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1404 Grady LLC
SW Grady Way Office and Shop Building
Technical
Information Report
Prepared for:
1404 Grady LLC
10650 9th Pl, Unit 1822
Bellevue, WA 98004
Contact: Dan Mendes
Phone: (206) 920-9104
Prepared by:
Sitts & Hill Engineers, Inc.
4815 Center Street
Tacoma, Washington 98409
Contact: Don Davis, P.E.
Phone: (253) 474-9449
July 2023
S&H Job Number 19,871
1404 Grady LLC
SW Grady Way Office and Shop Building
Technical Information Report
Prepared for:
1404 Grady LLC
10650 9th Pl, Unit 1822
Bellevue, WA 98004
Contact: Dan Mendes
Phone: (206) 920-9104
Prepared by:
Sitts & Hill Engineers, Inc.
4815 Center Street
Tacoma, Washington 98409
Contact: Don Davis, P.E.
Phone: (253) 474-9449
IN COMPLIANCE WITH CITY OF RENTON STANDARDS
July 2023 S&H Job Number 19,871
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TABLE OF CONTENTS
1.0 PROJECT OVERVIEW .............................................................................................................. 3
1.1 Scope ............................................................................................................................................................... 3
1.2 Existing Conditions ........................................................................................................................................ 4
1.3 Proposed Conditions ..................................................................................................................................... 4
2.0 Conditions and Requirements Summary .............................................................................. 6
2.1 Discussion of Core and Special Requirements ......................................................................................... 6
2.1.1 Core Requirement #1: Discharge at the Natural Location ................................................................ 6
2.1.2 Core Requirement #2: Off-site Analysis .............................................................................................. 6
2.1.3 Core Requirement #3: Flow Control ..................................................................................................... 6
2.1.4 Core Requirement #4: Conveyance System ....................................................................................... 6
2.1.5 Core Requirement #5: Erosion and Sediment Control ...................................................................... 6
2.1.6 Core Requirement #6: Maintenance and Operations ........................................................................ 6
2.1.7 Core Requirement #7: Financial Guarantees and Liability ............................................................... 7
2.1.8 Core Requirement #8: Water Quality ................................................................................................... 7
2.1.9 Core Requirement #9: On-site BMPs ................................................................................................... 7
2.1.10 Special Requirement #1: Other Adopted Area-Specific Requirements ........................................ 8
2.1.11 Special Requirement #2: Flood Hazard Area Delineation .............................................................. 8
2.1.12 Special Requirement #3: Flood Protection Facilities ....................................................................... 9
2.1.13 Special Requirement #4: Source Control .......................................................................................... 9
2.1.14 Special Requirement #5: Oil Control .................................................................................................. 9
2.1.15 Special Requirement #6: Aquifer Protection Areas ......................................................................... 9
3.0 OFF-SITE ANALYSIS .............................................................................................................. 12
3.1 Define and Map the Study Area ................................................................................................................. 12
3.2 Resource Review ......................................................................................................................................... 14
3.3 Field Inspection ............................................................................................................................................ 14
3.4 Drainage System Description and Problem Descriptions ...................................................................... 14
3.5 Mitigation of Existing or Potential Problems ............................................................................................. 14
4.0 FLOW CONTROL, LID, AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ..... 14
4.1 Existing Site Hydrology ............................................................................................................................... 14
4.2 Developed Site Hydrology .......................................................................................................................... 14
4.3 Performance Standards .............................................................................................................................. 15
4.4 Flow Control System .................................................................................................................................... 15
4.4.1 Flow Control Exemptions Check ......................................................................................................... 15
4.4.2 Flow Control Area .................................................................................................................................. 15
4.4.3 Flow Control Area Requirements and Exceptions ........................................................................... 15
4.4.4 Identify Applicable Flow Control BMPs per Core Requirement #9 ................................................ 15
4.5 Water Quality ................................................................................................................................................ 15
5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN ............................................................ 17
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6.0 SPECIAL REPORTS AND STUDIES ...................................................................................... 18
7.0 OTHER PERMITS .................................................................................................................... 19
8.0 CSWPPP ANALYSIS AND DESIGN ....................................................................................... 20
9.0 BOND QUANTITIES and R/D FACILITY SUMMARIES ........................................................ 21
9.1 Bond Quantities ............................................................................................................................................ 21
9.2 Facility Summaries ....................................................................................................................................... 21
10.0 OPERATIONS AND MAINTENANCE MANUAL .................................................................. 22
10.1 Purpose ....................................................................................................................................................... 22
10.2 Permanent Facilities Description ............................................................................................................. 22
10.3 Discussion of Maintenance....................................................................................................................... 22
10.4 Maintenance Frequency ........................................................................................................................... 22
10.5 Annual Cost Estimate ................................................................................................................................ 23
TABLE OF APPENDICES
A.1 TIR Worksheet
A.2 Bond Quantity Worksheet
A.3 Existing and Proposed Surface Coverage Exhibits
A.4 Stormwater Engineering Calculations
A.5 Geotechnical Engineering Report
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1.0 PROJECT OVERVIEW
1.1 Scope
This Technical Information Report (TIR) addresses site improvements associated with the proposed new
building located at 1404 SW Grady Way, Renton, WA (Parcel No. 2423049061). Please see Figure 1 for the
Site Location Map. This project is proposed to serve as an office and shop building, and with associated
site improvements including a parking lot, ramp for pedestrians and vehicles for access to adjacent
roadways, fencing, gates, and landscaping.
This Technical Information Report has been prepared in accordance with the 2022 City of Renton
Stormwater Design Manual (SWDM). A copy of the TIR Worksheet, which provides basic information
about the scope of this project, is included with this report in Appendix A.1.
Figure 1 – Site Location Map
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1.2 Existing Conditions
The subject site is located on King County parcel #2423049061, zoned as Medium Industrial (IM), with an
area of 0.62 acres of developed land. The site, as depicted on the topographical survey, is relatively flat.
The surface of the site is mainly gravel and there are no on-site stormwater drainage systems.
The existing site consists of a one-story building and parking for vehicle storage. The boundary on all sides
of the property is surrounded by chain link fence with exception to the northern side of the site. To our
knowledge, the north section of the property is not fenced off to provide access to utilities in the adjacent
parcel to the north.
Upon a visual examination of existing site conditions, stormwater runoff is infiltrated through the gravel
surfacing and potential stormwater water runoff will sheet towards the northeast corner of the property
and infiltrate through the soils on and off-site. Based upon a review of available information on the City
of Renton’s GIS, the northeast corner of the parcel is within a Special Flood Hazard Areas Zone (100-year
flood). The City of Renton’s Public Works Maps combined with King County GIS together indicate the site
is not located within or near any other critical areas.
1.3 Proposed Conditions
The purpose of site improvements for this project is to create access for vehicles and pedestrians to the
proposed office building and convey stormwater to a proposed on-site stormwater system. The proposed
stormwater conveyance system will discharge to the City’s conveyance system after it is treated on-site.
The project proposes grading, paving, utility, and drainage (water quality treatment devices and
conveyance piping) improvements for on-site and off-site areas. See Table 1 for a description of existing
and proposed surface conditions.
The project exceeds 5,000 SF new plus replaced pollution generating impervious surfaces and thus
stormwater runoff generated will be subject to enhanced water quality treatment before conveyed to the
conveyance system located within the City’s right-of-way. Stormwater runoff from the proposed building
roof area will be discharged directly into the on-site conveyance system prior to discharge into the City’s
right-of-way.
Please see Appendix A.3 for Existing and Proposed Surface Coverage Exhibits.
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Table 1. Existing and Developed Condition Description
Description On-site Off-site Total
Total Project Area (ft2)27,175 647 27,822
Existing impervious surface (ft2)27,175 647 27,822
Existing landscaping/lawn area (ft2)0 0 0
Total Project Area (ft2)27,175 647 27,822
Amount of new hard surface (ft2)0 0 0
Amount of new pollution generating hard surface (PGHS)
(ft2)0 0 0
Amount of replaced hard surface (ft2)24,256 647 24,903
Amount of replaced PGHS (ft2)12,618 503 13,121
Amount of new plus replaced hard surface (ft2)24,256 647 24,903
Amount of new plus replaced PGHS (ft2)12,618 503 13,121
Amount of existing hard surfaces converted to
vegetation/landscaping (ft2)2,919 0 2,919
Amount of Land Disturbed (ft2)27,175 647 27,822
Native Vegetation to Pasture (acres)0 0 0
Existing vegetation area to remain (ft2)0 0 0
Existing hard surface to remain unaltered (ft2)0 0 0
Value of proposed improvements ($)$1.6M 0 $1.6M
Amount to be Graded/Approx. FILL (C.Y.) ±1,200 CY 0 ±1,200 CY
Existing Conditions
Developed Conditions
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2.0 CONDITIONS AND REQUIREMENTS SUMMARY
2.1 Discussion of Core and Special Requirements
This is a Medium Industrial (IM) project that adds more than 2,000 square feet of new and replaced
impervious surface. Therefore, the project is subject to a full drainage review and must satisfy all core
requirements (1-9) and all special requirements (1-6) of the 2022 City of Renton Stormwater Design
Manual (SWDM). See “Figure 2 – Drainage Review Flow Chart” at the end of this Section. Below is a
description of each core requirement and how the project proposes to satisfy each requirement.
2.1.1 Core Requirement #1: Discharge at the Natural Location
Stormwater currently infiltrates on-site and potential stormwater runoff is conveyed to the northeast
corner of the parcel, which is within the 100-year flood hazard zone (see Figure 3). An on-site stormwater
system is proposed to reroute stormwater to avoid contributing stormwater flows to the flood plain and
neighboring properties.
2.1.2 Core Requirement #2: Off-site Analysis
The Off-Site Analysis included in Section 3.0 of this TIR will satisfy this Core Requirement.
2.1.3 Core Requirement #3: Flow Control
Please see Section 4.0 for a discussion of flow control for the project. The project proposes work within
the Peak Rate Flow Control Standards (Existing Site Conditions) Area. The project must match the
developed peak discharge rates to the existing site conditions peak discharge rates for the 2-, 10-, and
100-year return periods. Flow volumes are not expected to change after construction of the addition by
more than 0.15cfs, therefore flow control is not required.
2.1.4 Core Requirement #4: Conveyance System
Please see Section 5.0 of this TIR for the conveyance system analysis and design. This project proposes to
use a new on-site collection and conveyance system and associated enhanced water treatment device. In
existing conditions, there are no existing conveyance systems and the proposed conveyance system is
intended to meet the requirements listed in Volume 1 Section 1.2.4.1 of the City of Renton SWDM.
2.1.5 Core Requirement #5: Erosion and Sediment Control
A Temporary Erosion and Sediment Control Plan (TESC) and CSWPPP, under a separate cover, will be
prepared and included in the construction plan set and satisfy this requirement.
2.1.6 Core Requirement #6: Maintenance and Operations
Please see Section 10.0 of this TIR for the Operations and Maintenance Manual, prepared to satisfy this
Core Requirement. 1404 Grady LLC will be responsible for maintenance and operation of the proposed
on-site stormwater facilities upon completion. The City of Renton will continue to be responsible for
operation and maintenance of stormwater systems in the right-of-way.
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2.1.7 Core Requirement #7: Financial Guarantees and Liability
We anticipate that 1404 Grady LLC will be required to provide a Construction Bond to the City of Renton
prior to issuance of the permit. The contractor/owner will be responsible for all erosion and maintenance
liabilities during construction.
2.1.8 Core Requirement #8: Water Quality
Please see Section 4.0 for a discussion of water quality for the project. We propose to use a new enhanced
treatment device for water quality treatment.
2.1.9 Core Requirement #9: On-site BMPs
Target surfaces subject to Core Requirement #9 On-site BMPs include replaced impervious surfaces,
already mitigated with an approved on-site BMP. This site qualifies for the Large Lot BMP Requirements
per 1.2.9.2.2 of the City of Renton SWDM, since it is larger than 22,000 square feet. These requirements
state that all proposed pervious surfaces must implement the soil amendment BMP and roof downspout
connections must be perforated pipe connections. The soil amendment BMP will be implemented for
every pervious service affected by construction. We are not recommending the downspout BMP as the
soils are not suitable for infiltration.
In addition, these requirements require the consideration of the following BMPs: full dispersion, full
infiltration, limited infiltration, bioretention, permeable pavement, basic dispersion, reduced impervious
surface credit, native growth retention credit, tree retention credit. None of the listed BMPs are feasible
for implementation on the project site, however, tree retention credit will be feasible.
Full Dispersion – The application of this BMP depends on the sheet flow of runoff through an area of native
vegetation. The project site does not contain any native vegetation area (e.g., forested) in the existing or
proposed condition. Therefore, full dispersion is infeasible for this project.
Full Infiltration – Per Section C.2.2.2 of the Manual, full infiltration requires that “Existing soils must be
coarse sands or cobbles or medium sands and cannot be comprised of fill materials where the infiltration
device will be located.” However, the top layer of soils is undocumented fill and, in some areas, could be
very dense. The soil conditions are described in the Geotechnical Engineering Report prepared by PanGEO
Inc. (dated July 12, 2023) for the proposed project. Therefore, full infiltration is infeasible for this project.
Limited Infiltration – The infeasibility criteria for limited infiltration are the same as those for full
infiltration except that appropriate soils may be fine sands, loamy sands, sandy loams, or loams. Note that
Section C.2.3.2 of the Manual states “Silt and clay loams, and cemented till (hardpan) are not suitable for
limited infiltration systems.” However, the top layer of soils is undocumented fill and, in some areas, could
be very dense. Therefore, limited infiltration is infeasible for this project.
Bioretention – Bioretention is infeasible for this project since the on-site soils are not suitable for
infiltration. The top layer of soils is undocumented fill and, in some areas, could be very dense.
Permeable Pavement – The soil under a permeable pavement section must provide adequate treatment
for groundwater protection. The underlying soils should also infiltrate for this surfacing to be durable and
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effective. The requirements for adequate treatment are a minimum organic content of 1.0% and a
minimum cation exchange capacity of 8 milliequivalents per 100 grams. The uppermost soil layer on the
project site is made up of fill material and does not meet these requirements. Permeable Pavement is
infeasible for this project.
Basic Dispersion – The implementation of basic dispersion limits the area of impervious surface that can
run off to a dispersion structure to 700 square feet per structure. The proposed building addition will be
adding over 4,000 square feet, which would require seven separate flow dispersion structures. It is also
required for the dispersed stormwater to flow over a vegetated surface, but there are no existing or
proposed vegetated surfaces near the proposed addition. Such a flow path cannot be provided on the
project site without a drastic reduction in the number of parking stalls and vehicle paths. We see basic
dispersion as infeasible to the project.
Reduced Impervious Surface Credit – This BMP presents four possible methods of impervious surface
reduction: restricted footprint, wheel strip driveways, minimum disturbance foundation, and open grid
decking over pervious surface. The restricted footprint method requires less than 4,000 square feet of
impervious area, which is not feasible for the proposed use of the site. A wheel strip driveway is not
applicable for a parking lot. A minimum disturbance foundation is not feasible for an office and shop
building. Open grid decking over a pervious surface is also not applicable to a parking lot. The reduced
impervious surface credit is infeasible for this project.
Native Growth Retention Credit – The existing condition of the site does not contain any native growth.
Therefore, the native growth retention credit is infeasible for this project.
Tree Retention Credit – The existing condition of the site contains one on-site tree and one off-site tree
that will be affected by the current proposal. See Tree Retention Plan (Onsite and Offsite) for the
calculations.
2.1.10 Special Requirement #1: Other Adopted Area-Specific Requirements
The northeast corner project site is within a 100-year flood hazard zone; therefore, elements of the hazard
mitigation plan is incorporated to the proposed improvements. The proposed improvements include
rerouting stormwater runoff to the proposed conveyance system and mitigate stormwater runoff to the
neighboring properties and flooding problems. A master drainage plan, basin plan, salmon conservation
plan, stormwater compliance plan, lake management plan, and shared facility drainage plan is not
applicable to this project.
2.1.11 Special Requirement #2: Flood Hazard Area Delineation
According to City of Renton GIS Map, Figure 3, the northeast corner of the site is within a 100-year flood
hazard zone. and therefore flood-related delineation on the project site is required. The area of the site
within the flood hazard zone will be graded lower from the existing grade and a catch basin will be added
to a low point. No fill or construction will be within that flood hazard zone and the proposed
improvements will redirect stormwater runoff to reduce flooding problems.
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2.1.12 Special Requirement #3: Flood Protection Facilities
N/A. This project does not propose to rely on an existing flood protection facility nor does it modify or
construct a new flood protection facility.
2.1.13 Special Requirement #4: Source Control
1404 Grady LLC shall implement Operational and Structural Source Control BMPs that includes the
maintenance of stormwater drainage and treatment systems as described in the Operations and
Maintenance Manual, included in Section 10.0 of this report.
2.1.14 Special Requirement #5: Oil Control
This project does not propose to develop a high-use site as defined by City of Renton SWDM; therefore,
this Special Requirement is not applicable.
2.1.15 Special Requirement #6: Aquifer Protection Areas
This project is not located within an Aquifer Protection Area per King County GIS.
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Figure 2 – Drainage Review Flow Chart
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Figure 3 – City of Renton GIS Map
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3.0 OFF-SITE ANALYSIS
Per City of Renton SWDM Section 1.2.2, this project must provide an off-site analysis report that assesses
potential off-site drainage and water quality impacts associated with the redevelopment of the project
site. The level of analysis required depends on the specific site and downstream conditions. In accordance
with Section 1.2.2.1, a Level 1 Downstream Analysis has been performed.
3.1 Define and Map the Study Area
Based on the current topographic survey and our observations of the site, the site is generally flat with a
slight slope towards the northeast corner of the property. The site is mainly covered in dirt and gravel and
does not have an existing, private conveyance system. According to City of Renton GIS, the northeast
corner of the parcel is within a 100-year flood hazard zone. In existing conditions, Stormwater runoff
infiltrates with through the soils and any stormwater runoff will towards northeast corner of the parcel.
A topographic site map is featured in Figure 5 of this Report. In the proposed conditions, shown in Figure
4, the proposed conveyance system will convey stormwater to the City’s conveyance system which will
ultimately discharge to the Black River via Springbrook Creek.
Figure 4 - Downstream Flow Path
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Figure 5 – Topographic Survey
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3.2 Resource Review
A thorough review of the resources provided by the City of Renton Maps, as outlined on page 2-13 of the
SWDM, has been completed for the study area. The site is located within the Duwamish – Green River
Watershed, the Black River Basin, and the Springbrook Creek Sub Basin. Based on the City of Renton GIS,
the project area has not been defined as a sensitive area in exception to the northeast corner of the parcel
which lies within a Special Flood Hazard Areas (100-year flood). To our knowledge, there have not been
any reported drainage problems associated with the surrounding of the site. It was also found that the
site does not have a migrating river study, a 303d listing, or an adopted stormwater compliance plan
available. Please see Section 4.0 for a discussion of water quality for the project. A geotechnical report
completed by PanGEO can be found in Appendix A.6.
3.3 Field Inspection
During field inspections, the site was covered in a light layer of gravel, exposing some areas with soils.
From our knowledge, there is not any known flooding problems that occur on-site. We do not anticipate
any future problems with the proposed stormwater conveyance system as it will redirect stormwater
runoff and to be treated on-site and convey to the City’s stormwater system. In addition, proposed
stormwater improvements would mitigate any occurrences of ponding and flooding on-site. Please see
Section A.5 for the modeled areas in the predeveloped and mitigated scenarios.
Since it has been determined that there are no anticipated stormwater problems associated with this
project, Level 2 and Level 3 downstream analyses are not required.
No problems were found related to constrictions, capacity deficiencies, flooding, scouring, overtopping
hazards, sedimentation or erosion, aquatic organisms, or their habitation.
3.4 Drainage System Description and Problem Descriptions
N/A. There are no on-site drainage systems.
3.5 Mitigation of Existing or Potential Problems
The proposed project area does not have any existing or anticipated drainage problems as outlined in
Section 1.2.2.1 of the City of Renton SWDM.
4.0 FLOW CONTROL, LID, AND WATER QUALITY FACILITY ANALYSIS AND DESIGN
4.1 Existing Site Hydrology
The site currently has a one-story building with an asphalt driveway from the right-of-way and gravel
surfacing. The on-site stormwater runoff currently infiltrates onto the soils and any runoff potential will
sheet towards the northeast of the parcel. There are no existing private stormwater network and we are
not aware of any flooding problems.
4.2 Developed Site Hydrology
The proposed site will be comprised of a building, asphalt paved area, concrete walkways, and
landscaping. In the developed condition, approximately 9,418 sf of rooftop area and approximately 12,618
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sf of pollution generating hard surface. The project proposes to redirect the downstream flow path to the
City’s stormwater system.
4.3 Performance Standards
The site is within a Peak Rate Flow Control Standards (Existing Site Conditions) Area, which requires
matching the existing site conditions 2-, 10-, and 100- year peak flows. The predeveloped site is comprised
of gravel surfacing, rooftop surfacing, and asphalt driveway. The proposed site conditions include pervious
surfaces and less impervious surfaces.
In areas where conveyance features are required, they have been designed in accordance with Section
1.2.4 of the SWDM. The proposed private conveyance system includes conveyance piping from private
catch basin to water quality treatment device. Conveyance piping from the roof drains will connect to
proposed conveyance system where it will bypass the water quality treatment. The proposed conveyance
system will connect to the City’s stormwater system on the south side of SW Grady Way.
4.4 Flow Control System
Flow control is not required for this project.
4.4.1 Flow Control Exemptions Check
The project site is exempt from flow control due to an increase of less than 0.15 cfs in the 100-year storm
event. See Section 2.1.3 of this report for further discussion.
4.4.2 Flow Control Area
The site falls within a Peak Rate Flow Control Standard – Match Existing Area, based on the Flow Control
Application Map provided by the City of Renton (Figure 6 of this TIR).
4.4.3 Flow Control Area Requirements and Exceptions
Peak Rate Flow Control Standard – Match Existing – Areas must match existing site conditions 2-,10-, and
100-year peak rate runoff for areas draining to constructed (man-made) or highly modified drainage
systems so as to not create a downstream flooding problem. Per Section 1.2.3.1.A, Exception 1, of the
SWDM, the target surfaces subject to the Peak Rate Flow Control Standard Areas facility requirements will
generate no more than a 0.15-cfs increase in the existing site conditions 100-year peak flow. Therefore,
this project does not propose a flow control facility.
4.4.4 Identify Applicable Flow Control BMPs per Core Requirement #9
Please see Section 2.1.9 of this report for an evaluation of Flow Control BMPs per Core Requirement #9.
4.5 Water Quality
As mentioned in Section 4.3, the project proposes to satisfy the enhanced water quality requirement
through installation of a Biopod Biofilter.
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Figure 6- City of Renton Flow Control Application Map
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5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN
Proposed conveyance elements include conveyance piping to connect the new roof surface with the
existing stormwater system on-site.
Conveyance calculations are provided below per the Uniform Flow Analysis Method provided by the City
of Renton SWDM Section 4.2.1.2. The pipe is sized and sloped such that its barrel capacity at normal full
flow (computed by Manning’s equation) is equal to or greater than the design flow (25-year peak flow
rate).
𝑄= 1.49
𝑛𝐴𝑄2 3⁄𝑄1 2⁄
Where:
Q= Flow rate (cfs)
n = Manning’s Roughness coefficient
A = Area of the pipe (sf)
R = Hydraulic Radius (ft)
S = Channel Slope (ft/ft)
Per Section 4.2.1 of the SWDM, stormwater conveyance pipes must be either 8” or 12” with a minimum
slope of 0.5%. A cleansing full flow velocity of 3fps must be maintained. Manning’s roughness factor of is
assumed to be 0.013 for PVC piping. To comply with the requirements of the SWDM, 8” pipe must be at a
slope of 0.75%. This also yields a full flow volume of 1.118 cfs, which is higher than any flow volume
expected from the area that is being modified. In addition, the 12” pipe, with a slope of 1.14%, yields a
full flow volume of 4.065 cfs.
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6.0 SPECIAL REPORTS AND STUDIES
We are not aware of any site characteristics that are particularly sensitive to stormwater runoff.
A geotechnical report by PanGEO can be found in Appendix A.6 of this report.
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7.0 OTHER PERMITS
We anticipate that a Right-of-Way Use permit, Land Use Master Application, Civil Construction Permit
Building Permit, and an Environmental Review Permit (SEPA) will be required.
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8.0 CSWPPP ANALYSIS AND DESIGN
The Construction Stormwater Pollution Prevention Plan report will be included with the Civil Construction
Permit application.
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9.0 BOND QUANTITIES AND R/D FACILITY SUMMARIES
9.1 Bond Quantities
See Appendix A.2 for a copy of the City of Renton bond report.
9.2 Facility Summaries
This project does not propose to implement any new Retention / Detention (R/D) facilities.
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10.0 OPERATIONS AND MAINTENANCE MANUAL
10.1 Purpose
The purpose of this manual is to provide guidelines for maintaining the storm drainage system as a part
of the construction for the SW Grady Way Office and Shop Building. The site address is 1404 SW Grady
Way, Renton, WA 98057.
Storm utility improvements that have been proposed as a part of the project include:
o Oldcastle Infrastructure BioPod Biofilter
o Storm Drainage Piping
o Catch Basins
Each portion of the system has to be maintained in good working condition for the system to function
properly.
Operations and Maintenance of the private drainage systems will be the responsibility of the Owner, 1404
Grady LLC. Dan Mendes is the contact person at 1404 Grady LLC. His contact information is:
Dan Mendes
10650 9th Pl, Unit 1822
Bellevue, WA 98004
Phone: (206) 920-9104
The City of Renton will continue to be responsible for the Operation and Maintenance of public
improvements.
10.2 Permanent Facilities Description
Conveyance piping will convey stormwater from the new rooftop and paved surfaces to the existing
stormwater facilities on-site. The project proposes to redirect stormwater to the City’s s conveyance
system and will ultimately discharge to the Black River via Springbrook Creek.
10.3 Discussion of Maintenance
Any buildup of sediment, debris, vegetation, or trash that impedes the catch basins will reduce the storm
system capacity. As a result, care must be taken to keep all inlets clear of debris.
The applicable maintenance checklists and excerpts from the 2022 SWDM have been included with the
Operations and Maintenance Manual for review during routine maintenance inspections.
10.4 Maintenance Frequency
Following construction of the project, the storm drainage system shall be inspected and maintained
according to their respective maintenance checklists included at the end of this manual.
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Facilities will be inspected annually, or after every significant storm event where the precipitation is
greater than or equal to one inch in 24 hours
When deficiencies are noted, the problems are to be corrected as soon as possible. Any spill of hazardous
material (e.g. fuel, lubricant, herbicide, etc.) shall be cleaned up immediately and shall be reported to the
Division of Emergency Management (1-800-523-5044). Contaminated material will be disposed of
properly.
Any questions about the existence of a problem should be directed to a Professional Engineer.
10.5 Annual Cost Estimate
Annual maintenance costs for the proposed stormwater conveyance system are expected to increase the
costs of maintaining the private stormwater system by $1 for every linear foot of new piping, $1,000 for
each biopod biofilter and $500 for every catch basin. Approximately 389 linear feet of proposed pipe, 1
biopod biofilter and 4 catch basins will increase the cost of maintenance by $3,389.
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Cover Sheet for Inspection Forms
Name of Inspector:
_____________________________________________________________
Date of Inspection:
_____________________________________________________________
Number of Sheets Attached:
_____________________________________________________________
Inspector’s Signature:
_____________________________________________________________
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Maintenance Log
Action
Taken
Name Date How Procedure
Was Performed
Problems
Encountered
Additional Actions
Recommended
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A.1 TIR Worksheet
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A.2 Bond Quantity Worksheet
To be included in the TIR at time of Civil Construction Permit application.
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A.3 Existing and Proposed Surface Coverage Exhibits
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A.4 Stormwater Engineering Calculations
Flow Control
This project is in a location subject to meeting the Peak Rate Flow Control Standard, as described in Section
4.4. Therefore, we have prepared the following calculations to determine if flow control will be required
for this project.
No flow control will be required, or proposed, to be installed in this system, as the peak flow produced by
the 100-year storm does not increase by more than 0.15 cfs if the existing site conditions are assumed to
be gravel.
Predeveloped Conditions:
Based on the Location Map, shown in Figure 1, the site is occupied by a building and storage of R.V.s,
Conex boxes, boats, and vehicles surfaced with gravel. It Is assumed that the existing site condition is flat
road covering.
See the following excerpt from WWHM indicating the assumptions used in the “Predeveloped” Condition:
Mitigated Conditions:
The mitigated site coverage is comprised of asphalt pavement parking and the rooftop of the proposed
structure along with grass landscaping.
See the following excerpt from WWHM indicating the assumptions used in the “Mitigated” Condition:
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Flow Frequency Results:
The flow frequency table included on the following page indicates that the peak stormwater runoff from
the developed site will decrease due to more pervious surface. by less than 0.15 cfs for the 100-year storm
condition. As the flow is expected to change by less than 0.15 cfs, a flow control structure will not be
necessary.
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Water Quality
Since more than 5,000 square feet of impervious surface is being replaced during this project, water
quality treatment is required. Water quality treatment flows calculated by WWHM are shown below. The
proposed rooftop was not included in the water quality calculations as it is considered to not be a
pollution-generating surface and will bypass the treatment structure. Per Biopod Biofilter sizing
requirements listed on Washington State DOE, A hydraulic loading rate of 1.6 gpm per sf of media surface
area will be used. Using a peak 15-minute flow rate, approximately 23.25 sf of media is required.
Therefore, a 4’ x 6’ BioPod Underground with StormMix Media will be used as an enhance water quality
treatment device.
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A.5 Geotechnical Engineering Report
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