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Home My WebLink AboutRS_Preliminary_Technical_Information_Report_170503_v1Cedar Ridge Short Plat Renton, Washington Preliminary Technical Information Report May 03, 2017 Pacific Engineering Job No. 17006 PRELIMINARY TECHNICAL INFORMATION REPORT FOR Cedar Ridge Short Plat RENTON, WASHINGTON May o3, 207 PREPARED FOR Satwant Singh, Cedar Ridge, LLC. 24419 10511 Place SE Kent, WA 98030 Phone: (206) 391-3311 E-mail: pmvrsingh@gmail.com Pacific Engineering Design, LLC. 15445 53rd Avenue S Seattle, WA 98188 Phone: (206) 431-7970 '325 �£ST� �I'AL TABLE OF CONTENTS I. PROJECT OVERVIEW...............................................................................................3 Figure 1 Technical Information Worksheet to Follow...................................................4 Figure 2 Site Location Map to Follow...........................................................................5 Figure 3 Drainage Basin, Subbasin and Site Characteristics.......................................6 Figure4 Soils...............................................................................................................7 II. CONDITIONS AND REQUIREMENTS SUMMARY .................................................... 8 III. OFF SITE ANALYSIS...............................................................................................15 Task 1 Study Area Definition and Maps.....................................................................16 Task 2 Resource Review...........................................................................................17 Task 3 Field Inspection..............................................................................................18 Task 4 Drainage System Description and Potential Problems...................................19 Task 5 Mitigation of Existing or Potential Problems...................................................19 IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ...20 Part A Existing Site Hydrology...................................................................................22 Part B Developed Site Hydrology...............................................................................23 Part C Performance Standards.................................................................................. 32 Part D Flow Control System.......................................................................................33 Part E Water Quality System.....................................................................................57 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN (REVISED 6/26/2012).......6 .... 58 VI. SPECIAL REPORTS AND STUDIES.......................................................................59 VII. OTHER PERMITS...................................................................................................60 VIII. CSWPPP ANALYSIS AND DESIGN......................................................................61 X. BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION OF COVENANT................................................................................................................... 64 X. OPERATIONS AND MAINTENANCE MANUAL ....................................................... 65 2 I. Project Overview The proposed project will develop 6 single-family lots. The site is located at the southwest corner of the intersection of 156th Avenue SE and SE 2nd Place in the Renton Highlands north of the Cedar River. The address of the site is 13609 156th Avenue SE. The site area is 1.69 acres before Right of way dedication and 1.67 acres after Right of way dedication along 156th Avenue SE. The site consists of two existing parcels that form an overall rectangular piece of property that is approximately 484' x 152' with frontage on its eastern short side along 156th Avenue SE and frontage on its northern long side along SE 2nd Place. The project site includes both on-site development area and off-site improvements along 156th Ave SE and SE 2nd Place. The site is located in the City of Renton R4 zone. The surrounding parcels are all single-family residential also zoned R- 4. The site is located in the Lower Cedar River drainage basin. The site is located in the Duration with Forested conditions flow control area (Duration flow control with Forested site conditions) and Basic water quality control area. There are single-family residences and various outbuildings on the two existing parcels. All existing buildings will be demolished and removed for the proposed development. The remainder of the property is covered with grass and trees. The site is hilly with average slope of 11 % slopes westerly toward Grant Avenue South. There is no sensitive area on the site and no difficult conditions for the proposed development. For the onsite improvement, Restricted footprint and Basic dispersion for downspouts are used for each lots as Flow control BMPs. New plus replaced impervious area is approximately 0.49 acres before applying flow control BMP credits, new pervious area is approximately 1. 18 acres. A detention vault is proposed to provide the required Duration standard forested site conditions flow control. The offsite frontage improvements along SE 2�d Place and 156th Avenue SE remove approximately 4,390 square feet of existing impervious area and create approximately 6,090 square feet of new / replaced impervious area (1,632 square feet of it is pollution generating impervious area) and no new or replaced pervious area. For flow control, the new impervious area created by the SE 2nd Place offsite improvement is routed to the onsite detention vault and new impervious area created by the 156th Ave SE offsite improvement is counted as bypassed target area Per KCSWDM Section 1.2.3.2.E. The onsite detention vault is oversized, so that the developed onsite detained runoff plus the onsite and offsite bypassed runoffs meets the required Duration standard forested site conditions flow control requirements at the point of compliance (Near the intersection of 149th Place SE and SE 142nd Street). For water quality treatment, total new and replace pollution generating area (onsite plus offsite) is only 4,690 square feet (less than 5,000 square feet) and is counted as untreated discharge per 2017 Renton SWDM Section 1.2.8.2.D. No water quality treatment facility is required. 3 Figure 1 Technical Information Worksheet to Follow CITY OF RENTON SURFACE WATER DESIGN MANUAL 9 ❑ECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Project Owner S5 K DeVBGvdmemV r GL C Phone .206) 391 —331! Address Z �+1F1 °� I �S (� EGova S L Kent , WLR 180350 Project Engineer v P/ Company is % Phone 7476 t3f-700o Part 3 TYPE OF PERMIT APPLICATION © Land Use (e.g., SubdivisionSh&SFR © Building (e.g., M/F / Commercial ® Grading ® Right -of -Way Use ❑ Other Part 2 PROJECT LOCATION AND DESCRIPTION Project Name Cpoky Rtriee • Aolot i CED Permit # Location Township 13 Range D,5 Section 14 Site Address 1360° 156 to AVe Part 4 .:OTHER REVIEWS AND PERMITS ❑ DFW HPA ❑ Shoreline ❑ COE 404 Management ❑ DOE Dam Safety ❑ StructurW Rocker cult/ ❑ FEMA Floodplain Ll Section 7 ❑ COE Wetlands ❑ Other. Part 5 PLAN AND REPORT INFORMATION Technical Information Report Site Improvement Plan (Engr. Plans) 0 Full Type of Drainage Review ❑ Targeted Plan Type (check ® Full (check one): F] Simplified one): Ll Modified ❑ Large Project ❑ Simplified Date (include revision ❑ Directed Date (include revision dates): dates): Date of Final: Date of Final: 2017 City of Renton Surface Water Design Manual 12/12/2016 REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 6 SWDM ADJUSTMENT APPROVALS Type (circle one): Standard / Blanket Description: (include conditions in TIR Section 2) Approved Adjustment No. Date of Approval: Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: Completion Date: Describe: Re: SWDM Adjustment No. Part 8 SITE COMMUNITY AND DRAINAGE BASIN Community Plan: iV$Wc�s-t(� Special District Overlays: v v p Drainage Basin: LOW'P/1/ Stormwater Requirements: Part 9 ONSITE AND ADJACENT SENSITIVE AREAS 'I ❑River/Stream Ll Steep Slope ❑ Lake ❑ Erosion Hazard ❑ Wetlands ❑ Landslide Hazard ❑ Closed Depression ❑ Coal Mine Hazard ❑ Floodplain ❑ Seismic Hazard ❑ Other ❑ Habitat Protection El None, 12/12/2016 2017 City of Renton Surface Water Design Manual Part 10 SOILS Soil Type Ij � qG REFERENCE &A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Slopes 6 1.5 /U ❑ High Groundwater Table (within 5 feet) ❑ Sole Source Aquifer ❑ Other ❑ Seeps/Springs ❑ Additional Sheets Attached Part 11 DRAINAGE DESIGN LIMITATIONS Erosion Potential REFERENCE LIMITATION /SITE CONSTRAINT ® Core 2 — Offsite Analysis ❑ Sensitive/Critical Areas ❑ (Z EPA ❑ LID Infeasibility ❑ Other ❑ Additional Sheets Attached Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: SfrPcvw, +hpvt otYo1i%Yu5 io GOWP�✓ (name or description) Core Requirements (all 8 apply): Discharge at Natural Location Number of Natural Discharge Locations: 2� Offsite Analysis Level: 0/ 2 / 3 dated: J V Zv Flow Control (include facility Standard: f2Gl Y4j�tn ah �Ff',oW Coyt.eYr( Forest Site, summary sheet) or Exemption Number: Gvilp,{� -f�v►� ) On-site BMPs: d to i &mza d+5 eY5i01 Conveyance System Spill containment located at: Erosion and Sediment Control / CSWPP/CESCL/ESC Site Supervisor: Construction Stormwater Pollution Contact Phone: Prevention After Hours Phone: 2017 City of Renton Surface Water Design Manual Ref 8-A-3 12/12/2016 REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Maintenance and Operation Responsibility (circle one): Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: (D/ No Water Quality (include facility Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog summary sheet) or Exemption No. Special Requirements (as applicable): Area Specific Drainage Type: SDO / MDP / BP / Shared Fac. /G) Requirements Name: Floodplain/Floodway Delineation Type (circle one): Major / Minor / Exemption / one 100 -year Base Flood Elevation (or range): Datum: Flood Protection Facilities Describe: Source Control Describe land use: (commercial / industrial land use) Describe any structural controls: Oil Control High -Use Site: Yes /oNo Treatment BMP: Maintenance Agreement: Yes / No with whom? Other Drainage Structures Describe: 12/12/2016 2017 City of Renton Surface Water Design Manual REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS Type/Description MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION Type/Description AFTER CONSTRUCTION Clearing Limits ❑ Retaining Wall ❑ Stabilize exposed surfaces Cover Measures ❑ Rockery > 4' High © Remove and restore Temporary ESC Facilities Perimeter Protection ❑ Structural on Steep Slope © Clean and remove all silt and debris, ensure ❑ Traffic Area Stabilization ❑ Other. operation of Permanent BMPs/Facilities, restore tX C?A operation of BMPs/Facilities as necessary Sediment Retention ® Flag limits of sensitive areas and open space ® Surface Water Collection preservation areas ® Dewatering Control ❑ Other © Dust Control 0 Flow Control © Control Pollutants © Protect Existing and Proposed BMPs/Facilities ® Maintain Protective BMPs / Manage Project Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch) Part 15 EASEMENTS/TRACTS Part Flow Control Type/Description A Drainage Easement Water Quality Type/Description ® Detention ❑ Infiltration ❑ Regional Facility ❑ Shared Facility ® On-site BMPs ❑ Other 014YN' N0v%Tlow (ur-b�rol, ❑ Retaining Wall ❑ Vegetated Flowpath ❑ Wetpool ❑ Filtration ❑ Oil Control ❑ Spill Control ❑ On-site BMPs ❑ Other ❑ Rockery > 4' High ❑ Tract ❑ Structural on Steep Slope ❑ Other RESi�--Evo�pY' Fnr is cG►Tp,rSiov. ❑ Other. tX C?A 2017 City of Renton Surface Water Design Manual Ref 8-A-5 12/12/2016 16 STRUCTURAL ANALYSIS A Drainage Easement 91 Cast in Place Vault ❑ Covenant ❑ Retaining Wall ❑ Native Growth Protection Covenant ❑ Rockery > 4' High ❑ Tract ❑ Structural on Steep Slope ❑ Other ❑ Other. 2017 City of Renton Surface Water Design Manual Ref 8-A-5 12/12/2016 REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 17 SIGNATURE OF PROFESSIONAL ENGINEER I, or a civil engineer under my supervision, have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attached Technical Information Report. To the best of my knowledge the information provided here is accurate. S� Signed/Date 12/12/2016 2017 City of Renton Surface Water Design Mamial 8-A-6 Fit4ure 2 Site Location Map to Follow s 36th Sl � ' E88th 1 9E8gth Li wc A t I e m IN 30th St g ` �P � SE 95th WaY a Va N71t '~•• •� Lake Washington �. ;r �—• NE26tt St ` ~�+ ', •1• NE 241h St o `f• Seat e a o E 9ttcgt°c �t� a a` •� • b� m m s NE SLm S 114th t • rte• m 0th Ln ¢' • g NE 1SE 1161h St ^ a m a m NE 9fh 51 • S 1201h St w � m • w m ¢' NE 7th St S 1241 St N 61 St E NE 6th •r� ' n I°'� 9P 13I•, / m J• S128th St %a s/ E ..•' .J m I U11NE 4th St - SE 1281h SI 3d t x ■ � S132nd �•P heterUNW NEgtd St 1n rm HE tl Sf I 0 5135th Sl •W m E1st PI ~ANN... `\ SE yrd Gt 9 A•I N '. L• • •� 1E 135 hSt •�..�+ S�nae s3rd st st1 !! �..m.y 1.. ` feh SE htb -' i•� IN W SE 1381h PI`• �• , " Cedar River D Wish Waterway I SF Slh 3I ! tss, SITE SW 7th St t 'M Ise �.J•ti • c SfcOtrQ aa/ ya//,, '..i• • i SE 1451h 6cadYWa SE 121h St Hh Pl m - SE 1461h St 1405 rw a 515th St SE 16th PI -5`N oy'r � •� Renton N v T QJo frr Petle•�•� �.� ••~•�. tiPy' sfnan Walk 1 0` SE /581h Sl •�•�r• Gr ver j s ..J (/ • •r'•30 mok 760th PI Stra dere d I SE 1641h $1 SE 1647.57 SF Fa7�O SW 27th St �0 S7vd - S MINIM T k w i I i >< N 5F m 15 H V• I ¢ 5th P/ SE 168th St E 1701h St I m R- a v� v 134th Ave SE 0 a ¢ • SE I 5F S180th SSW 43 SI S 180th SI y Peo-Ovf7skyRtl _ St f y S 47th St SE 1841h St 3 �3j ydrq•� 184th PI SE K e n t 5192nd f •1I SE 192nd St - L e Youn S 196th St ; rSEtSt Department of Community Street Classification for Live Work Docket #11 ,�, &Economic Development Alex Pietsch, Administrator Zoning Designations Road Classification Data/GIS Analysis Services CN Commercial Neighborhood — Freeway AdrianaA, Johnson, Patrick Roduin R14 parcels adjacent arterials — Primary April 15, 2009 — Minor 0 11950 3,900 " Feet — Collector 1:50,000 Local Produced by City of Renton (c) 2009, the City of Renton all rights File Name: H:\CED\Plannin \GIS\GIS ro ects\docket items\ reserved. No warranties of any sort, including but not limited to 9 _p I accuracy, fitness or merchantability, accompany this productlive_work_D11\mxds\live work D11 selected_parcels.mxd Figure 3 Drainage Basin, Subbasin and Site Characteristics 0 Figure 4 Soils Reference 11-C Ago IIIIIININNIIIIIJ ANIM 1IalitEB EVB t f P< ? ~ C InC FEvO BFC ECD Pn Pn'Pn 4� - I w _ , ` EK IFITS E , E c 1t �• • NoId, 11 PITS AI F._ 'l l7 eoD T Ba� -"IE=-�uF,�F ,fi - % AF % �y� E B BIG i � n tR D \ - 9D Ft % D P9 \ _ F L - A4F -` Ago eec PY d"g TU Mc I r— Ev UW So B _ t - Sk o a no pgc % No Bk Sk N Ago FMB Sk Z Ago AI Sk Sk ANI I �I PmB PmB 00 , . EVB rI PITS PmB rO f ^9° / PyD /5D PGB AI To/ i f 140"M IN w... a SITE City o f R e n t o n Soil Survey Map Groundwater Protection A ea Boundary Aquifer Protection Area Zone 1 PublicWorks0 Q,CJ 1 Aquifer Protection Area Zone 1 Modified Surface Water Utility r city of , ( y I�..m G. Del ROSaf10 f !J��`JJ f '' Miles ILMur Renton City Limits 12/22/2009 II. Conditions and Requirements Summary CORE REQUIREMENTS - SECTION 1.2 OF KCSWDM 1.2.1 CORE REQUIREMENT #1: Discharge at the Natural I_ocatlon Overall topography throughout the drainage basin generally conveys flows from northeast4o-southwest and north -to -south. Streets and manmade conveyance systems within the vicinity of the site have broken up these flows, directing them in various directions that eventually flow to the same, original natural discharge point of the overall basin, which is a series of wooded ravines located on the south side of SE 142nd Street approximately 2,600 feet south of the project site. These ravines convey flows south off the Maplewood Heights / Renton Highlands to the valley below and connect to the Cedar River. Existing micro -topography on the project site generally slopes northeast to southwest in the general overall pattern of the drainage basin, directing surface flows from the site across neighboring downstream residential parcels toward 154th Ave SE. Surface flows in this direction are eventually collected by manmade conveyance systems in 154th Ave SE and directed south. There are several issues associated with releasing flows at the southwest corner of the site as a developed project: • This project will require installation of a detention vault and water quality facility. • There is no existing conveyance system located at the southwest corner of the site. • There is not adequate distance on-site to disperse flows from the detention vault to the surface toward the southwest corner of the site. • Parcels south and west of this site prohibit our ability to convey flows via pipe or swale C1 direction without easements across those parcels. • Emerging groundwater is already an existing problem on parcels immediately south of us along 156th Ave SE (see downstream analysis). • Conveyance systems in 154th Ave SE further south (outside city of Renton) are documented by homeowners in the area as overwhelmed in heavy and prolonged rain events. The overall topography in this area is virtually flat. For these reasons, we propose connecting our storm drainage system (post detention and water quality) to the piped conveyance system located in SE 2nd Place which flows west to Maplewood Park. At this location, the piped conveyance system discharges to an open conveyance channel / stream that flows west and south through the park before re- entering apiped conveyance system at SE 148tHPlace, travelling south along the 148tH / 149th rights-of-way to eventual discharge to the same wooded ravine south of SE 142nd that overland course from the site connects to. This is the natural discharge point of the overall basin. See' Fig.X included in section III, Task 3 for a map of the two drainage courses. 1.2.2 CORE REQUIREMENT #2: Off-site Analysis This core requirement has been addressed in Section III of this report. 1.2.3. CORE REQUIREMENT #3: Flow Control Per SWDM section 1.2.3.3 and 5. 2, Flow Control BMPs are required for the onsite development. See 1.2.9 CORE REQUIREMENT #9 of this report for Flow Control BMPs. Onsite flow control facility is provided by a detention vault to provide the required Duration standard forested site conditions flow control. 1.2.4 CORE REQUIREMENT #4: Conveyance System The new conveyance piping will be installed as needed. The new conveyance piping has been checked to confirm compliance with chapter 4 of the 2017 Renton SWDM. Per City of Renton 2017 SWDM Section 1.2.4.1: 1. New pipe system shall be designed with sufficient capacity to convey and contain (at the minimum) the 25 -year peak flow with minimum 6 inches of free board, assuming developed conditions for onsite tributary areas and existing conditions for any offsite tributary areas. 2. Pipe system structures may overtop for runoff that exceed the 25 -year design capacity, provided the overflow from a 100 -year runoff event does not create or aggravate a severe flooding problem or severe erosion problem as described in Core Requirement #2. Any overflow occurring onsite for runoff events up to and including the 100 -year event must discharge at the natural location for the project site. In residential subdivision, this overflow must be contained within an onsite drainage easement, tract, covenant, or public right-of-way. 3. The upstream end of a pipe system that receives runoff from an open drainage feature (pond, ditch, etc.) shall be analyzed as a culvert. The new conveyance system is designed to convey and contain the 25 - year peak flow with 6 inches of free board and the 100 -year peak flow and thus meets the requirements listed above. KCBW is used for Back water analysis following the requirements of City of Renton 2017 SWDM 4.2.1.2 and designed for the 100 -year peak flow. 1.2.5 CORE REQUIREMENT #5: Erosion and Sediment Control Erosion control will be installed as necessary for the frontage improvements and the on- site improvements. 1.2.6 CORE REQUIREMENT #6: Maintenance and Operations Any necessary maintenance of the onsite drainage system will be the responsibility of the property owner and manager. 60 1.2.7 CORE REQUIREMENT #7: Bonds and Liability Necessary bonds will be provided at the time the building permit plans are approved and the construction started. 1. 2.8 CORE REQUIREMENT #8: Water Quality The project site includes onsite improvement and frontage improvement (curb, gutter, sidewalk, planter strip) along both 156th Avenue SE and SE 2nd Place. Due to topography and existing drainage improvements, off-site flows do not drain onto the site and will not connect to the onsite detention vault. New sidewalk improvements along both 156th Ave SE and SE 2nd Place will drain to their adjacent streets and their respective existing conveyance systems. Total pollution generating area is 4,450 square feet and is counted as untreated discharge per 2017 Renton SWDM Section 1.2.8.2.D., no water quality treatment facility is required. 1.2.9 CORE REQUIREMENT #9: Flow Control BMPs Average lot size of this project is approximately 10,900 square feet, Small lot BMP requirements per 2007 Renton SWDM Section 1.2.9.2.1 apply to this project. BMPs must be implemented, at minimum, for an impervious area equal to at least 10% of the site/lot for site/lot size up to 11,000 square feet and at least 20% of the site/lot for site/lot size between 11,000 and 22,000 square feet. The feasibility and applicability of full dispersion was studied first. The study found full dispersion is not suitable for this site to fully disperse the new impervious areas and new non-native pervious areas because long native flow path is not available due to the dimensions of the overall site. Full infiltration is also not suitable for this site because onsite soil is till soil (Alderwood gravelly sandy loam, 6 to 15% slopes, AgC) according to City of Renton Soils Map. The following flow control BMPs are used to meet the requirements: 1. Restricted footprint. Impervious area coverage in each lots will be restricted to maximum 34% of their lot sizes for lots 1 through 5 and maximum 25% for lot 6. 2. Tree retention. 4 trees along the south property lines are preserved. 3. Basic dispersion for downspouts. Downspouts of the southeast corners of the houses on lots 1 through 5 up to 700 square feet per house are treated by Basic dispersion. Down spouts of the southeast and southwest corners of the house on lot 6 up to 1,400 square feet total are treated by Basic dispersion. Til SPECIAL REQUIREMENTS - SECTION 1.3 OF KCSWDM 1.3.1 Special Requirement #1: Other Adopted Area Specific Requirements No other area specific requirements are applicable. The site is not within a CDA, MDP, BP, SCP, SWCP, LMP, FHRPU or SFDP. 1. 3.2 Special Requirement #2: Flood Plain / Floodway Delineation Not applicable to this site. There is no flood hazard area in the site. The site is not within a floodplain or floodway. The site is not subject to inundation by the base flood or N hannel migration. 1.3.3 Special Requirement #3: Flood Protection Facilities Not applicable to this site. There is no flood hazard area in the site. The site does not rely on any flood protection measures. 1.3.4 Special Requirement #4: Source Controls This project is a single family short plat project. Source Controls are not required. 1.3.5 Special Requirement #5: Oil Control This project is a single family short plat project in R-4 zone and this site is not a high used site. Oil Control is not required. City of Renton Special Requirement #6: Aquifer Protection Area Not applicable to this site. The site is not located in the Aquifer Protection Areas (zone1, zone 1 modified and zone 2) shown on the City of Renton Aquifer Protection Zones Map. III. Off Site Analysis �5 Task 1 Study Area Definition and Maps The site is located on the east side of 156th Avenue Stand on the south side of SE Z" Place. The address of the site is 13609 156th Avenue SE. The parcel numbers of the 2 parcels making up the overall project site are 146340-0045 and 146340-0049. The onsite area is 1.67 acres. The site is located in the Lower Cedar River drainage basin. See attached Site Map and Topographical Map. Task 2 Resource Review The following resources have been reviewed for existing /potential problems in the study area. 1) Critical Drainage Area maps Do not apply in the City of Renton per City of Renton Surface Water Design Manual. 2) DNRP Drainage complaints and studies None. 3) Road drainage problems See description of downstream drainage system (King County) in 154th Avenue SE in Task 3 — Field Inspection. 4) U.S. Department of Agriculture, King County Soils Survey The King County Soils Survey map and City of Renton Soils Map show Alderwood soil on the site (AgD on the west portion of the site and AgC on the east portion of the site). See attached Soils map. 5) Wetland Inventory There is no wetland on the site and its adjacent areas. 6) Migrating river studies There is no migrating river within the study area. City of Renton Sensitive Areas Flood Hazard Public Works Department G. Zimmerrnan, Administrator Technical Services R. MacOnie, D.�lsneski Printed on May 21, 2009 Data Source: Public Warks, Utiliti es Systems, Technical Services ��D �ctryor, a r,mo s,eco (1_ ae rm, Cb Hazard Condition Flood Hazard Critical Infrastructure �� Police Department _= Fire Stations V Valley Medical Center � Schools City of Renton Sensitive Areas Erosion Hazards Public Works Department G. Zimmerman, Administrator Technical Services Donnaann Visneski, ES3 Printed on May 21, 2009 Data Source: Public Works, Utilities Systems, Technical Services 0 1,500 3,000' i r i ardpo+wmaaM�� m,asbn.aeeb �Jri rsMms crr w+e L. HAZARD CONDITION Critical Infrastructure " Police Department Fire Stati ons V Valley Medical Center � Schools City of Renton Sensitive Areas Public works Department Steep Slopes Percentage Range G. Zimmerman, Administrator ° td00 2800' Technical Services r >15% & <=25°/ R. MacOnie, D. �sneski Printed on May 21, 2009 a d".A :.«� TM.... d m >25°/ & <=a0% Data Source: Public Works, Utilities Systems, Technical Services � acrry°t � LJ� Renton City Limits City of Renton Sensitive Areas Landslide Hazard Public Works Department G. Zimmerman, Administrator Technical Services R. MaGunie, D. Vsneski Printed on May 21, 2009 Data Source: Public Works, Utilities Systems, Technical Services city Ofr l l l l ° t,zso 2,5°°' LANDSLIDE HAZARD CRITICAL FACILITIES Very High _ Police Department Hig_ •. tz r' Renton City Limits - Moderate � Fire Stations Mod Unclassified V Valley Medical Center Schools Task 3 Field Inspection Upstream Tributary Area Based on the general neighborhood layout and topography, there are no significant upstream flows that enter the site. Upstream runoff to the east is intercepted by the existing conveyance system (CBs and underground pipes on the east side of the street) in 156th Ave. SE and conveyed south past the project site. Upstream runoff to the north is intercepted by the existing conveyance system (ditch along the north side / CBs and underground pipe on the south side) in SE 2nd Place and conveyed west past the project site toward Maplewood Park. Downstream Analysis Surface runoff from the site currently travels overland in a southwesterly direction toward SE 3rd Place / 154th Ave. SE. While no standing water or water flows were observed on the project site, surface water (likely excess groundwater) was observed flowing off parcels on the east side of 154th Ave SE south of SE 3rd Place (approximately 350 feet downstream of the project site). A portion of this flow was crossing 154th Avenue SE in a wide band to the gutter on the west side of 154th Avenue SE where it was channeled to existing CBs in that flowline. The remainder of that flow was travelling south on the east side of 154th Avenue SE in a shallow to non-existent flowline to a CB located near the end of the paved portion of 154th Avenue SE (approximately 520 feet downstream of the property). Both pipe systems continue south through an unopened section of 154th Avenue SE where they connect to an existing series of shallow, grass -lined conveyance swales, roadside ditches and culverts (beginning approximately 1200 feet downstream of the site) in the southerly open portion of 154th Avenue SE. This open conveyance system continues south within the right-of-way for approximately 670 feet to the intersection of SE 142nd St. and 154th Ave. SE where it turns and continues west in SE 142nd Street (approximately 1870 feet downstream of site). This portion of downstream in 154th Avenue SE and SE 142nd Street is more completely described in the downstream analysis prepared for MeadowVue (LUA17-000106) by CPH Consultants. m IN o� s 0*1 Eu F ' 1 5�--PINTO a pi Ole _ i NJ UP ■ d NO NO03 UP �Mm __-• - Y - _Z. • irt r WN ININ '��t� -' ' AL ALP y� •sr _ � WIN Tau 1 r: p in ':Oc AMR: limmmirmilm" Now; a No r LOP JJ iron fit• .:. �-:� . •J3 A �'�-°7 �, � , ' r, '' IL , POP 1; too AN m =j '� .�! t -o L b IN o� s 0*1 Eu F ' 1 5�--PINTO a pi Ole _ i NJ UP ■ d NO NO03 UP �Mm __-• - Y - _Z. • irt r WN ININ '��t� -' ' AL ALP y� •sr _ � WIN Tau 1 r: p in ':Oc AMR: limmmirmilm" Now; a No r LOP JJ iron fit• .:. �-:� . •J3 A �'�-°7 �, � , ' r, '' IL , POP 1; too AN m =j '� .�! t -o L �—�• , I r r+i y 1 h I M1 `'rarm, _,; ', r°7 1 — �r� t r 1.4 1 Ali Alto �..r - Ai'% f r �. iAE I oz a LF pity Of Renton' t 'r.. �l� '� •�,i z Ij ~-a + . . r 1',`. 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ALI FlatJa AD in 111 LDso a € z ;' _ Fall 1 TV IDIOM; Mal ";Zjix.�Lwaamt .AV SAW o a ,•i 154th Ave SE F1 rt.Jim -�r A ;� .� , Overland Sheet Floi ,_ y r 4 ,.. _— .L 4 ", x`'_ w 11T � a,� Pipes [CBs :.�WEI twill f ILIst`` '� I -; Grass -Lined Swales / .CIrierts _. S,into ¢ a r' LL to ,: . - '•. ,4 :..' •,=-L• _ d� -i, ij_ .� i P a r SE 2nd Place FI h� w I i a IMF ri a i As +a' h r1. 1Vi s r7 r zr (All. Pipe I CBs)., ,.'�,�i ' WISI IF - - _ r Fall F �. r ky- r h- tDo, 14 AV • :{ , �y .■1 _ 5 , y.4 _ -IV LA 4 Who Z�r� AM '� 4F !I FILLs . i . :f X11 ��1Is AM •, _ _ OL ' •.-'1�.�' R .. �4 ._1,e1 1��'11a� !' ! �" t''• r -'� r_ - - • 7 , OF to I Irl - _ .: , r . 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' a d� ■�s` DOWNSTREAM CONDITIONS i,uuxui� �vu�ii aivu� i��r r-vvc. ter, (approximately 530 feet downstream of site). PACIFIC ENGINEERING DESIGN, LLC 15445 53RD AVE. S., #100 Seattle, WA. 98188 (206) 431-7970 www.p aceng com Cedar Ridge Short Plat Downstream 13609 156th Avenue SE Renton, WA 98059 SCALE: None I DATE: 3/20/17 1 SHEET: 4 OF 12 JOB NUMBER: FILE NAME: BY: LEL 17006 Photobase 4 DOWNSTREAM CONDITIONS >r t - - to It— . t Y. x r; A `jr foo food a 1 to of' ;t - _ ,Fhti14, TF - off - foo off. - of I:r ` toot., AL s1, 1% 1 ot I I V�p '. _ _ Wo of of to Iwo� of off r F I off .. .. r „k r foo, I or �ooI If or I of Looking south along the gutter on the west side of 154th Ave. SE (approximately 680 feet downstream of site). PACIFIC ENGINEERING DESIGN, LLC 000000000 15445 53RD AVE. S., #100 Seattle, WA. 98188 (206) 431-7970 www.pacen _ Cedar Ridge Short Plat Downstream 13609 156th Avenue SE Renton, WA 98059 SCALE: None DATE: 3/20/17 SHEET: 6 OF 12 JOB NUMBER: FILE NAME: BY: LEL 17006 Photobase 6 DOWNSTREAM CONDITIONS LVVlilll� SVULll 0.1Vllb' L11G WGSL S1UG Vl 1J`t LyVG. JL' (approximately 1680 feet downstream from site) PACIFIC ENGINEERING DESIGN, LLC 15445 53RD AVE. S., #100 Seattle, WA. 98188 (206) 431-7970 www.pacen.a .com Cedar Ridge Short Plat Downstream 13609 156th Avenue SE Renton, WA 98059 SCALE: one DATE: 3/20/17 SHEET: 10 OF 12 JOB NUMBER: FILE NAME: BY: LEL 17006 Photobase 10 or A `- A I A AT A JI . - _.` iff I c i- ` `-- -ISIOF�III I All L _ro S TA MAIL A"A, +y_ r'll' ALL L VIA Add, -, ,Ad ALL Ar kLAL tj. .-� \ —pe,eF - IT I�t f'!• ceA.l Vw, 1 r�,/, ,]}'Afl. orf _ t� k, tAim � Ar -': AWAL V. av ' ,,_ Ad iAIA A �f I, I Aij ALL do A— L IVA dr 7 LI A ' `, , ' t At TV "I Ad di A #Ad AV TJ I - =_ I AT TO A ` / Y?. A VA It V) k r j' (dd I < 7 z.4 i- r , i.. ! i.i / ..A JA x;.� z2'y .mak ,.:Al 11't`.'r '= A IT Y 's,. A DOWNSTREAM CONDITIONS Lvvnui� �vu�u aivii� uic ww� �iuc vl l�-r rvvc. aL (approximately 1950 feet downstream of site). PACIFIC ENGINEERING DESIGN, LLC 15445 53RD AVE. S., #100 Seattle, WA. 98188 (206) 431-7970 www.12aceng.co Ridge Short Plat Downstream 13609 156th Avenue SE Renton, WA 98059 SCALE: None DATE: 3/20/17 SHEET: 12 OF 12 JOB NUMBER: FILE NAME: BY: LEL 17006 Photobase 12 Task 4 Drainal4e System Description and Potential Problems There are no unsolved existing and potential drainage problems within 0.25 mile downstream of the site other than the observed groundwater surface flows along 154th Ave SE. Further south in the King County portion of 154th Ave SE (gravel road surface) approaching SE 142nd Street (0.25 — 0.36 miles downstream), the topography is quite flat with roadside swales and culverts. Discussions with residents in this unincorporated area of the county indicate minor flooding issues with this system during intense and /or prolonged rain / snowmelt events. Task 5 Mitigation of Existing or Potential Problems There are no unsolved existing and potential drainage problems within 0.25 mile downstream of the site. For the onsite improvement, Restricted footprint and Basic dispersion for downspouts are used for each lots as Flow control BMPs. New plus replaced impervious area is approximately 0.49 acres before applying flow control BMP credits, new pervious area is approximately 1.18 acres. A detention vault is proposed to provide the required Duration standard forested site conditions flow control. The offsite frontage improvements along SE 2nd Place and 156th Avenue SE remove approximately 4,390 square feet of existing impervious area and create approximately 63090 square feet of new / replaced impervious area (1,632 square feet of it is pollution generating impervious area) and no new or replaced pervious area. For flow control, the new impervious area created by the SE 2nd Place offsite improvement is routed to the onsite detention vault and new impervious area created by the 156th Ave SE offsite improvement is counted as bypassed target area Per KCSWDM Section 1.2.3.2.E. The onsite detention vault is oversized, so that the developed onsite detained runoff plus the onsite and offsite bypassed runoffs meets the required Duration standard forested site conditions flow control requirements at the point of convergence (Near the intersection of 149th Place SE and SE 142nd Street). For water quality treatment, total new and replace pollution generating area (onsite plus offsite) is only 4,690 square feet (less than 5,000 square feet) and is counted as untreated discharge per 2017 Renton SWDM Section 1.2.8.2.D. No water quality treatment facility is required. With connection to the piped conveyance system in SE 2nd Place, the proposed development will not create any adverse impact on the downstream drainage system in either direction between the site and the wooded ravine south of SE 142nd Street where the two downstream systems re -converge. 19 Downstream maps and Photos 20 V. Flow Control and Water Quality Facility Analysis and Design 21 Part A Existing Site Hydrology Duration standard forested site conditions flow control requires matching developed flow duration from 50% of pre -developed 2 -year peak to full 50 -year peak and matching peak discharge rates of developed 2 and 10 -year peaks with the existing 2 and 10 year peaks. Existing site condition is forest condition per City of Renton Flow Control Application Map. Offsite frontage improvement along SE 2"d Place This is an existing developed street Right of way. Total drainage area = 0.334 acres (the south half right of way along the frontage of the site) Total existing impervious area = 0.229 acres Total existing pervious area = 0.105 acres (till grass, soil group C) Offsite frontage improvement along 156t" Avenue SE This is an existing developed street Right of way. Total disturbed area = 0.050 acres Total existing impervious area = 0.005 acres Total existing pervious area = 0.045 acres The 156th Avenue SE drainage system has a different drainage path from the SE 2"d Place drainage system and the onsite drainage system. All three drainage path joins to a stream that drains to the Lower Cedar River approximately 0.75 miles downstream from the site (Point of compliance). Onsite improvements Scale factor = 1.167 (Seatac) Total onsite area = 1.67 acres (assume till forest, soil group C) 22 4V4VHM2Q12 SatwantRenton File Edit View Zoom Help ❑ u��ws-0or'aaa 23 ltr4NHM2012 SatwantRenton File Edit View Help Summar/ Report REM IC If LW ;IID :Surface I nterflow Ca raundwaker Flows To IChannell -----� Channel 1 -----1 Area in Basin f' Show Only Selected Available Pervious Acres ,available Impervious Acres _ r; A113, Forest, Flat 0 r ROADS/FLAT 10 'A1B. Forest, Mod + ROADSIMOD 10 r A113, Forest, Soep j ROADS/STEEP 10 _ " AIB, Pasture, Flat 10 r ROOF TOPS/F 10 -- - AIB, Pasture, Mod 0 r DRIVEWAYS/FLAT 10 F' A1B. Pasture, Skeep 10 DRIVEWAYSi 10 I—' A1B. Lawn, Flat' 10 DRIVEWAYS/ 10 A1B, Lawn, Mod 0 SIDEWALKS/FLA T 0 A113, Lawn, Steep 0� SIDEWALKSlMOD 0 C. Forest, Flat 10 r SIDEWALKS/STEEP 10 r: C, Forest, Mod 11.67 r PARKING/FLAT 10 • C, Forest, Steep 0 r PARKING1MaD .__ • C, Pasture, Flat 10 r PARKINGISTEEP 10 F' C, Pasture, Mod 0 r POND 1 r C. Pasture, Steep r Porous Pavemenk10 C Lawn Flat C. Lawn. Mod r' C. Lawn, Steep " SAT, Forest, Flat PerviousTotal 1.67 _J Acres Impervious Total 0 Acres Basin Total 1.ta7 Acres DeselectZer0 Select By. CO 24 ij VAUHtv12012 SatvrantRenton File Edit VieW Help Summary Report ry6�9 Eb Oft =) E . ubbasin Name_ Surface lnterFlow Groundwater Flows To: IChannell HChannell ----------- Area in Basin r Show Only Selected Available Pervious Acres I— Iv r r r r 1— r r I I— I' r r o r r AIB, Forest, Flak D VB, Forest, Mod ASB, Forest, Steep V13, Pasture, Flak ASB, Pasture, Mod AIB, Pasture, Steep VB, Lawn, Flat' ASB, Lawn, Mod VB, Lawn, Steep C, Forest, Flat C, Forest, Mod C, Forest, Steep C. Pasture, Flak C, Pasture, Mod C, Pasture, Steep C, Lawn, Flat C, Lawn, Mod 14 C, Lawn, Steep 10 Available Impervious ROADS/FLAT ROADS}MOD ROADS/STEEP ROOF TOPS/FLAT DRIVEWAYSN T 10 DRIVEWAYSlMOD 10 j— DRIVEWAYS/STEEP' SIDEWALKS/FLAT SIDEWALKS/MOD SIDEWALKS/STEEP PARKING/FLAT 0 " PARKING/MOD PARKING/STEEP POND Porous Pavement Acres 0 225 a � 0 -- 0 0 -- � 0 105 r SAT, Forest, Flat 0 PerviousTotal 0.10 Acres Impervious Total Basin Total D eseleGk Zero ti^1 Acres flares 25 Available Impervious Acres 0 225 a � 0 -- 0 0 -- � 0 105 r SAT, Forest, Flat 0 PerviousTotal 0.10 Acres Impervious Total Basin Total D eseleGk Zero ti^1 Acres flares 25 '- krtWHM2012 SatwantRenton File Edit View Help Summary Report iso Suhhasin Name_ Surface Interflow Groundwater Flows To IChannell IlChannell Area in Basin r Show Only Selected Available Pervious Acres Available Impervious Acres Emi 0 r A}B, Forest, ' AIB, Forest, Mod ASB, Forest, Steep AIB, Pasture, Flak j- A1B, Pasture, Mod AIB, Pasture, Steep J ' AIB, Lawn, Flat ' A/B, Lawn, Mod j- A1B, Lawn, Stee C, Forest, Flat C, Forest, Mod j� C, Forest, Steep r C. Pasture, Flat C, Pasture, Mod (C, Pasture, Steep j- C. Lawn, Flat C, Lawn, Mod j" C, Lawn, Steep SAL Forest, Flat PerviousTotal 0.045 Acres Impervious Total O.Q05 Acres' Basin Total O.D5 Acres DeselectZ ero IItaTelta�.Y��GTi7 �' DRIVEWAYSIMOD Q 1— DRIVEWAYS/STEEP 0 SIDEWALKS/FLAT 0 SIDEWALKS/MOD 0 SIDEWALKSISTEEP 10 _ PARKING/FLAT 0 - -- PARKING/MOD 0 PARKING/STEEP 0 J- POND 0 Porous Pavement 0 select By. � GO Flow Frequency Return Periods for Predeveloped. Return Period Flow(efs) 2 year 0. If ear 193946 5 0.276802 10 year 0.339937 25 year 0.4297 50 year 0.504201 100 year 0.585572 POC #1 Flat PerviousTotal 0.045 Acres Impervious Total O.Q05 Acres' Basin Total O.D5 Acres DeselectZ ero IItaTelta�.Y��GTi7 �' DRIVEWAYSIMOD Q 1— DRIVEWAYS/STEEP 0 SIDEWALKS/FLAT 0 SIDEWALKS/MOD 0 SIDEWALKSISTEEP 10 _ PARKING/FLAT 0 - -- PARKING/MOD 0 PARKING/STEEP 0 J- POND 0 Porous Pavement 0 select By. � GO Flow Frequency Return Periods for Predeveloped. Return Period Flow(efs) 2 year 0. If ear 193946 5 0.276802 10 year 0.339937 25 year 0.4297 50 year 0.504201 100 year 0.585572 POC #1 POC #1 Part B Developed Site Hydrology Offsite frontage improvement along SE 2"d Place This is an existing developed street Right of way. Total drainage area = 0.334 acres (the south half right of way along the frontage of the site, this area will be collected and conveyed to the onsite detention vault) Total existing impervious area to remain = 0.135 acres Total new plus replaced impervious area = 0.116 acres Total impervious area = 0.251 acres Total pervious area = 0.083 acres (till grass, soil group C) Offsite frontage improvement along 156t" Avenue SE This is an existing developed street Right of way. Total disturbed area = 0.05 acres (this area will be collected and conveyed to the existing storm drainage system that runs along the east side of 156th Avenue SE and bypass the onsite detention vault) Total new and replaced impervious area = 0.02 acres Total pervious area = 0.03 acres (till grass, group C) Onsite improvement Under developed condition, onsite runoffs will be collected and conveyed to the onsite detention vault. Onsite impervious area calculation (before applying Flow control BMP credits): Roofs of lot 1 through lot 5 = 3,000 sf per lot. Roofs of lot 6 = 2,400 sf. Private, driveway, walkway and parking for 6 lots = 3,600 sf. Driveway to detention vault = 480 sf. Total impervious area = 21,480 sf. = 0.493 acres Total onsite area = 1.67 acres Total onsite pervious area = 1.67 — 0.493 = 1.177 acres (till grass, group C soil) WWHM2012 SaMantRentanDer File Edit Viev Zoom Help r•: MVHM2012 SatwantRentonDev File Edit View Help Summary Summary Report ti61196bft IID Flows Ta T Surface Area in Basin Inkerllow groundwater Available Pervious Acres r AIB, Forest, Flat 0 r AIB, Forest, Mod 0 r AIB, Forest, Steep 0 r AIB, Pasture, Flat 0 r AIB, Pasture, Mod F r AIB, Pasture, Steep r AIB, Lawn, Flat , 0 r AIB, Lawn, Mod 0 r AIB, Lawn, Steep r C, Forest, Flat 0 jV C, Forest, Mod 0 r C. Forest, Steep r C, Pasture, Flat CI r C, Pasture, Mod 0 r C; Pasture, Steep 0 r C, Lawn, Flat 0 (V C; Lawn, Mod 1.177 r C. Lawn, Steep r SAT, Forest, Flat j PerviousTokal 1.177 Acres Impervious Total 0.493: Acres Basin Total 1.67 Acres Deselect Zero _] Select By_ Show Only Selected Available Impervious Acres ROADS/FLAT 'ROADS/MOD 094 r ROADS/STEEP C ROOFTOPSIFLAT .399 r DRIVEWAYS/FLAT I" DRIVEWAYSIMOD IV r PARKINGIFLAT r PARKINGIMOD r PARKING/STEEP POND r Porous Pavement 29 Wd WtNHM2012 SatwantRentonDev File Edit View Help Summary Report D Gi 6119 JP,a Surface Interflow Groundwater Flows To : lChannell 1� (Channel 1 Area in Basin r Show Only Selected Available Pervious AIB, Forest, Flat T AIB, Foresk, Mod r AIB, Forest, Steep j- AIB, Pasture, Flat r AIB, Pasture, Mo f' AIB, Pasture, Steep r AIB, Lawn, Flat r AIB, Lawn, Mod del )— C, Pasture; Flat j Acres C. Pasture, Mo J— Co Pasture, Steep j� C, Lawn, Flat V C, Lawn, Mod C. Lawn, Steep j ;SAT, Forest, Flat PerviousTotal �( Impervious Total Basin Total Deselect Zero Acres Acres Available Impervious ROADS/FLAT � ROADS/MOD j- ROADS/STEEP ROOF TOPSIFLAT DRIVEWAYS/FLAT j DRIVEWAYS/MOD DRIVEWAYSISTEEP SIDEWALKS/FLAT Acres ]� PARKINGISTEEP POND J` PorousPavement Selec# By_ � _GO VANHM2012 SatwantRentonDe%t File Edit View Help SummaryReport ; 64 Yo a� � A W WF5t, [Z ID Subbasin Name: lflMMMMM= — I h Designate as Bypass for POC:' Surface Interflow Groundwater Flows To: IChannel 1 IChannell I Area in Basin Show Only Selected Available Pervious Acres Available Impervious Acres . r AIB, Forest, Flat 0 r ROADS/FLAT 10 F AIB, Forest, Mod 0 ROADSIMOD 02 r AIB, Forest, Steep )- ROADS/STEEP 10 AIB, Pasture, Flat 'ROOF TOPS/FLAT 0 r AIB, Pasture, Mod 0 r DRIVEWAYS/FLAT � C, Foresk, Mod ] DRIVEWAYSIMOD'i C, Forest, steep 0� r C; Pasture, Flat 0 r C. Pasture, Mod r C; Pasture, Steep , 0 C Lawn, Flat � C, Lawn, Mod ,03 r C, Lawn, Steep 0 r SAT, Forest, Flat r` .Porous Pavement �" PerviousTotal q.03 Acres Impervious Total 0.02 Acres Basin Total 0.05 Acres Deselect Zero Select By. GD Flow Frequency Return Periods for Developed condition. POC #1 (No detention and no flow control BMPs) Return Period Flow(efs) 2 year 0.553387 5 year 0.76618 10 year 0.918046 25 year 1.122584 50 year 1.284265 100 year 1.454035 31 Part C Performance Standards The site is located in Duration NOW Control Area (Forest existing condition). Since no problem has been identified within the site and its downstream area, level 2 flow control (forest existing condition) is required. Per SWDM section 1.2.3.3 and 5.2, Flow Control BMPs are required for the onsite development. Flow control BMP's for more than 10% of each lot area is required for lots 1 through 5 and Flow control BMP's for more than 20% of the lot area is required for lot 6. The feasibility and applicability of full dispersion is studied first, the study found full dispersion is not suitable for this site to fully disperse the new impervious areas and new non-native pervious areas because long native flow path is not available. Full infiltration is also not suitable for this site because onsite soil is till soil (Alderwood gravelly sandy loam, 6 to 15% slopes, AgC) according to City of Renton Soils Map. The following flow control BMPs are used: 1. Restricted footprint. Impervious area coverage in each lots will be restricted to maximum 34% of their lot sizes for lots 1 through 5 and maximum 25% for lot 6. 2. Tree retention. 4 trees along the south property lines are preserved. 3. Basic dispersion for downspouts. Downspouts of the southeast corners of the houses on lots 1 through 5 up to 700 square feet per house are treated by Basic dispersion. Down spouts of the southeast and southwest corners of the house on lot 6 up to 1,400 square feet total are treated by Basic dispersion. For lots 1 through 5: Average lot size 10,655 sf. 10% of the lot size = 1,066 sf. Total impervious area in each lot is restricted to 3,600 sf. Total impervious area treated by Restricted foot print = 4,000 — 3,600 = 400 sf. Total impervious area treated by Basic dispersion for downspouts = 700 sf. Total impervious area treated by Flow control BMPs = 1,100 sf. > 1,066 sf., o.k. For lot 6: Lot size = 12,019 sf. 20% of the lot size = 2,404 sf. Total impervious area in this lot is restricted to 2,996 sf. Total impervious area treated by Restricted foot print = 4,000 — 2,996 = 1,004 sf. Total impervious area treated by Basic dispersion for downspouts = 1,400 sf. Total impervious area treated by Flow control BMPs = 2,404 sf., o.k. Final signed Flow Control BMP Covenant is required prior permit is issued and will be recorded with the Final Short Plat map. Onsite flow control facility is provided by a detention vault to provide the required Duration Flow Control (Forest existing condition) for onsite area and offsite improvement along SE 2nd Place. 32 Since total new plus replaced pollution generating impervious area is less than 5,000 square feet, water quality treatment facility is not required. The proposed detention vault provides 1' dead storage and 0.5' sediment storage which provides enough sediment control. See Section 2 of this report regarding special requirements, the only special requirement applicable to this site is special requirement 1.3.4 for source control. Dumpsters and recycle bins will be stored in the garages of each houses. Since the site is not a high use site, oil control is not required. The new onsite conveyance system is designed per chapter 4 of the 2017 Renton SWDM to convey the 25 -year peak with 6 inches of free board and the 100 -year peak flows. For offsite frontage improvement along 156th Avenue SE, as discussed in Section 1 of this report, no flow control or water quality treatment is required. 33 Part D Flow Control System Offsite frontage improvement along SE 2"d Place This is an existing developed street Right of way. Total drainage area = 0.334 acres (the south half right of way along the frontage of the site, this area will be collected and conveyed to the onsite detention vault) Total existing impervious area to remain = 0.135 acres Total new plus replaced impervious area = 0.116 acres Total impervious area = 0.251 acres Total pervious area = 0.083 acres (till grass, soil group C) Offsite frontage improvement along 156t" Avenue SE This is an existing developed street Right of way. Total disturbed area = 0.05 acres (this area will be collected and conveyed to the existing storm drainage system that runs along the east side of 156th Avenue SE and bypass the onsite detention vault) Total new and replaced impervious area = 0.02 acres Total pervious area = 0.03 acres (till grass, group C) Onsite improvement Total onsite area = 1.67 acres Total impervious area = 21,480 sf. = 0.493 acres (before applying Flow control BMP credits) Total impervious area treated by Basic dispersion of downspouts = 7* 700 = 4,900 sf. (credited as 909/o impervious area, 10% grass) For lots 1 and 2, dispersed flow from their southeast downspout and the back yards of these two lots sheet flow to the west adjacent lot bypassing the onsite detention vault. After apply the Flow control BMP credits, onsite drainage area draining to the detention vault = 1.408 acres Impervious area = 21,480 — 43900 + (5 * 700) * 0.9 = 19,730 sf. = 0.453 acres Pervious area = 1.408 — 0.453 = 0.955 acres (till grass, group C soil) Onsite bypassed area = 0.262 acres Impervious area = 2 * 700 * 0.9 = 1,260 sf. = 0.029 scres Pervious area = 0.262 — 0.029 = 0.233 acres (till grass, group C soil) Flow control facility: A detention vault is used to provide the required Level 2 flow control (forest existing condition). 2012 WWHM method with 15 -minute time step is used to size the detention vault. 34 The proposed detention vault (74' long x 36 wide x t live storage) actuary provides Level 3 Flow control (forest existing condition) performance. VVWHM1r12612 SatwantRenton File Edit View Zoom Help 35 MVHM2012 SatwantRenton File Edit View Help Summary Report D 0 6119 % oft (M Ar 1-�l KID �1 L%10 1C & I Subbasin Name_ ® ! mu' 1 Designate as Bypass for POC: Flows To T Surface Channel 1 Interflow Groundwater Channell 11 1 Available Pervious Acres J` A1B, Forest, Fla 0 j Ale, Forest, Mod 0 J— AB, Forest, Steep A16, Pasture, Flat A1B, Pasture, Mod j j A1B, Pasture, Steep C— A1B, Lawn, Flat 0 (� A1B, Lawn, Mod 0 A1B, Lawn, Steep 0 C Forest, Flat 0 ]V C; Forest, Mod C; Forest, Steep 0 J� C. Pasture, Flak j� C, Pasture, Mod 0 j- C. Pasture, Steep 0 l— C, Lawn, Flat 1 V C, Lawn, Mod .233 J- C. Lawn, Steep 0 F SAT, Forest, Flat PerviousTotal Acres Impervious Total 0.029 ' Acres Basin Total 0.262 Acres DeseleckZero ( Select By: t—` Show Only Selected Available Impervious Acres ROADSNLAT 0 ROADSlMOD 10 J' ROADS/STEEP (o r ROOF TOPSIFLAT 1.029 j DRIVEWAYS/FLAT D DRIVEWAYSIMOD 0 'DRIVEWAYS/STEEP SIDEWALKSIFLAT D 1— SIDEWALKSIM0D SIDEWALKSISTEEP O PARKING/FLAT D `PARKINGIMOD - 10 i— PARKINGISTEEF F `POND 1 Porous Pavement 0 36 VAVHlv12012 SatwantRenton File Edit View Help SummaryReport ;Q1 0% % oft I 01 �a LW.I [Nil If I Subbasin Name: - Surface Flows To ; lVault 1 Area in Basin Available Pervious y AIB, Forest, Flak J— AIB, Forest, Mod J" AIB, Forest, Steep r AIB, Pasture, Flat j- AIB, Pasture, Mod j- AIB, Pasture, Steep r AIB, Lawn, Flat AIB, Lawn, Mod AIB, Lawn, Steep iC, Forest, Flat lv C, Forest, Mod r C, Forest, Steep J— C, Pasture, Flat j— C, Pasture, Mod JJ C, Pasture, Steep j C, Lawn, Flat r ;C, Lawn, Mod r' 'C, Lawn, Steep T r ;SAT, Forest, Flat Designate as Bypass foj I nterflow 6 roundwater Vault 1 r Show Only Selected Avilable Impervi Acres aous ROADSIFLAT ROADSIMOD ROADUSTEEP ROOF TOPS/FLAT DRIVEWAYS/FLAT DRIVEWAYS/MOD ]— DRIVEWAYS/STEEP SIDEWALKS/FLAT SIDEWALKS/MOD (" SIDEWALKS/STEEP J � f Acres �' Porous Pavement: PerviousTotal 0.955:: Acres Impervious Total D.453 Acres Basin Total 1.4D8 Acres Deselect Zero Select By: � �� GO '` MVHN12012 SatwantRenton File Edit View Help Summary Report ;611x Subbasin Name: Surface Flows To Area in Basin Available Pervious r AtB, Forest, Flat r A/8, Forest, Mod I- A/B, Forest, Steep r' AIB, Pasture, Flak r AtB, Pasture, Mod r AJB, Pasture, Steep r A/B, Lawn, Flat r• AJB, Lawn, Mod F A/B, Lawn, Steep r C, Forest, Flat I✓ C,Forest, Mod r C. Forest, Steep Acres 1 1 L I- Designate as Bypass for POC::: Interflow Ciraundwater Vault i1 —I j— Show Only Selected Available Impervious Acres jJ 'C, Lawn, Mod � .083 Lawn, Steep T r SAT, Forest, Flat 1 PerviousTotal Impervious Total Basin Total Deselect Zero 0.083.: Acres 0.251 Acres 0.334 Acres Select By. J� ; ROOF TOPSJFLAT r DRIVEWAYS/FLAT r DRIVEWAYSJMOD (— ;PARKINGIFLAT r PARKING/MOD r 'PARKING/STEEP r POND r Porous Pavement ka kNNVHM2012 SatwantRenton File Edit View Help SummaryReport D ti Subbasin Mame:(— Designake as Bypass for PQC:' Surface Interflow Groundwater Flows To lChannell lChannell Area in Basin Show Only Selected Available Pervious Acres Available Impervious Acres +� A?B, Forest, Flat 0 r ROADS/FLAT 0 g ' uo 0 �` A1B, Pasture, 5keep � C; Forest, Mod C. Forest, Steep j— C. Pasture, Flat (- C, Pasture, Mod J" SATs Forest, Flat � 0 PerviousTotal 0.03 Acres Impervious Total 0.02 Acres Basin Total 0.05 Acres Deselect Zero Select By: GO 1+ ROOF TOPSIFLAT 'iDFiIVE1NAYSlMOD � j' DRIVEWAYS/STEEP j� SIDEWALKSND T SIDEWALKS}MOD SIDEWALKS/STEEP 39 MHM2012 SatwantRenton File Edit View Help Summary Report ry ( UV lil Facility Name Downs#ream Connection !Facility Dimensions Length [ft) 74 Width (ft] 36 Effective Depth (ft) I` Outlet 1 Outle# 2 Outlet 3 Channell 10 1 Auto Vault Quick V_ cult (- Fixed Width ForAuto Vault Facility Dimension Diaqram Outlet Structure Data j Riser Height (ft) ! f Riser Diameter (in) Riser Type Flat 0.7 Notch Type Infiltration N0 ;� Orifice Diameter Height Number (in) eft) 1 11,25 Fb '- 2 1.5 �v 3.ti 3 1.875 ' 4.7 Vault Volume at Riser Head (ac4t) .433 Show Vault Table Open Table Initial Stage (ft)j Tide Gate Time Series Demand u VMHM2012 SahvantRenton File Edit View Help SummaryRepart 00®11Eha r 1 t0E-4 10E3 t0E-2 1OE9 1 10 Pc+rcani Time Exceetling raatim ( UD Duration Fbvi Freouenw Water Qua' Evap + POC1__- _POC 2_� Al Datasets Fbw Staga Precip WVlHM2012 SaMiantRenton File Edit View Hdp Summary Report W1 ��' ID f.0 Cumulative ProbabilAy 1.0 `xx x x ,+, +++ _..+ + + + 501 tl x x x - E01 0.01 0.01 0.6 1 2 5 10 20 30 W 70 80 90 95 98 9999.51 SUeam Rded'wn Draatbn � LID Owalion Fb,w Frxxx.riru � Water Qua4v � HwLowach Analyze datasets CompactWDM Evap POC1 POC2 Al Datasets Fbw Stage Prec� Facility PASSP.D h Flox (c£s) Predev Mit Percentage Pass/Pail 0.0970 2945 F 65 Pass 040 0 1695 67 Pass 0.1052 0.30 O 71 J 0.1093 1929 0.20 1 t0E-4 10E3 t0E-2 1OE9 1 10 Pc+rcani Time Exceetling raatim ( UD Duration Fbvi Freouenw Water Qua' Evap + POC1__- _POC 2_� Al Datasets Fbw Staga Precip WVlHM2012 SaMiantRenton File Edit View Hdp Summary Report W1 ��' ID f.0 Cumulative ProbabilAy 1.0 `xx x x ,+, +++ _..+ + + + 501 tl x x x - E01 0.01 0.01 0.6 1 2 5 10 20 30 W 70 80 90 95 98 9999.51 SUeam Rded'wn Draatbn � LID Owalion Fb,w Frxxx.riru � Water Qua4v � HwLowach Analyze datasets CompactWDM Evap POC1 POC2 Al Datasets Fbw Stage Prec� Facility PASSP.D h Flox (c£s) Predev Mit Percentage Pass/Pail 0.0970 2945 1934 65 Pass 0.1011 2502 1695 67 Pass 0.1052 2182 3.564 71 Pass 0.1093 1929 1447 75 Pass 0.1134 1703 1324 77 Pass 0.1175 2503 1228 81 Pass 0.1217 1309 1128 86 Pass 0.1258 1178 1039 88 Pass 0.1299 1055 943 89 Pass 0.1340 945 849 89 Pass 0.1381 800 749 93 Pass 0.1422 708 665 93 Pass 0.1463 612 532 95 Pass 0.1504 544 506 93 Pass 7.1546 484 440 90 Pass 7.1587 440 366 83 Pass 7.1628 396 298 75 ..Pass 7.1669 357 250 70 Pass 0.1710 314 198 63 Pass 7.1751 277 173 62 Pass 0.1792 ::245 154 62 Pass ].1834 224 149 56 Pass ].1875 ::203 136 66 . Pass ].1916 155 128 69 Pass ].1957 163 119 73 Pass ].1998 .146 116 79 Pass ).2039 134 110 82 Pass ].2080 116 103 '88 Pass ].2121 111 98 88 Pass ].2163 104 92 88 : Pass 1.2204 95 87 91 Pass ].2245 :86 85 98 Pass ).2286 79 ED 101 .Pass ).2327 76 77 101 Pass v Plox Fregpenay Plox (ofs) Predeveloped Mitigated 2 Year - ::0.1939 0.1132 5 Year - 0.2768 0.1633 LO Year = 0.3399 0.2009 25 Year = 0.4297 0.2538 50 Year - 0.5042 0.2972 L00 Year = 0.5856 0.3442 4nnna1 Peaks 1949 0.2992 .0.1462 1950 0.2690 0.1510 1951 0.2085 0.1844 1952 0.1273 0.0752 1953 0.1029 0.0686 1954 0.1585 0.0896 1955 0.1638 '0.3007 1956 0.1911 0.1054 1957 .0.2114 0.1267 1958 0.1369 '..0.0788 1959 0.1277 :. 0.0750 1960 0.2375 0.1789 1961 0.1676 0.1055 1962 0.1012 0.0621 1963 0.1742 0.0987 1964 0.1798 0.1009 3965 0.1960 0.1067 1966 0.1380 0.0772 1967 0.2969 0.1542 3968 0.2205 0.1206 1969 .0.1654 0.1167 1970 0.1821 .0.1033 1971 0.1977 0.1274 1972 0.2382 0.1352 1973 0.1173 0.0746 1974 0.2130 0.1087 1975 0.2274 0.1345 197b 0.1810 0.1001 v 41 VNYMM2012 SatwantRenton File Edit Yew Help SummaryRepart CGo®1yoEheft DM M 0111 11. 10.0 Z- Cumulative Probabililj 0.1 0.5 1 7 25 Year 5.2430 Stream Protection Duation Stage Fregaenay 10.0 (feet) 1001 2 Year - 2.3245 5 Year - 3.4168 10 Year = 4.1969 5 10 20 30 b0 70 84 W 95 98 9999.5 LID Dwation 1999 .Flow Freouer I Waley Qua€ty I Hyc WWHM2012 PROJECT REPORT Project Name: SatwantRenton Site Name: SE 2nd Pl Short Plat Site Address: 13609 156th Ave SE City 0Renton Report Date: 5/1/2017 Gage &Seatac Data Start : 1948/10/01 Data End 2009/09/30 Precip Scale: 1.17 Version 2013/11/20 0.1 = 50 Year = 6.0646 L00 Year = 6.9213 Annna1 Peaks 1999 1.9492 1950 2.5722 1951 4.6324 1952 1.3771 1953 1.5089 1954 2.1788 1955 " 2.8071 1956 2.8218 1957 2.2144 1958 2.1719 1959 1.7973 1960 4.2545 1961 2.0844 1962 1.1768 1963 2.1187 1969 2.0016 1965 2.1971 1966 1.6352 1967 2.6043 1968 1.6684 1969 1.8640 1970 .1.9086 1971 2.4726 1972 3.6844 1973 1.7330 1979 2.0196 1975 2.6451 1976 2.3297 Low Flow Threshold for POC 1 50 Percent of the 2 Year High Flow Threshold for POC 1: 50 year PREDEVELOPED LAND USE Name Onsite Bypass: No Groundwater: No Pervious Land Use Acres 42 C, Forest, Mod 1.67 Pervious Total 1.67 Impervious Land Use Acres Impervious Total 0 Basin Total 1.67 Element Flows To: Surface Channel 1 Interflow Channel 1 Name SE 2nd Pl Frontage Bypass: No GroundWater: No Pervious Land Use Acres C, Lawn, Mod .105 Pervious Total 0.105 Impervious Land Use Acres ROADS MOD 0.229 Impervious Total 0.229 Basin Total 0.334 Element Flows To: Surface Channel 1 Interflow Channel 1 Name 156 Ave SE Front Bypass: No GroundWater: No Pervious Land Use Acres C, Lawn, Mod .045 Pervious Total 0.045 Impervious Land Use Acres ROADS MOD 0.005 Impervious Total 0.005 Groundwater Groundwater 43 Basin Total Element Surface Channel Flows To: 1 0.05 Interflow Channel 1 Name Channel 1 Bottom Length: 10.00 ft. Bottom Width: 5.00 ft. Manning's n: 0.03 Channel bottom slope l: 0 Channel Left side slope Channel right side slope Discharge Structure Riser Height: 0 ft. Riser Diameter: 0 in. .025 To 1 0: 3 To 1 2: 3 To 1 Element Flows To: Outlet 1 Outlet 2 Channel Hydraulic Table Groundwater Stage(ft) Area(ac) Volume(ac-ft) Discharge(cfs) Infilt(cfs) 0.0000 0.001 0.000 0.000 0.000 0.0222 0.001 0.000 0.069 0.000 0.0444 0.001 0.000 0.220 0.000 0.0667 0.001 0.000 0.435 0.000 0.0889 0.001 0.000 0.706 0.000 0.1111 0.001 0.000 1.028 0.000 0.1333 0.001 0.000 1.400 0.000 0.1556 0.001 0.000 1.818 0.000 0.1778 0.001 0.000 2.282 0.000 0.2000 0.001 0.000 2.791 0.000 0.2222 0.001 0.000 3.343 0.000 0.2444 0.001 0.000 3.938 0.000 0.2667 0.001 0.000 4.576 0.000 0.2889 0.001 0.000 5.257 0.000 0.3111 0.001 0.000 5.979 0.000 0.3333 0.001 0.000 6.743 0.000 0.3556 0.001 0.000 7.550 0.000 0.3778 0.001 0.000 8.398 0.000 0.4000 0.001 0.000 9.288 0.000 0.4222 0.001 0.000 10.22 0.000 0.4444 0.001 0.000 11.19 0.000 0.4667 0.001 0.000 12.21 0.000 0.4889 0.001 0.000 13.26 0.000 0.5111 0.001 0.000 14.36 0.000 0.5333 0.001 0.000 15.51 0.000 0.5556 0.001 0.000 16.69 0.000 0.5778 0.001 0.000 17.92 0.000 0. 6000 0.002 0.000 19.20 0.000 0.6222 0.002 0.001 20.51 0.000 0.6444 0.002 0.001 21.87 0.000 0.6667 0.002 0.001 23.28 0.000 0.6889 0.002 0.001 24.73 0.000 0.7111 0.002 0.001 26.22 0.000 0.7333 0.002 0.001 27.76 0.000 0.7556 0.002 0.001 29.34 0.000 0.7778 0.002 0.001 30.97 0.000 0.8000 0.002 0.001 32.64 0.000 0.8222 0.002 0.001 34.36 0.000 0.8444 0.002 0.001 36.13 0.000 0.8667 0.002 0.001 37.94 0.000 0.8889 0.002 0.001 39.81 0.000 0.9111 0.002 0.001 41.71 0.000 0.9333 0.002 0.001 43.67 0.000 0.9556 0.002 0.001 45.67 0.000 0.9778 0.002 0.001 47.73 0.000 1.0000 0.002 0.001 49.83 0.000 1.0222 0.002 0.001 51.98 0.000 1.0444 0.002 0.002 54.18 0.000 1.0667 0.002 0.002 56.43 0.000 1.0889 0.002 0.002 58.72 0.000 1.1111 0.002 0.002 61.07 0.000 1.1333 0.002 0.002 63.47 0.000 1.1556 0.002 0.002 65.92 0.000 1.1778 0.002 0.002 68.43 0.000 1.2000 0.002 0.002 70.98 0.000 1.2222 0.002 0.002 73.59 0.000 1.2444 0.002 0.002 76.24 0.000 1.2667 0.002 0.002 78.95 0.000 1.2889 0.002 0.002 81.72 0.000 1.3111 0.003 0.002 84.53 0.000 1.3333 0.003 0.002 87.41 0.000 1.3556 0.003 0.002 90.33 0.000 1.3778 0.003 0.002 93.31 0.000 1.4000 0.003 0.003 96.34 0.000 1.4222 0.003 0.003 99.43 0.000 1.4444 0.003 0.003 102.5 0.000 1.4667 0.003 0.003 105.7 0.000 1.4889 0.003 0.003 109.0 0.000 1.5111 0.003 0.003 112.3 0.000 1.5333 0.003 0.003 115.7 0.000 1.5556 0.003 0.003 119.1 0.000 1.5778 0.003 0.003 122.6 0.000 1.6000 0.003 0.003 126.1 0.000 1.6222 0.003 0.003 129.7 0.000 1.6444 0.003 0.003 133.4 0.000 1.6667 0.003 0.003 137.1 0.000 1.6889 0.003 0.003 140.9 0.000 1.7111 0.003 0.004 144.7 0.000 1.7333 0.003 0.004 148.6 0.000 1.7556 0.003 0.004 152.5 0.000 1.7778 0.003 0.004 156.5 0.000 1.8000 0.003 0.004 160.6 0.000 1.8222 0.003 0.004 164.8 0.000 1.8444 0.003 0.004 169.0 0.000 1.8667 0.003 0.004 173.2 0.000 1.8889 0.003 0.004 177.5 0.000 1.9111 ft. 12 in. Orifice 0.003 0.004 Orifice 2 Diameter: 181.9 1. 0.000 3 Diameter: 1.9333 1. 0.003 0.004 186.4 0.000 1.9556 0.003 0.004 190.9 0.000 1.9778 0.003 0.005 195.4 0.000 2.0000 0.003 0.005 200.1 0.000 2.0222 0.004 0.005 204.8 0.000 MITIGATED LAND USE Name Onsite to vault Bypass: No Groundwater: No Pervious Land Use Acres C, Lawn, Mod .955 Pervious Total 0.955 Impervious Land Use Acres ROADS MOD 0.094 ROOF TOPS FLAT 0.359 Impervious Total 0.453 Basin Total 1.408 Element Surface Vault 1 Flows To: Name Vault 1 Width 36 ft. Length : 74 ft. Depth: 7 ft. Discharcre Structure Riser Height: 7 Riser Diameter: 25 ft. 12 in. Orifice 1 Diameter: 1. Orifice 2 Diameter: 1. Orifice 3 Diameter: 1. Element Flows To: Outlet 1 Channel 1 Interflow Vault 1 Groundwater in. Elevation: 0 ft. 5 in. Elevation: 3.6 ft. 875 in. Elevation: 4.7 ft. Outlet 2 Vault Hydraulic Table Stage(ft) Area(ac) Volume(ac-ft) Diacharge(efa) Infilt(efa) 0.0000 0.061 0.000 0.000 0.000 0.0778 0.061 0.004 0.011 0.000 0.1556 0.061 0.009 0.016 0.000 0.2333 0.061 0.014 0.019 0.000 0.3111 0.061 0.019 0.022 0.000 0.3889 0.061 0.023 0.025 0.000 0.4667 0.061 0.028 0.028 0.000 0.5444 0.061 0.033 0.030 0.000 0.6222 0.061 0.038 0.032 0.000 0.7000 0.061 0.042 0.034 0.000 0.7778 0.061 0.047 0.036 0.000 0.8556 0.061 0.052 0.038 0.000 0.9333 0.061 0.057 0.039 0.000 1.0111 0.061 0.061 0.041 0.000 1.0889 0.061 0.066 0.042 0.000 1.1667 0.061 0.071 0.044 0.000 1.2444 0.061 0.076 0.045 0.000 1.3222 0.061 0.080 0.047 0.000 1.4000 0.061 0.085 0.048 0.000 1.4778 0.061 0.090 0.049 0.000 1.5556 0.061 0.095 0.051 0.000 1.6333 0.061 0.099 0.052 0.000 1.7111 0.061 0.104 0.053 0.000 1.7889 0.061 0.109 0.054 0.000 1.8667 0.061 0.114 0.056 0.000 1.9444 0.061 0.118 0.057 0.000 2.0222 0.061 0.123 0.058 0.000 2.1000 0.061 0.128 0.059 0.000 2.1778 0.061 0.133 0.060 0.000 2.2556 0.061 0.137 0.061 0.000 2.3333 0.061 0.142 0.062 0.000 2.4111 0.061 0.147 0.063 0.000 2.4889 0.061 0.152 0.064 0.000 2.5667 0.061 0.157 0.065 0.000 2.6444 0.061 0.161 0.066 0.000 2.7222 0.061 0.166 0.067 0.000 2.8000 0.061 0.171 0.068 0.000 2.8778 0.061 0.176 0.069 0.000 2.9556 0.061 0.180 0.070 0.000 3.0333 0.061 0.185 0.071 0.000 3.1111 0.061 0.190 0.072 0.000 3.1889 0.061 0.195 0.073 0.000 3.2667 0.061 0.199 0.074 0.000 3.3444 0.061 0.204 0.075 0.000 3.4222 0.061 0.209 0.075 0.000 3.5000 0.061 0.214 0.076 0.000 3.5778 0.061 0.218 0.077 0.000 3.6556 0.061 0.223 0.092 0.000 3.7333 0.061 0.228 0.100 0.000 3.8111 0.061 0.233 0.107 0.000 3.8889 0.061 0.237 0.112 0.000 3.9667 0.061 0.242 0.117 0.000 4.0444 0.061 0.247 0.121 0.000 4.1222 0.061 0.252 0.126 0.000 4.2000 0.061 0.256 0.129 0.000 4.2778 0.061 0.261 0.133 0.000 4.3556 0.061 0.266 0.137 0.000 4.4333 0.061 0.271 0.140 0.000 4.5111 0.061 0.275 0.143 0.000 4.5889 0.061 0.280 0.146 0.000 4.6667 0.061 0.285 0.149 0.000 47 4.7444 0.061 0.290 0.172 0.000 4.8222 0.061 0.294 0.187 0.000 4.9000 0.061 0.299 0.199 0.000 4.9778 0.061 0.304 0.209 0.000 5.0556 0.061 0.309 0.218 0.000 5.1333 0.061 0.313 0.226 0.000 5.2111 0.061 0.318 0.234 0.000 5.2889 0.061 0.323 0.242 0.000 5.3667 0.061 0.328 0.249 0.000 5.4444 0.061 0.333 0.255 0.000 5.5222 0.061 0.337 0.262 0.000 5.6000 0.061 0.342 0.268 0.000 5.6778 0.061 0.347 0.274 0.000 5.7556 0.061 0.352 0.280 0.000 5.8333 0.061 0.356 0.285 0.000 5.9111 0.061 0.361 0.291 0.000 5.9889 0.061 0.366 0.296 0.000 6.0667 0.061 0.371 0.301 0.000 6.1444 0.061 0.375 0.307 0.000 6.2222 0.061 0.380 0.312 0.000 6.3000 0.061 0.385 0.316 0.000 6.3778 0.061 0.390 0.321 0.000 6.4556 0.061 0.394 0.326 0.000 6.5333 0.061 0.399 0.331 0.000 6.6111 0.061 0.404 0.335 0.000 6.6889 0.061 0.409 0.340 0.000 6.7667 0.061 0.413 0.344 0.000 6.8444 0.061 0.418 0.349 0.000 6.9222 0.061 0.423 0.353 0.000 7.0000 0.061 0.428 0.357 0.000 7.0778 0.061 0.432 0.573 0.000 7.1556 0.000 0.000 0.963 0.000 Name Onsite Dispersed Bypass: No Groundwater: No Pervious Land Use Acres C, Lawn, Mod .233 Pervious Total 0.233 Impervious Land Use Acres ROOF TOPS FLAT 0.029 Impervious Total 0.029 Basin Total 0.262 Element Flows Surface Channel 1 To: Interflow Channel 1 Groundwater Name SE 2nd Pl Front Bypass: No Groundwater: No Pervious Land Use Acres C, Lawn, Mod .083 Pervious Total 0.083 Impervious Land Use Acres ROADS MOD 0.251 Impervious Total 0.251 Basin Total 0.334 Element Flows To: Surface Vault 1 Interflow Vault 1 Name 156th AVE SE Front Bypass: No Groundwater: No Pervious Land Use Acres C, Lawn, Mod .03 Pervious Total 0.03 Impervious Land Use Acres ROADS MOD 0.02 Impervious Total 0.02 Basin Total 0.05 Element Flows To: Surface Channel 1 Interflow Channel 1 Name Channel 1 Bottom Length: 10.00 ft. Bottom Width: 5.00 ft. Manning's n: 0.03 Channel bottom slope 1: 0.025 To 1 Channel Left side slope 0: 3 To 1 Groundwater Groundwater Channel right side slope 2: 3 TO 1 Discharge Structure Riser Height: 0 ft. Riser Diameter: 0 in. Element Flows To: Outlet 1 Outlet 2 Channel Hydraulic Table Stage(ft) Area(ac) Volume(ac-ft) Discharge(cfs) Infilt(cfs 0.0000 0.001 0.000 0.000 0.000 0.0222 0.001 0.000 0.069 0.000 0.0444 0.001 0.000 0.220 0.000 0.0667 0.001 0.000 0.435 0.000 0.0889 0.001 0.000 0.706 0.000 0.1111 0.001 0.000 1.028 0.000 0.1333 0.001 0.000 1.400 0.000 0.1556 0.001 0.000 1.818 0.000 0.1778 0.001 0.000 2.282 0.000 0.2000 0.001 0.000 2.791 0.000 0.2222 0.001 0.000 3.343 0.000 ).2444 0.001 0.000 3.938 0.000 0.2667 0.001 0.000 4.576 0.000 0.2889 0.001 0.000 5.257 0.000 0.3111 0.001 0.000 5.979 0.000 0.3333 0.001 0.000 6.743 0.000 0.3556 0.001 0.000 7.550 0.000 0.3778 0.001 0.000 8.398 0.000 0.4000 0.001 0.000 9.288 0.000 0.4222 0.001 0.000 10.22 0.000 0.4444 0.001 0.000 11.19 0.000 0.4667 0.001 0.000 12.21 0.000 0.4889 0.001 0.000 13.26 0.000 0.5111 0.001 0.000 14.36 0.000 0.5333 0.001 0.000 15.51 0.000 0.5556 0.001 0.000 16.69 0.000 0.5778 0.001 0.000 17.92 0.000 0.6000 0.002 0.000 19.20 0.000 0.6222 0.002 0.001 20.51 0.000 0.6444 0.002 0.001 21.87 0.000 0.6667 0.002 0.001 23.28 0.000 0.6889 0.002 0.001 24.73 0.000 0.7111 0.002 0.001 26.22 0.000 0.7333 0.002 0.001 27.76 0.000 0.7556 0.002 0.001 29.34 0.000 0.7778 0.002 0.001 30.97 0.000 0.8000 0.002 0.001 32.64 0.000 0.8222 0.002 0.001 34.36 0.000 0.8444 0.002 0.001 36.13 0.000 0.8667 0.002 0.001 37.94 0.000 0.8889 0.002 0.001 39.81 0.000 0.9111 0.002 0.001 41.71 0.000 0.9333 0.002 0.001 43.67 0.000 0.9556 0.002 0.001 45.67 0.000 0.9778 0.002 0.001 47.73 0.000 50 1.0000 0.002 0.001 49.83 0.000 1.0222 0.002 0.001 51.98 0.000 1.0444 0.002 0.002 54.18 0.000 1.0667 0.002 0.002 56.43 0.000 1.0889 0.002 0.002 58.72 0.000 1.1111 0.002 0.002 61.07 0.000 1.1333 0.002 0.002 63.47 0.000 1.1556 0.002 0.002 65.92 0.000 1.1778 0.002 0.002 68.43 0.000 1.2000 0.002 0.002 70.98 0.000 1.2222 0.002 0.002 73.59 0.000 1.2444 0.002 0.002 76.24 0.000 1.2667 0.002 0.002 78.95 0.000 1.2889 0.002 0.002 81.72 0.000 1.3111 0.003 0.002 84.53 0.000 1.3333 0.003 0.002 87.41 0.000 1.3556 0.003 0.002 90.33 0.000 1.3778 0.003 0.002 93.31 0.000 1.4000 0.003 0.003 96.34 0.000 1.4222 0.003 0.003 99.43 0.000 1.4444 0.003 0.003 102.5 0.000 1.4667 0.003 0.003 105.7 0.000 1.4889 0.003 0.003 109.0 0.000 1.5111 0.003 0.003 112.3 0.000 1.5333 0.003 0.003 115.7 0.000 1.5556 0.003 0.003 119.1 0.000 1.5778 0.003 0.003 122.6 0.000 1.6000 0.003 0.003 126.1 0.000 1.6222 0.003 0.003 129.7 0.000 1.6444 0.003 0.003 133.4 0.000 1.6667 0.003 0.003 137.1 0.000 1.6889 0.003 0.003 140.9 0.000 1.7111 0.003 0.004 144.7 0.000 1.7333 0.003 0.004 148.6 0.000 1.7556 0.003 0.004 152.5 0.000 1.7778 0.003 0.004 156.5 0.000 1.8000 0.003 0.004 160.6 0.000 1.8222 0.003 0.004 164.8 0.000 1.8444 0.003 0.004 169.0 0.000 1.8667 0.003 0.004 173.2 0.000 1.8889 0.003 0.004 177.5 0.000 1.9111 0.003 0.004 181.9 0.000 1.9333 0.003 0.004 186.4 0.000 1.9556 0.003 0.004 190.9 0.000 1.9778 0.003 0.005 195.4 0.000 2.0000 0.003 0.005 200.1 0.000 2.0222 0.004 0.005 204.8 0.000 ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC #1 Total Pervious Area:1.82 51 Total Impervious Area:0.234 Mitigated Landuse Totals for POC #1 Total Pervious Area:1.301 Total Impervious Area:0.753 Flow Frequency Return Return Period 2 year 5 year 10 year 25 year 50 year 100 year Periods for Flow (cfs) 0.193946 0.276802 0.339937 0.4297 0.504201 0.585572 Predeveloped. POC #1 Flow Frequency Return Periods for Mitigated. Return Period Flow(efs) Protection Duration 2 year 0.113206 Peaks for Predeveloped and 5 year 0.163253 Predeveloped Mitigated 1949 10 year 0.200891 0.146 25 year 0.253786 0.270 0.151 50 year 0.297213 0.209 100 year 0.344213 1952 0.127 Stream Protection Duration Annual Peaks for Predeveloped and Mitigated Year Predeveloped Mitigated 1949 0.299 0.146 1950 0.270 0.151 1951 0.209 0.184 1952 0.127 0.075 1953 0.103 0.069 1954 0.158 0.090 1955 0.164 0.101 1956 0.191 0.105 1957 0.211 0.127 1958 0.137 0.079 1959 0.128 0.075 1960 0.238 0.179 1961 0.168 0.105 1962 0.101 0.062 1963 0.174 0.099 1964 0.180 0.101 1965 0.196 0.107 1966 0.138 0.077 1967 0.297 0.154 1968 0.220 0.121 1969 0.165 0.117 1970 0.182 0.103 1971 0.198 0.127 1972 0.238 0.135 1973 0.117 0.075 1974 0.213 0.109 1975 0.227 0.134 1976 0.181 0.100 1977 0.144 0.075 POC #1 POC #1 52 1978 0.187 Mitigated 0.094 1 1979 0.193 0.3434 0.076 2 1980 0.429 0.2898 0.175 3 1981 0.172 0.2845 0.107 4 1982 0.311 0.2541 0.239 5 1983 0.184 0.2388 0.102 6 1984 0.135 0.2127 0.073 7 1985 0.138 0.2034 0.100 8 1986 0.215 0.1936 0.126 9 1987 0.207 0.1844 0.142 10 1988 0.112 0.1789 0.067 11 1989 0.169 0.1765 0.060 12 1990 0.596 0.1751 0.254 13 1991 0.376 0.1638 0.203 14 1992 0.164 0.1542 0.089 15 1993 0.131 0.1510 0.073 16 1994 0.102 0.1503 0.055 17 1995 0.150 0.1462 0.096 18 1996 0.347 0.1417 0.213 19 1997 0.230 0.1352 0.177 20 1998 0.183 0.1345 0.108 21 1999 0.430 0.1280 0.194 22 2000 0.179 0.1274 0.100 2001 0.156 0.086 2002 0.239 0.164 2003 0.298 0.128 2004 0.344 0.284 2005 0.184 0.115 2006 0.178 0.108 2007 0.498 0.290 2008 0.447 0.343 2009 0.255 0.150 Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated Rank Predeveloped Mitigated 1 0.5958 0.3434 2 0.4981 0.2898 3 0.4469 0.2845 4 0.4296 0.2541 5 0.4290 0.2388 6 0.3761 0.2127 7 0.3473 0.2034 8 0.3443 0.1936 9 0.3106 0.1844 10 0.2992 0.1789 11 0.2978 0.1765 12 0.2969 0.1751 13 0.2698 0.1638 14 0.2546 0.1542 15 0.2390 0.1510 16 0.2382 0.1503 17 0.2375 0.1462 18 0.2304 0.1417 19 0.2274 0.1352 20 0.2205 0.1345 21 0.2154 0.1280 22 0.2130 0.1274 POC #1 53 23 0.2114 0.1267 24 0.2085 2182 0.1264 1564 25 0.2069 0.1206 26 0.1977 1324 0.1167 1503 27 0.1960 0.1151 28 0.1931 1178 0.1087 1039 29 0.1911 0.1079 30 0.1871 849 0.1076 800 31 0.1841 0.1075 32 0.1839 0.1067 33 0.1832 0.1055 34 0.1821 0.1054 35 0.1810 0.1033 36 0.1798 0.1023 37 0.1793 0.1009 38 0.1784 0.1007 39 0.1742 0.1001 40 0.1717 0.1001 41 0.1693 0.0996 42 0.1676 0.0987 43 0.1654 0.0964 44 0.1639 0.0940 45 0.1638 0.0896 46 0.1585 0.0890 47 0.1561 0.0860 48 0.1498 0.0788 49 0.1437 0.0772 50 0.1380 0.0764 51 0.1377 0.0752 52 0.1369 0.0750 53 0.1348 0.0746 54 0.1312 0.0746 55 0.1277 0.0732 56 0.1273 0.0725 57 0.1173 0.0686 58 0.1116 0.0670 59 0.1029 0.0621 60 0.1024 0.0605 61 0.1012 0.0548 Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) 0.0970 Predev Mit 0.1011 0.1052 0.1093 0.1134 0.1175 0.1217 0.1258 0.1299 0.1340 0.1381 2945 1934 2502 1695 2182 1564 1929 1447 1703 1324 1503 1228 1309 1128 1178 1039 1055 943 945 849 800 749 Percentage 65 67 71 75 77 81 86 88 89 89 93 Pass/Fail Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass 54 0.1422 708 665 93 Pass 0.1463 612 582 95 Pass 0.1504 544 506 93 Pass 0.1546 484 440 90 Pass 0.1587 440 366 83 Pass 0.1628 396 298 75 Pass 0.1669 357 250 70 Pass 0.1710 314 198 63 Pass 0.1751 277 173 62 Pass 0.1792 245 154 62 Pass 0.1834 224 149 66 Pass 0.1875 203 136 66 Pass 0.1916 185 128 69 Pass 0.1957 163 119 73 Pass 0.1998 146 116 79 Pass 0.2039 134 110 82 Pass 0.2080 116 103 88 Pass 0.2121 111 98 88 Pass 0.2163 104 92 88 Pass 0.2204 95 87 91 Pass 0.2245 86 85 98 Pass 0.2286 79 80 101 Pass 0.2327 76 77 101 Pass 0.2368 70 71 101 Pass 0.2409 60 64 106 Pass 0.2451 57 58 101 Pass 0.2492 51 51 100 Pass 0.2533 47 48 102 Pass 0.2574 45 42 93 Pass 0.2615 40 31 77 Pass 0.2656 39 24 61 Pass 0.2697 36 17 47 Pass 0.2738 33 12 36 Pass 0.2780 32 9 28 Pass 0.2821 30 8 26 Pass 0.2862 29 5 17 Pass 0.2903 29 4 13 Pass 0.2944 29 3 10 Pass 0.2985 25 2 8 Pass 0.3026 23 2 8 Pass 0.3068 23 2 8 Pass 0.3109 22 2 9 Pass 0.3150 20 2 10 Pass 0.3191 17 1 5 Pass 0.3232 17 1 5 Pass 0.3273 14 1 7 Pass 0.3314 14 1 7 Pass 0.3356 14 1 7 Pass 0.3397 14 1 7 Pass 0.3438 14 1 7 Pass 0.3479 12 0 0 Pass 0.3520 11 0 0 Pass 0.3561 11 0 0 Pass 0.3602 10 0 0 Pass 0.3643 10 0 0 Pass 0.3685 10 0 0 Pass 0.3726 10 0 0 Pass 0.3767 9 0 0 Pass 0.3808 8 0 0 Pass 55 0.3849 and Volume for 8 0 0 Pass 0.3890 8 0 0 Pass 0.3931 7 0 0 Pass 0.3973 7 0 0 Pass 0.4014 7 0 0 Pass 0.4055 7 0 0 Pass 0.4096 7 0 0 Pass 0.4137 7 0 0 Pass 0.4178 7 0 0 Pass 0.4219 7 0 0 Pass 0.4260 7 0 0 Pass 0.4302 5 0 0 Pass 0.4343 5 0 0 Pass 0.4384 5 0 0 Pass 0.4425 5 0 0 Pass 0.4466 5 0 0 Pass 0.4507 4 0 0 Pass 0.4548 4 0 0 Pass 0.4590 3 0 0 Pass 0.4631 3 0 0 Pass 0.4672 3 0 0 Pass 0.4713 3 0 0 Pass 0.4754 3 0 0 Pass 0.4795 3 0 0 Pass 0.4836 3 0 0 Pass 0.4877 3 0 0 Pass 0.4919 2 0 0 Pass 0.4960 2 0 0 Pass 0.5001 1 0 0 Pass 0.5042 1 0 0 Pass Water Quality BMP Flow and Volume for POC #1 On-line On-line Adjusted Off-line Adjusted facility volume: facility target for 15 min: 0.0284 facility target for 15 min: 0.0189 0.0563 acre-feet flow: 0.0284 cfs. flow: 0.0189 cfs. cfs. cfs. LID Report LID Technique Used for Total Volumn Percent Water Quality Percent Comment Treatment? Needs Volumn Water Quality Treatment Infiltrated Treated (ac -ft Channel 1 POC N 255 18 0.00 Vault I 0.00 Total Volume Infiltrated 0.00 0.00 0% Compliance with LID Standard 8 Duration Analysis Result = Failed . N 221.44 Volumn Infiltration Cumulative Through Volumn Volumn Facility (ac -ft) Infiltration ac -ft) Credit N QN1 476.62 0.00 0.00 No Treat. Credit 56 Flow Frequency Return Periods for Return Period Flow(cfs) 2 year 0.193946 5 year 0.276802 10 year 0.339937 25 year 0.4297 50 year 0.504201 100 year 0.585572 Predeveloped. POC #1 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(efs) 2 year 0.113206 5 year 0.163253 10 year 0.200891 25 year 0.253786 50 year 0.297213 100 year 0.344213 Part E Water Quality System Total new plus replaced pollution generating impervious area is less than 5,000 square feet, no water quality treatment facility is required. All onsite driveways are treated by pervious concrete pavement Flow control BMP and can be consider treated. For offsite improvements total pollution generating impervious area is reduced and no new pervious area is created, no mitigation is required. s7 V. Conveyance System Analysis and Design Conveyance system calculation will be provided at the phase of construction design. VI. Special Reports and Studies Special Reports related to this project: • Geotechnical Report. Limited Stormwater &Geologic Hazard Evaluation prepared by Cobalt Geosciences, August 22, 2016 - updated April 12, 2017. • Arborist Report. Greenforest Incorporated, April 14, 2017 59 Vu. Other Permits Water Service through King County Water District #90 Sewer Service through City of Renton Right -of -Way permits through City of Renton Franchised utilities (power, cable, gas, etc.) through individual utility purveyors NPDES Permit Through WA State Department of Ecology VIII. CSWPPP Analysis and Design ESC Plan Analysis and Design (Part A) TEMPORARY EROSION AND SEDIMENT CONTROL 1. The grading for this project is limited to the onsite improvement and offsite frontage improvement. Temporary Erosion and Sedimentation Control will be provided by utilizing BMPs selected from the 2017 Renton Surface Water Design Manual. These BMPS will likely include, but are not necessarily limited to construction entrance for traffic stabilization, silt fencing for parameter protection, plastic sheeting of stockpiles, straw mulch, hydro -seeding of exposed areas, catch basin protection, etc. All new impervious areas and new pervious areas will be treated by a detention vault for Duration flow control (forest existing condition). At the beginning of the construction, construction entrance and silt fence along the grading limit will be installed. Then, combined detention/wet vault will be installed. Temporary erosion and sediment control facilities will be maintained during construction period and will be removed after construction is finished. Temporary erosion and sediment control plan, notes and details to be provided at construction plan stage. A Stormwater Pollution Prevention and Spill (SWPPS) plan will also be provided at construction plan stage. 2. The site is sloped, no sensitive area exists onsite. No special measure is proposed. Temporary sediment trap sizing: Q2y using WWHM method with 15 -minute time step: Flow Frequency Return Periods for Mitigated. POC #1 (Before detention) Return Period Flow(cfs) 2 year 0.419887 5 0.591157 0.712288 year 10 year 25 year 50 year 100 year Qty = 0.42 cfs Required surface area = 2080 *Q2y = 2080 * 0.42 = 874 sf. The proposed temporary sediment trap is located at the northwest corner of the site. A temporary overflow path is provided to over flow to the existing 12 storm that runs along SE 2nd Place. EROSION AND SEDIMENT CONTROL STANDARDS: ESC measures shall be applied and maintained to prevent, to the maximum extent practicable, the transport of sediment from the project site to downstream drainage systems or surface waters. This performance is intended to be achieved through proper 61 0.873986 1.000687 1.132724 Qty = 0.42 cfs Required surface area = 2080 *Q2y = 2080 * 0.42 = 874 sf. The proposed temporary sediment trap is located at the northwest corner of the site. A temporary overflow path is provided to over flow to the existing 12 storm that runs along SE 2nd Place. EROSION AND SEDIMENT CONTROL STANDARDS: ESC measures shall be applied and maintained to prevent, to the maximum extent practicable, the transport of sediment from the project site to downstream drainage systems or surface waters. This performance is intended to be achieved through proper 61 selection, installation, and operation of the above ESC measures as detailed in the ESC Standard (detached Appendix D) and approved by the City of Renton. PERMANENT EROSION AND SEDIMENT CONTROL For Permanent Erosion and Sedimentation Control, driveways and walkways will be paved. Landscape areas will be covered with grass, trees and ground covers. All onsite new imaervious areas and new oervious areas will be treated by the detention vault for Flow control (Duration, forest existing condition). 62 STORMWATER POLLUTION PREVENTION AND SPILL (SWPPS) PLAN (Part B) 63 X. Bond Quantities, Facility Summaries and Declaration of Covenant X. Operations and Maintenance Manual The onsite storm facilities will be maintained by the property owner and manager. 65