Talbot Urban Separator Overlay shall re uire dedication of fiftyercent b0°fo of the ross land area of that portion of the parcel or parcels located within the Urban Separator as anon- revocable open sace tract retained by the property owner. or dedicated to a homeowners association or other suitable organization as determined by the reviewing official. In order to satisN the dedication requirement, some of the area to be dedicated may consist of land abutting the Urban Separator, as determined by the Planning Director, on a case-by-case basis. Acreage in tracts may include critical areas and/or critical area buffers.- At a minimum, open space shall be connected to another contiguous open space parcel by a fifty foot (50) corridor. b. Existing residences, existing accessory uses and structures, existing above ground utilities located in the tract at the time of designation and new small and medium utilities shall not count toward the fifty percent (50%) gross land area calculation for open space except for storm water ponds designed with less than 3:1 engineered slopes and enhanced per techniques and landscape requirements set forth in the publication the "Integrated Pond" King County Land and Water Resources Division. c. Approval of a building permit for an addition of three hundred (300) square feet for a primary use structure or five hundred (500) square feet for an accessory structure shall require recordation of a conservation easement, protective easement or tract and deed restriction on critical areas and critical area buffers located within the contiguous open space corridor pursuant to RMC 4-3-050E4, Native Growth Protection Areas. d. Land dedicated as open space shall be located within the mapped contiguous open space corridor unless a modification is approved pursuant to subsection E6 of this Section. Denis Law Mayor C1 of EXHIBIT 11 %rte Department of Community and Economic Development November 10, 2009 Alex Pietsch, Administrator Tom Redding Bairna & Holmberg, Inc. 100 Front Street South Issaquah, WA 98027-3817 Subject: Wilson Park Preliminary Plat — LUA09-140 720 South 55th Street Street Modification requests Dear Mr. Redding: We have completed our review of your request for modifications to the street standards for the proposed Wilson Park. Preliminary Plat located at 720 South 55th Street. The proposed residential subdivision is for 13 single family building lots and four additional tracts. The subdivision will be served by two access roadways south of the site to South 556 Street, connecting to a new street through the proposed project. You have requested modification forthe internal roadway, including eliminating the required sidewalk from one side of the street, reducing the right-of-way width, and eliminating the requirement for a cul- de-sac. Clarification of the street improvement -requirements for the two off-site access roadways is also'requested. The proposal continues to be based on a waiver of the required connection to the north property line. The request to reduce the internal street right-of-way width to 37.5 feet is denied. However, the request to delete the sidewalk from one side of the internal street is approved, subject to providing an eight -foot (8') planting strip between the street and remaining sidewalk. The requirement for a cul-de- sac is modified to allow for a hammerhead turnaround and gated emergency access for secondary access. The proposal to waive the requirement to extend the public street to the north property line is also denied. City Cade 4-6-060 (Street Standards) requires full.street improvements for all adjacent rights-of-way for, within, and dedicated by a plat. The -City can modify street improvements for new plats if there are practical difficulties in carrying out the provisions of -the Street Improvement Ordinance. The Modification Procedures, as defined in Section 4-9-2SOD, clearly states the criteria for approval by the Department Administrator. In order for -a modification to be approved, the Department Administrator must find that a special individual reason make's the strict letter of fhis'Ordinance impractical, that the modification is iri conformity with the intent and purpose of this. Ordinance, and that such modification: (a) Will meet the objectives and. -safety, function, appearance, environmental protection and Maintainability intemded by this Ordinance, based upon sound engineering judgment; and (b) Will not be injurious to other property(s) in the vicinity; and Renton Crty Hall a 1055 South Grady Way • Renton, Washington 98057. 9 rentonwa_gov Mr. Tom Redding Wilson Park Preliminary flat Page 2 of 3 (c) Conform to the intent and purpose of the Code; and (d) Can be shown to be justified and required for the use and situation intended; and (e) Will not create adverse impacts to other properties in the vicinity. The request to reduce the right-of-way width to 37.5 feet cannot be approved. The code allows for consideration of reduction to 42 feet in width in cases where the additional area provides for a more reasonable lot configuration. The reduction to 42 feet in width is approved, but we fail.to find justification'to reduce the public right-of-way in this new residential neighborhood to a lesser standard. The request to eliminate the sidewalk along'the southerly side of the new internal roadway can be supported in this situation, provided there are equivalent value amenities provided in exchange for these improvements. This request is granted, subject to the provision of an eight- foot (8') wide planting : strip, including landscaping and street trees, on the northerly side of the street with the new sidewalk. The project site will be accessed by a single public street, which requires a cul-de-sac. The proposed secondary access will mitigate the dead-end roadway configuration for emergency vehicles, but will not be available for regular vehicles and delivery trucks. The requirement for a cul-de-sac is hereby waived, subject to providing a .full hammerhead turnaround in public right-of-way and emergency secondary access through an approved grated system. The function of a hammerhead turnaround will be provided with the extension of the street to the north property line, as addressed below. The proposed- street design for the plat fails to meet the requirement to extend the pubkic street system through the plat to the northerly property line. The property north of the site is large enough for future platting, and will be connected to the public street system approved for this plat. The regbirement far extension of the public street system through the proposed plat to the north property line remains. This extension is to be provided where Lot 8 is proposed, as an extension of the easterly north -south access roadway. The street improvements required for this preliminary plat, as modified in this decision, are as follows: Westerl off-site access padway between S. 55'h Stand the development site: This street section shall be in dedicated public right-of-way. The pavement width can be reduced to 26 feet (26') in width, allowing for parking on one side of the street. Curb and gutter shall be provided along the westerly edge pf the pavement. An eight -foot (8') wide planting strip shall be provided along the west side of the street, with a eve -foot (5') wide sidewalk. New internal street system: This street section shall be in a minimum 42 -foot width right-of-way. Additional right-of-way is also regUired at all the intersections and turns in the roadway configuration. These radius dedications shall be for a 15 -foot radius. The pavement width can be reduced to 26 feet in width, all for parking on one side of the street. Both sides of the street shall be improved with curb and gutter. A sidewalk is not required on the southerly side of the new street. The.face of the curb shall be installed three feet (3') from the southerly edge of the right-of-way: A five-foot (5') wide sidewalk shall be provided along the northerly and "outside" portion of the new internal street, with an Mr. Tom Redding Wilson Park Preliminary Plat Page 3 of 3 eight -foot (8') planting strip. The planting strip is to be landscaped, including street trees. Street lighting meeting code with required lighting levels shall be provided on the new internal street system. Street extension to north property line: A public street is required -in the approximate location -of proposed Lot 8. This street shall include a minimum of 42 feet in right -of -.way. The street improvements for this extension shall include 25 feet of pavement, and curb and gutter along both sides of the street_ Sidewalks are required along both sides of this street section, both five feet (5') in width. The sidewalk on the east side of the street can be constructed adjacent to the new curb. The west side of the street shall include a five-foot (5') planting strip laridscaped with street trees. -. Easterly off-site access roadway between S. .55th St and the d•evelopment-site: This street sectiori-is _--- initially to be used for secondary emergency access through a private roadway easement.. The pavement shall be a minimum of 20 feet in width through this roadway section. An emergency access gate, approved by the Renton Fire Department, can be installed where this roadway enters the new plat. If this private easement is replaced in the future with dedicated public right-of-way, the emergency access gateshall be removed. A note to this effect is to be included on the final plat. You have 14 days from the date of this letter to appeal the administrative determination in accordance with City code. Appeals are to be filed in writing; with the City Clerk, and require a filing fee in the amount of $250.00. Appeals must be fled with the City Clerk before Tuesday, November 24, 2009, at 5:00 P.M. You may contact Kayren Kittric_k.at (425) 430-7299 if you have any questions or need additional information. Sincerffely, f� �f r � Neil Watts, Director Development Services Division cc Alex Pietsch, Community & Economic Development Administrator Chip Vincent, Planning Director ifayren Kittrick, Development Engineering Supervisor Jerry Wasser, Associate P€anner WILSON PARK II LUA12-013 DEPARTMENT OF COMMUNITY AND ECONOMIC DEVELOPMENT 'C 'y of rc REPORT TO THE HEARING EXAMINER A. SUMMARY AND PURPOSE OF REQUEST: REPORT DATE: June 12, 2012 Project Name: Wilson Park II Owner/Applicant: Robert & Doravin Wilson, 21703 60t Street East, Lake Tapps, WA 98391 Contact., Darrell Offe, P.E.; Offe Engineers, PLLC, 13932 SE 159" Place, Renton, WA 98058 File Number: LUA12-013, ECF, PP, PPUD Project Manager: Jennifer Henning, Current Planning Manager Project Description: The applicant proposes to subdivide an existing 2.15 acre parcel into 10 lots for the eventual development of detached single family homes, and 1 tract for open space. The site is zoned Residential -14 du/ac (R-14) & Residential - 1 du/ac (R-1). The site contains 9,783 s.f. of protected slopes (>40%). Proposed density averages 6.4 dwelling units per acre across the site, with 8 lots proposed in the R- 14 area, & 2 lots proposed within the R-1 zone. A Planned Urban Development is proposed in order to modify minimum lots size and development standards for the R-1 and R-14 Zones. Access would be provided from South 55th Street via new street constructed as part of the approved Wilson Park I plat. A small hydrologically isolated, unregulated wetland is located on the western portion of the site. The site contains 82 trees, of which 21 would be removed for the construction of the new street serving Wilson Park #1. Ten (10) trees would be retained, and new trees would be planted including 2 new trees per lot. The project requires Environmental (SEPA) Review, Planned Urban Development (PUD) Review, and Preliminary Plat review. Project Location: 698 South 55th Street City of Renton Community and Economic Development Depariment Report to the Hearing Examiner KLSON PARK 11 PLA T & PUD LUA12-013, &CF, PP, PPUD PUBLIC HEARING DATE: June 12, 2012 Page 2 of 31 B. HEARING EXHIBITS: Exhibit 1: Neighborhood Map Exhibit 2: PUD/Plat Map (Sheet 1 of 1) Exhibit 3: Aerial Photo with Zoning Exhibit 4: Environmental Review Committee (SEPA) Report Exhibit 5. SEPA Determination Exhibit 6: SEPA Mitigation Measures and Advisory Notes Exhibit 7. Density Work Sheet Exhibit S: C-30 Administrative Policy/Code Interpretation Exhibit 9: Tree Retention Plan Exhibit 1a: Tree Retention Work Sheet Exhibit 11: Landscape Plan (Sheet L 1.1) Exhibit 12: Traffic Impact Analysis Report (Northwest Traffic Experts, 6/23/2009 & 1/25/2012) Exhibit 13: Drainage Utilities Plan Exhibit 14: Public Comment Letter: Witt/Vu/Nguyen/Dang/Duong (April 16, 2012) Exhibit 15: Topography Map Exhibit 16: Aerial Photo with City of Renton Slopes Exhibit 17: Road Profile/Grading Plan City ofRenion Community and Economic Development Department Reporl to the Hearing Examiner WILSON PARK IFPLAT&PUD LUA12-013, ECF, PP, PPUD P UBLIC HEARING DATE: .lune 12, 2012 Page 3 of 3l Exhibit 18: Geotechnical Engineering Study Exhibit 19: Proof of Mailing and Posting Exhibit 20: Wetland Verification for Wilson Park 2 (Altmann Oliver Associates, LLC (3/11/2011) Exhibit 21: Addendum to Technical Information Report Prepared for Wilson Park (LUA09-140) by Baima & Holmberg, Inc, dated May 5, 2009 (Darrell Offe, P.E., February 28, 2012) C. GENERAL INFORMATION: 1. Owner of Record. Robert & Doravin Wilson 2170360 th Street East Lake Tapps, WA 98391 2. Zoning Designation: Residential 1 dwelling units per net acre(R-1) and Residential 14 dwelling units per acre (R-14) 3. Comprehensive Plan Designation: Residential Single Family (RSF) and Residential Low Density (RLD) 4. Existing Site Use: Vacant S. Neighborhood Characteristics: North: Wilson Park I (undeveloped), R -14/R -1/R-8 zoning, portion of Geneva Park, detached single family homes zoned R-14 East: Single Family Residential, zoned R-8 South: South 55th Street and vacant property zoned R -14/R -1/R-8 West: Single Family Residential, zoned R-14 6. Proposed Orientation: Lots would orient east west along a new street, Road "A" 7. Site Area: 2.15 acres 8. Project Data: Existing Building Area: Not Applicable D. HISTORICAL/BACKGROUND: Action Land Use File No. Ordinance No. Date Annexation N/A Comprehensive Plan LUA08-145 5501 11/25/2009 Zoning LUA08-145 5191 11/25/2009 Wilson Park I Prelim Plat LUA09-140 N/A 8/16/2010 E. PUBLIC SERVICES: 1. Utilities: Water: Provided by Soos Creek Water and Sewer District Sewer: Provided by City of Renton Surface Water/Storm Water: Provided by City of Renton City of Renton Communtry and Economic Development Department Reporl to the Hearing Examiner WILSON PAkK11PLA T & PUD LUA12-013, ECF, PP, PPUD PUBLIC HEARING DATE. June 12, 2012 Page 4 of 31 2. Streets: South 55th Street is a Residential Access Street. 3. Fire Protection: City of Renton Fire Department F. APPLICABLE SECTIONS OF THE RENTON MUNICIPAL CODE: 1. Chapter 2 land Use Districts Section 4-2-020: Purpose and Intent of Zoning Districts Section 4-2-060: Zoning Use Table Section 4-2-110: Residential Development Standards Section 4-2-115: Residential Design and Open Space Standards 2. Chapter 3 Environmental Regulations and Overlay Districts Section 4-3-050: Critical Areas Regulations Section 4-3-100: Urban Separator Overlay Regulations 3. Chapter 4 Property Development Standards Section 4-4-030: Development Guidelines and Regulations Section 4-4-060: Grading, Excavation and Mining Regulations Section 4-4-070: Landscaping Section 4-4-080: Parking, Loading and Driveway Regulations Section 4-4-130: Tree Retention and Land Clearing Regulations 4. Chapter 6 Streets and Utility Standards Section 4-6-060: Street Standards S. Chapter 7 Subdivision Regulations Section 4-7-050: General Outline of Subdivision, Short Plat and Lot Line Adjustment Procedures Section 4-7-080: Detailed Procedures for Subdivision 5. Chapter 9 Procedures and Review Criteria Section 4-9-150: Planned Urban Development Regulations Section 4-9-250: Variances, Waivers, Modifications, and Alternates 6. Chapter 1.1 Definitions G. APPLICABLE SECTIONS OF THE COMPREHENSIVE PLAN: 1. Land Use Element— Residential Single Family 2. Community Design Element 3. Environment Element H. DEPARTMENT ANALYSIS: 1. Project Description/Background The applicant proposes to subdivide an existing 2.15 acre parcel into 10 lots for the eventual development of detached single family homes, and 1 tract (Tract A) for open space. The site is zoned Residential -14 du/ac (R-14) & Residential - 1 du/ac (R-1). The existing underlying parcel is 93,801 square feet in sire (2.15 acres) and contains 9,783 square feet of protected slopes (>40%). The R-1 City of Renton Community and Economic Development Department Report to the Hearing Examiner W=OY Pr1RKII PLAT & PUD LUA12-013, ECF, PP, PP UD P UBLIC HEARING DATE: June 12, 2012 Page 5 of 3I Zone comprises 38,326 square feet (including the steep slope area), and the R-14 portion of the site is 55,474 square feet. Proposed density averages 6.4 dwelling units per acre across the site, with 9 lots proposed in the R-14 area, & 1 lot proposed within the R-1. Site soils consist of glacial till. Grading is proposed for the project such that 820 cubic yards would be cut and 11,200 cubic yards of imported material would be used to fill the site. An underground stormwater vault was previously approved for Wilson Park I to be within the roadway on the subject site. The vault is being revised to accommodate the additional stormwater generated by the proposal. A Planned Urban Development is proposed in order to modify development regulations including minimum lots size within the R-1 Zone to create consistently sized lots for detached single family residential homes. Proposed lots would range in size from 5,560 square feet to 6,778 square feet. A portion of the site is subject to the Talbot Urban Separator Overlay Regulations. That portion of the site zoned R-1 is considered to be within the Urban Separator. Per RMC 4-3-110E2.a.ii, 50% of the area within the Urban Separator must be dedicated as irrevocable open space. The applicant proposes to retain 19,164 square feet, or 50% of the site as open space within Tract A. This tract would also provide for open space and recreation opportunities to serve the public and the residents of both Wilson Park developments. An approximate 350 square foot area would be provided with ornamental landscaping, a pergola or gazebo, and hard surface path. A soft -surface, 3 -foot wide walking path would be provided along the north and east boundaries of Lot 6, and along the east boundary of Lots 7 through 10. The path would wrap around the south boundary of Lot 10 and intersect with the sidewalk on the East side of Road A. Ornamental and native landscape plants are proposed within the tract. Access would be provided from South 55th Street via new street (Road A) constructed as part of the approved Wilson Park I plat. The street was identified as being within an easement across the subject site. With the project, the street would be dedicated and the easement would not be necessary. Street improvements including curb, gutter, 5 -foot sidewalks, an 8 -foot planting strip would be provided along both sides of Road A. This is considered to be a Residential Access street, and parking would be allowed on one side of the street. A small hydrologically isolated, unregulated wetland is located on the western portion of the site (Exhibit XX). The site contains 82 trees, of which 21 would be removed for the construction of the new street serving Wilson Park #1. An additional 51 trees would be removed for the project. Ten (10) trees would be retained, and new ornamental and native trees would be planted including two new trees per lot. 2. Environmental Review Pursuant to the City of Renton's Environmental Ordinance and SEPA (RCW 43.210, 1971 as amended), on May 7, 2012, the Environmental Review Committee issued a Determination of Non -Significance - Mitigated (DNS -M) for the Wilson Park II Plat and Planned Urban Development (Exhibits 4, 5). The DNS -M included 7 mitigation measures (Exhibit 6). A 14 -day appeal period commenced on May 11, 2012 and ended on May 25, 2012. No appeals of the threshold determination have been filed. City o Renton Communay and Economic Develo mens Department Re ort to the Hearin Examiner WYLSONPARK II PLA T& PUD LUA12-013, ECF, PP, PPUD PUBLIC HEARING DATE: June 12, 2012 Page b of 31 3. Compliance with ERC Conditions Based on an analysis of probable impacts from the proposal, the Environmental Review Committee (ERC) issued the following mitigation measures with the Determination of Non -Significance — Mitigated: 1. The applicant shall comply with the recommendations contained in the Geotechnical Engineering Study, prepared by Liu & Associates, Inc. dated November 22, 2404 and amended February 15, 2012, for the duration of project construction. 2. The applicant shall provide a Temporary Erosion and Sedimentation Plan designed pursuant to the Department of Ecology's Erosion and Sediment Control Requirements outlined in Volume II of the 2005 Stormwater Management Manual and provide staff with a Construction Mitigation Plan prior to issuance of construction permits. This mitigation measure shall be subject to review and approval of the Development Services Division. 3. The applicant shall provide weekly reports on the status and condition of the erosion control plan with any recommendations of change or revision to maintenance schedules or installation shall be submitted by the Project Engineer of record to the Public Works inspector. 4. Because of moisture -sensitive fine-grained soils mantling the site and the higher. gradient areas within the site the geotechnical study recommends that grading and foundation construction be carried out and completed within the dryer period of the year from April 1 through October 31 unless otherwise approved by the Development Services Division. Therefore, the applicant shall adhere to a construction schedule involving grading and foundation work during the dryer period of the year. S. The applicant shall pay a Parks Mitigation Fee based on $530.76 per each new single family lot prior to recording the final plat. 6. The applicant shall be required to pay a Traffic Mitigation Fee based on $75.00 per each new average daily vehicle trip associated with the proposed project prior to recording of the final plat. 7. The applicant shall be required to pay a Fire Mitigation Fee based on $488.00 per each new single family lot prior to recording the final plat. 4. Staff Review Comments Representatives from various City departments have reviewed the application materials to identify and address issues raised by the proposed development. These comments are contained in the official file, and the essence of the comments has been incorporated into the appropriate sections of this report and the Departmental Recommendation at the end of the report. City of Renton Community and Economic Development Department Report to the Hearimg Examiner WILSON PARX 1.1 PLA T& PUD - - — LUA12-013, ECF, PP, PPUD PUBLIC HEARING DATE: June 12, 2012 Page 7 of 31 5. Consistency with the Planned Urban Development Regulations a) Compliance with the Underlying Zoning Designation (Code provisions restricted from modification through the PUD process): The subject site is designated R-1 and R-14 on the City of Renton Zoning Map (Exhibit 2). The proposed development would allow for a 10 -lot, 1 -tract subdivision of an 2.15 acre site (Exhibit 3). i. Use: A planned urban development may not authorize uses that are inconsistent with those allowed by the underlying zone. The applicant is proposing the development of single family homes. Both the R-1 and R-14 Zones permit detached dwellings. ii. Density: The number of dwellings units shall not exceed the density allowances of the applicable base zone. The R-1 Zone allows a density of 1.0 dwelling units per gross acre. The R-14 Zone allows a maximum density of 14 dwelling units per net acre. According to the density worksheet (Exhibit 7) submitted with the application, the proposed project would have a net density of 6.4 dwelling units per net acre and, therefore, complies with the density requirement. Code Interpretation CI -30 (Exhibit 8) allows for properties with more than one zoning classification to be allowed to average residential density across the site provided this is accomplished through the Planned Urban Development process. This Code Interpretation has been posted on the City's webpage for a 14 -day comment period, and the appeal period for the interpretation ends at 5:00 pm on June 14, 2012. In order to ensure that only one dwelling unit is constructed on each lot within the R-14 Zone, staff recommends that the applicant be required to place a restrictive covenant on each of the lots indicating that only detached single family units could be constructed. b) Code Provisions That May Be Modified: In approving a Planned Urban Development, the City may modify any of the standards of chapters 4-2 Zoning Districts - Uses & Standards, 4-4 City -Wide Property Development Standards, and 4-7 Subdivision Regulations and RMC 4-6-060 Street Standards, except as listed above in subsection "a)". If all conditions of approval are complied with the proposed Wilson Park II Plat complies with all the City of Renton's development regulations including; chapters 4-2 Zoning Districts - Uses & Standards, 4-4 City -Wide Property Development Standards, and RMC 4-6-060 Street Standards, with the exception of the requested modifications identified in Table A below. Table A RE VEST£ Mt]1DIFJ RI=Oi FROM ROT, N MUNICIPAL CODE RMC _ - _ �� � _ _ ,rte � j'-�Sgu. Tr• ,��_ , .. _ ''� _ 1 RMC # Required per RMC Requested Modification RMC 4-2-110A: Minimum Lot Size R-1: 1 Acre, Except 10,000 sq. ft. R-1: Lots 5,560 to 6,778 sq. ft. for cluster development. R-14. Plat would include lots R-14: No minimum lot size; from 5,560 sq. ft.. to 5,909 sq. ft.; however developments over 9 all lots would be for detached lots shall incorporate a variety of single family homes. home sizes, lot sizes, and unit CiLy o Renton Community and Economic Development De arrmeni Report to the Hearin Examiner i4=ONPARKII PLAT & PUD LUA12-013, RCF, PP, PPUD PUBLIC HEARI_NC DATE: June 12, 2012 Page 8 of 31 RMC 4-2-11OA: Minimum Lot Width RMC 4-2-110A: Minimum Front Yard Setback clusters. R-1: 75 feet for interior lots; 85 feet for corner lots R-14: No minimum lot width Staff Comment: The applicant has not requested a modification from this standard. However, due to the small lot sizes requested above, staff believes a modification from this standard would be required to maintain a buildable lot - R -1: 30 feet R-14: Varies; however for lots with garage access from a street, require a minimum of 18 feet from the face of the garage to the back of the curb or sidewalk/path. RMC 4-2-110A: Minimum Side Yard I R-1: 15 feet R-14: 4 feet for detached units Staff Comment: Staff recommends that the applicant be subject to the standards of the R-8 Zone with regard to minimum lot width. R-1: Lots are proposed to be from 55 ft. to 66 ft. wide. R-14: Lots would be 55 ft. to 57 ft. wide. Staff Comment: Staff recommends requiring that the plot conform to the R-8 Development Regulations for minimum lot width. Minimum lot width would be 50 feet for interior lots and 60 feet for corner lots. Therefore, Lot 1, shown at 57.74 feet in width would need to be a minimum of 60 feet in width in order to conform to the R-8 standards for corner lots. None Proposed. Staff Comment: Staff recommends that the applicant be subject- to the minimum front yard standards of the R-8 Zone, which requires a 15 foot front yord setback. Staff further recommends that a minimum setback of 18 feet be required from the face of the garage to the back of the sidewalk to allow an appropriate area for parking. None Proposed. Staff Comment: Staff recommends that the applicant be subject to the standards of the R-8 Zone for minimum side Yard Setbacks, which is 5 feet. City of Renton Community and Economic Development Department Report to the Hearing Examiner WILSON PARK}I PLAT &PUD LUA12-013, ECF, PP, PPUD PUBLIC HEARING DATE: June 12, 2012 Page 9 of 31 RMC4-2-110: Minimum Side Yard R-1: 20 feet Along a Street R-14: n/a RMC 4-2-110A: Minimum Rear Yard R-1: 25 feet setback R-14: 12 feet RMC 4-2-11OA: Maximum Building Coverage RMC4-2-110A: Maximum Impervious Coverage R-1: 20% R-14: n/a Staff Comment: The applicant has not requested a modification from this standard. However, due to the small lot size requested above, staff believes a modification from this standard would be required to maintain a buildable lot. R-1: 30% R-14: 85% Staff Comment: The applicant has not requested a modification from this standard. However, due to the small lot size requested above, staff believes a modification from this standard would be required to maintain a buildable lot. None Proposed. Staff Comment: Staff recommends that the applicant be subject to the standards of the R-8 Zone for Minimum Side Yard Setback along a street, which is 15 feet (Lot 1). Further, staff recommends that the appropriate setback from Tract A and the pedestrian path within an easement be 5 feet. None Proposed. Staff Comment: Staff recommends that the applicant be subject to the standards of the R-8 Zone for the Rear Yard Setback, which is 20 feet. None Proposed. Staff Comment: Staff recommends that the applicant be subject to the standards of the R-8 Zone for Maximum Building Coverage. For lots larger than 5,000 s.f. this is 35% or 2,500 s.f. whichever is greater. None Proposed. Staff Comment: Staff recommends that the applicant be subject to the standards of the R-8 Zone for Maximum impervious Coverage, which is 75%. City of Renton Community and Economic Development Department Report to the Hearing Examiner WILSON PARK II PLAT & PUII L UA12-013, ECF, PP, PP UD PUBLIC HEARING DATE: June 12, 2012 Page 10 of31 RMC 4-2-115F.1. Site Design, Lot R-1: N/A Staff Comment., Staff Configuration recommends approval of the R-14: Developments of more requested deviation and than nine (9) detached dwellings recommends that the shall incorporate a variety of requirements of the R-8 home sizes, lot sizes, and unit Residential and Open Space clusters. Standards be followed. This standard requires that: 1. Lot width variation of 10 feet minimum of one per 4 abutting street fronting lots; or 2. Minimum of 4 lots sizes (minimum of 400 gross square feet size difference, or 3. A front yard setback variation of at least 5 feet minimum for at least every 4 abutting street fronting lots. RMC 4-2-115F.1. Site Design, R-1: N/A Staff Comment: Staff Garages recommends approval of the R-14: Recessed 8 feet from the requested deviation provided that front, or detached; garage similar the requirements of the R-8 to home; minimum 18 -foot Residential and Open Space driveway length from the face of Standards be followed. garage to the back of the sidewalk (unless accessed by This standard requires that the alley) garage be recessed at least 8 feet from the front of the house; or located so that the roof extends at least 5 feet; or located so that the entry does not face a public and/or private street or access easement, or sized so that it is no greater than 50% of the width of the front fagade at ground level, and that the portion wider than 26 feet wide is set back at least 2 feet. In addition; staff recommends City of Renton Community and Economic Development Department Report to the Hearing Examiner WILSON PARK II PLAT & P UD L UA12-013, ECF, PP, PPUD P UBLIC HEARING DATE: June 12, 2012 Page 11 of 31 RMC 4-2-115F.3. Residential Design, Scale, Bulk, and Character b) PUD Decision Criteria: R-1: N/A R-14: Primary building form shall be dominating; primary porch plate heights shall be one story; different colors shall be used to differentiate the same models and elevations; and no more than 2 of the same model and elevation shall be built on the same block frontage and shall not be abutting. . that there be a minimum of 18 feet of driveway length from the face of the garage to the back of the sidewalk. Staff Comment: Staff recommends approval of the requested deviation and recommends that the requirements of the R -S Scale, Bulk, and Character Standards be followed. This standard requires that: A variety of elevations and models that demonstrate a variety of floor plans, home sizes, and character shall be used. Additionally, both of the following are required: 1. A minimum of three (3) differing home models for each ten (10) contiguous abutting homes, and 2. Abutting houses must have differing architectural elevations. i. Demonstration of Compliance and Superiority: Applicants must demonstrate that a proposed development is in compliance with the purposes of the PUD regulations and with the Comprehensive Plan, that the proposed development shall be superior to that which would result without a planned urban development, and that the development will not be unduly detrimental to surrounding properties. Comment: If the conditions of approval are met, the applicant will have demonstrated compliance with the PUD regulations and the Comprehensive Plan. The applicant will have demonstrated that the development is superior to that which would result without a PUD and will not be detrimental to surrounding properties. The development of this site as a PUD results in a superior design than would result by the strict application of the Development Standards for many reasons. First, the proposed plat layout provides for a the protection of the steep slope area to the east. Second, the plat would provide for recreational amenities beyond code requirements. Third, the plat layout increases the quality of the internal circulation system throughout the development. Fourth, the City of Renton Community and Economic Development Department Report to the HearLnA Examiner WILSON PARK II PLAT & PUD LU,412-013, ECF, PP, PP UD PUBLIC HEARING DATE. June 12, 2012 Page 12 of 31 proposed subdivision is a significant improvement over a design that would meet both the R-1 and R-14 standards. This proposed design can provide for the aforementioned amenities because of the modifications requested in Table A above. ii. Public Benefit: The applicants shall demonstrate that a proposed development will provide specifically identified benefits that clearly outweigh any adverse impacts or undesirable effects of the proposed planned urban development, particularly those adverse and undesirable impacts to surrounding properties, and that the proposed development will provide one or more of the following benefits than would result from the development of the subject site without the proposed planned urban development: ➢ Critical Areas: Protects critical areas that would not be protected otherwise to the some degree as without a planned urban development, or ➢ Natural Features: Preserves, enhances, or rehabilitates natural features of the subject property, such as significant woodlands, native vegetation, topography, or noncritical area wildlife habitats, not otherwise required by other City regulations, or ➢ Public Facilities: Provides public facilities that could not be required by the City for development of the subject property without a planned urban development; or ➢ Use of Sustainable Development Techniques:, Design which results in a sustainable development, such as LEED certification, energy efficiency, use of alternative energy resources, low impact development techniques, etc.; or ➢ Overall Design: Provides a planned urban development design that is superior to the design that would result from development of the subject property without a planned urban development. A superior design may include the following: • Open Space/Recreation: (a) Provides increased open space or recreational facilities beyond standard code requirements and considered equivalent to features that would offset park mitigation fees in Resolution 3082, and (b) Provides a quality environment through either passive or active recreation facilities and attractive common areas, including accessibility to buildings from parking areas and public walkways; or • Circulation/Screening: Provides superior circulation patterns or location or screening of parking facilities; or • Landscaping/Screening: Provides superior landscaping, buffering, or screening in or around the proposed planned urban development, or • Site and Building Design: Provides superior architectural design, placement, relationship or orientation of structures, or use of solar energy; or • Al. leys: Provides alleys for proposed detached or attached units with individual, private ground related entries. CPty of Renton Community and Economic Development Department Report to the Hearing Examiner W=ON PARK 11 PLAIT & PUD — LU,412-013, ECF, PP, PP UD P UBLIC HEAFJNG DATE, June 12, 2012 Page 13 of 31 Table B CRITICAL AREAS: The site contains steep slopes greater than 40% which is termed to be a geotechnical hazard. The City critical areas regulations provide for protections to these features, however the proposed development increases these protections by protecting the steep slope within a tract that would also serve as the common open space and recreation area. A trail provided on the flat area of the tract would separate five of the new lots from the steep slope area. The open space tract would also connect to a comparable open space tract on Wilson Park I that was set aside to address requirements of the Urban Separator Overlay Regulations (RMC4-3-110E, 2.a.ii). Both. the subject plat and Wilson Park I are required to set aside 50% of the area of the site located within the Talbot Urban Separator as a non -revocable open space tract. For Wilson Park II, the Urban Separator is assigned to 38,326 square feet. The project proposes to set aside 19,164 square feet, or 50°% of this area. Staff recommends that the applicant record a Native Growth Protection Area Easement over the tract such that it is not disturbed. NATURAL FEATURES: The site is currently undeveloped. The site contains a total of 82 trees of 6 -inch caliper or larger, 21 are within the proposed public right-of-way, and 3 are located in critical areas and their buffers resulting in 58 protected trees on site (Exhibit 9, 10). Of these, 21 trees are within the R-1 zone, and 37 trees within the R-14 zoned portions of the property. The R-1 zone requires 30 percent tree retention of the protected trees on site, while the R-14 requires 10 percent tree retention. At a 30 percent retention rate in the R-1 zone, 6 trees would be required to be retained. At 10 percent retention rate in the R-14 zone, 4 trees would need to be retained. This is a total of 10 trees required to be retained. The applicant has identified 10 trees that would be retained thus meeting the requirement. In addition, the applicant proposes to plant 40 new trees on site, which includes street trees within the right-of-way and ornamental trees within Tract "A" the common open space and Native Growth Protection Area Easement. The applicant's provided conceptual landscape plan (Exhibit 11) indicates proposed ornamental trees, shrubs, and groundcover includes the proposed locations for the plantings. For the street trees, the applicant proposes Parrotia persica (Persian Ironwood trees), 1-1/2" caliper; with two planted for each of Lots 1 through 9. Cercis Canadensis (Forest Pansy Redbud trees), 1-1/2" caliper are proposed at the entrance to the plat along the south side of Lot 1 and within the right-of-way for Lot 10. Thuja plicata (Western Red Cedar trees), 6 -foot high, are proposed along the south boundary of Tract A/Lot 10, along the proposed walking path. Tsuga heterophylla (Western hemlock), 6 -foot high, are proposed between the common boundary between Lots 6, 7, 8 and the common open space tract, where the walking path is provided. The proposed plant palette also contains Mahonia aquifolium (Tall Oregon Grape), Ribes sanguineum (Red Flowering Currant) as shrubs and Arcostaphylos uva-ursi (Kinnikinnick), Gaultheria shallon (Salal) and Polystichum munitum (Sword fern) as ground cover. The conceptual landscape plan is acceptable provided that additional trees are proposed on the south side of Lot 1 within the right-of-way, and within the right-of-way for the street improvements along South 55th Street. As such, staff recommends as a condition of approval that the applicant provide a City of Renton Community and Economic Development Department Report to the Hearing Examiner R'IMSQN PARK 11 PLAT & .PUD L U,412-013, ECF, PP, PP UD PUBLIC HEARING D.4 TE: June 12, 2012 Page 14 of 31 detailed final landscape plan that shall be submitted and approved by the Current Planning Project Manager prior to final PUD approval. OVERALL DESIGN: 1. Open Space/Recreation: In addition to private open space provided on each proposed lot, the applicant has proposed to provide a passive recreation area primarily located on the eastern portion of the site, and wrapping around the north part of Lot 6 and the south boundary of Lot 10. This 19,164 square foot (0.44 acre) open space would include a pergola structure, landscaping and two picnic tables, a soft surface looped trail system through the development, and would also comprise the steep slope area beyond to the north and east. RMC 4-9-150E requires that PUD's provide large concentrated areas of open space, equivalent to 10% of the site's gross area. The site is 93,801 sq. ft. and the provided open space tract is 19,164 sq. ft, comprising approximately 20% of the site, and exceeding the open space standards by 9,784 square feet. The overall passive and active recreation opportunities proposed for the subject development are beyond the standard code requirements. The proposed open space and recreation on the site provide the opportunity for passive recreation. The looped trail system is approximately 510 lineal feet long, offering the opportunity for walking. However, it should be noted that the split -rail fence or pergola/gazebo designs are not reflected on the Landscape Plan or the Plat Plan, as such staff recommends a condition of approval that the applicant provide a detail of the proposed pergola/gazebo and fence design and location as a part. of the final detailed landscape plan. These details shall be submitted and approved by the Current Planning Project Manager prior to final PUD approval. 2. Circulation: The proposed preliminary plat provides for an appropriate pedestrian circulation system. In addition to the proposed soft surface pedestrian path, discussed above, the applicants have proposed sidewalks along Road A consistent with the residential character of the development. Comments received from surrounding property owners concern the ability of school buses to safely serve the Wilson Park II plat. The applicant has observed that presently school buses travel east on 55th Avenue South in the morning, stopping in 55th Avenue South to pick-up students. The buses then travel west in the afternoon, stopping in 55th Avenue South to drop-off students. However, upon inquiry with the Renton School District, it was determined that these are actually Kent School District (KSD) buses that serve students attending schools in the Kent School District, for properties on the south side of South 55th Street. The subject site is actually within the Renton School District (RSD). RSD busses do not travel on South 55th Street, and the closest school bus stop is located at the intersection of South 55th Street and Talbot Road South, approximately 700 feet to the west. Staff recommends that the project provide for an asphalt walking path from the entrance of the development (on the north side of South 55th Street) to the intersection of Talbot/S.55th, in order to facilitate walking to and from the bus stop. In addition to sidewalks and the proposed pedestrian path, the proposed preliminary plat also provides for appropriate vehicle circulation system. The road system connects with the Wilson Park Plat located immediately to the north. The road was originally approved as part of Wilson Park and has 'not yet been constructed. Wilson Park I is dependent upon the construction of this road, as is Wilson Park IL Staff recommends that if Wilson Park 11 moves forward prior to Wilson Park I, that the public street be constructed with an approved emergency turnaround. City of Renton Community and Economic Development Department Report to the Hearing Examiner WILSON PARK II PLAT & P UD L UA12-013, F_CF, PP, PP UD PUBLIC HEARNG DATE: Tune 12. 2012 Page 15 of31 3. Landscaping/Screening: The proposed landscape pian for the entire site, and in particular the open space tract is superior to what would be required by Renton's Municipal Code, as discussed above under "Natural Features". 4. Site and Building Design: The qualities of the proposed site design has been addressed above under, "Critical Areas", "Natural Features", and the subsections of "Overall Design". The above comments address such things as road design and pedestrian circulation, critical areas protection and enhancement, as well as increased landscaping and recreational opportunities. All these amenities contribute to the overall superior site design. The 10 proposed lots are accessed off a public street, and would be representative of a typical plat for detached single family horses. Homes would be subject to the Residential Design Standards, and as such no building design is required at this time. The proposal would protect the environmentally critical areas, and passive recreational opportunities are proposed. 5. The orientation of the lots allows for access to solar energy, as all of the lots are east/west. All homes will be subject to the residential design standards. Since the plat is most representative of plats designed to meet R-8 zone, staff recommends that the homes within the plat meet the R-8 residential design standards with minor modifications. For example, staff suggests that garages be setback a minimum of 18. feet from the back of the sidewalk to allow appropriate area for apron parking. Compliance with these standards will be reviewed at the time of building permit application. Due to the level of detail needed to identify compliance with the residential design standards this review is best left for building permit stage. 6. Alleys: The proposal is for a single two single tiers of lots front on an existing road easement approved as part of the Wilson Park I Plat. An alley configuration is not possible given the existing road location. iii. Building and Site Design: Perimeter: Size, scale, mass, -character and architectural design along the planned urban development perimeter provide a suitable transition to adjacent or abutting lower density/intensity zones. Materials shall reduce the potential for light and glare. Comment: Proposed landscaping on the south boundary of Lot 10 would provide some screening of when viewed from South 55th Street. Proposed plantings of the southeast corner of Lot 1 would provide some incremental screening for Lot 1 when viewed from 55th Avenue South. Additional planting within the right-of-way should be provided along 55th Avenue South. This would require dedication of additional right-of-way along the south boundary of the plat, between the new Road A west to the southwest corner of the site. The scale, mass, character and architectural design would be of a detached single family residential development. Due to the existing split zoning of the parcel (both R-1 and R- 14 Zone) staff recommends as a condition of approval that the project not conform to either the R-1 or the R-14 Residential Design standards; rather that the project be required to comply with the Residential Design Standards applied to the R -S Zone resulting in a compatible size, scale, mass, character and architectural design for the City of Renton Community and Economic Development Department Report to the Hearing Examiner WILSONPARK II PLAT & PUD LUA12-013, ECF, PP, PPUD PUBLIC HEARING DATE: June 12, 2012 Page 16 of 31 overall development. The proposed lot sizes are comparable with the R-8 Zone, and the development would be most like R-8 development. interior Design: Promotes a coordinated site and building design. Buildings in groups should be related by coordinated materials and roof styles, but contrast should be provided throughout a site by the use of varied materials, architectural detailing, building orientation or housing type. Comment, As mentioned above in Table B, the interior site design promotes quality pedestrian and vehicular circulation, increased critical area protection, promotes safety and by buffering the steep slopes area. All homes would be required to comply with the R-8 development design standards which would result in coordinated, yet varied roof styles and materials, architectural detailing, and a variety of home styles throughout the development. iv. Circulation: Provides sufficient streets and pedestrian facilities: The planned urban development shall have sufficient pedestrian and vehicle access commensurate with the location, size and density of the proposed development. All public and private streets shall accommodate emergency vehicle access and the traffic demand created by the development as documented in a traffic and circulation report approved by the City. Vehicle access shall not be unduly detrimental to adjacent areas. Comment: The subdivision would gain access from 55th Avenue South. A new street constructed for Wilson Park I bisects the two single tiers of lots and connects to the Wilson Park I site immediately abutting and north of Wilson Park 11. All of the proposed lots and the open space tract would have access to the public street. Proposed pavement width is 26 feet, which allows parking on one side of the street. Staff recommends that the parking be allowed on the east side of the street in order to address concerns expressed during SEPA review regarding the direction that vehicles would be parked based on travel patterns. Five-foot wide sidewalks and 8 -foot wide landscape strips are proposed on both sides of the street. In addition, a 3 -foot wide walking path is proposed across the north, east and south portions of the eastern tier of lots. Most of this path is within Tract A, with the exception of a section along the south boundary of Lot 10. The walking path would be concrete near the proposed gazebo on the north portion of the site and soft surface for the remainder of the pathway within the open space tract. Staff recommends that the section on the south side of Lot 10 be revised to meander within the landscaped area in the side yard of Lot 10. The PUD would have sufficient pedestrian and vehicle access based on the location, size and density of the development, if all conditions of approval are met. See Table B, "Public Benefit, subsection: Overall Design 2. Circulation above for additional discussion on pedestrian and vehicle circulation Frontage improvements are required along South 55th Street. The property has frontage in two locations, where the proposed street intersects South 55th Street, and where a portion of Tract A fronts on South 55th Street. In both cases, the applicant is required to construct curb, gutter, 5 -foot wide sidewalks, and an 8 -foot wide planting strip. The Cit of .Renton Community and Economic Development Department Report to the Hearing Examiner WILSON PARK 11 PLAT & PUD LUA12-013, ECF, PP, PPUD PUBLIC HEARING DATE. June 12, 2012 Page 17 of 31 applicant's proposal indicates a 5 -foot wide sidewalk along South 55th Street on the south side of Lot 1. No planting strip is proposed within the South 55th Street right-of- way. No street improvements are proposed within the right-of-way for South 55th Street for the portion where Tract A fronts on the street (Exhibit 2, 11). Staff recommends that the applicant be required to provide the required street improvements and landscaping, and that these be shown on the construction engineering plans, and final detailed landscape plan, during the Final PUD and Final Plat process. The internal street is designed to accommodate emergency vehicle access and the traffic generated by the project, provided that the street connects through Wilson Park I. In the event that Wilson Park I is not constructed concurrent or prior to Wilson Park li, then the applicant should be required to provide an emergency turnaround within the plat. Promotes safety: Promotes safety through sufficient sight distance, separation of vehicles from pedestrians, limited driveways on busy streets, avoidance of difficult turning patterns, and minimization of steep gradients. Comment: The applicant submitted a Traffic Impact Analysis Report (Exhibit 12) prepared by TraffEx (Northwest Traffic Experts, dated June 23, 2009 and supplemented January 25, 201.2). The report indicates that the proposal would utilize the same access to South 55th Street s the approved Wilson Park I Plat. The site access street intersects South 55th Street on the outside of a horizontal curve on South 55th Street to optimize sight distance in both the east and west direction for vehicles entering and exiting the site. The report also indicates that the horizon year for the study is considered to be 2014, as that is the year construction of both plats is anticipated. The study indicated the increase in traffic with the proposal and determined that the traffic would operate at acceptable levels at the intersection of South 55th Street and the new street within the plat. The Level -of -Service (LOS) with the project was determined to be LOS B for future 2014 conditions. Previously, the site distance on South 55th Street was evaluated as part of Wilson Park I. It was determined then that the City of Renton intersection and stopping sight distance requirements in both the east and west directions would be met. Comments received from surrounding property owners concern the ability of school buses to safely serve the plat (Exhibit 14). The applicant has observed that presently school buses travel east on South 55th Street in the morning, stopping in South 55th Street to pick-up students. The buses then travel west in the afternoon, stopping in South 55th to drop-off students. While it was originally anticipated that this practice would continue with the project, and that children would wait together for pick-up, an inquiry to the Renton School District (RSD) revealed that these are actually Kent School District buses, which do not serve the subject plat. RSD does not operate on South 55th Street, and would require that students walk approximately 700 feet to the west to be picked up at the corner of South 55th Street and Talbot Road South. In order to provide an appropriate safe route to schools, staff recommends that the applicant be required to provide a walking path within the improved right-of-way, with a minimum 5 -foot asphalt path, on the north side of South 55th Street, from the entrance to the plat to the intersection of South 55th Street and Talbot Road South separated from the traffic lane City of Renton Cornmuniiy and F,conomw Development Department Report to the Hearing Examiner WILSON PARK II PLA T&PUD LU.412-013, ECF, PP, PPUD PUBLIC HEARING DATE: June 11, 2012 Page 18 of 31 by C -curb. This should be installed at the time that street and utility improvements are being installed. A lighting plan was not included in the applicant's submittal packet; therefore, it is not clear how the proposed pedestrian pathways would be illuminated at night. Although, staff recommends that the area near the concrete path and pergola be illuminated at night, staff further recommends that the soft surface trail be unlit or minimally lit at night. Staff recommends, as a condition of approval, that the applicant submit a lighting plan for review and approval by the Current Planning Project Manager prior to utility construction. The lighting plan shall contain pedestrian lighting in addition to building and landscaping lighting if proposed. The proposed development would result in one driveway for each new lot. In addition, one access point is proposed from South 55th Street to the development, Road A. An additional emergency access is provided within Wilson Park I to South 55th Street. Based on the road width, parking would be permitted on one side of the new street. Staff recommends that parking be allowed on the east side, in order to acknowledge customary use and anticipated circulation. These design considerations/requirements would result in a circulation system that would avoid difficult turning patterns, minimizes steep gradients and minimize driveways on busy streets. Once the applicant has fulfilled the conditions of approval (noted above); the promotion of safety could be accomplished. Provision of a system of walkways: Walkways that tie residential areas to recreational areas, transit, public walkways, schools, and commercial activities. Comment: See Table B "Public Benefit, Subsection: Overall Design 1 and 2" above. The site is somewhat isolated and is constrained by topography. Street frontage improvements along 55th Avenue South would not tie into other existing sidewalk or walkway systems. The internal pathway would provide internal circulation and would connect to the sidewalks within the plat. There is no school bus stop for the Renton School District in close proximity. According to the Renton School District, the closest bus stop is located at the corner of Talbot Road and 55'h Ave South, approximately 700 feet to the west of the entrance road. The site is constrained by natural topographical features and connections to surrounding areas are difficult due to the topography and the 551h Ave South. The subject site is located on periphery of the City boundary, and is relatively isolated from commercial zoned property. There is no existing access to commercial development in or near the subject site and no new access proposed for pedestrians. Provides safe, efficient access for emergency vehicles: Comment: If the roadways are designed per recommended standards (Exhibit 2), the development would provide safe, efficient access for emergency vehicles. However, if the subject plat is constructed without Wilson Park I or prior to Wilson Park I, there would not be a sufficient turning radius for emergency vehicles and a temporary emergency vehicle turnaround would need to be provided on site. Therefore, staff recommends as a condition of approval that in the event that Wilson Park I is not constructed and recorded first or at all, Wilson Park 11 shall be required to provide City of Renton Community and Ecomomrc Development Department Report to the Hearing Examiner W=ON P.4 RK If PLA T& PUD LU412-013, ECF, PP, PPUD PUBLIC F115ARM-0 DATE: June 12, 2012 Page 19 of 3I appropriate emergency access, per the review and approval of the Development Service Project Manager and the Fire Marshal. This shall be accomplished by providing an acceptable emergency vehicle turnaround, prior to the recording of the plat. V. Infrastructure and Services: Provides utility services, emergency services, and other improvements, existing and proposed, which are sufficient to serve the development. Comment: Water service for the development would be provided by the Soos Creek Water and Sewer District. Water availability certificates will be required from the Soos Creek Water & Sewer District prior to Construction Permit. Based on the provided Conceptual Utilities Plan (Exhibit 13), there is an existing sewer main located in 55th Avenue South. The applicant has proposed to connect to this existing main and extend an 8 -inch sanitary sewer line to provide sewer to the development. This plan sheet also identifies an 8 -inch water line extension from 55th Avenue South through the subject plat and to the Wilson Park I plat located to the north. With receipt of the water availability certificate, the development could provide sufficient service to the lots. Fire protection would be provided by the City of Renton Fire Department. New impervious surfaces would result in surface water runoff increases. A Technical Information Report (dated May 5, 2009) was prepared by Baima and Holmberg Inc, for the previous Wilson Park I Plat. An addendum to this report was prepared by Qffe Engineers, PLLC on February 28, 2012 to consider the current proposal. The May 2009 report includes an analysis of upstream tributary drainage which states that the parcel to the east drains onto the site, with no problems related to runoff. The Level 1 Downstream Drainage Analysis in the report states that runoff from the site flows west into lots in the adjacent Geneva Court development. The majority of the existing runoff from Wilson Park II collects along the west property line via sheet flow and continues downstream over the vacant property to the west. This flow collects in a stormwater pond/bioswale facility located at the intersection of Talbot Road South and South 53rd Place approximately 750 feet downstream from the site. This facility outfalls through an 18 -inch pipe to the west side of Talbot Road South into a poorly defined channel flowing into the woods. The flows then pass through a 12 -inch culvert under a walking path and continue to flow west to a wooded wetland area more than a quarter mile downstream from the site. Flows into the ditch along South 55th Street continue west in a rock lined channel along the north side of the street to the intersection of Talbot Road South and South 55th Street. The channel is eroded and shows signs of flowing into the street. Flows from the ditch along Talbot Road South collect in the storm system about 850 feet downstream from the site eventually flowing into Springbrook Creek at about 1,800 feet downstream from the site. The Creek continues flowing west to about one-half mile downstream of the site where it enters a box culvert crossing SR 167. The Technical Information Report indicates that there are no apparent drainage problems. The amended February 28, 2012 report evaluates the addition of the subject 10 -lot plat. The original stormwater system for Wilson Park I and located within the street that would serve both Wilson Park I and 11 was sized to accommodate Wilson Park I lots and the new streets including the access street located within Wilson Park II. The addendum provides calculations intended to evaluate the sizing of the storm treatment facility for the two projects. The report notes that City of Renton's 2009 Drainage Manual requires City of Renton Community and Economic Development Department Report to [he_H_eariM Examiner WILSON PARK II PLAT & PUD LUA12-013, ECF, PP, PPUD PUBLIC HEARING DATE. June 12, 2012 Page 20 of 31 Best Management Practices (BMP's) for new developments. One BMP's is to restrict impervious areas on future lots to help reduce runoff, mitigate for development, and minimize the treatment system needed for the project. This is known as a "Restrictive Covenant" provision and was utilized as part of a preliminary sizing of the future system for both Wilson Park I and ll. The applicant intends to utilize the Restrictive Covenant provision and limit impervious surface on each of the new lots in both Wilson Park 1 and II to 3,300 square feet per lot. By limiting the impervious area for homes, patios, driveways and walkways, the proposed stormwater vault will be of an appropriate size to accommodate both developments. The applicant has also intended to develop both plats at the same time. Comments received from surrounding property owners (Exhibit 14) expressed concern as to whether the vault was sized appropriately to accommodate both projects. The applicant has stated that the vault is sized to the 2009 drainage manual and will provide the necessary volume and capacity for both projects. vi. Clusters or Building Groups and Open Space: An appearance of openness created by clustering, separation of building groups, and through the use of well-designed open space and landscaping, or a reduction in amount of impervious surfaces not otherwise required. Comment: The uniqueness of the zoning of the site, in addition to the area affected by steep slopes, results in a necessity to cluster development. The slope results in the preservation of open space in the form of a Native Growth Protection Area Easement as well as recreation space. The requested lot size and setback modification allow for a clustered R-8 development that provides increased protection of critical areas creating an appearance of openness. This also allows for a more cohesive design rather than attempting to design for two different residential density designations on one site. (See additional discussion above in Table B "Public Benefit, Subsections: Critical Areas and Natural Features".) As noted in the previous sections, the proposed development would have usable passive recreation, including open space and landscaping. In order to maintain sufficient separation between buildings, staff recommends that the applicant be required to meet the R-8 side yard setbacks, as such all structures will maintain a minimum of 10 feet of separation. This spacing allows for emergency access and sufficient fire separation. vii. Privacy and Building Separation: Provides internal privacy between dwelling units, and external privacy for adjacent dwelling units. Each residential or mixed use development shall provide visual and acoustical privacy for dwelling units and surrounding properties. Fences, insulation, walks, barriers, and landscaping are used, as appropriate, for the protection and aesthetic enhancement of the property, the privacy of site occupants and surrounding properties, and for screening of storage, mechanical or other appropriate areas, and for the reduction of noise. Windows are placed at such a height or location or screened to provide sufficient privacy. Sufficient light and air are provided to each dwelling unit. Comment: The context of the subdivision, it's location in relation to existing development, and the topography of the site provide for privacy. Within the subdivision, unit to unit privacy would be provided by the side yard setback requirement. Exhibit XX shows that applicant has indicated that a split -rail fence would be used to define the area City of Renton Community and Economic Development Department Report to the HEaring Ltamtner WILSON PARK II PLA T&PUD LUA12-613, ECF, PP, PPUD PUBLIC HEARING DATE. June I2, 2012 Page 21 of 3l between the back and side yard area of the lots and the soft surface pathway within Tract A. No specific fence detail has been provided, and there could be a tendency for future residents to construct privacy fences abutting the split -rail fence. Therefore staff recommends that the applicant provide a fence detail with the final landscape plan that is subject to the review and approval of the Current Planning Project Manager. Street trees are required either within the required landscape strip or in the front yard of the lot. As discussed above under Table B "Public Benefit, Subsections: Critical Areas and Natural Features". the proposed walkways and landscaping are appropriate for the protection and aesthetic enhancement of the property. All homes would be required to be designed to meet the residential design standards for the R-8 zone. These standards would require windows on the front of the home, 'increasing access to light and air for each dwelling unit. Furthermore, each lot would have private front, side and rear yards, enhancing each lot with landscaping and access to light and air. viii. Building Orientation: Provides buildings oriented to enhance views from within the site by taking advantage of topography, building location and style. Comment: The lots are arranged in into two tiers of single lots. The ten lots would be oriented east/west. The site topography slopes down from east to west, resulting in a terraced effect after site grading. The proposed layout maximizes the use of topography is appropriate. Views would be territorial and to lower elevations to the west. ix. Parking Area Design: Design: Provides parking areas that are complemented by landscaping and not designed in long rows. The size of parking areas is minimized in comparison to typical designs, and each area related to the group of buildings served. The design provides for efficient use of parking, and shared parking facilities where appropriate. Comment: Required parking would be provided within garages attached to each home. Additional guest parking would be provided on the driveway aprons for each lot. Staff has previously recommended that the applicant provide minimum 18 -foot garage aprons from the face of the garage to the back of the sidewalk to provide for parking that does not result in vehicles overhanging the sidewalk. On -street parking would be provided along the new internal road on one side. Staff further recommends that this parking be allowed on the east side of Road A. The proposed parking is designed to provide efficient use of the site and would be appropriately screen by the provided garages. Adequacy: Provides sufficient on-site vehicular parking areas consistent with the parking demand created by the development as documented in a parking analysis approved by the city. Comment: Parking regulations require a minimum of two off-street parking spaces for detached dwellings. As proposed each lot would have adequate area to provide two off- street parking spaces. Additional parking would be available on the internal road or in the drivetvays of each lot. Sufficient on-site vehicular parking would be provided consistent with the demand created by the development provided that conditions of approval are complied with. pryo Fenton Communes and Economic Development Department Report to the Hearing Examiner WILSON PARK II PLAT & P UD ,LUA12-013, ECF, PP, PPUD PUBLIC HEARING DATE: June 12, 2012 Page 22 of 31 X. Phasing: Each phase of the proposed development contains the required parking spaces, open space, recreation spaces, landscaping and utilities necessary for creating and sustaining a desirable and stable environment, so that each phase, together with previous phases, can stand alone. Comment: The applicant has not proposed to phase the subject development. As such, this criteria does not apply. A. Development Standards Common Open Space Standard: Open space shall be concentrated in large usable areas and may be designed to provide either active or passive recreation. Requirements for residential developments are described below. Residential: For residential developments open space must equal at least ten percent (1096) of the development site's gross land area. i. Open space may include, but is not limited to, the following: (a) A trail that allows opportunity for passive recreation within a critical area buffer (only the square footage of the trail shall be included in the open space area calculation), or (b) A sidewalk and its associated landscape strip, when abutting the edge of a critical area buffer and when a part of a new public or private road, or (c) A similar proposal as approved by the reviewing official. ii. Additionally, a minimum area equal to fifty (50) square feet per unit of common space or recreation area shall be provided in a concentrated space. Comment: The proposed development is located on an 2.15 acre site, of which a portion on the east is located in a critical area. The applicant has dedicated an Open Space Tract A which totals 19,164 square feet within which is a soft surface trail that equals approximately 1,530 square feet. The proposed development would have 10 lots; 50 square feet of common space or recreation areas is required per unit, resulting in a requirement of an additional 500 square feet. To partially fulfill the common space requirement the applicant has proposed to provide an approximate 350 square foot common park that includes a concrete path, pergola/gazebo and landscaping. Staff recommends that the applicant enlarge this area to be at least 500 square feet in order to meet the minimum requirement. Suggestions for added recreation opportunities may include a community garden or fire.circle or barbeque area. The park is iocated north of proposed Lot 5 and connects to the walking path through the remainder of Tract A. The overall location and design of the park, open space and trail are located as to create a quality open space/recreation area for the development, specifically if all conditions of approval are met. Private Open Space: Each residential unit in a planned urban development shall have usable private open space (in addition to parking, storage space, lobbies, and corridors) for the exclusive use of the occupants of that unit. Each ground floor unit, whether attached or detached, shall have private open space which is contiguous to the unit. The private open space shall be well demarcated and at least fifteen feet (15') in every Cite of Renion Community and Economic Development Department Report to the Hearing Examiner WILSaV PARKIIPLAT & PUD — - LU.412-013, ECF, PP, PPUD PUBLIC HEARNG DATE: June 12, 2012 Page 23 of 31 dimension (decks on upper floors can substitute for the required private open space). For dwelling units which are exclusively upper story units, there shall be deck areas totaling at least sixty (60) square feet in size with no dimension less than five feet (.5'). Comment: Each lot would have a private yard in both the front and the rear of the lot. The recommended setbacks would provide for a minimum 15 -foot front yard and a 20 - foot rear yard, which could result in a private open space yard meeting or exceeding the 15 foot in every dimension. Compliance with this standard shall be reviewed at building permit stage. Installation and Maintenance of Common Open Space: All common area and open space shall be landscaped in accordance with the landscaping plan submitted by the applicant and approved by the City. Comment: Prior to the recording of the plat, common landscaped areas and the open space landscaping, and street trees must be installed. The applicant would need to provide for the maintenance of the common areas through the establishment of a HomeOwners Association. Installation and Maintenance of Common Facilities: All common facilities not dedicated to the City shall be permanently maintained by the planned urban development owner by the property owners' association or the.agent(s) thereof- Comment: hereofComment: Staff recommends, as condition of approval, the applicant be required to establish a home owners' association for the development, which would be responsible for any common improvements, including but not limited to the soft surface trail, landscaping, and park within the PUD prior to Final PUD approval. All common facilities, not dedicated to the City, shall be permanently maintained by the PUD home owners' association. 6. Consistency with Preliminary Plat Criteria Approval of a plat is based upon several factors. The following preliminary plat criteria have been established to assist decision -makers in the review of the plat: a) Compliance with the Comprehensive Designation The site is designated Residential Single Family (RSF) and Residential Low Density (RLD) on the Comprehensive Plan Land Use Map. Land designated Residential Single Family is intended to be used for quality detached residential development organized into neighborhoods at urban densities. It is intended that larger subdivisions, infill development, and rehabilitation of existing housing be carefully designed to enhance and improve the quality of single-family living. Land designated Residential Low Density is intended for a range of low intensity residential and employment where land is either constrained by sensitive areas or where the City has the opportunity to add larger -lot housing stock at urban densities of 4-du/net acre, to its inventory: City o Renton Commmni and Economic 2evelo mens Department Re ort to the Hearin Examiner WILSON PARK II PLAT & PUD LUA12-013, ECF, PP, PPUD PUBLIC HEARING DATE: June 12, 2012 Page 24 of 31 RSF Policy LU -158. Net development densities should fall within a range of 4.0 to 8.0 dwelling units per acre in Residential Single Family Neighborhoods. ® Policy Objective Met ❑ Not Met Policy LU -159. Maximum height of structures should not exceed two (2) stories in single- family residential neighborhoods. ® Policy Objective Met ❑ Not Met Policy EN -19. Allow land alteration only for approved development proposal or approved mitigation efforts that will not create unnecessary erosion, undermine the support -of nearby land, or unnecessarily scar the landscape I areas subject to geologic hazards. ® Policy Objective Met ❑ Not Met Policy EN -28. Require trees and other vegetation along newly constructed or reconstructed streets to reduce impacts from development. ® Policy Objective Met ❑ Not Met Policy EN -36. Where appropriate combine environmentally sensitive areas with to provide public access and educational opportunities. ® Policy Objective Met ❑ Not Met Policy CD -1. integrate development into natural areas by clustering development and/or adjusting site plans to preserve wetlands, steep slopes, and notable stands of trees or other vegetation. Natural features should function as site amenities. Use incentives such as flexible lot size and configuration to encourage preservation and add amenity value. ® Policy Objective Met ❑ Not Met b) Compliance with the Underlying Zoning Designation See Consistency with the Planned Urban Development Regulations and Table A. The proposed development would allow for the future construction of 10 new single-family dwelling units. Density: The site is zoned both R-1. and R-14, and the zone line See Consistency with the Planned Urban Development Regulations, subsection aj. Lot Dimensions: See Consistency with the Planned Urban Development Regulations, Table A for requested modifications. As demonstrated in Table C below, all lots except Lot 1, meet the requirements for the requested minimum lot size, depth, and width as requested through the PUD. Lot 1 is a corner lot and would require that its minimum width be increased to 60 feet for meet the standard. There is sufficient room on the site to achieve this and keep the proposed lot count. City of Renton Community and Economic Development .Department Report to the Hearing Examiner KLSONPARK TIPLAT& PUD — — LUA12-013, ECF, PP, PPUD PUBLIC HEAPdNG DATE: June 12, 2012 Page 25 of 31 Table C As Proposed Lot Size Width Depth Lot 1 5,775 SF 57.74 feet 102.51 feet Lot 2 5,905 SF 57.60 feet 102.51 feet Lot 3 5,905 SF 57.60 feet 102.51 feet Lot 4 5,905 5F 57.60 feet 102.51 feet Lot 5 5,587 SF 57.47 feet 102.51 feet Lot 6 5,587 SF 55 feet 101 feet Lot 7 5,560 SF 55 feet 101 feet Lot 8 5,560 SF 55 feet 101 feet Lot 9 5,559 SF 55 feet 101 feet Lot 10 6,778 SF 66.41 feet 101feet In addition to the 10 proposed developable lots, the applicant has proposed 1 tract for, critical areas, recreation/open space, and access. For maintenance of the open space Tract A staff recommends as a condition of approval that all critical areas and their buffers be placed in a Native Growth Protection Easement (NGPE). However, such easement shall be written to provide access for the trail users. Furthermore, these areas shall be fenced with split rail fencing to separate the trail from the steep slope and to provide designated access points along the trail. Also, as a condition of approval staff recommends that a covenant shall be placed on all tracts restricting their separate sale and giving each lot owner within th-e plat an undivided interest in the tracts. This covenant should be recorded on the face of the plat, and/or concurrent with the plat recording, noting the recording number on the plat. Setbacks: See Consistency with the Planned Urban Development Regulations, Table A for requested modifications. Building Standards: See Consistency with the Planned Urban Development Regulations, Table A for requested modifications. City of Renton Community and Economic Development Department _ Report to the Bearing Examiner WILSON PARK 11 FLAT & PUD L UA12-013, ECF, PP, PPUD PUBLIC HEARING DATE: June 12, 2012 Page 16 of 31 c) Community Assets The site is sloped from the east to west and vegetated primarily with cottonwood, alder, maple, and fir trees. See Table B Public Benefit, subsection Natural Features and for discussion of tree retention, landscaping and plantings. The conceptual landscape plan submitted with the application includes the installation of street trees along the street frontage within the plat; however it does not show landscaping or street improvements for the street frontage on South 55th Street, as required by code. As such, staff recommends as a condition of approval that the street trees are shown on the final detailed landscape plan in compliance with the street tree standards. If the conditions of approval are complied with the development would demonstrate compliance with the landscaping regulations of the code. The applicant is required to submit and have approved a detailed landscape plan prior to final PUD and Final Plat recording. d) Compliance with Subdivision Regulations Streets: See Consistency with the Planned Urban Development Regulations, Table A for requested modifications and staff's recommendation for street development. In addition to the comments in the above Table A, street lighting meeting pedestrian lighting levels, in conformance with the residential street fighting interpretation, will be required for both the internal street sections. As such, staff recommends as a condition of approval, that a lighting plan be submitted with the construction permit application for review and approval by the Department of Community & Economic Development, Development Services project manager prior to building permit approval. All wire utilities shall be installed underground per the City of Renton UnderGrounding Ordinance. If three or more poles are required to be moved by the development design, all existing overhead utilities shall be placed underground. Construction of these franchise utilities must be inspected and approved by a City of Renton public works inspector prior to recording of the plat. Blocks: No new blocks will be created as part of the proposed plat. Lots: The shape, orientation, and arrangement of the proposed lots comply with the requirements of the Subdivision Regulations for the R-8 zone, subject to the requested modifications found in Table A above. in addition the proposal allows for reasonable redevelopment of land. All 10 lots are rectangular in shape and would provide sufficient building area. e) Reasonableness of Proposed Boundaries Access: The subdivision would gain access from South 55th Street at one access point, identified as "Road A". Road A would also provide access to Wilson Park I to the north. All of the proposed lots would be directly accessed off of Road A. Topography: The site is bounded by steep slopes east. The site contains areas of protected slopes (greater than 40%) in the northeastern portion of the property. This area City of Renton Communlfy and Feonomlc Development Department Report to the Hearing Examiner WILSON PARK I7 PLAT & PUD 1 U,412-013, ECF, PP. PPUD P U LIC HEARING DATE: June 12, 2012 Page 27 of 32 of protected slopes would be contained within Tract A. There is also a cut slope on the west portion of the property that slopes up to about 6 to 12 feet. This slope likely resulted from the original land grading. Both geotechnical reports submitted conclude that the subject site is stable and can support the development provided the recommendations of the November 22, 2004 report are fully implemented and observed during construction. Relationship to Existing Uses: See PUD criterion iii Budding and Site Design. f) Availability and Impact on Public Services (Timeliness) Police and Fire: Police and Fire Prevention staff indicates that sufficient resources exist to furnish services to the proposed development; subject to the condition that the applicant provides Code required improvements and potential impact fees, if applicable at the time of development/recording. Schools: According to the Draft Environmental Impact Statement for the City of Renton Land Use Element (January 15, 1992), the City of Renton has a student generation factor of 0.44 students per single-family residential dwelling. Based on the student generation factor, the proposed plat would result in 4 students (0.44 X 10 new lots = 4.4). It is anticipated that the Renton School district can accommodate the students generated by this proposal at the following schools: Benson Hill Elementary, Nelsen Middle School and Lindbergh High School. Renton Municipal Code provides for the collection of a school impact fee on behalf of the Renton School District, which is currently $6,392 per each new home, due at the time of building permit. Storm Water: New impervious surfaces would result in surface water runoff increases. A Technical Information Report (dated May 5, 2009) was prepared by Baima and Holmberg Inc, for the previous Wilson Park I Plat. An addendum to this report was prepared by Offe Engineers, PLLC on February 28, 2012 to consider the current proposal. The May 2009 report includes an analysis of upstream tributary drainage which states that the parcel to the east drains onto the site, with no problems related to runoff. The Level 1 Downstream Drainage Analysis in the report states that runoff from the site flows west into lots in the adjacent Geneva Court development. The majority of the existing runoff from Wilson Park 2 collects along the west property line via sheet flow and continues downstream over the vacant property to the west. This flow collects in a stormwater pond/bioswale facility located at the intersection of Talbot Road S and South 53rd Place approximately 750 -feet downstream from the site. This facility outfalls through an 18 -inch pipe to the west side of Talbot Road S into a poorly defined channel flowing into the woods. The flows then pass through a 12 -inch culvert under a walking path and continue to flow west to a wooded wetland area more than a quarter mile downstream from the site. Flows into the ditch along South 55th Street continue west in a rock lined channel along the north side of the street to the intersection of Talbot Road S and South 55th Street. The channel is eroded and shows signs of flowing into the street. Flows from the ditch along Talbot Road S collect in the storm system about 850 -feet downstream from the site eventually flowing into Springbrook Creek at about 1,800 -feet downstream from the site. The Creek continues flowing west to about one-half mile downstream of the site where it enters a box culvert City o Renton Community and Economic Development Department Report to the Hearing Examiner WILSON PARK 11 PLAT & PUD LUA12-0I3, RCF, PP, PPUD PUBLIC HEARING DATE: ,lune 12, 2012 Page 28 of 31 crossing SR 167. The Technical Information Report indicates that there are no apparent drainage problems. The amended February 28, 2012 report evaluates the addition of the subject 1.0 -lot plat. The original stormwater system for Wilson Park I and located within the street that would serve both Wilson Park I and 11 was sized to accommodate Wilson Park I lots and the new streets including the access street located within Wilson Park IL The addendum provides. calculations intended to evaluate the sizing of the storm treatment facility for the two projects. Water and Sanitary Sewer Utilities: See PUD criterion v. Infrastructure and Services. g) Compliance With Critical Area Regulations The project site includes areas with greater than 40% slope that are classified as critical areas. In addition, the site contains a small, isolated, unregulated wetland in the west portion of the site (Exhibit XX). The slopes are within the Talbot Urban Separator Overlay, and would be protected within Tract A, which would also include passive recreation in the form of a soft surface trail, pergola/gazebo, along with ornamental landscaping. In order to protect the critical area, the following conditions of approval are recommended by staff: 1. The common boundary between the native growth protection tract and the abutting land must be permanently identified. This identification shall include a permanent wood split rail fence and metal signs on treated or metal posts. The permanent wood split rail fence and signs shall be installed prior to Final Plat recording. 2. The following note shall appear on the face of the Final Plat and shall also be recorded as a covenant running with the land on the title of record for all affected lots on the title: "MAINTENANCE RESPONSIBILITY: All owners of lots created or benefitting from this City action abutting or including a native growth protection tract are responsible for maintenance and protection of the tract. Maintenance includes ensuring that no alterations occur within the tract and that all vegetation remains undisturbed unless the express written authorization of the City has been received." 1. RECOMMENDATIONS.- Staff ECOMMENDATIONS. Staff recommends approval of the Wilson Park Preliminary Plat and Preliminary PUD, Project File No. LUA12-013, ECF, PP, PPUD subject to the following conditions: 1. The applicant shall comply with the 7 mitigation measures issued as part of the Determination of Non -Significance Mitigated, dated May 7, 2012. 2. The applicant shall record a restrictive covenant on each of the lots indicating that only detached single family units may be constructed, and any future accessory units allowed per the R-8 Development Regulations. This covenant shall be subject to the review and approval of the Current Planning Project Manager and City Attorney, and shall be recorded prior to the recording of the Final Plat. Cid of Renton Community and Economic Development Department_ _ Repori to the Hearing Examiner WILSON PAPX11PLA T & PUD LU412-013, ECF, PP, PPUD PUBLIC HEARING DATE: June 12, 1012 Page 29 of 31 3. The project shall be subject to the Development Standards of the R-8 residential zone with respect to minimum lot size, minimum lot width, minimum side yard and side yard along a street setbacks, minimum rear yard setbacks, maximum building coverage, maximum impervious coverage. 4. The project shall be subject to the Development Standards of the R-8 zone with respect to the front yard setback, except that there shall be a minimum of 18 feet between the face of the garage and the back of the sidewalk. o,�_ e 5. The project small be subject to the Residential and Open Space Standards of the R-8 Zone, provided that there shall be a minimum of 18 feet of driveway length from the face of the garage to the back of the sidewalk. 6. The applicant shall establish and record a permanent and irrevocable Native Growth Protection Area Easement (NGPE) on the property title for all critical areas and their buffers prior to Final Plat recording. The protective easement shall be held by current and future property owners; shall run with the land; and shall prohibit development, alteration, and disturbance within the easement except for the purposes of habitat enhancement as a part of an enhancement project, access for the trail users and maintenance of the common recreation area. Furthermore, this area shall be fenced with split rail fencing. The NGPE shall be subject to the review and approval of the Current Planning Project Manager and the City Attorney, and shall be recorded prior to recording of the Final Plat. 7. The applicant shall submit'a detailed final landscape plan for review and approval by the Current Planning Project Manager prior to final PUD approval. The detailed final landscape plan shall include, but is not limited to the following: a. Proposed locations and design details of the pergola/gazebo, split -rail fence and interpretive signage proposed along the soft surface trail. b. Street trees shall be identified within the right-of-way in compliance with the City's street tree standards. (1 c. The plan shall indicate either 100 percent drought tolerant plantings or the applicant shall provide a final irrigation plan with the final detailed landscape plan. d. Provide a revised Landscape Plan indicating a Common Recreation area that is a minimum of 500 square feet that includes improvements providing for recreation by the public and area residents e. Redesign the trail on the south side of Lot 10 such that the trail meanders and is not abutting the edge of the split rail fence on Lot 10. S. The applicant shall provide a walking path within the right-of-way of South 55th Street that provides for a safe route to the nearest Renton School District bus stop. The path shall be asphalt with a minimum width of 5 feet and separated from the road travel lane by C -curbing as determined by the City's Development Services Division Project Manager. This improvement is required prior to the recording of the plat. Ci of Renton Community and Economic Devel2 ment Department Re ort to the Hearin Examiner WILSON PARD I1 PL4T & P UD LU.412-013, ECF, PP, PPUD PUBLIC HEARING DATE: June 12, 2012 Page 30 of 31 9. The applicant shall submit a lighting plan for review and approval by the Current Planning Project Manager prior to construction permit issuance. The lighting plan shall contain pedestrian lighting in addition to building and landscaping lighting if proposed. 10. In the event that Wilson Park I is not constructed and recorded first or not at all, Wilson Park II shall be required to provide appropriate emergency access, per the review and approval of the Development Service Project Manager and the Fire Marshal. This shall be accomplished by providing an acceptable emergency vehicle turnaround, prior to the recording of the plat. 11. The applicant shall establish a home owners' association for the development, which would be responsible for any common improvements, including but not limited to the soft surface trail, landscaping, and park within the PUD. The draft Codes, Covenants & Restrictions (CC&R's) shall be reviewed and approved by the City Attorney, prior to final PUD approval. All common facilities, not dedicated to the City, shall be permanently maintained by the PUD home owners' association. 12. The applicant shall revise the lot width for Lot 1 in order to provide the minimum`s corner lot width of 60 feet. This shall be shown on the final plat plan. 13. A covenant shall be placed on all tracts restricting their separate sale and giving each lot owner within the plat an undivided interest in the tracts. This covenant should be recorded on the face of the plat, and/or concurrent with the plat recording, noting the recording number on the plat. 14. A street lighting plan shall be submitted with the construction permit application for review and approval by the Plan Reviewer prior to construction permit approval. The applicant shall provide the Current Planning Project Manager, a water line installation plan, which complies with RMC 4-3-050L.8.b.i.(b) for review and approval, prior to final PUD approval. 16. The common boundary between the native growth protection tract and the abutting land must be permanently identified. This identification shall include a permanent wood split rail fence and metal signs on treated or metal posts. The permanent wood split rail fence and signs shall be installed prior to Final Plat recording. 17. The following note shall appear on the face of the Final Plat and shall also be recorded as a covenant running with the land on the title of record for all affected lots on the title: "MAINTENANCE RESPONSIBILITY: All owners of lots created or benefitting from this City action abutting or including a native growth protection tract are responsible for maintenance and protection of the tract. Maintenance includes ensuring that no alterations occur within the tract and that all vegetation remains undisturbed unless the express written authorization of the City has been received." ia. On -street parking shall be restricted to one side of Road A, on the east side of the road. No P ins shall be installed on the west side, .prior to final plat recording. DEPARTMENT OF COMMUNITY `' City Of. AND ECONOMIC DEVELOPMENT f ENVIRONMENTAL REVIEW COMMITTEE REPORT ERC MEETING DATE: May 7, 2012 Project Name: Wilson Park II Preliminary Plat and Preliminary PUD Owner: Robert Wilson and Doravin Wilson 219060th Street East Lake Tapps, WA 98391 Applicant: Same as owner Contact: Darrell Offee, P.E. Offee Engineers, PLLC 13932 SE 159th Place Renton, WA 98058 File Number: LUA122-013, ECF, PP, PPUD Project Manager: Jennifer Henning, Current Planning Manager Project5ummory: The applicant proposes to subdivide an existing 2..15 acre parcel into 10 lots for the eventual development of detached single family homes, and 1 tract for open space. The site is zoned Residential -14 du/ac (R-14) & Residential -1 du/ac (R-1). The site contains 9,783 s.f. of protected slopes (>40%). Proposed density averages G.4 dwelling units per acre across the site, with 9 lots proposed in the R-14 area, & 1 lot proposed within the R-1. A Planned Urban Development is proposed in order to modify minimum lots size within the R-1 Zone and provide larger lots within the R-14 zone. Access would be provided from South 55th Street via new street constructed as part of the approved Wilson Park #1 plat. A small hydrologically isolated, unregulated wetland is located on the western portion of the site. The site contains 82 trees, of which 21 would be removed for the construction of the new street serving Wilson Paris #1. Ten (10) trees would be retained, and new trees would be planted including 2 new trees per lot. The project requires Environmental (SEPA) Review, Planned Urban Development (PUD) Review, and Preliminary Plat review. Project Location: 698 South 55th Street Exist. Bldg. Area SF: N/A Proposed New Bldg. Area (footprint): N/A Proposed New Bldg. Area (gross): N/A Site Area: 2.15 acres. Total Building Area GSF. 93,801 s.f. STAFF Staff Recommends that the Environmental Review Committee issue a RECOMMENDATION: Determination of Non -Significance - Mitigated (DNS -M). EXHIBIT 4 | f/ > ,+a# ~� / -r.M'a |} 222'—=-;;3k((B)a!!§/ ` $a§§]t�aeEe[!s,)% e )}f(_' ,,,©,.�&E@@|EES$/f_ .■� \ /!3!£!�£ww=oo,=0000_ %2 IA_�. IL{ r : :s, ■ >■ .»mf e City of Renton Department of Community & Economic Development Environmental Review Committee Report WILSON PARK2 PRELIMINARY PLAT& PRELIMINARYPUD LUA12-013, PP,PPUD, ECF' Report of May 7, 2012 w Page 2 of 11 PART ONE: PROJECT DESCRIPTION /BACKGROUND The applicant proposes to subdivide a 2.15 acre parcel into 10 lots for the eventual development of detached single family homes, and 1 tract for open space. The site is zoned Residential -14 dwelling units per acre (R-14) and Residential --1 dwelling unit per acre (R-1). The R-1 portion of the site is considered to be Urban Separator, and as such 50% of the Urban Separator area is required to be dedicated as open space. New residential lots would range in size from 5,559 square feet to 6,778 square feet. The open space tract would be 19,164 s.f. in size. Proposed density averages 6.4 dwelling units per acre across the site, with 9 lots proposed for the portion within the R-14 Zone, and 1 residential lot proposed within the R-1 Zone. A Planned Urban Development is proposed in order to modify minimum lots sizes within the R-1 zone and to provide larger lots within the R-14 zone. Access would be provided from South 55th Street via a new street that would be constructed as part of the approved Wilson Park I subdivision (LUA09-140, PP, ECF). The topography of the site slopes upward from the west to the east; an area of steep protected slopes occurs on the eastern portion of the site. Site soils are comprised of Kame Terrace and Ground Moraine which are glacial till soils. Approximately 820 cubic yards of material would be excavated and 11,200 cubic yards of fill would be required to accomplish the project. A small wetland is located on the western portion of the site. This wetland is not regulated per Renton Municipal Code. Of the 82 trees onsite, 21 would be removed for the construction of the new street, 10 would be retained, and new trees would be planted, including 2 new trees per lot. The project requires Environmental (SEPA) Review, Planned Urban Development (PUD) Review, and Preliminary Plat review. n PART TWO: ENVIRONMENTAL REVIEW In compliance with RCW 43.210.240, the following environmental (SEPA) review addresses only those project impacts that are not adequately addressed under existing development standards and environmental- regulations. A. Environmental Threshold Recommendation Based on analysis of probable impacts from the proposal, staff recommends that the Responsible Officials: Issue a DNS -M with a 14 -day Appeal Period. B. Mitigation Measures 1. The applicant shall comply with the recommendations contained in the Geotechnical Engineering Study, prepared by Liu & Associates, Inc. dated November 22, 2004 and amended February 15, 2012, for the duration of project construction. Z, The applicant shall provide a Temporary Erosion and Sedimentation Plan designed pursuant to the Department of Ecology's Erosion and Sediment Control Requirements outlined in Volume li ERC Report.doc City of Renton Department of Community & Economic Development Environmental Review Committee Report WILSON PARK PRELIMINARY PLAT & PRELIMINARY PUD LUA1.2-013, PP,PPUD, ECF Report of May 7, 2012 Page 3 of it of the 2005 Stormwater Management Manual and provide staff with a Construction Mitigation Plan prior to issuance of construction permits. This mitigation measure shall be subject to review and approval of the Development Services Division. 3. The applicant shall provide weekly reports on the status and condition of the erosion control plan with any recommendations of change or revision to maintenance schedules or installation shall be submitted by the Project Engineer of record to the Public Works inspector. 4. Because of moisture -sensitive fine-grained soils mantling the site and the higher gradient areas within the site the geotechnical study recommends that grading and foundation construction be carried out and completed within the dryer period of the year from April .1 through October 31 unless otherwise approved by the Development Services Division. Therefore, the applicant shall adhere to a construction schedule involving grading and foundation work during the dryer period of the year. 5. The applicant shall pay a Parks Mitigation Fee based on $530.76 per each new single family lot prior to recording the final plat. 6. The applicant shall be required to pay a.Traffic Mitigation Fee based on $75.00 per each new average daily vehicle trip associated with the proposed project prior to recording of the final plat. 7. The applicant shall be required to pay a Fire Mitigation Fee based on $488.00 per each new single family lot prior to recording the final plat. C. Exhibits Exhibit 1 Zoning Map Exhibit 2 PUD/Plat Map Exhibit 3 Grading Plan Exhibit 4 Drainage/Utilities Plan Exhibit 5 Tree Retention Plan Exhibit 6 Landscape Plan Exhibit 7 Comment Letter (dated April 15, 2012) Exhibit 8 Aerial Photo D. Environmental Impacts The Proposal was circulated and reviewed by various City Departments and Divisions to determine whether the applicant has adequately identified and addressed environmental impacts anticipated to occur in conjunction with the proposed development. Staff reviewers have identified that the proposal is likely to have the following probable impacts: 1. Earth Impacts: The subject site is located on a broad moderate to steep westerly -sloping hillside. This downward slope is at grades of 13 to 39 percent. Steeper slopes greater than 40% are located on the eastern portion of the site. The higher gradient portions of the site generally lie within the eastern 100 to 200 feet and the western 150 to 200 feet of the site. Approximately 820 cubic yards ERC Report. doc City of Renton Department of Community & Economic Development Environmental Review Committee Report WILSON PARK 2 PRELIMINARY PLA T & PRELIMIIYAR Y PUD LUA12-013, PP,PPUO,, ECF Report of May 7, 2012 Page 4 of 11 of earth material would be cut and approximately 11,200 cubic yards of fill would be imported for the proposal. The applicant submitted a Geotechnical Engineering Study prepared by Liu & Associates, Inc. dated November 22, 2004 and amended February 15, 2012. The report identifies the soils on the site as Kame Terrace deposits underlain by Ground Moraine. Kame Terrace deposits consist mostly of silty sand and gravel to cobble. Locally, they may also contain lenses and pods of till and beds of sand, . silt and clay. According to the Geotechnical Report, these isolated lenses were not encountered on the subject site. Kame Terrace deposits are of moderately -high to high permeability and can provide good foundation support to structure in their native undisturbed state. Ground Moraine deposits are mostly thin ablation till over lodgment till, and were deposited during the retreat of glaciers during the last Ice Age, more than 14,000 years ago. Lodgment till is generally a compact mixture of unsorted clay, silt, sand, gravel and cobble, commonly referred to as "hard pan". Ablation Till is similar to lodgment till, but is much less compact and coherent. Lodgment Till is practically impervious, except local lenses of sand and gravel. It has the character of low-grade concrete and can stand in a steep natural or cut slope for long periods. This soil provides excellent foundation support with little settlement expected. Overlying ablation till is generally looser and is more compressible and permeable. The site contains areas of protected slopes (greater than 40%) in the northeastern portion of the property. This area of protected slopes would be contained within Tract A. There is also a cut slope on the west portion of the property that slopes up to about 5 to 12 feet. This slope likely resulted from the original land grading. Subsurface conditions on the site were explored in November 2004 via six (5) test pits on the western half of the site. The test pits sampled soil at depths ranging from 5.0 to 8.0 feet. The test pits identified a layer of loose, organic topsoil from 1.0 to 2.5 feet thick. The topsoil is generally underlain by a layer of brown Ablation Till soils of loose to medium -dense, silty fine sand, with a trace of gravel and occasional cobble and boulder, about 1.0 to 3.2 feet thick. Underlying the Ablation Till to the depths explored is a Lodgment Till deposit of light -brown to light -gray, dense to - very -dense, weakly -cement, silty fine sand with a trace of gravel. Additional test pits were explored for the eastern half of the site in February 2012. These recent test pits included a layer of loose, organic topsoil, from 8 to 10 inches thick, on the surface. The topsoil is underlain by a layer of brown to light -brown ablation till (weathered till) of medium - dense, silty fine sand, with a trace of to some gravel and occasional cobble and boulder, about 3.5 to 4.0 feet thick. Underlying the Ablation Till to the depths explored is a Lodgment Till (fresh till:) deposit of light -brown to light -gray, very -dense, weakly -cement, silty fine sand with some gravel. The soil conditions of added land are generally similar to that of the original land. Both report conclude that the subject site is stable and can support the development provided the recommendations of the November 22, 2004 report are fully implemented and observed during construction. The topsoil and loose to medium -dense weathered soils on-site are of low resistance to erosion. Erosion may occur in the weaker surficial soils over the higher gradient areas if they are devoid of vegetation. Progressive erosion can lead to shallow, skin -type mudflows. The geotechnical report recommends preservation and maintenance of vegetation outside of construction limits to mitigate this potential hazard.. The study also recommends that concentrated stormwater should not be discharged uncontrolled onto the ground. Stormwaterfrom impervious surfaces should be ERC Report.doc City of Renton Department of Community & Economic Development Environmental Review Committee Report WILSON PARK 2 PRELIMINARY PLAT& PRELIMINARYPUD LUA12-013, PP,PPUD, ECF Report of May 7, 2012 Page S of 11 captured by underground drain line systems connected to roof downspouts or by catch basins installed in roadways and driveways. Temporary erosion control measures are also recommended and these include: a thin layer of quarry spalls placed over excavated areas to protect the subgrade soils from disturbance by construction traffic; silt fences_ installed along the downhill sides of construction areas to prevent sediment from being transported onto adjacent properties or streets; and ditches or interceptor trench drains installed on the uphill sides of construction areas . to intercept and drain away storm runoff and near -surface groundwater seepage. In order to mitigate for potential geotechnical impacts such as erosion, staff recommends a mitigation measure which requires compliance with the recommendations. contained in the Geotechnical Engineering Study, prepared by Liu & Associates, Inc. dated November 22, 2004 and amended February 15, 2012. Staff also recommends,that the applicant provide a Temporary Erosion and Sedimentation Plan designed pursuant to the Department of Ecology's Erosion and Sediment Control Requirements outlined in Volume II of the 2005 5tormwater Management Manual and provide staff with a Construction Mitigation Plan prior to issuance of construction permits. This mitigation measure shall be subject to review and approval of the Development Services Division. Staff further recommends that weekly reports on the status and condition of the erosion control plan with any recommendations of change or revision to maintenance schedules or installation shall be submitted by the Project Engineer of record to the Public Works inspector. Because of moisture -sensitive fine-grained soils mantling the site and the higher gradient areas within the site the geotechnical study recommends that grading and foundation construction be carried out and completed within the dryer period of the year from April 1 through October 31 unless otherwise approved by the Development Services Division. Staff -recommends that as a mitigation measure that the applicant adhere to a construction schedule involving grading and foundation work during the dryer period of the year. Mitigation Measures: 1. The applicant shall comply with the recommendations contained in the Geotechnical Engineering Study, prepared by Liu & Associates, Inc. dated November 22, 2004 and amended February 15, 2012, for the duration of project construction. 2. The applicant shall provide a Temporary Erosion and Sedimentation Plan designed pursuant to the Department of Ecology's Erosion and Sediment Control Requirements outlined in Volume 11 of the 2005 Stormwater Management Manual and provide staff with a Construction Mitigation Plan prior to issuance of construction permits. This mitigation measure shall be subject to review and approval of the Development Services Division. 3. The applicant shall provide weekly reports on the status and condition of the erosion control plan with any recommendations of change or revision to maintenance schedules or installation shall be submitted by the Project Engineer of record to the Public Works inspector. 4. Because of moisture -sensitive fine-grained soils mantling the site and the higher gradient areas within the site the geotechnical study recommends that grading and foundation construction be carried out and completed within the dryer period of the year from April 1 through October 31 unless otherwise approved by the Development Services Division. Therefore, the applicant shall adhere to a construction schedule involving grading and foundation work during the dryer period of the year. ERC ReporLdoc City of Renton Deportment of Community & Economic Development Environmental Review Committee Report WILSON PARK2 PRELIMINARYPLAT & PRELIMINARYPUD LUA12-013, PP,PPUD, ECF Report of May 7, 2012 Page 6 of 11 Nexus: SEPA Environmental Regulations 2. Storm Water Impacts: A Technical Information Report (dated May 5, 2009.) was prepared by.Baima and Holmberg Inc, for the previous Wilson Park I Plat. An addendum to this report was prepared by'CC� Yr. g on February 28, 2012 to consider the current proposal. The May 2009 report includes an analysis of upstream tributary drainage which states that the parcel to the east drains onto the site, with no problems related to runoff. The Level 1 Downstream Drainage Analysis in the report states that runoff from the site flows west into lots in the adjacent Geneva Court development. The majority of these flows collect in a drain constructed along the back yards of the westernmost lots of the Geneva Court development and then flow into the storm system in South 53rd Place. This flow collects in a stormwater pond/bioswale facility located at the intersection of Talbot Road S and South 53`a Place approximately 750 -feet downstream from the site. This facility outfalls through an 18 -inch pipe to the west side of Talbot Road S into a poorly defined channel flowing into the woods. The flows then pass through a 12 -inch culvert under a walking path and continue to flow west to a wooded wetland area more than a quarter mile downstream from the site. Flows into the ditch along 5 55th Street continue west in a rock lined channel along the north side of the street to the intersection of Talbot Road S and S 55th Street. The channel is eroded and shows signs of flowing into the street. Flows from the ditch along Talbot Road S collect in the storm system about 850 -feet downstream from the site eventually flowing into Springbrook Creek at about 1,80.0 -feet downstream from the site. The Creek continues flowing west to about one-half mile downstream of the site where it enters a box culvert crossing SR 167. The Technical Information Report indicates that there are no apparent drainage problems. The amended February 28, 2012 report evaluates the addition of the subject 10 -lot plat. The original stormwater system for Wilson Park I and located within the street that would serve both Wilson Park I and II was sized to accommodate Wilson Park I lots and the new streets including the access street located within Wilson Park 11. The addendum provides calculations intended to evaluate the sizing of the storm treatment facility for the two projects. The report notes that City of Renton's 2009 Drainage Manual requires Best Management Practices (BMP's) for new developments. One'BMP's is to restrict impervious areas on future lots to help reduce runoff, mitigate for development, and minimize the treatment system needed for the project. This is known as a "Restrictive Covenant" provision and was utilized as part of a preliminary sizing of the future system for both Wilson Park I and 11, The applicant intends to utilize the Restrictive Covenant provision and limit impervious surface on each of the new lots in both Wilson Park I and 11 to 3,300 square feet per lot. By limiting the impervious area for homes, patios, driveways and walkways, the proposed stormwater vault will be of an appropriate size to accommodate both developments. The applicant has also intended to develop both plats at the same time. Comments received from surrounding property owners expressed concern as to whetherthe vault was sized appropriately to accommodate both projects. The applicant has stated that the vault is sized to the 2009 drainage manual and will provide the necessary volume and capacity for both projects. Mitigation Measures: No further mitigation necessary. Nexus: Not applicable. ERC Rep ort. doc City of Renton Department of Community & Economic Development Environmental Review Committee Report WILSON PARK 2 PRELIMINARY PLAT & PRELIMINARY PUD LUA12-013, PP,PPUD, ECF Report of May 7, 2012 Page 7 of 11 3. Water (Wetlands) Impacts: The applicant submitted a letter from Altmann Oliver Associates, LLC, dated March 11, 2011, that documents the wetland reconnaissance conducted on the subject property March 1, 2011. The primary focus of the reconnaissance was to verify the results of a wetland determination report prepared by Alder NW (dated October 19, 2004), which indicated the presence of a small '(less than 800 s.f.) hydrologically isolated wet area in the western portion of the site, immediately adjacent to a remnant foundation of an old loafing shed. The Alder NW report previously indicated that this small wetland area was unregulated as it was significantly disturbed. Altmann Oliver's reconnaissance concurred with the previous findings, describing the wetland as a small Category 3 wetland. Altmann also confirmed that the drainage course flowing from east to west through the southern portion of the site is from an outfall of a storm drain line that collects surface water runoff from South 192" a Street. Therefore, the drainage course is not considered to be stream and is not regulated by City of Renton. Mitigation Measures: No further mitigation required. Nexus: Not applicable. 4. Vegetation Impacts: The applicant submitted a Tree Inventory and Retention Plan and a Tree Retention with the project application. There are 82 total trees on the project site, of which 21 would be removed for construction of the roadway, and 3 trees are within the protected slope area. There are 21 trees within the R-1 zoned area of the site, and 37 trees within the R-14 zoned area. City Code requires that 30% of the trees in the R-1 (or 6.3 trees) and 10% of the trees in the R-14 (3.7 trees) be retained. The applicant is proposing to retain 10 trees and plant street trees and provide enhancedlandscaping in'the open space tract. The portion of the site zoned R-1 is within the Talbot Urban Separator Overlay. The purpose of the Urban Separator Overlay includes providing a continuous open space and wildlife corridor. The applicant proposes to retain trees within the critical area and buffer, to plant two trees per each new lot, and to enhance Tract A with native and ornamental trees, shrubs and groundcover. The enhancement area will be located proximate to the comparable area within Wilson Park I to provide for the continuous open space corridor. Mitigation Measures: No further mitigation necessary. Nexus: Not Applicable. S. Parks and Recreation Impacts: It is anticipated that the proposed development would generate future residents who would use City park and recreation facilities and programs. Staff recommends that the applicant be required to pay a Parks Mitigation Fee based on $530.76 per each new single family lot to be payable prior to recording the final plat. The fee is estimated at $5,307.60 (10 new lots x $530.76 = $5,307.60). Mitigation Measures: 1. The applicant shall pay a -Parks Mitigation Fee based on $530.76 per each new single family lot prior to recording the final plat. ERC Report.doc City of Renton Department of Community & Economic Development Environmental Review Committee Report WILSON PARK PRELIMINARY PLAT & PRELIMRVARYPUD LUA12-013, PP,PPUD, ECF Report of May 7, 2012 Page 8 of 11 Nexus: SEPA Environmental Regulations; Parks Mitigation Fee Resolution No. 3082, Ordinance No. 4527 4. Transportation Impacts: Access to the site would be from S 55th Street via a 50 -foot wide right-of-way that was identified on an access easement through the subject site for the Wilson Park I Plat. The roadway would be constructed to serve both plats (Wilson Park I and 11) and would be dedicated as a public right-of-way. The roadway will have two 13 -foot wide travel lanes, 8 -foot planter strips on each side, and 5 -foot wide sidewalks. The applicant submitted a Traffic Impact Analysis Report prepared by TraffEx (Northwest Traffic Experts, dated lune 23, 2009 and supplemented January 25; 2012). The report indicates that the proposal would utilize the same access to South 55th Street s the approved Wilson Park I Plat: The site access street intersects South 55th Street on the outside of a horizontal curve on South 55th Street to optimize sight distance in both the east and west direction for vehicles entering and exiting the site. The report also indicates that the horizon year for the study is considered to be 2014, as that is the year construction of both plats is anticipated. The study indicated the increase, in traffic with the proposal and determined that the traffic would operate at acceptable levels at the intersection of South 55th Street and the new street within the plat. The Level -of -Service (LOS) with the project was determined to be LOS B for future 2014 conditions. Previously, the site distance on South 55th was evaluated as part of Wilson Park I. It was determined then that the City of Renton intersection and stopping sight distance requirements in both the east and west directions would be met. Comments received from surrounding property owners concern the ability of school buses to safely serve the plat. The applicant has observed that presently the Renton School District buses travel east on South 55th in the morning, stopping in South 55th to pick-up students. The buses then travel west in the afternoon, stopping in South 55th to drop-off students. It is anticipated that this practice would continue with the project, and that children would wait together for pick-up. While this is not necessarily a concern for SEPA environmental review; staff will study the issue further and make recommendations to the Hearing Examiner during the Plat and Planned Urban Development Hearing. The proposal would result in an increase in traffic trips to the City's street system. Therefore, staff recommends that the applicant pay a Traffic Mitigation Fee based on a rate of $75.00 per additional average dailyvehicle trip. Each new residence is expected to generate 9.57 trips; credit is given for the existing residence on the subject property. The Traffic Mitigation Fee is estimated to be $7,177.50 (10 new lots x 9.57 trips x $75.00 = $7,177.50) and would be payable prior to recording the final plat. Mitigation Measures: 1. The applicant shall be required to pay a Traffic Mitigation Fee based on $75.00 per each new average daily vehicle trip associated with the proposed project prior to recording of the final plat. !Nexus: SEPA Environmental Regulations; Transportation Mitigation Fee Resolution No. 3100, Ordinance 4527 ERC Report. doc City of Renton Department of Community & Economic Development Environmental Review Committee Report WILSON PARK2 PRELIMINARYPLAT & PRELIMINARYPUD LUA12-013, PP,PPUD, ECF Report of May 7, 2012 Page 9 of 11 5. Fire & Police Impacts: Fire Prevention staff indicates that sufficient resources exist to furnish services to the proposed development subject to the condition that the applicant provides the required improvements and fees. As the proposal could potentially add 10 new residences, staff recommends that the applicant be required to pay a Fire Mitigation Fee in the amount of $488.00 per each new single family lot. The total fee is estimated to be $4,880.00 (10 new lots X $488.00 T $4,880.00). Mitigation Measures: 1. The applicant shall be required to pay a Fire Mitigation Fee based on $488.00 per each new single family lot prior to recording the final plat. Nexus: <add Nexus info here> E. Comments of Reviewing Departments The proposal has been circulated to City Department and Division Reviewers. Where applicable, their comments have been incorporated into the text of this report and/or "Advisory Notes to Applicant." V Copies of all Review Comments are contained in the Official File and may be attached to this report. Environmental Determination Appeal Process: Appeals of the environmental determination must be fled in writing on or before 5:00 PM, May 25, 2012. Renton Municipal Code Section 4-8-110.13 governs appeals to the Hearing Examiner. Appeals must be filed in writing at the City Clerk's office along with the required fee. Additional information regarding the appeal process may be obtained from the City Clerk's Office, Renton City Hall - 7th Floor, 1055 S. Grady Way, Renton WA 98057. ADvism NOTES TO APPLICANT The following notes are supplemental information provided in conjunction with the administrative land use action. Because these notes are provided as information only, they are not subject to the appeal process for the land use actions. Planning: 1. RMC section 4-4-030.0.2 limits haul hours between 8:30 am to 3:30 pm, Monday through Friday unless otherwise approved by the Development Services Division. 2. Commercial, multi -family, new single family and other nonresidential construction activities shall be restricted to the hours between seven o'clock (7:00) a.m; and eight o'clock (8:00) p.m., Monday through Friday. Work on Saturdays shall be restricted to the hours between nine o'clock (9:00) a.m. and eight o'clock (8:00) p.m. No work shall be permitted on Sundays. 3. Within thirty (30) days of completion of grading work, the applicant shall hydroseed or plant an appropriate ground cover over any portion of the site that is graded or FRC Report. doc City of Renton Deportment of Community & Economic Development Environmentol Review Committee Report WILSON PARK 2 PRELIMINARY PLAT & PRELIMINARY FUD LUA12-013, PP,PPUD, ECF Report of May 7, 2012 Page 10 of 11 cleared of vegetation and where no further construction work will occur within ninety (90) days. Alternative measures such as mulch, sodding, or plastic covering as specified in the current King County Surface Water Management Design Manual as adopted by the City of Renton may be proposed between the dates of November 1st and March 31st of each year. The Development Services Division's approval of this work is required prior to final inspection and approval of the permit. 4. A National Permit Discharge Elimination System (NPDES) permit is required when more than one acre is being cleared. 5. The applicant may not fill, excavate, stack or store any equipment, dispose of any materials, supplies or fluids, operate any equipment, install impervious surfaces, or compact the earth in any way within the area defined by the drip line of any tree to be retained. 6. The applicant shall erect and maintain six foot (6') high chain link temporary construction fencing around the drip fines of all retained trees, or along the perimeter of a stand of retained trees. Placards shall be placed on fencing every fifty feet (50') indicating the words, "NO TRESPASSING -- Protected Trees" or on each side of the fencing if.less than fifty feet (50'). Site access to individually protected trees or groups of trees shall be fenced -and signed. Individual trees shall be fenced on four (4) sides. In addition, the applicant shall provide supervision whenever equipment or trucks are moving near trees. Fire Prevention: 1. The Fire Mitigation Fees are applicable at the rate of $488.00 per single family unit. This fee is paid prior to the recording of the plat. 2. The fire flow requirement for a single family home is 1,000 gpm minimum for dwellings up to 3,600 square feet (including garage and basements). If the dwelling exceeds 3,600 square feet, a minimum of.1,500 gpm fire flow would be required. A minimum of one fire hydrant is required within 300-feeet of the proposed buildings and two hydrants if the fire flow goes up to 1,500 gpm. Existing hydrants can be counted toward the requirement as long as they meet current code, including 5 -inch storz fittings. 3. Fire Department apparatus access roadways are required to be minimum 20 -feet wide fully paved, with 25 -feet inside and 45 -feet outside turning radius. Fire access roadways shall be constructed to support a 30 -ton vehicle with 322 -psi point loading. Access is required within150-feet of all points on the buildings. Maximum grade of 15% is allowed. Dead end streets that exceed 150 -feet in length require an approved turnaround. Plan Review: Water 1. Water service will be provided by Soos Creek Water and Sewer District. A water availability certificate will be required to be submitted to the City with the .site plan application. Plan Review: Sanitary Sewer 1. Extension of an 8 -inch sewer main in the new roadway is required. Sewer stubs are required to be provided to each lot. 2. System development fees for sewer are based on the size of the new domestic waters to serve the new homes on the new lots. Sewer fee for a %- inch water meter is $1,591.00. Sewer ERC Report. doc City of Renton Deportment of Community & Economic Development Environmental Review Committee Report WILSON PARK2 PRELIMINARY PLAT & PRELIMINARY PUD LUA12-013, PP,PPUD, ECF Report of May 7, 2012 Page 11 of 11 fee for a 1 -inch water meter is $3,977.00. An"approved" water plan from Soos Creek Water and Sewer District will be required to be submitted to the City. Property Services: 1. See attached memo for comments from Property Services. ERC Report. doc DEPARTMENT OF COMMUNITY D Citvof Y AND ECONOMIC DEVELOPMENTa ;r DETERMINATION OF NON -SIGNIFICANCE -MITIGATED ADVISORY NOTES APPLICATION NO(S): LUA12-013, ECF, PP, PPUD APPLICANT: Robert & Doravin Wilson PROJECT NAME: Wilson Park 2 Preliminary Plat & PUD DESCRIPTION OF PROPOSAL: The applicant proposes to subdivide an existing 2.15 acre parcel into 10 lots for the eventual development of detached single family homes, and 1 tract for open space. LOCATION OF PROPOSAL: 698 S 55th Street LEAD AGENCY: The City of Renton Department of Community & Economic Development Planning Division Advisory Notes to Applicant: The following notes are supplemental information provided in conjunction with the environmental determination. Because these notes are provided as information only, they are not subject to the appeal process for environmental determinations. Planning: I. RMC section 4-4-030.C.2 limits haul hours between 8:30 am to 3:30 pm, Monday through Friday unless otherwise approved by the Development Services Division. Commercial, multi -family, new single family and other nonresidential construction activities shall be restricted to the hours between seven o'clock (7:00) a.m. and eight o'clock (8:00) p.m., Monday through Friday. Work on Saturdays shall be restricted to the hours between nine o'clock (9:00) a.m. and eight o'clock (8:00) p.m. No work shall be permitted on Sundays. 3. Within thirty (30) days of completion of grading work, the applicant shall hydroseed or plant an appropriate ground cover over any portion of the site that is graded or cleared of vegetation and - vwere nofu`rer— ccristruc ion work will occur within ninety—(90-) days. Alternative measures such as mulch, sodding, or plastic covering as specified in the current King County Surface Water Management Design Manual as adopted by the City of Renton may be proposed between the dates of November 1st and March 31st of each year. The Development Services Division's approval of this work is required prior to final inspection and approval of the permit. 4. A National Permit Discharge Elimination System (NPDES) permit is required when more than one acre is being cleared. 5. The applicant may not fill, excavate, stack or store any equipment, dispose of any materials, supplies or fluids, operate any equipment, install impervious surfaces, or compact the earth in any way within the area defined by the drip line of any tree to be retained. ERC Advisory Notes Page 1 of 2 The applicant shall erect and maintain six foot (6') high chain link temporary construction fencing around the drip lines of all retained trees,. or along the perimeter of a stand of retained trees. Placards shall be placed on fencing every fifty feet (50') indicating the words, "NO TRESPASSING — Protected Trees" or on each side of the fencing if less than fifty feet (50'). Site access to individually protected trees or groups of trees shall be fenced and signed. Individual trees shall be fenced on four (4) sides. In addition, the applicant shall provide supervision whenever equipment or trucks are moving near trees. Fire Prevention: J. The Fire Mitigation Fees are applicable at the rate of $488.00 per single family unit. This fee is paid prior to the recording of the plat. 2. The fire flow requirement for a single family home is 1,000 gpm minimum for dwellings up to 3,600 square feet (including garage and basements). If the dwelling exceeds 3,600 square feet, a minimum of 1,500 gpm fire flow would be required. A minimum of one fire hydrant is required within 304-feeet of the proposed buildings and two hydrants if the fire flow goes up to 1,500 gpm. Existing hydrants can be counted toward the requirement as long as they meet current code, including 5 -inch storz fittings. 3. Fire Department apparatus access roadways are required to be minimum 20 -feet wide fully paved, with 25 -feet inside and 45 -feet outside turning radius. Fire access roadways shall be constructed to support a 30 -ton vehicle with 322 -psi point loading. Access is required within150- feet of all points on the buildings. Maximum grade of 15% is allowed. Dead end streets that exceed 150 -feet in length require an approved turnaround. Plan Review: Water 1. Water service will be provided by Soos Creek Water and Sewer District. A water availability certificate will be required to be submitted to the City with the site plan application. Plan Review. Sanitary Sewer Extension of an 8 -inch sewer main in the new roadway is required. Sewer stubs are required to be provided to each lot. 2. System development fees for sewer are based on the size of the new domestic waters to serve the new homes on the new lots. Sewer fee for a %- inch water meter is $1,591.00. Sewer fee for a 1 -inch water meter is $3,977.00. An"approved" water plan from Soos Creek Water and Sewer District—wild be-req.uir-ed to-be-subm- ittedi -w t -he City Property Services: 1. See attached memo for comments from Property Services. ERC Advisory Notes Page 2 of 2 DEPARTMENT OF COMMUNITY d �Ityot AND ECONOMIC DEVELOPMENT o�� DETERMINATION OF NON -SIGNIFICANCE -MITIGATED MITIGATION MEASURES APPLICATION NO(S): LUA12-013, ECF, PP, PPUD APPLICANT: Robert & Doravin Wilson PROJECT NAME: Wilson Park 2 Preliminary Plat & PUD DESCRIPTION OF PROPOSAL: The applicant proposes to subdivide an existing 2.15 acre parcel into 10 lots for the eventual development of detached single family homes, and 1 tract for open space. LOCATION OF PROPOSAL: LEAD AGENCY: MITIGATION MEASURES: 698S55 th Street The City of Renton Department of Community & Economic Development Planning Division 1. The applicant shall comply with the recommendations contained in the Geotechnical Engineering Study, prepared by Liu & Associates, Inc. dated November 22, 2004 and amended February 15, 2012, for the duration of project construction. 2. The applicant shall provide a Temporary Erosion and Sedimentation Plan designed pursuant to the Department of Ecology's Erosion and Sediment Control Requirements outlined in Volume II of the 2005 Stormwater Management Manual and provide staff with a Construction Mitigation Plan prior to issuance of construction permits. This mitigation measure shall be subject to review and approval of the Development Services Division. 3. The applicant shall provide weekly reports on the status and condition of the erosion control plan with any recommendations of change or revision to maintenance schedules or installation shall be submitted by the Project Engineer of record to the Public Works inspector. 4. Because of moisture -sensitive fine-grained soils mantling the site and the higher gradient areas within the site the geotechnical study recommends that grading and foundation construction be carried out and com.pleted..with.io th__e d_r_y_e.r_per d__af th-e-y_oar rom_Aladti thro-ugh O- tQppr-31_unhess-tb-p-rwise ap-pm ed _ by the Development Services Division. Therefore, the applicant shall adhere to a construction schedule involving grading and foundation work during the dryer period of the year. 5. The applicant shall pay a Parks Mitigation Fee based on $530.76 per each new single family lot prior to recording the final plat. 6. The applicant shall be required to pay a Traffic Mitigation Fee based on $75.00 per each new average daily vehicle trip associated with the proposed project prior to recording of the final plat. 7. The applicant shall be required to pay a Fire Mitigation Fee based on $488.00 per each new single family lot prior to recording the final plat. EXHIBIT 6 ERC Mitigation Measures Page 1 of 1 City of DEPARTMENT OF COMMUNITY AND ECONOMIC DEVELOPMENT ENVIRONMENTAL (SEPA) DETERMINATION OF NON -SIGNIFICANCE - MITIGATED (DNS -M) APPLICATION NO(S): LUA12-013, ECF, PP, PPUD APPLICANT: Robert & Doravin Wilson PROJECT NAME: Wilson Park 2 Preliminary Plat & PUD DESCRIPTION OF PROPOSAL; The applicant proposes to subdivide an existing 2.15 acre parcel into 10 lots forthe eventual development of detached single family homes, and 1 tract for open space. LOCATION OF PROPOSAL: 698 5 551h Street LEAD AGENCY: City of Renton Environmental Review Committee Department of Community & Economic Development The City of Renton Environmental Review Committee has determined that it does not have a probable significant adverse impact on the environment. An Environmental Impact Statement (EIS) is not required - under RCW 43.21C.030(2)(c). Conditions were imposed as mitigation measures by the Environmental Review Committee under their authority of Section 4-6-6 Renton Municipal Code. These conditions are necessary to mitigate environmental impacts identified during the environmental review process. Appeals of the environmental determination must be filed in writing on or before 5:00 p.m. on May 25, 2012. Appeals must be filed in writing together with the required fee with: Hearing Examiner, City of Renton, 1055 South Grady Way, Renton, WA 98057. Appeals to the Examiner are governed by City of Renton Municipal Code Section 4-8- 110.6. Additional information regarding the appeal process may be obtained from the Renton City Clerk's Office, (425) 430-6510. PUBLICATION DATE: DATE OF DECISION: SIGNATURES: Gregg Zimmer n— dminj5trtor Public Works D partment Terry Higashiyama, Administrator Community Services Department May 11, 2012 May 7, 2012 Date Fire & Emergency Services t '5I-7 Iz , C.E. "Chip" Vincent, Interim Date Administrator/Planning Director Department of Community & Economic Development .- '7 / Date Date EXHIBIT 5 Nos11M IN39@a Yz o � � �.5 T szOWDNR a lAo z# >add NOSI I n o r F r 2 N c�'-6D�' W€w �.g R 8 R Lo - -----------...- C!% tE sk Rla 1L - 1 sser ss� s9. 71 _ 'ym' sstV ]LEI' 7. �6nlEwmpmtcmqpmqurmr r 1 � v! MEIN 'oEr(10 �� EXHIBIT 2 NOIDO14 YM 'NOiN3tl 2d O,1.I+i�ZI L/ xwNOSIM 30 AldZ) �,� City of Renton Community and Economic Development Department Report to the Hearing Examiner W7WNPARKIIPLAT & PUD LUA12-013, ECF, PP, PPUD PUBLIC HEARING DATE. June 12, 2012 Page 31 of 31 EXPIRATION PERIODS: Preliminary PUD: The developer shall, within two (2) years of the effective date of action by the Hearing Examiner to approve the preliminary plan, submit to the Department of Community and Econorrdc Development a final development plan snowing the ultimate design and specific details of the proposed planned urban development or the final phase or phases thereof; provided, however, that for a preliminary plan approved concurrent with a preliminary subdivision, the developer shall submit the final development plan within five (5) years of the effective date of action by the Hearing Examiner to approve the preliminary plan. Upon application by the developer, the Hearing Examiner may grant an extension of the approved preliminary plan for a maximum of twelve (12) months. Application for such extension shall be made at least thirty (30) days prior to the expiration date of preliminary plan approval. Only one such extension may be granted for a planned urban development. If a final development plan is not filed within the identified time limits or within the extended time period, if any, the planned urban development preliminary plan shall be deemed to have expired or been abandoned. To activate an expired or abandoned planned urban development, a new application is required. Preliminary Plat: Preliminary plat approval shall lapse unless a final plat based on the preliminary plat, or any phase thereof, is submitted within five (5) years from the date of preliminary plat approval. One one-year extension shall be granted to an applicant who files a written request with the Administrator at least thirty (30) days before the expiration of this five (5) year period, provided the applicant demonstrates that he/she has attempted in good faith to submit the final plat within the five (5) year period. Section 3: Offsite Analysis An upstream review and analysis has been performed to establish existing flows entering a new storm system being installed along South 55th Street. The upstream area is further reviewed within Section 5 of this report. Flows from the upstream areas were obtained from the "Rational Method" and KCRTS modeling, depending on basin size. Flows calculations will be found within Section 5. The upstream areas flow into an existing system of pipes and open channels along South 55th Street at the top of the hill. The upstream flow will be conveyed around the project within South 55`h Street. A downstream analysis was prepared for Wilson Park (LUA09-140) by Saima & Holmberg, Inc. dated May 5, 2009 (attached). This system was walked by Offe Engineers, PLLC in July 2013. Offe Engineers, PLLC concurs with the Baima & Holmberg review of the downstream system. The project is located in a "hillside" development area within the City of Renton. The downstream system has adequate grade and capacity for the additional impervious areas on these two projects. The proposed developed condition will collect the runoff from the roadway section and store the volumes for detention and water quality near the entry at South 55th Street. This new system will discharge into the off-site improvements (U13005791). The flows will be conveyed to the intersection of South 55th Street and Talbot Road South within 15" pipes and catch basins. At Talbot Road South (NE Corner) the new system will connect to the existing downstream system as analyzed for Wilson Park indicated above. BAIMA & HOLMBERG INC. LEVEL I DOWNSTREAM DRAINAGE REPORT for Wilson Plat January 23, 2009 Baima & Holmberg, Inc. Job No. 2687-001 Prepared For Robert Wilson 720 South 55th Street Renton, WA 98055 100 FRONT STREET SOUTH . ISSAQUAH • WASHINGTON • 98027-3817 • (425) 392-0250 • (425) 391-3055 Street Address 720 South 551h Street --- King County Tax Parcel No. 312305-9125 Project Overview This project involves developing a 2.5 -acre parcel into 13 single-family lots. The site currently is occupied with a single residence, lawn and wooded areas. The site is located about 250' north of South 55h Street, about 150' east of the east terminus of South 53rd Place, on the slope overlooking. SR 167, about 1/2 mile to the west. The site generally slopes down to the west at an average slope of approximately 20%. Per the SCS soil maps, the site is underlain with Alderwood soil, sandy loam over glacial till. Upstream Tributary Drainage A portion of the parcel to the east of the site drains onto the site. No problems related to this runoff was noted. Level 1 Downstream Drainage Analysis In general, runoff from the site flows west into lots in the adjacent development, Geneva Court (A). The majority of these runoff flows apparently collect in the drain behind an 8'± rockery (B) constructed along the back yards of the west -most lots of said development or in area drains in the back yards, then flow into the storm system in South 53rd Place (C & D). This flow collects in a stormwater pond/bioswale facility located at the intersection of South 53`d Place and Talbot Road South (E), about 750' downstream from the site. This facility outfalls through an 18" pipe to the west side of Talbot Road South into a shallow, poorly defined channel flowing west through the woods (F). The flows pass through a short 12" culvert (H) under a walking path then disappear into thick woods/brush, continuing to flow west to a wooded wetland area (1) beyond 1/4 mile downstream from the site. This wetland apparently drains to a 10' X 5't box culvert crossing under SR -167 (Q), about '/z mile downstream from the site. A small area of the south part of the site drains southwest across the south property line of the site into the adjacent parcel to the south (Z). These runoff flows through woods, collecting in a ditches along South 55'h Street (K)(about 350' downstream from the site) and/or Talbot Road South (L)( about 800' downstream from the site). Flows into the ditch along South 55d' Street (K) continue west in a 6"-12" rock -lined ditch channel along the north side of the street, passing through a couple of 12" driveway culverts on the way to the intersection of South 55`h Street and Talbot Road South (M). This ditch is eroded in areas and shows signs of overtopping and flowing into the street, presumably during the recent storms that caused widespread flooding in Western Washington. Flows from this ditch collect in an 18" storm system (M). Flows from the ditch along Talbot Road South (L) collect in the same storm system, about 850' downstream from the site. The 18" storm system continues west under Talbot Road South and west along the north side of South 192°d Street (N) to about 1200' downstream from the site where it apparently discharges into another shallow roadside ditch (0)(because of heavy vegetation the pipe outlet was not located). This ditch is poorly defined with flows drifting west along the road, where they enter Springbrook Creek at about 1800' downstream from the site (P). Springbrook Creek, with a channel generally about 5' wide and 3' deep (water depth of about 1') continues west to about'/2 mile downstream from the site (J) where it enters the aforementioned 10' X 5'± box culvert crossing under SR-167 (Q). The creek continues flowing west on the west side of SR- 167.Other than the overtopping ditch noted along South 55th Street, there were no apparent downstream drainage problems. A check of King County drainage complaints on their IMT website yielded no reported complaints along this downstream drainage path. 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The proposal is to mitigate on all the Lots using gravel filled trenches or dry wells at the time of building permit. The runoff from the "new" roadway section will be collected into a detention/Water Quality vault located near the entry of the project off of South 55th Street. The detention calculations are attached with a breakdown of the roadway sections contributing to the facility. The storm water pond sizing calculations are attached to this section. WATER QUALITY REVIEW The City Manual requires water quality treatment for projects that add 5,000 square feet or more of "new" pollution generating imperious surfaces (PCIS). The proposed developed (PCIS) exceed this requirement and therefore WQ treatment has been sized within the vault. The WQ portion of the vault is required to hold 4,419 cubic feet of "dead storage". Water Quality calculations are attached. DETENTION CALCULATIONS Wilson Park #1/#2 Area Breakdown Area Breakdown 4394 Cots 22 4,000 sq. ft. impervious max. (all BMP on lots) (74%) Roads lin. Feet 26'road section 325 (sidewalk both sides) 52' 26'road section 375 (sidewalk one side) 42' 26'road section 95 (sidewalk both sides) 42' 2O'road section 74 (sidewalk one side) 26' 20'road section 250' (Fire Lane) 20' Frontage 122 (sidewalk one side) 14' NPGEAreas Total Area Impervious Pervious Forest/NGPE ((RUN #Z)) Impervious Pervious Forest Tota/Areas . feet fsa feet? s ,feet 126068 0 0 INFILTRATION Area of R/W 16900 15750 3990 1924 1708 34273 200613 12506 4394 (74%) 11555 4095 (74%) 3431 559 (86%) 1847 77 (96%) 5000 (100%) 732 976 43% 455� 0` ? Ito 3���QG 5171 34273 10101 Existina Conditions 40 Land Use Summary Peak Flow Rates— -----Flow Area Flaw Rate Till Forest4.61 acres' Time of Till Pasture', 0.00 acres: - - Peaks Till Grass! 0.00 acres;. Return Outwash Forest; 0.00 acres. (CFS) Outwash Pasture' 0.00 8cres' r Outwash Grass' 0.00 acres!! (CFS) T Period Wetland 0.00 acres; f 0.291 lmperviousi 0.00 acres` 2/09/01 Total — 0.372 4.61 acres: i _ Scale Factor: 1.00 Hourly --Reduced 0.990 Time Series: JPredev.tsf 7 Compute Time Series 3:00 0.291 2 Modify User Input 0.960 0.216 4 File for computed Time Series [.TSF] 4 .:.-v't4:Mri{%..i.}v;A"Ful':'..'9.ri_'!�':{Kt-1RadEdKG: :n3n>ti. rv- '.eh'.r.,.4.h w. i'.A fro%.: .'-':._.'.a .yCf.:.. .4 {S•.:� Flow Frequency Analysis Time Series File:predev.tsf Project Location:5ea-Tac ---Annual Peak Flow Rates— -----Flow Frequency Analysis ------- Flaw Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.291 2 2/09/01 18:00 0.372 1 100.00 0.990 0.079 7 1/06/02 3:00 0.291 2 25.00 0.960 0.216 4 2/28/03 3:00 0.223 3 10.00 0.900 0.008 8 3/24/04 20:00 0.216 4 5.00 0.800 0.128 6 1/05/05 8:00 0.188 5 3.00 0.667 0.223 3 1/18/06 21:00 0.128 6 2.00 0.500 0.188 5 11/24/06 4:00 0.079 7 1.30 0.231 0.372 1 1/09/08 9:00 0.008 8 1.10 0.091 Computed Peaks 0.345 50.00 0.980 Developed Conditions 1._ ... 4anF} Use Siln'ImaI]/ Peak i Area ---_....._- Till Forest' 0.79 acres Till Pasture' 0,00 acres' Till Grass 0.23 acres: 3 Outwash Forest 0.00 acres; Outwash Pasture; 0.00 acres Peak Outwash Grass: 0.00 acres; Wetland! 0.00 acres; Imperviousi 0.81 acres. PTob 1.83 acres ................ Scale Factor: 1.00 Hourly Reduced Time Series: IDev.tsf Compute Time Series Modify User Input File for computed Time Series [.TSF] Mn+A''Qec-detiti�MXr�_,•s:9iea:K,4bi:P5.'i'i�A@>aF.'" - :Y�`Y4as'_'aD:-,`; fi kdas .'•�:�ix..;X�-.moi>x. Flow Frequency Analysis Time Series File:dev.tsf Project Location:5ea-Tac ---Annual Peak Flow Rates— -----Flow Frequency Analysis ------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return PTob (CFS) (CFS) Period 0.248 5 2/09/01 2:00 0.488 1 100.00 0.990 0.196 8 1/05/02 16:00 0.300 2 25.00 0.960 0.292 3 2/27/03 7:00 0.292 3 10.00 0.900 0.206 7 8/26/04 2:00 0.266 4 5.00 0.800 0.246 6 10/28/04 16:00 0.248 5 3.00 0.667 0.266 4 1/18/06 16:00 0.246 6 2.00 0.500 0.300 2 10/26/06 0:00 0.206 7 1.30 4.231 0.486 1 1/09/08 6:00 0.196 8 1.10 0.091 Computed Peaks 0.425 50.00 0.980 Detention Facility Design Facilky Definition Design Note: Detention is provided in the top 1 -ft of a 6 -ft diameter pipe. The total cross -sec tional storage area provided in the pipe is 3.097 sq. ft. The calculations below approximate a similar storage area. Only one orifice is proposed, so this is expected to be a reasonably accurate estimate. Retention/Detention Facility Type of Facility: Detention Vault Facility Length: 200.00 ft Facility Width: 3.00 ft Facility Area: 600. sq. ft Effective Storage Depth: 1.00 ft Stage 0 Elevation: 216.00 ft Storage Volume: 600. cu. ft Riser Head: 1.00 ft Riser Diameter: 12.00 inches Number of orifices; 1 Full Head Pipe orifice # Height Diameter Discharge Diameter (ft) (in) (CFS) (in) 1 0.00 1.50 0.211 Top Notch Weir: None Outflow Rating Curve: None Staao/ toraaeMiscra hae Performance Stage Elevation Storage Discharge Percolation (ft) (ft) (cu. ft) (ac -ft) (cfs) (cfs) 0.00 216.00 0. 0.000 0.000 0.00 0.02 216.02 12. 0.000 0.008 0.00 0.03 216.03 18. 0.000 0.011 0.00 0.05 216.05 30. 0.001 D.013 0.00 0.06 216.06 36. 0.001 0.015 0.00 0.08 216.08 48. 0.001 0.017 0.00 0.09 216.09 54. 0.001 0.019 0.00 0.11 216.11 66. 0.002 0.020 0.00 0.13 216.13 78. 0.002 0.022 0.00 0.18 216.18 108. 0.002 0.026 0-00 0.23 216.23 138. 0.003 0.029 0.00 0.28 216.28 168. 0.004 0.032 0.00 0.33 216.33 198. 0.005 0.035 0.00 0.38 216.38 228, 0.005 0.037 0.00 0.43 216.43 258. 0.006 0.040 0.00 0.48 216.48 288. 0.007 0.042 0.00 0.53 216.53 318. 0.007 0.044 0.00 0.58 216.58 348. 0.008 0.046 0.00 0.63 216.63 378. 0.009 0.048 0.0c 0.68 216.68 408. 0.009 0.050 0.00 0.73 216.73 438. 0.010 0.052 0.00 0.78 216.78 468. 0.011 0.054 0.00 0.83 216.83 498, 0.011 0.055 0.00 0.88 216.88 528. 0.012 0.057 0.00 0.93 216.93 558. 0.013 0.059 0.00 0.98 216.98 588- 0.013 0.060 0.00 1.00 217.00 600. 0.014 0.061 0.00 1.10 217.10 660, 0.015 0.372 0.00 1.20 217.20 720. 0.017 0.938 0.00 1.30 217.30 784. 0.018 1.670 0.00 1.4D 217.40 840. 0.019 2.460 0.00 1.50 217.50 900. 0.021 2.750 0.00 1.60 217.60 960. 0.022 3.010 0.00 1.70 217.70 1020. 0.023 3.240 0.00 1.80 217.80 1080. 0.025 3.460 0.00 1.90 217.90 1140. 0.026 3.670 0.00 2.00 218.00 1200. 0.028 3.670 0.00 Stage/Storaae/Discharne Performance at Significant Storm Event Hyd Inflow Outflow Peak Storage Target Calc Stage Elev (Cu -Ft) (Ac -Ft) 1 0.49 0.37 0.48 1.12 217.12 671_ 0.015 2 0.25 ******* 0.24 1.06 217.06 635. 0.015 3 0.27 ******* 0.25 1.06 217.06 636. 0.015 4 0.29 ***r*** 0.26 1.06 217.07 639. 0.015 5 0.25 ******* 0.23 1.06 217.06 633. 0.015 6 0.16 ******* 0.15 1.03 217.03 617. 0.014 7 0.20 ******* 0.17 1.04 217.04 622. 0.014 8 0.21 ******* 0.13 1.02 217.02 613. 0.014 Stage/Storaae/Discharge Performance Route Time Series through Facility Inflow Time Series File:dev.tsf Outflow Time Series File:RDOut Inflow/Outflow Analysis Peak Inflow Discharge: 0.488 CFS at 6:00 on Jan 9 in Year 8 Peak Outflow Discharge: 0.479 CES at 7:00 on Jan 9 in Year 8 Peak Reservoir Stage: 1.12 Ft Peak Reservoir Elev: 217.12 Ft Peak Reservoir Storage: 671. Cu -Ft 0.015 Ac -Ft Flow Duration from Time Series File:rdout.tsf Cutoff Count Frequency CDF Exceedence Probability CFS % % % 0.004 50662 82.619 82.619 17.381 0.174E+00 0.011 4350 7.094 89.713 10.287 0.103E+00 0.019 1985 3.237 92.950 7.050 0.705E-01 0.026 1357 2.213 95.163 4.837 0.484E-01 0.033 964 1.572 96.735 3.265 0.326E-01 0.041 617 1.006 97.741 2.259 0.226E-01 0.048 506 0.825 98.567 1.433 0.143E-01 0.055 319 0.520 99.087 0.913 0.913E-02 0.063 238 0.388 99.475 0.525 0.525E-02 0.070 38 0.062 99.537 0.463 0.463E-02 0.078 27 0.044 99.581 0.419 0.419E-02 0.085 31 0.051 99.631 0.369 0.369E-02 0.092 19 0.031 99.662 0.338 0.338E-02 0.100 25 0.041 99.703 0.297 0.297E-02 0.107 17 0.028 99.731 0.269 0.269E-02 0.114 16 0.026 99.757 0.243 0.243E-02 0.122 15 0.024 99.781 0.219 0.219E-02 0.129 14 0.023 99.804 0.196 0.196E-02 0.137 18 0.029 99.834 0.166 0.166E-02 0.144 13 0.021 99.855 0.145 0.145E-02 0.151 9 0.015 99.870 0.130 0.130E-02 0.159 8 0.013 99.883 0.117 0.117E-02 0.166 14 0.023 99.905 0.095 0.946E-03 0.173 3 0.005 99.910 0.090 0.897E-03 0.181 14 0.023 99.933 0.067 0.669E-03 0.188 6 0.010 99.943 0.057 0.571E-03 0.196 5 0.008 99.951 0.049 0.489E-03 0.203 7 0.011 99.962 0.038 0.375E--03 0.210 3 0.005 99.967 0.033 0.326E-03 0.218 4 0.007 99.974 0.026 0.261E-03 0.225 2 0.003 99.977 0.023 0.228E-03 0.232 4 0.007 99.984 0.016 0.163E-03 0.240 4 0.007 99.990 0.010 0.978E-04 0.247 2 0.003 99.993 0.007 0.652E-04 0.255 2 0.003 99.997 0.003 0.326E-04 0.262 1 0.002 99.998 0.002 0.163E-04 Duration Comparison Anaylsis Base File: predev.tsf New File: rdout.tsf Cutoff Units: Discharge in CFS Cutoff 0.065 0.082 0.100 0.117 0.135 0.152 0.169 0.187 0.204 0.222 0.239 0.257 0.274 -----Fraction of Time ----- Base New %Change 0.92E-02 0.50E-02 -45.3 0.62E-02 0.38E-02 -38.3 0.48E-02 0.30E-02 -38.3 0.37E-02 0.23E-02 -37.1 0.28E-02 0.17E-02 -38.7 0.22E-02 0.13E-02 -41.0 0.15E-02 0.95E-03 -34.8 0.98E-03 0.60E-03 -38.3 0.60E-03 0.38E-03 -37.8 0.34E-03 0.23E-03 -33.3 0.21E-03 0.98E-04 -53.8 0.16E-03 0.33E-04 -80.0 0.32E-04 0.00E+00 -100.0 There is no positive excursion ----------Check of Probability Base 0.92E-02 0.065 0.62E-02 0.082 0.48E-02 0.100 0.37E-02 0.117 0.28E--02 0.135 0.22E-02 0.152 0.15E-02 0.169 0.98E-03 0.187 0.60E-03 0.204 0.34E-03 0.222 0.21E--03 0.239 0.16E-03 0.257 0.82E-04 0.274 Maximum negative excursion = 0.032 cfs (-33.7%) occurring at 0.094 cfs on the Base Data:predev.tsf and at 0.062 cfs on the New Data:rdout.tsf Tolerance ------- New %Change 0.055 -15.1 0.060 -27.0 0.068 -32.2 0.086 -27.0 0.103 -23.5 0.123 -19.4 0.144 -14.8 0.165 -11.7 0.187 -8.5 0.207 -6.5 0.227 -5.1 0.233 -9.3 0.242 -11.6 Dauud - Duration Malys�s f:CRFS::. - - `Ys _ N M RDOut Our < Target.dur • N 4 N � O N O LL o cc j S N_ 00 CD c i, a R 4 � 8 p 0 E 10� 10� 10.3 10 10 10° . i ` Probability Exceedence WATER QUALITY CALCULATIONS Wetpool Sizing Calculations Per 2009 King County Stormwater Management Manual Project Name: Wilson Park 1 and 2 Project Number: Facility Description: DetentioNWQ treatment Step 1: Identify required wetpool volume factor (f). f = 3 Per KCSWDM 6.4.1.1 Step 2: Determine rainfall (R) for the mean annual storm. R = 4.47 Per KCSWDM Fig. 6.4.1.A Step 3: Calculate runoff from the mean annual storm (Vr) for the developed site. Vr = (0.9A, + 0.25Atg + 0.10Atr + 0.01 A,) x (R 112) where: A; = Impervious Surface Area= 36,171 s.f. At9 = Till Grass Area = 10,101 s.f. An = Till Forest Area = 34,273 s_f. Ao = Outwash Area = 0 s.f. Vr = 1,473 c.f. Step 4: Calculate required wetpool Volume (Vb). Vb=fxVr Vb = 4,419 cJ. Section 5: Conveyance System Analysis and Design An analysis of the new conveyance system is attached to this section. The new conveyance system was analyzed using the "Rational Method of Analysis" per section 3.2 of the King County Drainage Manual for the contributing areas to catch basin #16 and #18. These sub -basins were less than 10 acres in size. The larger sub -basins contributing to catch basin #20 and #24 are greater than 10 acres; therefore the KCRTS method, 15 minute intervals, was used. The entire on-site (Wilson Park & Wilson Park 2) conveyance systems were checked using a 25 year storm event flow rate of 6.2 cfs from runoff of the entire parcel. This is the amount of flow that would be contributing to CB #16 (point of discharge into the storm water vault). This is a conservative approach for this analysis. The on-site system is adequate at a 12" pipe because of the significant grade of the roads on the project. An upstream basin contributing to "new" CB #24 — located along the west side of the project within South 55th Street curves — is over 27 acres in size. The KCRTS model was used to produce a 25 year storm event flow rate of 12.33 cfs. This flow rate was used to check the new conveyance system from CB#24 to C8#18. At CB#18, an additional area around the curve, contributes to the "new" system. The "Rational Method" was used to calculate the flow from this 1.7 acre basin. At CB#18 the additional flow increases the 25 year flow rate within this system to 15.2 cfs. At the entry of the project with South 55th Street, the 25 year flow rate changes. At C13#20, the flows from the project together with the upstream flows from CB#24 and CB#18 combine. At this point, the contributing area exceeds the 10 acre minimum for the "Rational Method". The KCRTS model was used for the 25 year flow rate at C13#20. The 25 year flow rate at CB#20 is 15 cfs from the entire 35 acre upstream basin flowing into C13#20. Based upon the ".Stormwater Conveyance Backwater Calculatione attached, the new storm drainage system will handle the existing conditions for the upstream areas together with the developed conditions from the project site. v 00000000a M M � Odd 0 0 d o d 0 0 U,6.,=mow N LOLL 00000 O O O d Ln C .. 0. 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V} ,-•i ,--1 rt r -I r-1 W rl r-1 ri r1 L N CD ++ N Q O Ln N M N Ln M 00 00 M �-- d ,--1 r-1 Ln ,-4 w J rNv M M %D Q �a 00000 0 0 o Q N N N N N N N (V N N Ln to to tD to to to tD %D %D N M C M tD Ln M ,1 Q N 9 (L)*: ft u 4t: � to 4 dQ M ' O tD Ln M —4 Ln m r\ Ln N M N 4 -4 tnU 000000❑0❑ pp q m N N r\ -f n R N m Ln w rA W lL W m U M Uy -I Ln n +-1 M N M I- LLnn tD M .-i ,m-1 a% T M -1 00 +1 M -4 _ OD O +1 m r-� -1 00 N tD O M ui r,4 v tD r` 00 o .N1 N N N N N N N m M G W j 1a 0 0 0 0 Q Q (D c) C7 v= J w 0 0 0 0 0 0 0 Q Q n cn +� -4 —4 ,1 ,1 ,1 ,1 —1 ,1 —4 o ooQQQQQQQ (v •� CO = J -9 0 0 0 0 0 0 O Q Q L 00 -4 2 0 W w O C) 0 0 0 0 0 0 0 �. Q j M Q 00 N N. -1 O N m +1 Q a -'i+ C Q .� M n r1 N N CD ++ N Q) p w rNv M M %D Q M 0 +-1 U N N N N N N N M M M N 9 a✓ -4 to + 4 M-4 M Q Lin Ln C ww (qu) +--1 00 M r1 v m Q Ln to .�O ,1Nm mtDr.oDQ N N N N N N N N M O to ++ N N N N N N N N N v w J 0 0 Q O Q Q Q Q Q Ut o Ln m .1 Q d a-+ Q tD Ln m -i m r� Ln U N ,1-1 -4 ,1 � A* t� k # 44: 41� Mu) t p � O O M� aw Qoo c LU H N w aj U m Ln oo r` n L Lt. Q M N e W N M M LU M men O Lh +- Lf) n O H j p y M G %0 > a q�� U - = d CO Non C=) �+� qco M M M C5 M M ^ U m .N -r .N -i ,N -i o v m j=4� (D LII 4j H ^ L1 u N L Q rL u-) Lf) u-) 00 00 00 o W o .-. +1 +c rn m rn L 2 2 co < ci n Ul a qLU oaf H 00 M M M Ln 4� H 06 n ,-. ak >v Io rn ,-i CL)v o OLLJu M tor)M r 000 > o00 Q L N [V N M N .�ajz r .. v 4- ,-. CL L" J L Q Q H §" ,-. ~-' Ln IJ � W ED co N n m u N M N w Q E L .9 d L�N Z � 41 u ) 000 H N w `e U m Ln M L t1�/ M M M Go C) > a q�� = Lu w c M C5 M M LII 4j H °H' o o 0 0 n a H H 00 (5 Ln Q O Q m= J� o 0 0 r 4 o o Q Q c) Q .�ajz ,-. o co n n a>r w ooh -Ea� U M M M DL n N Ln �-. N > i Ln y 4� qy w a w o o � M M M x LAQ% —4 rd H HL6J u o00 V M N N E O L17 � Wilson Park & Park 2 Rational Method Runoff from Developed Basin P(25) 3.40 inches A(24) 27.5 acres A(20) 35. A acres A(16) 5.8 acres A(18) 1.7 acres (from attached Isopluvials Map) 25 Use KCRTS @ 15 minute routing 12.33 Combination ofA(24)+A(16)+A(18) - Use KCRTS .14,97 6,2 2.3 Area (16) Description of Flow Path L1 100 feet sl L2 950 feet s2 Composite Runoff Coefficient A(1) C(1) 0.90 0.92 acres A(2) C(2) 0.15 0.79 acres A(3) C(3) 0.25 4.09 acres 5.80 CO 0.92*0.90+0.79*0.15+4.09*0.25/5.8 Time of Concentration T(1) 100/60*{(7.0)*(0.05)**(0.5)3 T(2) 950/60*1(20.0)*(0.10)**(0.5)3 Compute iQ i@=(aR)*(Tc)**(-bR ft/ft 0.05 Lawn/Landscaping 0.10 Pipe Impervious Forest Grasses 0.34D 1.1 Minutes 2.5 Minutes 3.6 USE 5 Minutes i@=2.66*5**-0.65 0.93 Compute I(25) I(25)=P(25)*ICS 1(25)=3.40*0.93 3.16 Q(25)=C*I(25)*AM Q(25)=0.340*5.8*3.16 6.2 ds A(16) kp 7.0 20.0 Area (18) Description of Flow Path ft/ft k® L1 50 feet sl 0.05 pavement 20.0 L2 350 feet Q 0.10 forest 2.5 Composite Runoff Coefficient A(24) 5.50 12.00 A(1) C(1) 0.90 0.95 acres Impervious A(2) C(2) 0.15 0.75 acres Forest 1.70 Cp 0.95*0.90+0.75*0.15/1.7 0.570 Time of Concentration T(1) 50/60*{(20.0)*(0.05)**(0.5)} 0.6 Minutes T(2) 350/60*((2.5)*(0.10)**(0.5)} 7.3 Minutes 7.9 USE 8 Minutes Compute iQ i@=(aR)*(Tc)**(-bR) iQ=2.66*8**-0.65 0.69 Compute I(25) 1(25)=P(25)*IQ 1(25)=3.40*0.69 2.34 Q(25)=C*I(25)*A(T) Q(25)=0.57*1.70*2.34 2.3 cfs A(18) Area (20) A(20) = A(24) + A(18) + A(16) Basin Pasture Grass Impervious Forest A(24) 5.50 12.00 10.00 A(18) 0.95 0.75 A(16) 4.09 0.92 0.79 5.50 16.09 11.87 1.54 A(2O) UPSTREAM BASIN INTO CB#24 Flaw Frequency Analysis _----------------------------------------------------- ------------------------------------------- Time Series File:upstream basin cb#24.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis ---------- Flow Rate Rank Time of Peek - - Peaks - - Rank Return Prob (CFS) (CFS) Period 4.80 6 2/09/01 12:30 18.98 1 100.00 0.990 3.53 8 1/05/02 15:00 12.33 2 25.00 0.960 12.33 2 12/08/02 17:15 7.95 3 10.00 0,900 3.x,5 8/26/04 0:45 6.87 4 5.00 0.000 7.95 3 11/17/04 5:00 6.23 5 3.00 0.667 6.23 5 10/27/05 10:45 4.80 6 2,00 0,500 6.87 4 10/25/06 22:45 3.85 7 1.30 0.231 18.98 1 1/09/08 6:30 3.83 8 1.10 0.091 Computed Peaks 16.77 50.00 0.980 UPSTREAM BASIN INTO CB#20 Flow Frequency Analysis -------------------------------------------------------- Time Series File -upstream basins cb#20.tsf Traject Location:Sea-Tac ---Annual Peak Flow Rates_-- ___-_Flow Frequency Analysis ------- Flow Rate Rank Time of Peak - - Peaks - - Rank Returns Prob (CFS) (CFS) Period 5.91 6 2/09/01 12:30 23.39 1 100.00 0.990 4.63 7 1/05/02 15:00 1.4.97 2 25.00 0.960 14.97 2 4.60 8 12/08/02 8/26/04 17:15 0.45 9.99 8.22 3 4 10.00 5.00 0.900 0.800 _-,,` too 9.99 3 11/17/04 5:00 7.50 5 3,00 0.667 lfV 7.50 5 10/27/05 10:35 5.91 6 2.00 0.500 8.22 4 10/25/06 22:45 4.63 7 1.30 0.231 23.39 1 1/09/08 6:30 4.60 8 1.10 0.091 Computed Peaks 20.58 50.00 0.980 SECTION 3.2 RUNOFF COMPUTATION AND ANALYSIS MET IODS FIGURE 3.2. LC 25 -YEAR 24-HOURISOPLUVIA S SN KOMISH COUNTY KING COUNTY I f 1 f � x I C' `- I i� I j •U Cb '-` k ti WESTERN KING COUNTY 25 -Year 24 -Hour Precipitation in Inches �. KsxT L - d T •�. f r t . I w„- I�fns— I i.,KING COUNTY •�. f PIERCE COUNTY 44 N h � 4.S eb* co • -,. L _ fir` 0 2 2 4 Miles Cb o�- 1/9/2009 2009 Surface Water Design Manual 3-16 } � K k�1 A h� SN KOMISH COUNTY KING COUNTY I f 1 f � x I C' `- I i� I j •U Cb '-` k ti WESTERN KING COUNTY 25 -Year 24 -Hour Precipitation in Inches �. KsxT L - d T •�. f r t . I w„- I�fns— I i.,KING COUNTY •�. f PIERCE COUNTY 44 N h � 4.S eb* co • -,. L _ fir` 0 2 2 4 Miles Cb o�- 1/9/2009 2009 Surface Water Design Manual 3-16 3.2.1 RATIONAL METHOD TABLE 3.2.1.A ,.RUNOFF COEFFICIENTS -,`C" VALUES FOR THE RATIONAL METHOD General Land Covers Single Family Residential Areas+ Land Cover C Land Cover Density C Dense forest 0.10 0.20 DUIGA (1 unit per 5 ac.) 0.17 Light forest 0.15 0.40 DUIGA (1 unit per 2.5 ac.) 0.20 Pasture 0.20 0.80 DUIGA (1 unit per 1.25 ac.) 0.27 Lawns 0.25 1.00 DUIGA 0.30 Playgrounds 0.30 1.50 DUIGA 0.33 Gravel areas 0.80 2.00 DUIGA 0.36 Pavement and roofs 0.90 2.50 DUIGA 0.39 Open water (pond, lakes, 1.00 3.00 DUIGA 0.42 wetlands) 3.50 DUIGA 0.45 4.00 DUIGA 0.48 4.50 DUIGA 0.51 5.00 DUIGA 0.54 5.50 DUIGA 0.57 6.00 DUIGA 0.60 " Based on average 2,500 square feet per lot of impervious coverage. For combinations of land covers listed above, an area -weighted "C,:x A," sum should be computed based on the equation Cl: x A, = (Cl x Al) + (C2X Az) + ...+(C„x A.), where A, = (,41+,42 + ...+Aj, the total drainage basin area. 4"Ek 3 Z .t COEFFICIENTS FOR THERATIONAL METH " OD "iREQUATION Design Storm Return Frequency aR 6R 2 years 1.58 0.58 5 years 2.33 0.63 10 years 2.44 0.64 25 years 2.66 0.65 50 years 2.75 0.65 100 years 2.61 0.63 2009 Surface Water Design Manual 1!912009 3-13 m Section 6: Special Reports and Studies Geotechnical Study attached prepared by Liu & Associates, Inc. + Dated February 24, 2009 • Dated February 15, 2012 LTU & ASSOCIATES, INC. GeotecJ-n ca! En=ineering Erg ree-in= Geokuc - Ea -kr: $c;ence 1, tbrtwi-N t 5. Ill 12 Mr. Robert Wilson 7-'O South 55th Street Lake Tapp s. WA 9 191 Dcar'vIr. Wilson - Subject: Addendum No. l to I €.22::2004 Geotechnical Deport Cieolechnical Engineering Sttidv Proposed Re-sidential DeVelopment SoLah 551h Strcct and TvIorris Avenut South Renton. W ashing.t('O L&A Job -No- 4A 1 34 I N TR0 Di.: C'TIO*N We prt viously COITIpleted a gcatcci}nical end=ineering study for the site of a proposed 4-10t short plat, located at the abovc address in Renton, WArington. with our finch -IUs. cNtclttsions and reconzrnendations presented in our 11:1-1:22004 report titled '*Gcotechnical Engineering Study. Proposed 4 -Lot Short Platt. 99�,,-, South 192`j Street - Renton. Washinoton_.. We Understand that expansion of the stabject project to include more land to the east of the original site is bcin cnntenlplated. This added land generally rises moderately (o the cast_ The purpose of this addtndum is to explore subsurface condition of this added land and evaltr�lte its ;tahiiity to assure the geotechnical recommendations for P-radinn_ stirtace land Bound water control. erosion abatement. site stahill/-ation. and foundation design and construction}resented it) our l geotechnical report are also applicable to the det elopincnt of the added land. Prescntcd in this addendum are Utir findings and conclusions. 19213 Kenlake Place NE - Kenmore, Washington 98028 Phone (425) 483-9134 � Fax (425) 486-2748 February 1 �,_ 0 12 AddendUm No. I - Proposed Residential Dtx elopmn3 nt L&, A Job N(-). A 13 4 Pa, -,e PROJECT DESCRIPTION fhe project site is to be accessed from its scwth side by a roadway off South Street it►Wing north�� arca into the sire. The original land will be lying on the wcsl side of this read and the added land Iving east of thc. road. The original land is gcnerall,,flat. while thti added land -,]apes Lapti� and easterly moderaiel� . The added land is flanked by a stoop slope tap ro about 6 to l' feel hiLTh on its -,;est side ,vhich appears to tic a Cut slope rtladc .Cars auo to allow the origin land bei -n{, #traded '17te added land is dotting by tall Enature. deciduous and evcrarcen trees and co-*ered bv dense brush and vinc. The tree.-, are all straight N%ith no bents in the trttnks or dkmnhill leaning. No sign.5 of erosion or Steil movement ha- e been noted within the added. land, SURFACE CONI)ITIONS Substjrface condition of the added land \� pis explored with three test pits cxca ated on February ?R_ -2011. to depth; from 6_0 to 6.5 feet. fhc approximate lacaflolls of the test pits are shown on Plate 1 - Site and ENploraticm Location Platt. Tlie test pits were located with either a tape measure or b� -isual reference to exi; ting topographic features in the field and on the topographic swvc-v inap, and their locations should be considcred only 'Crccurare to The m asuring methi►d used. A «eotechnieal enaincer from OUr ofike ��as present during suhsurlace exploration. who examined the soil and 2colm-6c conditions ertcountered and completed logs of test pits, Sail sampics obtained fro n elac:h sail unit in the test pits were visualIN clati>ilied in tireneral accordance. v0th 17nited Soil Classitic�ation System. a cope of i0ich is presented LIU & ASSOCIATES, INC. Feb1,Lia - 15 - 01 Addendiun NO, I - Prorosed Residential L�e� cl �unlzrr L&A Job o- 4AI-04 on Plate i. Detailed descriptions of sail units encourilered during site, cxploratik)n ,ire Prescr1Cccl in tlIc tc�t }pit logs On Plate: 3 through 4. The Fest lits enccjuntcrcd a layer of looseorgunic topsoil. liori, C to lii inches thick_ on the surfs :e. The topsail B ur7derlain ht' a l;r�cr of brown To light-brukvn_ ablation till f eat}ycred till) of medium-dentiC. silty fine sand. �,Vtll a trace of to Some {uravol and Occasional cobble and b0LIlder, abow 3.5 to 4.2 feet thick. Undo -riving the "dilation till io the depths exp[ored is a lodomorit till (fresh till) depositul' €i�lit-hio-wn to ligl7t-grj,�, terN-dense. weakly -cement. silty line sand tiitit sonic g a\td. Thc soil condidon of added land is generally simikir to that of the original land. GROUNDWATER CONDITION Grouuck%iter s.epage -was not encountered its my of the test pits cxc,-j%att cd on the added lune{, DISCUSSION AND CONCLUSION- Based ONCLUSION Based on the ScrbSUrface (soil .incl groundwater) conclition encountered in the test pit, excavated 011 the added larid_ the gcotechnic;11 in our 11:?2 ?fate -coLechnical report simuld also be applictible to the de,elopment oFthe added land_ It is our opiniot] Chet added kmd should be gUite stable quid geologies haztr€ls over the added land should be minimal if the rcci>n=endations in our 11:''?.'� 00 4 report are mull% implemented and ubwer%ecl daring, c:onstn101011. LIU & ASSOCIATES, INC. I ebrualy 15. _'0I ? :NddendtmiNo- l - Proposed Residential Development 1,&A Job No. -SA I -14 Pa2c DRAINAGE INTPROV EMF NIT A drainage coursc of surfacc eater Nous observed c:omistg down the hillside On The eastern ialf ni' the soLith Side of the aitc, then lloN�ing through is cttivert into a ditch along.the north sire of Sowh 55' Street. The %%aTer in this drainage course gyp., o cars to be . sion uwater relejsed fri,)m the devc1opment cast of the pr,,�iec( sitc and dumped oilto the surjw site. 1t is our opinion that this stun-11watev should he collectcd and )'e -routed in a pipe off the proicct site. CLOSURE We arc pleased to be ofser,-iec to you Ertl this prujcct. Please feel frcc to contact us ifVOLI hay t any gtiestions regarding, this report �:)r need further consultation. Four phmes auaclied Yours very trtuly_ LII_. & A-SSOC 1ATE�. INC. J. �. �Ju11an) Liu. Ph. D_ P.T'. Constultirig. Geotechnical hnehice.r LII,; & ASSOCIATES, INC:. f i � a•.aa --1 � i � , �to r a 41 _ }.r -, T1&' SAF. * * C4-� �TR D P i I t I' In, i5.`.C� vim' a:` .a.� L of �- 4 r ti 4xa� za sva S F, I a � �•-- � tl�C K �';� ZI I a LV ?� ,�JTIL17Y EA , ., > T F i t l F ~ TF 2 pt 4k SITE AND EXPLORATION LOCATION PLAN tT & ASSOCIATES, INC. RESIDENTIAL DEVELOPMENT S_ 55TH STREET AND MORRIS AVENUE S. RENTON, 'WASHINGTON s! .o N -C. 4 ;134 sA i E _ 3 5 241't ?LATE:T71 UNIFIED SOIL CLASSIFICATION SYSTEM MAJOR DIVISIONS GROUP GROUP NAME SYMBOL GRAVE— CLEAN COARSE- :el :1.,=TI-,.[4 5 ;1. = GRAVEL 0v uR�..EL GRAINED GRAVEL', 7HI GM SOILS RE-µ.!MEC ON NO LSIE':m j 7fNES GC — SAND CLEAN SW vV7LL-,�R;lD=D SAND =INE—, w D:�RS= 5,AND rv"?r=THu.'v E,tk t:^ r�E 'AN CF SAND SP �rirlaLw_�Pa�= S"'x SM JiLTJ SAND RF7Ali4Er' 01•J THE C0ARSH=PY•wT.: N' SAND INI r H =G.55-JN5',.. 45:E':= I-INES t 1 S'v 4 L"-S'r`i=1' a,�`'•"" FINE- SIL- AND CLAY INORGA, ir, CL GRAINEDLIQ LJ!� LIMIT SOILS CESS T;-!a.w; 5c ORGANIC OL si_= GR �.r�{v ;r_a.•: Fi4ra 5��s, SILTY AND CLAY INORGANIC � MH SIL7 -'F - Gw p .asrICIT� E-ASric S CH CLAfiY C:F - a4H OL.4STICi''� =A- C PASS!NG O's THxLl . , I- D _ °.SIT OH - RGAI•JIC S _ 1P,GANIw S!!-- rrf.:' ._, c::�'•„rg a.(;?k OR ave,-= ,I r ORGA` 'SC HIGHLY ORGIIANIC SOILS PT F_4J -', CTH.E? �4;GHLY _O _S NOTES: SOIL MOISTURE MODIFIERS, r.=L'J c: LE'G''PJti,'IS' T�G..P:l`.; Tii'ti,;:1.r;e' _jr-E _—STY.DF:' M _ 5. _ '; 7E%'z::Z ;L ".0 ORCG ;:"= ?ATH �l D2j'33_83 YHE *r,Ll 11 �. = siL ,L ASS IF:�-'A ION i SIN � _•'E'-:R�.-,DF%Y TENS iS E.: S 1-TL . .. T `w1 . S : - DA MIF 4:. 4r7, tiIF?Lc dv' `= c, r - � MIL ��. ,p _�.Y ' F.E - .: K7 DuJ-AP r'.I t:3 -�= FELT v - J=2 D , .` _FPPE- SLI.L_ ET- ::IS S-E r'HE :'vATE:t _.R S,, v 72�TE7 v r=, 4_L;`L IJ C137LiY.r=D F=.7-.hrl 'V,'-%TEP -.ASLE LII & ASSOCIATES, INC. UNIFIED SOIL CLASSIFICATION SYSTEM reering -rig -aer;ng c;-�-,#,-; Err!-i __ PLATE 2 Logged By: JSL TEST PIT NO. Date: Z28,20'! 1 1 Grund EI. Dep -h - s "iscS CLASS So:. Description Sai-pFe N_. yr 0*her J' Brush and cuff on surface 1 — — — — loose, organic; silty fine SAND, 4w h fine roots. 5N! -Dark-drown, �- \ r oist tiTDPS,D Lj # __---------------------------- 2 Brown tolight-brown, medium -dense, sivy fine SAND, trace gravel, occasional rooks. moist (weathered VASHON TILL) 3 4 Y --------------------------------_-------- ---- —_Ski SRM Light -gray, very -dense. silty fine SAND, some gravel. weakly - moist (fresh VASHON TILL) Test pit terminated at 6.5 fl! groundwater not ancouniered Test pit terminated at 6.0 ft: ground,,vater not erroountered a 1;r iG i' Logged By. JSL TEST PIT NO, Date: 2f28J2011 Ground EI. i I Depth ft. i I USCS1 CLASS, Sol; Description Sar--ple Ny. w ala Other Tes; OL Vine and duff on surface 1 — — — — \Dark -brow n, oose, organic, silty fine SAND. with Tine roors, -- StA `,_moist TOPStDIL�__________--------_-- -- E Light-brown, medium -dense, silty fine SAND, tram to some gravel, occasional cobble and boulder, moist tweathered VASHON TILL} 3 4 6 ---- —_Ski Light -gray, very -dense. silty fine SAND, some gravel, weakly -cemented. moist fresh VASHON TILL) Test pit terminated at 6.0 ft: ground,,vater not erroountered a 1;r LIU & ASSOCIATES, INC. Geetechriva E't-girseern!3 - Enainearing Geology • Earth Science TEST PIT LOGS RESIDENTIAL DEVELOPMENT S. 55TH STREET & MORRIS AVENUE S. RENTON, WASHINGTON JOB NO. 4A334 1 oATE 316i201" PLATc 3 GEOTECHNICAL INVESTIGATION WILSON PLAT 720 SOUTH 55T" STREET RENTON, WASHINGTON L&A Job No. 9AO08 Date: February 24, 2009 Prepared for: Mr. Robert Wilson 21703 — 60th Street East Lake Tapps, WA 98391 Prepared By: Liu & Associates, Inc. 19213 Kenlake Place NE Kenmore, Washington 98028 UU & ASSOCIATES, INC. Geotechnical Engineering Engineering Geology Earth Science February 24, 2009 Mr. Robert Wilson 720 South 55th Street Renton, WA 98055 Dear Mr. Wilson: Subject: Geotechnical Engineering Study Wilson Plat 720 South 55"' Street Renton, Washington L&A Job No. 9AO06 INTRODUCTION We have completed a geotechnical engineering study for the site of the subject plat, located at the above address in Renton, Washington. The general location of the project site is shown on Plate 1 --- Vicinity Map. We understand that the proposed development for the site is to plat it into 16 single-family residential lots, with supporting infrastructure. The purpose of this study is to characterize the subsurface conditions of the site and provide geotechnical recommendations for grading, slope stabilization, erosion mitigation, surface and ground water drainage control, foundation design and construction, etc., for the proposed development of the site. Presented in this report are our findings, conclusions and recommendations. PROJECT DESCRIPTION For our use in this study, you provided us with a set of topographic survey and plat plan of the proposed development for the site. According to this plan, the subject site is an rectangle -shaped land about 526 feet wide (east -west) by about 207 feet deep (north -south), lying to the north of South 55th Street. The platted building lots are to be accessed from 55'hAvenue South to the south side of the site via a new roadway entering the site near its southwest corner and an existing gravel driveway at about 120 feet west of the southeast corner. These roadway/driveway are to 19213 Kenlake Place NE - Kenmore, Washington 98028 Phone (425) 483-9134 • Fax (425) 486-2746 February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page 2 gravel driveway at about 120 feet west of the southeast corner. These roadway/driveway are to connect a paved road running mainly east -west down the middle of the site. Individual infiltration facilities will be used to dispose stormwater onsite for the residential buildings wherever suitable and a concrete detention vault, designed to supplement the infiltration facilities, is to be located at tTYe nord west comer o�the-site to store storm runoff collected over the impervious surfaces of the proposed development. We understand that grading for the proposed development of the site will include cutting down the eastern high -ground area some what and filling up the western low- lying area to some degree. Retaining walls and/or rockery walls may be required to support or line the cut banks and/or fill embankments along the east, west and part of the south boundaries of the site. SCOPE OF SERVICES Our scope of services for this study comprises specifically the following: I Review the geologic and soil conditions at the site based on a published geologic map. 2. Explore the site for subsurface conditions with backhoe test pits to a firm bearing soil stratum or to the maximum depth (about 12 feet) capable by the backhoe used in excavating the test pits, whichever occurs first. 3. Perform necessary geotechnical analyses and provide geotechnical recommendations for grading, slope stabilization, erosion mitigation, surface and ground water drainage control, design and construction for building foundations and stormwater detention vault, etc., based on subsurface conditions encountered in the test pits and results of our geotechnical analyses. 4. Prepare a written report to present our findings, conclusions, and recommendations for the proposed development of the subject plat site. LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page 3 SITE CONDITIONS SURFACE CONDITIONS The subject site is situated on a broad, moderate to steep, westerly -declining hillside. It is backed into undeveloped wooded lands to the north and east, and adjoined by a single-family residence and undeveloped land to the south and a subdivision to the west. The site generally slopes down westerly at grades from 13 to 39 percent. The higher gradient portions of the site generally lie within the eastern 100 to 120 feet and the western 150 to 200 feet of the site, while the more moderate area lies in about the middle third of the site where the building pad and the yard of an existing residence are located_ The existing residence is accessed from South 55'" Street via a long gravel driveway. The unpaved area around the existing house is covered with lawn grass. The higher gradient eastern and western areas of the site is dotted with tall, mature evergreen trees with few mature deciduous trees mixed in between. The eastern steeper area is covered with thick brush, while the western steeper area is covered by sporadic brush and dense ivy. GEOLOGIC SETTING The Geologic Map of the Lake Stevens Quadrangle, Snohomish County,Washinpton, by James P. Minard, published by U_ S. Geological Survey in 1985, was referenced for the geologic and soil conditions of the subject site. According to this publication, the surficial soil units at and in the vicinity of the site are mapped as Kame Terrace (Qit) deposits underlain by Ground Moraine (Qgt). The geology of the Puget Sound Lowland has been modified by the advance and retreat of several glaciers in the past and subsequent deposits and erosion. The latest glacier advanced to the Puget Sound Lowland is referred to as the Vashon Stade of the Fraser Glaciation, which has occurred LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page 4 during the later stages of the Pleistocene Epoch and retreated from the region some 14,500 years ago. The Kame terrace deposits were laid down by ice -marginal streams flowing between higher ground on one side and an ice margin on the other side during the last glaciation. They consist mostly of silty sand and gravel to cobble. The Kame terrace deposits also contain lenses and pods of till and beds of sand, silt and clay locally. The Kame terrace deposits are of moderately -high to high permeability and can provide good foundation support to structures in their native undisturbed state. The ground moraine soil unit, underlying the Kame deposits, is composed of a thin layer of ablation till over lodgmont till sediments, deposited by Puget glacial lobe of the Vashon Stade of the Fraser Glaciation. The lodgmont till is generally a compact mixture of unsorted clay, silt, sand, gravel and cobble, commonly referred to as "hard pan". The ablation till is similar to lodgmont till, but is much less compact and coherent. The thickness generally varies from 2 to 4 feet for the ablation till deposit, and 5 to 30 feet for the lodgmont till deposit. The lodgmont till deposit is practically impervious, except local lenses of sand and gravel. It has a compressive strength comparable to that of low-grade concrete and can stand in steep natural or cut slopes for a long period. The lodgmont till can provide excellent foundation support with little settlement expected to structures. The overlying ablation till is generally in a loose to medium -dense state, and is more compressible and permeable. SOIL CONDITIONS Subsurface conditions of the site were explored with seven test pits excavated within the site. These test pits were excavated on February 4, 2009, with a tract -mounted backhoe to depths from 6.5 to 9.5 feet. The approximate locations of the test pits are shown on Plate 2 - Site and Exploration Location Plan. The test pits were located with either a tape measure or by visual LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page 5 reference to existing topographic features in the field and on the topographic survey map, and their locations should be considered only accurate to the measuring method used. A geotechnical engineer from our office was present during subsurface exploration, who examined the soil and geologic conditions encountered and completed logs of test pits. Soil samples obtained from each soil unit in the test pits were visually classified in general accordance with United Soil Classification System, a copy of which is presented on Plate 3. Detailed descriptions of soils encountered during site exploration are presented in test pit logs on Plates 4 through 7. The test pits encountered a layer of loose, organic topsoil, from about 10 to 24 inches thick, mantling the site. In Test Pits 1 and 2, located in the eastern high ground area, the layer of topsoil was found underlain by a layer of ablation till of brown, medium -dense, silty, fine to medium sand with a trace of gravel, from 2.3 to 3.5 feet thick. This ablation till is underlain to the depths explored by a lodgmont till deposit of brown to brown -gray, dense, silty fine sand, with some gravel and occasional cobble. Test Pits 3 and 4, located at the downhill fringe of the moderately -sloped middle section of the site, encountered a Kame terrace deposit underlying the topsoil. The top 1.7 to 2.0 feet of this Kame terrace deposit is weathered to a loose to medium -dense state and is composed of brown, fine to medium sand, locally with some silt and/or gravel. The fresh Kane terrace deposit underneath is medium -dense to dense, and is composed of brown -gray to light -gray, fine to medium sand with a trace of gravel. This clean sandy deposit should be of high permeability. Test Pits 5, 6 and 7. Located near at the west end of the site, encountered a weathered and/or fresh Kame terrace deposit, up to about 9.1 feet thick, underlying the topsoil. The Kame terrace deposits were found underlain by a lodgmont till deposit in Test Pits 5 and 7 at a depth of 5.0 and 9.0 feet, respectively. LTU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page 6 GROUNDWATER CONDITION Groundwater seepage was not encountered by any of the seven test pits excavated on the subject plat site. The topsoil, ablation till, and weathered and fresh Kame terrace deposits are loose to medium -dense, and would allow some storm runoff to seep into the ground. The underlying dense to weakly -cemented lodgmont till deposit is of extremely low permeability and would perch stormwater infiltrating into the more permeable surficial soils. The amount of and the depth to this perched groundwater would fluctuate seasonally, depending on precipitation, surface runoff, ground vegetation cover, site utilization, and other factors. The perched groundwater may dry up completely during the dryer summer months and accumulate and rise in the wet winter months. The test pits excavated in the heart of winter did not encountered any groundwater. Therefore, it is our opinion that any groundwater encountered under the subject plat site during construction should be minimal and minor even in the winter months of the year. DISCUSSIONS AND RECOMMENDATTONS GENERAL Based on the soil conditions encountered by the test pits excavated on the site, it is our opinion that the site is suitable for the proposed development from the geotechnical engineering viewpoint, provided that the recommendations in this report are fully implemented and observed during construction. Due to moisture -sensitive fine-grained soils mantling the site and the local higher gradient areas within the site, we recommend that grading and foundation construction work for the proposed development be carried out and completed during the dryer period from April 1 through October 31. If grading work has to proceed beyond the above dryer period, the measures for slope stabilization, erosion mitigation, and surface and ground water drainage control recommended in this report should be in place and operational on a daily basis during construction. LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page 7 Surficial unsuitable soils, including topsoil and loose to medium -dense weathered soils mantling the site, should be stripped down to the medium -dense to dense, fresh Kame terrace and/or lodgmont till soils within the building pads of the lots and the roadways. The underlying fresh Kame terrace and/or lodgmont till soils are of high to moderately -high to high strength and are capable of providing adequate foundation support to the proposed residential buildings, roadways and stormwater detention vault. Conventional footing foundations constructed on or into the above competent basal soils may be used to support the proposed residential building and stormwater detention vault. Structural fill, if required for site grading, should be placed on proof- rolled, roofrolled, underlying undisturbed, competent basal soils following the stripping of the surficial unsuitable soils. GEOLOGIC HAZARDS AND REMEDIATIN Landslide Hazard The medium -dense to dense, fresh Kame terrace and lodgmont till soils underlying the site at shallow depth are of moderately -high to high shear strength and have good to excellent resistance against slope failures. Therefore, it is our opinion that the potential for deep-seated landslides to occur on the site should be minimal, provided the recommendations in this report are fully implemented and complied with during construction. Erosion Hazard The topsoil and loose to medium -dense weathered soils are of low resistance against erosion. Erosion may occur in the weaker surficial soils over the higher gradient areas of the site if they are devoid of vegetation cover and overly saturated. Progressive erosion can lead to shallow, skin - type mudflows in the higher gradient areas of the site. To mitigate such erosion hazard, vegetation outside of construction limits should be preserved and maintained. Unpaved exposed ground within the site resulted from construction activities should be re -seeded and re -vegetated as soon as possible. Concentrated stormwater should not be discharged uncontrolled onto the ground within the site. Stormwater over impervious surfaces, such as roofs and paved roadways LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page S and driveways, should be captured by underground drain line systems connected to roof downspouts or by catch basins installed in paved roadways and driveways_ Water collected by these drain line systems should be tightlined to discharge into a storm sewer or a suitable stormwater disposal facility. Areas devoid of vegetation cover should be re -seeded and re - vegetated as soon as possible, and should be covered with clear plastic sheets until the vegetation is fully established. Seismic Hazard and Design Consideration The Puget Sound region is in an active seismic zone. The subject site is underlain at shallow depth by medium -dense to dense, fresh Kame terrace and lodgmont till soils of moderately -high to high shear strength. There is a lack of continuous, extensive, static groundwater table at shallow depth under the site. The combination of the above makes it rather unlikely for seismic hazards, such as landslides, liquefaction or soil lateral spreading, to occur on the site during strong earthquakes. Therefore, the seismic hazard of the site should be minimal. The residential buildings to be constructed on the site, however, should be designed to withstand seismic forces induced by strong earthquakes. Based on the soil conditions encountered by the test pits, it is our opinion that Seismic Use Group I and Site Class D should be used in the seismic design of the proposed residential buildings in accordance with the 2006 International Building Code (IBC). SITE PREPARATION AND GENERAL GRADING Vegetation within construction limits should be cleared and grubbed. Loose surficial soils, including topsoil and loose weathered soils, should be completely stripped down to the medium - dense to dense, fresh Karne terrace and/or lodgmont till soils within the building pads of the proposed residential buildings and roadways. The exposed soils should be compacted to a non - yielding state with a vibratory compactor and proof -rolled with a piece of heavy earthwork equipment. LW & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page 9 TEMPORARY EROSION CONTROL The onsite surficial soils contain a high percentage of fines, and are sensitive to moisture and can be disturbed easily by construction traffic when saturated. A layer of clean, 2 -to -4 -inch, quarry spalls should be placed over excavated areas and areas of frequent traffic, such as the entrance to the site, as required, to protect the subgrade soils from disturbance by construction traffic. Silt fences should be installed along the downhill sides of construction areas to prevent sediment from being transported onto adjoining properties or streets by storm runoff The bottom edge of silt fences should be folded inward and ballasted with onsite soils. Ditches or interceptor trench drains should be installed on the uphill sides of construction areas, as required, to intercept and drain away storm runoff and near -surface groundwater seepage. Water captured by such ditches or interceptor trench drains should be discharged into onsite detention/settling ponds or nearby storm inlets. The storm inlets, if into which stormwater is to be to be discharged, should be covered with a filter sock to prevent sediment from entering the storm sewer system_ The filter socks should be cleaned frequently during construction to prevent clogging, and should be removed after completion of construction. EXCAVATION AND FILL SLOPES Under no circumstance should excavation slopes be steeper than the limits specified by local, state and federal safety regulations if workers have to perform construction work in excavated areas. Unsupported temporary cuts greater than 4 feet in height should be no steeper than 1H: IV in topsoil, loose to medium -dense weathered Kame terrace and ablation till soils, no steeper than 3/4H: IV in medium -dense to dense Kame terrace deposits and may be vertical in lodgment -till soils if the overall depth of excavation is no more than 15 feet. Otherwise, temporary cut in lodgment till should be no steeper than 1/2H: IV. Unsupported permanent cuts should be no steeper than 2H:1 V in topsoil, loose to medium -dense weathered Kame terrace and ablation till soils, no steeper than 1-3/4H: IV in medium -dense to dense Kame terrace deposits, and no steeper than 1-1/2H:1V in lodgment till soils_ LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No, 9AO06 Page 10 A 5 -foot -wide level bench should be built into temporary or permanent cut slopes to keep the vertical rise between the benches no more than 15 feet. The soil units into which cut slopes and the stability of the cut slopes are to be made should be verified by a geotechnical engineer during excavation. Permanent fill embankments required to support structural or traffic load should be constructed with compacted structural fill placed over undisturbed, proof -rolled, firm, native, fresh Kame terrace and/or lodgment till soils after the surficial unsuitable soils are completely stripped. Permanent fill to be placed over slopes steeper than 15 percent grade should be retained structurally. The exposed ground exceeding 15 percent grade should be benched with vertical steps not exceeding 4 feet tall after stripping of surftcial unsuitable soils and prior to placing structural fill. The slope of permanent fill embankments should be no steeper than 2H:1 V_ Upon completion, the sloping face of permanent fill embankments should be thoroughly compacted to a non -yielding state with a hoe -pack. The above recommended cut and fill slopes are under the assumption that groundwater seepage would not be encountered during construction. If groundwater is encountered, the cut and fill earthwork should be immediately halted and the slope stability re-evaluated. The slopes may have to be flattened and other measures taken to stabilize the slopes. Stormwater should not allowed to flow uncontrolled over cut and fill slopes. Permanent cut slopes or fill embankments should be seeded and vegetated as soon as possible for erosion protection and long -terra stability, and should be covered with clear plastic sheets, as required, to protect them from erosion until the vegetation is fully established. STRUCTURAL FILL Structural fill is the fill that supports structural or traffic load. Structural fill should consist of clean granular soils free of organic, debris and other deleterious substances and with particles not larger than three inches. Structural fill should have a moisture content within one percent of its LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page 11 optimum moisture content at the time of placement. The optimum moisture content is the water content in the soils that enable the soils to be compacted to the highest dry density for a given compaction effort. Onsite clean silty sand to gravelly sand soils, meeting the above requirements, may be used as structural fill. Imported material to be used as structural fill should be clean, free -draining, granular soils containing no more than 5 percent by weight finer than the No. 200 sieve based on the fraction of the material passing No. 4 sieve, and should have individual particles not larger than three inches. The ground over which structural fill is to be placed should be prepared in accordance with recommendations in the SITE PREPARATION AND GENERAL GRADING and EXCAVATION AND FILL SLOPES sections of this report. Structural fill should be placed in lifts no more than 10 inches thick in its loose state, with each lift compacted to a minimum percentage of the maximum dry density determined by ASTM D1557 (Modified Proctor Method) as follows: Application Within building pads and under foundations Roadway/driveway subgrade Retaining/foundation wall backfill Utility trench backfill STORMWATER DETENTION VAULT % of Maximum Dry Density 95% 95% for top 3 feet and 90% below 92% 95% for top 4 feet and 90% below An underground concrete detention vault, designed to supplement onsite infiltration systems, is to be constructed at the northwest corner of the site to store stormwater collected over impervious surfaces of the proposed development of the site. Two test pits (Test Pits 5 and 6) were LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9A006 Page 12 excavated within the footprint of the proposed vault, and these test pits encountered dense lodgment till soils and/or medium -dense to dense fresh Dame terrace deposit at depths about 4.0 to 5.0 feet. The vault may be supported on footings founded on these competent basal soils. An allowable soil bearing pressure not exceeding 3,500 psf may be used for the design of the vault footing foundations. A drain line consisting of perforated, rigid PVC, drain pipe or slotted, corrugated ADS, drain pipe, at Ieast 6 inches in diameter, should be installed at a few inches below bottom of the perimeter footings of the vault walls to intercept and drain away groundwater which may flow towards the vault. The drain line should have sufficient slope (0.5% minimum) to generate flow by gravity, and water collected in the drain line should be tightlined to discharge into a storm sewer or a suitable stormwater disposal facility. The vault footing drain line should be completely embedded in washed gravel wrapped in a layer of non -woven filter fabric, such as 140N by Mirafi Inc. or approved equal_ A vertical drainage blanket at least 12 inches thick horizontally, consisting of clean 314 to 1 -112 -inch washed gravel or crushed rock, should be placed against the perimeter vault walls. The remaining backfill should be constructed of structural fill. Alternatively, a vertical drain mat, such as N iradrain 6000 by Mirafi Inc. or equivalent, may be placed against the perimeter vault walls as the vertical drainage blanket. The vertical drainage blanket or drain mat should be hydraulically connected to the drain line at the base of the vault perimeter walls. Sufficient number of cleanouts at strategic locations should be installed for periodical cleaning of the vault wall drain line to prevent clogging. The perimeter walls of the detention vault would also serve as retaining walls to support cut banks and backfill. The perimeter walls of the vault capped with a lid would be restrained at their top from horizontal movement and should be designed for at -rest lateral soil pressure. For the condition that groundwater behind the perimeter vault walls can be fully drained by the drain line provided at the base of the walls, we recommend an at -rest soil pressure of 50 pd equivalent fluid density (EFD) be used for the design of vault perimeter walls. To counter the at -rest soil LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9A006 Page 13 pressure, a passive lateral soil pressure of 375 pcf EFD may be used, except that the passive pressure within the top 12 inches of the finish subgrade should be ignored. The above passive pressure assumes the backslope of the walls is level or ascending away from the walls. The at -rest soil pressure may also be resisted by the friction force between the footings and the subgrade soils based on a coefficient of friction of 0.55. If the site grades are such that it is not feasible to completely drain groundwater behind the vault walls with a gravity drain line system, the hydrostatic pressure on the perimeter vault walls should also be taken into consideration for the design of the vault perimeter walls. For the condition that a perimeter drain line has to be placed higher than the footing level, the perimeter vault walls should be designed for a lateral soils pressure of 50 pcf EFD above the drain line level and a combined lateral soil and hydrostatic pressure of 80 pcf EFD below the drain line level. The above lateral pressures on the walls may be countered by a passive soil pressure of 375 pcf EFD above the drain line and 210 pcf EFD below. The detention vault should also be designed for seismic loading based on a 100 -year seismic event. For seismic design of the detention vault walls, a pseudo static soil pressure diagram of inverted triangle from the finished ground level to the bottom of the foundations should be used_ Based on the soil conditions in the detention vault area, we recommend the lateral soil pressure at the top of the triangle be 8H psf for a 100 -year seismic event, where H is the height from finish grade over top of the vault to bottom of footings in feet. A one-third increase in the above recommended allowable soil bearing pressure may be used when considering the seismic loading condition. The above design parameters are unfactored ultimate values. Proper factors of safety should be applied for the design of the vault walls against sliding and overturning failures. LIU & ASSOCIATES, INC, February 24, 2009 Wilson Plat L&A Job leo. 9AO06 Page 14 PAVED ROADWAYS AND DRIVEWAYS Performance of roadway and driveway pavement is critically related to the conditions of the underlying subgrade soils. We recommend that the subgrade soils under the roadways/driveways be treated and prepared as described in the SITE PREPARATION AND GENERAL EARTHWORK section of this report. Prior to placing base material, the subgrade soils should be compacted to a non -yielding state with a vibratory roller compactor and proof -rolled with a piece of heavy construction equipment, such as a fully4oaded dump truck. Any areas with excessive flexing or pumping should be over -excavated and re -compacted or replaced with structural fill or crushed rock placed and compacted in accordance with the recommendations provided in the STRUCTURAL FILL section of this report. We recommend that a Iayer of compacted, 7/8 -inch crushed rock base (CRB), be placed for the roadways/driveways. This crushed rock base should be at least 6 inches for the public roadways and 4 inches for the private driveways. The crushed rock base should be overlain with a 3 -inch asphalt treated base (ATB) topped by a 2 -inch -thick Class B asphalt concrete (AC) surficial course for public roadways and overlain by a 3 -inch -thick Class B asphalt concrete (AC) surficial course for the private driveways. BUILDING SETBACK The purpose of building setback from the top or toe or an overly steep portion of a slope is to establish a safe buffer such that if a slope failure should occur the stability of the structure can be maintained and damages to the structure minimized. In general, the greater the setback, the lower the risk for the structure to sustain damages from a slope failure. To maintain stability, the residential buildings to be constructed on the site should be sufficiently setback from the top or toe of slopes of 40% gradient or more. We recommend the buildings be set back at least 15 feet from top or toe of slopes with grades 40% or more. If footing foundations are used to support the new residences of future development, the footing LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page 15 foundations should be embedded at least one foot into the underlying, medium -dense to dense, fresh Kame terrace or lodgment till soils. If the buildings are to be constructed on the slopes with grades 40% or more, the footing foundations should be extended downward to such elevation that the horizontal distance from the edge of footings to the face of slopes should be at least 15 feet, and that a plane drawn from the edge of footings to the toe of slopes of 40% or more gradient sbould be no steeper than 2.511: IV. BUILDING FOUNDATIONS Conventional footing foundations may be used to support the residential buildings to be constructed on the site. The footing foundations should be placed on or into the underlying, medium -dense to dense, fresh Kame terrace or lodgmont soils, or on structural fill placed over these undisturbed competent basal soils. Water should not be allowed to accumulate in excavated footing trenches. Disturbed soils in footing trenches should be completely removed down to undisturbed, competent basal soils and the basal soils should be thoroughly compacted to a non - yielding state with a vibratory mechanical compactor prior to pouring concrete for the footings. If the above recommendations are followed, our recommended design criteria for footing foundations are as follows: * The allowable soil bearing pressure for design of footing foundations, including dead and live loads, should be no greater than 3,000 psf if constructed on or into native, undisturbed, competent basal soils, and no greater than 2,500 psf if constructed on structural fill placed over competent basal soils. The footing bearing soils should be verified by a geotechnical engineer after the footing trenches are excavated and before the footings poured. LIU & ASSOCIATES, INC, February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page 16 • The minimum depth to bottom of perimeter footings below adjacent final exterior grade should be no less than 18 inches. The minimum depth to bottom of the interior footings below top of floor slab should be no less than 12 inches. • The minimum width should be no less than 16 inches for continuous footings, and no less than 24 inches for individual footings, except those footings supporting light -weight decks or porches. A one-third increase in the above recommended allowable soil bearing pressure may be used when considering short-term, transitory, wind or seismic loads. For footing foundations designed and constructed per recommendations above, we estimate that the maximum total post -construction settlement of the buildings should be 314 inch or less and the differential settlement across building width should be 1/2 inch or less. Lateral loads on the proposed residential buildings may be resisted by the friction force between the foundations and the subgrade soils or the passive earth pressure acting on the below -grade portion of the foundations. For the latter, the foundations must be poured "neat" against undisturbed soils or backfilled with a clean, free -draining, compacted structural fill. We recommend that an equivalent fluid density (EFD) of 325 pcf (pounds per cubic foot) for the passive earth pressure be used for lateral resistance. The above passive pressure assumes that the backfill is level or inclines upward away from the foundations for a horizontal distance at least 1.5 times the depth of the foundations below the final grade. A coefficient of friction of 0.55 between the foundations and the subgrade soils may be used_ The above soil parameters are unfactored values, and a proper factor of safety should be used in calculating the resisting forces against lateral loads on the new garage. SLAB -ON -GRADE FLOORS Slab -on -grade floors, if used for the residential buildings to be constructed on the site, should be placed on firm subgrade soils prepared as outlined in the SITE PREPARATION AND LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page 17 GENERAL EARTHWORK and the STRUCTURAL FILL sections of this report. Where moisture control is critical, the slab -on -grade floors should be placed on a capillary break which is in turn placed on the compacted subgrade. The capillary break should consist of a minimum four - inch -thick layer of clean, free -draining, 718 -inch crushed rock, containing no more than 5 percent by weight passing the No_ 4. sieve. A vapor barrier, such as a 6 -mil plastic membrane, may be placed over the capillary break, as required, to keep moisture from migrating upwards. BASEMENT AND ClIP CONCRETE RETAL"NG WALLS Building basement walls would be required to support backfill. Cast -in-place concrete walls may be used to retain fill embankments along the west and part of the south boundaries of the site. Basement walls restrained horizontally at the top are considered unyielding and should be designed for a lateral soil pressure under the at -rest condition; while cast -in-place concrete retaining walls free to move at the top should be designed for active lateral soil pressure. We recommend that a lateral soil pressure of 55 pcf EFD be used for the design of basement walls restrained at the top; and 40 pcf EFD for retaining walls unrestrained at the top. These lateral soils pressures are applicable to walls with level backslope. With a backslope rising away from the walls, an additional pressure of 0.75 pcf per degree of angle of the backslope above horizontal should be added to the above pressures. To counter the active soil or at -rest pressure, a passive lateral soil pressure of 300 pcf EFD may be used, except that the passive pressure within the top 12 inches of the finish subgrade should be ignored. The above passive pressure is applicable to walls with level backslope. The above lateral soil pressures are under the assumption that groundwater behind the walls is fully drained. To resist against sliding, the friction force between the footings and the subgrade soils may be calculated based on a coefficient of friction of 0.55. The above soil parameters are ultimate values, and proper factors of safety should be used in the design of the basement and retaining walls against sliding and overturning failures. Basement walls or retaining walls may be supported on footing foundations seated on or into the underlying, medium -dense to dense, fresh Kame terrace or lodgment till soils, with an allowable soil bearing pressure not to exceed 3,000 psf. LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No, 9A006 Page 21 Design Soil Parameters We recommend that the precast concrete block walls to be constructed to support fill embankments be designed for a fully drained condition in accordance with the following soil perimeters: The block walls should be designed for a minimum factor of 1.5 against sliding failure and 1.7 against overturning failure under the static loading condition. The Puget Sound region is in an active seismic zone and the block walls should also be designed under the seismic loading condition for a 100 -year seismic event. The peak ground acceleration is about 0.39 (g = gravity force) for such an event in the Puget Sound region_ The block walls, however, are built with interlocking concrete blocks with relatively high flexibility, and the blocks do not move in unison during earthquakes. Therefore, for design of the block wail under the seismic loading condition, the ground acceleration may be reduced to 0.2g. The block walls should designed for a factor of safety of at least 1.15 against sliding and overturning failures under the seismic loading condition. Heavy equipment or material storage should not be allowed within 10 feet of the block walls; otherwise, the walls should be designed for 250 psf of uniform load. Construction of Precast Concrete Block Walls Vegetation within construction limits of the block walls and its backfill should be cleared and roots thoroughly grubbed. Unsuitable surficial soils, such as topsoil and loose to medium -dense weathered sand soils within the block walls and backfill footprint should be stripped down to the LIU & ASSOCIATES, INC. Reinforced Retained Foundation Leveling A5 Rock Base Unit Weight, Y, pcf 130 120 135 135 Angle of Internal Friction, 36 33 36 40 �, degrees Cohesion, c, psf 0 0 0 0 The block walls should be designed for a minimum factor of 1.5 against sliding failure and 1.7 against overturning failure under the static loading condition. The Puget Sound region is in an active seismic zone and the block walls should also be designed under the seismic loading condition for a 100 -year seismic event. The peak ground acceleration is about 0.39 (g = gravity force) for such an event in the Puget Sound region_ The block walls, however, are built with interlocking concrete blocks with relatively high flexibility, and the blocks do not move in unison during earthquakes. Therefore, for design of the block wail under the seismic loading condition, the ground acceleration may be reduced to 0.2g. The block walls should designed for a factor of safety of at least 1.15 against sliding and overturning failures under the seismic loading condition. Heavy equipment or material storage should not be allowed within 10 feet of the block walls; otherwise, the walls should be designed for 250 psf of uniform load. Construction of Precast Concrete Block Walls Vegetation within construction limits of the block walls and its backfill should be cleared and roots thoroughly grubbed. Unsuitable surficial soils, such as topsoil and loose to medium -dense weathered sand soils within the block walls and backfill footprint should be stripped down to the LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page 22 medium -dense to dense, fresh Kame terrace and/or lodgment till soils. Over -excavation down to these competent basal soils should be backfilled with structural fill. The keyway trench for the block walls should be cut into native, undisturbed, medium -dense to dense, fresh Kame terrace and/or lodgment till soils, capable of rendering an allowable bearing pressure of at least 3,000 psf. The soils exposed at bottom of the keyway trench should be compacted to a non -yielding state with a vibratory compactor. A minimum 4 -inch layer of 7/8 - inch -minus crushed rock leveling base, compacted to a non -yielding state, should be placed over firm subgrade soils supporting the block walls. The base -course blocks are to be placed on this crushed rock base with an embedment at least 10 inches below the adjacent finish grade in front of the block wall_ The precast concrete blocks should be stacked tightly against one another. A minimum 6 -inch perforated, rigid, PVC drain line fitted in a non -woven filter fabric sock should be laid in the keyway trenches behind the base -course blocks. The bottom of keyway trenches and the drain line should have sufficient slope (0.5 percent minimum) to generate flow by gravity. The drain pipes should be tightlined to discharge into a storm sewer or a suitable stormwater disposal facility. A minimum 10 -inch -thick (horizontally) vertical drainage blanket, constructed of clean 3/4 to 1 -1/2 -inch washed gravel crushed rock, should be placed against the back of the block wall facing. The vertical drainage blankets should be hydraulically connected to the drain lines at the base behind the block walls. The wall backfill behind the vertical drainage blankets should consist of structural fill. The vertical drainage blanket and structural fill should be constructed in lifts after each course of blocks is completed. Each layer of geogrid mesh should be laid on level backfill surface, with one end securely anchored between two rows of concrete blocks, stretched tight, and the other end staked down prior to the placement of the next lift of wall backfill. Overlaps of geogrid mesh in the direction of the wall alignments should be at least 12 inches, overlaps in the direction perpendicular to the wall alignments should not be allowed. LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page 24 The infiltration trenches should be set back at least 10 feet from adjacent buildings and 5 feet from property lines. The schematic presentation of an infiltration trench with a single dispersion pipe to serve the residential buildings is shown on Plate 9. The infiltration trenches should be at least 24 inches wide. The bottom of infiltration trenches should be excavated at least 6 inches into the underlying clean, fresh, gravelly sand Kame terrace deposit. The side walls of the trenches should be lined with a layer of non -woven filter fabric. The trench is then filled with clean 314 to 1 -1/2 - inch washed gravel or crushed rock to within about 8 inches of the finish grade_ The dispersion pipes should be constructed of 4 -inch rigid or 6 -inch flexible perforated PVC pipes and laid level in the gravel or crushed rock filled trenches at about 16 inches below the top of trenches. The top of the gravel or crushed rock fill should also be covered with the filter fabric liner. The remaining trench should then be filled with compacted on-site soils. Stormwater captured over impervious surfaces should be routed into a sediment control structure/oil-water separator structure before being released into the infiltration trenches. Building Footprint Excavation Building footprint excavation for the proposed residential buildings, if encountering groundwater seepage, should have the bottom of excavation sloped and ditches excavated along bases of the cut banks to direct collected groundwater into sump pits from which water can be pumped out. A layer of 2 -inch crushed rock should be placed over footing bearing subgrade soils, as required, to protect the soils from disturbance by construction traffic. This crushed rock base should be built to a few inches above groundwater level, but not less than 6 inches thick. The crush rock base should be compacted in 12 -inch lifts to a non -yielding state with a vibratory mechanical compactor. Runoff over Impervious Surfaces Storm runoff over impervious surfaces, such as roofs and paved roadways/driveways, should be collected by underground drain line systems connected to downspouts and by catch basins LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9A006 Page 25 installed in paved roadways/driveways- Stormwater thus collected should be tightlined to discharge into a storm sewer or suitable stormwater disposal facilities. Building Footing Drains A subdrain should be installed, around the perimeter footings of each of the residential buildings. The subdrains should consist of a 4 -inch -minimum -diameter, perforated, rigid, drain pipe, laid a few inches below bottom of the perimeter footings of the buildings. The trenches and the drain lines should have a sufficient gradient (0.5% minimum) to generate flow by gravity_ The drain lines should be wrapped in a non -woven filter fabric sock and completely enclosed in clean washed gravel. The remaining trenches may be backfilled with clean onsite soils. Water collected by the perimeter footing subdrain systems should be tightlined, separately from the roof and surface stormwater drain lines, to discharge into a storm sewer or suitable stormwater disposal facility. Surface Drainage Water should not be allowed to stand in any areas where footings, on -grade slabs, or pavement is to be constructed. Finish ground surface should be graded to direct surface runoff away from the residential buildings. We recommend the finish ground be sloped at a gradient of 3 percent minimum for a distance of at least 10 feet away from the buildings, except in the areas to be paved. Cleanouts Sufficient number of clea.nouts at strategic locations should be provided for underground drain lines. The underground drain lines should be cleaned and maintained periodically to prevent clogging. LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9AO06 Page 26 RISK EVALUATION STATEMENT The subject site is underlain at shallow depth by medium -dense to dense Kame terrace and/or lodgmont till soils. These soils are of moderately -high to high shear strength and groundwater was not encountered by the test pits excavated on the site. Therefore, the site should be quite stable. The key to maintain site stability during and after completion of construction is to have proper and adequate erosion and drainage controls. It is our judgment that provided the recommendations in this report are fully implemented and observed during construction, the areas disturbed by construction will be stabilized and will not increase the potential for soil movement. In our opinion, the risk of damage to the proposed development and from the development to adjacent properties due to soil instability should be minimal. LIMITATIONS This report has been prepared for the specific application to this project for the exclusive use by Mr. Robert Wilson and his associates, consultants and contractors. We recommend that this report, in its entirety, be included in the project contract documents for the information of the prospective contractors for their estimating and bidding purposes and for compliance with the recommendations in this report during construction. The conclusions and interpretations in this report, however, should not be construed as a warranty of the subsurface conditions. The scope of this study does not include services related to construction safety precautions and our recommendations are not intended to direct the contractor's methods, techniques, sequences or procedures, except as specifically described in this report for design considerations. Our recommendations and conclusions are based on the geologic and soil conditions encountered in the test pits, and our experience and engineering judgment_ The conclusions and 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 this area. No warranty, expressed or implied, is made. LIU & ASSOCIATES, INC, February 24, 2409 Wilson Plat L&.A Job No. 9A006 Page 27 The actual subsurface conditions of the site may vary from those encountered by the test pits excavated on the site. The nature and extent of such variations may not become evident until construction starts. If variations appear then, we should be retained to re-evaluate the recommendations of this report, and to verify or modify them in writing prior to proceeding further with the construction of the proposed development of the site. CLOSURE We are pleased to be of service to you on this project_ Please feel free to call us if you have any questions regarding this report or need further consultation. Nine plates attached ) S. EXPIRES 7/17/ Yours very truly, LIU GCIATES, INC. J_ S. (Juli n) Liu, Ph.D., P.E. Consulting Geotechnical Engineer LIU & ASSOCIATES, INC. 'T� yaps �'7,7�SE 174TH PL J SE -' ��}•"r."^'�C •RU� > a 190TH.'.X 5E�F `. (SE 18VT I 1TI ST) 5ST Bni pp, 90TH SE F J 1.�� .�ivi S�-���' ..=- !�, SE '7 182ND �, sE 32 ��5� 183RD 3� 5T .o +� .., 184TH 1� o a 16aPD cT SE PL 'a t r V�4 ST. _ SE 184TH 184TH z I Qy r a LN PL ils + t :t T. N sE 185TH p1 wH SE 8b - -..Q1 SL 187TH ST ST H SE g S S 188TH S7 m .li ,�; CSE 167TH ` w - se 1 ST 4 SE a R sE 100TH r� P~ tg7 I cr PROJECT ST 54 1 T( � s u �t h T s iso SITE sE d SE 189TH ST r 1�T �. . SE 19arH� ST 9L sE 190TH ST 1agTH ~ sr ry 190TH P t SE sE 190 H PL y SID ND ST H � 190TH PLa T �.rJ . 4r .' - .r. 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WILSON PLAT 720 SOUTH 55TH STREET Geotechnical Engineering • Engineering Geology • Earth Science RENTON, WASHINGTON JOB NO_ 9A006 TDATE 9/1 212 00 9 1 PLATE 1 60OZ/Z 616 3iVG I 90046 -ON 90f NOIJNIHSVM `NO1N3�1 133HIS H1g5 Hinos OZL lb'ld NOSIIM Nbrld NOUVOOl NOUVb 10ldX3 (INV 3115 8 Ly 00 -os o0 71 \ IaS£ fl" r,n i f ti � } aoua$og Aboloao Buuaau U3 leoiupa}oaE) 03M `SaZVIDOSSV v IlIZ Pqp�3A 0££ J J J O dglo.ae�r�.r �9f �77VM 138 '.)NO,) 4 y OZ£ n -T' fZoN �- 19-4 77 V) tx 90f -off` �Q4 N L r _ —ODMs _ —� — _ _ J 300 OOH L — 1-1 — — — J I 11 11�9E y/� C'—�4a0�—� JT- �ea z£ z—I- DLZ�_ 69 / (�= —gsz- zcz o�Oz xzr,s/L,oj` . a 0 '3's V1 Ys ;9ZS 3 W 'M 4q 3 2h3� tib. .pox l'ilo1z" r 99 Zge �� 1 �k ry 9SZ _ bsz rsz z£z u7 � !1 r fry w z o J 00£ 77VM 4011 3[38. N00 i l'ilo1z" r 99 Zge �� 1 �k ry 9SZ _ bsz rsz z£z UNIFIED SOIL CLASSIFICATION SYSTEM NOTES: SOIL MOISTURE MODIFIERS. 1. FIELD CLASSIFICATION IS BASED ON VISUAL EXAMINATION DRY - ABSENCE OF MOISTURE, DUSTY, DRY TO OF SOIL IN GENERAL ACCORDANCE WITH ASTM D2488-83. THE TOUCH 2. SOIL CLASSIFICATION USING LABORATORY TESTS IS BASED SLIGHTLY MOIST - TRACE MOISTURE, NOT DUSTY ON ASTM D2487-83. MOIST - DAMP, BUT NO VISIBLE WATER 3. DESCRIPTIONS OF SOIL DENSITY OR CONSISTENCY ARE VERY MOIST - VERY DAMP, MOISTURE FELT TO THE TOUCH BASED ON INTERPRETATION OF BLOW -COUNT DATA, VISUAL WET -VISIBLE FREE WATER OR SATURATED, APPEARANCE OF SOILS, ANDIOR TEST DATA. USUALLY SOIL IS OBTAINED FROM BELOW WATER TABLE LIU & ASSOCIATES, INC. Geotechnical Engineering - Engineering Geology • Earth Science UNIFIED SOIL CLASSIFICATION SYSTEM PLATE 3 MAJOR DIVISIONS GROUP GROUP NAME SYMBOL GRAVEL CLEAN GW WELL -GRADED GRAVEL, FINE TO COARSE GRAVEL COARSE- MORE THAN 50% OF GRAVEL GP POORLY -GRADED GRAVEL GRAINED COARSE FRACTION GRAVEL WITH GM SILTY GRAVEL SOILS RETAINED ON NO. 4 SIEVE FINES GC CLAYEY GRAVEL SAND CLEAN SW WELL -GRADED SAND, FINE TO COARSE SAND MORE THAN 50% MORE THAN 50% OF SAND SP POORLY -GRADED SAND RETAINED ON THE COARSE FRACTION SAND WITH SM SILTY SAND NO. 200 SIEVE PASSING NO. 4 SIEVE FINES SC CLAYEY SAND FINE- SILT AND CLAY INORGANIC ML SILT GRAINED LIQUID LIMIT CL CLAY SOILS LESS THAN 50% ORGANIC OL ORGANIC SILT, ORGANIC CLAY MORE THAN 50% SILTY AND CLAY INORGANIC MH SILT OF HIGH PLASTICITY, ELASTIC SILT PASSING ON THE LIQUID LIMIT CH CLAY OF HIGH PLASTICITY, FAT CLAY NO. 200 SIEVE 50% OR MORE ORGANIC OH ORGANIC SILT, ORGANIC SILT HIGHLY ORGANIC SOILS PT PEAT AND OTHER HIGHLY ORGANIC SOILS NOTES: SOIL MOISTURE MODIFIERS. 1. FIELD CLASSIFICATION IS BASED ON VISUAL EXAMINATION DRY - ABSENCE OF MOISTURE, DUSTY, DRY TO OF SOIL IN GENERAL ACCORDANCE WITH ASTM D2488-83. THE TOUCH 2. SOIL CLASSIFICATION USING LABORATORY TESTS IS BASED SLIGHTLY MOIST - TRACE MOISTURE, NOT DUSTY ON ASTM D2487-83. MOIST - DAMP, BUT NO VISIBLE WATER 3. DESCRIPTIONS OF SOIL DENSITY OR CONSISTENCY ARE VERY MOIST - VERY DAMP, MOISTURE FELT TO THE TOUCH BASED ON INTERPRETATION OF BLOW -COUNT DATA, VISUAL WET -VISIBLE FREE WATER OR SATURATED, APPEARANCE OF SOILS, ANDIOR TEST DATA. USUALLY SOIL IS OBTAINED FROM BELOW WATER TABLE LIU & ASSOCIATES, INC. Geotechnical Engineering - Engineering Geology • Earth Science UNIFIED SOIL CLASSIFICATION SYSTEM PLATE 3 TEST PIT NO. 1 Logged By: JSL Date, 2/4/2009 Ground El. + Depth ft. USCS CLASS. Soil Description Sample No. W % Other Test OL Fern bushes and duff on surface Dark -brown, loose, organic, silty fine SAND, with roots to 114 -inch diameter, moist (TOPSOIL) 2 SM Brown, medium --dense, sElty fine SAND, fr—a cW gravel and abundant — roots, moist 3 (ABLATION TILL) 4 — -- -------------------------- 5 SM Brown, dense, silty fine SAND, trace to some gravel, very -weakly - cemented, moist (LODGMONT TILL) 6 7 S 9 Test pit terminated at 8.5 ft, groundwater not encountered_ 10 TEST PIT NO. 2 Logged By: JSL Date: 2/4/2009 Ground EI. # Depth USCS Sample W Other ft. CLASS. soil Description No. % Test OL Berry bushed and duff on surface 1 Dark -brown, loose, organic, silty fine SAND, with roots to 314 -inch diameter, moistiTOPSQILj. — _ _ _ _ _ _ _ _ _ _ 2 SM Brown, medium -dense, silty, fine to medium SAND, with trace — T gravel and cobble and abundant roots, moist 3 (KAME TERRACE) 4 SM Brown -gray, dense, silty fine SAND, some gravel and occasional T 6 cobble, very -weakly -cemented, moist (LODGMONT TILL) 7 8 9 Test pit terminated at 7,5 ft, groundwater not encountered, 10 TEST PIT LOGS LIU & ASSOCIATES, INC. WILSON PLAT 720 SOUTH 55TH STREET Geotechnical Engineering - Engineering Geology_ Earth Science RENTON, WASHINGTON JOB No. 9AO06 I DATA= 9/10/20091 PLATE 4 Logged By: JSL TEST PIT NO. Date: 2/4/2009 I Ground EI. ± Depth USCS Sample W Other ft. CLASS. Soil Description No. % Test OL Berry bushes on surface 1 Dark -brown, loose, organic, silty fine SAND, with fine roots, moist — — (TOPSOIL) 2 SP ` f Frown, la'ose,graveAy,'fine tomedium SAN 7�, slightly moist (weathered KAME TERRACE) SP t-gra Lighy, medi-ur er se to dense, fine to medium SAND, trace 4 gravel, slightly moist (KAME TERRACE) 5 B 7 8 Test pit terminated at 6.5 ft, groundwater not encountered. 9 10 TEST PIT NO. 4 Logged By: JSL Date: 2/4/2009 Ground El. ± Depth USCS Sample W Other ft. CLASS. Soil Description No. % Test OL Berry bushes on surface t Dark -brown to black, loose, organic, silty fine SAND, with roots to 112 -inch diameter, moist (TOPSOIL) 2 SMISP Brown, loose to medium dense, sGgdtly silty, fine to medium — s SAND, few roots, slightly moist (weathered KAME TERRACE) 4 SP Brown -gray, medium -dense to dense, fine to medium SAND, moist 5 (KAME TERRACE) 6 7 9 Test pit terminated at 7.0 ft, groundwater not encountered. 10 TEST PIT LOGS LIU & ASSOCIATES, INC, WILSON PLAT 720 SOUTH 55TH STREET Geotechnical Engineering - Engineering Geology - Earth Science RENTON, WASHINGTON JOB NO. 9A00$ I DATE 911012009 FpLATE 5 Logged By; JSL TEST PIT NO. Date: 2/4/2009 5 Ground EI. t Depth USCS Sample W Other ft. CLASS. Soli Description No. % Test OL Ivy on,surface _ _ Dark -brown to black, loose, organic, silty fine SAND, with fine roots, moist (TOPSOIL) — 2 SM/Sp Brawn, medium -dense to dense,silty to slightly silty, fine SAND, trace gravel, moist (KAME TERRACE) 3 4 5 SM Brown -gray, dense, sffty fine SAND, trace gavel, very -weakly- 6 cemented, moist (LODGMONT TILL) 7 8 9 Test pit terminated at 8.0 ft, groundwater not encountered. 10 TEST PIT NO. 6 Logged By JSL Date: 2/4/2009 Ground El. t Depth USCS Sample W Other ft. CLASS. Soil Description No. % Test OL Brush on surface 1_ _ Dark -brown, loose, organic, silty fine SAND, with roots to 112 -inch SMISP -1diameter, moist (TOPSOIL) 2 Brown, med urF--dense, sli htl—y si! fine tc medium SAND, trace 9 Y ty, — — — — — gravel, moist (weathered KAME TERRACE) 3 4 SP Light -gray, medium -dense to densefne to medium SAND, trace — 5 gravel, moist (KAME TERRACE) s 7 8 9 Test pit terminated at 8.0 ft, groundwater not encountered. 10 TEST PIT LOGS LIU & ASSOCIATES, INC, WILSON PLAT 720 SOUTH 55TH STREET Geotechnical Engineering - Engineering Geology , Earth Science RENTON, WASHINGTON JOB NO. 9A008 I DATE 9/10/2009 PLATE 6 TEST PIT NO. 7 LIU & ASSOCIATES, INC. Geotechnical Engineering - Engineering Geology - Earth Science TEST PIT LOGS WILSON PLAT 720 SOUTH 55TH STREET RENTON, WASHINGTON JOB NO. 9AO06 I DATE 9/10/2009 FP7TE 7 Logged By: JSL Date: 2/4/2009 Ground El. + Depth USCS Sample W Other ft. CLASS. Soil Description No. % Test OL Brush and duff on surface 1 — — Dark -brawn, loose, organic, silty fine SAND, with fine roots, SMISP _ I moist (TOPSOIL) I 2 frown, Inose to medium' -dense, sligffl silty, fine to medium SAND, trace gravel, slightly moist (weathered KAME TERRACE) 3 4 -- ------------------------------ SP Brown -gravel, medium -dense to dense, gravelly, fine to medium SAND, moist (KAME TERRACE) 6 7 8 9 SM Light-gray, dense, silty Fine SAND, trceato some gravel, 10 very -weakly -cemented, moist (LODGMONT TILL) 11 Test pit terminated at 9.5 ft, groundwater not encountered. 12 TEST PIT NO. Logged By. Date: _ Grnrrnri FI + LIU & ASSOCIATES, INC. Geotechnical Engineering - Engineering Geology - Earth Science TEST PIT LOGS WILSON PLAT 720 SOUTH 55TH STREET RENTON, WASHINGTON JOB NO. 9AO06 I DATE 9/10/2009 FP7TE 7 ex (s -r, . % I a IZ11 !Mils, -JE r� 1 mItj� . LpM PAG'��P or151TE ori (: Ibit -0H rC.k ) ODr4 -u1oJc�;t! r -c LTA �AE5f2( C., T&PAk DfZA,14 KoG�, err 600(ZSI✓ (�jI TO ,rzd c,K 6 rA(�L_ �--1 Lt�) MEN, F�- PVC D A•l�I FIFO l=iTTG-p tom!1 A I✓1C-Tgol� Fp.&KI C �pc iC NOTES: 1. Rockery construction shall comply with Standard Rockery Construction Guidelines published by the Association of Rockery Contractors. 2. Rock material shall be hard, well -cemented, sound, durable and free of cracks, fissures, air boles and other defects. 3. Rockery construction shall start immediately following completion of cut banks and keyway trenches. 4_ Drain lines shall consist of 6 -inch minimum, perforated, rigid, PVC pipes fitted with a filter fabric sock. Keyway trenches and drain lines shall have sufficient slope (0.5% minimum) to generate flow by gravity_ 5. Keyway trenches shall be at least 12 inches deep and free of loose soils and standing water. Base -course facial stones shall be placed on firm, undisturbed soils with an allowable bearing pressure at least 3,000 psf. 6. Facial stones shall be as nearly rectangular as possible and stacked tightly against one another to minimize voids between rocks. Excessive voids shall be chinked with smaller rocks from behind. 7. Each facial stone shall be firmly supported on the stones below_ Facial stones shall be tilted back at a slope no steeper than 6V:1 H. S. Drain rock shall consist of 2 -to -4 -inch quarry spalls, placed in lifts after completion of each course of facial stones. ROCK SIZE AND WEIGHT SCHEDULE ROCKERY FACIAL. STCINF S( -MF :nt rr F Rode Size Weight, Pounds Avg. Dimension, Ft. Small to Large 1 -Man 50-200 0.75-1-25 Small to Large 2 -Man 200-700 1,25-2.0 Small to Large 3 -Man 700-2000 2.0-2,75 Small to Large 4 -Man 2000-4000 2.75-3.5 5 -Man 4000-6000 4.0-4.5 6 -Man 6000-8000 4.5 TQ 5.0 LIU & ASSOCIATES, INC. Geotechnical Engineering - Engineering Geology - Earth Science Wall Height Facial Stone Size H, Ft. Base Course Lower Third Middle Third Upper Third 4 S 3 -Man L to S 2 -Man L to S 1 -Man L to S 1 -Man 6 Large 3 -Man Small 3 -Man L to S 2 -Man L to S 1 -Man 8 Small 4 -man Large 3 -Man L to S 3 -Man L to S 2 -Man 10 Large 4 -Man Small 4 -man Large 3 -Man L to S 3 -Man 12 Small 5 -Man L to S 4 -man Small 4 -Man L to S 3 -Man 14 Large 5 -Man Large 4 -man L to S 4 -Man Large 3 -Man 16 L to S 6 -Man L to S 5 -man L to S 4 -Man Large 3 -Man TYPICAL SECTION - ROCKERY LINING CUT BANK WILSON PLAT 720 SOUTH 55TH STREET RENTON, WASHINGTON PLAN VIEW NTS 4" rigid or 6" flexible perforated pipe - ---- •- ------- in filtrati on trench PLAN VIEW NTS overflow 4" rigid or 6" flexible splash block perforated pipe V:. ------ ----------------------------------- J1. ---------------------------------- iwashed rock — 1 112"-314" o no fine mesh screen varies A k 6 a -wove# com PA4-[C-_P P I [.TER FpRL,Rl G ��,GiCF[LI. roof drain sump wlsolid lid roof drain 5-0' CB sump wlsolid lid LIU & ASSOCIATES, INC. Geotechnical Engineering - Engineering Geology • Eacth Scic= INFILTRATION TRENCH -- SINGLE DISPERSION PIPE WILSON PLAT 720 SOUTH 55TH STREET RENTON, WASHINGTON JOB NO- 9Aa06 I SATE 2/18/2009 PLATE 9 } d 0 �, 0 p lam"xr �t-E wed a �7 '0 '40 ❑ f I'[P'v v Iq{] kf�.sEf�v K041 {r •P = f of 3/�}-" I1/ GL.� � 24".r�,t�. Sods SECTION A NTS LIU & ASSOCIATES, INC. Geotechnical Engineering - Engineering Geology • Eacth Scic= INFILTRATION TRENCH -- SINGLE DISPERSION PIPE WILSON PLAT 720 SOUTH 55TH STREET RENTON, WASHINGTON JOB NO- 9Aa06 I SATE 2/18/2009 PLATE 9 Section 7: Other Permits City of Renton permits needed to finalize construction: • Electrical Permit to install Street Lighting System • Franchise Utility permits to cross South 551h Street • Building permit for: o Retaining Wall over 4' in height o Stormwater vault • Right of Way Use permit to connect to existing water system (Soon Creek) Others Section 8: CSWPPP Analysis and Design The proposed development consists of 4.62 acres of developed area. A DQE NPDES permit and SWPPP will be required for this development at the time of construction. The Owner, Robert Wilson, is planning to sell the property prior to issuance of the utility permits. The new buyer will be required to obtain and provide the necessary permits from the Department of Ecology. A temporary storage facility (pond) has been shown to be installed to reduce runoff during the construction period. This pond was sized using the 2 year storm event, from the KCRTS model. The calculations are attached to this section. A Certified Erosion Control Expert will be required by the DOE permit. This Expert will be needed during construction verify if the erosion control is adequate during construction. The erosion control shown on the approved plans is not intended to be the only improvements necessary to reduce and/or eliminate silt -laden runoff from leaving the project. Additional erosion control will be required as construction is phased and weather conditions change. Wilson Park & Park 2 TESC pond sizing j Area _ J Till Forest! 4.61 acres Till Pastured 0.00 acres Till Grass{ 0.00 acres! Outwash Forest= 0.00 acres' Outwash Pastare� 0.00 acres! Outwash Grass, 8.00 acres Wetlandi 0.00 acres; Impervious; 0.00 acres/ FTota1._.__._ _..... 4.61 acres; Scale Factor: 1,00 15 -Min Reduced Time Series: Wilson TESC sizing ?? Compute Time Series Modify User Input File. for computed Time Series I.TSFI '" Heb► ! Fitea KCR T :.` .. Flow Frequency Analysis Time Series File:wilson test Project i.ocation:Sea-Tac Prob ---Annual Peak Flaw bates ---- Flow Rate Rank Time of Peak (CFS) 0.990 0.300 2 2/09/01 17:15 0,096 7 1/06/02 2:30 0.213 4 3/06/03 18:45 0.011 8 3/08/04 18:45 0.143 6 1/05/05 7:30 0.231 3 1/18/06 20:15 0.196 5 11/24/06 5:15 0.505 1 1/09/08 9:30 Computed Peaks 0.231 sizing. tsf ------Flow Frequency Analysis _------ - - Peaks - - Rank Return Prob (CFS) Period 0.505 1 100.00 0.990 0.300 2 25.00 0.960 0.231 3 10.00 0.900 0.213 4 5.00 0.800 0.196 5 3.00 0.667 0.143 6 2.00 0.500 0.090 7 1.30 0.231 0.011 8 1.10 0.091 0.437 50.00 0.980 - LEJ3 JI A �/ s �rb - "I-- fD �) I Avv1 screra. a. o. ooz7 0.1 O rt vS� 2N� Section 9: Bond Quantities, Facility Summaries, and Declaration of Covenant Bond Quantity Worksheet • Declaration of Covenant for Inspection and Maintenance BOND QUANTITY WORKSHEET Z K cn ro m o °n y� ❑ 0z z m O O m Z M M v Z I sw O z D G) z u m -4 r- T M m b an � - my CD 00 T M Q, mo y � � z as r- z (D 6) v r �I r+ 0 3 0 [Q 3 CD !T W 0 Q �-h �s 1 0 fA 0 0 i --F X C X. fD Q 3 = o 0 n' m 3 ° N CL @ Pe o' 7 3 fD oa A3 m 0 m CD 3 3 CD 0 P. 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Cl 0 0 0 0 • � o m oho o cr 0- Q C] C] C7 C] O O C7 0 p o O o O 0 O O o o - C C 0 0 4 4 4 4 4 4 ...00 C 61 � y m� O 0 C. 0 0 0 0 0 0 0 0 4 4 4 4 4 0. 4 0 0 C7 4 4 o O O O cs 0 cq C7 C CD m m o a M so a e 0 N = C C C C C7 4 C 4 4 Q 00 0 0 0 0 0 C. 0 0 - 0 0 0 0 0 0 0 0 4 4 4.. 4 V / CD 3 O CDC 3 CDO 3 CL C 3 O 1 '77'h V• 3 CD CD DECLARATION Of COVENANT RECORDING REQUESTED BY AND WHEN RECORDED MAIL TO: CITY CLERK'S OFFICE CITY OR RENTON 1055 SOUTH GFADY WAY RENTON, WA 98057 DECLARATION OF COVENANT FOR INSPECTION AND MAINTENANCE OF STORMWATER FACILITIES AND BMPS Grantor: Grantee: City or Renton 4 �p� r� Legal Description: cM "[ ! Additional Legal(s) on: Assessor's Tax Parcel ID#: Ze72 0?7?zO t f Ll IN CONSIDERATION of the approved City or Renton A 11; permit for application file No. LUA/SWP V P? - Zj (pf7 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 or Renton, a political subdivision 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 10 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 stormwater facilities and best management practices ("BMPs") identified in the plans and specifications submitted to King County for the review and approval of permit(s) 4: . Stormwater facilities include pipes, swales, tanks, vaults, ponds, and other engineered structures designed to manage stormwater on the Property. Stormwater BMPs include dispersion and infiltration devices, native vegetated areas, permeable pavements, vegetated roofs, rainwater harvesting systems, reduced impervious surface coverage, and other measures designed to reduce the amount of stormwater runoff on the Property. 2. City or 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 other activities specified in this Declaration of Covenant and in accordance with RMS 4-6-030. This right of ingress and egress, right to inspect, and right to perform required maintenance or repair as provided for in Section 3 below, shall not extend over those portions of the Property shown in Exhibit "A." 3. If City of Renton determines that maintenance or repair work is required to be done to any of the stormwater facilities or BMPs, City of Renton shall give notice of the specific maintenance and/or repair work required pursuant to RMC 4-6-030. The City shall also set a reasonable time in which such work is to be completed by the Owners. If the above required maintenance or repair is not completed within the time set by the City, the City may perform the required maintenance or repair, and hereby is given access to the Property, subject to the exclusion in Paragraph 2 above, 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 maintenance and/or repair work will begin immediately. 4. If at any time the City of Renton reasonably determines that a stormwater facility or BMF on the Property creates any of the hazardous conditions listed in ICC 9.04.130 or relevant municipal successor's codes as applicable and herein incorporated by reference, The City may take measures specified therein. 5. The Owners shall assume all responsibility for the cost of any maintenance or repair work completed by the City as described in Paragraph 3 or any measures taken by the County to address hazardous conditions as described in Paragraph 4. Such responsibility shall include reimbursement to the County within thirty (30) days of the receipt of the invoice for any such work performed. Overdue payments will require payment of interest at the current legal rate as liquidated damages. If legal action ensues, the prevailing party is entitled to costs or fees. 6. The Owners are hereby 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 stormwater facilities and BMPs referenced in this Declaration of Covenant. 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 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 Stormwater Facilities and BMPs is executed this day of 120 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 SECTION C.2 FLOW CONTROL BMPs 3. The depression overflow point must be at least 6 inches below any adjacent pavement area and must be situated so that overflow does not cause erosion damage or unplanned inundation. 4. The depression side slopes must be no steeper than 3 horizontal to 1 vertical. 5. Spacing between multiple infiltration depressions shall be a minimum of 4 feet. 6. Infiltration depressions must be setback at least IS feet from buildings with crawl space or basement elevations that are below the overflow point of the infiltration depression. 7. Infiltration depressions may be any size or shape provided the above specifications and the minimum requirements in Section C.2.2.1 are met. 8. The ground surface of the infiltration depression must be vegetated with grass or other dense ground cover. 0.2.2.6 MAINTENANCE INSTRUCTIONS FOR FULL INFILTRATION If the full infiltration flow control BMP is proposed for a project, the following maintenance and operation instructions must be recorded as an attachment to the required declaration of covenant and grant of easement per Requirement 3 of Section C.1.3.3 (p. C-18). The intent of these instructions is to explain to future property owners, the purpose of the BMP and how it must be maintained and operated. These instructions are intended to be a minimum; DDES may require additional instructions based on site- specific conditions. Also, as the County gains more experience with the maintenance and operation of these BMPs, future updates to the instructions will be posted on King County's Surface Water Design Manual website. ❑ TEXT OF INSTRUCTIONS Your property contains a stormwater management flow control BMP (best management practice) called "full infiltration," which was installed to mitigate the stormwater quantity and quality impacts of some or all of the impervious surfaces on your property. Full infiltration is a method of soaking runoff from impervious area (such as paved areas and roofs) into the ground. If properly installed and maintained, full infiltration can manage runoff so that a majority of precipitation events are absorbed. Infiltration devices, such as gravel filled trenches, drywells, and ground surface depressions, facilitate this process by putting runoff in direct contact with the soil and holding the runoff long enough to soak most of it into the ground. To be successful, the soil condition around the infiltration device must be reliably able to soak water into the ground for a reasonable number of years. The infiltration devices used on your property include the following as indicated on the flow control BMP site plan: ❑ gravel filled trenches, ❑ drywells, ❑ ground surface depressions. The size, placement, and composition of these devices as depicted by the flow control BMP site plan and design details must be maintained and may not be changed without written approval either from the King County Water and Land Resources Division or through a future development permit from King County. Infiltration devices must be inspected annually and after major storm events to identify and repair any physical defects. Maintenance and operation of the system should focus on ensuring the system's viability by preventing sediment -laden flows from entering the device. Excessive sedimentation will result in a plugged or non-functioning facility_ If the infiltration device has a catch basin, sediment accumulation must be removed on a yearly basis or more frequently if necessary. Prolonged ponding around or atop a device may indicate a plugged facility. If the device becomes plugged, it must be replaced. Keeping the areas that drain to infiltration devices well swept and clean will enhance the longevity of these devices. For roofs, frequent cleaning of gutters will reduce sediment loads to these devices. 1/9/2009 2009 Surface Water Design Manual — Appendix C C-44 House House C.2.2 FLIL INFILTRATION FIGURE C.2.2.0 TYPICAL DRYWELL INFILTRATION SYSTEM Roof Downspout Catch Basin (Yard Brain) Roof flow Downspout 0 DRY WELL 48 Inch Diameter Hale Filled with PLAN VIEW 112-3"Washed Drain Rock NTS Roof Downspout flow �� Fine Mesh Screen Catch Basin (Yard Drain) Sides of Hole Lined with Filter Fabric Mark Center of Hole with 1" Capped PVC or Other means Flush with Surface 1' min. Varies Min. 1' above Seasonal DRY WELL High Grou ndwate r Table SECTION NTS 2009 Surface Water Design Manual — Appendix C 1/9/2009 C-47 C.2.2 FULL INFILTRATION FIGURE C.2.2.A TYPICAL TRENCH INFILTRATION SYSTEM ME w \1 LllrSll 4" rigid or 5" flexible perforated pipe ---------------- ----------------• infiltration trench PLAN VIEW NTS overflow 4" rigid or 6" flexible splash block perforated pipe 6" . . ........... 6' r eve i2' ti,n �•— washed rack n 1 1I2"-314„ fine mesh crraan varies - A filter fabric -- 2,V' SECTION A NTS i roof �} drain i sump wlsolid fid 1' min 5.0' min_; 11'min C8 sump w/solid lid compacted backtill 4" rigid or 6" flexible perforated pipe washed rock 1 1/2"-314" 2009 Surface Water Design Manual — Appendix C 1/9/2009 C-45 Section 10: Operation and Maintenance Manual The Operation and Maintenance of the individual BMP's for each lot is attached. SECTION C.2 FLOW CONTROL J3MPs other types of soils or fill materials if designed by a civil engineer in accordance with the infiltration facility standards in Section 5.4 of the SWDM. b) For purposes of determining whether full infiltration of roof runoff is mandatory as outlined in Section C.1.3, the depth of soil to the maximum wet season water table or hardpan must be at least 3 feet. For any optional or mandatory application of full infiltration, the depth of soil to the maximum wet season water table or hardpan must be at least 1 foot below the bottom of a gravel filled infiltration system and at least 3 feet below the bottom of ground surface depression used for full infiltration. 2. For purposes of determining whether full infiltration of roof runoff is mandatory as outlined in Section C.1.3, one of the following infiltration devices must be used in accordance with the design specifications for each device set forth in Sections C.2.2.3, 0.2.2.4, and 0.2.2.5. Note: full infiltration may be possible using other types and sizes of infiltration devices if designed by a civil engineer in accordance with the infiltration facility standards in Section 5.4 of the SWDM. • Gravel filled trenches (see Section 0.2.2.3, p. G-42) • Drywells (see Section C.2.2.4, p. C-43) • Ground surface depressions (see Section C.2.2.5, p.C43) 3. A minimum 5 -foot setback shall be maintained between any part of an infiltration device and any structure or property line. Larger setbacks from structures may be specified in the design specifications for each infiltration device. Infiltration devices may not be placed in sensitive area buffers. A 50 -foot setback is required between an infiltration device and a steep slope hazard area or landslide hazard area (this may be reduced if approved by a geotechnical engineer or engineering geologist and DDES. 4. Infiltration devices are not allowed in critical area buffers or on slopes steeper than 25% (4 horizontal to 1 vertical). Infiltration devices proposed on slopes steeper than 15% or within 50 feet of a landslide hazard area or steep slope hazard area must he approved by a geotechnical engineer or engineering geologist unless otherwise approved by the DDES staff geologist. 5. For sites with septic systems, infiltration devices must be located downgradient of the primary and reserve drainfield areas. DDES permit review staff can waive this requirement if site topography clearly prohibits subsurface flows from intersecting the drainfield. 6. The infiltration of runoff must not create flooding or erosion impacts as determined by DDES. If runoff is infiltrated near a landslide hazard area, erosion hazard area, steep slope hazard area, or a slope steeper than 15%, DDES may require evaluation and approval of the proposal by a geotechnical engineer or engineering geologist. 0.2,2.3 USE OF GRAVEL FILLED TRENCHES FOR FULL INFILTRATION Gravel filled trenches (also called "infiltration trenches") are a good option where the depth to the maximum wet -season water table or hardpan is between 3 and 6 feet. Figure C.2.2.A (p. C45) and Figure C.2.2.13 (p. C-46) illustrate the specifications for gravel filled trench systems as outlined below: 1. When located in coarse sands or cobbles, infiltration trenches must be at least 20 feet in length per 1,000 square feet of impervious surface served. When located in medium sands, infiltration trenches must be at least 30 feet in length per 1,000 square feet of impervious surface served. 2. Maximum trench length must not exceed 100 feet from the inlet sump. 3. The trench width must be a minimum of 2 feet. 4. The trench must be filled with at least 18 inches of 314 -inch to 1112 -inch washed drain rock. The drain rock may be covered with backfill material as shown in Figure C.2.2.A or remain exposed at least 6 inches below the lowest surrounding ground surface as shown in Figure 0.2.2.8. 1/9/2009 2009 Surface Water Design Manual —Appendix C C-42 C.2.2 FULL INFILTRATION 5. Filter fabric (geotextile) must be placed on top of the drain rock (if proposed to be covered with backfill material) and on the trench sides prior to filling with the drain rock. 6. Spacing between trench centerlines must be at least 6 feet. 7. Infiltration trenches must be setback at least 15 feet from buildings with crawl space or basement elevations that are below the overflow point of the infiltration system. 8. To prevent damage to overlying pavement, trenches located beneath pavement shall be constructed such that the trench pipe is connected to a small yard drain or catch basin with a grate cover so that if the trench infiltration capacity is exceeded, the overflow would occur out of the catch basin at an elevation at least one foot below that of any overlying pavement, and in a location that provides a safe path for the overflow. 9. Runoff from roadways, driveways, and parking areas shall pass through a yard drain or catch basin fitted with a down -turned elbow prior to entering the infiltration trench (see Figure C.2.2.13, p. C- 46). The elbow is intended to trap spilled material in the catch basin sump so that the spilled material can be cleaned up more easily by the homeowner. C.2.2.4 USE OF DRYWELLS FOR FULL INFILTRATION Drywells are gravel filled holes as opposed to trenches and therefore may allow for a more compact design in areas where the depth to the maximum wet -season water table is relatively deep (e.g., 6 feet or greater). Figure C.2.2.0 on page C-47 illustrates the specifications for drywell infiltration systems as outlined below: 1. When located in coarse sands and cobbles, drywells must contain a volume of gravel equal to or greater than 60 cubic feet per 1,000 square feet of impervious surface served. When located in medium sands, drywells must contain at least 90 cubic feet of gravel per 1,000 square feet of impervious surface served. 2. Drywells must be at least 48 inches in diameter and deep enough to contain the gravel amounts specified above for the soil type and impervious surface area served. 3. The gravel used for drywells must be 1112 -inch to 3 -inch washed drain rock. The drain rock may be covered with backfill material as shown in Figure C.2.2.0 (p. C47) or remain exposed at least 6 inches below the lowest surrounding ground surface. 4. Filter fabric (geotextile) must be placed on top of the drain rock. (if proposed to be covered with backfill material) and on the drywell sides prior to filling with the drain rock. 5. Spacing between drywells shall be a minimum of 10 feet. 6. Drywells must be setback at least 15 feet from buildings with crawl space or basement elevations that are below the overflow point of the drywell. C.2.2.5 USE OF GROUND SURFACE DEPRESSIONS FOR FULL INFILTRATION Ground surface depressions (also called "infiltration depressions") are another option for full infiltration if the maximum wet -season water table or hardpan is at least 3 feet below the bottom of the depression. Figure C.2.2.13 illustrates the specifications for infiltration depressions as outlined below: I. When located in coarse sands or cobbles, infiltration depressions must be able to store at least 40 cubic feet of stormwater per 1,000 square feet of impervious surface served. When located in medium sands, ground surface depressions must be able to store at least 60 cubic feet of stormwater per 1,000 square feet of impervious surface served. This volume of water storage must be achieved through the excavation of existing native soil, not through the construction of berms. 2. The stormwater storage areas of infiltration depressions must be at least 12 inches in depth with a minimum 6 inches of freeboard before overflow. 2009 Surface Water Design Manual —Appendix C 1/9/2409 C-43 SFCTION C.2 FLOW CONTROL BMPs 3. The depression overflow point must be at least 6 inches below any adjacent pavement area and must be situated so that overflow does not cause erosion damage or unplanned inundation. 4. The depression side slopes must be no steeper than 3 horizontal to 1 vertical. 5. Spacing between multiple infiltration depressions shall be a minimum of 4 feet. 6. In -filtration depressions must be setback at least 15 feet from buildings with crawl space or basement elevations that are below the overflow point of the infiltration depression. 7. Infiltration depressions may be any size or shape provided the above specifications and the minimum requirements in Section C.2.2.1 are met. 8. The ground surface of the infiltration depression must be vegetated with grass or other dense ground cover. C.2.2.6 MAINTENANCE INSTR INFILTRATION If the full infiltration flow control BMP is proposed for a project, the following maintenance and operation instructions must be recorded as an attachment to the required declaration of covenant and grant of easement per Requirement 3 of Section C.1.3.3 (p. C-18). The intent of these instructions is to explain to future property owners, the purpose of the BMP and how it must be maintained and operated. These instructions are intended to be a minimum; DDES may require additional instructions based on site- specific conditions. Also, as the County gains more experience with the maintenance and operation of these BMPs, future updates to the instructions will be posted on King County's Surface Water Design Manual website. 0 TEXT OF INSTRUCTIONS Your property contains a stormwater management flow control BMP (best management practice) called "full infiltration," which was installed to mitigate the stonnwater quantity and quality impacts of some or all of the impervious surfaces on your property. Full infiltration is a method of soaking runoff from impervious area (such as paved areas and roofs) into the ground. If properly installed and maintained, full infiltration can manage runoff so that a majority of precipitation events are absorbed. Infiltration devices, such as gravel filled trenches, drywells, and ground surface depressions, facilitate this process by putting runoff in direct contact with the soil and holding the runoff long enough to soak most of it into the ground. To be successful, the soil condition around the infiltration device must be reliably able to soak water into the ground for a reasonable number of years. The infiltration devices used on your property include the following as indicated on the flow control BMP site plan, Q gravel filled trenches, 0 drywells, U ground surface depressions. The size, placement, and composition of these devices as depicted by the flow control BMP site plan and design details must be maintained and may not be changed without written approval either from the King County Water and Land Resources Division or through a future development permit from King County. Infiltration devices must be inspected annually and after major storm events to identify and repair any physical defects. Maintenance and operation of the system should focus on ensuring the system's viability by preventing sediment -laden flows from entering the device. Excessive sedimentation will result in a plugged or non-functioning facility. If the infiltration device has a catch basin, sediment accumulation must be removed an a yearly basis or more frequently if necessary. Prolonged ponding around or atop a device may indicate a plugged facility. If the device becomes plugged, it must be replaced. Keeping the areas that drain to infiltration devices well swept and clean will enhance the longevity of these devices. For roofs, frequent c4eaning of gutters will reduce sediment loads to these devices. 1/9/2049 2409 Surface Water Design Manual - Appendix C C-44 C.2.2 FULL 1NFILTRA11ON FIGURE C.2.2.A TYPICAL TRENCH INFILTRATION SYSTEM roof drain PLAN VIEW NTS 4" rigid or 6" flexible perforated pipe -------------------------- - -------- infiltration trench sump w/solid lid PLAN VIEW roof drain NTS overflow 4" rigid or S"flexible splash block perforated pipe 6" e°ol v L o e 1' min 5.0' min [� washed rock I . 12" h 1 112"-314" 1' min fine mesh CB sump w/solid lid A c.+rncn varies----.— filter fabric — 6„ 24" 1 2" ❑o y❑a c n °P a °7 6 P�4 d 7 O J O � p 7 0 7 ., a 24' I SECTION A NTS compacted backfill 4" rigid or 6" flexible perforated pipe washed rock 1 112"-3/4" 2009 Surface Water Design Manual – Appendix C 1/9/2009 C-45 I pvtf FA C.2.2 FULL INFILTR4TICN FIGURE C.2.2.0 TYPICAL DRYWELL INFILTRATION SYSTEM SppgEpx of gpvu DbLdi !Cbtjo )7bm!Esbjo* flow S ppg Epx of gpvu DRY WELL MTS SppdEpx of gpvu House pvf W Tgrht i !CgDd flow ",�T Gjof !N f ti !Tdsf f o Dbuf !Cbt jo )2bse!E�bjo* 15' min. DRY WELL SECTION NTS O 59!.bdi !Ejbn f Lf s I pprh!(4nfne!x ju 2 .4AXbtife E9ajo!Spol / N bd Of otf dpcjl prft x ju !2)iDbggf e!CYO pslPufsin fbot ! Lpgt pjm Gvit i !xjd !Tv#df _ 1' min. N jo/!54ejbl Q\AD!Cigf 59!.bdi !Ejbn f Lf s lryft Tjef t !p9l pdn 2 I pth!gnfoe!x ju Mof e!x ju g V03.49X bt i f e Cjni sl(bcgd Esbjo!Spol o Min. 1' above Seasonal High Groundwater Table t 2009 Surface Water Design Manual — Appendix C 1/9/2009 C47