19126788-R-Rev0-RPA GNP Lk McDonald Rpt-04172020.pdf

REPORT

Geotechnical Investigation and HDD Engineering

Recommendations Lake McDonald, Glacier National Park

WFL Geotechnical Report No. 03-20

Submitted to:

Jeff Key Robert Peccia & Associates Inc.

PO Box 5653

Helena, MT 59604

Submitted by:

Golder Associates Inc.

18300 NE Union Hill Road, Suite 200, Redmond, Washington, USA 98052

+1 425 883-0777

19126788

April 2020

April 2020 19126788 i

Distribution List Electronic Copy

Jeff Key - Robert Peccia & Associates Inc.

ii

Table of Contents

1.0 INTRODUCTION

1.1 Project Description

1.2 Scope of Work

1.3 Project Alignment

2.0 PROJECT SETTING

2.1 Regional Geologic Setting

2.2 Project Stratigraphy and Groundwater (HDD Crossing 1, 2, 3, 5, 18, and 19)

2.2.1 Crossing 1: STA 20+50 to STA 24+50

2.2.2 Crossing 2: STA 29+25 to STA 33+00

2.2.3 Crossing 3: STA 33+50 to STA 39+00

2.2.4 Crossing 5: STA 70+50 to STA 73+00

2.2.5 Crossing 18: STA 267+75 to STA 269+75

2.2.6 Crossing 19: STA 290+00 to STA 296+00

3.0 FIELD INVESTIGATIONS

3.1 Borehole Locations

3.1.1 Lake McDonald Lift Station

3.1.2 Horizontal Directional Drilling Locations

3.1.3 Subgrade Investigation

3.1.4 Kelly Camp Bridge

4.0 LABORATORY TESTING

5.0 ENGINEERING ANALYSIS FOR LAKE MCDONALD LIFT STATION

5.1 General

5.2 Seismic Design

5.2.1 Site Class

5.2.2 Ground Motion Parameters

5.2.3 Liquefaction Potential

iii

5.2.4 Seismic Surcharge on Walls

5.3 Shallow Foundation Design Criteria

5.4 Permanent Wall Design Criteria

5.5 Lift Station Construction Considerations

5.5.1 Temporary Cut Slopes

5.5.2 Temporary Shoring Recommendations

5.5.2.1 Lagging

5.5.3 Foundation Construction Recommendations

5.5.4 Site Drainage and Dewatering

5.5.5 Site Preparation and Topsoil Removal

5.5.6 Use of onsite soils

5.5.7 Structural Fill placement and Compaction

5.5.7.1 Materials

5.5.7.2 Placement

6.0 HDD INSTALLATION FEASIBILITY AND ANALYSIS

6.1 Proposed HDD Layouts

6.2 Pull Tension Prediction

6.3 Potential for Drilling Fluid Loss

6.3.1 General

6.3.2 Inadvertent Drilling Fluid Return Evaluation

6.4 HDD Installation Recommendations

6.4.1 General

6.4.2 Hole Stability

6.4.3 Ground Settlement

6.4.4 Additional Recommendations

7.0 CLOSING

8.0 REFERENCES

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TABLES

Table 1: Summary of Boreholes

Table 2: Design Ground Motion Parameters

Table 3: Geotechnical Design Parameters for Temporary Cantilever Shoring

Table 4: Evaluation of Ground Conditions

Table 5: Proposed Crossing Greater Than 150 Feet in Length

No table of figures entr ies found .

FIGURES

Figure 1: Project Overview Map

Figure 2 Through Figure 8: Subsurface Exploration Locations

Figure 9: Lateral Earth Pressure Diagram: Temporary Cantilever Shoring

Figure 10: Lateral Earth Pressure Diagram: Surcharges Acting on Temporary and Permanent Walls

APPENDICES

APPENDIX A

Record of Boreholes

APPENDIX B

Laboratory Testing

APPENDIX C

Evaluation of Installation Loads v

ACRONYMS AND ABBREVIATIONS

bgs below ground surface

BP before present

CDF controlled density fill

FHWA Federal Highway Administration

GTSR Going-to-the-Sun-Road

HDD Horizontal Directionally Drilled

HDPE High-Density Polyethylene

IBC International Building Code ksf kips per square foot

MADFP maximum allowable drilling fluid pressure

NPS National Park Service pcf pounds per cubic foot psf pounds per square foot

SPT Standard Penetration Test

USGS United States Geological Survey

WFLHD Western Federal Lands Highway Division

1.0 INTRODUCTION

1.1 Project Description

The Federal Highway Administration (FHWA) and the National Park Service (NPS) intend to replace utilities in the corridor between the Lake McDonald Lodge and Apgar Village within Glacier National Park. The proposed project comprises an 11-mile section of Sanitary Sewer, Phone, and Electric line replacement, with roadway reconditioning. The extent of the project (from north to south) is from the Lake McDonald Lodge pump house, along the Lake McDonald spur road to the Lake McDonald Lodge access road, from the intersection of the access road and the Going-to-the-Sun-Road (GTSR) south, and the intersection of GTSR and Apgar Road (SE corner of

Lake McDonald) to the Apgar lift station. Because of the subsurface investigation work associated with this project, it was also requested that Golder collect bridge borings for the Kelly Camp Bridge located (upper

McDonald Creek Bridge), samples to be submitted directly to the Western Federal Lands Highway Division

(WFLHD) of the FHWA.

WFLHD has selected Robert Peccia & Associates (RPA) to provide engineering services for the project. RPA has contracted with Golder Associates Inc. (Golder) to conduct the geotechnical investigation and provide initial comments on geotechnical engineering issues.

1.2 Scope of Work

The scope of work for the 2019 Glacier National Park geotechnical investigation included:

Prepare a geotechnical exploration plan and submit to FHWA and NPS for compliance review and concurrence.

Exploration Staking and Locates – locate boreholes and stake or mark locations in the field. Notify utility companies of proposed ground disturbance via MT No-dig.

Conduct a field investigation and testing of materials, in support of roadway reconditioning, Horizontal

Directionally Drilled (HDD) sewer installations, and Lake McDonald Lift Station. Investigate subsurface conditions at the Kelly Camp Bridge and provide samples to WFLHD.

HDD sewer Feasibility and Design Support of nominal 8-inch High-Density Polyethylene (HDPE) sewer pipe.

Prepare a preliminary geotechnical memorandum.

Following the review of the preliminary geotechnical memorandum, prepare a Geotechnical Report (This document).

1.3 Project Alignment

This report is based on the proposed Force Main alignment and stationing provided by RPA on September 12, 2019, referred to as the alignment. Both borings in support of the roadway and HDD crossings reference this alignment. The proposed alignment ranges from Station 00+00 (Begin project) to Station 466+76 (end project).

The elevations values in the report are based on the surface modeled provided by RPA also on September 12, 2019. Borehole locations were not surveyed in and should be considered approximate, +/-30 feet.

2.0 PROJECT SETTING

The project is in northeastern Flathead County Montana, along the eastern shoreline of Lake McDonald within

Glacier National Park. The topography of the area is characterized by mountainous terrain to the south east of the alignment and a glacially scoured linear valley to the northwest, occupied by Lake McDonald. The alignment generally follows the GTSR along the eastern side of the lake. Water from Lake McDonald Creek flows into Lake

McDonald on the northeastern end of the lake and exits at Apgar Village on the southwest end of the lake. The project location is shown on Figure 1.

2.1 Regional Geologic Setting

The project site (which includes the western portion of the GTSR adjacent to Lake McDonald, the North Lake

McDonald Road bridge area, an area adjacent to the existing sanitary sewer pump station next to the Lake

McDonald Lodge, and the northeastern section of Apgar Loop) is located within the greater McDonald River/Lake

McDonald valley. The valley is a northeast to southwest trending valley in the western slopes of the Rocky

Mountains of northwestern Montana, specifically within the boundaries of Glacier National Park.

As shown in the geologic map of Glacier National Park (Whipple 1992), a limited portion of the project area is underlain by scattered surficial and near surface bedrock. The majority of the project area however is underlain by varied, glacially derived or post glacially derived sediments, deposited directly by a large valley occupying, alpine glacier or in streams, lakes, and mass wasting areas associated with the glacier. This large alpine glacier fed a nearby continental ice sheet to the immediate west. The valley glacier occupied the project area from approximately 20,000 years before present (BP) to approximately 12,000 years BP.

The bedrock outcrops and near surface bedrock encountered in the project area consist of two main rock types.

The first and oldest bedrock is the Prichard Formation. The second, slightly younger bedrock is the Helena

Formation.

The Prichard Formation is a weakly metamorphosed, sedimentary based Siltite (Siltstone) which was observed in the two borings (BH19-61K and BH19-62K) drilled near the North McDonald Road bridge and in nearby outcrops, north of the bridge, along the banks of the McDonald River. The Prichard Formation is part of the Meso-

Proterozoic of the Pre-Cambrian and is interpreted to have been deposited between 1.7 and 1.33 billion years BP.

The Helena Formation is a weakly metamorphosed, sedimentary based Limestone which was observed in borings

BH19-33, BH19-34, BH19-35, BH19-36, BH19-38, and BH19-58; in road cuts; and adjacent outcrops along the

GTSR near the southwest end of lake McDonald. The Helena Formation is also part of the Meso-Proterozoic of the Pre-Cambrian and is interpreted to have been deposited between 1.5 and 1.6 billion years BP.

2.2 Project Stratigraphy and Groundwater (HDD Crossing 1, 2, 3, 5, 18, and 19)

Geologic units encountered in Golder borings associated with the six longer proposed directional drilling areas included fill, fluvial deposits, glacial till, lacustrine deposits, and debris flow deposits. General descriptions of these units are presented below. Figures 2 through 8 show the approximate locations of the borings. Summary boring logs are included in Appendix A.

2.2.1 Crossing 1: STA 20+50 to STA 24+50

Fill – The fill unit refers to soils placed by human activity such as those placed during road construction. The two borings (BH19-03 and BH19-04) encountered fill just below the road’s pavement. The fill appeared to extend from approximately 0.8 feet to 10 feet below the ground surface (bgs) in both borings. The fill material consisted of gravel and sand with generally low fines content and scattered cobbles. The density of the fill material was generally medium dense based on N-values derived from Standard Penetration Tests (SPTs) and observations of the drill action. The N-value is an indication of the relative density of cohesionless soils and the consistency of cohesive soils.

Fluvial Deposit – Fluvial deposits (including older glaciofluvial and younger recent fluvial deposits) are derived from sediment deposited by glacial ice melt, rivers, or streams, and usually consist of mixtures of stratified sand, gravel, and cobbles. Materials interpreted as fluvial deposits were encountered in borings BH19-03 and BH19-04 below the fill. The fluvial deposits in these two borings extended from approximately 10.7 feet to their termination depths of 31.5 feet bgs. In general, the fluvial deposit was medium dense to very dense, based on N-values derived from SPTs and observations of the drill action. The fluvial deposits encountered in these two borings consisted of non-stratified to weakly stratified sand containing trace to little amounts of gravel and trace amounts of silt.

Groundwater – Groundwater was encountered below approximately 16.0 feet while drilling BH19-03 and below approximately 18.4 feet while drilling BH19-04. When groundwater was suspected, the drilling operation was halted for approximately 10 to 15 minutes and the water level was then measured within the open bottom, hollow stem auger. No wells or piezometers were installed, and these reported groundwater depths are based on the limited time allowed for the water to enter the auger. Fluctuations in groundwater depths are expected with seasonal changes in the area wide groundwater table, as affected by rainfall and snowmelt.

2.2.2 Crossing 2: STA 29+25 to STA 33+00

Fill – The fill unit refers to soils placed by human activity such as those placed during road construction. The two borings (BH19-05 and BH19-06) encountered fill just below the road’s pavement. The fill appeared to extend from approximately 0.8 feet to 7 feet bgs in BH19-05 and from 0.8 to 5 feet bgs in BH19-06. The fill material consisted of sand and gravel with generally low fines content and scattered cobbles. The density of the fill material was generally medium dense to dense based on N-values derived from SPTs and observations of the drill action.

Fluvial Deposit – Fluvial deposits (including older glaciofluvial and younger recent fluvial deposits) are derived from sediment deposited by glacial ice melt, rivers, or streams, and usually consist of mixtures of stratified sand, gravel and cobbles. Materials interpreted as fluvial deposits were encountered in borings BH19-05 and BH19-06 below the fill. The fluvial deposits extended from approximately 7.0 to 31.0 feet bgs in BH19-05 and from 5.0 to

31.5 feet bgs in BH19-06. Both borings were terminated in the fluvial deposit. In general, the fluvial deposit was medium dense to very dense, based on N-values derived from SPTs and observations of the drill action. The fluvial deposits encountered in these two borings consisted of non-stratified to weakly stratified sand containing trace to little amounts of gravel and trace amounts of silt.

Groundwater – Groundwater was encountered below approximately 14.25 feet while drilling BH19-05 and below approximately 16.8 feet while drilling BH19-06. When groundwater was suspected, the drilling operation was halted for approximately 10 to 15 minutes and the water level was then measured within the open bottom, hollow stem auger. No wells or piezometers were installed, and these reported groundwater depths are based on the limited time allowed for the water to enter the auger. Fluctuations in groundwater depths are expected with seasonal changes in the area wide groundwater table, as affected by rainfall and snowmelt.

2.2.3 Crossing 3: STA 33+50 to STA 39+00

Fill – The fill unit refers to soils placed by human activity such as those placed during road construction. The two borings (BH19-07 and BH19-08) encountered fill just below the road’s pavement. The fill appeared to extend from approximately 0.8 feet to 7 bgs in both borings. The fill material consisted of gravel and sand with generally low fines content and scattered cobbles. The density of the fill material was generally medium dense based on

N-values derived from SPTs and observations of the drill action.

Fluvial Deposit – Fluvial deposits (including older glaciofluvial and younger recent fluvial deposits) are derived from sediment deposited by glacial ice melt, rivers, or streams, and usually consist of mixtures of stratified sand, gravel and cobbles. Materials interpreted as fluvial deposits were encountered in boring BH19-07 below the fill.

The fluvial deposits in this boring extended from approximately 7 feet to the boring’s termination depth of 31.5 feet bgs. In general, the fluvial deposit was medium dense to dense, based on N-values derived from SPTs and observations of the drill action. The fluvial deposit encountered in this boring consisted of non-stratified to weakly stratified sand and gravel containing trace to little amounts of silt.

Debris Flow Deposit – This debris flow deposit appears to be derived from sediment deposited by high energy mass wasting possibly related to the withdrawal of adjacent supporting glacial ice and consisted of a variable mixture of a non-stratified clay matrix supporting variable and somewhat random amounts of sand, gravel, cobbles, and boulders. Material interpreted as a debris flow deposit was encountered in boring BH19-08 below the fill. The debris flow deposit in this boring extended from approximately 7 feet to the boring’s termination depth of 31.5 feet bgs. In general, the debris flow deposit was stiff to hard, based on N-values derived from SPTs and observations of the drill action.

Groundwater – Groundwater was encountered approximately below 19.0 feet while drilling BH19-07. Limited amounts of perched groundwater were encountered while drilling BH19-08 between approximately 4.5 and

7.0 feet bgs. When groundwater was suspected, the drilling operation was halted for approximately 10 to

15 minutes and the water level was then measured within the open bottom, hollow stem auger. No wells or piezometers were installed, and these reported groundwater depths are based on the limited time allowed for the water to enter the auger. Fluctuations in groundwater depths are expected with seasonal changes in the area wide groundwater table, as affected by rainfall and snowmelt.

2.2.4 Crossing 5: STA 70+50 to STA 73+00

Fill – The fill unit refers to soils placed by human activity such as those placed during road construction. The two borings (BH19-10 and BH19-11) encountered fill just below the road’s pavement. The fill appeared to extend from approximately 0.8 feet to 9 feet bgs in boring BH19-10 and from 0.5 to 5.5 feet bgs boring BH19-11. The fill material consisted of gravel and sand with generally low fines content and scattered cobbles. The density of the fill material was generally medium dense based on N-values derived from SPTs and observations of the drill action.

Fluvial Deposit – Fluvial deposits (including older glaciofluvial and younger recent fluvial deposits) are derived from sediment deposited by glacial ice melt, rivers, or streams, and usually consist of mixtures of stratified sand, gravel and cobbles. Materials interpreted as a fluvial deposit were encountered in boring BH19-10 below a lacustrine deposit from approximately 29.0 to 31.5 feet bgs. Materials interpreted as a fluvial deposit were encountered in boring BH19-11 below the fill. The fluvial deposit in boring BH19-11 extended from approximately

5.5 feet to approximately 7.5 bgs. In general, the fluvial deposit encountered in BH19-11 was dense, based on

N-values derived from SPTs and observations of the drill action. The fluvial deposit encountered in boring

BH19-11 consisted of non-stratified to weakly stratified sand containing some gravel and trace amounts of silt.

The fluvial deposit encountered in BH19-10 was a medium dense silt containing some clay and trace amounts of gravel and sand.

Lacustrine Deposit – Lacustrine deposits (including older glaciolacustrine and younger, recent lacustrine deposits) are derived from sediment deposited in fresh water, deep, low energy glacially or otherwise impounded water in kettles, bogs, ponds, and lakes and usually consist of clay and silt and may contain limited amounts of organics such as peat or peat like materials. Materials interpreted as glaciolacustrine deposits were encountered in both boring BH19-10 and BH19-11. The glaciolacustrine encountered in BH19-10 was located below the fill at approximately 9 feet bgs and extended down to approximately 29 feet bgs at the top of the fluvial deposit. The glaciolacustrine deposit in BH19-11 was encountered between the debris flow at approximately 9.5 feet bgs and extended down to the top of a boulder sitting atop the glacial till at approximately 14.5 feet bgs. In general, the encountered lacustrine deposit was stiff to very stiff, based on N-values derived from SPTs and observations of the drill action. The lacustrine deposit encountered in these two borings consisted of non-stratified clay containing variable though generally low amounts of disseminated silt, sand, gravel. No cobbles or boulders were encountered in these two borings they but could exist in this deposit in the form of iceberg rafted drop stones. No organic material was observed.

Debris Flow Deposit – This debris flow deposit appears to be derived from sediment deposited by high energy mass wasting possibly related to the withdrawal of adjacent supporting glacial ice and consisted of a variable mixture of a non-stratified silt matrix supporting variable and somewhat random amounts of sand, gravel and cobbles. Material interpreted as a debris flow deposit was encountered in boring BH19-11 below the fluvial deposit. The debris flow deposit in this boring extended from approximately 7.5 feet to 9.5 feet bgs. In general, the debris flow deposit was medium dense, based on N-values derived from SPTs and observations of the drill action.

Glacial Till – Glacial till deposits (including both overridden, higher blow count “lodgement” and non-overridden

“ablation” till) are derived from sediment deposited directly by glacial ice and usually consist of variable mixtures of non-stratified clay, silt, sand, gravel, cobbles, and boulders. Materials interpreted as a glacial lodgement till were encountered in boring BH19-11 below a lacustrine deposit, from approximately 15.1 feet to the boring’s termination at 30.2 feet bgs. The glacial lodgement till encountered in BH19-11 was generally very dense, based on N-values derived from SPTs and observations of the drill action. The glacial lodgement till encountered in boring BH19-11 consisted of non-stratified sand containing some silt, little amounts of gravel and trace amounts of scattered cobbles and boulders.

Groundwater – No groundwater was encountered while drilling borings BH19-10 and BH19-11.

2.2.5 Crossing 18: STA 267+75 to STA 269+75

Fill – The fill unit refers to soils placed by human activity such as those placed during road construction. The two borings (BH19-24 and BH19-25) encountered fill just below the road’s pavement. The fill appeared to extend from approximately 0.8 feet to 7 feet bgs in boring BH19-24 and from 0.9 to 5.0 feet bgs boring BH19-25. The fill material in BH19-24 consisted of silty sand generally low amounts of gravel over silty clay containing low amounts of sand and gravel. The density of the fill material in BH19-24 was generally medium dense in the upper sandy portion and medium stiff in the lower clay portion based on N-values derived from SPTs and observations of the drill action.

Fluvial Deposit – Fluvial deposits (including older glaciofluvial and younger recent fluvial deposits) are derived from sediment deposited by glacial ice melt, rivers, or streams, and usually consist of mixtures of stratified sand, gravel and cobbles. Materials interpreted as a fluvial deposit were encountered in boring BH19-24 below the fill from approximately 7.0 feet bgs to the boring’s termination depth at 31.5 feet bgs. Materials interpreted as a fluvial deposit were encountered in boring BH19-25 below a glacial till deposit at approximately 12 feet bgs and extended to BH19-25’s termination depth of 31.5 feet bgs. In general, the fluvial deposit encountered in BH19-24 and BH19-25 was loose to medium dense, based on N-values derived from SPTs and observations of the drill action. The fluvial deposit encountered in these two borings consisted of non-stratified to weakly stratified variable sand and gravel containing trace amounts of silt and trace amounts of scattered cobbles.

Glacial Till – Glacial till deposits (including both overridden, higher blow count “lodgement” and non-overridden

“ablation” till) are derived from sediment deposited directly by glacial ice and usually consist of variable mixtures of non-stratified clay, silt, sand, gravel, cobbles, and boulders. Materials interpreted as a glacial ablation till were encountered in boring BH19-25 below the fill at approximately 5 feet bgs and extended down to approximately

12 feet bgs where the fluvial deposit was encountered. In general, the glacial ablation till encountered in BH19-25 was loose to medium, based on N-values derived from SPTs and observations of the drill action. The glacial ablation till encountered in boring BH19-25 consisted of non-stratified sandy silt and silt sand containing trace amounts of gravel.

Groundwater – Groundwater was encountered below approximately 14.6 feet bgs while drilling BH19-24 and

14.3 feet bgs while drilling BH19-25. When groundwater was suspected, the drilling operation was halted for approximately 10 to 15 minutes and the water level was then measured within the open bottom, hollow stem auger. No wells or piezometers were installed, and these reported groundwater depths are based on the limited time allowed for the water to enter the auger. Fluctuations in groundwater depths are expected with seasonal changes in the area wide groundwater table, as affected by rainfall and snowmelt.

2.2.6 Crossing 19: STA 290+00 to STA 296+00

Fill – The fill unit refers to soils placed by human activity such as those placed during road construction. The two borings (BH19-26 and BH19-27) encountered fill just below the road’s pavement. The fill appeared to extend from approximately 0.7 feet to 7.0 feet bgs in both borings. The fill material consisted of silty sand in BH19-26 and low fines content sands and gravels in BH19-27. The density of the fill material was generally medium dense to dense based on N-values derived from SPTs and observations of the drill action.

Fluvial Deposit – Fluvial deposits (including older glaciofluvial and younger recent fluvial deposits) are derived from sediment deposited by glacial ice melt, rivers, or streams, and usually consist of mixtures of stratified sand, gravel and cobbles. Materials interpreted as fluvial deposits were encountered in borings BH19-26 and BH19-27 below the fill. The fluvial deposits in these two borings extended from approximately 7.0 feet bgs to their termination depths of 31.5 feet bgs. In general, the fluvial deposit was medium dense to very dense, based on

N-values derived from SPTs and observations of the drill action. The fluvial deposits encountered in these two borings consisted of non-stratified to weakly stratified sand containing little amounts of gravel and trace amounts of silt.

Groundwater – Groundwater was encountered below approximately 18.8 feet bgs while drilling BH19-26 and below approximately 18.6 feet bgs while drilling BH19-27. When ground water was suspected, the drilling operation was halted for approximately 10 to 15 minutes and the water level was then measured within the open bottom, hollow stem auger. No wells or piezometers were installed, and these reported groundwater depths are based on the limited time allowed for the water to enter the auger. Fluctuations in groundwater depths are expected with seasonal changes in the area wide groundwater table, as affected by rainfall and snowmelt.

3.0 FIELD INVESTIGATIONS

Prior to the start of field work, Golder prepared a preliminary schedule for the exploration work, exploration locations, anticipated testing, and list of subcontractors working on the project. A draft exploration plan was submitted on September 13, 2019 and later revised to address comments made during a site meeting with RPA and WFLHD on September 17, 2019. A final version of the exploration plan was submitted on September 26, 2019 (Golder 2019).

Kyle Obermiller of Golder visited the project site on September 16, 2019 to review the HDD Crossings and to mark proposed borehole locations in support of roadway reconditioning, HDD crossings, and the Kelly Camp

Bridge. Facility operators were given notice of our intent to drill through the UDIG public utility locator service immediately following the boring field markings. Private locator services were also employed at the Kelly Camp

Bridge and Lake McDonald Lodge lift station, out of an abundance of caution, to verify our proposed boring locations were clear of utilities.

Drilling of the 62 borings occurred between October 1, 2019 and November 16, 2019. Borings were advanced using a CME-75 truck mounted drill rig, operated by Haz-Tech Drilling, Inc. (Haztech). The exploration was conducted under the full-time observation of Golder Geologist, John Coleman. The Kelly Camp Bridge borings were advanced using hollow-stem drilling to approximately 30 feet bgs and then casing advancer thereafter. All other borings were conducted using hollow-stem drilling methods.

Sampling

Drilling and sampling were performed in general accordance with Golder Technical Procedure TP-1.2-5, Drilling, Sampling, and Logging of Soils (Golder 1996). Pertinent information was recorded on field logs and included;

sample depths, stratigraphy, groundwater occurrence, and engineering characteristics. SPTs were generally performed at 2.5-foot intervals to 30 feet bgs and then on 5-foot intervals thereafter using a standard 2-inch diameter split-spoon sampler advanced in accordance with ASTM D-1586 which consisted of a 140-pound auto-hammer falling a distance of 30 inches for each strike. The number of hammer blows for each 6-inches of penetration was recorded. The standard penetration resistance (N) is the sum of the number of blows required for the final 12 inches of sampler penetration. The N-value is an indication of the relative density of cohesionless soils and the consistency of cohesive soils. Representative samples were collected from the split-spoon sampler and placed into plastic bags that were sealed to reduce moisture loss and transported to a local laboratory for storage.

Select soil samples were selected for additional index testing. Grab samples from the subgrade borings were collected by carefully loosening roadway base materials with the auger and placing all base material in a sample bag. Grab samples and SPT samples collected were described in general accordance with ASTM Standard

D2488.

Digital gINT borehole records were later created from the field forms using the WFLHD’s electronic gINT library.

Note - The stratigraphic contacts shown on the borehole logs represent the approximate boundaries between soil units; actual transitions may be more gradual.

Backfill

The boreholes were abandoned at the target depth or when bedrock was encountered, except at the Kelly Camp

Bridge borings where the bedrock was cored 10 feet. All samples [soil and rock] collected from the Kelly Camp

Bridge borings were sent to the Materials Lab at Federal Highway Division, attention Evan Garich.

The lift station borings (BH19-01 and BH19-02) were backfilled with bentonite chips to just below the ground surface, then cuttings added to blend with the ground surface. Boreholes in support of the HDD crossings

(BH19-03 to BH19-38) were backfilled with a cement-bentonite grout mixture to within a few feet the surface.

Cuttings where then added and topped with a few inches of cold patch asphalt and hand tamped. The roadway boreholes (BH19-39 to BH19-60) were backfilled with bentonite chips to within a few feet the surface. Cuttings where then added and topped with a few inches of cold patch asphalt and hand tamped. In both cases the cuttings were compacted by pressing the auger down with the truck. Bridge boring BH19-61K and BH19-62K were backfilled with a cement-bentonite grout mixture to within a few feet the surface, BH19-61K then had cuttings added and blend with the ground surface. Cuttings added to borehole BH19-62K were compacted by pressing the auger down with the truck, then topped with a few inches of cold patch asphalt and hand tamped.

3.1 Borehole Locations

The proposed borings in support of the Lake McDonald lift station, HDD crossings, and roadway reconditioning were prescribed in statement of work DTFH7015D00007, Task Order No. 69056719F000134. At the time of this report, the borehole locations had not been surveyed and their locations are considered approximate. Table 1 provides a summary of the boring locations, depth explored, date drilled, and depth of groundwater.

3.1.1 Lake McDonald Lift Station

The lift station borings (BH19-01 and BH19-02) are in support of a new sanitary sewer lift station at the Lake

McDonald Lodge. The new lift station will be roughly in the same location as the existing lift station. Borehole

BH19-01 was drilled north of the Northwest corner of the existing structure in a gravel walkway/road that leads from the lake to the lodge. During auger removal and backfill, a void extending from 1.5 to 4.5 feet bgs and 2 to

3 feet wide was observed in the sidewall about 1.5 feet bgs. The sidewalls of the void contained boulders up to

3 feet and some brick fragments. It did not appear to be a result of drilling (no surface subsidence, nor was water/sewage observed) but rather developed during placement of the fill material. BH19-02 was drilled south of the existing structure along the gravel access road.

SPT soil samples were generally collected at 2.5 intervals to 15 feet bgs then on 5 feet intervals thereafter to a depth of 40 feet.

3.1.2 Horizontal Directional Drilling Locations

Borings BH19-03 through BH19-38 were in support of the 30 proposed HDD crossings. Depending on the length of the crossing, exploratory borings were drilled at the beginning and the end of the crossing. Shorter crossings had a single boring located roughly at the midpoint. SPT soil samples were generally collected on 2.5-foot intervals to 15 feet bgs then on 5 feet intervals thereafter to a depth of 30 feet.

3.1.3 Subgrade Investigation

Borings BH19-39 through BH19-60 were completed in support of the roadway reconditioning. The borings were carried out in a manner that avoided contaminating materials of different layers in the first five feet. This was achieved by slowly advancing a 15-inch auger and laying out the spoils for inspection. Distinct strata, where encountered, were classified and bagged together. SPT samples were then collected on 2.5-foot intervals to a depth of 15 feet bgs.

3.1.4 Kelly Camp Bridge

As prescribed in the Task Order, the Kelly Camp Bridge borings were to be located 20 feet +/- north and 20 feet

+/- back from edge of riverbank on top of slope. However, the eastern location was not accessible due to vegetation and topography. An old cut bank parallels the road at this location and therefore the boring was drilled from the existing westbound lane, on the east side of the bridge.

In general, SPT samples were collected on 2.5-foot intervals to a depth of 30 feet bgs then on 5-foot intervals to

150 feet bgs or bedrock. When bedrock was encountered, the rock was cored 10 feet. All soil samples and rock core collected were shipped directly to WFLHD, no testing was performed by Golder.

Table 1: Summary of Boreholes

Boring Depth Date Latitude Longitude Depth to

Groundwater

BH19-01 41.5 10/29/2019 N048° 37' 01.68" W113° 52' 48.15" 12

BH19-02 41.5 10/29/2019 N048° 37' 01.63" W113° 52' 48.35" 17

BH19-03 31.5 10/2/2019 N048° 36' 44.36" W113° 52' 51.52" 16

BH19-04 31.5 10/2/2019 N048° 36' 40.89" W113° 52' 54.14" 18.4

BH19-05 31 10/3/2019 N048° 36' 36.26" W113° 52' 54.86" 14.5

BH19-06 31.5 10/3/2019 N048° 36' 32.73" W113° 52' 56.54" 16.8

BH19-07 31.5 10/4/2019 N048° 36' 32.25" W113° 52' 56.72" 19

BH19-08 31.5 10/4/2019 N048° 36' 27.82" W113° 53' 01.22" 4.5

BH19-09 16.5 10/5/2019 N048° 36' 21.73" W113° 53' 04.56" --

BH19-10 31.5 10/6/2019 N048° 35' 58.88" W113° 53' 15.68" --

BH19-11 30.2 10/7/2019 N048° 35' 56.62" W113° 53' 17.12" --

BH19-12 30.4 10/7/2019 N048° 35' 35.52" W113° 53' 26.65" --

BH19-13 30.5 10/8/2019 N048° 35' 32.48" W113° 53' 28.13" --

BH19-14 31 10/9/2019 N048° 35' 18.25" W113° 53' 44.05" 19.6

BH19-15 30.3 10/9/2019 N048° 35' 15.17" W113° 53' 47.14" 6.8

BH19-16 31.5 10/10/2019 N048° 34' 44.87" W113° 54' 15.47" --

BH19-17 31.5 10/25/2019 N048° 34' 34.75" W113° 54' 30.89" --

BH19-18 31.5 10/26/2019 N048° 34' 33.89" W113° 54' 33.96" --

BH19-19 31.5 10/27/2019 N048° 34' 18.74" W113° 54' 50.74" --

BH19-20 31.5 10/27/2019 N048° 34' 16.89" W113° 54' 56.39" --

BH19-21 31.4 10/27/2019 N048° 34' 15.31" W113° 54' 59.71" --

BH19-22 31.5 11/7/2019 N048° 34' 06.91" W113° 55' 09.85" --

BH19-23 31.5 11/7/2019 N048° 33' 55.73" W113° 55' 29.15" --

BH19-24 31.5 11/8/2019 N048° 33' 36.34" W113° 56' 13.19" 14.6

BH19-25 31.5 11/8/2019 N048° 33' 34.82" W113° 56' 15.08" 14.3

BH19-26 31.5 11/9/2019 N048° 33' 18.38" W113° 56' 29.86" 18.8

BH19-27 31.5 11/9/2019 N048° 33' 12.63" W113° 56' 31.02" 18.6

BH19-28 31.5 11/10/2019 N048° 33' 02.17" W113° 56' 46.50" 15

Boring Depth Date Latitude Longitude Depth to

Groundwater

BH19-29 31.5 11/14/2019 N048° 32' 53.27" W113° 57' 03.26" --

BH19-30 31.5 11/14/2019 N048° 32' 51.03" W113° 57' 07.97" --

BH19-31 31.5 11/15/2019 N048° 32' 23.46" W113° 57' 51.68" 23.7

BH19-32 31.5 11/15/2019 N048° 32' 21.03" W113° 57' 55.09" 24

BH19-33 15.2 11/16/2019 N048° 32' 06.33" W113° 58' 14.66" --

BH19-34 18 11/16/2019 N048° 32' 01.34" W113° 58' 20.10" --

BH19-35 17.7 11/16/2019 N048° 31' 53.94" W113° 58' 27.36" --

BH19-36 11.6 11/16/2019 N048° 31' 51.44" W113° 58' 28.93" --

BH19-37 31.5 11/12/2019 N048° 31' 46.40" W113° 58' 32.31" 19

BH19-38 7.6 11/12/2019 N048° 31' 42.85" W113° 58' 34.86" --

BH19-39 16.5 10/1/2019 N048° 36' 44.70" W113° 52' 50.98" 14.1

BH19-40 16.5 10/4/2019 N048° 36' 26.92" W113° 53' 01.82" --

BH19-41 16.5 10/5/2019 N048° 36' 08.83" W113° 53' 11.53" --

BH19-42 16.5 10/7/2019 N048° 35' 50.30" W113° 53' 21.03" --

BH19-43 16.5 10/8/2019 N048° 35' 31.44" W113° 53' 28.57" 5

BH19-44 16.5 10/9/2019 N048° 35' 15.96" W113° 53' 46.24" 9.6

BH19-45 15.9 10/25/2019 N048° 34' 59.08" W113° 54' 01.49" --

BH19-46 16.5 10/25/2019 N048° 34' 42.34" W113° 54' 16.92" 12.3

BH19-47 16.5 10/26/2109 N048° 34' 29.32" W113° 54' 37.03" 10

BH19-48 16.5 10/26/2019 N048° 34' 16.30" W113° 54' 57.58" --

BH19-49 15.9 11/7/2019 N048° 34' 01.48" W113° 55' 16.20" --

BH19-50 16.5 11/7/2019 N048° 33' 48.16" W113° 55' 37.32" --

BH19-51 16.5 11/8/2019 N048° 33' 41.43" W113° 56' 04.68" --

BH19-52 16.5 11/8/2019 N048° 33' 25.48" W113° 56' 20.08" --

BH19-53 16.5 11/9/2019 N048° 33' 09.11" W113° 56' 33.22" --

BH19-54 16.5 11/14/2019 N048° 32' 56.22" W113° 56' 55.54" 11.7

BH19-55 16.5 11/14/2019 N048° 32' 45.81" W113° 57' 20.51" --

BH19-56 16.5 11/15/2019 N048° 32' 30.73" W113° 57' 38.82" --

BH19-57 16.5 11/15/2019 N048° 32' 16.25" W113° 57' 57.33" 4.7

BH19-58 7.3 11/16/2019 N048° 32' 02.84" W113° 58' 18.42" --

BH19-59 16.5 11/12/2019 N048° 31' 45.71" W113° 58' 32.68" --

BH19-60 16.5 11/10/2019 N048° 31' 41.50" W113° 58' 57.76" 12.2

BH19-61K 154.9 10/22/2019 N048° 38' 07.93" W113° 52' 02.50" 18.2

BH19-62K 126 11/5/2019 N048° 38' 06.60" W113° 51' 59.26" 16.1

4.0 LABORATORY TESTING

Soil samples collected in the field by Golder personnel were submitted to Alpine Geotechnical located in Kalispell, Montana for testing with some samples sent to additional laboratories. Laboratory tests were conducted to characterize engineering index properties of the site soils. Results of the laboratory testing were provided to

Golder, who then updated borehole logs with the data. Testing consisted of the following:

Gradation Testing (AASHTO T 11/T 27)

Moisture Content (AASHTO T 265)

Atterberg Limits (AASHTO T 89/T 90)

Aggregate Durability Index (AASHTO T 210)

Resistance to Degradation (AASHTO T 96)

Organic Content (MT 412-04)

A summary of the sieve, moisture content, Atterberg, and organic content tests can be found in Appendix B

Table B.1, results of the laboratory testing are also provided in Appendix B.

5.0 ENGINEERING ANALYSIS FOR LAKE MCDONALD LIFT STATION

5.1 General

This section presents recommendations for design of the proposed Lake McDonald Lift Station structures. It is our understanding from the preliminary utility plans that the lift structure will consist of an above ground structure housing two pumps, with a fully buried wet well structure below. The above ground structure will be approximately

24 by 16 feet, while the wet well will be 14 by 14 feet wide, extend to a depth of 15.5 feet bgs and will be located partially beneath the above ground structure. Where the above ground structure is not located directly over the wet well, it will be supported by strip footings along the wall perimeter and a slab on grade floor. The wet well will be supported by a mat slab foundation.

5.2 Seismic Design

The 2018 International Building Code (IBC) seismic design section provides information to be used as the basis for seismic design of structures.

5.2.1 Site Class

Section 1613 of the 2018 IBC provides information on earthquake loads and site ground motion needed for liquefaction potential assessment. Based on the IBC design criteria, sites are classified according to the average soil profile properties in the first 100 feet bgs. The deepest borehole in the proposed Lake McDonald Lift Station site was advanced to a depth of 41.5 feet bgs, but the properties below 41.5 feet bgs are expected to be similar or denser than the soils at the bottom depths of explorations. The site should be classified as Site Class D site based on the nearby borehole corrected N-values (assumed 80% efficiency).

5.2.2 Ground Motion Parameters

Ground motion parameters used for design per ASCE 7-16 include the site coefficient and mapped spectral accelerations, provided in the United States Geological Survey (USGS) Seismic Design Maps. The interpolated probabilistic ground motion values in percent gravity were obtained from the ASCE 7 online hazard tool based on the USGS US Seismic Design Maps (https://asce7hazardtool.online/). The results shown in Table 2 were obtained for latitude 48.617 and longitude -113.880 (a point located near the center of the site) assuming an occupancy category of III and a default Site Class D (see Section 11.4.3 of ASCE 7-16).

Table 2: Design Ground Motion Parameters

Ground Motion Parameter Acceleration (g)

Peak Ground Acceleration (PGA) 0.212

Modified PGA (PGAM) 0.295

Short (0.2 second) Spectral Response (SS) 0.477

1.0 Second Spectral Response (S1) 0.151

Modified Short Spectral Response (SMS) 0.676

Modified 1.0 Second Spectral Response (SM1) 0.347

Design Short Spectral Response (SDS) 0.451

Design 1.0 Second Spectral Response (SD1) 0.232

Note: Modified and design spectral response values provided for default Site Class D soil condition (see Section 11.4.3 of

ASCE 7-16).

5.2.3 Liquefaction Potential

Loose soils below the water table could liquefy during seismic shaking. Based on the soil and groundwater conditions encountered in BH19-01, we estimate between 1 to 2 inches of liquefaction induced settlement at the lift station under the design earthquake.

5.2.4 Seismic Surcharge on Walls

A seismic surcharge should be added to the earth pressures on below grade basement walls. Golder recommends a uniform lateral seismic surcharge equal to 6H (6 times H [service level]) in pounds per square foot

(psf), where H is the wall height in feet for walls design based on at-rest earth pressure conditions.

5.3 Shallow Foundation Design Criteria

The foundations for the proposed lift station structures may consist of shallow isolated and continuous spread footings. Based on the conceptual plans for the project, the lift station will be supported by a mat foundation at the base of the lift station wet well and a continuous strip footing below the walls of the above ground structure, where the walls are not over the below ground vault. The estimated elevation of the bottom of the planned spread footing for the lift wet well is at approximately elevation 3,149.67 feet, with a footing thickness of 18 inches. The bottom of the strip footing beneath the walls is at approximately elevation 3,164.37 feet.

Based on explorations in the area, the footing elevations are expected to be in fill consisting of loose to medium dense gravel or loose to medium dense native sands. The groundwater table is expected to be at approximately elevation 3,155 feet from measurements in BH19-01, however it should be noted that these explorations took place in the fall when water levels are generally lowest. We anticipate that this is a minimum groundwater elevation.

The subgrade soil encountered should be over-excavated and replaced in accordance with recommendations contained in Section 5.5. If the lift station foundations are placed on properly placed and compacted structural fill significant long-term settlement is not expected at the site.

Conventional shallow isolated or continuous foundations placed on compacted structural fill should be designed based on the following recommendations. Please refer to Section 5.5 for construction recommendations pertaining to spread footings. The foundation recommendations are based on our current understanding of the conceptual plans (sheets E.1 and E.2). If the configuration of the lift station changes, Golder should be notified to review the updated plans and revise the foundation recommendations accordingly.

Design isolated footings for a maximum allowable bearing pressure of 4 kips per square foot (ksf) assuming a minimum footing width of 3 feet and a maximum footing width of 6 feet.

Design mat foundation or footing equal to the footprint of the lift station for a maximum allowable bearing pressure of 2 ksf to limit settlement to less than 1 inch.

A subgrade modulus of 200 pounds per cubic inch can be used for the mat foundation bearing on the well-graded sand.

Design continuous footings using a maximum allowable bearing pressure of 4 ksf assuming a minimum footing width of 2 feet and maximum footing width of 4 feet.

The maximum allowable bearing pressures meet the required factor of safety according to IBC.

The recommended maximum allowable pressures are gross bearing pressures.

The recommended maximum allowable bearing pressures will result in less than 1 inch of total settlement.

The values presented may be increased by one-third for short-term wind and seismic loading.

Both isolated and continuous footings should be embedded a minimum of 3 feet below adjacent finished grade for frost protection.

The above recommendations are based on concentric pressures applied at the base of the footings. In the case of eccentric pressures (e.g., due to lateral stress), Golder may need to re-evaluate the recommended pressures.

A qualified geotechnical engineer should observe the foundation subgrade soils prior to placement of structural fill to verify that the foundation subgrade soils are consistent with the soils encountered at the time of this study.

Lateral loads due to earth pressures, wind, and seismic events can be resisted simultaneously by:

Base Friction: An allowable friction coefficient value of 0.35 can be assumed for base friction between the soil and spread footings. This value includes a factor of safety of 1.5. The allowable base friction value may be increased by one-third for the seismic loading.

Passive Resistance on Basement Walls and Sides of Shallow Footings Founded Against Soil: An equivalent fluid density of 280 pounds per cubic foot (pcf) should be used for soils above the groundwater table, and

140 pcf for soil below the groundwater table. These values include a factor of safety of 1.5. These values can be increased by one-third for seismic loads.

Design criteria presented in this section assume walls are backfilled with free draining material and the site is graded to direct water away from walls and structures.

5.4 Permanent Wall Design Criteria

The design lateral pressure on permanent basement walls depends on the construction methods used and the allowable movement. Based on the project plans, we expect that no excavation shoring will be used for the permanent structure—all walls will be backfilled after construction of the wall. Further, based on project plans we expect all permanent walls to be braced against rotation and should be designed using at-rest earth pressures.

The wet well walls should be designed for an at-rest earth pressure equivalent to a fluid with a density of 59 pcf above, and 29 pcf below, the permanent groundwater table. These earth pressures assume a freely draining condition above the permanent groundwater table, and level grades behind the wall. The wall should be designed to resist the lateral earth pressures in addition to hydrostatic pressures below the groundwater table.

A seismic surcharge pressure, as described in this section, Seismic Design (Section 5.2.3), should be added to the above earth pressures.

The site should be graded to provide drainage away from walls.

5.5 Lift Station Construction Considerations

These sections present recommendations for earthworks as part of the lift station construction. Site activities will include surface drainage and erosion control, subgrade and footing preparation, and construction of temporary excavation shoring and/or sloping.

5.5.1 Temporary Cut Slopes

Safe temporary cut slopes are the responsibility of the contractor. Based on the gravelly fill soil conditions, a slope angle no steeper than 1.5 horizontal to 1 vertical (1.5H:1V) is recommended. If groundwater seepage is encountered, 2H:1V or gentler slopes will likely be required to prevent sloughing.

5.5.2 Temporary Shoring Recommendations

If space constraints do not allow for open cuts, cantilever soldier pile shoring is feasible for the soil conditions encountered and proposed excavation depth.

The shoring system should be designed to support the earth pressure and lateral surcharge loads from construction equipment/materials, any adjacent structures or utilities, and roads or parking areas. If the shoring is designed to provide permanent support for the vault structure, then seismic load cases should be considered in designing the shoring. The shoring design should consider the construction sequence at the site.

The earth pressure diagram recommended for design of soldier piles is shown in Figure 9. Earth pressure coefficients and other design parameters for design of temporary cantilever soldier pile shoring are presented in

Table 3.

Table 3: Geotechnical Design Parameters for Temporary Cantilever Shoring

Design Parameter Value

Active Earth Pressure Coefficient (Ka) 0.28

At-Rest Earth Pressure Coefficient (K0) 0.44

Passive Earth Pressure Coefficient (Kp) 3.25

Total Unit Weight (γ1) 125 pcf

Submerged Unit Weight (γ2) 70 pcf

Notes:

1. Value for passive earth pressure coefficient is un-factored. Application of a Factor of safety of 1.5 is recommended.

2. Use Total Unit Weight above design groundwater elevation. Use submerged unit weight combined with hydrostatic pressure below design groundwater elevation. A design groundwater elevation for construction and therefore temporary shoring design is at the bottom of excavation.

3. If sensitive structures are located near the excavation, design of temporary shoring for at-rest earth pressures to reduce potential ground movement.

We anticipate that use of active earth pressures will limit deformation to less than 1 inch. If such deformation is not acceptable, at-rest earth pressures should be used for the shoring system design, in which case we anticipate deformation less than 0.25 inch.