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HomeMy WebLinkAboutRS_TIR_20210112_v3 furrengineering.com Technical Information Report ROPPE SINGLE FAMILY RESIDENCE Renton, Washington – King County Parcel # 1423059097 14005 160TH Ave. SE For: Vicki and Dale Roppe July 21, 2020 Revised: October 05, 2020 Revised: January 07, 2021 Prepared by: Dean A. Furr, P.E. FES Project #20053 01/07/2021 R G G N A FU R SEF O R P I ANO EL T S GE SI N ERE DEEATDSNTAWFO . SAHI INREENOTR46937 Table of Contents 1.0 PROJECT OVERVIEW ..................................................................................................... 1 TECHNICAL INFORMATION REPORT WORKSHEET ............................................................. 2 2.0 CONDITIONS AND REQUIREMENTS SUMMARY .......................................................... 8 Analysis of the Nine Core Requirements .......................................................................... 8 Analysis of the Five Special Requirements .....................................................................10 3.0 OFF-SITE ANALYSIS ......................................................................................................12 DEFINE AND MAP THE STUDY AREA ..........................................................................12 RESOURCE REVIEW ....................................................................................................14 Lower Cedar River Basin ................................................................................................14 No mapped floodplains exist on site. ...............................................................................14 Drainage Complaints ......................................................................................................16 Field Inspection ...............................................................................................................22 Drainage System Description and Problem Description ..................................................22 4.0 STORMWATER ANALYSIS AND DESIGN .....................................................................25 Existing Site Hydrology ...................................................................................................25 Developed Site Hydrology...............................................................................................26 Fontage Improvements: ................................................................................................................................... 26 100-year Peak Runoff Exception ...................................................................................................................... 27 Small Lot BMP Evaluation ............................................................................................................................... 27 Water Quality ..................................................................................................................28 Flood Plain ......................................................................................................................28 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN.......................................................33 6.0 SPECIAL REPORTS AND STUDIES ...............................................................................35 7.0 OTHER PERMITS ............................................................................................................36 8.0 ESC ANALYSIS AND DESIGN ........................................................................................37 9.0 BOND QUANTITIES ........................................................................................................38 10.0 OPERATIONS AND MAINTENANCE MANUAL ..............................................................54 Page 1 1.0 PROJECT OVERVIEW The Roppe Single Family Residence project is in Renton, Washington. The site is bound by rural residential homes to the west, north and south and 106th Ave SE to the east. More generally, the site is located within the SW 1/4 of the SE ¼, Section 14, Township 23 North Range 5 East WM. The project area consists of a single parcel #1423059097, 14005 160TH Ave. SE and approximately 0.5ac in size. The site takes access from an existing driveway along the south property line to 160th Ave SE. The site can be characterized as sloping to the southeast and is covered with grass and some trees, typical of rural/urban landscaping. Stormwater runoff flows to the southeast and enters the existing drainage system within the street. Per the Geotechnical Evaluation performed by NGA, Inc., the site is underlain by 3 feet of undocumented fill. Underlying the fill is native glacial till. A pit test was performed on 4ft x 3ft x 45ft deep infiltration pit. The infiltration test was performed in accordance with the 2017 City of Renton Surface Design Manual. Due to the perched groundwater and dense nature of the underlying glacial till, the geotechnical opinion is that “infiltration within the site is not feasible”, see page 10 of the report. The proposal is to construct a Single Family Residence, includes off-site frontage improvements (curb, gutter and sidewalk and driveway cut), landscaping and associated utilities. The existing on-site paved driveway will remain. The project on-off site plans on disturbing approximately 14,327sf and 6,352sf of new+replaced impervious surface. The project is required to utilize on-site stormwater management techniques to the maximum extent feasible. The parcel is under 22,000sf and is considered “Small Lot” per Appendix C, Forested land cover over Group C soil. The facility will be sized to Flow Control Duration Standard – Matching Forested Conditions using WWHM 2012. The project stormwater discharge will be analyzed and mitigated in accordance with the 2017 City of Renton Surface Water Design Manual (CoRSWDM). Page 2 TECHNICAL INFORMATION REPORT WORKSHEET Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 2.0 CONDITIONS AND REQUIREMENTS SUMMARY Hearing Examiners TBD Analysis of the Nine Core Requirements Core Requirement #1: Discharge at the Natural Location The intent of this requirement is to “prevent adverse impacts to downstream properties caused by diversion of flow from one flowpath to another, and to discharge in a manner that does not significantly impact downhill properties or drainage systems,”. The existing site drains to the east into the existing drainage system along 160th Ave SE. The proposed discharge will maintain the same natural drainage pattern. Core Requirement #2: Off-Site Analysis The intent of this requirement is to identify and evaluate off-site flooding and erosion problems that may be created or aggravated by the proposed project and to ensure appropriate measures are provided for preventing creation or aggravation of those problems. A complete of-site analysis is located in Section 2 of this report Core Requirement #3: Flow Control The intent is to ensure the minimum level of control needed to protect downstream properties and resources from increases in peak, duration, and volume of runoff generated by new development. Basic Exemption: 1. Less than 5,000sf of new plus replaced impervious surface AND 2. Less than ¾ acres of new pervious surface will be added The project must COMPLY with CR#3 because the 6,352sf (new+replaced) impervious surface is greater than 5,000sf. Conservation Flow Control is waived for any Threshold Discharge Area in which there is no more than 0.15cfs difference (WWHM 15min) modeling. 100yr Exist. flow = 0.0513cfs (15min) 100yr Dev. flow = 0.1641cfs (15min) The difference is 0.11cfs, therefore, Conservation Flow Control is not required. Core Requirement #4: Conveyance System The intent of this requirement is to ensure proper design and construction of engineered conveyance system elements. Page 9 The conveyance system will be designed to convey the 25-yr and 100yr storm events. See Section 5.0 of this report. Core Requirement #5: Erosion and Sediment Control The intent of this requirement is to prevent the transport of sediment and other impacts, such as increased runoff, related to land disturbing activities. A temporary Erosion and Sedimentation Control (TESC) Plan has been prepared as part of the Civil Plan Set. The TESC Plan will identify BMP’s that will aid in controlling the transport of sediment and turbid stormwater to downstream surface waters and adjacent properties in accordance with all the applicable standards of the CORSWDM and the Department of Ecology Stormwater Management Manual.. Core Requirement #6: Maintenance and Operations The intent is to ensure that the maintenance responsibility for drainage facilities is clearly assigned and that these facilities will be properly maintained and operated in perpetuity. Operations and Maintenance instructions are included in Section 10.0. Core Requirement #7: Financial Guarantees and Liability This requirement is intended to ensure financial guarantees are posted to sufficiently cover the cost of correcting, if necessary, incomplete or substandard drainage facility construction work, and to warrant for two years the satisfactory performance and maintenance of those newly-constructed drainage facilities to be assumed by PRIVATE OWNERSHIP for maintenance and operation. Applicable guarantees will be provided for the project as required by the city. Core Requirement #8: Water Quality The intent of the water quality requirement is "to require an efficient, cost-effective level of water quality treatment tailored to the sensitivities and resource protection needs of the downstream receiving water to which the project site drains." and "Core Requirement No. 8 requires that water quality treatment facilities be provided to remove pollutants from runoff discharging from the project site." Basic Exemption: 1. Less than 5,000sf of new plus replaced PGIS AND 2. Less than ¾ acres of new PGPS will be added The project is EXEMPT from CR#8 because the project proposes to add 690sf PGIS. See Section 4.4 of this report Core Requirement #9: Flow Control BMP’s The intent of the flow control BMP’s is to provide mitigation of hydrologic impacts that are not possible/practical to mitigate with a flow control facility. Flow control BMP’s seek to Page 10 reduce runoff volumes and flashiness and increase groundwater recharge by reducing imperviousness and making use of the pervious portions of the development sites to maximize infiltration and retention of stormwater onsite. The goal is to apply flow control BMP’s to new impervious and pervious surfaces, replaced impervious surfaces, and existing impervious surfaces added since January 8, 2001 to the maximum extent feasible without causing flooding or erosion impacts. The proposed project WILL utilize “Small Lot” BMP because the lot is 21,785sf. See Section 4.0 The project site soils are not conducive to infiltration. Analysis of the Five Special Requirements Special Requirement No. 1: Other Adopted Area-Specific Requirements. The following is a list of other possible adopted area-specific requirements according to the CORSWDM: Critical Drainage Areas: This development is not located within a critical drainage area. Master Drainage Plan: There are no special requirements for the existing storm drainage system associated with this project. Salmon Conservation Plan: A Salmon Conservation Plan does not apply to this development. Lake Management Plan: This development is not located with a Lake Management Plan. Shared Facility Drainage Plan: The project does not propose to connect to a shared detention facility system or create a shared facility. This plan does not apply. Special Requirement No. 2: Flood Hazard Area Delineation. Review of the FEMA Flood Map shows the site is outside of the 100 year floodplain. Special Requirement No. 3: Flood Protection Facilities. Special Requirement No. 3 is not applicable to the proposed site because the site does not meet either of the conditions set forward in the CORSWDM: • Contains or is adjacent to a Class 1 or 2 stream that has an existing flood protection facility (such as a levee, revetment, or berm). • Proposed to construct a new or to modify an existing flood protection facility. The design of the site will not affect any existing flood protection facilities. Special Requirement No. 4: Source Control. Page 11 Special Requirement No. 4 will be met through a variety of on-site source control BMPs. This includes the good housekeeping practices and maintenance. Special Requirement No. 5: Oil Control. The proposed building/site is not classified as a high-use site as defined in the CORSWDM. Special Requirement No. 6: Aquifer Protection Area (APA) Special Requirement #6 is not applicable because the project site is not located within an APA. Page 12 3.0 OFF-SITE ANALYSIS DEFINE AND MAP THE STUDY AREA The offsite Analysis was prepared in accordance with Core Requirement #2, of the 2017 City of Renton Surface Water Design Manual (Manual). The site is located at 14005 160TH Ave. SE, Renton. Bound to the south, west and north by single family residences and the east by 160th Ave. SE. The site is covered with landscaping, typical for urban development. The project is located on the east side of ridge located along the west property line. The project slopes to the southeast at 3% slope. There is insignificant runon from the west or north. See Figure 1 and Figure 2 for maps of the study area. Figure 1: King County Vicinity Map Page 13 Figure 2: King County IMAP TOPOGRAPHY Page 14 RESOURCE REVIEW Adopted Basin Plans: Lower Cedar River Basin Floodplan/Floodway (FEMA) Map No mapped floodplains exist on site. Other Offsite Analysis Report: As part of the research, we have reviewed the Downstream Drainage Analysis for the Mindy’s Place Developed on the east side of the 160th. Sensitive Areas Folio Maps Review of the Environmentally Sensitive Areas Maps on King County’s IMAP website and other Reports o A Potential landslide hazard area (2016) is NOT on or adjacent to a the project o A Potential landslide hazard area 50-foot buffer (2016) is NOT on, adjacent or downstream of the project o A Landslide hazard (1990) is NOT on, adjacent or downstream of the project o A Potential steep slope hazard area (2016) is NOT on, adjacent or downstream of the project o A LOW Basin Condition (2005 CAO) IS located within the project o A Shoreline condition (2005 CAO) is NOT on, adjacent or downstream of the project o A Erosion hazard (1990 SAO) is NOT on, adjacent or downstream of the project o A Seismic hazard (1990 SAO) is NOT on, adjacent or downstream of the project o A Coal mine hazard (1990 SAO) is NOT on, adjacent or downstream of the project o A Stream (1990 SAO) is NOT on or adjacent to the project. o The project is NOT on or adjacent to a Wetland (1990 SAO). o The project is NOT on or adjacent to properties that have Sensitive area notice on title. o A Chinook distribution is NOT on, adjacent or downstream of the project o A Wildlife network is NOT on, adjacent or downstream of the project o A Channel migration hazard area is NOT on, adjacent or downstream of the project Groundwater o A Groundwater source IS located adjacent to the project. Page 15 o Well Detail Well ID S_472836122073701 Location Name OUIMET Well Type Well Well Depth (ft) 32 Surface Elevation (ft) 390 X Coord (WAN-SPF) 1320522.5 Y Coord (WAN-SPF) 176564.015625 Has Water Level Data? No Has Water Quality Data? No Local Number 23N/05E-14Q01 Ecology Well Tag Unknown Parcel Number GWMA Code Other Basin Lower Cedar River CARA Area None City King County o A Groundwater quality sampling site is NOT on, adjacent or downstream of the project o The project is NOT within the King County Groundwater management area o The project IS located on, adjacent or downstream of a LOW Area susceptible to groundwater contamination o The project is NOT within A Critical aquifer recharge area. o The project is NOT within a Sole source aquifer. Page 16 o A Wellhead protection area (one year) is NOT on, adjacent or downstream of the project o A Wellhead protection area (five year) is NOT on, adjacent or downstream of the project o The project IS within a Wellhead protection area (ten year). o The project IS within the King County Water District 90 Water District. Drainage Complaints Review of IMAP shows there are several drainage complaints on and downstream of the project site. It appears that all of the complaints have been closed. Figure 3: Downstream Drainage Map\Drainage complaints The drainage complaints listed below begin with the project parcel and continue in order of downstream drainage path and terminates a ¼ mile downstream. Page 17 Parcel: 1457500105 Drainage complaints Drainage complaints Complaint number 2002-0766 Complaint number 1997-0423 Complaint type C Complaint type CL Date received Date received Problem DTA Problem FLDG Date closed 12/25/2002 Date closed 12/17/1997 Address 14028 160TH AVE SE Address 14028 160TH AVE SE Parcel 1457500105 Parcel 1457500105 Comments COMPLAINANT REQUESTED TECHNICAL ASSISTANCE TO RESOLVE HISTORIC FLOODING PROBLEM. INFOR PROVIDED AND WILL SEND TO ROADS FOR THEIR REVIEW Comments ROADSIDE DITCH OVERFLOW-160TH AVE SE Tracker ID 27594 Tracker ID 22021 Complaint number 1997-0203 Complaint number 2001-0344 Complaint type C Complaint type WQC Date received Date received Problem FLDG Problem WQO Date closed 2/10/1997 Date closed 6/21/2001 Address 14028 160TH AVE SE Address 13644 160TH AVE SE Parcel 1457500105 Parcel 1457500090 Comments OVERFLOW FROM D/W CULV IMPACT PVT PROP Comments IRON OXIDE DISCHARGE FROM PIPE OUTLET Tracker ID 21791 Tracker ID 25868 Complaint number 1982-0520 Complaint number 2000-0322 Complaint type C Complaint type WQC Page 18 Date received Date received Problem FLDG Problem WQI Date closed 2/24/1982 Date closed 5/25/2000 Address 13612 160TH AVE SE Address 13612 160TH AVE SE Parcel 1457500085 Parcel 1457500085 Comments Comments APPARENT IRON OXIDE BACTERIA IN DISCHARGE FROM PIIPE. SOURCE OF FLOW TO PIPE NOT IDENTIFIED Tracker ID 3578 Tracker ID 2160 Parcel: 5547540080 Drainage complaints Drainage complaints Complaint number 2000-0322 Complaint number 1982-0520 Complaint type WQC Complaint type C Date received Date received Problem WQI Problem FLDG Date closed 5/25/2000 Date closed 2/24/1982 Address 13612 160TH AVE SE Address 13612 160TH AVE SE Parcel 1457500085 Parcel 1457500085 Comments APPARENT IRON OXIDE BACTERIA IN DISCHARGE FROM PIIPE. SOURCE OF FLOW TO PIPE NOT IDENTIFIED Comments Tracker ID 2160 Tracker ID 3578 Complaint number 2001-0344 Complaint type WQC Date received Problem WQO Date closed 6/21/2001 Address 13644 160TH AVE SE Parcel 1457500090 Comments IRON OXIDE DISCHARGE FROM PIPE OUTLET Page 19 Tracker ID 25868 Parcel: 1457500115 Drainage complaints Complaint number 2000-0322 Complaint number 2001-0344 Complaint type WQC Complaint type WQC Date received Date received Problem WQI Problem WQO Date closed 5/25/2000 Date closed 6/21/2001 Address 13612 160TH AVE SE Address 13644 160TH AVE SE Parcel 1457500085 Parcel 1457500090 Comments APPARENT IRON OXIDE BACTERIA IN DISCHARGE FROM PIIPE. SOURCE OF FLOW TO PIPE NOT IDENTIFIED Comments IRON OXIDE DISCHARGE FROM PIPE OUTLET Tracker ID 2160 Tracker ID 25868 Complaint number 1982-0520 Complaint type C Date received Problem FLDG Date closed 2/24/1982 Address 13612 160TH AVE SE Parcel 1457500085 Comments Tracker ID 3578 Parcel: 1397510110 Drainage complaints Complaint number 2018-0946 Complaint type R Date received Page 20 Problem DTA Date closed 8/29/2018 Address 15845 SE 143RD ST Parcel 1397510110 Comments RUNOFF FROM CUL-DE-SAC. - TA PROVIDED FOR IMPROVED INFILTRATION/DISPERSION. Tracker ID 43540 Parcel: 1472230200 Drainage complaints Drainage complaints Complaint number 2009-0163 Complaint number 2009-0349 Complaint type FI Complaint type FIR Date received Date received Problem REM Problem REM Date closed 2/18/2009 Date closed 7/8/2019 Address 16023 SE 144TH ST Address 16023 SE 144TH ST Parcel 2323059044 Parcel 2323059044 Comments 18.6%. Comments STOPPED BY SITE ON JUNE 23, 2009 AND EXPLAINED TO BILL SPIRY SPECIFICALLY WHAT I NEEDED IN ORDER TO CONSIDER THIS SITE RESIDENTIAL. Tracker ID 33804 Tracker ID 33996 Complaint number 2009-0349 Complaint type FIH Date received Problem REM Date closed 7/8/2019 Address 16023 SE 144TH ST Parcel 2323059044 Page 21 Comments STOPPED BY SITE ON JUNE 23, 2009 AND EXPLAINED TO BILL SPIRY SPECIFICALLY WHAT I NEEDED IN ORDER TO CONSIDER THIS SITE RESIDENTIAL. Tracker ID 34326 Page 22 Field Inspection Date: April 29, 2020 Time: 12:00pm Weather Observation: mostly sunny, 58ºF, 3mph wind in a SSW direction 24-hour precipitation: 0.04 inches (wunderground website) Monthly Precipitation: 1.7 inches (wunderground website) Precipitation 10/1/19 to 4/1/20: 29.79 inches (wunderground website) A field investigation was performed by Dean A. Furr, P.E. of Furr Engineering Services to determine the existing upstream and downstream storm drainage patterns. Drainage System Description and Problem Description Upstream There is no significant upstream drainage, because it the west edge of the site is on a North to South ridge, where the ground slopes down to the south east. Downstream Stormwater sheet flows 52ft “A” and enters a CB “B” on the west side which is the beginning of the existing drainage system within 160th Ave SE. Stormwater flows south within a 12” pipe “C” for 60lf and enters a CB “D”. Stormwater flows through a 12” pipe “E” for 62ft and enters a CB “F”. Stormwater continues to flow south through a 12” pipe “G” for 75ft and discharges “H” into a vegetated ditch “I” and flows for 30ft. The stormwater enters a 12” culvert inlet “J” and flows south through a 12” pipe “K” and enters a CB “L”. The stormwater flows southeast under 160th Ave SE through a 12” pipe “M” for 68ft and discharges through a culvert outlet “N”. Stormwater enters onto private property and flows through a vegetated ditch “O” in a southeast direction for approximately 955ft to the terminus of the quarter mile downstream. See the exhibit and table in the following this pages. 4,538 378 Roppe SFR Downstream This map is a user generated static output from an Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. None 5/22/2020 Legend 2570129 THIS MAP IS NOT TO BE USED FOR NAVIGATION Feet Notes 257 WGS_1984_Web_Mercator_Auxiliary_Sphere Information Technology - GIS RentonMapSupport@Rentonwa.gov City and County Labels City and County Boundary Addresses Parcels Network Structures Access Riser Inlet Manhole Utility Vault Clean Out Unknown Control Structures Pump Stations Discharge Points Water Quality Detention Facilities Pond Tank Vault Bioswale Wetland Other Stormwater Mains Culverts Open Drain Facility Outlines A SITE B C D E F G H I J K L M N O 1/4MILE Basin Lower Cedar River Subbasin Name:Subbasin Number: DrainageDrainage ComponentSlopeDistanceExisting PotentialObservations of field inspectorComponent Type, Descriptionfrom siteProblemsProblemsresource reviewer, or residentName, and SizedischargeType: sheet flow, swale,constrictions, under capacity, ponding, see mapstream, channel, pipe, drainage basin, vegetation, cover, %1/4 mi = 1,320 ftovertopping, flooding, habitat or organismtributary area, likelihood of problem, pond; Size: diameter,depth, type of sensitive area, volumedestruction, scouring, bank sloughing,overflow pathways, potential impacts.surface areasedimentation, incision, other erosionSITE DISCHARGE0'A sheet flow Asphalt 3.5% 52 none observed none observed Ditch is functioning as intendedB Catch Basin Catch Basin w/standard grate - 0 none none observed Grate is functioning as intendedC 12" Pipe 60LF betweein catch basins ? 112 none none No noticable obstructionsD Catch Basin Catch Basin w/standard grate - 0 none none Grate is functioning as intendedE 12" Pipe 62LF pipe between catch basins ? 174 none none No noticable obstructionsF Catch Basin Catch Basin w/standard grate - 0 none none Grate is functioning as intendedG 12" Pipe 75LF pipe discharge into ditch ? 249 none nonecouldn't lift the CB cover, assume the pipe is functioningH Culvert outlet 12" outlet into vegetated ditch - 0Pipe outlet is partially burriedrestricted flow excavate ditch to outlet IEI Ditch 30lf vegetated roadside ditch ? 280 none noneDitch is functioning as intended, but should be excavated to create a new flow line from outlet IEJ Culvert inlet Inlet to 12" pipe - 0 none debris blockage No noticable obstructionsK 12" Pipe 17LF pipe between ditch and cb ? 297 none none No noticable obstructionsL Catch Basin Catch Basin w/standard grate - 0 none none Grate is functioning as intendedM 12" Pipe68LF pipe between CB and outfall on east side of road? 365 none none No noticable obstructionsN Culvert outlet12" outlet into vegetated ditch onto privat property- 0 vegetated outlet restricted flow excavate ditch to outlet IEO Vegetated Channelchannel on private property - unable to inspect? 1320 nonedebris blockage, scouringchannel on private property - unable to inspectthe termination of the 1/4mi. (1,320ft)OFF-SITE ANALYSIS DRAINAGE SYSTEM TABLESurface Water Design Manual, Core Requirement #2Symbol Page 25 4.0 STORMWATER ANALYSIS AND DESIGN The project is required to utilize on-site stormwater management techniques to the maximum extent feasible. The parcel is under 22,000sf and is considered “Small Lot” per Appendix C, Forested land cover over Group C soil. The facility will be sized to Flow Control Duration Standard – Matching Forested Conditions using WWHM 2012. The project stormwater discharge will be analyzed and mitigated in accordance with the 2017 City of Renton Surface Water Design Manual (CoRSWDM). Existing Site Hydrology The project area consists of a single parcel #1423059097, 14005 160TH Ave. SE and approximately 0.5ac in size. The site takes access from an existing driveway along the south property line to 160th Ave SE. The site can be characterized as sloping to the southeast 3% and is covered with grass and some trees, typical of rural/urban landscaping. Stormwater runoff enters the existing drainage system within the street. Per the Geotechnical Evaluation performed by NGA, Inc., the site is underlain by 3 feet of undocumented fill. Underlying the fill is native glacial till. A pit test was performed on 4ft x 3ft x 45ft deep infiltration pit. The infiltration test was performed in accordance with the 2017 City of Renton Surface Design Manual. Due to the perched groundwater and dense nature of the underlying glacial till, the geotechnical opinion is that “infiltration within the site is not feasible”, see page 10 of the report, please see the Geotechnical Report in Section 6.0. See the following existing conditions area breakdown table and the Existing Conditions Exhibit at the end of this section. EXISTING CONDITIONS sf ac PARCEL AREA 21,785.40 0.50 ON-SITE DISTURBED AREA 12,065 0.28 OFF-SITE DISTURBED AREA 2,262 0.05 ON-SITE sf ac IMPERVIOUS 9,408 0.22 HOUSE(TBR) 3,270 0.08 GARAGE 519 0.01 CARPORT(TBR) 243 0.01 SHED 1 251 0.01 SHED 2(TBR) 191 0.00 SHED 3(TBR) 16 0.00 GAZEBO 101 0.00 EX. CIRCULAR DRIVE(TBR) 1,361 0.03 MAIN DRIVEWAY (SOUTH) 3,457 0.08 Page 26 PERVIOUS (LS) 12,377 0.28 OFF-SITE sf ac DRIVEWAY/PAVING 1,167 0.03 PGIS PERVIOUS (LS) 1,095 0.03 Table 1: Existing Conditions area breakdown Developed Site Hydrology The proposal is to construct a Single Family Residence, includes frontage improvements (curb, gutter and sidewalk and driveway cut). The existing ON-SITE paved driveway will remain and is not included in the following area breakdown. TOTAL ON/OFF-SITE DEV sf ac DISTURBED AREA 14,327 0.33 IMPERVIOUS 6,352 0.146 >> 5,000sf CR #3 REQ’D HOUSE 4,701 0.108 SIDEWALK 961 0.022 DRIVEWAY 690 0.016 PGIS << 5,000sf PERVIOUS (LS) 7,975 0.183 Modeled as Pasture because it is amended soil Table 2: Lot area break down Fontage Improvements: The project is required to widen the 160th Ave. SE., which will require the existing drainage ditch at the north east corner to be shortened and install a new CB, 54” Type 2 along the flow line inline of the existing 24” SD and re-align a new 24” SD pipe culvert. The reconstructed driveway will add 690sf. See Developed Conditions Exhibit at the end of this section. The project requires frontage improvements. See the following OFF-SITE break down table. PROP. OFF-SITE DEVELOPMENT sf ac DISTURBED AREA 2,262 0.05 IMPERVIOUS 1,287 0.030 DRIVEWAY/CG (PGIS) 690 0.016 PGIS << 5,000sf SIDEWALK 597 0.014 PERVIOUS (LS) 975 0.022 Table 3: Proposed Off-site area breakdown Page 27 100-year Peak Runoff Exception The facility requirement in Conservation Flow Control Areas is waived for a TDA in which there is no more than a 0.15-cfs difference (when modeled using 15 min. time steps) for the 100-yr peak flows. See the following tables showing the existing and developed runoff using WWHM 2012 (15min. time steps) Flow Frequency Flow Frequency Flow(cfs) 0501 15m Flow(cfs) 0801 15m 2 Year = 0.0129 2 Year = 0.0726 5 Year = 0.0213 5 Year = 0.0944 10 Year = 0.0276 10 Year = 0.1098 25 Year = 0.0365 25 Year = 0.1306 50 Year = 0.0437 50 Year = 0.1469 100 Year = 0.0513 100 Year = 0.1641 0.11cfs<<0.15cfs Table 4: existing and developed runoff The previous table shows a 0.11cfs increase in runoff, which is less than 0.15cfs threshold for . The developed runoff also assumes that the all pervious areas within the disturbed area will be treated with the Post Construction Soil Amendment and is modeled as pasture. Small Lot BMP Evaluation The area will be analyzed against C.1.2.9.2.1 SMALL LOT BMP. 1. Full Dispersion: The feasibility of full dispersion has been evaluated and the area does not comply, because the impervious area percentage is greater than 15% compared to the NGPA tract area as well as, the sum of the impervious and pervious area is greater than 35%. Furthermore, the site does not contain native vegetation. 2. Full Infiltration of Roof Runoff: The geotechnical opinion is that “traditional stormwater infiltration within the site is not feasible”, see page 10 of the report. 3. If Requirements of #1 and #2 above can’t be mitigated, then the site must be evaluated per the following list below. a. Full Infiltration: The geotechnical opinion is that “traditional stormwater infiltration within the site is not feasible”, see page 10 of the report. b. Limited Infiltration: The geotechnical opinion is that “traditional stormwater infiltration within the site is not feasible”, see page 10 of the report. c. Rain Garden: The impermeable layer “Glacial Till” makes this BMP infeasible. The geotechnical opinion is that “traditional stormwater infiltration within the site is not feasible”, see page 10 of the report. Page 28 d. Bioretention: The impermeable layer “Glacial Till” makes this BMP infeasible. The geotechnical opinion is that “traditional stormwater infiltration within the site is not feasible”, see page 10 of the report. e. Permeable Pavement: The impermeable layer “Glacial Till” makes this BMP infeasible. The geotechnical opinion is that “traditional stormwater infiltration within the site is not feasible”, see page 10 of the report. 4. If Requirements #1, #2, #3 above can’t be mitigated, then the site must be evaluated per the Basic Dispersion List below. a. Splash Block: This BMP will be used on two portions (700sf) of the roof section shown on the developed conditions exhibit which have a 50ft vegetated flow path. b. Rock Pad: This BMP will not be used because a splash block is recommended. c. Graveled Fill Trench: This BMP will be used on 3,301sf of roof area. The vegetated flow path will be maintained for the 47ft dispersion trench. d. Sheet Flow: A small portion of the sidewalk will be mitigated by this BMP. 5. If Requirements #1, #2, #3 and #4 above can’t be mitigated, then the site must be evaluated per the Basic Dispersion List below. NOT EVALUATED 6. Soil Amendment: Feasible. All disturbed pervious areas will be amended per KCC 16.82, either using post-construction standard OPTION 2, 3 OR 4. Water Quality This site is not subject to Basic Water Quality treatment, because it has less than 5,000sf of PGIS. Flood Plain Review of the King County Flood map shows that this property is outside of the 100-year flood Zone. BSBLBSBL BSBL BSBLBSBL CARPORTTBRSHED3TBRASPHALT TBRph 206.890.82914715 142nd Pl. SW #B,Edmonds, WA 9802640202010FEETSCALE:01 INCH = 20DAF5/7/202020053NEXISTING CONDITIONS DITCH ALONG 160th AVE SE RDRDRDRDRDRDRDRD RDRD RD RD RDBSBLBSBL BSBL BSBLBSBL PROPOSEDHOUSEPORCHPORCHRD25.0'VEGETATED FLOW PATHph 206.890.82914715 142nd Pl. SW #B,Edmonds, WA 9802640202010FEETSCALE:01 INCH = 20DAF5/13/202020053NDEVELOPED CONDITIONS NEW INLET INTO EXISTNGSTORM SYSTEMLANDSCAPNGWITH STREETTREESLEGEND700SF OF NW CORNER TO SPLASH BLOCK3,301SF PORTION OF ROOF TO 47LF DISPERSION TRENCH700SF OF NORTH SECTION TO SPLASH BLOCK47LF DISPERION TRENCHYARD DRAIN50LF VEGETATED FLOW PATHSPLASH BLOCKNEW 24"SD PIPENEW 54" SDMHCONNECTED TO EXISTING24"SD PIPE Page 31 WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: EX vs DEV Site Name: Roppe SFR Site Address: City : Renton Report Date: 1/7/2021 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.17 Version Date: 2019/09/13 Version : 4.2.17 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Flat .33 Pervious Total 0.33 Impervious Land Use acre Impervious Total 0 Basin Total 0.33 Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Pasture, Flat .183 Page 32 Pervious Total 0.183 Impervious Land Use acre ROOF TOPS FLAT 0.108 DRIVEWAYS FLAT 0.016 SIDEWALKS FLAT 0.022 Impervious Total 0.146 Basin Total 0.329 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.33 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.183 Total Impervious Area:0.146 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.012892 5 year 0.021254 10 year 0.027602 25 year 0.036473 50 year 0.043668 100 year 0.051344 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.072611 5 year 0.094396 10 year 0.109843 25 year 0.130567 50 year 0.146911 100 year 0.164052 ___________________________________________________________________ Page 31 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN The project proposes to use on-site bmps that are prescriptive and do not need conveyance analysis. The project proposes to install a new 24” CPEP culvert at the end of the existing ditch along 160th Ave SE and connected to a 54”SDMH along the flow line of the new curb line. The Mindys Place development across the street was required to upgrade the storm system for the discharge of the ditch. Review of the Mindys Place analysis of the upstream flow (see following this sheet) determined that the developed flow is approximately 20.16cfs (100 yr). The project proposes to install a 24” CPEP, N12 at 3.20% to proposed 54”SDMH and connect to the existing 24” CPEP system within 160th Ave SE.. Using Mannings equation Mannings equation D(in) 24 D(ft) 2.000 S (ft/ft) 0.0320 n 0.012 R (ft) 0.500 R (ft) 0.500 The Qfull flow for the 24” pipe is 43.96cfs and the 60% full is 26.38cfs which is greater than 20.16cfs. So it can be said that the proposed pipe has capacity. Page 32 Figure 4: Upstream Analysis along 160th Ave SE, by DMP, Inc. dated 9/18/2015 Page 33 6.0 SPECIAL REPORTS AND STUDIES Geotechnical Engineering Evaluation, by NGA, Inc. Roppe Residence Development, dated March 9, 2020. Page 34 7.0 OTHER PERMITS The following permits and/or approvals are thought to be required as part of this project: • Clearing and Grading Permit • Right-Of-Way use Permit • Land Use Permit Page 35 8.0 ESC ANALYSIS AND DESIGN TESC measures are put into place to prevent sediment from leaving the site. The site is generally flat. The proposed TESC plan will include, but not be limited to, the following guidelines set in the 2016 CORSWDM in order to comply with Core Requirement No. 5. A SWPPP will be provided at Final Approval 1. Clearing Limits – Clearing limits specify the boundary of the work to be done. Clearing are defined on the TESC plans and will be flagged in the field. 2. Cover Measures – Cover measures are involved (typically) with the means to control erosion of exposed soil and are specified on the TESC plans. 3. Perimeter Protection – Perimeter protection keeps site sediment from leaving the construction site. This type of protection typically involves a silt fence. The silt fence and clearing limits are shown on the TESC plans. 4. Traffic Area Stabilization – Traffic area stabilization is addressed by a stabilized construction entrance. 5. Sediment Retention – Retention will be established by silt fences around the perimeter and catch basin inserts that will control of the on-site sediment-laden water. 6. Surface Water Collection – An interceptor ditch with check dams is shown in the plans and will be implemented in the field if necessary. 7. Dewatering Control – Any water from dewatering shall be filtered or contained so sediment can filter out prior to discharge downstream. 8. Dust Control – Dust control will be provided by sprinkling. 9. Wet Season Construction – Construction will be conducted according to the jurisdiction’s standards during the wet season. 10. Construction Within Sensitive Areas and Buffers - Any construction within the wetland buffer will be subject to sensitive areas restrictions and is contained in the TESC notes. 11. Maintenance – Maintenance requirements are detailed in the TESC notes within the engineering plans. 12. Final Stabilization – Upon completion of the project, all disturbed areas will be stabilized and Best Management Practices removed. Page 36 9.0 BOND QUANTITIES See the following Bond Quantities Worksheets Page 37 Page 38 Page 39 Page 40 Page 41 Page 42 Page 43 Page 44 Page 45 Page 46 Page 47 Page 48 Page 49 Page 50 Page 51 Page 52 10.0 OPERATIONS AND MAINTENANCE MANUAL The drainage facilities on this project will be private facilities owned and maintained by the Owner. See the following. Page 53 Page 54 Page 55