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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
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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
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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.
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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
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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
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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
___________________________________________________________________
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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.
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Figure 4: Upstream Analysis along 160th Ave SE, by DMP, Inc. dated 9/18/2015
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6.0 SPECIAL REPORTS AND STUDIES
Geotechnical Engineering Evaluation, by NGA, Inc. Roppe Residence Development,
dated March 9, 2020.
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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
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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.
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9.0 BOND QUANTITIES
See the following Bond Quantities Worksheets
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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.
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