HomeMy WebLinkAboutSKIDMORE SHOP - GEO General - 3/4/2026 Geotechnical Report
Skidmore Shop
XXX E Mystic Court, Union
Parcel No. 42114-43-90120
Mason County,Washington
March 4, 2024
I
Project#24036
Prepared For:
David Skidmore
300 E Mystic Court
Union,Washington 98592
Prepared By:
Envirotech Engineering, PLLC
PO Box 984
Belfair,Washington 98528
Phone: 360-275-9374
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MASON COUNTY St,t s itt i Checklist
COMMUNITY SERVICES Geotechnical Report
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Instructions:
This checklist must be submitted with a Geotechnical Report and completed,signed, and stamped by the licensed
professional(s)who prepared the Geotechnical Report for review by Mason County pursuant to the Mason County
Resource Ordinance. If an item is found not applicable,the report should explain the basis for the conclusion.
Note: Unless specifically documented, this report does not provide compliance to the International Residential
Code Sections R403.1.7 for foundations on or adjacent to slopes, Section R403.1.8 for expansive soils or section
1808.7.1 of the International Building Code Section for Foundations on or adjacent to slopes.
Applicant/Owner David Skidmore Parcel#42114-43-90120
Site Address XXX E Mystic Court, Union
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(1) (a) A discussion of general geologic conditions in the vicinity of the proposed development,
Located on page(s) 5
(b) A discussion of specific soil types,
Located on page(s) 6
(c) A discussion of ground water conditions,
Located on page(s) 7
(d) A discussion of the upslope geomorphology,
Located on page(s) 3
(e) A discussion of the location of upland waterbodies and wetlands,
Located on page(s) 3
(f) A discussion of history of landslide activity in the vicinity, as available in the referenced maps and
records.
Located on page(s) 8
(2) A site plan which identifies the important development and geologic features.
Located on Map(s) Geotechnical Site Plan—Appendix A
(3) Locations and logs of exploratory holes or probes.
Located on Map(s) Geotechnical Site Plan and Soil Logs(Appendix B)
(4) The area of the proposed development,the boundaries of the hazard,and associated buffers and
setbacks shall be delineated(top, both sides,and toe)on a geologic map of the site.
Located on Map(s) Geotechnical Site Plan
(5) A minimum of one cross section at a scale which adequately depicts the subsurface profile,and
which incorporates the details of proposed grade changes.
Located on Map(s) Soil Profile(Appendix B)
(6) A description and results of slope stability analyses performed for both static and seismic loading
conditions.Analysis should examine worst case failures.The analysis should include the Simplified
Bishop's Method of Circles.The minimum static safety factor is 1.5,the minimum seismic safety
factor is 1.1,and the quasi-static analysis coefficients should be a value of 0.15.
Located on page(s) 10 Page 1 of 40
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(7) (a) Appropriate restrictions on placement of drainage features,
Located on page(s) 19
(b) Appropriate restrictions on placement of septic drain fields,
Located on page(s) 20 r
(c) Appropriate restrictions on placement of compacted fills and footings,
Located on page(s) 14 and 16
(d) Recommended buffers from the landslide hazard areas shoreline bluffs and the tops of other slopes.
Located on page(s) 19
(e) Recommended setbacks from the landslide hazard areas shoreline bluffs and the tops of other slopes.
Located on page(s) 18
(8) Recommendations for the preparation of a detailed clearing and grading plan which specifically identifies
vegetation to be removed, a schedule for vegetation removal and replanting, and the method of vegetation
removal.
Located on page(s) 19
(9) Recommendations for the preparation of a detailed temporary erosion control plan which identifies the specific
mitigating measures to be implemented during construction to protect the slope from erosion, landslides and
harmful construction methods.
Located on page(s) 10
(10) An analysis of both on-site and off-site impacts of the proposed development.
Located on page(s) 13
(11) Specifications of final development conditions such as,vegetative management,drainage,erosion control,and
buffer widths.
Located on page(s) 14-20
(12) Recommendations for the preparation of structural mitigation or details of other proposed mitigation.
Located on page(s) 20
(13) A site map drawn to scale showing the property boundaries,scale, north arrow,and the location and nature
of existing and proposed development on the site.
Located on Map(s) Geotechnical Site Plan
I, Michael Staten, hereby certify under penalty of perjury that I am a civil engineer licensed in the State of Washington
with specialized knowledge of geotechnical/geological engineering or a geologist or engineering geologist licensed in
the State of Washington with special knowledge of the local conditions. I also certify that the Geotechnical
�t cus'bt.sr Report,dated March 4, 2024 ,and entitled Skidmore
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Shop meets all the requirements of the Mason County
cc lief,
Resource Ordinance,Geologically Hazardous Areas Section,
43045 , � is complete and true,that the assessment demonstrates
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Ssf�NAL 04 conclusively that the risks posed by the landslide hazard can
3/4/24
be mitigated through the included geotechnical design •
Disclaimer:Mason County does not recommendations,and that all hazards are mitigated in such a
certify the quality of the work done in manner as to prevent harm to property and public health and
this Geotechnical Report. safety. Page 2 0f 2
TABLE OF CONTENTS
1.0 INTRODUCTION 1
1.1 PROJECT INFORMATION 1
1.2 PURPOSE OF INVESTIGATION AND SCOPE OF WORK 1
2.0 SURFACE CONDITIONS 3
2.1 TOPOGRAPHY 3
2.1.1 Upslope Geomorphology 3
2.2 SURFACE DRAINAGE 3
2.2.1 Upland Water Bodies 3
2.3 SLOPE AND EROSION OBSERVATIONS 3
3.0 SUBSURFACE INVESTIGATION 5
3.1 FIELD METHODS,SAMPLING AND FIELD TESTING 5
3.2 GEOLOGIC CONDITIONS 5
3.3 SPECIFIC SUBSURFACE CONDITIONS 6
3.3.1 Groundwater 7
4.0 ENGINEERING ANALYSES AND CONCLUSIONS 8
4.1 SLOPE STABILITY 8
4.1.1 Slope Stability Analysis 9
4.2 EROSION 10
4.3 SEISMIC CONSIDERATIONS AND LIQUEFACTION 11
4.3.1 Liquefaction 11
4.4 LANDSLIDE,EROSION AND SEISMIC HAZARDS CONCLUSIONS 11
4.5 LATERAL EARTH PRESSURES 12
4.6 ON-SITE AND OFF-SITE IMPACTS 12
5.0 ENGINEERING RECOMMENDATIONS 14
5.1 BUILDING FOUNDATION RECOMMENDATIONS 14
5.1.1 Bearing Capacity 14
5.1.2 Settlement 15
5.1.3 Concrete Slabs-on-Grade 15
5.2 EARTHWORK CONSTRUCTION RECOMMENDATIONS 15
5.2.1 Excavation 15
5.2.2 Placement and Compaction of Native Soils and Engineered Fill 16
5.2.3 Retaining Wall Backfill 17
5.2.4 Wet Weather Considerations 17
5.3 BUILDING AND FOOTING SETBACKS 18
5.4 SURFACE AND SUBSURFACE DRAINAGE 18
5.5 VEGETATION BUFFER AND CONSIDERATIONS 19
5.6 TEMPORARY AND PERMANENT EROSION CONTROL 19
5.7 SEPTIC DRAINFIELDS 20
5.8 STRUCTURAL MITIGATION 20
6.0 CLOSURE 21
Appendix A—Geotechnical Site Plan
Appendix B-Soil Information
Appendix C-Slope Stability
Appendix D—Erosion Control
1.0 INTRODUCTION
Envirotech Engineering, PLLC. (Envirotech) has completed this geotechnical report for a
property located at XXX E Mystic Court, Union, identified as parcel number 42114-43-
90120 in Mason County,Washington.
As presented herein, this report includes information pertaining to the project in this
Introduction Section; observations of the property and surrounding terrain in the Surface
Conditions Section; field methods and soil descriptions in the Subsurface Investigation
Section; supporting documentation with relation to slope stability, erosion, seismic
considerations, and lateral earth pressures in the Engineering Analyses and Conclusions
Section; and, recommendations for foundation, settlement, earthwork construction,
retaining walls, erosion control, drainage, and vegetation in the Engineering
Recommendations Section.
An initial geotechnical evaluation of the project was conducted by Envirotech on January
23, 2024. It was determined that slopes in excess of 40% with a vertical relief of at least
10 feet were present within 300 feet of the planned development. Based on this site
characteristic, the proposed development will require a geotechnical report pursuant to
Landslide Hazard Areas of Mason County Resource Ordinance (MCRO) 8.52.140.
During the site visit by Envirotech, surface and subsurface conditions were assessed.
After completion of the field work and applicable project research, Envirotech prepared
this geotechnical report which, at a minimum, conforms to the applicable MCRO.
1.1 Project Information
Information pertaining to the project was provided by the proponent of the property, and
observations from a field visit by Envirotech. The proposed development is expected to
consist of a shop on an existing developed single family residential lot, and other
ancillary features typical of this type of development . Approximate site development
footprint with relation to existing geological site features are illustrated in the Geological
Site Plan in Appendix A of this report.
1.2 Purpose of Investigation and Scope of Work
The purpose of this geotechnical investigation is to assess geological hazards, and
evaluate the project in order to provide geotechnical recommendations that should be
implemented during development. The investigation included characterizing the general
project surface and subsurface conditions, and evaluating the suitability of the soils to
support the planned site activities.
In order to fulfill the purpose of investigation, the geotechnical program completed for
the proposed improvements of the project include:
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Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 4, 2024
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• Review project information provided by the project owner and/ or owner's
representative; '
• Conduct a site visit to document the site conditions that may influence the
construction and performance of the proposed improvements of the project;
• Define general subsurface conditions of the site by observing subsoils within test
pits and/ or cut banks, review geological maps for the general area, research
published references concerning slope stability, and review water well reports
from existing wells near the project;
• Collect bulk samples, as applicable, at various depths and locations;
• Perform soils testing to determine selected index and/or engineering properties of
the site soils;
• Complete an engineering analysis supported by the planned site alterations, and
the surface and subsurface conditions that were identified by the field
investigation, soil testing, and applicable project research; and,
• Establish conclusions based on findings, and make recommendations for
foundations, drainage, slope stability, erosion control, earthwork construction
requirements, and other considerations.
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Vicinity Map from Mason County Website
Envirotech Engineering Geotechnical Report
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Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 4, 2024
2.0 SURFACE CONDITIONS ti
Information pertaining to the existing surface conditions for the project was gathered on
January 23, 2024 by a representative with Envirotech. During the site visit, site features
were documented that may reveal potential geological hazards.
This Surface Conditions Section provides information on topography, drainage and slope/
erosion conditions for the project and surrounding areas. An aerial photo of the project
and immediate vicinity is provided on the following page.
2.1 Topography
The topographic information provided in this section was extrapolated from a public lidar
source, and incorporated observations and field measurements. Where necessary, slope
verification included measuring slope lengths and inclinations with a cloth tape and
inclinometer. See the Geological Site Plan in Appendix A for an illustration of the
general slope indicators with respect to the planned development.
Maximum sloping grades within 300 feet of the proposed development area with a
vertical relief in excess of at least 10 feet were observed to be 100%.
2.1.1 Upslope Geomorphology
The landform that is upland from property is considered a hillside and crest of
glacial origin with centuries of weathering overburden. Additional
geomorphology that is pertinent to both upslope and downslope areas are
provided in the Subsurface Investigation Section of this report.
2.2 Surface Drainage
The majority of the stormwater runoff originating upslope from the anticipated
development is expected to be minimal to moderate . Significant scour, erosion and
sediment transport was not apparent near the project.
2.2.1 Upland Water Bodies
There are no apparent water bodies or wetlands located upslope from the planned
development that would significantly influence the project.
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2.3 Slope and Erosion Observations
The existing moderate slopes near the project signal a potential landslide or erosion
hazard area. Some indicators that may suggest past slope movements include:
Envirotech Engineering Geotechnical Report =�
PO Box 984 page 3 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County, Washington
Ph. 360-275-9374 March 4, 2024
• Outwash of sediments near the bottom of the slope,
• Fissures, tension cracks or naturally stepped land masses on the face or top of the
slope, and parallel to the slope,
• Fine, saturated subsurface soils,
• Old landslide debris,
• Significant bowing or leaning trees, or,
• Slope sloughing or calving.
Trees that were leaning and bowing on the slope were observed indicating some land
movement over time.
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Aerial Photo from Mason County Website
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Envirotech Engineering Geotechnical Report
PO Box 984 page 4 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County, Washington
Ph. 360-275-9374 March 4, 2024
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3.0 SUBSURFACE INVESTIGATION
Information on subsurface conditions pertaining to the project was gathered during
research and a site reconnaissance. The site visit was accomplished on January 23, 2024
by a representative with Envirotech. Specific information on field methods, sampling,
field testing, subsurface conditions, and results from soil testing are presented in this
section of the report. See Appendix B for a soil profile cross-sections, soil logs, and other
appropriate information as necessary.
3.1 Field Methods,Sampling and Field Testing
Information on subsurface conditions for the project was accomplished by probing
anticipated foundation areas with hand tools, and observing soils within test pit
excavations and/ or earth cuts. Information on subsurface conditions also included
reviewing geological maps within the project vicinity, and water well reports originating
from nearby properties. No soil samples were collected for this project. Envirotech
measured the relative density of the in-situ soils by gauging the resistance of hand tools.
3.2 Geologic Conditions
In general, soils at the project are composed of materials from glacial advances. The
geologic conditions as presented in the "Geologic Map of Washington," compiled by J.
Eric Schuster, 2002 indicates Quaternary sediments, Qg. Quaternary sediments are
generally unconsolidated deposits, and dominantly deposited from glacial drift, including
alluvium deposits. This project is located within the Puget Lowland. Typically, "lower
tertiary sedimentary rocks unconformably overlie the Crescent Formation." as revealed in
the Geologic Map. Initial sedimentary rocks were formed from shales, sandstones and
coal deposits from rivers. During the Quaternary period, the Puget Lowland was covered
by numerous ice sheets, with the most recent being the Fraser glacier with a peak of
approximately 14,000 years ago. Upon the glacial retreat, the landscape was formed by
glacial erosion glacial drift deposits. More specifically for the project location, a caption
from the Washington State Department of Natural Resources is as follows:
Map Unit: Qga
Age: Quaternary
GeoMaterial: Alluvial sediment
Description: Glaciofluvial sand and gravel and lacustrine clay, silt, and sand deposited
during the advance of glaciers; sandy units commonly thick, well sorted, and fine
grained, with interlayered coarser sand, gravel, and cobbles; locally contains nonglacial
sediments and deposits mapped as transitional between glacial and nonglacial.
Envirotech Engineering Geotechnical Report
PO Box 984 page 5 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County, Washington
Ph. 360-275-9374 March 4, 2024
3.3 Specific Subsurface Conditions
The following subsurface conditions are estimated descriptions of the project subgrade
utilizing information from the depth of penetration at all testing, sampling, observed and
investigated locations.
Soils for this project were described utilizing the Unified Soil Classification System
(USCS). Using the USCS in conjunction with estimated relative densities and other it
anticipated engineering properties of the soil, susceptibility for potential landslides,
erosion and seismic hazards may be assessed.
The project is primarily composed of undisturbed, native soils, with indications of
significant fill sidecast over the top of slope. Within native, undisturbed areas, competent
bearing soils were encountered at 12 inches below the existing ground surface in
locations where the ground was probed. For engineering purposes, these native soils
consist of distinguishable layers, as presented below.
Soils within the upper 13 feet of natural ground were observed to be primarily moist,
brown silty sand with gravel (SM) and poorly graded sand with gravel (SP) . Soils below
this upper soil strata were observed to be very dense glacial outwash. The outwash is
believed to extend to depths of at least 50 feet. This is based on nearby well reports, site
geology, and/or knowledge of the general area.
Not withstanding the potential for any old fill, the relative densities are suitable for
foundations as provided above. Expanded and specific subsurface descriptions, other than
what is provided in this section, are provided within additional soil information located in
Appendix B of this report.
According to the "Soil Survey of Mason County," by the United States Department of
Agriculture, Soil Conservation Service (SCS), the site soils are described as Alderwood
gravelly sandy loam with 30% - 50% slopes. See the soil map below.
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Envirotech Engineering Geotechnical Report
PO Box 984 page 6 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 4, 2024
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Soil Survey From USDA Natural Resources Conservation Service
3.3.1 Groundwater
From the water well report(s) and knowledge of the general area, permanent
groundwater is at least 50 feet below the current ground surface. Surface seepage
or perched groundwater at shallow depths was not observed on-site, nor indicated
on the well reports.
Envirotech Engineering Geotechnical Report
PO Box 984 page 7 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 4, 2024
1411
4.0 ENGINEERING ANALYSES AND CONCLUSIONS
441
The following section includes slope stability, erosion, seismic considerations, and
impacts to both on-site and off-site properties.
4.1 Slope Stability
Landslides are natural geologic processes, and structures near slopes possess an inherent
risk of adverse settlement, sliding or structural damage due to these processes.
Geotechnical engineering cannot eliminate these risks for any site with sloping grades 44411
because gravity is constantly inducing strain on the sloping soil mass. Excessive wet
weather and/ or earthquakes will exacerbate these strains. Geotechnical engineering
considers excessive wet weather and `design' earthquakes in order to provide an
acceptable factor of safety for developing on or near sloping terrain with relation to
current engineering protocol. These factors of safeties are based on engineering standards
such as defining engineering properties of the soil, topography, water conditions, seismic
acceleration and surcharges. Surface sloughing or other types of surficial slope
movements usually do not affect the deep-seated structural capability of the slope.
However, repeated surficial slope movements, if not repaired, may present a threat to the
structural integrity of the slope. If any slope movement arises, the slope should be
inspected by an engineer. Subsequently, maintenance may be required in order to prevent
the possibility of further surficial or deep seated slope movements that may be damaging
to life and property.
According to the Coastal Zone Atlas of Mason County, Washington, the project is 414
outside of its mapping limits. A Stability Map from the Coastal Zone Atlas for the
general area of this project is provided below:
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Map from Washington State Department of Ecology Website
Envirotech Engineering Geotechnical Report
PO Box 984 page 8 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County, Washington
Ph. 360-275-9374 March 4, 2024
N
According to the Resource Map from the Washington State Department of Natural
Resources (DNR), the project is within terrain labeled `highly unstable' relating to soils.
DNR labeled portions of this project as medium and high slope instability with relation to
slopes. A Resource Map from the DNR Forest Practices Application Review System is
provided below:
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4.1.1 Slope Stability Analysis
The Simplified Bishop Method, utilizing `STABLE' software, was used to
analyze the static stability of the site slopes. Seismic conditions were estimated
utilizing worst case scenario values from the static analysis, a quasi-static analysis tii
coefficient of at least 0.15, and applying the applicable values to STABLE
software. Various radii's and center points of the circle were automatically
selected, and produced factor of safeties in a graphical and tabular format. Worst
case scenario values were used in the slope stability analysis in regards to
topography, surcharges, water content, internal friction and cohesion of the site
soils. STABLE software has been repeatedly checked with manual calculations,
and consistently proved to be a very conservative program. The following soil
ti
Envirotech Engineering Geotechnical Report
PO Box 984 page 9 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County, Washington
Ph. 360-275-9374 March 4, 2024
1
properties were used in the analysis, and are based on observed conditions, known
geology, and/or published parameters:
Upper 5 feet soil depth
Soil unit weight: 132 pcf
Angle of internal friction: 30 degrees
Cohesion: 200 psf
Soils below 5 feet in depth
Soil unit weight: 138 pcf
Angle of internal friction: 38 degrees
Cohesion: 200 psf
Based on the slope stability analysis, unacceptable factors of safety could be
present on and near the critical slope, but do not reflect conditions where
development is expected to occur. For this project, at the location of the proposed
development, minimum factor of safeties for static and dynamic conditions were
estimated to be at least 1.5 and 1.1, respectively. See the slope stability
information in Appendix C for a depiction of minimum factors of safety away
from the project.
4.2 Erosion
Based on the USCS description of the project soils, the surface soils are considered
moderately erodible. According to the Resource Map from the Washington State DNR, as
provided above, the project is not within terrain labeled `highly erodible.' This project is
within an erosion hazard area as defined by the MCRO. Erosion hazard areas are those
with USDA SCS designations of River Wash (Ra), Coastal Beaches (Cg), Alderwood
Gravelly Sandy Loam on slopes 15% or greater (Ac and Ad), Cloquallum Silt Loam on
slopes 15% or greater (Cd), Harstine Gravelly Sandy Loam on slopes 15% or greater
(Hb), and Kitsap Silt Loam on slopes 15% or greater(Kc).
It is our opinion that minor erosion control recommendations provided in this report is
sufficient for the development of this project, and additional engineered erosion control
plans are not required. Temporary and permanent erosion control measures are required
for site development. Extents of temporary erosion control will mostly depend on the
timeliness of construction, moisture content of the soil, and amount of rainfall during
construction. Soil erosion typical to the existing site conditions and planned disturbance
of the project include wind-borne silts during dry weather, and sediment transport during
prolonged wet weather. Sediment transport could be from stormwater runoff or tracking
off-site with construction equipment.
Envirotech Engineering Geotechnical Report
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Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 4, 2024
I
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The Temporary and Permanent Erosion Control Section (Section 5.6) of this report
consist of specific erosion controls to be implemented. Additional erosion control
information and specifications may be found in the latest addition of the "Stormwater
Management Manual for Western Washington," prepared by the Washington State
Department of Ecology Water Quality Program.
4.3 Seismic Considerations and Liquefaction
There are no known faults beneath this project. The nearest Class 'A' or 'B' fault to this
property is the Hood Canal Fault Zone , which is not located on the property or adjacent
properties. This information is supported by the USGS Quaternary Fault and Fold
Database for the United States.
Potential landslides due to seismic hazards have been considered, and are addressed in
the Slope Stability Analysis Section provided earlier in this report.
Soils immediately below the expected foundation depth for this project are generally '441
Type D, corresponding to the International Building Code (IBC) soil profiles. According
to the IBC, the regional seismic zone is 3 for this project. The estimated peak ground
acceleration ranges from 0.50g to 0.60g. This estimation is based on the United States
Geological Survey (USGS) National Seismic Hazard project in which there is an
estimated 2% probability of exceedance within the next 50 years.
4.3.1 Liquefaction
The potential for liquefaction is believed to be low for this project. This is based,
in part, on the subsurface conditions such as soil characteristics and the lack of a
permanent shallow water table. Subgrade characteristics that particularly
contribute to problems caused from liquefaction include submerged, confined,
poorly-graded granular soils (i.e. gravel, sand, silt). Although gravel- and silt-
sized soil particles could be problematic, fine and medium grained sands are
typically subjected to these types of seismic hazards. No significant saturated sand
stratifications are anticipated to be within the upper 50 feet of the subsoil for this
project.
4.4 Landslide,Erosion and Seismic Hazards Conclusions
DNR did not indicate historic landslide activity near the project. Mapped slope
conditions, as delineated by the Departments of Ecology and/or Natural Resources, were
considered in our slope stability assessment. Based on the proximity and severity of
mapped delineations with respect to the proposed development, results of the aforesaid
slope stability analysis, observed surface conditions, and other pertinent information, it is
our opinion that the proposed development may occur in accordance with the
recommendations in this geotechnical report.
Envirotech Engineering Geotechnical Report
PO Box 984 page 11 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County, Washington
Ph. 360-275-9374 March 4, 2024
1
4.5 Lateral Earth Pressures
Retaining walls may be utilized for this project. The lateral earth pressures exerted
through the backfill of a retaining wall are dependent upon several factors including
height of retained soil behind the wall, type of soil that is retained, degree of backfill
compaction, slope of backfill, surcharges, hydrostatic pressures, earthquake pressures,
and the direction and distance that the top of the wall moves.
An equivalent fluid unit weight used for structural design may be estimated as the
product of the backfill soil unit weight and the earth pressure coefficient for at-rest
pressures. Retaining walls should be designed to resist a lateral earth pressure based on
an equivalent fluid unit weight of the following:
At-Rest Active
Native Soils 49 pcf 32 pcf
Engineered Fill Soils 45 pcf 28 pcf
The values provided above shall be increased by 1 pcf for every 1 degree of backfill/
natural slope angle. These equivalent fluid unit weight values do not include lateral earth
pressures induced by earthquakes, groundwater, or surcharges from live loads.
Earthquake pressures should be added to the wall analysis, and treated as an inverted
pressure triangle where the resultant pressure is located at 2/3 of the wall height, or other
method approved by a structural engineer. The following resultant earthquake pressures
as a function of the wall height(H) may be utilized:
At-Rest Active
Native Soils 15.411 psf 9.8H psf
Engineered Fill Soils 13.611 psf 8.2H psf
See the Earthwork Construction Recommendations Section for details concerning the use 40
of native soils,engineered fill and placement of backfill.
4.6 On-Site and Off-Site Impacts
From a geotechnical position, it is Envirotech's opinion that the subject property and
adjacent properties to the proposed development should not be significantly impacted if
all recommendations in this report are followed. This opinion is based on the expected
a
Envirotech Engineering Geotechnical Report
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Ph. 360-275-9374 March 4, 2024
site development, existing topography, existing nearby development, land cover, and
adhering to the recommendations presented in this report. Future development or land
disturbing activities on neighboring properties or properties beyond adjacent parcels that
are upslope and/or downslope from the subject property could cause problems to the
subject property. For this reason, future development or land disturbance near the subject
property should be evaluated by a geotechnical engineer.
Envirotech Engineering Geotechnical Report
PO Box 984 page 13 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County, Washington
Ph. 360-275-9374 March 4, 2024 441
5.0 ENGINEERING RECOMMENDATIONS
The following sections present engineering recommendations for the proposed
improvements of the project. These recommendations have been made available based on
the planned improvements as outlined in the Introduction Section of this report; general
observations including drainage and topography as recapitulated in the Surface
Conditions Section; soil/ geologic conditions that were identified from the geotechnical
investigation that is summarized in the Subsurface Investigation Section; and, project
research, analyses and conclusions as determined in the Engineering Analysis and
Conclusions Section. Recommendations for the project that is provided herein, includes
pertinent information for building foundations, earthwork construction, building and/ or
footing setbacks, drainage, vegetation considerations, and erosion control.
5.1 Building Foundation Recommendations
The recommended allowable bearing capacities and settlements as presented below,
consider the probable type of construction as well as the field investigation results by
implementing practical engineering judgment within published engineering standards.
Evaluations include classifying site soils based on observed field conditions and soil
testing for this project. After deriving conservative relative densities, unit weights and
angles of internal friction of the in-situ soils, the Terzhagi ultimate bearing capacity
equation was utilized for determining foundation width and depth. Foundation parameters
provided herein account for typical structural pressures due to the planned type of
development. A structural analysis is beyond the scope of a geotechnical report, and a
structural engineer may be required to design specific foundations and other structural
elements based on the soil investigation. Stepped foundations are acceptable, if warranted
for this project. Continuous, isolated, or stepped foundations shall be horizontally level
between the bottom of the foundation and the top of the bearing strata. The frost
penetration depth is not expected to extend beyond 12 inches below the ground surface
for this project under normal circumstances and anticipated design features.
5.1.1 Bearing Capacity
Existing in-situ soils for this project indicates that the structure can be established
on shallow, continuous or isolated footings. Foundations shall be established on
relatively undisturbed native soil that is competent and unyielding. Alternatively,
foundations may be constructed on selective re-compacted native soil or
compacted engineered fill as described in the Earthwork Construction
Recommendations Section of this report. #r
For a bearing capacity requirement of no more than 1500 psf, a minimum
continuous footing width of 12 inches shall be placed at a minimum of 12 inches
below the existing ground surface atop unyielding soils and away from any
potential old fill or disturbed soils. Foundation recommendations are made
Envirotech Engineering Geotechnical Report
PO Box 984 page 14 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 4, 2024
available based on adherence to the remaining recommendations that are provided
in this report. Alterations to the aforementioned foundation recommendations may
be completed upon a site inspection by a geotechnical engineer after the
foundation excavation is completed.
5.1.2 Settlement
Total and differential settlement that a structure will undergo depends primarily
on the subsurface conditions, type of structure, amount and duration of pressure
exerted by the structure, reduction of pore water pressure, and in some instances,
the infiltration of free moisture. Based on the expected native soil conditions,
anticipated development, and construction abides by the recommendations in this
report, the assumed foundation system may undergo a maximum of 1.0 inch total
settlement, and a maximum differential settlement of 0.75 inch.
5.1.3 Concrete Slabs-on-Grade
Interior slabs, if utilized, should be supported on a minimum of 4 inches of
compacted coarse, granular material (Retained on U.S. Sieve #10 or greater) that
is placed over undisturbed, competent native subgrade or engineered fill per the
Earthwork Recommendations Section below.
The recommendations for interior concrete slabs-on-grade as presented herein are
only relevant for the geotechnical application of this project. Although beyond the
scope of this report, concrete slabs should also be designed for structural integrity
and environmental reliability. This includes vapor barriers or moisture control for
mitigating excessive moisture in the building.
5.2 Earthwork Construction Recommendations
Founding material for building foundations shall consist of undisturbed native soils to the
specified foundation depths. Compacted engineered fill, or selective re-compacted native
soils may be used to the extents provided in this Earthwork Construction
Recommendations Section. The following recommendations include excavations,
subgrade preparation, type of fill, and placement of fill for building foundations.
1M
5.2.1 Excavation
Excavation is recommended to remove any excessive organic content, old fills/
disturbed soils or other deleterious material, if present,beneath foundations and to
achieve appropriate foundation depth. Additional sub-excavation will be required
for this project if the soils below the required foundation depth are loose,
saturated, not as described in this report, or otherwise incompetent due to
inappropriate land disturbing, or excessive water trapped within foundation ^r
Envirotech Engineering Geotechnical Report
PO Box 984 page 15 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County, Washington
Ph. 360-275-9374 March 4, 2024
q
excavations prior to foundation construction. All soils below the bottom of the
excavation shall be competent, and relatively undisturbed or properly compacted
fill. If these soils are disturbed or deemed incompetent, re-compaction of these ay
soils below the anticipated footing depth is necessary. Excavations shall be
completely dewatered, compacted, and suitable before placement of additional
native soil,engineered fill or structural concrete.
5.2.2 Placement and Compaction of Native Soils and Engineered Fill
For engineered fill or disturbed native soils that will be utilized as fill material
directly beneath foundations, observation and/ or geotechnical testing is required
prior to foundation construction. The following placement and compaction
requirements are necessary.
For disturbed native soils or engineered fill beneath foundations, limits of
compacted or re-compacted fill shall extend laterally from the bottom edge of the
foundation at a rate of one horizontal foot for each foot of compacted or re-
compacted fill depth beneath the foundation. See the illustration below.
FOOTING
COMPACTED
NATIVE SOILS
OR ENGINEERED 1
FILL 1
II UNDISTURBED SUBGRADEI
Both engineered fill and native soils used as compacted fill should be free of roots
and other organics, rocks over 6 inches in size, or any other deleterious matter.
Because of moisture sensitivity, importing and compacting engineered fill may be
more economical than compacting disturbed native soils. Engineered fill shall
include having the soils retained on the No. 4 sieve crushed (angular), and should
consist of the following gradation:
U.S. Standard Sieve %Finer(by weight)
6" 100
3" 60— 100
No. 4 20—60
No. 200 0- 8
Table 1
Particle Size Distribution of Engineered Fill
Compaction shall be achieved in compacted lifts not to exceed 6 inches for both
native soils and engineered fill, respectively. Each lift should be uniformly
Envirotech Engineering Geotechnical Report
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Belfair,Washington 98528 Mason County, Washington
Ph. 360-275-9374 March 4, 2024
compacted to at least 95% of the modified Proctor maximum dry density (ASTM
D 1557) and within 3% of optimum moisture content. Each lift surface should be
adequately maintained during construction in order to achieve acceptable
compaction and inter-lift bonding.
Temporary and permanent earth cuts and fill slopes exceeding 4 feet in height
should be limited to a slope of 2:1 (horizontal:vertical). Utility trenches or other
confined excavations exceeding 4 feet should conform to OSHA safety
regulations. Permanent cut and fill slopes shall be limited to a slope of 2:1, unless
otherwise approved by an engineer.
5.2.3 Retaining Wall Backfill
Native soils may be used as retaining wall backfill for this project if the total wall
height is 4 feet or less and the recommendations below are followed. Native soils
for retaining walls exceeding 4 feet in height must be approved by the local
authority or evaluated by an engineer. Backfill may consist of engineered fill, as
presented in this report, or borrow material approved by a geotechnical engineer.
Compaction of these materials shall be achieved in compacted lifts of about 12
inches. Each lift should be uniformly compacted to at least 85%, and no more
than 90% of the modified Proctor maximum dry density (ASTM D 1557). If
pavement or building loads are planned to be located within retaining wall
backfill, then 90% compaction is required. In addition, heavy construction
equipment should be at a distance of at least ' the wall height. Over-compaction
and limiting heavy construction equipment should be prevented to minimize the
risk of excess lateral earth pressure on the retaining structure. Envirotech
recommends that retaining wall backfill is compacted with light equipment such
as a hand-held power tamper. If clean, coarse gravel soils are utilized as
engineered fill, and surcharges will not influence the retaining wall, compaction
may be achieved by reasonably densifying granular soils with construction
equipment.
5.2.4 Wet Weather Considerations
Due to the types of subsurface soils, additional provisions may be required during
prolonged wet weather. Every precaution should be made in order to prevent free
moisture from saturating the soils within excavations. If the bottom of excavations
used for footing placement changes from a moist and dense/hard characteristic as
presented in this report to muck or soft, saturated conditions, then these soils
become unsuitable for foundation bearing material. If this situation occurs, a
geotechnical engineer should be notified, and these soils should be completely
removed and replaced with compacted engineered fill or suitable native material
as presented in this section.
Envirotech Engineering Geotechnical Report
PO Box 984 page 17 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 4, 2024
5.3 Building and Footing Setbacks
Provided that assumptions relating to construction occur and recommendations are
followed as presented in this report, the factor of safety for slope stability is sufficient for
a 50 feet footing setback from the face of the nearby descending slopes exceeding 40%. ,ii
The secondary critical slope as depicted on the site plan requires a 10 feet building
setback. See the figure below and the Site Plan in Appendix A for an illustration of the
setbacks.
STRUCTURE
TOP OF
SLOPE SLOPE
FACE
I I-I I I -I I
1.1
kSETBACK FOOTING
From the illustration above, structures may be located closer to the top of slope by
extending the foundation deep enough to maintain the recommended setback. In addition,
the required setback may be reduced by implementing pin piles or other deep foundation
system. Deeper foundations of 5 feet below the ground surface may encroach 6 feet of
setback. Only foundations within the encroachment area need to have deeper foundations.
This encroachment formula may be used for any reduction, such as a 10 feet footing
depth would allow a 12 foot setback reduction.
5.4 Surface and Subsurface Drainage
Positive drainage should be provided in the final design for all planned residential
buildings. Drainage shall include sloping the ground surface, driveways and sidewalks
away from the project structures. All constructed surface and subsurface drains should be
adequately maintained during the life of the structure. If drainage problems occur during
or after construction, additional engineered water mitigation will be required
immediately. This may include a combination of swales, berms, drain pipes, infiltration
facilities, or outlet protection in order to divert water away from the structures to an
appropriate protected discharge area. Leakage of water pipes, both drainage and supply
lines, shall be prevented at all times.
If impervious thresholds are exceeded per the prevailing agency code, then engineered
stormwater management plans are required for this project. The drainage engineer must
coordinate with a geotechnical engineer for input with relation to slope stability prior to
submitting drainage plans. If stormwater management plans are not required for this
project,then the following recommendations should be followed.
For this project, we recommend that infiltration is avoided in order to maintain slope
stability, and that roof downspout dispersion on splash blocks are employed for all point
Envirotech Engineering Geotechnical Report
PO Box 984 page 18 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County, Washington
Ph. 360-275-9374 March 4, 2024
discharges located at least 50 feet from the top of slope. If slope encroachment is
necessary,then roof water should be tightlined to the toe of slope.
5.5 Vegetation Buffer and Considerations
For this project, we believe that a detailed clearing and grading plan is not warranted
unless the prevailing agency thresholds are exceeded, and basic vegetation management
practices should be adhered to.
Vegetation Buffer—Vegetation shall not be removed from the face of the critical slope or
within a distance of 10 feet beyond the top of the slope. The secondary steep slope may
have a zero foot setback from the top. However, any tree deemed hazardous to life or
property shall be removed. If tree removal is necessary, then stumps and roots shall
remain in place, and the underbrush and soil shall remain undisturbed as much as
possible. Any disturbed soil shall be graded and re-compacted in order to restore the
terrain similar to preexisting conditions and drainage patterns. See the Site Plan in
Appendix A of this report for a depiction of the vegetation buffer.
5.6 Temporary and Permanent Erosion Control
Erosion control during construction should include minimizing the removal of vegetation
to the least extent possible. Erosion control measures during construction may include
stockpiling cleared vegetation, silt fencing, intercepting swales, berms, straw bales,
plastic cover or other standard controls. Although other controls may be used, if
adequate, silt fencing is presented in this report as the first choice for temporary erosion
control. Any erosion control should be located down-slope and beyond the limits of
construction and clearing of vegetation where surface water is expected to flow. If the
loss of sediments appears to be greater than expected, or erosion control measures are not
functioning as needed, additional measures must be implemented immediately. See
Appendix D for sketches and general notes regarding selected erosion control measures.
The Site Plan in Appendix A depicts the recommended locations for erosion control
facilities to be installed as necessary.
Permanent erosion control is necessary if substantial vegetation has not been established
within disturbed areas upon completion of the project. Temporary erosion control should
remain in place until permanent erosion control has been established. Permanent erosion
control may include promoting the growth of vegetation within the exposed areas by
mulching, seeding or an equivalent measure. Selected recommendations for permanent
erosion control are provided in Appendix D. Additional erosion control measures that
should be performed include routine maintenance and replacement, when necessary, of
permanent erosion control, vegetation, drainage structures and/or features.
Envirotech Engineering Geotechnical Report
PO Box 984 page 19 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County, Washington
Ph. 360-275-9374 March 4, 2024
5.7 Septic Drainfields
Septic drainfields were considered in our geotechnical evaluation. This includes septic
drainfields with relation to the observed soil conditions, expected vegetation removal,
and existing and proposed topography. Based on the aforesaid parameters, the septic
drainfields are not expected to adversely influence critical slopes if located at least 30 feet
from top of slopes.
5.8 Structural Mitigation
With respect to landslide alleviation or slope improvements, structural mitigation is not
necessary for this project unless setback encroachment is needed. This determination is
based on the anticipated improvements of the project, engineering conclusions, and
compliance with all recommendations provided in this report.
i
Mr
41
Envirotech Engineering Geotechnical Report
PO Box 984 page 20 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 4, 2024
6.0 CLOSURE
Based on the project information provided by the owner, the proposed development, and
site conditions as presented in this report, it is Envirotech's opinion that additional
geotechnical studies are not required to further evaluate this project.
Due to the inherent natural variations of the soil stratification and the nature of the
geotechnical subsurface exploration, there is always a possibility that soil conditions
encountered during construction are different than those described in this report. It is not
recommended that a qualified engineer performs a site inspection during earthwork
construction unless fill soils will influence the impending foundation. However, if native,
undisturbed subsurface conditions found on-site are not as presented in this report, then a
geotechnical engineer should be consulted.
This report presents geotechnical design guidelines, and is intended only for the owner,
or owners' representative, and location of project described herein. This report should not
be used to dictate construction procedures or relieve the contractor of his responsibility.
Any and all content of this geotechnical report is only valid in conjunction with the
compliance of all recommendations provided in this report. Semantics throughout this
report such as `shall,' `should' and `recommended' imply that the correlating design
and/or specifications must be adhered to in order to potentially protect life and/ or
property. Semantics such as `suggested' or `optional' refer that the associated design or
specification may or may not be performed, but is provided for optimal performance. The
recommendations provided in this report are valid for the proposed development at the
issuance date of this report. Changes to the site other than the expected development,
changes to neighboring properties, changes to ordinances or regulatory codes, or
broadening of accepted geotechnical standards may affect the long-term conclusions and
recommendations of this report.
The services described in this report were prepared under the responsible charge of
Michael Staten, a professional engineer with Envirotech. Michael Staten has appropriate
education and experience in the field of geotechnical engineering in order to assess
landslide hazards,earthquake hazards, and general soil mechanics.
Al
Please contact Michael Staten at 360-275-9374 if you have any questions, comments, or
require additional information.
Sincerely,
Envirotech Engineering
716411 ne
Michael Staten,P.E.
Geotechnical Engineer
Envirotech Engineering Geotechnical Report
PO Box 984 page 21 Parcel 42114-43-90120
Belfair,Washington 98528 Mason County,Washington
Ph. 360-275-9374 March 4, 2024
ti
APPENDIX A
GEOTECHNICAL SITE PLAN
n
TEP OF CRITICAL SLEE+E , J
EXEEE IIINFL AA%
SCALE 1 INCH=AR FEET
II' VEC£rAT[ON BtvrER FRLYI
111P IT CRITICAL SLOPE MIBI
a PD AS
AZs91A'Ts1>N'i y ! r
14\)
jpfi 9P" EtkTlf I_ J
i' ?1 \ \., 0 \\\\,,, C--.
/11
�JIL�DI4G SETDAE.1�[t1Y ''-T� OF $ECONIYOS'f?' SLOPE
I IGE EtT&N1CAL O FETL EXCE rATI AGd ZERO
+ GE0TE.'SH,�NIC-f+LP0RT ,, r v'EGErATION B4t�ER
r / d
T `.�� jj a '"_ /,_ ~�":A' BUILDING SETBACK FREM
' ."***... '' 1 f .'" „ TOE OF SEC(1NIIA&T SL0P£''::/,,
N t / _.., /.....
\ -, ,, \\,,,,si \\\
‘' 's\\,) \ - , - , \ ''''?„ ' :'
III(i -I
\ ci i,;,, 4 ((/4//,
/
\\\‘\\\-‘ 1/)if 2\ ,11 ' '.. ! t' , \\\\
~ ' x`. O1` 1)/) f' i; :a
d
f
NOTES,
L EROSION ONTROL NAY 1E REQUIRED FCR PHIS SITE,CAMERAL LOCATIONS
ARE DEPICTED,AND ALTERNATIVES MAY BE ;.ITIL]FEl AS EXPLAID IN TI-E
GEOTECHNICAL REPS'..
2,CON[TP.FS WERE NOT PREPARED ST A LICENSED LAND SURNEYDA
CONTOLRS WERE FX.HAP(L ATE D FRI7M A Pulls LIDAI SOURCE.AND
INCORPORATED-FIELD NEASUNENENTS AR EXPLA]NEC [N THE CIEITTECHNCLAL LEGEND
READRY.
3, N P DARIES'MERE NOT PREPARED BY A LICENSED SURVEYOR LIENTI NS TE[PORARY ETDI]NEE'
OF SITE FEATURES THAT ARE SHOWN FERE, SUJI AS TIT IT SLOPES.TEE -i--4-�EREIBBBN CDYTRO.. ENVDR0TETH ENGGRFEERINE
OF %LIPES. WATER FEATURES.ETC..WITH RELATION TO TIE PROPERTY PO BOX 904
LINES MIST HE VERIFIED BY THE OWNER,RE`.ONIENOATIONS IN THE -_� SCIPL IND CATOR BELFAIR, WASHINGTON H8SHH
SEOTECHNICAL [IEPOF1 %PROVIDE SETBACKS. $.FFE]FS, LEPTHS, ETC. WITH 3{. 2i$1jBT4
RELATED. TO GEOLOGIC` FEATURES,NOT Pi�ERTY LINES,THESE GEOLOGIC B6'_. EMISTI CONTOUR
FEATURES NAx HE LOCATED ON Of SUBJECT PRIPERTT CR A£IPHBEIRI f PZ TEST HIIS. SITE PLANPRO'ERT,ES. x
o s a t I III do A
4
qu
APPENDIX B
SOIL INFORMATION
ti
vRe:JL.AO beFFneTti SEA.[?
ECALD 1 MiH-W rat
PROPOSED SHOW—
EXISTING AND
EXISTING FILL /PROPOSED GRADE
`� ADVANCE OLTWASH
STREAM SECTION A-A
CONVERGENCE
MOTE5
EHI7fEEW
11 40POR r&Anc CHANGES REWIRED IN ORDER TO ACHIEVE CMVIROTECH ENGINEERING
mOS[i'NE MANAGE PO )OK 984
SOIL PROFILE 1S AGCtRATE FUR THE DEPTH OF 6ELFAIIR. WASHINGTON 985
THE D)1•$ERVER TEST PITS AT THE SPECIFIED LCCATI:RE W-275-9774
LOWER DEPTHS ARE!ABED ON SITE GEELELy,
vELL LOCASI, MINER EXPERIENCE EN TIE GENEPAL AREA SOIL PROFILE
TEST PIT LOG
(TP-1)
Date of Log: January 23, 2024
Location: XXX E Mystic Court,Union
Logged By: MCS
Depth USCS Description
0- 13ft SM-SP Poorly Graded Silty Sand with Gravel. +�
Medium brown and moist
Loose to medium dense.
Gravel is primarily coarse and subrounded
Sand is mostly medium and coarse
No plasticity
Density increases with depth
Glacial Outwash
APPENDIX C
SLOPE STABILITY
n ; -
hcs
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R i . .. -
M
d • :
/ : ` \ . . . . .
o . �
m
. . . . . .
�
\ \ \ \
' . 0 . \» _
0 « 0 % a } W S0
o , : coc00000
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:
.
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5 1 9e
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—.
Slope Sailty: Static
%
4111
14,
APPENDIX D
EROSION CONTROL
S
GEOTEXTILE FABRIC
WRAP AROUND TRENCH
TO AT LEAST ENTIRE
BOTTOM OF TRENCH
BEFORE PLACING GRAVEL 2'x2'x5' WOOD POST OR
12' DEEP, 8' WIDE TRENCH EQUIVALENT OR BETTER
FILLED WITH 3/4' TO 1 1/2'
WASHED GRAVEL OR VEGETATION
1i 25 FT
DIRECTION OF r EXISTING
WATER FLOW GROUND SURFACE
12•
T� 2S FT
I 8.
SILT FENCE - CROSS SECTION
N,T,S.
2'x2° WOOD POST (TYP) GEOTEXTILE FABRIC
OR EQUIVALENT OR BETTER AND WIRE MESH
@ 6 FT MAX, O,C, 6 FT Ir 49►T
EXISTING ` •
....:..,............... ................................. t
GROUND SURFACE $.1,,Xaio....•.....•.v.•.:a..o.....on.........u....w..
.••••i1•4tl.•.••,•••.i PSI"..••O..ip.•••q..g••VAI p/O•
12' DEEP, 8' WIDE ' • �' •��•'� •
.. :'2 '�_" .. 1 FT
TRENCH FILLED WITH «' ''. : . r iye«'. '. iZP
3/4° TO 1 1/2' .,�,:. io i4: '?,ii i::' 2.3 FT
WASHED GRAVEL OR VEGET•TIN• 4116,
BOTTOM EXTENTS OF
GEOTEXTILE FABRIC SILT FENCE - DETAIL
N.T.S.
PROVIDE FULL WIDTH
INGRESS/EGRESS
3/4 IN TO 1 1/
CRUSHED GRAVEL I�
PLACED AT 6 IN
MINIMUM DEPTH
WELL-DRAINED
SOILS
-0.02 IN/MIN FULL LENGTH
R=25 FT MIN
FL
ACCESS ROAD
STABILIZED CONSTRUCTION ENTRANCE
N.T.S.
O
S
PERMANENT EROSION CONTROL NOTES,
3EPERAL NOTES,
SEEDING FOR RAW SLOPES
L SIU,LD THE TEMPORARY EROSION AND SEDIMENT CONTROL MEASURES SHOWN ON
THESE PLANS PROVE TO BE INADEQUATE DURING CONSTRUCTION,THE CONTRACTOR 1. BEFORE SEEDING, INSTALL NEEDED SURFACE RUNOFF CONTROL
SHALL INSTALL ADDITIONAL EROSION AND SEDIMENT CONTROL FACILITIES. MEASURES SUCH AS GRADIENT TERRACES,INTERCEPTOR DIKES,
2.ALL EROSION AND SEDIMENT CONTROL FACILITIES AND DEVICES SHALL BE SWALES, LEVEL SPREADERS AND SEDIMENT BASINS,
INSPECTED DAILY AND IMMEDIATELY MAINTAINED,IF NECESSARY. 2.TIE SEED BED SHALL BE FIRM WITH FAIRLY FINE SURFACE.
3,ALL EROSION AND SEDIMENT CONTROL FACILITIES AND DEVICES SHALL BE LEFT IN FOLLOWING SURFACE ROUGHENING.PERFORM ALL OPERATIONS ACCROSS 41,,
PLACE UNTIL TIE UPSLOPE AREAS HAVE BEEN PERMANENTLY STABILIZED. OR PERPENDICULAR TO THE SLOPE.
3, SEEDING RECOM4ENDATICNS, AS SHOWN BELOW, AND SHOULD BE
TEMPORARY EROSION CONTROL NOTES, APPLIED AT THE RATE OF 120 POUNDS PER ACRE.
4.SEED BEDS PLANTED BETWEEN MAY 1 AND OCTOBER 31 WILL
'OR ALL AREAS WHICH HAVE BEEN STRIPPED OF VEGETATION OR EXPERIENCED LAND REQUIRE IRRIGATION AND OTHER MAINTENANCE AS NECESSARY TO
DISTURBING ACTIVITIES, AND WHERE NO FURTHER WORK IS ANTICIPATED FOR A FOSTER AND PROTECT THE ROOT STRUCTURE.
ERIOD EXCEEDING THE LISTED CRITERIA BELOW,ALL DISTURBED AREAS MUST BE 5. SEED BEDS PLANTED BETWEEN NOVEMBER 1 AND APRIL 30,
MMEDIATELY STABILIZED WITH MULCHING,GRASS PLANTING OR OTHER APPROVED ARMORING OF THE SEED BED WILL BE NECESSARY, (e.g.,
'ROSION CONTROL TREATMENT APPLICABLE TO THE TIME OF YEAR.GRASS SEEDING GEOTExTILES, JUTE MAT,CLEAR PLASTIC COVERING).
%LONE WILL ONLY BE ACCEPTABLE DURING THE MONTHS OF APRIL THROUGH 6.FERTILIZERS ARE TO BE USED ACCORDING TO SUPPLIERS'
≥EPTEMBER. HOWEVER, SEEDING MAY PROCEED WHENEVER IT IS IN THE INTEREST OF RECOMMENDATIONS.AMOUNTS SHOULD BE MINIMIZED,ESPECIALLY
THE OWNER/CONTRACTOR, BUT MUST ALSO BE AUGMENTED WITH MULCHING, NETTING ADJACENT TO WATER BODIES AND WETLANDS.
IR OTHER APPROVED TREATMENT.
USE TIE FOLLOWING RECOMMENDED SEED MIXTURE FOR EROSION
DRY SEASON CMAY 1 THRU SEPTEMBER 30)--THE CLEARING OF LAND, INCLUDING THE CONTROL, OR A COUNTY APPROVED ALTERNATE SEED MIXTURE.
REMOVAL OF EXISTING VEGETATION OR OTTER GROUND COVER, MUST BE LIMITED TO
ONLY AS MUCH LAND AS CAN RECEIVE APPROPRIATE PROTECTIVE COVER OR BE PROPORTIONS PURITY GERMINATION
OTHERWISE STABILIZED,AFTER HAVING BEEN CLEARED OR OTHERWISE DISTURBED , NAME BY WEIGHT(%) (X) (X)
BY NI LATER THAN SEPTEMBER 30 OF A GIVEN YEAR. UNLESS IMMEDIATE
ITABILIZATION IS SPECIFIED IN THE EROSION AND SEDIMENT CONTROL PLAN, ALL REDTOP (AGROSTIS ALBA) 10 92 90
%READ CLEARED OR OTHERWISE DISTURBED MUST BE APPROPRIATELY STABILIZED ANNUAL RYE (LOLIUM MILTIFLORUM) 40 98 90
THROUGH THE USE OF MULCHING,NETTING, PLASTIC SHEETING,EROSION BLANKETS. CHEWING FESUE 40 97 00
"REE DRAINING MATERIAL,ETC., BY SEPTEMBER 30 OR SOONER PER THE APPROVED (FESTUCA RUBRA COMMUTATA)
'LAN OF ACTION, UNLESS OTHERWISE APPROVED BY THE COUNTY, SEEDING. (JAMESTOWN, BANNER, SHADOW.KIIKET)
IRTILIZING AND MULCHING OF CLEARED OR OTHERWISE DISTURBED AREAS SHALL BE WHITE DUTCH CLOVER 10 96 90
ERFORMED DURING THE FOLLOWING PERIODS,MARCH 1 TO MAY 15,AND AUGUST 15 TO CTRIFOLIUM REPENS)
OCTOBER L SEEDING AFTER OCTOBER 1 WILL BE DONE WHEN PHYSICAL COMPLETION
IF THE PROJECT IS ImINENT AND TIE ENVIROENTAL CONDITIONS ARE CONDUCIVE MULCHING
TO SATISFACTORY GROWTH IN THE EVENT THAT PERANENT STABILIZATION IS NOT
'OSSIBLE,AN ALTERNATIVE METHOD OF GROUND COVER, SUCH AS MULCHING, NETTING,1.MATERIALS USED FOR MULCHING ARE RECOMMENDED TO BE WOOD
'LASTIC SHEETING,EROSION BLANKETS,ETC.,MUST BE INSTALLED BY NCI LATER THAN FIBER CELLULOSE, AND SHOULD BE APPLIED AT A RATE OF 1000
SEPTEMBER 30. POUNDS PER ACRE,
2. MULCH SHOULD BE APPLIED IN ALL AREAS WITH EXPOSED SLOPES
IN TIE EVENT THAT CONSTRICTION ACTIVITIES OR OTHER SITE DEVELOPMENT GREATER THAN 2,1(IORIZONTAL,VERTICAL),
RCTIVITIES ARE DISCONTINUED FEE AT LEAST 4 CONSECUTIVE DAYS, THE 3.MULCHING SFOLID BE USED IMMEDIATELY AFTER SEEDING OR IN
INNER/CONTRACTOR SHALL BE RESPONSIBLE FOR THE INSPECTION OF ALL EROSION AREAS WHICH CANNOT BE SEEDED BECAUSE OF THE SEASON,ALL
AND SEDIMENT CONTROL FACILITIES IMMEDIATELY AFTER STORM EVENTS, AND AT AREAS REQUIRING MULCH SHALL BE COVERED BY NOVEMBER 1.
_EAST ONCE EVERY WEEK. THE OWNER/ CONTRACTOR SHALL BE RESPONSIBLE FOR
THE MAINTENANCE AND REPAIR OF ALL EROSION AN SEDIMENT CONTROL FACILITIES. TOPSOILING AN
AT SEASON (OCTOBER 1 TIIRU APRIL 30)--ON SITES WHERE UNINTERUPTED L TOPSOIL SHOULD BE USED FOR THIS PROJECT DUE TO HIGHLY
'INSTRUCTION ACTIVITY IS IN PROGRESS, THE CLEARING OF LAND, INCLUDING THE DENSE EXPOSED SOILS.
REMOVAL OF EXISTING VEGETATION AND OTHER GROUND COVER, SHALL BE LIMITED 2 TOPSOIL SHOULD DE PLACED ON SLOPES NOT EXCEEDING 20,
TO AS MUCH LAND AREA AS CAN BE COVERED OR STABILIZED WITHIN 24 HOURS IN 3, STRIPPING AND STOCKPILING ON-SITE SOILS SHALL ONLY BE
THE EVENT A MAJOR STORM IS PREDICTED AND/ OR EROSION AND SEDIMENT PERMITTED IF TOPSOIL IS FRIABLE AND LOAMY (LOAM, SANDY LOAM,
TRANSPORT OTT-SITE IS OBSERVED. SILT LOAM, SANDY CLAY LOAM,CLAY LOAM),
4. STRIPPING SHALL BE UNFITTED TO THE IMMEDIATE CONSTRUCTION
ILL CLEARED OR DISTURBED AREAS SHALL RECEIVE APPROPRIATE PROTECTIVE
;OVER OR BE OTHERWISE STABILIZED, SUCH AS MULCHING, NETTING,PLASTIC DEPTH A FIVR TO SIX INCH STRIPPING DEPTH IS SOIL A, BUT
>MEETING,EROSION BLANKETS, FREE DRAINING MATERIAL,ETC., WITHIN 5 DAYS AFTER DEPTH MAY VARY DEPENDING ON THE PARTICULAR SOIL ALL
HAVING BEEN CLEARED OR OTHERWISE DISTURBED IF NOT BEING ACTIVELY WORKED, SURFACE RUNOFF CONTROL STRUCTURES SHALL BE IN PLACE BEFORE
SILT FENCING, SEDIMENT TRAPS. SEDIMENT PONDS,ETC., WILL NOT BE VIEWED AS STRIPPING.
ADEQUATE COVER IN AND OF THEMSELVES.IN THE EVENT THAT ANY LAND AREA NOT
BEING ACTIVELY WORKED REMAINS UNPROTECTED OR HAS NOT BEEN APPROPRIATELY
STABILIZED 5 DAYS AFTER HAVING BEEN CLEARED.ALL CONSTRUCTION ACTIVITY ON
THE SITE,EXCEPT FOR APPROVED EROSION AND SEDIMENT CONTROL ACTIVITY, SHALL
IMMEDIATELY CEASE UNTIL SUCH A TIME AS AFOREMENTIONED LAND AREA HAS BEEN
IPPRIPRIATELY PROTECTED OR STABILIZED.
STOCKPLE MANAGIYENT
1.STOCKPILE SHALL DE STAIILIZEO(WITH PLASTIC COVERING OR OTHER APPROVED DEVICE)DAILY BETWEEN HIIVEMBER I AND MARCH
31,
2.IN ANY SEASON,SEDIMENT LEACHING FROM STOCK PILES MUST BE PREVENTED,
a TOPSOIL SHALL MIT BE PLACED AILS IN A FROZEN OR BUDDY CONDITION,WHEN THE SUBGRADE IS EXCESSIVELY WET,IN WHEN
CONDITIONS EXIST THAT MAY OTHERWISE BE DETRIMENTAL TO PROPER GRADING OR PROPOSED SODDING OR SEEDING.
4.PREVIOUSLY ESTABLISHED GRADES CN THE AREAS TO BE TDESOILED SHALL BE MAINTAINED ACCORDING TD 10E APPROVED PLANS.
STABILIZED CONSTRUCTION ENTRANCE
L MATERIAL SHALL BE 4 INCH TO 8 INCH QUARRY SPALLS (4 TO 6 INCH FOR RESIDENTIAL SINGLE FAMILY LOTS)AND MAY BE
TOP-DRESSED WITH 1 INCH TO 3 INCH ROCK.(STATE STANDARD SPECIFICATIONS, SECTION 8-15.)
2.THE ROCK PAD SHALL BE AT LEAST 12 INCHES THICK AND 50 FEET LONG(20 FEET FOR SITES WITH LESS THAN 1 ACRE OF
DISTURBED SOIL).WIDTH SHALL BE FILL WIDTH OF TIE VEHICLE INGRESS AND EGRESS AREA.SMALLER PADS MAY DE APPROVED
FOR SINGLE-FAMILY RESIDENTIAL AND SHALL COMMERCIAL SITES.
3.ADDITIONAL ROCK SHALL BE ADDED PERIODICALLY TO MAINTAIN PROPER FUNCTION OF THE PAD.
4.IF THE PAD DOES NOT ADEQUATELY REMOVE THE MUD FROM THE VEHICLE WHEELS, THE WHEELS SHALL BE HOSED OFF BEFORE
THE VEHICLE ENTERS A PAVED STREET.THE WASHING SHALL BE DONE ON AN AREA COVERED WITH CRUSHED ROCK AND WASH
WATER SHALL DRAIN TO A SEDIMENT RETENTION FACILITY OR THROUGH A SILT FENCE.
SILT FENCE
1.GEOTEXTILE FILTER FABRIC TYPE SHALL BE PER SPECIFIED IN DE 'STIIRMWATER MANAGEMENT MANUAL
FOR THE PUGET SOUND BASIN; OR APPLICABLE COUNTY STANDARDS
2.GEOTEXTILE FILTER FABRIC SHALL BE PURCHASED IN A CONTINUOUS ROLL CUT TO THE LENGTH OF
EACH BARRIER TO AVOID USE OF JOINTS.IF JOINTS ARE NECESSARY, FILTER FABRIC SHALL BE SPLICED
TOGETHER ONLY AT A SUPPORT POST WITH A MINIMUM 6-INCH OVERLAP AND SECURELY FASTENED AT
BOTH ENDS TO THE POST,
3.STANDARD FILTER FABRIC SHALL BE FASTENED USING 1' STAPLES OR TIE WIRES (HOG RINGS) B 4 IN
SPACING,
4,POSTS SHALL BE SPACED AND PLACED AT DEPTHS INDICATED IN THE DETAILS ON THIS SHEET,AND
DRIVEN SECURELY INTO THE GROUND.
5. VIRE MESH SHALL BE 2'X2'014 GAUGE OR EQUIVILENT.THE WIRE MESH MAY BE ELIMINATED IF
EXTRA-STRENGTH FILTER FABRIC OAONOFILAMENT), AND CLOSER POST SPACING IS USED.
6.A TRENCH SHALL BE EXCAVATED ACCORDING TO THE DETAILS ON THIS SHEET ALONG THE LINE OF THE
POSTS AND UPSLOPE FROM THE SILT FENCE,
7,SILT FENCES SHALL BE LOCATED DOWNSLOPE FROM THE CLEARING LIMITS OF THE PROJECT.
SY
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