HomeMy WebLinkAboutGeotachnical Report (Application Materials and Site Plan)CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
PRELIMINARY GEOLOGIC HAZARD ASSESSMENT &
GEOTECHNICAL ENGINEERING REPORT
Hawkins Lane Subdivision
2870 Hawkins Lane
Eugene, Oregon 97405
Lane County Parcel No. 1804024304600
Prepared for:
Mr. Michael Sorric
Pineridge Construction, LLC
CORE GeoEngineering Project No. 26-1156
August 20, 2026
Preliminary Geologic Hazard Assessment and Geotechnical Engineering Report
Hawkins Lane Subdivision, Eugene, Oregon
i | P a g e CORE GeoEngineering, Project No. 26-1156
Version 2.0, August 20, 2026
TABLE OF CONTENTS
1.0 PROJECT INFORMATION ................................................................................................................................................... 1
2.0 SITE AND PROJECT DESCRIPTION ...................................................................................................................................... 1
2.1 Eugene Site Development Standards: Geological and Geotechnical Analysis .................................................................. 1
2.1.1 Level Two Analysis EC 9.6710(5)(b) ........................................................................................................................ 2
2.1.2 Clear and Objective Housing EC 9.6710(6) ............................................................................................................. 2
2.1.3 South Hills Study Policies EC 9.9630(3)(c) .............................................................................................................. 3
3.0 REGIONAL GEOLOGIC MAPPING ....................................................................................................................................... 4
4.0 REGIONAL SEISMIC SETTING ............................................................................................................................................. 5
4.1 Cascadia Subduction Zone ................................................................................................................................................ 5
5.0 FIELD EXPLORATION AND SUBSURFACE CONDITIONS ...................................................................................................... 5
5.1 Soil Descriptions ................................................................................................................................................................ 6
5.2 Expansive Soils and Shrink Swell Potential ........................................................................................................................ 7
5.3 Depth to Groundwater ...................................................................................................................................................... 8
6.0 GEOLOGIC HAZARD REVIEW ............................................................................................................................................. 9
6.1 Earthquake Hazard Review ............................................................................................................................................... 9
6.2 Seismic Site Class and Earthquake Ground Motion Parameters ....................................................................................... 9
6.3 Soil Liquefaction .............................................................................................................................................................. 11
6.4 Landslides and Global Slope Stability .............................................................................................................................. 11
6.4.1 LiDAR Review ........................................................................................................................................................ 12
6.5 Flood Hazard ................................................................................................................................................................... 12
6.6 Erosion Hazard ................................................................................................................................................................ 12
6.7 Radon Hazard .................................................................................................................................................................. 13
7.0 PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS .............................................................................................. 13
7.1 Preliminary Site Preparation Recommendations ............................................................................................................ 13
7.2 Keyways, Benching, and Subdrains for Fill Slopes ........................................................................................................... 14
7.3 Engineered Fill Recommendations .................................................................................................................................. 15
7.4 Excavation Conditions and Utility Trench Backfill Recommendations ............................................................................ 16
7.5 Wet Weather Earthwork Recommendations .................................................................................................................. 16
7.6 Lateral Earth Pressures ................................................................................................................................................... 17
7.7 Preliminary Foundation Recommendations ................................................................................................................... 19
7.8 Concrete Slabs-on-Grade ................................................................................................................................................ 20
7.9 Potential Retaining Walls ................................................................................................................................................ 21
7.10 Foundation Drains ........................................................................................................................................................... 21
8.0 ROADWAY CONSTRUCTION ............................................................................................................................................ 22
8.1 Subgrade Preparation ..................................................................................................................................................... 22
8.2 Wet Weather Construction Pavement Section ............................................................................................................... 23
9.0 LIMITATIONS ................................................................................................................................................................... 24
10.0 REFERENCES .................................................................................................................................................................... 25
Preliminary Geologic Hazard Assessment and Geotechnical Engineering Report
Hawkins Lane Subdivision, Eugene, Oregon
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LIST OF APPENDICES
Figures
Exploration Logs
Soils Laboratory Results
Site Plans
Site Research
Photographic Log
LIST OF FIGURES
1 Site Location Map
2 Site Aerial and Exploration Map
3 Site Plan and Exploration Map
4 LiDAR Imagery
5 LiDAR Imagery and Landslide Inventory
6 Typical Keyway, Benching, and Fill Slope
7 Typical Perimeter Footing Detail
Preliminary Geologic Hazard Assessment and Geotechnical Engineering Report
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1.0 PROJECT INFORMATION
This report presents the findings and conclusions of a preliminary geologic hazard assessment and
geotechnical engineering study conducted by CORE GeoEngineering, LLC (CORE) for the referenced
project. The purpose of the study was to assess subsurface conditions, characterize geologic and
geotechnical conditions, and provide recommendations for the proposed development. The investigation
was performed in accordance with Proposal No. P26-1154, dated July 17, 2026, and subsequent approvals
of our proposal and General Terms and Conditions.
2.0 SITE AND PROJECT DESCRIPTION
As indicated on Figures 1 through 3, the subject site is located at 2870 Hawkins Lane in the South Eugene
area of Eugene, Lane County, Oregon, and is identified as Lane County Tax Lot 4600 (Assessor's Map No.
18-04-02-43; Tax Lot 1804024304600). The property encompasses approximately 2.98 -acres and is
bordered to the west and northwest by Hawkins Lane, to the east by existing residential properties, and
to the south by undeveloped land. The site was previously developed with a single-family residence and
associated improvements that were removed sometime after 2005, and the property is currently
undeveloped and vegetated with mixed trees, brush, and grasses. Topography across the site slopes
moderately down to the north and northwest, with elevations ranging from approximately 722 to 807
feet AMSL (NAVD 88). The property is located in the SW ¼ of the SE ¼ of Section 2, Township 18 South,
Range 4 West, Willamette Meridian. The site latitude and longitude are 44.026381, -123.137337. The site
is zoned R-1, Low Density Residential, and the regulatory jurisdictional agency is the City of Eugene,
Oregon.
Based on our review of the preliminary site plan prepared by A & O Engineering, L.L.C., dated August 12,
2026 (see Site Plans in report appendix), CORE understands that the proposed development will consist
of a 10-Lot residential subdivision supporting construction of new single-family homes, a new public street
(Videra Drive) extending east from Hawkins Lane, new underground utilities, and a stormwater facility
located within Tract A. The planned homes are expected to be two-story structures constructed with wood
framing above typical spread footings. Individual lots are anticipated to be left at existing grade at the
time of plat development, with lot grading to be performed by others during the individual home
construction process. We anticipate cuts and fills associated with the proposed development. At this time
site planning is preliminary and a grading plan has not yet been prepared. We understand that retaining
walls may be proposed as part of the development. Once a grading plan has been prepared, we
recommend that site-specific retaining wall design be performed. During home building we recommend
that lot by lot geotechnical evaluation be conducted on a case-by-case basis relative to the proposed
development plans and soil conditions at each building lot.
2.1 Eugene Site Development Standards: Geological and Geotechnical Analysis
CORE understands that, based on site topography and geologic hazard mapping, a geological and
geotechnical analysis is required as part of the tentative subdivision application, in compliance with City
of Eugene Code (EC) 9.6710, Geological and Geotechnical Analysis. Because the site is a proposed
subdivision with slopes equal to or greater than 10 percent, a Level Two Analysis is required under EC
9.6710(5)(b). This report presents a compilation of record geological data, analysis of site characteristics,
subsurface investigation and testing to establish soil types and distribution, and a discussion of site and
Preliminary Geologic Hazard Assessment and Geotechnical Engineering Report
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soil characteristics in relation to the proposed development, including identification of potential problems
and recommendations for design and construction techniques consistent with the standards applicable
to the development. We further understand the applicant intends to pursue approval under the Clear and
Objective Housing provisions of EC 9.6710(6). Accordingly, this report has been prepared to also address
the items described under EC 9.6710(6)(a) through (6)(c). In addition, this report provides a review of the
anticipated on-site and off-site impacts of the proposed development by a qualified engineering geologist,
in compliance with the South Hills Study Policies of EC 9.9630(3)(c). The subsections below cross-reference
each required item to the report section where it is addressed. The results of our study and
recommendations for site development are presented below.
2.1.1 Level Two Analysis EC 9.6710(5)(b)
A Level Two Analysis under EC 9.6710(4)(b) consists of a compilation of record geological data, analysis of
site characteristics, subsurface investigation and testing to establish soil types and distribution, and a
report that includes site and soil characteristics in relation to the proposed development, identification of
potential problems, and recommendations for design and construction techniques. The report sections
addressing each required item are identified below.
• Compilation of record geological data, including published geologic mapping, soil survey data, and
geologic hazard mapping, is presented in Section 3, Regional Geologic Mapping; Section 6,
Geologic Hazard Review; and the Site Research Appendix.
• Analysis of site characteristics is presented in Section 2, Site and Project Description; Section 3,
Regional Geologic Mapping; Section 4, Regional Seismic Setting; Section 5, Field Exploration and
Subsurface Conditions; and Section 6, Geologic Hazard Review.
• Subsurface investigation and testing to establish soil types and distribution is presented in Section
5, Field Exploration and Subsurface Conditions, with supporting exploration logs and laboratory
results in the Appendix.
• Site and soil characteristics in relation to the proposed development and identification of
potential problems are presented in Section 5, Field Exploration and Subsurface Conditions;
Section 6, Geologic Hazard Review; and Section 7, Preliminary Conclusions and
Recommendations.
• Recommendations for design and construction techniques are presented in Section 7, Preliminary
Conclusions and Recommendations, including Section 7.1, Preliminary Site Preparation
Recommendations; Section 7.7, Preliminary Foundation Recommendations; and Section 7.9,
Potential Retaining Walls.
2.1.2 Clear and Objective Housing EC 9.6710(6)
The applicant intends to pursue approval under the Clear and Objective Housing provisions of EC
9.6710(6). The report sections addressing each item required under EC 9.6710(6) are identified below.
• Identification of any portion of the site located in an area of moderate or high landslide
susceptibility on the Eugene Landslide Hazard Map, as required under EC 9.6710(6)(a), is
Preliminary Geologic Hazard Assessment and Geotechnical Engineering Report
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presented in Section 6.4, Landslides and Global Slope Stability, with supporting hazard mapping
in the Site Research Appendix.
• The statement regarding stability problems and the site conditions listed under EC 9.6710(6)(b),
including slopes 20 percent or greater, springs or seeps, depth of soil to bedrock, soil types,
variations in soil types, open drainage ways, and fill, is addressed in Section 5, Field Exploration
and Subsurface Conditions, and Section 6.4, Landslides and Global Slope Stability.
• Review of the suitability of the proposed lot layout, street locations, and proposed locations for
utilities, driveways, parking areas, and buildings, as required under EC 9.6710(6)(c)(1), is
presented in Section 6.4, Landslides and Global Slope Stability; Section 7.1, Preliminary Site
Preparation Recommendations; and Section 7.7, Preliminary Foundation Recommendations.
• Recommended modifications to the proposed lot layout, street locations, and building locations
to mitigate the identified hazards and site conditions, as required under EC 9.6710(6)(c)(2), are
presented in Section 7.7, Preliminary Foundation Recommendations, including slope setback
recommendations for Lots 6, 7, and 10, and Section 7.9, Potential Retaining Walls.
• Methods for safely addressing the identified landslide hazards and site conditions, as required
under EC 9.6710(6)(c)(3), are presented in Section 6.6, Erosion Hazard; Section 7.1, Preliminary
Site Preparation Recommendations; Section 7.7, Preliminary Foundation Recommendations; and
Section 7.9, Potential Retaining Walls.
• Recommendations for additional geotechnical analysis for future buildings or improvements on
the development site and on the proposed lots, as required under EC 9.6710(6)(c)(4) and (5), are
presented in Section 7.7, Preliminary Foundation Recommendations.
2.1.3 South Hills Study Policies EC 9.9630(3)(c)
EC 9.9630(3)(c) requires review of both on-site and off-site impacts of the proposed development by a
qualified engineering geologist. This review is provided in Section 6, Geologic Hazard Review, and Section
7, Preliminary Conclusions and Recommendations. The report sections addressing this requirement are
identified below.
• Review of on-site and off-site slope stability and landslide impacts, including the mapped
landslides in the site vicinity and the steep slope within Tract B, is presented in Section 6.4,
Landslides and Global Slope Stability, and Section 6.4.1, LiDAR Review, with supporting hazard
mapping in the Site Research Appendix.
• Review of on-site geologic hazards, including seismic, liquefaction, flood, erosion, and radon
hazards, is presented in Sections 6.1 through 6.7, Geologic Hazard Review.
• Recommendations for site development to address the identified on-site and off-site impacts,
including grading, drainage, erosion control, slope setbacks, and site preparation, are presented
in Section 7, Preliminary Conclusions and Recommendations, including Section 6.6, Erosion
Hazard; Section 7.1, Preliminary Site Preparation Recommendations; and Section 7.7, Preliminary
Foundation Recommendations.
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Because a grading plan has not yet been prepared for the proposed development, this review of on-site
and off-site impacts is preliminary and is based on the existing site conditions and the preliminary site
plan. Once a grading plan has been prepared, CORE should conduct additional review of the proposed
grading, cut and fill slopes, and drainage to complete the evaluation of on-site and off-site impacts and to
provide any additional recommendations necessary to address those impacts.
3.0 REGIONAL GEOLOGIC MAPPING
The property is located within the southern portion of the Willamette Valley, a broad structural and
depositional basin bounded by the Coast Range to the west and the Western Cascades to the east. The
regional geology consists primarily of Quaternary alluvial and fluvial deposits derived from the Willamette
and McKenzie Rivers, composed of unconsolidated sand, gravel, silt, and clay deposited in channel,
overbank, and floodplain environments. These surficial sediments typically overlie Tertiary volcanic and
sedimentary rocks associated with the Western Cascades and marine sequences of the Coast Range. The
region’s geologic framework reflects the long-term influence of Cascadia Subduction Zone tectonics,
which have produced broad uplift, folding, and associated earthquake hazards. Additionally, Pleistocene
glacial outwash, episodic flooding, and volcanic input have contributed to the heterogeneous character
and variable engineering properties of near-surface soils throughout the Eugene area.
Geologic mapping1 indicates that the site is directly underlain by volcanic rocks of the western Cascade
Range (Tvw), of Miocene and Oligocene age. This unit consists of lava flows, tuff, breccia, pyroclastic
material, and volcaniclastic sediments of variable composition, and composes much of the western
Cascade Range in the study area. It includes the Little Butte Volcanics of Peck and others (1964) in Oregon,
and is locally intruded by small stocks, dikes, and sills. Consistent with this mapping, our subsurface
exploration encountered weathered claystone and siltstone bedrock beneath residual fat clay soils across
the site, grading from soft, weathered rock (ODOT hardness R1) at shallow depth to harder, less
weathered rock (R2 to R4) with depth.
The Web Soil Survey (United States Department of Agriculture, Natural Resources Conservation Service
[USDA NRCS, 2026 Website]) indicates that near-surface soils at the site are mapped predominantly as
Dixonville silty clay loam, 3 to 12 percent slopes (map unit 41C), with Philomath cobbly silty clay, 12 to 45
percent slopes (map unit 108F) mapped along the eastern portion of the property. Both series are poorly
drained and are assigned to Hydrologic Soil Group D, indicating a very slow infiltration rate and high runoff
potential. The Dixonville series is mapped with depth to bedrock of approximately 66 centimeters and
depth to the seasonal high-water table greater than 200 centimeters, while the Philomath series is
mapped with a shallower depth to bedrock of approximately 36 centimeters. Based o n our observations
during subsurface exploration, the mapped boundary of the 108F unit appears to extend too far east
relative to actual conditions, and the highly expansive fat clay soils encountered on-site are more
consistent with the eastern portion of the property than the mapped unit boundaries indicate.
1 Generalized Geologic Map of the Willamette Lowland, US Department of the Interior, US Geological Survey, Professional
Paper 1424-A, Gannett and Caldwell, 1998.
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4.0 REGIONAL SEISMIC SETTING
At least one major fault zone capable of generating damaging earthquakes is thought to exist in the vicinity
of the subject site consisting of the Cascadia Subduction Zone.
4.1 Cascadia Subduction Zone
The Cascadia Subduction Zone is a major geological feature that extends from northern California through
Oregon to British Columbia, where the Juan de Fuca Plate is being subducted beneath the North American
Plate. Located approximately 50 to 70 miles off the coast of Oregon, this subduction process has shaped
the region's tectonic activity and geologic history, created the Cascade Range, and contributed to
significant historic volcanic and seismic activity. The collision between these tectonic plates builds
immense pressure that is periodically released in powerful earthquakes releasing centuries of
accumulated tectonic stress, including the potential for devastating megathrust earthquakes.
Additionally, the subduction process has generated uplift and deformation of coastal areas, as well as
driving volcanism in the Cascade Range.
The Cascadia Subduction Zone has the potential to produce extremely large earthquakes, with
magnitudes reaching up to 9.0 or higher. Geological evidence from sediment cores, tsunami deposits, and
coastal uplift suggests that the Cascadia Subduction Zone has experienced repeated cycles of large
earthquakes, with the last major event occurring in 1700. Models based on past events indicate that the
zone could produce an earthquake with a magnitude ranging between 8.0 and 9.0, causing widespread
damage not only in Oregon but throughout the Pacific Northwest. This high-magnitude earthquake could
trigger powerful tsunamis, liquefaction, landslides, and severe shaking, significantly impacting both
coastal and inland areas. Scientists consider the Cascadia Subduction Zone one of the greatest seismic
hazards in North America.
5.0 FIELD EXPLORATION AND SUBSURFACE CONDITIONS
Subsurface explorations for this report were conducted on August 6, 2026. Six exploratory test pits (TP-1
through TP-6) were excavated at the site using a Komatsu PC138 US LC tracked excavator equipped with
rock teeth, reaching a maximum depth of approximately 13 feet below ground surface (bgs). A CORE
engineering geologist provided full-time observation during the explorations, recording key data such as
soil sample depths, stratigraphy, soil engineering characteristics, and groundwater occurrence. Soils were
classified according to the Unified Soil Classification System (USCS) and the ODOT rock hardness
classification system. Samples collected during the explorations were stored in relatively air-tight plastic
bags. After each test, the pits were loosely backfilled with onsite soil. The approximate exploration
locations are shown on Figures 2 and 3.
It is important to note that the exploration locations were determined in the field by pacing or measuring
distances from visible property corners and other site features indicated on the provided plans. Therefore,
the exploration locations should be considered approximate. Summary exploration logs are attached. The
stratigraphic contacts shown on the individual subsurface logs represent approximate boundaries
between different soil types, but actual transitions may be more gradual. The soil and groundwater
conditions described are specific to the dates and locations of the explorations and may not be
Preliminary Geologic Hazard Assessment and Geotechnical Engineering Report
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representative of other areas or times. A summary of the soil and groundwater conditions encountered
during the explorations is provided below.
5.1 Soil Descriptions
Topsoil: At the locations of our subsurface explorations, the ground surface was primarily vegetated with
grasses, Rhododendrons, poison oak, and Oak trees. Test pit exploration indicated that the near-surface
soils primarily consist of approximately 14 to 24 inches of brown, soft, moist, moderately to highly organic
topsoil containing abundant fine and coarse roots. At test pits TP-1 and TP-3, the topsoil classified as
Organic Fat CLAY (OH); at test pits TP-4, TP-5, and TP-6, the topsoil classified as Lean CLAY (OL). The depth
of the organic topsoil layer should be expected to increase where trees are present, as coarse roots were
observed extending to depths of approximately 24 inches below the ground surface at the location of test
pit TP-1. No topsoil was observed at test pit TP-2, which was located at the former home site.
Undocumented Fill: Undocumented fill was encountered beneath the topsoil at the locations of test pits
TP-4, TP-5, and TP-6, and at the ground surface at test pit TP-2, located at the former home site. The
approximate extent of the identified undocumented fill is shown on Figures 2 and 3. The fill encountered
at test pits TP-4, TP-5, and TP-6 consisted of medium stiff, dry, low-plasticity Lean CLAY containing
abundant basaltic cobbles and boulders up to approximately 36 inches in diameter, extending to
approximate depths of 3 to 5 feet below the ground surface (bgs). The fill at test pit TP-6 also contained
3/4-inch-minus crushed aggregate and remnants of old gas and storm piping. The fill encountered at test
pit TP-2 consisted of demolition debris, including subrounded gravel and concrete fragments within a silty
soil matrix, extending to a depth of approximately 2.5 feet bgs. The distribution and variable character of
the undocumented fill across the site suggests multiple fill events of differing source materials associated
with prior site development. The fill material is not considered suitable for support of planned
improvements in its existing condition and will require removal or remediation prior to construction.
Fat CLAY (CH): Underlying the topsoil at test pits TP-1 and TP-3, soils consisted of red brown, stiff to very
stiff, moist, highly plastic, highly expansive Fat CLAY (CH). The soil type was observed to extend to
approximate depths of 5 feet bgs. The anticipated extent of the highly expansive Fat CLAY is shown on
Figures 2 and 3. Pocket penetrometer measurements indicated unconfined compressive strengths ranging
from approximately 2.0 to greater than 4.5 tons/ft². Sieve analysis conducted in accordance with ASTM
D6913 and D1140, Standard Test Methods for Particle-Size Distribution (Gradation of Soils Using Sieve
Analysis), indicated 87.0 percent passing the No. 200 sieve. Atterberg Limit testing conducted in
accordance with AASHTO T-89 and T-90 indicated a liquid limit of 81 and a plasticity index of 51. An in-
situ moisture content of 28.4 percent was measured on a representative sample collected from test pit
TP-1. The soil type classified as A-7-5(51) according to AASHTO standards.
Weathered CLAYSTONE / SILTSTONE: Underlying the Fat CLAY and undocumented fill, soils transitioned
to weathered claystone and siltstone bedrock. At test pit TP-1, the material consisted of red brown,
medium dense, moist, high-plasticity CLAYSTONE (CH) with blocky fragments and a waxy texture,
displaying ODOT rock hardness increasing from R1 to R3 with depth, in accordance with the ODOT Rock
Hardness Classification System (Table 1). At test pits TP-3, TP-4, TP-5, and TP-6, the material consisted of
light brown, weathered, medium dense to dense, non-plastic SILTSTONE (ML) with blocky fragments and
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orange staining that broke apart with a hammer, displaying ODOT rock hardness increasing from R1 to R4
with depth. At test pit TP-2, the material consisted of light brown, dense, cemented sandstone
conglomerate containing dark, angular basalt gravel to cobbles, displaying ODOT rock hardness of R2 to
R4; this conglomerate was observed only at test pit TP-2. Digging conditions became progressively harder
with depth, with practical refusal of excavation encountered at approximately 7 to 9 feet bgs at test pits
TP-2, TP-5, and TP-6. Sieve analysis indicated 53.9 to 90.0 percent passing the No. 200 sieve. Atterberg
Limit testing indicated the CLAYSTONE at test pit TP-1 classified as A-7-6(29) with a liquid limit of 56 and
a plasticity index of 28, while the SILTSTONE at test pit TP-4 was non-plastic and classified as A-4(0). In-
situ moisture contents of 24.4 and 17.2 percent were measured on representative samples collected from
test pits TP-1 and TP-4, respectively. See the attached test pit logs provided in the appendix of this report
and the ODOT Rock Hardness Classification Chart presented in Table 1 for additional detail.
Table 1. Oregon Department of Transportation (ODOT) Rock Hardness Classification Chart
ODOT Rock
Hardness Rating Field Criteria
Unconfined
Compressive
Strength
Typical Equipment Needed for Excavation
Extremely Soft (R0) Indented by thumbnail <100 psi Small excavator
Very Soft (R1) Scratched by thumbnail,
crumbled by rock hammer 100-1,000 psi Small excavator
Soft (R2)
Not scratched by
thumbnail, indented by
rock hammer
1,000-4,000 psi Medium excavator
(slow digging with small excavator)
Medium Hard (R3) Scratched or fractured by
rock hammer 4,000-8,000 psi
Medium to large excavator (slow to very slow
digging, typically requires chipping with
hydraulic hammer or mass excavation)
Hard (R4) Scratched or fractured w/
difficulty 8,000-16,000 psi Slow chipping with hydraulic hammer and/or
blasting
Very Hard (R5)
Not scratched or fractured
after many blows,
hammer rebounds
>16,000 psi Blasting
5.2 Expansive Soils and Shrink Swell Potential
As noted above, subsurface explorations encountered highly plastic, highly expansive Fat CLAY (CH) soils
at test pits TP-1 and TP-3, generally beneath approximately 1.5 feet of surface soils and extending to
approximate depths of 4 to 4.5 feet below ground surface. Atterberg Limit testing on a representative
sample from test pit TP-1 indicated a liquid limit of 81 and a plasticity index of 51, corresponding to a
"high" to "very high" expansion potential. The anticipated extent of the highly expansive Fat CLAY across
the site is shown on Figures 2 and 3; however, expansive soils may be present outside of these mapped
areas, and the boundaries shown are approximate and based on our test pit observations. These soils
exhibit significant volume change with variations in moisture content, shrinking as they dry and swelling
as they become wet. This shrink-swell behavior can generate vertical and lateral ground movement,
particularly where seasonal moisture fluctuations occur within the active zone beneath a structure. If left
unmitigated, this movement can lead to differential heave and settlement, cracking and distress in
foundations, slabs-on-grade, pavements, and flatwork, and damage to shallow utilities.
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Because this report is preliminary and home construction is to be undertaken by others, individual lots
will require evaluation on a case-by-case basis at the time of building permit application. For lots within
the areas of anticipated highly expansive Fat CLAY shown on Figures 2 and 3, we recommend that
additional expansion index testing be conducted in accordance with ASTM D4829 to characterize the
expansion potential at each building site. Where highly expansive soils are confirmed beneath planned
structures, we recommend that the expansive Fat CLAY be over-excavated to a depth of at least 4 feet
below the bottom of footings and replaced with 3/4-inch-minus crushed aggregate compacted to at least
95 percent of the maximum dry density as determined by AASHTO T-180. The over-excavation and
structural fill pad should extend laterally at least 4 feet beyond the foundation on all sides. This approach
is intended to remove the expansive soils from the zone influenced by foundation loading and from the
zone in which seasonal moisture change would otherwise generate vertical and lateral pressures against
the foundation elements.
The recommendations presented herein are contingent on the expansive Fat CLAY being fully removed
from beneath and adjacent to the foundation elements to the limits specified above. CORE should observe
the foundation over-excavation at the time of construction on each affected lot to verify that the
expansive Fat CLAY has been removed to the specified limits and that the exposed bearing materials are
consistent with the conditions anticipated in this report. If expansive soils are encountered at or below
the planned over-excavation depth, the over-excavation will need to be deepened, or the foundation
recommendations revised, at CORE's direction. If subsurface conditions are found to differ from those
described in this report, CORE should be contacted to review the conditions and update or revise our
recommendations as necessary.
5.3 Depth to Groundwater
Subsurface explorations were conducted on August 6, 2026, during the dry season typical of late summer
in western Oregon. Observed soil moisture conditions were moist throughout the near-surface soils at all
exploration locations. No groundwater seepage was observed in any of the six test pits, which extended
to depths of up to approximately 13 feet below ground surface. The absence of observed groundwater is
consistent with the dry-season timing of our explorations and the low-permeability, fine-grained soils and
weathered bedrock encountered at the site.
Although groundwater was not encountered during our explorations, seasonal perched water conditions
should be anticipated during the wet season, particularly at the contact between the overlying low-
permeability fine-grained soils and the underlying weathered bedrock. The USDA NRCS Web Soil Survey
maps a shallow seasonal high-water table for portions of the site vicinity, and perched water may develop
where downward infiltration is impeded by the expansive Fat CLAY and weathered claystone and
siltstone. Perched water conditions may require management in trench and foundation excavations
performed during the wet season.
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6.0 GEOLOGIC HAZARD REVIEW
We conducted a preliminary review of mapped geologic hazards at the property to evaluate potential
risks, including seismic activity, landslide susceptibility, slope stability, erosion, flooding, and groundwater
conditions that could affect the safety and feasibility of future development. Our assessment involved
analyzing a range of geological data sources, including the Oregon Department of Geology and Mineral
Industries (DOGAMI) geohazard database, available geologic maps, geotechnical reports, and site-specific
investigation through field reconnaissance and subsurface exploration. The conclusions and
recommendations offered are intended to help guide development strategies aimed at promoting the
safety and stability of the proposed project. A summary of our findings from the geologic hazard review
is outlined below. Hazard mapping and other site research are presented in the Site Research Appendix.
6.1 Earthquake Hazard Review
The DOGAMI Oregon HazVu: Statewide Geohazards database was reviewed to evaluate seismic hazards
at the subject site. The DOGAMI Cascadia Subduction Zone Earthquake (CSZE) instrumental intensity map
indicates the site would experience Very Strong (MMI VII) ground shaking during a full Cascadia
Subduction Zone rupture. For the probabilistic 2,475-year return period earthquake (2 percent probability
of exceedance in 50 years), which incorporates ground shaking contributions from all regional seismic
sources, the site is mapped within a Severe (MMI VIII) intensity zone. The DOGAMI probability of
damaging earthquake shaking map estimates a 5 to 10 percent probability of damaging shaking at the
site.
6.2 Seismic Site Class and Earthquake Ground Motion Parameters
The DOGAMI Oregon HazVu: Statewide Geohazards Viewer indicates the site is located in an area
designated as seismic Site Class C. Our subsurface explorations extended to a maximum depth of
approximately 13 feet below ground surface, and we reviewed available well logs from the site vicinity.
Based on our subsurface observations, document review, and the shallow weathered claystone and
siltstone bedrock encountered during exploration, we recommend Site Class C as defined in ASCE 7-22,
Chapter 20, Table 20.2-1, which is characterized by average shear wave velocities (Vs) of greater than
1,450 to 2,100 ft/s in the upper 100 feet. This recommendation is consistent with the DOGAMI seismic
site class mapping for the subject site. Site class determination may be confirmed by shear wave velocity
testing per ASCE 7-22, Chapter 20, Section 20.3 if required by the project design team. Design seismic
parameters for the site were determined using the USGS Seismic Design Maps tool (ASCE 7 -22) and are
summarized in Table 2 below based on Site Class C.
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Table 2: Recommended Earthquake Ground Motion Parameters (ASCE 7-22)
Parameter Value Description
Location (Lat, Long) Degrees: 44.026381, -123.137337 Site coordinates
Risk Category: II Seismic risk category
Site Class: C Site classification based on soil conditions
Seismic Design Category D Determined based on Risk Category, SDs, and
SD1, per ASCE 7-22 Table 11.6-1 and 11.6-2
VS30 ~530 m/s The shear-wave velocity used for the user-
specified site class, in units of m/s
PGAM 0.47 g
The Geometric-Mean Maximum Considered
Earthquake (MCEG) peak ground acceleration
for the user-specified Site Class, in units of g.
Mapped Spectral Response Acceleration Parameters:
0.2 Sec Short Period, Ss 0.87 g The MCER spectral response acceleration at 0.2
seconds for Site Class BC, in units of g.
1.0 Sec Period, S1 0.39 g The MCER spectral response acceleration at 1
second for Site Class BC, in units of g.
Risk-Targeted Maximum Considered Earthquake (MCE R) Spectral Response Acceleration Parameters:
SMS 1.0
SMS = 1.5x SDS, the risk targeted maximum
considered earthquake (MCER) spectral
response acceleration for short periods and
the user-specified site class.
SM1 0.56
SM1 = 1.5x SD1, the MCER spectral response
acceleration for 1 second and the user-
specified site class.
Design Spectral Response Acceleration Parameters:
SDs 0.67 g
The design spectral response acceleration for
short periods and the user-specified site class,
in units of g.
SD1 0.37 g
The design spectral response acceleration for 1
second and the user-specified site class in,
units of g.
Additional Parameters:
TS 0.557 S TS = SD1/ SDs in seconds, for construction of
the two-period design spectrum.
T0 0.111 S T0 = 0.2 x TS, in seconds, for construction of the
two-period design response spectrum.
TL 16 S
The long-period transition period, in seconds,
for construction of the two-period design
response spectrum.
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6.3 Soil Liquefaction
The DOGAMI Oregon HazVu: Statewide Geohazards Viewer indicates the risk of soil liquefaction at the
subject site is very low to none during a design earthquake event. Liquefaction occurs when saturated,
cohesionless soils such as loose sands and non-plastic silts lose strength due to earthquake-induced pore
pressure buildup, causing the soil to temporarily behave as a viscous fluid. Liquefaction susceptibility is
primarily controlled by soil type, relative density, plasticity characteristics, depth to groundwater, and
intensity of ground shaking. Subsurface explorations at the site encountered stiff to very stiff, highly
plastic Fat CLAY (CH) soils and undocumented fill underlain by weathered claystone and siltstone bedrock,
with practical refusal of excavation encountered at depths of approximately 7 to 13 feet below ground
surface. Clay soils of high plasticity are generally not susceptible to liquefaction due to their cohesive
nature and resistance to pore pressure buildup during seismic loading, and competent bedrock is not
subject to liquefaction. No groundwater was observed within the explorations.
Based on the clayey soil conditions, the presence of shallow weathered bedrock, and the lack of
groundwater observed within the explorations, the overall potential for soil liquefaction at the site is
considered low. The potential for liquefaction-induced ground surface rupture and lateral spreading is
also considered low, given the shallow bedrock and the cohesive, high-plasticity nature of the overlying
soils.
6.4 Landslides and Global Slope Stability
The DOGAMI Statewide Landslide Information Layer for Oregon (SLIDO) and the Eugene Landslide Hazard
Map were reviewed to evaluate landslide hazards at the subject site. SLIDO does not map any active or
pre-historic landslide deposits on the subject property. Two pre-historic (greater than 150 years old)
mapped landslides are identified in the site vicinity, Eugene No. 658 (complex movement, approximately
22-foot failure depth) and Eugene No. 1073 (earth flow, approximately 25-foot failure depth), both
located several hundred feet east of the property and not encroaching onto the site. The Eugene Landslide
Hazard Map identifies the site as having a Moderate relative landslide risk. DOGAMI landslide
susceptibility mapping indicates the site has Moderate susceptibility to deep-seated landslides and Low
to Moderate susceptibility to shallow landslides, with areas of Moderate to High shallow susceptibility
mapped along the steeper slopes to the north and east.
The majority of the developable portion of the site consists of gently to moderately sloping ground
underlain by expansive fine-grained soils and weathered claystone and siltstone bedrock. A steep slope
of approximately 45 percent is present within Tract B along the northern and eastern portion of the
property, which was not explored as part of this investigation and is proposed to remain undeveloped. No
indications of active instability, such as scarps, tension cracks, hummocky ground, or displaced vegetation,
were observed within the developable portion of the site during our field reconnaissance. Based on our
review of hazard mapping, the absence of mapped landslides on the property, our subsurface findings,
and our site observations, it is our qualitative opinion that the potential for deep-seated slope instability
affecting the developable portion of the site is low, provided that development avoids or is appropriately
set back from the steep slopes within Tract B. Grading, cut and fill slopes, and surface and subsurface
drainage should be designed to maintain stability, and the steep slope area within Tract B should be
protected from concentrated drainage, undercutting, and placement of uncontrolled fill. Footing-to-slope
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setbacks for buildings constructed near the top of descending slopes should be determined on a case-by-
case basis at the time of individual lot development.
6.4.1 LiDAR Review
We reviewed available LiDAR (Light Detection and Ranging) imagery of the site and surrounding area
utilizing DOGAMI LiDAR data as shown in Figures 4 and 5. LiDAR imagery is highly effective for identifying
landslide features and subtle geomorphic indicators due to its ability to capture precise topographic
details, even in vegetated areas. By removing vegetation and other surface obstructions, LiDAR creates a
bare-earth model that enhances the visibility of geologic features including scarps, hummocky terrain,
and displaced material that may be indicative of past or active slope instability.
The LiDAR imagery depicts the developable portion of the subject property as gently to moderately sloping
terrain. A steep slope of approximately 45 percent is evident within Tract B along the northern and eastern
portion of the property, descending toward Hawkins Lane, consistent with the topography observed
during our field reconnaissance. The surrounding area is characterized by hillside terrain typical of the
South Eugene hills.
No distinct landslide head scarps, arcuate failure features, hummocky terrain, or other indicators of past
or active slope movement are evident within the developable portion of the subject property. The two
pre-historic landslides mapped in the site vicinity (Eugene No. 658 and No. 1073) are visible in the LiDAR
imagery several hundred feet east of the property and do not encroach onto the site, as shown in Figure
5. The terrain morphology within the developable portion of the site is relatively smooth and consistent
with natural hillslope processes, and the LiDAR imagery is consistent with the landslide susceptibility
mapping reviewed for the site.
6.5 Flood Hazard
The DOGAMI Oregon HazVu: Statewide Geohazards database indicates that the site is located outside of
the FEMA 100-Year flood zone.
6.6 Erosion Hazard
During our field exploration, we did not observe soil or topographic conditions that would be highly
susceptible to erosion. In our opinion, the primary erosion risk will arise during construction in areas
where vegetation has been cleared. Erosion can be minimized by implementing the project's erosion
control plan, which should include the use of straw wattles, fiber rolls, and silt fences. These measures
should remain in place throughout site preparation and construction. Particular attention should be given
to erosion control along the steep slope within Tract B and at the interface between disturbed areas and
the descending slope, where concentrated runoff should be prevented from discharging onto the slope
face. Additionally, erosion and sedimentation can be further reduced by promptly re-vegetating disturbed
areas and staging construction to limit the exposure of large portions of the site at one time. Immediate
or temporary protection can be provided by covering exposed areas with mulch or erosion control netting,
while permanent stabilization should be achieved by seeding with an approved grass mix or hydroseeding
with a seed-mulch-fertilizer blend.
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6.7 Radon Hazard
The DOGAMI radon hazard zoning mapping indicates that the subject site is located within an area of low
radon potential. Radon is a naturally occurring, colorless, and odorless radioactive gas produced by the
decay of uranium in soil and rock, which can accumulate in enclosed spaces such as basements and crawl
spaces. Based on the low mapped radon potential, radon is not considered a significant hazard at the
subject site. Notwithstanding the low mapped potential, radon concentrations can vary locally, and testing
of completed structures by a qualified radon measurement professional can be performed if desired by
the property owner or builder.
7.0 PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS
Our site investigation indicates that the proposed residential subdivision is geotechnically feasible,
provided that the recommendations outlined in this report are incorporated into the design and
construction of the project. Based on our understanding of existing site conditions and the proposed
development, the primary geotechnical concerns are the presence of highly expansive Fat CLAY (CH) soils
across portions of the site and the presence of undocumented fill soils, both as depicted on Figures 2 and
3, along with the steep slope within Tract B. Because this report is preliminary and home construction is
to be undertaken by others, individual lots will require site-specific evaluation at the time of building
permit application, as described in the following sections.
7.1 Preliminary Site Preparation Recommendations
All proposed construction areas and locations designated for engineered fill should be thoroughly cleared
of organic and inorganic debris. Remnants of the former home site, including the existing well house,
demolition debris, and any associated buried structures or utilities, should be removed from areas
proposed for development. Any inorganic debris and organic matter generated during clearing should
either be removed from the site or stockpiled for use in landscaping and non-structural areas. Organic-
rich soils and root zones should be stripped from all construction areas and areas designated for
engineered fill and structural foundations. All stripping and clearing operations should be observed and
documented by the soil engineer or their representative.
The depth of topsoil stripping is expected to range between approximately 14 and 24 inches, with the
final removal depth determined through field observation following stripping. Stripping depths will likely
increase where trees are present, with stumps and root zones potentially extending to at least 3 feet
below the ground surface (bgs). Undocumented fill was encountered at test pits TP-2, TP-4, TP-5, and
TP-6, extending to depths of approximately 2.5 to 5 feet bgs, as depicted on Figures 2 and 3. The
undocumented fill soils are not considered suitable for support of structures, roadways, or engineered fill
in their existing condition and should be thoroughly removed from areas proposed for grading, building
construction, and roadway construction prior to placement of structural fill or building elements. The fill
soils may potentially be suitable for reuse as engineered fill, provided they are processed to remove
oversized material and debris, moisture-conditioned to within 2 percent of optimum moisture, free of
organic material exceeding approximately 5 percent by weight, and compacted in accordance with the
project specifications described in Section 7.3, Engineered Fill Recommendations.
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Highly plastic, highly expansive Fat CLAY (CH) soils were encountered across portions of the site as
depicted on Figures 2 and 3. Because this report is preliminary and home construction is to be undertaken
by others, lots within the areas of anticipated highly expansive Fat CLAY will require site-specific
evaluation and additional expansion index testing at the time of building permit application. Where highly
expansive soils are confirmed beneath planned structures, we recommend that the expansive Fat CLAY
be over-excavated to a depth of at least 4 feet below the bottom of footings and replaced with 3/4 -inch-
minus crushed aggregate compacted to at least 95 percent of the maximum dry density as determined by
AASHTO T-180. The over-excavation and structural fill pad should extend laterally at least 4 feet beyond
the foundation on all sides. The completed over-excavation should be observed by the soil engineer prior
to placement of aggregate to verify that the expansive Fat CLAY has been removed to the specified limits
and that the exposed bearing materials are consistent with the conditions anticipated in this report.
Additional detail is provided in Section 7.7, Foundation Recommendations.
Areas designated for placement of structures and engineered fill should be scarified and recompacted
before structural fill is placed. Keying and benching may be necessary in portions of the project where
engineered fill is placed on existing slopes of 15 percent or steeper, as described in this report. Prior to
placing engineered fill, the underlying soils should be moisture-conditioned to within 2 percent of
optimum moisture content and recompacted in accordance with project specifications for engineered fill.
The native soils are moisture-sensitive and may become difficult to work during wet conditions.
Excavation and subgrade preparation are best performed during dry weather. If subgrade stabilization
proves challenging, options such as over-excavation, placement of granular material, or cement or lime
treatment of the subgrade may be considered. Excavation spoils consisting of the native Fat CLAY are
considered unsuitable for reuse as structural engineered fill and should be removed or used only in
landscaping and non-structural areas. CORE GeoEngineering should be present on site to observe
subgrade preparation prior to placement of engineered fill.
7.2 Keyways, Benching, and Subdrains for Fill Slopes
Keying and benching may be necessary for this project where engineered fills are proposed on hillsides.
Engineered fill placed on existing slopes with an incline of approximately fifteen percent or steeper should
be constructed using keyways and benches, as illustrated in the attached Typical Keyway, Benching, and
Fill Slope Detail (Figure 6). Keyways should have a minimum depth of three feet on the downhill side, to
be field verified by the soil engineer, and a minimum width of ten feet. They should be excavated at the
toe of the fill slope and extend perpendicular to the downslope direction. If weakened or soft soils are
encountered during construction, additional removal may be required. Benches and keyways should
generally be horizontal in the downslope direction but may slope up to ten percent along a topographic
contour. If keyways slope more than fifteen percent along a topographic contour, benching or alternative
configurations approved by the soils engineer or their designated representative will be necessary. Fill
slopes should be overbuilt a minimum of three feet and trimmed back to competent material to achieve
the final 2H:1V maximum slope face. The exact dimensions, design, and locations of keyways should be
finalized during construction under the soil engineer's guidance.
If groundwater seepage is encountered during excavation, subdrain trenches should be installed at the
back of each bench and keyway as determined by the soil engineer based on field observations during
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grading. Subdrains should consist of a minimum 3-inch-diameter ADS Heavy Duty grade (or equivalent)
perforated plastic pipe enveloped in a minimum of 3 cubic feet per lineal foot of 2-inch to ½-inch open-
graded gravel drain rock wrapped in non-woven geotextile filter fabric (Mirafi 140N or equivalent). A
minimum gradient of 0.5 percent should be maintained throughout all subdrain pipes and outlets. CORE
should inspect keyways, benching, and subdrain installations prior to placement of fill. Subdrains may be
omitted at the discretion of the soils engineer.
7.3 Engineered Fill Recommendations
All grading for the proposed construction should be performed as engineered grading in accordance with
the applicable building code at the time of construction, with the exceptions and additions noted in this
report. Site grading must follow the 2024 International Building Code (IBC) and the 2025 Oregon Structural
Specialty Code (OSSC), Chapter 18 and Appendix J. Before placing structural fill, areas designated for fill
should be scarified and recompacted. CORE GeoEngineering or a designated representative should
observe and document site preparation, soil stripping, and grading activities. Proper testing frequency
and earthwork documentation typically require daily observation and testing during stripping, rough
grading, and placement of engineered fill.
CORE GeoEngineering or a designated representative should be provided with samples of all soil types
submitted for use as structural fill prior to placement. We anticipate that structural fill will primarily
consist of imported granular crushed aggregate. The undocumented fill soils may potentially be suitable
for reuse as engineered fill, provided they are processed to remove oversized material and debris,
moisture-conditioned to within 2 percent of optimum moisture, free of organic material exceeding
approximately 5 percent by weight, and compacted in accordance with the project specifications
described herein. The highly expansive Fat CLAY (CH) soils are not considered suitable for reuse as
structural engineered fill and should be removed or used only in landscaping and non-structural areas.
Imported fill material must be approved by the soil engineer prior to being imported to the site. Oversize
material greater than 6 inches in size should not be used within 3 feet of foundation footings, and material
greater than 12 inches in diameter should not be used in engineered fill.
Engineered fill should be compacted in horizontal lifts no thicker than 12 inches using standard
compaction equipment. Engineered fill should be compacted to at least 95 percent of the maximum dry
density as determined by the Standard Proctor test method (ASTM D698). Field density testing should
adhere to ASTM D6938 standards. One density test should be performed for every 2 vertical feet of fill
placed. Since testing is conducted on an on-call basis, the earthwork contractor should be held
contractually responsible for scheduling and ensuring the required testing frequency.
Site earthwork may be affected by soil moisture and wet weather conditions. Performing earthwork
during wet weather will likely require significant use of additional crushed aggregate, cement or lime
treatment, or other special measures, resulting in substantially higher costs compared to earthwork
conducted in dry conditions.
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7.4 Excavation Conditions and Utility Trench Backfill Recommendations
We anticipate that onsite soils can generally be excavated using conventional heavy equipment. However,
weathered claystone and siltstone bedrock and difficult excavation conditions should be anticipated, with
practical refusal of excavation encountered at depths of approximately 7 to 13 feet bgs during our
explorations. See the attached test pit logs for detail. The weathered bedrock displayed ODOT rock
hardness increasing from Very Soft (R1) to Hard (R4) with depth, in accordance with the ODOT Rock
Hardness Classification System (Table 1). We anticipate that small or medium-sized excavators will largely
be sufficient but may encounter difficulty or even refusal in portions of the site. Large excavators and
hydraulic chipping may be needed in some areas.
Maintenance of safe working conditions, including temporary excavation stability, is the responsibility of
the contractor. Actual slope inclinations at the time of construction should be determined based on safety
requirements and actual soil and groundwater conditions. All temporary cuts in excess of 4 feet in height
should be sloped in accordance with U.S. Occupational Safety and Health Administration (OSHA)
regulations (29 CFR Part 1926) or be shored. The existing native soils classify as Type B Soil and temporary
excavation side slope inclinations as steep as 1H:1V may be assumed for planning purposes. These cut
slope inclinations are applicable to excavations above the water table only.
Shallow, perched groundwater may be encountered at the site during the wet season and should be
anticipated in excavations and utility trenches. Vibrations created by traffic and construction equipment
may cause some caving and raveling of excavation walls. In such an event, lateral support for the
excavation walls should be provided by the contractor to prevent loss of ground support and possible
distress to existing or previously constructed structural improvements.
Underground utility pipes should be installed in accordance with the procedures specified in ASTM D2321
and City of Eugene standards. We recommend that structural trench backfill be compacted to at least 95
percent of the maximum dry density obtained by the Modified Proctor (ASTM D1557) or equivalent. Initial
backfill lift thicknesses for a 3/4-inch-minus crushed aggregate base may need to be as great as 4 feet to
reduce the risk of flattening underlying flexible pipe. Subsequent lift thickness should not exceed 1 foot.
If imported granular fill material is used, then the lifts for large vibrating plate-compaction equipment
(e.g., hoe compactor attachments) may be up to 2 feet, provided that proper compaction is being achieved
and each lift is tested. Use of large vibrating compaction equipment should be carefully monitored near
existing structures and improvements due to the potential for vibration-induced damage.
Adequate density testing should be performed during construction to verify that the recommended
relative compaction is achieved. Typically, at least one density test is taken for every 4 vertical feet of
backfill on each 100-lineal-foot section of trench.
7.5 Wet Weather Earthwork Recommendations
Onsite soils are likely to be moisture-sensitive, making them challenging to handle or navigate with
construction equipment during wet or freezing weather. Conducting earthwork during dry weather is
generally more cost-effective. If earthwork is performed during wet conditions, costly measures, such as
the use of imported granular material will be needed to achieve the recommended compaction standards
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for fill areas. If earthwork or fill placement must occur during wet weather or when controlling soil
moisture is difficult, the following recommendations should be included in the contract specifications.
1. Earthwork should be conducted in small sections to reduce exposure to wet conditions.
Excavation and the removal of unsuitable soils should be immediately followed by the placement
and compaction of clean engineered fill. Equipment size and type may need to be adjusted to
avoid disturbing the soil, and in some cases, a backhoe may be required to minimize subgrade
disruption from equipment movement.
2. The construction site should be graded to allow surface water runoff and prevent pooling.
3. Engineered fill material should be clean, granular soil with less than 5 percent passing the No. 200
sieve, and fines should be non-plastic. Alternatively, cement treatment of on-site soils may be
used to facilitate work during wet weather.
4. The ground surface should be sealed with a smooth drum vibratory roller or similar equipment,
and under no circumstances should it be left uncompacted and exposed to moisture. Soils that
become too wet for compaction should be removed and replaced with clean granular material.
5. A CORE representative should oversee excavation and fill placement to ensure unsuitable
materials are removed and proper compaction and drainage are achieved.
6. Erosion control measures, such as geotextile silt fences, straw wattles, and fiber rolls, should be
strategically placed to manage runoff and erosion.
7.6 Lateral Earth Pressures
Lateral earth pressures on below-grade foundation retaining walls are influenced by several factors,
including the slope inclination of adjacent terrain, type of backfill material, level of wall restraint, method
and degree of backfill compaction, drainage conditions, and the magnitude and location of any nearby
surcharge loads. Active pressure occurs when the wall is allowed to move or rotate slightly away from the
soil, reducing the lateral force exerted by the soil. This condition typically results in lower pressures and
is used in the design of walls that can tolerate some movement. At-rest pressure applies to walls that are
fully restrained and cannot move, such as basement walls, leading to higher lateral forces due to the lack
of flexibility. Passive pressure, on the other hand, is the resistance exerted by the soil in front of the wall
when it is pushed into the ground.
The design recommendations presented in Table 3 are valid for static loading cases only and are based
upon in situ soil conditions or compacted granular fill. The recommended earth pressures do not include
surcharge loads, hydrostatic pressures, or seismic loads, and assume level backfill and a relatively level
base below the wall. These values assume that the recommended drainage provisions are incorporated,
and hydrostatic pressures are not allowed to develop against the wall.
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Table 3: Recommended Lateral Earth Pressures: Level Backfill
Backfill Material
Equivalent Fluid Pressure
for Level Backfill Wet Density
Drained
Internal Angle
of Friction At-rest Active Passive
Onsite Soils 55 pcf 35 pcf 320 pcf 120 pcf 28°
Imported Granular Crushed
Aggregate 52 pcf 32 pcf 568 pcf 135 pcf 38°
A minimum continuous 12 to 18-inch-thick zone of free-draining, open-graded drain rock and a 3-inch
perforated gravity drainpipe is assumed behind retaining walls. Geotextile filter fabric should be placed
between the drain rock and backfill soil. The recommended equivalent fluid densities are based on the
assumption of free-draining conditions behind the walls to prevent the buildup of hydrostatic pressure.
Perforated plastic drainpipes should be installed at the base of the wall and connected to an appropriate
discharge point to drain water from the gravel zone. The drainpipe should be wrapped in filter fabric, such
as Mirafi 140N or an equivalent, to reduce the risk of clogging.
A coefficient of friction of 0.42 may be assumed at the interface between the wall footing base and the
underlying subgrade soils. The recommended coefficient of friction and passive earth pressure values are
provided without a safety factor, so a suitable safety factor should be incorporated into the design.
Furthermore, the top 12 inches of soil should be disregarded in passive pressure calculations unless it is
protected by pavement or concrete slabs.
If the walls are subjected to surcharge loading within a horizontal distance equal to or less than the height
of the wall, they should be designed to account for the additional horizontal pressure. For uniform
surcharge loads, a lateral pressure equal to 0.3 times the surcharge pressure should be added to the
design. For traffic surcharges, an additional vertical load of 250 psf may be applied, in accordance with
local standards and practices.
We recommend using the Mononobe-Okabe method for evaluating seismic loading on retaining walls.
This method provides a well-established analytical approach for calculating the additional lateral earth
pressures induced by seismic forces. It takes into account key factors such as wall height, backfill material,
and the seismic acceleration specific to the site. The Mononobe-Okabe method is particularly useful for
designing retaining walls to withstand earthquake-induced loads by estimating the active or at-rest
pressures under static conditions, and then adding an incremental seismic load. This approach offers a
reliable and practical solution for ensuring that retaining walls maintain stability during seismic events.
During a seismic event, the lateral earth pressures on below-grade structural walls will increase by an
additional amount due to earthquake forces. Using the Mononobe-Okabe method and peak horizontal
accelerations appropriate for the site, seismic loading should be modeled by applying the active or at-rest
earth pressures previously recommended, along with an additional rectangular-shaped seismic load of
6.5H, where H represents the total height of the wall.
Structures should be located a horizontal distance of at least 1.5H away from the back of the retaining
wall, where H is the total height of the wall. CORE should be contacted for additional foundation
recommendations where structures are located closer than 1.5H to the top of any wall.
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7.7 Preliminary Foundation Recommendations
CORE understands that the proposed development consists of a 10-lot residential subdivision, and that
the lots are to be left close to natural grade and sold to builders who will grade the individual lots to their
specifications at a later date. The planned homes are anticipated to be one- and two-story wood-framed
structures supported on conventional spread footings. Because this report is preliminary and home
construction is to be undertaken by others, the recommendations below are provided for planning
purposes, and each lot will require site-specific evaluation and a final geotechnical report or lot
verification at the time of building permit application.
The proposed structures may be supported on shallow spread foundations bearing on competent native
soil, weathered bedrock, or engineered fill, provided they are properly designed and constructed
according to the recommendations in this report. Foundation design, construction, and setback
requirements must adhere to the applicable building codes in effect at the time of construction. To
optimize bearing capacity and prevent frost heave, spread footings should be embedded at least 12 inches
below the lowest adjacent exterior grade. If soft or disturbed soil is encountered at the footing subgrade
elevation, it should be excavated and replaced with compacted onsite engineered fill or crushed
aggregate.
The anticipated allowable soil bearing pressure is 1,500 lbs/ft² for footings constructed on competent
native soil or engineered fill. This allowable bearing pressure may be increased by one-third for short-
term, transient conditions such as wind or seismic loading. The coefficient of friction between the on-site
soil and poured-in-place concrete is 0.42, without applying any factor of safety. Excavations near
structural footings should not encroach within a 1H:1V plane projected downward from the bottom edge
of the footings.
As described in Section 7.1, lots within the areas of anticipated highly expansive Fat CLAY (CH) shown on
Figures 2 and 3 will require additional expansion index testing and, where highly expansive soils are
confirmed beneath planned structures, over-excavation of at least 4 feet below the bottom of footings
and replacement with 3/4-inch-minus crushed aggregate compacted to at least 95 percent of the
maximum dry density as determined by AASHTO T-180, extending laterally at least 4 feet beyond the
foundation on all sides. Footings bearing on the 4-foot-thick crushed aggregate pad constructed where
the expansive Fat CLAY has been over-excavated and replaced may use an allowable bearing pressure of
2,500 lbs/ft². This allowable bearing pressure may be increased by one-third for short-term, transient
conditions such as wind or seismic loading. Maximum anticipated total and differential footing
movements are expected to be 1 inch and 3/4 inch over a span of 20 feet, respectively, provided the
expansive soil mitigation described herein is implemented. Most of the estimated settlement is
anticipated to occur during construction as loads are applied.
Where homes are constructed near the top of descending slopes, appropriate footing-to-slope setbacks
should be developed on a case-by-case basis at the time of individual lot development to maintain
foundation support and slope stability. Lots 6, 7, and 10, which are located adjacent to the steep slope
within Tract B along the eastern portion of the site, are anticipated to require particular attention to slope
setbacks, and building placement on these lots should be evaluated by CORE at the time of building permit
Preliminary Geologic Hazard Assessment and Geotechnical Engineering Report
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application. Setbacks should be measured in accordance with the applicable building code and confirmed
by the soil engineer based on the proposed building location, foundation type, and actual slope conditions
exposed during construction.
Footing excavations should extend through topsoil, undocumented fill, and any disturbed soil to reach a
competent subgrade capable of providing adequate bearing support. All excavations should be neatly
trimmed, and any loose or softened soil must be removed from the bottom of the excavation before
placing reinforcing steel. Given the moisture sensitivity of the native soils, foundations constructed during
wet weather may require over-excavation of the footings, followed by backfilling with compacted crushed
aggregate to ensure stability.
Following development of the individual lots, a Final Soil Report should be prepared by CORE for each lot
to confirm or revise these recommendations as necessary. Additional geotechnical studies and laboratory
testing will likely be necessary at the time of individual lot development, particularly on lots within the
areas of anticipated highly expansive Fat CLAY.
7.8 Concrete Slabs-on-Grade
Subgrade preparation for concrete slab-on-grade floors should follow the procedures outlined in Section
7.1, Site Preparation Recommendations, and Section 7.7, Foundation Recommendations. During
excavation for foundations and slabs, care should be taken to avoid disturbing the subgrade soils. If the
subgrade is compromised whether due to wet weather or construction activity the affected upper soils
should be scarified to a depth of at least 8 inches, moisture-conditioned to within approximately 3 percent
of the optimum moisture content and compacted in accordance with engineered fill specifications. As an
alternative, disturbed soils may be removed entirely and replaced with compacted crushed aggregate to
restore subgrade support.
For evaluation of the concrete slab-on-grade floors using the beam on elastic foundation method, a
modulus of subgrade reaction of 150 kcf (87 pci) should be assumed for the compacted crushed aggregate
anticipated to be present at foundation subgrade elevation following adequate site preparation as
described above. This value assumes the concrete slab system is designed and constructed as
recommended herein, with a minimum thickness of 8 inches of 1½”-0 crushed aggregate beneath the slab.
The total thickness of crushed aggregate will be dependent on the subgrade conditions at the time of
construction and should be verified visually by proof-rolling. Under-slab aggregate should be compacted
to at least 95 percent of its maximum dry density as determined by ASTM D1557 (Modified Proctor) or
equivalent.
In areas of the proposed structure where moisture could damage floor coverings or sensitive equipment,
suitable vapor barriers and damp-proofing measures should be incorporated into the design. A typical
system includes a 10-mil polyethylene vapor barrier placed directly over the capillary break layer.
Alternative vapor or moisture control systems may also be appropriate, depending on project -specific
requirements. Consultation with qualified design professionals is recommended for selecting and
detailing vapor barriers, damp-proofing systems, ventilation strategies, moisture-resistant building
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materials, and mold prevention measures, as these considerations fall outside the scope of CORE’s
geotechnical services.
7.9 Potential Retaining Walls
Based on the sloping site topography and the proposed subdivision grading, we understand that retaining
walls may be constructed as part of the subdivision improvements, including road and utility construction,
as well as during future lot development performed by others. At this preliminary stage, no retaining wall
locations, heights, or configurations have been established. Retaining walls up to 4 feet in height retaining
level backfill with no surcharge loading may generally be constructed as standard, non-engineered walls
in accordance with the applicable building code and manufacturer recommendations. Retaining walls
exceeding 4 feet in height (measured from the bottom of the footing to the top of the wall), or any wall
of any height that supports sloping backfill, surcharge loads, or foundation loads, should be designed by
a qualified engineer once a specific wall layout and grading plan are proposed. Site-specific design
parameters, including lateral earth pressures, bearing capacity, sliding resistance, and global stability
considerations, will be provided by CORE at that time based on the proposed wall geometry, retained and
foundation materials, and any applicable surcharge conditions.
All retaining walls should be provided with adequate subsurface drainage to prevent the buildup of
hydrostatic pressure behind the wall, including a perforated drain pipe at the base of the wall discharged
to an appropriate outlet. The backfill zone behind retaining walls should consist of crushed aggregate,
typically 3/4-inch-minus. The highly expansive Fat CLAY (CH) and other fine-grained onsite soils are not
considered suitable for use within the retaining wall backfill zone and should not be placed within the
zone of influence behind retaining walls. CORE should review the proposed retaining wall plans and
provide design recommendations, and should observe wall construction, whether the walls are
constructed as part of the subdivision improvements or during future lot development.
7.10 Foundation Drains
Construction should incorporate standard measures for managing subsurface water beneath the
structures, including ensuring proper crawlspace drainage with a low-point drain exiting the foundation,
covering exposed crawlspace ground with visqueen, and providing adequate crawlspace ventilation
through foundation vents. The homeowners should be informed that some slow-moving water in
crawlspaces is normal and, with these design features in place, is not typically harmful to the structure.
Additionally, downspouts and roof drains should be kept separate from footing drains to minimize the risk
of clogging. Roof drainage should be directed to an appropriate discharge point and stormwater system,
well away from the building foundations.
In accordance with Section 1805.4.2 of the 2025 Oregon Residential Specialty Code (ORSC) and Section
1805.4.2 of the 2024 International Building Code (IBC), perimeter drains should be installed around
foundations constructed with gravel or crushed stone that contains no more than 10 percent material
passing through a No. 4 (4.75 mm) sieve. These provisions apply specifically to foundations that retain
earth and enclose habitable or usable spaces below grade. The drains must discharge into an approved
drainage system either by gravity or mechanical means. An exception allows for the omission of a drainage
Preliminary Geologic Hazard Assessment and Geotechnical Engineering Report
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system if the foundation is placed on well-drained ground or soils composed of a sand and gravel mixture.
The soil conditions at the subject site do not appear to meet the criteria for this exception.
Perimeter footing drains should be installed for the proposed homes and constructed following the
attached Typical Perimeter Footing Detail (Figure 7). These drains consist of 3-inch perforated plastic pipe,
embedded in at least 1 cubic foot of clean drain rock per linear foot. The drainpipe and rock should be
wrapped in non-woven geotextile fabric (e.g., Mirafi 140N or equivalent) to reduce clogging and prevent
soil loss. A minimum slope of 0.5 percent should be maintained throughout the system, including the non-
perforated outlet pipe. Footing drains can discharge at the curb or, if slope is insufficient, on the backside
of the lots.
8.0 ROADWAY CONSTRUCTION
As described above and as indicated on the attached site plans, CORE understands that the proposed
development will include construction of new streets to serve the Hawkins Lane subdivision. We
understand that the structural pavement section design will be performed by the project civil engineer.
Accordingly, the recommendations provided in this section are limited to subgrade preparation and wet-
weather construction considerations relevant to the site soils. CORE should be provided with the proposed
pavement sections and traffic loading assumptions for review, and should observe subgrade preparation
prior to placement of aggregate base, to confirm that the exposed subgrade is consistent with the
conditions anticipated in this report.
8.1 Subgrade Preparation
Roadway subgrade soils should be compacted and inspected by CORE prior to the placement of crushed
aggregate base for pavement. Typically, a proofroll with a fully loaded water or haul truck is conducted by
travelling slowly across the grade and observing the subgrade for rutting, deflection, or movement. Any
pockets of organic debris or loose fill encountered during ripping or tilling should be removed and replaced
with engineered fill. In order to verify subgrade strength, we recommend proof-rolling directly on
subgrade with a loaded dump truck during dry weather and on top of base course in wet weather. Soft
areas that pump, rut, or weave should be stabilized prior to paving.
As noted above, portions of the site contain variable undocumented fill soils. Subgrade over-excavation
may be required to remove these materials. Depending on the final subgrade elevations, additional
granular structural fill or cement-treated soil may be needed to achieve the design subgrade elevation
and a stable base for the new roadways.
If pavement areas are to be constructed during wet weather, the subgrade and construction plan should
be reviewed by the project geotechnical engineer at the time of construction so that condition-specific
recommendations can be provided. The moisture-sensitive subgrade soils make the site a difficult wet
weather construction project. General recommendations for wet weather pavement sections are
provided below.
Preliminary Geologic Hazard Assessment and Geotechnical Engineering Report
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23 | P a g e CORE GeoEngineering, Project No. 26-1156
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During placement of pavement section materials, density testing should be performed to verify
compliance with project specifications. Generally, one subgrade, one base course, and one asphalt
compaction test is performed for every 100 to 200 linear feet of paving.
8.2 Wet Weather Construction Pavement Section
This section presents our recommendations for wet weather pavement sections and construction for new
pavement sections at the project. These wet weather pavement section recommendations are intended
for use in situations where it is not feasible to compact the subgrade soils to project requirements, due to
wet subgrade soil conditions, and/or construction during wet weather. Based on our site review, we
recommend a wet weather section with a minimum subgrade deepening of 6 to 12 inches to
accommodate a working subbase of additional 1½”-0 crushed rock. Geotextile fabric, Mirafi 500x or
equivalent, should be placed on subgrade soils prior to placement of base rock.
In some instances, it may be preferable to use a subbase material in combination with over-excavation
and increasing the thickness of the rock section. CORE should be consulted for additional
recommendations regarding use of additional subbase in wet weather pavement sections if it is desired
to pursue this alternative. Cement treatment of the subgrade may also be considered instead of over-
excavation. For planning purposes, we anticipate that treatment of the onsite soils would involve mixing
cement powder to approximately 6 percent cement content and a mixing depth on the order of 12 to 18
inches.
With implementation of the above recommendations, it is our opinion that the resulting pavement section
will provide equivalent or greater structural strength than the dry weather pavement section currently
planned. However, it should be noted that construction in wet weather is risky and the performance of
pavement subgrades depend on a number of factors including the weather conditions, the contractor’s
methods, and the amount of traffic the road is subjected to. There is a potential that soft spots may
develop even with the implementation of the wet weather provisions recommended in this report. If soft
spots in the subgrade are identified during roadway excavation, or develop prior to paving, the soft spots
should be over-excavated and backfilled with additional crushed rock.
During subgrade excavation, care should be taken to avoid disturbing the subgrade soils. Removals should
be performed using an excavator with a smooth-bladed bucket. Truck traffic should be limited until an
adequate working surface has been established. We suggest that the crushed rock be spread using
bulldozer equipment rather than dump trucks, to reduce the amount of traffic and potential disturbance
of subgrade soils. Care should be taken to avoid over-compaction of the base course materials, which
could create pumping, unstable subgrade soil conditions. Heavy and/or vibratory compaction efforts
should be applied with caution. Following placement and compaction of the crushed rock to project
specifications (95 percent of Modified Proctor), a finish proof-roll should be performed before paving.
The above recommendations are subject to field verification. CORE should be on-site during construction
to verify subgrade strength and to take density tests on the engineered fill, base rock and asphaltic
pavement materials.
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24 | P a g e CORE GeoEngineering, Project No. 26-1156
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9.0 LIMITATIONS
This report has been prepared specifically for the owner and their consultants for use in the design of this
project. While it may be shared in full with prospective contractors for bidding and estimation purposes,
the conclusions and interpretations within should not be taken as a guarantee of subsurface conditions.
It is important to note that soil and groundwater conditions can vary significantly even over short
distances. Variations may exist between exploration points that may not be detected in a geotechnical
study. Should site conditions encountered during construction differ significantly from those described in
this report, CORE should be contacted to review and, if necessary, revise the recommendations.
Adequate geotechnical monitoring, testing, and consultation should be conducted during construction to
ensure that the site conditions align with those indicated by the exploration. If conditions encountered
during construction differ from expectations, we will provide revised design recommendations and ensure
that the geotechnical aspects of construction comply with the contract plans and specifications.
Within the constraints of the project’s scope, schedule, and budget, CORE has performed these services
in accordance with the generally accepted standards of geotechnical engineering and engineering geology
at the time the report was prepared. No warranty, express or implied, is provided. This work did not
include environmental assessments or evaluations of wetlands, hazardous substances, or toxic materials
in the soil, surface water, or groundwater at the site.
We appreciate the opportunity to assist with this project.
Sincerely,
CORE GeoEngineering, LLC.
EXP 12/31/2026
Benjamin L. Cook, R.G., C.E.G.
Principal Engineering Geologist
Preliminary Geologic Hazard Assessment and Geotechnical Engineering Report
Hawkins Lane Subdivision, Eugene, Oregon
25 | P a g e CORE GeoEngineering, Project No. 26-1156
Version 2.0, August 20, 2026
10.0 REFERENCES
Gannett, Marshall W., and Caldwell, Rodney R., Generalized Geologic Map of the Willamette Lowland, U.S. Department of the interior,
U.S. Geological Survey, 1998.
Geomatrix Consultants, Inc., 1995, Seismic design mapping, State of Oregon: Final report to Oregon Department of Transportation,
Salem, Oregon, under Contract 11688, January 1995, unpaginated, 5 pls., scale 1:1,250,000.
Geology of the Southern and Southwestern Border Areas of the Willamette Valley, H.E. Vokes, Parke D. Snavely Jr., and Donald
A. Myers, United States Department of the Interior Geologic Survey, Oregon State Department of Geology and
Mineral Industries, Oil and Gas Investigations Map OM 110, 1951.
Goldfinger, C., Kulm, L.D., Yeats, R.S., Appelgate, B, MacKay, M.E., and Cochrane, G.R., 1996, Active strike-slip faulting and folding of
the Cascadia Subduction-Zone plate boundary and forearc in central and northern Oregon: in Assessing earthquake hazards
and reducing risk in the Pacific Northwest, v. 1: U.S. Geological Survey Professional Paper 1560, P. 223-256.
Oregon Department of Geology and Mineral Industries, Statewide Geohazards Viewer, Oregon.gov/dogami/hazvu.
Oregon Department of Geology and Mineral Industries, Statewide LiDAR Viewer, gis.dogami.oregon.gov/maps/lidarviewer.
Oregon Department of Geology and Mineral Industries, Statewide Landslide Information Database, Oregon.gov/dogami/slido.
Seismic Design Maps, seismicmaps.org.
United States Geological Survey, USGS Earthquake Hazards Program Website (earthquake.usgs.gov).
Web Soil Survey, Natural Resources Conservation Service, United States Department of Agriculture.
www.websoilsurvey.nrcs.usda.gov/app/
Yeats, R.S., Graven, E.P., Werner, K.S., Goldfinger, C., and Popowski, T., 1996, Tectonics of the Willamette Valley, Oregon: in Assessing
earthquake hazards and reducing risk in the Pacific Northwest, v. 1: U.S. Geological Survey Professional Paper 1560, P. 183-
222, 5 plates, scale 1:100,000.
CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
Project No. 26-1156 CORE GeoEngineering
Hawkins Lane Subdivision, Eugene, Oregon August 20, 2026
FIGURES
CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
Project No. 26-1156 CORE GeoEngineering
Hawkins Lane Subdivision, Eugene, Oregon August 20, 2026
EXPLORATION LOGS
CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
Project No. 26-1156 CORE GeoEngineering
Hawkins Lane Subdivision, Eugene, Oregon August 20, 2026
SOILS LABORATORY RESULTS
UNIFIED SOIL CLASSIFICATION SYSTEM
UNIFIED SOIL CLASSIFICATION AND SYMBOL CHART
COARSE-GRAINED SOILS (more than 50% of material is larger than No. 200 sieve size.)
GRAVELS More than 50% of coarse fraction larger than No. 4 sieve size
SANDS 50% or more of coarse fraction smaller than No. 4 sieve size
Clean Gravels (Less than 5% fines)
GW
GP
Well-graded gravels, gravel-sand mixtures, little or no fines
Poorly-graded gravels, gravel-sand mixtures, little or no fines
Gravels with fines (More than 12% fines)
GM
GC
Silty gravels, gravel-sand-silt mixtures
Clayey gravels, gravel-sand-clay mixtures
Clean Sands (Less than 5% fines)
SW
SP
Well-graded sands, gravelly sands, little or no fines
Poorly graded sands, gravelly sands, little or no fines
Sands with fines More than 12% fines
SM Silty sands, sand-silt mixtures
SC Clayey sands, sand-clay mixtures
FINE-GRAINED SOILS (50% or more of material is smaller than No. 200 sieve size.)
SILTS
AND
CLAYS Liquid limit less than 50%
SILTS
AND
CLAYS Liquid limit 50% or greater
HIGHLY ORGANIC SOILS
ML
CL
OL
MH
CH
OH
PT
Inorganic silts and very fine sands, rock flour, silty of clayey fine sands or clayey silts with slight plasticity
Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays
Organic silts and organic silty clays of low plasticity
Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts
Inorganic clays of high plasticity, fat clays
Organic clays of medium to high plasticity, organic silts
Peat and other highly organic soils
GW
GP
GM
GC
SW
SP
SM
SC
LABORATORY CLASSIFICATION CRITERIA
cu D 50 D 30 = --greater than 4; Cc = between 1 and 3 D 10 010 x D50
Not meeting all gradation requirements for GW
Atterberg limits below "A" Above "A" line with P.I. between line or P.I. less than 4 4 and 7 are borderline cases Atterberg limits above "A" requiring use of dual symbols line with P. I. greater than 7
cu D 50 D 30 = --greater than 4; Cc = between 1 and 3
D 10 01o xD60
Not meeting all gradation requirements for GW
Atterberg limits below "A" Limits plotting in shaded zone line or P.I. less than 4 with P.I. between 4 and 7 are
Atterberg limits above "A" borderline cases requiring use line with P. I. greater than 7 of dual symbols.
Determine percentages of sand and gravel from grain-size curve. Depending on percentage of fines (fraction smaller than No. 200 sieve size), coarse-grained soils are classified as follows: Less than 5 percent .................................... GW, GP, SW, SP More than 12 percent .................................. GM, GC, SM, SC 5 to 12 percent ................... Borderline cases requiring dual symbols
PLASTICITY CHART
60 ,,/ � � 50
� CH / /
>< 40 V" ALINE: Vp1 = on(LL-20) � 30 >-CL ,,/ MHloH 20 / j:: / 10 ...J CL+ML ./ ML&OL II.. 0 0 I 10 20 30 40 50 60 70 80 90 100
LIQUID LIMIT (LL) (%)
SOIL DESCRIPTION AND CLASSIFICATION GUIDELINES
Particle-Size Classification
ASTM/USCS AASHTO
COMPONENT
size range sieve size range size range sieve size range
Cobbles > 75 mm greater than 3 inches > 75 mm greater than 3 inches
Gravel 75 mm – 4.75 mm 3 inches to No. 4 sieve 75 mm – 2.00 mm 3 inches to No. 10 sieve
Coarse 75 mm – 19.0 mm 3 inches to 3/4-inch sieve - -
Fine 19.0 mm – 4.75 mm 3/4-inch to No. 4 sieve - -
Sand 4.75 mm – 0.075 mm No. 4 to No. 200 sieve 2.00 mm – 0.075 mm No. 10 to No. 200 sieve
Coarse 4.75 mm – 2.00 mm No. 4 to No. 10 sieve 2.00 mm – 0.425 mm No. 10 to No. 40 sieve
Medium 2.00 mm – 0.425 mm No. 10 to No. 40 sieve - -
Fine 0.425 mm – 0.075 mm No. 40 to No. 200 sieve 0.425 mm – 0.075 mm No. 40 to No. 200 sieve
Fines (Silt and Clay) < 0.075 mm Passing No. 200 sieve < 0.075 mm Passing No. 200 sieve
Consistency for Cohesive Soil
CONSISTENCY
SPT N-VALUE
(BLOWS PER FOOT)
POCKET PENETROMETER
(UNCONFINED COMPRESSIVE
STRENGTH, tsf)
Very Soft
Soft
Medium Stiff
Stiff
Very Stiff
Hard
Very Hard
2
2 to 4
4 to 8
8 to 15
15 to 30
30 to 60
greater than 60
less than 0.25
0.25 to 0.50
0.50 to 1.0
1.0 to 2.0
2.0 to 4.0
greater than 4.0
-
Relative Density for Granular Soil
RELATIVE DENSITY
SPT N-VALUE
(BLOWS PER FOOT)
Very Loose
Loose
Medium Dense
Dense
Very Dense
0 to 4
4 to 10
10 to 30
30 to 50
more than 50
Moisture Designations
TERM FIELD IDENTIFICATION
Dry No moisture. Dusty or dry.
Damp Some moisture. Cohesive soils are usually below plastic limit and are
moldable.
Moist
Grains appear darkened, but no visible water is present. Cohesive soils
will clump. Sand will bulk. Soils are often at or near plastic limit.
Wet Visible water on larger grains. Sand and silt exhibit dilatancy. Cohesive
soil can be readily remolded. Soil leaves wetness on the hand when
squeezed. Soil is much wetter than optimum moisture content and is
above plastic limit.
AASHTO SOIL CLASSIFICATION SYSTEM
TABLE 1. Classification of Soils and Soil-Aggregate Mixtures
Granular Materials Silt-Clay Materials
General Classification (35 Percent or Less Passing .075 mm) (More than 35 Percent Passing 0.075)
Group Classification A-1 A-3 A-2 A-4 A-5 A-6 A-7
Sieve analysis, percent passing:
2.00 mm (No. 10) - - -
0.425 mm (No. 40) 50 max 51 min - - - - -
0.075 mm (No. 200) 25 max 10 max 35 max 36 min 36 min 36 min 36 min
Characteristics of fraction passing 0.425 mm (No. 40)
Liquid limit 40 max 41 min 40 max 41 min
Plasticity index 6 max N.P. 10 max 10 max 11 min 11 min
General rating as subgrade Excellent to good Fair to poor
Note: The placing of A-3 before A-2 is necessary in the "left to right elimination process" and does not indicate superiority of A-3 over A-2.
TABLE 2. Classification of Soils and Soil-Aggregate Mixtures
Granular Materials Silt-Clay Materials
General Classification (35 Percent or Less Passing 0.075 mm) (More than 35 Percent Passing 0.075 mm)
A-1 A-2 A-7
A-7-5,
Group Classification A-1-a A-1-b A-3 A-2-4 A-2-5 A-2-6 A-2-7 A-4 A-5 A-6 A-7-6
Sieve analysis, percent passing:
2.00 mm (No. 10) 50 max - - - - - - - - - -
0.425 mm (No. 40) 30 max 50 max 51 min - - - - - - - -
0.075 mm (No. 200) 15 max 25 max 10 max 35 max 35 max 35 max 35 max 36 min 36 min 36 min 36 min
Characteristics of fraction passing 0.425 mm (No. 40)
Liquid limit 40 max 41 min 40 max 41 min 40 max 41 min 40 max 41 min
Plasticity index 6 max N.P. 10 max 10 max 11 min 11 min 10 max 10 max 11 min 11min
Usual types of significant constituent materials Stone fragments, Fine
gravel and sand sand Silty or clayey gravel and sand Silty soils Clayey soils
General ratings as subgrade Excellent to Good Fair to poor
Note: Plasticity index of A-7-5 subgroup is equal to or less than LL minus 30. Plasticity index of A-7-6 subgroup is greater than LL minus 30 (see Figure 2).
AASHTO = American Association of State Highway and Transportation Officials
GROUP SYMBOL GROUP NAME
<5% fines Cu≥4 and 1≤Cc≤3 GW <15% sand Well-graded gravel
≥15% sand Well-graded gravel with sand
Cu<4 and/or 1>Cc>3 GP <15% sand Poorly graded gravel
≥15% sand Poorly graded gravel with sand
fines = ML or MH GW-GM <15% sand Well-graded gravel with silt
Cu≥4 and 1≤Cc≤3 ≥15% sand Well-graded gravel with silt and sand
fines = CL, CH,GW-GC <15% sand Well-graded gravel with clay (or silty clay)
GRAVEL (or CL-ML)≥15% sand Well-graded gravel with clay and sand
% gravel >5-12% fines (or silty clay and sand)
% sand
fines = ML or MH GP-GM <15% sand Poorly graded gravel with silt
Cu<4 and/or 1>Cc>3 ≥15% sand Poorly graded gravel with silt and sand
fines = CL, CH,GP-GC <15% sand Poorly graded gravel with clay (or silty clay)
(or CL-ML)≥15% sand Poorly graded gravel with clay and sand
(or silty clay and sand)
fines = ML or MH GM <15% sand Silty gravel
≥15% sand Silty gravel with sand
>12% fines fines = CL or CH GC <15% sand Clayey gravel
≥15% sand Clayey gravel with sand
fines = CL-ML GC-GM <15% sand Silty, clayey gravel
≥15% sand Silty, clayey gravel with sand
<5% fines Cu≥6 and 1≤Cc≤3 SW <15% gravel Well-graded sand
≥15% gravel Well-graded sand with gravel
Cu<6 and/or 1>Cc>3 SP <15% gravel Poorly graded sand
≥15% gravel Poorly graded sand with gravel
fines = ML or MH SW-SM <15% gravel Well-graded sand with silt
Cu≥6 and 1≤Cc≤3 ≥15% gravel Well-graded sand with silt and gravel
fines = CL, CH,SW-SC <15% gravel Well-graded sand with clay (or silty clay)
SAND (or CL-ML)≥15% gravel Well-graded sand with clay and gravel
% sand ≥5-12% fines (or silty clay and gravel)
% gravel
fines = ML or MH SP-SM <15% gravel Poorly graded sand with silt
Cu<6 and/or 1>Cc>3 ≥15% gravel Poorly graded sand with silt and gravel
fines = CL, CH,SP-SC <15% gravel Poorly graded sand with clay (or silty clay)
(or CL-ML)≥15% gravel Poorly graded sand with clay and gravel
(or silty clay and gravel)
fines = ML or MH SM <15% gravel Silty sand
≥15% gravel Silty sand with gravel
>12% fines fines = CL or CH SC <15% gravel Clayey sand
≥15% gravel Clayey sand with gravel
fines = CL-ML SC-SM <15% gravel Silty, clayey sand
≥15% gravel Silty, clayey sand with gravel
GROUP SYMBOL GROUP NAME
< 30% plus No. 200 < 15% plus No. 200 Lean clay
15-29% plus No. 200 % sand ≥ % gravel Lean clay with sand
Pl > 7 and plots CL % sand < % gravel Lean clay with gravel
on or above % sand ≥ % gravel < 15% gravel Sandy lean clay
"A"-line ≥ 30% plus No. 200 ≥ 15% gravel Sandy lean clay with gravel
% sand < % gravel < 15% sand Gravelly lean clay
≥ 15% sand Gravelly lean clay with sand
< 30% plus No. 200 < 15% plus No. 200 Silty clay
15-29% plus No. 200 % sand ≥ % gravel Silty clay with sand
4 ≤ Pl ≤ 7 and CL-ML % sand < % gravel Silty clay with gravel
Inorganic plots on or above % sand ≥ % gravel < 15% gravel Sandy silty clay
"A"-line ≥ 30% plus No. 200 ≥ 15% gravel Sandy silty clay with gravel
% sand < % gravel < 15% sand Gravelly silty clay
≥ 15% sand Gravelly silty clay with sand
< 30% plus No. 200 < 15% plus No. 200 Silt
LL < 50 15-29% plus No. 200 % sand ≥ % gravel Silt with sand
Pl < 4 or plots ML % sand < % gravel Silt with gravel
below "A"-line % sand ≥ % gravel < 15% gravel Sandy silt
≥ 30% plus No. 200 ≥ 15% gravel Sandy silt with gravel
% sand < % gravel < 15% sand Gravelly silt
LL -ovendried ≥ 15% sand Gravelly silt with sand
Organic -------------------- < 0.75 OL
LL -not dried
< 30% plus No. 200 < 15% plus No. 200 Fat clay
15-29% plus No. 200 % sand ≥ % gravel Fat clay with sand
Pl plots on or CH % sand < % gravel Fat clay with gravel
above "A"-line % sand ≥ % gravel < 15% gravel Sandy fat clay
≥ 30% plus No. 200 ≥ 15% gravel Sandy fat clay with gravel
% sand < % gravel < 15% sand Gravelly fat clay
Inorganic ≥ 15% sand Gravelly fat clay with sand
< 30% plus No. 200 < 15% plus No. 200 Elastic silt
15-29% plus No. 200 % sand ≥ % gravel Elastic silt with sand
LL ≥ 50 Pl plots below MH % sand < % gravel Elastic silt with gravel
"A"-line % sand ≥ % gravel < 15% gravel Sandy elastic silt
≥ 30% plus No. 200 ≥ 15% gravel Sandy elastic silt with gravel
LL -ovendried % sand < % gravel < 15% sand Gravelly elastic silt
Organic -------------------- < 0.75 OH ≥ 15% sand Gravelly elastic silt with sand
LL -not dried
Flow Chart for Classifying Coarse-Grained Soils (More Than 50% Retained on No. 200 Sieve)
Flow Chart for Classifying Fine-Grained Soil (50% or More Passes No. 200 Sieve)
Tested By: G. Leatham Checked By: B. Cook
Particle Size Distribution Report
ASTM D6913 & D1140
PERCENT FINER0
10
20
30
40
50
60
70
80
90
100
GRAIN SIZE - mm.
0.0010.010.1110100
% +3"% Gravel Coarse
% Sand
Fine Silt
% Fines
Clay
0.0 5.1 3.0 4.9 87.06 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200Test Results (ASTM D6913 & D1140)Material Description
Atterberg Limits
Coefficients
Classification
Test Remarks
Sample Date:
Location: Test Pit TP-1
Sample Number: S26-056 Depth: 4 feet
Client:
Project:
Project No:Figure
Sieve Size
or
Diam. (mm.)
Finer
(%)
Spec.*
(%)
Out of
Spec.
(%)
Pct.
of
Fines
Fat CLAY (CH)
3
2
1.5
1
.75
.375
#4
#10
#20
#40
#60
#100
#140
#200
100.0
100.0
100.0
100.0
100.0
99.4
97.2
94.9
93.2
91.9
90.7
88.9
88.4
87.0
30 81 51
0.2057
CH A-7-5(51)
In situ moisture: 28.4%
8/6/2026
Pineridge Construction, LLC
Hawkins Lane Subdivision
26-1156
PL=LL=PI=
D90=D85=D60=
D50=D30=D15=
D10=Cu=Cc=
USCS=AASHTO=
*(no specification provided)
CORE GeoEngineering
Portland, Oregon
Tested By: G. Leatham Checked By: B. Cook
LIQUID AND PLASTIC LIMITS TEST REPORT
PLASTICITY INDEX0
10
20
30
40
50
60
LIQUID LIMIT
0 10 20 30 40 50 60 70 80 90 100 110
CL-ML
CL or
O
L
CH or
O
H
ML or OL MH or OH
Dashed line indicates the approximate
upper limit boundary for natural soils
47
WATER CONTENT74
75
76
77
78
79
80
81
82
83
84
NUMBER OF BLOWS
5 6 7 8 9 10 20 25 30 40
MATERIAL DESCRIPTION LL PL PI %<#40 %<#200 USCS
Project No.Client:Remarks:
Project:
Location: Test Pit TP-1
Sample Number: S26-056 Depth: 4 feet
CORE GeoEngineering
Portland, Oregon Figure
Fat CLAY (CH)81 30 51 91.9 87.0 CH
26-1156 Pineridge Construction, LLC
In situ moisture: 28.4%Hawkins Lane Subdivision
Tested By: G. Leatham Checked By: B. Cook
Particle Size Distribution Report
ASTM D6913 & D1140
PERCENT FINER0
10
20
30
40
50
60
70
80
90
100
GRAIN SIZE - mm.
0.0010.010.1110100
% +3"% Gravel Coarse
% Sand
Fine Silt
% Fines
Clay
0.0 2.6 5.0 2.4 90.06 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200Test Results (ASTM D6913 & D1140)Material Description
Atterberg Limits
Coefficients
Classification
Test Remarks
Sample Date:
Location: Test Pit TP-1
Sample Number: S26-057 Depth: 8 feet
Client:
Project:
Project No:Figure
Sieve Size
or
Diam. (mm.)
Finer
(%)
Spec.*
(%)
Out of
Spec.
(%)
Pct.
of
Fines
Claystone (CH)
3
2
1.5
1
.75
.375
#4
#10
#20
#40
#60
#100
#140
#200
100.0
100.0
100.0
100.0
100.0
100.0
99.9
97.4
93.9
92.4
91.6
90.9
90.5
90.0
28 56 28
0.0766
CH A-7-6(29)
In situ moisture content: 24.4%
8/6/2026
Pineridge Construction, LLC
Hawkins Lane Subdivision
26-1156
PL=LL=PI=
D90=D85=D60=
D50=D30=D15=
D10=Cu=Cc=
USCS=AASHTO=
*(no specification provided)
CORE GeoEngineering
Portland, Oregon
Tested By: G. Leatham Checked By: B. Cook
LIQUID AND PLASTIC LIMITS TEST REPORT
PLASTICITY INDEX0
10
20
30
40
50
60
LIQUID LIMIT
0 10 20 30 40 50 60 70 80 90 100 110
CL-ML
CL or
O
L
CH or
O
H
ML or OL MH or OH
Dashed line indicates the approximate
upper limit boundary for natural soils
47
WATER CONTENT52
53
54
55
56
57
58
59
60
61
62
NUMBER OF BLOWS
5 6 7 8 9 10 20 25 30 40
MATERIAL DESCRIPTION LL PL PI %<#40 %<#200 USCS
Project No.Client:Remarks:
Project:
Location: Test Pit TP-1
Sample Number: S26-057 Depth: 8 feet
CORE GeoEngineering
Portland, Oregon Figure
Claystone (CH)56 28 28 92.4 90.0 CH
26-1156 Pineridge Construction, LLC
In situ moisture content: 24.4%Hawkins Lane Subdivision
Tested By: G. Leatham Checked By: B. Cook
Particle Size Distribution Report
ASTM D6913 & D1140
PERCENT FINER0
10
20
30
40
50
60
70
80
90
100
GRAIN SIZE - mm.
0.0010.010.1110100
% +3"% Gravel Coarse
% Sand
Fine Silt
% Fines
Clay
0.0 1.3 12.2 32.6 53.96 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200Test Results (ASTM D6913 & D1140)Material Description
Atterberg Limits
Coefficients
Classification
Test Remarks
Sample Date:
Location: Test Pit TP-4
Sample Number: S26-058 Depth: 6 feet
Client:
Project:
Project No:Figure
Sieve Size
or
Diam. (mm.)
Finer
(%)
Spec.*
(%)
Out of
Spec.
(%)
Pct.
of
Fines
Siltstone (ML)
3
2
1.5
1
.75
.375
#4
#10
#20
#40
#60
#100
#140
#200
100.0
100.0
100.0
100.0
100.0
100.0
100.0
98.7
93.8
86.5
78.1
66.1
60.0
53.9
NP NV NP
0.5673 0.3797 0.1062
ML A-4(0)
In situ moisture content: 17.2%
8/6/2026
Pineridge Construction, LLC
Hawkins Lane Subdivision
26-1156
PL=LL=PI=
D90=D85=D60=
D50=D30=D15=
D10=Cu=Cc=
USCS=AASHTO=
*(no specification provided)
CORE GeoEngineering
Portland, Oregon
CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
Project No. 26-1156 CORE GeoEngineering
Hawkins Lane Subdivision, Eugene, Oregon August 20, 2026
SITE PLANS
Microsoft, Vantor, State of Oregon, State of Oregon GEO, Esri, HERE, Garmin, iPC, Lane
County GIS, Lane County, LCOG
Lane County, Oregon
0 50 10025
Feet
±The information on this map was derived from digital databases on the Lane
County regional geographic information system. Care was taken in the creation
of this map, but is provided “as is”. Lane County cannot accept any responsibility
for errors, omissions or positional accuracy in the digital data or the underlying
records. Current plan designation, zoning, etc., for specific parcels should be
confirmed with the appropriate agency. There are no warranties, expressed
or implied, accompanying this product. However, notification of any errors will be appreciated.
2870 Hawkins Lane, Eugene, Oregon
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PROJECT No:
HORIZ:
VERT:
DRAWN BY:
SCALE:
DATE:REVISIONS:
DESIGNED BY:
REVIEWED BY:
SUBMITTALS:A & O Engineering L.L.C.
380 Q ST. SUITE 200
SPRINGFIELD, OR. 97477
PHONE: (541) 302-9790
info@ao-engr.com
CIVIL ENGINEERING & SITE
DEVELOPMENT CONSULTING
EXPIRES 12/26
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PROJECT No:
HORIZ:
VERT:
DRAWN BY:
SCALE:
DATE:REVISIONS:
DESIGNED BY:
REVIEWED BY:
SUBMITTALS:A & O Engineering L.L.C.
380 Q ST. SUITE 200SPRINGFIELD, OR. 97477PHONE: (541) 302-9790info@ao-engr.com
CIVIL ENGINEERING & SITEDEVELOPMENT CONSULTING
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9.6710 Geological and Geotechnical Analysis.
(1) Purpose of Geological and Geotechnical Analyses. The purpose of geological and geotechnical analyses is to
ensure that public and private facilities in developments in areas of known or potential unstable soil conditions
are located, designed, and constructed in a manner that provides for public health, safety, and welfare.
(2) Geological and Geotechnical Analysis Required. Except for those activities exempted under EC 9.6710(3)
Exemptions from Geological and Geotechnical Requirements, a geological and geotechnical analysis, prepared by
an Oregon licensed Engineering Geologist or an Oregon licensed Civil Engineer with geotechnical experience,
conforming with standards, procedures and content as defined in the Standards for Geological and Geotechnical
Analysis adopted by the city in the manner set forth in EC 2.019 City Manager – Administrative and Rulemaking
Authority and Procedures, is required for any of the following:
(a) All proposed tentative planned unit development, site review, or subdivision applications on properties
with slopes equal to or greater than 5%.
(b) All proposed development that includes dedication or construction of a public street or alley or the
construction of public drainage systems or public wastewater sewers.
(3) Exemptions from Geological and Geotechnical Analysis Requirements. The following activities are exempt from
the requirements of this section:
(a) Maintenance, operation, reconstruction of existing streets, driveways, and utility lines, provided soil
disturbance is limited to a standard utility trench width or the area beneath street and driveway structures.
(b) Emergency actions which must be undertaken immediately or for which there is insufficient time for full
compliance when it is necessary to prevent or abate any of the following:
1. An imminent threat to public health or safety.
2. An imminent danger to public or private property.
3. An imminent threat of serious environmental degradation.
(c) Street and alley dedications that widen existing public right-of-way are exempt from requirements of
9.6710(2)(b).
(d) A residential building permit for a lot or parcel that was subject to previous reports and assessments.
(e) New construction, building alterations and building additions that will not result in soil disturbance.
(f) Activities on land included on the city’s acknowledged Goal 5 inventory.
Site Development Standards | Eugene Code Page 1 of 3
The Eugene Code is current through Ordinance 20738, passed May 11, 2026.
(4)Categories of Geological and Geotechnical Analysis. The analysis required in geological and geotechnical
analyses is based on the following categories, and shall be prepared in the manner required in the rules
referenced in subsection (2) of this section:
(a)A Level One Analysis shall consist of a compilation of record geotechnical data, on-site verification of the
data and site conditions, and a report discussing site and soil characteristics in relation to the proposed
development and other applicable standards.
(b)A Level Two Analysis shall consist of a compilation of record geological data, analysis of site
characteristics, sub-surface investigation and testing to establish soil types and distribution, and a report that
includes site and soil characteristics in relation to the proposed development, identification of potential
problems, and recommendations for design and construction techniques and standards consistent with other
standards applicable to the development proposal.
(c)A Level Three Analysis shall consist of a Level Two Analysis and additional site-specific geotechnical
design of facilities such as, but not limited to, streets, foundations, utilities, retaining walls and structures due
to geologic constraints.
(5)Applicability of Different Categories of Geological and Geotechnical Analysis. Unless exempt under 9.6710(3), the
category of geotechnical analysis required is based on the following:
(a)A Level One Analysis shall be required on:
1.All development sites with slopes less than 10% that include construction of public improvements;
2.Subdivision, site review, and planned unit development applications for development sites with
slopes greater than or equal to 5% and less than 10%.
(b)A Level Two Analysis shall be required on:
1.All development sites with slopes greater than or equal to 10% that include construction of public
improvements;
2.Subdivision, site review, and planned unit development applications for development sites with
slopes greater than or equal to 10%.
(c)A Level Three Analysis shall be required on development sites where the Level One or Two Analysis
reveals evidence of existing or potential stability problems or where site conditions such as springs or seeps,
depth of soil to bedrock, variations in soil types, or a combination of these conditions, in the opinion of the
professional, impact the design parameters of the structure.
(6)Clear and Objective Housing. Unless exempt under 9.6710(3), in lieu of compliance with subsections (2), (4), and
(5)of this section, applications proposing housing to be reviewed with clear and objective approval criteria shall
include a certification from an Oregon licensed Engineering Geologist, an Oregon licensed Geotechnical Engineer,
or an Oregon licensed Civil Engineer with geological experience, prepared within ten years of the date of
application, that includes the following information:
Site Development Standards | Eugene Code Page 2 of 3
The Eugene Code is current through Ordinance 20738, passed May 11, 2026.
The Eugene Code is current through Ordinance 20738, passed May 11, 2026.
Disclaimer: The city recorder’s office has the official version of the Eugene Code. Users should contact the city
recorder’s office for ordinances passed subsequent to the ordinance cited above.
City Website: www.eugene-or.gov
Hosted by General Code.
(a) Identification of any portion of the proposed development site that is located in an area of moderate or
high landslide susceptibility as shown on the city’s adopted Eugene Landslide Hazard Map.
(b) A statement that the proposed development will not be impacted by existing or potential stability
problems or any of the following site conditions: slopes 20 percent or greater, springs or seeps, depth of soil
bedrock, soil types, variations in soil types, open drainage ways, fill, or a combination of these conditions.
(c) If proposed development will be located in an area identified as moderately or highly susceptible to
landslides pursuant to (a), or will be impacted by existing or potential stability problems or any of the site
conditions listed in (b), the certification must also include:
1. A review of the suitability of the proposed lot layout, street locations, and proposed locations for
utilities, driveways, parking areas, and buildings given the landslide hazards, stability problems, and/or
site conditions identified in the certification;
2. Any recommended modifications to the proposed lot layout, street locations, and proposed
locations for utilities, driveways, parking areas, and buildings that in the engineer’s opinion, would
mitigate the landslide hazards, stability problems, and/or site conditions identified in the certification;
3. Methods for safely addressing the landslide hazards and/or site conditions identified in (a) and (b);
and
4. Recommendations, if any, for additional geotechnical analysis for future buildings or improvements
on the development site.
5. Recommendations, if any, for additional geotechnical analysis for future buildings or improvements
on proposed lots or parcels.
If certification is submitted under (6)(c), the application shall include the applicant’s statement that it will develop
in accordance with the Engineer’s certification.
(Section 9.6710, see chart at front of Chapter 9 for legislative history from 2/26/01 through 6/1/02; amended by
Ordinance No. 20297, enacted August 11, 2003, effective September 10, 2003; Ordinance No. 20679, enacted
November 30, 2022, effective January 1, 2023.)
Site Development Standards | Eugene Code Page 3 of 3
The Eugene Code is current through Ordinance 20738, passed May 11, 2026.
CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
Project No. 26-1156 CORE GeoEngineering
Hawkins Lane Subdivision, Eugene, Oregon August 20, 2026
SITE RESEARCH
Soil Map—Lane County Area, Oregon
(2870 Hawkins Ln., Eugene, Oregon)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/16/2026
Page 1 of 34874710487474048747704874800487483048748604874890487492048747104874740487477048748004874830487486048748904874920488810488840488870488900488930488960488990489020489050489080489110489140
488810 488840 488870 488900 488930 488960 488990 489020 489050 489080 489110 489140
44° 1' 38'' N 123° 8' 22'' W44° 1' 38'' N123° 8' 7'' W44° 1' 31'' N
123° 8' 22'' W44° 1' 31'' N
123° 8' 7'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84
0 50 100 200 300
Feet
0 20 40 80 120
Meters
Map Scale: 1:1,560 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:20,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Lane County Area, Oregon
Survey Area Data: Version 24, Sep 10, 2025
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: May 17, 2023—Jun
3, 2023
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Soil Map—Lane County Area, Oregon
(2870 Hawkins Ln., Eugene, Oregon)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/16/2026
Page 2 of 3
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
41C Dixonville silty clay loam, 3 to
12 percent slopes
6.4 52.9%
102C Panther silty clay loam, 2 to 12
percent slopes
1.0 8.3%
108F Philomath cobbly silty clay, 12
to 45 percent slopes
4.7 38.8%
Totals for Area of Interest 12.1 100.0%
Soil Map—Lane County Area, Oregon 2870 Hawkins Ln., Eugene, Oregon
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/16/2026
Page 3 of 3
Depth to Water Table—Lane County Area, Oregon
(2870 Hawkins Ln., Eugene, Oregon)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/16/2026
Page 1 of 34874710487474048747704874800487483048748604874890487492048747104874740487477048748004874830487486048748904874920488810488840488870488900488930488960488990489020489050489080489110489140
488810 488840 488870 488900 488930 488960 488990 489020 489050 489080 489110 489140
44° 1' 38'' N 123° 8' 22'' W44° 1' 38'' N123° 8' 7'' W44° 1' 31'' N
123° 8' 22'' W44° 1' 31'' N
123° 8' 7'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84
0 50 100 200 300
Feet
0 20 40 80 120
Meters
Map Scale: 1:1,560 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
0 - 25
25 - 50
50 - 100
100 - 150
150 - 200
> 200
Not rated or not available
Soil Rating Lines
0 - 25
25 - 50
50 - 100
100 - 150
150 - 200
> 200
Not rated or not available
Soil Rating Points
0 - 25
25 - 50
50 - 100
100 - 150
150 - 200
> 200
Not rated or not available
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:20,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Lane County Area, Oregon
Survey Area Data: Version 24, Sep 10, 2025
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: May 17, 2023—Jun
3, 2023
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Depth to Water Table—Lane County Area, Oregon
(2870 Hawkins Ln., Eugene, Oregon)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/16/2026
Page 2 of 3
Depth to Water Table
Map unit symbol Map unit name Rating (centimeters)Acres in AOI Percent of AOI
41C Dixonville silty clay
loam, 3 to 12 percent
slopes
>200 6.4 52.9%
102C Panther silty clay loam,
2 to 12 percent slopes
15 1.0 8.3%
108F Philomath cobbly silty
clay, 12 to 45 percent
slopes
>200 4.7 38.8%
Totals for Area of Interest 12.1 100.0%
Description
"Water table" refers to a saturated zone in the soil. It occurs during specified
months. Estimates of the upper limit are based mainly on observations of the
water table at selected sites and on evidence of a saturated zone, namely
grayish colors (redoximorphic features) in the soil. A saturated zone that lasts for
less than a month is not considered a water table.
This attribute is actually recorded as three separate values in the database. A
low value and a high value indicate the range of this attribute for the soil
component. A "representative" value indicates the expected value of this attribute
for the component. For this soil property, only the representative value is used.
Rating Options
Units of Measure: centimeters
Aggregation Method: Dominant Component
Component Percent Cutoff: None Specified
Tie-break Rule: Lower
Interpret Nulls as Zero: No
Beginning Month: January
Ending Month: December
Depth to Water Table—Lane County Area, Oregon 2870 Hawkins Ln., Eugene, Oregon
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/16/2026
Page 3 of 3
Hydrologic Soil Group—Lane County Area, Oregon
(2870 Hawkins Ln., Eugene, Oregon)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/16/2026
Page 1 of 44874710487474048747704874800487483048748604874890487492048747104874740487477048748004874830487486048748904874920488810488840488870488900488930488960488990489020489050489080489110489140
488810 488840 488870 488900 488930 488960 488990 489020 489050 489080 489110 489140
44° 1' 38'' N 123° 8' 22'' W44° 1' 38'' N123° 8' 7'' W44° 1' 31'' N
123° 8' 22'' W44° 1' 31'' N
123° 8' 7'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84
0 50 100 200 300
Feet
0 20 40 80 120
Meters
Map Scale: 1:1,560 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:20,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Lane County Area, Oregon
Survey Area Data: Version 24, Sep 10, 2025
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: May 17, 2023—Jun
3, 2023
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Hydrologic Soil Group—Lane County Area, Oregon
(2870 Hawkins Ln., Eugene, Oregon)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/16/2026
Page 2 of 4
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
41C Dixonville silty clay
loam, 3 to 12 percent
slopes
D 6.4 52.9%
102C Panther silty clay loam,
2 to 12 percent slopes
D 1.0 8.3%
108F Philomath cobbly silty
clay, 12 to 45 percent
slopes
D 4.7 38.8%
Totals for Area of Interest 12.1 100.0%
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive
precipitation from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (A/D, B/D, and C/D). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when
thoroughly wet. These consist mainly of deep, well drained to excessively
drained sands or gravelly sands. These soils have a high rate of water
transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well
drained soils that have moderately fine texture to moderately coarse texture.
These soils have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of
water transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a claypan or clay
layer at or near the surface, and soils that are shallow over nearly impervious
material. These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in
their natural condition are in group D are assigned to dual classes.
Hydrologic Soil Group—Lane County Area, Oregon 2870 Hawkins Ln., Eugene, Oregon
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/16/2026
Page 3 of 4
2870 Hawkins Lane, Eugene, Oregon, Seismic Site Class Mapping
Vantor
NEHRP_Site_Class_Map
C
D
E / F
August 12, 2026
0 0.15 0.30.07 mi
0 0.2 0.40.1 km
1:12,000
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Lane County Area, Oregon 2870 Hawkins Ln., Eugene, Oregon
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/16/2026
Page 4 of 4
Depth to Bedrock—Lane County Area, Oregon
(2870 Hawkins Ln., Eugene, Oregon)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/16/2026
Page 1 of 44874710487474048747704874800487483048748604874890487492048747104874740487477048748004874830487486048748904874920488810488840488870488900488930488960488990489020489050489080489110489140
488810 488840 488870 488900 488930 488960 488990 489020 489050 489080 489110 489140
44° 1' 38'' N 123° 8' 22'' W44° 1' 38'' N123° 8' 7'' W44° 1' 31'' N
123° 8' 22'' W44° 1' 31'' N
123° 8' 7'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84
0 50 100 200 300
Feet
0 20 40 80 120
Meters
Map Scale: 1:1,560 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
0 - 25
25 - 50
50 - 100
100 - 150
150 - 200
> 200
Not rated or not available
Soil Rating Lines
0 - 25
25 - 50
50 - 100
100 - 150
150 - 200
> 200
Not rated or not available
Soil Rating Points
0 - 25
25 - 50
50 - 100
100 - 150
150 - 200
> 200
Not rated or not available
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:20,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Lane County Area, Oregon
Survey Area Data: Version 24, Sep 10, 2025
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: May 17, 2023—Jun
3, 2023
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Depth to Bedrock—Lane County Area, Oregon
(2870 Hawkins Ln., Eugene, Oregon)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/16/2026
Page 2 of 4
Depth to Bedrock
Map unit symbol Map unit name Rating (centimeters)Acres in AOI Percent of AOI
41C Dixonville silty clay
loam, 3 to 12 percent
slopes
66 6.4 52.9%
102C Panther silty clay loam,
2 to 12 percent slopes
107 1.0 8.3%
108F Philomath cobbly silty
clay, 12 to 45 percent
slopes
36 4.7 38.8%
Totals for Area of Interest 12.1 100.0%
Depth to Bedrock—Lane County Area, Oregon 2870 Hawkins Ln., Eugene, Oregon
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/16/2026
Page 3 of 4
Description
The term bedrock in soil survey refers to a continuous root and water restrictive
layer of rock that occurs within the soil profile.
There are many types of restrictions that can occur within the soil profile but this
theme only includes the three restrictions that use the term bedrock. These are:
1) Lithic Bedrock
2) Paralithic Bedrock
3) Densic Bedrock
Lithic bedrock and paralithic bedrock are comprised of igneous, metamorphic,
and sedimentary rocks, which are coherent and consolidated into rock through
pressure, heat, cementation, or fusion. Lithic bedrock represents the hardest type
of bedrock, with a hardness of strongly coherent to indurated. Paralithic bedrock
has a hardness of extremely weakly coherent to moderately coherent. It can
occur as a thin layer of weathered bedrock above harder lithic bedrock. Paralithic
bedrock can also be much thicker, extending well below the soil profile.
Densic bedrock represents a unique kind of bedrock recognized within the soil
survey. It is non-coherent and consolidated, dense root restrictive material,
formed by pressure, heat, and dewatering of earth materials or sediments.
Densic bedrock differs from densic materials, which formed under the
compaction of glaciers, mudflows, and or human-caused compaction.
If more than one type of bedrock is described for an individual soil type, the depth
to the shallowest one is given. If no bedrock is described in a map unit, it is
represented by the "greater than 200" depth class.
Depth to bedrock is actually recorded as three separate values in the database.
A low value and a high value indicate the range of this attribute for the soil
component. A "representative" value indicates the expected value of this attribute
for the component. For this soil property, only the representative value is used.
Rating Options
Units of Measure: centimeters
Aggregation Method: Dominant Component
Component Percent Cutoff: None Specified
Tie-break Rule: Lower
Interpret Nulls as Zero: No
Depth to Bedrock—Lane County Area, Oregon 2870 Hawkins Ln., Eugene, Oregon
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/16/2026
Page 4 of 4
2870 Hawkins Lane, Eugene, Oregon, LIDAR Imagery
Vantor
August 12, 2026
0 0.04 0.080.02 mi
0 0.07 0.140.04 km
1:3,600
2870 Hawkins Lane, Eugene, Oregon, Landslide Inventory and LiDAR Imagery
Vantor
Scarp Head Scarp Deposits
Landslide
August 12, 2026
0 0.09 0.170.04 mi
0 0.1 0.20.05 km
1:7,200
2870 Hawkins Lane, Eugene, Oregon, Landslide Hazard Zoning: Deep Seated Susceptibility
Microsoft, Vantor
Deep Susceptibility
Low susceptibility to deep landslides
Moderate susceptibility to deep landlides
August 12, 2026
0 0.03 0.050.01 mi
0 0.04 0.090.02 km
1:2,400
2870 Hawkins Lane, Eugene, Oregon, Landslide Hazard Zoning: Shallow Susceptibility
Vantor
Shallow Susceptibility
Low susceptibility to shallow landslides
Moderate susceptibility to shallow landslides
High susceptibility to shallow landslides
August 12, 2026
0 0.04 0.080.02 mi
0 0.07 0.140.04 km
1:3,600
2870 Hawkins Lane, Eugene, Oregon, DOGAMI Earthquake Hazard Zoning, P2475 Intensity Map
Vantor
P2475_Instrumental_Intensity_Map
Severe (VIII)
Violent (IX)
August 12, 2026
0 0.15 0.30.07 mi
0 0.2 0.40.1 km
1:12,000
2870 Hawkins Lane, Eugene, Oregon, DOGAMI Earthquake Hazard Zoning, CSZ Intensity Map
Vantor
CSZE_Instrumental_Intensity_Map
Strong (VI)
Very Strong (VII)
August 12, 2026
0 0.15 0.30.07 mi
0 0.2 0.40.1 km
1:12,000
2870 Hawkins Lane, Eugene, Oregon, Seismic Liquefaction Hazard Zoning
Vantor
Liquefaction_Susceptibility_Map
None
Moderate
Very High
August 12, 2026
0 0.09 0.170.04 mi
0 0.1 0.20.05 km
1:7,200
2870 Hawkins Lane, Eugene, Oregon, DOGAMI Probability Damaging Earthquake Shaking
Vantor
Probability_of_Damaging_Shaking_Map
5% - 10%
20% - 30%
August 12, 2026
0 0.09 0.170.04 mi
0 0.1 0.20.05 km
1:7,200
2870 Hawkins Lane, Eugene, Oregon, Radon Hazard Zoning
Vantor
Radon Potential
Low
August 12, 2026
0 0.04 0.080.02 mi
0 0.07 0.140.04 km
1:3,600
CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
Project No. 26-1156 CORE GeoEngineering
Hawkins Lane Subdivision, Eugene, Oregon August 20, 2026
PHOTOGRAPHIC LOG
CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
Project No. 26-1156 CORE GeoEngineering
Hawkins Lane Subdivision, Eugene, Oregon August 20, 2026
Test Pit TP-1
Test Pit TP-1
CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
Project No. 26-1156 CORE GeoEngineering
Hawkins Lane Subdivision, Eugene, Oregon August 20, 2026
Facing south, old home location, cut bank on east side
CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
Project No. 26-1156 CORE GeoEngineering
Hawkins Lane Subdivision, Eugene, Oregon August 20, 2026
Test pit TP-2
CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
Project No. 26-1156 CORE GeoEngineering
Hawkins Lane Subdivision, Eugene, Oregon August 20, 2026
Existing well house
CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
Project No. 26-1156 CORE GeoEngineering
Hawkins Lane Subdivision, Eugene, Oregon August 20, 2026
Test pit TP-3
Test pit TP-3
CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
Project No. 26-1156 CORE GeoEngineering
Hawkins Lane Subdivision, Eugene, Oregon August 20, 2026
Test pit TP-4
Test pit TP-4
CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
Project No. 26-1156 CORE GeoEngineering
Hawkins Lane Subdivision, Eugene, Oregon August 20, 2026
Test pit TP-5
CORE GEOENGINEERING
4207 SE Woodstock Blvd
Portland, Oregon 97206
T. (503) 509-9115
www.core-geoengineering.com
Project No. 26-1156 CORE GeoEngineering
Hawkins Lane Subdivision, Eugene, Oregon August 20, 2026
Test pit TP-6
Test pit TP-6