HomeMy WebLinkAboutC25004016 TIR
Gill Single Family Residence
Technical Information Report
City of Renton Permit No.: B25001833
July 16, 2025
For: Manjit Gill
551 Orcas Ave NE
Renton, WA 98059 Prepared By: Interlaken Engineering and Design, PLLC
7001 Seaview Ave NW, Suite 160-388, Seattle, WA 98117 (206) 470-9572 www.interlakenengineering.com
B25001833_V2
RECEIVED
07/23/2025 striplett
BUILDING DIVISION
Surface Water Enginering
jfarah 10/28/2025
DEVELOPMENT ENGINEERING
HHuynh 11/05/2025
Interlaken Engineering and Design, PLLC
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TABLE OF CONTENTS Section 1 – Project Overview...……………………………………………………………3 Section 2 – Conditions and Requirements Summary ......................................................... 4 Core Requirement #1: Discharge at the Natural Location. ............................................. 4
Core Requirement #2: Offsite Analysis. ......................................................................... 4 Core Requirement #3: Flow Control............................................................................... 4 Core Requirement #4: Conveyance System. .................................................................. 4 Core Requirement #5: Erosion and Sediment Control. .................................................. 4 Core Requirement #6: Maintenance and Operation........................................................ 4
Core Requirement #7: Financial Guarantees and Liability. ............................................ 4 Special Requirement #4: Source Control. ....................................................................... 5 Proposed Flow Control BMPs ........................................................................................ 5 Section 3 – Offsite Analysis ............................................................................................... 6 Section 4 – Conveyance System Analysis and Design ....................................................... 7
Section 5 – Special Reports and Studies ............................................................................. 9 Section 6 – Other Permits ................................................................................................... 9 Section 7 – CSWPPP Analysis and Design ........................................................................ 9 Section 8 – Facility Summaries, and Declaration of Covenant ........................................ 10 Section 9 – Operation and Maintenance Manual .............................................................. 10
Interlaken Engineering and Design, PLLC
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Section 1 – Project Overview
The project site (Parcel No. 273920-0110; 551 Orcas Ave NE, Renton) is a rectangular 0.22-acre lot located on the west side of Orcas Ave NE. The lot is zoned R-4. The abutting properties are developed residential lots. The lot is presently vacant and covered by grasses and shrubs. A new single-family residence is proposed for the central portion of the lot. Access will be provided by a driveway extending west into the site from Orcas Ave NE. The subject lot has approximately 72’ of frontage along the west side of Orcas Ave NE. The lot slopes to the southwest at magnitudes of about 7-15%. The total relief on-site is about 10 feet.
Under existing conditions flows disperse and infiltrate across the site. Runoff that does not infiltrate on site flows overland west across the project site and is collected by the existing City of Renton drainage system in Nile Ave NE. According to the Geotechnical Report prepared by Pacific Geo Engineering dated February 6th, 2025; the site is underlain by dense glacial till. Heavy groundwater seepage was observed at
shallow depths. Infiltration is infeasible. The full geotechnical report has been included in the appendices. The applicant proposes to construct a new SFR with 3,313 sf of roof, 342 sf of uncovered deck, 233 sf of on-site walkway, and 957 sf of on-site paved driveway/parking area. The total proposed on-site hard surface area for this project is 4,845 sf. Total site disturbance will be approximately 7,200 sf. Because the subject lot is smaller than 22,000 square feet, it is subject to the Small Lot BMP Requirements in Appendix C of the 2022 City of Renton Surface Water Design Manual. The project proposes less than 5,000 sf of impervious area. However, due to the proposed
modification of a 12” storm pipe this project is subject to Targeted Drainage Review, Category 2.
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Section 2 – Conditions and Requirements Summary
According to City of Renton Surface Water Design Manual (hereafter CORSWDM) Figure 1.1.2.A Flow Chart for Determining Type of Drainage Review Required and Section 1.1.2.2 Targeted Drainage Review, the proposed project is subject to Core
Requirements (hereafter CR) #1-2 & 4-7 and Special Requirement (hereafter SR) #4 as
outlined below with a brief summary of how it will be met:
Core Requirement #1: Discharge at the Natural Location.
Under existing conditions flows disperse and infiltrate across the site. Runoff that does not infiltrate on site flows overland west across the project site and is collected by the
existing City of Renton drainage system in Nile Ave NE. The same drainage pattern will
remain under developed conditions. Runoff from the proposed roof, walkway, deck and on-site driveway will be collected and routed via tightlines to a dispersion trench to the west of the proposed SFR. This maintains existing drainage patterns to the greatest extent feasible.
Core Requirement #2: Offsite Analysis.
Minimal to no offsite flows enter the site. The upstream properties are similar small residential lots. Runoff from the project site infiltrates and disperses across the project site. Runoff that does not infiltrate on site flows overland west across the project site and is collected by the existing City of Renton drainage system in Nile Ave NE.
Core Requirement #3: Flow Control.
Not required for Targeted Drainage Review Category 2.
Core Requirement #4: Conveyance System.
Short sections of 6" PVC storm drain pipe will be used to convey runoff from downspouts to the proposed drywell. Calculations are included in Section 5.
Core Requirement #5: Erosion and Sediment Control.
The Construction Storm Water Pollution Prevention Plan (CSWPPP) for this project includes the Erosion and Sediment Control (ESC) Plan and Stormwater Pollution Prevention and Spill Control Measures. Temporary erosion control measures will include silt fences, construction fences, a temporary construction entrance, catch basin
protections and plastic covers (if any are present). See Section 8 for an ESC plan and
CSWPPP attached.
Core Requirement #6: Maintenance and Operation.
O&M will be as stated in 2022 RDWDM Pre-Approved Plans Policy. The on-site BMPs will be maintained by the property owners. Standard maintenance and operation practices
for all proposed on-site structures have been included in Section 10.
Core Requirement #7: Financial Guarantees and Liability.
The owner and/or developer will provide all Financial Guarantees and Liability.
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Special Requirement #4: Source Control.
The proposed project does not require a commercial building or commercial site
development permit. (2022 CORSWDM 1.3.4)
Proposed Flow Control BMPs
To address the requirements for mitigation of target impervious surface, the applicability
and feasibility of the on-site BMPs were evaluated based on the order described per Section C.1.3. The following summarizes the feasibility analysis: 1) Full Dispersion: Full dispersion is infeasible because the site cannot meet the 15% ratio of fully dispersed impervious area to native vegetated surface. 2) Full Infiltration: Full infiltration is infeasible. According to the Geotechnical
Report prepared by Pacific Geo Engineering dated February 6th, 2025 sf the site is underlain by dense glacial till. Heavy groundwater seepage was observed at shallow depths. Infiltration is infeasible. 3) Rain Gardens: Rain gardens are infeasible. According to the Geotechnical Report prepared by Pacific Geo Engineering dated February 6th, 2025 sf the site is
underlain by dense glacial till. Heavy groundwater seepage was observed at shallow depths. Infiltration is infeasible. Bioretention: Bioretention is infeasible. According to the Geotechnical Report prepared by Pacific Geo Engineering dated February 6th, 2025 sf the site is underlain by dense glacial till. Heavy groundwater seepage was observed at
shallow depths. Infiltration is infeasible. Permeable Pavement: Permeable pavement is infeasible. According to the Geotechnical Report prepared by Pacific Geo Engineering dated February 6th, 2025 sf the site is underlain by dense glacial till. Heavy groundwater seepage was observed at shallow depths. Infiltration is infeasible.
4) Basic Dispersion: Basic dispersion is feasible and proposed to the maximum extent practicable. In accordance with CORSWDM C.2.4.4 up to 3,500 sf of impervious surface may be drained to a 50-foot trench with notch board. A 50’ dispersion trench is proposed to the west of the proposed residence with a 25’ vegetated flow path. This dispersion trench will mitigate runoff from the proposed
roof. In the absence of feasible BMPs, runoff from the proposed driveway will sheet flow to the right-of-way where it will be collected by the existing City of Renton storm system. 5) BMPs must be implemented, at a minimum for an impervious surface are equal to at least 10% of the site/ lot for site/ lot sizes up to 11,000 sf. Basic Dispersion is
proposed to mitigate flows from 3,500 sf of roof area, which is 36% of the subject lot. Additional BMPs are not required.
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Section 3 – Offsite Analysis
Task 1 Study Area Definition and Maps The project is located in Renton on a 9,626 sf (0.22 acre) rectangular lot zoned R-4 (Parcel No. 273920-0110) located on the west side of Orcas Ave NE.
Task 2 Resource Review There are no landslide hazards on the site or in the immediate vicinity. There are no erosion hazards on the site or in the immediate vicinity. There are no Wetlands on the site or in the immediate vicinity.
There are no potential steep slope hazards on the site or in the immediate vicinity.
There are no critical aquifer recharge areas on the site or in the immediate vicinity. The project site is mapped as low susceptibility to groundwater contamination.
Task 3 Field Inspection
Upstream Tributary Area The adjacent properties on all sides are similar developed small residential lots. Minimal offsite flows enter the project site.
Downstream Drainage
Under existing conditions any runoff that does not disperse and infiltrate on-site flows overland west across the project site and is collected by the existing City of Renton drainage system in Nile Ave NE.
Task 4 Drainage System Description and Potential Problems
Flows onsite generally infiltrate and disperse onsite. There are no known downstream drainage issues. Task 5 Mitigation of Existing and Potential Problems
Downstream Drainage Problems Requiring Special Attention
Type 1 – Conveyance System Nuisance Problems There are no known, reported, or observed current downstream conveyance problems. Type 2 – Severe Erosion Problems There are no known, reported, or observed current downstream severe erosion problems.
Type 3 – Severe Flooding Problems
There are no known, reported, or observed current downstream severe flooding problems.
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Section 4 – Conveyance System Analysis and Design
Onsite storm pipes will have sizes of 6” and minimum slopes of 2%. Offsite storm pipes will have sizes of 12” and have been set to a slope of 2.5% to match existing pipe inverts.
The system is designed to convey the 25-year peak flows and checked for flooding
conditions at the 100-year event per the 2022 City of Renton Surface Water Design Manual. The rational method is used to calculate the 25 and 100 year 24-hour runoff peaks. Roof drains are connected to the Basic Dispersion BMP to the west of the residence. New storm main pipes within project frontage to the east are connected to
existing City of Renton stormwater pipes at the north and south extents of the subject lot.
ROW impervious area calculation is as follows:
320 ft length of Upstream Orcas Ave X (26 ft pavement width + (2) 0.5 ft curbs + (2) 5 ft sidewalks) =
11,840 sf ≈ 0.2718 ac Upstream lots along Orcas Ave impervious area calculation is as follows:
66676 sf (total area of neighboring lots) X 50% (maximum impervious surface area per Renton Municipal Code - Table 4-2-110A) = 33,338 sf ≈ 0.7653 ac
Pipe Calculations Precipitation P25y = 3.4 inches, P100y = 3.90 inches Time of concentration = 6.3 minutes iR = aR x Tc (-bR)
aR = 2.66 for 25 year – 24-hour storm
aR = 2.61 for 100 year – 24-hour storm bR = 0.65 for 25 year – 24-hour storm bR = 0.63 for 100 year – 24-hour storm iR = 2.66 x 6.3(-0.65) = 0.804 for 25 year – 24-hour storm
iR = 2.61 x 6.3(-0.63) = 0.819 for 100 year – 24-hour storm
IR = iR x PR = 2.733 inches for 25 year – 24-hour storm = 3.194 for 100 year – 24-hour storm
Q = C * IR *A
Impervious area
(acres)
C = 0.90
Pervious area
(acres)
C = 0.25
Q25y
(cfs)
Q100y
(cfs)
SFR Roof 0.0803 0 0.198 0.231
Paved ROW
+ Neighboring Lots Impervious
1.037
0.934
3.189
3.727
Interlaken Engineering and Design, PLLC
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Full pipe capacity using Manning’s method:
Pipe size (in.) Pipe slope % Manning’s n Full pipe capacity (cfs) Q25y (cfs) Q100y (cfs) SFR Roof 6 2.00 0.012 0.860 0.198 0.231
Paved ROW + Neighboring Lots Impervious
12 2.50 0.012 6.102 3.189 3.727
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Section 5 – Special Reports and Studies
Geotechnical Report prepared by Pacific Geo Engineering dated February 6th, 2025.
Section 6 – Other Permits
Other permits required include water connection permits, septic permit and building permits for the proposed residence.
Section 7 – CSWPPP Analysis and Design
This project requires only simple measures for ESC because this project will disturb less than 1 acre of land. In order to prevent erosion and trap sediments within the project site, the following BMPs
will be used as shown on the ESC plan:
• Clearing limits will be marked by high visibility fencing, tape or other means on the ground. Silt fencing will be placed along slope contours at the downslope limit of clearing.
• The driveway will be constructed and graveled immediately. A rocked construction entrance will be placed at the entrance of the site.
• Plastic covers may be used to protect cut and fill slopes and stockpiles. Mulch will be spread over all cleared areas of the site when they are not being worked.
Mulch will consist of air-dried straw and chipped site vegetation. Cleared areas
accepting sheet flow from the driveway and footprint of the proposed residence will be seeded and mulched.
• Haybales and silt fence will be placed at the downstream end of slopes.
• Runoff will not be allowed to concentrate, and no water will be allowed to point discharge onto the slopes.
• Dust is to be controlled on construction site with a water truck. Dust will be controlled on paved roadways with the use of a sweeper with water if deemed
necessary.
• Silt fencing will be placed along slope contours at the downslope limit of clearing.
• Pollutant control will be monitored by designated ESC supervisor.
• Existing and proposed flow control BMPs will be monitored by the contractor. The limits of proposed drywells and permeable paving will be marked prior to commencement of construction.
• The general contractor will maintain BMPs and manage the project.
Additionally, the following SWPPS measures will be implemented:
• Effective pollutant handling and disposal procedures will be followed.
• Cover and containment for materials, fuel, and other pollutants will be provided.
• Site will be protected from spills and drips of petroleum and other pollutants.
• The overapplication or untimely application of chemicals and fertilizers will be avoided.
• Stormwater runoff from pH modifying sources will be prevented.
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Section 8 – Facility Summaries, and Declaration of Covenant
Following approval of plans a Flow Control and Water Quality Facility Summary Sheet and Sketch will be prepared and submitted.
The applicant will provide the County with an original signed copy of the maintenance
agreement and license to enter prior to issuance of a Building permit.
Section 9 – Operation and Maintenance Manual
The maintenance standards for the following flow control BMPs applied on this project include: Basic Dispersion
GEOTECHNICAL ENGINEERING STUDY
For
NEW SFR
551, ORCAS AVENUE NE
RENTON, WA 98059
Prepared For
MANJIT GILL
551, ORCAS AVENUE NE
RENTON, WA 98059
Prepared By
P.O. BOX 1419, ISSAQUAH, WASHINGTON 98027
PGE PROJECT NUMBER 24-797
February 6, 2025
February 6, 2025
Client: Manjit Gill
551, Orcas Avenue NE
Renton, WA 98059
Re: Single Family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, WA 98059
Parcel # 273920-0110
PGE Project No. 24-797
Dear Mr. Gill:
As per the request, Pacific Geo Engineering, LLC (PGE) has completed the geotechnical engineering
study for the subject property in Renton, Washington, which is shown in Figure 1, Vicinity Map. The study
includes soil investigation and development of geotechnical engineering recommendations pertinent to the
geotechnical aspect of the proposed new residence. This geotechnical engineering study report summarizes
the results of our evaluation and the recommendation.
This study is completed in accordance with the scope of services described in our final executed
proposal no. 24-12-862, dated December 17, 2024, which was authorized on December 19, 2024 by Mr. Gill.
The scope of services was developed based on the preliminary understanding of the proposed new residence
obtained from the client. Our scope of services is planned to obtain as much subsurface information as
possible within the time and budgetary constraints of the project.
The primary purposes of our limited geotechnical study were to perform site reconnaissance, explore
and characterize subsurface soil and groundwater conditions in the site, perform laboratory testing of native
soil, review of available local geologic maps and geotechnical literatures, and to use the data and the
information obtained from the above as a basis for formation of our geotechnical recommendations for the
proposed new residence.
Our recommendations are provided for the design and construction of the proposed residence,
allowable bearing capacity value, slab-on-grade floor, subgrade preparation, site preparation, grading and
earthwork operation, overexcavation, fill placement and compaction, and site drainage and erosion control
measures. Also, evaluations were made on site’s susceptibility to liquefaction under seismic conditions and
infiltration feasibility of the site soil.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 2 of 40
The conclusions and recommendations contained in this report are based upon our current
understanding of the proposed development. We recommend that PGE should be allowed to review the final
design grades and the actual features of the proposed development, and the construction plans after the final
design phase and the construction plans are completed, which will help PGE to verify that the
recommendations provided in this report are included in the final design and plan, and that, if necessary, to
reevaluate and modify the conclusions and the recommendations contained in this report. PGE also
recommends that PGE should be retained for the construction-time testing, inspection, and monitoring of the
geotechnical aspect of the proposed development. If PGE is not retained to provide the above mentioned
geotechnical engineering service continuity, then PGE cannot be responsible for the remaining phases of the
project and any misinterpretation of our recommendations; in this case the selected geotechnical firm by the owner
and the contractor shall become the engineer-of-record for administering PGE’s recommendations.
1.0 Proposed Development
The general location of the site is shown in Figure 1, Vicinity Map. The existing site features and the
surroundings are shown in Figure 2, Site & Exploration Plan, available from Mr. Gill. Based on the current
development plan and the information from the client we understand that a triple-story, single-family
residence with a partial daylight basement floor facing towards west will be built in the open vacant land of
the subject property. The proposed development will have a concrete paved walkway from the Orcas Avenue
NE to provide access to the new residence. The existing structures will be demolished and the trees will be
removed.
Based on our conversation with Mr. Gill we understand that the final grades of the proposed new
residence will be almost at the same grade as the current native grades without any significant grade changes
within the proposed new residence footprint area. Based on the presence of the topsoils, upper loose native
soils, and the existing undocumented loose fills, we assume that there will be some overexcavation to be
required to remove the above soils and the existing fills and backfilling the void areas with new imported
structural fills up to the final subgrade levels. The overexcavation and backfilling depths will be decided on-
site during the actual constriction of the project, which may be found varying across the site.
Based on our experience with similar type of residence, we anticipate that wall loads will be in the
range of 2 to 3 kips per lineal foot, isolated column loads in the range of 40 to 60 kips, and slab-on-grade
floor loads of 150 pounds per square foot (psf).
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 3 of 40
2.0 Engineering Evaluation
Based on the scope of this geotechnical study delineated in the contract agreement, the following
items are accomplished - field exploration, laboratory soil testing, engineering evaluation of the field and
laboratory data, grading recommendations, and foundation recommendations.
The scope of our work did not include any wetland study, or any environmental analysis or evaluation
to find the presence of any hazardous or toxic materials in the soil, surface water, groundwater, or air in or
around this site.
Subsurface Conditions
• Descriptions of the soil and the groundwater conditions;
• Soil Test Pit Logs;
• Depth to water table and any sign of high water table, if encountered;
• Laboratory soil index property test results.
• Native soil Classification as per USCS system;
• USGS Soil unit;
General Site Development & Earthwork & Grading
• Grading and earthwork including site preparation, and fill placement and compaction;
• Use of on-site soils as structural fills;
• Imported structural fill requirements;
• Underground utility structure trench backfilling and pipe bedding;
• Temporary and permanent excavation slopes;
• Temporary construction dewatering;
• Site drainage including permanent subsurface drainage systems and temporary groundwater
control measures, if necessary;
• Dry and wet weather construction;
• Erosion control measurements;
• Infiltration evaluation;
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 4 of 40
Structure
• Foundation type recommendation - conventional shallow spread footings;
• Allowable bearing capacity value for supporting the proposed footings and the cottage;
• Estimated total and differential settlements of the footings;
• Frictional and passive values for the resistance of lateral forces;
• Subgrade preparation for spread footings;
• Slab-on-grade for the proposed building, and the subgrade preparation for slab-on-grade;
• Modulus of subgrade reaction for the design of the slab-on-grade floor;
• Seismic design recommendations, including the site co-efficient as per ASCE7-16 Standard &
2018 IBC;
Geologic Hazard Mitigations
• Geologic hazards evaluation: erosion, seismic, and landslide;
• Liquefaction potential evaluation of native soil;
• Erosion control measures.
3.0 Surface and Subsurface Features
3.1 Site Location
The subject property is located west of the Orcas Avenue NE, in Renton, as shown in Figure 1,
Vicinity Map. The property is a rectangular shaped land, which is bounded by single-family residences on
the north, south, and west, and Orcas Avenue NE on the east. The site has accesses from the Orcas Avenue
East.
3.2 Site Descriptions
The subject property is located within a region dominated by densely populated single family
residences. The site is currently an open vacant land with some temporary structures like fence, wooden play
structure in the backyard. The site is covered with landscape grasses and small to large trees in the backyard.
The property has two distinct topographies; the front yard is at higher level almost at the same grade as the
Orcas Avenue NE, and the backyard is at a relatively lower level. As per Figure 2, the elevation at the
frontyard is approximately 502 feet and the elevation at the backyard is approximately 494 feet. The
transition between the two levels is a minor downhill slope from the frontyard to the backyard.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 5 of 40
4.0 Field Investigation
Soil investigation was performed at three (3) locations in the site as shown in Figure 2, Site &
Exploration Plan. The test pit locations were selected by PGE’s on-site geotechnical engineer and Mr. Gill.
The test pit locations plotted in Figure 2 should be considered accurate only to the degree implied by the
measuring methods.
The test pits were advanced at the site on January 12, 2024, using an excavating machine hired by
the owner. The test pits were excavated up to approximately 5 to 9 feet depths in the test pits below the
grades.
The specific number and location of the test pits were selected in relation to the existing and
proposed site features, accessibility to the open spaces of the property, underground utility conflicts, purpose
of evaluation, budget considerations, and after the consultation and approval of the owner.
A geotechnical engineer from PGE observed the field explorations including the test pit excavations,
soil sampling, continually logging the subsurface conditions in the test pits, collecting representative bulk
samples from different soil layers at different depths of the test pits, and visually-manually classifying the
soil samples in the field as per the methods described in the ASTM D-2488-93 (based on soil samples'
density/consistency, moisture condition, grain size, and plasticity estimations) and the 'Key to Exploration
Logs' figure in Appendix A. The engineer also observed the pertinent site features and took notes. The soil
samples were designated according to the test pit number and sampling depth, stored in watertight plastic
containers, and later on transported to our laboratory for further visual examination and testing.
Results of the field investigation are presented in the soil test pit logs (Appendix A). The final
exploration logs were prepared with our observation and interpretation of the test pit excavation, and visual
examination of the samples in the field and later on in the laboratory. The soils were classified according to
the methods presented in figure 'Key to Exploration Logs' in Appendix A. This figure also provides a legend
explaining the symbols and abbreviations used in the soil exploration logs. The soil logs indicate the depth
where the soils change. It should be noted that the indicated stratification lines on the logs represent the
approximate boundaries between soil types. The actual transitions of varying soil strata may be more gradual
in the field.
5.0 Laboratory Testing
Laboratory tests were conducted on several selected representative soil samples to evaluate the
general physical properties and the engineering characteristics of the soils encountered. The bulk samples
were visually-manually classified in the laboratory following the procedure described in ASTM D-2488-17
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 6 of 40
(based on the soil samples' density/consistency, moisture condition, grain size, and plasticity estimations),
and later on the soil samples' classifications were supplemented by laboratory tests data in accordance with
the procedure described in ASTM D-2487-17.
Moisture content tests were conducted on the samples in accordance with ASTM D-2216-10
procedures. The results of the moisture content tests are provided in the test pit logs, Appendix A.
6.0 Site Soil and Groundwater Conditions
The explored area was covered with landscape grasses, which is underlain by topsoils for
approximately 12 inches thickness below the current grades.
TP-1
The topsoil is underlain by undocumented existing fill consisting of brown, very moist, loose, silty sand
with gravel (USCS Soil Classification: SM) and cobble, and some debris that continued up to approximately 2.5
depth below the grade. The fill was then underlain by native soil consisted of light gray, very moist, loose to
medium dense at shallow depth and very dense at greater depth, sand with gravel, and occasional cobble and
boulder (USCS Soil Classification: SP) extended up to the bottom of the test pit at approximately 9 feet depth
below the grade.
TP2 & TP-3
The topsoil is underlain by native soil comprised of brown, very moist, loose, silty sand with gravel
(USCS Soil Classification: SM), that continued up to approximately 2.5 depth below the grades. The above soil
was then underlain by light gray, wet, loose, sand with gravel up to approximately 4 feet depth below the grade
and then by moist, very dense, glacial till comprising of sand with gravel, and occasional cobble and boulder
(USCS Soil Classification: SP) extended up to the bottom of the test pits at approximately 5 feet depth below the
grades.
Hydrogeologic Condition
TP-1
Very minor perched water seepage was noticed at approximately 2.5 feet depth below the grade at
the bottom of the existing fill, and in the native soil at the bottom of the test pit TP-1.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 7 of 40
TP-2 & TP-3
Heavy groundwater seepage was noticed within the exploration depths of the test pits TP-2 and TP-3
at approximately 2.5 feet below the grade. Heavy mottling signs (oxidized soils) were noticed in the soils
above the glacial till. Mottling signs (oxidized soils) are indicative of accumulation of seasonal perched
groundwater above the underlying denser deposit.
Perched water is defined when stormwater permeates through the upper, less denser soils, and
accumulates on top of the underlying denser, less permeable soils, like glacial till, which is very typical in the
Puget Sound area. Typically, perched water presents in a spatial manner above the denser deposit like glacial
till. It is to be noted that fluctuations in the perched water amount and level may be expected due to the
seasonal variations in the amount of rainfall, surface runoff, and other factors not apparent at the time of our
explorations. Typically, the perched water level rises higher and the flow rate increases during the wet winter
months, which are evidenced by the signs of mottling.
The preceding discussion on the subsurface conditions of the site is intended as a general review to
highlight the major subsurface stratification features and material characteristics. For more complete and
specific information at individual test pit location, please review the Soil Test Pit Log (Figure A-1, A-2, and
A-3) in Appendix A. The log includes soil descriptions, stratification, and location of the samples, and the
laboratory test results. It should be noted that the stratification lines shown on the logs represent the
approximate boundaries between various soil strata; actual transitions may be more gradual or more severe.
The subsurface explorations made as part of the site evaluation indicate the subsurface conditions at
test pit location only and as such the actual subsurface conditions may vary in other areas of the site. The
actual nature and extent of such variation would not become evident until additional explorations are
performed in the site or until construction activities have begun.
7.0 Local Geologic Literature & Map Review
7.1 Regional Geology
The site lies within the Puget Sound Lowland, which is part of a regional north-south trending
structural and topographic trough or depression lying between Olympic Mountains on the west and Cascade
Mountains on the east and extends from southwestern British Columbia to near Eugene, Oregon. The lowland
depression experienced successive glaciation and nonglaciation activities over the time of Pleistocene period.
During the most recent Fraser glaciation, which advanced from and retreated to British Columbia between
13,000 and 20,000 years ago, the lowland depression was buried under about 3,000 feet of continental glacial
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 8 of 40
ice. During the successive glacial and nonglacial intervals, the lowland depression, which is underlain by
Tertiary volcanic and sedimentary bedrock, was filled up above the bedrocks to the present-day land surface
with Quaternary sediments, which consisted of Pleistocene glacial and nonglacial sediments. The glacial
deposits include concrete-like lodgement till, lacustrine silt, fine sand and clay, advance and recessional
outwash composed of sand or sand and gravel, and some glaciomarine materials. The nonglacial deposits
include largely fluvial sand and gravel, overback silt and clay deposits, and peat attesting to the sluggish stream
environments that were apparently widespread during nonglacial times.
7.2 USGS Soil Unit
As per the WA State DNR map (Interactive Geologic Information Portal), provided in Figure 4, the
site is underlain by Pleistocene (Quaternary) Continental Glacial Drift (geologic Map Unit - Qgd). The
glacial drift soils were deposited during the Vashon Stade of the Fraser Glaciation, approximately 12,000
to 15,000 years ago. As per the above map the deposit is described as Pleistocene till and outwash clay,
silt, sand, gravel, cobbles, and boulders deposited by or originating from continental glaciers, locally
includes peat, nonglacial sediments, modified land, and artificial fills. The undocumented existing fills,
and the underlying native soils consisted of sand and gravel with varying amounts of silt and glacial till
encountered in the test pits match with the above descriptions.
7.3 WA State DNR Portal Map – Liquefaction Potential Map
As per the WA State DNR map (Interactive Geologic Information Portal), Figure 4, the seismic site
class is categorized as ‘C’, representing ‘very dense soil and soft rock’, and the site has ‘very low’ potential
for liquefaction.
8.0 Geologic Hazards
As per the King County Code, the potential geologic hazards i.e., the landslide, seismic, and erosion in
the subject property are evaluated, which are discussed in the following subsections.
8.1 Landslide Hazard
Based on the topography of the site, the site is almost a level flat ground with minor slope hence the
potential for landslide hazard in this site is considered nil.
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 9 of 40
8.2 Seismic Hazard
Liquefaction Potential
Earthquake-induced geologic hazards may include liquefaction, lateral spreading, slope instability,
and ground surface fault rupture. Liquefaction is a phenomenon, which takes place due to the reduction or
complete loss of soil strength due to an increase in pore water pressure in soils during the seismic vibrations
induced by a major earthquake event. Liquefaction primarily affects geologically recent deposits of loose,
fine-grained sands and granular silts that are below the groundwater table. Based on our review of the soil
and groundwater conditions in the test pits, it is our opinion that the on-site soils are not prone to liquefaction
because of the presence of till at shallow depths and the absence of groundwater within the explored depths.
Also, as per WA State DNR map (Interactive Geologic Information Portal), Figure 4, the seismic site class is
designated as ‘C’, representing ‘very dense soil and soft rock’, and the site has ‘very low’ potential for
liquefaction. Therefore, potential for widespread liquefaction and its associated hazards over the site during a
seismic event is almost none. Therefore, the subsurface conditions do not warrant additional mitigation
techniques relating to liquefaction hazards.
While the site is relatively near the Seattle Fault zone, no evidence of ground fault rupture was
observed in the subsurface explorations or our site reconnaissance. Therefore, the potential for ground surface
is also low.
Regional Seismicity
The site is located in the Puget Sound region of western Washington, which is seismically active.
Seismicity in this region is attributed primarily to the interaction between the Pacific, Juan de Fuca and North
American plates. The Juan de Fuca plate is subducting beneath the North American plate at the Cascadia
Subduction Zone (CSZ). This produces both intercrustal (between plates) and intracrustal (within a plate)
earthquakes. In the following sections we discuss the design criteria and potential hazards associated with the
regional seismicity. Provided the design criteria listed below are followed, the proposed structure should
have no greater seismic risk damage than other appropriately designed structures in the Puget Sound area.
Seismic Design Parameters
As per the WA State DNR map (Interactive Geologic Information Portal), Seismic Map, the NEHRP
Seismic Site Class is mapped as Site Class ‘C’, which is described as very dense deposit. According to the
SEA OSHPD Seismic Design Maps, and as per the 2016 ASCE 7-16 code standards, Table 20.3-1, for the
seismic Site Class ‘C’, the following seismic design parameters should be used for the structural design of
the building.
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 10 of 40
Table 1 - Seismic Design Parameters
Spectral Response Acceleration (SRA) and Site Coefficients Short Period (0.2 sec)
Maximum Considered Earthquake (MCE) Ss = 1.356g
Site Response Coefficient (Site Class C) Fa = 1.2
Adjusted Spectral Response Acceleration (SRA) of MCE SMS = Ss x Fa = 1.663g
Design SRA SM1 = 2/3 x SMS = 0.7g
Spectral Response Acceleration (SRA) and Site Coefficients One Second Period (1 sec)
Maximum Considered Earthquake (MCE) S1 = 0.474g
Site Response Coefficient (Site Class C) Fv = 1.5
Adjusted Spectral Response Acceleration (SRA) of MCE SDS = 1.108
Design SRA SD1 = 0.474
Peak Ground Acceleration
The mapped peak ground acceleration (PGA) for this site is 0.59g. To account for site class, the PGA
is multiplied by a site amplification factor (FPGA) of 1.2. The resulting site modified peak ground acceleration
(PGAM) is 0.708g.
8.3 Erosion Hazard
Typically, uncontrolled surface water with runoff over unprotected site surfaces during construction
activities is considered the single most important factor that impacts the erosion potential of a site. The
erosion process may be accelerated significantly when factors such as soils with high fines, sloped surface,
and wet weather combines together. Taking into consideration the almost level grades of the subject property
where the proposed new residence will be built, and if the proposed construction will take place during dry
summer period it is our opinion that the potential for erosion hazard of the site soils is not a limiting factor
for the proposed development. This possibility will be further reduced if appropriate erosion control
measures are installed and maintained as recommended below. These measurements must be kept in place
and to be maintained throughout the earthwork and the grading activities.
Though special mitigations are not necessary, a temporary erosion and sediment control (TESC) plan
should be created and implemented during site construction. It is our opinion that implementation of a
relatively basic erosion control plan will prevent off site sediment transport. The proper use of “best
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 11 of 40
management practices” (BMPs) should be utilized during development of the building to minimize the
potential for erosion and sediment off of the property due to clearing, grading and construction traffic.
Implementation of a TESC plan will likely be a requirement of the clearing and grading or building
permit. The City of Renton will perform TESC inspections during construction to verify compliance with the
TESC plan and permit conditions.
Erosion Control Measures & Mitigations
All erosion sediment control measures must conform to the City of Renton requirements. As a
minimum, we recommend implementing the following erosion and sediment control Department of Ecology
(DOE) best Management Practices (BMPs) prior to, during, and immediately after clearing and grading
activities at the site.
• Mass grading activities and the earthwork should be completed within the dry summer period since
the near surface site soils containing some silts may pose some erosion related problems.
• Limit disturbance to areas where construction is imminent. If possible, site clearing and grading
should be performed in stages, with successive stages not being cleared until erosion control
measures for the previous stages are in place.
• Determine staging areas for temporary stockpiles of excavated soils as part of the excavation
planning.
• Provide temporary cover for denuded areas including cut slopes and soil stockpiles during periods of
inactivity. From October 1 to April 30, no soil shall remain un-stabilized for more than 48 hours.
From May 1 to September 13, no soil shall remain un-stabilized for more than seven days.
Temporary cover may consist of straw mulch or plastic sheeting that is securely anchored to the
ground surface. Plastic covering should be placed and anchored, as specified in BMP C123 provided
in Chapter 4.1 of the Stormwater Management Manual for Western Washington. Mulching should be
conform to the guide lines outlined in the BMP C121 provided in Chapter 4.1 of the Stormwater
Management Manual for Western Washington
• Establish permanent covers for exposed areas that will not be worked for period of 30 days or more
by seeding in conjunction with a mulch cover or appropriate hydroseeding. Seeding should conform
to the specifications outlined in BMP C120 provided in Chapter 4.1 of the Stormwater Management
Manual for Western Washington.
• Measurements such as the control of surface water must be maintained during construction.
• Vegetation clearing must be kept very limited in this site to reduce the exposed surface areas. It is
recommended that following the clearing of the vegetations, grading the open exposed areas should
be covered with mulch or hydroseed.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 12 of 40
• No disturbance or removal of the existing vegetations, tress, and undergrowths should be made
beyond the proposed construction area.
• Temporary erosion and sedimentary control (TESC) plan, as a part of the Best Management
Practices (BMP) must be developed and implemented as well. The TESC plan should include the use
of geotextile barriers (silt fences) along any down-slope, straw bales to de-energize downward flow,
controlled surface grading, limited work areas, equipment washing, storm drain inlet protection, and
sediment traps. The TESC plan may need to be reviewed and modified periodically to address the
changing site conditions during ongoing progress of the construction and the weather.
• A permanent erosion control plan is to be implemented following the completion of the construction.
Permanent erosion control measurements such as establishment of landscaping, replantation of trees
and groundcover vegetations as soon as feasible in areas that are necessarily disturbed by earthwork
activities, control of downspouts and surface drains, control of sheet flow over the excavation slope,
prevention of discharging water over the excavation slope and at the toe of the slope are to be
implemented following the completion of the construction.
• Install temporary or permanent tightline pipes, where necessary and practical, to convey stormwater
from above slope to appropriate downslope facilities on flatter terrain.
• Install permanent stormwater runoff diversion systems, such as swales, curbs, berms, or pipes, to
prevent flow directly over any final slope grades.
• We recommend that completed graded-areas be restricted from traffic or protected prior to wet
weather conditions. The graded areas may be protected by paving, placing asphalt-treated base, a
layer of free-graining material such as pit run sand and gravel or clean crushed rock material
containing less than 5 percent fines, or some combination of the above.
Containment
• Install a silt fence along the downhill side of the construction area that will be disturbed. The silt
fence should be placed before cleaning and grading is initiated and should conform to the
specifications outlined in BMP C233 provided in Chapter 4.2 of the Stormwater Management
Manual for Western Washington.
• Construct interceptor dikes and shallow drainage swales to intercept surface water flow and route the
flow away from the construction tare to be stabilized and approved point of controlled discharge.
Some small detention ponds with pipe slope drains may be incorporated with the swales in order to
collect and transport the runoff to the discharge point.
• Provide on-site sediment retention for collected runoff. Runoff should not flow freely over the top of
the slope or off the site.
• The on-site contractor should perform daily review and maintenance of all erosion and sedimentation
control measures at the site to ensure their proper working order.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 13 of 40
Provided the recommended erosion and sedimentation control BMP’s are properly implemented and
maintained, it is our opinion that the planned development will not increase the potential for erosion at the
site or on adjacent properties.
9.0 Executive Summary
Based on this study, the subject site is considered suitable for the proposed development, if the
geotechnical recommendations provided in this report are properly understood and interpreted, and
implemented during the design and construction phases of the proposed development.
It should be noted that if the subsurface conditions are found to be different in the unexplored areas
of the site than what it is found in the explored areas then the recommendations provided in this report may
need to be revisited and altered to incorporate the changes. This may calls for possible changes in the final
design of the project as well. A contingency plan should be in place by the owner considering the above
scenario.
The existing fill is found in the frontyard of the property in test pit TP-1 up to approximately 2.5 feet
depth below the current grade. Below the fill the native soil comprised of light gray sand with gravel, cobble,
and boulder was in very moist and loose condition up to approximately 4 feet depth below the grade. The fill
and the native soil are not considered strong enough and reliable for supporting any type of loading like footing,
slab-on-grade floor, and new fill pad since the existing fill and the native soil may undergo significant amount of
settlement under the above loading. Based on the test pit TP-1 soil profile, the native soil at approximately 4 feet
depth below the grade was noticed as medium dense deposit, which in our opinion, is considered suitable for
supporting footing and new fill pad. PGE recommends that the existing fill and the loose, very moist native soil
must be completely removed up to approximately 4 feet depth below the grade and the void area to be crated
must be backfilled with adequately compacted, new imported structural fill (fill pad) up to the final subgrade
level of the footing and the slab-on-grade floor. The depth of the overexcavation of the existing fill and the loose
native soil may vary in the unexplored area within the footprint area of the proposed residence. Following the
removal of the existing fill and the loose native soil the native subgrade should be prepared as ‘competent’
native subgrade prior to placing new ‘fill pad’. The final native subgrade is described as ‘competent’ when the
subgrade will display firm and unyielding conditions under the subgrade preparation activity recommended
here, which will include ‘redensification’ and ‘proofrolling’ as described later in Section 10.1.3, 'Subgrade
Preparation' of this report.
Heavy groundwater seepage was observed at shallow depth above the glacial till in the lower level
backyard of the property at approximately 2.5 feet depth below the current grade. The native soil above the
glacial till and the upper transition soil in the till were found in very moist and loose condition up to
approximately 4 feet depth below the grade. The combination of the above geological factors in test pit TP-2 and
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 14 of 40
TP-3 prohibit the footing to be placed directly over the very dense glacial till deposit encountered at
approximately 4 feet depth below the grade. It should be noted that the footing cannot be placed directly above
the till deposit because of the presence of heavy seepage above the till deposit; as per the UBC code, for this
condition, the footing must be placed at least 3 feet above the highest groundwater level. Also, the very moist,
loose native soil up to approximately 4 feet depth are not considered strong enough and reliable for supporting
any type of loading like footing, slab-on-grade floor, and new fill pad since the above native soil may undergo
significant amount of settlement under the above loading. The glacial till at approximately 4 feet depth below
the grade was noticed as very dense deposit, which in our opinion, is considered suitable for supporting footing,
and new fill pad. PGE recommends that the loose, very moist native soil must be completely removed up to
approximately 4 feet depth below the grade and the void area to be crated must be backfilled with adequately
compacted, new imported structural fill (fill pad) up to the final subgrade level of the footing and the slab-on-
grade floor. The new fill pad will also help raising the final footing subgrade to 3 feet height above the
groundwater level. The depth of the overexcavation of the existing fill and the loose native soil may vary in the
unexplored area within the footprint area of the proposed residence. Following the removal of the existing fill
and the loose native soil the native subgrade should be prepared as ‘competent’ native subgrade prior to placing
new ‘fill pad’. The final native subgrade is described as ‘competent’ when the subgrade will display firm and
unyielding conditions under the subgrade preparation activity recommended here, which will include
‘redensification’ and ‘proofrolling’ as described later in Section 10.1.3, 'Subgrade Preparation' of this report.
The preparation of the final ‘competent’ native subgrades, redensification and proofrolling, and new
fill compaction may be accomplished by using either a big single- or double-drum vibratory roller.
The new, imported, structural fill material to be used to fill the void area above the final ‘competent’
native subgrade must be granular material, which should be constructed of clean, crushed rock or crushed
gravel, and sand that is fairly well graded between coarse and fine as described later on in Section 10.1.6
‘Structural Fills’ of this report. The new fill must be placed and compacted as per the recommendations
provided later on in Section 10.1.7, 'Fill Placement and Compaction Requirements' of this report. The new
structural fill must be compacted adequately to firm and unyielding condition to achieve 95% or more of fills’
dry density value to be determined from the ASTM Test Designation D-1557 (Laboratory Modified Proctor)
method. The new fill compaction may be accomplished by using either a big single- or double-drum vibratory
roller or a walk-behind, heavy-duty, vibratory plate compactor (similar to TMG-PC330K Reversible Plate
Compactor with 14HP Kohler Engine).
The footing to be supported directly on the medium denser native soil in the frontyard of the property
and on the new ‘fill pad’ in the backyard of the property will be able to provide an allowable bearing capacity
value of 1500 psf for supporting the building footing and keeping the total settlement and differential settlement
of the footing within the allowable limit of 1 inch or less and ½ inch or less, respectively. The footing for the
new residence can be comprised of perimeter wall strip footing and interior isolated column spread footing.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 15 of 40
The slab-on-grade floor should bear directly over the new ‘fill pad’. After the final native subgrade
preparation will be completed as ‘competent’ subgrades and to be accepted by the geotechnical engineer, the
new imported structural fill should be placed and compacted up to the final floor subgrade. The new
structural fill and the new fill placement and compaction should be as per the recommendations provided
earlier in Section 10.1.6, ‘Structural Fills’, and 10.1.7, ‘Fill placement & Compaction’, respectively.
The proposed concrete sidewalk and patio, and driveway should be bearing on a minimum of 12
inches thick new, imported, structural ‘fill pad’.
The horizontal limits of the fill placement under any load-bearing structure should extend laterally
beyond the each side of the fill pad for a horizontal distance equal to the depth of the fill pad. This is to avoid
the loading from the structure (which is assumed exerts pressure through an imaginary line at 1H:1V
inclination or at 450 angle from below the footings) to pass through the fill thickness instead the loading line to
pass below the fill thickness.
The actual overexcavation depth across the proposed construction area should be evaluated by PGE’s
on-site geotechnical engineer during the actual construction. The depth and the degree of the competence of
the final native subgrade may vary across the site, which must be verified and approved on-site by the PGE’s
on-site geotechnical engineer. The redensification of the final native subgrade, proofrolling and preparation
of the final native subgrade as ‘competent’ native subgrades, the new imported structural fill, and the fill
placement and compaction must be monitored and approved by the on-site geotechnical engineer prior to
placing the new fill, and the footing, slab-on-grade floor, concrete paved driveway, side-walk, and concrete
patio directly above new fill.
The heavy-root, organic reach topsoils must be removed completely from the proposed
development area prior to start the cut and fill operations in this site. The topsoils cannot be used structural
fills and be stockpiled for later use in the landscaping areas. The guidelines for reuse of the native soils are
discussed later on in Section 10.1.5, ‘Reuse of Native Soils’ of this report. The recommendations for the
new, imported structural fills are provided later on in Section 10.1.6, ‘Structural Fills’ of this report.
The site does not appear suitable for considering a below grade infiltration system for managing the
stormwater runoff from the proposed new residence because of the presence of heavy groundwater seepage and
the glacial till at shallow depths in the site. We have recommended other option in Section 11.0, ‘Stormwater
Runoff Management’ of this report.
The remainder of this section (10.0) presents specific engineering recommendations on the pertinent
geotechnical aspects that are anticipated for the design and construction of the proposed development. These
recommendations should be incorporated into the final design and drawings, and construction specifications.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 16 of 40
10.0 Conclusion & Recommendations
10.1 Site Preparation
Preparation of the site should involve clearing, stripping, subgrade preparation and proofrolling,
cutting, filling, excavations, and drainage installations. The following paragraphs provide specific
recommendations on these issues.
10.1.1 Clearing and Grubbing
Initial site preparation for the site preparation requires stripping of the topsoil from the proposed
construction area. We anticipate topsoil stripping depth of about 12 inch, however, thicker layer of topsoil
may be present in unexplored portions of the site. It should be realized that if the stripping operation takes
place during wet winter months, it is typical a greater stripping depth might be necessary to remove the near-
surface moisture-sensitive silty soils disturbed during the stripping; therefore, stripping is best performed
during dry weather period. Stripped vegetation debris should be removed from the site. Stripped organic
topsoil will not be suitable for use as structural fill but may be used for future landscaping purposes.
10.1.2 Overexcavations of Fills
Once the clearing of the vegetation and the topsoil from the proposed development area will be
completed, the existing fill from the frontyard of the property must be completely removed up to the
underlying denser native material encountered at approximately 2.5 feet depth below the current grade. The
overexcavation of the fill from the proposed new construction area must be verified by PGE’s on-site
geotechnical engineer. The overexcavation should be performed using smooth-edged bucket to limit the
disturbances of the potential final native subgrade. All loose or disturbed soil should be removed from the
overexcavation area. Following the removal of the unsuitable material, the exposed native subgrade should
be prepared as recommended in the following Section 10.1.3, ‘Subgrade Preparation’. After the subgrade
preparation is completed and approved by the geotechnical engineer the new fill placement should be
initiated. The new fill must be placed and compacted as described later on in Section 10.1.7, ‘Fill Placement
& Compaction Requirements’ of this report.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 17 of 40
10.1.3 Subgrade Preparation
Redensification
After the clearing of the vegetation and topsoil, and following the completion of the overerxcavation
of the existing fill up to the final native subgrade, as a part of the subgrade preparation, we recommend that
all final native subgrade that is supposed to be supporting the new ‘fill pad’ and the footing should be
redensified to enhance the in-situ density of the final native subgrade, improving its bearing capacity hence
reducing its potential of undergoing settlement. Typically, the redensification is effective for the upper one to
two feet of soil below the final native subgrade. The depth of the in-situ density increase depends on the
compaction equipment to be used. Typically, the redensification of the final native subgrades is done using a
big, heavy-weight, single- or double-drum, vibratory roller. The redensification is achieved by having the
compaction equipment make several passes as to be found necessary by the on-site geotechnical engineer.
One pass is considered to consist of a passage of the compactor in each direction, forwards and backwards,
over the same strip of subgrade. The redensification process should be carried out over the whole of the
excavated native subgrade.
Proofrolling
Any exposed subgrade that is intended to provide direct support for new construction and/or require
new fill should be adequately proofrolled to evaluate their condition and to identify the presence of any
isolated soft and yielding area and to verify that stable subgrade is achieved to support the proposed
structures, and any new fills. Typically, the proofrolling of the final native subgrades is done using a big,
heavy-weight, single- or double-drum, vibratory roller. The proofrolling should be done under the
supervision of PGE’s on-site geotechnical engineer. If it is found by the on-site geotechnical engineer that
the soil is too wet near the subgrade to be proofrolled or it not feasible to proofroll the subgrade, then an
alternative method (i.e., visual evaluation and probing with a 1/2-inch diameter steel T-probe) can be used by
the geotechnical engineer to identify the presence of any isolated soft and yielding areas and to verify that
stable subgrades are achieved to support the proposed structures and any new fill.
The final native subgrade should not be exposed to standing water. If water is present in the final native
subgrade it must be removed completely to bring the subgrade into dry condition before placing new fill and
the geogrid layer. Protection of exposed soil, such as placing a 6-inch thick layer of crushed rock or a 3- to 4-
inch layer of lean-mix concrete, could be used to limit disturbance to bearing surfaces.
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 18 of 40
If the base of an overerxcavated area is excessively soft and wet and needs stabilization then we
recommend considering a 6 to 12-inch layer of additional ballast rock or quarry spalls should be placed to
form a base on which the recommended 4 feet of ‘fill pad’ can be placed. Ballast rock should meet the
requirements for Class B Foundation Material in Section 9-03.17 and quarry spalls should meet the
requirements in Section 9-13.1(5) of the 2024 WSDOT Standard Specifications. The ballast rock or quarry
spalls should be pushed into the subgrade with the back of a backhoe bucket or with the use of a large-
vibratory steel drummed roller without the use of vibration. Such decision should be made the on-site
geotechnical engineer during the actual construction of the project.
10.1.4 Backfilling of Test Pit Area
The loosely backfilled soils in exploratory test pits should be overexcavated completely to the firm
native soils and backfilled with adequately compacted new, imported structural fill to the final grade. The
new, imported structural fill should be granular materials like sand and gravel meeting the requirements
provided in Section 10.1.6, ‘Structural Fills’ of this report. The fills should be placed and compacted
following the procedures described later on in Section 10.1.7, 'Fill Placement and Compaction Requirements'
of this report. Prior to placing the new fills the final native subgrades at the bottom of the overexcavated
areas must be proofrolled adequately to firm and unyielding conditions as recommended earlier in Section
10.1.3, ‘Subgrade Preparation’ of this report and accepted by PGE’s on-site geotechnical engineer prior to
placing new fill.
10.1.5 Reuse of Native Soils as Structural Fills
The ability to use native soils as structural fills, to be obtained during the mass grading activities, will
depend on the factors such as the quality of the native soils, i.e., the presence of excessive roots and organics,
fines content, larger-size particles, moisture content, soil types and their gradation, and the prevailing weather
conditions during the time of the construction i.e., dry or wet weather. The weather plays a significant role in
determining if the native soils can be compacted adequately during the wet weather period, especially when the
native soils content higher percentages of fines.
Typically, native soils containing unsuitable materials such as the excessive roots and organics are not
considered suitable for use as structural fills.
No existing fills of uncontrolled and undocumented nature and containing any type of debris can be
used as new structural fills.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 19 of 40
If the native soils contain percentage of fines equal to or less than the allowable percentage of fines
(typically 5% or less) recommended for ‘imported structural fills’ then the native soils are not considered as
moisture insensitive soils and can be reused as structural fills.
The native soils contain higher percentages of fines compared to the typical ‘imported structural fills’
that contains 5% or lesser fines, therefore the native soils should be considered as moisture sensitive soils,
which can only be reused based on the weather conditions and following a careful evaluation of the native soils
by a geotechnical engineer. Typically, when the fines content (that portion passing the U.S. No. 200 sieve) of
soil increases, the soil becomes increasingly sensitive to small changes in moisture content, which makes the
soils’ compaction more difficult or impossible. Soils containing more than about 5 percent fines by weight
cannot be consistently compacted to the recommend degree when the moisture content is more than about 2
percent above or below the optimum. Especially, if the soils with higher fines content are used during the wet
weather period, typically between October and May, significant reduction in the soils strength and support
capabilities occur. Also, when these soils become wet they may be slow to dry and thus significantly retard the
progress of grading and compaction activities. Therefore, the native soil containing higher percentage of fines
cannot be used as structural fills during the wet weather period. However, this type of native soil can be used as
borrow materials for general filling purposes during the dry season, provided the optimum moisture content of
the soils can be maintained during the compaction.
In addition to the higher percentage of fines, if the native soils are found in excessively over the
optimum moisture content, then the soils would pose problems during their compaction. This may require
moisture conditioning of the native soils prior to their placement and compaction.
Other criteria that is to be considered prior to use native soils as structural fills is the presence of
significant amount of larger-size particles such cobbles and boulders. Typically, this type of soil is not
considered suitable to use as structural fills, since the cobbles and the boulders pose problems during the
compaction of the fills. Therefore, the native soils if considered to be used as borrow materials then the cobbles
and the boulders must be removed from the native soils. This can be accomplished either by screening the
native soils on-site or by selectively handpicking the larger-size particles, whichever methodology is feasible
and economical. The PGE’s on-site geotechnical engineer should inspect the final fill product to verify that the
fills do not contain larger size particles. The final fills should contain a maximum of 2 to 3-inch particle
diameter for being able to be adequately compacted.
The suitability of using the native soils should be verified and approved by the on-site geotechnical
engineer prior to their use. If the native soils cannot be used after the inspection and asked by PGE’s on-site
geotechnical engineer to discard then imported new structural fills are to be brought in to the site for backfilling
purposes. In the event that whether the fill materials are to be imported to the site, we recommend that the
imported fill materials be verified and approved by the on-site geotechnical engineer prior to their use. We
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 20 of 40
recommend that a contingency plan should be in place in the project budget if the native soils are to be exported
out and new structural fills need to be imported into the site.
10.1.6 Structural Fill
General Requirements
Typically, excavated native soils containing topsoil, unsuitable materials such as excessive roots and
organics, wood debris and pieces, trash, left over construction debris are not considered suitable for use as
structural fills, and should be properly disposed offsite.
If the native soils are found unsuitable for using as structural fills then we recommend that imported
structural fill should be used for backfilling purposes. The workability of material for use as structural fill
will depend on the gradation and moisture content of the soil. Structural fill is defined as non-organic soil,
free of any debris and deleterious materials, and well-graded and free-draining granular material, such as
sand and gravel or crushed rock with a maximum particle size of 3 inches for any individual particle and less
that 5 percent fines by weight based on the minus ¾-inch fraction. We recommend that washed crushed rock
or select granular fill, as described below, be used for structural fill during wet weather. If prolonged dry
weather prevails during the earthwork phase of construction, materials with somewhat higher fines content
may be acceptable. Weather and site conditions should be considered when determining the type of import
fill materials purchased and brought to the site for use as structural fill. Frozen material should not be used as
structural fills. All materials should be approved by the project geotechnical engineer prior to use. A sample
of each fill material type should be submitted to the project geotechnical engineer for evaluation and
approval prior to use.
A typical gradation for structural fill is presented in the following table.
Table 2 - Structural Fill
U.S. Standard Sieve Size Percent Passing by Dry Weight
3 inch 100
¾ inch 50 –100
No. 4 25 – 65
No. 10 10 – 50
No. 40 0 – 20
No. 200 5 Maximum*
* Based on the ¾ inch fraction.
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 21 of 40
WSDOT Structural Fills
For reference purpose, the following table provides the specifications for various types of structural
fills that can be considered in this site for use as new, imported structural fills.
Table 3 - WSDOT 2024 Structural Fills Specifications
Fill Type Recommended Materials
Structural Fill
9-03.9(1) Ballast
9-03.9(3) Crushed Surfacing Base Course
9-03-12(1)A Gravel Back fill for Foundation Class A
9-03.14(1) Gravel Borrow
Common Fill Section 9-03.14(3) Common Borrow
Free-draining Granular Fill
9-03.9(2) Permeable Ballast
9-03.12(2) Gravel Backfill for Walls
9-03.12(4) Gravel Backfill for Drains
For most applications, we recommend that structural fill consist of material similar to ‘Gravel
Borrow’ or ‘Select Borrow’ as described in Section 9-03.14(1) or Section 9-03.14(2), respectively, of the
WSDOT 2024 Standard Specifications.
Select Granular Fill
Imported materials with gradation characteristics similar to WSDOT 2024 Standard Specification 9-
03.9 (Aggregates for Ballast and Crushed Surfacing), or 9-03.14 (Gravel Borrow) is suitable for use as select
granular fill, provided that the fines content is less than 5 percent (based on the minus ¾-inch fraction) and
the maximum particle size is 6 inches.
Other Fill Materials
Other materials may also be considered suitable for use as structural fill provided they are approved
by the project geotechnical engineer. Such materials typically used include clean, well-graded sand and
gravel (pit-run); clean sand; various mixtures of gravel; crushed rock; controlled-density-fill (CDF, it should
meet the requirements in Section 2-09.3(1)E of the WSDOT 2024 Standard Specifications); and lean-mix
concrete (LMC). Recycled asphalt, concrete, and glass, which are derived from pulverizing the parent
materials also potentially useful as structural fill in certain applications. These materials must be thoroughly
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 22 of 40
crushed to a size deemed appropriate by the geotechnical engineer (usually less than 2 inches). The structural
fills should have a maximum 2 to 3-inch particle diameter.
Stabilization Material
Stabilization rock should consist of pit or quarry run rock that is well-graded, angular, crushed rock
consisting of 4- or 6-inch-minus material with less than 5 percent passing the US Standard No. 4 Sieve. The
material should be free of organic matter and other deleterious material. WSDOT SS 9-13.(15) - Quarry
Spalls can be used as a general specification for this material with the stipulation of limiting the maximum
size to 6 inches.
10.1.7 Fill Placement and Compaction Requirements
Generally, quarry spalls, controlled density fills (CDF), lean mix concrete (LMC) do not require
special placement and compaction procedures. In contrast, clean sand, crushed rock, soil mixtures and
recycled concrete should be placed under special placement and compaction procedures and specifications
described here.
The new ‘fill pad’ should be built up in uniform loose lifts not exceeding 12 inches in thickness for a
big, heavy-weight, single- or double-drum, vibratory roller or a walk-behind, heavy-duty, vibratory plate
compactor (similar to TMG-PC330K Reversible Plate Compactor with 14HP Kohler Engine).
.
No heavy compaction equipment such as hoe pack or big vibratory roller should be used to compact
the backfills to be placed behind the footing stem walls, within the horizontal distance equal to the heights of
the walls. Use of the heavy compaction equipment will impose excess surcharge load on the walls, which
may cause permanent lateral instability to the walls. We recommend that the fills behind the footing stem
walls should be placed in 4 inches lifts and to be compacted with a hand held standard vibratory plate
compactor.
Each lift of fills whether 12 inches or 4 inches or 6 inches should be compacted to a minimum of 95
percent of the fill’s maximum dry density as to be determined in the laboratory by ASTM Test Designation
D-1557 (Modified Proctor) method, or to the applicable minimum City or County standard, whichever is the
more conservative.
The fill should be moisture conditioned such that its final moisture content at the time of compaction
should be at or near (typically within about 2 percent) of its optimum moisture content, as determined by the
ASTM Test Designation D-1557 (Modified Proctor) method. This should help enhance the compatibility of
the materials and avoid the risks involved with wet, moisture sensitive soils. Fills should not be placed on
frozen subgrades.
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 23 of 40
If the fill materials are on the wet side of optimum, they can be dried by relatively inexpensively
periodic windrowing and aeration or by intermixing lime or cement powder to absorb excess moisture. An
ordinary Portland cement powder can be used in this regard. In using cement, we have found that the
hydration of the cement not only results in water absorption, but also develops some “concrete-like” strength
within the soil and cement matrix. In our experience the soil cement matrix can sometimes generates a
compressive strength in excess of two thousand (2,000) psi. If this option is selected, we recommend that for
a preliminary estimation purpose, the cement powder may be intermixed at a rate of about 3% by weight of
the soil. The actual cement content should be decided during the mass grading activity depending on the wet
weather, soils’ natural moisture content, and the soil types. This form of soil treatment is not suitable for any
type soils that are considered as free-daring backfills.
The compacted structural ‘fill pad’ should extend outside all foundations and other load bearing
structures elements for a minimum distance equal to the thickness of the ‘fill pad’.
We recommend that any and all structural fills and /or load bearing backfills be tested for
determining the in-place density and the water content of the fills as per the Nuclear Density Gauge method
(ASTM D6938). This test results will help to verify that the backfills have the achieved the appropriate
degree of compaction and the moisture content. We recommend that compaction of the fills be tested
periodically throughout the fill placement. A field compaction testing program should be prepared by the
geotechnical engineer with the assistance from the project geotechnical engineer. If field density tests
indicate that the last lift of compacted fills has not been achieved the required percent of compaction or the
surface is pumping and weaving under loading, then the fill should be scarified, moisture-conditioned to near
optimum moisture content, re-compacted, and re-tested prior to placing additional lifts.
We recommend that a minimum of one test be performed for one hundred (100) square feet of
compacted or backfill surface area or for every one hundred (100) cubic feet of fill or backfill, whichever
generates the greater number of compaction tests.
10.1.8 Dry Weather Construction
Since the near surface soils have higher fines content, we prefer the proposed construction should be
completed during the dry season to mitigate any erosion related issues that may otherwise arise during the
construction activities in the wet season. Erosion particularly happens, when uncontrolled surface runoff is
allowed to flow over unprotected excavation areas of the site during the wet winter months.
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 24 of 40
10.1.9 Wet Weather Construction
If the construction takes place during the wet weather, the near surface soils, which is anticipated as to
be moisture sensitive, will be found susceptible to degradation and disturbed when get wet. Therefore, it may
be necessary to adopt some remedial measures to enhance the subgrade conditions in this site if the
construction takes place in the winter. The contractor should include a contingency in the earthwork budget for
this possibility. The appropriate remedial measure is best determined by the geotechnical engineer during the
actual construction of the project. The following remedial measures may be considered in this regard:
• The earth contractor must use reasonable care during site preparation and excavation so that the
subgrade soils are remained firm, unyielding, and stable.
• Removal of the affected soil that is already wet exposing suitable bearing subgrades and replacing
with imported free-draining materials as structural fills that can be compacted.
• Aeration of the surficial materials during favorable dry weather by methods such as scarifying or
windrowing repeatedly and expose to sunlight to dry near optimum moisture content prior to
placement and compaction
• Chemical modification of the subgrades with admixtures like hydrated lime or Portland cement,
depending on the soil type.
• Limiting the size of areas that are stripped of topsoil and left exposed.
• Limiting construction traffic over unprotected soils.
• Sloping excavated surfaces to promote runoff.
• Limiting the size and type of construction equipment used.
• Providing gravel or quarry spalls “working mat” over areas of protected subgrade.
• Removing wet surficial soil prior to commencing fill placement each day.
• Sealing the exposed ground surface by rolling with a smooth drum compactor or rubber-tired
roller at the end of each day.
• Providing upgradient perimeter ditches or low earthen berms and using temporary sumps to
collect runoff and prevent water from ponding and damaging exposed subgrades.
• Mechanical stabilization with a coarse crushed aggregate (such as sand and gravel, crushed rock, or
quarry spalls) compacted into the subgrade, possibly in conjunction with a geotextile fabric, such as
Mirafi 500X.
• In the event earthwork takes place during the wet season, we recommend that special precautionary
measurements should be adopted to minimize the impact of water and construction activities on the
moisture sensitive soils.
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 25 of 40
• It is recommended that earthwork be progressed part by part in small sections to minimize the soil’s
exposure to wet weather. Traversing of construction equipment can cause considerable disturbance to
the exposed subgrades, therefore, should be restricted within the specific drive areas. This will also
prevent excessive widespread disturbance of the subgrades. Construction of a new working surface
from an advancing working surface could be used to avoid trafficking the exposed subgrade soils.
• Any excavations or removal of unsuitable soils should be immediately followed by the placement of
backfill or concrete in footings.
• At the end of each day, no loose on-site soils and exposed subgrades be left uncompacted or properly
tamped, which will help seal the subgrade and thereby to minimize the potential for moisture
infiltration into the underlying layers of fills or subgrades.
• In case site filling must proceed during wet weather the contractor should include a contingency in the
earthwork budget for the possibility of using imported clean, granular fill. For general structural fill
purposes, we recommend that using well-graded sand and gravel, such as ‘Ballast’ or ‘Gravel Borrow’
per 2024 WSDOT Standard Specifications 9-03.9(1) and 9-03.14(1), respectively. Alternatively, ‘free-
draining’ soil similar to the one described earlier in the Structure Fill Table may also be considered
suitable as filling material for the wet weather construction. This type of fill refers to soils that have a
fines content of 5 percent or less (by weight) based on the minus ¾-inch soil fraction.
10.1.10 Subgrade Degradation Prevention
The near surface subgrade soils when will be subjected to construction activity during the wet winter
months may degrade. To protect against the subgrade degradation we recommend a ‘working mat’ be placed
over final prepared subgrades. We recommend this ‘working mat’ consists of 12 inches thick free draining
materials consist of crushed rocks or quarry spalls, possibly in conjunction with a geotextile fabric, such as
Mirafi 500X placed underneath the crushed rocks or quarry spalls layer. Construction traffic should be limited
to these ‘working mat’ areas. The stabilization materials can be as per the requirements recommended later on
in Section 10.1.6, ‘Stabilization Materials’.
10.2 Site Drainage
Surface Drainage
The final site grades of the finished development must be such that surface runoff will flow by
gravity away from the building and other structure, such as the pavement and sidewalks, using sloped and
drainage gradients towards the local stormwater collection system. We recommend providing a minimum
drainage gradient of about 2% for a minimum distance of about 10 feet from the building perimeter. Surface
water should not be allowed to pond and soak into the ground surface near buildings or paved areas during or
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 26 of 40
after constructions. A combination of using controlled surface drainage and capping of the building
surroundings by concrete, asphalt, or low permeability silty soils will help minimize or preclude surface
water infiltration around the perimeter of the building and beneath the garage basement floor slab. Paved
areas should be graded to direct runoff to catch basins and or other collection facilities. Collected water
should be directed to the on-site drainage facilities by means of properly sized smooth walled PVC pipe.
Interceptor ditches or trenches or low earthen berms should be installed along the upgrade perimeters of the
site to prevent surface water runoff from precipitation or other sources entering in to the lower area of the lot.
It should be noted that surface water runoff from precipitation flows as a sheet flow over slope is considered
to be the primary cause of surficial sloughing and triggering slope failure. Therefore, the surface drainage
system should be designed in such a way that stormwater runoff over the finished lot must not create any
sheet flow over the sloped areas of the site; instead, the stormwater runoff must be collected in drain pipes to
discharge in approved discharge points at the toe of the slope. Surface drainage system and the water
collection facilities should be designed by a professional civil engineer.
Footing Excavation Drain
Water must not be allowed to pond in the foundation excavations or on prepared subgrades either during
or after construction. If due to the rainfall, runoff, seasonal fluctuations, groundwater seepage is encountered
within footing depths, we recommend that the bottom of excavation should be sloped toward one corner to
facilitate removal of any collected rainwater, groundwater, or surface runoff, and then direct the water to ditches,
and to collect it in prepared sump pits from which the water can be pumped and discharged into an approved
storm drainage system. Water handling needs will typically be lower during the summer and early fall months.
Footing Drain
Footing drains should be used where (1) crawl spaces or basements will be below a structure, (2) a
slab below the outside grade, and (3) the outside grade does not slope downward from a building. To reduce
the potential for groundwater and surface water to seep into the interior spaces of the building we
recommend that an exterior footing drain system be constructed around the perimeter of the building footings
as shown in Figure 5, ‘Footing, Floor Slab, & Footing Drain’ of this report. The drains must be laid with a
gradient sufficient to promote positive flow by gravity to a controlled point of approved discharge. The
foundation drains should be tightlined separately from the roof drains to this discharge point. Footing drains
should consist of at least 6-inch diameter, heavy-walled, perforated PVC pipe or equivalent. The pipe should
be surrounded by at least 6 inches of free-draining gravel over the pipe and 3 inches of free-draining gravel
below the pipe. The free-draining material may consist of open-graded drain rocks consisted of ¾” minus
washed gravels should be wrapped up by a non-woven geotextile filter fabric (Mirafi 140N) to limit the
ingress of fines into the gravel and the pipe. The free-draining material should contain less than 2 percent by
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 27 of 40
weight passing the U.S. Standard No. 200 sieve (based on a wet sieve analysis of that portion passing the
U.S. Standard No. 4 sieve). The drains should be located along the outside perimeter of the spread footings
or the footing stem walls. Also, the invert of the footing pipe should be placed at approximately the same
elevation as the bottom of the footing or 12 inches below the adjacent floor slab grade, whichever is deeper,
so that water will not seep through walls or floor slabs. The footing drains should discharge to an approved
drain system and include cleanouts to allow periodic maintenance and inspection.
Downspout or Roof Drain
These should be installed once the building roof in place. They should discharge directly in tightlines to
a positive, permanent stormwater collection system. Under no circumstances connect these tightlines to the
perimeter footing drains. The drain is shown in Figure 5 of this report.
10.3 Construction Dewatering
As discussed earlier in Section 6.0, heavy groundwater seepage was noticed at approximately 2.5
feet depth below the current grades in test pit TP-2 and TP-3 at the time of the test pit excavations.
Therefore, seepage may be encountered within the overexcavation depth during the construction, especially
if the overexcavation takes place in the wet winter months. Standing water should not be allowed to
accumulate within the overexcavation depth any time when the construction will take place. Therefore, we
recommend that if water is encountered then temporary measures such as typical sump excavations and
sump pumps will be used to de-water the areas for short term work. The construction areas must be
maintained in a complete dry condition throughout the excavation and the construction period, and to prevent
the excavation face and the foundation subgrades against degradation. In our opinion, dewatering techniques
involving some positive elements such as interceptor trenches, collection ditches, and directing water flow to
sumps where water can be removed by conventional filtered sump pumps, can be adopted in this regard.
Also, surface water from seepage must not be allowed to flow over slope area or pond near the top of the
slope, instead the water should be directed away from the slope via ditches or trenches or drain pipes to
approved discharge points at the toe of the slope. If the situation seems severe, then more specialized
dewatering techniques, such as vacuum wells, well points, etc., may be needed. The contractor and its civil
engineer should be responsible for the design and adoption of appropriate dewatering system in this regard.
We recommend that to minimize the possibility of any water conditions during the excavation and the
construction period, the construction should take place during the dry summer months.
10.4 Temporary Excavations
As we understand from the project plan that the proposed site development is likely to involve
overexcavations of existing fills, original topsoils, and loose native soils, and for installing underground
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 28 of 40
utility lines. The overexcavations depths may be 4 to 5 feet below the current grades. The inclination of the
overexcavation embankment should be made as per the recommendations provided below.
As a general rule, all temporary soil excavations in excess of 4 feet in height and less than 20 feet in
depth, the side slopes should be adequately sloped back or properly shored in accordance with Safety Standards
for Construction Work Part N, WAS 296-155-657 to prevent sloughing and collapse. As for the current
estimation purposes, in our opinion, the side slopes in the native soils (OSHA soil Type C) should be laid back
at a minimum slope inclination of 1.5:1 (Horizontal:Vertical), and the side slopes in the native soils (OSHA soil
Type B) should be laid back at a minimum slope inclination of 1:1 (Horizontal:Vertical), for up to almost 6 feet
depth below the grades from the crest to the toe of the slope. However, estimation of the proper inclination of
excavation side slopes should be made on-site after inspecting the soil and groundwater conditions, which will
be revealed during the actual construction in the site.
It should be recognized that slopes of the above gradients do ravel and require occasional maintenance.
All temporary exposed slopes and excavations should be protected as soon as possible using appropriate
methods to prevent erosion to occur during periods of wet weather. This can be achieved by installing a durable
reinforced plastic membrane, jute matting, or other erosion control mats with proper anchorage to the ground.
In addition, we recommend that experienced personnel of the contractor should regularly check the slope
condition to notice if any signs of raveling or sloughing off is underway to prevent any catastrophic slope
failure.
All temporary soil cuts greater than 4 feet in height, if cannot be sloped back because of the limited
horizontal distance to be available between the top of the excavation line and the property line, a properly
shoring system is to be considered to prevent sloughing and collapse of the slope.
Any excavation side inclinations will assume that the ground surface behind the cut slopes is level, that
surface loads from equipment and materials are kept a sufficient distance away from the top of the slope. If
these assumptions are not valid, we should be contacted for additional recommendations. Flatter slopes may be
required if soils are loose or caving and/or water, are encountered along the slope faces. If such conditions
occur and the excavation cannot stand by itself, or the excavation slope cannot be flattened because of the space
limitations between the excavation line and the boundary of the property, temporary shoring may be
considered. The shoring will assist in preventing slopes from failure and provide protection to field personnel
during excavation. Because of the diversity available of shoring stems and construction techniques, the design
of temporary shoring is most appropriately left up to the contractor engaged to complete the installation. We
can assist in designing the shoring system by providing with detailed shoring design parameters including
earth-retaining parameters, if required.
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 29 of 40
Where sloped embankments are used, the top of the slopes should be barricaded to prevent vehicles
and storage loads within 10 feet of the top of the slopes. Greater setbacks may be necessary when
considering heavy vehicles, such as concrete trucks and cranes. If the temporary construction embankments
are to be maintained during the rainy season, berms are suggested along the top of the slopes to prevent
runoff water from entering the excavation and eroding the slope faces. All temporary slopes should be
protected from surface water runoff.
The owner and the contractor should be aware that in no case should the excavation slopes be greater
than the limits specified in local, state, and federal safety regulations, particularly, the Occupational Safety
and Health Administration (OSHA) regulations in the “Construction Standards for Excavations, 29 CFR, part
1926, Subpart P, dated October 31, 1989” of the Federal Register, Volume 54, the United States Department
of Labor. As mentioned above, we also recommend that the owner and the contractor should follow the local
and state regulations such as WSDOT Section 2-09.3(3) B, Washington Industrial Safety and Health Act
(WISHA), Chapter 49.17RCW, and Washington Administrative Code (WAC) Chapter 296-115, Part N.
These documents are to better insure the safety of construction worker entering trenches or excavation. It is
mandated by these regulations that excavations, whether they are for utility trenches or footings, be
constructed in accordance with the guidelines provided in the above documents. We understand that these
regulations are being strictly enforced and, if they are not closely followed, both the owner and the contractor
could be liable for substantial penalties.
Stability of temporary excavations is a function of many factors including the presence of, and
abundance of groundwater and seepage, the type and density of the various soil strata, the depth of excavation,
surcharge loadings adjacent to the excavation, and the length of time and weather conditions while the
excavation remains open. It is exceedingly difficult under these unknown and variable circumstances to pre-
establish a safe and maintenance-free temporary excavation slope angle at this time of the study. We therefore,
strongly recommend that all temporary, as well as permanent, cuts and excavations in excess of 4 feet be
examined by a representative of PGE during the actual construction to verify that the recommended slope
inclinations are appropriate for the actual soil and groundwater seepage conditions exposed in the cuts. If the
conditions observed during the actual construction are different than anticipated during this study then, the
proper inclination of the excavation and cut slopes or requirements of temporary shoring should be determined
depending on the condition of the excavations and the slopes.
The above information is provided solely for the benefit of the owner and other design consultants,
and under no circumstances should be construed to imply that PGE assumes responsibility for construction
site safety or the contractor’s activities; such responsibility is not being implied and should not be inferred.
Therefore, the contractor is solely responsible for designing and constructing stable, temporary excavations
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 30 of 40
and should shore, slope, or bench the sides of the excavations as required to maintain stability of both the
excavation sides and bottom. The contractor’s “responsible person”, as defined in 29 CFR Part 1926, should
evaluate the soil exposed in the excavations as part of the contractor’s safety procedures.
We expect that the excavation can be completed using conventional equipments such as bulldozers
or backhoes.
10.5 Utility Support and Backfill
Based on the soils encountered at the site within the exploration depths, the majority of the soils appear
to be adequate for supporting utility lines; however, softer soils may be encountered at isolated locations, where,
it should be removed to a depth that will provide adequate support for the utility. A major concern with utility
lines is generally related to the settlement of the trench backfill along utility alignments and pavements. The
trench backfill settlement causes misalignment of the utility lines and breaking apart of the joints. Therefore, it is
important that each section of utility be adequately supported on proper bedding material and properly
backfilled. We recommend that the on-site geotechnical engineer should evaluate the final subgrades of the
bottom of the utility trench to verify if the subgrade is competent to support the utility lines and the backfills, or
the subgrades need some proofrolling and recompaction, or require overexcavation of unsuitable loose fills and
replacement with suitable structural fills.
We recommend that if needed the bottom grades of the utility trench must be adequately proofrolled
and compacted to firm and unyielding conditions. A layer of geo-grid such as Mirafi 500X or equivalent should
be placed on the proofrolled subgrades prior to placing the bedding materials and laying the utility lines. This
should be decided on-site by the geotechnical engineer on-site based on the observed subgrade conditions at the
bottom of the trench.
It is recommend that utility trenching, installation, and backfilling conform to all applicable Federal,
State, and local regulations such as WISHA and OSHA for open excavations.
Pipe Bedding & Pipe Zone
Trench backfill to be placed beneath, adjacent to, and for at least 2 feet above utilities line should
consist of well-graded granular material with a maximum particle size of 1 inch and less than 10 percent by dry
weight passing the US Standard No. 200 Sieve, and should meet the standards of ‘Gravel Backfill for Pipe
Zone Bedding’ described in Section 9-03.12(3) of the 2024 WSDOT Standard Specifications. Trench backfill
must be free of debris, organic material and rock fragments larger than 1 inch. The bedding materials should be
hand tamped to ensure support is provided around the pipe haunches. Trench backfill should be carefully placed
and hand tamped to about 12 inches above the crown of the pipe before any heavy compaction equipment is
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Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 31 of 40
brought into use. In order to reduce the potential for damaging the utilities, heavy compaction equipment
should not be permitted to operate directly over utilities until a minimum of two (2) feet of backfill will be
placed. In general, pipe bedding should be placed in loose lifts not exceeding 6 inches in thickness and
compacted to at least 90 percent of the fills’ maximum dry density value as to be determined by the laboratory
Modified Proctor (ASTM D1557) test method. The fill materials within the pipe bedding and pipe zone, their
thicknesses and compactions should be suitable for the utility system and materials installed, and in accordance
with any applicable manufacturers' recommendations or local building department. Pipe bedding materials
should be placed on relatively undisturbed native soil. Based on our field explorations, we anticipate relatively
coarse-grained soils comprised of poorly graded gravel with cobbles. Some overexcavation and removal of
cobbles should be anticipated at the pipe invert elevation to maintain a uniform grade for the utility installation.
Where overexcavation is needed, additional pipe bedding materials should be placed to restore the grade.
Trench Backfills
We recommend that the backfills to be placed 2 feet above the pipe and upto the final pavement
subgrade level should be consisted of materials similar to ‘Gravel Borrow’ described in Section 9-03.14(1) or
‘Select Borrow’ as described in Section 9-03.14(2), of the 2024 WSDOT Standard Specifications. Where
excavations occur in the wet, alternative such as ‘Select Granular Fill’ described earlier in Section 10.1.6,
Structural Fills’ should be considered. Trench backfill must be free of roots, debris, organic matter and rock
fragments larger than 3 inches. Other materials may be appropriate depending on manufacturer specifications
and/or local jurisdiction requirements. For site utilities located within the City of Renton right-of-ways,
bedding and backfill should be completed in accordance with the city specifications. As a minimum, 5/8 inch
pea gravel or clean sand may be used for bedding and backfill materials. The trench backfills to be placed 2
feet above the pipe and upto the final pavement subgrade level should be compacted to 95 percent of the
fills’ maximum dry density value as to be determined by the laboratory Modified Proctor (ASTM D-1557)
test method. The backfill should be placed in lifts not exceeding 4 inches if compacted with hand-operated
equipment or 8 inches if compacted with heavy equipment. Catch basins, utility vaults, and other structures
installed flush with the pavement should be designed and constructed to transfer wheel loads to the base of
the structure.
The utility trenches should not be left open for extended periods to prevent water entry,
accumulation, and softening of the subgrade. Should soft soils be encountered at the bottom of the trench, it
should be overexcavated and replaced with select fills. As an alternative to undercutting, a Geotextile fabric
or crushed rock may be used to stabilize the trench subgrade. Where water is encountered in the trench
excavations, it should be removed prior to fill placement. Alternatively, quarry spalls or pea gravel could be
used below the water level if allowed by the local authority or the project specifications.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 32 of 40
10.6 Foundation Recommendations
As mentioned earlier, the footings of the proposed new residence can be supported on conventional
shallow spread footings for interior isolated columns and continuous strip footings for perimeter walls.
The footing may be placed directly over the medium dense native soil to be prepared as final
‘competent’ native subgrade in the higher level frontyard of the property expected to be encountered at
approximately 4 feet depth below the grade (TP-1). Alternatively, the footing may also bear directly over the
new ‘fill pad’ to be placed over the medium dense final ‘competent’ native subgrade.
The footing should bear over the new ‘fill pad’ to be placed over the very dense glacial till to be
prepared as final ‘competent’ native subgrade in the backyard of the property, expected to be encountered at
approximately 4 feet depth below the grade (TP-2 and TP-3). The new fill pad must be placed over the final
‘competent’ native subgrade.
Allowable Bearing Capacity
The footings to be placed directly over the final ‘competent’ native subgrade and over the new fill
pad may be designed for an allowable net bearing capacity value of 1500 psf. The “net allowable bearing
pressure” refers to the pressure that can be imposed on the soil at foundation level resulting from the total of
all dead loads plus the long-term live loads, exclusive of the weight of the footing or any backfill placed
above the footing, i.e., these loadings can be ignored in calculating footing sizes.
For short-term loads, such as wind and seismic (earthquake), a 1/3 increase in the above net allowable
capacity can be used. We recommend that continuous footings have a minimum width of 18 inches and
individual column footings a minimum width of 24 inches. All exterior footings should bear at least 18 inches
below the final adjacent finish grade to provide adequate confinement of the bearing materials and frost
protection.
Settlement
Based on our settlement potential evaluation of the shallow foundation options, we anticipate that
properly designed and constructed foundations supported on the recommended bearing materials should
experience total settlement of less than 1 inch for the allowable bearing pressures presented above. Differential
settlement could be on the order of ¼ to ½ inch between similarly loaded foundations over a distance of 50 feet
of continuous footings. This estimation was done without the aid of any laboratory consolidation test data, but on
the basis of our experience with similar types of structures and subsoil conditions. The soil response to applied
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 33 of 40
stresses caused by building and other loads is expected to be predominantly elastic in nature with most of the
settlements occurring during construction as loads are applied; however, due the fines content of the site soils,
the estimated settlements could occur over a longer time, and disturbance of the foundation subgrades during
construction could result in larger settlements than predicted.
Lateral Load Resistance
Lateral loads due to wind and seismic forces transferred to the footings may be resisted by friction
between the foundation base and the bearing soil, and by passive earth pressure acting on the vertical face of
the footings embedded below the current grades. We recommend using a coefficient of friction of 0.35 to
calculate friction between the concrete, and the ‘fill pad’ soils. For passive earth pressure, the available
resistance may be determined using an equivalent fluid pressure of 300 pcf, which includes a factor of safety
of 1.5. This value assumes the foundations are cast "neat" against the undisturbed native soils or structural
fills placed and compacted as recommended in Section 10.1.7, ‘Fill Placement & Compaction’ of this report.
We recommend disregarding the upper 12 inches of soil while computing the passive resistance value
because this depth can be affected by weather or disturbed by future grading activity. To achieve the
adequate passive resistance from the embedded soils as well as for frost and erosion protection, we
recommend that all exterior footings must be embedded at least 18 inches below the final adjacent outside
grades consisted of either the undisturbed native soils or structural fills placed and compacted as
recommended in Section 10.1.7, ‘Fill Placement and Compaction Requirements’ of this report. The passive
earth pressure and friction components may be combined provided that the passive component does not
exceed two-thirds of the total resistance. The passive earth pressure and friction components may be
combined provided that the passive component does not exceed two-thirds of the total resistance.
Footing Subgrade Inspection
We recommend that PGE representative examine the bearing materials prior to placing forms or
rebar. Variations in the quality and strength of the potential bearing soils can occur with depth and distance
away from the test pits. Therefore, a careful evaluation of the bearing material and the design bearing
capacity value as recommended in this report must be verified at the proposed footing locations at the time of
footing construction.
10.7 Slab-on-grade Floor
Slab-on-grade floor for the new residence should not be placed over topsoils, uncontrolled existing
fills, loose and yielding native soils, or any soils containing heavy roots.
The slab-on-grade floor should bear directly on the new ‘fill pad’ in the frontyard and backyard areas
of the property. After the final native subgrade preparation will be completed as ‘competent’ subgrades and
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 34 of 40
to be accepted by the geotechnical engineer, the new imported structural fill should be placed and compacted
up to the final subgrades. The new structural fill and the new fill placement and compaction should be as per
the recommendations provided earlier in Section 10.1.6, ‘Structural Fills’, and 10.1.7, ‘Fill placement &
Compaction’, respectively.
After the final subgrade for supporting the slab will be achieved the slab should be provided with a
capillary break to retard the upward wicking of ground moisture beneath the floor slab. The capillary break
would consist of a minimum of 6-inch thick clean, free-draining sand or pea gravel. The structural fill
requirements specified in Section 10.1.6, ‘Structural Fills’, could be used as capillary break materials except
that there should be no more than 2 percent of fines passing the no. 200 sieve. Alternatively, ‘Gravel Backfill
for Drains’ per 2023 WSDOT Standard Specifications 9-03.12(4) can be used as capillary break materials.
This layer should be placed and compacted to an unyielding condition. Where moisture by vapor
transmission is undesirable, we recommend the use of a vapor barrier such as a layer of durable plastic
sheeting (such as Crossstuff, Moistop, or Visqueen) between the capillary break and the floor slab to prevent
the upward migration of ground moisture vapors through the slab. This is particularly importance where
moisture migration through the slab is an issue, such as where adhesives are used to anchor carpet or tile to
the slab. During the casting of the slab, care should be taken to avoid puncturing the vapor barrier. At
owner’s or architecture’s discretion, the membrane may be covered with 2 inches of clean, moist sand as a
‘curing course’ to guard against damage during construction and to facilitate uniform curing of the overlying
concrete slab. The addition of 2 inches of sand over the vapor barrier is a non-structural recommendation. A
cross-sectional view of the slab-on-grade floor showing the above features is provided in Figure 5, Footing,
Floor Slab, Footing Drain of this report.
The final slab subgrade consisted of adequately compacted, new imported structural fills, a modulus
of subgrade reaction value of about 150 pounds per cubic inch (pci) can be used to estimate slab deflections,
which could arise due to elastic compression of the subgrades
11.0 Infiltration Potential Evaluation
As a part of the scope of this geotechnical study the permeability characteristic of the native soil was
evaluated to assess the feasibility of using a below grade infiltration system in this site for managing the
stormwater runoff from the proposed new residence. To achieve this, the surface and subsurface conditions in
the proposed new infiltration system area was observed as a basis for evaluating the feasibility of below grade
infiltration system in the subject site.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 35 of 40
In our opinion, the presence of heavy groundwater seepage and glacial till at shallow depth in the
backyard of the property are considered unacceptable for considering any type of below grade infiltration
system in the site. The glacial till is considered as ‘restrictive layer’ for the functioning of a below grade
infiltration system.
Considering the above geological conditions, we recommend that the guideline provided in the newly
revised Western Washington Storm Water Manual should be used. As per the manual, a design model has
recommended to incorporate the idea of many small point discharges over an area using splash blocks
commonly known as basic dispersion system. The stormwater runoff from the home and the roof can be
discharged onto the ground through the splash blocks to be placed at the down-spout location, as close as
possible to the location where it is collected. This water is then allowed to disperse through the lawn areas in
the property simulating the prevailing natural conditions as much as possible. Regarding the impact of the
stormwater runoff from the above system the lawn area should be able to act to break up and slow any overflow
sheet flow from the site.
The above options should be discussed with the local city authority. The final decision in evaluating
the suitability of any particular stormwater management system in this site specific to the proposed
development requirement should be made by the project civil engineer. Also, the various aspects of the
design requirements described in the 2022 City of Renton Surface Water Design Manual should be
incorporated into the system design.
12.0 Construction Monitoring
Problems associated with earthwork and construction can be avoided or corrected during the progress
of the construction if proper inspection and testing services are provided. Since this project involves so many
aspects of geotechnical engineering related construction activities such as the identification of the
undocumented existing fill and its removal, removal of topsoils, final native subgrades preparation and
proofrolling, fill placement and compaction, slab-on-grade-floor installation, footing embedment depth, and
verification of allowable bearing capacity value, we recommend that PGE’s geotechnical engineer should
inspect and monitor all the above construction activities. A list of inspection items are provided in the following
section ‘Geotechnical Special Inspection’ of this report. PGE’s involvement during the construction-phase of
the project will help in completing the project more efficiently, cost-effectively, timely manner since PGE has
the prior knowledge, familiarity, and better understanding with the subsurface conditions and our
recommendations.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 36 of 40
Geotechnical Special Inspection
The construction of the proposed development in this site involves several aspects of the geotechnical
engineering that are considered to be critical for the successful completion of the project and continue that
throughout the project life. Therefore, PGE recommends that the following geotechnical special inspection
services to be performed during the construction of the proposed development. According to PGE, the following
items should be considered as a minimum but not limited to.
• A professional geotechnical engineer should be retained to provide geotechnical consultation,
material testing, and construction monitoring services during the construction of the project.
• A pre-construction meeting should be held on-site to discuss the geotechnical aspects of the
development and the special inspection services to be performed during the construction.
• The site preparation activities including but not limited to stripping, cut and filling, final subgrade
preparation for foundation, floor slab, paved driveway, and retaining wall be monitored by a
geotechnical engineer or his representative under the engineer’s supervision.
• A list of the possible items that require special geotechnical inspection and approval by the
geotechnical engineer is as follows:
➢ Stripping of topsoils.
➢ Removal of loose, native soils, and undocumented existing fills.
➢ Redensification and proofrolling of final (competent) native subgrades that are intended to provide
direct support for any load bearing structure such as the building footings, slab-on-grade floor, and
new ‘fill pad’.
➢ Any structural fills to be used in this site, and structural fills placement and its compaction.
➢ Temporary or permanent excavation inclinations, and excavation stability.
➢ The footing bearing materials, bearing capacity value, and the embedment depth of the footings
prior to placing forms and rebars.
➢ Subgrade preparation for soil supported slab-on-grade floors.
➢ Subgrade preparation for paved driveways.
➢ Compaction of CSBC, CSTC, and laying of concrete pavement in driveway.
➢ Site drainage.
➢ Installation of drainage system such as footing excavation drain and footing drain, and daylighting
of such drains and downspout or roof drains.
➢ Bedding and the backfilling materials, and backfilling of utility lines.
➢ Any other items specified in the approved project plans to be prepared by other consultants
relevant to the geotechnical aspect of the project.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 37 of 40
13.0 Additional Services
Additional services described below can be performed by PGE in the event the project requires such
services. These services will be performed upon written authorization of the client or the civil engineer, and
with additional cost to perform such services, under a separate contract between PGE and the client.
13.1 Design Phase Engineering Services
PGE can provide additional engineering recommendations to the project team during the design
phase of the project, if necessary.
13.2 Final Plan Review Service
As the geotechnical engineer of record for the proposed development, at owner’s option, PGE can
perform a review of the geotechnical aspect of the final project plans and specifications to verify that the
geotechnical recommendations provided in this report have been properly interpreted and incorporated into the
project final design and specifications. PGE’s review of the final plan would allow re-evaluating the
geotechnical recommendations provided in this report, and if necessary, modifying the recommendations
before the construction begins. We believe this would be helpful for the project’s speedy completion and
success.
13.3 Construction-time Testing and Inspection
As recommended earlier in Section 12.0, ‘Construction Monitoring’ of this report, as the
geotechnical engineer of record for the subject project, at owner’s option, PGE can provide geotechnical
consultation, material testing, and construction monitoring services during the construction of the project.
These services are important for the project to confirm that the earthwork and the general site development
are in compliance with the general intent of design concepts, specifications, and the geotechnical
recommendations presented in this report. Also, participation of PGE during the construction will help PGE
engineers to make on-site engineering decisions in the event that any variations in subsurface conditions are
encountered or any revisions in design and plan are made.
PGE can assist the owner before construction begins to develop an appropriate monitoring and
testing plan to aid in accomplishing a fast and cost-effective construction process.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 38 of 40
14.0 Report Limitations
The conclusions and recommendations presented in this report are based on our soil investigation,
the laboratory test results, and our engineering evaluation. The study was performed using a mutually agreed-
upon scope of work between PGE and the client.
It should be noted that PGE cannot take the responsibility regarding the accuracy of the information
provided in the project plan prepared by other consultants. If any of the information considered during this
study is not correct or if there are any revisions to the plans for this project, PGE should be notified
immediately of such information and the revisions so that necessary amendment of our geotechnical
recommendations can be made. If such information and revisions are not notified to PGE, no responsibility
should be implied on PGE for the impact of such information and the revisions on the project. Such revision
work and amendment of the geotechnical recommendations and conclusions would be additional work
beyond the current scope of work for this study.
Variations in subsurface (soil and groundwater) conditions may reveal during the construction of the
proposed below grade infiltration system. The nature and the extent of the subsurface variations may not be
evident until construction occurs. If any subsurface conditions are encountered at the site that are different
from those described in this report, we should be notified immediately to review the applicability of our
recommendations if there are any changes in the project scope. Such revision work and necessary
amendment of the geotechnical recommendations and conclusions would be additional work beyond the
current scope of work for this study.
This report may be used only by the client and for the purposes stated, within a reasonable time from
its issuance. Land use, site conditions (both off and on-site), or others factors including advances in our
understanding of applied science, may change over time and could materially affect our findings. Therefore,
this report should not be relied upon after 24 months from its issuance. PGE should be notified if the project
is delayed by more than 24 months from the date of this report so that we may review to determine that the
conclusions and recommendations of this report remain applicable to the changed conditions.
The scope of our work does not include services related to construction safety precautions. Our
recommendations are not intended to direct the contractors' method, techniques, sequences or procedures,
except as specifically described in our report for consideration in design. Additionally, the scope of our work
specifically excludes the assessment of environmental characteristics, particularly those involving hazardous
substances.
This report including its evaluation, conclusions, specifications, recommendations, or professional
advice has been prepared for planning and design purposes for specific application to the proposed project in
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 39 of 40
accordance with the generally accepted standards of local practice at the time this report was written. No
warranty, express or implied, is made.
This report is the property of our client Mr. Manjit Gill, and has been prepared for the exclusive use
of our client and its authorized representatives for the specific application to the proposed development at the
subject site in Renton, Washington.
It is the client's responsibility to see that all parties to this project, including the civil engineer,
designer, contractor, subcontractor, future homeowner, etc., are made aware of this report in its entirety. We
recommend that the information contained in this report, in its entirety, should be included in the bidding
documents and project contract documents at the owner’s or contractor's option. Any party other than the
client who wishes to use this report shall notify PGE of such intended use and for permission to copy this
report. Based on the intended use of the report, PGE may require that additional work be performed and that
and updated report be reissued. Noncompliance with any of these requirements will release PGE from any
liability resulting from the use this report.
___________________________________________________________________________________________________________________________
Manjit Gill Sing-family Residence
Geotechnical Engineering Study
551, Orcas Avenue NE
Renton, King County, WA 98059
PGE Project No. 24-797
February 6, 2025
Page 40 of 40
Closure
We trust the information presented in this report is sufficient for your current needs. We appreciate
the opportunity to provide the geotechnical services at this phase of the project and look forward to continued
participation during the design and construction phase of this project. Should you have any questions or
concerns, which have not been addressed, or if we may be of additional assistance, please do not hesitate to
call us at 425-218-9316 or 425-643-2616.
Respectfully submitted,
Santanu Mowar, MSCE, P.E.
D:\Geotechnical\2024-proj\24-797
Attachments: Figure 1 Vicinity Map
Figure 2 Site & Exploration Plan
Figure 3 Proposed Residence Plan
Figure 4 WA State DNR Map - USGS, Seismic Site Class, Liquefaction
Figure 5 Footing, Floor Slab, Footing Drain
Figure 6 Notes
Appendix A Soil Test Pit Log
02-06-25 Expires 01-01-26
N VICINITY MAP
Not to Scale
Project No: 24-797 PROJECT
New SFR
551, Orcas Avenue NE
Renton, WA 98059
Date: February 6, 2025
Drawn by:
Client: Manjit Gill Figure 1
Site
N
SITE & EXPLORATION PLAN
Not to Scale
Project No: 24-797 PROJECT
New SFR Addition
551, Orcas Avenue NE
Renton, WA 98059
Date: February 6, 2025
Drawn by:
Client: Manjit Gill Figure 2
TP 1
TP 2
Existing Residence
TP 3
N PROPOSED RESIDENCE PLAN
Not to Scale
Project No: 24-797 PROJECT
New SFR
551, Orcas Avenue NE
Renton, WA 98059
Date: February 6, 2025
Drawn by:
Client: Manjit Gill Figure 3
Existing Residence
N
WA DNR USGS MAP
Not to Scale
Project No: 24-797 PROJECT
New SFR
551, Orcas Avenue NE
Renton, WA 98059
Date: February 6, 2025
Drawn by:
Client: Manjit Gill Figure 4
Site
FOOTING, SLAB-ON-GRADE, & FOOTING DRAIN
Conceptual only
(not a construction drawing)
Footing Wall
Slope backfill w/ minor slope
C
J
DK
A
Floor Level
F
Concrete slab-on-grade
B
6" min. gravel on pipe top
H G
E
L
Vapor Barrier
Capillary Break Layer
Footing subgrade on new fill pad to be
compacted adequately following the procedures
provided in PGE’s geotechnical text report 24-
797; allowable bearing capacity of 1500 psf must
be verified on-site by PGE’s geotechnical
engineer
Drain Rocks
Drain Pipe
Mirafi 140N
Footing Excavation Slope
Compacted Backfills
Roof Drain
New, imported structural
fill pad below footing & slab
IFills must be placed & compacted
as per PGE’s geotechnical text
report 24-797; fills placement &
compaction must be inspected by
PGE’s geotechnical engineer
Curing Sand Layer
Figure 5 Not to Scale
Project No. –24-797
Project – Manjit Gill Site – New SFR
551, Orcas Avenue NE, Renton, WA 98059
3" min. gravel below pipe
Final native subgrade must be
prepared as ‘competent’
subgrade prior to placing new
fill pad following the
procedures provided in PGE’s
geotechnical text report 24-
797, which must be verified
on-site by PGE’s geotechnical
engineer
FOOTING, SLAB-ON-GRADE, & FOOTING DRAIN
Final native subgrades supporting the new structural fill pad directly must be thoroughly ‘redensified’ and adequately ‘proofrolled’ to firm & unyielding conditions to prepare
the final native subgrades as ‘competent’ native subgrades, which must be verified on-site by PGE’s geotechnical engineer prior to placing the new fill pad.
Excavation face slope should be determined based on the actual soil and groundwater conditions to be exposed during the construction.
Non-woven Geotextile Filter Fabric -Mirafi 140 N must wrap around the drain rocks to be placed around the footing drain pipe and the vertical drainage layer to be installed against
the wall, to prevent migration of fines into the drain rocks.
A
B
C
D
K
Capillary Break layer – min. 6" thk, of free-draining 5/8-inch crushed rocks containing no more than 2% fines or pea-gravel. Slab-on-grade floor should be placed directly on a
capillary break layer in unheated areas e.g., garage, storage rooms.
E
H
L
NOTES:-
F
G
Drain rocks -the drain pipe must be enveloped by drain rocks consisted of ¾” minus washed gravel (free draining).
Stormwater roof drain,must be tightlined and must not be connected to footing drain. Pipe should be sloped towards approved discharge point so that no backflow should occur
into the pipe.
J
Curing Sand Layer -as an additional layer can be placed above the vapor barrier or plastic membrane to guard the
membrane against damage during construction and to facilitate uniform curing of the overlying concrete slab.
Vapor Barrier – a durable 10 to 15-mil. plastic membrane be placed over capillary break layer as a vapor retarder.
Fill placement & compaction -void areas on both sides of the footing stem wall & the footing to be created due to the overexcavations through the native soils or the exiting fills for
installting the footing wall & footing, and also below the floor slab, must be backfilled with approved new structural fills. The fills must be compacted to 95% of fills’ max. dry
density value (to be determined as per the laboratory Mod. Proctor Test ASTM D1557). The fills to be placed should be compacted with care within the horizontal distance equal to
the height of the footing stem wall to avoid over compaction and overstressing the footing stem wall & the footing. No heavy compaction equipment such as vibratory roller or hoe-
pac be used to compact the fills because these equipment may impose excess surcharge loading on the wall, causing lateral instability to the footing stem wall & the footing. Fills to be
placed adjacent to the footing stem wall and the footing must be placed not exceeding 4 to 6 inches thick loose lifts of fills and to be compacted with a walk-behind, hand-held,
regular vibratory plate compactor. The new imported structural fills should be used as per the recommendations provided in PGE’s geotechnical text report 24-797.
Wall Footing Drain - 6" minimum diameter, perforated or slotted rigid concrete, metal, or plastic pipe with tight plastic joints, with a positive gradient (~2%) towards thee
discharge ends sufficient to generate gravity flow w/out backflow to occur into the pipe, and provided with accessible cleanouts at regular intervals. The pipe must be taken to final
discharge point (approved). The pipe must be placed as low as possible, at least 6 inches below footing or crawl space. Perforations (¼” max. diameter) to be in lower half of pipe,
with lower quadrant segment un-perforated to facilitate water flow. Slotted pipe to have 1/8" maximum width slots. Must NOT be tied to roof downspout or perimeter footing grain
lines. The drain pipe must be enveloped w¾” minus washed gravels (free draining), which then be wrapped around with Mirafi 140N to prevent migration of fines into the din rocks
and clog the pipe.
New imported structural fills – The new must fills must of and to be placed and compacted as described in the item above. Fills must be placed & compacted as per the
recommendations provided in I A
Figure 6 Not to Scale
Footing subgrades supporting the footings must be compacted adequately to firm and unyielding conditions that can provide allowable bearing capacity value of 1500 psf to
support the footings. The final footing subgrades must be verified on-site by PGE’s geotechnical engineer prior to placing rebars and forms.
Project No. –24-797
Project – Manjit Gill Site – New SFR
551, Orcas Avenue NE, Renton, WA 98059
Appendix A
Soil Test Pit Log
Figure A-1 Not to Scale
TEST PIT – TP-1
0 ft
1 ft
2 ft
3 ft
4 ft
5 ft
6 ft
0 ft
Soil Layer Descriptions
Laboratory Test
ResultsSample
Depth
Sample
Nos.Moist.
Content - #200 Sieve
Soil
Layer
Depth
USCS
Soil
Class
Test
Pit
Depth4 ft4 ft
Test Hole Width
Surface Elev. Ft.Date of Excavation
Test Pit Depth
Water/Seepage Depth
Mottling Depth
Ground Cover
Cave in Depth
Notes -
Grass
9 ft None
Landscape Top Soil -Blk. Silt w/
Hevay roots and organics
Wet, Soft
0 –1 ft
2
1
V. minor seepage below fill @ approx. 2.5 ft & 9 ft below
below grade
12/24/2024
Test Pit Location See site plan
Permeability
None
Fills: Brn., Silty Sand w/ small to
med. size Gravel, Cobble
some small debris
V. Moist, Loose
2
Project No. –24-797
1
1 ft – 2.5 ft SM
7 ft
8 ft
Project – Manjit Gill Site SFR
551, Orcas Avenue NE, Renton, WA 98059
Field Logging by ASTM D5434-12 Soil Sampling by ASTM D-75-19 Visual-Manual Soil Identification by ASTM D2488-17
9 ft
10 ft
26.5%S-1 @ 2 ft
Native Soil:Lt. Gray, Sand w/ Gravel,
occasional Cobble & Boulder
V. Moist & Loose up to approx. 4 ft
below grade & Moist & V. Dense
below this depth
V. difficult digging was encountered
32.5 ft –9 ft SP 18.2%S-2 @ 6 ft 3
Figure A-2 Not to Scale
TEST PIT – TP-2
0 ft
1 ft
2 ft
3 ft
4 ft
5 ft
6 ft
0 ft
Soil Layer Descriptions Laboratory Test
ResultsSample
Depth
Sample
Nos.Moist.
Content - #200 Sieve
Soil
Layer
Depth
USCS
Soil
Class
Test
Pit
Depth4 ft4 ft
Test Hole Width
Surface Elev. Ft.Date of Excavation
Test Pit Depth
Water/Seepage Depth
Mottling Depth
Ground Cover
Cave in Depth
Notes -
Grass
5 ft None
Landscape Top Soil -Blk. Silt w/
hevay roots and organics
Wet, Soft
0 –1 ft
2
1
Heavy seepage above till, approx. rate 1 gpm
12/24/2024
Test Pit Location See site plan
Permeability
None
Native Soil: Brn., Silty Sand w/ small
to med. size Gravel, Cobble
V. Moist, Loose
2
Project No. –24-797
1
1 ft – 2.5 ft SM
7 ft
8 ft
Project – Manjit Gill Site SFR
551, Orcas Avenue NE, Renton, WA 98059
Field Logging by ASTM D5434-12 Soil Sampling by ASTM D-75-19 Visual-Manual Soil Identification by ASTM D2488-17
9 ft
10 ft
Native Soil:Lt. Gray, Sand w/ Gravel,
occasional Cobble & Boulder
(Glacial Till)
Wet & Loose up to 4 ft below grade
& Moist & V. Dense below this depth
V. difficult digging was encountered
in Till
32.5 ft –5 ft SP 3
Figure A-3 Not to Scale
TEST PIT – TP-3
0 ft
1 ft
2 ft
3 ft
4 ft
5 ft
6 ft
0 ft
Soil Layer Descriptions Laboratory Test
ResultsSample
Depth
Sample
Nos.Moist.
Content - #200 Sieve
Soil
Layer
Depth
USCS
Soil
Class
Test
Pit
Depth4 ft4 ft
Test Hole Width
Surface Elev. Ft.Date of Excavation
Test Pit Depth
Water/Seepage Depth
Mottling Depth
Ground Cover
Cave in Depth
Notes -
Grass
5 ft None
Landscape Top Soil -Blk. Silt w/
hevay roots and organics
Wet, Soft
0 –1 ft
2
1
Heavy seepage above till, approx. rate 1 gpm
12/24/2024
Test Pit Location See site plan
Permeability
None
Native Soil: Brn., Silty Sand w/ small
to med. size Gravel, Cobble
V. Moist, Loose
2
Project No. –24-797
1
1 ft – 2.5 ft SM
7 ft
8 ft
Project – Manjit Gill Site SFR
551, Orcas Avenue NE, Renton, WA 98059
Field Logging by ASTM D5434-12 Soil Sampling by ASTM D-75-19 Visual-Manual Soil Identification by ASTM D2488-17
9 ft
10 ft
Native Soil:Lt. Gray, Sand w/ Gravel,
occasional Cobble & Boulder
(Glacial Till)
Wet & Loose up to 4 ft below grade
& Moist & V. Dense below this depth
V. difficult digging was encountered
in Till
32.5 ft –5 ft SP 3
KEY TO EXPLORATION LOG
Sample Descriptions:
Classification of soils in this report is based on visual field and laboratory observations, which include density/consistency,
moisture condition, grain size, and plasticity estimates, and should not be construed to imply field or laboratory testing unless
presented herein. Visual-manual classification methods in accordance with ASTM D-2488-17 were used as an identification
guide. Where laboratory data available, soil classifications are in general accordance with ASTM D2487-17. Soil
density/consistency in borings is related primarily to the Standard Penetration Resistance values. Soil density/consistency in test
pits is estimated based on visual observations of excavations. Undrained shear strength = ½ unconfined compression strength.
RELATIVE DENSITY OR CONSITENCY VS. SPT N-VALUE
COARSE GRAINED SOILS: SAND OR GRAVEL
FINE GRAINED SOILS: SILT OR CLAY
Density N
(Blows/ft.)
Approx. Relative Density
(%)
Consistency N (Blows/ft.) Approx. Undrained
Shear Strength (psf)
Very Loose 0 – 4 0- 15 Very Soft 0 – 2 <250
Loose 4 – 10 15 – 35 Soft 2 – 4 250 –500
Medium Dense 10 – 30 35 – 65 Medium Stiff 4 – 8 500 – 1000
Dense
30 – 50 65 – 85 Stiff 8 – 15 1000 – 2000
Very Dense >50 85 – 100 Very Stiff
Hard
15 – 30
> 50
2000 – 4000
> 4000
MOISTURE CONTENT DEFINITIONS
Dry Absence of moisture, dusty, dry to the touch
Moist Damp but no visible water
Wet Visible free water, from below water table
DESCRIPTIONS FOR SOIL STRATA AND STRUCTURE
General Thickness or Spacing
Structure
General Attitude
Parting
< 1/16 in Pocket Erratic, discontinuous deposit of limited extent Near Horizontal 0 - 10 deg
Seam
1/16 - 1/2 in Lens Lenticular deposit Low Angle 10 - 45 deg
Layer
½ - 12 in Varved Alternating seams of silt and clay High Angle 45 - 80 deg
Stratum
> 12 in Laminated Alternating seams Near Vertical 80 - 90 deg
Scattered
< 1 per ft Interbedded Alternating Layers
Numerous
> 1 per ft Fractured Breaks easily along definite fractured planes
Slickensided
Polished, glossy, fractured planes
Blocky, Diced
Breaks easily into small angular lumps
Sheared
Disturbed texture, mix of strengths
Homogeneous
Same color and appearance throughout
DEPARTMENT OF COMMUNITY
AND ECONOMIC DEVELOPMENT
Page 1 of 3 | Published: 1/19/2024
Development Engineering Division | 1055 South Grady Way | Renton, WA 98057 | 425-430-7240
Website: rentonwa.gov
ENGINEERING IMPROVEMENT DETERMINATION
RESULTS
Published : 1/19/2024
Project Address/Location: _____________________________ Parcel #(s): ________________________________
Determination results are based on the information provided by the Applicant. Deviations from the submitted information may require that
a new Determination Request form be submitted and result in additional requirements.
ROADWAY IMPROVEMENTS
Street Name(s): __________________________ Roadway Classification(s): ___________________________
NO Right of Way Dedication and NO Street Frontage Improvements Required as the project falls within RMC
4-6-060 Street Standards exemption criteria.
Right of Way Dedication and/or Street Frontage Improvements Required per RMC 4-6-060.
Fee-in-Lieu Allowed for Street Frontage Improvements (see City Fee Schedule for $/LF of frontage)
Modified Right of Way Dedication and/or Street Frontage Improvements Recommended.
Fee-in-Lieu Allowed for Street Frontage Improvements (see City Fee Schedule for $/LF of frontage)
551 Orcas Ave NE 273920-0110
Orcas Ave NE Residential Access
Orcas Ave NE is classified as a Residential Access street with an existing right-of-way (ROW)
width of 60 feet according to the King County Assessors map. To meet the City's complete
street standards for Residential Access streets, a minimum ROW of 53 feet is required. Per
RMC 4-6-060, half street improvements shall include a pavement width of 26 feet (13 feet from
the centerline), a 0.5 foot curb, an 8 foot planting strip, a 5 foot sidewalk, street trees and storm
drainage improvements. Sewer is not currently available. A sewer main extension or Public
Health Approval for Septic will be required. No Right of Way dedication is required.
4
ENGINEERING IMPROVEMENT DETERMINATION RESULTS (CONT’D)
Page 2 of 3 | Published: 1/19/2024
Project Address/Location: _____________________________ Parcel #(s): _________________________________
Determination results are based on the information provided by the Applicant. Deviations from the submitted information may require
that a new Determination Request form be submitted and result in additional requirements.
STORM DRAINAGE REVIEW TYPE (See City of Renton Surface Water Design Manual Figure 1.1.2.A for Reference)
Basic Drainage Evaluation (Less than 2,000 Square Feet of New or Replaced Impervious Surface)
Simplified Drainage Review (Renton Surface Water Design Manual, Appendix C)
Targeted Drainage Review due to ____________________________________________________
Directed Drainage Review
ANTICIPATED SUBMITTAL ITEMS
Required Waived All Checklists/Studies/Reports Required Unless Waived by City Staff
_____ Civil Construction Permit Application
_____ Residential Drainage Application
_____ Deed of Dedication
_____ Real Estate Excise Tax Affidavit (REETA) – (See Example REETA Form)
_____ Modification Application and Supporting Documents
_____ Fee-in-Lieu of Street Improvements Application
_____ Soils Report (See Renton Surface Water Design Manual Appendix C, Section C.1.3)
_____ Written Drainage Assessment (See Example Simplified Drainage Review)
_____ Storm Drainage Covenant (See Example Storm Drainage Covenant)
_____ Water Availability from:
_____ Sewer Availability from:
RESULT PROVIDED BY:
Determination expires six (6) months following the date of the Determination Results provided that City codes have not changed
within this period that would affect this determination. A new Determination Request will need to be submitted following this
expiration. The applicant is cautioned that information contained in this summary is preliminary and non-binding and may be
subject to modification and/or concurrence by official City decision-makers.
RESOURCES
Definitions
Renton Surface Water Design Manual (RSWDM)
City of Renton Standard Details
City of Renton Forms
Electronic File Standards
551 Orcas Ave NE 273920-0110
Water District 90 - info@kcwd90.com
City of Renton - developmentengineering@rentonwa.gov
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DEVELOPMENT ENGINEERING
hpowers 12/06/2024
ENGINEERING IMPROVEMENT DETERMINATION RESULTS (CONT’D)
Note: This handout shall not be used as a substitute for code and regulations. The applicant is responsible for compliance with all codes and regulations, whether or
not described in this document.
Page 3 of 3 | Published: 1/19/2024
Project Address/Location: _____________________________ Parcel #(s): _________________________________
Determination results are based on the information provided by the Applicant. Deviations from the submitted information may require
that a new Determination Request form be submitted and result in additional requirements.
INFORMATION PROVIDED BY APPLICANT:
551 Orcas Ave NE 273920-0110