Preliminary Geotechnical Report West Olympia/US 101 Access Improvements

Olympia, Washington

November 25, 2015

Submitted To: Mr. Owen Kikuta, P.E.

Parametrix 719 2

nd Avenue, Suite 200

Seattle, Washington 98104

By: Shannon & Wilson, Inc.

400 N 34th Street, Suite 100

Seattle, Washington 98103

21-1-22058-001

TABLE OF CONTENTS

Page

1.0 INTRODUCTION ..................................................................................................................1

2.0 SITE AND PROJECT DESCRIPTION .................................................................................1

3.0 GEOLOGY AND SUBSURFACE CONDITIONS ...............................................................2 3.1 Regional Geology .......................................................................................................2 3.2 Subsurface Conditions ................................................................................................3

4.0 PRELIMINARY ENGINEERING CONCLUSIONS AND RECOMMENDATIONS ........3 4.1 Foundations ................................................................................................................4 4.2 Retaining Walls ..........................................................................................................4 4.3 Stormwater Infiltration ...............................................................................................4

5.0 ADDITIONAL SERVICES ...................................................................................................4

6.0 LIMITATIONS ......................................................................................................................5

7.0 REFERENCES .......................................................................................................................7

FIGURES 1 Vicinity Map 2 Site Plan

APPENDIX

Important Information About Your Geotechnical/Environmental Report

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PRELIMINARY GEOTECHNICAL REPORT WEST OLYMPIA/US 101 ACCESS IMPROVEMENTS

OLYMPIA, WASHINGTON

1.0 INTRODUCTION

This report presents the results of preliminary geotechnical engineering studies performed for the West Olympia/US 101 access improvement project in Olympia, Washington. Our geotechnical studies included evaluating subsurface conditions and formulating geotechnical engineering recommendations for use in the preliminary design of the proposed project.

Our scope of geotechnical services included:

Reviewing geologic maps;

Reviewing geotechnical data available from the Washington State Department of Natural Resources;

Performing a field reconnaissance of the project site;

Evaluating the subsurface conditions;

Developing preliminary geotechnical design recommendations; and

Preparing this report.

We developed our recommendations in general accordance with the Washington State Department of Transportation (WSDOT) Geotechnical Design Manual (WSDOT, 2014a).

Our services were for preliminary design only. Additional geotechnical explorations and analyses will be required for final design and construction.

We provided our services in general accordance with our consultant agreement as authorized by Parametrix on March 4, 2015.

2.0 SITE AND PROJECT DESCRIPTION

US 101 runs along the southwest side of Olympia, as shown in Figure 1. The segment of US 101 from Black Lake Boulevard SW to Evergreen Parkway NW is a limited access highway with two traffic lanes and a shoulder in each direction. Interchanges exist at Black Lake Boulevard SW and Evergreen Parkway NW. The Kaiser Road SW overpass bridge crosses US 101 about 2,000 feet east of Evergreen Parkway NW. Yauger Way SW currently dead ends about 600 feet north of US 101, near a detention pond. The detention pond is on the north side of US 101,

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about 2,700 feet west of the Black Lake Boulevard SW interchange. Figure 2 shows the existing site features.

The ground surface along the project alignment is generally level; major terrain features are related to US 101 and its interchanges. Fill embankments support interchange ramps and bridge approaches. Embankment side slopes are typically 2 horizontal to 1 vertical (2H:1V).

The proposed project includes widening US 101, adding a half-diamond interchange at Kaiser Road SW, adding a ramp to Yauger Way SW, and constructing stormwater facilities. The US 101 widening would include one additional 12-foot-wide lane in each direction between the Kaiser Road SW and Black Lake Boulevard SW interchanges. The project team does not anticipate major cuts or fills associated with the widening of US 101.

The proposed US 101/Kaiser Road SW interchange includes:

Widening the existing Kaiser Road SW overpass;

Constructing fill walls up to about 30 feet tall on the west side of Kaiser Road SW to accommodate the road widening; and

Constructing fill walls up to about 30 feet tall on both sides of the proposed ramp from westbound US 101.

The proposed Yauger Way SW ramp would include cut walls up to about 10 feet tall.

The project team will evaluate the location and size of the proposed stormwater facilities based on the recommendations contained in this report. Based on discussions with the project team, we understand that stormwater infiltration ponds are planned.

3.0 GEOLOGY AND SUBSURFACE CONDITIONS

We evaluated the subsurface conditions based on a literature review, a field reconnaissance, and reviewing available subsurface data. We did not perform new subsurface explorations for this project.

3.1 Regional Geology

The project is located in the central portion of the Puget Lowland, an elongated, north-south depression situated between the Olympic Mountains and the Cascade Range. Repeated glaciation in this region influenced the present-day topography, geology, and groundwater conditions in the project area.

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Geologists generally agree that the Puget Lowland was subjected to six or more major glacial events, five of which may have overridden the Olympia area. Glacial ice from these glaciations originated in the British Columbia Coast Range and Canadian Rockies, and generally flowed southward into the Puget Lowland. Each glaciation deposited new sediment and partially eroded previous sediments. During the intervening periods when glacial ice was not present, normal geomorphic processes, such as streams, wave action, and landsliding, eroded and reworked some of the glacially derived sediment.

During the most recent glaciation that covered the Puget Lowland (termed Vashon), glacial ice is estimated to have been about 1,500 feet thick in the project area (Thorson, 1989). As the ice advanced southward, meltwater streams deposited sand and gravel (advance outwash). Beneath the glacier, an unstratified mixture of silt, sand, and gravel (glacial till) was deposited. The weight of the glacial ice compacted (overconsolidated) the glacial and nonglacial soil, including the glacial till and advance outwash. Subglacial meltwater streams eroded into overconsolidated soil, forming north-trending valleys.

As the Vashon glacier receded north, meltwater from the glacier deposited recessional glacial outwash and lacustrine sediment in valleys. The recessional glacial deposits are overlain by younger (Holocene), relatively loose and soft, post-glacial soil.

3.2 Subsurface Conditions

A geologic map of the region (Walsh and others, 2003) suggests that the project site is underlain by Vashon recessional deposits, including relatively clean fine to medium sand, sand and gravel, and local silt/clay. Walsh and others (2003) show outcrops of glacial till on the south side of US 101 near Kaiser Road SW.

Soil borings performed for the Black Lake Boulevard SW interchange encountered medium dense to very dense, slightly silty to silty sand and gravel to depths of about 65 feet below ground surface (bgs).

The borings encountered wet soil about 25 to 35 feet bgs. This depth to groundwater roughly corresponds to the water surface elevation of Simmons Lake, which is about 1,000 feet south of the project alignment.

4.0 PRELIMINARY ENGINEERING CONCLUSIONS AND RECOMMENDATIONS

We evaluated suitable foundations, retaining walls types, and stormwater infiltration rates based on the mapped geology at the project site. Additional subsurface explorations are required for final design.

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4.1 Foundations

In our opinion, shallow foundations, such as spread footings, would likely be suitable for the proposed project structures.

4.2 Retaining Walls

In our opinion, suitable wall types for fill retaining walls include cast-in-place concrete (CIPC) walls or structural earth walls (SEWs).

In our opinion, suitable wall types for cut retaining walls include CIPC walls, SEWs, or cantilever soldier pile walls. Constructing CIPC walls or SEWs for cut walls would require temporary slopes. For planning purposes, we recommend assuming that temporary slopes would be 1.5H:1V.

4.3 Stormwater Infiltration

We evaluated stormwater infiltration rate for Vashon recessional deposits based on guidance in the 2014 WSDOT Highway Runoff Manual (WSDOT, 2014b), and hydraulic conductivity testing performed by the U.S. Geological Survey (Drost and others, 1999). We recommend considering a long-term design infiltration rate on the order of 0.5 to 2 inches/hour for preliminary design. Infiltration rate depends on many factors, including:

Grain size distribution and texture of the soil deposits at the infiltration site;

Thickness and lateral extent of the infiltration soil;

Groundwater elevation; and

Presence of low permeability soil layers near the bottom of the infiltration facility and within the infiltration soil.

Additional explorations and in situ testing should be performed at the proposed stormwater infiltration site to evaluate the infiltration rate for final design.

The project alignment crosses a drinking water protection area, defined by the City of Olympia. Constructing stormwater infiltration facilities in this area will likely require coordination with City of Olympia officials.

5.0 ADDITIONAL SERVICES

Additional subsurface explorations and testing will be required to meet WSDOT (2014a) requirements for design. We recommend that Shannon & Wilson, Inc. be retained to perform the

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additional exploration and testing, and use those results to develop recommendations for final design.

When final design is complete, we recommend that Shannon & Wilson, Inc. be retained to review those portions of the plans and specifications pertaining to geotechnical aspects of construction to evaluate if they are consistent with our recommendations. We also recommend that we observe the geotechnical aspects of construction, which will allow us to verify the subsurface conditions as they are exposed during construction and to evaluate if the work is accomplished in accordance with our recommendations.

6.0 LIMITATIONS

This report was prepared for the exclusive use of Parametrix and the project team for preliminary design of the project. This report should not be used for final design, and should not be made available to prospective contractors. This report is not a warranty of subsurface conditions such as those interpreted from geologic maps and presented in the discussions of subsurface conditions included in this report.

Within the limitations of the scope, schedule, and budget, the analyses, conclusions, and recommendations presented in this report were prepared in accordance with generally accepted professional geotechnical engineering principles and practice in this area at the time this report was prepared. We make no other warranty, either express or implied.

The analyses, conclusions, and recommendations contained in this report are based on site conditions as they presently exist, and further assume that the subsurface conditions reported in explorations performed by others, and geologic maps are representative of the subsurface conditions throughout the project sites; that is, the subsurface conditions everywhere are not significantly different from those disclosed by the explorations/maps. Our conclusions and recommendations are based on our understanding of the project as described in this report and the site conditions as interpreted from the explorations/maps.

If, during final design and construction, subsurface conditions different from those assumed are observed or appear to be present, we should be advised at once so that we could review these conditions and reconsider our recommendations where necessary. If there is substantial lapse of time between the submission of this report and the start of work at the site, or if conditions have changed because of natural forces or construction operations at or adjacent to the site, we recommend that this report be reviewed to determine the applicability of the conclusions and recommendations concerning the changed conditions or the time lapse.

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7.0 REFERENCES

Drost, B. W.; Ely, D. M.; and Lum, W. E., II, 1999, Conceptual model and numerical simulation of the ground-water-flow system in the unconsolidated sediments of Thurston County, Washington: U.S. Geological Survey Water-Resource Investigations Report 99-4165, 254 p.

Thorson, R.M., 1989, Glacio-isostatic response of the Puget Sound area, Washington: Geological Society of America Bulletin, v. 101, no. 9, p. 1163-1174.

Walsh, T. J; Logan, R. L.; Schasse, H. W.; and Polenz, Michael, 2003, Geologic map of the Tumwater 7.5-minute quadrangle, Thurston County, Washington: Washington State Division of Geology and Earth Resources Open-File Report 2003-9, scale 1:24,000.

Washington State Department of Transportation (WSDOT), 2014a, Geotechnical Design Manual: Olympia, Wash., WSDOT, Manual M 46-03.10, 1 v., August, available: http://www.wsdot.wa.gov/Publications/Manuals/M46-03.htm

Washington State Department of Transportation (WSDOT), 2014b, Highway runoff manual: Olympia, Wash., WSDOT, Manual M 31-16.04, 1 v., April, available: http://www.wsdot.wa.gov/Environment/WaterQuality/Runoff/HighwayRunoffManual.htm

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VICINITY MAP

FIG. 1

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LEGEND

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APPENDIX

IMPORTANT INFORMATION ABOUT YOUR

GEOTECHNICAL/ENVIRONMENTAL REPORT

Page 1 of 2 1/2015

SHANNON & WILSON, INC. Geotechnical and Environmental Consultants

Dated:

Attachment to and part of Report 21-1-22058-001

Date: November 25, 2015

To: Mr. Owen Kikuta, P.E.

Parametrix

IMPORTANT INFORMATION ABOUT YOUR GEOTECHNICAL/ENVIRONMENTAL REPORT

CONSULTING SERVICES ARE PERFORMED FOR SPECIFIC PURPOSES AND FOR SPECIFIC CLIENTS.

Consultants prepare reports to meet the specific needs of specific individuals. A report prepared for a civil engineer may not be

adequate for a construction contractor or even another civil engineer. Unless indicated otherwise, your consultant prepared your report

expressly for you and expressly for the purposes you indicated. No one other than you should apply this report for its intended

purpose without first conferring with the consultant. No party should apply this report for any purpose other than that originally

contemplated without first conferring with the consultant.

THE CONSULTANT'S REPORT IS BASED ON PROJECT-SPECIFIC FACTORS.

A geotechnical/environmental report is based on a subsurface exploration plan designed to consider a unique set of project-specific

factors. Depending on the project, these may include: the general nature of the structure and property involved; its size and

configuration; its historical use and practice; the location of the structure on the site and its orientation; other improvements such as

access roads, parking lots, and underground utilities; and the additional risk created by scope-of-service limitations imposed by the

client. To help avoid costly problems, ask the consultant to evaluate how any factors that change subsequent to the date of the report

may affect the recommendations. Unless your consultant indicates otherwise, your report should not be used: (1) when the nature of

the proposed project is changed (for example, if an office building will be erected instead of a parking garage, or if a refrigerated

warehouse will be built instead of an unrefrigerated one, or chemicals are discovered on or near the site); (2) when the size, elevation,

or configuration of the proposed project is altered; (3) when the location or orientation of the proposed project is modified; (4) when

there is a change of ownership; or (5) for application to an adjacent site. Consultants cannot accept responsibility for problems that

may occur if they are not consulted after factors which were considered in the development of the report have changed.

SUBSURFACE CONDITIONS CAN CHANGE.

Subsurface conditions may be affected as a result of natural processes or human activity. Because a geotechnical/environmental report

is based on conditions that existed at the time of subsurface exploration, construction decisions should not be based on a report whose

adequacy may have been affected by time. Ask the consultant to advise if additional tests are desirable before construction starts; for

example, groundwater conditions commonly vary seasonally.

Construction operations at or adjacent to the site and natural events such as floods, earthquakes, or groundwater fluctuations may also

affect subsurface conditions and, thus, the continuing adequacy of a geotechnical/environmental report. The consultant should be kept

apprised of any such events, and should be consulted to determine if additional tests are necessary.

MOST RECOMMENDATIONS ARE PROFESSIONAL JUDGMENTS.

Site exploration and testing identifies actual surface and subsurface conditions only at those points where samples are taken. The data

were extrapolated by your consultant, who then applied judgment to render an opinion about overall subsurface conditions. The actual

interface between materials may be far more gradual or abrupt than your report indicates. Actual conditions in areas not sampled may

differ from those predicted in your report. While nothing can be done to prevent such situations, you and your consultant can work

together to help reduce their impacts. Retaining your consultant to observe subsurface construction operations can be particularly

beneficial in this respect.

Page 2 of 2 1/2015

A REPORT'S CONCLUSIONS ARE PRELIMINARY.

The conclusions contained in your consultant's report are preliminary because they must be based on the assumption that conditions

revealed through selective exploratory sampling are indicative of actual conditions throughout a site. Actual subsurface conditions can

be discerned only during earthwork; therefore, you should retain your consultant to observe actual conditions and to provide

conclusions. Only the consultant who prepared the report is fully familiar with the background information needed to determine

whether or not the report's recommendations based on those conclusions are valid and whether or not the contractor is abiding by

applicable recommendations. The consultant who developed your report cannot assume responsibility or liability for the adequacy of

the report's recommendations if another party is retained to observe construction.

THE CONSULTANT'S REPORT IS SUBJECT TO MISINTERPRETATION.

Costly problems can occur when other design professionals develop their plans based on misinterpretation of a

geotechnical/environmental report. To help avoid these problems, the consultant should be retained to work with other project design

professionals to explain relevant geotechnical, geological, hydrogeological, and environmental findings, and to review the adequacy of

their plans and specifications relative to these issues.

BORING LOGS AND/OR MONITORING WELL DATA SHOULD NOT BE SEPARATED FROM THE REPORT.

Final boring logs developed by the consultant are based upon interpretation of field logs (assembled by site personnel), field test

results, and laboratory and/or office evaluation of field samples and data. Only final boring logs and data are customarily included in

geotechnical/environmental reports. These final logs should not, under any circumstances, be redrawn for inclusion in architectural or

other design drawings, because drafters may commit errors or omissions in the transfer process.

To reduce the likelihood of boring log or monitoring well misinterpretation, contractors should be given ready access to the complete

geotechnical engineering/environmental report prepared or authorized for their use. If access is provided only to the report prepared

for you, you should advise contractors of the report's limitations, assuming that a contractor was not one of the specific persons for

whom the report was prepared, and that developing construction cost estimates was not one of the specific purposes for which it was

prepared. While a contractor may gain important knowledge from a report prepared for another party, the contractor should discuss

the report with your consultant and perform the additional or alternative work believed necessary to obtain the data specifically

appropriate for construction cost estimating purposes. Some clients hold the mistaken impression that simply disclaiming

responsibility for the accuracy of subsurface information always insulates them from attendant liability. Providing the best available

information to contractors helps prevent costly construction problems and the adversarial attitudes that aggravate them to a

disproportionate scale.

READ RESPONSIBILITY CLAUSES CLOSELY.

Because geotechnical/environmental engineering is based extensively on judgment and opinion, it is far less exact than other design

disciplines. This situation has resulted in wholly unwarranted claims being lodged against consultants. To help prevent this problem,

consultants have developed a number of clauses for use in their contracts, reports and other documents. These responsibility clauses

are not exculpatory clauses designed to transfer the consultant's liabilities to other parties; rather, they are definitive clauses that

identify where the consultant's responsibilities begin and end. Their use helps all parties involved recognize their individual

responsibilities and take appropriate action. Some of these definitive clauses are likely to appear in your report, and you are

encouraged to read them closely. Your consultant will be pleased to give full and frank answers to your questions.

The preceding paragraphs are based on information provided by the

ASFE/Association of Engineering Firms Practicing in the Geosciences, Silver Spring, Maryland