HomeMy WebLinkAboutEX09_TIR
Western Washington Division Eastern Washington Division
165 NE Juniper St., Ste 201, Issaquah, WA 98027 407 Swiftwater Blvd, Cle Elum, WA 98922
Phone: (425) 392-0250 Fax: (425) 391-3055 Phone: (509) 674-7433 Fax: (509) 674-7419
www.EncompassES.net
PRELIMINARY TECHNICAL INFORMATION REPORT
For
Bonsai Estates Short Plat
XXXXX & 12816 156th Avenue SE
Renton, WA 98059
January 9th, 2024
01/09/2024
Prepared by:
Gabe Garner
Encompass Engineering Job No. 21657
Prepared For:
Juan Carlos Morales
P.O. Box 18211
Seattle, WA 98118
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Table of Contents
I. PROJECT OVERVIEW ................................................................................................................ 1
II. CONDITIONS AND REQUIREMENTS SUMMARY ...................................................................... 7
III. DOWNSTREAM ANALYSIS ........................................................................................................ 10
IV. FLOW CONTROL, LOW IMPACT DEVELOPMENT AND WATER QUALITY FACILITY ANALYSIS
AND DESIGN ........................................................................................................................... 14
V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN ..................................................................... 16
VI. SPECIAL REPORTS AND STUDIES ............................................................................................ 16
VII. OTHER PERMITS ..................................................................................................................... 16
VIII. CSWPP ANALYSIS AND DESIGN .............................................................................................. 16
IX. BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION of COVENANT ................... 16
X. OPERATION AND MAINTENANCE MANUAL .......................................................................... 16
List of Figures
Figure 1 – TIR Worksheet
Figure 2 – Vicinity Map
Figure 3 – Soils Map and Legend
Figure 4 – Existing Conditions Map
Figure 5 – Developed Conditions Map
Figure 6 – Drainage Review Flow Chart
Figure 7 – Downstream Map
Appendix A
Geotechnical Engineering Study by Earth Solutions NW, LLC dated November 24, 2021
Appendix B
WWHM Output
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I. PROJECT OVERVIEW
Project: Morales Short Plat
Site Address: XXXXX & 12816 156th Ave SE, Renton, WA 98059
Tax Parcel #: 366450-0170 & 366450-0175
Zoning District: R-4 (single-family residential)
Site Area: 46,483 SF (1.07 AC) – as surveyed
Site Location: The site is in the City of Renton within the NE quarter of Section 14,
Township 23 North, Range 5 East, W.M., King County, Washington.
The site is located on the east side of 156th Ave SE, south of the
intersection of 156th Ave SE and SE 128th St.
Figure 2: Vicinity Map
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Pre-developed Site Conditions
The project site is located in the City of Renton on a 46,483 SF (1.07 AC) site that is zoned R-4
(single-family residential). The site is accessed from 156th Avenue SE, south of the intersection of
156th Avenue SE and SE 128th Street. The site is bordered to the west by 156th Avenue SE, and to
the north, south, and east by single-family residences.
The site includes a 2,035 SF single-family residence (roof area), 350 SF of uncovered concrete
walkways/pads, 955 SF of uncovered gravel, and 1,566 SF of on-site uncovered asphalt driveway.
Additionally, 261 SF of asphalt driveway apron is located off-site in the public right-of-way (ROW).
The total existing on-site impervious surface coverage is 4,906 SF, which is 10.55% of the total
site area. Apart from these existing structures, the site is primarily covered with vegetation (lawn,
trees, etc.).
An Existing Conditions Map is included as Figure 4 at the end of this Section.
Critical Areas
According to King County iMap, there are no critical areas located on site, or on any adjacent
sites.
Soils
Per the US Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS)
Web Soil Survey (WSS) information, the entire project site is underlain with Alderwood gravelly
sandy loam (See Figure 3 on the following page). A Geotechnical Engineering Study prepared by
Earth Solutions NW, LLC (Appendix A) confirms this soil classification across the site, with the
study indicating that the site is underlain primarily by glacial till deposits .
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Figure 3: Soil Map and Legend
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Developed Site Conditions
The project proposes the development of three (3) single-family lots within the 46,483 SF (1.07
AC) site, a stormwater tract, and a ROW dedication. The 9,683 SF (0.22 AC) stormwater tract
(Tract A) is located in the western-most portion of the site. Lot 1 is 9,524 SF (0.22 AC) and is
located directly east of Tract A. Lot 2 is 9,520 SF (0.22 AC) and is located directly east of Lot 1. Lot
3 is 9,516 SF (0.22 AC) and is located east of Lot 2. The 8,242 SF ROW dedication borders the
western and northern property boundaries. The parcel is zoned R-4, which allows for a maximum
building coverage of 35% and a maximum impervious surface coverage of 50%. The maximum
allowable building/impervious surface for each lot is discussed below:
• Lot 1: The maximum allowable building coverage for Lot 1 is 9,524 SF * 0.35 = 3,333
SF, and the maximum impervious surface coverage is 9,524 SF * 0.50 = 4,762 SF. The
final site layout of Lot 1 has not been determined at this stage; therefore, this report
assumes that the future impervious surfaces required to construct the residence on
Lot 1 will use the maximum coverages stated above.
• Lot 2: The maximum allowable building coverage for Lot 2 is 9,520 SF * 0.35 = 3,332
SF, and the maximum impervious surface coverage is 9,520 SF * 0.50 = 4,760 SF. The
final site layout of Lot 2 has not been determined at this stage; therefore, t his report
assumes that the future impervious surfaces required to construct the residence on
Lot 2 will use the maximum coverages stated above.
• Lot 3: The maximum allowable building coverage for Lot 3 is 9,516 SF * 0.35 = 3,331
SF, and the maximum impervious surface coverage is 9,516 SF * 0.50 = 4,758 SF. The
final site layout of Lot 3 has not been determined at this stage; therefore, t his report
assumes that the future impervious surfaces required to construct the residence on
Lot 3 will use the maximum coverages stated above.
Additionally, there will be a 415 SF hammerhead/turnaround located on-site, as well as 9,779 SF
of pavement widening, 876 SF of driveway aprons, and 2,072 SF of concrete sidewalk proposed
off-site and in the right-of-way (ROW) dedication.
Stormwater runoff from the proposed development will be collected and conveyed to a Contech
CMP detention system. The feasibility of other flow control BMPs will be evaluated with final
engineering.
Section II and Section IV of this TIR for additional discussion on stormwater BMPs. A Developed
Conditions Map is provided as Figure 5 at this end of this Section.
156TH AVE SE
NORTH
1 of 1EXISTING CONDITIONSEXISTING IMPERVIOUS AREAS:MORALES SHORT PLAT
XXXXX & 12816 156TH AVE SE
RENTON, WA 98059
REVISIONS JOB NO.
DATE
SCALE SHEET
Encompass
Eastern Washington Division
407 Swiftwater Blvd. ▪ Cle Elum, WA 98922 ▪ Phone: (509) 674-7433
Western Washington Division
165 NE Juniper Street, Suite 201 ▪ Issaquah, WA 98027 ▪ Phone: (425) 392-0250
ENGINEERING & SURVEYING
156TH AVE SETRACT ALOT 1LOT 2LOT 3ROW DEDICATIONNORTH
1 of 1PROPOSED CONDITIONSPROPOSED IMPERVIOUS AREAS:MORALES SHORT PLAT
XXXXX & 12816 156TH AVE SE
RENTON, WA 98059
REVISIONS JOB NO.
DATE
SCALE SHEET
Encompass
Eastern Washington Division
407 Swiftwater Blvd. ▪ Cle Elum, WA 98922 ▪ Phone: (509) 674-7433
Western Washington Division
165 NE Juniper Street, Suite 201 ▪ Issaquah, WA 98027 ▪ Phone: (425) 392-0250
ENGINEERING & SURVEYING
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II. CONDITIONS AND REQUIREMENTS SUMMARY
The 2022 City of Renton Surface Water Design Manual (RSWDM) was utilized to determine and
address all core and special requirements. Based on the criteria specified in Figure 1.1.2.A of the
RSWDM, the project falls under Full Drainage Review. Per Section 1.1.2.4 of the RSWDM, the
project must meet all nine (9) core and all six (6) special requirements. See Figure 6 below for
more information on how the type of drainage review was determined.
Figure 6: Drainage Review Flow Chart
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Core Requirements
Core Requirement #1: Discharge at the Natural Location
The proposed development will discharge stormwater runoff towards the natural
discharge area in the southwestern portion of the site. Refer to the Level 1 Downstream
Analysis in Section III of this TIR for a complete description of the existing drainage paths.
Core Requirement #2: Downstream Analysis
A Level 1 Downstream analysis has been completed for the site and no existing or
potential problems have been identified. This analysis is included in Section III of this TIR.
Core Requirement #3: Flow Control Facilities
Based on the City of Renton’s flow control application map, the project site is located
within the Peak Rate Flow Control Standard (Existing Site Conditions). Flow control
facilities are required to match the developed peak discharge rates to existing site
conditions peak discharge rates for 2-, 10- and 100-year return periods. This project
proposes a Contech CMP detention system to control flow rates leaving the site. A
preliminary discussion on the design of this facility is included in Section IV of this TIR.
Core Requirement #4: Conveyance System
Conveyance in compliance with the requirements detailed in Section 1.2.4.1 of the City
of Renton 2017 SWDM will be provided with final engineering.
Core Requirement #5: Construction Stormwater Pollution Prevention
A temporary erosion and sediment control (TESC) plan providing details on best
management practices (BMPs) to be implemented during construction is included in the
engineering plan set. A Construction Stormwater Pollution Prevention Plan (CSWPPP) will
be provided with final engineering. Please refer to Section VIII of this TIR for additional
discussion.
Core Requirement #6: Maintenance and Operations
An Operation and Maintenance Manual will be provided with final engineering.
Core Requirement #7: Financial Guarantees and Liability
The owner will arrange for any financial guarantees and liabilities required by the permit.
Core Requirement #8: Water Quality Facilities
This project proposes over 5,000 SF of pollution generating impervious surfaces (PGIS),
therefore water quality treatment is required. A Contech StormFilter will be proposed to
meet this requirement. This will be designed with final engineering.
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Core Requirement #9: Flow Control BMPs
Flow control BMPs are not proposed at this time. The feasibility of these will be evaluated
with final engineering. A permanent Contech CMP detention system will serve to control
flows during the construction process.
Special Requirements
Special Requirement #1: Other Adopted Area-Specific Requirements
Critical Drainage Area – N/A
Master Drainage Plan – N/A
Basin Plan – N/A
Lake management Plan – N/A
Shared Facility Drainage Plan – N/A
Special Requirement #2: Flood Hazard Area Delineation
The limits of this project do not lie within a delineated FEMA 100-year floodplain.
Special Requirement #3: Flood Protection Facilities
This project does not rely on or propose to modify/construct a new flood protection
facility.
Special Requirement #4: Source controls
The project is a preliminary short plat; therefore, this requirement is not applicable.
Special Requirement #5: Oil Control
This project is not considered high-use in need of oil control.
Special Requirement #6: Aquifer Protection Area
This site is not located within an Aquifer Protection Area.
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III. DOWNSTREAM ANALYSIS
A Level 1 Downstream analysis has been conducted per the requirements in Section 1.2.2.1 of
the RSWDM. Please see Tasks 1 through 4 below for a summary of the results.
Task 1: Define and Map the Study Area
The area of analysis extends from the site discharge point (southern portion of the site) and along
156th Avenue SE until reaching approximately a quarter-mile downstream. A Downstream Map
is provided in Figure 7 below.
Figure 7: Downstream Map
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Task 2: Review All Available Information on the Study Area
Per King County and City of Renton resources, there have been no significant drainage complaints
within a quarter-mile downstream of the site.
Task 3: Field Inspect the Study Area
A field inspection was performed by Encompass Engineering & Surveying on June 22nd, 2023.
Please refer to Task 4 for a detailed description of the downstream drainage system and analysis.
Task 4: Describe the Drainage System
Runoff leaves the site through one NDA, creating a single TDA for the site. Stormwater starts by
sheet flowing downhill over lawn surfaces towards the southern/southwestern portion of the
site (A). Once exiting the site, the stormwater immediately enters the roadside drainage ditch on
the eastern edge of 156th Ave SE (B). After entering the ditch, the runoff gets conveyed to the
south through a series of different driveway culverts. After about 800 FT, the runoff passes by
the intersection of SE 132nd Street & 156th Ave SE and continues being conveyed to the south
within the drainage ditch (C). From here, the runoff continues south within the drainage ditch
until the ¼ mile downstream limit is reached (D). Images of the downstream flow path can be
found on the following pages.
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Element A – Runoff sheet flows towards southern/southwestern portion of property
Element B – Runoff enters drainage ditch along eastern side of 156th Ave SE
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Element C – Runoff continues south past intersection of SE 132nd Street & 156th Ave SE
Element D – Runoff reaches ¼ mile limit and continues south within drainage ditch
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IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN
Part A: Existing Site Hydrology
The 46,483 SF (1.07 AC) site is currently developed with a single-family residence accessed from
156th Avenue SE via an asphalt driveway located in the western portion of the site. Stormwater
runoff from the site generally sheet flows to the southwest, following the topography of the lawn
surfaces with slopes ranging from 2-5%. Shortly after the runoff from the site gathers on 156th
Avenue SE, it enters the existing grass-lined drainage ditch located along the eastern side of the
street.
The property is located in the Lower Cedar River Drainage Basin, within the Cedar River/Lake
Washington Watershed. All stormwater runoff from the site ultimately discharges into the Cedar
River. See full downstream analysis in Section III of this Preliminary Technical Information Report
(TIR).
The Geotechnical Engineering Study prepared by Earth Solutions NW, LLC (Appendix A) confirms
the NRCS Alderwood gravelly sandy loam on the site (glacial till deposits), and has determined
infiltration to be infeasible.
WWHM 2012 was used to model the existing condition within the limits of disturbance as forest.
A discussion of this analysis is included under Parts C and D below.
Part B: Developed Site Hydrology
The project proposes the development of three (3) single-family lots within the 46,483 SF (1.07
AC) site, a stormwater tract, and a ROW dedication. The 9,683 SF (0.22 AC) stormwater tract
(Tract A) is located in the western-most portion of the site. Lot 1 is 9,524 SF (0.22 AC) and is
located directly east of Tract A. Lot 2 is 9,520 SF (0.22 AC) and is located directly east of Lot 1. Lot
3 is 9,516 SF (0.22 AC) and is located east of Lot 2. The 8,242 SF ROW dedication borders the
western and northern property boundaries.
Stormwater runoff from the proposed development will be collected and conveyed to a Contech
CMP detention system (the feasibility of other flow control BMPs will be evaluated with final
engineering). The Contech CMP detention system was sized using WWHM, and a breakdown of
the facility sizing is included under Parts C and D below.
Part C: Performance Standards
Based on the City of Renton’s flow control map, the project site is located within the Flow Control
Duration Standard Matching Forested Condition Area. Flow control facilities are required to
match the flow duration of predeveloped rates for forested (historical) site conditions over the
range of flows extending from 50% of 2-year up to the full 50- year flow AND matches peaks for
the 2- and 10-year return periods.
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Flow Control BMPs are not proposed at this time. The feasibility of these will be evaluated with
final engineering. A permanent Contech CMP detention system will serve to control flows during
and following the construction process. This facility, located in a designated stormwater tract,
will maintain the site’s existing discharge point. All stormwater runoff from the site shall be
collected and conveyed to the proposed Contech CMP detention system. The stormwater
detention and water quality volume for the proposed development were determined using
WWHM2012. The basin area breakdown is included below in Table 1 and full WWHM output is
included in Appendix B.
Area Breakdown
Existing Proposed
Condition Measured (AC) Modeled (AC) Measured (AC) Modeled (AC)
Forest: 1.169 1.169 0.000 0.000
Roof: 0.000 0.000 0.328 0.328
Road: 0.000 0.000 0.244 0.244
Sidewalk: 0.000 0.000 0.067 0.067
Lawn: 0.000 0.000 0.530 0.530
Total Area: 1.169 1.169 1.169 1.169
Table 1: Area Breakdown
The required water storage volume for this site is 17,598 CU-FT (0.404 AC-FT). The proposed
system has a provided water storage volume of 18,624 CU-FT.
Part D: Flow Control System
A preliminary analysis was performed to make sure a Contech CMP detention system would work
within the proposed stormwater tract. Further design of the system and outfall will be performed
with final engineering.
Part E: Water Quality System
The site falls within a Basic Water Quality treatment area in accordance with Section 1.2.8.1.A of
the RSWDM. A Contech StormFilter is proposed to meet this requirement. This facility will be
sized with final engineering.
V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN
A conveyance system analysis will be provided with final engineering.
VI. SPECIAL REPORTS AND STUDIES
• Geotechnical Engineering Study by Earth Solutions NW, LLC dated November 24, 2021
(Appendix A).
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VII. OTHER PERMITS
• Civil Construction Permit
• Final Short Plat
• Building Permits
• Right-of-Way Use Permit
VIII. CSWPP ANALYSIS AND DESIGN
A CSWPPP will be provided with final engineering.
IX. BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION of
COVENANT
Bond Quantities, Facility Summary and Declaration of Covenant will be provided with final
engineering.
X. OPERATION AND MAINTENANCE MANUAL
An Operation and Maintenance Manual will be provided with final engineering.
Bonsai Estates Short Plat Preliminary Technical Information Report
Appendix A
Geotechnical Engineering Study by Earth Solutions NW, LLC dated November 24, 2021
EarthSolutionsNWLLC
EarthSolutions
NW LLC
15365 N.E.90th Street,Suite 100 Redmond,WA 98052
(425)449-4704 Fax (425)449-4711
www.earthsolutionsnw.com
Geotechnical Engineering
Construction Observation/Testing
Environmental Services
GEOTECHNICAL ENGINEERING STUDY
PROPOSED MORALES SHORT PLAT
12816 –156 AVENUE SOUTHEAST
RENTON,WASHINGTON
ES-8222
TH
PREPARED FOR
MR. JUAN CARLOS MORALES
C/O MR. JIM HOWTON
November 24, 2021
__________________________
Scott S. Riegel, L.G., L.E.G.
Senior Project Manager
__________________________
Kyle R. Campbell, P.E.
Principal Engineer
GEOTECHNICAL ENGINEERING STUDY
PROPOSED MORALES SHORT PLAT
12816 – 156TH AVENUE SOUTHEAST
RENTON, WASHINGTON
ES-8222
Earth Solutions NW, LLC
15365 Northeast 90th Street, Suite 100
Redmond, Washington 98052
Phone: 425-449-4704 | Fax: 425-449-4711
www.earthsolutionsnw.com
11/24/2021
11/24/2021
Geotechnical-Engineering Report
Important Information about This
Subsurface problems are a principal cause of construction delays, cost overruns, claims, and disputes.
While you cannot eliminate all such risks, you can manage them. The following information is provided to help.
The Geoprofessional Business Association (GBA)
has prepared this advisory to help you – assumedly
a client representative – interpret and apply this
geotechnical-engineering report as effectively as
possible. In that way, you can benefit from a lowered
exposure to problems associated with subsurface
conditions at project sites and development of
them that, for decades, have been a principal cause
of construction delays, cost overruns, claims,
and disputes. If you have questions or want more
information about any of the issues discussed herein,
contact your GBA-member geotechnical engineer.
Active engagement in GBA exposes geotechnical
engineers to a wide array of risk-confrontation
techniques that can be of genuine benefit for
everyone involved with a construction project.
Understand the Geotechnical-Engineering Services
Provided for this Report
Geotechnical-engineering services typically include the planning,
collection, interpretation, and analysis of exploratory data from
widely spaced borings and/or test pits. Field data are combined
with results from laboratory tests of soil and rock samples obtained
from field exploration (if applicable), observations made during site
reconnaissance, and historical information to form one or more models
of the expected subsurface conditions beneath the site. Local geology
and alterations of the site surface and subsurface by previous and
proposed construction are also important considerations. Geotechnical
engineers apply their engineering training, experience, and judgment
to adapt the requirements of the prospective project to the subsurface
model(s). Estimates are made of the subsurface conditions that
will likely be exposed during construction as well as the expected
performance of foundations and other structures being planned and/or
affected by construction activities.
The culmination of these geotechnical-engineering services is typically a
geotechnical-engineering report providing the data obtained, a discussion
of the subsurface model(s), the engineering and geologic engineering
assessments and analyses made, and the recommendations developed
to satisfy the given requirements of the project. These reports may be
titled investigations, explorations, studies, assessments, or evaluations.
Regardless of the title used, the geotechnical-engineering report is an
engineering interpretation of the subsurface conditions within the context
of the project and does not represent a close examination, systematic
inquiry, or thorough investigation of all site and subsurface conditions.
Geotechnical-Engineering Services are Performed
for Specific Purposes, Persons, and Projects,
and At Specific Times
Geotechnical engineers structure their services to meet the specific
needs, goals, and risk management preferences of their clients. A
geotechnical-engineering study conducted for a given civil engineer
will not likely meet the needs of a civil-works constructor or even a
different civil engineer. Because each geotechnical-engineering study
is unique, each geotechnical-engineering report is unique, prepared
solely for the client.
Likewise, geotechnical-engineering services are performed for a specific
project and purpose. For example, it is unlikely that a geotechnical-
engineering study for a refrigerated warehouse will be the same as
one prepared for a parking garage; and a few borings drilled during
a preliminary study to evaluate site feasibility will not be adequate to
develop geotechnical design recommendations for the project.
Do not rely on this report if your geotechnical engineer prepared it:
• for a different client;
• for a different project or purpose;
• for a different site (that may or may not include all or a portion of
the original site); or
• before important events occurred at the site or adjacent to it;
e.g., man-made events like construction or environmental
remediation, or natural events like floods, droughts, earthquakes,
or groundwater fluctuations.
Note, too, the reliability of a geotechnical-engineering report can
be affected by the passage of time, because of factors like changed
subsurface conditions; new or modified codes, standards, or
regulations; or new techniques or tools. If you are the least bit uncertain
about the continued reliability of this report, contact your geotechnical
engineer before applying the recommendations in it. A minor amount
of additional testing or analysis after the passage of time – if any is
required at all – could prevent major problems.
Read this Report in Full
Costly problems have occurred because those relying on a geotechnical-
engineering report did not read the report in its entirety. Do not rely on
an executive summary. Do not read selective elements only. Read and
refer to the report in full.
You Need to Inform Your Geotechnical Engineer
About Change
Your geotechnical engineer considered unique, project-specific factors
when developing the scope of study behind this report and developing
the confirmation-dependent recommendations the report conveys.
Typical changes that could erode the reliability of this report include
those that affect:
• the site’s size or shape;
• the elevation, configuration, location, orientation,
function or weight of the proposed structure and
the desired performance criteria;
• the composition of the design team; or
• project ownership.
As a general rule, always inform your geotechnical engineer of project
or site changes – even minor ones – and request an assessment of their
impact. The geotechnical engineer who prepared this report cannot accept
responsibility or liability for problems that arise because the geotechnical
engineer was not informed about developments the engineer otherwise
would have considered.
Most of the “Findings” Related in This Report
Are Professional Opinions
Before construction begins, geotechnical engineers explore a site’s
subsurface using various sampling and testing procedures. Geotechnical
engineers can observe actual subsurface conditions only at those specific
locations where sampling and testing is performed. The data derived from
that sampling and testing were reviewed by your geotechnical engineer,
who then applied professional judgement to form opinions about
subsurface conditions throughout the site. Actual sitewide-subsurface
conditions may differ – maybe significantly – from those indicated in
this report. Confront that risk by retaining your geotechnical engineer
to serve on the design team through project completion to obtain
informed guidance quickly, whenever needed.
This Report’s Recommendations Are
Confirmation-Dependent
The recommendations included in this report – including any options or
alternatives – are confirmation-dependent. In other words, they are not
final, because the geotechnical engineer who developed them relied heavily
on judgement and opinion to do so. Your geotechnical engineer can finalize
the recommendations only after observing actual subsurface conditions
exposed during construction. If through observation your geotechnical
engineer confirms that the conditions assumed to exist actually do exist,
the recommendations can be relied upon, assuming no other changes have
occurred. The geotechnical engineer who prepared this report cannot assume
responsibility or liability for confirmation-dependent recommendations if you
fail to retain that engineer to perform construction observation.
This Report Could Be Misinterpreted
Other design professionals’ misinterpretation of geotechnical-
engineering reports has resulted in costly problems. Confront that risk
by having your geotechnical engineer serve as a continuing member of
the design team, to:
• confer with other design-team members;
• help develop specifications;
• review pertinent elements of other design professionals’ plans and
specifications; and
• be available whenever geotechnical-engineering guidance is needed.
You should also confront the risk of constructors misinterpreting this
report. Do so by retaining your geotechnical engineer to participate in
prebid and preconstruction conferences and to perform construction-
phase observations.
Give Constructors a Complete Report and Guidance
Some owners and design professionals mistakenly believe they can shift
unanticipated-subsurface-conditions liability to constructors by limiting
the information they provide for bid preparation. To help prevent
the costly, contentious problems this practice has caused, include the
complete geotechnical-engineering report, along with any attachments
or appendices, with your contract documents, but be certain to note
conspicuously that you’ve included the material for information purposes
only. To avoid misunderstanding, you may also want to note that
“informational purposes” means constructors have no right to rely on
the interpretations, opinions, conclusions, or recommendations in the
report. Be certain that constructors know they may learn about specific
project requirements, including options selected from the report, only
from the design drawings and specifications. Remind constructors
that they may perform their own studies if they want to, and be sure to
allow enough time to permit them to do so. Only then might you be in
a position to give constructors the information available to you, while
requiring them to at least share some of the financial responsibilities
stemming from unanticipated conditions. Conducting prebid and
preconstruction conferences can also be valuable in this respect.
Read Responsibility Provisions Closely
Some client representatives, design professionals, and constructors do
not realize that geotechnical engineering is far less exact than other
engineering disciplines. This happens in part because soil and rock on
project sites are typically heterogeneous and not manufactured materials
with well-defined engineering properties like steel and concrete. That
lack of understanding has nurtured unrealistic expectations that have
resulted in disappointments, delays, cost overruns, claims, and disputes.
To confront that risk, geotechnical engineers commonly include
explanatory provisions in their reports. Sometimes labeled “limitations,”
many of these provisions indicate where geotechnical engineers’
responsibilities begin and end, to help others recognize their own
responsibilities and risks. Read these provisions closely. Ask questions.
Your geotechnical engineer should respond fully and frankly.
Geoenvironmental Concerns Are Not Covered
The personnel, equipment, and techniques used to perform an
environmental study – e.g., a “phase-one” or “phase-two” environmental
site assessment – differ significantly from those used to perform a
geotechnical-engineering study. For that reason, a geotechnical-engineering
report does not usually provide environmental findings, conclusions, or
recommendations; e.g., about the likelihood of encountering underground
storage tanks or regulated contaminants. Unanticipated subsurface
environmental problems have led to project failures. If you have not
obtained your own environmental information about the project site,
ask your geotechnical consultant for a recommendation on how to find
environmental risk-management guidance.
Obtain Professional Assistance to Deal with
Moisture Infiltration and Mold
While your geotechnical engineer may have addressed groundwater,
water infiltration, or similar issues in this report, the engineer’s
services were not designed, conducted, or intended to prevent
migration of moisture – including water vapor – from the soil
through building slabs and walls and into the building interior, where
it can cause mold growth and material-performance deficiencies.
Accordingly, proper implementation of the geotechnical engineer’s
recommendations will not of itself be sufficient to prevent
moisture infiltration. Confront the risk of moisture infiltration by
including building-envelope or mold specialists on the design team.
Geotechnical engineers are not building-envelope or mold specialists.
Copyright 2019 by Geoprofessional Business Association (GBA). Duplication, reproduction, or copying of this document, in whole or in part, by any means whatsoever, is strictly
prohibited, except with GBA’s specific written permission. Excerpting, quoting, or otherwise extracting wording from this document is permitted only with the express written permission of
GBA, and only for purposes of scholarly research or book review. Only members of GBA may use this document or its wording as a complement to or as an element of a report of any kind.
Any other firm, individual, or other entity that so uses this document without being a GBA member could be committing negligent or intentional (fraudulent) misrepresentation.
Telephone: 301/565-2733
e-mail: info@geoprofessional.org www.geoprofessional.org
November 24, 2021
ES-8222
Mr. Juan Carlos Morales
c/o Mr. Jim Howton
11047 Southeast 62nd Place
Bellevue, Washington 98006
Dear Mr. Howton:
Earth Solutions NW, LLC (ESNW) is pleased to present this geotechnical engineering study that
supports the construction of a residential short plat in Renton, Washington. Based on the results
of our investigation, construction of the proposed residential subdivision is feasible from a
geotechnical standpoint. Our study indicates the site is underlain primarily by glacial till deposits.
In general, typical residences up to three stories in height may be supported on conventional
continuous and spread footing foundations bearing on competent native soil, recompacted native
soil, or new structural fill placed directly on competent native soil. In general, competent native
soil, suitable for support of the new foundations, will likely be encountered beginning at depths of
about one to two feet below the existing ground surface. Where loose or unsuitable soil
conditions are exposed at foundation subgrade elevations, compaction of soils to the
specifications of structural fill, or overexcavation and replacement with suitable structural fill, will
be necessary. Because no design details were available at the time of this report, ESNW should
review the project details to confirm the recommendations in this report are applicable.
Infiltration is not feasible from a geotechnical standpoint due, in part, to the variable but low
infiltration capacity of the native soil deposits encountered across much of the site.
We appreciate the opportunity to be of service to you on this project. If you have questions
regarding the content of this geotechnical engineering study, please contact us.
Sincerely,
EARTH SOLUTIONS NW, LLC
Scott S. Riegel, L.G., L.E.G.
Senior Project Manager
15365 N.E. 90th Street, Suite 100 • Redmond, WA 98052 •(425) 449-4704 • FAX (425) 449-4711
Earth Solutions NW LLC
Geotechnical Engineering, Construction
Observation/Testing and Environmental Services
Earth Solutions NW, LLC
Table of Contents
ES-8222
PAGE
INTRODUCTION ................................................................................. 1
General..................................................................................... 1
Project Description ................................................................. 1
SITE CONDITIONS ............................................................................. 2
Surface ..................................................................................... 2
Subsurface .............................................................................. 2
Topsoil and Fill ............................................................. 2
Native Soil ..................................................................... 2
Geologic Setting ........................................................... 2
Groundwater ................................................................. 3
GEOLOGICALLY HAZARDOUS AREAS ........................................... 3
DISCUSSION AND RECOMMENDATIONS ....................................... 3
General..................................................................................... 3
Site Preparation and Earthwork ............................................. 4
Temporary Erosion Control ......................................... 4
Stripping ....................................................................... 4
Excavations and Slopes .............................................. 5
In-situ and Imported Soils ........................................... 5
Wet-Season Grading .................................................... 5
Structural Fill ................................................................ 6
Foundations ............................................................................ 6
Seismic Design ....................................................................... 7
Slab-on-Grade Floors ............................................................. 8
Retaining Walls ....................................................................... 8
Landscape Retaining Walls ......................................... 9
Drainage................................................................................... 9
Infiltration Evaluation ................................................... 9
Preliminary Stormwater Vault Design Recommendations .. 10
Utility Support and Trench Backfill ....................................... 11
Preliminary Pavement Sections ............................................. 11
LIMITATIONS ...................................................................................... 12
Additional Services ................................................................. 12
Earth Solutions NW, LLC
Table of Contents
Cont’d
ES-8222
GRAPHICS
Plate 1 Vicinity Map
Plate 2 Test Pit Location Plan
Plate 3 Retaining Wall Drainage Detail
Plate 4 Footing Drain Detail
APPENDICES
Appendix A Subsurface Exploration
Test Pit Logs
Appendix B Laboratory Test Results
Earth Solutions NW, LLC
GEOTECHNICAL ENGINEERING STUDY
PROPOSED MORALES SHORT PLAT
12816 – 156TH AVENUE SOUTHEAST
RENTON, WASHINGTON
ES-8222
INTRODUCTION
General
This geotechnical engineering study (study) was prepared for the proposed residential
development to be constructed off the east side of 156 th Avenue Southeast in Renton,
Washington. The purpose of this study was to develop geotechnical recommendations for the
proposed project. The scope of services for completing this study included the following:
Subsurface exploration consisting of test pit excavations;
Laboratory testing of soil samples collected at the test pit locations;
Engineering analyses and recommendations for the proposed development, and;
Preparation of this report.
The following documents and maps were reviewed as part of preparing this study:
Site Plan, prepared by Encompass Engineering, dated August 5, 2021;
Geologic Map of the Renton 7.5’ Quadrangle, King County, Washington;
Renton Municipal Code (RMC) 4-3-050 Critical Areas Regulations, and;
Web Soil Survey (WSS), provided by the United States Department of Agriculture (USDA),
Natural Resources Conservation Service.
Project Description
Based on review of the referenced site plan, the property will be redeveloped with four residential
lots, an access roadway, a stormwater management facility and utility improvements.
Based on existing grades, we anticipate mass grading activities will include minor cuts and fills
of up to about five feet. Perimeter footing loads will likely be 1 to 2 kips per lineal foot. Slab-on-
grade loading is anticipated to be approximately 150 pounds per square foot (psf).
Mr. Juan Carlos Morales ES-8222
c/o Mr. Jim Howton Page 2
November 24, 2021
Earth Solutions NW, LLC
If the above design assumptions are incorrect or change, ESNW should be contacted to review
the recommendations provided in this report. ESNW should review final designs to confirm that
our geotechnical recommendations have been incorporated into the plans.
SITE CONDITIONS
Surface
The subject site is located off the east side 156th Avenue Southeast in Renton, Washington. The
approximate location of the property is illustrated on Plate 1 (Vicinity Map). The site consists of
two adjoining tax parcels (King County Parcel Numbers 366450-0170 and -0175) totaling about
one acre. The property is occupied by a residence and landscaping and sparse trees. The site
topography generally descends very gently to the southwest with about five feet of total elevation
change.
Subsurface
A representative of ESNW observed, logged, and sampled five test pits excavated across the
overall project area, on October 25, 2021 using a mini-trackhoe and operator retained by our firm.
The test pits were completed for purposes of assessing soil conditions, classifying site soils, and
characterizing near-surface groundwater conditions within the overall development area. The
approximate locations of the test pits are depicted on Plate 2 (Test Pit Location Plan). Please
refer to the test pit logs provided in Appendix A for a more detailed description of subsurface
conditions. Representative soil samples collected at the test pit locations were analyzed in
general accordance with Unified Soil Classification System (USCS) and USDA methods and
procedures.
Topsoil and Fill
Topsoil generally extended to a depth of about six inches below the existing ground surface (bgs).
The topsoil was characterized by the observed dark brown color, the presence of fine organics,
and root intrusions extending into the shallow, weathered soils.
Fill was not encountered during our exploration; however, fill is likely present near the existing
development areas of the site.
Native Soil
Underlying topsoil, native soils encountered on the subject site were consisting primarily of silty
sand with gravel (USCS: SM) that extended to the maximum exploration depth of about nine feet
below existing grades.
Geologic Setting
The referenced geologic map resource identifies glacial till (Qvt) deposits as the primary geologic
unit underlying the site and surrounding areas. The referenced WSS map resource identifies
Alderwood gravelly sandy loam (Map Unit Symbol: AgB) across the property. The Alderwood
series soils formed in glacial till plains.
Mr. Juan Carlos Morales ES-8222
c/o Mr. Jim Howton Page 3
November 24, 2021
Earth Solutions NW, LLC
Based on our field observations, the majority of the native soils encountered during our fieldwork
are consistent with glacial till deposits.
Groundwater
During our subsurface exploration completed on October 2021, groundwater seepage was not
encountered at the test pit locations. However, perched seepage should be expected within the
weathered zone of soils on this site depending on the time of year grading occurs. In general,
groundwater flow rates and elevations are higher during the winter, spring, and early summer
months.
GEOLOGICALLY HAZARDOUS AREAS
Based on our review of the referenced Renton municipal code section and site conditions
encountered during our fieldwork, there are no geologic hazard areas (erosion, landslide, seismic,
or mine hazards) on or within 300 feet of the subject site. Standard development BMPs may be
used for this site development plans.
DISCUSSION AND RECOMMENDATIONS
General
Based on the results of our investigation, construction of typical single-family residences on this
site is feasible from a geotechnical standpoint. The primary geotechnical considerations
associated with the proposed development include site grading, foundation support, slab-on-
grade subgrade support, and the suitability of using on-site soils as structural fill.
Typical single-family residences may be supported on conventional continuous and spread
footing foundations bearing on competent native soil, recompacted native soil, or new structural
fill placed directly on competent native soil. In general, competent native soil, suitable for support
of the new foundations, will likely be encountered beginning at depths of about one to two feet
bgs. Where loose or unsuitable soil conditions are exposed at foundation subgrade elevations,
compaction of soils to the specifications of structural fill, or overexcavation and replacement with
suitable structural fill, will be necessary. ESNW should review the proposed plans to confirm the
recommendations in this report remain applicable.
Due to the low infiltration capacity of the glacially consolidated soils on this site, infiltration on the
site is not recommended.
This study has been prepared for the exclusive use of Mr. Juan Carlos Morales, Jim Howton, and
their representatives. A warranty is neither expressed nor implied. This study has been prepared
in a manner consistent with the level of care and skill ordinarily exercised by other members of
the profession currently practicing under similar conditions in this area.
Mr. Juan Carlos Morales ES-8222
c/o Mr. Jim Howton Page 4
November 24, 2021
Earth Solutions NW, LLC
Site Preparation and Earthwork
Initial site preparation activities will consist of installing temporary erosion control measures,
establishing grading limits, removing structural improvements, and clearing and stripping the site.
Subsequent earthwork activities will involve site grading and related infrastructure improvements.
Temporary Erosion Control
The following temporary erosion control measures are offered:
Temporary construction entrances and drive lanes, consisting of at least six inches of
quarry spalls, should be considered to both minimize off-site soil tracking and provide a
stable access entrance surface. Placing geotextile fabric underneath the quarry spalls will
provide greater stability, if needed.
Silt fencing should be placed around the site perimeter.
When not actively graded, soil stockpiles should be covered or otherwise protected.
Temporary measures for controlling surface water runoff, such as interceptor trenches,
sumps, or swales, should be installed prior to beginning earthwork activities.
Dry soils disturbed during construction should be wetted to minimize dust and airborne soil
erosion.
Additional Best Management Practices (BMPs), as specified by the project civil engineer and
indicated on the plans, should be incorporated into construction activities. Temporary erosion
control measures should be actively managed and may be modified during construction as site
conditions require, to ensure proper performance.
Stripping
Topsoil was generally encountered within the upper approximately six inches at the test pit
locations. The organic-rich topsoil should be stripped and segregated into a stockpile for later
use on site or to haul off site. The material remaining immediately below the topsoil may have
some root zones and will likely be variable in composition, density, and/or moisture content. The
material exposed after initial topsoil stripping will likely not be suitable for direct structural support
as is and will likely need to be compacted in place or stripped and stockpiled for reuse as fill;
depending on the time of year stripping occurs, the soil exposed below the topsoil may be too
wet to compact and may need to be aerated or treated. ESNW should observe initial stripping
activities to provide recommendations regarding stripping depths and material suitability.
Mr. Juan Carlos Morales ES-8222
c/o Mr. Jim Howton Page 5
November 24, 2021
Earth Solutions NW, LLC
Excavations and Slopes
Based on the soil conditions observed at the subsurface exploration locations, the maximum
allowable temporary slope inclinations provided below may be used. The applicable Federal
Occupation Safety and Health Administration and Washington Industrial Safety and Health Act
soil classifications are also provided.
Areas exposing groundwater seepage 1.5H:1V (Type C)
Loose soil; fill 1.5H:1V (Type C)
Medium dense to dense native soil 1H:1V (Type B)
Permanent slopes should be planted with vegetation to both enhance stability and minimize
erosion. The presence of perched groundwater may cause localized sloughing of temporary
slopes. An ESNW representative should observe temporary and permanent slopes to confirm
the slope inclinations are suitable for the exposed soil conditions and to provide additional
excavation and slope recommendations as necessary. If the recommended temporary slope
inclinations cannot be achieved, temporary shoring may be necessary to support excavations.
In-situ and Imported Soils
The majority of the near-surface soils encountered during our subsurface exploration have a high
sensitivity to moisture and were generally in a damp to moist condition at the time of the
exploration (October 2021). Exposed soils will degrade rapidly if exposed to wet weather and/or
construction traffic. In general, soils encountered during site excavations that are more than
about 3 percent over the optimum moisture content will require aeration or treatment prior to
placement and compaction. Conversely, soils that are substantially below the optimum moisture
content will require moisture conditioning through the addition of water prior to use as structural
fill. A representative of ESNW should determine the suitability of in-situ soils for use as structural
fill at the time of construction.
Imported soil intended for use as structural fill should consist of a well-graded, granular soil with
a moisture content that is at (or slightly above) the optimum level. During wet weather conditions,
imported soil intended for use as structural fill should consist of a well-graded, granular soil with
a fines content of 5 percent or less (where the fines content is defined as the percent passing the
Number 200 sieve, based on the minus three-quarter-inch fraction).
Wet-Season Grading
Because the site soils are highly sensitive to moisture, grading during the rainy season will be
very difficult. If grading takes place during the winter, spring, or early summer months, a
contingency in the project budget should be included to allow for export of native soil and import
of wet-weather structural fill.
Mr. Juan Carlos Morales ES-8222
c/o Mr. Jim Howton Page 6
November 24, 2021
Earth Solutions NW, LLC
Structural Fill
Structural fill is defined as compacted soil placed in foundation, slab-on-grade, roadway,
permanent slope, retaining wall, utility trench, and vault backfill areas. Soils placed in structural
areas should consist of a granular material devoid of deleterious debris and organics, placed in
loose lifts of 12 inches or less and compacted to a relative compaction of 95 percent, based on
the laboratory maximum dry density as determined by the Modified Proctor Method (ASTM D-
1557).
Foundations
Typical two to three story residential structures may be supported on conventional spread and
continuous footings bearing on competent native soil, recompacted native soil, or new structural
fill placed directly on competent native soil. In general, competent native soil suitable for the
support of foundations will likely be encountered at depths of about one to two feet bgs. ESNW
should evaluate the design subgrade conditions to confirm suitable conditions are exposed and
to provide additional preparation recommendations, where necessary. Where loose, organic, or
otherwise unsuitable soil conditions are observed at foundation subgrade elevations, compaction
of the soils to the specifications of structural fill, or overexcavation and replacement with granular
structural fill, will likely be necessary.
Provided residential structures will be supported as described above, the following parameters
can be used for design of the new foundations:
Allowable soil bearing capacity 2,500 psf
Passive earth pressure 300 pcf (equivalent fluid)
Coefficient of friction 0.40
The passive earth pressure and coefficient of friction values include a safety factor of 1.5. A one-
third increase in the allowable soil bearing capacity may be assumed for short-term wind and
seismic loading conditions. With structural loading as expected, total settlement in the range of
1 inch is anticipated, with differential settlement of about 0.5 inch. The majority of settlement
should occur during construction, as dead loads are applied.
Mr. Juan Carlos Morales ES-8222
c/o Mr. Jim Howton Page 7
November 24, 2021
Earth Solutions NW, LLC
Seismic Design
The 2018 International Building Code (2018 IBC) recognizes the most recent edition of the
Minimum Design Loads for Buildings and Other Structures manual (ASCE 7-16) for seismic
design, specifically with respect to earthquake loads. Based on the soil conditions encountered
at the boring locations, the parameters and values provided below are recommended for seismic
design per the 2018 IBC.
Parameter Value
Site Class C*
Mapped short period spectral response acceleration, S S (g) 1.373
Mapped 1-second period spectral response acceleration, S 1 (g) 0.47
Short period site coefficient, Fa 1.2
Long period site coefficient, Fv 1.5
Adjusted short period spectral response acceleration, S MS (g) 1.648
Adjusted 1-second period spectral response acceleration, S M1 (g) 0.705
Design short period spectral response acceleration, S DS (g) 1.099
Design 1-second period spectral response acceleration, S D1 (g) 0.47
* Assumes very dense soil conditions, encountered to a maximum depth of nine feet bgs during the October 2021
field exploration, remain very dense or better to at least 100 feet bgs. Based on our experience with the project
geologic setting (glacial till) across the Puget Sound region, soil conditions are likely consistent with this
assumption.
Further discussion between the project structural engineer, the project owner (or their
representative), and ESNW may be prudent to determine the possible impacts to the structural
design due to increased earthquake load requirements under the 2018 IBC. ESNW can provide
additional consulting services to aid with design efforts, including supplementary geotechnical
and geophysical investigation, upon request.
Liquefaction is a phenomenon where saturated or loose soil suddenly loses internal strength and
behaves as a fluid. This behavior is in response to increased pore water pressures resulting from
an earthquake or another intense ground shaking. In our opinion, site susceptibility to liquefaction
may be considered negligible. The absence of a shallow groundwater table and the relatively
dense characteristics of the native soil were the primary bases for this opinion.
Mr. Juan Carlos Morales ES-8222
c/o Mr. Jim Howton Page 8
November 24, 2021
Earth Solutions NW, LLC
Slab-on-Grade Floors
Slab-on-grade floors should be supported on a firm and unyielding subgrade consisting of
competent native soil or new structural fill. Unstable or yielding areas of the subgrade should be
recompacted or overexcavated and replaced with suitable structural fill prior to construction of
the slab. A capillary break, consisting of a minimum of four inches of free-draining crushed rock
or gravel, should be placed below the slab. The free-draining material should have a fines content
of 5 percent or less defined as the percent passing the number 200 sieve based on the minus
three-quarters inch fraction. In areas where slab moisture is undesirable, installation of a vapor
barrier below the slab should be considered. If used, the vapor barrier should consist of a material
specifically designed to function as a vapor barrier and should be installed in accordance with the
manufacturer’s specifications.
Retaining Walls
Retaining walls must be designed to resist earth pressures and applicable surcharge loads. The
following parameters may be used for design:
Active earth pressure (unrestrained condition) 35 pcf (equivalent fluid)
At-rest earth pressure (restrained condition) 55 pcf
Traffic surcharge (passenger vehicles) 70 psf (rectangular distribution) *
Passive earth pressure 300 pcf (equivalent fluid)
Coefficient of friction 0.40
Seismic surcharge 8H psf**
* Where applicable
** Where H equals the retained height (in feet)
The above design parameters are based on a level backfill condition and level grade at the wall
toe. Revised design values will be necessary if sloping grades are to be used above or below
retaining walls. Additional surcharge loading from adjacent foundations, sloped backfill, or other
relevant loads should be included in the retaining wall design, where applicable. A safety factor
of 1.5 is included in the passive earth pressure and coefficient of friction values.
Retaining walls should be backfilled with free-draining material that extends along the height of
the wall and a distance of at least 18 inches behind the wall. The upper 12 inches of the wall
backfill can consist of a less permeable soil, if desired. A sheet drainage product can also be
used for retaining wall drainage. A perforated drainpipe should be placed along the base of the
wall and connected to an approved discharge location. A typical retaining wall drainage detail is
provided on Plate 3. If drainage is not provided, hydrostatic pressures should be included in the
wall design.
Mr. Juan Carlos Morales ES-8222
c/o Mr. Jim Howton Page 9
November 24, 2021
Earth Solutions NW, LLC
Landscape Retaining Walls
Based on the existing site grades, retaining walls may be used along the portions of the lots to
raise grades for new building pads. Final wall heights, alignments and facing materials have not
been determined at the time of this report. Walls over four feet in total height, including toe
embedment will require building permits supported by an engineered design. ESNW can prepare
and engineered retaining wall design, upon request. ESNW should review the final grading plans
to confirm the recommendations are incorporated and to provide additional recommendations
where appropriate.
Drainage
Groundwater seepage was not encountered during our exploration; however, groundwater
seepage will likely be encountered within site excavations, particularly utility trenches and deeper
excavations such as detention vault/pond areas. Temporary measures to control surface water
runoff and groundwater during construction would likely involve passive elements, such as
interceptor trenches and sumps. ESNW should be consulted during preliminary grading to
identify areas of groundwater and to provide recommendations to reduce the potential for
instability related to groundwater effects. Depending on the flow volumes encountered during
grading, an interceptor trench drain system may be warranted along the up-slope perimeter of
the work area to help mitigate or otherwise control shallow perched groundwater flows.
Finish grades must be designed to direct surface water away from the new structures and/or
slopes for a distance of at least 10 feet or as setbacks allow. Water must not be allowed to pond
adjacent to the new structures and/or slopes. A typical foundation drain detail is provided on
Plate 4.
Infiltration Evaluation
The site soils consist predominately of silty sand with gravel, glacially consolidated deposits that
exhibit fines contents ranging from about 18 to 33 percent (passing the U.S. No. 200 sieve).
These soils are not suitable for infiltration.
Mr. Juan Carlos Morales ES-8222
c/o Mr. Jim Howton Page 10
November 24, 2021
Earth Solutions NW, LLC
Preliminary Stormwater Vault Design Recommendations
Detention vault foundations should be supported on competent native soil or crushed rock placed
directly on a competent native subgrade. Final stormwater vault designs must incorporate
adequate space from property boundaries such that temporary excavations to construct the vault
structure can be successfully completed or shoring will be required. Perimeter drains should be
installed around the vault and conveyed to an approved discharge point. The presence of
perched groundwater seepage should be anticipated during excavation activities for the vault.
The following parameters can be used for preliminary stormwater vault design:
Allowable soil bearing capacity (dense native soil) 5,000 psf
Active earth pressure 35 pcf
Active earth pressure (hydrostatic) 80 pcf
At-rest earth pressure (restrained) 55 pcf
At-rest earth pressure (restrained, hydrostatic) 100 pcf
Coefficient of friction 0.40
Passive earth pressure 300 pcf
Seismic surcharge 8H*
* Where H equals the retained height.
Vault walls must be backfilled with at least 18 inches of free-draining material or suitable sheet
drainage that extends along the height of the walls. The upper one foot of the wall backfill can
consist of a less permeable soil, if desired. A perforated drain pipe should be placed along the
base of the vault wall and connected to an approved discharge location. If the elevation of the
vault bottom is such that gravity flow to an outlet is not possible, the portion of the vault below the
drain should be designed to include hydrostatic pressure. Design values accounting for
hydrostatic pressure are included above.
ESNW should observe grading operations for the vault and the subgrade conditions prior to
concrete forming and pouring to confirm conditions are as anticipated, and to provide
supplemental recommendations as necessary. Additionally, ESNW should be contacted to
review final vault designs to confirm that appropriate geotechnical parameters have been
incorporated.
Mr. Juan Carlos Morales ES-8222
c/o Mr. Jim Howton Page 11
November 24, 2021
Earth Solutions NW, LLC
Utility Support and Trench Backfill
The native soils observed at the test pit locations are generally suitable for support of utilities;
however, the native soils may not be suitable for use as structural backfill in the utility trench
excavations unless the soil is at or near the optimum moisture content at the time of placement
and compaction. Moisture conditioning or cement treatment of the soils may be necessary at
some locations prior to use as structural fill. If utility backfill occurs during wet weather, cement
treatment of native soils or import of a suitable material will likely be necessary. Utility trench
backfill should be placed and compacted to the specifications of structural fill provided in this
report, or to the applicable requirements of presiding jurisdiction.
Preliminary Pavement Sections
The performance of site pavements is largely related to the condition of the underlying subgrade.
To ensure adequate pavement performance, the subgrade should be in a firm and unyielding
condition when subjected to proofrolling with a loaded dump truck. Structural fill in pavement
areas should be compacted to the specifications detailed in the Site Preparation and Earthwork
section of this report. It is possible that soft, wet, or otherwise unsuitable subgrade areas may
still exist after base grading activities. Areas of unsuitable or yielding subgrade conditions may
require remedial measures such as overexcavation and replacement with structural fill or thicker
crushed rock sections prior to pavement.
For lightly loaded pavement areas subjected primarily to passenger vehicles such as driveways,
the following preliminary pavement sections may be considered:
A minimum of two inches of hot mix asphalt (HMA) placed over four inches of crushed
rock base (CRB), or;
A minimum of two inches of HMA placed over three inches of asphalt treated base (ATB).
Heavier traffic areas generally require thicker pavement sections depending on site usage,
pavement life expectancy, and site traffic. For preliminary design purposes, the following
pavement sections for occasional truck traffic areas may be considered:
Three inches of HMA placed over six inches of crushed rock base (CRB), or;
Three inches of HMA placed over four-and-one-half inches of ATB.
The HMA, CRB and ATB materials should conform to WSDOT specifications.
If pavement areas will include an inverted crown, additional drainage should be used to effectively
convey water that may enter the subgrade toward the storm drainage system. ESNW can provide
recommendations for enhanced drainage upon request.
Mr. Juan Carlos Morales ES-8222
c/o Mr. Jim Howton Page 12
November 24, 2021
Earth Solutions NW, LLC
LIMITATIONS
The recommendations and conclusions provided in this study are professional opinions
consistent with the level of care and skill that is typical of other members in the profession
currently practicing under similar conditions in this area. A warranty is neither expressed nor
implied. Variations in the soil and groundwater conditions observed at the test locations may
exist and may not become evident until construction. ESNW should reevaluate the conclusions
provided in this study if variations are encountered.
Additional Services
ESNW should have an opportunity to review final project plans with respect to the geotechnical
recommendations provided in this report. ESNW should also be retained to provide testing and
consultation services during construction.
Geotechnical Engineering,Construction
Observation/Testing and Environmental Services
Drwn.CAM
Checked SSR Date Nov.2021
Date 11/22/2021 Proj.No.8222
Plate 1
Earth Solutions NWLLCEarthSolutionsNWLLC
EarthSolutions
NW LLC
Vicinity Map
Morales Short Plat
Renton,Washington
Reference:
King County,Washington
OpenStreetMap.org
NORTH
NOTE:This plate may contain areas of color.ESNW cannot be
responsible for any subsequent misinterpretation of the information
resulting from black &white reproductions of this plate.
Renton
SITE
Geotechnical Engineering,Construction
Observation/Testing and Environmental Services
Drwn.CAM
Checked SSR Date Nov.2021
Date 11/22/2021 Proj.No.8222
Plate 2
Earth Solutions NWLLCEarthSolutionsNWLLC
EarthSolutions
NW LLC
TP-1
TP-2 TP-3
TP-4
TP-5
Lot 1
Lot 2
Lot 3Lot4
House
Sheds156thavenues.e.Alley
Gravel
Asphalt Driveway
Concrete464
464
466
466
468
468
470
470
4 7 0
0 3 0 6 0 1 2 0
Sc ale in Feet1"=6 0 '
NOTE:This plate may contain areas of color.ESNW cannot be
responsible for any subsequent misinterpretation of the information
resulting from black &white reproductions of this plate.
NOTE:The graphics shown on this plate are not intended for design
purposes or precise scale measurements,but only to illustrate the
approximate test locations relative to the approximate locations of
existing and /or proposed site features.The information illustrated
is largely based on data provided by the client at the time of our
study.ESNW cannot be responsible for subsequent design changes
or interpretation of the data by others.
LEGEND
Approximate Location of
ESNW Test Pit,Proj.No.
ES-8222,Oct.2021
Subject Site
Existing Building
Proposed Lot Number
TP-1
NORTH
Lot 1
Test Pit Location Plan
Morales Short Plat
Renton,Washington
Geotechnical Engineering,Construction
Observation/Testing and Environmental Services
Drwn.CAM
Checked SSR Date Nov.2021
Date 11/22/2021 Proj.No.8222
Plate 3
Earth Solutions NWLLCEarthSolutionsNWLLC
EarthSolutions
NW LLC
NOTES:
Free-draining Backfill should consist
of soil having less than 5 percent fines.
Percent passing No.4 sieve should be
25 to 75 percent.
Sheet Drain may be feasible in lieu
of Free-draining Backfill,per ESNW
recommendations.
Drain Pipe should consist of perforated,
rigid PVC Pipe surrounded with 1-inch
Drain Rock.
LEGEND:
Free-draining Structural Backfill
1-inch Drain Rock
18"Min.
Structural
Fill
Perforated Rigid Drain Pipe
(Surround in Drain Rock)
SCHEMATIC ONLY -NOT TO SCALE
NOT A CONSTRUCTION DRAW ING
Retaining Wall Drainage Detail
Morales Short Plat
Renton,Washington
Geotechnical Engineering,Construction
Observation/Testing and Environmental Services
Drwn.CAM
Checked SSR Date Nov.2021
Date 11/22/2021 Proj.No.8222
Plate 4
Earth Solutions NWLLCEarthSolutionsNWLLC
EarthSolutions
NW LLC
Slope
Perforated Rigid Drain Pipe
(Surround in Drain Rock)
18"Min.
NOTES:
Do NOT tie roof downspouts
to Footing Drain.
Surface Seal to consist of
12"of less permeable,suitable
soil.Slope away from building.
LEGEND:
Surface Seal:native soil or
other low-permeability material.
1-inch Drain Rock
SCHEMATIC ONLY -NOT TO SCALE
NOT A CONSTRUCTION DRAW ING
Footing Drain Detail
Morales Short Plat
Renton,Washington
Earth Solutions NW, LLC
Appendix A
Subsurface Exploration
Test Pit Logs
ES-8222
Subsurface conditions at the subject site were explored on October 25, 2021 by excavating five
test pits using a mini-trackhoe and operator retained by our firm. The approximate locations test
pits are illustrated on Plate 2 of this study. The test pit logs are provided in this Appendix. The
maximum exploration depth was approximately nine feet bgs and were terminated in firm native
soils.
The final logs represent the interpretations of the field logs and the results of laboratory analyses.
The stratification lines on the logs represent the approximate boundaries between soil types. In
actuality, the transitions may be more gradual.
GRAVEL
AND
GRAVELLY
SOILS
CLAYEY GRAVELS, GRAVEL - SAND -
CLAY MIXTURES
WELL-GRADED SANDS, GRAVELLY
SANDS, LITTLE OR NO FINES
POORLY-GRADED SANDS,
GRAVELLY SAND, LITTLE OR NO
FINES
SILTY SANDS, SAND - SILT
MIXTURES
CLAYEY SANDS, SAND - CLAY
MIXTURES
INORGANIC SILTS AND VERY FINE
SANDS, ROCK FLOUR, SILTY OR
CLAYEY FINE SANDS OR CLAYEY
SILTS WITH SLIGHT PLASTICITY
INORGANIC CLAYS OF LOW TO
MEDIUM PLASTICITY, GRAVELLY
CLAYS, SANDY CLAYS, SILTY CLAYS,
LEAN CLAYS
ORGANIC SILTS AND ORGANIC
SILTY CLAYS OF LOW PLASTICITY
INORGANIC SILTS, MICACEOUS OR
DIATOMACEOUS FINE SAND OR
SILTY SOILS
INORGANIC CLAYS OF HIGH
PLASTICITY
SILTS
AND
CLAYS
MORE THAN 50%
OF MATERIAL IS
LARGER THAN
NO. 200 SIEVE
SIZE
MORE THAN 50%
OF MATERIAL IS
SMALLER THAN
NO. 200 SIEVE
SIZE
MORE THAN 50%
OF COARSE
FRACTION
PASSING ON NO.
4 SIEVE
MORE THAN 50%
OF COARSE
FRACTION
RETAINED ON NO.
4 SIEVE
SOIL CLASSIFICATION CHART
(APPRECIABLE
AMOUNT OF FINES)
(APPRECIABLE
AMOUNT OF FINES)
(LITTLE OR NO FINES)
FINE
GRAINED
SOILS
SAND
AND
SANDY
SOILS
SILTS
AND
CLAYS
ORGANIC CLAYS OF MEDIUM TO
HIGH PLASTICITY, ORGANIC SILTS
PEAT, HUMUS, SWAMP SOILS WITH
HIGH ORGANIC CONTENTS
LETTERGRAPH
SYMBOLSMAJOR DIVISIONS
COARSE
GRAINED
SOILS
TYPICAL
DESCRIPTIONS
WELL-GRADED GRAVELS, GRAVEL -
SAND MIXTURES, LITTLE OR NO
FINES
POORLY-GRADED GRAVELS,
GRAVEL - SAND MIXTURES, LITTLE
OR NO FINES
SILTY GRAVELS, GRAVEL - SAND -
SILT MIXTURES
CLEAN
GRAVELS
GRAVELS WITH
FINES
CLEAN SANDS
(LITTLE OR NO FINES)
SANDS WITH
FINES
LIQUID LIMIT
LESS THAN 50
LIQUID LIMIT
GREATER THAN 50
HIGHLY ORGANIC SOILS
DUAL SYMBOLS are used to indicate borderline soil classifications.
The discussion in the text of this report is necessary for a proper understanding of the nature
of the material presented in the attached logs.
GW
GP
GM
GC
SW
SP
SM
SC
ML
CL
OL
MH
CH
OH
PT
Earth Solutions NW LLC
MC = 18.0%
MC = 8.2%
MC = 6.3%
TPSL
SM
Dark brown TOPSOIL, minimal root intrusions
Brown silty SAND with gravel, medium dense, moist (Weathered till)
-becomes gray, dense, damp
-weakly cemented
-unweathered till
-becomes very dense
Test pit terminated at 8.0 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
0.5
8.0
NOTES Depth of Topsoil & Sod 6": grass
LOGGED BY SES
EXCAVATION METHOD
EXCAVATION CONTRACTOR NW Excavating
CHECKED BY SSR
DATE STARTED 10/25/21 COMPLETED 10/25/21
GROUND WATER LEVEL:
GROUND ELEVATION +-468 ft
LONGITUDE -122.13219 LATITUDE 47.48726
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
PAGE 1 OF 1
TEST PIT NUMBER TP-1
PROJECT NUMBER ES-8222 PROJECT NAME Morales Short Plat
GENERAL BH / TP / WELL - 8222.GPJ - GRAPHICS TEMPLATE.GDT - 11/22/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 10.6%
Fines = 18.3%
MC = 9.0%
Fines = 32.8%
TPSL
SM
Dark brown TOPSOIL, minimal root intrusions
Brown silty SAND with gravel, medium dense, damp
-becomes gray, dense
[USDA Classification: very gravelly coarse sandy LOAM]
-becomes very dense, weakly cemented
[USDA Classification: gravelly sandy LOAM]
Test pit terminated at 9.0 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
0.5
9.0
NOTES Depth of Topsoil & Sod 6": grass
LOGGED BY SES
EXCAVATION METHOD
EXCAVATION CONTRACTOR NW Excavating
CHECKED BY SSR
DATE STARTED 10/25/21 COMPLETED 10/25/21
GROUND WATER LEVEL:
GROUND ELEVATION +-469 ft
LONGITUDE -122.13191 LATITUDE 47.48721
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
PAGE 1 OF 1
TEST PIT NUMBER TP-2
PROJECT NUMBER ES-8222 PROJECT NAME Morales Short Plat
GENERAL BH / TP / WELL - 8222.GPJ - GRAPHICS TEMPLATE.GDT - 11/22/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 15.0%
MC = 8.3%
MC = 7.3%
TPSL
SM
Dark brown TOPSOIL, minimal root intrusions
Brown silty SAND with gravel, medium dense, moist
-becomes gray, dense, damp
-becomes weakly cemented
-becomes very dense
Test pit terminated at 8.0 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
0.5
8.0
NOTES Depth of Topsoil & Sod 6": grass
LOGGED BY SES
EXCAVATION METHOD
EXCAVATION CONTRACTOR NW Excavating
CHECKED BY SSR
DATE STARTED 10/25/21 COMPLETED 10/25/21
GROUND WATER LEVEL:
GROUND ELEVATION +-470 ft
LONGITUDE -122.13121 LATITUDE 47.48721
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
PAGE 1 OF 1
TEST PIT NUMBER TP-3
PROJECT NUMBER ES-8222 PROJECT NAME Morales Short Plat
GENERAL BH / TP / WELL - 8222.GPJ - GRAPHICS TEMPLATE.GDT - 11/22/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 22.4%
Fines = 21.9%
MC = 12.8%
TPSL
SM
Dark brown TOPSOIL, root intrusions to 1'
Brown silty SAND with gravel, medium dense, wet
[USDA Classification: gravelly sandy LOAM]
-becomes gray, dense, moist
-becomes weakly cemented
-becomes very dense
Test pit terminated at 8.5 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
0.5
8.5
NOTES Depth of Topsoil & Sod 6": grass
LOGGED BY SES
EXCAVATION METHOD
EXCAVATION CONTRACTOR NW Excavating
CHECKED BY SSR
DATE STARTED 10/25/21 COMPLETED 10/25/21
GROUND WATER LEVEL:
GROUND ELEVATION +-468 ft
LONGITUDE -122.13127 LATITUDE 47.4869
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
PAGE 1 OF 1
TEST PIT NUMBER TP-4
PROJECT NUMBER ES-8222 PROJECT NAME Morales Short Plat
GENERAL BH / TP / WELL - 8222.GPJ - GRAPHICS TEMPLATE.GDT - 11/22/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 29.8%
MC = 12.0%
MC = 12.4%
TPSL
SM
Dark brown TOPSOIL, root intrusions to 1'
Brown silty SAND with gravel, medium dense, wet
-becomes gray, dense, moist
-becomes very dense, weakly cemented
Test pit terminated at 8.0 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
0.5
8.0
NOTES Depth of Topsoil & Sod 6": grass
LOGGED BY SES
EXCAVATION METHOD
EXCAVATION CONTRACTOR NW Excavating
CHECKED BY SSR
DATE STARTED 10/25/21 COMPLETED 10/25/21
GROUND WATER LEVEL:
GROUND ELEVATION +-466 ft
LONGITUDE -122.13219 LATITUDE 47.48696
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
PAGE 1 OF 1
TEST PIT NUMBER TP-5
PROJECT NUMBER ES-8222 PROJECT NAME Morales Short Plat
GENERAL BH / TP / WELL - 8222.GPJ - GRAPHICS TEMPLATE.GDT - 11/22/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
Earth Solutions NW, LLC
Appendix B
Laboratory Test Results
ES-8222
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.0010.010.1110100
3
D100
140
Specimen Identification
1
fine
6
HYDROMETER
304
18.3
32.8
21.9
101/2
COBBLES
Specimen Identification
4
coarse
20 401.5 8 14
USDA: Gray Very Gravelly Coarse Sandy Loam. USCS: SM.
USDA: Gray Gravelly Sandy Loam. USCS: SM.
USDA: Brown Gravelly Sandy Loam. USCS: SM with Gravel.
6 60
PERCENT FINER BY WEIGHTD10
0.215
0.131
1.508
0.366
1.147
GRAIN SIZE DISTRIBUTION
100
LL
TP-02
TP-02
TP-04
3/4
U.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS
GRAVEL SAND
9.5
19
19
%Silt
TP-02
TP-02
TP-04
2 2003
Cc CuClassification
%Clay
16
PID60 D30
coarse SILT OR CLAYfinemedium
GRAIN SIZE IN MILLIMETERS
3/8 50
4.0ft.
9.0ft.
2.0ft.
4.00ft.
9.00ft.
2.00ft.
PL
PROJECT NUMBER ES-8222 PROJECT NAME Morales Short Plat
GRAIN SIZE USDA ES-8222 MORALES SHORT PLAT.GPJ GINT US LAB.GDT 11/16/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
Earth Solutions NW, LLC
Report Distribution
ES-8222
EMAIL ONLY Mr. Juan Carlos Morales
c/o Mr. Jim Howton
11047 Southeast 62nd Place
Bellevue, Washington 98006
Bonsai Estates Short Plat Preliminary Technical Information Report
Appendix B
WWHM Output
WWHM2012
PROJECT REPORT
CMP Sizing 1/9/2024 9:14:31 AM Page 2
General Model Information
Project Name:CMP Sizing
Site Name:
Site Address:
City:
Report Date:1/9/2024
Gage:Seatac
Data Start:1948/10/01
Data End:2009/09/30
Timestep:15 Minute
Precip Scale:1.167
Version Date:2019/09/13
Version:4.2.17
POC Thresholds
Low Flow Threshold for POC1:50 Percent of the 2 Year
High Flow Threshold for POC1:50 Year
CMP Sizing 1/9/2024 9:14:31 AM Page 3
Landuse Basin Data
Predeveloped Land Use
Basin 1
Bypass:No
GroundWater:No
Pervious Land Use acre
C, Forest, Mod 1.169
Pervious Total 1.169
Impervious Land Use acre
Impervious Total 0
Basin Total 1.169
Element Flows To:
Surface Interflow Groundwater
CMP Sizing 1/9/2024 9:14:31 AM Page 4
Mitigated Land Use
Basin 1
Bypass:No
GroundWater:No
Pervious Land Use acre
C, Lawn, Mod 0.53
Pervious Total 0.53
Impervious Land Use acre
ROADS MOD 0.244
ROOF TOPS FLAT 0.328
SIDEWALKS MOD 0.067
Impervious Total 0.639
Basin Total 1.169
Element Flows To:
Surface Interflow Groundwater
Contech CMP 1 Contech CMP 1
CMP Sizing 1/9/2024 9:14:31 AM Page 5
Routing Elements
Predeveloped Routing
CMP Sizing 1/9/2024 9:14:31 AM Page 6
Mitigated Routing
Contech CMP 1
Element Flows To:
Outlet 1 Outlet 2
CMP Sizing 1/9/2024 9:14:31 AM Page 7
Analysis Results
POC 1
+ Predeveloped x Mitigated
Predeveloped Landuse Totals for POC #1
Total Pervious Area:1.169
Total Impervious Area:0
Mitigated Landuse Totals for POC #1
Total Pervious Area:0.53
Total Impervious Area:0.639
Flow Frequency Method:Log Pearson Type III 17B
Flow Frequency Return Periods for Predeveloped. POC #1
Return Period Flow(cfs)
2 year 0.04818
5 year 0.081888
10 year 0.108691
25 year 0.147667
50 year 0.18044
100 year 0.216451
Flow Frequency Return Periods for Mitigated. POC #1
Return Period Flow(cfs)
2 year 0.026323
5 year 0.037487
10 year 0.046515
25 year 0.060002
50 year 0.071713
100 year 0.084988
Annual Peaks
Annual Peaks for Predeveloped and Mitigated. POC #1
Year Predeveloped Mitigated
1949 0.070 0.021
1950 0.075 0.026
1951 0.095 0.051
1952 0.031 0.019
1953 0.027 0.023
1954 0.038 0.024
1955 0.059 0.024
1956 0.055 0.029
1957 0.048 0.024
1958 0.044 0.024
CMP Sizing 1/9/2024 9:15:10 AM Page 8
1959 0.038 0.022
1960 0.075 0.040
1961 0.036 0.025
1962 0.025 0.018
1963 0.036 0.024
1964 0.049 0.023
1965 0.037 0.029
1966 0.030 0.022
1967 0.082 0.024
1968 0.045 0.022
1969 0.043 0.021
1970 0.034 0.022
1971 0.045 0.025
1972 0.074 0.036
1973 0.034 0.028
1974 0.045 0.025
1975 0.058 0.023
1976 0.042 0.024
1977 0.018 0.020
1978 0.034 0.025
1979 0.020 0.018
1980 0.132 0.043
1981 0.030 0.023
1982 0.077 0.034
1983 0.050 0.024
1984 0.031 0.021
1985 0.018 0.022
1986 0.077 0.029
1987 0.071 0.035
1988 0.030 0.021
1989 0.019 0.021
1990 0.223 0.041
1991 0.102 0.039
1992 0.040 0.025
1993 0.036 0.021
1994 0.015 0.018
1995 0.047 0.025
1996 0.125 0.050
1997 0.090 0.102
1998 0.035 0.021
1999 0.143 0.038
2000 0.034 0.025
2001 0.009 0.018
2002 0.048 0.032
2003 0.082 0.022
2004 0.077 0.053
2005 0.053 0.025
2006 0.052 0.027
2007 0.171 0.127
2008 0.173 0.066
2009 0.074 0.029
Ranked Annual Peaks
Ranked Annual Peaks for Predeveloped and Mitigated. POC #1
Rank Predeveloped Mitigated
1 0.2225 0.1274
2 0.1732 0.1022
3 0.1706 0.0660
CMP Sizing 1/9/2024 9:15:10 AM Page 9
4 0.1429 0.0528
5 0.1316 0.0514
6 0.1254 0.0500
7 0.1016 0.0433
8 0.0945 0.0407
9 0.0897 0.0400
10 0.0821 0.0390
11 0.0820 0.0382
12 0.0771 0.0362
13 0.0769 0.0348
14 0.0765 0.0337
15 0.0755 0.0319
16 0.0751 0.0295
17 0.0741 0.0294
18 0.0736 0.0291
19 0.0713 0.0286
20 0.0702 0.0276
21 0.0592 0.0266
22 0.0580 0.0255
23 0.0546 0.0254
24 0.0530 0.0252
25 0.0521 0.0252
26 0.0503 0.0252
27 0.0492 0.0251
28 0.0480 0.0251
29 0.0478 0.0248
30 0.0474 0.0248
31 0.0455 0.0245
32 0.0453 0.0244
33 0.0447 0.0243
34 0.0442 0.0243
35 0.0426 0.0242
36 0.0421 0.0239
37 0.0400 0.0238
38 0.0384 0.0238
39 0.0376 0.0235
40 0.0372 0.0234
41 0.0364 0.0226
42 0.0356 0.0226
43 0.0355 0.0224
44 0.0348 0.0223
45 0.0343 0.0223
46 0.0342 0.0221
47 0.0339 0.0218
48 0.0339 0.0216
49 0.0314 0.0212
50 0.0308 0.0211
51 0.0302 0.0210
52 0.0298 0.0210
53 0.0296 0.0210
54 0.0265 0.0208
55 0.0247 0.0205
56 0.0202 0.0201
57 0.0195 0.0192
58 0.0180 0.0183
59 0.0177 0.0181
60 0.0153 0.0181
61 0.0088 0.0180
CMP Sizing 1/9/2024 9:15:10 AM Page 10
CMP Sizing 1/9/2024 9:15:10 AM Page 11
Duration Flows
The Facility PASSED
Flow(cfs)Predev Mit Percentage Pass/Fail
0.0241 16206 16196 99 Pass
0.0257 14127 9672 68 Pass
0.0272 12198 7702 63 Pass
0.0288 10515 6385 60 Pass
0.0304 9163 5392 58 Pass
0.0320 7965 4336 54 Pass
0.0336 6951 3559 51 Pass
0.0351 6143 2984 48 Pass
0.0367 5450 2524 46 Pass
0.0383 4860 2108 43 Pass
0.0399 4359 1547 35 Pass
0.0415 3918 1111 28 Pass
0.0430 3482 632 18 Pass
0.0446 3084 440 14 Pass
0.0462 2731 407 14 Pass
0.0478 2417 371 15 Pass
0.0494 2160 342 15 Pass
0.0509 1931 291 15 Pass
0.0525 1761 256 14 Pass
0.0541 1597 222 13 Pass
0.0557 1392 200 14 Pass
0.0573 1246 186 14 Pass
0.0588 1118 178 15 Pass
0.0604 1035 170 16 Pass
0.0620 942 160 16 Pass
0.0636 875 144 16 Pass
0.0652 788 130 16 Pass
0.0667 713 106 14 Pass
0.0683 631 102 16 Pass
0.0699 545 97 17 Pass
0.0715 465 93 20 Pass
0.0730 391 90 23 Pass
0.0746 349 87 24 Pass
0.0762 309 82 26 Pass
0.0778 265 79 29 Pass
0.0794 218 75 34 Pass
0.0809 184 71 38 Pass
0.0825 152 68 44 Pass
0.0841 126 65 51 Pass
0.0857 113 61 53 Pass
0.0873 93 57 61 Pass
0.0888 80 54 67 Pass
0.0904 67 52 77 Pass
0.0920 60 47 78 Pass
0.0936 49 43 87 Pass
0.0952 44 36 81 Pass
0.0967 41 32 78 Pass
0.0983 34 30 88 Pass
0.0999 30 28 93 Pass
0.1015 25 23 92 Pass
0.1031 20 15 75 Pass
0.1046 18 13 72 Pass
0.1062 12 10 83 Pass
CMP Sizing 1/9/2024 9:15:10 AM Page 12
0.1078 12 4 33 Pass
0.1094 11 3 27 Pass
0.1110 11 3 27 Pass
0.1125 10 3 30 Pass
0.1141 9 3 33 Pass
0.1157 9 2 22 Pass
0.1173 9 2 22 Pass
0.1188 9 2 22 Pass
0.1204 9 2 22 Pass
0.1220 9 1 11 Pass
0.1236 9 1 11 Pass
0.1252 9 1 11 Pass
0.1267 8 1 12 Pass
0.1283 8 0 0 Pass
0.1299 8 0 0 Pass
0.1315 7 0 0 Pass
0.1331 6 0 0 Pass
0.1346 6 0 0 Pass
0.1362 6 0 0 Pass
0.1378 6 0 0 Pass
0.1394 6 0 0 Pass
0.1410 6 0 0 Pass
0.1425 6 0 0 Pass
0.1441 5 0 0 Pass
0.1457 5 0 0 Pass
0.1473 5 0 0 Pass
0.1489 5 0 0 Pass
0.1504 5 0 0 Pass
0.1520 5 0 0 Pass
0.1536 5 0 0 Pass
0.1552 5 0 0 Pass
0.1568 4 0 0 Pass
0.1583 4 0 0 Pass
0.1599 4 0 0 Pass
0.1615 4 0 0 Pass
0.1631 4 0 0 Pass
0.1646 4 0 0 Pass
0.1662 4 0 0 Pass
0.1678 4 0 0 Pass
0.1694 4 0 0 Pass
0.1710 3 0 0 Pass
0.1725 3 0 0 Pass
0.1741 1 0 0 Pass
0.1757 1 0 0 Pass
0.1773 1 0 0 Pass
0.1789 1 0 0 Pass
0.1804 1 0 0 Pass
CMP Sizing 1/9/2024 9:15:10 AM Page 13
Water Quality
Water Quality BMP Flow and Volume for POC #1
On-line facility volume:0 acre-feet
On-line facility target flow:0 cfs.
Adjusted for 15 min:0 cfs.
Off-line facility target flow:0 cfs.
Adjusted for 15 min:0 cfs.
CMP Sizing 1/9/2024 9:15:10 AM Page 14
LID Report
CMP Sizing 1/9/2024 9:16:44 AM Page 15
Model Default Modifications
Total of 0 changes have been made.
PERLND Changes
No PERLND changes have been made.
IMPLND Changes
No IMPLND changes have been made.
CMP Sizing 1/9/2024 9:16:44 AM Page 16
Appendix
Predeveloped Schematic
CMP Sizing 1/9/2024 9:16:47 AM Page 17
Mitigated Schematic