Loading...
The URL can be used to link to this page
Your browser does not support the video tag.
Home
My WebLink
About
03619 - Technical Information Report
,t 4. 1 Encompass . N 0) ENGINEERING & Sit` ■ V co �3 � o Jvin TECHNICAL INFORMATION REPORT for Harmony Grove October 3, 2011 lt11,,mv /Z1q(1) Gvf � 6 D I (1 (o1 lZ I _-- p,MES +t 4,V -<< w s,y/ < it 9ts i = ,,, O co,0/ RE A4,/e , s ,147 1� V;i8, 13/!l tttt;``oNA;`N`'_� Encompass Engineering Job No. 115171 Prepared For PNW Holdings, LLC 9725 SE 36th Street, Suite 214 Mercer Island, WA 98040 CITY of RENTON RECEIVED JAN 2 3 201a BUILDING DIVISION Western Washington Division Eastern Washington Division 165 NE Juniper St.,Ste 201, Issaquah, WA 98027 108 East 2nd Street,Cle Elum, WA 98922 Phone:(425)392-0250 Fax:(425)391-3055 Phone: (509)674-7433 Fax: (509)674-7419 www.EncompassES.net 3 Ce,/9 TABLE OF CONTENTS SECTION TITLE 1 PROJECT OVERVIEW 2 CONDITIONS AND REQUIREMENTS SUMMARY 3 OFFSITE ANALYSIS 4 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN 5 CONVEYANCE SYSTEM ANALYSIS AND DESIGN 6 SPECIAL REPORTS AND STUDIES 7 OTHER PERMITS 8 ESC ANALYSIS AND DESIGN 9 BOND QUANTITIES, FACILITY SUMMARIES,AND DECLARATION OF COVENANT 10 OPERATIONS AND MAINTENANCE MANUAL SECTION 1 PROJECT OVERVIEW Site Address 13502 162' Avenue Tax Parcel No. 145750-0040 Project Overview The Harmony Grove Plat (formerly called Threadgill) is a 15-lot single-family project on a 4.01- acre parcel. The property address is 13502 162°d Avenue in Renton, Washington(Tax Parcel No. 1457500040). The project is located east of 162nd Avenue SE and is bordered by SE 135th Street on the north and by 164th Avenue SE on the east. Cover types on the site include a single-family residence with a shop and lawn, mature forest, and two Class 3 wetlands. Slopes on the site range from 1 to 20 percent, with the steeper slopes in the eastern portion of the property. Based on the King County Soil Survey (U.S. Department of Agriculture, 1973)the site consists of Alderwood soils, sandy loam over glacial till. The site has two subbasin, including a 1.5-acre area that drains to the southwest and a 2.5-acre area that drains to the southeast. The westerly subbasin is tributary to the Maplewood and Orting Hills subbasin of the Cedar River(King County Department of Natural Resources, 1997). The easterly subbasin is tributary to the Lower Mainstem subbasin of the Cedar River . The westerly portion of the site drains to a Class 3 wetland in the southwest corner of the property. The easterly portion of the site drains to both a Class 3 wetland in the southeast corner of the site and a roadside ditch along the east property boundary. The easterly wetland appears to be a closed depression with a 2 to 3-foot depth. The natural outlet of the wetland appears to be in its southeast corner, which in the event of overflow,would tie into the ditch on the east property line. But an approved drainage adjustment allows the discharge point to be in SE 136th Street R/W about 200' east of the site Drainage Control Per approved Drainage Adjustment 2011-02, a single combination Level 3 detention pond/Basic water quality pond will provide the required flow control/water quality for the project. The pond will outfall to the aforementioned existing drainage ditch located in the SE 136th Street R/W about 200' east of the site. Five lots on the west side of the project will discharge directly to the remaining wetland for recharge. / J Airmili _41, I .Mr ' are EH,OTEDII N 88'48'53" W S.E. 135 STR 4/IMMIll 91 .. EMEND. �6 �•W I 15' �' `U ,.. Y ti 1UY 6 1111110117110 Yii HI v a' � ��II% 1111 •Uig piii •Z. .. i ILA 011116 1SOO —•,e--. 91 �JJ.II Ilillu�{I �� _el�1e`:_gar.'r� � IA q�i�tl��wi+oas�av��wasi ani'AMIN"si. Lei III NNW -71-1111r'Olilliffill AP 14 11 :1.1- .- ? Fl p. ,'I ----' \- ,�a, 0 � 1 \_\ 1®,_.rte. ''�� + .I �. o. =TR CT E+ D �' - Q I \ I �� II1 1 . a . aiii--........-- )11:. 4' r. sig"--4— /-- , „ • N ' " W 92.E �� . •.on ' i•14( df N., _ : E542 . JP4t . - - _- 5 IX • Site Plan 1" = 100' King County Department of Development and,Environmental Services TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECTOWNER AND ;Part 2 PROJECT LOCATION AND PROJECT ENGINEER :DESCRIPTION - • Project Ower. Project Name t?'JW itOtivcc LLQ gik6 Address Location 21i ST 3/777) .y�;-501- Z(4 Township 23 Phone f"4 — t 5 C-A'.D tod(t ¶6 fo 'co& SSS— Range S Project Engineer Section 14 --T FfPD" Company . ✓ .. / IV Address/Phone 5- .3'1 Z D Z W Part 3 TYPE OF RERMIT • APPLICATION Part 4 :'OTHER REVIEWS AND_PERMITS ':-... ;' .;: _. . . Subdivison DFW HPA Shoreline Management Short Subdivision COE 404 Rockery Grading DOE Dam Safety Structural Vaults Commercial FEMA Floodplain Other Other COE Wetlands • Part 5 SITE COMMUNITY AND DRAINAGE BASIN = Community -if/ © 12,6 Drainage Basin oibmt Part 6 SITE;CHARACTERISTICS River Floodplain WetlandsTik)? 0.01/0644D.S 014 Stream Seeps/Springs -1E, Critical Stream Reach High Groundwater Table Depressions/Swales Groundwater Recharge Lake Other Steep Slopes Part 7':SOILS • Soil Type Slopes Erosion Potential Erosive Velcoties Additional Sheets Attached ;Part 8: DEVELOPMENT'LIMITATIONS REFERENCE LIMITATION/SITE CONSTRAINT Ch. 4—Downstream Analysis 'a I it.. • 'rd 6 r ar <AJI IZ I N Additional Sheets Attached =Part9 ESC REQUIREMENTS r ' MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION AFTER CONSTRUCTION ✓Sedimentation Facilities /Stabilize Exposed Surface ✓Stabilized Construction Entrance /Remove and Restore Temporary ESC Facilities /Perimeter Runoff Control - ✓ Clean and Remove All Silt and Debris t/Clearing and Graing Restrictions ✓ sure Operation of Permanent Facilities Cover Practices Flag Limits of SAO and open space preservation areas Construction Sequence Other Other 'Part 10 :SURFACE:WATER SYSTEM Grass Lined Tank Infiltration Method of Analysis Channel �G LRr`5 Vault Depression Pipe System Compensation/Mitigati Energy Dissapator Flow Dispersal on of Eliminated Site Open Channel Storage Wetland Waiver Dry Pond • Stream Regional /( Wet Pond Detention Brief Description of System Operation C13( 1)9E- Ci9 v t' f y •, G , 1 . #' .��1 �� 1 , t__ I 715wn, Facility Related Site Limitations PO PI> Reference Facility Limitation Part11 :STRUCTURAL ANALYSIS Part 12 EASEMENTS/TRACTS r- Cast in Place Vault )(Drainage Easement Retaining Wall Access Easement ?(' Rockery>4' High Native Growth Protection Easement Structural on Steep Slope Tract Other Other Part-13:`SIGNATUREOF 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. G( � — 19(3/,/ Signed/Date 'A �� 121st tIt . l'i '- t' 4th ° if 124th „ l 124th o c'lpf Stit ' .-k-ff‘i. -';i.,.-z1 kk i * 27th co t co t t .:.:. 1 3S N. \\ M 128th ' v- o' t- -I 1 x' b.. ^- ?: 130th to 131st 43t 131st 132nd 132nd 132nd 132nd 133rd 5 e � 133rd 13 134th 134th .r 135th ' Project Site ! 136th L___ o. 135th 4 ir 137th 137th 137th £ 138th i 11311I1 v o N r n. 139th m 1444 141st c c4 c ,ff) eo ma 142nd 14'74'3 142nd 142nd m , 142nd m 143rd r 143rd t t iiico 0 . 144th 144th w t n ,to �co 145th t1 146th t = m A. ; \\,% .s\s,) 1,45111 a 146th �:; h 147th _.. r 148th 149th # 149th N ' To74 P I` r py'- RI ti. 1 Soils Map 0Ed McCarthy PE.PS a„ Threadgiil Downstream Drainage 9957171st Avenue SE 11/15!05 Plat Analysis 1,000 Renes.Washington 98059 King County,Washington I Feet � (425)271-5794 Figure 2 (425)2713432 SECTION 2 CONDITIONS AND REQUIRMENTS SUMMARY PUBLIC WORKS DEPARTMENT � Alton 8 DEVE:,I,c EU! CL MEMOR ANDUM Ci"`r OF KAI ON JUL 26 2011 DATE: July 21, 2011 R ;` CEIVFD TO: Jan lllian, Plan Reviewer FROM: INRon Straka,Surface Water Utility Supervisor,x7248 STAFF CONTACT: Hebe Bernardo, Surface Water Utility Engineer,x7264 SUBJECT: Threadgill Plat Adjustment 2011-02 The City of Renton Surface Water Utility has completed review of the adjustment request for the Threadgill Plat in accordance with City adopted 2005 King County Surface Water Design Manual (KCSWDM). Our review of the information leads us to understand that the applicant's engineering is requesting an adjustment from the 2005 King County Surface Water Design Manual to core requirement#1 (section 1.2.1), Discharge at the Natural Location. Our review of the information provided by the applicant engineer on June 21, 2011 provides the following findings: 1. The proposed Threadgill Plat is located at 13502162"d Ave SE. The 15 lot, 4.01 acres proposed subdivision is filed under LUA 08-125. 2. The site has two subbasins, including a 1.5-acre area that drains to the southwest and a 2.5-acre area that drains to the southeast. The westerly subbasin is tributary to the Maplewood and Ortin Hills subbasin of the Cedar River. The easterly subbasin is tributary to the Lower Mainstem subbasin on the Cedar River. 3. Hearing Examiner Conditions(January 29, 2008), required the project to comply with the following: a. Surface water discharge from the west basin is required to follow its existing drainage course. b. To mitigate flooding problems identified downstream of the west basin of the Threadgill Plat, and along 1446 St., a level 3 flow control facility designed in accordance with section 1.2.3 was required for the west subbasin. Final engineering plans should provide for level 3 detention of surface water runoff prior to leaving the west basin of the proposed development and should re-examine the discharge of the existing flow Jan Milan Page 2 of 4 July 21,2011 from the west basin to determine the extent to which any existing flows are conveyed south along 162"d Ave SE rather than west along the alignment of SE 136th St., during major storm events. c. To mitigate for the flooding problems, in addition to the level 3 flow control facility,the applicant proposed three options for Improvements along SE 144th St. d. If any of the surface water flow from the west basin of the Threadgill Plat is found to travel south along 162nd Ave SE under existing conditions, proposed drainage plans for reconstruction of 162"d Ave SW and its extension shall be required to accommodate those flows and assure that there is no diversion to the water to the west. 4. The downstream analysis identified flooding problems downstream of the west basin as well as the east basin. 5. The west basin of the Threadgill Plat contributes to the hydrology of the wetland located in the Liberty Grove Contiguous Plat. 6. The applicant proposed to discharge runoff from proposed lots 1 and 2 directly into a wetland to maintain wetland hydrology. 7. The proposal is to collect much of the runoff from the project site (3.75 acres) and direct it to a single combined detention and water quality facility located in the east portion of the site. The allowed release would then discharge through an improve conveyance system into the right-of-way of 164th Ave SE,from there the surface water will be conveyed south to the alignment of SE 136th St.,then east to the location where current flow from the east basin enters SE 136th St at the existing channel. 8. The Department of Development and Environmental Services approved an adjustment to core requirement 1 of the 2005 King County Surface Water Design Manual to allow for the diversion of run-off from the on-site facility to discharge to a new closed pipe system on 164th Ave and SE 136th St instead of SE 135th St. Adjustment was approved in April 24, 2008. 9. The proposed detention facility was designed as a level 3 storm water facility for the entire basin using the east basin as the existing(forested) site conditions. Facility was designed in accordance with section 1.2.3 of the 2005 KCSWDM. Based on these understandings,findings and per section 1.2.1 of the 2005 Surface Water Design Manual,the adjustment to allow the diversion of runoff to a single H:\Elle Sys\SWP-Surface Water Projects\SWP-27-Surface Water Projects(CIP)\27-3129 Renton Stormwater Manual\ADJUSTMENTS\2011-2 Threadgill Plat.doc\Hl3ah Jan lllian Page 3 of 4 July 21,2011 combined stormwater flow control and water quality treatment facility draining to SE 164th Ave is approved with the following conditions: 1. The release rate from the detention facility will be based on all of the tributary area being directed to the facility. Tributary area discharging to the on-site wetland (located on the west basin) as needed may be removed from this calculation. 2. The volume of the stormwater detention facility shall be based on all flows directed to the facility at full development under current zoning. The detention volume shall be sized using Level 3 Flood Problem Flow Control Standards in the 2005 KCSWDM. The pre-developed condition runoff rates for the sizing of the facility shall be based only on the east basin using forested site conditions. The TIR shall include all required documentation detailed in chapter 2 of the 2005 KCSWDM for the sizing of the facility. 3. A wetland report shall be provided. The report shall include a hydrologic assessment prepared in accordance with Reference 5 of the 2005 KCSWDM. The wetland hydroperiod under existing pre-development and anticipated post development conditions shall be measured or estimated and included in the report. This assessment should be performed with the aid of a qualified hydrologist. The report shall also include recommendations for maintaining the pre-developed wetland hydroperiod under developed conditions. 4. The water quality facility shall be sized based on the entire proposed subdivision draining to the facility including any required frontage improvements. 5. Additional storm drainage requirements identified by the King County Office of Hearing Examiner or SEPA will apply to this project. 6. Please note that the approval of this adjustment does not relieve the applicant from other conditions stipulated in previously approved adjustments,city, state, or federal requirements. Notes to applicant: 1. All lots within the Threadgill Plat are required to provide flow control BMPs in accordance with figure C.1.3.A of the 2005 KCSWDM. Flow control BMP credits in accordance with section 1.2.3 of the 2005 KCSWDM may be used to reduce the size of the required flow control facility. The feasibility to implement full dispersion BMPs and full infiltration BMPs shall be verified first. If Implementation of full dispersion BMPs and full infiltration BMPS are not feasible alternatives,then any of the BMPs listed in figure C.1.3.A shall be H:\File Sys\SWP-Surface Water Protects\SWP-27-Surface Water Projects(CIP)\27-3129 Renton Stormwater Manual\ADJUSTMENTS\2011-2 Threadgill Plat.doc\HBah Jan Illian Page 4 of 4 July 21,2011 provided. The selected flow control BMP to be implemented on each lot shall be shown on the construction plans. Drainage calculations for the sizing of the proposed BMPs to be constructed on each lot shall be included in the TIR. Construction of the proposed flow control BMPs may be differed for construction on the lot at time of building permit. 2. To allow the City access to inspect proposed drainage facilities within the Threadgill Plat and designate maintenance responsibility, a declaration of covenant for the maintenance and inspection of flow control facilities and BMPs shall be recorded with King County prior to final inspection. The required declaration of covenant for the maintenance and inspection of drainage facilities and BMPs shall be reviewed by the City prior to recording. If you have any questions about this adjustment, please contact Hebe Bernardo or me. cc: Lys Hornsby,P.E.,Utility Systems Director Kayren Kittrick,Development Services Supervisor File H:\Fite Sys\SWP-Surface Water Projects\SWP-27-Surface Water Projects(CIP)\27-3129 Renton Stormwater Manual\ADJUSTMENTS\2011-2 Threadgill Nat.doc\HBah s• Denis Law Mayor city of ti1Y0 t • August 31,2011 Department of Community and Economic Development Alex Pietsch,Administrator Justin Lagers Director of Land Acquisition&.Development American Classic Homes 9725 SE 36th Street,Suite 214 Mercer Island, WA 98040 Subject: Minor Amendment Approval-Threadgill Preliminary Plat 13502—162nd Avenue Southeast Dear Mr.Lagers: We have reviewed your request to allow an alternate solution to the required off-site pedestrian school route improvements. We have also reviewed your request for credit toward traffic mitigation/impact fees for the installation of enhanced street improvements for the project. Finally, we have reviewed the list of project conditions established by the King County Hearing Examiner prior to annexation,and are approving revisions to the wording of the plat conditions to clarify Renton requirements for approval of the final plat. These requests and revisions are all approved as part of a minor amendment to the preliminary plat,as allowed by Renton Municipal Code(RMC)4-7-080M. A copy of the approved. revisions to the project conditions is attached. These revisions include the approved modifications to the street standards, approval for the traffic impact fee credit request,and approval of the requested alternate school walkway installation. If you have any further questions regarding street improvement or drainage requirements for this project, please contact Jan lIlian at 425-430-7216 or lillianPrentonwa.gov. Sincerely, 1,1a Neil Watts, Director ,Development Services Director cc: Kayren Kittrick Jennifer Henning Jan Illian Rocale Timmons Renton City Hall • 1055 South Grady Way • Renton,Washington 98057 • rentonwa.gov Amended Conditions of Approval for the Threadgill Preliminary Plat, as of August 10, 2011 The proposed subdivision of Threadgill Plat, as revised and received December 11, 2006, is granted preliminary approval, subject to the following conditions of final plat approval: 1. Compliance with all platting provisions of Title 19A of the King County Code. Revision: Compliance with all platting provisions of the Renton Municipal Code (RMC)4-8-110. 2. All persons having an ownership interest in the subject property shall sign on the face of the final plat a dedication that includes the language set forth in King County Council Motion No. 5952. Revision: Delete this condition. King County staff have been unable to provide any information on the content or intention of the referenced King County Council Motion No. 5952. 3. The plat shall comply with the base density and minimum density requirements of the R-4 zone classification. All lots shall meet the minimum dimensional requirements of the R-4 zone classification or shall be as shown on the face of the approved preliminary plat, whichever is larger, except that minor revisions to the plat which do not result in substantial changes may be approved at the discretion of the Department of Development and Environmental Services. Any plat boundary discrepancies shall be resolved to the satisfaction of DDES prior to the submittal of the final plat documents. As used in this condition, "discrepancy" is a boundary hiatus, an overlapping boundary or a physical appurtenance which indicates an encroachment, lines of possession or a conflict of title. Revision: The plat shall comply with the base density and minimum density requirements of the R-4 zone classification in place in King County on December 11, 2006. All lots shall meet the minimum dimensional requirements of said R-4 zone classification or shall be as shown on the face of the approved preliminary plat, whichever is larger, except that minor revisions to the plat which do not result in substantial changes may be approved at the discretion of the City of Renton Planning Division. Any plat boundary discrepancies shall be resolved to the satisfaction of the Renton Planning Division prior to the submittal of the final plat documents. As used in this condition, "discrepancy" is a boundary hiatus, an overlapping boundary or a physical appurtenance which indicates an encroachment, lines of possession or a conflict of title. 4. All construction and upgrading of public and private roads shall be done in accordance with the King County Road Standards established and adopted by Ordinance No. 11187, as amended (1993 KCRS). Revision: All construction and upgrading of public and private roads shall be done in accordance with the King County Road Standards established and adopted by Ordinance No. 11187, as amended (1993 KCRS),or as otherwise modified by the City of Renton Development Services Division per RMC 4-9-250D. 5. The applicant must obtain the approval of the King County Fire Protection Engineer for the adequacy of the fire hydrant, water main, and fire flow standards of Chapter 17.08 of the King County Code. Revision: The applicant must obtain the approval of the Renton Fire Department for the adequacy of the fire hydrant,water main, and fire flow standards of RMC 4-5-070. 6. Final plat approval shall require full compliance with the drainage provisions set forth in King County Code 9.04. Compliance may result in reducing the number and/or modifying the location of lots or tracts as shown on the preliminary approved plat. Preliminary review has identified the following conditions of approval which represent portions of the drainage requirements. All other applicable requirements in K.C.C.9.04 and the Surface Water Design Manual (SWDM) must also be satisfied during engineering and final review. a. Drainage plans and analysis shall comply with the 2005 King County Surface Water Design Manual and applicable updates adopted by King County. DDES approval of the drainage and roadway plans is required prior to any construction. b. A surface water drainage adjustment shall be applied for to permit discharge from the Tract B (east) pond to 164th Avenue Southeast, at approximately the location shown on exh. No. 29, from where surface water shall be conveyed south to Southeast 136th Street, then approximately 160 feet east along Southeast 136th Street (preferably within the southern portion of the right-of-way) to the existing channel where the present flow from the east basin of the Threadgill property enters Southeast 136th Street. The adjustment application shall request that King County accept for maintenance the new conveyance system to be constructed within the public right-of-way. In the event a surface water adjustment that permits utilization of Option 1 substantially as presented in exh. No. 29 is denied, the hearing on this application shall be reopened for the limited purpose of reevaluating surface water drainage alternatives for the east basin. c. Engineering plans for the west basin shall provide for detention of surface water to the Level 3 standard. The conveyance of water discharged from the west basin shall be reexamined to determine the extent, if any, to which existing flow travels south along the alignment of 162nd Avenue Southeast, south of Southeast 136th Street. No proportion of surface water that currently travels south on 162"d Avenue Southeast shall be diverted to the west along Southeast 136th Street. d. To implement the required Best Management Practices (BMP's) for treatment of storm water, the final engineering plans and technical information report (TIR) shall clearly demonstrate compliance with all applicable design standards. The requirements for best management practices are outlined in Chapter 5 of the 2005 KCSWDM. The design engineer shall address the applicable requirements on the final engineering plans and provide all necessary documents for implementation. The final recorded plat shall include all required covenants, easements, notes, and other details to implement the required BMP's for site development. Revisions: The adjustment discussed in (b) will be reviewed and subject to the approval of Renton Development Services. The rest of Condition#6 remains unchanged, . 7. The following road improvements are required to be constructed according to the 1993 King County Road Standards(KCRS): a. Road A shall be improved at a minimum to the urban minor access street standard. b. FRONTAGE: The frontage along 162nd Ave SE (east side) shall be improved at a minimum to the urban subcollector street standard. c. The Applicant shall widen 162nd Avenue SE, from the intersection of SE 136th Street to the northeasterly curb return of the intersection of SE 137th Place (the plat street for the Liberty Lane subdivision) to provide adequate walkway conditions for students who will walk to Liberty High School, and Maywood Middle School. These improvements shall consist of a minimum of 22-foot wide roadway together with a walkway that is: (i) Eight feet wide if directly abutting the traveled-way, or (ii) Five (5) feet wide if separated from the vehicle travel lane by an extruded curb (which requires an additional 1-foot shy distance from the shoulder edge of the northbound travel lane —i.e., 162nd Avenue SE would need to be at least 23-feet wide) or, (iii) Five (5) feet wide if physically separated from the vehicle travel lane by a gravel shoulder. These improvements may include construction of full urban improvements (curb, gutter, and sidewalk) in lieu of these options. Note: It is expected that similar improvements will also be conditions of approval for the proposed plats of Liberty Gardens L04P0034 and Cavalla L06P0001, on appropriate portions of 162nd Avenue Southeast. d. The applicant shall provide an improved walkway within the right-of-way of Southeast 135th Street or Southeast 136th Street to 164th Avenue Southeast, and continuing east, as necessary,to 166th Avenue Southeast to provide safe walking conditions for students who will walk to Brierwood Elementary School to the north. These improvements shall be the minimum necessary determined by DDES to provide safe walking conditions for elementary school students. e. Tract D shall be improved to the joint use driveway standard per Section 3.01 of the KCRS. This Tract shall be owned and maintained by the Lot owners served. f. Thirty feet of additional R/W shall be dedicated along the frontage of SE 135th Street; along with R/W radii at the northwest corner of Lot 15 and the northeast corner of Tract B. g. R/W radii shall also be dedicated at the southwest corner of Tract E and the southeast corner of Lot 6. h. Modifications to the above road conditions may be considered according to the variance provisions in Section 1.08 of the KCRS. i. A conceptual frontage road improvement plan for the future construction of SE 136th Street, to the neighborhood collector street standard, shall be submitted with the engineering plans. This plan shall show the necessary R/W width for future construction of the road. Additional R/W needed to construct the future road shall be dedicated with the final plat. The intent of this condition is to insure that, following development, sufficient R/W will exist for future construction of SE 136th Street to the east. Revision: The following road improvements are required to be constructed according to the 1993 King County Road Standards (KCRS), or as modified per Renton Municipal Code 4-9-250D. a. The new internal roadway for the plat shall be constructed to City of Renton residential street standards, including a 26 foot pavement section, vertical curbs, eight foot planting strips and five foot sidewalks. b. The frontage along 162nd Ave SE (east side) shall be improved at a minimum to the 1993 KCRS urban subcollector street standard. c. The applicant shall widen 162nd Avenue SE from the intersection of SE 136th Street to the northeasterly curb return of the intersection of SE 137th Place (the plat street for the Liberty Lane subdivision) to provide adequate walkway conditions for students who will walk to Liberty High School, and Maywood Middle School. These improvements shall include a minimum of 22 feet of pavement width, and either an eight foot walkway adjacent to the pavement, a five foot walkway with a curb separation from the traveled lane, or a five foot walkway separated from the travel lane by a gravel shoulder. These improvements may include construction of full urban improvements(curb,gutter, and sidewalk) in lieu of these options. d. The applicant shall provide an improved walkway within the right-of-way of Southeast 135th Street or Southeast 136th Street to 164th Avenue Southeast, and continuing east, as necessary,to 166th Avenue Southeast to provide safe walking conditions for students who will walk to Brierwood Elementary School to the north. In lieu of these off-site improvements, the applicant has the option of installing full urban street level improvements for the south side of SE 136th Street west of 160th Avenue SE, with a minimum 20 foot pavement section, vertical curb and a six foot sidewalk linking the existing sidewalk sections east and west of the this missing pedestrian sidewalk link. e. Tract D shall be improved to the joint use driveway standard per Section 3.01 of the KCRS. This Tract shall be owned and maintained by the Lot owners served. f. To meet City of Renton right-of-way width requirements, the applicant shall dedicate eighteen (18)feet of additional right-of-way along the frontage of SE 135th Street; along with right-of-way radii at the northwest corner of Lot 15 and the northeast corner of Tract B. g. Right-of-way radii shall also be dedicated at the southwest corner of Tract E and the southeast corner of Lot 6. h. Modifications to the above road conditions may be considered according to the modification provisions in Section 4-9-250D of the RMC C i. The existing right-of-way width for SE 136th Street adjacent to the project is 60 feet in width, which is sufficient to accommodate future construction of street improvements to the current City of Renton standards. No further design work or right-of-way dedication is required for the section of SE 136th Street for this project. 8. All utilities within proposed rights-of-way must be included within a franchise approved by the King County Council prior to final plat recording. Revision: All utilities within proposed rights-of-way must be built and approved per RMC 4-7-200 prior to final plat recording. 9. The applicant or subsequent owner shall comply with King County Code 14.75, Mitigation Payment System (MPS), by paying the required MPS fee and administration fee as determined by the applicable fee ordinance. The applicant has the option to either: (1) pay the MPS fee at the final plat recording, or (2) pay the MPS fee at the time of building permit issuance. If the first option is chosen, the fee paid shall be the fee in effect at the time of plat application and a note shall be placed on the face of the plat that reads, "All fees required by King County Code 14.75, Mitigation Payment System (MPS), have been paid." If the second option is chosen, the fee paid shall be the amount in effect as of the date of building permit application. Revision: The applicant or subsequent owner shall comply with the applicable City of Renton traffic mitigation fee schedule or applicable impact fee schedule in place at time of fee payment. The applicant has the option to either: (1) pay the traffic mitigation or impact fee at the final plat recording, or(2) pay the mitigation or impact fee at the time of building permit issuance. If the first option is chosen, the fee paid shall be the fee in effect at the time of final plat application and a note shall be place on the face of the plat that reads, " All traffic mitigation or impact fees required by Renton Municipal Code have been paid." If the second option is chosen, the fee paid shall be the amount in effect as of the date of building permit application. The applicant has the option to improve the new internal roadway to City of Renton street standards, including providing 4" of asphalt for the street paving. The City will grant a credit toward the project traffic mitigation fees for the increased construction costs for this upgrade to the street standards. The credit granted is for up to $22002.50, and shall not exceed the total traffic mitigation fees for the project. 10. Lots within this subdivision are subject to King County Code 21A.43, which imposes impact fees to fund school system improvements needed to serve new development. As a condition of final approval, fifty percent (50%) of the impact fees due for the plat shall be assessed and collected immediately prior to the recording, using the fee schedules in effect when the plat receives final approval. The balance of the assessed fee shall be allocated evenly to the dwelling units in the plat and shall be collected prior to the building permit issuance. Revision: Lots within this subdivision are subject to Renton Municipal Code 4-1-160, which imposes impact fees to fund school system improvements needed to serve new development. As a condition of final approval, fifty percent (50%) of the impact fees due for the plat shall be assessed and collected immediately prior to the recording, using the fee schedules in effect when the plat receives final approval. The balance of the assessed fee shall be allocated evenly to the dwelling units in the plat and shall be collected prior to the building permit issuance. 11. There shall be no direct vehicular access to or from SE 135th Street or Southeast 136th Street from those lots which abut those streets. A note to this effect shall appear on the engineering plans and the final plat. Revision: Condition#11 remains unchanged. 12. The proposed subdivision shall comply with the Critical Areas Code outlined in K.C.C. 21A.24. Permanent survey marking and signs as specified in K.C.C. 21A.24.160 shall also be addressed prior to final plat approval. Temporary marking of critical areas and their buffers (e.g., with bright orange construction fencing) shall be placed on the site and shall remain in place until all construction activities are completed. All offsite construction required as conditions of final plate approval shall likewise comply with the CAC. Revision: The proposed subdivision shall comply with the Critical Areas Code procedures outlined in RMC 4-3-050E. Permanent survey marking and signs as specified in RMC 4-3-050E shall also be addressed prior to final plat approval. Temporary marking of critical areas and their buffers (e.g., with bright orange construction fencing) shall be placed on the site and shall remain in place until all construction activities are completed. All offsite construction required as conditions of final plate approval shall likewise comply with the General Performance Standards outlined in RMC 4-3-050E. 13. Preliminary plat review has identified the following specific requirements which apply to this project. All other applicable requirements from K.C.C. 21A.24 shall also be addressed by the applicant. Wetlands A. Wetland A is a Category IV and requires a 50 foot buffer. The wetland is located in the southeastern portion of the site. The wetland is less than 2500 square feet and may be filled as shown on the site plan dated December 11, 2006. Mitigation is required for the wetland and buffer impacts. B. Wetland B is a Category IV wetland and requires a 50 foot buffer. The wetland is located in the southwestern portion of the site. A portion of the wetland and buffer is located within unimproved right-of-way. This portion of the wetland and buffer may be impacted for required road improvements, as shown on the site plan dated December 11, 2006, subject to an approved mitigation plan. C. The 50 foot buffer for Wetland B may be reduced to 25 feet with an approved buffer enhancement/mitigation plan. D. All remaining wetlands and buffers shall be placed within Critical Areas Tracts (CAT) for long term protection. A split-railed fence or similar barrier shall be installed along the tract boundary. E. A 15 foot building set back line (BSBL) is required from the edge of CAT's and shall be shown on all affected lots. F. Additional road improvements are required within the unimproved 162nd Avenue right-of-way (ROW) located south of the proposed plat. Critical areas and buffers are located within this ROW. Impacts within the ROW may be permitted with mitigation. A mitigation plan will be required during engineering review. G. The engineering plans shall be routed to Critical Areas staff for review and approval of the critical area conditions. RESTRICTIONS FOR CRITICAL AREA TRACTS AND CRITICAL AREAS AND BUFFERS Dedication of a critical area tract/critical area and buffer conveys to the public a beneficial interest in the land within the tract/critical area and buffer. This interest includes the preservation of native vegetation for all purposes that benefit the public health, safety and welfare, including control of surface water and erosion, maintenance of slope stability, and protection of plant and animal habitat. The critical area tract/critical area and buffers imposes upon all present and future owners and occupiers of the land subject to the tract/critical area and buffer the obligation, enforceable on behalf of the public by King County, to leave undisturbed all trees and other vegetation within the tract/critical areas and buffer. The vegetation within the tract/critical area and buffer may not be cut, pruned, covered by fill, removed or damaged without approval in writing from the King County Department of Development and Environmental Services or its successor agency, unless otherwise provided by law. The common boundary between the tract/critical area and buffer and the area of development activity must be marked or otherwise flagged to the satisfaction of King County prior to any clearing, grading, building construction or other development activity on a lot subject to the critical area tract/critical area and buffer. The required marking or flagging shall remain in place until all development proposal activities in the vicinity of the sensitive area are completed. No building foundations are allowed beyond the required 15-foot building setback line, unless otherwise provided by law. Revision: Preliminary plat review has identified the following specific requirements which apply to this project. All other applicable requirements from Renton Municipal Code 4-7-110 shall also be addressed by the applicant. The rest of Condition #13 remains unchanged for sections A through F. Section G is revised as follows: G. The engineering plans shall be routed to Renton Development Services Division staff for review and approval of the critical area conditions. RESTRICTIONS FOR CRITICAL AREA TRACTS AND CRITICAL AREAS AND BUFFERS Dedication of a critical area tract/critical area and buffer conveys to the public a beneficial interest in the land within the tract/critical area and buffer. This interest includes the preservation of native vegetation for all purposes that benefit the public health, safety and welfare, including control of surface water and erosion, maintenance of slope stability, and protection of plant and animal habitat. The critical area tract/critical area and buffers imposes upon all present and future owners and occupiers of the land subject to the tract/critical area and buffer the obligation, enforceable on behalf of the public by the City of Renton, to leave undisturbed all trees and other vegetation within the tract/critical areas and buffer. The vegetation within the tract/critical area and buffer may not be cut, pruned, covered by fill, removed or damaged without approval in writing from the Renton Development Services Division or its successor agency, unless otherwise provided by law. The common boundary between the tract/critical area and buffer and the area of development activity must be marked or otherwise flagged to the satisfaction of the City of Renton prior to any clearing, grading, building construction or other development activity on a lot subject to the critical area tract/critical area and buffer. The required marking or flagging shall remain in place until all development proposal activities in the vicinity of the sensitive area are completed. No building foundations are allowed beyond the required 15-foot building setback line, unless otherwise provided by law. 14. Suitable recreation space shall be provided consistent with the requirements of K.C.C. 21A.14.180 and K.C.C. 21 A.14.190(i.e., sports court[s], children's play equipment, picnic table[s], benches, etc.). a. A detailed recreation space plan (i.e., location, area calculations, dimensions, landscape specs, equipment specs, etc.) shall be submitted for review and approval by DDEs and King County Parks prior to or concurrent with the submittal of engineering plans. b. A performance bond for recreation space improvements shall be posted prior to recording of the plat. Revision: Suitable recreation space shall be provided consistent with the requirements of K.C.C. 21A.14.180 and K.C.C. 21 A.14.190 (i.e., sports court[s], children's play equipment, picnic table[s], benches, etc.). a. A detailed recreation space plan (i.e., location, area calculations, dimensions, landscape specs, equipment specs, etc.) shall be submitted for review and approval by Renton Development Services Division and the Renton Community Services Department prior to or concurrent with the submittal of engineering plans. b. A performance bond for recreation space improvements shall be posted prior to recording of the plat 15. A homeowners' association or other workable organization shall be established to the satisfaction of DDES which provides for the ownership and continued maintenance of the recreation and critical area tract(s). Revision: A homeowners' association or other workable organization shall be established to the satisfaction of Renton Development Services Division which provides for the ownership and continued maintenance of the recreation and critical area tract(s). 16.Street trees shall be provided as follows (per KCRS 5.03 and K.C.C. 21A.16.050): a. Trees shall be planted at a rate of one tree for every 40 feet of frontage along all roads. Spacing may be modified to accommodate sight distance requirements for driveways and intersections. b. Trees shall be located within the street right-of-way and planted in accordance with Drawing No. 5-009 of the 1993 King County Road Standards, unless King County Department of Transportation determines that trees should not be located in the street right-of-way. c. If King County determines that the required street trees should not be located within the right- of-way, they shall be located no more than 20 feet from the street right-of-way line. d. The trees shall be owned and maintained by the abutting lot owners or the homeowners association or other workable organization unless the county has adopted a maintenance program. Ownership and maintenance shall be noted on the face of the final recorded plat. e. The species of trees shall be approved by DDES if located within the right-of-way, and shall not include poplar, cottonwood, soft maples, gum, any fruit-bearing trees, or any other tree or shrub whose roots are likely to obstruct sanitary or storm sewers, or that is not compatible with overhead utility lines. f. The applicant shall submit a street tree plan and bond quantity sheet for review and approval by DDES prior to engineering plan approval. g. The applicant shall contact Metro Service Planning at (206) 684-1622 to determine if 162"d Avenue SE is on a bus route. If 162nd Avenue SE is a bus route, the street tree plan shall also be reviewed by Metro. h. The street trees must be installed and inspected, or a performance bond posted prior to recording of the plat. If a performance bond is posted, the street trees must be installed and inspected within one year of recording the plat. At the time of inspection, if the trees are found to be installed per the approved plan, a maintenance bond must be submitted or the performance bond replaced with a maintenance bond, and held for one year. After one year, the maintenance bond may be released after DDES has completed a second inspection and determined that the trees have been kept healthy and thriving. Revision: Street trees shall be provided as follows: to a. Trees shall be planted at a rate of one tree for every 40 feet of frontage along SE 184 Place. Spacing may be modified to accommodate sight distance requirements for driveways and intersections. b. Trees shall be located within the street right-of-way and planted in accordance with Drawing No. 5-009 of the 2007 King County Road Standards, unless the City of Renton Department of Public Works determines that trees should not be located in the street right-of-way. c. If the City of Renton determines that the required street trees should not be located within the right-of-way, they shall be located no more than 20 feet from the street right-of-way line. d. The trees shall be owned and maintained by the abutting lot owners or the homeowners association or other workable organization unless the City of Renton has adopted a maintenance program.This shall be noted on the face of the final recorded plat. e. The species of trees shall be approved by the City of Renton Community& Economic Development Department if located within the right-of-way,and shall not include poplar, cottonwood, soft maples,gum, any fruit-bearing trees,or any other tree or shrub whose roots are likely to obstruct sanitary or storm sewers, or that is not compatible with overhead utility lines. f. The applicant shall submit a street tree plan and bond quantity sheet for review and approval by the City of Renton Community& Economic Development prior to engineering plan approval. g. The street trees must be installed and inspected, or a performance bond posted prior to recording of the plat. If a performance bond is posted,the street trees must be installed and inspected within one year of recording of the plat. At the time of inspection, if the trees are found to be installed per the approved plan, a maintenance bond must be submitted or the performance bond replaced with a maintenance bond, and held for one year. After one year, the maintenance bond may be released after the Community& Economic Development Department has completed a second inspection and determined that the trees have been kept healthy and thriving. h. A landscape inspection fee shall also be submitted prior to plat recording. 17. A landscape inspection fee shall also be submitted prior to plat recording. The inspection fee is subject to change based on the current county fees. Revision: A landscaping inspection fee shall be submitted prior to plat recording is the City of Renton fee schedule includes this type of fee at the time of recording. 18. The following have been established by SEPA as necessary requirements to mitigate the adverse environmental impacts of this development. The applicants shall demonstrate compliance with these items prior to final approval. a. In order to address the incremental impacts of the development of the Threadgill plat, and the cumulative impacts with other pending development proposals in the area (Liberty Gardens, DDES File L04P0034, and Cavalla, DDES File LO6P0001), on the High Accident Location (HAL) at the intersection of SE 128th Street/160th Avenue SE), the Applicant shall individually or jointly with the other developers in the area construct an offsite extension of 162nd Avenue SE in general conformance with the conceptual plan submitted to DDES (dated: July 2, 2007) for the plat of Cavalla, from the current south terminus of 162nd Avenue SE (near the SE 138xx block) to SE 144th Street. These improvements shall include no less than 22 feet of roadway paving, plus all associated appurtenances, and all storm drainage conveyance/detention/treatment facilities as determined by DDES. These improvements shall include a tight-lining of the existing water- course located on the westerly half of the 162nd Avenue SE right-of-way. (KCC 14.80.030B). Note: A multi-party agreement between the three pending plat applicants (Threadgill, Liberty Gardens, and Cavalla) has been reached to implement this requirement. Portions of this improvement are located along the frontage of the Liberty Gardens and Cavalla plats, and will require additional roadway frontage improvements as conditions of those plats' approvals. b. In order to address the incremental impacts of the Threadgill development, by itself, on the HAL at the intersection of SE 128th Street/160th Avenue SE, this applicant shall — in addition to the requirements of the preceding SEPA condition — dedicate any additional right-of-way required along the SE 136th Street margin of the site needed to construct — in the future, by others (private or public) — an extension of SE 136th Street from 162nd Avenue SE to 166th Avenue SE. The required additional right-of-way, as needed, may be based upon the preliminary road profile prepared by Baima & Holmburg dated 4/18/2005, and based upon a future 32-foot wide roadway with curb, gutter and sidewalks meeting applicable King County Road Standards, and any cut/fill slopes or retaining walls needed to allow others to construct this roadway. Any additional R/W needed to comply with this condition shall be determined prior to engineering plan approval and then shown as dedication on the final plat. (KCC 14.80.030B) Revision: The SEPA condition for the extension of 162nd Avenue SE has been amended by the City of Renton for this project, and Condition #18.a is no longer applicable for this project. The City of Renton does not plan on extending 162nd Avenue SE south of the proposed Liberty Garden preliminary plat, due to steep topography, wetlands and other critical areas along this corridor. 19. To implement K.C.C. 21A.38.230 which applies to the site, a detailed tree retention plan shall be submitted with the engineering plans for the subject plat. The tree retention plan (and engineering plans) shall be consistent with the requirements of K.C.C. 21A.38.230. No clearing of the subject property is permitted until the final tree retention plan is approved by LUSD. Flagging and temporary fencing of trees to be retained shall be provided, consistent with K.C.C. 21A.38.230.B.4. The placement of impervious surfaces, fill material, excavation work, or the storage of construction materials is prohibited within the fenced areas around the preserved trees, except for grading work permitted pursuant to K.C.C. 21A.38.230.B.4.d.(2). Revision: To implement appropriate tree retention standards under RMC 4-4-130, a detailed tree retention plan shall be submitted with the engineering plans for the subject plat. The tree retention plan (and engineering plans) shall be consistent with the requirements of RMC 4-4-130. No clearing of the subject property is permitted until the final tree retention plan is approved by Renton Development Services Division. Flagging and temporary fencing of trees to be retained shall be provided, consistent with RMC 4-4-130. The placement of impervious surfaces, fill material, excavation work, or the storage of construction materials is prohibited within the fenced areas around the preserved trees, except for grading work permitted pursuant to RMC 4-4-130. 20. A note shall be placed on the final plat indicating that the trees shown to be retained on the tree retention plan shall be maintained by the future owners of the proposed lots, consistent with the K.C.C. 21A.38.230.B6. (Note that the tree retention plan shall be included as part of the final engineering plans for the subject plat.) Revision: A note shall be placed on the final plat indicating that the trees shown to be retained on the tree retention plan shall be maintained by the future owners of the proposed lots, consistent with RMC 4-4-130. (Note that the tree retention plan shall be included as part of the final engineering plans for the subject plat.) RECEIVED c,PR 98 2008 King County Department of Development BARNA&HOLMtG1NO4 and Environmental Services 900 Oakesdale Avenue Southwest Renton, WA 98057-5212 206-296-6600 lT'206-296-7217 www.kinocountv.aov April 24, 2008 Randy Goodwin Shupe Holmberg,P.E. Eagle Creek Land Development LLC Baima& Holmberg 15215 SE 272" St. Suite 101 100 Front St. South Kent, WA 98042 Issaquah, WA 98027 RE: Threadgill Subdivision 2005 KCSWDM Adjustment Request(File No. LO8V0017i Dear Applicant and Engineer: The Department of Development and Environmental Services (DDES), Land Use Services Division (LUSD), Site Engineering Review Section, has completed review of the adjustment request for the Threadgill Subdivision. You are requesting approval for an adjustment from the 2005 King County Surface Water Design Manual (SWDM) Section 1.2.1, Discharge at the Natural Location. Our review of the information provides the following findings: 1. The proposed Threadgill subdivision is located at 13502 162"Avenue SE in Renton. The 15 lot, 4.01 acre, proposed subdivision is filed under Land Use Services Division (LUSD) file number L05P0026. 2. The Threadgill subdivision is located in the Cedar River Drainage Basin. The site is subject to the Conservation flow control and Basic water quality requirements of the 2005 KCSWDM. Additionally, Hearing Examiner's Decision 6c states, `Engineering plans for the west basin shall provide for detention of surface water to the Level 3 standard. The conveyance of water discharged from the west basin shall be re-examined to determine the extent, if any, to which existing flow travels south along the alignment of 162" Avenue Southeast, south of Southeast 136th Street. No proportion of surface water that currently travels south on 162"Avenue Southeast shall be diverted to the west along Southeast 136th Street." 3. Currently the site has two subbasins, west and east. The west subbasin sheet flows to a Class 3 wetland in the southwest corner of the property. The westerly subbasin is not part of this diversion. Water discharges from the wetland to a 12-inch diameter pipe that crosses under SE 136th Street. Stormwater then leaves a Type 1 catch basin from the south side of SE 136th Street and discharges to a shallow ditch on the west side of 162nd Avenue SE. The property at this location is currently under plat construction. The L08V0017 April 24,2008 Page 2 Liberty Grove plat (DDES Files Nos. L03P005 and L0374401) drainage plan shows that runoff from the Threadgill property will be collected in a 12-inch diameter storm drain pipe and conveyed through the Liberty Grove site, separate from runoff collected at •Liberty Grove. Stormwater from this pipe will discharge to the wetland on Tract C of Liberty Grove. From the Tract C wetland, runoff flows to a ditch on the property to the south and is conveyed to a 12-inch diameter pipe. This pipe conveys runoff about 150 feet to the south and discharges to a section of open channel. Runoff then passes through a 12-inch diameter concrete pipe and is collected by a shallow driveway ditch which then flows a short distance before passing through a 12-inch diameter driveway culvert at a distance of 1,270 feet from the project site. Drainage then enters a grass-lined channel and then a flat forested area. The conveyance system ultimately discharges to Tributary 0307, over one mile from the project site, which then discharges to the Cedar River. The east basin sheet flows both to a Class 3 wetland in the southeast corner of the site and a roadside ditch along the east property boundary. The easterly wetland appears to be a closed depression with a 2 to 3 foot depth. The natural outlet of the wetland appears to be in its southeast corner, which in the event of overflow, would tie into the ditch on the east property line (west side of 164th Avenue SE). Runoff from a portion of SE 136th Street and the road right of way appears to sheet flow to the east along SE 136th Street. Runoff which is not caught by the ditch along the west side of 164th Avenue SE continues to sheet flow to the east. Runoff sheet flows from the east edge of 164th Avenue SE and then down a grass slope and gravel driveway. Runoff that flows along this drainage course would join with the conveyance path from the site. The ditch on the west side of 164th Avenue SE leads to a 12-inch diameter concrete pipe that conveys drainage to the east side of 164th Avenue SE. The culvert outlets to a grass-lined ditch on the south side of SE 135th Street. The ditch discharges to a 12-inch diameter pipe and turns to the southeast at a catch basin. The pipe outlets to a concrete sump on the west property boundary of the adjacent residence and a 12-inch pipe then continues due south. The pipe outfalls on the south property boundary of the residence and is collected by a shallow channel. The channel conveys flow over a small embankment at which point the flow path becomes dispersed. Runoff collects further down gradient and merges with a well-established channel that flows in from the east. The channel meanders through a forested area before entering a short section of 30-inch diameter concrete pipe at the north property fence line of Liberty High School. Stormwater is conveyed through a short section of open channel and into a 30-inch diameter Corrugated Metal Pipe(CMP) with trash rack that apparently discharges to the school's stormwater pond. However, the outlet end of this pipe was not found. A control structure at the south end of the pond includes an 18-inch CMP inlet pipe. A 20-inch overflow pipe is also located at the south end of the pond. The pond discharges to a ravine at the south end of the football field. The 42-inch diameter outfall pipe discharges to a well-established low-gradient channel. The channel meanders through a forested area in the ravine bottom. The channel did not have signs of any significant erosion. 4. The east basin is proposing an off-site diversion of the natural discharge location. The proposal is to collect most runoff from the east basin and direct it to a single detention L08V0017 April 24, 2008 Page 3 and water quality facility located at the northeast corner of the property. The allowed release would then be discharged to a new closed pipe system that crosses 164th Avenue SE to the east and then turns south along the east side of 164th Avenue SE, then turns east on the north side of 136th Street. The diversion would eliminate flows to the existing ditch on the east side of 164th Ave SE flowing north, which then turns east on the south side of SE 135th Street, then flows southeast to recombine with the proposed discharge location. The existing ditch between Locations 23 through 24 has high spots and could overflow with high flows,presenting risk of flooding to the residence to the south. The west basin is not part of this diversion because the natural discharge location will be maintained. 5. No decorative ponds or shallow wells have been identified that would be affected by the proposed diversion. 6. No currently relevant flooding complaints have been reported along the downstream drainage course with ''A mile of the project site. 7. A consolidation of facilities for the proposed subdivision will be more economical in long term maintenance. 8. Hearing Examiner's Decision 6b states,"A surface water drainage adjustment shall be applied for to permit discharge from the Tract B (east)pond to 164th Avenue Southeast, at approximately the location shown on exh. No. 29, from where surface water shall be conveyed south to Southeast 136th Street,then approximately 160 feet east along Southeast 136th Street(preferably within the southern portion of the right-of-way)to the existing channel where the present flow from the east basin of the Threadgill property enters Southeast 136th Street. The adjustment application shall request that King County accept for maintenance the new conveyance system to be constructed within the public right-of-way. In the event a surface water adjustment that permits utilization of Option 1 substantially as present in exh.No. 29 is denied, the hearing on this application shall be reopened for the limited purpose of re-evaluating surface water drainage alternatives for the east basin." 9. King County Roads Maintenance policy is to maintain conveyance systems within roads that are King County maintained. Southeast 136th Street and 164th Avenue SE is King County Right-of-way but is not maintained. 10. King County Water and Land Resources Maintenance policy is to maintain conveyance systems up to the next structure downstream of the King County maintained stormwater drainage facility. Based on these findings, we hereby approve this adjustment to allow the diversion of runoff to on-site facility(draining to a new closed pipe system on 164th Ave and SE 136th Street) with the following conditions: L08V0017 April 24, 2008 Page 4 1. The release rates for the detention facility will be based on the land naturally draining from the site in all directions. 2. The volume for the detention facility will be based on all flows directed to the facility at full development under current zoning. The allowed release rate will be reduced by any undetained flows that would bypass the proposed subdivision drainage facilities. The detention volume shall be sized using the Conservation flow control standard in the 2005 KCSWDM. The design Technical Information Report shall state the factor of safety selected and the basis of that determination. 3. Water quality facilities must be sized based on the entire proposed subdivision draining to the facilities including any required frontage improvements. 4. The onsite drainage facilities must be located in a public right-of-way, recreation space tract with easement or storm drainage tract dedicated to King County. 5. Conveyance (from the R/D facility) in a closed pipe system must be in accordance with Core Requirement#4. 6. Additional storm drainage requirements identified by SEPA or the plat hearing review will apply to this project. The applicant retains all rights and privileges afforded in Section 1.4. 7. An extended right-of-way use permit for the proposed off-site conveyance system in unmaintained right-of-way shall be submitted for review and approval by DDES concurrent with the submittal of engineering plans. A homeowners' association or other workable organization shall be established to the satisfaction of DDES which provides for the ownership and continued maintenance of the proposed off-site conveyance system in unmaintained right-of-way. If you have any further questions regarding the SWDM variance or the design requirements, please contact Claire Jonson at(206) 296-6641. Sincerely, #07 Jim Sanders, P.E. Mark Bergam, P.E. Supervising Development Engineer Site Engineering and Planning Supervisor Land Use Services Division Building Services Division cc: Curt Crawford,P.E.,Supervising Engineer,Local Drainage Services,KCDNR Bruce Whittaker,Engineer III,Engineering Review Section,LUSD Chad Tibbits,Project/Program Manager III,Current Planning Section,LUSD Claire Jonson,P.E.,Engineer III,Engineering Review Section,LUSD Web Date: 11/16/2005 QSURFACE WATER DESIGN MANUAL King County • -RQUIREMENTS I.STANDARDS Department of Development and Environmental Services ADJUSTMENT* _REQUEST 900 Oakesdale Avenue Southwest Renton,Washington 98055-1219 206-296-6600 TTY 206-296-7217 For alternate formats, call 206-296-6600. Project Name: ODES Project File No: L05P0026 L !/oov 7 Threadgill Plat ODES Engineer/Planner Name: Bruce W ittaker/Chad Tibbits Project Address: Design Engineer: Phone: 13502 162nd Ave SE Shupe Holmberg (425)392-0250 Applicant/Agent"*: Phone: Signatu of Desi n n ineer: Date: 21114 Randy•odwin (253) 850-7220 (425)392 .4011 Alai Si• - - of Appl :nt/Ag o Date: Engineers Fir ame: A - Baima & Holmberg 're•s: / • City, State,ZIP: Address: City, State,ZIP: 15215 SE 272nd St.Ste 101 Kent,WA 98042-4215 100 Front St.South Issaquah,WA 98027 INSTRUCTIONS TO APPLICANT/DESIGN ENGINEER: Please be sure to include all materials(Level One Downstream Analysis, Certification of Applicant Status, sketches,photos, and maps)that may assist in complete review and consideration of this adjustment request. Failure to provide all pertinent information may result in delayed processing or denial of request. Please submit two complete copies of this request, application form, and applicable fee to the Department of Development and Environmental Services, 900 Oakesdale Ave. SW, Renton,WA 98055-1219. For more information, contact Mark Bergam, P.E., at 206-296-7270. **Applicant/Agent is the individual financially responsible for all fees EFER.TO GH RTFR`9, ECTIONVOZ ITHE°SURF, ICE;I/t/ATER<1JE5/GN M.ANUAL'FOR ADJUSTOENTa .:: DESCRIPTION OF ADJUSTMENT REQUEST: ®Standard 0 Complex 0 Experimental 0 Blanket D Pre-application Permission is being requested to divert the east basin R/D pond outlet to bybass a 450' portion of the downstream drainageway(maintaining east basin discharge) APPLICABLE VERSION KCSWDM: 0 1990 (11/95)* ❑ 1998 (9/98) ®2005(1/05) *(Note: the term"variance"replaced by"adjustment") . [� (� APPLICABLE SECTION(S) OF STANDARDS: 1;rr F D C__ F. li`,l 1L; 1998 KCSWDM Section 1.2.1 Discharge at the Natural Location MAR 0 3 2008 JUSTIFICATION PER KCSWDM SECTION 1.4.2: 0 See attachments listed below. K.C. D,D.E.S. The proposed diversion will bypass a potential east basin downstream drainage problem. The proposed diversion will route the pond outfall around a low-capacity, pieced-together, private storm system and keep in the public R/W. The proposed diversion will return the flows into the natural discahrge location, about 450'downstream from the plat.The outfall diversion will eliminate the potential of the adjacent private system being adversely affected by this project. AUTHORIZATION SIGNATURES: DETERMINATION: 0 Approval Conditional Approval(see below) ❑ Denial ❑DNRP/WLRD Approval Signed: Date: (Experimental&Blanket only) ODES Staff Recommendation Signed: Date: 4 • 24 •oc12 Conditions of Approval: /� See attached memo dated: ei. �l'c4i DDES DIRECTOR/DESIGNEE DD, ee Review Supervisor: // DDES, 8S■,Site/ gi a ng&Planning Supervisor Si Cr--ned:� "� Date: 4/��/ Signed: / /te ✓ " - Date: t f.741 p�' Check out the DDES Web site at www.metrokc.gov/ddes SurfWaterDesManRegStdsAdjRegFORM.doc le-info-surwa-adj.pdf 11/16/2005 Page 1 of 1 • PORTION OF THE SE 1/4, OP THE NE 1/4 OF SEC. 14,TWN.23 N., RNG 5 E.,WM 01 KING COUNTY,WASHINGTON 5is tit 4 • i ) v. 1 I 1 T.l.f32745Aa15 : • _ ,>,. 1'.- ti t' / `w'F° Ta.+_.F--7t!, TL ".3333 ! . 'CV ' ><.w. —_.__. 88'44.33.w S.E.t35 i.STREE J �j�Y;'/ y I ; b.� t cAp• •a^ _ ""r ". I , v.�_�. `�`� 1�� VICINITY MAP I li` r "' _ eil I I 0 itA �" I �:!� .N.y ., ` des • *"'k,--.-• '' 2. I, P4tat.%-illk uF t-.a0' . .r. 4�-: ct� - s def. ,•j li.11 b .v:+c \, ..r _. ---- f.R ,7E,fi..,... eae.. air'" , ate,..7� ��Er, .:- ..n,: e is.1j.ip -'!L5 r_4 4:,.....,... ..,,i 11: ! A C £ o..ucrexa., ,Flat' +.• ±I�1a.: - ` ..__-. 4 -[I ` , e , ' -1 If r,,,, .-,-. iiit....,4 1 :---,, ••-, .,,,..k.. , - „„......,, ,:, • • .,„ .„.. ,.. ii* d 46 i‘t- e_' �.aea�.aww `� y,i7 �':� 1I i ,` e� .^•^S�`*,'I` \ '.Ift _!C� E'} 8 ..9' 2 1,,Izj : V r fJ, ••/ ,. . �, r� 1; tiz' �y y PL x Rt1 (tytf d I / I 't . k.. • fzfr l `I.1'11 11 ; ' -l�� 6� °� . 3 _ _ „a rty_ ` u .�_ _,.>< _: L.0GP �m 1 j '`..". -tom -----.4, ear v 1 gi ,- �,e�. - - ` L _ s Ma �iMYA 'f .1 r Y.. 1•s:1:�• ....... .. T.L.165%100:115 '1 I .- . :+.:..... t I C t I • CEDAR ri "MAC :b rt _I L.T:S"77S:f • .: 1:.5iae72S 1 r:,SRS`57+C5 (t i Ssra...% _ -x,.15..:35 a4 - 1 I i o,?+t. s i 1 ' - 0 a .4 _1 a • ...tea 1/-110111%./F001-191i.Yc1110 le s:lawn IEF.I[000!41Th 0 11,fm Yc.a-R a 11130.9 s e)w.` ,11, • **r-hawl1m.Tw-b1 11,awv FM ..K..eN..Mee/1.,1..1 15!1 M:4-O.. .K•wt a-VCP�:rNnK1 N"iN wKµx,Y.R w�V�c�R.a cc �d1¢ - V. ",traa,;n c., 0..<411111121--- 41 Tart I L4M4hI7 '1 « 1 a W-50\45••0E6\aq\a5-0$P d.s MAWS ta.tj WHOM) 3:2111 Pat w' January 29,2008 OFFICE OF THE HEARING EXAMINER KING COUNTY,WASHINGTON 400 Yesler Way,Room 404 Seattle, Washington 98104 Telephone(206)296-4660 Facsimile(206)296-1654 Email: hearex@metrokc.gov REPORT AND DECISION SUBJECT: Department of Development and Environmental Services File No. L05P0026 Proposed Ordinance No. 2007-0620 THREADGILL SUBDIVISION Preliminary Plat Application Location: 13502— 162nd Avenue Southeast Applicant: Eagle Creek Development,LLC represented by Bill H.Williamson Williamson Law Office 701 -5th Avenue Seattle, Washington 98139 Telephone: (206)292-0411 Facsimile: (206)292-0313 Intervenor: Citizen's Alliance for a Responsible Evendell represented by Gwendolyn High P.O. Box 2936 Renton,Washington 98056 Telephone: (425)336-4059 King County: Department of Development and Environmental Services(DDES) represented by Chad Tibbits 900 Oakesdale Avenue Southwest Renton,Washington 98055 Telephone: (206)296-7194 Facsimile: (206)296-7051 SUMMARY OF RECOMMENDATIONS/DECISION: Department's Preliminary Recommendation: Approve subject to conditions Department's Final Recommendation: Approve subject to conditions(modified) Examiner's Decision: Approve subject to conditions(modified) L05P0026—Threadgill Subdivision 2 EXAMINER PROCEEDINGS: Hearing Opened: December 18,2007 Hearing Closed: January 22,2008 Hearing Re-opened(for administrative purposes)and Closed: January 25,2008 Participants at the public hearing and the exhibits offered and entered are listed in the attached minutes. A verbatim recording of the hearing is available in the office of the King County Hearing Examiner. ISSUES AND TOPICS ADDRESSED: Surface water drainage Traffic safety Student safe walking conditions Complete application SUMMARY OF DECISION: A subdivision of 15 lots on 4.01 acres in the urban area is approved, subject to conditions. FINDINGS,CONCLUSIONS&DECISION: Having reviewed the record in this matter,the Examiner now makes and enters the following: FINDINGS: 1. General Information: Applicant: Eagle Creek Land Development, LLC Randy Goodwin 13701 SE 253`d Street Kent, WA 98042 206-730-9145 Engineer: Ed McCarthy, P.E.,P.S. 9957-171st Avenue SE Renton, WA 98059 425-271-5734 STR: 14-23-05 Location: The site is located at 13502-162nd Avenue SE,at the southeast corner of 162nd Avenue SE and SE 135th Street intersection. Zoning: R-4 Acreage: 4.01 acres Number of Lots: 15 Density: Approximately 3.74 units per acre Lot Size: Approximately 6,000 to 10, 000 square feet in size Proposed Use: Single Family Detached Dwellings Sewage Disposal: The City of Renton Water Supply: King County Water District No.90 Fire District: King County Fire District No. 39 School District: Issaquah School District No.411 Complete Application Date: December 13, 2005 L05P0026—Threadgill Subdivision 3 2. Except as modified herein,the facts set forth in the King County Land Use Services Division's preliminary report to the King County Hearing Examiner for the December 18,2007,public hearing are found to be correct and are incorporated herein by this reference. The LUSD staff recommends approval of the application, subject to conditions. The division's recommended conditions were modified at the January 8 and 22,2008 public hearings. 3. The mitigated determination of environmental non-significance(MDNS)issued on November 9, 2007 was appealed by the applicant. On December 18,2007,the applicant withdrew its appeal. The conditions of the November 9,2007 MDNS are now incorporated in the proposed action. 4. Section F 3 of the preliminary report for the December 18,2007 public hearing erroneously refers to the Soos Creek Subbasin of the Green River drainage basin. The subject property lies within the Maplewood,Orting Hills and Mainstem sub-basins of the Lower Cedar River basin. This error had no effect on the review of the proposed plat by DDES. 5. Section H of the preliminary report for the December 18,2007 public hearing was revised by the Land Use Services Division at the January 8,2008 public hearing. The revised section is set forth in exhibit no. 18 in the hearing record. 6. In a letter dated January 7,2008(exh. no. 24)the applicant proposed revisions to the surface water drainage system. These revisions are, in part,a response to a recent hydraulic study prepared for Southeast 144th Street,and also respond to downstream concerns identified by residents of the neighborhood. To mitigate flooding problems identified downstream of the west basin of the Threadgill plat,and along Southeast 144th Street,the applicant's revised proposal is to provide Level 3 flow control of surface water discharged from the detention pond to be located in the southwest corner of the property. In addition,three options are offered by the applicant to address concerns downstream from the east basin of the subject property. Option 1 would bypass potential drainage problem areas immediately downstream from the northeast corner of the site. Option 2 would utilize a new storm pipe system within the right-of-way of Southeast 135th Street,and would provide improvements on private property to convey water from Southeast 135th Street to Southeast 136th Street. Option 3 would provide increased detention capacity(Level 3 flow control)for the east basin,but would not provide downstream improvements. The applicant and all nearby property owners who have expressed an opinion prefer that Option 1 be utilized for the discharge and conveyance of stormwater from the east basin. The review engineer also supports that option,and recommends that King County accept for maintenance the new conveyance system that would be constructed within the public right-of-way from the discharge point on 164th Avenue Southeast to the point on Southeast 136th Street where the new conveyance system will intersect with the current north-south channel approximately 160 feet east of 164th Avenue Southeast. A drainage adjustment is required for implementation of Option 1. 7. The downstream analysis provided by the applicant for surface water runoff from the west basin indicates that water is now discharged from the Threadgill property at its southwest corner,then crosses 162nd Avenue Southeast and travels to the west along Southeast 136th Street. It then turns south and travels to a wetland within the Plat of Liberty Grove Contiguous. Evidence presented by a property owner to the south states that the current drainage from the Threadgill Plat west basin now travels south on 162nd Avenue Southeast,and does not enter the Liberty Grove Contiguous wetland. L05P0026—Threadgill Subdivision 4 There are current flooding problems to the south,that are exacerbated by excessive water discharging from the Liberty Grove Contiguous wetland during certain storm events. Surface water discharge from the Threadgill property's west basin is required to follow its existing drainage course, unless a surface water adjustment is approved. A catch basin exists in the right-of-way of 162nd Avenue Southeast at Southeast 136th Street, from which a pipe leads west within Southeast 136th Street. However, it is possible that existing runoff from the southwest basin also travels, at least in part, south on 162nd Avenue Southeast within existing road side ditches. Diversion to the west of any portion of the surface water runoff that in fact flows south on 162nd Avenue Southeast would aggravate existing downstream problems and would conflict with SWDM requirements. The actual path of surface water from the west basin of the Threadgill property during various storm events can be determined during the process of reviewing final drainage plans. 8. The proposed development of 15 lots has received a certificate of traffic concurrency from the King County Department of Transportation. The number of trips generated during any peak hour by the Threadgill Plat is 16. This is below the thirty peak hour trips at any intersection which is the minimum threshold required to call for mitigation of traffic impacts at an affected intersection. The MDNS requires participation by this proposed development in the construction of 162nd Avenue Southeast from its present southerly terminus(near Liberty Gardens)to Southeast 144th Street. This requirement will enhance the interconnectivity of streets serving the neighborhood, and will reduce the number of vehicles traveling to and from this subdivision that will travel through the high accident location of Southeast 128th Street and 160th Avenue Southeast. 9. The proposed development does not include construction of either Southeast 135th Street or Southeast 136th Street from 162nd Avenue Southeast to 164th Avenue Southeast. Although right-of-way will exist adjacent to this plat on both Southeast 135th and Southeast 136th Streets to allow for future construction,any decision to construct improvements to either the Southeast 135th Street or Southeast 136th Street rights-of-way between 162nd Avenue Southeast and 164th Avenue Southeast will be subject to future consideration. The Threadgill Plat will be served solely by a cul-de-sac street from 162nd Avenue Southeast to a"dead end"within the subject property. 10. It is proposed by King County Department of Transportation,and agreed by the applicant,to provide safe walking conditions for students who will walk to Liberty High School and Brierwood Elementary School by constructing a walkway on 162nd Avenue Southeast, from the southwest corner of the Threadgill subdivision to Southeast 137th Place within the Plat of Liberty Lane. Within Liberty Lane, Southeast 137th Place connects with a path to the east boundary of that property on the alignment of 164th Avenue Southeast,adjacent to Liberty High School. This route is reasonable and suitable for Liberty High School students. However, from Southeast 137th Place,Brierwood Elementary students would have to cross the high school grounds to 166th Avenue Southeast,then turn back north to reach Brierwood Elementary. It is unlikely that elementary school students would, in fact,walk south approximately 200 yards from the Threadgill plat entrance road to Liberty Lane,then retrace those 200 yards going back north on 166th Avenue Southeast. It is substantially more likely that the undeveloped right-of- way of Southeast 135th Street,or the undeveloped right-of-way of Southeast 136th Street,would be utilized to travel east and connect with 166th Avenue Southeast. The final engineering plans can identify what, if any, improvements are necessary and acceptable to King County DDES to provide safe walking conditions on either Southeast 135th Street or Southeast 136th Street to L05P0026—Threadgill Subdivision 5 166th Avenue Southeast for students who will walk from the Threadgill subdivision to Brierwood Elementary School. 11. KCC 20.24.040 provides that DDES shall not commence review of any application until the applicant has submitted the materials and fees required for a complete application. The Intervenor in this proceeding contends that the Threadgill preliminary plat application was incomplete for failure to provide a certificate of water availability,a certificate of sewer availability, a certificate of transportation concurrency,density calculations and a tree inventory. (The Intervenor's contention includes a claim that certain certificates,that may have been valid when submitted, subsequently expired.) A King County Certificate of Water Availability for this property(then proposing a subdivision of 23 lots)was issued by King County Water District No. 90 on December 13,2004, and was filed with DDES with this subdivision application on December 13,2005. The certificate was renewable after one year. A certificate of sewer availability for 15 lots on the property was issued by the City of Renton Wastewater Utility on July 14,2005,and was also filed with DDES on December 13,2005. The Certificate of Water Availability was re-issued by King County Water District No.90 on January 7, 2008, and the Certificate of Sewer Availability issued by the City of Renton was confirmed as still valid by the issuer on January 7, 2008. A Certificate of Transportation Concurrency was issued by King County Road Services Division for 16 dwelling units on the Threadgill property on December 2, 2005 and was received by DDES on December 13,2005. Subdivision Density and Dimension Calculations dated December 5,2005 were filed by the applicant with DDES on December 13,2005, and were re-filed on a revised DDES form on January 2,2008. A site plan identifying the trees on the subject property was filed with DDES on December 13, 2005, as Sheet 2 of the subdivision plan. A tree retention plan and landscape plan are required with engineering plans for plat development. DDES determined that the subject application was complete on December 13, 2005. CONCLUSIONS: 1. If approved subject to the conditions recommended below,the proposed Threadgill subdivision will comply with the goals and objectives of the King County Comprehensive Plan, subdivision and zoning codes,and other official land use controls and policies of King County. 2. If approved subject to the conditions recommended below,this proposed subdivision will make appropriate provision for the public health, safety and general welfare, and for open spaces, drainage ways,streets,other public ways,transit stops,potable water supply, sanitary waste, parks and recreation,playgrounds, schools and school grounds and safe walking conditions for students who walk to school; and it will serve the public use and interest. 3. The conditions for final plat approval recommended below and contained in the mitigated determination of environmental non-significance are in the public interest and are reasonable and L05P0026—Threadgill Subdivision 6 proportionate requirements necessary to mitigate the impacts of the development upon the environment. 4. The dedications of land or easements within and adjacent to the proposed plat,as required for final plat approval or as shown on the revised proposed preliminary plat submitted by the Applicant on December 11,2006,are reasonable and necessary as a direct result of the development of this proposed plat, and are proportionate to the impacts of the development. 5. The applicant should apply for a surface water drainage adjustment to allow for the discharge of surface water from the east basin of the subject property to the right-of-way of 164th Avenue Southeast approximately as shown in exh. no. 29, from where the surface water would be conveyed south to the alignment of Southeast 136th Street,then east to the location where current flow from the east basin enters Southeast 136th Street at the existing channel. This adjustment would allow for the bypassing of current problem areas that could be impacted by additional flows from the Threadgill plat. As part of the surface water drainage application,the developer should request that King County accept and maintain the new conveyance system to be constructed within the public right-of-way of 164th Avenue Southeast and Southeast 136th Street. 6. Final engineering plans should provide for Level 3 detention of surface water prior to leaving the west basin of the proposed development,and should re-examine the discharge of existing flow from the west basin to determine the extent to which any existing flows are conveyed south along 162nd Avenue Southeast,rather than west along the alignment of Southeast 136th Street,during major storm events. This re-examination should be specifically reviewed by the DDES review engineer,to assure that no flow of surface water from 162nd Avenue Southeast is redirected to the west and enters the wetland within the Plat of Liberty Grove Contiguous. If any of the surface water flow from the west basin of the subject property is found to travel south along 162nd Avenue Southeast under existing condition,drainage plans for reconstruction of 162nd Avenue Southeast and its extension shall be required to accommodate those flows and assure that there is no diversion of surface water to the west. 7. The proposed development,with the conditions of the MDNS and the conditions of final plat approval set forth in this decision, improves road connectivity in the neighborhood in a manner that fully and proportionately mitigates the impacts of this development on traffic and vehicle safety at high accident locations on the Southeast 128th Street corridor. 8. Final engineering plans should provide a walkway to the east on the alignment of either Southeast 135th Street or Southeast 136th Street,to be utilized by students who will walk to Brierwood Elementary School,to provide a safe connection to 166th Avenue Southeast, for travel north to Brierwood. These walkways improvements should be reviewed by DDES for consistency with applicable King County standards for a safe walkway,and should be constructed,as approved,with the plat improvements. 9. The Threadgill application for preliminary plat approval meets the requirements of KCC 19A.08.150 and KCC 20.20.040. DDES correctly determined that this application was complete on December 13,2005. The subsequent expiration and renewal of certificate of water and sewer availability did not affect the completeness of the application. The certificate of transportation concurrency was in effect at the time this application for subdivision approval was filed,and, therefore,remains valid while review of the application is pending. Appropriate density calculations and a tree inventory were submitted with the application. Modifications made to a L05P0026—Threadgill Subdivision 7 proposal during its review do not require submission of revised documents to maintain a complete application for the purpose of considering an application's eligibility for preliminary approval. DECISION: The proposed subdivision of Threadgill Plat,as revised and received December 11,2006 is granted preliminary approval, subject to the following conditions of final plat approval: 1. Compliance with all platting provisions of Title 19A of the King County Code. 2. All persons having an ownership interest in the subject property shall sign on the face of the final plat a dedication that includes the language set forth in King County Council Motion No. 5952. 3. The plat shall comply with the base density and minimum density requirements of the R-4 zone classification. All lots shall meet the minimum dimensional requirements of the R-4 zone classification or shall be as shown on the face of the approved preliminary plat,whichever is larger,except that minor revisions to the plat which do not result in substantial changes may be approved at the discretion of the Department of Development and Environment Services. Any plat boundary discrepancies shall be resolved to the satisfaction of DDES prior to the submittal of the final plat documents. As used in this condition, "discrepancy" is a boundary hiatus,an overlapping boundary or a physical appurtenance which indicates an encroachment, lines of possession or a conflict of title. 4. All construction and upgrading of public and private roads shall be done in accordance with the King County Road Standards established and adopted by Ordinance No. 11187, as amended (1993 KCRS). 5. The applicant must obtain the approval of the King County Fire Protection Engineer for the adequacy of the fire hydrant, water main, and fire flow standards of Chapter 17.08 of the King County Code. 6. Final plat approval shall require full compliance with the drainage provisions set forth in King County Code 9.04. Compliance may result in reducing the number and/or modifying the location of lots or tracts as shown on the preliminary approved plat. Preliminary review has identified the following conditions of approval which represent portions of the drainage requirements. All other applicable requirements in K.C.C. 9.04 and the Surface Water Design Manual(SWDM) must also be satisfied during engineering and final review. a. Drainage plans and analysis shall comply with the 2005 King County Surface Water Design Manual and applicable updates adopted by King County. DDES approval of the drainage and roadway plans is required prior to any construction. b. A surface water drainage adjustment shall be applied for to permit discharge from the Tract B (east)pond to 164th Avenue Southeast, at approximately the location shown on exh.no. 29,from where surface water shall be conveyed south to Southeast 136th Street, then approximately 160 feet east along Southeast 136th Street(preferably within the southern portion of the right-of-way)to the existing channel where the present flow from the east basin of the Threadgill property enters Southeast 136th Street. The adjustment application shall request that King County accept for maintenance the new conveyance L05P0026—Threadgill Subdivision 8 system to be constructed within the public right-of-way. In the event a surface water adjustment that permits utilization of Option 1 substantially as presented in exh. no.29 is denied,the hearing on this application shall be reopened for the limited purpose of re- evaluating surface water drainage alternatives for the east basin. c. Engineering plans for the west basin shall provide for detention of surface water to the Level 3 standard. The conveyance of water discharged from the west basin shall be re- examined to determine the extent, if any,to which existing flow travels south along the alignment of 162nd Avenue Southeast, south of Southeast 136th Street. No proportion of surface water that currently travels south on 162nd Avenue Southeast shall be diverted to the west along Southeast 136th Street. d. To implement the required Best Management Practices(BMP's)for treatment of storm water,the final engineering plans and technical information report(TIR)shall clearly demonstrate compliance with all applicable design standards. The requirements for best management practices are outlined in Chapter 5 of the 2005 KCSWDM. The design engineer shall address the applicable requirements on the final engineering plans and provide all necessary documents for implementation. The final recorded plat shall include all required covenants, easements,notes,and other details to implement the required BMP's for site development. 7. The following road improvements are required to be constructed according to the 1993 King County Road Standards(KCRS): a. Road A shall be improved at a minimum to the urban minor access street standard. b. FRONTAGE: The frontage along 162nd Ave SE(east side)shall be improved at a minimum to the urban subcollector street standard. c. The Applicant shall widen 162"d Avenue SE,from the intersection of SE 136th Street to the northeasterly curb return of the intersection of SE 137th Place(the plat street for the Liberty Lane subdivision)to provide adequate walkway conditions for students who will walk to Liberty High School,and Maywood Middle School. These improvements shall consist of a minimum 22-foot wide roadway together with a walkway that is: (i) eight feet wide if directly abutting the traveled-way,or (ii.) five(5)feet wide if separated from the vehicle travel lane by an extruded curb (which requires an additional 1-foot shy distance from the shoulder edge of the northbound travel lane—i.e., 162nd Avenue SE would need to be at least 23-feet wide)or, (iii) five(5)feet wide if physically separated from the vehicle travel lane by a gravel shoulder. These improvements may include construction of full urban improvements (curb, gutter and sidewalk) in lieu of these options. L05P0026—Threadgill Subdivision 9 Note: it is expected that similar improvements will also be conditions of approval for the proposed plats of Liberty Gardens L04P0034 and Cavalla L06P0001,on appropriate portions of 162nd Avenue Southeast. d. The applicant shall provide an improved walkway within the right-of-way of Southeast 135th Street or Southeast 136th Street to 164th Avenue Southeast, and continuing east, as necessary,to 166th Avenue Southeast to provide safe walking conditions for students who will walk to Brierwood Elementary School to the north. These improvements shall be the minimum necessary determined by DDES to provide safe walking conditions for elementary school students. e. Tract D shall be improved to the joint use driveway standard per Section 3.01 of the KCRS. This Tract shall be owned and maintained by the Lot owners served. f. Thirty feet of additional R/W shall be dedicated along the frontage of SE 135th St;along with R/W radii at the northwest corner of Lot 15 and the northeast corner of Tract B. g. R/W radii shall also be dedicated at the southwest corner of Tract E and the southeast corner of Lot 6. h. Modifications to the above road conditions may be considered according to the variance provisions in Section 1.08 of the KCRS. i. A conceptual frontage road improvement plan for the future construction of SE 136th St, to the neighborhood collector street standard, shall be submitted with the engineering plans. This plan shall show the necessary R/W width for future construction of the road. Additional R/W needed to construct the future road shall be dedicated with the final plat. The intent of this condition is to insure that, following development, sufficient R/W will exist for future construction of SE 136th St to the east. 8. All utilities within proposed rights-of-way must be included within a franchise approved by the King County Council prior to final plat recording. 9. The applicant or subsequent owner shall comply with King County Code 14.75, Mitigation Payment System(MPS),by paying the required MPS fee and administration fee as determined by the applicable fee ordinance. The applicant has the option to either: (1)pay the MPS fee at the final plat recording,or(2)pay the MPS fee at the time of building permit issuance. If the first option is chosen,the fee paid shall be the fee in effect at the time of plat application and a note shall be placed on the face of the plat that reads, "All fees required by King County Code 14.75, Mitigation Payment System(MPS),have been paid." If the second option is chosen,the fee paid shall be the amount in effect as of the date of building permit application. 10. Lots within this subdivision are subject to King County Code 21A.43,which imposes impact fees to fund school system improvements needed to serve new development. As a condition of final approval, fifty percent(50%)of the impact fees due for the plat shall be assessed and collected immediately prior to the recording,using the fee schedules in effect when the plat receives final approval. The balance of the assessed fee shall be allocated evenly to the dwelling units in the plat and shall be collected prior to building permit issuance. L05P0026—Threadgill Subdivision 10 11. There shall be no direct vehicular access to or from SE 135th Street or Southeast 136th Street from those lots which abut those streets. A note to this effect shall appear on the engineering plans and the final plat. 12. The proposed subdivision shall comply with the Critical Areas Code as outlined in K.C.C. 21A.24. Permanent survey marking and signs as specified in K.C.C.21A.24.160 shall also be addressed prior to final plat approval. Temporary marking of critical areas and their buffers (e.g.,with bright orange construction fencing)shall be placed on the site and shall remain in place until all construction activities are completed. All offsite construction required as conditions of final plat approval shall likewise comply with the CAC. 13. Preliminary plat review has identified the following specific requirements which apply to this project. All other applicable requirements from K.C.C. 21A.24 shall also be addressed by the applicant. Wetlands A. Wetland A is a Category IV and requires a 50 foot buffer. The wetland is located in the southeastern portion of the site. The wetland is less than 2500 square feet and may be filled as shown on the site plan dated December 11,2006. Mitigation is required for the wetland and buffer impacts. B. Wetland B is a Category IV wetland and requires a 50 foot buffer. The wetland is located in the southwestern portion of the site. A portion of the wetland and buffer is located within unimproved right-of-way. This portion of the wetland and buffer may be impacted for required road improvements,as shown on the site plan dated December 11, 2006, subject to an approved mitigation plan. C. The 50 foot buffer for Wetland B may be reduced to 25 feet with an approved buffer enhancement/mitigation plan. D. All remaining wetlands and buffers shall be placed within Critical Areas Tracts(CAT) for long term protection. A split-railed fence or similar barrier shall be installed along the tract boundary. E. A 15 foot building set back line(BSBL)is required from the edge of CAT's and shall be shown on all affected lots. F. Additional road improvements are required within the unimproved 162nd Avenue right- of-way(ROW)located south of the proposed plat. Critical areas and buffers are located within this ROW. Impacts within the ROW may be permitted with mitigation. A mitigation plan will be required during engineering review. G. The engineering plans shall be routed to Critical Areas staff for review and approval of the critical area conditions. RESTRICTIONS FOR CRITICAL AREA TRACTS AND CRITICAL AREAS AND BUFFERS Dedication of a critical area tract/critical area and buffer conveys to the public a beneficial interest in the land within the tract/critical area and buffer. This interest includes the L05P0026—Threadgill Subdivision 11 preservation of native vegetation for all purposes that benefit the public health, safety and welfare, including control of surface water and erosion,maintenance of slope stability,and protection of plant and animal habitat. The critical area tract/critical area and buffer imposes upon all present and future owners and occupiers of the land subject to the tract/critical area and buffer the obligation,enforceable on behalf of the public by King County,to leave undisturbed all trees and other vegetation within the tract/critical area and buffer. The vegetation within the tract/critical area and buffer may not be cut,pruned,covered by fill,removed or damaged without approval in writing from the King County Department of Development and Environmental Services or its successor agency,unless otherwise provided by law. The common boundary between the tract/critical area and buffer and the area of development activity must be marked or otherwise flagged to the satisfaction of King County prior to any clearing, grading,building construction or other development activity on a lot subject to the critical area tract/critical area and buffer. The required marking or flagging shall remain in place until all development proposal activities in the vicinity of the sensitive area are completed. No building foundations are allowed beyond the required 15-foot building setback line,unless otherwise provided by law. 14. Suitable recreation space shall be provided consistent with the requirements of K.C.C. 21A.14.180 and K.C.C. 21A. 14.190(i.e., sport court[s],children's play equipment,picnic table[s],benches,etc.). a. A detailed recreation space plan (i.e., location,area calculations, dimensions, landscape specs,equipment specs,etc.)shall be submitted for review and approval by DDES and King County Parks prior to or concurrent with the submittal of engineering plans. b. A performance bond for recreation space improvements shall be posted prior to recording of the plat. 15. A homeowners'association or other workable organization shall be established to the satisfaction of DDES which provides for the ownership and continued maintenance of the recreation and critical area tract(s). 16. Street trees shall be provided as follows(per KCRS 5.03 and K.C.C.21A.16.050): a. Trees shall be planted at a rate of one tree for every 40 feet of frontage along all roads. Spacing may be modified to accommodate sight distance requirements for driveways and intersections. b. Trees shall be located within the street right-of-way and planted in accordance with Drawing No. 5-009 of the 1993 King County Road Standards, unless King County Department of Transportation determines that trees should not be located in the street right-of-way. c. If King County determines that the required street trees should not be located within the right-of-way,they shall be located no more than 20 feet from the street right-of-way line. d. The trees shall be owned and maintained by the abutting lot owners or the homeowners association or other workable organization unless the county has adopted a maintenance program. Ownership and maintenance shall be noted on the face of the final recorded plat. L05P0026—Threadgill Subdivision 12 e. The species of trees shall be approved by DDES if located within the right-of-way, and shall not include poplar, cottonwood, soft maples,gum,any fruit-bearing trees,or any other tree or shrub whose roots are likely to obstruct sanitary or storm sewers,or that is not compatible with overhead utility lines. f. The applicant shall submit a street tree plan and bond quantity sheet for review and approval by DDES prior to engineering plan approval. g. The applicant shall contact Metro Service Planning at(206)684-1622 to determine if 162nd Avenue SE is on a bus route. If 162nd Avenue SE is a bus route,the street tree plan shall also be reviewed by Metro. h. The street trees must be installed and inspected,or a performance bond posted prior to recording of the plat. If a performance bond is posted,the street trees must be installed and inspected within one year of recording of the plat. At the time of inspection,if the trees are found to be installed per the approved plan,a maintenance bond must be submitted or the performance bond replaced with a maintenance bond,and held for one year. After one year,the maintenance bond may be released after DDES has completed a second inspection and determined that the trees have been kept healthy and thriving. 17. A landscape inspection fee shall also be submitted prior to plat recording. The inspection fee is subject to change based on the current county fees. 18. The following have been established by SEPA as necessary requirements to mitigate the adverse environmental impacts of this development. The applicants shall demonstrate compliance with these items prior to final approval. a. In order to address the incremental impacts of the development of the Threadgill plat, and the cumulative impacts with other pending development proposals in the area (Liberty Gardens, DDES File L04P0034,and Cavalla,DDES File LO6P0001),on the High Accident Location(HAL)at the intersection of SE 128th Street/ 160th Avenue SE), the Applicant shall individually or jointly with other developers in the area construct an offsite extension of 162nd Avenue SE in general conformance with the conceptual plan submitted to DDES(dated: July 2,2007)for the plat of Cavalla,from the current south terminus of 162Nd Avenue SE(near the SE 138xx block)to SE 144th Street. These improvements shall include no less than 22 feet of roadway paving,plus all associated appurtenances,and all storm drainage conveyance/detention/treatment facilities as determined by DDES. These improvements shall include a tight-lining of the existing water-course located on the westerly half of the 162nd Avenue SE right-of-way.(KCC 14.80.030B) Note: a multi-party agreement between the three pending plat applicants(Threadgill,Liberty Gardens, and Cavalla)has been reached to implement this requirement. Portions of this improvement are located along the frontage of the Liberty Gardens and Cavalla plats,and will require additional roadway frontage improvements as conditions of those plats' approvals. b. In order to address the incremental impacts of the Threadgill development,by itself,on the HAL at the intersection of SE 128th Street/ 160th Avenue SE,this applicant shall—in addition to the requirements of the preceding SEPA condition—dedicate any additional right-of-way required along the SE 136th Street margin of the site needed to construct— L05P0026—Threadgill Subdivision 13 in the future,by others(private or public)—an extension of SE 136th Street from 162nd Avenue SE to 166th Avenue SE.The required additional right-of-way,as needed,may be based upon the preliminary road profile prepared by Baima&Holmburg dated 4/18/2005,and based upon a future 32-foot wide roadway with curb,gutter and sidewalks meeting applicable King County Road Standards,and any cut/fill slopes or retaining walls needed to allow others to construct this roadway.Any additional R/W needed to comply with this condition shall be determined prior to engineering plan approval and then shown as dedication on the final plat.(KCC I4.80.030B) 19. To implement K.C.C.21A.38.230 which applies to the site,a detailed tree retention plan shall be submitted with the engineering plans for the subject plat. The tree retention plan(and engineering plans) shall be consistent with the requirements of K.C.C. 21A.38.230. No clearing of the subject property is permitted until the final tree retention plan is approved by LUSD. Flagging and temporary fencing of trees to be retained shall be provided,consistent with K.C.C. 21A.38.230.B.4. The placement of impervious surfaces, fill material,excavation work,or the storage of construction materials is prohibited within the fenced areas around preserved trees, except for grading work permitted pursuant to K.C.C.21A.38.230.B.4.d.(2). 20. A note shall be placed on the final plat indicating that the trees shown to be retained on the tree retention plan shall be maintained by the future owners of the proposed lots,consistent with K.C.C.21A.38.230.B.6. (Note that the tree retention plan shall be included as part of the final engineering plans for the subject plat.) ORDERED this 29th day of January, 2008. James N.O'Connor King County Hearing Examiner pro tem NOTICE OF RIGHT TO APPEAL In order to appeal the decision of the Examiner,written notice of appeal must be filed with the Clerk of the King County Council with a fee of$250.00(check payable to King County Office of Finance)on or before February 12,2008. If a notice of appeal is filed,the original and six(6)copies of a written appeal statement specifying the basis for the appeal and argument in support of the appeal must be filed with the Clerk of the King County Council on or before February 19,2008. Appeal statements may refer only to facts contained in the hearing record;new facts may not be presented on appeal. Filing requires actual delivery to the Office of the Clerk of the Council, Room 1025, King County Courthouse, 516 3`d Avenue, Seattle,Washington 98104,prior to the close of business(4:30 p.m.)on the date due. Prior mailing is not sufficient if actual receipt by the Clerk does not occur within the applicable time period. The Examiner does not have authority to extend the time period unless the Office of the Clerk is not open on the specified closing date, in which event delivery prior to the close of business on the next business day is sufficient to meet the filing requirement. If a written notice of appeal and filing fee are not filed within fourteen(14)calendar days of the date of this report,or if a written appeal statement and argument are not filed within twenty-one(21)calendar days of the date of this report,the decision of the hearing examiner contained herein shall be the final decision of King County without the need for further action by the Council. L05P0026 -Threadgill Subdivision 14 MINUTES OF THE DECEMBER 18,2007,JANUARY 8 AND 22,2008 PUBLIC HEARING ON DEPARTMENT OF DEVELOPMENT AND ENVIRONMENTAL SERVICES FILE NO.L05P0026. James N.O'Connor was the Hearing Examiner in this matter. Participating in the hearing were Barbara Heavey,Chad Tibbits,Kristen Langley,Nick Gillen and Bruce Whittaker representing the Department; Bill H. Williamson and Shupe Holmberg,representing the Applicant; Gwendolyn High,Intervenor and Ty Pendergraft,Ed Sewell,Ed McCarthy,Doris Yepez,Michelle Hohlbein,John N.Case,Ed McCarthy, Henry Perrin,Keith Brown,and Gary Norris. The following Exhibits were offered and entered into the record on December 18,2007: Exhibit No. I Prepared remarks on the pre-hearing conference on CARE's petition to intervene Exhibit No. 2 Citizen's statements of support of the CARE petition to intervene Exhibit No. 3 Letter from Mary and Donald Hamblin to the Hearing Examiner's Office dated December 17,2007 in support of the petition to intervene by CARE Exhibit No. 4 Threadgill vicinity development map The following Exhibits were offered and entered into the record on January 8,2008: Exhibit No.4A Annotated Threadgill vicinity development map by Shupe Holmberg Exhibit No. 5 Department of Development and Environmental Services File No. L05P0026 Exhibit No. 6 Department of Development and Environmental Services preliminary report dated December 18,2007 Exhibit No. 7 Application dated December 13,2005 Exhibit No. 8 Environmental Checklist dated December 13,2005 Exhibit No.9 SEPA Mitigated Determination of Non-Significance dated November 9,2007 Exhibit No. 10 Affidavit of Posting indicating January 25, 2006 as date of posting and January 26, 2006 as the date the affidavit was received by DDES Exhibit No. 11 Revised preliminary plat map and site plan dated December 11,2006 Exhibit No. 12 Revised Level 1 Downstream Analysis prepared by Baima&Holmberg, Inc., received December 11,2006 Exhibit No. 13 Revised Critical Areas Report prepared by Sewall Wetland Consulting,Inc.,received December 11, 2006 Exhibit No. 14 Revised Traffic Impact Analysis prepared by Gary Norris,received December 11, 2006 Exhibit No. 15 Landscape Plan(Conceptual Recreation Space Plan)prepared by Lane&Associates, received December 11,2006 Exhibit No. 16 King County Water District No.90 Certificate of Water Availability dated December 13,2004 Exhibit No. 17 Submittal package by the Citizen's Alliance for a Responsible Evendell dated January 4,2008 Exhibit No. 18 Drainage narrative Exhibit No. 19 King County Department of Assessments Map Exhibit No. 20 Density and Dimension Calculations Exhibit No.21 Email from Ty Pendergraft to Bill Williamson, Shupe Holmberg and the Goodwins dated January 7,2008,re: Sewer Availability Exhibit No. 22 King County Certificate of Water Availability Exhibit No. 23 Response to C.A.R.E. issues/concerns Exhibit No. 24 Letter to Bruce Whittaker of DDES from Baima&Holmberg, Inc. dated January 7, 2008 re: Proposed Stormwater Control Exhibit No.25 Report from Ed McCarthy, PE,re: Downstream Drainage Analysis Exhibit No. 26 Aerial photograph showing the downstream conveyance system Exhibit No.27 Basin map L05P0026—Threadgill Subdivision 15 Exhibit No. 28 Liberty Grove and Liberty Grove Contiguous Street and Storm Drainage Plan(2 sheets) Exhibit No.29 Sheet titled Option 1 —Alternate Storm Outfall Exhibit No. 30 Preliminary Road Improvement Plan Exhibit No. 31 Delivery Record/Receipts(3 pages) Exhibit No. 32 Letter to John&Nenita Ching,Donald&Andrea Gragg,Norm&Patricia Gammel from Curt W.Crawford,Manager,King County Stormwater Services Section dated April 13,2007 Exhibit No. 33 DDES Permit Approval Actions Report Exhibit No. 34 Letter to James N.O'Connor from Peter H. Eberle dated December 17,2007 Exhibit No. 35 Email to C.A.R.E. from Don&MaryEllen Hamblin dated December 17,2007 Exhibit No. 36 Email to C.A.R.E. from Susan Oord dated December 16,2007 Exhibit No. 37 Email to C.A.R.E. from Mike Ritchey dated December 16,2007 Exhibit No. 38 Memo to DDES from Bob&Lynn Wilmot dated January 8,2008 Exhibit No. 39 Letter to C.A.R.E. from John&Nenita Ching dated January 7,2008 The following Exhibits were offered and entered into the record on January 22,2008: Exhibit No.40A Photo of Liberty Grove Contiguous drainage pond(under construction) Exhibit No.40B Photo of path to the east on SE 135th Street alignment Exhibit No.40C Photo of Hohlbein property Exhibit No.41 HALS/HARS List Exhibit No.42 Student walkways The following exhibit was entered into the record on January 25,2008: Exhibit No.43 CARE: Threadgill Hearing prepared comments(January 22,2008)with attachments JNOC:gao L05P0026 RPT DEPARTMENT OF COMMUNITY lb, City AND ECONOMIC DEVELOPMENT lt© , 01:74 ADDENDUM TO ENVIRONMENTAL (SEPA) DETERMINATION OF NON-SIGNIFICANCE (DNS-M) - MITIGATED Pursuant to WAC 197-11-600(4)(c) and WAC 197-11-625 Addendum to the Threadgill Preliminary Plat as Addended by the City of Renton (LUA08-125) Determination of Non-Significance - Mitigated (DNS-M) Date of Addendum: May 23, 2011 Date of Original Issuance of SEPA Threshold Determination: November 9, 2007 Proponent: Encompass Engineering&Surveying Project Number: LUA08-125, PP, ECF Project Name: Threadgill Preliminary Plat Proposal/ Purpose of Addendum: The 15-lot residential subdivision was approved by King County DDES prior to annexation to the City. As part of the original approval the applicant was required, pursuant to a SEPA mitigation measure,to provide an offsite extension of 162nd Ave SE from its current south terminus to SE 144th St in order to provide relief to a HAL at the intersection of SE 128th St and 160th Ave SE. The mitigation measure would have been applied to other approved development proposals in the area (Cavalla, LUA08-097/DDES LO6P0001 and Liberty Gardens, LUA08-093/DDES L04P0034) in order to jointly improve the extension of 162nd Ave SE to SE 144th St. However, Environmental 'SEPA' Review for both Cavalla and Liberty Gardens did not include mitigation measures requiring the extension of 162nd Ave SE. Alternatively, a mitigation measure requiring the applicants to provide secondary access suitable for domestic, emergency and pedestrian safety was required. Both applicants are proposing to provide and east/west connection through their respective plat from 162nd Ave SE to 164th Ave SE with an extension of 164th Ave SE to 144th Ave SE in order to provide secondary access. Therefore the Encompassing Engineering&Surveying is requesting an addendum SEPA addendum in order to remove the mitigation measure requiring the applicant to improve an extension of 162nd Ave SE as such an extension has been forgone by neighboring plats since annexation. It has been determined that the environmental impacts of the new proposal are adequately addressed under the analysis of significant impacts contained within the previously adopted Addendum to Environmental(SEPA)Review • Page 2 of 3 May 23,2011 DNS-M. Based on WAC 197-11-600(4) c,the addendum process may be used if analysis-or information is added that does not substantially change the analysis of significant impacts and alternatives in the existing environmental document. The proposal will not change the analysis or impacts in the 1995 State Environmental Policy Act (SEPA) Review. The City of Renton is hereby issuing a SEPA Addendum pursuant to WAC 197-11-600. This Addendum is appropriate because it contains only minor information not included in the original Determination and there no environmental impacts related to inclusion of the new information. Location: 13502162"dAve SE Lead Agency: City of Renton, Department of Community& Economic Development Review Process: Addendum to previously issued Determination of Non-Significance- Mitigated (DNS-M) Additional Information: If you would like additional information, please contact Rocale Timmons, Planning Manager, City of Renton Planning Division, Department of Community& Economic Development at (425) 430-7219. There is no comment period for this Addendum, dated May 23, 2011 issued by the City of Renton Environmental Review Committee. Addendum to Environmental(SEPA)Review Page 3 of 3 May 23,2011 ENVIRONMENTAL REVIEW COMMITTEE SIGNATURES: "1/3/71 r\i 5ii3/2.0// Gregg merria ,Adm trator Date Public Works De artm t 'I ;_____. ------ x12314-, Terry Higashiyama, Administrator Date Community Services Department 2 72,74_4) LA/ 612.r(/) Mark Peerson Administrator 1 Date Fire& Emergency Services Department 17\A/V.11.-) 47-) IL , n )7.2A ,, Alex Pietsch, Administrator Date Department of Community& E nomic Development • , PORTION OF THE SE 1/4, OF THE NE 1/4 OF SEC. 14, TWN.23 N., RNG 5 E.,WMa KING COUNTY, WASHINGTON a It i 11 1 i I, Ii p_ , Ii i sJsra_ aat. P 1 1 SCALE 1•.101Y I . �" I I I I ' ' 1 I I VICINITY MAP -i! ! II ,II , I1 , i 1 1 I 1 I.--..... , ; 1 , ; «,n..� (_ .1.1.1.1... ROM INA 11R IIi1S r «wnram +@@@ •RK•O I I I I I i ! N4 n HOPCf z ec rPNt - 'Tp --7----- _—.... I —.--..—...-r---- ;, _, I—'----- \ J 1- -1 •------.1-----.�-..__ r+,i.�. .1.1.1.1 ........ .ev ! I 1 —F-1---; �I I }---_•.-7 .1.1.1,.1, i , I I T—...-_' 1 i 0.14]1 f I I II _-- i i i ' ,i-----1.-- !„ I 1 I. I !tf j I L_..........L. ! I I �---.1.1.1.1..—..! j I-..«,.•I I I ../-'sem•""s,ta LAPS U �_ • wg 1 i..,..y 1--._�...--i----1------1-------i2---'I I ; ! -- _-•__•..; I I 1 ; .. i 1 OO 1,211HJ021'IR c 3.33 .C o V t..._—.� I I i I ' I �__�.W'I n..u_ I __ ! ! usr!. i .a--i I n� Ii! . L_._i.� . J ! L-I _.. ... ._ — \y1l i ! I t' I.j I ; ! ' 1 1111111011I� f i 1: I ! I ! b.tan ... ......,.a as :it t• a E ;__ , i IL�- 5 n I, i , I roman hc!u. I. s;II 4 II i ; aaas imaw zm.bls:M. P ,, .11t L-.1.1.1.1.!_... ._._._. L. . .w CONT..NIT M•.c,,. x I j r_.._I — — ���.1.1.1.1�.�. J J I .w.I..u--w .curl •-saa 1 ...I r. .76 hi=! I 1....._:....---.1..! sA,_r ,.,n ! I ! .r.r i ,.�. .1_~.1.10 L.......,1 i I ......... i I 1i i = L ! III —I I 1 ! ; I 1 III I I III MCI O5 V I I I x'.....1a.en...- w •-0• lice _1 ti ! I I I 1 I »..,T .•�w.��.roartvw-w OS KOu�a:o mF I , 1 I I ! I 1 I I +.� -o.,.. ,N4d.1.'..1,,0.10." o za ! o I 1________._— .—III`— — — I ! _ I .N, _�,>, K: �.41.4a,.,,...a Z a Ill I 1 /I .11 r—••.— .. _---•_•--......J < p< yl 1 CC W I1�- - - - -==- . W U I li II 1 " i ' 1 I { i '/ I 1W i O,A____ JOB NO 1,1=11O13___ ac'0.�>-olvn f1F[1 1 oa 2 k e - . PORTION OF THE SE 114, OF THE NE 1/4 OF SEC. 14, TWN.23 N., RNG 5 E., WM 3X KING COUNTY, WASHINGTON .' . . 4.q-... -• . I . -- .... . 01 I r--- i li ;Ii. i t , , 1 , ,-, ' T- 155 I ' i I .§ i 1 I - $-7.2'..,,r.P... SIMI sin.: ; . %,..:1:1e.Reg'i : I r0.00..m.t As ....tr ...-- ' , ---, , J V ..f... , I 5 1 I S.E. 135 STR I 5%1Z8/011/01=11 9 41;* */ I • . ___ . riPIIIIIWgi---- e 1 m. . .'11.01.1111Malliin&VnilairlilliS i' 1 m VICINITY MAP I ' ! I!,,:r_.! i, ANIII asi lip p i ir f-----f,w,rte...... ....::.,-4,,,_ Mk liNNMEN IDEng!riUP.ST -;'''' ' gin 1c 1 .1 mg.M 1161,04 CIO MM.mg Lair srAcm Armond no Of MAP Mr,;COMO a R 1 •ai. VO.nq :•4 ; •,'•. M • VW.3 01 RAM MM M.MLLE.M LM .1 ,;'. .,_ , ! , • 1 111 K.- r 1 ........_ . _ ,,,,, = ,it ,,,, - .v.-. 0 . 1,,,,ifiCV , r -1 i, . k- --T.:'qj Ilitiriii,,,,--- .-..,_.q gil iral_rg.1....IMPOn 1...."....., .f.' .4.." ... - I .4 A 1 N.„N---1— 4. ,... ....., ,.. , ,_,....r, ---;-4 -$16 •.:60,.,..tiLlig- , -.414,0 ---- •.-- .„. 11$11.,,, . --- ,f,.0,0..0:„. 1,4-i, ---1 t:, , AEggpiwf:__41...rtz,ort,;,.1,-1137-Q--aGIVAvna cY..^rearz.:si,-4 -1r--'i) -iia -116ialr 1-- illikil- ' ; C CVIM••••• C 1 Lt;i .. 1, WIZ&,- :';:MMZ;•,..!;116ATM:t t.,,A.,...r$,L,.;;; ;;MMieg ir,',„,..t.,,r527,1110:1111_10024#1 ,-.._;•ih: .-- ' M MM.nu. 1 kil plit.,‘,17mn---- ..- ...---___,-.7...................„.....„,...........„, aoRcAi4,„,,,,;41-,-.2„..-i.J--.==;-=-0-t--, -0 mig ma. ' i g ..p .' J'''' P r Adilit °.'669111"' ,,,,,.... .i.1,,,,,,o, ge Y.',. ' „,.. ./. /Lt.!If 1 Nigi,p/i,..dr I Kean 132 1g' c0 ,41' , '" 1 . N....n...... ..0 .gf / ,. 1 r ';*451 167,:vi I,±,1 1 ,,, . -. 7424,CUb6 . E .- .. ,,,, ......,v . _ .; I 't , . A i I 1 - V A WI!)1'1 I . I../.4.' 0 •P ... .7" roan arm,.c. gm MO 1 .at " 4. 'if. 1: il . . • i I ti, L I o5 H. 0 ,..e ) . 1.V.— L ji , , • , 1, ki , El, - - _ WIMP '1.• 4,3 1 ....3 -21--- - -"'- •ant ....- • Mr. i 3 1- t. t.s .__1.9--' • ..._-.-.;;;";:".1 1 ,...iille:ii ..P.i-: FiVE .•1.:.:PF. li -J T 1. tileThr.i.,05i 1 I • -.1 L 145MCritt "I. .P-3..1! ,. -49717.V:E3 1 ' .•:'i' ,k,".1.: HIVE: T I V.57501.4 ' 1415. 0 ... -J 6 o z oi3 -01- ' r • ' hi 0 W Fr-ii---. - Ul 0 a ' .,--7"'''.= la---1.---t-,-_.-,--2L"` -4---"••••••••• .- -.1 Nan v.now tow.-va N ortK.,o,o Inkr carrIg V M.V gam,cmovm Mal V-MOSAtim VAX•10 V Mogen•gam..re "c,..:4VVC.11r,Pg ; ar.-,e1V.MTIMOMM cease r: ! i.r.roorgrIM OrMil Cgir 1,-N.M.roc FACCM•VE gsmargr• 100.0 V-...T...NM,-IV la LIMO AILMIMCJ 31. g=1117;;;;IM=.10.6 1 W i :i AMJSMILE OATE AZULM__ a•MITAMOMMLYCOM. I'M M.'"fa'a lan."":"." go• . JOS tatb-oes ROAD A SECTION CMG 1 IC .5-00., •L• WEI 1 Or 1 RAO-SOW-0N\0•0.45 -pe .-g UTAITZ5.0.g 1C/16/2007 31V1:13 PM PDT • maw— .ma.K PORTION OF THE SE 1/4 OF THE NE 1/4 OF # ;ry:; �' y I 1 SEC. 14, TWN 3 N I RNG 5 E. WM 111::,-.;.,"::4"‘".: .a..� �: 4m 1. MUI.'iT., r >! _ --- `' "°" "'° KING COUN'''Y,WASHINGTON y t.LIT _-- I. V • Lk • lik , . L c 1 • 1• .. I• \ , Irx n..wm - j r:.wa•wm I ell 0.10 t I1 m . It I � do4 __ 1116 =3 '. I : f / . •,•-•••••7-- I SE HST R 0.— ... —... --- 'Z V-If MI■ I ' 4 - J J ti i .- _ ..... Oro •__4Y _.. - ,rm ,4q t1-0 m.m am NSO m wTa °' "Atr ho - .- _... ._ I w.rc•nlroe EAGLE CREEK LAND DEVELOPLIEN`, LLC Baima & Holmberg Inc. - •-- ._ 1.17-01- 1,110.20 ENGINEERS • oSYNY[TONS THREADGILL NAT :+T..e.,.. >r .w..m+ I*.• •••••• w s.m .I♦ _•_ I www.•_r w sen camber, off EHEC • ..—.«, 1.40. Spn S.E. 136TH STREET PROFILE '"' ..0/..0/40 i9' J..,•• a"r. L,rc .n "w am w¢ 1 0 1 SECTION 3 OFFSTIE ANALYSIS Threadgill Plat LEVEL 1 DOWNSTREAM DRAINAGE ANALYSIS DDES FILE No. Prepared by: Baima & Holmberg Inc. 100 Front Street South Issaquah, WA 98027-3817 Tel. (425)392-0250 Fax (425)391-3055 Ed McCarthy, P.E., P.S. 9957 171st Avenue SE Renton, WA 98059 Tel. (425) 271-5734 Fax (425) 271-3432 $Pa� ,WA Submitted to: w�Q �� King County DDES r �- 900 Oakesdale Avenue S.W. Renton, WA 98055 roe, �, .8576 O 4 a/6/06 November 18, 2005 EXPIRES: 2/19/, , Revised December 5, 2006 TABLE OF CONTENTS Task 1: Study Area Definition and Maps 1 Task 2: Resource Review 1 Task 3: Field Inspection 2 Task 4: Drainage System Description and Problem Descriptions 5 Task 5: Mitigation of Existing or Potential Problems 6 References 17 Appendix A. Downstream Drainage System Appendix B. Overflow Conveyance Analysis for the East Pond Appendix C. Onsite Basin Map LIST OF TABLES Table 1. Description of Downstream Conveyance System 11 LIST OF FIGURES Figure 1. Vicinity Map 7 Figure 2. Soils Map 8 Figure 3. Basin Map 9 Figure 4. Downstream Conveyance System 10 Threadgill Plat-November 2005 TASK 1: STUDY AREA DEFINITION AND MAPS Site Description `5 The Threadgill Plat is a proposal for development to build-Mingle-family homes on a 4-acre tract.The property address is 13502 162"d Avenue in Renton,Washington(Tax Parcel No. 1457500040)(Figure 1).The project is located east of 162nd Avenue SE and is bordered by SE 135th Street on the north and by 164th Avenue SE on the east. Cover types on the site include a single-family residence with a shop and lawn,mature forest,and two Class 3 wetlands(Photos 1 and 2 in Appendix A.2). Slopes on the site range from 1 to 20 percent,with the steeper slopes in the eastern portion of the property. The elevation of the site ranges from about 500 feet(NAVD 88)in the northwest portion of the site to 472 feet in the northeast corner. Based on the King County Soil Survey(U.S. Department of Agriculture, 1973)the site consists of Alderwood soils (Figure 2). The site has two subbasins, including a 1.5-acre area that drains to the southwest and a 2.5-acre area that drains to the southeast. The westerly subbasin is tributary to the Maplewood and Orting Hills subbasin of the Cedar River(King County Department of Natural Resources, 1997). The easterly subbasin is tributary to the Lower Mainstem subbasin of the Cedar River(Figure 3). The westerly portion of the site drains to a Class 3 wetland in the southwest corner of the property. The easterly portion of the site drains to both a Class 3 wetland in the southeast corner of the site and a roadside ditch along the east property boundary. The easterly wetland appears to be a closed depression with a 2 to 3-foot depth.The natural outlet of the wetland appears to be in its southeast corner,which in the event of overflow,would tie into the ditch on the east property line. TASK 2: RESOURCE REVIEW Based on a review of available resources,including the County's Sensitive Areas Map Folio(King County Department of Parks,Planning,and Resources, 1990),the site and downstream system within 1 mile from the site are characterized as follows: • Critical Drainage Area Map Both subbasins on the site are tributary to the Cedar River.The drainage course from the west basin merges with Tributary 0307 more than 1 mile from the site.The drainage course from the east basin also discharges to the Cedar River,well over 1 mile downstream from the site. • Floodplain/Floodway(FEMA)Maps. The site is not within a mapped 100-year floodplain.The site is tributary to floodplains associated with Tributary 0307 and the Cedar River,both of which are well over 1 mile from the project site. 1 Threadgill Plat-November 2005 • Offsite Analysis Reports The downstream analysis for Evendell Plat(Haozous Engineering,PS,June 15,2001) was used in assessing the subbasin to the west of the project site.The stormwater engineering plans for Liberty Grove(L03P005 and L0374401)a residential plat located along the westerly drainage course,was consulted. Liberty Grove is currently under construction. • Basin Plans The site is within the Cedar River watershed. The Current&Future Conditions Report for the Cedar River(King County Department of Natural Resources, 1993) describes characteristics of subbasins to which the site contributes. The Lower Cedar River Basin and Nonpoint Pollution Action Plan(King County Department of Natural Resources, 1997)lists several programmatic stormwater recommendations for the Maplewood and Orting Hills subbasin and the Lower Cedar Mainstem subbasin. • Sensitive Area Information Based on IMAP from the King County website and the Sensitive Areas Map Folio,the site is not located within a coal mine, 100-year floodplain,seismic, erosion,landslide,or wetland area. The downstream drainage course does pass through an erosion area within 1 mile of the project site(Figure 3). There are landslide and seismic areas associated with the Cedar River,more than 1 mile from the project site. • SWM Drainage Complaints A map and copy of registered drainage complaints are included in Appendix A.1. • King County Soils Map Based on the King County Soil Survey(U.S.Department of Agriculture, 1973)the site consists of Alderwood soils(Figure 2). TASK 3: FIELD INSPECTION A downstream drainage analysis for the site is presented in this section.The site discharges to two downstream drainage courses.The westerly subbasin is tributary to the Maplewood and Orting Hills subbasin of the Cedar River(King County Department of Natural Resources, 1997).The easterly subbasin is tributary to the Lower Mainstem subbasin of the Cedar River(Figure 3).The drainage courses from the site were assessed on 11/16/05. The downstream conveyance systems are described below and illustrated in Figure 4. Further descriptions of drainage features are summarized in Table 1. Upstream Drainage There does not appear to be any offsite areas contributing runoff to the project site.Along the north boundary of the site,a roadside ditch along the north side of SE 135th Street intercepts runoff from 2 Threadgtll P/at—November 2005 the north and conveys it to the east and west(Locations 1 and 2 in Table 1 and in Figure 4).A roadside ditch along the west side of l62"d Avenue SE Street collects runoff from the west and conveys it to the south and then west along SE 136th Street(Location 3). Runoff from lawns bordering the south boundary of the site either sheet flows to the south or is intercepted by SE 136`h Street before reaching the project site(Location 4). Downstream Drainage Course—Maplewood and Orting Hills Subbasin Runoff from the western portion of the site discharges to a Class 3 wetland in the site's southwest corner(Location 5).Water discharges from the wetland to a 12-inch diameter pipe that crosses under SE 136`h Street(Location 6). Stormwater leaves a Type 1 catch basin from the south side of SE 136th Street and discharges to a shallow ditch on the west side of 162"d Avenue SE(Location 7).The property at this location is currently under plat construction.The plat, Liberty Grove(DDES Files Nos. L03P005 and L0374401),will have 36 lots on 7.9 acres.The drainage plan for the plat shows that runoff from the Threadgill property will be collected in a 12-inch diameter storm drain pipe and conveyed through the Liberty Grove site,separate from runoff collected at Liberty Grove. Stormwater from this pipe will discharge to the wetland on Tract C of Liberty Grove(Location 8). From the Tract C wetland, runoff flows to a ditch on the property to the south and is conveyed to a 12-inch diameter pipe(Location 9).This pipe conveys runoff about 150 feet to the south and discharges to a section of open channel(Location 10). Runoff then passes through a 12-inch diameter concrete pipe(Location 11)and is collected by a shallow driveway ditch which then flows a short distance before passing through a 12-inch diameter driveway culvert at a distance of 1,270 feet from the project site(Location 12). From Location 12,drainage enters a grass-lined channel(Location 13;Photo 3 in Appendix A.2) and then enters a flat forested area(Location 14;Photo 4 in Appendix A.2).The flow path through the forested area is not well-defined and has dense briars in sections. South of Location 14 the flow path has sections where it becomes more defined and then again less distinct. Eventually,the channel becomes more consistently defined(Location 15)as it increases in gradient and continues to flow through a forested area. The channel continues through mature forest with little sign of erosion(Location 16)and eventually leaves the wooded area along the back yard of a single-family residence(Location 17). The channel widens prior to entering an 18-inch diameter culvert(Location 18)that crosses under SE 144th Street. On the south side of SE 144th Street,the storm pipe system turns to the west(Location 19). The 18-inch diameter pipe system continues to the west through a series of catch basins. The field assessment was ended at Location 20,a distance of 3,960 feet from the project site. Based on subbasin maps for the watershed(King County Department of Natural Resources, 1997),the conveyance system ultimately discharges to Tributary 0307,over one mile from the project site,which then discharges to the Cedar River. King County staff has reported that the culvert at Location 18 has flooded in the recent past as a result of either blockage or lack of conveyance capacity.The trash rack at the inlet of the 18-inch diameter culvert at Location 18 was observed to be partially blocked with leaf debris on 12/5/06. 3 Threadgill Plat-November 2005 The forested channel upstream from the culvert has potential to carry leaf and tree branch debris to the culvert crossing. More frequent routine maintenance of the culvert inlet is likely needed at this location. The recent past flooding event at Location 18 was reported to have overtopped the culvert and then turned to the west in the ditch on the north side of SE 144th Street.This drainage course was observed on 12/5/06. The drainage course consists of a roadside ditch(width= 1.5 feet,depth= 1.5 feet, side slopes=2:1)and a number of 12-inch diameter driveway culverts. The ditch system conveys flows to the west for a distance of 600 feet and then enters a 12-inch diameter pipe network just east of 160`h Avenue SE.The pipe system crosses under SE 144th Street and joins the pipe system on the south side of the road at Location 20.The pipe network downstream from Location 20 is 18-inch diameter CMP. Downstream Drainage Course—Lower Cedar River Mainstem Subbasin Runoff from the south part of the eastern portion of the site discharges to a Class 3 wetland in the site's southeast corner(Location 21). Runoff from this wetland and the remaining areas in the eastern portion of the site flows to a roadside ditch on the west side of 164th Avenue SE. Runoff from a portion of SE 136th Street and the road right of way appears to sheet flow to the east along SE 136`h Street. Runoff which is not caught by the ditch along the west side of 164th Avenue SE continues to sheet flow to the east. Runoff sheet flows from the east edge of 164th Avenue SE and then down a grass slope and gravel driveway(Location 21A). Although there were signs of recent surface runoff,no signs of erosion were evident along this flow path. Runoff that flows along this drainage course would join with the conveyance path from the site at Location 26. The ditch on the west side of 164`h Avenue SE leads to a 12-inch diameter concrete pipe (Location 22)that conveys drainage to the east side of 164th Avenue SE. The culvert outlets to a grass-lined ditch on the south side of SE 135th Street(Location 23). The ditch discharges to a 12- inch diameter pipe and turns to the southeast at a catch basin(Location 24).The pipe outlets to a concrete sump(Location 25)on the west property boundary of the adjacent residence and a 12- inch pipe then continues due south.The pipe outfalls on the south property boundary of the residence and is collected by a shallow channel (Location 26; Photo 5 in Appendix A.2). The channel conveys flow over a small embankment at which point the flow path becomes dispersed (Location 27). Runoff collects further down gradient and merges with a well-established channel that flows in from the east(Location 28; Photo 6 in Appendix A.2).The channel meanders through a forested area before entering a short section of 30-inch diameter concrete pipe (Location 29)at the north property fence line of Liberty High School. Shortly downstream,water is conveyed through a short section of open channel(Location 30)and into a 30-inch diameter CMP with trash rack(Location 31)that apparently discharges to the school's stormwater pond (Location 32).However,the outlet end of this pipe was not found. A control structure at the south end of the pond(Location 33)includes an 18-inch CMP inlet pipe. A 20-inch overflow pipe is also located at the south end of the pond.The pipe from the pond discharges to a ravine at the south end of the football field(Location 34).The 42-inch diameter outfall pipe discharges to a well-established low-gradient channel. The channel meanders though a forested area in the ravine bottom(Location 35).The channel did not have signs of any significant erosion. 4 Threadgill Plat—November 2005 On December 5, 2006,the drainage course downstream from Location 35 was verified in the field.The drainage course passes through a King County stormwater pond prior to crossing under SE 144th Street(Location 36). At the time of the site visit,the trash rack on the 24-inch CMP inlet to the pond's control structure was blocked with leaf debris.The outlet pipe from the control structure conveys drainage to the south,to catch basins along 167 Place SE.The pipes along 167 Place SE are relatively shallow and appear to be squashed CMP. The pipe system turns to the west along the north side of SE 1451 Street.The pipe system along SE 145th Street is 18-inch diameter CMP. A ditch and culvert system on the south side of the street flows parallel to the pipe system(Location 38). The pipe system crosses under 164th Place SE and then shortly turns to the south under SE 145th Street(Location 39). On the south side of the street stormwater pipes enter a Type 2 catch basin from the north,west,and east. A 24-inch diameter concrete pipe exits the structure to the south through a right-of-way among the residential properties(Location 40).The field assessment was ended at Location 40,a distance of about 1 mile from the project site. TASK 4: DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS Downstream Drainage Complaints Drainage complaints along the downstream system were investigated at King County Water and Land Resource Division.Copies of registered drainage complaints are listed in Appendix A.1. A summary of the drainage complaints is provided in Table A.1 of Appendix A.1. Based on available information,the drainage-related complaints that are relevant to the study reach would likely be classified as Type 1 problems,or conveyance system nuisance problems. There are a number of drainage complaints associated with the stormwater pond(D91941)that is located 1 mile downstream from the project site along the easterly drainage course(Figure 4). These drainage complaints include 91-1147,97-1493,00-066,and 04-0607. Road flooding has evidently occurred at the intersection of 164th Avenue SE and SE 145th Street.This flooding may have been documented in drainage complaints prior to 1990.The class of the flooding at the intersection could not be determined based on available information. The drainage problems associated with complaints 93-0724 and 95-0715 appear to have been resolved. Several of the reported drainage complaints summarized in Table A.1 are not relevant to the study reach. 5 Threadgill Plat-November 2005 TASK 5: MITIGATION OF EXISTING OR POTENTIAL PROBLEMS Stormwater Design Under developed conditions,stormwater from the plat will be collected and treated onsite in combined stormwater detention/wetponds. The two natural discharge locations from the site will be maintained;therefore it is likely that the plat will have two stormwater ponds. Conservation flow control standards are required based on the county's flow control applications map(King County Department of Natural Resources,2005).In my opinion,conservation flow control standards are adequate for the proposed Threadgill Plat.This opinion is based on the following: • No currently relevant flooding complaints have been reported along the downstream drainage course within 1/4 mile of the project site. • The downstream drainage analysis for both drainage courses from the site did not reveal any reach of channel with erosion problems. • Conservation flow control standards assume forest cover types for the target flow duration in the pond design. Peak flow rates from the project site will be reduced compared to existing conditions. Based on my observations of the easterly downstream drainage course, I recommend that the proposed pond in the easterly basin discharge to a tightline or to a new culvert and re-graded ditch that replaces the existing culvert and ditch at Locations 23 through 24(Figure 4). The existing ditch between Locations 23 through 24 has high sots and could overflow with high flows,presenting risk of flooding to the residence to the south. If a tightline is used to replace the existing system,catch basins with grate inlets should be included at the outlet of the existing road culvert and at the inlet of the existing pipe at the downstream connection point. Providing these catch basins would allow drainage from the surrounding road to be collected.Alternatively,the existing culvert could be replaced and the roadside ditch re-graded to eliminate the high points. The re-graded ditch should have dimensions with at least a 1-foot bottom width, 1-foot depth and 2:1 side slopes.If this alternative is selected,a rock pad should be installed at the outlet of the culvert and a trash rack should be installed at the inlet of the 12-inch pipe located at the downstream end of the improved ditch section. Based Manning's formula,a 12-inch diameter pipe sloped at 3 to 10 percent would have a conveyance capacity ranging from 6.7 to 12.2 cubic feet per second. An improved ditch,sloped at 3 to 10 percent would have a conveyance capacity ranging from 14.8 to 27.0 cubic feet per second (Appendix B.1).The 100-year 15-minute overflow rate from the pond has been estimated to be 2.1 cubic feet per second,assuming that the pond manages runoff from about 2.5 acres(Appendix B.2). The suggested downstream improvements would have adequate capacity for potential pond overflow and for runoff from surrounding roads. 6 Threadgill Plat-Novetnher 2005 17th -a G \ n 17th 107th a) 8 r 107th li A. v 15th S0k ` S ", a dim \ me Va/ m ets��eK z \ . /ey 108th coo `���tey �s f2c m 12th N3----- i2th 112th 111th 9� �� y c \ = c 112th o ? m Alto \u� in 113th 1121 3 $, m 8 , 3 114th a C = D $ �, May Vall 10th c c 016th 116th w m N / co �° 10th 9th < 117th ? 116th �' 9th 9th o t _ �0 j .400 4.,„ .1 .�. 9/h V r S O1 w / 118th r b 8th ( 71 a �s x 7th j c 8th �\ ��� 120th 120th o sfh m m 7th 121st Unnamed 1, 120th 3 6th 6th6t 6th 122nd Ll .�ry a El d L 121st v 6th ,` 124th f J co 124th >,61_-...c r,ar .., \__ n 0th o 5th 125th Unnamed $ w �t'v 124th E 226th c //� Ea_ \ 4th a `Q 4thr °D 4th------- („Ii-,--- - 127th 1 co r 128th a 29th L__.._ _ _ _ _. m 8th S 3rd co 2nd 131st a 130th - r 2nd 2nd 132nd t 131st 1st -c v- 3rd 133rd2nd r 132nd 132nd 132nd N. 1st 13 th 1S3W1 Vashon 135th 13 134th Project Site ! 134th 2nd 2nd 136 M r ot 135th Unnamed 951° td o 136th co 136th ; 135th 9 sovt -, .c 38th 137th 137th At` p, co 138th 138th rn c 139th r co N 139th y 139th N.n "v„ v v t ' 141st c 140th 142nd 142nd in aco 1g1St o= o = v jq2�a 142nd 142nd \142nd / co v A v 143rd 143rd 143rd 5 4/ a 145th OS y \� 144th t �S r° 144th /e V h "\ " X40. 145th 1 c__ �� _V r r r 451h1 \ 1„� 148 r r N co m ^ 1\ co I ,s a CN:� 149th o �49t1' � 4,,, a;to = t c_:�1 Refit,Maple vary .,r �”�`., r a 'lento a cfl co a, ,9�rh a^-`cr an Maple Valley z ry _.,;:� p c tl w np ' 1 1 m c: o cg co 158th J 159th 159th 159th 159th 160th 160th h m .400 160th m C 7 r ,0 csi el F 's/S/ c v 162nd is-0) r'�/h ,w p 1c1 'sora' v No Vicinity Map0 Ed McCarthy,PE,PS Thread ill Downstream Drainage ��11/15l05 Threadgill 9 9957171st Avenue SE Plat Analysis 2,000 Renton,Washington 98059 PhoKing County,Washington I I Feet Fax. (425)271-5734 Figure 1 Fax (425)271-3432 L co 121st L m 4 � \)4C3' — F 14th �° 410 L 2 } c. ' 124th124th r�2 :If \it in Lo L 127th i. co n v L 128th co to L r • s IIN c 130th Lo 700Nt. 'Itilt.Lekk 131st co 131st t. `v m L in n 132nd 132nd 132nd 132nd 133rd CI co 133rd 1330 134th \ 134th 135th I Project Site P. 136th a 135th ...` ' 137th 137th t,,,t f~ 137th It(i g 13 N 138th n. 139th ccoo N\ 140 0 141st c CNI L CO ( )co (o 142nd `` \ 14°6 142nd 142nd , 142nd co 143rd 143rd t 8 144th 144th L .-L. �6 n7 145th ,w in 0- 45t L , ,- ticr EvB r 146th °' 146th c� "' P }vis N n co Lo 147th 148th 149th `x - .c �6, a M� 149th 7 -EP m Cr) ^°' e o w CO CO 4 7 Pc Lo pro No Soils Map0 Ed McCarthy,PE,PS ..„ Threadgili Downstream Drainage 9957171st Avenue SE 11/15/05 Plat Analysis 1,000 Renton,Washington 98059 King County,Washington I I Feet Phone (425)271-5734 Figure 2 Fax (425)271-3432 • 133rd s ` Basin Boundary CO 134th 134th r 134th v Project Site a) 135thcv o Downstream k Flow Path 136th Catchment of the _ '` Lower Cedar River Mainstem ,' 1 Subbasin ; • Area = 122 AC I !i `S t37111 1/4 Mile v N I ‘ , 138th 1 G t , N r i , 1 i , ! i 7;, I 1 Catchment of the �. t 1 Ii Maplewood& Orting Hills ', t 1/4 Mile �� Subbasin `� i r4 Area =51 AC ,-AK:-r- 140th �` ��' 141st Site is 2%of `"� Basin Area o `\ .e , . � 142n(1 s , r 1/2 Mile / , i 142nd t i 1/2 Mile - Erosion , 143rd fSensitive Area i i, I � s c Site is 3%of •� ,` • 143rd r m Basin Area ,'r t t I CO I - - - - - - - - - -' ', 144th C a 145th - r ` _ G'') 1 145th a ,' 1 Mile 0 'm 146th .0 r r Lm t-, N a to <n CO- r 03 -- 147th 148th 0 up b w c MN 149th ?491 J�7 • co -zo c i h p. w <o 0 Erosion Sensitive Area PMN. Basin Map0 Ed McCarthy,PE,PS - Threadgill Downstream Drainage 9957 171st Avenue SE 12/5/06 Plat Analysis 600 Renton,Washington 98059 King County,Washington I 1 Feet Phone: (425, 71:3432 Figure 3 • I . �,„i. Prove 't Site +.4 �f 4< 1 t.."-- t. •; '''',.:•4471-, ti :. ..; :1 .25 °+-.sic ' s 1 i' i-1” °. .:;%: .,. __....1,, .c. ,.... 26 • .,_ ti,":, ,." - .''.,.,. 1° .t .: . I `s,- .V;'. ."' .' N:%.' ,. .',..... '‘.''',.. . .41-,,q t4,11,,,. ----I' 7' '.. ...:' `).: t , t- ''' ,, 4,, ..• .• • ',01D ' :, ; 1 1044i 1 30 t pip/Agit vv., . : .41.1 P. it _.. . . .0 ..-T".....', vim' Si--,A ti..),,4 *--,1 ' 4 V r 1). r. 7, ' ' 44ils .- .4,. . .� • y ) !r...„t„,i., ,, ., ,:..,..,, .-,. �ft-i.,-,- t.k,,,,..e.N. • . ,..._ „,. : .Az - lir',u-: -, r. ‘41.. i T �t,r 1 .. .411 1 I p 111, , �, t t _,fir s : '.,01,0"11.1(4.s,, w ...44.......: /• . C 14 • j. ',.11;,' r p,". r0 - r .."4•5 } Ca fix. r .` , - ' 1 M el.9 .' , z y s e; ,, • '•, V� •� !•. . 1t��� r� '�- '1, ,T�7,�3s �' Y"•� � ,•� _ 1' t.� y�+ I �8 •t' .�y : • r 1s 11 • 1 1.Y a 1 4 , _..,.'.., Y'.i Ynit,� `}}j .v'• I ` Y S zY I 1 r. ,:'� w 1 }y }' 42 , ` 1 fn 1J .f I1 l i > 4 s • wfre /. r.,. c vj . ti if'1.w;.fi 'j�9, 1 y� to i, ' ti1.> ' glit ', i. �O" .. 'vy "i • "-411,= `.1 1 39 .A. _l�' `�" L • ., 'v . ',;,....1'.7',- ' f - - 4. • , ✓Tom+ -' f { •a f 1 ; +,'T/ i,,� ,1 O d Y.._' 38 Z� l+ �''. ' i.:liki. .r i3 . ' , i.. c , - . .,.....,.,. „.._.,.. .. , • .f. ..., . . ... .. .- - -: ,.. ,,,,.,4„ 7..,.. . _ , mi,,? t_sa,.-, 3,:,.... . . . }' '\f'.n'j{• , '�4 p, 111 \ - e � ..4 �.� ., . ,..--...t .. .R 11/; ----. ...0::-..,-...-7 I' i qp. ><� 31 .. ` + . •t ,. { Ss 7'_�i.j-. s; r,,,,,z,,,,,,,74.1.:-...- . a.: .s a f-7.1.-'. z i11.7,..: }.. ,}},%�`'� `ir- 'P .e ... 4 ! .- 1'. I l� g'1' ' 1-1. .#� - t fCE a.t a. i. Ar. ii.+ 4,444, tittki, / p : .. I ,viihr .• 1! .• x.r ; �• b W r.t w „NC� £ 'I•-•-• 3 s` + g „afeta .1. Downstream Conveyance System Ed McCarthy,PE,PS 0Wti12/5/06 Threadgill Downstream Drainage 9957 171st Avenue SE Plat Analysis 500 Renton,Washingtcn 98959 King County,Washington I IFeet Ft (25)2»34 Figure 4 Table 1.Description of Downstream Conveyance System Site Visits on 11/16/05 and 12/5/06 Basin: Westerly Basin—Maplewood and Orting Hill Subbasin(including upstream areas) Weather:Overcast Location Drainage Drainage Slope Distance from Existing Potential Observations of Field ID Component Type, Component Site Discharge Problems Problems Inspector,Resource Name,and Size Description Reviewer,or Resident See Fig.4 Type:sheet flow,swale, drainage basin, 1/4 mile=1,320 ft constrictions,under capacity,ponding, tributary area,likelihood of stream,channel,pipe. vegetation,cover,depth, (%) (FT) overtopping,scouring,bank sloughing, problem,overflow Size:diameter,width type of sensitive area sedimentation,incision,other erosion pathways,potential impacts 1 Roadside ditch Grass-lined ditch 4 North boundary Offsite drainage from with driveway culverts of site north is intercepted by ditch and conveyed to the east 2 Roadside ditch Grass-lined ditch 1 North boundary Offsite drainage from of site north is intercepted by ditch and conveyed to the west 3 Roadside ditch Grass-lined ditch 2 West boundary Offsite drainage from with driveway culverts of site west is intercepted by ditch and conveyed to the south 4 Sheet flow Gravel road intercepts 2 South boundary Offsite drainage from sheet flow from of site south is conveyed away adjacent lots from site to south or east 5 12"-inch diameter Onsite wetland l Southwest corner Class 3 wetland concrete pipe of site discharges to pipe in southwest corner of site 6 Type 1 CB w/grate 1 60 Pipe flows to west 12"-inch diameter pipe 7 Pipe outfall Shallow channel and 2 200 See drainage No problems Liberty Grove under sheet flow;new pipe complaints 00- foreseen;new pipe construction system to be 0322 and 01-0344 system will convey constructed drainage through new plat Table 1 (continued) Basin: Westerly Basin—Maplewood and Orting Hill Subbasin(including upstream areas) Location Drainage Drainage Slope Distance from Existing Potential Observations of Field ID Component Type, Component Site Discharge Problems Problems Inspector,Resource Name,and Size Description Reviewer,or Resident See Fig.4 Type:sheet flow,swale, drainage basin, 1/4 mile=1,320 ft constrictions,under capacity,ponding, tributary area,likelihood of stream,channel,pipe. vegetation,cover,depth, (%) (FT) overtopping,scouring,bank sloughing, problem,overflow Size:diameter,width type of sensitive area sedimentation,incision,other erosion pathways,potential impacts 8 Location of future pipe Wetland discharges to 1 870 Tract C Liberty Grove outfall in Liberty Grove a ditch along adjacent wetland property line to the south 9 12-inch diameter CP Basin at inlet to pipe 2 1,070 Pipe conveys runoff to south property line of parcel 10 Open channel Grass-lined ditch 2 1,070 Width:3' Depth:3' Side slope:2:1 11 12-inch diameter CP Outlet end of culvert 1 1,230 Damaged outlet of Culvert discharges to Length=20' is damaged culvert may shallow ditch along constrict higher north side of gravel flows driveway 12 12-inch diameter CP Driveway culvert 1 1,270 Length=20' Table 1 (continued) Basin: Westerly Basin—Maplewood and Orting Hill Subbasin(including upstream areas) Location Drainage Drainage Slope Distance from Existing Potential Observations of Field ID Component Type, Component Site Discharge Problems Problems Inspector,Resource Name,and Size Description Reviewer,or Resident See Fig.4 Type:sheet flow,swale, drainage basin, 1/4 mile-1,320 ft constrictions,under capacity,ponding, tributary area,likelihood of stream,channel,pipe. vegetation,cover,depth, (%) (FT) overtopping,scouring,bank sloughing, problem,overflow Size:diameter,width type of sensitive area sedimentation,incision,other erosion pathways,potential impacts 13 Open channel Grass-lined 1 1,485 Channel enters forested Width:2-3' area and becomes Depth: 1-1.5' dispersed Side slope:3:1 14 Open channel Leaf/earth bottom 1 1,780 Width:2' Depth:0.3' Side slope:6:1 15 Open channel Sand and gravel 1 2,110 In certain reaches,flow Width:2' substrate;forested path becomes less Depth:0.3' area distinct Side slope:6:1 16 Open channel Sand and gravel 3 2,500 Channel becomes well- Width:3' substrate;forested defined with increasing Depth: 1.0' area gradient Side slope:2:1 17 Open channel Earth and grass-lined 4 2,890 Channel borders forest Width: 1.5' and back portion of Depth:2.0' residential lot Side slope: 1:1 18 18-inch diameter CMP Pipe crosses under SE 1 3,170 County staff has reported blockage and Inlet partially blocked w/trash rack 144th Street flooding at this location with leaf debris on 12/5/06 19 18-inch diameter CMP Conveys drainage 1 3,270 and catch basins west 20 18-inch diameter CMP Conveys drainage 1 3,960 west Table 1 (continued) Basin: Easterly Basin—Lower Cedar River Mainstem Subbasin Location Drainage Drainage Slope Distance from Existing Potential Observations of Field ID Component Type, Component Site Discharge Problems Problems Inspector,Resource Name,and Size Description Reviewer,or Resident See Fig.4 Type:sheet flow,swale, drainage basin, 1/4 mile-1,320 ft constrictions,under capacity,ponding, tributary area,likelihood of stream,channel,pipe. vegetation,cover,depth, (%) (FT) overtopping,scouring,bank sloughing, problem,overflow Size:diameter,width type of sensitive area sedimentation,incision,other erosion pathways,potential impacts 2 l Closed depression Onsite wetland 2 Southeast corner Overflow from wetland of site would be intercepted by ditch on west side of 164th Avenue SE 21A Sheet flow to east Grass and gravel 10-15 0-100 No signs of high Likely receives runoff driveway flow rates from a portion of SE 136th Street 22 12-inch diameter CP Conveys drainage 3 0 Debris blocking under 164t Avenue inlet of culvert • SE 23 Channel Grass-lined 5 60 Channel could Width: 1.5' have limited Depth: 1.0' capacity for pond Side slope:3:1 emergency overflow 24 Type 1 CB w/grate 2 170 See drainage 12-inch diameter pipe complaints 93- 0724 and 95-0715 25 Concrete sump 390 12-inch diameter pipe 26 Channel Earth and gravel-lined 1 550 Flow path not Width:2' well-defined Depth:0.2' Side slope: 10:1 27 Sheet flow and Forested/shrub 6 640 No erosion Signs of high flow dispersed channel embankment observed evident Table 1 (continued) Basin: Easterly Basin—Lower Cedar River Mainstem Subbasin Location Drainage Drainage Slope Distance from Existing Potential Observations of Field ID Component Type, Component Site Discharge Problems Problems Inspector,Resource Name,and Size Description Reviewer,or Resident See Fig.4 Type:sheet flow,swale, drainage basin, 1/4 mile=1,320 ft constrictions,under capacity,ponding, tributary area,likelihood of stream,channel,pipe. vegetation,cover,depth, (%) (FT) overtopping,scouring,bank sloughing, problem,overflow Size:diameter,width type of sensitive area sedimentation,incision,other erosion pathways,potential impacts 28 Stream channel Gravel substrate; 1 700 No signs of Channel meanders Width:4-6' forested area erosion through forested area Depth: 1.0' Side slope: 1:1 29 30-inch diameter CP Culvert crosses under 3 860 Length=40' school yard fence 30 Stream channel Shallow grass-lined 2 880 Width:4' ditch Depth: 1.5' Side slope: 1:1 31 30-inch diameter CMP Pipe conveys flow to 2 940 Outfall of pipe not found w/trash rack R/D pond in pond;could be a submerged outlet 32 RID Pond Heavy wetland 0 1,130 RID pond to high school vegetation 33 R/D Pond outlet 0 1,270 18-inch diameter CMP structure and overflow inlet to control structure pipe 34 42-inch diameter CP Pipe outfalls to stream 2 2,100 4-inches of sediment outfall w/trash rack channel accumulation 35 Stream channel Low-gradient channel 1 2,290 No signs of Channel meanders Width:3.5' erosion through forested area at Depth: 1.5' bottom of ravine Side slope:2:1 Table 1 (continued) Basin: Easterly Basin—Lower Cedar River Mainstem Subbasin Location Drainage Drainage Slope Distance from Existing Potential Observations of Field ID Component Type, Component Site Discharge Problems Problems Inspector,Resource Name,and Size Description Reviewer,or Resident See Fig.4 Type:sheet flow,swale, drainage basin, 1/4 mile=1,320 ft constrictions,under capacity,ponding, tributary area,likelihood of stream,channel,pipe. vegetation,cover,depth, (%) (FT) overtopping,scouring,bank sloughing, problem,overflow Size:diameter,width type of sensitive area sedimentation,incision,other erosion pathways,potential impacts 36 King County Pond D- 24"CMP inlet pipe 3 3,500 Trash rack to inlet Recommend cleaning 90832 Serena with trash rack to pipe was blocked debris from inlet pipe Park/Outlet control control structure with leaf debris structure on 12/5/06 37 15"x24"CMP;system 2 CMP is corroded turns into 18"CMP further downstream 38 Ditch and culvert 2 system on south side of SE 145`h Street 39 CB with 18"x24"CMP 1 crossing under SE 145th Street 40 CB with 24"CP exiting 1 5,000 12"CP enters CB from to south west 41 King County Pond D- 1 5,300 91941 REFERENCES Haozous Engineering,PS. June 15,2001.Evendell Plat-Preliminary Technical Information Report. DDES File No. L98P0047. Renton,Wash. King County Department of Natural Resources,2005. King County Surface Water Design Manual. Seattle. King County Department of Natural Resources, 1997. Lower Cedar River Basin and Nonpoinl Pollution Action Plan. Seattle. King County Department of Natural Resources, 1993. Current&Future Conditions Report for the Cedar River. Seattle. King County Department of Parks,Planning,and Resources, 1990. Sensitive Areas Map Folio. Seattle. U.S. Department of Agriculture, Soil Conservation Service, 1973. Soil Survey of King County Area, Washington. Seattle. 17 Threadgill Plat—November 2005 SECTION 4 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN Encompass Engineering & Surveying 77f,2 i c (H'/LLiQJ29(/4' ) �oB �9P�- -C / Now Partnered with Baima&Holmberg Western Washington Division SHEET NO. OF /// 165 NJu(42r)3.Suite201.I (4 S) WA 98027 7/ / Phone(425)392-0250 Fax:(42S)391-3055 CALCULATED BY � DATE '[/,`/ Eastern Washington Division 108 East 2'd Street.Cie Elum.WA 98922 CHECKED BY DATE Phone:(509)674-7433 Fax:(509)674-7419 SCALE I ... . I D 0 A cci v.. Z .cdi - . ., I im E AtiltiosiRwr i /49 (t --0 z-r effrci-ircV Pt .(. v A,t... To Lb Viet /9/144jp p1, .,..�ijii 'Toi -.A. I 1 . iriiit. PNELE14-eitt, - WI.L..L ---b• i .. 1 op vg, .. ,( 1--iiii)c.0 -0.6 (A/5 61.27 ri7ti . : i 1 -•. .kV 1 — (--- )P--,:i FI.OPLI .89113boa, 1 * 1414Q 0 04.0 ; f ..... ! i 1� i 170(Pyik..) ei,F 1 ,.. ., . ..t. t •.. .t.. r GTS I h ' ...! i i i 1 ! i 1 • ) ) 7 ) . . . . . . IA/VrtAND A. 0 ti RIPuc:17o/us Ild MA-0 4.aF.-- 128L.F71-s7L -413CM). 5 ,_,_ I 1)(21M5!t 3 1 t ! t ! ! 1 1 : : : : i f 3 1 3 1 i I 1 1 5 f • ! .•••••• ! i i } i i 1 1 3 3 1 1 3 S 1 i 1 1 1 f 3 ! 3 ! 3 S 3 3 Encompass Engineering & Surveying JOB Cts LT Now Partnered with Baima&Holmberg Western Washington Division SHEET NO. OF 165 NE juniper St..Suite 201,tssap)ah,WA 98027 Phone(425)392-0250 Fax:(425)391-3055 CALCULATED BY 712---- DATE C1 f �f vJ 711 J Eastern Washington Division 108 East 2 Street.Cle Elm,WA 98922 CHECKED BY DATE Phone:(509)674-7433 Fax:(509)674-7419 SCALE I I fri°14/* E regUA 1;?FP 5/4 A) •I • ---- A(, t, ,:p. p aarec,r- I tvavi), l fri-oA.05T___ t .. c i4 tA.L C 7-vek ,?fi r ail' ik pia4.1.t, 7-e) wE12,4tim) , tie_ ,Reeeviitrie4&_I I hi :..-. F-4,4,4_, rfte_,_: c7--- • te: ...4_6(or fiticcA/p0.--4, 1><At69:.9N . I AI .- r Z•r.. -- �- 3 i 5 ., - &J 44 (g40)... I ,.. L = o r 1.�,...2.. i.. ,...y. . .I. .z4.- , l A-L s z.• 731/15/ - =.. . ;0' ,mc, tA� z 4j. r 410, = 3... 5& _Q 0 = z:•??4ci- I --7--> AagA -1??. .E-0,g7r/fuir..i? ' . . . i : . . . . . . ! v4: Irci......f -r.. . I. �a . i I 1 1 I t ! i 3 ! ) ) } y } y ! ) y } . . . . . . . . . . . . . . . . . . . . I 1 1 ! ! I3 • • • • • 3 i i i } i f ! } 3 ! } i i } : : : i : : iiii } 3 . . . . . . . . . . . . . . . . . . . . . . . . Encompass Engineering & Surveying JOB eaGG L 1t S/ 7--- Now Partnered with Baima&Holmberg Western Washington Division SHEET NO. OF 165 N 'wiper St.3Suite 20Is(425) WA 98027 g 1,.�'' Phone(425)392-0250 Fax:(425)391-3055 CALCULATED BY � DATE C ` 7/ Eastern Washington Division 108 East 2"°Street.Cle FJum.WA 98922 CHECKED BY DATE Phone:(509)674-7433 Fax:(509)674-7419 SCALE I : : r .�.. ~ 191 iv yam. 1..o i 'c C A4) IV --.: - i 45 H t F i 9 ett-- - etElzki:.triiirt-, /3.,:.2) ctrisiE. Retj I T ?- '. .1 kJ 4C:./•6 Al- ,- I Ij .. .. .d,. ' : ;..Q r Ar f-4 . 17 11- (77 1-(....j. -11--iAr2F.:7") 1 t.1 i Al et, . V;IC Zr.5 ( V.,,E,-f/' ii^.4.7. 2 d_ 13 I 0'2- -"*.-- 01 (D110 Z,) , . g6 --- 0 , ( 05. 6, A t to 14/4--e7oe- po .,42) i...=...�...., 5 or-' . • • . ' I :s • I 1214)Air4c-c •ific7pgpfir, z---- ST I tic) I1 1 1 1 1 • j ; • ; ! ! ! ! ! 3 I 1 1 1 1 } 1 1 f ! 3 1 ! ) ) ) I • 7 . . . . . . . . . . . . . . . . . . f i 3 } 3 1 j j i 1 j i i 3 ) } 3 j : : : : : : : : : : : : : : : i3> 7 Encompass Engineering& Surveying JOB Now Partnered with Baima&Holmberg Western Washington Division SHEET NO. OF 165 NE Juniper St.,Suite 201.Issaquah.WA 98027 Phone(425)392-0250 Fax:(425)391-3055 CALCULATED BYillDATE 10-1"--1/ Eastern Washington Division 108 East 2'1 Street.Ck Elum.WA 98922 CHECKED BY DATE Phone:(509)674-7433 Fax:(509)674-7419 SCALE I t rVitti42.a is C #4( ins 5 Er 1 i .TV-Ierii/FlexAdirf-K•.4.- 1 ilfir?-,t4i1HgJ r Apel .. DW, r r 3�. Q... : r 00•,: ,� l. . .. ... A.-zg.s 1 V ... -r-/ -r- s) P : , (F-A6Admitv j: }meq r Svc f.v • 1 ---4- I ....g..1.0 ser op --= 1.,x...1..A. .(L."rx i , A-f• 4 l g'.�.- - LAI l..vat...A r./ w j ! • vi:I.uti , Je-C,d7: . ..r 0 rp:(./.004?LeD . • 1 f 1 1 1 ! ! ! ; i 1 ! ! ` ` - I. eFiz; Li 66 • . . i • CP' to r 0 , 6 6 5 or---5 : . jet, • ?O6 ' ( , ( t C .... I 1 1 1 ! 1 3 1 1 1 ! 1 1 1 1 I 3I. 1 3 . . . . . . . . . . . . . 1 1 1 1 1 3 1 3 3 } 1 ••••• i I 1 / ; i i 3 3 I I ••••i 1 , I i 1 1 1 1 7 1 , 3 1 Encompass Engineering & Surveying JOB I t ci Now Partnered with Baima&Holmberg Western Washington Division SHEET NO. OF 165 NE juniper St..Suite 201,Laaeyah,WA 98027 Phone(425)392-0250 Fax:(425)391-3055 CALCULATED BY DATE 013//Y Eastern Washington Division 108 East P°Street.Cle FJum,WA 98922 CHECKED BY DATE Phone:(509)674-7433 Fax:(509)674-7419 SCALE I I .DICIrrfrallehk Q .Lip_____ I --.--pip- r v./L 7)1. N/77 cQ t\/ Rev 19 2,1 t 0 4 /00 w_,roil:r...,p1.49mi.5 .m.rr I fc, (0 I ....i....„4-- i> v cr 2.►- pix/-I-7, .fes mOT-611111 I i --p_xr_q ti), : I 1?Eqv 4_ 0,,,,,, 4) Ir..' imams :... .... I it qio.. fro ,� I Rac . 1( . ÷-, ,. g.1.00 ,-:: 0 II'15 Cr1107 I 4-100 -r41144 . . . . . . . . . . . . . . . • ; i t i i i ; ; ; I • ) r ct,..... K r5 ( & p! I'w7!V . . . . . . }!/1 !. . . . . . . . . . 1 I . Ritgly vet*410 =--- 5 7--,63rEe.e.t.-- ... ... Pe-,/:!/ . } 3 y . I . . 1 , 3 1 1 } , > f1 1 , i I 1 / f 1 7 i } 3 3 3 3 f 3 • i Encompass Engineering & Surveying JOB Now Partnered with Baima&Holmberg Western Washington Division SHEET NO. OF 165 NE Juniper St..Suite 201.Issamfah.WA 98027 Phone(425)392-0250 Fax:(425)391-3055 CALCULATED BY DATE._ Eastern Washington Division 108 East 2id Street.Cle Elum.WA 98922 CHECKED BY DATE Phone:(509)674-7433 Fax:(509)674-7419 SCALE :::n-W1 (__ zwf_21) if ; /,490 $P /*/°> Css15°:1 ePi ftiv/PE-2? S(1 ,tv i !/b , o )..'.11.6i3V o : 1 3,00 F 141W1141Z' e,2, ...... .-..-0.....e....„ . nye, ; • II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I • 1 f f ; • ) 3 > 7 f ; ; ii i { 3 3 3 f 3 3 ) f i } r ii f 3 i ) ) f ) 1 t f ) ••••••• 3 3 3 Encompass Engineering & Surveying JOB ( (5 f Now Partnered with Baima&Holmberg Western Washington Division SHEET NO. OF 165 NE juniper S3.Suite 201 (42 ah.WA 98027 /i j Phone(425)392-0250 Fax: (425)391-3055 CALCULATED BY_Tr _I 0/DATE ./ Eastern Washington Division 108 East 2 Street.Cle Hum.WA 98922 CHECKED BY DATE Phone:(509)674-7433 Fax:(509)674-7419 SCALE P64141P1--- 11 f/It._..1...1,4 laile-4-4/ ~mew 1/6X ZWATit9 AO CP"1.9 � wMee fp •�•V+1 ii.i = 3.o ..Al c, ie Ago titi360.z9 02T cieret, A4 I. i / bffly I..448 .4r> . .. ..4.1,0 (41 ,.! .., f 44 > 6'7i f i.."'- il 3 i i • • . . . : : : : : : : : : : : a : • • f 1 i i ! 1 1 1 1 ! } ! } ! i ! ! 3 } I i 1 ! ! ) 1 i i } 3 i } ! } ! 3 } > 7 } } } • i 1 1 } } ) ! I } } i i i i } 3 i 3 1 i i Encompass Engineering & Surveying JOB U51 _1 Now Partnered with Baima&Holmberg Western Washington Division SHEET NO. OF 165 NE Nniper St..Suite 201.Issaquah,WA Phone(425)392-0250 Fax:(425)391-3055 CALCULATED BY Tfc DATE I 7153// ( Eastern Washington Division 108 East 2"'Street,Cle Elum,WA 98922 CHECKED BY DATE Phone.(509)674-7433 Fax:(509)674-7419 SCALE 1 3 1‘.41 •• = ve IL v.14.172t9 ypr. , i •••••••• •• •......., e S Lor CA)1 CO !.' V i:4.11./Ai 1?1..P4Ore--11- lb T.14.t. udievr.-Lo..&0 ii14.......?._, Le.i,.e peziliz.p5. --irgAti.s.r;-_-, ic... ......7.0... P.t..5.124.k.51/.01‘) A-b..1) Ti-mr..... 1 tfc..i2v) A--rrramti6.i- oJ iir - -rt-tt . f.2N1)..P.(0:•/=- fi.4 IA) I tiq ii.c. ra.s. 714$ 7..-trAPD.,....ki..6 -131.44 ;p5. fra(t ywitt$ 7-74iti, t-61-5 11 v2 it. i .. I _----.1,. . rH-E- 7 . -001..N.t.iv.ti 1. 0 C,0171 A-1)094-4./A,LI rl. . ...iv.u. 1_ . ... ..thl:ve..- . 6/14. 12 -? I/7 0 hum) -F 1 0-10.1-no A) FP1s.-7, L -1 / --e-- I. fuLt- .1.2!, P1*.r24/zo fs., TW cif"). f.: -. TH.t filfpOce 7.7" fpwi &A!evi...4 LOT Wit rare. polm.eri.8.4-, I :i.ci,.1 F.v.4_, 1;,.1.. (ple.03 11-7-b m47)1.E.0.1.z. Liezfi2ip?.0) CA)3.:Ff.tiu.kp.O. 1r4.c.r.!? :.D.o./.1.1:- c.atiti97, plyg:45/:f4) gr5.0 .7.-.15.41-4_..: ' i , , : : i 1)(4(-- i if,j1-___:MtnidLAI yr)z. -a-ilk 194e/ImP9 : . :.. : : . ..., iAy41,..Aeo.g.im. 4.71111)1i- ": 00 ec,:i.111(11%), 6 4PF: ilet --rili..1. ifiZtqle12,1-11CAL4 A/49ner I i 13.4.- ..4. 1 1 I elOP:afi.51.0/\) • 4Aei r;711 1 C.. 13°.74.4*. !F/Q! 4 .....1.11M111.011.1111Mill.a.1 6:i=;;46., m.....i...."I'r . I . . . . . . . . . . . . . . • . . . • ! ! ! : Encompass Engineering & Surveying JOB I i 5 ( 7- ( Now Partnered with Baima&Holmberg Western Washington Division SHEET NO. OF 165 NE Juniper St.,Suite 201.Issactuah,WA 98027 Phone(425)392-0250 Fax:(425)391-3055 CALCULATED BY Tn— DATE I—4(8fr Eastern Washington Division 108 East 2Street,Cle Bum,WA 98922 CHECKED BY DATE Phone.(509)674-7433 Fax:(509)674-7419 SCALE 1: 1041t.C..,, 7 L 469E/21 I OL? 31P4u.t1LEI) Fgrz, i°4-. I a J l/A- re0E- gc0F5 oee (i 14c. r-o ,f;$ 4 104 e2E TWE l-e71- talEA-s 1-14E ii-VE1(44L-. ... A.ara/c1 .49F-- 74 lt 0 49-73 -re, 1.1tetm.e0„, --om..171s ...L. 6,..33.5..*--*:77; I "PlimI1%.r.1) I rott_ Eylsp . c t;0 I mtect.mir,--72#%-4 li• --.&14ey i COUCkOuri ulsar V4F1514734e.k...:1S..er .t.c.„, I Pi. relis.4a4t) )Zi2-- .telcki •6? NE ir zedv7s--1/15 .13 1 . . J : 54-ia1/4i774r oleig w-- 7:27/1j'16 .-i /6 I neli Id (6•9i * 4 , 1 ilFamirzz? Hobtrig,Ri • (Di ! : • t , 010 5.40-A-50trkte,-- V,t ii -- ..e : I P , r---y— j, H (T) ..,141-._„,____,(0. I ! , . „ , i i, it, _ ,,- 'ilic/.40-19 F-40k1 pg.ni- ir404P'll-- i :! :! !: . 1 -- ------ - - . . • . , . . . . . . . f ? ? ' : ? . . . . . . . . . . . . . 7' Deep Level 3 Detention Pond Retention/Detention Facility Type of Facility: Detention Pond Side Slope: 2. 00 H: 1V Pond Bottom Length: 100. 00 ft Pond Bottom Width: 57. 65 ft Pond Bottom Area: 5765. sq. ft Top Area at 1 ft. FB: 11834. sq. ft 0.272 acres Effective Storage Depth: 7.00 ft Stage 0 Elevation: 0.00 ft Storage Volume: 57634. cu. ft 1.323 ac-ft Riser Head: 7.00 ft Riser Diameter: 12. 00 inches Number of orifices: 2 Full Head Pipe Orifice # Height Diameter Discharge Diameter (ft) (in) (CFS) (in) 1 0.00 0. 69 0.034 2 6.00 1.56 0.066 4 .0 Top Notch Weir: None Outflow Rating Curve: None Stage Elevation Storage Discharge Percolation Surf Area (ft) (ft) (cu. ft) (ac-ft) (cfs) (cfs) (sq. ft) 0. 00 0.00 0. 0. 000 0.000 0. 00 5765. 0. 01 0.01 58 . 0. 001 0.002 0. 00 5771. 0. 02 0.02 115 . 0. 003 0.002 0. 00 5778. 0.03 0.03 173. 0. 004 0.002 0. 00 5784. 0.04 0.04 231. 0. 005 0. 003 0. 00 5790. 0. 05 0.05 289. 0. 007 0. 003 0. 00 5797. 0. 06 0.06 347 . 0. 008 0. 003 0.00 5803. 0. 18 0.18 1048 . 0. 024 0.005 0. 00 5879. 0. 30 0.30 1758 . 0. 040 0.007 0. 00 5956. 0. 42 0.42 2477 . 0.057 0.008 0. 00 6033. 0. 54 0.54 3206. 0.074 0.009 0. 00 6110. 0. 66 0. 66 3944 . 0. 091 0.010 0. 00 6188. 0.78 0.78 4691. 0. 108 0.011 0.00 6267. 0.89 0.89 5384 . 0. 124 0.012 0.00 6339. 1.01 1 .01 6150. 0. 141 0.013 0.00 6418. 1. 13 1 .13 6925. 0. 159 0.014 0. 00 6498. 1.25 1.25 7709. 0. 177 0.014 0. 00 6578. 1. 37 1 .37 8504. 0. 195 0.015 0. 00 6659. 1. 49 1.49 9308. 0.214 0.016 0. 00 6740. 1. 61 1. 61 10121. 0.232 0.016 0. 00 6822. 1.73 1.73 10945. 0.251 0.017 0. 00 6904. 1. 84 1 .84 11708 . 0.269 0.017 0. 00 6979. 1. 96 1. 96 12551. 0.288 0.018 0. 00 7062. 2.08 2 .08 13403. 0. 308 0. 018 0. 00 7146. 2.20 2.20 14266. 0.327 0. 019 0.00 7230. 2. 32 2 .32 15138. 0.348 0. 020 0. 00 7314. 2. 44 2 . 44 16021. 0.368 0.020 0.00 7399. 2.56 2 .56 16914. 0.388 0.020 0.00 7484. 2. 67 2 . 67 17742. 0. 407 0.021 0. 00 7563. 2 .79 2.79 18655. 0. 428 0.021 0. 00 7649. 2. 91 2 . 91 19578. 0. 449 0. 022 0.00 7736. 3. 03 3.03 20511. 0. 471 0. 022 0.00 7823. 3. 15 3.15 21455. 0.493 0.023 0.00 7910. 3.27 3.27 22410. 0.514 0.023 0. 00 7998. 3. 39 3.39 23375. 0. 537 0.024 0. 00 8087. 3.51 3.51 24350. 0.559 0.024 0. 00 8176. 3. 62 3.62 25254. 0.580 0.024 0. 00 8257. 3.74 3 .74 26250. 0. 603 0.025 0.00 8347. 3.86 3.86 27257. 0. 626 0.025 0.00 8438. 3. 98 3. 98 28275. 0. 649 0.026 0. 00 8528. 4. 10 4 . 10 29304. 0. 673 0.026 0. 00 8619. 4.22 4 .22 30344. 0. 697 0.026 0. 00 8711. 4. 34 4 .34 31395. 0.721 0.027 0. 00 8803. 4. 45 4 .45 32368. 0.743 0.027 0. 00 8888. 4 . 57 4 .57 33440. 0.768 0.027 0. 00 8981. 4. 69 4 . 69 34523. 0.793 0.028 0. 00 9074. 4. 81 4 .81 35618 . 0.818 0.028 0. 00 9168. 4. 93 4 . 93 36724. 0.843 0.028 0. 00 9263. 5.05 5.05 37841. 0. 869 0.029 0. 00 9358. 5. 17 5. 17 38970. 0. 895 0.029 0. 00 9453. 5.28 5.28 40014. 0. 919 0. 029 0.00 9541. 5. 40 5. 40 41165. 0. 945 0. 030 0. 00 9637. 5.52 5 .52 42327. 0. 972 0. 030 0. 00 9733. 5. 64 5 .64 43501. 0. 999 0.030 0. 00 9831. 5.76 5 .76 44687. 1.026 0.031 0. 00 9928. 5.88 5.88 45884. 1. 053 0. 031 0.00 10026. 6. 00 6.00 47093. 1. 081 0.031 0.00 10125. 6. 02 6.02 47295. 1. 086 0. 032 0. 00 10141. 6. 03 6.03 47397. 1. 088 0.033 0.00 10149. 6. 05 6.05 47600. 1. 093 0.036 0. 00 10166. 6. 07 6.07 47804. 1 . 097 0.040 0. 00 10182. 6.08 6.08 47905. 1. 100 0.044 0. 00 10191. 6. 10 6.10 48109. 1. 104 0.050 0. 00 10207. 6. 11 6.11 48211. 1. 107 0. 054 0. 00 10215. 6. 13 6. 13 48416. 1. 111 0.056 0. 00 10232. 6. 15 6. 15 48621. 1. 116 0.057 0. 00 10248. 6.27 6.27 49857 . 1. 145 0.066 0. 00 10348. 6. 38 6.38 51000. 1. 171 0.073 0. 00 10439. 6.50 6.50 52259. 1.200 0. 080 0.00 10540. 6. 62 6.62 53529. 1.229 0.085 0.00 10641. 6.74 6.74 54812 . 1.258 0.090 0. 00 10742. 6.86 6.86 56108 . 1.288 0.095 0. 00 10844. 6. 98 6. 98 57415. 1. 318 0.099 0. 00 10946. 7.00 7 .00 57634. 1 .323 0. 100 0. 00 10963. 7. 10 7 . 10 58735. 1 .348 0. 412 0. 00 11049. 7 .20 7 .20 59844 . 1. 374 0. 978 0.00 11135. 7. 30 7 .30 60962. 1. 399 1.710 0. 00 11221. 7. 40 7 .40 62088 . 1. 425 2 . 510 0. 00 11308. 7. 50 7 .50 63223. 1 . 451 2 .790 0. 00 11395. 7. 60 7.60 64367 . 1. 478 3.050 0. 00 11482. 7.70 7.70 65519. 1. 504 3.290 0.00 11569. 7.80 7.80 66681. 1. 531 3.510 0.00 11657. 7. 90 7 . 90 67851. 1 . 558 3.720 0.00 11745. 8. 00 8.00 69030. 1.585 3. 910 0.00 11834. 8. 10 8. 10 70218 . 1. 612 4 . 100 0. 00 11923. 8.20 8.20 71414 . 1. 639 4 .280 0. 00 12012. 8. 30 8 .30 72620. 1. 667 4 . 450 0. 00 12101. 8. 40 8.40 73835. 1. 695 4 . 610 0. 00 12191. 8. 50 8.50 75058 . 1 . 723 4 .770 0. 00 12281. 8. 60 8.60 76291. 1.751 4 .930 0.00 12372. 8.70 8 .70 77533. 1.780 5.080 0. 00 12462. Hyd Inflow Outflow Peak Storage Target Cale Stage Elev (Cu-Ft) (Ac-Ft) 1 0.55 0.17 0.07 6. 32 6.32 50375. 1. 156 100-yr 2 0. 66 ******* 0. 07 6.30 6. 30 50164. 1. 152 3 1. 12 0.10 0.07 6.27 6.27 49875. 1. 145 10-yr 4 0.56 ******* 0.03 5. 62 5. 62 43269. 0. 993 5 0.35 ******* 0. 03 3. 97 3. 97 28212. 0. 648 6 0.45 0.06 0.02 3. 35 3.35 23075. 0.530 2-yr 7 0.59 ******* 0.03 4 .38 4. 38 31737. 0.729 8 0.49 ******* 0. 02 2 . 53 2.53 16693. 0.383 Route Time Series through Facility Inflow Time Series File: 115171.tsf Outflow Time Series File: rdout Inflow/Outflow Analysis Peak Inflow Discharge: 1. 12 CFS at 6:00 on Jan 9 in Year 8 Peak Outflow Discharge: 0. 136 CFS at 21 :00 on Feb 9 in Year 1 Peak Reservoir Stage: 7.01 Ft Peak Reservoir Elev: 7 .01 Ft Peak Reservoir Storage: 57761. Cu-Ft 1.326 Ac-Ft Flow Frequency Analysis Time Series File:rdout.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- Flow Frequency Analysis Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) (ft) Period 0. 136 1 2/09/01 21: 00 0. 136 7.01 1 100.00 0. 990 0.028 6 1/14/02 1: 00 0. 092 6.79 2 25.00 0. 960 0. 092 2 3/06/03 23: 00 0.066 6.27 3 10.00 0. 900 0. 020 8 8/26/04 9: 00 0. 031 5.76 4 5. 00 0. 800 0.028 5 1/08/05 6: 00 0.028 4 .74 5 3.00 0. 667 0. 027 7 1/23/06 4 : 00 0.028 4.71 6 2.00 0.500 0.031 4 11/28/06 14 :00 0.027 4.56 7 1 .30 0.231 0.066 3 1/09/08 20:00 0. 020 2 .53 8 1. 10 0.091 Computed Peaks 0. 122 7.01 50.00 0. 980 Flow Duration from Time Series File:rdout.tsf Cutoff Count Frequency CDF Exceedence_Probability CFS ° s o a 0. 002 22585 36.831 36.831 63. 169 0. 632E+00 0.006 7610 12 . 410 49.242 50.758 0.508E+00 0. 010 7056 11.507 60.749 39.251 0.393E+00 0.013 4778 7 .792 68 . 540 31. 460 0.315E+00 0.017 7467 12. 177 80.718 19.282 0. 193E+00 0.021 5190 8.464 89. 181 10.819 0. 108E+00 0.025 2968 4 .840 94 .022 5. 978 0.598E-01 0.029 2769 4 .516 98 . 537 1.463 0. 146E-01 0. 032 676 1.102 99. 640 0.360 0.360E-02 0.036 10 0.016 99. 656 0.344 0.344E-02 0.040 9 0. 015 99. 671 0.329 0.329E-02 0.044 7 0.011 99. 682 0.318 0. 318E-02 0.048 4 0.007 99. 689 0.311 0. 311E-02 0.051 5 0.008 99. 697 0.303 0. 303E-02 0. 055 6 0.010 99.706 0.294 0.294E-02 0.059 19 0.031 99.737 0.263 0.263E-02 0.063 21 0.034 99.772 0.228 0.228E-02 0.067 19 0.031 99. 803 0. 197 0. 197E-02 0. 071 15 0.024 99. 827 0. 173 0. 173E-02 0. 074 11 0.018 99. 845 0. 155 0. 155E-02 0. 078 8 0.013 99. 858 0. 142 0. 142E-02 0.082 10 0. 016 99. 874 0. 126 0. 126E-02 0.086 12 0.020 99. 894 0. 106 0. 106E-02 0.090 13 0.021 99. 915 0.085 0.848E-03 0. 093 17 0.028 99. 943 0.057 0. 571E-03 0.097 17 0.028 99. 971 0.029 0.294E-03 0. 101 14 0.023 99. 993 0.007 0. 652E-04 0. 105 0 0.000 99. 993 0.007 0. 652E-04 0. 109 2 0. 003 99. 997 0.003 0.326E-04 0 . 112 0 0.000 99. 997 0.003 0. 326E-04 0. 116 0 0.000 99. 997 0.003 0.326E-04 0. 120 0 0.000 99. 997 0.003 0. 326E-04 0. 124 1 0.002 99. 998 0.002 0. 163E-04 0. 128 0 0.000 99. 998 0.002 0. 163E-04 0. 131 0 0.000 99. 998 0 .002 0. 163E-04 0. 135 0 0.000 99. 998 0.002 0. 163E-04 .Paused-Duration Analysis-KCRTS 11E1 iit X i CO o rdout.dur c //,, target.dur •W O N_ O \-___ O R +, )e--------.0-_____:. U �` a) co 4 rn O 1 170° o CI (L O O • ♦ O O 00 ♦ • N ♦ O • O ♦ + ♦ O O O 0- I 1 111111 1 1 1 1 1 1 111 1 1 1111111 I I 1 1 1 1 1 1 1 1 1 1 1111 1 1 10 -5 10 -4 10 -3 10 -z 10 100 Probability Exceedence UrZ c NJ C(112- PS SECTION 5 CONVEYANCE SYSTEM ANALYSIS AND DESIGN Encompass Engineering & Surveying JOB l 51 / Now Partnered with Baima&Holmberg Western Washington Division SHEET NO. OF 165 NE Juniper St..Suite 201,Issaapah,WA 98027 / Phone(425)392-0250 Fax:(425)391-3055 CALCULATED BY DATE 1/14, 11 14)1 7, Eastern Washington Division / 108 East 2 Street.Cie Elum.WA 98922 CHECKED BY DATE Phone:(509)674-7433 Fax:(509)674-7419 SCALE CO.NVir rt+kiCE, Cilte30 -j.i- . Ten- itIV 1, /5 pEaThal4-1.E l 7 t. .rL Wrvs nF Z..,.,.....sP t410161 4. rgcr7- 1.• �....1.. 4 r 1 0 , .1.o.... .. ) i NT pENAJ-0 ..... �• 1(1 : -ft4t polo i rtn -Tri 1411-1-, �l 2 , fOO( AiI .v RLL Q.C.00. :- .RP14-5 U4D 1 )(4- • -165t4g-P RP 7-147-ea/ ritistet_ WiL ' r..1 pr,,y013 P ar-49.1.11)fici) )9A4) CA 5 Fg .. rakle..kw Nq. .....' �- - 1:10-- oc. Pfil/U5 1-#41) 211-5/rve; 04P 04-r- • . s...... .L.11-1 2 .. 70 ..... . . . . . . . . . . . . . . . . . . . . 0 ° 4 01144-4- 6,P 1 1_ R ---.,; ,, le ins) ilpt _ it 2- STA. 0+54, 13.25'RT .Na I, CB/ 1, TYPE M a - RIM=493.95 INV=490.95 STA. 1+89, 14.00'RT O �1 I! CB/2, TYPE II-48" lithe 1 „W/SOLID LOCKING UD _ a RIM=496.80 I >;� �- sIN r "INV=490.28 b1.11.4 (ti - STA. 2+80, 14.0O'RT '3'S 3f1N3AV - _� CB/3, TYPE I N 02'08'26" W 326.17' Y ,.t RIM=498.75 ` I uN1 §li! N '. INV=495.00 � �i 'rx_' ST/ , TY 1II-48T t,:c'1 71 q ST 4, TYPE II-48" � � RIM-496.04 l<s�=��- �= R I giit - 050,E25RT ��„� ` R9604_� Z �� I INV=493.00 • STA. 2+42.45, 11.391T I /- ' �� �� �� a• T. -I CB/6, TYPE 11-48" ‘.1.f,. ` r • '-\ s RIM=495.98 8d �� \ INV=489.15 I I. lit ailSTA. 2+42.45, 12.25'RT �--- gg -- 11141 CB/ 7, TYPE I i 9 kR t m \ A /J RIM=495.98 SII sk I . / INV=492.50 i 'pi I r--- -- 1 4 .w ______y STA. 3+84.37, 12.25'LT F CB/8, TYPE I NI Iib I Im RIM=492.47 -I I alCei__ ii I ~ Io INV=488.44 IL 1-1 1-- - I I In STA. 3+84.37, 12.25 RT cc L_ ! - - -- 3CB/ 9, TYPE1 1 � RIM=492.47 il I 11_--- -- 0 ,: r1 �' I< s_ INV=488.70 1f+ -r U -- - STA. 4+87.84, 2O.O0'LT V-1 r RE ,� z I_ CB/ 10, TYPE I � N w RIM=489.60 N I � b ii INV=485.60 I -- . F 3 ( - friiii 't .� ----� CB/ 11, TYPE II-48" �� I ', � g R I x W/BIRDCAGE OVERFLOW zI CO I r----i!I-di " ^ / ii Iii' I • 1-rg RIM=485.20 r) INV=477.58 3$ g ki -- - 14 STA. 6+66, 11.6'LT III ; Cl) CB/ 12, TYPE 1 e4II '-' 9 / I - RIM=473.0± I r---_ �r .�v: 7+ i �' (MATCH GROUND) bel 1 '_ / i ! I° 1 INV=468.50 Z `1 e3Rty I I f 00. ,� W ` a_ STA. 7+66, 11.6'LT �� � CB/ 13, TYPE I zE, `•+-1 RIM=457.0± 11: g 18�: B_ \.` ~ /i ,,, I '� (MATCH GROUND) I . le:2 _ S ::` v t . _ INV=452.50 t. � ),_ - .. e CONTROL MANHOLE VOIr .0%...........„40-,k, . -10. TYPE II-54" yuv,as.r-P W/SOLID LOCKING UD RIM=492.00 • ,,,,Fac M ,.SS,£b.10 N ( O.F.=485.00 G� INV=478.00 '3•S 3f1N3AV QM 1 iii : Lq ill -) a ; il24 C ow retitiee , kil , R 1 M A to n+,: 1d6, 1 Backwater Analysis of 12" Conveyance Pipe System from CB#1 to Pond using KCBW(conservatively assume full 100-yr flow through all CB's/pipe and pond is full) CB# 10 PIPE NO. 1: 90 LF- 12"CP @ 10.67% OUTLET:476.00 INLET: 485.60 INTYP: 5 JUNC NO. 1: OVERFLOW-EL:489.60 BEND: 30 DEG DIA/WIDTH: 2.0 Q-RATIO: .00 Depth of flow Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.12 .56 486.16 * .012 .45 .21 9.00 9.00 .45 ***** .56 CB#8 Og• ' 41 PIPE NO. 2: 104 LF- 12"CP @ 2.74% OUTLET: 485.60 INLET: 488.45 INTYP: 5 JUNC NO. 2: OVERFLOW-EL: 492.47 BEND: 0 DEG DIA/WIDTH: 2.0 Q-RATIO: .00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.12 .59� 489.04 * .012 .45 .29 .56 .56 .45 ***** .59 CB#6 PIPE NO. 3: 142 LF- 12"CP @ .49% OUTLET: 488.45 INLET:489.15 INTYP: 5 JUNC NO. 3: OVERFLOW-EL: 495.98 BEND: 0 DEG DIA/WIDTH:4.0 Q-RATIO: .00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.12 .67 489.82 * .012 .45 .45 .59 .59 .45 .67 .60 CB#4 PIPE NO.4: 190 LF- 12"CP @ .50% OUTLET: 489.15 INLET:490.10 INTYP: 5 JUNC NO.4: OVERFLOW-EL: 496.04 BEND: 30 DEG DIA/WIDTH: 4.0 Q-RATIO: .00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.12 .67 490.77 * .012 .45 .45 .67 .67 .45 .67 .61 le CB#2 PIPE NO. 5: 36 LF- 12"CP @ .50% OUTLET: 490.10 INLET: 490.28 INTYP: 5 JUNC NO. 5: OVERFLOW-EL: 496.80 BEND: 90 DEG DIA/WIDTH: 4.0 Q-RATIO: .00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.12 .70 490.98 * .012 .45 .45 .67 .67 .52 .70 .64 CB#1 PIPE NO. 6: 135 LF- 12"CP @ .50% OUTLET: 490.28 INLET:490.95 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.12 .70 491.65 * .012 .45 .45 .70 .70 .45 .70 .63 LBackwater Analysis of 12" Conveyance Pipe System from Pond to Outfall discharge point using KCBW (conservatively assume full undetained 100-yr flow through all CB's/pipe and pond is full) CB#13 PIPE NO. 1: 100 LF- 12"CP @ 14.50% OUTLET:438.00 INLET:452.50 INTYP: 5 JUNC NO. 1: OVERFLOW-EL:457.00 BEND: 0 DEG DIA/WIDTH: 2.0 Q-RATIO: .00 Depth of flow Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.12 .53 453.03 * .012 .45 .19 .50 .50 .45 ***** .53 0P 41- 110 ' CB#12 PIPE NO. 2: 100 LF- 12"CP @ 16.00% OUTLET:452.50 INLET: 468.50 INTYP: 5 JUNC NO. 2: OVERFLOW-EL: 473.00 BEND: 10 DEG DIA/WIDTH: 2.0 Q-RATIO: .00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.12 .53 469.03 * .012 .45 .19 .53 .53 .45 ***** .53 p. CB#11 PIPE NO. 3: 123 LF- 12"CP @ 7.38% OUTLET:468.50 INLET:477.58 INTYP: 5 JUNC NO. 3: OVERFLOW-EL:485.20 BEND: 30 DEG DIA/WIDTH: 4.0 Q-RATIO: .00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.12 .57 478.15 * .012 .45 .23 .53 .53 .45 ***** .57 V Ctrl MH PIPE NO. 4: 85 LF- 12"CP @ .49% OUTLET:477.58 INLET:478.00 INTYP: 5 JUNC NO. 4: OVERFLOW-EL: 492.00 BEND: 90 DEG DIA/WIDTH: 4.5 Q-RATIO: .00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.12 .778.71 * .012 .45 .45 .57 .57 .45 .71 .64 Pond Inlet Pipe-this pipe is assumed submersed in full pond PIPE NO. 5: 45 LF- 12"CP @ -6.67% OUTLET: 478.00 INLET: 475.00 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.12 3.83 478.83 * .012 .45 .00 .71 .71 3.78 3.83 .67 ole.., 31 •Ase4ED iNpotit. Encompass Engineering & Surveying JOB Now Partnered with Baima&Holmberg Western Washington Division SHEET NO. OF 165 NE Iuniper St..Suite 201,Issac jah,WA 98027 Phone(425)392-0250 Fax:(425)391-3055 CALCULATED BY DATE Eastern Washington Division 108 East 2i0 Street,Cle Hum,WA 98922 CHECKED BY DATE Phone:(509)674.7433 Fax:(509)674-7419 SCALE Ik O V i '',1 .._' coy volim.4e aitoc./e.___ .I I • fa-e 144-41- 1eti&G 4.i._,,, pe /6. it /2-ci' .4. a102- 1-' 021-' C ' ...4/62/1/01` .--(--.'i X/ ` :.. r , (NJ stIA-1,Lernek,i07- c- .: I c-t; 4 t o at 0 :,-... 48 et 4 0 > q i woe/v(4.h r r N ill.'"="403 . I".I .e 1-967 4t_9 , I P:j, °1140 40-11414, . . . . . . r -,I . CA. ... til ( Ic.f f ..) 7 r. / 9 ; ; if ; i . . . . . . . i 'CArg4q . q.c.9‘ P-- • : i i 1. i it • ... • i i I ! . . . . . . . . . . . . . . . t I t I I i f 3 rr : : : 4.3.1 CULVERTS METHODS OF ANALYSIS FIGURE 4.3.1.B HEADWATER DEPTH FOR SMOOTH INTERIOR PIPE CULVERTS WITH INLET CONTROL —180 —10,000 -—168 -8 ,000 EXAMPLE (1) (2) (3) ENTRANCE TYPE _156 —6 00o D=42 inches (3.0 feet). Q=120cfs _ 5 _ 'SQUARE EDGE WITH —144 —5,000 HEADWALL - —4,000 ►+w' HW —132 - D (feet) - - —3,000 (1) 2.5 8.8 —120 - (2) 2.1 7.a - - I I - ,T•2,000 (3) 2.2 7.7 4. _ I I —108 - - - D in feet - ) 3. 1 —96 -1,000 _ 3• - _ PLAN (1 GROOVE END WITH —800 - _y _ _ . - HEADWALL —600 --84 2 :r•. - —500 - - I :'I 2. - _ I —72 —400 0 - - _ I _ - -300 �jPj/ _ . — 1.5 — 1.5 I I Z 60 LL —200 / ¢ — 1.5 : :? — Z U w - PLAN (2) Z - w - GROOVE END 0 —54 a - - - PROJECTING CC —48 p_ o - - _ ti80 x UO. / _ —60 I— _ — 1.0 _ 1.0 / LL �2 a) —50 HW ENTRANCE 0 _ / i — 1.0 / O —40 D S ALE TYPE cc (3) 36 .9 Lu - — .9 H —30 (1) Square edge with Q W - headwall — •9 - Q —33 Q _ 7-20 (2) Groove end with W —30 headwall = — •8 — ,8 (3) Groove end '$ _ —27 _ projecting - - —248 — .7 6 To use scale (2) or(3) project - —/".".. .\\ —5orizontally to scale (1), then - -4se straight inclined line through and a scales, or reverse as3lustrated.— 2kOtib' ^) 1'0 - - _ - — : 1.0 12 2005 Surface Water Design Manual 1/24/2005 4-45 SECTION 6 SPECIAL REPORTS AND STUDIES Technical Memorandum Re: Harmony Grove—Onsite Wetland Hydrology Assessment Project: Harmony Grove Project Location: Renton, WA Prepared by: Ed McCarthy, PE, PS Prepared for: American Classic Homes Date: 12-12-11 Harmony Grove —Onsite Wetland Hydrology Assessment Methods The hydrology of an onsite wetland at the proposed Harmony Grove plat(Figure 1)was evaluated for existing and proposed developed conditions. The hydrologic model WWHM4 was used to simulate the hydrology of the wetland and to determine if the wetland's hydroperiod, following development of the site,was within an acceptable range as outlined in Reference#5 of the King County Surface Water Design Manual(2005). Basin Hydrology A hydrologic assessment of basins contributing to the onsite wetland was conducted to characterize flow regimes and stage fluctuations in the wetland. A single basin draining to the wetland was delineated under both existing and proposed developed conditions. A node was added in the hydrology model to allow flow statistics to be computed at the wetland. The area of the contributing basin was broken down into categories of land cover type, hydrologic soil group, and slope. Categories of land cover types included forest, pasture, lawn and impervious. These areas were delineated using a color aerial photograph and the project's topographic map. Hydrologic soil groups included Group C/D, representing poorly drained soil series with relatively a high amount of surface runoff. The assignment of this hydrologic soil groups was based on the SCS mapped soils series(Figure 2)(SCS, 1973). In addition, slope categories were defined for flat(0-5 percent), moderate(5-15 percent), and steep slopes(>15 percent). Data for the basin were input to the Western Washington Hydrologic Model (WWHM4 Pro Version). WWHM4 is a continuous hydrologic model that develops runoff time series for historic rainfall record. Rainfall data for the Seatac area rain gage,which includes a 50-year period of record, were used in the hydrologic modeling of the wetland. The WWHM4 program generates statistical reports for several hydrologic parameters including peak flow rates for estimated return periods, flow durations,wetland stage and other data useful in evaluating wetland hydrology. The hydrology of the wetland was evaluated for two scenarios including i) existing conditions and ii) proposed developed conditions. Under existing conditions,the basin contributing to the wetland was modeled in its current state. The wetland was modeled as a reservoir with water levels controlled by a single 12-inch diameter culvert at the wetland's outlet. Under proposed developed conditions, the basin contributing to the wetland was modeled in its proposed 1 developed state.Under the development plan, some of the wetland's basin would be collected in the plat's stormwater system and conveyed away from the wetland. The runoff from five single- family lots surrounding the wetland would be collected and dispersed into the wetland buffer. As for existing conditions,water levels in the wetland were assumed to be controlled by the existing 12-inch diameter culvert at the wetland's outlet. The stage-storage relationship in the wetland was based on the topographic map for the site. The stage-discharge relationship for the wetland was developed using a nomograph for a corrugated 12-inch diameter pipe, assuming inlet control. Results The total area of the basin draining to the wetland under existing conditions was estimated to be • 1.96 acres(Table 1). The majority of the basin is currently forested but includes two residential structures and areas of lawn/pasture (Figure 3). Under proposed developed conditions,the wetland's basin area would be 1.40 acres, including 5 single-family residential lots (Figure 4). The average annual rainfall for the 50-year period of simulation record was 37.6 inches with a minimum amount of 23.8 inches in 1952 and a maximum amount of 54.6 inches in 1950 (Figure 5). Predicted wetland stages, for both existing and developed conditions, are compared in Figures 6 through 8 for a wet year, a dry year, and an average year of precipitation. Peak wetland stages were calculated for a range of return periods, including 2-, 5-, 10-, 25-, 50-, and 100-year frequencies for both existing and developed conditions (Table 2).Modifying the basin area contributing to the wetland under proposed developed conditions slightly increased the peak stages in the wetland for return periods ranging from the 2-year to 100-year events (Table 2). The 2-year peak stage was estimated to be 0.08 foot under existing conditions versus 0.16 foot under developed conditions. The 100-year peak stage was estimated to be 0.26 foot under existing conditions versus 0.41 foot under developed conditions. The mean annual stage fluctuation in the wetland over the 50-year period was predicted to be 0.26 foot under existing conditions versus 0.48 foot under developed conditions (Appendix A.2). This represents a 0.22 foot increase in the mean annual stage fluctuation. On a monthly basis, stage fluctuations increased as a result of the proposed wetland modifications by up to 0.06 foot in the wetter months(November through February) and 0.04 foot in the drier months(March through October) of the year. In general, the model predicted wetter conditions in the wetland under the proposed development plan. The proposed plan for maintaining the wetland's hydrology will meet the King County's criteria for allowable stage fluctuations.No stage excursions greater than 0.5 foot were predicted during thesimulation period. Furthermore, no stage excursions greater than 0.24 foot were predicted during the amphibian breeding season (February 1 -May 31)throughout simulation period. In addition, criteria for the change in the number of dry periods in the wetland were also satisfied as determined by the WWHM4 modeling results (Appendix A.2).No total dry period, defined as when the wetland pool draws down to the soil surface, was predicted to change by more than 14 days in any year. 2 Table 1. Summary of basin areas draining to wetland. Existing Conditions Forest Pasture Lawn Imperv. Total Till Till Till (AC) (AC) (AC) (AC) (AC) Total 1.34 0.51 0.00 0.11 1.96 Developed-Conditions Forest Pasture Lawn Imperv. Total Till Till Till (AC) (AC) (AC) (AC) (AC) Residential Lots 0.39 0.34 0.73 Wetland/Other 0.63 0.04 0.67 Total 0.63 0.00 0.39 0.38 1.40 Table 2. Peak stage in wetland. Return Period Peak Stage- Peak Stage- (Years) Existing Developed Conditions Conditions (FT) (FT) 2 0.08 0.16 5 0.12 0.21 10 0.15 0.25 25 0.19 0.31 50 0.23 0.36 100 0.26 0.41 3 i � i rS!ii•IF'1' ,�, '� s�/N i� am- �i/ peak tea. P4 ii-Vil r.�� n■■.:.,.� s 1.1 i ArA ` Nwi, C6t,, , r-- Ell , mmE.m M i?� l r-it di - ms's/ii..41♦j Ra \ t NE N71,- 2th St NE 9f•. TA amil- 0 • sue Via i a � �� s�Lr ..i■ii •_ E.1 nr :fi d I lq,La. rr SE 112th .t �� r—� ■01■f uy .ail i� filth St NE 11th S 1 �I :■� , w NE o � .. ..■1 1 ra.rincrr�" r1� � t Mil ���nn� � �I�.�ias. � , p_kl NEE 10th Pt r SP'16th �:■1111111111W—mo �1111111643114141*ik‘ � 111111-114-617:41c- t_ t i M ■P !lp 'cc /Illi .I-�' ILNE 9th St Ll I'�i .' ,,.6sri NE 10[hSt w �� ■fi,��e:�- I ,��� _I : fl .,.Irk\ ,i N-%. ''AIL ,�-s'✓. NE 8th \--4:-2 JS S aw t►ill -� 1 _ ����� ,� t�►�N'�m -1.1t ■. E 7th \, t t , ' Aiii i il:w� 11_ _■i� i I In IfigAVA C IIII il mifas ri En F - NE 6th St a \tido* nll■■ . ria .. s ,. " � NE 5th St SE 125th St . •� 1 , ,. °�Imt`.�� �1 Igen_ .1 E 5th St _46 �I �imp p 4: ■f 11 �v I ,W1 L r I� a c �b ani_ pokPIIn ME EN EN , �1)1,116114 4,: 1 in._ W', - �_ o NE 4th St_ 1111 ....6110,1 ■=_■i NI irro:VP,1'� .. {1 s. NE 3rd C1 29th PI w ill ii imili•Lcx ■• w mi �I���'s■r It■� ir� �r ` N E 2 • ao ■um dm -ILII 11i1N . =i • '-rl I '. - JJ i�Nln ��.�� e j ■ CP rl NE 2n• � I NE SE 132nd St Q' mom —Ifh __ !lN �C\ `'3�■ ..... J "�li' aNE 1 - 1 ) 1--c 11'J.3PErti` Vi Mitilid=n 11 W1aA , m�6; , ,3 to' oq m w SE 1st P! �_ w Sf _ -Neal ■ n �1_ non 1-t-- _ n ti ■ ■nu' w •qiu�H Project Site S ns o li CM"1 n _ f34th n >SE2nd Pl � ��=Nrrypaa �� o E d ��� viii_ +SE 1 .1 'a�istu ■ li.n, 'J NI�or 1 i ;i ill .. ■ S S , ■ �■.I= .SE Aires Vitra :t�llln_�-It+.i taloa • �a '- n■ —;Iuui rtrATI " a N n. y' ' s •n 11 I'ini a �I :L�iw �� . um ,_ 40 rgo=1=�� 1. .etailmuz_�i 1 Lttk 1■mt miiii„ .. ,A,,lilt c�:'� ��-_ :_���:asl►w.imm NN �I,rl ;TM oth S <<r.1 Jnr _ ��- dt —SE 'low. c-E 4 dpPati•• !�.po . _..� trirm.t �a:1{i�G A al � r..Y.7i �•�i:3� •_� L. . �,w iii IN ii I /�j ., ,'a►• ■_a �:;=� P -1 g Nd „'E 143rd Sf ,�' IliriA r'��-"1—a' 1I1i• 1 ili�.__ • i simm Int is __lin X11 2._.. Va ��.,; ____■I.o?I.� I .1111111■1 M0,0/ y . is �� S a� ' c.► �� � � Ildl �.ts3 i y �1 �.iii IJ-� .,.� .- E 4.:7 N1 S� 6.�d� Ii7 1 ,71:2 \, i II I j' << : G.* --,V1- I■n .sl /, 1.0, i. 'Hi VII._�� U RI_1 1 Ra �' lib, 1/��.t• �s�+ WIEN u t=Allow al - .4-4 IN flu Liras13 1; 0 2 i M�sau i kv\`P,e Pve SE ��4�000000 �/•iii2i . rat r ..'..,,,,-l.■ 1 �i � ' Smil Inv E 515tS •. , .s i;` QCs �hk C- /0 ----,-,.----!-=.------` SE Jon - - AI' p 0l1 ` I y SF�S6th `..1.'y' r 1 ''ngk - o r CF k ��� SE 158th St '' ;�1� ,•I�H v 1 (\..fik I n. �.1���►��/ \, `l SE 159th PI :;_t N - `' SE 's7.9e. -SE 162nd PI SE 164th St 163rd St Rq No Vicinity Map Ed McCarthy,PE,PS ,,,,e Harmony Grove Wetland Hydrology 99571715tAoenueSE 12/12/11 Plat Analysis 2,000 Renton,Washington 98059 Phone: (425)271-5734 Figure 1 King County, Washington 1 I Feet Fax (425)271-3432 ?7121St �I 1 A) `� • /rte .1.- _---:--__. lir � A `tel 4.I ` ■ _i7 .a, ' APPIf� — ri; ii r 11116,- ilmi 11 ifi IN IN au i -/� ■ 7th 1!$ 4II _.1 pu IN : .1 ,-. 111. .111 11112 " 3 ' .moi 1 � is i ■ = 11'x!91 p (116n c.1 • lk 1 —11 fim•■ 6 - 111!1 ■■■■■■■ : A■■ Egin v von, F •�'.�11 I :I, . ■■��i■■_� ! ■ i���7 I _ = 3-nd �� :1111 F I 1 3rd '-- t— L/� = � : = 13 rd � I --L 134th — III —� 1 IIIA INN_ FITF14 h ■ ■ I �.•UI Project Site - : L UM ■1111 .._ M l.. 111111 I i I [ 13 X11111 _ — - : Mil �_ ---------- -�_r:11 . go Mg MN _ �_( ■■■■ ■ z7r 1 ■, � �i�i — 3 th.,, im hmumq oral in 4 113..._ #1I o - TE: _ - E, , � 6 �m mg ■ _ IIIIM ■ --- 0I ' ] 1 away ! 1, a • .-� _ _ 2 r ��' �I1/ j ■■■fit. mum_ I. ��►. L —�— ' J�`� (\., - .. —7 ' 1 1 M iiit -11'itit:E : - 1111 ; Is . _" _ ■ _ "too■ ■111in 40.- lr V 1 Law :-.ii. i 4 Ltdiar. ilk 14)111! In mi= Irl : -_-- : ', - -a/J M t`.Imp -1■..11■ a ilir *,% - . itit\14• _- gag ilibilcl�l * MI yy a,_ ., 'gm: PI Soils Map Ed McCarthy, PE,PS a, Harmony Grove Wetland Hydrology 9957171stAvenueSE 12/12/11 Plat Analysis 1,000 Renton,Washington 98059 King County, Washington Feet �'o"e (425)271-5734 Figure 2 I I I T.L. 145750-0037 — — I I I I T.L. 145750-0038 } I / ----IL:1/ S 18 TO BE DEDICATED 8 — _ T' CITY or REN70N N 88'48'53" W 1 a . .1 .. i 4,F I , • SHOP I 4A i yp4 I -'17*---.)\ ® ( y02 I . L. . ' r 500, N 49 . . . .: I - CYCLONE k.', , I s.0 ' ,AIL . el!.._ • in Are• — . ' 6 A - ' I I \ =° to M ,�, \ fid^ ,-- li C'' yo a �� \ 4 oti I z # �. . . �. 0 'IL e at. D EX. 4.32SMH per' 1 RIM-494.32 / .62 (8'PVC-W) Q y 11-12 4,, 4... .,,,, 7 , _ .r��c_,mss INC. _ ° �t� - y�':. 0.35 -- Ti-� 0 0.•' 11-, Ink +0. sa, 2+00 .. nam 492.78 �'� , .,. ®4, WOOD 488.93 (12'HEPE '• / ,.r, RAIL FENCE - - RIM-493.78 491.18(i122" -E) 'kill 'R •31 v1.oe (12•CMP-N 3.18 T.L. 1457500126 I NV=491.48 (12"CMP-N) I • I INV=491.38 (12"CMP-W) • i \ \ . T.L. 1457500128 \*".--.. fI I If I I I 1"-30. Figure 3. Existing Wetland Basin o 15 30 60 T.L. 145750-0037 I I 1 I I T.L. 145750-0038 I - – I I - - - - - - - - - - - — / „ In ¢---a1�—GP--.'ter—CFP--CUP——--Or-- 01.-- 18 TO BE DEDICATED g — i _ _ _ r r, arr OF RENTON N 88'48'53" w S.E. 135 1 - - : - - — 498 �� 502 LTJ15 I 13 3 12 I 11 D5,701 SF ©„200 SF Z 5„201 5,372 SF 6,132 SF 6,1 11.1 I > 504 Q 1 - I DRAINAGE L 1 5•PRIVA I I y02'I I Q \ jI 1 EASEMENT 5•PRIVATE Z N � DRAINAGE 500 M� Illir 1 — 1 49 '11+00 ---�_ 1.'. 1 / B �sirh\ • ea •1 .40 • =r- \ \ - _ 7..:\,._, a °ryh I Z :' ge-e e-e I °�°° I ~ TR• T E — Q ° IA e. ENS,VE AREA Fo a 16,859 S' D I. 3 EX. SSMH y,�' 1 I 2 k9$ -496- RIM=494.328"Pvc-w) 1 e-a 1 .62 (8"PVC-W) Q „a / 500-- _ - _ 5,932 SF5 PRIVATE 57 . 494 ® / 0p,NO / / �ASfll£N7„ii' 5. 2 SF _ �` a — _ _ jr-••100•=17.4=- --46:r -� M a; - 1•111118NMI»� • — . . $$75'4: INC. ' 0.35 _ _ Aad , #. . V •�6 81 .t 6+00 Wit/ s, _� + 2+00 9�� _ '�1 - . Pte. Q - TREE cbti 492.78 Ei / , - - ® 488.93(12"HDPEE •- / . ':'.-- ' EX. CB oP" -• RIM=493.78 _ • 491.18(12'CMP-E) �@ Ex:.•_•3,19' '. ••`x~ T.L. 1457500126 I 1 .08 (12 CMP-N) NV=491.48 (12'CMP-N) A 141 I INV=491.38 (12'CMP-W) \ T.L. 1457500128 \ V II 8 I I \ I/ ! I I ”-30' Figure 4. Developed Wetland Basin 0 15 30 60 It 60 up O N U) Y7 Y] 6D (p m 50 CD vlird n4- N o v - o Z 40 �- T. o --/-��`. O_ V)CO ca CSI A CS/ rr, C v a+ cam) Y th VC,r _ 7 0 cE 7 E 30 m `c 20 - R a c 0 3'al,..� r' r r—r --- --r Calendar Year Figure 5.Annual rainfall amounts used in hydrologic model.Based on Seatac precipitation gage with 1-hour time increments. 8 0.2 Wetland Stage-1950-Wet Year Existing Developed H LL O)0.1 lC co T. d !, ?„ U OL 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 Julian Day Figure 6. Wetland stage for a wet year. Values plotted are daily average stage. 0.2 Wetland Stage-1952 -Dry Year Existing Developed 1- u- 1:” A 0.1 N o \At , I I I I 4 .akk, C d 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 Julian Day Figure 7. Wetland stage for a dry year. Values plotted are daily average stage. 9 0.2 Wetland Stage-1986 -Average Year of Rainfall Existing Developed i- U- m0 1 65 C l4 d '; I 0 'N.J $ , ems' t< ' ' 'vr ' ` i " ' �, 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 Julian Day Figure 8. Wetland stage for an average year. Values plotted are daily average stage. 10 References King County Department of Natural Resources, 2005. King County Surface Water Design Manual. Seattle. U.S. Department of Agriculture, Soil Conservation Service, 1973. Soil Survey of King County Area, Washington. Seattle. 11 Appendix A. WWHM4 Model Input/Output Appendix A.I WWHM Project Report Appendix A.2 Wetland Stage Analysis Appendix B. Wetland Stage-Storage-Discharge Appendix C. Julian Day Calendar Appendix A.1 WWHM4 Project Report WWHM4 PROJECT REPORT Project Name: Harmony Grove Site Name Harmony Grove Site Address: City Renton Report Date : 12/12/2011 Gage Seatac Data Start 1948/10/01 Data End 1998/09/30 Precip Scale: 1.17 Version 2011/06/09 PREDEVELOPED LAND USE Name Existing Bypass: No GroundWater: No Pervious Land Use Acres C, Forest, Flat 1.34 C, Pasture, Flat .51 Impervious Land Use Acres DRIVEWAYS FLAT 0.11 Element Flows To: Surface Interflow Groundwater SSD Table 1 SSD Table 1 Name SSD Table 1 Depth: 2.35 ft. Element Flows To: Outlet 1 Outlet 2 SSD Table Hydraulic Table Stage Area Volume (ft) (ac) (ac-ft) Manual NotUsed NotUsed NotUsed NotUsed 0.000 0.004 0.000 0.000 0.000 0.000 0.000 0.000 0.350 0.005 0.001 0.500 0.000 0.000 0.000 0.000 2.350 0.183 0.186 4 .500 0.000 0.000 0.000 0.000 13 MITIGATED LAND USE Name Developed Bypass: No GroundWater: No Pervious Land Use Acres C, Forest, Flat .63 C, Lawn, Flat .39 Impervious Land Use Acres DRIVEWAYS FLAT 0.38 Element Flows To: Surface Interflow Groundwater SSD Table 1 SSD Table 1 Name SSD Table 1 Depth: 2.35 ft. Element Flows To: Outlet 1 Outlet 2 14 Appendix A.2 Wetland Stage Analysis Wetland Fluctuation Analysis Program [A]Comparing Datasets: 1001 SSD Table 1 STAGE Predeveloped 1003 SSD Table 1 STAGE Mitigated [B] Current Mean Annual Fluctuation: 0.259596536938961 ft Future Mean Annual Fluctuation: 0.47993500272815 ft Change in Annual Fluctuation : 0.2203 ft [C] Mean Annual Excursions : 0.000 [D] Mean Monthly Fluctuations (Feet) Month Current Future Difference January 0.055 0. 102 0.047 February 0. 058 0. 099 0.041 March 0.046 0. 08 0.033 April 0.039 0.077 0.038 May 0. 029 0. 061 0.032 June 0. 016 0. 047 0.031 July 0. 015 0. 048 0.033 August 0. 01 0. 034 0.023 September 0. 014 0. 048 0.034 October 0. 017 0.058 0.041 November 0. 027 0. 084 0.057 December 0. 045 0. 103 0.058 [E] Year Events >72hr Events Events During >24hr Events Dry Period New Amph Breeding For Non- Amph (Current-Future) Dry Periods Months Breeding Months 1949 0 0 0 0 6 0 1950 0 0 0 0 4 0 1951 0 0 0 0 10 0 1952 0 0 0 0 13 0 1953 0 0 0 0 2 0 1954 0 0 0 0 8 0 1955 0 0 0 0 13 0 1956 0 0 0 0 7 0 1957 0 0 0 0 6 0 1958 0 0 0 0 5 0 1959 0 0 0 0 9 0 1960 0 0 0 0 9 0 1961 0 0 0 0 10 0 1962 0 0 0 0 10 0 1963 0 0 0 0 9 0 1964 0 0 0 0 11 0 1965 0 0 0 0 6 0 1966 0 0 0 0 0 0 1967 0 0 0 0 11 0 1968 0 0 0 0 2 0 1969 0 0 0 0 12 0 1970 0 0 0 0 4 0 1971 0 0 0 0 3 0 1972 0 0 0 0 5 0 15 • 1973 0 0 0 0 1 0 1974 0 0 0 0 13 0 1975 0 0 0 0 1 0 1976 0 0 0 0 9 0 1977 0 0 0 0 12 0 1978 0 0 0 0 7 0 1979 0 0 0 0 3 0 1980 0 0 0 0 5 0 1981 0 0 0 0 0 0 1982 0 0 0 0 13 0 1983 0 0 0 0 10 0 1984 0 0 0 0 12 0 1985 0 0 0 0 0 0 1986 0 0 0 0 1 0 1987 0 0 0 0 7 0 1988 0 0 0 0 3 0 1989 0 0 0 0 12 0 1990 0 0 0 0 5 0 1991 0 0 0 0 5 0 1992 0 0 0 0 0 0 1993 0 0 0 0 3 0 1994 0 0 0 0 5 0 1995 0 0 0 0 1 0 1996 0 0 0 0 10 0 1997 0 0 0 0 9 0 1998 0 0 0 0 10 0 /*/ indicates falure to comply with wetland fluctuation criteria. [A] Comparing datasets. The first is considered "Current" and the second is considered "Future" in this program. [B] Mean annual water level fluctuations (WLF) should not exceed 20 cm. This is the mean/average fluctuation for all the data years. [C] Compare existing and future continuous hydrographs and record all events in which there was a difference of more than 0.5 ft. Determine the mean annual number of these events. [D] Mean Monthly Fluctuations (Feet) . Compare existing and future mean monthly WLF for each month of the year (ie compare existing and future for January, compare existing and future for February, etc.) . 1 2 3 4 5 6 7 [E] Year Events >72hr Events Events During >24hr Events Dry Period Dry Period Amph Breeding For Non- Amph (Current) (Future) Months Breeding Months 1 Data year. 2 All events in which there was a difference of more than 0.5 ft. (Allowed: 6) 3 All events in which there was a difference of more than 0.5 ft with a duration > 72 hours. ( Allowed: 0 ) 4 All events in which there wasa difference of more than 0.26 ft the amphibian breeding period (February 1st through May 31st) . (Allowed: 0) 5 All events in which there was a difference of more than 0.26 ft with a duration > 24 hours within any 30 day period outside the amphibian breeding period. (Allowed: 0) 6 Difference between current & future dry periods (stage < 0.001 ft) . (Allowed: 14 days) 7 Dry periods in future conditions where there were none in current conditions. (Allowed:0) 16 Appendix B. Wetland Stage-Storage-Discharge Existing/Developed Conditions Stage SA Storage Discharge (FT) (AC) (AC-FT) (CFS) Method of Flow Estimate 0.00 0.0040 0.0000 0.00 0.35 0.0045 0.0007 0.50 HW/D inlet control 2.35 0.1830 0.1860 4.50 HW/D inlet control 17 Appendix C. Julian Day Calendar Regular years: (2001, 2002, 2003, 2005, 2006, 2007, 2009, 2010, ...) Jan Feb Mar AprMay Jun Jul Aug Sep Oct Nov Dec I 1 1 1 32 60 91 121 152 182 213 244 274 305 335 [i2531 61 921122 153 183 214 45 275 306 336 r3 I 3 34 62 93 123 154 184 215 246 276 307 337 1 4 4 35 63 94 124 1551185 216 247 277 308 338 15 r 5 36 64 95 125 156 186 217 248 278 309 339 1 6� 6 37 65 96 126 157 187 218 249 279 310 340 17 38 66 97 127 158 188 219 250 280 311 341 8 8 9 67 98 128 159 189 220 251 281 312 342 19 9 401 68 99 129 160 190 221 252 282 313 343 110 I0 41 69 100 130 1611 191 222 253 283 314 344 11 11 42 70 101 131 162 192 223 254 284 3151345 12 l2 43 7l (02 132 163 193 224 255 285 316 346 13 13F1:4-1-72:1-165.1ThITal11941225 256 286 317 347 1414 45 73 104 134 165 195 22612571287 318 48 1111 46 74 105 135 166 196 227 258 288 319 349 1 16 47 75 1061 136 167 19712-2-8- 259 289 320 50 17 17 .18177T1-67711371168119812291- 21 351 W1 .81 49 77 108 138 169 199 230 261 291 322 52 19 9 3 78 109 139 170 200 231 262 22 3231353 20 20 51 79 1101 140 171120112321263 293 324 354 21 21 52 80 111 141 172 202 233 264 294 325 355 122 1 221 53 81 112 142173 203 234 265 295 326 356 23 23 54 82F1- 11,1314121412T21-2-9- 1357 24 241 55 831114 144 175 205 2361267 297 328 358 125r-231--5.- 25 56 84F, i31145 176 206 237 2681298 329 359 126 1 26T-571 85l146[ [ [360 27 27 58 86 117 147 178 208 239 270 300 331 361 28 28 59 87 118 14811791-5-39-12401271W3321 ,36 F2-9-1 291-1 881119 149 180 210 241 272 302 333 363 30 301— 89 120 150 181 211 242 273 303 334 364 31 311— 901— 1511— 212 243 304 365 18 PREPARED FOR PNW HOLDINGS, LLC August 30, 2011 Stephen H. Avril Staff Geologist • ' e¶,, :14,/15z� ' "IoNAL k" Kyle R. Campbell, P.E. Principal GEOTECHNICAL ENGINEERING STUDY PROPOSED THREADGILL RESIDENTIAL PLAT 162nd AVENUE SOUTHEAST RENTON, WASHINGTON ES-2023 Earth Solutions NW, LLC 1805 - 136th Place Northeast, Suite 201 Bellevue, Washington 98005 Phone: 425-449-4704 Fax: 425-449-4711 Toll Free: 866-336-8710 Earth 'Solutions NW ► August 30, 2011 Earth Solutions NW LLC ES-2023 • Geotechnical Engineering • Construction Monitoring • Environmental Sciences PNW Holdings, LLC 9725 Southeast 36th Street, Suite 214 Mercer Island, Washington 98040 Attention: Mr. Justin Lagers Dear Mr. Lagers: Earth Solutions NW, LLC (ESNW) is pleased to present this report titled "Geotechnical Engineering Study, Proposed Threadgill Residential Plat, 162nd Avenue Southeast, Renton, Washington". In general, the site is underlain by a weathered soil zone grading to firm sandy glacial till deposits. Fill soil was encountered at one test pit location. In our opinion, the proposed residential buildings can be supported on conventional continuous and spread footing foundations bearing on competent native soils, re-compacted native soils, or structural fill. Competent soils suitable for support of foundations should be encountered at depths of between one to three feet below existing grades at most locations. Where loose or unsuitable soil conditions are exposed at foundation subgrade elevations, compaction of the soils to the specifications of structural fill, or overexcavation and replacement with a suitable structural fill material will be necessary. Groundwater seepage was observed at the majority of the test pit locations. The groundwater seepage can be characterized as a perched condition and was observed at variable depths throughout the exposed soil stratigraphy. Seepage should be expected during grading activities. Recommendations for foundation design, site preparation, drainage, and other pertinent recommendations are provided in this study. We appreciate the opportunity to be of service to you on this project. If you have questions regarding the content of this geotechnical engineering study, please call. Sincerely, EARTH S LUTIO S NW, LLC )r i, Stephen H. •ril Staff Geologist 1805 136th Place N E.. Suite 201 • Bellevue,WA 98005 • (425)449-4704 • FAX(4251449-4711 TABLE OF CONTENTS ES-2023 PAGE INTRODUCTION 1 General 1 Project Description 1 SITE CONDITIONS,. 2 Surface 2 Subsurface 2 Fill 2 Topsoil . ....... ... 2 Native Soil 3 Geologic Setting 3 Groundwater ...,. . . 3 DISCUSSION AND RECOMMENDATIONS 3 General 3 Site Preparation and General Earthwork 4 Wet Season Grading 5 In-situ Soils 5 Imported Soils 5 Structural Fill. 5 Foundations . 6 Seismic Design Considerations .. 6 Slab-On-Grade Floors 6 Retaining Walls 7 Drainage 7 Excavations and Slopes 8 Utility Trench Backfill 8 Pavement Sections 8 LIMITATIONS 9 Additional Services •• 9 Earth Solutions NW, LLC TABLE OF CONTENTS Cont'd ES-2023 GRAPHICS PLATE 1 VICINITY MAP PLATE 2 TEST PIT LOCATION PLAN PLATE 3 RETAINING WALL DRAINAGE DETAIL PLATE 4 FOOTING DRAIN DETAIL APPENDICES Appendix A Subsurface Exploration Test Pit Logs Appendix B Laboratory Test Results Earth Solutions NW,LLC GEOTECHNICAL ENGINEERING STUDY PROPOSED THREADGILL RESIDENTIAL PLAT 162nd AVENUE SOUTHEAST RENTON, WASHINGTON ES-2023 INTRODUCTION General This geotechnical engineering study was prepared for the proposed residential development to be constructed between 162nd and 164th Avenue Southeast on the north side of Southeast 136th Street in Renton, Washington. The purpose of this study was to explore subsurface conditions across the site and develop geotechnical recommendations for the proposed development. Our scope of services for completing this geotechnical engineering study included the following: • Conducting subsurface explorations within accessible portions of the development envelope; • Laboratory testing of soil samples obtained from the subsurface exploration; • Engineering analyses, and; • Preparation of this report. The following documents/maps were reviewed as part of our report preparation: • Conceptual Utility Plan, prepared by Encompass Engineering and Surveying, dated February 24, 2011; • Geologic Map of Washington, Northwest Quadrant, Dragovich, Logan, et al, 2002, and; • King County USDA Soil Conservation Survey (SCS). Project Description We understand the subject site will be developed with 15 residential lots, access roadways, and associated utility improvements. The remainder of the site will be developed with general landscaping, a storm water retention pond, and asphalt paved driveways. Given the limited topographic change across the site, we anticipate the residential structures will be constructed near existing site grades. Grading activities will likely involve relatively minimal cuts and fills (on the order of five feet or less) to establish the final design grades. Stormwater will be conveyed to a detention pond located in the eastern portion of the property. PNW Holdings, LLC ES-2023 August 30, 211 Page 2 Building construction is anticipated to consist of relatively lightly loaded wood framing and slab- on-grade floors. Perimeter foundation loading is expected to range from approximately one to two kips per foot. Slab-on-grade loading is expected to be on the order of 150 psf. If the above design assumptions are incorrect or change, ESNW should be contacted to review the recommendations in this report. ESNW should review the final design to confirm that our geotechnical recommendations have been incorporated. SITE CONDITIONS Surface The site is located between 162nd and 164th Avenue Southeast the north side of Southeast 136th Street in Renton, Washington. The approximate location of the property is illustrated on Plate 1 (Vicinity Map) included in this study. The site is rectangular in shape and consists of one tax parcel totaling five acres in size. The site is currently occupied with a residential trailer and workshop structure along Southeast 135th Street, and is bordered by 162nd Avenue Southeast to the West, to the south by Southeast 136th Street, and to the east by 164th Avenue Southeast. The existing site topography descends very gently to the east between elevations of about 500 in the northeast and 480 feet in the southeast. Vegetation consists primarily of forested areas and landscaped lawn areas around the existing trailer located along the northern portion of the property. Subsurface An ESNW representative observed, logged and sampled six test pits excavated using a trackhoe and operator provided by the client. The approximate locations of the test pits are depicted on the Test Pit Location Plan (Plate 2). Please refer to the test pit logs provided in Appendix A for a more detailed description of the subsurface conditions. Fill Fill was encountered at test pit location TP-6; and consisted of a brown silty sand with gravel (Unified Soil Classification SM). This fill material was observed at depths ranging from six inches below existing site elevations to one and a half feet. There is the potential for limited amounts of fill surrounding the existing residential structure and workshop. The fill is not suitable for support of foundations. Topsoil Topsoil was encountered at all test pit locations extending to depths of between about 6 to 14 inches. Topsoil is not suitable for use as structural fill nor should it be mixed with material to be used as structural fill. Topsoil or otherwise unsuitable material can be used in landscaping areas if desired. Earth Solutions NW,LLC PNW Holdings, LLC ES-2023 August 30, 211 Page 3 Native Soil Underlying the topsoil and fill soil at TP-6, native soils consisting primarily of medium dense to dense silty sand (SM) deposits were encountered extending to the maximum exploration depth of seven and a half feet below existing grades. Test pits excavated near the proposed retention pond area included a layer of glacial till consisting of a very dense silty sand with gravel (SM) at a depth of six feet below existing site elevations at that location. Geologic Setting The referenced geologic map resource identifies glacial till (Qgt) deposits across the site and surrounding areas. The referenced SCS soil survey identifies Alderwood series soils across the entirety of the site. Alderwood soils formed in glacial till and typically present a slight to moderate erosion hazard and slow to medium runoff. The soil conditions observed at the test pit locations are generally consistent with glacial till deposits. Groundwater Perched groundwater was observed at the majority of the test pits during the fieldwork (May 2011). The groundwater was perched at variable depths within most test pits; therefore, seepage should be expected in all grading activities at this site, particularly during the winter, spring and early summer months. Typically, the seepage was present at the base of the weathered native soil and where soil conditions became dense. We would expect seepage to persist year-round given the extent of perched groundwater observed and the surrounding topographic features. Groundwater seepage rates and elevations fluctuate depending on many factors, including precipitation duration and intensity, the time of year, and soil conditions. In general, groundwater flow rates are higher during the wetter, winter months. DISCUSSION AND RECOMMENDATIONS General In our opinion, construction of the proposed residential development is feasible from a geotechnical standpoint. The proposed residential buildings can be supported on conventional continuous and spread footing foundations bearing on competent native soils, re-compacted native soils, or structural fill. Slab-on-grade floors should be supported on dense native soil or structural fill. Competent soils suitable for support of foundations should be encountered at depths of between one to three feet below existing grades. Where loose or unsuitable soil conditions are exposed at foundation subgrade elevations, compaction of the soils to the specifications of structural fill, or overexcavation and replacement with a suitable structural fill material will be necessary. Recommendations for foundation design, site preparation, drainage, and other pertinent geotechnical recommendations are provided in the following sections of this study. Earth Solutions NW,LLC PNW Holdings, LLC ES-2023 August 30, 211 Page 4 This study has been prepared for the exclusive use of American Classic Homes and their representatives. No warranty, expressed or implied, is made. This study has been prepared 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. Site Preparation and Earthwork Site preparation activities will involve removal of existing structures, site clearing and stripping, and implementation of temporary erosion control measures. The primary geotechnical considerations associated with site preparation activities include building pad subgrade preparation, underground utility installations, and preparation of pavement subgrade areas. Temporary construction entrances and drive lanes, consisting of at least 12 inches of quarry spalls can be considered in order to minimize off-site soil tracking and to provide a stable access entrance surface. Erosion control measures should consist of silt fencing placed along the down gradient side of the site. Soil stockpiles should be covered or otherwise protected to reduce soil erosion. Temporary sedimentation ponds or other approaches for controlling surface water runoff should be in place prior to beginning earthwork activities. Topsoil and organic-rich soil was encountered generally within the upper 6 to 14 inches at the test pit locations. Topsoil and organic-rich soil is not suitable for foundation support, nor is it suitable for use as structural fill. Topsoil or organic-rich soil can be used in non-structural areas if desired. Over-stripping of the site, however, should be avoided. A representative of ESNW should observe the initial stripping operations, to provide recommendations for stripping depths based on the soil conditions exposed during stripping. Subgrade conditions expected to be exposed throughout the proposed building and pavement areas will likely be comprised of silty sand deposits. After the completion of site stripping and rough grading activities ESNW recommends a proofroll utilizing a fully loaded solo dump truck in order to determine the suitability of the exposed native soils for support of foundations and roadways. ESNW should be retained during this phase of earthwork to observe the proofroll and other earthwork activities. The soils exposed throughout subgrade areas should be compacted to structural fill specifications prior to constructing the foundation, slab, and pavement elements. The subgrade throughout pavement areas should be compacted as necessary and exhibit a firm and unyielding condition when subjected to the proofrolling with a loaded solo dump truck. Structural fill soils placed throughout foundation, slab, and pavement areas should be placed over a firm base. Loose or otherwise unsuitable areas of native soil exposed at subgrade elevations should be compacted to structural fill requirements or overexcavated and replaced with a suitable structural fill material. Where structural fill soils are used to construct foundation subgrade areas, the soil should be compacted to the requirements of structural fill described in the following section. Foundation subgrade areas should be protected from disturbance, construction traffic, and excessive moisture. Where instability develops below structural fill areas, use of a woven geotextile below the structural fill areas may be required. A representative of ESNW should observe structural fill placement in foundation, slab, and pavement areas. Earth Solutions NW, LLC PNW Holdings, LLC ES-2023 August 30, 211 Page 5 Wet Season Grading Perched groundwater was present at the majority of the test pits and at variable depths. This condition coupled with the high moisture sensitivity of the soil will make grading during periods of rain difficult or impossible. Mass grading should take place during the late summer months when conditions are more favorable. If grading takes place during the wetter winter or spring months, a contingency in the project budget should be included to allow for export of native soil and import of structural fill as described below. In-situ Soils The soils encountered throughout the majority of the test sites have a sensitivity to moisture and were generally in a moist to wet condition at the time of the exploration (May 2011). In this respect, the in-situ soils may not be suitable for use as structural fill if the soil moisture content is above the optimum level at the time of construction. In general, soils encountered during site excavations that are excessively over the optimum moisture content will require moisture conditioning (aeration) prior to placement and compaction. Conversely, soils that are below the optimum moisture content will require moisture conditioning through the addition of water prior to use as structural fill. If the in-situ soils are determined to not be suitable for use as structural fill, then use of a suitable imported soil may be necessary. In our opinion, a contingency should be included in the project budget for exporting unsuitable soil and importing structural fill. Imported Soils Imported soil intended for use as structural fill should consist of a well graded granular soil with a moisture content that is at or near the optimum level. During wet weather conditions, imported soil intended for use as structural fill should consist of a well graded granular soil with a fines content of 5 percent or less defined as the percent passing the #200 sieve, based on the minus three-quarter inch fraction. Structural Fill Structural fill is defined as compacted soil placed in foundation, slab-on-grade, and roadway areas. Fills placed to construct permanent slopes and throughout retaining wall and utility trench backfill areas are also considered structural fill, Soils placed in structural areas should • be placed in loose lifts of 12 inches or less and compacted to a relative compaction of 90 percent, based on the laboratory maximum dry density as determined by the Modified Proctor Method (ASTM D-1557). Soil placed in the upper 12 inches of slab-on-grade, utility trench, and pavement areas should be compacted to a relative compaction of at least 95 percent. Additionally, more stringent compaction specifications may be required for utility trench backfill zones, depending on the responsible utility district or jurisdiction. Earth Solutions NW,LLC PNW Holdings, LLC ES-2023 August 30, 211 Page 6 Foundations Based on the results of our study, the proposed residential structures can be supported on conventional spread and continuous footings bearing on competent native soils, re-compacted native soils, or structural fill. Based on the soil conditions encountered at the test sites, competent native soils suitable for support of foundations should be encountered at depths of between one to three feet below existing grades. Where loose or unsuitable soil conditions are exposed at foundation subgrade elevations, compaction of the soils to the specifications of structural fill, or overexcavation and replacement with structural fill, may be necessary. Provided foundations will be supported as described above, the following parameters can be used for design of new foundations: • Allowable soil bearing capacity 2,500 psf • Passive earth pressure 350 pcf (equivalent fluid) • Coefficient of friction 0.4 A one-third increase in the allowable soil bearing capacity can assumed for short-term wind and seismic loading conditions. The above passive pressure and friction values include a factor-of- safety of 1.5. With structural loading as expected, total settlement in the range of one inch and differential settlement of about one-half inch is anticipated. The majority of the settlements should occur during construction, as dead loads are applied. Seismic Design Considerations The 2009 International Building Code specifies several soil profiles that are used as a basis for seismic design of structures. Based on the soil conditions observed at the test sites, Site Class C, from table 1613.5.2, should be used for design. In our opinion, the site has a low susceptibility to liquefaction based on the relative density of the native soils. Slab-On-Grade Floors Slab-on-grade floors for residential buildings constructed at this site should be supported on a firm and unyielding subgrade. Where feasible, the existing native soils exposed at the slab-on- grade subgrade level can be compacted in place to the specifications of structural fill. Unstable or yielding areas of the subgrade should be recompacted or overexcavated and replaced with suitable structural fill prior to construction of the slab. A capillary break consisting of a minimum of four inches of free draining crushed rock or gravel should be placed below the slab. The free draining material should have a fines content of 5 percent or less (percent passing the #200 sieve, based on the minus three-quarter inch fraction). In areas where slab moisture is undesirable, installation of a vapor barrier below the slab should be considered. If a vapor barrier is to be utilized it should be a material specifically designed for use as a vapor barrier and should be installed in accordance with the manufacturer's specifications. Earth Solutions NW,LLC PNW Holdings, LLC ES-2023 August 30, 211 Page 7 Retaining Walls Retaining walls must be designed to resist earth pressures and applicable surcharge loads. The following parameters can be used for retaining wall design: • Active earth pressure (yielding wall) 35 pcf(equivalent fluid) • At-rest earth pressure (restrained wall) 55 pcf • Traffic surcharge for passenger vehicles 70 psf (rectangular distribution) (where applicable) • Passive resistance 350 pcf (equivalent fluid) • Coefficient of friction 0.4 • Seismic surcharge 6H (where H equals retained height) Additional surcharge loading from adjacent foundations, sloped backfill, or other loads should be included in the retaining wall design. Drainage should be provided behind retaining walls such that hydrostatic pressures do not develop. If drainage is not provided, hydrostatic pressures should be included in the wall design. Retaining walls should be backfilled with free draining material that extends along the height of the wall, and a distance of at least 18 inches behind the wall. The upper one foot of the wall backfill can consist of a less permeable soil, if desired. A perforated drain pipe should be placed along the base of the wall, and connected to an approved discharge location. A typical retaining wall drainage detail is provided on Plate 3. Drainage Perched groundwater was observed during the fieldwork (May 2011). As such, groundwater should be anticipated in site excavations. Temporary measures to control surface water runoff and groundwater during construction would likely involve interceptor trenches and sumps. ESNW should be consulted during preliminary grading to identify areas of seepage and to provide recommendations to reduce the potential for instability related to seepage effects. In our opinion, foundation drains should be installed along building perimeter footings. A typical foundation drain detail is provided as Plate 4. Based on the presence of glacial till (hardpan) deposits and perched groundwater, in our opinion infiltration on the site or individual lots is not feasible. Earth Solutions NW,LLC PNW Holdings, LLC ES-2023 August 30, 211 Page 8 Excavations and Slopes The Federal Occupation Safety and Health Administration (OSHA) and the Washington Industrial Safety and Health Act (WISHA) provide soil classification in terms of temporary slope inclinations. Based on the soil conditions encountered at the test pit locations, the weathered native soils encountered in the upper approximately four feet of the test pit locations and where groundwater seepage is exposed are classified as Type C by OSHA/WISHA. Temporary slopes over four feet in height in Type C soils must be sloped no steeper than 1.5H:1V (Horizontal:Vertical). Medium dense to dense native soils encountered below about four feet where no groundwater seepage is exposed would be classified as Type B by OSHA/WISHA. Temporary slopes over four feet in height in Type B soils must be sloped no steeper than 1H:1V. The presence of perched groundwater may cause caving of the temporary slopes due to hydrostatic pressure. ESNW should observe site excavations to confirm the soil type and allowable slope inclination. If the recommended temporary slope inclination cannot be achieved, temporary shoring may be necessary to support excavations. Permanent slopes should maintain a gradient of 2H:1V, or flatter, and should be planted with vegetation to enhance stability and to minimize erosion. A representative of ESNW should observe temporary and permanent slopes to confirm the slope inclinations, and to provide additional excavation and slope recommendations, as necessary. Utility Support and Trench Backfill In our opinion, the soils anticipated to be exposed in utility excavations should generally be suitable for support of utilities. Organic or highly compressible soils encountered in the trench excavations should not be used for supporting utilities. The native soils are moisture sensitive and will therefore be difficult to use as structural trench backfill if the moisture content of the soil is high. Moisture conditioning of the soils will likely be necessary prior to use as structural backfill. Utility trench backfill should be placed and compacted to the specifications of structural fill provided in this report, or to the applicable City of Renton specifications. Seepage should be anticipated within utility trench excavations. Caving of the trench sidewalls due to hydrostatic pressure should be anticipated and temporary shoring should be included in site designs and budget. Pavement Sections The performance of site pavements is largely related to the condition of the underlying subgrade. To provide adequate pavement performance, the subgrade should be in a firm and unyielding condition when subjected to proofrolling with a loaded dump truck. Structural fill in pavement areas should be compacted as recommended in the "Site Preparation and Earthwork" section of this report. It is possible that soft, wet, or otherwise unsuitable subgrade areas may still exist after base grading activities. Areas of unsuitable or yielding subgrade conditions will require remedial measures such as overexcavation, placement of a geotextile and thicker crushed rock or structural fill sections prior to pavement. Earth Solutions NW,LLC PNW Holdings, LLC ES-2023 August 30, 211 Page 9 For lightly loaded pavement areas subjected primarily to passenger vehicles, the following preliminary pavement sections can be considered: • Two inches of hot-mix asphalt (HMA) placed over four inches of crushed rock base (CRB), or; • Two inches of HMA placed over three inches of asphalt treated base (ATB). For relatively high volume, heavily loaded pavements subjected to moderate to high, loaded truck traffic, the following preliminary pavement sections can be considered: • Three inches of hot-mix asphalt (HMA) placed over six inches of crushed rock base (CRB), or; • Three inches of HMA placed over four and one half inches of asphalt treated base (ATB). The AC, ATB and CRB materials should conform to WSDOT specifications. All soil base material should be compacted to at least 95 percent of the maximum dry density. Final pavement design recommendations can be provided once final traffic loading has been determined. Given the presence of shallow perched groundwater, in our opinion, additional drainage measures should be considered for pavement subgrade areas. Such drainage measures could include the installation drainlines along the sides of crowned roadways and along the centerline for roadways with inverted crowns. If areas of seepage are exposed in roadway excavations, drains should be installed in these areas to allow removal of the water. Specific recommendations and details for roadway drainage can be provided upon request. LIMITATIONS The recommendations and conclusions provided in this geotechnical engineering study are professional opinions consistent with the level of care and skill that is typical of other members in the profession currently practicing under similar conditions in this area. A warranty is not expressed or implied. Variations in the soil and groundwater conditions observed at the test locations may exist, and may not become evident until construction. ESNW should reevaluate the conclusions in this geotechnical engineering study if variations are encountered. Additional Services ESNW should have an opportunity to review the final design with respect to the geotechnical recommendations provided in this report. ESNW should also be retained to provide testing and consultation services during construction. Earth Solutions NW,LLC 4.1.41. Y. .i evi ‘ Ir.'- , sta rL ;Ii r `a= - k 'i" ct j- .3.a-r 9 #° * illIII' 1.14 INitig rilll.al, t 5 s 4. _ „ s l y -i4Z East Renton , 4L .• ' .t; sr - Hi hl fids - n r: l 1*��r ST,44. M_ 9 7 ry P' s. ;.-,. .1 ► {'2ar11� _ �w - 1i t C T! s�.e..aew.•. t M4- /5.! F- t ,�;* Ltj 4;;,=131451411'2'1 A Lake N 6r # ry SES ` Sr tri ti, SS 13h.15T _ c b d y -'` ,' Ka Klee s Yd..1 ; sa ti '1113,714',. t: ler�a,k, i � ' mss;_ •># e x 7 } .ii I �F ttt . 1Mit'n +4 y !i9�N VW 7 C�� U =`.114',.` it rtr3 g ,,,- r l 2 ag i et i .} 1 .3u P liRt�1 0"--.'` 1 t .1 : r;r .,t t sr, 4• . ;Irtt i3itk t {i, tv. el,,, r .�G ' — v C , �,�:. '" t- .11' �/ `1'.Z _ ter.-ar at; ,t M1 Gi.4,6. ti h: .-:3 ,*•S: 1_ h N.S.1.4;0k-144i w. '11' M'.lf'i •I'i-i:`.' r4 Ifot�w fi^I, IA' tam nt'nil n P S' M1 I� . fit *V �. .. 4 Y m 'F'4 r. ..:4t 4 CC S t —.S r S;71.i1 t: s r. ? t 1 i,ldtit 1, ,.. t•.lt 41 tuft ,..- es .S_'_.'.aq,1 a--., #pbl !p4 r t ,a cl =" f:1-:kg.;2 f , ' i! i to R 4 x.k 41't. 4. L4 1441 yt ' _st......g.• { . 1t , it `a, . a , E ' ha t .,f S I !AN,,,4 a9 y.c l;.- a c. ^ 7` '3,- m a. `7 SI 11, 14. .i Lr rI 47W $ s0 *A.. ."-+;-.11.S. ';',61° }1a. F---- _ is I� - sz r K. !`' ' rc 7 • i*PilV4 WiF4F MAIItY HG "^-` `';- +*,;' n, • tw, ,.c , wA - ,!.:. NORTH Earth rth Solutions NW«c • Solutions Reference: APPwill% NW Lucethnical Engineering,Construction Monitoring King County, Washington ale Environmental Sciences Map 657 By Thomas Brothers Maps Vicinity Map Dated 2009 Proposed Threadgill Residential Plat King County, Washington NOTE:This plate may contain areas of color.ESNW cannot be Drwn. GLS Date 05/18/2011 Proj. No. 2023 responsible for any subsequent misinterpretation of the information resulting from black&white reproductions of this plate. Checked SA Date May 2023 Plate 1 ie 0 I3 , 0 mg1iOf I I NORTH c • m 0 I a m _. ,112 �: `-01 'P1 .� p.'vf ao '11'M...'1f NO a� �n al as 0_ N 3 _,_. `.., -\ ,'_, 7�1'r-\ +Nt T-Jam'_'•-1 I------ N a c5 --- - -n- - _ ` , ,Th,-,– , l - ——- -II --- n —t,t-- Tr rr ,.,--‘7.-.t. ~ N C ew I Y _-L 'I III / A' r II i �_J r I 1 11'Z_/ r I 1 , \✓ ji ---—_- Oa. I l,ki 1 1 h t1' _l'' / t 1\,1,11 =J; ( `�I I I 0 40 80 160 2 TP-6.' 1J 1 i 1 1 ft , .- tl r �, O'll '4. `, , a �' t n 0.�� d , , 1r 1'=80' ITC',fs ..na'-',„ f3 ,`\ t2 1 \ I I ,.o '^'1' , I, 7 '`--1;11,-4,1,‹ I�I19/.4�:u#.',n ITP., . im Scale in Feet '/1p' i .. , vj ~1iY;{ \,,A'�,ei,1\''1-„.1-1-1 - I , _,_,,11,---,_ _ ---_ ,fs 1 ,, ;errs "d4a,t�, '? r I 1+`v it - r I ''\ 1 r K w ' —J--,—,— ITP•5 �, _ ,_' ;1'i fI yyFFr= 1''' s > —- — -� -— I' r , f )' 14'4i 4',0"t' `'` \'SO LEGEND I� '..�JP_2 \ I , ,y�r r, ,i,ip"u1� 1, Q ------�- I _ ----'' "_i—-_ _r_L v ,-, n f✓j rttr dell/, \` I •'u .r f I r'/ - — ` �� \I'—. a' r\ ��n'y�rdiif it ,y4'A"gi `yam 1 I V) — ...._i� 4 z , . ✓• " r^Iya44% y'1�1M1 I TP-1—i—Approximate Location of .",1,,,*‘ " y I rP 1 I I 1il' i'a'"'I °1'1 a„1 ESNW Test Pit,Proj.No. i4 �� —IT�-3' I '` rT\ ; ' ' .'e �.r 1"-y,Iwr411, y^p1:u1oi ' % ES-2023,May 2011 I , i._w� y 1'�,k*`k i -', I i lovi 1 •I 1 , 1 I ' . I' 1,A'�+i 141,pIr' ,I r d' 1 iv.' /�` ��',k i-4- ,1 , i `ri 1 \ I 1 1 ,,r ` ,01,.x:14 , h�11d111 r r , �-- k k � I % I ( i I r Mo �1,1,11,�1ji�r--�„f11iu1' 1, _ — Subject Site v r4 T -–— _-—- k_ � ; I% I r '.1----1:7=--=—:—.-------:.---'1-1—„.1),'1 Existing Building /ik Jr J AU '16 IN' 111 -- �4 T--,-T-I-,Ail'Ls,—y '-'`.:77- 496 T c— ,_ `—-- -- N6 O' OT 100 4111 NIS Lot Number � --- f Ii(, Iil - ! l- It i "' \”' - `\ —__-___ _ Pond Area T* 0 Existing Wetland Area ‘,,IL I (Delineated By Others) W f z Drwn.By — — — - GLS , NOTE:The graphics shown on this plate are not intended for design Checked B 1 I purposes or precise scale measurements,but only to illustrate the y I approximate test locations relative to the approximate locations of SA I existing and I or proposed site features.The information illustrated Date is largely based on data provided by the client at the bore of our study.ESNW cannot be responsible for subsequent design changes 08/01/2011 or interpretation of the data by others. Prof.No. NOTE:This plate may contain areas of color.ESNW cannot be 2023 responsible for any subsequent misinterpretation of the information Plate resulting from black 8 white reproductions of this plate. 2 18" Min. 4111 ° 0 ° ° 0 ° mo 000000o ° ° d °° °o °° 0 0 ° 0 0 °°° bo00 . °/�°° ° O 0 0-�,ll G O 0 0 (5 o 00 0 0 ° 0 0 ° ' o ° oOo o ° ° ° - 00 0 0 0 000 ° 0 o° °o 0o 0 o ° 00 00 °O °° 0 o ° °o 0g 00 °0 . ° Structural 0 . 0 0 ° °° °° Fill 0 "• ° -00 0 o 00 0 °0 g ° O 0 O 0 . 0 0 0 Q o 0 00°0 ° o ° 00 0 V0 0 • , °000 00 0 0 ° 00 O 0 °0 ° 0 0 0 00 0 1 1 1 -1 1 1 °° ° ° ° 00 ° 000 0 0° g 0 0 o°° oa ° 11 I 0000 0 ° e.,. o L• •ti•L 171: 0 L• S Perforated Drain Pipe NOTES: (Surround In Drain Rock) • Free Draining Backfill should consist of soil having less than 5 percent fines. Percent passing#4 should be 25 to 75 percent. • Sheet Drain may be feasible in lieu SCHEMATIC ONLY- NOT TO SCALE of Free Draining Backfill, per ESNW NOT A CONSTRUCTION DRAWING recommendations. • Drain Pipe should consist of perforated, rigid PVC Pipe surrounded with 1" Drain Rock. • LEGEND: w` Earth 0:00 0 Solutions NWr Lc 0 op°° Free Draining Structural Backfill NW��c �,w, 'Construction Monitoring • 0 '°s ental Sciences •r:ti:tir titi 1 inch Drain Rock RETAINING WALL DRAINAGE DETAIL ..P.0.0••••• Proposed Threadgill Residential Plat King County, Washington Drwn. GLS Date 05/24/2011 Proj. No. 2023 1 ' Checked SA Date May 2011 Plate 3 . , r Slope :•:41•:18 :777: :7777'.77.-.---.--- •:is 111,1K•1.1• _ .....% 1 r1..�1. 2" (Min.) Perforated Rigid Drain Pipe (Surround with 1" Rock) NOTES: • Do NOT tie roof downspouts to Footing Drain. • SCHEMATIC ONLY- NOT TO SCALE Surface Seal to consist of NOTA CONSTRUCTION DRAWING 12"of less permeable, suitable soil. Slope away from building. LEGEND: Surface Seal; native soil or other low permeability material. 5 Earth / ions NW«C ••••y'.•,.• Solutions ,,fa. , 1.1.1.1• 1" Drain Rock Construction Monitoring J•r•r•r• N W LLC ,,.��.<, •1.1.1.1• �, [Sciences FOOTING DRAIN DETAIL Proposed Threadgill Residential Plat King County, Washington Drwn. GLS Date 05/24/2011 Proj. No. 2023 / Checked SA Date May 2011 Plate 4 APPENDIX A SUBSURFACE EXPLORATION ES-2023 The subsurface conditions at the site were explored by excavating a total of six test pits across accessible portions of the property. The subsurface explorations were completed on May 6, 2011. The approximate test pit locations are illustrated on Plate 2 of this report. Logs of the test pits are provided in this Appendix. The test pits were excavated to a maximum depth of seven and a half feet below existing grades. Earth Solutions NW,LLC Earth Solutions NWLLC SOIL CLASSIFICATION CHART MAJOR DIVISIONS SYMBOLS TYPICAL GRAPH LETTER DESCRIPTIONS CLEAN ' •i` WELL-GRADED GRAVELS,GRAVEL- GRAVEL GRAVELS ie b•� i, GW SAND MIXTURES,LITTLE OR NO AND i.••11 s FINES GRAVELLY pettfoetu Of O.Of POORLY-GRADED GRAVELS, SOILS (LITTLE OR NO FINES) >o DQo DC GP GRAVEL-SAND MIXTURES,LITTLE ,00000 OR NO FINES COARSE '°' ; GRAINED GRAVELS WITH ;C\ I SILTY GRAVELS,GRAVEL-SAND- SOILS MORE THAN 50% FINES o • • D GM SILT MIXTURES OF COARSE 30'S n,6 a FRACTION �:, � RETAINED ON NO. ;1'• ./!+ 4 SIEVE (APPRECIABLE r'.;"'°'• •� GC CLAYEY GRAVELS,GRAVEL-SAND- AMOUNT OF FINES) f��/' :I CLAY MIXTURES DED SANDS,G MORE THAN 50% SAND CLEAN SANDS •��• SW SANDS,WELL-GLITTLE OR NO F NREASVELLY OF MATERIAL IS AND .::i::::::::::::::. , LARGER THAN SANDY POORLY-GRADED SANDS, NO.200 SIEVE SOILS GRAVELLY SAND,LITTLE OR NO SIZE (LITTLE OR NO FINES) y'P FINES SANDS WITH •,::::..::•%-:,.':',,": SM SILTY SANDS,SAND-SILT MORE THAN 50% FINES MIXTURES OF COARSE FRACTION PASSING ON NO. 4 SIEVE (APPRECIABLE sc CLAYEY SANDS,SAND-CLAY AMOUNT OF FINES) MIXTURES INORGANIC SILTS AND VERY FINE ML SANDS,ROCK FLOUR,SILTY OR CLAYEY FINE SANDS OR CLAYEY SILTS WITH SLIGHT PLASTICITY SILTS INORGANIC CLAYS OF LOW TO FINE LIQUID LIMIT MEDIUM PLASTICITY,GRAVELLY GRAINED CLAYS LESS THAN 50 CLAYS,SANDY CL CLAYS,LEAN CLAYSS,SILTY SOILS _ OL ORGANIC SILTS AND ORGANIC -------------- SILTY CLAYS OF LOW PLASTICITY MORE THAN 50% INORGANIC SILTS,MICACEOUS OR OF MATERIAL IS MH DIATOMACEOUS FINE SAND OR SMALLER THAN SILTY SOILS NO.200 SIEVE SIZE SILTS 0 AND LIQUID LIMIT INORGANIC CLAYS OF HIGH CLAYS GREATER THAN 50 CH PLASTICITY ..w�: w ORGANIC CLAYS OF MEDIUM TO OH HIGH PLASTICITY,ORGANIC SILTS t IV! L PEAT,HUMUS,SWAMP SOILS WITH HIGHLY ORGANIC SOILS PT HIGH ORGANIC CONTENTS L 1,1 .L,, , DUAL SYMBOLS are used to indicate borderline soil classifications. The discussion in the text of this report is necessary for a proper understanding of the nature of the material presented in the attached logs. Earth Earth Solutions NW TEST PIT NUMBER TP-1 'solution 1805 136th Place N.E.,Suite 201 PAGE 1 OF 1 f�1N �c Bellevue,Washington 98005 Telephone: 425-284-3300 CLIENT American Classic Homes PROJECT NAME Proposed Threadgill Residential Plat PROJECT NUMBER 2023 PROJECT LOCATION King County,Washington DATE STARTED 5/6/11 COMPLETED 5/6111 GROUND ELEVATION 480 ft TEST PIT SIZE EXCAVATION CONTRACTOR Client Provided GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION — LOGGED BY SHA CHECKED BY SHA AT END OF EXCAVATION — NOTES Depth of Topsoil&Sod 12"-14":blackberries AFTER EXCAVATION — w a. Nfi Vi • F-x W e TESTS o_O MATERIAL DESCRIPTION o_ ¢z 0 CO 0 •- Brown silty SAND with gravel,loose,moist MC=17.00% SM Fines=18.30% 4.0 476.0 - Brown silty SAND with gravel,medium dense,moist(Weathered Till) SM - MC=11.10% 4 -becomes dense to very dense,light seepage I7 0 473.0 Test pit terminated at 7.0 feet below existing grade.Groundwater seepage encountered at 6.0 feet during excavation. Bottom of test pit at 7.0 feet. U) z z ri oN w}J O. I I LO . Lt Earth Solutions NW TEST PIT NUMBER TP-2 'Solution: 1805 136th Place N.E.,Suite 201 PAGE 1 OF 1 tilirccc Bellevue,Washington 98005 Telephone: 425-284-3300 CLIENT American Classic Homes PROJECT NAME Proposed Threadgill Residential Plat PROJECT NUMBER 2023 PROJECT LOCATION King County,Washington DATE STARTED 5/6/11 COMPLETED 5/6/11 GROUND ELEVATION 500 ft TEST PIT SIZE EXCAVATION CONTRACTOR Client Provided GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION — LOGGED BY SHA CHECKED BY SHA AT END OF EXCAVATION — NOTES Depth of Topsoil&Sod 8"-10":blackberries AFTER EXCAVATION — w a U a a co O MATERIAL DESCRIPTION 0 z 0 0 Brown silty SAND with gravel,loose,moist SM -becomes dense with iron oxide staining,light seepage f i gp 497.0 Brown silty SAND with gravel,dense to very dense, moist(Weathered Till) - - MC=13.60% SM - 17 5 492.5 MC=11.80% Test pit terminated at 7.5 feet below existing grade.Groundwater seepage encountered at 2.5 feet during excavation. Bottom of test pit at 7.5 feet. I i 0 0 U, z 0- 0-4 O N J • a rift Earth Solutions NW TEST PIT NUMBER TP-3 'So IUUoii. 1805 136th Place N.E.,Suite 201 PAGE 1 OF 1 • !a1V:ic Bellevue,Washington 98005 Telephone: 425-284-3300 CLIENT American Classic Homes PROJECT NAME Proposed Threadgill Residential Plat PROJECT NUMBER 2023 PROJECT LOCATION King County,Washington DATE STARTED 5/6/11 COMPLETED 5/6/11 GROUND ELEVATION 496 ft TEST PIT SIZE EXCAVATION CONTRACTOR Client Provided GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION — LOGGED BY SHA CHECKED BY SHA AT END OF EXCAVATION NOTES Depth of Topsoil&Sod 16":ferns AFTER EXCAVATION --- w ao • 0 cn w TESTS O MATERIAL DESCRIPTION w" o- 2z D 0 Brown silty SAND with gravel,loose,moist MC=28 10% iron oxide staining,light seepage -Till Contact,becomes very dense SM s -light seepage - - MC= 17.90% 0.5 489.5 Test pit terminated at 6.5 feet below existing grade. Groundwater seepage encountered at 2.0 and 5.5 feet during excavation. Bottom of test pit at 6.5 feet. m o of I- r i ( a C7 N 0 N 'JSL t- m � w Iz Ea rth Earth Solutions NW TEST PIT NUMBER TP-4 .solution _ 1805 136th Place N.E.,Suite 201 PAGE 1 OF 1 %iilt Bellevue,Washington 98005 Telephone: 425-284-3300 CLIENT American Classic Homes PROJECT NAME Proposed Threadgill Residential Plat PROJECT NUMBER 2023 PROJECT LOCATION King County,Washington DATE STARTED 5/6/11 COMPLETED 5/6/11 GROUND ELEVATION 499 ft TEST PIT SIZE EXCAVATION CONTRACTOR Client Provided GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION -- LOGGED LOGGED BY SHA CHECKED BY SHA AT END OF EXCAVATION -- NOTES Depth of Topsoil&Sod 12":ferns AFTER EXCAVATION w p — r rn d r w• TESTS oaf p MATERIAL DESCRIPTION rn 7 J 0 Brown silty SAND with gravel,loose,moist MC= 15.70% -becomes medium dense SM -Till Contact,becomes dense 5 MC=12.90% 7 0 492.0 Test pit terminated at 7.0 feet below existing grade.No groundwater encountered during excavation. Bottom of test pit at 7.0 feet. 0 0 0 CO z z 0 a of N 0 wJy CO Earth Earth Solutions NW TEST PIT NUMBER TP-5 '~mutton 1805 136th Place N.E.,Suite 201 PAGE 1 OF 1 Wu( Bellevue,Washington 98005 Telephone: 425-284-3300 CLIENT American Classic Homes PROJECT NAME Proposed Threadqill Residential Plat PROJECT NUMBER 2023 PROJECT LOCATION King County,Washington DATE STARTED 5/6/11 COMPLETED 5/6/11 GROUND ELEVATION 496 ft TEST PIT SIZE EXCAVATION CONTRACTOR Client Provided GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION --- LOGGED BY SHA CHECKED BY SHA AT END OF EXCAVATION -- NOTES Depth of Topsoil&Sod 12":ferns AFTER EXCAVATION -- w }�F- vi U in _ w I- 2 u TESTS O MATERIAL DESCRIPTION 0 o Qz 0 U) 0 Brown silty SAND with gravel,loose,moist -heavy iron oxide staining,light seepage - - MC=26.20% -Till Contact SM 5 - MC=13.50% - 65 489.5 Test pit terminated at 6.5 feet below existing grade.Groundwater seepage encountered • at 1.5 feet during excavation. • Bottom of test pit at 6.5 feet. m F- 0 O NJ a C- m i-- l E.Irtti Earth Solutions NW TEST PIT NUMBER TP-6 Sulutinn 1805 136th Place N.E.,Suite 201 PAGE 1 OF 1 ti1i X14 Bellevue,Washington 98005 Telephone: 425-284-3300 CLIENT American Classic Homes PROJECT NAME Proposed Threadgill Residential Plat PROJECT NUMBER 2023 PROJECT LOCATION Kinq County,Washington DATE STARTED 5/6/11 COMPLETED 5/6/11 GROUND ELEVATION 501 ft TEST PIT SIZE EXCAVATION CONTRACTOR Client Provided GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION -- LOGGED BY SHA CHECKED BY SHA AT END OF EXCAVATION ___ NOTES Depth of Topsoil&Sod 8":grass AFTER EXCAVATION — w ui — w co TESTS U n O MATERIAL DESCRIPTION - aM vi �9 z (7 0 .•++ Brown silty SAND with gravel,medium dense,moist(Fill) SM ,+:;. - MC=5.40% i'+4 •••••• Vis 4e9s Brown silty SAND with gravel,medium dense,moist(Native) 5 _ -becomes very dense -light iron oxide staining MC=18.20% Fines=37.10% 1 7.5 _ 493.5 Test pit terminated at 7.5 feet below existing grade.No groundwater encountered during excavation. Bottom of test pit at 7.5 feet. i3 a. tl APPENDIX B LABORATORY TEST RESULTS ES-2023 Earth Solutions NW, LLC I.trih Earth Solutions NW GRAIN SIZE DISTRIBUTION '.olutWrIIs 1805-136th Place N E.,Suite 201 `.%,it Bellevue,WA 98005 Telephone: 425-2843300 CLIENT American Classic Homes PROJECT NAME Threadgill Plat ___ __ PROJECT NUMBER ES-2023 __ PROJECT LOCATION Renton, U.S.SIEVE OPENING IN INCHES I U.S.SIEVE NUMBERS I HYDROMETER • 4 3 2 •' 314 1/2318 3 4 • 610 14116 20 30 40 5066 100140200 100 r I I 1 I 1/23/I I 1 1 1 1 l . f I t 95 I'- • �. _ _ - 1 90 \\\I 4 • '--.6, — - ,..--11_, 85 — r 80 r __. 75----- - I - t--T 70 - - -, r r..1 IS. E- 65 (-9 60 4 - r — >- 55 . - CO W50 : 1 I - r Z Z45 -- --- , r r a.,..1.. 4 - 1 T r. I r---1 Lii ° 40. �.4, - -' I - ' w 30 , - 0 r+-- 25 ' r _ , , -\cti...4-,..-r-.--- , 20 - ---�+ 15 r —_--...-,....--,-.1._—r. ► T- 10 .�_. 1 r 5,---I . �I --4-..........--.-...---------....---._ _ 0 3 100 10• 1• 0.1 0.01 0.001 GRAIN SIZE IN MILLIMETERS COBBLES GRAVEL SAND SILT OR CLAY coarsetine coarse medium 1 fine -_ • Specimen identification Classification LL PL ~PI Cc Cu E p TP-1 2.0ft._ Brown silty SAND with gravel,SM 5i El TP-6 7.0ft. Gray silty SAND with gravel,SM , 1 n Specimen Identification D100 D60 D30 D10 _ %Gravel ' %Sand %Silt %Clay O TP-1 2.0ft. 37.5 5.374 0.268 41.7 40.0 18.3 TP-6 7.Oft. _ 37.5 0.313 15.7 47.1 37.1 u, REPORT DISTRIBUTION ES-2023 EMAIL ONLY PNW Holdings, LLC 9725 Southeast 36th Street, Suite 214 Mercer Island, Washington 98040 Attention: Mr. Justin Lagers Earth Solutions NW,LLC SECTION 7 OTHER PERMITS SECTION 8 ESC ANALYSIS AND DESIGN Encompass Engineering & Surveying JOB Now Partnered with Baima&Holmberg Western Washington Division SHEET NO. OF 165 NE Juniper St..Suite 201.Issatpah.WA 98027 Phone(425)392-0250 Fax:(425)391-3055 CALCULATED BY TR DATE Eastern Washington Division 108 East 2nd Street.Cie EJum.WA 98922 CHECKED BY DATE Phone:(509)674-7433 Fax:(509)674-7419 SCALE r r CiteF ro --/ w *. '/ W - pow -TeFfelAvkityli . . F/poiiiiiikl‘-7-(2,/qe (150..„ C y.tYC/Es CeA/9 b 11. r ......... .(9.IZ. .rt . N . pokiiti5ini/941 4f. :) r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I1 1 1 } 1 1 } ) } 3 7 f 3 J 1 } } } SECTION 9 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL STORMWATER FACILITY SUMMARY SHEET Development /192ft' 9fr((' I(nJ lit Date 1(9/3/ Location `` / ENGINEER DEVELOPER Name T�7 KED,1 N4 Name DIV tA/ (-tori I • C-i-cd Finn E ivC ?MigsS ZINC[ . Finn 11-2 5 _se ?6,7H sr--Stir Z14.- Address,6 5 n/�J"JNi pole J7-AAA,/ Address itA�scfl,L. 1411itp (11$ - IS4va� W R- q WO Z-7- 1 e Phone /4 7,5 ?,9 Z—CZ 512Phones 2(p00 -1!'/?-- Developed Site: Acres 4 D I A-(� Number of lots t <j Number of detention facilities on site: Number of infiltration facilities on site: 1 ponds ponds vaults vaults tanks tanks Flow control provided in regional facility(give location) No flow control required Exemption number Downstream Drainage Basins _ Immediate Major Basin Basin A Basin B Basin C Basin D. Number&type of water quality facilities on site: biofiltration swale(regular/wet/or sand filter(basic or large?) continuous inflow?) sand filter,linear(basic or large?) • ycombined detention/WQ pond sand filter vault(basic or large?) (WQ portio ba tc large?) combs detention/wetvault stormwater wetland compost filter wetpond(basic or large?) filter strip wetvault flow dispersion farm management plan landscape management plan oil/water separator(baffle or coalescing plate?) catch basin inserts:Manufacturer • pre-settling pond pre-settling structure:Manufacturer flow-splitter catchbasin DESIGN INFORMATION • INDIVIDUAL BASIN A B C D Water Quality design flow Water Quality treated volume or wetpond Vr 09, I)icf GF% • 1998 Surface Water Design Manual 9/1/S 1 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL - DESIGN TOTAL INDIVIDUAL BASIN INFORMATION,cont'd Drainage basin(s) A B C D Onsite area 2..g/. A� Offsite area Type of Storage Facility PO op Live Storage Volume 3- 63tf C,- PredeveIoped Runoff Rate 2-year p,n&rj CAr 10-year Q,t 05cr- 100-year CJ. lLi, Developed runoff rate 2-year 0155 / 10-year B .6 6 scr-s 100-year I Al,L Gf`' Type of restrictor Size of orifice/restriction No. 1 1 I/16" No.2 1 NW/ No.3 No.4 FLOW CONTROL&WATER QUALITY FACILITY SUMMARY SHEET SKETCH All detention,infiltration and water quality facilities must include a sketch per the following criteria: • 1. Heading for the drawings should be located at the top of the sketch(top right-hand corner). The heading should contain: • North arrow(point up or to left) • D9# • Plat name or short plat number . •Address(nearest) • Date drawn(or updated) •Thomas Brothers page,grid number 2. Label CBs and MHs with the plan and profile designation. Label the control structure in writing or abbreviate with C.S. Indicate which structures provide spill control. 3. Pipes--indicate: • Pipe size Pipe length Flow direction Use s single heavyweight line 4. Tanks--use a double,heavyweight line and indicate size(diameter) 5. Access roads • Outline the limits of the road • Fill the outline with dots if the road is gravel. Label in writing if another surface. 6. Other Standard Symbols: • Bollards: ® • OO 4 ■ ■ 11 • Rip rap 000000 000000 Fences --x---x---x---x---x---x--- • Ditches 7. Label trash racks in writing. 8. Label all streets with the actual street sign designation. If you don't know the actual street name,consult the plat map. 9. Include easements and lot lines or tract limits when possible. 10. Arrange all the labeling or writing to read from left to right or from bottom to top with reference to a properly oriented heading. 11. Indicate driveways or features that may impact access,maintenance or replacement. 9/1/98 1998 Surface Water Design Manual 2 SECTION 10 OPERATIONS AND MAINTENANCE MANUAL k(tor ({) N1 G v 'Foy a KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL KING COUNTY, WASHINGTON SURFACE WATER DESIGN MANUAL APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE AND WQ FACILITIES Section No. Subject 1 Detention Ponds 2 Infiltration Facilities 3 Detention Tanks and Vaults 4 Control Structure/ Flow Restrictor 5 Catch Basins 6 Debris Barriers 7 Energy Dissipaters 8 Fencing 9 Gates 10 Conveyance Pipes and Ditches 11 Grounds (Landscaping) 12 Access Roads 13 Basic Biofiltration Swale 14 Wet Biofiltration Swale 15 Filter Strip 16 Wetpond 17 Wetvault 18 Sand Filter Pond 19 Sand Filter Vault 20 StormFilter® 21 StormFilter®(Cartridge Type) 22 Baffle Oil/Water Separator 23 Coalescing Plate 24 Catch Basin Insert 1/24/2005 KING COUNTY, WASHINGTON. SURFACE WATER DESIGN MANUAL APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES NO. 1 - DETENTION PONDS Maintenance Defect or Problem Conditions When Maintenance Is Needed Results Expected When Component Maintenance Is Performed General Trash&Debris Any trash and debris which exceed 1 cubic foot Trash and debris cleared from site. per 1,000 square feet(this is about equal to the amount of trash it would take to fill up one standard size office garbage can). In general, there should be no visual evidence of dumping. Poisonous Vegetation Any poisonous or nuisance vegetation which may No danger of poisonous vegetation or Noxious Weeds constitute a hazard to County personnel or the where County personnel or the public. public might normally be. Coordination with Seattle-King County Health Department Contaminants and Oil,gasoline,or other contaminants of one gallon No contaminants present other than Pollution or more,or any amount found that could: a surface film. (Coordination with 1)cause damage to plant,animal,or marine life; Seattle/King County Health 2)constitute a fire hazard;or 3)be flushed Department) downstream during rain storms. Unmowed If facility is located in private residential area, When mowing is needed, Grass/Ground Cover mowing is needed when grass exceeds 18 grass/ground cover should be inches in height. In other areas,the general mowed to 2 inches in height. policy is to make the pond site match adjacent Mowing of selected higher use areas ground cover and terrain as long as there is no rather than the entire slope may be interference with the function of the facility. acceptable for some situations. Rodent Holes Any evidence of rodent holes if facility is acting Rodents destroyed and dam or berm as a dam or berm,or any evidence of water repaired. (Coordination with piping through dam or berm via rodent holes or Seattle/King County Health other causes. Department) Insects When insects such as wasps and hornets Insects destroyed or removed from interfere with maintenance activities. Mosquito site. Mosquito control: Swallow complaints accompanied by presence of high nesting boxes or approved larvicide mosquito larvae concentrations(aquatic phase). applied. Tree Growth Tree growth threatens integrity of berms acting Trees do not hinder maintenance as dams,does not allow maintenance access,or activities. Harvested trees should interferes with maintenance activity(i.e.,slope be recycled into mulch or other mowing,silt removal,vectoring,or equipment beneficial uses(e.g., alders for movements). If trees are a threat to berm firewood). integrity or not interfering with access,leave trees alone. 2005 Surface Water Design Manual—Appendix A 1/24/2005 A-1 APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL,CONVEYANCE,AND WQ FACILITIES NO. 1 - DETENTION PONDS Maintenance Defect or Problem Conditions When Maintenance Is Needed Results Expected When Component Maintenance Is Performed Side Slopes of Pond Erosion Eroded damage over 2 inches deep where cause Slopes should be stabilized by using of damage is still present or where there is appropriate erosion control potential for continued erosion. measure(s);e.g.,rock reinforcement,planting of grass, Any erosion observed on a compacted berm compaction. embankment. If erosion is occurring on compacted berms a licensed civil engineer should be consulted to resolve source of erosion. Storage Area Sediment Accumulated sediment that exceeds 10%of the Sediment cleaned out to designed designed pond depth. pond shape and depth;pond reseeded if necessary to control erosion. Liner Damage Liner is visible and has more than three/-inch Liner repaired or replaced. (If Applicable) holes in it. Pond Berms(Dikes) Settlement Any part of berm that has settled 4 inches lower Dike should be built back to the than the design elevation. Settling can be an design elevation. indication of more severe problems with the berm or outlet works. A licensed civil engineer should be consulted to determine the source of the settlement. Emergency Tree Growth Tree growth on emergency spillways create Trees should be removed. If root Overflow/Spillway blockage problems and may cause failure of the system is small(base less than 4 and Berms over 4 berm due to uncontrolled overtopping. inches)the root system may be left feet in height. in place. Otherwise the roots should Tree growth on berms over 4 feet in height may be removed and the berm restored. lead to piping through the berm which could lead A licensed civil engineer should be to failure of the berm. consulted for proper berm/spillway ) restoration. Emergency Rock Missing Only one layer of rock exists above native soil in Replace rocks to design standards. Overflow/Spillway area five square feet or larger,or any exposure of native soil at the top of out flow path of spillway. Rip-rap on inside slopes need not be replaced. ) 1/24/2005 2005 Surface Water Design Manual—Appendix A A-2 APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL,CONVEYANCE,AND WQ FACILITIES NO. 4-CONTROL STRUCTURE/FLOW RESTRICTOR Maintenance Defect or Problem Condition When Maintenance is Needed Results Expected When Component Maintenance is Performed General Trash and Debris Distance between debris build-up and bottom of All trash and debris removed. (Includes Sediment) orifice plate is less than 1.5 feet. Structural Damage Structure is not securely attached to manhole Structure securely attached to wall wall and outlet pipe structure should support at and outlet pipe. least 1,000 lbs of up or down pressure. Structure is not in upright position(allow up to Structure in correct position. 10%from plumb). Connections to outlet pipe are not watertight and Connections to outlet pipe are water show signs of rust. tight;structure repaired or replaced and works as designed. Any holes—other than designed holes—in the Structure has no holes other than structure. designed holes. Cleanout Gate Damaged or Missing Cleanout gate is not watertight or is missing. Gate is watertight and works as designed. Gate cannot be moved up and down by one Gate moves up and down easily and maintenance person. is watertight. Chain/rod leading to gate is missing or damaged. Chain is in place and works as designed. Gate is rusted over 50%of its surface area. Gate is repaired or replaced to meet design standards. Orifice Plate Damaged or Missing Control device is not working properly due to Plate is in place and works as missing,out of place,or bent orifice plate. designed. Obstructions Any trash,debris,sediment,or vegetation Plate is free of all obstructions and blocking the plate. works as designed. Overflow Pipe Obstructions Any trash or debris blocking(or having the Pipe is free of all obstructions and potential of blocking)the overflow pipe. works as designed. Manhole See"Detention Tanks See"Detention Tanks and Vaults"Table No. 3 See"Detention Tanks and Vaults" and Vaults" Table No.3 2005 Surface Water Design Manual–Appendix A 1/24/2005 A-5 APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL,CONVEYANCE,AND WQ FACILITIES NO. 5-CATCH BASINS Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed General Trash&Debris Trash or debris of more than'/2 cubic foot which No Trash or debris located (Includes Sediment) is located immediately in front of the catch basin immediately in front of catch basin opening or is blocking capacity of the basin by opening. more than 10%. Trash or debris(in the basin)that exceeds 1/3 the No trash or debris in the catch depth from the bottom of basin to invert the basin. lowest pipe into or out of the basin. Trash or debris in any inlet or outlet pipe blocking Inlet and outlet pipes free of trash or more than 1/3 of its height. debris. Dead animals or vegetation that could generate No dead animals or vegetation odors that could cause complaints or dangerous present within the catch basin. gases(e.g., methane). Deposits of garbage exceeding 1 cubic foot in No condition present which would volume. attract or support the breeding of insects or rodents. Structure Damage to Corner of frame extends more than%inch past Frame is even with curb. Frame and/or Top curb face into the street(If applicable). Slab Top slab has holes larger than 2 square inches Top slab is free of holes and cracks. or cracks wider than'/4 inch(intent is to make sure all material is running into basin). Frame not sitting flush on top slab, i.e., Frame is sitting flush on top slab. separation of more than' inch of the frame from the top slab. Cracks in Basin Cracks wider than'/2 inch and longer than 3 feet, Basin replaced or repaired to design Walls/Bottom any evidence of soil particles entering catch standards. basin through cracks,or maintenance person judges that structure is unsound. Cracks wider than 1/2 inch and longer than 1 foot No cracks more than 1/4 inch wide at at the joint of any inlet/outlet pipe or any the joint of inlet/outlet pipe. evidence of soil particles entering catch basin through cracks. Settlement/ Basin has settled more than 1 inch or has rotated Basin replaced or repaired to design Misalignment more than 2 inches out of alignment. standards. Fire Hazard Presence of chemicals such as natural gas,oil No flammable chemicals present. and gasoline. Vegetation Vegetation growing across and blocking more No vegetation blocking opening to than 10%of the basin opening. basin. Vegetation growing in inlet/outlet pipe joints that No vegetation or root growth is more than 6 inches tall and less than 6 inches present. apart. Pollution Nonflammable chemicals of more than 1/2 cubic No pollution present other than foot per three feet of basin length. surface film. Catch Basin Cover Cover Not in Place Cover is missing or only partially in place.Any Catch basin cover is closed open catch basin requires maintenance. Locking Mechanism Mechanism cannot be opened by on Mechanism opens with proper tools. Not Working maintenance person with proper tools. Bolts into frame have less than 1/2 inch of thread. Cover Difficult to One maintenance person cannot remove lid after Cover can be removed by one Remove applying 80 lbs.of lift;intent is keep cover from maintenance person. sealing off access to maintenance. Ladder Ladder Rungs Unsafe Ladder is unsafe due to missing rungs, Ladder meets design standards and misalignment,rust, cracks,or sharp edges. allows maintenance person safe access. 1/24/2005 2005 Surface Water Design Manual—Appendix A A-6 APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL,CONVEYANCE,AND WQ FACILITIES NO. 5-CATCH BASINS Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed Metal Grates Unsafe Grate Grate with opening wider than 7/8 inch. Grate opening meets design (If Applicable) Opening standards. Trash and Debris Trash and debris that is blocking more than 20% Grate free of trash and debris. of grate surface. Damaged or Missing. Grate missing or broken member(s)of the grate. Grate is in place and meets design standards. NO. 6- DEBRIS BARRIERS (E.G., TRASH RACKS) Maintenance Defect or Problem Condition When Maintenance is Needed Results Expected When Component Maintenance is Performed. General Trash and Debris Trash or debris that is plugging more than 20% Barrier clear to receive capacity of the openings in the barrier. flow. Metal Damaged/Missing Bars are bent out of shape more than 3 inches. Bars in place with no bends more Bars. than 3/4 inch. Bars are missing or entire barrier missing. Bars in place according to design. Bars are loose and rust is causing 50% Repair or replace barrier to design deterioration to any part of barrier. standards. } NO. 7-ENERGY DISSIPATERS Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed. External: Rock Pad Missing or Moved Only one layer of rock exists above native soil in Replace rocks to design standards. Rock area five square feet or larger,or any exposure of native soil. Dispersion Trench Pipe Plugged with Accumulated sediment that exceeds 20%of the Pipe cleaned/flushed so that it Sediment design depth. matches design. Not Discharging Visual evidence of water discharging at Trench must be redesigned or Water Properly concentrated points along trench(normal rebuilt to standards. condition is a"sheet flow"of water along trench). Intent is to prevent erosion damage. Perforations Plugged. Over Y%of perforations in pipe are plugged with Clean or replace perforated pipe. debris and sediment. Water Flows Out Top Maintenance person observes water flowing out Facility must be rebuilt or of"Distributor"Catch during any storm less than the design storm or redesigned to standards. Basin. its causing or appears likely to cause damage. Receiving Area Over- Water in receiving area is causing or has No danger of landslides. Saturated potential of causing landslide problems. Internal: Manhole/Chamber Worn or Damaged Structure dissipating flow deteriorates to'/z or Replace structure to design Post. Baffles,Side of original size or any concentrated worn spot standards. Chamber exceeding one square foot which would make structure unsound. 2005 Surface Water Design Manual—Appendix A 1/24/2005 A-7 APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL,CONVEYANCE,AND WQ FACILITIES NO. 8- FENCING Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed General Missing or Broken Any defect in the fence that permits easy entry to Parts in place to provide adequate Parts a facility. security. Erosion Erosion more than 4 inches high and 12-18 No opening under the fence that inches wide permitting an opening under a fence. exceeds 4 inches in height. Wire Fences Damaged Parts Post out of plumb more than 6 inches. Post plumb to within 11/2 inches. Top rails bent more than 6 inches. Top rail free of bends greater than 1 inch. Any part of fence(including post,top rails,and Fence is aligned and meets design fabric)more than 1 foot out of design alignment. standards. Missing or loose tension wire. Tension wire in place and holding fabric. Missing or loose barbed wire that is sagging Barbed wire in place with less than more than 21/2 inches between posts. 3/4 inch sag between post. Extension arm missing,broken,or bent out of Extension arm in place with no shape more than 11/2 inches. bends larger than'/,inch. Deteriorated Paint or Part or parts that have a rusting or scaling Structurally adequate posts or parts Protective Coating condition that has affected structural adequacy. with a uniform protective coating. Openings in Fabric Openings in fabric are such that an 8-inch No openings in fabric. diameter ball could fit through. NO. 9- GATES ) Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed General Damaged or Missing Missing gate or locking devices. Gates and Locking devices in place. Members Broken or missing hinges such that gate cannot Hinges intact and tubed.Gate is be easily opened and closed by a maintenance working freely. person. Gate is out of plumb more than 6 inches and Gate is aligned and vertical. more than 1 foot out of design alignment. Missing stretcher bar,stretcher bands,and ties. Stretcher bar,bands,and ties in place. Openings in Fabric See"Fencing"Table No.8 See"Fencing"Table No.8 1/24/2005 2005 Surface Water Design Manual—Appendix A A-8 APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL,CONVEYANCE,AND WQ FACILITIES NO. 10- CONVEYANCE PIPES AND DITCHES Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed Pipes Sediment&Debris Accumulated sediment that exceeds 20%of the Pipe cleaned of all sediment and diameter of the pipe. debris. Vegetation Vegetation that reduces free movement of water All vegetation removed so water through pipes. flows freely through pipes. Damaged Protective coating is damaged;rust is causing Pipe repaired or replaced. more than 50%deterioration to any part of pipe. Any dent that decreases the cross section area Pipe repaired or replaced. of pipe by more than 20%. Open Ditches Trash&Debris Trash and debris exceeds 1 cubic foot per 1,000 Trash and debris cleared from square feet of ditch and slopes. ditches. Sediment Accumulated sediment that exceeds 20%of the Ditch cleaned/flushed of all design depth. sediment and debris so that it matches design. Vegetation Vegetation that reduces free movement of water Water flows freely through ditches. through ditches. Erosion Damage to See"Detention Ponds"Table No. 1 See"Detention Ponds"Table No. 1 Slopes Rock Lining Out of Maintenance person can see native soil beneath Replace rocks to design standards. Place or Missing(If the rock lining. Applicable). NO. 11 - GROUNDS (LANDSCAPING) Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed General Weeds Weeds growing in more than 20%of the Weeds present in less than 5%of (Nonpoisonous, not landscaped area(trees and shrubs only). the landscaped area. noxious) Safety Hazard Any presence of poison ivy or other poisonous No poisonous vegetation present in vegetation. landscaped area. Trash or Litter Paper,cans,bottles,totaling more than 1 cubic Area clear of litter. foot within a landscaped area(trees and shrubs only)of 1,000 square feet. Trees and Shrubs Damaged Limbs or parts of trees or shrubs that are split or Trees and shrubs with less than 5% broken which affect more than 25%of the total of total foliage with split or broken foliage of the tree or shrub. limbs. Trees or shrubs that have been blown down or Tree or shrub in place free of injury. knocked over. Trees or shrubs which are not adequately Tree or shrub in place and supported or are leaning over,causing exposure adequately supported;remove any of the roots. dead or diseased trees. 2005 Surface Water Design Manual—Appendix A 1/24/2005 A-9 APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL,CONVEYANCE,AND WQ FACILITIES NO. 12-ACCESS ROADS Maintenance Defect or Problem Condition When Maintenance is Needed Results Expected When Component Maintenance is Performed General Trash and Debris Trash and debris exceeds 1 cubic foot per 1,000 Roadway free of debris which could square feet(i.e.,trash and debris would fill up damage tires. one standards size garbage can). Blocked Roadway Debris which could damage vehicle tires(glass Roadway free of debris which could or metal). damage tires. Any obstruction which reduces clearance above Roadway overhead clear to 14 feet road surface to less than 14 feet. high. Any obstruction restricting the access to a 10-to Obstruction removed to allow at 12-foot width for a distance of more than 12 feet least a 12-foot access. or any point restricting access to less than a 10- foot width. Road Surface Settlement, Potholes, When any surface defect exceeds 6 inches in Road surface uniformly smooth with Mush Spots, Ruts depth and 6 square feet in area. In general,any no evidence of settlement,potholes, surface defect which hinders or prevents mush spots,or ruts. maintenance access. Vegetation in Road Weeds growing in the road surface that are more Road surface free of weeds taller Surface than 6 inches tall and less than 6 inches tall and than 2 inches. less than 6 inches apart within a 400-square foot area. Modular Grid Build-up of sediment mildly contaminated with Removal of sediment and disposal Pavement petroleum hydrocarbons. in keeping with Health Department recommendations for mildly contaminated soils or catch basin sediments. Shoulders and Erosion Damage Erosion within 1 foot of the roadway more than 8 Shoulder free of erosion and Ditches inches wide and 6 inches deep. matching the surrounding road. / Weeds and Brush Weeds and brush exceed 18 inches in height or Weeds and brush cut to 2 inches in hinder maintenance access. height or cleared in such a way as to allow maintenance access. 1/24/2005 2005 Surface Water Design Manual—Appendix A A-10 APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL,CONVEYANCE,AND WQ FACILITIES NO. 16-WETPOND Maintenance Defect or Problem Condition When Maintenance is Needed Recommended Maintenance to Component Correct Problem Pond Area Water Level First cell empty,doesn't hold water. Line the first cell to maintain at least 4 feet of water. Although the second cell may drain,the first cell must remain full to control turbulence of the incoming flow and reduce sediment resuspension. Defective Vegetation Vegetation such as grass and weeds need to be Vegetation should be mowed to 4 to mowed when it starts to impede aesthetics of 5 inches in height. Trees and pond. Mowing is generally required when height bushes should be removed where exceeds 18 inches. Mowed vegetation should be they are interfering with pond removed from areas where it could enter the maintenance activities;that is,at the pond,either when the pond level rises,or by inlet,outlet and near engineered rainfall runoff. structures. Algae Mats When algae mats develop over more than 10% Algae mats that cover more than of the water surface,they should be removed. 10%of the surface of any cell Also remove mats in the late summer before fall should be removed. A rake or rains,especially in Sensitive Lake Protection mechanical device should be used Areas. Excessive algae mats interfere with to remove the algae. Removed dissolved oxygen content in the water and pose a algae can be left to dry on the pond threat to downstream lakes if excess nutrients slope above the 100-year water are released. surface. Trash and Debris Accumulation that exceeds 1 cubic foot per 1000 Trash and debris removed from square foot of pond area. pond. Sediment Sediment accumulations in pond bottom that Removal of sediment from pond Accumulation exceeds the depth of sediment zone plus 6 bottom. inches,usually in the first cell. Oil Sheen on Water Prevalent and visible oil sheen. Remove oil from water by use of oil- absorbent pads or by vactor truck. Refer problem to locate source and correct. If chronic low levels of oil persist,plant wetland plants such as Juncus effusus (soft rush)which can uptake small concentrations of oil. Erosion Erosion of the pond's side slopes and/or Slopes should be stabilized by using scouring of the pond bottom,that exceeds 6 proper erosion control measures, inches,or where continued erosion is prevalent. and repair methods. Pond Dike/Berm Settlement Any part of these components that has settled 4 Dike/berm is repaired to inches or lower than the design elevation,or specifications. inspector determines dike/berm is unsound. Internal Berm Concentrated Flow Berm dividing cells should be level. Build up low areas of berm or lower high areas so that the berm surface is level and water flows evenly over the entire length of the berm from the first cell to the second. Inlet/Outlet Pipe Sediment and Debris Inlet/Outlet pipe clogged with sediment and/or No clogging or blockage in the inlet debris material. and outlet piping. Overflow Spillway Rock Missing Rock is missing and soil is exposed at top of Replace rocks to specifications. spillway or outside slope. T 2005 Surface Water Design Manual-Appendix A 1/24/2005 A-13 APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL,CONVEYANCE,AND WQ FACILITIES NO. 24-CATCHBASIN INSERT Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed Catch Basin Inspection Inspection of media insert is required. Effluent water from media insert is free of oils and has no visible sheen. Sediment When sediment forms a cap over the insert No sediment cap on the insert Accumulation media of the insert and/or unit. media and its unit. Trash and Debris Trash and debris accumulates on insert unit Trash and debris removed from Accumulation creating a blockage/restriction. insert unit. Runoff freely flows into catch basin. Media Insert Water Saturated Catch basin insert is saturated with water,which Remove and replace media insert no longer has the capacity to absorb. Oil Saturated Media oil saturated due to petroleum spill that Remove and replace media insert. drains into catch basin. Service Life Exceeded Regular interval replacement due to typical Remove and replace media at average life of media insert product. regular intervals,depending on insert product. 1/24/2005 2005 Surface Water Design Manual—Appendix A A-20