ATT E - Engineering Geology Report.pdf

ENGINEERING GEOLOGY REPORT

Culvert Repair Investigation US 101 Oregon Coast Highway

MP 303

Curry County, Oregon

Key 24015

EA E1243204

April 2025

REGION 3 TECH CENTER, GEO/ENVIRONMENTAL UNIT

1.0 INTRODUCTION

1.1 PROJECT DESCRIPTION

1.2 SCOPE OF WORK

2.0 SITE DESCRIPTION

2.1 BACKGROUND

2.2 REGIONAL GEOLOGY

2.3 GEOMORPHOLOGY

2.4 GEOLOGIC HAZARD - LANDSLIDES

3.0 SITE CHARACTERIZATION

3.1 SUBSURFACE INVESTIGATION

3.1.1 LABORATORY DATA

3.1.2 GROUNDWATER

3.1.3 SLOPE MOVEMENT

3.1.4 MATERIAL UNITS

4.0 SUMMARY AND CONCLUSIONS

5.0 LIMITATIONS

6.0 REFERENCES

7.0 SIGNATURES

FIGURES

Figure 1 – Vicinity Map (in report text) Figure 2a – Regional Geologic Map (in report text) Figure 2b – Geologic Map Units and Symbols (in report text) Figure 3 – Formation of Southwest Oregon Figure 4 – LiDAR Site Image GA-04 – Geotechnical Data (Site Plan) GA-05 – Geotechnical Data (Section A-A) GA-06 – Geotechnical Data (Section B-B) GA-07 – Geotechnical Data (Drill Holes Not Shown on Sections)

TABLES

Table 1: Drill Hole Summary Table 2: Drill Hole Survey Data Table 3: Groundwater Data Summary Table 4: Inclinometer Data Summary

APPENDICES

Appendix A – Drill Hole Logs Appendix B – Rock Core Photographs Appendix C – Laboratory Data Appendix D – Groundwater Data Graph Appendix E – Slope Inclinometer Plots

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M22022 US 101 Oregon Coast Highway MP 303 April 2025

1.0 INTRODUCTION

1.1 Project Description

This report presents the results of an engineering geological investigation of a culvert experiencing damage due to slope failure at milepost 303 of US101, Oregon Coast

Highway #009, Key Number 24015. Located about 1.5 miles south of the City of Port

Orford, Oregon, US101 crosses an unnamed creek using a culvert and substantial fill.

Culvert ID D041264 is covered by 53 feet at the inlet and 90 feet at the outlet. This unnamed creek delineates the right lateral (north) margin of the Rocky Creek Landslide.

Realignment of the culvert is being considered using either a traditional open cut or a trenchless method. The general location of the site is shown in Figure 1, Vicinity Map.

Figure 1 – Vicinity Map showing the location of the US 101 MP 303 Culvert Investigation. Image obtained from ODOT’s TransGIS mapping system.

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M22022 US 101 Oregon Coast Highway MP 303 April 2025

1.2 Scope of Work

Geologic investigation of the proposed culvert realignment included review of existing geologic data and a geotechnical subsurface investigation. The scope of work for this investigation included the following tasks:

• Review of available geologic and remote sensing information, including:

o Previous subsurface investigations o Culvert Video Log (2024) o Geologic maps and geologic hazard maps, o Aerial photographs, and o LiDAR data,

• Subsurface investigation included seven (7) drill holes located near the existing damaged culvert. The drill holes ranged in depth from 115.3 to 135.0 feet below the ground surface (bgs) and spanned elevations ranging from 178.4 to -55.1 feet mean sea level.

• Laboratory testing to assess engineering characteristics of the subsurface materials, and

• Geologic analysis of information from the data review, subsurface exploration, and laboratory testing.

2.0 SITE DESCRIPTION

2.1 Background

The existing culvert at MP 303 is not recorded in the ODOT Bridge Data System (BDS);

however, it is recognized as Drainage Facility ID D041264 in ODOT’s TransGIS (2025).

In this system, the culvert is described as a 36-inch corrugated metal pipe (CMP) totaling

302 feet in length, however, a recent video inspection revealed that the diameter of the pipe is 42 inches. Plans from 1946 (Federal Works Agency) indicate that the initial cross-drain built at this site was a concrete box culvert measuring 4 feet in height and 4 feet in width, extending over a length of 318 feet. The box culvert was subsequently lined with the present 42-inch CMP within the past two decades, following the displacement and

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M22022 US 101 Oregon Coast Highway MP 303 April 2025 shearing of certain sections (Oregon Department of Transportation, 2022). The 42-inch

CMP has subsequently experienced displacement and partial shearing, resulting in water escaping the system and saturating the adjacent soils. This problem has led to piping erosion, which in turn has impacted the roadway shoulder and created cracking in the travel lane as well as a significant void in the embankment adjacent to the highway. The present alignment of the culvert is located adjacent to the northern right lateral margin of the Rocky Point Landslide.

This area has undergone multiple investigations via subsurface exploration and site assessments conducted by ODOT staff and personnel from the US Army Corps of

Engineers. These investigations have been the result of roadway and ground displacement that have posed maintenance challenges for over five decades. The key studies concerning the alignment of this culvert comprise two investigations that led to the drilling and instrumentation of three drill holes conducted between 1998 and 2001.

The drill holes and related data were presented in metric units since ODOT utilized the metric system during that period of data collection. Drill hole logs for two of the three holes were located, along with inclinometer displacement plots for all three instruments in the

ODOT files. Additionally, some information was obtained from the US Army Corps of

Engineers report related to the Rocky Creek Coastal Protection Project (2002).

Inconsistencies are present in the naming conventions for the drill holes and instruments.

Therefore, we have compiled a list of the different names associated with these three instruments, along with relevant information for each:

• DH 01-06, also listed as DH-6 o Reported collar elevation 81.0 feet o Installed to a depth of approximately 44.2 meters (145 feet) bgs (below ground surface) o Readings collected from 4/25/01 to 2/21/02, when the instrument reportedly closed to probe at approximately 115 feet bgs on 2/21/02 (33 feet below sea level)

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M22022 US 101 Oregon Coast Highway MP 303 o Last reading prior to tube closing showed approximately 4 millimeters (0.15 inches) of cumulative displacement between 4/25/01 and 10/17/01 at a depth of 115 feet bgs

• DH 98-02, also listed as 99303-02 o Reported collar elevation 28.16 meters (92.4 feet) o Installed to a depth of approximately 24.38 meters (80 feet) bgs o Readings collected from 7/17/98 to 12/2/03, when the instrument reportedly sheared or plugged near its base (approximately 12 feet above sea level) o Last reading prior to tube closing showed minimal displacement at the depth of shearing/plugging, but suggested a shear plane at approximately 47 feet bgs (45 feet above sea level) with approximately 175 millimeters (7 inches) of cumulative displacement measured over the approximately 5 year monitoring period

• DH 98-03, also listed as 99303-03 o Reported collar elevation 24.84 meters (81.5 feet) o Installed to a depth of approximately 24.5 meters (80.4 feet) bgs o Readings collected from 7/17/98 to 8/5/02, no data was found beyond this date, but no explanation was given to why readings would have been discontinued o Readings did not suggest distinct failure planes but instead showed a total cumulative displacement of approximately 25 millimeters (1 inch; combined along the entire depth of the inclinometer casing) during the approximately

4 year monitoring period.

ODOT surveyors reported the collar elevation for DH 01-06 to be based on the NAVD 88 vertical datum. Collar elevations for DH98-02 and DH98-03 were documented in the drill hole logs; however, the associated vertical datum was not specified. The only Drill Hole

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M22022 US 101 Oregon Coast Highway MP 303 April 2025 relevant to the current investigation, DH-02 (99303-02), is included in the site characterization section of this report.

Culvert Investigation

The existing 42-inch CMP was video logged on March 19, 2024, after roadway movement was noticed near the culvert. The logging indicated that the pipe wall and slope conditions within the culvert remained relatively uniform from the inlet to about 180 feet downstream, as measured by the track-mounted inspection camera during the assessment. At a distance of 180 feet from the inlet, the angle of the pipe's slope dropped significantly, revealing signs of corrosion at the bottom, along with a visible hole in the pipe wall.

Between 180 and approximately 215 feet from the inlet the culvert showed signs of vertical shearing or displacement at multiple points. It appears that there is a total cumulative displacement of more than 5 feet within this 35-foot section. The inspection camera could not proceed past 195 feet from the culvert inlet. However, it was observed that daylight was visible reflecting off the pipe wall approximately 20 feet from the camera's stopping point. This indicates that there is likely no significant displacement of the pipe from that location to its outlet.

2.2 Regional Geology

Geologic mapping of the area (McClaughry, et al., 2013) depicts geologic units within the culvert replacement investigation area consisting of artificial (roadway) fill, landslide debris, terrace deposits, and “bedrock” assigned to the Rocky Point Formation of lower

Cretaceous geologic age. Clipped images show the Regional Geologic Map and the

Explanation of Map Units and Symbols in Figures 2A and 2B.

Two landslides are mapped in the vicinity: a larger landslide, locally known as Rocky Point

Landslide, and a smaller unnamed landslide. The terrane above and surrounding the

Rocky Point Landslide is comprised of Indian Creek terrace sediments according to mapping by McClaughry, et al. The Indian Creek terrace is described by Kelsey (1990) as a once broad marine terrace platform that is now highly dissected. The wave-cut platform has a thick 100 to 120-foot sediment cover consisting of offshore to relatively

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M22022 US 101 Oregon Coast Highway MP 303 April 2025 deep nearshore deposits near its outer edge grading upwards to nearshore to beach to eolian dune deposits further east.

Geologic mapping conducted by McClaughry, et al. indicates that there is no exposed bedrock within the immediate vicinity of the site. However, exposures mapped within stream canyons to the north, south and east of the site indicate that the terrace sediments are underlain by a pseudo “bedrock” assigned to the Rocky Point Formation of Lower

Cretaceous geologic age. The Rocky Point Formation is broadly characterized by Ramp, et al. (1977) as consisting of graded sandstone, mudstone, and conglomerate. The formation can be more precisely characterized as a ‘block-in-matrix’ mélange that comprises variably sized blocks of sandstone and conglomerate in a highly sheared mudstone matrix. Formed in the accretionary wedge between the North American and the Juan de Fuca plate, these components are part of the accreted terrane found within the Elk Subterrane, which is a segment of the larger Western Klamath Terrane (Oregon

Department of Geology and Mineral Industries, 2013).

The published mapping and as-built construction plans (Federal Works Agency, 1936) reveal that a substantial and comparatively deep roadway fill prism is situated beneath

US 101. This fill occupies the unnamed stream canyon for which the existing culvert serves as a connecting cross drain. At road level, the fill stretches approximately 800 feet north of the culvert site and extends to around 840 feet south of that point, resulting in a total length of approximately 0.3 miles.

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Figure 2a – Regional Geologic Map: Image modified from the Geologic Map of the Port Orford OE W7.5’ Quadrangle, and Part of the Father Mountain 7.5’ Quadrangle, Curry County, Oregon, Plate 4 of Geologic map of the southwestern Oregon coast between Crook Point and Port Orford, Curry County, Oregon, 2013, by McClaughry, et al. Map shows the project site. Scale as shown.

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2.3 Geomorphology

The MP303 Culvert and fill prism lie at the western margin of the Klamath Mountains physiographic province of Southwest Oregon. The Klamath Mountains are formed from multiple accreted terranes composed of Paleozoic to Mesozoic ocean crust and volcanic

Figure 2b – Explanation of Map Units and Symbols, to accompany Figure 2a, Images modified from the Geologic Map of the Port Orford OE W7.5’ Quadrangle, and Part of the Father Mountain 7.5’ Quadrangle, Curry County, Oregon, Plate 4 of Geologic map of the southwestern Oregon coast between Crook Point and Port Orford, Curry County, Oregon, 2013, by McClaughry, et al.

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M22022 US 101 Oregon Coast Highway MP 303 April 2025 island arcs curving in a northeast to southwest direction with the oldest terranes inland and the youngest toward the Pacific Ocean (Orr and Orr, 2012).

These terranes are distinguished from each other by age, petrography, geochemistry, metamorphism, and fossils. With the eastern advancement of the Juan de Fuca plate, the terranes were rafted toward the western boundary of the North American Continent. As these terranes impacted the North American Continent, they were compressed, folded, faulted, and thrust beneath one another in an accretionary wedge, which formed the

Klamath Mountain province. The result is something similar to a fanned-out deck of playing cards, slid together from the bottom-most card as shown in the Formation of

Southwest Oregon Geology – Figure 3. These terranes were transported northward by thrust faults from sites in California in the early Cretaceous period. The southern Oregon coastline is composed of the youngest of these terranes.

The coastline geology from Port Orford south to Sisters Rock State Park that encompasses the MP303 and fill prism is a chaotic amalgamation of the geologic formations created during the accretion of these terranes in the late Jurassic to early

Cretaceous periods. Tremendous forces within the earth’s crust have altered seafloor sedimentary and volcanic material, hardening some rock through metamorphic recrystallization and weakening others through intense folding, faulting, and shearing.

The result of this process is a “block-in-matrix” (BIM) or mélange environment of mixed and heterogeneous formations of competent blocks embedded in a weaker matrix material. This largely accounts for the differential erosion along the coast (Ernest H. Lund, The Ore Bin Volume 37, No.4 April 1975).

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Figure 3: Formation of Southwest Oregon Geology. Images taken from Orr and Orr sixth edition (2012), pg. 51. Images show the orientation and the various terranes that make up southwest Oregon.

2.4 Geologic Hazard - Landslides

Geologic hazards in the form of landslides are present within the vicinity of the proposed culvert replacement. Two landslides are shown on published geologic reports and a third

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M22022 US 101 Oregon Coast Highway MP 303 April 2025 landslide is within the subject fill prism encompassing a portion of the culvert. These three landslides are discussed below.

Rocky Creek Landslide: The most prominent geologic feature at the site is the Rocky

Point Landslide of Holocene geologic age, which occupies the coastline near the location of the existing culvert south for a distance of about ½ mile and extends ¼ mile east from the coastline at its widest point. This landslide exhibits creeping movement with both rotational and translational characteristics.

Unnamed Landslide: The Oregon Department of Geology and Mineral Industries

(DOGAMI) (State of Oregon HazVu: Statewide Geohazards Viewer, 2021) has identified another landslide located directly north of the Rocky Point Landslide. This landslide may exhibit a comparable failure mechanism, as indicated by its geomorphological characteristics, but does not appear to impact the road fill prism or the adjacent Rocky

Creek Landslide. This landslide is significantly smaller than the Rock Creek Landslide with a width of approximately 300 feet and a length of approximately 200 feet. It is located west of the highway and north of the subject unnamed drainage. Mapping conducted by

McClaughry, et al. categorizes this feature as a significantly younger landslide, dating to the Anthropocene (Recent) geological period, in contrast to the Holocene-age Rocky

Point Landslide.

Road Prism Fill Failure: A crack at the center line of the highway indicates the headscarp of this landslide with the toe terminating at the right lateral limit of the Rocky Creek

Landslide. Dimensions of the landslide measure approximately 150 ft in the direction of movement and approximately 100 feet in width. Deformation and shearing of the culvert provide a good indication of the slide plane elevation at the culvert. Based on the culvert video log described in Section 2.1, deformation of the culvert starts around 180 feet from the inlet, while the culvert shear is situated about 215 feet from the inlet. This suggests that the slide plane elevations are 75 feet and 70 feet, respectively. The southwestern portion of the existing fill prism appears to extend into the northern edge of the Rocky

Point Landslide mass. The cause of failure is interpreted to be related to movement of the

Rocky Point Landslide. Movement of the Rocky Point Landslide is likely removing toe

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M22022 US 101 Oregon Coast Highway MP 303 April 2025 support of the fill prism, causing this secondary failure to develop. Further damage to the road prism has been caused by water escaping the damaged culvert, which has caused erosion and surficial failures in the area directly adjacent to the southbound pavement surface. At the time of this report update, 4/21/2025, the culvert has nearly completely sheared and water has impounded on the inlet side. Blockage and subsequent impoundment began on 3/16/2025. Water has been observed causing piping and erosion within the fill prism near the shear location. An annotated LiDAR Site Image in Figure 4 shows the approximate failure limits of the landslides relative to the roadway fill, and the existing culvert.

Figure 4 – LiDAR Site Image shows limits of landslides, limits of roadway failure expression, approximate roadway fill limits, and approximate location of the damaged culvert. Image obtained from Oregon Department of Geology and Mineral Industries, 2025.

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M22022 US 101 Oregon Coast Highway MP 303 April 2025

3.0 SITE CHARACTERIZATION

Several subsurface investigations have been conducted at or adjacent to the subject location. Two previous investigations led to the drilling and instrumentation of three drill holes conducted between 1998 and 2001. One drill hole from those investigations, drill hole 99303-02, is interpreted to be relevant to the current investigation. It has been included with data from the recent (2024) subsurface investigation. This recent subsurface investigation was conducted to assess subsurface variability at the site and to provide engineering parameters for the geotechnical system design of the proposed repair/replacement culvert. The subsurface investigation included drilling exploration, sampling the earth materials beneath the site, and laboratory testing of selected samples obtained from the drilling.

3.1 Subsurface Investigation

A recent (2024) subsurface exploration included sampling of earth materials at the site.

Sampling was performed between September 16 and October 6, 2024 and included seven (7) drill holes as shown on GA-04 – Geotechnical Data (Site Plan). The drill holes were situated within the fill prism, in the adjacent Rocky Creek landslide, and extending beyond the existing culvert alignment. The proposed culvert alignment and fill prism geometry are shown on GA-05 – Geotechnical Data.

Drilling was accomplished using a CME-850X track-mounted drill rig. Drilling methods consisted of Mud Rotary Advancer (either 4 ⅞ inch or 3 ⅞ inch tricone bit), and HQ3 rock wireline coring with a diamond-impregnated bit. Samples within the fill were collected at five (5)-foot intervals using a two (2)-inch outside diameter split barrel sampler in general conformance with ASTM D1586-11, also known as the Standard Penetration Test (SPT).

The sampler was driven with a 140-pound auto hammer and blow counts were recorded for every six (6)-inch interval of penetration. Samples were logged in according to guidance provided by Chapter 5 of the ODOT Geotechnical Design Manual, Soil and

Rock Classification and Logging (Oregon Department of Transportation, 2024). Additional data, including backfill information and material descriptions, are summarized on logs of

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M22022 US 101 Oregon Coast Highway MP 303 April 2025 the drill holes provided in Appendix A. Photographs of the rock cores are provided in

Appendix B. The drill holes were advanced through fill and “bedrock” to total depths ranging between 32.0 and 37.0-feet below ground surface (bgs). Drill hole depths were determined in consultation with the Region 3 Geotechnical Engineer during drilling based on subsurface conditions A summary of the drill hole data is provided in Table 1 and survey information for each drill hole is listed in Table 2.

Table 1: Drill Hole Summary Drilling Contractor: Various

Drill Hole Number

Date Completed

Maximum Depth

(feet bgs2) Instrumentation

24015-01 9/24/2024 120.1 SI & VWT1

24015-02 9/18/2024 120.0 SI & VWT1

24015-03 9/20/2024 120.3 SI & VWT1

24015-04 10/3/2024 135.0 SI & VWT1

24015-05 9/22/2024 125.1 SI & VWT1

24015-06 10/6/2024 115.3 SI & VWT1

24015-07 10/4/2024 131.5 SI & VWT1

99303-02 7/15/1998 80.0 SI & VWT1

1) Slope Inclinometer and Vibrating Wire Transducers

2) Below Ground Surface

Table 2: Drill Hole Survey Data Drilling Contractor: Various

Drill Hole Number

Collar Elevation1

(feet) Northing2 Easting2

24015-01 149.1 474873.35 329358.42

24015-02 64.90 474797.59 329206.1992

24015-03 71.58 474740.52 329285.80

24015-04 148.12 474798.56 329425.85

24015-05 84.95 474629.28 329366.62

24015-06 137.47 474642.83 329560.85

24015-07 141.68 474616.53 329503.11

99303-02 94.0 474698.81 329357.95

1) NAVD 88 Vertical Datum

2) Oregon Coordinate Reference System (OCRS) – Oregon Coast Zone

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M22022 US 101 Oregon Coast Highway MP 303 April 2025

3.1.1 Laboratory Data

Select rock samples were tested for engineering properties at the ODOT Materials

Laboratory in Salem, Oregon. The following tests were conducted:

• Resistivity

• Sulfate Determination

• Chloride Determination

• pH

• Moisture Content

• Particle Size

• Atterberg Limits

• Unconfined Compressive Strength of selected rock core samples

A laboratory summary table is included with the laboratory test results in Appendix C.

Select laboratory test results are also included on the Drill Logs in Appendix A.

3.1.2 Groundwater

Two Vibrating Wire Transducers (VWTs) were installed in each drill hole following drilling to measure subsurface pore water pressure. Instrumentation was grouted in place following OWRD regulations. Subsequent monitoring was performed by Region 3

Geology personnel using a Geokon on-site data logger and manual data collection.

Transducer elevation, maximum and minimum groundwater elevation, and range of reading dates are summarized in Tables 3A and 3B. Groundwater data graphs for each

VWT are included in Appendix D.

At the time of this report update, 4/21/2025, the culvert was nearly completely sheared and water has impounded at the inlet. Blockage caused by the shearing and subsequent impoundment began on 3/16/2025. Groundwater data in Table 3A summarizes maximum and minimum groundwater elevations through 3/15/2025 and Table 3B summarizes the maximum and minimum groundwater elevation for dates following 3/15/2025. Data

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M22022 US 101 Oregon Coast Highway MP 303 April 2025 following 3/15/2025 may present artificially elevated groundwater elevations not representative of normal seasonal conditions.

Table 3A: Groundwater Data Summary (through 3/15/2025)

Drill Hole Number

Transducer Elevation

(feet)

Groundwater Maximum Elevation

(feet)

Groundwater Minimum Elevation

(feet)

Data Date Range

24015-01 (Shallow) 115.1 118.73 116.2 10/8/2024 – 1/14/2025

24015-01 (Deep) 74.1 105.7 100.7 10/8/2024 – 3/15/2025

24015-02 (Shallow) 39.9 43.92 40.07 10/8/2024 – 3/15/2025

24015-02 (Deep) 9.9 13.00 12.13 10/8/2024 – 3/15/2025

24015-03 (Shallow) 62.6 73.11 69.38 10/8/2024 - 3/15/2025

24015-03 (Deep) 42.6 47.50 42.18 10/8/2024 – 3/15/2025

24015-04 (Shallow) 112.1 111.26 109.68 10/8/2024 – 3/15/2025

24015-04 (Deep) 92.1 102.04 95.03 10/8/2024 – 3/15/2025

24015-05 (Shallow) 45.0 56.39 47.23 10/8/2024 – 3/15/2025

24015-05 (Deep) 10.0 51.35

46.65 10/8/2024 – 3/15/2025

24015-06 (Shallow) 78.5 86.99 84.58 10/8/2024 – 3/15/2025

24015-06 (Deep) 27.5 85.06 79.90

10/8/2024 – 3/15/2025

24015-07 (Shallow) 96.7 98.57 98.57 10/8/2024

24015-07 (Deep) 71.7 77.57 73.95 10/8/2024 – 3/15/2025

99303-02 Not Available Not Available Not Available Not Available

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Table 3B: Groundwater Data Summary (3/16/2025 – 4/22/2025)

Drill Hole Number

Transducer Elevation

(feet)

Groundwater Maximum Elevation

(feet)

Groundwater Minimum Elevation

(feet)

Data Date Range

24015-01 (Shallow) 115.1 116.19 116.19 4/22/2025

24015-01 (Deep) 74.1 104.53 104.53 4/22/2025

24015-02 (Shallow) 39.9 47.57 42.17 3/16/25 – 4/22/25

24015-02 (Deep) 9.9 12.98 11.64 3/16/25 - 4/22/25

24015-03 (Shallow) 62.6 74.99 69.2 3/16/25 – 4/22/25

24015-03 (Deep) 42.6 45.87 42.80 3/16/25 – 4/22/25

24015-04 (Shallow) 112.1 111.41 110.13 3/16/25 – 4/22/25

24015-04 (Deep) 92.1 106.17 95.63 3/16/25 – 4/22/25

24015-05 (Shallow) 45.0 69.83 52.24 3/16/25 – 4/22/25

24015-05 (Deep) 10.0 62.63 49.83 3/16/25 – 4/22/25

24015-06 (Shallow) 78.5 113.73 85.57 3/16/25 – 4/22/25

24015-06 (Deep) 27.5 81.06 80.28 3/16/25 – 4/22/25

24015-07 (Shallow) 96.7 101.57 100.31 4/9/2025 - 4/22/2025

24015-07 (Deep) 71.7 77.43 74.26 3/16/25 – 4/22/25

99303-02 Not Available Not Available Not Available Not Available

Pore water pressure measurements obtained from the VWTs during the periods outlined in Table 3A reveal an average maximum groundwater gradient of approximately 0.31 in the southwest direction. This generally conforms to the expected flow toward the unnamed stream valley at the location of the existing culvert. A review of the regional rainfall data indicates a higher-than-normal rainfall year, culminating in approximately 16 more inches of rain in March 2025 than normal. Table 3A represents the period prior to the storm event of March 16, 2025. Following the storm event of 3/16/2025 and resulting water impoundment, the gradient represented by data in Table 3B decreased to an average of about 0.26, due primarily to an increase in the overall groundwater elevation.

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M22022 US 101 Oregon Coast Highway MP 303 April 2025

The overall groundwater in the area of the existing culvert inlet increased up to about 27 feet during the impoundment.

An analysis of the highest recorded groundwater level in relation to the site's topographic contours indicates a possible intersection of the groundwater with the ground surface in a limited area located just north of the current culvert outlet. A lower piezometric surface detected from pore pressure readings of the deeper VWTs generally has the same gradient patterns as the upper maximum groundwater level with some close convergence of the higher and lower gradients at or near the location of the stream valley prior to the storm event of March 16, 2025.

3.1.3 Slope Movement

Slope inclinometers were installed in each of the seven drill holes. Data plots from these as well as the data from drill hole 99303-02 are provided in Appendix E. The deepest observed slide plane is summarized for the dates given in the inclinometer summary on

Table 4 below.

Table 4: Inclinometer Summary Data

Drill Hole Number

Initial Reading

Date

Most Recent

Reading Date

Collar Elevation1

(feet)

Approximate Depth to Deepest

Slide Plane (feet bgs)

Resulting Approximate Slide Plane

Elevation, (feet)

24015-01 10/7/2024 3/25/2025 149.1 N/A N/A

24015-02 9/26/2024 1/30/2025** 64.90 10 (sheared)

24015-03 9/26/2024 3/25/2025 71.58 74 -5

24015-04 10/5/2024 3/25/2025 148.12 45 105

24015-05 9/26/2024 1/14/2025** 84.95 90 (sheared)

-5

24015-06 10/7/2024 2/25/2025 137.47 N/A N/A

24015-07 (B) 12/5/2024 3/25/2025 141.68 27* 115

99303-02 9/2/1998 12/2/2003 92.4 50-80 (sheared)

40-12

*Not a distinct slide plane, ** Sheared as of 3/25/2025.

Data collection issues resulted in a corrected plot of 24015-07, titled 24015-07 (B). Data from 24015-07 (B) is not a distinct slide plane and appears to show more ‘drift’ rather than a distinct slide plane. This is thought to be caused by the installation of the slope

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M22022 US 101 Oregon Coast Highway MP 303 April 2025 inclinometer at the margin of the failure where the slide plane is interpreted to be near vertical.

3.1.4 Material Units

Earth materials identified within the drill holes at the US 101 MP 303 culvert replacement site are classified as roadway fill, marine terrace deposits, landslide debris, and mélange

“bedrock”. For convenience, the various earth materials have been grouped into numbered soil and rock units within these four geologic classifications based on their engineering similarities. These units match the descriptions provided on the drill hole logs, which present more detailed soil descriptions within each unit. Subsurface information is provided on GA-05, GA06, and GA-07.

• Unit 1 – Roadway Pavement Section:

o Asphalt – Unit 1A: A2 to 7-foot-thick section of asphaltic concrete roadway pavement (Asphalt – Unit 1A) was measured at drill holes 24015-04 and

24015-07. Drill holes 24015-04 and 24015-07 are located within the southbound lane of Highway 101, all other drill holes are located outside of this Section.

o Access Road Fill – Unit 1B: The fill in this unit is derived from the cut bank slopes for a drill access road. Fill was observed at the surface to approximately

10 feet bgs in drill hole 24015-02. Unit 1B consisted of Sandy SILT, that was wet and very loose, with non-plastic fines and organic material (roots).

o Base Aggregate Fill – Unit 1C: Base aggregate was observed immediately below the pavement section to approximately 13 feet bgs in drill holes 24015-

04, 24015-07 and from the surface to approximately 9.5 feet bgs in drill hole

24015-06. Unit 1C consisted of angular GRAVEL to Clayey Silty Sandy

GRAVEL to Gravelly SAND, that was damp to wet, loose to dense, with non-plastic to low plasticity fines.

o Fill, Derived from Marine Terrace Deposits– Unit 1D: Marine terrace fill was observed in drill holes 24015-04, 24015-06 and 24015-07 from approximately

Engineering Geology Report Page 20 of 27

10 to 46 feet bgs. Unit 1D consisted of Sandy SILT to Clayey, Silty SAND that was wet to dry, medium stiff to stiff and loose to medium dense, with non-plastic to low plasticity fines and fine to coarse grained sand with trace sub-rounded gravels and organics.

o Fill, Derived from Marine Terrace Deposits – Unit 1E: Marine terrace fill was observed in drill holes 24015-04, 24015-06 and 24015-07 at various intervals bgs. Unit 1E consisted of Clayey SAND to Sandy SILT that was wet to dry, medium stiff to stiff and loose to medium dense, with non-plastic to low plasticity fines and fine to coarse grained sand with trace sub-rounded gravels and organics.

o Wood – Unit 1F: Fresh wood was observed in drill hole 24015-06 at approximately 55 feet bgs.

• Unit 2 – Marine Terrace Deposits: Marine terrace materials were observed in drill holes 24015-01 and 24015-02 from the surface to various intervals bgs.

o Marine Terrace Deposits – Unit 2A: Marine terrace material was observed in drill hole 24015-01 from the surface to approximately 7.5 bgs. Unit 2A consisted of CLAY with trace Sand that was moist and stiff with high plasticity fines and coarse grained sand.

o Marine Terrace Deposits – Unit 2B: Marine terrace material was observed in drill hole 24015-01 immediately below Unit 2A. Unit 2B consisted of Sandy

SILT that was damp to moist and soft to medium stiff with non-plastic to low plasticity fines and fine grained sand.

o Marine Terrace Deposits – Unit 2C: Marine terrace material was observed in drill holes 24015-01 and 24015-02 immediately below Unit 2B and Unit 1B respectively. Unit 2C consisted of Clayey to Silty SAND that was wet to moist and loose to dense with non-plastic to low plasticity fines and fine grained sand with trace coarse rounded gravel and organics.

Engineering Geology Report Page 21 of 27

• Unit 3 – Landslide Debris: Landslide materials derived from marine terraces and mélange were observed in drill holes 24015-03, 24015-05 and 24015-07 from the surface to various intervals bgs.

o Landslide Debris, Derived from Marine Terrace Deposit – Unit 3A:

Landslide debris derived from marine terrace material was observed in drill hole

24015-03 from the surface to approximately 9.5 feet bgs. Unit 3A consisted of marine terrace material that remold to Sandy CLAY to Clayey SAND to Silty

SAND that was moist and soft to medium stiff to loose with low plasticity fines and organics.

o Landslide Debris, Derived from Mélange – Unit 3B: Landslide debris derived from mélange material was observed in drill hole 24015-03, 24015-05 and

24015-07 from the surface to various intervals bgs. Unit 3B consisted of mélange that remolds to Clayey, Sandy GRAVEL to Clayey, Silty, Sandy

GRAVEL to Clayey, Silty SAND with some Gravel to Sandy CLAY that was wet to dry and medium dense to very dense and hard with non-plastic to low plasticity fines and weak Siltstone/Mudstone.

• Unit 4 – Mélange: Mélange materials were observed in all the drill holes underlying the fill, marine terrace deposits and landslide deposits. Mélange is generally described as a siltstone/mudstone matrix with inclusions of more resistant blocks

(block in matrix).

o Where disturbed by drilling and sampling methods, the material is described with a wide range of properties. As such, Unit 4 consisted of a wide range of materials from Clayey SAND to Silty GRAVEL, wet to dry, medium dense to very dense and very hard, with non-plastic to medium plasticity, with moderate cemented Siltstone/Mudstone.

o Where encountered, the blocks exhibited slight to moderate weathering and displayed a rock strength ranging from extremely weak to weak (R0 to R2).

Core was obtained in 24015-02 and one sample was attempted but fell apart before testing could be completed.

Engineering Geology Report Page 22 of 27

M22022 US 101 Oregon Coast Highway MP 303 April 2025

4.0 SUMMARY and CONCLUSIONS

The following items summarize the findings and conclusions determined from review of existing geologic data and a geotechnical subsurface investigation related to culvert replacement at US101 MP303 Culvert. This review included published geologic reports, historical documents, aerial photography, LiDAR imagery, subsurface investigations, laboratory testing, and geologic analysis. The summary and conclusions are as follows:

1. Subsurface geological materials in the vicinity of the proposed alignment for the replacement culvert consist of roadway fill and mélange.

a. Roadway Fill: The material used for the roadway fill was derived mainly from marine terrace deposits, consisting of sandy silt and silty to clayey sand (Units

1D & 1E). This material exhibited non-plastic to low plasticity characteristics and ranged from medium stiff to hard, or from loose to medium dense. Grain size ranged from fine to coarse sand with some gravel.

Wood fragments (Unit 1F) were encountered at the interface between the roadway fill and mélange in drill hole 24015-06 at approximately 55 feet bgs.

Wood fragments at this location were approximately 2-2.5 feet thick. Wood fragments are possible at the base of the fill, especially near the former stream thalweg.

b. Mélange: Mélange materials located immediately below the roadway fill consist primarily of siltstone blocks within a sheared mudstone matrix. (Unit

4). The matrix materials exhibit non-plastic to medium plasticity, varying from medium density to very dense or extremely hard, with a degree of moderate cementation present. The siltstone blocks exhibited slight to moderate weathering and displayed a rock strength ranging from extremely weak to weak (R0 to R2). Mud rotary methods were used to advance all holes, except

24015-02 and the previously drilled 99303-02. Of the 12 feet advanced with

HQ3-wireline coring in 24015-02, only one (1) foot of low-discontinuity core was collected. The rest was rubble or washed from the sample.

Engineering Geology Report Page 23 of 27

2. Analysis and interpretation of geological contacts from the subsurface exploration indicate that the proposed alignment for the replacement culvert will be fully situated within the fill, mélange, and landslide debris materials previously described (Unit 1D, Unit 1E, Unit 3A, Unit 3B & Unit 4). These materials, as described, should present no specific constraints to trenchless type excavation.

It is important to note that the mélange may include oversized rock material that was not detected in any of the drill holes during this investigation, and this should be considered when assessing the impact on excavation.

3. Landslides.

a. The analysis of the Rocky Point Landslide failure plane, based on its surface manifestation, slope inclinometer readings, and landslide debris identified in the drill holes, suggests that the planned alignment for the replacement culvert is situated adjacent to the larger movement of the Rocky Point

Landslide. This is predicated on the continued creep-type movement of the landslide and does not account for more catastrophic movement, which could cause instability within the materials to the north of the landslide.

b. Surface manifestation and slope inclinometer readings indicate that the proposed culvert alignment is situated very close to or within the active Road

Prism Fill Failure. Movement of the Rocky Point Landslide is interpreted to be the cause of this failure as it relates to removal of support at the toe of the fill slope. Additional mitigation measures should be considered, such as horizontal drains and/or structural slope stabilization to protect the culvert for the long-term.

4. Maximum groundwater levels in the summer months when construction is likely to occur are unknown. Projection of maximum groundwater gradient for winter months, prior to the storm event of March 16, 2025, indicates that nearly the entire length of proposed culvert will be below the groundwater table. Additional

Engineering Geology Report Page 24 of 27 groundwater level readings would be required to determine the groundwater response for an entire year.

5.0 LIMITATIONS

The analyses presented in this report and its appendices are based on the data obtained from geologic mapping, research, site visits, and the subsurface exploration performed at the locations indicated on GA-04, Geotechnical Data (Site Plan). Subsurface exploration has provided detailed information at specific locations in the project area however, variations in soil and rock conditions may exist in other areas. Data shown in the logs of the drill holes applies only to that drill hole on the date indicated and is not intended to be conclusive as to the character of any material or conditions beyond the drill hole location.

Any interpretation or evaluation of this report by individuals outside of the Oregon

Department of Transportation is done at the sole risk of the individuals.

The nature and extent of any variations in subsurface materials or conditions may not become evident until construction. If subsurface conditions differ from those identified in the drill hole logs, the Geotechnical Engineer and Project Engineering Geologist should be advised at once so that they can observe, review, and reconsider the design recommendations.

Engineering Geology Report Page 25 of 27

M22022 US 101 Oregon Coast Highway MP 303 April 2025

6.0 REFERENCES

Federal Works Agency, Public Roads Administration, 1937, Plans for the Proposed Project No. 10-D1, Grading, Surfacing & Bit Surfacing, Oregon Coast Highway, Route No. 10 – 31.4 Miles Class 1, Port Orford to Gold Beach, Forest Highway System, Siskiyou National Forest, Curry County, Oregon, sheet 8 of 20.

Federal Works Agency, Public Roads Administration, Division No. 8, 1946, Plans for the Proposed Project No. 10-D1, E Clearing & Box Culverts, Oregon Coast Highway, Route No. 10 – 31.4 Miles Class 1, Port Orford to Gold Beach, Forest Highway System, Siskiyou National Forest, Curry County, Oregon, sheet 6 of 12.

Kelsey, H.M., 1990, Late Quaternary Deformation of Marine Terraces on the Cascadia Subduction Zone Near Cape Blanco, Oregon, Tectonics, Vol. 9, No. 5, pages 983-1014, October 1990.

McClaughry, J.D., Ma, Lina, Jones, C.B., Mickelson, K.A., and Wiley, T.J., 2013, Geologic map of the southwestern Oregon coast between Crook Point and Port Orford, Curry County, Oregon, Oregon Department of Geology and Mineral Industries, Open-File Report O-2013-21

Oregon Department of Geology and Mineral Industries, 2013 (areas along the southern Oregon coast), Geologic Map of Oregon, interactive map https://www.oregon.gov/ dogami/geologicmap/pages/index.aspx.

Oregon Department of Geology and Mineral Industries, 2025, DOGAMI Lidar Viewer, https://gis.dogami.oregon.gov/maps/lidarviewer/.

Oregon Department of Transportation, Geographic Information Services (GIS) Unit, 2024, ODOT TransGIS, Version 4.10.0.

Oregon Department of Transportation, 2024, Geotechnical Design Manual, Chapter 5, Soil and Rock Classification and Logging.

Oregon Department of Transportation, 2022, US101: MP 303.0 Culvert Repair Project, Oregon Coast Highway, Curry County, June 2022, Plan/Set Number 55V-090.

Orr, E.L. and Orr, W.N., 2012, Oregon Geology: Corvallis, Oregon, Oregon State University Press, 304 p.

Ramp, L., Schlicker, H.G., and Gray, J.J., 1977, Geology, mineral resources, and rock material of Curry County, Oregon Department of Geology and Mineral Industries, Bulletin 93, Map Scale: 1:125,000.

https://www.oregon.gov/dogami/geologicmap/pages/index.aspx https://www.oregon.gov/dogami/geologicmap/pages/index.aspx https://gis.dogami.oregon.gov/maps/lidarviewer/

Engineering Geology Report Page 26 of 27

M22022 US 101 Oregon Coast Highway MP 303 April 2025

State of Oregon, Department of Geology and Mineral Industries, 2021, Oregon HazVu:

Statewide Geohazards Viewer, https://gis.dogami.oregon.gov/maps/hazvu/, accessed August 20, 2024.

US Army Corps of Engineers, Portland District, 2002, Rocky Creek Coastal Protection Project, (Port Orford, Oregon).

Engineering Geology Report Page 27 of 27

M22022 US 101 Oregon Coast Highway MP 303

7.0 SIGNATURES

POR: Colin E. Cunningham, C.E.G.

Engineering Geologist

QC Reviewed by: Jill DeKoekkoek, C.E.G.

Senior Region Engineering Geologist

Figures

40'

45'

50'

55'

60'

65'

70'

75'

80'

80'

85'

85'

90'

95'

100'

105'

5'

110'

115'

5'

120'

125'

5'

130'

0'

135'

5'

140'

140'

140'

0'

5'

145'

145'

150'

150'

150'

150'

155'

155'

155'

160'

0'

165'

170'

175'

0'

A"

A"

A"

A"

A"

A"

A"

A"

57V-111

OF TRANSPORTATION

OREGON DEPARTMENT

Checker:Drafter:

Designer:

SHEET NO.

Reviewer:

AVAILABLE UPON REQUEST

FINAL ELECTRONIC DOCUMENT

CURRY COUNTY

OREGON COAST HIGHWAY

CULVERT REPAIR PROJECT

US101: MP 303.06 EMERGENCY

F O

T N

E

MTRAPED

N

O G

E R

O

N

OI

T

ATROPS

N A

R T

Brad Hayes

N/A

Tomsen Reed

Dan Faas

GEOTECHNICAL DATA

over 20 ft. depth

HDPE Culvert, Solid-Wall

48" Diameter

Existing culvert99303-02

24015-

24015-03

24015-01

24015-04

24015-07

24015-06

PLAN

Minor Contour Interval =1'

Major Contour Interval = 5'

1"=60'Scale:

24015-05

= Drill hole

LEGEND

A A

= Extg. guardrail

= Edge. of pavement

= Edge. of gravel

= Cross-Section Line

= Edge. of berm

= Storm Pipe

GA04

A

B

B

A

Jill DeKoekkoekColin Cunningham

Dan Faas

GT_M22022_gtpl_01.dgn :: GA004 5/13/2025 4:04:35 PM hwye35z

57V-111

OREGON

RE

GI

ST

ERE

D PROFESSIONALEN

GINEER

101431PE

RENEWS: 12-31-2025

NES

M

O

T DEER

M

A R . 14, 2

OF TRANSPORTATION

OREGON DEPARTMENT

Checker:Drafter:

Designer:

SHEET NO.

Reviewer:

AVAILABLE UPON REQUEST

FINAL ELECTRONIC DOCUMENT

CURRY COUNTY

OREGON COAST HIGHWAY

CULVERT REPAIR PROJECT

US101: MP 303.06 EMERGENCY

F O

T N

E

MTRAPED

N

O G

E R

O

N

OI

T

ATROPS

N A

R T

Brad Hayes

N/A

Tomsen Reed

Dan Faas

GEOTECHNICAL DATA

CROSS-SECTION A-A

1"=30'Scale:

= Core sample

R.Q.D.

C-1

50/1st #"

Uncorrected N value

= Standard Penetration Test -

= Drill hole

= Rock Quality Designation

LEGEND

= Standard Penetration Test refusal length

= Maximum Groundwater Elevation = Date of Maximum Ground Water LevelX/X/XXXX

00.00'

= Maximum Groundwater

UNIT DESCRIPTION

ASPHALT(ASPHALT-Unit 1A) coarse gravel. (Aggregate Fill-Unit 1C) plasticity, damp to wet, loose to dense, angular, GC-SP, gray to black to brown, nonplastic to low

SAND, GP-GC-SP, gray to black to gravelly SAND, GP-

GRAVEL to Clayey Silty Sandy GRAVEL to gravelly

Deposits, Unit 1E) native fill. (FILL, derived from Marine Terrace subrounded gravel, organics / rootlets, stratified to medium dense, fine to coarse grained sand, trace plasticity, wet to dry, medium stiff to stiff and loose yellow to orange to brown to gray, nonplastic to low

Sandy SILT to Clayey or Silty SAND, SC-SM-ML, from Marine Terrace Deposits-Unit 1E) trace weathered sedimentary gravel (FILL, derived wet to dry, medium dense and very stiff to hard, and red brown mottled, low plasticity to nonplastic, gravel, SM-SC-ML, brown to blue to black to gray

Silty to clayey SAND to Sandy SILT with trace to some from Mélange-Unit 3B) extreamly to weak (R0-R2) (Landslide Debris, derived gray to dark gray, slightly to moderatly weathered, dense and very hard; and SILTSTONE/MUDSTONE, to low plasticity, wet to dry, medium dense to very gravel, GC-GM-SC-SM-CL, gray to green, nonplastic

SAND with some gravel to Sandy CLAY with some

Clayey SAND with some to trace gravel to Clayey Silty to Clayey Sandy GRAVEL to Silty Sandy GRAVEL to some sand to GRAVEL with some sand and trace clay

Sandy GRAVEL with some clay to Clayey GRAVEL with

LANDSLIDE DEBRIS derived from Mélange remolds to mudstone(Mélange-Unit 4) extreamly weak to weak (R0-R2), slickensided moderately weathered to slightly weathered, MUDSTONE/SILTSTONE, gray to dark gray, dense and very hard, moderate cementation; and medium plasticity, dry to wet, very dense to medium

SP-ML-GM-GC-GP-GC, brown to gray, nonplastic to

Sandy GRAVEL to with some sand and clay, SC-SM-

Sandy GRAVEL to Sandy Clayey GRAVEL to Clayey Silty

GRAVEL with some clay to Gravelly SILT to Clayey

Sandy GRAVEL to Sandy Silty GRAVEL to Sandy

SAND to Sandy SILT with trace gravel to SILT to Silty

SAND to Silty Gravely SAND to Clayey Silty Gravelly

Gravelly SAND with some clay to Clayey Gravelly trace gravel, Silty Clayey SAND with trace gravel to with some gravel to Clayey Silty SAND with some to

MELANGE remolds to Clayey SAND to Clayey SAND

0+00

% Rec.

R0-R2

R0-R2

R0-R2

R0-R2

R.Q.D.Core Hardness

C1

C2

C3

C4

1' except as noted.

reported for an interval of

D1586-18, N values are

2. In accordance with ASTM the Engineering Geology report.

is available on the drill logs in

More detailed subsurface data terminology from the drill logs.

information and/or revision in drawing are a consolidation of

1. Geotechnical data shown on this

GENERAL NOTES

2+00

99303-02 surface ground

Extg.

50/6

50 1st 5

50/3

50 1st 5

50 1st 3

50 1st 3

50/5

50 1st 5

50 1st 3

50 1st 6

50 1st 6

50/5

50 1st 3

50 1st 5

50 1st 5

50 1st 2

50 1st 3

50/0

50/0

11.6ft

1/11/25

111.260' MSL

24015-04

10/3/2024

148.1ft

75/11

50 1st 5

50 1st 5

50 1st 5

50/4

50 1st 5

50 1st 5

50/2

50/2

50 1st 4

50 1st 2

50 1st 4

50 1st 1

50 1st 1

-40.1ft

1/4/25

56.393' MSL

24015-05

9/22/24

85.0ft

1+00

-20

-10

-40

-30 proposed 48" diameter culvert

Approximate centerline of

-20

-10

-40

-30

C-1

C-2

C-3

C-4

12.4ft

Offset Right 31'

99303-02

07/15/98

92.4ft

2+90 diameter culvert of proposed 48"

Approximate springline

GA05

Jill DekoekkoekColin Cunningham

Tracey Parker

GT_M22022_gtpl_01.dgn :: GA005 - Section A-A 5/13/2025 4:04:36 PM hwye35z

57V-111

OREGON

RE

GI

ST

ERE

D PROFESSIONALEN

GINEER

101431PE

RENEWS: 12-31-2025

NES

M

O

T DEER

M

A R . 14, 2

OF TRANSPORTATION

OREGON DEPARTMENT

Checker:Drafter:

Designer:

SHEET NO.

Reviewer:

AVAILABLE UPON REQUEST

FINAL ELECTRONIC DOCUMENT

CURRY COUNTY

OREGON COAST HIGHWAY

CULVERT REPAIR PROJECT

US101: MP 303.06 EMERGENCY

F O

T N

E

MTRAPED

N

O G

E R

O

N

OI

T

ATROPS

N A

R T

Brad Hayes

N/A

Tomsen Reed

Dan Faas

GEOTECHNICAL DATA

CROSS-SECTION B-B

1"=30'Scale:

= Core sample

R.Q.D.

C-1

50/1st #"

Uncorrected N value

= Standard Penetration Test -

= Drill hole

= Rock Quality Designation

LEGEND

length

= Standard Penetration Test refusal

= Maximum Groundwater Elevation

Level

= Date of Maximum Ground Water X/X/XXXX

00.00'

= Maximum Groundwater

0+00

1' except as noted.

reported for an interval of

D1586-18, N values are

2. In accordance with ASTM the Engineering Geology report.

is available on the drill logs in

More detailed subsurface data terminology from the drill logs.

information and/or revision in drawing are a consolidation of

1. Geotechnical data shown on this

GENERAL NOTES

2+00

Extg. ground surface

50/6

50 1st 5

50/3

50 1st 5

50 1st 3

50 1st 3

50/5

50 1st 5

50 1st 3

50 1st 6

50 1st 6

50/5

50 1st 3

50 1st 5

50 1st 5

50 1st 2

50 1st 3

50/0

50/0

11.6ft

1/11/25

111.26' MSL

24015-04

10/3/2024

148.1ft

1+00 proposed 48" diameter culvert

Approximate centerline of proposed 48" diameter culvert

Approximate springline of

3+00

50 1st 5

50 1st 2

50 1st 1

50 1st 4

50 1st 5

50 1st 3

50 1st 2

50 1st 5

50 1st 3

50 1st 4

50 1st 2

50 1st 3

50 1st 2

50 1st 1

50 1st 1 58.3ft

1/4/25

118.70' MSL

24015-01 178.4ft

E 329358.4ft

N 474873.4ft

50/11

50 1st 6

50 1st 3

50 1st 6

50 1st 3

86/11

50 1st 5

50 1st 5

50 1st 3

50 1st 2

50 1st 6

50 1st 1

50 1st 4

10.2ft

10/8/24

98.57' MSL

24015-07

10/4/2024

141.7ft

E 329503.1ft

N 474616.5ft

UNIT DESCRIPTION

ASPHALT(ASPHALT-Unit 1A) coarse gravel. (Aggregate Fill-Unit 1C) plasticity, damp to wet, loose to dense, angular, GP-GC-SP, gray to black to brown, nonplastic to low

SAND, GP-GC-SP, gray to black to gravelly SAND, GRAVEL to Clayey Silty Sandy GRAVEL to gravelly derived from Marine Terrace Deposits, Unit 1D) organics / rootlets, stratified native fill.