HomeMy WebLinkAboutStudies APPLICANT 6/1/2020 (2)Geotechnical Investigation and
Seismic Hazard Study
SUB South Hills 4"' Level Reservoir
Springfield, Oregon
Prepared for:
Springfield Utility Board
Springfield, Oregon
January 15, 2020
Foundation Engineering, Inc.
Foundation Engineering, Inc.
Professional Geotechnical Services
Steven Wages, P.E. January 15, 2020
Springfield Utility Board - Water Division
202 S. 1 Bt" Street
Springfield, Oregon 97477
SUB South Hills 4' Level Reservoir Project 2191041
Geotechnical Investigation and Seismic Hazard Study
Springfield, Oregon
Dear Mr. Wages:
We have completed the requested geotechnical investigation for the
above -referenced project in Springfield, Oregon. Our report includes a description
of our work, a discussion of the site conditions, a summary of laboratory testing,
and a discussion of engineering analyses. Recommendations for the design and
construction of new tank foundations are also provided.
A seismic hazard study was completed to identify potential geologic and seismic
hazards and evaluate the effect those hazards may have on the proposed site. The
study fulfills the requirements presented in the 2019 Oregon Structural Specialty
Code (OSSC 2019) for site-specific seismic hazard reports for essential and
hazardous facilities, and major and special occupancy structures. The OSSC (2019)
is based on the 2018 International Building Code (IBC) and ASCE 7-16: Minimum
Design Loads and Associated Criteria for Buildings and Other Structures. Results of
the study indicate there are no geologic or seismic hazards that require special design
consideration. These findings are summarized in the analysis provided herein and
the Seismic Hazard Study provided in Appendix C.
It has been a pleasure assisting you with this phase of your project. Please do not
hesitate to contact us if you have any questions or if you require further assistance.
Sincerely,
FOUNDATION ENGINEERING, INC.
Jonathan C. Huffman, P.E., G.E.
Senior Geotechnical Engineer
JCH/mw
enclosure
820 NW Cornell Avenue s Corvallis, Oregon 97330 s 641-767-7646
7867 SW Cirrus Orive, Bid 24 8 Beaverton, Oregon 97008 4 603-643-1641
GEOTECHNICAL INVESTIGATION
SUB SOUTH HILLS 4" LEVEL RESERVOIR
SPRINGFIELD, OREGON
BACKGROUND
The Springfield Utility Board (SUB) plans to construct a new water reservoir with a
nominal capacity of 460,000 gallons as part of the improvements to their East Systems
service area. The reservoir will be located south and uphill from the existing South
Hills Reservoir. The proposed site is forested and currently accessed via a walking
path that extends south from the terminus of S. 66' Place and Jessica Drive. The
project area is identified on the Vicinity Map (Figure 1A, Appendix A). The site layout
and proposed tank location are shown on Figure 2A (Appendix A).
We understand a ± 50 -foot diameter circular tank is proposed. The tank will include
a ring foundation extending 3 feet beyond the tank walls. The base of the tank will
be constructed at ± EI. 1 11 5.5. The top of water surface elevation will be ± EI. 1147,
resulting in a ±31 .5 -foot water column. The overflow elevation will be ±EI. 1148.
SUB is the project owner. Murraysmith is the civil designer and Branch Engineering is
the surveyor. SUB retained Foundation Engineering as the geotechnical consultant.
Our initial scope of work was summarized in a proposal dated March 27, 2019. The
scope was later revised in a letter dated July 22, 2019, to include an additional
exploration. Our work was authorized by SUB Purchase Order PO 0200004930 dated
March 29, 2018.
Foundation Engineering has completed investigations for existing reservoirs north of
the current project site, including SUB's South Hills Reservoir and 67' Street Reservoir.
Information from those studies was used to supplement the current investigation,
where applicable.
LOCAL GEOLOGY
Detailed discussions of the local and regional geology, tectonic setting, local faulting,
and historical seismicity are presented as part of the Seismic Hazard Study
(Appendix C). References cited in this section are also in Appendix C. An
abbreviated discussion of local geology is provided below.
The proposed reservoir site is located on an irregular -surfaced, north -facing slope at
the southeast edge of Springfield. Local geologic mapping indicates the project site
and immediately surrounding area is generally underlain by volcaniclastic rocks
overlain by basaltic andesite (Hladky and McCaslin, 2006; McClaughry et al., 2010).
Landslide deposits have been mapped at and in the vicinity of the site (Yeats et al.,
1996; Hladky and McCaslin, 2006; McClaughry et al., 2010; DOGAMI, 2018). The
geologic mapping is generally consistent with the subsurface conditions in our
explorations, which encountered a thin topsoil/duff layer followed by colluvium
consisting primarily of silty to clayey gravel, cobbles and boulders. The colluvium
represents possible landslide debris extending ±33 feet below the tank site. The
underlying bedrock consists of weathered tuff.
SUB South Hills 4'h Leval Reservdr January 16, 2020
Geotechnical Investigation and Seismic Hazard Study 1. Project 2191041
Springfield, Greg. Springfield Utility Board
PRIOR GEOTECHNICAL WORK
Foundation Engineering completed an investigation at the South Hills Reservoir in
2013 as part of a seismic evaluation for the existing tank. The South Hills Reservoir
is located ±600 feet north and downslope of the current project site. The
investigation included exploratory borings adjacent to and upslope of the tank. The
upslope boring was located near the east terminus of Jessica Drive. We reviewed
this work in preparation for the current study. Our previous explorations typically
encountered ± 10 to 20 feet of colluvium over residual soil and decomposed to highly
weathered bedrock composed of tuff or siltstone.
RECONNAISANCE AND SUBSURFACE EXPLORATION
Reconnaissance
We completed a multi -phase reconnaissance. The first phase included a site visit
with Steven Wages, P.E. (SUB) on March 18, 2019, to observe the area and develop
a scope for new explorations. Jon Huffman, P.E., G.E., and Brooke Running, R.G.,
C.E.G. (Foundation Engineering) returned to the site on April 19, 2019, to complete
the reconnaissance and initial subsurface explorations.
During the reconnaissance, we traversed the site to observe surface conditions at
the proposed tank location and the surrounding area. The project site is located
within sloping terrain. We observed areas both upslope and downslope of the
proposed tank site. Details of our observations are provided in subsequent sections
of this report and the Seismic Hazard Study (Appendix C).
Explorations
Test Pits
We dug five exploratory test pits (TP -1 through TP -5) on April 19, 2019, using a
John Deere 49OD tracked excavator. TP -1 and TP -2 were dug north of the proposed
tank to document subsurface conditions downslope of the tank site. TP -3, TP -4,
and TP -5 were dug within or adjacent to the proposed tank footprint. The test pit
locations were surveyed by Branch Engineering and are shown on Figure 2A
(Appendix A).
The test pits extended to maximum depths ranging from ±4 to 13 feet. Within
each test pit, the subsurface profiles were logged, and representative samples were
obtained for further examination at our office. Upon completion, the test pits were
backfilled with the excavated soils. The test pit logs are provided in Appendix B.
Borehole
The test pits did not encounter bedrock. Therefore, a deeper boring was drilled on
August 27, 2019, using a Terra Sonic TSi 150 track -mounted drill rig. The boring
(BH -1 ) was located within the footprint of the proposed tank, as shown on Figure 2A.
SUB South Hills 4'h Leval Reservdr January 16, 2020
Geotechnical Investigation and Seismic Hazard Study 2. Project 2191041
Springfield, Greg. Springfield Utility Board
BH -1 was drilled using roto -sonic drilling techniques and extended ±45 feet below
the ground surface. Roto -sonic drilling includes continuous sampling. Ten runs
were completed, ranging in length from ±0.5 to 5 feet, to obtain soil and bedrock
samples. Sampling was also completed at selected depths by driving a split -spoon.
The Standard Penetration Test (SPT), which is performed when the split -spoon is
driven, provides an indication of the relative stiffness or density of the foundation
soil.
The boring was continuously logged by a Foundation Engineering representative.
The soil and rock profile encountered in the boring is shown in the boring log
(Appendix B) and discussed below. The log includes sample intervals, which are
designated by run number or split -spoon ("SS") sample designation.
DISCUSSION OF SITE CONDITIONS
Surface Conditions and Site Topography
The project site is located within hillside terrain that generally slopes down to the
north. Topographic information was established based on Branch Engineering's
survey data included in Figure 2A. The area is forested and includes trees of various
variety and age. Abundant ferns, brambles, bushes, and similar undergrowth are
present across the forest floor.
The tank will be constructed on a relatively level bench near the southern extent of
SUB's property. The ground surface within the tank footprint is estimated to range
from ±EI. 1119 to EI. 1121. The northernmost portion of the tank footprint is set
back ± 15 feet from the crest of a local slope. The local slope extends north ± 80 to
90 feet at a ±2:1 (H:V) slope to another relatively level bench at ±EI. 1077. The
lower bench extends ±240 to 250 feet north of the tank before the ground surface
slopes moderately to steeply down again towards Jessica Drive. The south edge of
pavement for Jessica Drive is estimated to be ±480 to 490 feet north of the
proposed tank location.
The ground surface near the proposed tank also slopes down to the east and west
from the bench, but more gently compared to the sloping terrain north of the tank
site (see Figure 2A).
Subsurface Conditions
The explorations encountered relatively similar conditions across the site. The
following describes the soil units encountered. More details are provided on the logs
in Appendix B.
• Topsoi/. A topsoil and/or duff layer was encountered in each of the
explorations. This unit is typically comprised of clayey silt or silt with
scattered organics consisting of roots, woody debris, and/or plant matter.
The topsoil was soft and damp to moist at the time of the exploration. Within
the tank footprint, the topsoil was encountered to depths ranging from ±6 to
14 inches.
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Geotechnical Investigation and Seismic Hazard Study 3. Project 2191041
Springfield, Greg. Springfield Utility Roard
• Clayey SILT (Colluvium). At TP -1, medium stiff grading to very stiff, medium
plasticity clayey silt with scattered gravel -sized rock fragments was
encountered beneath the topsoil, extending to ± 10 feet. Similar soil was not
encountered in the other explorations. TP -1 was located ± 170 feet north
and downslope from where the tank is planned.
• Si7ty to Clayey GRAVEL, COBBLES and BOULDERS (Colluvium)- In each
exploration we encountered medium dense to dense, silty to clayey rock
fragments. The rock fragments are angular to subrounded and range from
gravel to boulder -sized. The colluvial rock fragments are comprised of
basaltic andesite. Similar intact bedrock is exposed across the top of the
hillside, ±500 to 600 feet south of the proposed tank site. The intact
bedrock appears to be the parent material for the gravel to boulder -sized
colluvial rock fragments encountered in the explorations.
Colluvial rock fragments were typically encountered at shallow depths (except
at TP -1) and extended to the bottom of the test pits. In TP -1, the silty to
clayey rock fragments were encountered below the clayey silt at a depth of
± 10 feet. In TP -2, TP -4 and TP -5, it was encountered below the topsoil at
a depth of ±6 to 8 inches. In TP -3, stiff gravelly clay to medium dense
clayey gravel (colluvium) was encountered from ±0.5 to 3 feet, followed by
gravel to boulder -sized rock fragments.
In BH -1, silty gravel and cobbles with scattered boulders was encountered
below the topsoil and extended to a depth of ±32.8 feet. This approximately
corresponds to ±EI. 1087 based on surface elevations provided in Figure 2A.
• Silty CLAY (Residua/ Soil)- Residual soil comprised of stiff, medium plasticity
silty clay with fine sand was encountered beneath the colluvium in BH -1 from
±32.8 to 33.3 feet. Residual soil is bedrock that has weathered in place to
a soil -like consistency. Below ±33.3 feet, the residual soil transitions to
weathered bedrock.
• TUFF (Bedrock)- Extremely weak (RO), decomposed to highly weathered tuff
was encountered in BH -1 below ±33.3 feet. The tuff grades to highly
weathered below ±39 feet and is extremely weak to very weak (RO to 131)
from ±44 to 45 feet (the bottom of BH -1).
Tuff is an igneous rock that forms from explosive volcanic eruptions and is
typically a mix of blasted rock, ash, and magma. Similar rock is exposed in
the hillside cut along the south side of Jessica Street (±500 feet north of
BH -1 ) and was encountered in previous borings drilled adjacent to and upslope
of the existing South Hills Reservoir.
Ground Water
No ground water was encountered to the maximum depth of the explorations,
including the deeper boring. The sloping terrain across the site may create
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Geotechnical Investigation and Seismic Hazard Study 4. Project 2191041
Springfield, Greg. Springfield Utility Roard
preferential channels for surface drainage. However, we did not observe any
surface drainage or ponded water at the time of the explorations and reconnaissance.
LABORATORY TESTING
Most of the retained samples were comprised of gravel to cobble -sized rock
fragments, limiting the available laboratory tests. An Atterberg limits test was
completed on sample 5-1-2 to help classify the fine-grained colluvium encountered
in TP -1. The results are summarized in Table 1. Non -tested samples were visually
classified in accordance with ASTM D2488 -09a and ASTM D2487-11.
Table 1. Natural Moisture Content and Atterberg Limits
Sample
Sample
Natural
USCS
Designation
Depth
Moisture
LL
PL
pl
Classification
(ft)
Content (%)
5-1-2
2.0-3.0
35.5
60
44
16
MH
SEISMIC DESIGN
A detailed discussion of the local seismic hazards is provided in the Seismic Hazard
Study (Appendix C). The recommendations provided in this section are limited to
the design response spectrum based on OSSC (2019) seismic parameters. A brief
discussion of the liquefaction hazard is also provided.
Seismic Response Spectrum
A site response spectrum was developed for the site in accordance with OSSC
(2019), which is based on IBC (2018) and ASCE 7-16. OSSC 2019 Section 1613.2
stipulates seismic ground motion parameters Ss and S1 (i.e., 0.2 and 1.0 -second risk -
targeted Maximum Considered Earthquake (MCER) spectral acceleration values on
bedrock) be based on mapped values determined using the Applied Technology
Council (ATC) Hazards by Location Tool at http://hazards.council.org with
ASCE 7-16 selected as the "Reference Document'.
The proposed reservoir location is underlain by a relatively deep deposit of medium
dense to dense silty to clayey rock fragments, followed by highly weathered bedrock.
Based on these conditions, the Site Class could fall between a Site Class C or D using
the definitions provided in ASCE 7-16 Section 20.3. Therefore, we recommend
designing based on a Site Class D profile. Shear wave velocity testing (e.g., ReMi,
MASK or similar methods) could be completed to further define Site Class, if it would
be beneficial for design.
When developing the design response spectrum for a Site Class D, ASCE 7-16
Section 11.4.8 requires a ground motion hazard analysis be performed in accordance
with ASCE 7-16 Section 21.2 at sites where S1 is greater than or equal to 0.2g.
The ATC Hazard Tool indicates S1 equal to 0.363g for the project location in
Springfield.
SUB South Hills 4'h Level Reservdr January 16, 2020
Geotechnical Investigation and Seismic Hazard Study 5. Project 2191041
Springfield, Oregon Springfield Utility Board
An exception in Section 11 .4.8 stipulates a ground motion hazard analysis is not
required when the seismic response coefficient Cs is calculated based on Eq. 12.8-2
for values of T < 1.5Ts and taken as equal to 1.5 times the value computed using
either Eq. 12.8-3 for T > 1.5Ts or Eq. 12.8-4 for T >_ 1.5TL (where T is the
fundamental period of the structure, Ts = Sot/SDS, and TL is the long -period transition
period shown on Figure 22-14 in Chapter 22). The TL value for Oregon is
16 seconds. The adjustment in the Cs value is intended to better model long -period
spectral accelerations for softer soils coupled with strong ground motions.
However, the adjustment applies only to the design of long -period structures
(i.e., typically structures with a height of five stories or greater). For the proposed
new water reservoir, we understand the period of interest for the structure will be
less than 1.5Ts (based on input from the structural designer). Therefore, no
adjustment to Cs is required when using the exception in ASCE 7-16 Section 11.4.8.
The site response spectrum shown on Figure 3A (Appendix A) was developed using
the mapped MCER ground motions and the general procedure in ASCE 7-16
Section 11.4.6 with F. selected based on OSSC 2019 Table 1613.2.3(1) and F�
selected based on Table 1613.2.3(2).
Liquefaction
Liquefiable soils typically consist of saturated, loose sands and non -plastic or low
plasticity silt (i.e., a PI of less than 12). Such soils were not encountered.
Therefore, soil liquefaction is not considered a hazard at this site.
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Discussion of Hazards and Site Observations
The proposed tank site is located within sloping terrain underlain by colluvial soils.
The Oregon Department of Geology and Mineral Industries (DOGAMI) identifies the
area as being within mapped landslide topography. Figure 4A (Appendix A) includes
output from DOGAMI's interactive hazard map, HazVu, showing the project site and
surrounding area (DOGAMI, 2018). The limits of the landslide topography extend
over a relatively large area that include SUB's South Hills Reservoir and the
67" Street Reservoir to the north. The geology and documented site conditions
suggests potential risk for landslides and/or slope instability that could affect the
proposed new tank location.
To address these concerns, we traversed the proposed tank site and surrounding
area to observe and document potential indicators of recent or on-going instability.
At that time, we observed the following:
• Large benches (i.e., flat ground adjacent to sloping terrain) located at the
proposed tank site and further north and downslope of the site are consistent
with the location of historic scarps identified by DOGAMI. However, no
apparent active slumps, fresh scarps, or similar signs of recent mass soil
movement are present.
SUR South Hills 4'h Leval Reservdr January 16, 2020
Geotechnical Investigation and Seismic Hazard Study 6. Project 2191041
Springfield, Greg. Springfield Utility Roard
• No ground water seeps or springs were observed that could indicate potential
destabilizing forces along the slopes.
• No areas of vegetation consistent with year-round standing water (e.g., wetland
vegetation) near the crest or toe of adjacent slopes were observed.
• Older, larger -diameter fir trees growing on and adjacent to the slopes are
generally straight.
• We observed some recently fallen trees and broken branches, which we believe
were caused by large snowstorms that occurred in late February 2019.
The terrain within the project area includes alternating areas with natural benches
adjacent to moderate to steep slopes, which could be the result of previous landslide
activity. However, our above -noted observations suggest no recent or on-going
instabilities in the immediate vicinity of the proposed tank site. We previously noted
similar conditions when evaluating the existing South Hills and 67' Street Reservoir
locations.
Slope Stability Analysis
The proposed tank will be set back ± 15 feet from a slope that extends north and
downhill from the tank. We completed slope stability analysis to evaluate the slope
and the potential effect the tank could have on the overall stability.
Limit equilibrium analysis was completed using the program Slide2 by Rocscience.
A representative cross-section with interpreted soil and bedrock profile was
developed based on the available survey data (see Figure 2A) and the subsurface
explorations. The cross-section is shown with the analysis output in Figures 5A and
6A (Appendix A).
The general subsurface profile includes a relatively thin layer of fine-grained soil
followed by silty to clayey gravel to boulder -sized rock fragments (colluvium).
Residual soil and bedrock were encountered in BH -1 but not in the test pits.
Therefore, the depth of the residual soil and bedrock were estimated based the
depths measured in BH -1 and the maximum depth of colluvium noted in the test pits.
Strength parameters for each layer were based on the observed conditions in the
boring and test pits. Typical Mohr -Coulomb strength parameters were assumed for
the soil layers. The colluvial gravel to boulder -sized rock fragments were observed
to be medium dense to dense. However, we assumed a relatively low friction angle
in = 34 degrees) to represent the soil strength in order to account for potential
variability of the soil unit with depth. Hoek -Brown (2002) criteria was used to
characterize the global bedrock strength parameters. The assumed strength
parameters are indicated in Figures 5A and 6A.
Ground water was not observed in the explorations and was not included in the slope
stability model. Ground water should not affect the stability of the slope at the
proposed tank location unless it is very shallow. Based on the observed site and
subsurface conditions, we believe that very shallow ground water beneath the tank
is unlikely.
SUR South Hills 4'h Leval Reservdr January 16, 2020
Geotechnical Investigation and Seismic Hazard Study 7. Project 2191041
Springfield, Greg. Springfield Utility Roard
The load from the tank was represented as a uniform stress applied over the tank
area. We assumed a nominal uniform stress of 3,500 psf to account for the weight
of the water and structural loads. The actual average stress could vary and is
expected to be lower away from the concentrated footing loads (note: the uniform
weight from a full reservoir with 31.5 -foot water column is ± 1,965 psf).
Slope stability analyses were conducted for static and seismic loading conditions.
The pseudo -static force representing seismic load was estimated as kh = O.5As,
where As is the peak ground surface acceleration. OSSC/IBC refers to ASCE 7 for
estimating ground acceleration, which calculates As as the peak ground acceleration
(PGA) on rock multiplied by the site factor, FPGA. At this site, the mapped PGA is
O.33g and the site factor, FPGA, is 1.17 assuming a Site Class D profile. Therefore,
the design As was assumed equal to +0.39g and kh is +0.19g.
The results of the slope stability analysis are shown in Figure 5A for static conditions
and Figure 6A for seismic conditions. Both circular and block failure surfaces were
analyzed, along with different methods of analysis. The results are provided for a
block surface with Bishop's Simplified method. Other methods indicated similar
results. The analysis indicates a factor of safety (FS) between ±1.4 and 1.5 for
static analysis and FS between ±1.0 and 1.1 for seismic analysis. These results
suggest adequate performance of the slope with the tank in place under static and
seismic loading conditions.
ENGINEERING ANALYSIS FOR TANK FOUNDATIONS
The structure will be supported on a perimeter ring foundation. It was unknown at the
time this report was prepared if the foundation system would also include a slab or
interior footings. Additional recommendations can be provided, as necessary, as the
design progresses.
Based on the proposed bottom of tank elevation (± EI. 1115.5) and the existing site
grades, we anticipate site preparation for the tank will include minor cuts on the order
of a few feet beneath the tank area.
Bearing Capacity
The analysis provided herein assumes a minimum footing width of 24 inches. We
understand the perimeter ring foundation will likely be wider than 24 inches. The base
of all footings should be constructed at least of 18 inches below grade. We also
recommend all footings (and slabs, if present) be underlain by at least 12 inches of
compacted crushed gravel or rock meeting the specifications for Select Fill, as defined
in the Recommendations sections of this report.
Footing excavations should terminate in medium dense to dense, silty to clayey rock
fragments. We assumed an effective internal friction angle (01 of 34 degrees to
represent this material. This value is based on the observed conditions in the test pits
and accounts for potential variability across the tank area and with depth.
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Geotechnical Investigation and Seismic Hazard Study 8. Project 2191041
Springfield, Greg. Springfield Utility Hoard
The rock fragments are expected to range from gravel to boulder -sized. Boulders
extending above the bottom of the footing excavation should be removed and any voids
backfilled with additional compacted Select Fill, as necessary. If zones of soft silt or
clay are present, the material should be overexcavated and replaced with additional
Select Fill. A representative of Foundation Engineering should be present at the time
of the footing excavations to confirm the suitability of the foundation soils and the need
for any additional excavation.
Provided the foundations are designed and constructed as recommended herein, we
recommend using an allowable bearing pressure of 3,500 psf for design. This
includes a nominal factor of safety of 3. The allowable bearing pressure may be
increased by one-third to evaluate short-term (e.g., seismic or wind) loads.
Settlement
The predominantly granular foundations soils have low compressibility
characteristics. Therefore, foundation settlement should be limited to ± Y: inch or
less if the foundations are designed using the allowable bearing pressure and
constructed as recommended herein. Any settlement should occur relatively quickly
as the footings are loaded.
Sliding Coefficient and Passive Resistance
A coefficient of friction of 0.5 is recommended for evaluating the sliding resistance
between the base of the concrete footings and the underlying Select Fill.
Passive resistance will develop on the sides of the footings in response to lateral
loading. Based on the foundation soils, we recommend assuming an allowable
lateral resistance of 200 psf/ft. The passive resistance should only be considered if
the foundation embedment depth can be confirmed for the entire life of the footing.
Concrete Slab
If the reservoir base is supported on a slab, we recommend a modulus of subgrade
reaction, k., of 200 pci for slab design. This value assumes the slab is supported
on at least 12 inches of compacted Select Fill over medium dense to dense granular
subgrade. Slabs should be reinforced with rebar instead of wire mess to limit the
risk of cracking or warping.
DRAINAGE CONSIDERATIONS
We understand Murraysmith is considering options for conveying stormwater runoff
and tank drainage from the site. One option is to utilize overland dispersion in lieu of
piping the runoff or constructing roadside ditches. Murraysmith has suggested using
level spreader techniques or a similar method to provide low-velocity dispersion in the
forested area to limits the risk of erosion.
We believe overland dispersion using a level spreader or similar method can be used
successfully at the site. However, to avoid increasing the risk of slope instability, we
recommend discharging flow further west of the reservoir, away from steeper slopes
SUR South Hills 4'h Level Reservoir January 16, 2020
Geotechnical Investigation and Seismic Hazard Study 9. Project 2191041
Springfield, Oregon Springfield Utility Board
and the area of mapped landslide topography. The terrain west of the existing walking
path has relatively gradual sloping terrain that slopes down to the north and west away
from the tank location. Therefore, we recommend directing flow from the tank via
solid pipe extending ±20 to 30 feet west of the walk path. From there, low-velocity
overland dispersion may be used to drain water to the west to northwest. A schematic
is provided in Figure 7A (Appendix A).
To further limit the risk of slope instability, we recommend limiting tank drainage to
volumes that don't exceed typical storm events. Draining of the reservoir should also
not coincide with periods of significant rainfall.
RECOMMENDATIONS
The construction recommendations provided below assume earthwork will occur
during dry weather. Depending on the actual time of year construction begins,
modifications to the respective recommendations may be required.
General Earthwork and Material Recommendations
1 . Select Fill as defined in this report should consist of 1 or '%-inch minus,
clean (i.e., less than 5% passing the #200 U.S. Sieve), well -graded,
crushed gravel or rock.
2. Compact the Select Fill in loose lifts not exceeding 12 inches. Thinner
lifts (e inches or less) will be required where light or hand -operated
equipment is used. Compact the Select Fill to a minimum of 95%
relative compaction. The maximum dry density of ASTM D 698 should
be used as the standard for estimating relative compaction. Field density
tests should be run frequently to confirm adequate compaction of the fill.
During wet weather, it may be necessary to increase the thickness of the
initial lift of fill to ± 18 to 24 inches to reduce the risk of subgrade
pumping. The need for a thickened initial lift will need to be verified by
a Foundation Engineering representative at the time of construction.
3. If trenches are required for below -grade construction, provide shoring to
protect workers from sloughing or caving soils. An OR -OSHA Type C
soil should be assumed for planning utility trenching and/or shoring (OR -
OSHA, 2011). Shoring and safety is the exclusive responsibility of the
contactor.
Site Preparation
We recommend the foundation area under the reservoir be prepared during dry
weather as follows:
4. Strip the existing ground ±6 to 12 inches, or as required to remove roots,
sod, or other deleterious material. Deeper grubbing may be needed
where trees or thick brambles are present. Dispose of all strippings
outside of construction areas, including pavements.
SUR South Hills 4'h Leval Reservdr January 16, 2020
Geotechnical Investigation and Seismic Hazard Study 10. Project 2191041
Springfield, Greg. Springfield Utility Board
5. Grade the finished ground surface surrounding all structures to promote
runoff away from the foundations.
6. Fill used for grading beneath and adjacent to the reservoir should consist
of Select Fill, placed and compacted as specified in Item 2. Finished fill
slopes adjacent to foundations should be graded at 4:1 (H:V) or flatter
and include erosion control.
7. Finished excavations for footings (or slabs) should be completed using a
hoe equipped with a smooth bucket to minimize subgrade disturbance.
The excavations should terminate in medium dense to dense,
predominantly gravel to boulder-sized rock fragments.
The required excavation depths will need to be confirmed at the time of
construction. Any areas of softened fine-grained soils (i.e., silt or clay)
or boulders extending above the planned excavation depth should be
overexcavated and replaced with additional compacted Select Fill. All
footing excavations should be evaluated by a Foundation Engineering
representative prior to backfilling.
B. Areas of loosened or disturbed granular foundation soils should be
compacted prior to backfilling. A walk-behind plate compactor should
suffice for smoothing and compacting the surface within the foundation
excavations.
9. Backfill the excavations to the planned foundation grade with compacted
Select Fill. At least 12 inches of Select Fill should be provided beneath
the foundations (and slab, if necessary) to help protect the underlying
soil. The fill thickness may need to be increased if construction occurs
during wet weather.
Foundation Design
We recommend new footings be designed in accordance with the following
recommendations.
10. Design footings using an allowable bearing pressure of 3,500 psf. A
one-third increase in the allowable bearing pressure may be assumed for
transient (i.e., wind and seismic) loading. This value assumes footings
will be constructed on a minimum of 12 inches of Select Fill underlain by
medium dense to dense, predominantly gravel to boulder-sized rock
fragments. The foundation soil should be confirmed by a representative
of Foundation Engineering at the time of construction.
11. Assume new footings could settle up to Y2 inch. This also represents
the potential differential settlement between the foundations.
12. Use a coefficient of friction of 0.5 for footings bearing on compacted
Select Fill for sliding analysis.
SUR South Hills 4'h Leval Reservdr January 16, 2020
Geotechnical Investigation and Seismic Hazard Study 11. Project 2191041
Springfield, Greg. Springfield Utility Roard
13. Use an allowable passive resistance of 200 psf/ft if the footings are
backfilled with compacted Select Fill. The passive resistance should only
be considered if the foundation embedment depth can be confirmed for
the entire life of the footing.
14. Use a modulus of subgrade reaction, Ike, of 200 pci, if necessary, for slab
design.
DISCUSSION OF ADDITIONAL PROJECT ELEMENTS
Access to the proposed reservoir location will require a new road and/or extension
of the existing road that currently terminates at the intersection of S. 66' Place and
Jessica Drive. An access road through the sloping terrain is likely to require modest
cuts and/or fills. Our present work focused solely on the new reservoir and does
not address any design or construction considerations for an access road. We are
available to complete additional explorations and provide design guidance, as
necessary, as the project progresses, and a preferred access route is identified.
We did not identify potential instability concerns at the proposed reservoir location.
However, that does not preclude similar concerns arising at other locations where an
access road may cross, particularly when cuts or fills are required.
DESIGN REVIEW/CONSTRUCTION OBSERVATION/TESTING
Foundation Engineering should be provided the opportunity to review all drawings
and specifications that pertain to site preparation and foundation construction. Site
preparation will require field confirmation of foundation soils. Mitigation of any
subgrade pumping will also require engineering review and judgment. That
judgment should be provided by one of our representatives. Frequent field density
tests should be run on all engineered fill. We recommend we be retained to provide
the necessary construction observation.
VARIATION OF SUBSURFACE CONDITIONS, USE OF THIS REPORT AND WARRANTY
The analyses, conclusions and recommendations contained herein assume the soil
conditions encountered in the test pits are representative of the site conditions. The
above recommendations assume we will have the opportunity to review final
drawings and be present during construction to confirm the assumed foundation
conditions. No changes in the enclosed recommendations should be made without
our approval. We will assume no responsibility or liability for any engineering
judgment, inspection or testing performed by others.
This report was prepared for the exclusive use of the Springfield Utility Board and
their design consultants for the SUB South Hills 4" Level Reservoir project in
Springfield, Oregon. Information contained herein should not be used for other sites
or for unanticipated construction without our written consent. This report is
intended for planning and design purposes. Contractors using this information to
estimate construction quantities or costs do so at their own risk. Our services do
not include any survey or assessment of potential surface contamination or
SUB South Hills 4'h Leval Reservdr January 16, 2020
Geotechnical Investigation and Seismic Hazard Study 12. Project 2191041
Springfield, Greg. Springfield Utility Board
contamination of the soil or ground water by hazardous or toxic materials. We
assume those services, if needed, have been completed by others.
Our services do not include any survey or assessment of potential surface
contamination or contamination of the soil or ground water by hazardous or toxic
materials. We assume that those services, if needed, have been completed by
others.
Our work was done in accordance with generally accepted soil and foundation
engineering practices. No other warranty, expressed or implied, is made.
REFERENCES
ASCE, 2017, 7-16: Minimum Design Loads and Associated Criteria for Buildings and
Other Structures, American Society of civil Engineers (ASCE), ISBN 978-0-
7844-7996-4.
ASTM, 2011, Standard Test Method for Classification of Soils for Engineering
Purposes (Unified Soil Classification System, USCS): American Society of
Testing and Materials (ASTM) International, ASTM Standard D2487, DOI:
1O. 152O/D2487-11, 11 p.
ASTM, 2009, Standard Test Method for Description and Identification of Soils
(VisualManualProcedure): American Society of Testing and Materials (ASTM)
International, ASTM Standard D2488, DOI: 1O. 1520/D2488 -09A, 11 p.
DOGAMI, 2018, Oregon Haz Vu: Statewide Geohazards Viewer: Oregon
Department of Geology and Mineral Industries (DOGAMI), web site:
http://www.oregongeology.org/hazvu, updated March 13, 2018, accessed
June 2019.
IBC, 2018, International Building Code: International Code Council, Inc.,
OR -OSHA, 2011, Oregon Administrative Rules, Chapter 437, Division 3 -
Construction, Subdivision P — Excavations: Oregon Occupational Safety and
Health Division (OR -OSHA).
OSSC, 2019, Oregon Structural Specialty Code (OSSC): Based on the International
Code Council, Inc., 2018 International Building Code (IBC), Section 1613 and
1803.
USGS, 2008, National Seismic Hazard Mapping Project, US Seismic Design Maps:
USGS website: http://earthquake.usgs.gov/designmaps/us/application.php.
See Appendix C for geologic references noted herein.
SUR South Hills 4'h Leval Reservdr January 16, 2020
Geotechnical Investigation and Seismic Hazard Study 13. Project 2191041
Springfield, Greg. Springfield Utility Roard
Appendix A
Figures
Foundation Engineering, Inc.
Professional Geotechnical Services
FOUNDATION ENGINEERING INC. VICINITY MAP FIGURE N0.
PROMSIORAL GFATECIR(ICa SERVICES
ROD "CQR ' A' SUB South Hills 4th Level Reservoir 1 A
CORYMUS. OR 990
%-4517
Rus.(5417757_7 FAR (541)757-7e50 Springfield, Oregon
FILE NAME:
SCALE IN FEET
40' 80' 160
U
\QI
1. BASE MAP WITH SURVEYED TEST PIT LOCATIONS AND PROPOSED
DATE InaN9
RESERVOIR WAS PROVIDED BY BRANCH ENGINEERING.
FOUNDATION ENGINEERING INC.
DwN. JCH
SITE LAYOUT AND EXPLORATIONS
FIGURE NO.
2. SEE REPORT FOR A DISCUSSION OF SITE AND SUBSURFACE
vrsar 10N.u. Gsarec Cm SERWEs
APPR
CONDITIONS.
_ anNrcORi n7exue
c0N7"u.m, ort 97330-45n
RENS
PROJECT N0.
SUB South Hills 4th Level Reservoir
2A
eue. (5.) 737 -?M M(5u) 737-7959
219109
Springfield, Oregon
FILE NAME:
0.7
M
a 0.5
U?
N
CF
.r
0.4
`w
v
4 0.3
m
U
d
Or 0.2
0.1
ASCE 7-161055(3 2019
0 0.5 1 1.5 2 2.5 3
Period (seconds)
Nates:
1. The Design Response Spectrum is based on ASCE 7-16 Section 11.4.
2. The fallowing parameters are based on the modified USGS 2014 maps and the
ATC Hazards by Location Tod (based on ASCE 7-16):
Site Class= D Damping = 5%
Sa= 0.63 Fa= 1.30 Sue= 0.81 SDs= 0.54
Sr = 0.36 F,= 1.94 Su, = 0.70 SDI = 0.47
3. Sc and Sr values indicated in Note 2 are the mapped, risk -targeted maximum considered
earthquake spectral aederations for 2% probability of exeeedence in 50 years.
4. F. and F, were established based on OSSC 2019 Tables 1613.2.3(1) and 1613.2.3(2)
using the selected Sc and Sr values. SDs and Sm values include a 213 reduction on
Sas and Sul as discussed in ASCE 7-16 Sector, 11.4.5.
5. Site location is: Latitude 43.0331, Longitude -122.9105.
FIGURE 3A.
ASCE 7-16/OSSC 2019 SITE RESPONSE SPECTRUM
SUB South Hills 4th Level Reservoir
Springfield, Oregon
Project 2191041
Figure 4A Oregon HazVu: Springfield South Hills
June 21, 2019
— Scarp
0 Head Scarp
Deposits
0 Talus -Colluvium
0 Fan
1:10,800
0 0.05 0.1 0.2 rtv
0 0.1 02 0.4 km
ElLandslide Source Ead, HERE, Gi , (c) Opm9mIM{p xn S, GIS w
Oregon Department of Geology and Mineral Industries (DOGAMI)
Oregon HazVu: Statewide Geohazards Viewer
http://gis.dogami.oregon.gov/maps/hazvu/
Figure SA.
1.460
Global Stability - Static Analysis
Results for Bishops Simplified Method.
Showing minimum FS and surfaces with
10 lowest FS values.
n
Assumed tank load
3500.0016/112 3500.001b/fl2
Me au"dense to dense
g
Sal to clayey GRAVEL, 'oBBLES
Medium stiff to very stiff
a�nd uvim)
Clayey SILT (colluvim)
34 deg. 7=125pcf
Su=O.Sksf y=115pcf
Stiff silty CLAY ------ ---
soil)
S(residual
Su = 1.0 ksf RO to R1 TUFF (bedrock)
y=115 pcf UCS= 14.4 ksf(100 psi)
GSI = 20
mi=13
D=0
a
-25 0 25 50 ]5
100 125 150 1]5 200 225 250
�
Figure 6A.
1.067
Horizontal seismic coefficient, ka
\
\i
Global Stability -
019
Pseudo -static Seismic Analysis
Results for Bishops Simplified Method.
Showing minimum FS and surfaces with
10 lowest FS values.
n
Assumed tank load
3500.0016/t2 3500.001b/*2
N
I�
Me ium denseto dense
g
Sil to clayey GRAVEL, BBLES
Medium stiff to very stiff
and 0ULDERS (colluvium)
Clayey SILT (colluvium)
34 deg. deg. y=125 pcf
Su=0.8 lest 7— 115
-----
Stiff silty CLAY —
,
(residual soil)
- -
S
Su— 1.0 ksf RO to Rl TUFF (bedrock)
y=115 pet UCS=14.4kef(100psi)
GSI = 20
mi=13
D=O
a
-25 0 25 50 75
100 125 150
175 200 225 250
rn r MAur
FOUNDATION ENGINEERING INC.
DWN. �_
SITE DRAINAGE
SCHEMATIC
FIGURE N0.
PB MSIONAL GEOncmcA SERVICES
APPR_
Aso" como:a. AVENUE
Ile
SUB South Hills 4th
Level Reservoir
srm (eu) vev-xu - (nu% M'
2191041
NO x1p -i3
Oregon
X+1
,Discharge via overland dispersion using
','level spreader or similar technique.
- - ----- x -
— - - - ---
- _ _'
--
IDirect all flow away from area within
+++
historic landslide, as mapped b DOG4M1.
x
PROPOSED
X RESERVOI
I+Vo
x
X++
+N
X +
X
.J
'.,Pipe to direct tank drainage and runoff west
of
reservoir. Extend pipe 120 to -30
feet west
of
x' x cuc
XX
walking path.
NOTES:
1. DISCUSSION AND RECOMMENDATIONS PROVIDED HEREIN ARE
PRELIMINARY AND SHOULD BE
CONFIRMED IN THE FIELD.
2. SEE REPORT FOR ADDITIONAL
DISCUSSION OF SITE DRAINAGE.
3. BASE MAP WAS PROVIDED BY
BRANCH ENGINEERING.
rn r MAur
FOUNDATION ENGINEERING INC.
DWN. �_
SITE DRAINAGE
SCHEMATIC
FIGURE N0.
PB MSIONAL GEOncmcA SERVICES
APPR_
Aso" como:a. AVENUE
RENS
PROJECT NO.
SUB South Hills 4th
Level Reservoir
srm (eu) vev-xu - (nu% M'
2191041
Springfield,
Oregon
rn r MAur
Appendix B
Boring and Test Pit Logs
Foundation Engineering, Inc.
Professional Geotechnical Services
DISTINCTION BETWEEN FIELD LOGS AND FINAL LOGS
A field log is prepared for each boring or test pit by our field representative. The log contains information concerning
sampling depths and the presence of various materials such as gravel, cobbles. and fill, and observations of ground water.
It also contains our interpretation of the soil conditions between samples. The final logs presented in this report represent
our interpretation of the contents of the Feld loge and the results of the sample examinations and laboratory test results.
Our recommendations are based on the contents of the final logs and the information contained therein and not on the
field logs.
VARIATION IN SOILS BETWEEN TEST PITS AND BORINGS
The final log and related information depict subsurface conditions only at the specific location and on the date indicated.
Those using the information contained herein should be aware that soil conditions at other locations or on other dates
may differ. Actual foundation or subgrade conditions should be confirmed by us during construction.
TRANSITION BETWEEN SOIL OR ROCK TYPES
The linea designating the interface between soil, fill or rock on the final logs and on subsurface profiles presented in the
report are determined by interpolation and are therefore approximate. The transition between the materials may be
abrupt or gradual. Only at boring or test pit locations should profiles be considered as reasonably accurate and then
only to the degree implied by the notes thereon.
SAMPLE OR TEST SYMBOLS
SH -1-4
SOIL
Sample Number
C — Pavement Core Sample
Sand
CS — Rack Core Sample
Boring or Test Pit Number
Sample Type
OS — Grab Sa Sample (3—inch split—spoon)
W — Well Graded
S — Grob Sample
Top of Sample Attempt
SH — Thin—walled Shelby Tube Sample
S —
SS —Standard Penetration Teat Sample (split—spoon)
Recovered Portion
♦ Standard Penetration Test Resistance equals the number of
Unrecovered Portion
blows a 140 Ib. weight falling 30 in. is required to drive a
M —
standard split—spoon sampler 1 ft. Practical refusal is
Bottom of Sample Attempt
equal to 50 or more blows per 6 in. of sampler penetration.
• Water Content (%).
UNIFIED
SOIL
CLASSIFICATION SYMBOLS
®Concrete
Sand
FIELD SHEAR STRENGTH TEST
G —
Grovel
W — Well Graded
®Clay
®Silt
Shear strength measurements on test pit aide
S —
Sand
P — Pooriy Graded
walla, blocks of soil or Shelby tube samples
M —
SIR
L — Low Plasticity
are typically made with Torvane or Field Vane
C —
Clay
H — High Plasticity
shear devices.
Pt—
Peat
0 — Organic
TYPICAL
SOIL/ROCK
SYMBOLS
®Concrete
Sand
Basalt
®Organics
Gravel
Sandstone
®Clay
®Silt
Siltstone
WATER TABLE
_ Water Table Location
(1/31/16) Date of Measurement
FOUNDATION ENGINEERING INC.
PROFESSIONAL GEOTECIRRCAL SERVICES
SYMBOL KEY
em xr tarsus ewxue men OF teem Bsm BRUNNO 24 EXPLORATION LOGS
animus, OP YIYA B61w81oX. 0e VNN
Y (441) 'm -7W sue (mi xr-wt
Explanation of Common Terms Used in Soil Descriptions
* SPT N—value in blows per foot (bpf)
•� Undrained shear strength
Term
Cohesive Soils
Granular Soils
Field Identification
Dry to the touch.
Damp
SPT*
Su (tsf)
Term
SPT*
Term
Contains shears and partings
Easily penetrated several inches
0 — 2
< 0.125
Very Soft
0 — 4
Very Loose
by f st.
remolded. Soil leaves wetness on the hand when squeezed.
Lensed
Soil is wetter than the optimum moisture content and above the plastic limit.
finger
Easily penetrated several inches
2 — 4
0.125-0.25
Soft
4 — 10
Loose
by thumb.
Can be Denetrated several inches
4 — 8
0.25 — 0.50
Medium Stiff
10 — 30
Medium
by thumb with moderate effort.
Dense
Readily indented by thumb but
8 — 15
0.50 — 1.0
Stiff
30 — 50
Dense
penetrated only with great effort.
Readily indented by thumbnail.
15 — 30
1.0 — 2.0
Very Stiff
> 50
Very Dense
Indented with difficulty by
>30
> 2.0
Hard
thumbnail.
,
* SPT N—value in blows per foot (bpf)
•� Undrained shear strength
Term
Soil Moisture Field Description
Dry
Absence of moisture. Dusty.
Dry to the touch.
Damp
Soil has moisture. Cohesive
soils are below plastic limit and usually moldable.
Moist
Grains appear darkened, but
no visible water. Silt/clay will clump. Sand will bulk. Soils
Contains shears and partings
are often at or near plastic
limit.
Wet
Visible water on larger grain
surfaces. Sand and cohesionless silt exhibit dilatancy.
Breaks into small lumps that resist
Cohesive soil can be readily
remolded. Soil leaves wetness on the hand when squeezed.
Lensed
Soil is wetter than the optimum moisture content and above the plastic limit.
Term PI Plasticity Field Test
Non—plastic 0 — 3 Cannot be rolled into a thread at any moisture.
Low Plasticity 3 — 15 Can be rolled into a thread with some difficulty.
Medium Plasticity 15 — 30 Easily rolled into thread.
High Plasticity > 30 Easily rolled and re—rolled into thread.
Term
Soil Structure Criteria
Stratified
Alternating layers at least 74 inch
Breaks under
thick.
Laminated
Alternating layers less than
pressure.
34 inch thick.
Fissured
Contains shears and partings
Breaks under
along planes of weakness.
Slickensided
Partings appear glossy or striated.
Blocky
Breaks into small lumps that resist
further breakdown.
Lensed
Contains pockets of different soils.
Term
Soil Cementation
Criteria
Weak
Breaks under
light
finger
pressure.
Moderate
Breaks under
hard
finger
pressure.
Strong
Will not break
with
finger
pressure.
FOUNDATION ENGINEERING INC.
PRUFRaaIoNn GROWCHIUM SER14CRe
COMMON TERMS
wemramma.. .Rxwoeswens Romwsw SOIL DESCRIPTIONS
ORxwu % OR BOOR s u lsew OR VNat
m. (au) am-rou Rea (ma) wt-.
Explanation of Common Terms Used in Rock Descriptions
Field Identification
Weathering Field Identification
UCS (psi)
Strength
Hardness
rock fabric.
Slightly
Rock mass is generally fresh. Discontinuities are stained and may contain clay. Some
Weathered
(ODOT)
Indented by thumbnail.
RO
< 100
Extremely Weak
Extremely Soft
Crumbles under firm blows with geological
R1
100-1,000
Very Weak
Very Soft
hammer, can be peeled by a pocket knife.
Rock mass is completely decomposed. Original rock 'fabric may be evident (relict texture).
3 ft. — 10 ft.
May be reduced to soil with hand pressure.
`
Can be peeled by a pocket knife with difficulty, shallow
R2
1,000-4,000
Weak
Soft
indentations made by firm blow with geological hammer.
Cannot be scraped or peeled with a pocket knife, specimen
R3
4,000-8,000
Medium Strong
Medium Hard
con be fractured with a single blow of geological hammer.
Specimen requires more than one blow of
R4
8,000-16,000
Strong
Hard
geological hammer to fracture it.
Specimen requires many blows of
R5
>16,000
Very Strong
Very Hard
geological hammer to fracture it.
Term
Weathering Field Identification
Fresh
Crystals are bright. Discontinuities may show some minor surface staining. No discoloration in
Bedding/Foliation
rock fabric.
Slightly
Rock mass is generally fresh. Discontinuities are stained and may contain clay. Some
Weathered
discoloration in rock fabric.
Moderately
Significant portions of rock show discoloration and weathering effects. Crystals are dull and show
Weathered
visible chemical alteration. Discontinuities are stained and may contain secondary mineral deposits.
Highly
Rock can be excavated with geologist's pick. All discontinuities exhibit secondary mineralization.
Weathered
Complete discoloration of rock fabric. Surface of core is friable and usually pitted due to
(Predom. Decamp.)
washing out of highly altered minerals by drilling water.
Decomposed
Rock mass is completely decomposed. Original rock 'fabric may be evident (relict texture).
3 ft. — 10 ft.
May be reduced to soil with hand pressure.
`
>
Spacing
(meters)
Spacing
Spacing Term
Bedding/Foliation
<
0.06
< 2 in.
Very Close
Very Thin (Laminated)
0.06
— 0.30
2 in. — 1 ft.
Close
Thin
0.30
— 0.90
1 ft. — 3 ft.
Moderately Close
Medium
0.90
— 3.0
3 ft. — 10 ft.
Wide
Thick
>
3.0
> 10 ft.
Very Wide
Very Thick (Massive)
Vesicle Term
Volume
Some vesicles
5 — 25%
Highly vesicular
25 — 50%
Scoriaceous
> 50%
Stratification lerm Description
Lamination <1 cm (0.4 in.) thick beds
Fissile Preferred break along laminations
Parting Preferred break parallel to bedding
Foliation Metamorphic layering and segregation of minerals
FOUNDATION ENGINEERING INC.
PROFESSIONAL GEOTECRNICA6 SERVICES
COMMON TERMS
eon xr caravi. •veare vesv el C. Dave euamm se ROCK DESCRIPTIONS
sus tsu1 vevcxm sre. se)Du� ss�.
RQD %
Designation
RQD %percentage. Designation
Rock Quality Designation (RQD)
is the
cumulative length of intact pieces 4 inches or
longer excluding breaks caused by drilling and
0 — 25
Very Poor
75 — 90 Good
25 — 50
Poor
90 — 100 Excellent
handling divided by run length,
expressed as a
50 — 75
Fair
FOUNDATION ENGINEERING INC.
PROFESSIONAL GEOTECRNICA6 SERVICES
COMMON TERMS
eon xr caravi. •veare vesv el C. Dave euamm se ROCK DESCRIPTIONS
sus tsu1 vevcxm sre. se)Du� ss�.
DePdn
Sail anti Rack Description
Flew.
A SFT,
• Ma&rae. %
Eusea l/
Lag
Samples
N Valva
leta /
Feel
Corais
Dgah
0 Recovmy ® ROD.,%
Verr
1121.2
0
So
100
Soff clayey SILT, am a graystsizetl nock fragments
DO
RUN
Cappetl with
1
,an organics (MH); retl-0rmvn, tlry toclamp, metlium
fv
1119.0
sal
2
Iplasficiy, fnelocoarsesubangulargrevst,organics
I B
1'2
�.
onsisl of woody dams, (lapsclgtlul�
Fwigs and .
Cd9
3
Medium dense to dense silly GRAVEL and
?:......=•....='.Y.:
.= ....:........:...
4
COBBLES, scattered boulders(GM);retl-brownlo
5
grey, tlry to clamp, low to medium plasticity all, fine to
i
RUN
- -
-
- - -
ccarsesubangulargravel toboulder-sized slightly to
0
RUN
Backfilled
B
moderately weathered basaltic andesite rock
with
7
fragments, (alluvium).
viu
uSS-1-1
bentonite
- -
-
-
chips
8
9
a
RUN
1
- -
- - - -
12
13
14
&
-
15
Dampbel.115fest.
t
RUN
18
17
18
°
19
9
20
RUNG
j
21
9
SS-1-3
22
24
25
RUN ]
26
SS-1J
0
28
RUN 8
31
:.-
087.4
L), yediumpfigticity n
Slid ally CLAed,
32.
39
dam tonnoi
lantl iron-stained, clly
I'_ ]
1089.8
35
tfine sang rel-wlcanitlasfic texture, (resi--soip._(]_�'�
33.3
Extremelyweak (RO) TUFF; yellowish light brmvn antl
>:
RUNS
-
inonstained, decomposed to highly weathered, fine
:.?'�
SS-1-5
37
sand-sized volcanic clasts.
'1-
38
esstained joints below 133.8 fest.
Occasional mangane
1�.,-,j j--'s
4
39
>:
..
"
Highly weathered below t39 feet.
RUN 10
41
SS-16
42
21
43
IF
z
Extremely weak to very weak (R0 to R1) bebwd44':
1075.2
Project No.: 2191041 Boring Log: BH -1
surface B.H. 1120.2 feet(Approx.) SUB South Hills 4th Level Reservoir
Dale of Boring: August 27, 2019 Springfield, Oregon
!! Foundation Engineering, Inc. Page 1 of 1
Camnras
s
-
sail and Rod, Description
Camnnh
€
E
�
;
p
Stl1 arch Rods Oescriprion
Surface: fans, brambles, and similar
ddd
A
m
F
Soft SILT, some organics (ML); dark brown, clamp to moist, tau
Surface: Thick fans and underbrush
1_
0.5°
Soft clayey SILT to SILT, some clay, mattered organics (ML to
}
MH); dark brown to brown, clamp to moist, metlium plasticity,
Abundant fine rods extend to 36
2-
51-1
blocky, organics consist d primarily rods, (topsoiVduff).
inches and scattered fine rods up to
r
o z.a
—---------------------------
31 -inch diameter extend to 31.5 feel.
S -i 2
2.0
Medium stili clayey SILT, scattered rock fragm ants (MH);
4
orange-brovm,mdsi, medium plasticity, gravel -sized rock
Rootsu to 3l YAnch diameter extend
p
51-3
fragments up to 38tinch diameter, (collumm).
to 33 feel.
4-
Becomes stiff to vay stiff below 23.5 feet.
-
5-
6-
&7-
No seepage or groundwater
7-
encountered to the limit d exploration.
8
&
&
069.5
o-
John Deere 49DDexcavator
1964.9
°
10.0
encountered practkal digging refusal x111-
S1J
10.0
Meoium tlense to tlense silly to clayey GRAVEL, COBBLES, antl
310 feet, likely on a boulder.
11_
BOULDERS (GM to GC); grey to broom, clamp to moist, me win
1z-
plastery silt and clay, angular to subangular gravel to
12-
broker -sized rock fragments up to t2 -foot diam elec rock
No seepage or ground water
Surface Elevation: 1079.5 feet(Approx.) SUB South Hills 4th Level Reservoir
Date of Test Pit: April 19, 2019 Springfield, Oregon
1061.9
fragments are slightly to moderately weathered basaltic an desite,
encwntered to the limitderplcralion.
1&
(cdlutium).
13.0
BOTTOM OF EXPLORATION
Project No.: 2191041 Test Pit Log: TP -1
surface Elevation: 1074.9 feet(Approx.) SUB South Hills 4th Level Reservoir
Date of Test Pit: April 19, 2019 Springfield, Oregon
Camnras
s
-
sail and Rod, Description
S
Surface: fans, brambles, and similar
1079.0
M4 1
Soft SILT, some organics (ML); dark brown, clamp to moist, tau
underbrush
1_
0.5°
plasticity, organics consist d rods, wV9dy debris, and plant
�n a_Popsoiutlufn__________________J
Abundant fine rods extend to 36
2-
S-2-1
Medium dense to dense silly to clayey GRAVEL, COBBLES, and
inches and scattered fine rods up to
}
BOULDERS (GM to GC); brain to grey, clamp to add, tau to
31 -inch diameter extend to 31.5 feel.
medium plasticity sill and clay, angular to subrounded gravel to
4
honker -sized rock fragments up to 32. 5 -foot diam eler, rock
fragments are sightly to moderately weathered basaltic an desite,
5-
(ccllumm).
7 -
No seepage or groundwater
&
encountered to the limit d exploration.
g_
10-
069.5
BOTTOM OF EXPLORATION
John Deere 49DDexcavator
10.0
encountered practkal digging refusal x111-
310 feet, likely on a boulder.
1z-
1&
Project No.: 2191041 Test Pit Log: TP -2
Surface Elevation: 1079.5 feet(Approx.) SUB South Hills 4th Level Reservoir
Date of Test Pit: April 19, 2019 Springfield, Oregon
r
Sd1arM Rock Description
Camnrh
€
E
y
p
Soil antl Rock Oescriplicn
Surface: fans, well haesnag, and
ddd
A
m
F
Solt clayey SILT, scattered rock fragments and organics (MIN);
Surface: fans, moss, small Mlgs, and
1-
1129A
°
Solt clayey SILT, some organics, scattered gravel -sized rock
siniaruntlabrush
}
0.5
fragmenls,(ML); dark brown, clamp to mdsi, low to medium
2-
S31
plasticity, ocaree subangular gravelof co
, organics consist ols
Abundant fine rteredrods dtl to 38
in&.
intoes and rods up to
2-
S41
�tlwoc�
ntlebns,(topsoil/alluvium).____
Abundant fine rock edend to 38
intoes
1117.9
-
Sliltgravelly CLAY, some cobbles to medium dense clayey
4
3.0
°
GRAVEL (CL to GC); orange -brown to grey, damp to moist,
4
(metlium plasticity clay, angular to subrounded gravel to I
Scalleretl roots up to 33inch diameter
rf
Icabble-sized rock fragments up to 1110 -inch diameter, rock I
edend to t3 feel.
5-
Ihagmenls are slightly to moderately weathered basaltic andesite,l
((colluvium).
&
Dense ally to clayey GRAVEL antl COBBLESbltlars
, same oc
No seepage or ground water
8 -
(GM to GC); orange -brown to grey, clamp to mdsi, low to
encountered to the limit of exploration.
]-
1110.8
metlium plasticity clay, an gular to subrounded gravel to
BOTTOM OF EXPLORATION
boulder -sized rock fragments up to t1&inch diameter, rock
&
fragments are slightly to mod mately weathered basaltic an desite,
&
(colluvium).
to-
sa 2
11-
Project No.: 2191041 Test Pit Log: TP -4
1z
Dale aTed Pit: April 19, 2019 Springfield, Oregon
No seepage to ground wader
encocnleretl to the limit of erplaralioc.
en
13-
1107.9
BOTTOM OF EXPLORATION
13.0
Project No.: 2191041 Test Pit Log: TP -3
Surface E.N. 1120.9 feet(Approx.) SUB South Hills 4th Level Reservoir
Dale ofTesl Pit: April 19, 2019 Springfield, Oregon
r
Sd1arM Rock Description
Surface: fans, well haesnag, and
1118.9
Solt clayey SILT, scattered rock fragments and organics (MIN);
underbrush
1-
0.7dark
°
b, mdsi, medium plasticity, coarse angular to
rownIsubangulargraveFsizetl
rock fragments, organics consist ofrodsl
2-
land decaying plant matter, (topsoillallumm).--------1
Abundant fine rteredrods dtl to 38
in&.
intoes and rods up to
}
S41
--
se to denseulde to clayey GRAVEL AND
diameter
f1%inch diameter extentl 1032 feel.
COBBLES,
COBBLES, scattered boulders (GM GC); orange -brown to
4
grey, clamp to moist, low to medium plasticity sift and clay,
angular to subrounded gravel to boulder -sized rock fragments up
rf
to 11&inch diameter, rock fragments are slightly to moderately
weathered basaltic antlesile, (colluvium).
7 -
No seepage or ground water
8 -
encountered to the limit of exploration.
&
1110.8
BOTTOM OF EXPLORATION
9.0
10-
11-
1z-
1}
Project No.: 2191041 Test Pit Log: TP -4
surface Et.u. 1119.6 feet(Approx.) SUB South Hills 4th Level Reservoir
Dale aTed Pit: April 19, 2019 Springfield, Oregon
$
�
o
cornrerms
b
Sall and Roar Descdpicn
m
Surface: fans, small "s, leases, antl
1120.4
Solt tlayey SILT, scattered organics (MN); dark brown, moist,
underbrush}
0.5
°
medium pladicily, organics
anics owed ofrools, woody claims, antl
Llan)
.
matter, (lopaoi/tlufn--------------- J
Y --
&
SS1
Medium dense siXy to tlayey GRAVEL AND COBBLES,
scattered boulders (GM to GC); aangetrewn to grey, clamp to
No seepage or grountl water
most, low to medium plasticity clay, angular to subrounded
encountered to the limit of exploration
4
1116.9
gravel to boulder -sized rock fragments up to 212 -inch diameter,
4.0ro
k fragments are slightly to m oderately weathered basaltic
rf
tlasile, (cduNum).
BOTTOM OF EXPLORATION
]-
8
9-
o-
10-
11-
11-
Project No.: 2191041 Test Pit Log: TP -5
Project
Surface B.N. 1120.9 feet(Approx.) SUB South Hills 4th Level Reservoir
Dale ctTed Pit: April 19, 2019 Springfield, Oregon
Appendix C
Seismic Hazard Study
Foundation Engineering, Inc.
Professional Geotechnical Services
SEISMIC HAZARD STUDY
SUB SOUTH HILLS4" LEVEL RESERVOIR
SPRINGFIELD, OREGON
INTRODUCTION
This seismic hazard study was completed to identify potential geologic and seismic
hazards and evaluate the effect those hazards may have on the proposed project. The
study fulfills the requirements presented in the 2019 Oregon Structural Specialty Code
(OSSC), Section 1803 for site-specific seismic hazard reports for essential and
hazardous facilities and major and special -occupancy structures (OSSC, 2019).
The following sections provide a discussion of the local and regional geology, seismic
and tectonic setting, earthquakes, and seismic hazards. A detailed discussion of the
subsurface conditions at the project location, including exploration logs, is provided in
the main report.
LITERATURE REVIEW
Available geologic and seismic publications and maps were reviewed to characterize
the local and regional geology and evaluate relative seismic hazards at the site. The
literature review included information from previous geotechnical and seismic hazard
investigations completed by Foundation Engineering in the Springfield area.
Investigations reviewed included subsurface conditions for two existing SUB reservoirs
to the north or down slope of this proposed reservoir.
Regional Geology
The project site lies within the Willamette Valley, which is a broad, north -south -
trending basin separating the Coast Range to the west from the Cascade Range
(Western and High Cascade Ranges) to the east. The proposed reservoir is along the
western foothills of the Western Cascades near the southern extent of the Willamette
Valley.
At the western margin of Oregon is the Cascadia Subduction Zone (CSZ). The CSZ is
a converging, oblique plate boundary where the Juan de Fuca oceanic plate is being
subducted beneath the western edge of the North American continental plate
(Geomatrix Consultants, 1995). The CSZ extends from central Vancouver Island, in
British Columbia, Canada, through Washington and Oregon to Northern California in
the United States (Atwater, 1970). The movement of the subduction zone has
resulted in accretion, folding, faulting, and uplift of oceanic and other sediments on
the western margin of the North American plate.
In the early Eocene 1±55 million years ago), the Willamette Valley was part of a broad
continental shelf extending west from the Western Cascades beyond the present
coastline. Basement rock underlying most of the north -central portion of the Valley
includes the Siletz River Volcanics (early to middle Eocene, ±50 to 58 million years
old), which erupted as part of a submarine oceanic island -arc (Bela, 1979; Yeats et
al., 1996; Wiley, 2008).
SUB South Hills 4t' Level Reservoir January 16, 2020
Seismic Hazard Study 1 Project 2191041
Springfield, Oregon Springfield Utility Board
The island -arc collided with, and was accreted to, the western margin of the
converging North American plate near the end of the early Eocene. Volcanism
subsided and a forearc basin was created and infilled with marine sediments
throughout the late Eocene and Oligocene (Wiley, 2008). The thickness of the
basement volcanic rock is unknown. However, it is estimated to be ±3 to 4 miles
thick (Yeats et al., 1996).
After emerging from a gradually shallowing ocean, the marine sediments were covered
by Columbia River Basalt (CRB) which poured through the Columbia Gorge from
northeastern Oregon and southeastern Washington and spread as far south as Salem,
Oregon (±17 to 10 million years ago, middle to late Miocene). Uplift and folding of
the Coast Range and the Western Cascades during the late Miocene formed the
trough-like configuration of the Willamette Valley. (Orr and Orr, 1999; O'Connor et
al., 2001; Wiley, 2008; McClaughry et al., 2010)
Following the formation of the Willamette Valley, thick layers of Pliocene gravel filled
the Southern Valley (Madin and Murray, 2006; McClaughry et al., 2010). The deposits
were then incised by the Willamette River, forming alluvial terraces. In the Pleistocene
1± 1.6 million to 10,000 years ago), the Central and Southern Valley was refilled with
fan -delta gravel, originating from the melting glaciers in the Cascade Range. The
Willamette and McKenzie Rivers incised deeply into the fan -delta deposits during the
Quaternary and deposited recent alluvium adjacent to the river banks and major
tributaries (Madin and Murray, 2006).
Also during the Pleistocene, catastrophic flood deposits (over 15,000 years ago)
mantle the Willamette Valley floor as far south as Eugene (Hampton, 1972; Yeats et
al., 1996; O'Connor et al., 2001; McClaughry et al., 2010). These deposits originated
from a series of glacial -outburst floods that periodically drained Glacial Lake Missoula
in western Montana (Allen et al., 2009).
Local Geology
Springfield is located between the McKenzie River and Middle Fork of the Willamette
River. The reservoir site is located on an irregular -surfaced north -facing slope at the
southeast edge of Springfield. The location is up slope (south) from the existing South
Hills Reservoir and Jessica Drive.
Local geologic mapping indicates the project site and immediate surrounding area is
generally underlain by volcaniclastic rocks overlain by basaltic andesite (Hladky and
McCaslin, 2006; McClaughry et al., 2010). Landslide deposits have been mapped at
and in the vicinity of the site (Yeats et al., 1996; Hladky and McCaslin, 2006;
McClaughry et al., 2010; DOGAMI, 2018). The geologic mapping is generally
consistent with the subsurface conditions in our explorations, which encountered a
thin topsoil/duff layer followed by colluvium consisting primarily of silty to clayey
gravel, cobbles and boulders. The colluvium represents possible landslide debris
extending ±33 feet below the tank site. The underlying bedrock consists of
weathered tuff that is similar to the bedrock exposed in hillside cuts adjacent to Jessica
Drive and in previous borings completed for the South Hills Reservoir. Details of the
SUB South Hills 4'h Level Resewok January 16, 2020
Seismic Hazard study 2 Protect 2191041
Springfield, Oregon Springfield Utility Board
subsurface conditions are provided in the Subsurface Conditions section of the main
report and in the exploration logs (Appendix B).
A search of other explorations and water wells near the proposed reservoir site did not
locate any explorations at or immediately near the site. A boring completed by
DOGAMI at 69' and Ivy (±0.4 miles down slope to the NEI indicates the subsurface
conditions include fill and landslide deposits to ± 1 B.5 feet, followed by vitric tuff to
±29.5 feet (maximum depth of the boring).
Tectonic Setting
Springfield and vicinity is located ±120 miles inland from the surface expression of
the CSZ, a converging, oblique plate boundary where the Juan de Fuca plate is being
subducted beneath the western edge of the North American continent (Geomatrix
Consultants, 1995). The CSZ extends from central Vancouver Island in British
Columbia, Canada, through Washington and Oregon to Northern California (Atwater,
1970). It is estimated that the average rate of subduction of the Juan de Fuca plate
under the North American plate is ±37 mm/year northeast, based on Pacific and Mid -
Ocean Ridge velocities, geodetic studies of convergence, and magnetic anomalies of
the Juan de Fuca plate (Personius and Nelson, 2006; DeMets et al., 2010).
Available information indicates the CSZ is capable of generating earthquakes within
the descending Juan de Fuca plate (intraplate), along the inclined interface between
the two plates (interface or subduction zone), or within the overriding North American
Plate (crustal) (Weaver and Shedlock, 1996). Therefore, western Oregon is located in
an area of potentially high seismic activity due to its proximity to the CSZ, and all three
earthquakes sources could potentially affect the site.
Local Faulting
The US Geological Survey (USGS) has defined four fault classifications based on
evidence for Quaternary displacement I<1.6 million years) in their US fault database
(Personius et al., 2003). The fault classes are defined as follows:
• Class A faults have geologic evidence supporting tectonic movement in the
Quaternary known or presumed to be associated with large -magnitude
earthquakes.
• Class B faults are of non -tectonic origin (e.g. volcanic activity) or demonstrate
less evidence of tectonic displacement.
• Class C faults are crustal features that lack evidence of a tectonic fault,
Quaternary slip, or deformation of a known fault.
• Class D faults are features that are not tectonic faults and include joints, joint
zones, landslides, erosional or scarp surfaces, and lacustrine shorelines.
Class A and B faults are included in the USGS fault database and interactive fault map.
USGS considers 17 features in Oregon to be Class C faults (USGS, 2006a). The
Class C Harrisburg anticline is ±20 miles northwest of Springfield. The USGS does
not consider any features in Oregon as Class D (USGS, 2006a).
SUB South Hills 4'h Laval Reservoir January 16, 2020
Seismic Hazard study 3 Proieot 2191041
Springfield, Oregon Springfield Utility Board
A review of nearby faults was completed to evaluate the seismic setting and the
potential seismic sources. Several concealed and inferred crustal faults are located
within ±10 miles of the site; however, none of the faults show any evidence of
movement in the last ± 1 .6 million years (Geomatrix Consultants, 1995; Personius et
al., 2003; USGS, 2006a).
Two potentially active Quaternary (<1.6 million years or less) crustal fault zones have
been mapped within ±40 miles of the site (Geomatrix Consultants, 1995; Personius et
al., 2003; USGS, 2006a) and are listed in Table 1 C. The approximate surface projection
locations of these faults in the southern Willamette Valley are shown on Figure 1C
(attached) (Personius et al., 2003). Of the listed faults, the Owl Creek fault is the only
US Geologic Survey (USGS) Class A fault. The Upper Willamette River fault zone is
considered a Class B fault by the USGS. None of the local crustal faults show any
evidence of movement within the last ± 1.6 million years (Geomatrix Consultants,
1995; USGS, 2006a). Additional fault information is available in the literature (Personius
et al., 2003; USGS, 2006a). For a more detailed list and discussion of regional folds
and faults associated with the CSZ, readers are directed to visit:
http://earthquake.usgs.gov/hazards/qfaults/or/index.php.
Table 1C. USGS Class A and Class B Crustal Faults
within a ±40 -mile Radius of the Site (USGS, 2006) X11
IA Fault data based on Personius at al., 2003, USGS, 2006 and USGS, 2017.
'a To nearest surface projection of the fault or fault zone.
'01 Quaternary time period defined at <1.6 million years based on the 1963 Geologic Time Seale (Palmer,
19831
Historic Earthquakes
No significant interface (subduction zone) earthquakes have occurred on the CSZ in
historic times. However, several large -magnitude (>M —8.0, M = unspecified
magnitude scale) subduction zone earthquakes are thought to have occurred in the
past few thousand years. This is evidenced by tsunami inundation deposits, combined
with evidence for episodic subsidence along the Oregon and Washington coasts
(Peterson et al., 1993; Atwater et al., 1995).
The estimated maximum magnitude of a CSZ interface earthquake is up to a moment
magnitude (Mrv) 9.3 (Petersen et al., 2014a). The fault rupture may occur along a
portion or the entire length of the CSZ (Weaver and Shedlock, 1996).
SUB South Hills 4'h Level Reservoir
January 16, 2020
Seismic Hazard Study 4
Approximate
Springfield, Oregon
Springfield Utility Board
Approximate
Last KnownFault
Name
Fault
Distance and
Slip Rate
LengthDeformation
and Class
Number
Direction from Site
'a,
(mm/yr)
y
(miles)
(Years)
(miles)'zI
Upper Willamette
<1.6 million
g63
+27
+18 SE
<0.20
River (B)
—
—
years
Owl Creek Al
870
±9
±4W
<750,000
I <0.20
IA Fault data based on Personius at al., 2003, USGS, 2006 and USGS, 2017.
'a To nearest surface projection of the fault or fault zone.
'01 Quaternary time period defined at <1.6 million years based on the 1963 Geologic Time Seale (Palmer,
19831
Historic Earthquakes
No significant interface (subduction zone) earthquakes have occurred on the CSZ in
historic times. However, several large -magnitude (>M —8.0, M = unspecified
magnitude scale) subduction zone earthquakes are thought to have occurred in the
past few thousand years. This is evidenced by tsunami inundation deposits, combined
with evidence for episodic subsidence along the Oregon and Washington coasts
(Peterson et al., 1993; Atwater et al., 1995).
The estimated maximum magnitude of a CSZ interface earthquake is up to a moment
magnitude (Mrv) 9.3 (Petersen et al., 2014a). The fault rupture may occur along a
portion or the entire length of the CSZ (Weaver and Shedlock, 1996).
SUB South Hills 4'h Level Reservoir
January 16, 2020
Seismic Hazard Study 4
Project 2191041
Springfield, Oregon
Springfield Utility Board
Numerous detailed studies of coastal subsidence, tsunami, and turbidite deposits
estimate a wide range of CSZ earthquake recurrence intervals. Turbidite deposits in
the Cascadia Basin have been investigated to help develop a paleoseismic record for
the CSZ and estimate recurrence intervals for interface earthquakes (Adams, 1990;
Goldfinger et al., 2012). A study of turbidites from the last ± 10,000 years suggests
the return period for interface earthquakes varies with location and rupture length.
That study estimated an average recurrence interval of ±220 to 380 years for an
interface earthquake on the southern portion of the CSZ, and an average recurrence
interval of ±500 to 530 years for an interface earthquake extending the entire length
of the CSZ (Goldfinger et al., 2012). Older, deep-sea cores have been re-examined
more recently and the findings may indicate greater Holocene stratigraphy variability
along the Washington coast (Atwater et al., 2014). Additional research by Goldfinger
for the northern portion of the CSZ suggests a recurrence interval of ±340 years for
the northern Oregon Coast (Goldfinger et al., 2016). The most recent CSZ interface
earthquake occurred ±319 years ago (January 26, 1700) (Nelson et al., 1995; Satake
et al., 1996).
Intraplate (Intraslab or Wadati-Benioff Zone) earthquakes occur within the Juan de
Fuca plate at depths of ±28 to 37 miles (Weaver and Shedlock, 1996). The maximum
estimated magnitude of an intraplate earthquake is about Mw 7.5 (Petersen et al.,
2014b). The available record for intraplate earthquakes in Oregon is limited. The
available data indicates a Mb = 4.6 event occurred in 1963, located ±23 miles east
of Salem at a depth of ±29 miles (Barnett et al., 2009). Based on its depth, this
earthquake may be considered an intraplate event. The Puget Sound region of
Washington State has experienced three intraplate events in the last ±70 years,
including a surface wave magnitude (Me) 7.1 event in 1949 (Olympia), a Ms 6.5 event
in 1965 (Seattle/Tacoma) (Wong and Silva, 1998), and a Mw 6.8 event in 2001
(Nisqually) (Dewey et al., 2002).
Crustal earthquakes dominate Oregon's seismic history. Crustal earthquakes occur
within the North American plate, typically at depths of ±6 to 12 miles. The estimated
maximum magnitude of a crustal earthquake in the Willamette Valley and adjacent
physiographic regions is about Mw 7.0 (Petersen et al., 2014b). Only two major crustal
events in Oregon have reached Richter local magnitude (ML) 6 (the
1936 Milton-Freewater ML 6.1 earthquake and the 1993 Klamath Falls ML
6.0 earthquake) (Wong and Bott, 1995). The majority of Oregon's larger crustal
earthquakes are in the ML 4 to 5 range (Wong and Bott, 1995).
Table 2C summarizes earthquakes with a M of 4.0 or greater or Modified Mercalli
Intensity (MMI) of V or greater has occurred within a ±50 -mile radius of Springfield in
the last ± 186 years (Johnson et al., 1994; NCEDC, 2014; USGS, 2016). Note that
the referenced earthquake catalogs are a composite of different earthquake catalogs
and seismic networks; therefore, data errors may exist. Complete historic earthquake
records may not yet be included in the referenced earthquake catalogs. Therefore, it
is possible some earthquakes may not be included in Table 2C.
SUB South Hills 4'^ Level Reservoir
January 16, 2020
Seismic Hazard Study 6
Project 2191041
Springfield, Oregon
Springfield Utility Board
Table 2C. Historic Earthquakes Within a ±50 -mile Radius of Springfield 11'
Year
Month
Day
Hour
Minute
Latitude
Longitude
Depth
(miles)
Magnitude or
Intensity I31
1921
02
25
20
00
44.4
-122.4
unknown
MMI -V
1942
05
13
01
52
44.5
-123.3
unknown
MMI -V
1961
08
19
04
56
44.7
-122.5
unknown
M = 4.5
2015
07
04
15
42
44.1
-122.8
4.9
ML = 4.1
^ The site is located at Lettuce 44.03303 and Longitude -122.910674.
"' M —unspecified magnitude, Mh —compressional body wave magnitude, M. = primary coda magnitude, ML = local Fichte
magnitude, and MMI = Modified Mercalli Intensity at or near epicenter.
It should be noted that seismic events in Oregon were not comprehensively
documented until the 1840's (Wong and Bott, 1995). Earthquake epicenters located
in Oregon from the late 1920's to 1962 were limited due to the number of and the
distance between seismographs, the number of recording stations, and uncertainty in
travel times. Therefore, information recorded during that time suggests that only
earthquakes with magnitudes > 5 would be recorded in Oregon (Bela, 1979). Oregon
State University (OSU) likely had the first station installed in 1946, and the first modern
seismograph was installed at OSU in 1962 (Wong and Bott, 1995; Barnett et al.,
2009). According to Wong and Bott (1995), seismograph stations sensitive to smaller
earthquakes (ML <4 to 5) were not implemented in northwestern Oregon until 1979
when the University of Washington expanded their seismograph network to Oregon.
The local Richter magnitude (ML) of events occurring prior to the establishment of
seismograph stations have been estimated based on correlations between magnitude
and MMI. Some discrepancy exists in the correlations.
Table 3C summarizes distant, strong earthquakes felt in the Springfield area (Wiley et
al., 1993; Wong and Bott, 1995; Black, 1996). None of these events caused
significant, reportable damage in Springfield or surrounding area.
Table 3C. Distant Earthquakes Felt in the Springfield Area
Earthquake
Modified Mercalli Intensities
(MMI)
2001 Nisqually, Washington
II to III
1993 Klamath Falls, Oregon
IV
1993 Scotts Mills, Oregon
IV
1965 Seattle - Tacoma, Washington
I to IV
1962 Portland, Oregon
I to IV
1961 Lebanon/Albany, Oregon
IV
1949 Olympia, Washington
IV
1873 Crescent City, California
V
SUB South Hills 4'h Leyel Feservair January 16, 2020
Seismic Hazard Study 6 Proieot 2191041
Springfield, Oregon Springfield Utility Board
Seismic and Geologic Hazards
Section 1803.6.1 of the 2019 OSSC requires the evaluation of risks from a range of
seismic hazards including local ground motion amplification, earthquake -induced
landslides, liquefaction and lateral spread, fault rupture, tsunami/seiche, or earthquake -
induced flooding.
We have developed conclusions regarding the seismic hazards based on the subsurface
profiles encountered in our explorations at the project site. The conclusions are also
based on our knowledge of the site geology, a review of previous geotechnical and
seismic studies performed in the area, and available geologic hazard maps (including
information available from DOGAMI).
DOGAMI has completed geologic and seismic hazard studies, which include Lane
County (Burns et al., 2008), and provides online hazard information through HazVu,
LiDAR, and SLIDO viewers (DOGAMI, 2016, 2017, 2018). The above-mentioned
maps refer to some, but do not cover all, of the seismic hazards. The reviewed
information is only considered a guide and does not have precedence over site-specific
evaluations. In the following sections, information from the available seismic hazard
maps is provided along with our site-specific evaluations for comparison.
The relative earthquake hazard is based on the combined effects of ground shaking
amplification and earthquake -induced landslides with a range in hazard from Zone A
(highest hazard) to Zone D (lowest hazard). Based on the relative earthquake hazard
mapping, the site is within Zone D (lowest hazard) for the overall, relative earthquake
hazard at the site (Black et al., 2000). To the immediate southeast of the proposed
site is a Zone B hazard (intermediate to high hazard), likely due to the existing landslide
hazard, and to the immediate east/southeast of the proposed site is a Zone C (low to
intermediate hazard), likely due to the steeper slopes and moderate slope instability
hazard.
Local Ground Motion Amplification. Ground motion amplification is the influence of a
soil deposit on the earthquake motion. As seismic energy propagates up through the
soil strata, the ground motion is typically increased (i.e., amplified) or decreased
(i.e., attenuated) to some extent. Based on the presence of deep colluvial deposits
with predominantly medium dense to dense soils, it is our opinion the amplification
hazard is moderate and is consistent with a Site Class D soil profile. The DOGAMI
hazard study (Burns et al., 2008) indicates the amplification susceptibility for the site
is low to moderate (NEHRP Site Class B to C). The site is expected to experience strong
ground shaking during a CSZ earthquake due to its proximity to the CSZ (DOGAMI,
2018).
Landslides and Earthquake-lnduced Landslides. The proposed reservoir site is located
on a north -facing slope near the top of the ridge. Much of the site and surrounding
slopes are mapped as landslide deposits (Hladky and McCaslin, 2006; DOGAMI,
2016). The landslide hazard or susceptibility is mapped as moderate to very high
(likely to possible landsliding) (Black et al., 2000; Burns et al., 2008; DOGAMI, 2018).
Landslide topography was observed during our reconnaissance and colluvial deposits
were encountered in our explorations.
SUB South Hills 4'^ Level Resewok
January 16, 2020
Seismic Hazard Study 7
Project 2191041
Springfield, Oregon
Springfield Utility Board
Any development within hillside terrain includes inherent risk of slope instability,
particularly hillside terrain with mapped landslide topography. However, no recent or
on-going active slope instability features were observed during the exploration phase.
Based on our observations and the results of the slope stability discussion and analysis
in the main report, we believe the risk of landslides or earthquake -induced landslides
(with design -level earthquake loads) is low.
Liquefaction, Settlement, and Lateral Spread. Liquefiable soils, where liquefaction
triggering has been documented, typically consist of saturated, loose, clean sand, and
non -plastic to low plasticity silt with a plasticity index (PI) typically less than B. These
soils were not encountered in our explorations. Therefore, we do not believe there is a
risk for liquefaction at the project site. The DOGAMI hazard report and HazVu site
indicate liquefaction susceptibility is moderate in the project area (Burns et al., 2008;
DOGAMI, 2018).
Lateral spread is a liquefaction -induced hazard which occurs when soil or blocks of soil
are displaced down slope or toward a free face (such as a riverbank) along a liquefied
layer. A lateral spread hazard does not exist at the site since there is no liquefaction
hazard.
Subsidence. The Oregon Seismic Safety Policy Advisory Committee (OSSPAC) has
prepared a report describing the hazards associated with CSZ earthquakes (OSSPAC,
2013). The report includes a map showing the estimated ground subsidence as a
result of large-scale plate bending associated with a Mw 9 CSZ earthquake. The map
indicates the ground in the Springfield area could subside up to 1 foot during a Mw 9
CSZ earthquake.
Fault Rupture. The risk of fault rupture is expected to be low due to the lack of known
active faulting beneath the site (Yeats et al., 1996; Personius et al., 2003; Hladky and
McCaslin, 2006; USGS, 2006b, a; McClaughry et al., 2010). The closest potentially
active crustal fault is the Owl Creek fault and general fault information for this fault
can be found in Table 1 C.
Tsunami/Seiche or Earthquake -Induced Roodinp. Tsunami are waves created by a
large-scale displacement of the sea floor due to earthquakes, landslides, or volcanic
eruptions (Priest, 1995). Tsunami inundation is not applicable to this site because
Springfield is not on the Oregon Coast. Seiche (the back and forth oscillations of a
water body during a seismic event) is also not a local hazard due to the absence of
large bodies of water near the site.
According to HazVu, there is no localized flood potential for the Effective FEMA
100 -year flood at or near the site (DOGAMI, 2018). Earthquake -induced flooding
related to the failure of other structures or shallow ground water and subsidence does
not apply to the site. Oregon dams are regulated through the Association of State
Dam Safety Officials and OWRD and evaluation of the risk of dam failure is not part
of our work scope.
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SEISMIC DESIGN
Design Earthquakes
The 2019 OSSC, Section 1803.3.2.1, requires the design of structures classified as
essential or hazardous facilities and of major and special occupancy structures to
address, at a minimum, the following earthquakes:
Crustal: A shallow crustal earthquake on a real or assumed fault near the site
with a minimum Mw 6.0 or the design earthquake ground motion
acceleration determined in accordance with the 2019 OSSC Section
1613.
Intraplate: A CSZ intraplate earthquake with Mw of at least 7.0.
Interface: A CSZ interface earthquake with a Mw of at least 8.5.
The design maximum considered earthquake ground motion maps provided in the
2019 OSSC, which are based on modified (risk -targeted) 2014 maps prepared by the
USGS for an earthquake with a 2% probability of exceedance in 50 years (i.e., a
±2,475 -year return period) for design spectral accelerations . The modifications
include factors to adjust the spectral accelerations to account for directivity and risk.
The 2014 USGS maps were established based on probabilistic studies and include
aggregate hazards from a variety of seismic sources. The interactive deaggregation
search tool on the USGS National Earthquake Hazard Mapping website allows the
breakdown of earthquake sources to be identified (USGS, 2014).
Interactive deaggregation of the 2,475 -year return period USGS spectral acceleration
maps indicates the seismic hazard at the site is dominated by the CSZ, contributing
79% to the overall aggregate hazard. Crustal earthquakes were included in the studies
but were not considered to be a principal seismic hazard at this site. The CSZ scenarios
considered ranged from Mw 8.7 to 9.3, located ±44 to 81 miles west of the site.
The earthquake magnitudes and source -to -site distances used to generate the
2014 USGS maps satisfy the requirements of 2019 OSSC. Seismic design parameters
and 2019 OSSC design response spectrum are discussed in the Site Response section
of the main report and are shown on Figure 3A (Appendix A).
CONCLUSION
Based on the findings presented herein, it is our opinion there are no geologic or seismic
hazards that would preclude the design and construction of the proposed project. This
site-specific hazard investigation for the SUB South Hills 4' Level Reservoir in
Springfield, Oregon, was prepared by Brooke Running, R.G., C.E.G.
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SUB South Hills 4'^ Level Reservoir January 16, 2020
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Reducing Risk in the Pacific Northwest, U.S. Geological Survey (USGS),
Professional Paper 1560, p. 183-222.
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NOTES:
1. POR71ON OF MAP BASED ON MAP OF QUATERNARY FAULTS AND FOLDS IN OREGON (PERSONIUS ET AL., 2003).
2. SEE SITE-SPECIFIC SEISMIC HAZARD STUDY FOR A DISCUSSION OF LOCAL FAULTING.
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