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Home My WebLink About03735 - Technical Information Report - Drainage Vl � Wilson Park & Wilson Park # 2 �' � `� LUA09- 140 & 12-013 �� 720 South 55t" Street Renton, Washington 98055 DRAINAGE REPORT � � �3�35 November 5, 2013 }�r o� � Updated May 13, 2014 Prepared for: R��pN Robert Wilson, Owner ,�.�oF � 21703 60"' Street East � c��,C�� Lake Tapps, Washington 98391 1,� 2p14 Doravin@comcast.net �uN ,v`5,0� �v,��,�G o �� ` L. O�, Prepared by: `` �.yc � � � . Offe Engineers, PLLC Darrell Offe, P.E. � 13932 SE 159�' Place �� '��' Renton, Washington 98058-7832 �IONALE � /� (425) 260-3412 office � (425) 227-9460 fax (?7 � darrell.offe@comcast.net � ,3 73 S 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 8: 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 Part 2 PROJECT LOCATION AND PROJECT ENGINEER DESCRIPTION Project Owner: Robert Wilson Project Name: Wilson Park& Address: 21703 60�' Street East Wilson Park 2 Lake Tapps,WA 98391 � ; Phone: (253) 208-3263 Location � � Project Engineer. Darrell Offe, P.E. Township: 23 North - Company: Offe Engineers, PLLC Range: 5 East � Address/Phone: 13932 SE 159th Place Section: 31 � Renton, WA 98058 425 260-3412 Part 3 TYPE OF PERMIT Part 4 OTHER REVIEWS AND PERMITS APPLICATION Subdivision , ❑ DFW HPA C Shoreline Mana ement 9 X 2 / /P A ats UD ❑ COE 404 X Rockery - ❑ Grading ❑ DOE Dam Safety X Structural Vaults ❑ Commercial � �� - � FEMA Flood lain X Other NPDE p S - ❑ Other I' ' ❑ COE Wetlands _ � r'� � Part 5 SITE COMMUNITY AND DRAINAGE BASIN Community South Renton Drainage Basin Springbrook Creek / Green River / Puget Sound Part 6 SITE CHARACTERISTICS ❑ River � Floodplain ❑ Seeps/Springs ❑ Stream ❑ High Groundwater Table ` ❑ Critical Stream Reach ❑ Groundwater Recharge ❑ Depressions/Swales � ❑ Lake X Other_Steep Terrain_ X Steep Slopes Part 7 SOILS Soii Type Slopes Erosion Potential Erosive Velocities SM 15-40% moderate ❑ Additional Sheets Attached Part 8 DEVELOPMENT LIMITATIONS REFERENCE LIMITATION/SIT CONSTRAINT " ��-�y��v, c�S;�� i ❑ Ch. 4—Downstream Analvsis " V , ❑ ��/ � I ❑ i ❑ � ❑ I , ❑ ❑ Additional Sheets Attached Part 9 ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION AFTER CONSTRUCTION �, Sedimentation Facilities C Stabilize Exposed Surface � Stabilized Construction Entrance �+ Remove and Restore Temporary ESC Facilities � Perimeter Runoff Control � Clean and Remove All Silt and Debris '�: Clearing and Grading Restrictions � Ensure Operation of Permanent Facilities � Cover Practices � Flag Limits of SAO and open space _ �Construction Sequence preservation areas _ C Other ❑ Other i� Part 10 SURFACE WATER SYSTEM ❑ Grass Lined Dispersion � Infiltrati Method of Analysis Channel J Depression 2009 City of Renton ❑ Energy Dissipater Manual Pipe System � �/ettand � Flow Dispersal Open Channel ❑ Waiver Compensation/Mitigati ❑ Stream on of Eliminated Site ❑ Dry Pond ❑ Regional Storage Detention Bnef 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 ' Part 12 EASEMENTS/TRACTS Cast in Place Vault � � � Tract � Retaining Wall � - �Rockery>4' High ❑ Other ��, �� j Structural on Steep Slope II - ❑ 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. I _ , 2�G'! � � �� Signed/Date ( 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 55"' Street is required. This widening improvement ofF � site was submitted as a separate permit, U13005791. The two projects will be constructed from these plans. , �� r ��, �_� ; �I � I. ,.( II (� 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. Co�e Requirement No, 1 -Discharge at Natura/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 55�' 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 55tn, following the natural discharge point for the property. Core Requi�ement No. 2-Offsite Ana/ysis 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. SSth 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-F/ow Conino/ 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 by using infiltration dry wells or trenches at time of building permits; collection of the roadway section into catch basins and a stormwater facility to treat for detention and water quality. This new vault will be located at the entry of the project and connect into the existing downstream, system at the intersection of Talbot Road South and South 55th 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 i 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 Requi�ement No. 5-Erosion and Sediment Contro/ 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 Ope�ations � 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-Financia/Guarantees and Liabi/ity 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. �� '�, � ;_, � .-,� -1 - .i ,:: � '� ( ` WILSON PARK LUA 09-140 � ' i I, r' � �� i �— s, ; � � � r'� � �� r PUBLIC Cityof Renton Department of Community and Economic Development HEARING PRELIMIIVARY REPORT TO THE HFARING EXAM/NER A. SUMMARYAND PURPOSE OF REQUEST: PUBUC HEAR/NG DATE: M a rch 16, 2010 Project Name: Wilson Park Preliminary Plat Applicont/Owner: Robert Wilson; 21703 60�'Street East; Lake Tapps, WA 98391 Contact: Shupe Holmberg; Baima & Holmberg Inc., 100 Front Street; Issaquah,WA 98027 File Number: LUA09-140, PP, ECF ProjQct Manoger: Gerald Wasser,Associate Planner ProjectSummory: The applicant is requesting approval of a Preffminary Plat tor the subdivision of a 108,h�_ square foot (2.5 acrej parcel in the R-1, R-8 and R-14 zones and in the Urban Separatc Overlay. The original proposal encompassed 13-lots and 4-tracts (for open space an : storm detention). The revised proposal encompasses 12-lots and 3-tracts (for ope� space). A portion of proposed Lot 12 would also contain an open space easement. '� , proposed stormwater vault would be located under the proposed access road. Propose : �, lots range in size from 4,500 to 13,006 square feet with a density of 7.99 dwelling unit I per acre. The proposed lots are intended for the future construction of single famil. �I residences. Slopes generally range from 13% to 39% and the southwestern portion c- � the site contains a small area of protected slopes (over 409'0). Access to the propose : 1i lots would be via a new street off of South 55th Street; a secondary access fc- �, emergency vehicles is also proposed. Grading would involve approximately 17,000 cub�: � yards of cut with approximately 6,000 cubic yards used as structural fIL ;��,�proxim��;rl��; I ' S�0 cubic yards of crushed rock fill would be used for road construction. �, ------ ' Project Location: 720 South 55`h Street I�I j � :� e��- � ��-��y'�' ��_,� ; :�.�_= * � j.� ;'�".��i�r��*�-` � ++�c.� �`� I ,�i�i�o�++_`.��c - �`� �.. -r� �:�-r��.. . . � � � 'lt I �� ui�i(�.I � . "�3...^j" �f`�� S-�'tzt4 f r _. ,. e, ,. fSS��FF�'�CF{t� � � � z [ -x �� .� ��,�� ` , t , �. �`- _ - - a �1'�.�a��F� I� p�I -�� „�r ,�` � , � �� r� �t� ��;� :� I � ��=��\ �oL� `^�' , �.,� �� {� �� - `�'��e��:.�d��e� i .�_: �_ e � ProjedLocation Map LUA09-140,ECF,PP I City of Renton Community and Economic Development Departmenf Preliminary Report to the Hearing Examiner _ WILSON PARK PRELIM/NARY PLAT LUA09-140,PP,ECF PUBLlC HEARlNG DATE Morch 16,2010 Page 3 of 23 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 REIVTON MUN/C/PAL CODE: 1. Chapter 2 Land Use Districts a. Section 4-2-020: Purpose and Intent of Zoning Distrir_ts 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 47-150: 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 S. Chapter 9 Procedures and Review Criteria 6. Chapter il Definitions G. APPLlCABLE SECTIONS OF THE COMPREHENSIVE PLAN: 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. DEPARTMENFANALYSIS: 1. Proiect Description/Back�round 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 PRELIMJNRRY PLAT LUA09-140,PP,ECF PUBLIC NEARING DATE March 36,2010 Page S of 13 - 5. Weekly reports on the status and condition of the erosion control p(an 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 1 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. 8. The applicant shall be required to pay a Parks Mitigation Fee based on $530J6 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 t_rip associated wrth the_proposed projectprior 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 �n $488.00 per each new single family lot prior to recording the final plat (with credit given for the existing housej. 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 I�, Representatives from various departments have reviewed the application materials to identify and III 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. Consistencv with Preliminarv 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 Plan 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 presenration and add amenity value. ✓Policy Objective Met ❑Not Met Poticy CD-22. During land division, all lots sh�uld front streets or parks. Discourage single tier lots with rear yards backing onto a street. Where a single-tier plat is the only LUA09-140,ECF,PP City of RenYon Community and Economic Development Department Preliminary Report to the Hearing Ezaminer WILSON PARK PRELlM11UARY PLAT LUA09-140,PP,ECF PUBUC HEARlNG 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. Lot Area(sq.ft.) Width/Depth (ft.l Notes 1 4,594 63/75 R-8 Zone; abuts open space Tracts B &D 2 4,500 60/75 R-8 Zone 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/iZ0 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-S and R-1 Zones 12 13,006(net lot area 108/90 Ft. R-1 Zone; includes 4,884 8,12z) 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 rear yard. 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 Hearing Fxaminer WILSON PARK PREL/M/NARY PL4T LUA09-140,PP,ECF PUBLlC HEAR/NG 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: 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 Po�icy/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, 4,195 sf in Tract C, 2,400 sf in Tract D, and 4,884 sf in the open space easement as part of proposed Lot 12). eJ 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 classification5 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 R�ad A. Staff recommends as a LUA09-140,ECF,PP i City of Renton Community and Economic Development Department Preliminary Report to the Hearing Examiner WILSON PARK PRfL1M/NARY PLAT LUA09-140,PP,ECF PUBLIC HEARlNG DATE March 16,2010 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 Geotechni�al 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. Relationship 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. g) Availability and Impoct on Public Services(Timeliness) Police and Fire: Police and Fire Prevention staff indicated that sufficient resources exist to furnish services to the proposed development. Due 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 potentiafly impact the City's Police and Fire Emergency Services. Staff recommended through SEPA Environmental Review as a condition of approval to mitigate for these impacts that requires the applicant t� 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 accomm�date 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 Le�el 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 53`d Place approximately 750-feet downstream from the site. This facility outfalls through an 18-inch pipe to the west side of Talbot Road 5 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 Communrty and Economic DevelopmentOepartment Preliminary Report to the Hearing Examiner _ - WlLSON PARK PRELIMIIYARY PLAT LUA09-140,PP,ECF PUBLlC HEARlNG DATE March 16,2010 Page 13 of 13 G. RECOMMENDATlONS: 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 Re�iew Committee on February 22, 2010 for Project File No. WA09-140, 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 Native Growth Protection Easement (NGPE) shall.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. 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 f�r 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 4-7-080.L I � ` i -.�-� � 1 � r__ -J LUA09-140,ECF,PP � � PORTION OF THE SE 1/4 OF SEC. 31, TWN. 23 N. RNG 5 E. 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' � a.�� ' I Z4 ---- - 6.�.,� _ �' 1 ; ; N — _ _ J '__ � 'R-8� I� H � � 5se�91 � M e.eas i �.' i : i ; � �s ps o . � ; --.. Y� M s R-8 �,�j �"q �a a�— — S�R- — 3 : --R ; _ � �_—S.y�� SSOm4 � ; ; : . . s � � " �T��& R-14 :..�__..---�,.,.,a----- . . S�"�, a f � 5�s — — a �_a5�as — -- ��-- v,_i4 `5' � ,�__` -- _=s€+�a= ;�: ----- S t i� — -----— R-1 - - � � _ --� � �,�g p__ �• � � — -- — 'i� _ N � . >. �, � — '� � 55�5 •. ¢ s sw'� —��—, R-1 R-4 : -R ZONING MAP BOOK J3 - 06 T22N R�E E 1/2 PW TECHNICALSERVICES �� PRINTED ON 11/13/09 � ,�,�..e...��.m,� �..s..b,...r.�n..r.e�e a k r..d..�arnkaerd.�rew ,n.�w.Y...retroaa.a..o.o.as+. 0 200 4D0 ' �Feet 31 T23N RSE E 1/2 - _._ �C'��`��i ��`�.,-�,` 1:4�800 5331 f � � 50%of the area as open space is a hardship. By requiring 509�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 Tafbot Urban Separator will be required to dedicate 50% of the gross land area in the Urban Separator as open space, rather than ' S0%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 I information on the appeal process. i� ' _ CODE i AMENDMENTS ' NEEDED TO IMPLEMENT I ' DETERMINATIONS: RMC 4-3-110.E.2 should be amended to read as shown on Attachment A. I CI-05 Page 2 of 2 Denis Law - I - MaYo� �— City of EXHIBIT 11 w �� , � -.- ; : : �` _ -- �__- - . ._ _ _.. .. . . a��lS 'i r r Department of Community ar�d Economic Development November 10, 2009 Alex Pietsch,Administrator Tom Redding . Bairt�a & Holmberg, inc. � 100 Front Street South Issaquah, WA 98027-3817 � Subject: Wilson Park Preliminary Plat—LUA09-140 720 South 55"'Street Street Modification requests Dear Mr. Redding:- - - __ --- --- � We have completed our reuiew of your reques#for modifications to the street standards far the . proPosed Wilson Park Freliminary Plat located at 720 South 55t"Street. The proposed residential subdivision is for 13 single family b�ilding lots and four additional tracts. The subdivision will be served by two access roadways south of the site to South 55th Street, connecting to a n-ew street thro_ugh the propDsed project. You have requested modifcation forthe internal ro.adway, including efiminating the required sidewalk from one side of the street,�reducing tMe right-of-way width, and eliminating the requirement for a cul- �� de-sac. Clarifca�ion of the street improvement requirements for the two off-site access roadways is �� also.requested_ The proposal contin�es to be based on a waiver of the required connection to the north � - property line. . �� The request to recfuce the internal street right-of-way wadth to 37.5 feet is denied. However,the � request to delete the sidewalk from one side of the ir�ternal street is ap{�roved,subject to providing an eight-foot (8') planting st�ip 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 pr�posal to waive th�requirement to extend the public street to the north property line is ; � also denied. . � i - I - : City Cade 4-6-060 (Street Standardsj requires full.street improdements for afl adjacent rights-of-way for, within, and dedicated by a plat. . � � � The�City can modify street improvements for new plats if there are practical diffieulties in carrying out the provisions of the Street Imprpvement Ordinance. The Modification Procedures, as defined in Section 4-9-250D, clearfy states the criieria for approval by the Department Administrator. In order for - -a modifcation to be approved,the Department Administrator must find that a special individual reason makes the strict letter of this Ordinance impcactical,that the modification is iri conformity with the irrtent and purpose of this Ordinance; and that such modificatior�: (a} WiIF meet the ob�ectives and. safety, function, appearance, environmental protection and rimaintainability intended by this Ordinance, based upon sound engineering judgment; and (b) Will c�ot be injurious to other property(s) in the v"icinity; and . _ _ Renton Gty Hall • 1055 South Cxady Way • Renton,Washington 98057. • rentonwa.gov 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. Streef . (ighting meeting code with required (ighting 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 improvem?r�` for this extension shall include 26 feet Df pa�ement, and curb and gutter along both sides of the stre� Sidewalk's are required along both sides of this street section, both five feet(5') in width. The sidew� on the east side of the street can be constructed adjacent to the new curb. The west side of the stre shall include a five-faot(S') planting strip landscaped with s� : °� Easterlv off-site access roadwav tietween 5:55�St and the c � . ; 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 ne::� plat. If this private easement is replaced in the future with dedicated public right-of-way, the emergency access gate shall 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.�0. Appeals must be filed with the City Clerk before Tuesday, November 24, 2D09, at 5:00 p.m. You may contact Kayren Kittrick.at(425)430-7299 if you have any questions or need additional information. � � Sincerely, - �� L/Vd . � � Neil Watts, Director Development Services Division cc Alex Pietsch,Community&Economic Development Administrator Chip Vir�cent,Planning Diredor Kayren Kittrick, Development Engineering SuRervisor Jerry Wasser,Associate Planner WILSON PARK II LUA12-013 DEPARTMENT OF COMMUNITY _ �- __.c'�'°f� � __ ;, �, II ^.. , � �c'; ('�� C",�' ('� =��> AND ECONOMIC DEVELOPMENT �.s.._.,,� .. ,.... REPORT TO THE HEARING EXAMINFR A. SUMMARY AND PURPOSE OF REQUEST: REPORT DATE: J u n e 12, 2012 Project IVame: Wilson Park II Owner/Applicant: Robert & Doravin Wilson, 21703 60th Street East, Lake Tapps, WA 98391 Contact: Darrell Offe, P.E.; Offe Engineers, PLLC, 13932 SE 159t 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 �ots 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 Department Report to the Hearing Examiner WILSONPARKII PLAT&PL,IJ LL'AI2-013,ECF,PP,PPUD PUBZ.IC HEARING DATE: June 12,2012 Page 3 of 31 Exhibit I8: 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) Exhibit2l: 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 21703 60th 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 Designotion: Residential Single Family (RSF) and Residential Low Density (RLD) 4. Existing Site Use: Vacant 5. Neighborhood Characteristics: North: Wilson Park 1(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. HISTORlCAL/SACKGROUND: Action Land Use File No. Ordinance No. Date Annexation N/A Comprehensive Plan LUA08-145 5501 11/25/2009 Zon i n g LUA08-145 5191 11/25/2009 Wilson Park I Prelim Plat LUA09-140 N/A 8/16/2010 E. PUBLIC SERVlCES: 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 Ciry of Renton Community and Economic Developrnenl Department Report to the HearinAExaminer WILSONPARKII PLAT&PGD LUA72-013,ECF,PP,PPUD PUBLIC HE�4RING DATE: June 12,2012 Page S 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 site zoned R-1 is considered to be within the Urban Separator. Per RMC 4-3-110E2.a.ii, 50°% area within the Urban Separator must be dedicated as irrevocable open space. The applica� proposes to retain 19,164 square feet, or 50%of the site as open space within Tract A. This would also provide for open space and recreation opportunities to serve the public and the res of both Wilson Park developments. An approximate 350 square foot area would be provided w�ti� 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 43.21C, 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 Urbari 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 of Renton Cornmunrty and Economic Develapment Department Report to the Hearing Examiner WILS0IV PARK II PLAT&PLD LG'AI2-013,ECF,PP,PPUD PUBLIC HEARING DATE: June 12,2012 Page 7 of 31 5. Consistencv with the Planned Urban Development Re�ulations aJ 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 co�enant on each of the lots indicating that only detached single family units could be constructed. 6J 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 "aJ". 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 = REt2UESTED MODIFICATIONS FROM RENTON MUNICIPAL CODE (RMC� - 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 incorparate a variety of single family homes. home sizes, lot sizes, and unit Ciry of Renton Commu�zity a»d Economic Development Department Report to ihe Hearing Examiner WILSON PARK II PLAT&PUD L UA12-013,ECF,PP,PP UD PUBLIC HEARA'G D.4TE: June 12,2012 Page 9 of 31 RMC4-2-110: Minimum Side Yard R-1: 20 feet None Proposed. Along a Street R-14: n/a Staff Comment: Staff recommends that the applicant be su6ject to the standards of the R-S Zone for Minimum Side Yard Setback along a street, which is 15 feet(Lot 1). Further, staff recommends that the appropriote - setback from Tract A and the " pedestrian poth within an easement be 5 feet. RMC 4-2-110A: Minimum Rear Yard R-1: 25 feet None Proposed. setback R-14: 12 feet Staff Comment: Staff recommends that the a licant PP be subject to the standards of the R-S Zone for the Rear Yard Setback, which is 20 feet. RMC 4-2-110A: Maximum Building R-1: 20% None Proposed. Coverage Sta Comment: Sto R-14: n/a � ff recommends that the applicanr Staff Comment: The applicant has be su6ject to the standards of the not requested a modification from R-8 Zone for Maximum Building this standard. However, due to Coverage. For fots larger than the small lot size requested 5,000 s.f. this is 35%or 2,500 s.f. above, staff believes a whichever is greater. modification from this standard would be required to maintain a 6uildable lot. RMC4-2-110A: Maximum R-1: 30% None Proposed. Impervious Coverage R-14: 85% Staff Comment: Staff recommends that the applicanr I Staff Comment: The applicant hos be subject to the standards of the '� not requested a modification from R-8 Zone for Maximum 'i this standard. However, due to lmpervious Coveroge, which is the small lot size requested �$�• above, staff believes a modification from this standard would be required to mainrain a buildable lot. City of Renfon Community and Ecanomic Development Department Report to the Hearin�Examiner WILSONPARKII PLAT&PUD LUA12-013,ECF,PP,PPUD PUBLIC HF.fIRING DATE: June 12,2012 Page 11 af 31 that there be a minimum of 18 feet of driveway length from the face of the garage ro i-he back of the sidewalk. RMC 4-2-115F.3. Residential Design, R-1: N/A Staff Comment: Staff Scale, Bulk, and Character recommends approval of the � R-14: Primary building form shall requested deviation and be dominating; primary porch recommends that the , plate heights shall be one story; requirements of the R-8 Scale, different colors shall be used to gulk, and Character Standards be differentiate the same models followed. This standard requires and elevations; and no more than that: A variety of elevations and 2 of the same model and models that demonstrate a elevation shall be built on the variety of floor plans, home sizes, same block frontage and shall not and character shall be used. _ be abutting. . Additionally, both ofthe r following are required: l. A minimum of three (3) - differing home models for each ten (10) contiguous abutting homes, and ' 2. Abutting houses must have � differing architectural elevations. 6J PUD Decision Criteria: i. Demonstration of Compliance and Superiority: Applicants must demonstrate that o proposed development is in compliance with the purposes of the PUD regulations and with rhe Comprehensive Plan, that the proposed development shall be superior to that- which would result without a planned urban development, and that the development wi!!not be unduly derrimental to surrounding properties. Comment: If the conditions of approval are met, the applicant will ha�e 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 Econornic Development Department Report to tFre Hearing F.xaminer � WILSONPARKII PLAT&PUD LUA12-013,ECF,PP,PPUD P UBLIC HEARING DATE: June 12,2012 Page 13 of 31 Table B _ ,- - .- : =- - _ _ � =_ _ PUBLIC BENEFIT PROVIDED: CRITICAL AREAS;NATURAL FEATURES &OVERALL DESIG_N ,; 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 addcess 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 lronwood 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 WILSONPARKII PLAT&PUD LUA12-013,ECF,PP,PPL'D PUBLIC HEARING DfITE: June 12,2012 Page I S of 31 3. Landscaping/Screenin�: The proposed landscape plan 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 Buildin� Desi�n: 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 homes. 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 home5 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: Perrmeter: Size, scale, mass, character and architectural design along the plonned urban development perimeter provide o suitable transition to adjacent or abutting lower density/intensity zones. Materials shal!reduce the potentia!for light ond 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 55Lh 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-8 Zone resulting in a compatible size, scale, mass, character and architectural design for the Ciry of Renton Cammunit}-and Economic Development Departrnent Report to the Hearin�Examiner YYILSONPARKII PLAT&PUD LG'All-013,ECF,PP,PPUD PUBLIC HF.,4RING DATE: June Il,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 i the applicant be required to pravide 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 II, then the applicant should be required to provide an emergency turnaround within the plat. Promotes safety: Promotes safety thro�gh sufficient sight distance, separation of vehicles from pedestrians, Iimited driveways on busy streets, avoidance of difficult turning � pat�ems, 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, 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 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 tra�el east on South 55th Street in the morning, stopping in South 55tn 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 i ,\ 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 Communiry and Econamic Development Department Report to the Hearing Examiner ' WILSON P.4RK II PLAT&PUD LUA12-013,ECF,PP,PP UD � PUBLIC HErfRING DATE: June 12,2012 Page 19 of 31 ', - 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 ro 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 55tn 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 A�enue 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 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 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 53�d 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 II 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 oJRenton Communiry and Economic Development Department Report to the Hearing Examiner - WILSONPARKIIPLAT&PG'D LUA12-013,ECF,PP,PPUD P UBLIC HEARING DATE: June 12,2012 Page 21 of 31 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 'Publlc Benefit, Subsections: Critical Areas ond Naturol Feotures'; 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 pri�ate front, side and rear yards, enhancing each lot with landscaping and access to light and air. viii. Building Orientation: Provides buildings oriented to enhance yiews from within the site by taking advantage of topogrophy, 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: Desi�n: 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 ro the group of buildings served. The design pravides for efficient use of parking, and shared porking 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 porking oreos consrstent with the porking � demand created by the development as documented in a parking analysis approved by i-he I _ �ft.�,• 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 drive�rvays of each lot. Sufficient on-site vehicular parking would be provided ' _ consistent with the demand created by the development provided that conditions of � approva) are complied with. City of Renton Community and Economic Development Department Report to the Hearing Examiner i�'7LSON PARK II PLAT&PUD LUA12-013,ECF,PP,PPUD PUBLIC HE�iR7_NG DATE: June Il,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 shal! be deck areas totaling at least sixty(60J square feet in size with no dimension less than five feet(S'). 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: A!I common areo ond open space shall be landscaped in occordance with the londscaping 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 HomeOwner's Association. Installation and Maintenance of Common Facilities: AII common facilities not dedicoted to the City shall be permanently maintained by the planned urban development owner by the property owners'association or the ogent(s) thereof. Comment: 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 RUD 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 Preliminarv 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: aJ Compliance with the Comprehensive Designation The site is designated Residential Single Family (RSF) and Residentiol Low Density (RLDJ on the Comprehensive Plan Land Use Map. Land designated Residential Single Family is intended to be used for quality detached residential development organized inro neighborhoods at urban densities. !t is intended that/arger subdivisions, infrl!development, and rehabilitation of existing housing be carefully designed to enhance and improve the quality of single family living. Cand desrgnated 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/arger-lot housing stock at urban densities of 4-du/net acre, to its inventory: Ciry ofRenton Comrnunity and Economic Development Deparirnenl Report to the Hearing Ezaminer Yf7LSOA'PARKIIPLAT&PUD LUA12-013,ECF,PP,PPUD PL'BLIC HEARI.�'G D.4TE. June 12,2011 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 SF 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 sha►I 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 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. Setbacks: See Consistency with the Planned Ur6an Development Regulations, Table A for requested modifications. Building Standards: See Consistency with the Planned Urbon Development Regulotions, Table A for requested modifications. City of Renton Communiry and Econornic Development Depamnent Repart to the Hearin,q Fxaminer - YG7LSONPARKIIPLAT&PUD LUAI2-013,ECF..PP,PPL%D , PUBLIC HEARPJG DATE: June 12,2012 Page 27 of 31 ��, of protected slopes would be contained within Tract A. There is also a cut slo e on the P 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 i �- report are fully implemented and obser�ed during construction. Relationship to Existing Uses: See PUD criterion iii Building and Site Design. fl Availability and/mpact on Public Services(TimelinessJ 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 16, 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 studPnts 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 imperviaus 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 53�d 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 ofRenton Community and Economic Developmen!Department Report to the Hearing Ezaminer WILSOA'PARKII PL4T&PUD LUA12-013,ECF,PP,PPL�D PUBLIC HEfIRl.�JG DATE: June 12,2012 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 sidewaNc. '�t� � ��,r 5. The project shall 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 n�, 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 G �V � City's street tree standards. �'0 �,� c. The plan shall indicate either 100 percent drought tolerant plantings or th � � � aPP�,. ._t , �_.,,� .__._ ., �,._ ,� �__� „ ..� ... ��. ��,, r,.._� ., ,.,:�._..� � ,...,-. _ . plai C�. PfOV1C]L-' d f�VI��U Ldf1C]�l":d�C I'Idfl If1C]ICdLi�l� d L.UfllfliUfl i�el:fCdLlUfl di�d Lfl:�:' � minimum of 500 square feet that includes improvements providing � recreation by the public and area residents � e. Redesign the trail on the south side of Lot 10 such that the trail meanders , � not abutting the edge of the split rail fence on Lot 10. � 8. The applicant shall provide a walking path within the right-of-way of South 55 � that provides for a safe route to the nearest Renton School District bus stop. Tf path shall be asphalt with a minimum width of 5 feet and separated from the ro�� travel lane by Gcurbing as determined by the City's Development Services Div��- ProjPct Manaaer. This imorovement is required prior to the recordinQ of the pl�t _ -- ------_ DEPARTMENT OF COMMUN{TY ;-; r,`=��"ci�y°f. . , _ \ � -,� E ! �, � �_-. f �. -,- -"� ._ AND ECONOMIC DEVELOPMENT """ - - { `J � ! ' ' � �' � ->---. - - _. _ ._ v __� _ ._ -.�1� ENVIRONMENTAL REVIEW COMMITTEE REPORT ERC MEFTING DATE: May 7, 2012 Project Nome: Wilson Park II Preliminary Plat and Preliminary PUD Owner: Robert Wilson and Doravin Wilson 21�$60th 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 ' Number: LUA122-013 ECF PP PPUD File , , , ifer Hennin Current Plannin Mana er Pro'ect Mana er: lenn g, g g l 9 Pro'ectSumma : The a licant ro oses to subdivide an existin 2.15 acre arcel into 10 lots for 1 rY P p P p g P 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 9 lots proposed in the R-14 area, & 1 lot proposed within the R-1. A Planned Urban De�elopment 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 p[at. 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) Re�iew, Planned Urban Development (PUD) Review, and Preliminary Plat review. Project Location: 698 South 55th Street Exrst. 81dg. Area SF: N/A Proposed New Bldg. Area (footprintJ: N/A � Proposed New B/dg. Area (grossJ: 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 RECOMMENDATlON: Determination of Non-Significance- Mitigated (DNS-M). EXHIBIT 4 City of Renton Department of Community&Economic Development Environmenta!Review Committee Report WILSON PARK 2 PREUM/NARY PLAT&PRELIM!lVARY PUD LUAIZ-013,PP,PPUD,ECF Report of May 7,201� 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. . PART TWO: ENVIRONMENTAL REVIEW In compliance with RCW 43.21C.240,the following environmental (SEPA) review addresses only those project impacts that are not adequately addressed under existing development standa.rds 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. 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 ERC Report.doc City of Renton Department of Community&Economic Development Environmental Review Committee Report WILSON PARK Z PRELIMIIVARY PLAT&PRELIMINARY PUD LUA12-013,PP,PPUD,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-hig�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 gravef. 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 6 to 12 feet. This slope likely resulted from the original land grading. Subsurface conditions on the site were explored in November 2004 via six (6)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�ne 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 incfuded 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 inedium- 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. I 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. Stormwater from impervious surfaces should be ERC Report.doc City of Renton Department of Community&Economic Development Environmental Review Committee Report WILSON PARK 2 PRFLIM/NARY PLAT&PRELIMlIVARY PUD 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 Hoimberg Inc, for the previous Wilson Park I Plat. An addendum to this report was prepared by D.(�C '�f'S. 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�d 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 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 downstrearn 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 anci 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 II, The applicant intends to utilize the Restrictive Covenant provision and fimit impervious surface on each of the new Iots in both Wilson Park I 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 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. _ Mitigation Measures: No further mitigation necessary. Nexus: Not applicable. ERC Report.doc City of Renton Department of Community&Economic Development Environmental Review Committee Report WILSON PARK 2 PRELIMIIVARY PIAT&PRELIMINARY PUD LUAIZ-013, PP,PPUD,ECF Report of May 7, 2012 Page 8 of 11 Nexus: SEPA Envir�nmental Regulations; Parks Mitigation Fee Resolution No. 3082, Ordinance No. , 4527 I 4. Transportation � tmpacts: Access to the site would be from S 55th Street via a 5Q-foot wide right-of-way that was , , I� identifed 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 II) 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 June 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 55t�'Street on the outside of a horizontal curve on Sauth 55tn ;� ' 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 55�'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 Schoof District buses travel east on South 55th in the morning, stopping in South 55th to pick-up students. The buses then � trave_I 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 neeessarily a concern for SEPA environmental review; staff will study the issue further �I 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 I recommends that the applicant pay a Traffic Mitigation Fee based on a rate of$75.00 per additional average daily vehicle 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 an $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, i , Ordinance 4527 I, ; '� ;_ ERC Report.doc City of Renton Department of Community&Economic Development Environmental Review Commi�tee Report WILSON PARK 2 PRELIM/NARY PLAT&PRELIMINARY PUD 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 lines of all retained trees, or along the perirrieter 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 lie 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 wifl 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 pfan application. Plan Review: Sanitary Sewer 1. Extension of an 8-inch sewe�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 DEPARTMENT OF COMMUNITY D citvaf ;;Y �, AND ECONOMIC DEVELOPMENT ��0� ��.�{`` 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 PROP�SAL: 698 S 55th Street LEAD AGENCY: The City of Renton Department of Community & Economic Development Planning Division r Advisory Notes to Applicant: ` The followinq notes are supplemental information provided in conjunction with the environmental determination. Because these notes are provided as informafion only, they are not subject to rhe appeal process for environmental determinations. Plannin�: 1. 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. - 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 I' appropriate ground cover over any portion of the site that is graded or cleared of vegetation and where no furfher cons ruc ion work wi11 occur wi�hin nine y (-9-0�days. A7tema ive 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 DEPARTMENT OF COMMUNITY D cityof ,;,. �. AND ECONOMIC DEVELOPMENT ��O�l�l �rr,'Y`� ` 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: 698 S 55th Street LEAD AGENCY: The City of Renton Department of Community & Economic Development Planning Division 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 II of the 2005 Stormwater Management Manual and provide staff with a Construction Mitigation Plan prior to issuance of construction permrts. 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 th_e_dr_y_er period of_tf_te Xear�rom_April 1 through Oc�ober 31 un_less othelwise approved_ ��, by the Development Services Division. Therefore, the applicant shall adhere to a construction schedule 'I involving grading and foundation work during the dryer period of the year. I �' S. The applicant shall pay a Parks Mitigation Fee based on $530J6 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. 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I �� / •.�' � � � � � ,y s.ns+ So.Ff. 5 � � �� oi.oe' � ' � � ° �'• � � �07.h GflEATER SLOPE Y � � J lo�i � i:�e•:eait�, .. � � ��.. � r' �.- n.as' i y / � � ��'.%.. - 1�-.,.. i � AREA=9�783 50.Ff. Q� J � . •n,,, ` ' �� ... I n wii•ee � i �'� b lot ia }/.� ;/ /� . .. , . ,I � � Y � ��L ��=5 6n0h/-50.FC M� r' �� - ZONING BOUNOhRY a 3 � �..,.. . .�..:., /\ � " xe7�� ,•. n � A � ;/ � h � . . nnaw' ,/ _ � � CpdSTRUGi�N�,`� �-�s ot; .. H /`� I :, �.�. �. -�� --n.lr]tl1. . . e I / . - _..._�R/W-- - � - - � oza'� ' .._- . . . .- _�_r.�i /' - �• ( � � ' SOU7H SSIh STREEf%.,," C. i��, _ �/---- � ----- -'--' . � m a , ,� ''�is'/uta��uscnrtNr _ '�-- --- -- �!i � �O � � � , �: �. . �. n�Camm��iiziw�ee 1 . � . � a .. .�,. . . ' .;�. � � � ._ ;.. .. :-. �� '.`i � . 10'SEWEN FASEMEM .;.. �r� .. � �� ' � � ,. i •, '` . RECOROING�7EITIEON/ . _., � • , � N ,,•;�.,'"� � � ., „, � � � � �,� a,,,�,� o �o eo izo +oe xo. TAX PMCEL�J12305-9119 ov.'o wo. . - SLALE� P=�0' 1 �F 1 _ 1 � . 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 55"' 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 55"' Street at the top of the hill. The upstream flow will be conveyed around the project within South 55r'' Street. A downstream analysis was prepared for Wilson Park(LUA09-140) by Baima &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 55"' Street. This new system will discharge into the off-site improvements (U13005791). The flows will be conveyed to the intersection of South 55"' Street and Talbot Road South within 15"pipes and catch basins. At Talbot Road South (NE corner) the new system will wnnect to the existing downstream ', � system as analyzed for Wilson Park indicated above. ; � � ;,__; '� �-� � � � � � � �� _'�� '��I ' J � -�, i � �._� l I `-J ; � � , � I , II BAIMA & HOLMBERG INC. LEVEL 1 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 • ISSAC�UAH • WASHINGTON • 98027-3817 • (425} 392-0250 • (425)391-3055 �'�l ,--� Street Address 720 South SSth 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 55�' Street, about 150' east of the east terminus of South 53rd Place, on the slope overlooking SR 167, about '/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. r 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 yazds, 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`a 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(I) beyond 1/4 mile downstream from the site. This wetland apparently drains to a 10' X 5'f box culvert crossing under SR-167 (Q), about '/2 mile downstream from the site. � A small area of the south part of the site drains southwest across the south property line I� of the site into the adjacent parcel to the south (Z). These runoff flows through woods, i collecting in a ditches along South 55�' Street(K)(about 350' downstream from the site) 'I and/or Talbot Road South (L)( about 800' downstream from the site). Flows into the � ; ;- ditch along South SSth Street(K) continue west in a 6"-12" rock-lined ditch channel I�, . '��1 ' .� : °� . , ,, along the north side of the street, passing through a couple of 12" driveway culverts on the way to the intersection of South 55`� 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 (IVn. 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 'h mile downstream � from the site (� where it enters the aforementioned 10' X 5'f 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 55`� Street, there were no appazent downstream drainage problems. A check of King County drainage complaints on their IMAP website yielded no reported complaints along this downstream drainage path. A i I � .. ' �— ...._ .:. � �"^Y •.t . . . _, i, � � �,! ,:�7�'��, 7 �j 1 j' � * . f��~� ; �'y� - , r ' �... �r � �I . . , ��' .'S ! � . ' � .,. .�.. � . .�s,..:.. . y .Y � „ �Y y . � ��y�� y, . , �. . • ' . _ �� . .. ' ` r ; �'lx , �'.. -.:� . . � � si . . �.�.. ;a � . . . � �. �! . , . . �. ;... �` ,,,,�; r,- . __ j � .. 5 ,��..:_ �.�. . . . � � � r ._ , ... . .. , ., . , . , �,, ,_. _ _ . ; �, _ _ . . ,. � � �+i��a .. .. . � P . I �. ..3 .. 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('�� `\;`\�� i ��' i � �� `��-� �� \;,� ) 1 � I� l��i'� � � `.% n �\ �, �i. i 1 iN:�....,.,, . l '`d. . , .� � � `r�am Drainage Map " 1" = 250' Section 4: Flow Control and Water Quality Facility Analysis and Design i ' FLOW CONTROL REVIEW Based upon the City Drainage Manual, the following steps are required to determine the mitigation of storm water runoff of the developed project: Full Dispersion- N/G (no good)-the property does not have 100 feet of flow path available on each new lot; Full Infiltradon -Acceptable -The soils on the project will allow for infiltration of the individual lots. See attached compliance letter from Geotechnical Engineer. 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 treatrnent for projects that add 5,000 square feet or more of"new" pollution generating imperious surfaces (PGIS). The proposed developed (PGIS) exceed this requirement and therefore WQ treatrnent 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. � � Z O � � U J V Z ��.�1 F Z W F W � Wi/son Pa�k#i/#Z ((RUN#Z)) Area Breakdown Impervious Pervious forest Area Breakdown Tota/Areas s , feet s , feet s , feet Lot�s 22 i,��8 O O �.��,690�sq. ft. impervious max. «`� INFILTR.4TION � (all BMP on lots) Roads lin, Feet Area of R/W 26'road section 325 16900 12506 4394 (sidewalk both sides) 52' (74%) 26'rivad section 375 15750 11655 4095 (sidewalk one side) 42' (74%) 16'road section 95 3990 3431 559 (sidewalk b�th sides) 42' (86%) 20'road section 74 1924 1847 77 (sidewalk one side) 26' (96%J ZO'road section 250' SO00 (Fire Lane) 20' (100%) � Frontage 122 1708 732 976 (sidewalk one side) 14' (43%) NPGEAreas 34273 a-�1��. Tota/Area 2006i3 ` ��2�jQL- Impervious 3517i � � �.7�a�" Pervious IOI01 ForestJNGPE 34273 , � _::I , �, ; , Existin_q Conditions ,,. .��,. .�� --� .. - � tand Use Surnm,ary• - ,;-,. a=f -�.` _� � _ -.- `..: � Area Till Farest �.61 acres Till Pasture 0.�0 acres Till Grass 0.00 acres Ouiwash For�est �•�0 acres Ouiwash Pasture 0.00 acres s Outwash Grass O.OQ a�res R Wetland 0.00 acres Imper�ious 0.�0 acres Total _ . � 4.61 acres - _ _ ----- � Scale Factor : 1.00 Hourly Reduced � � Time Series: Predev.#sf s Compute Time Series � � Madiiy User Input � £ -�____ ___: - -- - _ -.:: __ _ _ ! File for camputed Time Series [.TSF] � �.. `'F.z55.+v5},t�-' ' -'.�4i� a_.��. r.�:-+�tii�3.:�.�a�_. ..-�..a...�.�=ts�.z �,:� , ..-.- � __. : I� Flow Frequency Analysis Time Series File:predev.tsf Project Location:Sea-Tac I . ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- I � Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob I (CFS) (CFS) Period 0.291 2 2/09/Ol 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 0.904 0.008 8 3/24/04 20:00 0.216 4 5.00 0.800 0.128 6 1/OS/O5 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 I ,��_ . s �_� � . � Land tfse Summary ,- --- _ -�_ . � � � ,�..� �� -:: Area Till Forest 0.79 acres , Till Pasture 0.00 ecres ' Till Grass 0.23 acres Ouiwash Forest U.00 acres � Ouiwash Pasture 0.�0 acres Outwash Grass 0.00 acres �!i � � � WeNand 0.00 acres � Imperrrious 0.81 acres � Tota I =; 1.83 acres' � _ _ _ � Scale Fac#or: 1.00 Hourly Reduced Time Series: �De�.tsf I $ Compute Time Series � � I � � Modiiy User Input � � . � _ _ _ ., _ - - -- —- -- _ - - - - _- -- - -- � � File for computed Time Series [.TSF] .,. _,:_. F�._ �- ,_,�� ,. , �.:.�;�.�.-�,:.�..;,W. �_.�. .-:.n -. :...... . .... ,_. ._ ._ , . . 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 Prob (CFS) (CFS) Period 0.298 5 2/09/O1 2:00 0.4B8 1 100.00 0.990 0.196 8 1/O5/02 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 9 5.00 0.800 0.296 6 10/28/04 16:00 0.298 S 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 0.231 0.488 1 1/09/08 6:00 0.196 8 1.10 0.091 Computed Peaks 0.425 50.00 0.960 i Detention Facilitv Desi_qn Facilitv 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 Sto=age 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 �I ,° Outflow Rating Curve: None Staae/StoraaelDischarae Performance Stage Elevation Storage Discharge Percolation ift) (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 0.013 0.00 0.06 216.06 36. 0.001 0.015 0.00 0.08 216.08 98. 0.001 0.017 O.DO 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 0.93 216.43 258. 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 0.56 216.58 398. 0.008 0.046 0.00 0.63 216.63 378. 0.009 0.048 0.00 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.�0 0.83 216.83 49@. 0.011 0.055 0.00 0.88 216.88 526. 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 1.30 217.30 780. 0.018 1.670 0.00 1.40 217.40 840. 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 I 1.70 217.70 1020. 0.023 3.240 0.00 I 1.80 217.80 1080. D.025 3.460 0.00 1.90 217.90 1140. 0.026 3.670 0.00 2.00 218.00 1200. 0.028 3.870 0.00 ; 'j Staae/StoraqelDischame Performance at Siqnificant Storm EveM 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 ******* 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. 0.019 7 0.20 ******* 0.17 1.04 217.09 622. 0.014 8 0.21 ******* 0.13 1.02 217.02 613. 0.014 Staue/StoraQelDischarqe 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 CFS 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 1a.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 0.336 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 99.809 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.B70 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 �.090 0.897E-03 0.181 14 0.023 99.933 0.067 0.669E-03 0.188 6 0.010 99.993 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 �i 0.232 4 0.007 99.984 0.016 0.163E-03 ' 0.240 4 0.007 99.990 0.010 0.9�8E-04 i 7 2 7 - ! � 0.29 0.003 99.993 0.00 0.652E 04 2 7 - � 0.255 a.003 99.99 0.003 0.326E Q4 0.262 1 0.002 99.998 0.002 0.163E-04 � Duration Com arison Ana lsis I P Y i I I �i � I Base File: predev.tsf New File: rdout.tsf Cutoff Units: Discharge in CFS -----Fraction of Time----- ---------Check of Tolerance------- Cutoff Base New $Change Probability Base New �Change 0.065 I 0.92E-02 0.50E-02 -95.3 I 0.92E-02 0.065 0.055 -15.1 0.082 I 0.62E-02 0.38E-02 -38.3 � 0.62E-02 0.082 0.060 -27.0 0.100 I 0.48E-02 0.30E-02 -38.3 � 0.48E-02 0.100 0.068 -32.2 0.117 � 0.37E-02 0.23E-02 -37.1 � 0.37E-02 0.117 0.086 -27.0 0.135 I 0.28E-02 0.17E-02 -38.7 � 0.28E-02 0.135 0.103 -23.5 0.152 I �•22E-02 0.13E-02 -41.0 � 0.22E-02 0.152 0.123 -19.4 0.169 � 0.15E-02 0.95E-03 -39.8 I 0.15E-02 0.169 0.149 -19.8 0.187 � 0.98E-03 0.60E-03 -38.3 I 0.98E-03 0.187 0.165 -11.7 0.204 � 0.60E-a3 0.38E-03 -37.8 � 0.60E-03 0.204 0.187 -8.5 0.222 I 0.34E-03 0.23E-03 -33.3 I 0.34E-03 0.222 0.207 -6.5 0.239 � 0.21E-03 0.98E-04 -53.8 I 0.21E-03 0.239 0.227 -5.1 0.257 I 0.16E-03 0.33E-04 -80.0 I 0.16E-03 0.257 0.233 -9.3 0.279 � 0.82E-04 O.00E+00 -100.0 � 0.82E-04 0.274 0.242 -11.6 There is no positive excursion 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 A �Pauzed-Ouraticn Analysis-KCiiTS ' �- �•:.-` .�'-�':[].�� N ('7 � n:_'�i1t�.if . Target.Cur • � N O i � � -- �.�_ :� I N � . � I O ' � �� ^ o N 9 � p U : � � s a, � � o : � � ; v ` !A N � 5j o 0 � , : � � � i Q R � -- - o 0 0 o - o � 10� 10d 10-3 10�2 10�� 10° Probability Exceedence ; WATER QUALITY CALCULATIONS � � ' _,� , , i , ) �� . _� ,_-� � � � , `� � _.� � , � _� i ' -�> \) � �� - � I ;--, � . - Wetpool Sizing Calculations 'I - Per 2009 King County Stormwater Management Manual Project Name: `�Ison Park 1 and 2 I�, Project Number: ' Facility Description: Detention/WQ 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= 0.47 Per KCSWDM Fig. 6.4.1.A Step 3: Calculate runoff from the mean annual storm (V,)for the developed site. V�_ (0.9A;+ 025A�9+0.10A�+0.01Ao)x(R/ 12) where: A; = Impervious Surface Area= 35,171 s.f. A�9=Till Grass Area = 10,101 s.f. A� =Till Forest Area = 34,273 s.f. Ao = Outwash Area = 0 s.f. V�= 1,473 c.f. Step 4: Calculate required wetpool volume(Vb). Vb= f x V� Vb= 4,419 c.f. ) 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.z 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 inter�als, 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 CB#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 55"' Street, the 25 year flow rate changes. At CB#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 CB#20. The 25 year flow rate at CB#20 is 15 cfs from the entire 35 acre upstream basin flowing into CB#20. Based upon the'�Stormrvater Conveyance Backwater Ca/cu/ations"attached, the new storm drainage system will handle the existing conditions for the upstream areas together with the developed conditions from the project site. STORMWATER CONVEYANCEBACKWATER CALCULATIONSHEET (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (il) (12) (13) Barrel Entrance Entrance Pipe 25 year Pipe Outlet Inlet Barrel Barrel Velocity TW Friction HGL Head Segment Q Length Pipe "n" Elev Elev Area Velocity Head Elev Loss Elev Loss CB to CB (cfs) ft Size Value feet) feet s . feet f s (feet (feet (feet (feet) feet O-1/O-2 15.0 210 15" 0.011 125.40 147.00 1.23 1Z.Z0 0.19 I26,40 1.95 128.35 0.04 O-2/O-3 15.0 140 15" 0.011 147.00 163.86 1.23 12.20 0.19 147.60 1.30 148.90 0.04 0-3/O-4 15.0 162 15" 0.011 163.86 188.00 1.23 12.20 0.19 164.46 1.51 165.97 0.04 O-4/O-5 15.0 90 15" 0.011 188.00 202.00 1.23 12.20 0.19 188.60 0.84 189.44 0.04 O-5/CB#20 15.0 47 15" 0.011 202.00 209.50 1.23 12.20 0.19 202.60 0.44 203.04 0.04 #20-#19 15.2 15 15" 0.011 209.50 211.80 1.23 12.36 0.19 210.33 0.14 210.47 0.04 #19-#18 15.2 120 15" 0.011 211.80 228.00 1.23 12.36 0.19 212.53 1.13 213.66 0.04 #18-#23 12.9 142 15" 0.011 228.00 269.00 1.23 10.49 0.16 228.64 1.14 229.77 0.03 #23-#24 12.9 95 15" 0.011 269.00 284.00 1.23 10.49 0.16 269.73 0.76 270.49 0.03 126.40 ASSUME at 18"oulfa//pipe (14) (15) (16) (17) (18) (19) (20) (21) Exit Outlet Inlet Approach Bend Junction Pipe Head Control Control Velocity Head Head HW RIM ELEV Segment Loss Elev Elev Head Loss Loss Elev UPSTREAM CB to CB feet (feet feet feet) feet feet feet cg 0-1/O-2 0.19 128.58 147.60 0 0 0 147.60 151.00 OK.� O-2/0-3 0.19 149.13 164.46 0 0 0 164.46 167.86 OK.� O-3/0-4 0.19 166.19 188.60 0 0 0 188.60 192.00 OK.� O-4/0-5 0.19 189.66 202.60 0 0 0 202.60 206.00 OK.� O-5/CB#20 0.19 203.26 210.10 0 0.08 0.15 210.33 214.00 OK.� #20-#19 0.19 210.70 212.40 0 0.13 0 212.53 215.80 OK.� #19-#18 0.19 213.90 228.60 0 0.0 0.04 228.64 233.00 OK.� #18-#23 0.16 229.97 269.60 0 0.13 0 269.73 274.00 OK! #23-#24 0.16 270.69 284.60 0 0.11 0 284.71 290.00 OK.� STORMWATER CONVEYANCEBACKWATER CALCULATIONSHEET (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) Barrel Entrance Entrance Pipe 25 year Pipe Outlet Inlet Barrel Barrel Velocity TW Friction HGL Head Segment Q Length Pipe "n" Elev Elev Area Velocity Head Elev Loss Elev Loss CB to CB (cfs) ft Size Value feet feet) (sq. feet fps) feet (feet) feet feet feet #20-#16 6.20 104 12" 0.011 209.50 227.28 OJ9 7.85 0.12 210.33 0.62 210.95 0.02 #16-#15 6.20 44 12" 0.011 227.28 232.42 0.79 7.85 0.12 227.89 0.26 228.15 0.02 #15-#13 6.20 72 12" 0.011 232.42 239.57 0.79 7.85 0.12 233.04 0.43 233.47 0.02 #13-#11 6.20 135 12" 0.011 239.57 253.71 0.79 7.85 0.12 240.19 0.81 241.00 0.02 #l i-#10 6.20 70 12" 0.011 253.71 262.10 0.79 7.85 0.12 254.33 0.42 254.75 0.02 #10-#9 6.20 55 12" 0.011 262.10 269.57 0.79 7.85 0.12 262.71 0.33 263.04 0.02 #9-#7 6.20 98 12" 0.011 269.57 283.19 0.79 7.85 0.12 270.18 0.59 270.76 0.02 #7-#5 6.20 188 12" 0.011 283.19 305.61 0.79 7.85 0.12 283.81 1.12 284.93 0.02 #5-#6 6.20 35 12" 0.011 305.61 312.00 0.79 7.85 0.12 306.23 0.21 306.44 0.02 (14) (15) (16) (17) (18) (19) (20) (21) Exit Outlet Inlet Approach Bend Junction Pipe Head Control Control Velocity Head Head HW RIM ELEV Segment Loss Elev Elev Head Loss Loss Elev UPSTREAM CB to CB feet feet feet feet (feet feet feet ca #20-#16 0.12 211.10 227.88 0 0.01 0.00 227.89 231.28 OK.� #16-#15 0.12 228.30 233.02 0 0.01 0.01 233.04 236.42 OK.� #15-#13 0.12 233.62 240.17 0 0.01 0.01 240.19 243.57 OK.� #13-#11 0.12 241.14 254.31 0 0.01 0.01 254.33 257.71 OK.� #11-#10 0.12 254.89 262.70 0 0.01 0.00 262.71 266.17 OK.� #10-#9 0.12 263.18 270.17 0 0.01 0.00 270.18 273.57 OK.� #9-#7 0.12 270.91 283.79 0 0.01 0.01 283.81 287.19 OK.� #7-#5 0.12 285.08 306.21 0 0.01 0.01 306.23 311.35 OK.� #5-#6 0.12 306.58 312.60 0 0.01 0.00 312.61 315.28 OK.� STORMWATER CONVEYANCE BACKWATER CALCUL4 TIDN SHEET (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) Barrel Entrance Entrance Pipe 25 year Pipe Outlet Inlet Barrel Barrel Velocity TVU Friction HGL Head Segment Q Length Pipe "n" Elev Elev Area Velocity Head Elev Loss Elev Loss CB to CB cfs ft Size Value feet feet s . feet f s feet (feet (feet feet feet #5-#3 6.20 59 12" 0.011 305.61 307.38 0.79 7.85 0.12 306.23 0.35 306.58 0.02 #3-#21 6.20 179 12" 0.011 307.38 309.17 0.79 7.85 0.12 308.00 1.07 309.07 0.02 #21-#22 6.20 100 12" 0.011 309.17 310.17 0.79 7.85 0.12 309.78 0.60 310.37 0.02 (14) (15) (16) (17) (18) (19) (20) (21) Exit Outlet Inlet Approach Bend Junction Pipe Head Control Control Velocity Head Head HW RIM ELEV Segment Loss Elev Elev Head Loss Loss Elev UPSTREAM CB to CB feet feet feet feet feet feet (feet ca #5-#3 0.12 306.73 307.98 0 0.01 0.01 308.00 313.05 OK.� #3-#21 0.12 309.22 309.77 0 0.01 0 309.78 315.26 OK.� #21-#22 0.12 310.52 310.77 0 0.01 0 310.78 313.17 OK.� I Wi/son Park&Park Z Rational Method Runoff from Developed Basin P(25) 3.40 inches (from attached Isopluvials Map) ZS A(24) 27.5 acres Use KCRTS Ca� IS minute routing 12.33 A(20) 35.0 acres Combination ofA(24)fA(16)+A(18) -Use KCRTS 14.97 A(16) 5.8 acres 6.2 A(18) 1.7 acres 2.3 Area(16) Description of Flow Path ft/ft k0 Ll 100 feet sl 0.05 Lawn/Landscaping 7.0 L2 950 feet s2 0.10 Pipe 20.0 Composite Runoff Coefficient A(1) C(1) 0.90 0.92 acres Impervious A(2) C(2) 0.15 0.79 acres Forest A(3) C(3) 0.25 4.09 acres Grasses 5.80 ' C�O 0.92*0.90+OJ9*0.15+4.09*0.25/5.8 0.340 Time of Concentration ' T(1) 100/60*{(7.0)*(0.05)**(0.5)} 1.1 Minutes T(2) 950/60*{(20.0)*(0.10)**(0.5)} 2.5 Minutes 3.6 USE 5 Minutes Compute i0 i�=(aR)*(Tc)**(-bR) i�=2.66*5**-0.65 0.93 Compute I(25) I(25)=P(25)*IOO I(25)=3.40*0.93 3.16 Q(25)=C*I(25)*A(� Q(25)=0.340*5.8*3.16 6.2 cfs A(16) Ar�ea(18) Descri�tion of Flow Path ft/ft k� Ll 50 feet sl 0.05 pavement 20.0 L2 350 feet s2 0.10 forest 2.5 Composite Runoff Coefficient I A(1) C(1) 0.90 0.95 acres Impervious i A(2) C(2) 0.15 0.75 acres Forest 1.70 COO 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 i0 iQ=(aR)*(Tc)**(-bR) iQQ=2.66*8**-0.65 0.69 Compute I(25) I(25)=P(ZS)*IOO I(25)=3.40*0.69 Z.34 Q(25)=C*I(25)*A(� Q(25)=0.57*1.70*2.34 2.3 cfs A(18) Area(20) A(ZO) = A(24) + A(18) + A(16) Basin Pasture Grass Im�ervious Forest A(24) 5.50 12.00 10.Q0 A(18) 0.95 0.75 A(16) 4.09 0.92 0.79 5.50 16.09 11.87 1.54 A(ZO) UPSTREAM BASIN INTO CB#24 '. ..47R�� '`..?�'!`a�..� . . . . �� Area ?� Till Forest U.00 acres Till Pasture 5.50 acres Till Grass i 2.00 acres Outwash Forest O.Ofl acres Dutwash Pasture 0.00 acres Outwash Grass 0.00 acres Wetland 0.00 acres " lmpervious 10.00 acres Tota l 27.50 acres Scale Factor: i.00 15-Min Redaced Edit Flow Paths i Time Series: Upstream Basin CB#24 » Compute Time Series � Modity tlser Input � File for computed Time Series [.iS� :,, �.� a: � ��'�`�� = _ .JJ� �+'-n --� - . .. � Flo�.* Frequency Atialysi� -------------------------------------------------------- Time Series File:upstream basin cb#24. tsf Praject Zocation:Sea-Tac l ---Annuai Peak Flow Rates--- -----Flow Frer�uency nIldl'y'S1S------- Flow Rate Ra.nk Time of Feak - - PcaY.s - - F.ank P.eturn Prob !CFS} (CFS) Period � � 4.80 6 2i09i01 12: 30 18.9g 1 100.00 0 950 '�!� 3.83 8 1i05�02 15 OU 12. 33 � -� 12.33 Z 12i08i02 17:15 ?.95 3 10.00 0.900 3.SS ? 8i26iU4 U:45 6.27 9 5.00 Ci .800 � 9.95 3 i1�1i�04 5:00 Ei.23 5 3.00 0.6f,i 6.23 5 10i27iC15 10:45 4 .80 6 2.00 0.500 6.3? � 10i25iGb 22 .45 3.85 7 1.30 0.231 lP 98 1 1%09i08 6 ?Ci 3 83 $ 1 10 O U91 C�_�rnput.ed F'e.,ks 15 . . 5ii iiQ 0.'��0 � � � � ► I UPSTREAM BASIN INTO CB#20 �' - �� _ ,,. , Are a ?� Til1 Forest 1.54 acres Till Pasture 5.50 acres Till Grass 16•09 acres Outwash Forest D.00 acres Outwash Pasture O.DU acres �I Ouhvash Grass 0.00 acres I Wetland 0.00 acres j impervious 1 i.87 acres _ __.__ _ Total 35.OQ acres _ __ ScaEe Factor: i.00 i 5-Min Reduced Edit Ftow Paths � Time Series: Upstream Basin CB#20 » Campute Time Series � Modify User Input � _ _ _ _ _ _ _ _ . __. ___ _ .._ . ____. File fior eomputed Time Series [.TSF] `,�4 . _ � _ �. . �..:�, ..-�, -._ _ . .. . , . . .. �� Flow Frequency Analysis -------------------------------------------------------- Tirae Series File:upstream basin cb�20.tsf Project Location:Sea-Tac ---Annual Peak Fiow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS} PEriod 5.91 6 2i09i01 12:30 23.39 1 100.00 0.990 � 4. 63 7 1i05i02 15:�0 1�.97 2 25.00 0.960 14.9? 2 12i08i02 17: 15 � 9.99 3 10.00 U.900 4.60 8 8i26iO4 0:45 8.22 9 5.00 0.800 9.99 3 11i17i09 S:OQ 7.50 S 3.00 0.667 7.50 5 10i27i05 10:45 5.91 6 2.00 O.S00 8.22 4 10i25i06 22:d5 4.63 7 1.30 0.231 23.39 1 1i09i08 6:30 4.fi0 8 1 .10 0.091 Computed Peaks 20.58 50.00 0.920 � +I I ► i SECTION 3.2 RUNOFF COMPUTATION AND ANALYSIS METHODS I FIGiJRE 3.2.1.0 25-YEAR 24-HOUR ISOPLLIVIALS 2S --" - -- _ SN HOMISH COUNTY �� S 5.�i�" �� a iiE _ __ __ __ _— C, - ' KING GOUNTY ?� Rr s - J � 28 � -� _'I �� ' _ _ �h �� - - - 3� r.,Rx_ _- _ __ � _ l� �' .� -- EIIID 4 � ,�S =_�,_ _ - �� o � h. . _ . � r_ . _. _- �;6 � 3 _ _�ei.._ � °7 ' _ ' --f�,y, �i . ' p7'�-�� _ _ 1 � ,) _ s. ��' `. � f ' _ � i - _ '- _ � - _ '``� 5.0 ,.,r, ; F _ - _ � ,�_. . . -��.� - . - , - �Y �. -- , _ _ . . �. �-.� � ___ ,� � '� � � � ��,� - - - � � r /I � � ��\ o - 't.7+ .�, __. � .�.w�� - i. � � �' r; � __– � s�., I � _ � � � 1� _� _ �� w� ,�� ; � -- 1/I yC��;, � � � � 1 � .. . . (� . . - P . �� , . _ .___ ... �' � u _ 1 a _ (/^� � -_ ' c _� � _�,., ro._ � _ s,,� � _ — __ �� ri - � � - - �� . � � - �' .�,�. 'S - a: - ..:' ^ � L' _ e � ryj `� "��.f � � -._ � _ o. � �` - - - - �• � � `\ � � � � - � - �• A. �_ uii=aw____ -KING COUNTV � V' �• PIERLE COUNTV WESTERN � �_ �. �� KING COUNTY �,�; -- _ - _ Ss N -- - 50 � 4.5 25-Year 24-Hour � � � � ,� r'-� Precipitation � � �� o -��_,�� in Inches °�M`�� , 1/9/2009 2009 Surface Water Design Manual 3-16 3.2.1 RATTONAL METHOD TABLE 3.2.1.A RUNOFF COEFFICIENTS- "C"VALLTES FOR TAE RATIONAL METHOD General Land Covers Single Family Residential Areas� Land Cover C Land Cover Density C Dense forest 0.10 0.20 DU/GA(1 unit per 5 ac.) 0.17 Light forest 0.15 0.40 DU/GA(1 unit per 2.5 ac.) 0.20 Pasture 0.20 0.80 DU/GA(1 unit per 1.25 ac.) 0.27 Lawns 0.25 1.00 DU/GA 0.30 Playgrounds 0.30 1.50 DU/GA 0.33 Gravel areas 0.80 2.00 DU/GA 0.36 Pavement and roofs 0.90 2.50 DU/GA 0.39 Open water(pond, lakes, 1.00 3.00 DUIGA 0.42 wetlands) 3.50 DU/GA 0.45 4.00 DU/GA 0.48 4.50 DU/GA 0.51 5.00 DU/GA 0.54 5.50 DU/GA 0.57 6.00 DU1GA 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 C�:x A,_ (C,x A,)+(CZ x Az)+_..+(C�x An),where A8=(A,+AZ+ ...+A�),the total drainage basin area. TABLE 3.2.1.B COEFF`ICIENTS FOR THE RATIOI�'AL METHOD"iR" EQUATION Design Storm Return Frequency aR bR 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 2J5 0.65 I 100 years 2.61 0.63 TABLE 3Z.1.0 kR VALUES FOR Tr LSING THE RATIONAL METHOD Land Cover Category kR Forest with heavy ground litter and meadow 2.5 Fallow or minimum tillage cultivation 4.7 Short grass pasture and lawns 7.0 Nearty bare ground 10.1 Grassed waterway 15.0 Paved area (sheet flow)and shallow gutter flow 20.0 2009 Surface Water Design Manual 1/9/2009 3-13 r ,i N'i 14bJ'J�1,"'�g�x..-!,ue"co. 06� r � I � ___ �''�10�sst 137262 � _. r `�caoa au�138 m � .. 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I I „ �'ClG-� Ci�ut:.�hni��ii lZr�ori C;��techr.ic��l �n�ii�LcrinQ Sn��fv 1'rc�posc�! RcSidential De�elc�pment �t>ulh ��ch 5tr�ii�'�rid T�iorris .'i�enue S��ull� R�riton_ �'va5l�in+�ti?n L��:� i�-,b �;��_ �:��l�-� I\TRC?llt C'TTO� '��e pr��iot��h� co�zlpletecl a �catcelinical en��inrrrin� stut��- fii�r tl�� 5ite i?f.3 rr��+��scd -�-lut , :hc>r� pl,jt. I��Gatcd at ihz abo��c addre55 in Kencot�. ��'asf�inL�c]n. �ti-i�I� aur tindin��, cnnclusiuns and r�c�fn�lneriCl3ti�n5 �rr>�n[e� irl �u�• I 1 `'? _(►C�� repurt title�f -'(;��technical �n�i�e��-in� Stu�s-. Pro}�t�sec� �-Lut �h{�rt Plat, 9�� 5outh 19?�� Strcct. k�nt��n. 44�a�hinoton_"� ��'4 under:t��nd that exp�tn5ion ofi the ;�tbjeCt �r��jcct t�� inc:lt�dc morc 1�3nd �i� th� east ��f the uri�in��l sii� i� �ein^ ��ntemplat�t�. Thi, added 1:3nt� `�cn�r�i]l� ri5es Illlfl�CC3te�� lU the �ast. The �urpu�z ��f this add�n�il►m is i�i c�pl��r� subsurfac� c��nditi��n ��i' tlii5 addcd iand ��nd evalua�4 its >tabilit� t� �3usur< <he �J�at��}�nica� rz�c�rn�l�ci�datic�ns tor ot'<3dtt1R, tiUfl�:ll:e �ind ��uund �z-ater c�lntr��l. ert�,i��n ahat�meni. sicc �tabiii�atiun. and fi�und�tiim c3e5i�n �nd constr�tction �r�senied in c�ur 1 I ?"'.�UC►-� _�ot�cf�nEcal r��rt ,3r� c3tst� ap}�licaht� tc� the cl��lupm�t�t of the addeci land. Yrescntc� in tl�is sddcndwl� are t�ur tir�din�; an� c��ncliisic}ns. 19213 Kenlake Place NE • Kenmore, Washington 98028 Phane (425) 483-9'!34 • Fax (425) 486-2746 i�l�i'U�31`t. (ti. �k_�l � ��dc3enc3um '�la. 1 - 1'rupc��rcl I��sidz��tial Dr�elc�pmerit L�.�A Jub�u. �:�17� 1'�l`.?C � PROJECT DESCR1PT101 lhe prujecl Si1e i� Lu b� <i�c�ss��l fr�7�� it� s�n�th �ic�e b�� a r�a��z-��- ��ff S��uth ��' Sti•cct `<<�in� nc.�rth�+arei into the sit�. rf�e ori�inal land «�ill bc l��in� l�Il T}lC 1'��CSt SI�C tlf'tI11S C��3� t�nd th� tici�iec� l.intl l��inG c��st of thc r��d. Thc ori�inal I�ni-i is ocn�rall} tlat. «�hilr the added lail� �3t�pe5 up«<�r�l ea;terl�� mc�tl�r.jteh�. l�he ��dd�d Iantj is fl3nkcd h�- a >tcc� sln�e up ;�� ,�ho�it 6 t�� 1? t��l �llL�l �,�3 i�s �ces� siclz .�hie:h �ippe�ir� t�� be a �ut s!�}pc rnadc �'cars <<��u tc> ,�llot�� ih� origin lanc� h�in�� rad�d 1lat. �lhe ac3ded 1;�nc1 is d��ttino 1��- ta(f �tiature, �ie�i�iuc�us anc3 e�'�rgr�cn tr�es and c�-��ec•ed h� densr brush and �-inc. T}�c tre�s arr alt �ir�ci�,ht ��iih nt� �±cnts in th� tr�t��E:s c�r d��«nhill lraniri+. �To signs ��t� erc�,ic�n c�r ;uil i110t"C1?l�ill �1:1�C I�een ili�t�.�l �z�iih ir-� t'i� added '��nci, SL�RFACE CUNi)TTT(�NS �ubstirtacc �t>naili��n ��f t}i� adde� lanel ��::� c�pl��n�i ��iil� tl�►-ee ittit pit5 c�ca�atr�� n rebruan• ?R_ ?C}l l. t� il�pth; fr�m 6.11 tc� (�.� feet. 1'h� a�prt�xin��t� lc,+ca�i��ns �f t1�c te�[ ��ii• ��r� sho�z-n on P1ate 1 - 5ite �nd E�{�lora�iun Lc�c�fti��n Y1a11. Tli� te5t pit� �j-cre loclt��I ;�ith either a t,3pe tT�easure �r b� �i�u�ll rCf�r�nce to exi;lin�: t��pt�gra�hir (eatures in t1�� 'icl� ant� �n the tc��i.�vr.Zphic it1�-C�� ma�. and ih�ir lOC�3Ti��nS sl��uld hz cun�ider�:d ��itlz- ._:c��:r��te t�� t1;� r1��a�ur�n�� m�thu�j it�zd. _� �*ec�crchni��l �n�inccr tY:�m uur ��tti�:e ��; pre�ent dtirin� sul�surlac;z �xplurti[it�n. «-h�� :imine�i c�le soi[ an� �ecy)c��ic i;��n�litiems �neot�ntered at��i co�z�pleted lc}�� tfi� teST pit�. �uil s��mpl�s cfhtaine� f'rom each 5c.�il Lillll in the te�t pit5 «-erc �-isuall� cla�>ili�d iZ _Trner��I :3e�ord��nee «-ith ['nited Sc�il C:l�issitic�ition ��-ste�11. � �:�ry�� f tt 11t��1 i� p]'e5etfi�t� LIU & ASSOCIATF.�, [i�C. f��]'Lls'31"�� l�_ 411i, .a��ienc�t�m \o. 1 - ['r�,,��,;ec� RG�iclriiti�l L)e�,cl;_to��r;- Lc�A Job '��_ �.�I,� p�it�i i i�l� 1��3�-C �', �tt�111�tj i�t.4CCl�tl(?tl� ��t �i?t{ l.l[ll�� c'I1Ct>UI1lC'f�Ci� ill]T1I1`1 �I'C i�'�rlt�1-�ilt�ii ;;i�C ��r�-tr�Twc3 in t}3c �4�t pit 3�� :�� Pl�ttL: � lI1I't"�Ll�h -+, T�le iC�l ��{l� �il�i'�ll�l[�C�� ;� :��r ui lui��_ �_�I''��tlll� i�:>��tJl�. �1'c�1Tl i Tl� �if it�C�lti* t�'.ICh_ i�fl thti Sllli.3�e. Th� to�s�til i� un�jerlai�� t- ti l:i�er c�f brim-n t�� litTl�t-t�rt�1�-r�_ ��L�l�ttion till +:1�eathcretl cill) ►�t ri��lit�m-ciensL. �ilt•� tinc s�md, u�itf� a tr�ic�e �-�f to ;ome L 1'3Z'l`I an�� t�cc�:sion�i] ci�hhEc �nd hc7��lder, �b��u� i_� to �? teet tfii�k. L'nciEr�z•ina ti'�e .�l�latit?r� ti�I tu the d�p�h5 c�;�l«recl ia �� fo��rri0ni ti1] (fr��h till) �ic�i�tiii «1� li�l�x-hr��iin t� ii�l3t-�r�ti. `rr�-�le��c. i�-e:�kiti-�emcnt, sil� linc ��tt� ��it�� Sc�rnt �?rij��l. �(-hc ;oil c�nciiti��n of��ieci �'i]tj iti '��i2�]'t�ift- :itlli�iti It? 1�1�t1 �lt t��C' ��I?��?T1�11. 13i1i�'. (�:lZpl��-D�'4'A7'ER CONDITTt)ti _rl1l,':�il��'.C:�.t-:� ti` �i \\�ii\ � 1[ � t ; `.� �' �' i �' � tT :p:�_ t7=�t en�c l��:c.�cd r� ,:�ri_ �� tl-:� �e.,; � t, �,�c�i�.�t�c3 ��.� th�� aud�{� l�inti, ll1�C��5SIc�� .aNU C.-[_)�C'Lt-SIO'ti T�;.�S�l� ilI] Z�it' �U��UTI�ILC �.�11i� c131C� �Ct�llt7t��Z�3t�r) CC1Ili�llli)il Cl�::i?Lll7l�.t'�L� 1;1 LIi: �C�T ('It� r�c�«<<<e� �}n the acidzd land_ thc gcE�r.cchnic:il rL�unulienci�tti��s in i>ut• l 1 ?? �'t�l)� ��c��tcchnica] rcp�rt �h�uid als�� hc s�pplicak�le t« thz ci��elc�pmz,�t i�f'tl�z ac�cied ]a�ld. It i� ��t�r �pir�ic�n th��t adclee� I<�n� shti��lci �� uit� 5ta�+le and �:.��l��ic h�zards rn�er the addcd I<ir�d �11i�u1�� b� I111I11[11K'�! if cfi� re�c�rnmen�l��tio�.� in c}cir 1 I '??'?OU� rep��rE �+re liall� i[11�+��.I17:_111�,Cj c:l1i( t?��}�1-�Ll� �14JI'lII:�T �:t�1lilZt3�:lt�.}1l, LIU � :��5(1GI_�TE�, ��, , I-�l�nian� 1`. �Cl l� :ldcirndui��'�1��. I - 1'r�pos�d Re�ider_tic�� L)c�e3c>pnlent I.�.A i��b �{�_ -�.�1�-� �'t1�C -� nRAI\aGE 1_1�TPROti`E!�1FNT .-'� c3r:31I]3Q� ��rSC oi�;�irl,tC� t��ater u�i� ��CCZC[� �'t3I111I2° di?��n t�1C fli�la.de �}2l t)�� es5tet�1 �:�aif c�i' the tit�Lli�l si�ie o#' th� si[�. tf��n 1luuinQ tl�rt�u�h �� l.i�t-ert into a :iiicl� �ll��t�� the nt�rth tiide ��f South ��`~ StreeT. Tl�e �tiutcr in thi� c�rain�� our,e a�p��3rs tu �e �tc�r_��ater r�ICaSed 1r��2Ti the d�ti�Cl��rEn4nt e<�st oi` ►_hC pr��ie�t �it� arzd L�UITI�'?�� t�nt� thi �ubj�4i site. lt i� t�L1I U�1i11C?!l ��]�ji t�ii; stonn�t�atcr sh�crld he c��lle�tcd anc� r�-r��u��c3 in a j�int ��tt i)1: '?''��jCCt tiil�. CLCl�t:RE �� e ar� ��le<<��cl t�� be ur 5er�ii� to t ctiu u�� This pruj.ct. Ple��sc terl fine tc� ��ntact u; if�-e�� f7:1'�� .�11'�" �]t1Cy�li�flti 1"C�'31"�417�� 1��15 t"��t?1"t l`t' 1��zU IIirCEICf" �l�Il`U�i31li.}ll. 4' - r�� `�` ~°a �l l�lir� �f.'C\ CI1�jt_ -:�'��. � -�� LTI_- �. .��Sc.>Ci.�TL-S. 1'�C. � � � � k � �` �l'+, �a� __ � e� p " .1. S. �Tulian► L.iu_ PI;.D.. P.T'_ � �. �r=. .. C��nsultin� C�i�uizehnical �nvinccr .,-x'' - _:'t. ti- ..�y.,�--�5��.f�.. . -.. -.- _ F��ur �l��tes �in.ac��d LIL & A�S(�CTATES, INC. t . �•.aa i � ; , .s ' ` �� ' #� � . ' � � : � � �� µ 1 S�iC9 Sq �1� � =,�7C1 5R �t w S,�C14`-�4� f ��s....» -- - -- - -��--�_.�i �te.' '7,�,`�Ft � 1 J � ;f , � ,�',� �.lf SaR"�'� = � � s� � ' �`— ., _ ' i 1_ , �.. ^, � � , � �y"�-CyT „-.,+� �+-�.�.-. �.t�——-�--. � i,..��. .� �,1 C--. e$ ^e7 �Trifl �' � L..j��? _ �} � �.431'!S��3.56' �'"•i,+� �-�p- • L�r �� b�0 � :�z.�-�`c_ _ . .a. ..�• 1` � �. � �iF's -' -"-- -�lA�M� '" _,� ,��r.- +_ �_,�:r+��:.—y�-.r rai+e��.�. 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Grc�.VE� `�,f��1TH i �71Vf =iLT1` ��'cH'y'F_ I S�IL� �E—�,��.!€� �r�.r�a� .;iF��._ i ��PJE� ' GC . _ j �'r E' �"f�r.'� _ _ �.�I�G' 4L�Mf �''1�r' .Y=LL-��fi�.-�=D 5�.:� =i"v�-� ��,�PS� 5'-' � ,�',�.�N�r SP ! ?r��'�v _F.�.�=�� C"',-^i s{�_JF_ ��"'��. i .C_t._I<N. Fl�'ti!'—J,F ..3.4�c�l;-'�+�_'�F � �=;.�,Ira€��t�THE c^��__��: ., , S�ND `�`i H SF�I `.�T' �� _Y��s_:=_ =��fra� ... ��d- �1rJ�s ' �' — -- _ � �,� „Ln ; � �AL _ =11�a�- i �lL� nND GLr.Y IN�RG��:C "" - GR�a"a�G G� =:�^-• LI+}I.}iT}ll°v11T �C��L� �_��;�.�su�� rJRvr"4�4C �iL _4 i yi_ C`�:�. f1f f' ' �,R:�r•FJ ; ?v J=t:=TH�'_��14'i�s� ��L I T �i:V3J L.r�� IlY�IZlsT11V�� tvfn �ILT Jr - =�y �_.KST�C.T?` --"C-j� �.� - .. Fr.SG!^d�:i;�`�� l.H CL�.'r'�F :. �_.�;�Tir` �r = Li..� �+_::4;T � s_� c;�•.,�� -�v� ��R►,n� _ �R�.�ti-.� �H ::R�r,r�ic � = v�s�tai� �, - � ` ;��f��,7` Q��t��i�� 1�,� r'"�-'� F=.4T �TEa�� r,HL7 . r-. _ :�� _:� l��-,TE�:: S�;�� 'V'_�:I�T�:�C� P�1��I�IER.�: - _�.., v�.�'.L:i' .J..i i� . �ti�:�.S�r. _,� ,!��.;Y.�C4�:-.�.�i.�.., _��+. � f -.��F`.ti: . �. ��TI_ii1= -,._:I T ❑F` �� _ _ _.., vE =�.�L '-vCGRC . ,�= ,;ITH=il'�,�1D2�;-u3 � cT=�U�r ��?�'�'.3ti 3? �;;�,�r =-_,� - _-. - -�'li s1�..5�tF_� •''I��, _LEfI:� _..��-:P . =:RYTE�T� i� -� �= _" ,� - - 1 , =-t.�. _� "--_ ,.,+v � -�A'.�'F R 1-�:G' . 5i��_',+`u.�T�- i , -=-�� ` -:la� v- -- - �='� ' -- '- _ - �, ._�� .=-� �,"_'�- ,=t='i"L��.t.{�¢ tli:;i::- ^�=-=L?-_ --_ . r -- � _;s=D �°'. .--�'F�= ;?��, -:F �t��:. ..�-�':':��Tfi . �i.F�._ .,_T •:'i� �_= F�._E .';.r:7E? =R �,..-�R�TE= -_ , - `_ -- ..t.i� ..--�_ _ -. . - _ _i`,:={L,.. v� -. ':=�' r .�{`,"�_�_ . ,,.r-- -�-- _ .. �" =LC Ltl' � ��I.�TES, I?��. ur�,��a �c�i� c��sss�i�,��i�r� ��_�� -.. ....-��:.,si =-y r%='iryQ . _�9:.,�Yit1�_f_�;,inj4� €_"'^�.,...��c.F � F'_r,T� �: i TEST PIT N4. 1 L�gged sy: JSL �7at2. 2.�28;'�"v'1 Gr�u1.^. E1. ± � C'B'J:h ij�`GS $BTpic L'd �tF2! � - G�1ScJ. S��`. �v��rlptlQ!1 Nn. "�'c TB�t ' Q'_ BNSn 211d C��f�f1 SUtf2C8 i ---- �Dark-brotfr, loase, organ�c.siltyf:^e SAhD, •rr:;h=�,�e roots. ,--� S�� moist{'TGPS��iLi -------- J� z Brown tc.ight-brown, medium-dense, siE,ry fine S�NC.t.*aee gr�vel, occssio�a+ roc-ts moist{w�atherec V�SHON TILL: o � � ; e F �� __'r��_�_��`��'��____ Y 5hd Light-gray, very-dense. silty�ne SA�V�. some g�av�l.w2akly- � 5 mcist r.�resr v�SNOy TiLI�) � � � � ' d -est pit ter,ninated �t�.5�; graundwater n�t enco�niared 8 � 14 t t• ��ST PIT NO. 2 Lagged By JSL Date Zi28�2��11 Grcund EL t , �ea:h USCS Sa-rpie w O:�er n. CLf1SS SOf' �aCrl il0'1 N•�. `>: T�S: pL b'ine ar,d duff on sur�ace 1 ---- �Dark-a�own, :oos2. organic. �ilty nne SRND. w��h 5ne roots ,-- S►yq � most{70PSLlLi ______�' �' ___ '� -- L Light-brown, medium-dense, sitty fsne SAtvD,trac�to some gravel. occasional eob�le and boufder,moist fweath2red VASHON TIL�y 3 4 � � ---- -----------------�----------------- I � SM Light-gray. very-dense, silty fine SAND, some gravEl.weakiy- 5 �eme�ted. mo�st�fresh`4'HS�ON TItL) T�S�pit terrninated at 6.0 ft: graundwater nok er.countered I 0 V I � � 1� � � TE�T PlT LOGS LTI� & aSSC)C1aT�S, INC�. RESIDENTIAL DEVEL�PMENT _ _ S. 55TH STRE�T $� MURRIS AVENUE S. ve�techri�a E��i-,eerrg cr;inesring Gc:dogy Ear.h S��crc� RENTON. WASHINGTON - - - J��B N0. 4r�'.;,t aATE 3,��,'2�1° �LAT� 3 TEST PiT NU. 3 �ogged By: JtiL Date: 2r�28;'201' Graursd �i. ± aea:h UuCS Sam,^le 'vV flTnef it. C�ss. Soif ��s~r+�:ion ��. -lo TAs. �L Lr.,�sh an�du�r on surfaee 1 ____ `Cark-brflwn, laose. arganic. si:!�f fin�5P:NQ.�with roots, �—— Sh� � moi�t{?��501L'; __�' � Lkght-brown;� yes!�wish-br4vm, medium-dense. silty yne �AhID. trace grarel and occas�ona!cobble a�d �oultier, moist i 5 (w2ather��J,�SHOfV TILL; � Sh.t Li�ht-gray, very-de�se. sil#y fne Sr,t�D: �n7e gra�el weakiy 0 1 6 moist ifires�VASHON-1LL} Test o�t�em�irated a�6.5�t:groundwa�er n�#encauntered. � � E 'I 1 TEST PiT Nts. Logc�d By �SL �ate Gr�unti EI, ± �e^:h llSGS Sdmp;e W Qtre� ' t ft.j CLAS� Soil Descr}}tlDn No �'lo �est j 1 i � � 4 � � h a a � '0 � TEST PIT L4GS LIIT c4z t1S��►�ES, I�iC. R�SIDENTI�L DEVELOFMENT S_ S�TH STR�ET & M4RR1� AVENUE S. i�4r�re�h�;cF� Eng ree•in_ E�gin��•rg uea:oay Ea�n S�i��;,� RENT�N, WASHINGTON __ - - -— J�B N0 �A13d !�ATE 3:r�r2�1" �Lr,7� d GE�TECHNICAL INVESTIGATION WILSON PLAT 720 SOUTH 55� ST'REET RENTON, WASHINGTON L&A Job No. 9A008 Date: February 24, 2009 Prepared for: Mr. Robert Wilson 21703 —60`� Street East Lake Tapps, WA 98391 Prepared By: Liu& Associates, Inc. . 19213 Kenlake Place NE Kenmore, Washington 98028 LIU & ASSOCIATES, INC. Geotechnical Engineering Engineering Geology Earth Science February 24, 2009 Mr. Robert Wilson 720 South 55'� Street Renton, WA 98055 Dear Mr. Wilson: Subject: Geotechnical Engineering Study Wilson Plat 720 South S St'' Street Renton, Washington L&A 7ob No. 9A006 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 ± grading, slope stabilization, erosion mitigation, surface and ground water drainage contr � foundation design and construction, etc., for the proposed development of the site. Presented �n this report are our findings, conclusions and recommendations. II PROJECT DESCRIPTION For our use in this study, you provided us with a set of topogaphic 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 55�' Street. The platted building lots are to be accessed from 55�` Avenue South to the south side of the site via a new roadway entering the site near its southwest corner and an existing i gravel driveway at about 120 feet west of the southeast corner. These roadway/driveway aze to 19213 Kenlake Place NE • Kenmore, Washington 98028 Phone (425) 483-9134 • Fax (425) 486-2746 i February 24, 2009 Wilson Plat LBcA Job No. 9A006 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 the northwest corner of 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: 1 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. 9A006 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 fram 13 to 39 percent. The higher gradient portions of the site generally lie within the eastern 100 to 120 feet and the westem 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 e�cisting 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 Geolo 'g,�c Map of the Lake Stevens Quadrang,le, Snohomish County, Washin t�on, 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 Mora.ine (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. 9A006 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. I 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 glaciallobe of the Vashon Sta.de of - the Fraser Glaciation. The lodgmont till is generally a compact mixture of unsorted clay, silt, sand, gravel and cobble, commonly refened to as "hard pan". The ablation till is similaz 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 appro�mate locations of the test pits aze 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. 9A006 Page 5 reference to e�sting 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 ea.ch 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 eastem high ground area, the layer of topsoil -1 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 tenace 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 tenace 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 ?. Located near at the west end of the site, encountered a weathered andlor 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. LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat _ L&A Job No. 9A006 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 RECOMMENDATIONS 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. 9A006 Page 7 Surficial unsuitable soils, including topsoil and loose to medium-dense weathered soils mantlmg i, 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 i and stormwater detention vault. Conventional footing foundations constructed on or into the I above competent basal soils may be used to support the proposed residential building and I stormwater detention vault. Structural fill, if required for site grading, should be placed on proof- rolled, 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 tenace 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 ow 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. 9A006 -- Page 8 i 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. j x ' 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, e�rtensive, static goundwater 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 topsoi� and loose weathered soils, should be completely stripped down to the medium- dense to dense, fresh Kame tenace 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. � LIU & ASSOCIATES, INC. �1 � I February 24, 2009 Wilson Plat _ L&A Job No. 9A006 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 area.s 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 neaz-surface groundwater seepage. Water captured by such ditches or interceptor trench drains should be discharged into onsite detention/settling ponds or neazby 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:1V in topsoil, loose to medium-dense weathered Kame terrace and ablation till soils, no steeper than 3/4H:1V 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 112H:1 V. 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:1V in medium-dense to dense Kame terrace deposits, and no steeper than 1-1/2H:1V in lodgmenttill soils. LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9A006 � 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 ta11 after stripping of surficial 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 I � 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-term stability, and I 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. � ` I February 24, 2009 Wilson Plat ^ L&A Job No. 9A006 Page 1 l 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 ofthe maximum dry density deternuned by ASTM D1557 (Modified Proctor Method) as follows: i: Apnlication % of Maximum Dry Densitv Within building pads and under foundations 95% Roadway/driveway subgrade 95%for top 3 feet and 90%below Retaining/foundation wall backfill 92% Utility trench backfill 95% for top 4 feet and 90% below STORMWATER DETENTION VAULT 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 Kame terrace deposit at depths about 4.0 to 5.0 feet. The vault may be supported on footings founded on these comgetent 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 least 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 NI'irafi Inc. or approved equal. A vertical drainage blanket at least 12 inches thick horizontally, consisting of clean 3/4 to 1-1/2-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 Miradrain 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 wa11s of the detention vault would also serve as retaining walls to support cut banks and bacl�ll. The perimeter walls of the vault capped with a lid would be restra.ined 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 pcf equivalent fluid density (EFD) be used for the design of vault perimeter walls. To counter the at-rest soii LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9A006 Page 13 � presswe, a passive lateral soil pressure of 375 pcf EFD may he used, except that the passive I 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 r-, ' based on a coefficient of friction of 0.55. t! 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 ta.ken 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 azea, 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 No. 9A006 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 roadwaysldriveways �I 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 constn,iction equipment, such as a fully-loaded 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 layer 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 I,&A Job No. 9A006 Page 15 foundations should be embedded at lea.st 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 founda.tions should be e�ended 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 should be no steeper than 2.SH:1 V. 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. 9A006 Page 16 , • The minimum depth to bottom of perimeter footings below adjacent final e�erior 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 tota.l post-construction settlement of the buildings should be 3/4 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 fi-iction 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 f- 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. 9A006 Page 17 GENERAL EARTHWORK and the STRUCTLJRAL FILL sections of this report. Where moisture control is critical, the slab-on-grade floors should be placed on a ca.pillary 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, 7/8-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 CIP CONCRETE RETAINING WALLS Building basement walls would be required to support backfill. Cast-in-place concrete wa11s may be used to retain fill embankments along the west and part of the south baundaries of the site. Basement walls restrained horizontally at the top aze 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 wa11s restrained at the top; and 40 pcf EFD for retaining walls unrestrained at the top. These lateral soils pressures are applicable to wa11s with level backslope. With a backslope rising away from the wa11s, 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 axe 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 overtuming 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 18 , k A drain line consisting of perforated, rigid PVC, drain pipe or slotted, corrugated ADS, drain pipe, at least 4 inches in diameter, should be installed at a few inches below bottom of basement �, ` or retaining wa11s to intercept and drain away groundwater flowing towa.rds the walls. The drain 4 lines should have sufficient slope (0.5 percent 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 drain lines 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, consisting of clean, 3/4 to 1-1/2-inch, washed gravel or crushed rock, should be placed against the walls. Alternatively, a vertical drain mat, such as Miradrain 6000 by Mirafi Inc. or equivalent, may be placed against the wa11s as the vertical drainage blanket. The vertical drainage blanket or drain mat should be hydraulically connected to the drain lines at the base of the perimeter walls. ROCKERY WALLS General Rockery walls may be used to line the cut banks along the east boundary of the site. Rockery by nature is not an engineered retaining wall, such as a reinforced concrete wall. Although a rockery wall can provide some degree of retention capability, its main function is to serve as a protective facing to retard weathering and erosion process to the earth bank behind the rockery. To achieve a satisfactory rockery wall, the earth bank behind the wall must be stable by itself on a long-term basis. In addition, the rockery wall should be constructed in a proper way to assure long-term stability of the cut bank or fill embankment. The medium-dense to dense, fresh Kame terrace and/or lodgment till deposit underlying the site at shallow depth is of moderately-high to high shear strength. It is our opinion that cut banks in these sail deposits will be able to maintain long- term stability if lined by properly constructed rockery. Our design of rockery walls lining cut banks in these competent deposits is shown on Plate 8 attached hereto. LIU & ASSOCIATES, INC. February 24, 2009 , Wilson Plat L&A Job No. 9A006 � Page 19 � I Rockery Material and Construction I Rock material used for rockery construction should be hard, well-cemented, sound, durable and �� free of cracks, fissures, joints, air holes and other defects. Construction of rockery walls should �, be in compliance with the Standard Rockery Construction Guidelines published by Associated I Rockery Contractors. �! Subgrade and Keyway Trench Preparation Construction of the rockery walls should start immediately following completion of cut banks and keyway trenches. The keyway trenches should be cut into medium-dense to dense, fresh Kame terrace and/or lodgment till soils capable of rendering an allowable bearing capacity of at least 3,000 psf. The keyway trenches should be at least 12 inches deep below the finish grade in front of the rockery wall and should be wide enough such that the heel of the keyway trenches would be at least 12 inches from the back of the base-course facial stones. Keyway trenches should be free of loose disturbed soils or standing water and the exposed soils at bottom of keyway trenches should be compacted to a non-yielding state with a vibratory mechanical compactor prior to rockery installation. Groundwater Drainage Control A drain line should be placed in the keyway trenches behind the base-course facial stones to collect and drain away groundwater flowing toward the rockery walls. The drain lines should consist of minimum 6-inch, perforated, rigid, PVC pipes, wrapped in a filter fabric sock. The bottom of the keyway trench and the drain line should have sufficient slope (0.5 percent minimum) to generate flow by gravity. Water collected in the drain lines should be tightlined to discharge into a storm sewer or a suitable stormwater disposal facility. Faciai Stones Facial stones of the rockery walls should be as nearly rectangular as possible with the long dimension of the stones placed perpendicular to the wa11 alignment. Facial stones should be LIU & ASSOCIATES, INC. February 24, 2009 , Wilson Plat ' — L&A Job No. 9A006 '' — Page 20 � stacked tightly against one another to minimize voids between the stones. Excessive openings between the facial stones should be chinked with smaller rock from behind. The rockery walls should be constructed such that the facial stones of each successive course would be staggered over and firmly supported on stones of the previous course. Facial stones of the rockery walls should be tilted back at an inclination no steeper than 6V:1H. Drain Rock Course A drain rock course, consisting of 2-to-4-inch rock spalls, should be installed between the facial stones and the cut bank in lifts as each course of the facial stones is completed. The horizontal thickness of the drain rock course should be at least 12 inches. The purpose of the drain rock course is to retain soils in place while allowing groundwater to bleed out. PRECAST CONCRETE BLOCK WALLS General Precast concrete block walls may be used to support fill embankments to be constructed.along the west and part of the south boundaries of the site. These walls may be constructed with commercially available precast concrete blocks, such as by Keystone, Lock Block or Redi Rock. Loose topsoil and loose to medium-dense weathered soils within the keyway trenches of the walls should be over-excavated down to medium-dense to dense, fresh Kame terrace and/or lodgment till soils. The block walls should be constructed with geogrid mesh reinforcement anchored to the block wa11s and embedded in the wall bacl�ll. The wall should be founded on a minimum 4-inch layer, 7/8-inch crushed rock, leveling base, placed over firm undisturbed bearing soils capable of rendering an allowable bearing capacity of at least 3,000 psf. A vertical drainage blanket should be placed against the back of the concrete block facing and hydraulically connected to the drain lines at the base Qf the wa11s. The remaining wa11 bacl�ll behind the vertical drainage blanket should consist of compacted structural fill consisting of clean granular soils. 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: Reinforced Retained Foundation Leveling Soils � �oi1s RQ�k B�s� Unit Weight, Y, pcf 130 120 135 135 Angle of Internal Friction, 36 33 36 40 �, degees , 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 gound acceleration is about 0.3g (g = gravity force) for such an event in the Puget Sound region. The block wa11s, 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 wall 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 Walis Vegetation within construction limits of the block wa11s 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. 9A006 Page 22 medium-dense to dense, fresh Kame terrace andlor 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 iaid 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 bacl�ill 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. 9A006 Page 23 DRAINAGE CONTROL Onsite Stormwater Disposal The moderately-sloped mid-section and the low-lying western portion of the subject plat site are underlain by fresh Kame terrace deposit of clean, gavelly, fine to medium sand deposit and infiltration of stormwater into this soil stratum is feasible for the residential buildings to be constructed in these areas. The impervious lodgmont till deposit, however, was found underlying �� "Tract A", located at the northwest corner of the site, at a depth as less as 5 feet below the �; existing grade. Therefore, we do not recommend a concentrated infiltration facility in "Tract A" to dispose a large amount of stormwater into the ground. This is because the large amount of concentrated disposed stormwater in this tract may increa.se the potential of groundwater seepage " downhill off the subject site where the lodgmont till may be e�osed or near the ground surface. ;` Increased groundwater seepage may elevate the possibility of erosion, sloughing and la.ndlside. , � Appendix C — Small Project Drainage Requirements, of the King CountX. Washing;ton Surface Water Design Manua1,, January 24, 2005, allows stormwater collected on 2,000 or more but not � more than 10,000 square feet of impervious surfaces of small residential projects to be disposed onsite with infiltration or dispersion method. The "full infiltration" method specified in Section C.2.2 — Full Infiltration of the above design manual can be used on sites underlain by medium sand or coarse sand or gravel and cobble. The moderately-sloped mid-section and the low-lying western portion of the subject plat site are underlain by fresh Kame terrace deposit of clean gravelly, fine to medium sand deposit and are qualified for using Full Infiltration method to dispose stormwater for the residential buildings in these areas. According to the above design manual, infiltration trenches installed into clean gravelly sand soils should be designed to be at least 30 feet long for every 1000 s.f. of impervious surFace served (with a 2-foot-wide trench). The length of infiltration trenches may be shortened proportionally with increased trench width. � LIU & ASSOCIATES, INC. February 24, 2009 Wilson Plat L&A Job No. 9A006 Page 24 The infiltration trenches should be set back at least 10 feet from adjacent buildings and 5 feet from property lines. The schematic presentarion 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 3/4 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. � _ i , �i �' Building Footprint Ezcavation �� 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 ti 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 I Wilson Plat L&A Job No. 9A006 �I Page 25 ��, installed in paved roadways/driveways. Stormwater thus collected should be tightlined to II 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 i lines should have a sufficient gradient (0.5% minimum) to generate flow by gravity. The drain I� lines should be wrapped in a non-woven filter fabric sock and completely enclosed in clean washed gravel. The remaining trenches may be bacl�illed with clean onsite soils. Water collected by the perimeter footing subdrain systems should be tightlined, separately from the roof and I' 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 cleanouts 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. 9A006 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 recommendaxions in this report during construction. The conclusions and interpretarions 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, 2009 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. �C3 ,s Yours very truly, ,�'�i�o�w�s�cr LIU OCIATES, INC. �� ; c� � �' �, ,� 27589 J. S. (Juli )Liu, Ph.D., P.E. � ��3isc�� ' Consulting Geotechnical Engineer �01Vp1,Y� ' ; � '.FXPI�/17/ " Nine plates attached � �;� > I _ � '� .r� , � � -� � LIU & ASSOCIATES, INC. ��•� ;?' a d�� : � r O � '. 5a. �� .'�. �vuter .n > � 'S\ o �� K-¢��,✓ . :+�1,1 � -� Z ?�� il"l �i � � t �.^lU..v��'''; � '' F�a'.I �� SE 179TH PL ,^I� � a ��k7Jry � .�` � ¢`� y��' -a� ,arcx-� ��. 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' UNIFIED SOIL CLASSIFICATION SYSTEM MAJOR DIVISIONS GROUP GROUP NAME SYMBOL GRAVEL CLEAN GW WELL-GRADED GRAVEL,FINE TO COARSE GRAVEL COARSE- MORE THAN 50°k 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�OARSE 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 c�aY SOILS LESS THAN 50% ORGANIC OL ORGANIC SILT,ORGANIC CLAY MORE THAN 50% SILTY AND CLAY INORGANIC MH SILT OF HIGH PLASTICITY,EIASTiC SILT PASSING ON THE LIQUID LIMIT CH CLAY OF HIGH PLASTICITY,FAT CLAY NO.200 SIEVE 50°/a OR MORE ORGANIC OH ORGANIC SILT,ORGANIC SIIT HIGHLY ORGANIC SOILS PT PEAT AND OTHER HIGHLY ORGANIC SOILS NOTES: SOIL MOISTURE MODIFIERS: �I 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 CIASSIFICATION 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,AND/OR TEST DATA. USUALLY SOIL IS OBTAINED FROM BELOW WATER TABLE LIU & ASSOCIATES, INC. UNIFIED SOIL CLASSIFICATION SYSTEM __ Geotechnical Engineering • Engineering Geology Earth Science PLATE 3 TEST PIT NO. 1 Logged By: JSL Date: 2/4/2009 Ground EI. t Depth USCS Sample W Other ft. ctAss. Soil Descri tion No. % Test OL Fem bushes and duff on surface 1 Dark-brown, loose,organic,silty fine SAND,with roots to 1/4-inch diameter, moist(TOPSOIL) 2 SM Brown, medium-dense, silty fine SAND,trace 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 8 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 n. c�a,ss. Soil Desc�iption No. % Test OL Berry bushed and duff on surface 1 Dark-brown, loose, organic, silty fine SAND,with roots to 314-inch _ diamete�moistLTOPSOILZ_ � 2 SM Brown, medium-dense, silty, fine to medium SAND,with trace gravel and cobble and abundant roots, moist 3 (KAME TERRACE) a 5 -- ------------- SM Brown-gray, dense, silty fine SAND, some gravel and occasional 6 cobble, very-weakly-cemented, moist(LODGMONT TILL) 7 B 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 - -------- - - — ---- ------ -- �os No. 9A006 DATE 9/10/2009 PLATE 4 TEST PIT NO. 3 Logged By: JSL Date: 2/4/2009 Ground EI. t Depth USCS Sample W Other I n. cv+ss. Soil Descri tion No. % Test ! OL Berry bushes on surface � Dark-brown, loose,organic,siity fine SAND,with fine roots, moist -- -, {TOPSOIL) -------------� 2 SP Brown, loose, graveliy, fne to medium SAND,slightly moist (weathered KAME TERRACE) 3 SP Light-gray, medium-dense to dense,fine to medium SAND,trace 4 gravel, slightly moist(KAME TERRACE) 5 6 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 EI. ± Depth USCS Sample W Other ft. c�+ss. Soil Description No. % Test OL Berry bushes on surFace 1 Dark-brown to black, loose, organic, silty fine SAND,with roots to 1/2-inch diameter, moist(TOPSOIL) 2 SM/SP Brown, loose to medium-dense, slightly silty,fine to medium 3 SAND, few roots, slightly moist(weathered KAME TERRACE) 4 SP Brown-gray, medium-dense to dense,fne to medium SAND, moist 5 (KAME TERRACE) s � a 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. 9A006 DATE 9/10/2009 PLATE 5 ) TEST PIT NO. 5 Logged By: JSL Date: 2/4/2009 Ground EI. t Depth USCS Sample W Other n. c�ass. Soil Descri tion No. % Test OL Ivy on surface 1 Dark-brown to black, loose,organic, silty fine SAND,with fine � roots, moist(TOPSOIL) � �———————————————————————— 2 SM/SP Brown, medium-dense to dense, silty to slightly silty, fine SAND, trace gravel, moist(KAME TERRACE) 3 4 5 SM Brown-gray, dense, silty fne SAND,trace gavel, very-weakly- 6 cemented, moist (LODGMONT TILL) 7 - 8 I 9 II Test pit terminated at 8.0 ft,groundwater not encountered. 10 TEST PIT NO. 6 Logged By: JSL Date: 2/4/2009 Ground EI. ± � Depth USCS Sample W Other ft. CLASS. SOII D@SCfI t1011 No. % Test OL Brush on surface 1 Dark-brown, loose, organic,silty fine SAND,with roots to 1/2-inch SM/SP � diameter, moist(TOPSOIL) � �————————————————————————� 2 Brown, medium-dense,slightly silty,fine to medium SAND,trace gravel, moist(weathered KAME TERRACE) 3 4 SP Light-gray, medium-dense to dense,fine to medium SAND,trace 5 gravel, moist(KAME TERRACE) s _ � 8 9 Test pit terminated at 8.0 ft,groundwater not encountered. �0 TEST PIT LOGS LIU & ASSOCIATES, INC. WILSON PLAT - -- - - - -- - --_ _---- 720 SOUTH 55TH STREET Geotechnical Engineering Engineering Geology� Earth Science RENTON, WASHINGTON --- - - ____ - -- —----_ _------ --- _ JOB NO. 9A006 DATE 9/10/2009 PtATE 6 � TEST PIT NO. 7 Logged By: JSL Date: 2/4/2009 Ground EI. ± Depth USCS Sample W Other ft. CLASS. SOII Description No. % Test OL Brush and duff on surface i __ �Dark-brown, loose,organic,silty fine SAND,with fine roots, SM/SP � moist(TOPSOIL) I 2 Brown, loose to medium�lense, slightly silty, fine to medium SAND,trace gravel, slightly moist(weathered KAME TERRACE) 3 q —— —————————————————————————— SP Brown-gravel, medium-dense to dense, gravelly,fine to medium 5 SAND, moist(KAME TERRACE) 6 7 8 9 —— —————————————————————————— SM Light-gray, dense, silty fine SAND,trace to some gravef, �0 very-weakly-cemented, moist(LODGMONT TILL) 11 Test pit terminated at 9.5 ft,groundwater not encountered. 12 TEST PIT NO. Logged By: Date: Ground EI. ± Depth USCS Sample W Other ft. CLASS. SOII Description No. % Test 1 2 3 __ 4 5 6 7 8 TEST PIT LOGS LIU & ASSOCIATES, INC. WILSON PLAT _ - - - --- --- -- - ---- - 720 SOUTH 55TH STREET Geotechnical Engineering Engineering Geology EaRh Science RENTON, WASHINGTON _ _ __ _ _----- — ---- ___- - ---- -—-- — JOB NO. 9AOO6 DATE 9/1O/2009 P�TE 7 � � � � � �� _ � , _f; � r r � �'� � •� � C�M PAG'(�D Or15 I TE GXIST� / / .�' ., � 50(L F�LL�C �g�� , �(ZA� ' / � ` TH«K) d��d� ��I rlor�-ulo�1�1 Fc�T� �oa � �A�R( c� . � I �d � / � J' t�v-� �A�l k X r/ jN � f2 M�N� � , ��a�� Gov�ZsE(�� -ro�{.►r �20�-�G S�P.�l.- F�w� _ � , � _ �� a n l2" M��l. � �'r�M{h1. �PF�F PVG - ��.��l p�P� F�rTc-fl �r � . ` 1f /� �tLTEK Fp.R�P�I L �D�k � z _ �, _ � � NOTES: 1. Rockery construction shatl comply with Standard Rockerv 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 holes and other defects. 3. Rockery construction shall start immediately following completion of cut banks and keyway t�enches. 4. Drain lines shall consist of 6-inch minimum, perforated, rigid, PVC pipes fitted with a fi{ter 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 �east 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 smalte�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. 8. Drain rock shall consist of 2-to-4-inch quarry spalls, ptaced in lifts after completion of each course of facial stones. ROCK SfZE AND WEiGHT SCHEDULE ROCKERY FACfAL STONE SCHEDULE Rock Size Weight,Pounds Avg.Dimension,Ft. Wall Height Facial Stone Size -- Small to Large 1-Man 50-200 0.75- 1.25 H, Ft. Base Course Lower Third Middle Third Upper Third Small to Large 2-Man 200-700 1.25-2.0 4 S 3-Man L to S 2-Man L to S 1-Man L to S 1-Man Small to Large 3-Man 700-2000 2.0-2.75 6 Large 3-Man Small 3-Man l to S 2-Man L to S 1-Man Small to Large 4Man 2000-4000 2.75-3.5 8 Small 4-man Large 3-Man L to S 3-Man L to S 2-Man 5-Man 4000-6000 4.0-4.5 10 Large 4Man Small 4man Large 3-Man L to S 3-Man 6-Man 6000 -80d0 4.5 TO S.Q 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 LIU & ASSOCIATES, INC. TYPICAL SECTION - ROCKERY LINING CUT BANK WILSON PLAT 720 SOUTH 55TH STREET Geotechnical Engineering�Engineering Geology� EaRh Science RENTON, WASHINGTON J JOB NO. 9AOQ6 PLATE NO. 8 1 - roo( drain PLAN VIEW 4"rigid or 6'flexible NTS perforated pipe --------------------------------------•---- ---. ------------•------•-----------------------•---' infiltration trench sump wlsolid lid PLAN VIEW roof drain NTS overflow 4'rigid or 6'flexible splash block perforated pipe _$i� - � T � �� : � gu :o o"----- op i �� 0 washed rock �, 4o p o°p C ''min 5.0'min _ :' �— 1 1/2"-3/4' .":.^ Q o o� o' �min . • o 00 ' � '--------- ---------------------�Q--°--n-----�f" fine mesh � CB sump w/solid lid screen varies A t.lo a-W ovGrJ C.vM PAcTF� F l L�CER Pp,�R1 L F,�/�.GKFI LL . . I ! � '+�'. , ':e- , � (I� �'I� . .e�, ••' -� � �' .� � � V 90 � a lU � ' � , -- �{-�` R i G i� o� � � '�aa` Q�Q � �"�xi�� `? � n�d a p � �� PEr�FoP�T�D ; a" a O L] I �IP� . � V ��M ia� - , �d°Q �q W�� r�� ;li - _ _ Ill 3/4�� - ��i� � C l.�A�1 �At�D =24" M�a. �ocLs - SECTION A � NTS INFILTRATION TRENCH - SINGLE DISPERSION PIPE LIU & ASSOCIATES, INC. WILSON PLAT 720 SOUTH 55TH STREET GeotechnicalEngineering�EngineeringGeology�EacthScienoe RENTON, WASHINGTON JOB NO. 9A006 DATE 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 55"' Street ' • Building permit for: o Retaining Wall over 4' in height o Stormwater vault I • Right of Way Use permit to connect to existing water system (Soos Creek) ', • Others ; . 1 , I� i 'I _` . � _., ; ; Section 8: CSWPPP Analysis and Design The proposed development consists of 4.62 acres of developed area. A DOE 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 F�cpert 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 rnnditions change. ,.� Wilson Park & Park 2 TESC pond sizing � �� . Qrea � Till Farest d.61 acres Till Pasture 0.00 acres Tiil Grass 0.00 acres ', Outwash Farest 0.00 acres Outwash Pasture U.00 acres Outwash Grass 0.00 acres Wetland (i.00 acres impervious 0.00 acres --- --- Total - 4.6i acres Scale Fador : 1.00 15-Min Reduced Time Series: Wilson TESC sizing » �ompute Time Series � Mvdiiy User Input I _._..�____ _ _ _ _ __._ __ _ _------ File #or computed Time Series [.TSFJ '' �� ,�. , � =1oJ J � Flow Frequency Analysis -------------------------------------------------------- Time Series File:wilson tesc sizing.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow FrcquencT� Analysis------- Flow Rate Rank Tirae of Peak - - Peaks - - Rank Return Prob (CFS) (CFS} Periad 0 .300 2 Zi09i01 17:15 0.505 1 100.00 0.99Q �J .090 7 1i06i02 2:30 0.300 2 25.00 0.960 0.213 4 3i06iO3 18:45 0.231 3 10.00 0. 900 0.011 $ 3i08iO4 18:45 0.213 4 5.00 0. 800 0.143 6 1i05i05 7:30 0.196 S 3.00 0. 667 , 1�,�� 0 .231 3 1i18i06 20:15 0.143 6 2.00 0.500 v�� 0 . 196 5 11i24i06 5:15 0.090 7 1 .30 0. 231 0 . 505 1 1i09i08 9:30 0.011 8 1.10 0.091 Computed Peaks 0.437 50 .00 0. 980 � �� ► ;; I i I I �I I � � � � � � � �� .�. a L`4 = N I � �� Lz� � a = � �,-�.�` - °� ��°' � �� -� = Q-� 15 �� " � , a � c��'�-�;�i �� '� Cl� , l�a �? - 'S� 01- - ---- ��.��4 -�--�'I.l.�p � - i :..� � � ��1�' :�� 1�2 =- �� I : � �� o �0 �� = t � � �� .�� '�'v�� a��d ��!��- Section 9: Bond Quantities, Facility Summaries, and Declaration of Covenant • Bond Quantity Worksheet • Declaration of Covenant for Inspection and Maintenance ,� �� , � , H W W _ � Y � O 3 � z a � a c z 0 m Site Improvement Bond Quantity Worksheet Original bond com utations prepared by: ', „— ^�`� /i/ Name: �fr�Z%r,�� ,%L, Date: � �7i Gv C`7 PE Registration Number. �'"'� �� Tel.#: ` � ' Firm Name: ��j � ��'�.) ��(,..�j Address: �� =jC, ��'if� � �_�., Project No: ��, c�,�,Pr _ ROAD IMPROVEMENTS&DRAINAGE FACILITIES FINANCIAL GUARANTEE REQUIREMENTS PERFORMANCE BOND',** PUBLIC ROAD&DRAINAGE AMOUNT MAINTENANCE/DEFECT BOND'," Stabilization/Erosion Sediment Control(ESC) (A) $ - Existing Right-of-Way Improvements (B) $ - Future Public Road Improvements&Drainage Facilities (C) $ - Private Improvements (D) $ - Construction Bond"Amount (A+B+C+D) = TOTAL (T) $ - Minimum bond'amount is$1000. (B+C)X Maintenance/Defect Bond"Total 0.20= $ - NAME OF PERSON PREPARING BOND"REDUCTION: Date: `NOTE: The word"bond"as used in this document means any financial guarantee acceptable to the City of Renton. ""NOTE:All prices include labor,equipment,materials,overhead and profit. Prices are from RS Means data adjusted for the Seattle area or from local sources if not included in the RS Means database. REQUIRED BOND'AMOUNTS ARE SUBJECT TO REVIEW AND MODIFICATION BY RDSD Page 1 of 1 Unit prices updated: 2/12/02 Version:4/22/02 REF 8-H BOND QUANTITY WORKSHEET.xIs Report Date: 1/19/2010 Site Improvement Bond Quantity Worksheet Existing Future Public Private Quantity Completed Right-of-Way Road Improvements Improvements (eond Reduction)* &Drainage Facilities Quant. nit rice nit uant. ost uant. ost uant. ost Complete Cost GENERAL ITEMS No. Backfill&Compaction-embankment GI-1 $ 5.62 CY 0.00 0.00 0.00 0.00 Backfill 8 Compaction-trench GI-2 $ 8.53 CY 0.00 0.00 0.00 0.00 Clear/Remove Brush,by hand GI-3 $ 0.36 SY 0.00 0.00 0.00 0.00 Clearing/Grubbing/Tree Removal GI-4 $8,876.16 Acre 0.00 .00 0.00 0.00 Excavation-bulk GI-5 $ 1.50 CY 0.00 0.00 0.00 0.00 Excavation-Trench GI-6 $ 4.06 CY 0.00 0.00 0.00 0.00 Fencing,cedar,6'high GI-7 $ 18.55 LF 0.00 0.00 0.00 0.00 � Fencing,chain link,vinyl coated, 6'high GI-8 $ 13.44 LF 0.00 0.00 0.00 0.00 � Fencing,chain link,gate,vinyl coated, 2 GI-9 $1,271.81 Each 0.00 0.00 0.00 0.00 I Fencing,split rail,3'high GI-1 $ 12.12 LF 0.00 0.00 0.00 0.00 Fill&compact-common barrow GI-11 $ 22.57 CY 0.00 0.00 0.00 0.00 I Fill&compact-gravel base GI-1 $ 25.48 CY � 0.00 0.00 0.00 0.00 � Fill&compact-screened topsoil GI-1 $ 37.85 CY 0.00 0.00 0.00 0.00 Gabion,12"deep,stone filled mesh GI-1 $ 54.31 SY 0.00 0.00 0.00 0.00 Gabion,18"deep,stone filled mesh GI-1 $ 74.85 SY 0.00 0.00 0.00 0.00 Gabion,36"deep,stone filled mesh GI-1 $ 132.48 SY 0.00 0.00 0.00 0.00 Grading,fine,by hand GI-1 $ 2.02 SY 0.00 0.00 0.00 0.00 Grading,fine,with grader GI-1 $ 0.95 SY 0.00 0.00 0.00 0.00 I Monuments,3'long GI-1 $ 135.13 Each 0.00 0.00 0.00 0.00 Sensitive Areas Sign GI-2 $ 2.88 Each 0.00 0.00 0.00 0.00 Sodding, 1"deep,sloped ground GI-21 $ 7.46 SY 0.00 0.00 0.00 0.00 Surveying,line&grade GI-2 $ 788.26 Day 0.00 0.00 0.00 0.00 Surveying,lot location/lines GI-2 $1,556.64 Acre 0.00 0.00 0.00 0.00 Traffic control Crew(2 flaggers) GI-2 $ 85.18 HR (7 0.00 0.00 0.00 0.00 Trail,4"chipped wood GI-2 $ 7.59 SY 0.00 0.00 0.00 0.00 Trail,4"crushed cinder GI-2 $ 8.33 SY 0.00 0.00 0.00 0.00 Trail,4"top course GI-2 $ 8.19 SY 0.00 0.00 0.00 0.00 Wall,retalning,concrete GI-2 $ 44.16 SF 0.00 . 0 0.00 0.00 Wall,rockery I-2 � 0. 0 Page 2 of 7 SUBTOTAL 0.00 O.DO 0.00 0.00 4 I � I�=�� ?.�j� l�7(sa�'� lri,7(v S Unit prices updated: 2/12/02 Version:4/22/02 RFF R-H R�Nn nl IANTITY WORKSHFET xls Report Date: 1/19l2010 Site Improvement Bond Quantity Worksheet Existing Future Publfc Private Bond Reduction" Right-of-way Road Improvements Improvements 8�Drainage Facilities Quant. Unit Price Unit Quant. Cost Quant. ost uant. ost Complete Cost ROADIMPROVEMENT No. AC Grinding,4'wide machine<1000sy RI-1 $ 23.00 SY 0.00 0.00 0.00 0.00 AC Grinding,4'wide machine 1000-2000 RI-2 $ 5.75 SY 0.00 0.00 0.00 0.00 AC Grinding,4'wide machine>2000sy RI-3 $ 1.38 SY 0.00 0.00 0.00 0.00 AC Removal/Disposal/Repair RI-4 $ 41.14 SY 0.00 0.00 0.00 0.00 Barricade,type I RI-5 $ 30.03 LF 0.00 0.00 0.00 0.00 Barricade,type III(Permanent) RI-6 $ 45.05 LF 0.00 0.00 0.00 0.00 Curb&Gutter,rolled RI-7 $ 13.27 LF 0.00 0.00 0.00 0.00 Curb&Gutter,vertical RI-8 $ 9.69 LF 0.00 0.00 0.00 0.00 Curb and Gutter,demolition and disposal RI-9 $ 13.58 LF 0.00 0.00 0.00 0.00 Curb,extruded asphalt RI-1 $ 2.44 LF 0.00 � 0.00 0.00 0.00 Curb,extruded concrete RI-11 $ 2.56 LF 0.00 0.00 0.00 0.00 Sawcut,asphalt,3"depth RI-12 $ 1.85 LF 0.00 0.00 0.00 0.00 Sawcut,concrete,per 1"depth RI-13 $ 1.69 LF 0.00 0.00 0.00 0.00 Sealant,asphalt RI-1 $ 0.99 LF 0.00 D.00 0.00 0.00 Shoulder,AC, (see AC road unit price) RI-1 $ - SY 0.00 0.00 0.00 0.00 Shoulder,gravel,4"thick RI-16 $ 7.53 SY 0.00 0.00 0.00 0.00 ' Sidewalk,4"thick RI-1 $ 30.52 SY 0.00 0.00 0.00 0.00 Sidewalk,4"thick,demolition and dispos RI-18 $ 27.73 SY 0.00 0.00 0.00 0.00 Sidewalk,5"thick RI-19 $ 34.94 SY 0.00 D.00 0.00 0.00 Sidewalk,5"thick,demolition and dispos RI-2 $ 34.65 SY 0.00 0.00 0.00 0.00 Sign,handicap RI-21 $ 85.28 Each 0.00 0.00 0.00 0.00 Striping,per stall RI-22 $ 5.82 Each 0.00 0.00 0.00 0.00 Striping,thermoplastic,(for crosswalk) RI-23 $ 2.38 SF 0.00 0.00 0.00 0.00 triping,4' re ectorized ne -2 0.25 LF - 0.00 0.00 0.00 . Page 3 of 7 SUBTOTAL 0.00 0.00 0.00 0.00 '�� '�� Unit prices updated: 2/12/02 Version:4/22/02 RFF A-H RnNn�UANTITY WnRKSHEET xls Re�ort Date: 1/19/2010 Site Improvement Bond Quantity Worksheet Existing Future Public Private Bond Reduction" Right-of-way Road Improvements Improvements 8 Drainage Facilities Quant. Unit Price Unit Quant. ost uant. Cost Quant. Cost Complete Cost - - 1 For KCRS'93,(additional 2.5"base)add:RS-1 $ 3.60 SY 0.00 0.00 0.00 0.00 AC Overlay,1.5"AC RS-2 $ 7.39 SY 0.00 0.00 0.00 0.00 AC Overlay,2"AC RS-3 $ 8.75 SY 0.00 0.00 0.00 0.00 AC Road,2",4"rock,First 2500 SY RS-4 $ 17.24 SY .00 0.00 0.00 0.00 AC Road,2",4"rock,Qty.over 2500SY RS-5 $ 13.36 SY 0.00 0.00 0.00 0.00 AC Road,3",4"rock,First 2500 SY RS-6 $ 19.69 SY 0.00 0.00 0.00 0.00 AC Road,3",4"rock,Qty.over 2500 SY RS-7 $ 15.81 SY 0.00 0.00 0.00 0.00 AC Road,5",First 2500 SY RS-8 $ 14.57 SY 0.00 0.00 0.00 0.00 AC Road,5",Qty.Over 2500 SY RS-9 $ 13.94 SY 0.00 0.00 0.00 0.00 AC Road,6",First 2500 SY S-1 $ 16.76 SY 0.00 0.00 0.00 0.00 AC Road,6",Qty.Over 2500 SY S-1 $ 16.12 SY 0.00 0.00 0.00 0.00 Asphalt Treated Base,4"thick S-1 $ 9.21 SY 0.00 0.00 0.00 0.00 Gravel Road,4"rock,First 2500 SY S-1 $ 11.41 SY 0.00 0.00 0.00 0.00 Gravel Road,4"rock,Qty.over 2500 SY S-1 $ 7.53 SY 0.00 0.00 0.00 0.00 PCC Road,5",no base,over 2500 SY S-1 $ 21.51 SY 0.00 0.00 0.00 0.00 PCC Road, 6",no base,over 2500 SY S-1 $ 21.87 SY 0.00 0.00 0.00 0.00 Thickene Edge -1 . 0.00 ' 0.00 00 Page 4 of 7 SUBTOTAL 0.00 0.00 0.00 0.00 ZZ� �'�2�- ��j� �b� Unit prices updated: 2/12/02 Version:4/22/02 REF 8-H BOND QUANTITY WORKSHEET.xIs Reqort Date: 1/19/2010 Site Improvement Bond Quantity Worksheet Existing Future Public Private Bond Reduction* Right-of-way Road Improvements Improvements &Dralnage Facilities Quant. Unit Price rnt Quant. Cost uant. ost Quant. Cost Complete Cost R � /,� - r For Culvert prices, Average of 4'cover was assumed.Assume pertorated PVC is same price as solid pipe. Access Road,R/D D-1 $ 16.74 SY 0.00 0.00 0.00 0.00 Bollards-fixed D-2 $ 240.74 Each 0.00 0.00 0.00 0.00 Bollards-removable D-3 $ 452.34 Each 0.00 - 0.00 0.00 0.00 "(CBs include frame and lid) CB Type I D-4 $1,257.64 Each 0.00 0.00 0.00 0.00 CB Type IL D-5 $1,433.59 Each ", � 0.00 0.00 0.00 0.00 CB Type II,48"diameter D-6 $2,033.57 Each 0.00 0.00 0.00 0.00 for additional depth over 4' D-7 $ 436.52 FT 0.00 0.00 0.00 0.00 CB Type II,54"diameter D-8 $2,192.54 Each 0.00 0.00 0.00 0.00 for additional depth over 4' D-9 $ 486.53 FT 0.00 0.00 0.00 0.00 CB Type II,60"diameter D-10 $2,351.52 Each 0.00 0.00 0.00 0.00 for additional depth over 4' D-11 $ 536.54 FT 0.00 0.00 0.00 0.00 CB Type I1,72"diameter D-12 $3,212.64 Each 0.00 0.00 0.00 0.00 for additional depth over 4' D-13 $ 692.21 FT 0.00 0.00 0.00 0.00 Through-curb Inlet Framework(Add) D-14 $ 366.09 Each 0.00 0.00 0.00 0.00 Cleanout,PVC,4" D-15 $ 130.55 Each 0.00 0.00 0.00 0.00 Cleanout,PVC,6" D-16 $ 174.90 Each 0.00 0.00 0.00 0.00 Cleanout,PVC,8" D-17 $ 224.19 Each 0.00 0.00 0.00 0.00 Culvert,PVC,4" D-18 $ 8.64 LF 0.00 0.00 0.00 0.00 Culvert,PVC,6" D-19 $ 12.60 LF 0.00 0.00 0.00 0.00 Culvert,PVC, 8" D-20 $ 13.33 LF 0.00 0.00 0.00 0.00 Culvert,PVC, 12" D-21 $ 21.77 LF 0.00 0.00 0.00 0.00 Culvert,CMP,8" D-22 $ 17.25 LF 0.00 0.00 0.00 0.00 Culvert,CMP, 12" D-23 $ 26.45 LF 0.00 0.00 0.00 0.00 Culvert,CMP,15" D-24 $ 32.73 LF 0.00 0.00 0.00 0.00 Culvert,CMP,18" D-25 $ 37.74 LF 0.00 0.00 0.00 0.00 Culvert,CMP,24" D-26 $ 53.33 LF 0.00 0.00 0.00 0.00 Culvert,CMP,30" D-27 $ 71.45 LF 0.00 0.00 0.00 0.00 Culvert,CMP,36" D-28 $ 112.11 LF 0.00 0.00 0.00 0.00 Culvert,CMP,48" D-29 $ 140.83 LF 0.00 0.00 0.00 0.00 Culvert,CMP,60" D-30 $ 235.45 LF 0.00 0.00 0.00 0.00 ulvert, D-31 0.00 0. 0 0.00 0.00 Page 5 of 7 SUBTOTAL 0.00 0.00 0.00 0.00 �L�-� �Zf.�i �7�� Unit prices updated: 2/12/02 Version:4/22/02 REF 8-H BOND QUANTITY WORKSHEET.xIs Re�ort Date: 1/19/2010 Site Improvement Bond Quantity Worksheet Existing Future Public Private Bond Reduction` Right-of-way Road Improvements Improvements DRAINAGE CONTINUED &Drainage Facilities Quant. No. Unit Price Unit Quant. Cost Quant. Cost Quant. Cost Complete Cost Culvert,Concrete,8" D-32 21.02 LF 0 0 0 0 Culvert,Concrete, 12" D-33 $ 30.05 LF 0 0 0 0 Culvert,Concrete, 15" O-34 $ 37.34 LF 0 0 0 0 Culvert,Concrete,18" D-35 $ 44.51 LF 0 0 0 0 Culvert,Concrete,24" D-36 $ 61.07 LF 0 0 0 0 Culvert,Concrete,30" D-37 $ 104.18 LF 0 0 0 0 Culvert,Concrete,36" D-38 $ 137.63 LF 0 D 0 0 Culvert,Concrete,42" D-39 $ 158.42 LF 0 0 0 0 Culvert,Concrete,48" D-40 $ 175.94 LF 0 0 0 � Culvert,CPP,6" D-41 $ 10.70 LF 0 0 0 0 Culvert,CPP,8" D-42 $ 16.10 LF 0 0 0 0 Culvert,CPP,12" D-43 $ 20.70 LF 0 � 0 0 0 Culvert,CPP,15" D-44 $ 23.00 LF 0 0 0 0 Culvert,CPP,18" D-45 $ 27.60 LF 0 0 0 0 Culvert,CPP,24" D-46 $ 36.80 LF 0 0 0 0 Culvert,CPP,30" D-47 $ 48.30 LF 0 0 0 0 Culvert,CPP,36" D-48 $ 55.20 LF 0 0 0 � Ditching D-49 $ 8.08 CY 0 0 0 0 Flow Dispersal Trench (1,436 base+) D-50 $ 25.99 LF French Drain (3'depth) D-51 $ 22.60 LF 0 0 0 0 Geotextile,laid in trench,polypropylene D-52 $ 2.40 SY 0 0 0 0 Infiltration pond testing D-53 $ 74.75 HR 0 0 0 0 Mid-tank Access Riser,48"dia, 6'deep D-54 $1,605.40 Each 0 0 0 � Pond Overflow Spillway D-55 $ 14.01 SY 0 0 0 D Restrictor/Oil Separator, 12" D-56 $1,045.19 Each 0 0 0 0 Restrictor/Oil Separator,15" D-57 $1,095.56 Each 0 0 0 0 Restrictor/Oil Separator,18" D-58 $1,146.16 Each 0 0 0 0 Riprap,placed D-59 $ 39.08 CY 0 0 0 0 Tank End Reducer(36"diameter) D-60 $ 1,000.50 Each 0 0 0 0 Trash Rack,12" D-61 $ 211.97 Each 0 0 0 0 Trash Rack,15" D-62 $ 237.27 Each 0 0 0 0 Trash Rack,18" D-63 $ 268.89 Each 0 0 0 0 Trash Rac ,21" - 4 06.84 ach 0 0 0 Page 6 of 7 SUBTOTAL 0 Z, ��) 0 0 0 � , r�� Unit prices updated:2/12/02 Version:4/22/02 �F A_H RnND nUANTITY WORKSHEET.xIs Report Date: 1/19/2010 Site Improvement Bond Quantity Worksheet Existing Future Public Private Bond Reduction' Right-of-way Road Improvements Improvements 8 Drainage Facilities Quant. Unit rice nit Quant. Price uant. Cost uant. ost Complete Cost PARKING LOT SURFACING No. 2"AC,2"top course rock&4"borrow PL-1 $ 15.84 SY 0 0 0 0 2"AC, 1.5" top course&2.5"base cour PL-2 $ 17.24 SY 0 0 0 0 4"select borrow PL-3 $ 4.55 SY 0 0 0 0 1.5"top course rock&2.5"base course PL-4 $ 11.41 SY 0 0 0 0 WRITE-IN-ITEMS (Such as detention/water quality vaults.) NQ WI-1 Each 0 0.00 0.00 0.00 WI-2 SY 0 0.00 0.00 0.00 WI-3 CY 0 0.00 0.00 0.00 WI-4 LF 0 0.00 0.00 0.00 WI-5 FT 0 0.00 0.00 0.00 WI-6 0 0.00 0.00 0.00 WI-7 0 0.00 0.00 0.00 WI-8 0 0.00 0.00 0.00 WI-9 0 0.00 0.00 0.00 WI-10 �.�0 0.�� 0. SUBTOTAL � /��0.00 0.00 0.00 0.00 SUBTOTAL(SUM ALL PAGES�: ?/�� O'� J 0.00 �G[/��`� 0.00 I��S 0.00 0.00 30%a CONTINGENCY 8 MOBILIZATION: r(C�� 0.00 ��G�-��J 0.00 ��t.� 0.00 0.00 -r GRANDTOTAL: ��il�l�� 1� 0.00 �f///') �/� 0.00 ��/`�`�� 0.00 0.00 COLUMN: B C D E Page 7 of 7 Unit prices updated: 2/12/02 Version:4/22/02 REF 8-H BOND QUANTITY WORKSHEET.xIs Renqrt Date: 1/19/2010 H Z Q Z W � � U � O Z O �Q �G g v W � �----- ��'�(1 rfJ(I RECORDING REQUESTED BY AND WHEN RECORDED MAIL TO: CITY CLERK'S OFFICE CITY OR RENTON 1055 SOUTH GRADY WAY RENTON, WA 98057 DECLARATION OF COVENANT FOR INSPECTION AND MAINTENANCE OF STORMWATER FACILITIES AND BMPS Grantor: Grantee: Ciry or Renton Legal Description: �� 'T � �7 �V�- S� �� k� �-�. SE �'� � � � y� -k�� w;`�. -��z��- �t� 1� � c�•�. ,�u.� l .o� 1.�- �-d-� �d�c, �8 �.a-�- Additional Legal(s)on: (,�i� 1�'1 ��2�%1(m !� . �{n�� Z�! Cj��'. Assessor's T'ax Parcel ID#: �I Z?j OS ' 1 � 2� � �f��f�� " 1 � l.� IN CONSIDERATIOI� of the approved City or Renton � [ �` permit for application file No. LUA/SWP � ��7' ��Lj�Z relating to the real property ("Property") described above, the Grantor(s), the owner(s) in fee of that Propert_y, hereb_y 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)ar 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)#: . Stormwater facilities include pipes, swales,tanks,vaults,ponds,and other engineered structures designed to manage stormwater on the Properry. 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 BMI's, 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 statin the Ci ' ' g ty s mtention 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 BMP on the Property creates any of the hazardous conditions listed in KCC 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 snch 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. I! 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 beriveen 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. T'his Declaration of Covenant shall run with the land and be binding upon Grantor(s),and Grantor's(s')successors in interest,and assigns. 3 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 , 20 GRANTOR, owner of the Property GRANTOR, owner of the Property STATE OF WASHINGTON ) COL'IVTY 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 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 C2.2.1 are met. 8. The ground surface of the infiltration depression must be vegetated with grass or other dense ground cover. l� � C.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.133 (p. G18). The intent of these instructions is to explain to �� ' future property owners,the purpose of the BMI'and how it must be maintained and operated. These instructions are intended to be a minunum;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 osted on Kin Coun 's Sur ace Water Desi P g tY .f Sn Manual website. ❑ TEXT OF INSTRUCTIONS Your ro ert contains a stormwater mana ement fl w con r I BMP m o t o best ana ement ractice called P P Y 9 � 9 P ) "full infiltration,"which was installed to mitigate the stormwater quantity and quality impacts of some or all I � 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 ravel filled trenches d ells n r a d ound surtace de ressions facilitate this rocess b � uttin runoff in 9 , � , 9 p , P YP 9 . direct contact with the soil and holdin the runoff lon enou h to soak most of it into the r n 9 9 9 9 ou d. T o 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 �'� I . 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 Vl�ater Desigc►Manual—Appendix C C-44 C.2.? FLZ,L I'��F'ILTRATIOti FIGURE C.2.2.0 TYPICAL DRYWELL LYFILTRATION SYSTEM �Roof Downspout House Catch Basin �(Yard Drain) / �RooF f�ow Downspout � DRY WELL 48lnch Diameter Hole Filled with PLAN VIEW 1�12-3�washed Drain Rock NTS Roof Downspout Mark Center of Hole with 1"Capped PVC House �Overflow or Other means Splash Block Topsoil Flush with Surface - 1 - - - -- - -- - - - -- 1' min. —► _ ..,- . . „ ,.,_; flow � ��Q�r�°��p L ao "2� �0 27 ��c ao o a o a �o Fine Mesh Screen I Min.4"dia. ° op��pop��°= op PVC Pipe �aoa�9�° ��^,�o� Catch Basin �C'`�� '�o (Yard Drain) � `x 48 Inch Diameter � Varies Sides of Hole �� Hole Filled with ; Lined with �� 1��2-3"Washed � Filter Fabric o� Drain Rock � 8�0, '� 15' min. �,o�,_p_, ,�G� �° bpo.,[�° �'�°�,L�a�D Min. 1'above Seasonal DRY WELL HighGroundwaterTable SECTION � NTS ?009 Surface�5'a�er Design 1�lanual—�ppendizc C U9/2009 c-a� C.2.2 F[II.L INFIL.TRATION FIGURE C.2.2.A TYPICAL TRENCH INFII,TRATION SYSTE�VI � � � roof � drain j RLAN VIEW ! �T� —4"rigid or 6' flexible ' ;%� perforated pipe i ------•a_._�-------------•--•-------- - �_�t1 i �.�� '----------------------------------•--------•--'"� .� infiitration trench �sump w/solid lid PLAN V{EW roof drain � NTS i overflow —, 4"rigid or 6'flexible Spl�sh blocK,� `'�� ! - ;�periorated pipe . .. / i r.�v ,., �;`�%'; � ♦1\ ��\f\'� 1� ��.f��1\�t\�\/\•Zf�✓\�; �-- :i,,:��,.' � . 6, i,:rflr,:i,!i,. ; �r;:i��r`-1,�i�;�i.�J:;.:��:.., , - ; --�------•.;�------------•------•-------------- - �,�� ;��°� v ^ 1 T1'min 4�� '�. waShed roCk l'>� - -= - - ��+ 5.0'mi� 12"i �--- 1 1/2"-3i4" �= '-✓=" - f min _ .. _, _,. ,. _ ' , �. • � L-- ------ ---------------------�---�..�='------ • � �, fine mesh — CB sump+n�,"solid '�id .. , �� cr�roc,n 4'1f165 A filter fabric---� � ' ,.--- -- compactec backfill � 6„ r\ �/', _ � , � �` `' •' 4A rigid or 6"flexible � - -_ ` perfor�ted pipe 24" • �� `� _ � :. � � � .�r ` �•�� 12" :�'("� 3 L�;� -,i i v t� washed raCk f .{ � a .. `, 1 1/2"-3;4° I + i��>,-`��;�.�y;.; �'' ,�,:..;�;�;�y>. j4�i�r/,••!:,'.:i I��24" SECTI{}N A -- NT� --__ 2009 Surface Water Design 141anual-Appendi�c C 1/9/ZQpy C-�l5 Section 10: Operation and Maintenance Manuai ' The Operation and Maintenance of the individual BMP's for each lot is attached. SECTION C.2 FLOW CONTROL BMPs other types of soils or f ll 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.13,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 hazdpan 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 deternuning whether full infiltration of roof runoff is mandatory as outlined in Secrion 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.2.23,C.22.4,and C.2.2.5. Note:full infrltration may be possible using other rypes a»d srzes of infrltration devices if designed by a civil engineer in accordance with the infltration facility standards in Section 5.4 of the SWDM. • Gravel filled trenches(see Section C.2.2.3,p.C-42) • Drywells(see Section C.2.2.4,p. C-43) • Ground surface depressions(see Section C.2.2.5,p.C-43) 3. A minimum 5-foot setback sha(1 be maintained between any part of an infiltration device and any structure or pmperty line. Lazger setbacks from structures may be specified in the design specifications for each infiltration device. Infiltration devices may not be placed in sensitive azea 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 � [ands[ide hazard area or steep slope hazard area must be 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 pemut review staff can waive this requirement if site topography clearly prohibits subsurface flows from intersecting the drainfield. 6. The infiltration of runoffmust not create flooding or erosion impacts as determined by DDES. If runoff is infiltra#ed near a landslide hazard area,erosion hazard area,steep slope hazard area,or a slope steeper than 15%,DDES may require evalua.tion and approval of the proposal by a geotechnical engineer or engineering geologict. G2.2.3 USE OF GRAVEL FILLED TRENCHES FOR FULL INFILTRATION Gravel filled trenches(also called"infiltration trenc6es")aze a good option where the depth to the ma�cimum wet-season water table or hardpan is between 3 and 6 feet Fignue C.2.2.A(p.C-45)and Figure C.2.2.B(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 lengt6 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. Maaimum 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 3/4-inch to 11/2-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 C.2.2.B. 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. I 7. Infiltration trenches must be setback at least 15 feet from buildings with crawl space or basement elevations that aze 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 pazking 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.B,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 aze gravel filled holes as opposed to trenches and therefore may allow for a more compact design in azeas where the depth to the rnaximum wet-season water table is relarively 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 11/Z-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.C-47)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 maacnnum wet-season water table or hardpan is at least 3 feet below the bottom of the depression. Figure C.2.2.D illustrates the specifications for infiltration depressions as outlined below: L 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 e�cisting native soil,not through the construcrion of berms. 2. The stormwater storage areas of infiltration depressions must be at least 12 inches in depth witb a minimum 6 inches of freeboazd before overflow. 2009 Surface Water Design Manual—Appendix C I!9i2009 C-43 SECTION C.2 FLOW CONTROL BMPs 3. The depression overtlow point must be at least 6 inches below any adjacent pavement area and must be situated so that overflow dces not cause erosion damage or unplanned inundation. 4. The depression side slopes must be no steeper than 3 horizontal to 1 veRical. 5. Spacing between multiple infiltration depressions shall be a minimum of 4 feet. 6. Infiltration depressions must be setback at least 15 feet from buildings with crawl space or basement elevations tUat 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 aze met. 8. The ground surface of the infiltration depression must be vegetated with grass or other dense ground cover. C.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 Secrion C.1.3.3 (p.C-18). The intent of these instcvctions is to explain to future property owners,the purpose of the BMP and how it must be maintained and operated. These instructions aze 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 operarion 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 oontrol 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 infi�ration is a method of soaking runoff from impervious area(such as paved areas and roofs) irrto the ground. If properly installed and maintained,full infiltration can manage runoff so that a majority of preapitation 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 oondition around the infiltration de�ice 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 faality. If the device becomes pfugged, 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 deaning of gutters will reduce sediment loads to these devices. 1/9i2009 2009 Surface Water Design Manual-Appendix C G44 C.2.2 FCTLL INFILTRATION ' FIGURE C.2.2.A TYPICAL TRENCH INFILTRATION SYSTEM n V j roof �drain � PLAN VIEW � NT$ ,�4"rigid or 6"flexibie / perforated pipe j ---------------•---------•--------•------/�- � � '�•-----••-•-------------•-------••-•--•-------•. infiltration trench �sump w/soiid lid ! i PLAN VIEW roof drain � NTS ; overtlow � 4"rigid or 6"(lexible splash block � /-perforated pipe � i i i ri�i�i i i i 6" �i;�i��i;�i��i; / %i;�%�i�;�%�i�?�%��i:�i��%��i� ::�:� --V-------�'--------------•----••-•-------•---•. 6., l c o C ' � V �2„� N�� — washed rock � �°a�� o ��j"" 5.0'min � 1 1/2"-3l4" o ' � C�uo� j1'min �--- `-------- ----------------------'�-�--=`-----�'-'� ( fine mesh � CB sump w/solid Iid c�rcnn I varies - A filter fabric i ,;` .� compacted backfill 6A /� 4� i � � .� � 4"rigid or 6"flexible ` U�' ° �a, perforated pipe 24" `''� ° °� • o o v �n o O r7 �'2s �� p� '�° ��n� washed rock i yC �° o��`�� 7� 1 1/2"-3/4" ; , r.° 7o �u i/\`!\\�\`\\-_\v\ j�y��/��/\i�\//\ :i�i�✓.�i�i:i r= 24" SECTION A NTS 2009 Surface R�ater Design Manual-Appendix C 119/2009 C-45 C.2.2 FULL IIVFILTRATION FIGURE C.2.2.0 TYPICAL DRYWELL INFILTRATION SYSTEM �Spp�Epx ot qpvu I pvtf Dbtdi !Cbt jo �)�se!E�jo' / flow �SPP9 E px ot qpv u � DRY WELL 59!.bdi !Ejbn f�f s I rfi.qfiie.x ju PLAN VIEW ��4�lX bt i f e E�jo!Spd NTS ' Spp�Epx ot qpvu N b� !Df o�f slp�l pfi x ju !2�lDbqqf e!(IVID House /—p,�� pslPti f sln f bot! Tqrlot i lCrpol �qt PJm �i !x ju !Tvs�df - � ; - - - - - - 1' min. _� ..'nr.o ,";� ❑�'Gd7cL-,�=- flow �,� ��cc�� r�°°�,^,�D L � C O?I�'p�oOo p U�o�� C�of!Nf t i !Tdsf f o Njo/.5�ejb/ ;,�,,��p�� op I (1�illpl4qf �' o.9�� 9�� Dbuii !Cbt jo L��^4 '�� )�se!E�jo" a� �� x 59f.bd !Ejbn f�f s � t Tjef t!P�I Prfn �� I fi!Cjrfie!x ju ', A�Jof e!x ju �� 4>�X bt i f e ? gr�i�C�c�d =�� E�jo!Spol � 15'min. ��o�i�—__.. - - 0�9 C5�`�CD`,C��Co�;��C Min. 1' above Seasonal DRY WELL High Groundwater Table SECTION � NTS 2009 Surface Water Design Manual—Appendix C 1/9/2009 C-47 ' �I