Final_Spruce_Trail_Geotechnical_Memorandum_5-03-2017.pdf

ALASKA

CALIFORNIA

COLORADO

FLORIDA

MISSOURI

OREGON

WASHINGTON DC

WASHINGTON STATE

WISCONSIN

3990 COLLINS WAY, SUITE 100

LAKE OSWEGO, OREGON 97035-3480

PHONE: (503) 210-4750

FAX: (503) 210-4890

www.shannonwilson.com 24-1-04087-001

May 3, 2017

Mr. Tom Gut, PE

AECOM

1111 Third Avenue, Suite 1600 Seattle, Washington 98101

RE: GEOTECHNICAL MEMORANDUM

WESTERN FEDERAL LANDS SPRUCE RAILROAD TRAIL, SEGMENT A

CONTRACT NO. DTFH7015D00001, TASK ORDER NO. DTFH7016F01005

OLYMPIC NATIONAL PARK, WASHINGTON

Dear Mr. Gut:

This memorandum presents our reconnaissance-based preliminary geotechnical recommendations for the proposed improvements to Segment A of the Spruce Railroad Trail in Olympic National Park, Washington. No boring or test pit explorations were performed for this project due to difficult and potentially cost-prohibitive drilling conditions. We understand that the Western Federal Lands Highway Division (WFLHD) of the Federal Highway Administration (FHWA) is planning improvements to an approximately 0.853-mile length of the Spruce Railroad Trail, designated Segment A. The location of Segment A is shown on the Vicinity Map, Figure 1, and its general layout is shown on the Site Plan, Figure 2. We understand that the proposed improvements, which extend from project station 10+51 to 55+00 include excavation, grading, drainage modifications, placement of aggregate base, possible construction of retaining walls, and mitigation of landslide and rock fall hazards as necessary to make the trail accessible and reasonably safe for bicycle and pedestrian use. The completed trail is anticipated to be 12 feet wide and accommodate a design speed of 15 miles per hour for bicycle traffic. After Segment B is constructed, the 8-foot width on the Lake Crescent side of the trail will be paved, and the remaining width will be gravel surfaced. AECOM Technical Services, Inc. (AECOM) is providing design engineering for the project, and Shannon & Wilson, Inc., is providing geotechnical support as a subconsultant to AECOM. Shannon & Wilson’s scope of services included literature review, site reconnaissance, and development of preliminary geotechnical recommendations for the proposed Segment A improvements. This memorandum summarizes our literature review, field observations, and preliminary recommendations.

Final Spruce Trail Geotechnical Memorandum 24-1-04087-001

REGIONAL GEOLOGIC SETTING

The Spruce Railroad Trail Segment A lies along the north side of Lake Crescent, in the north-central portion of the Olympic Mountains Physiographic Province of northwestern Washington.

Bedrock along the project alignment has been mapped by Schasse (2003) as early to middle Eocene (53- to 45-million-year-old) marine basaltic rocks of the Crescent Formation. The Crescent Formation generally includes pillow basalts and basalt breccias, volcaniclastic sandstones and conglomerates, minor basalt flows, and minor gabbroic dikes and sills. The formation is generally interpreted to represent a marginal rift-basin sequence (marine volcanic and sedimentary rocks) that have been scraped off the ocean floor and onto the North American continent during subduction of the oceanic crust. The convergence between the North American tectonic plate and adjacent, subducting oceanic plates has led to uplift, contortion, and extensive faulting of the accreted rocks, producing the rugged peaks of Olympic National Park.

The modern-day valleys at and near the project site were shaped partly by glaciers during the last ice age. The most recent glacial period occurred from about 110,000 to 10,000 years ago, and the last major glaciation of that period, within the vicinity of the project area, is known as the Fraser Glaciation. The Fraser Glaciation occurred between about 25,000 and 10,000 years ago.

The Vashon ice sheet of the Fraser Glaciation advanced from Canada and into the project area around 18,000 to 17,500 years ago, reaching its maximum extent about 17,000 years ago (Porter and Swanson, 1998). The Vashon ice sheet bifurcated as it advanced southward, with part of it following the Puget Lowland and part of it following the Strait of Juan de Fuca. The Crescent Valley, which originated along the parallel Crescent Thrust Fault, was further carved out by ice associated with the Juan de Fuca Lobe of the Vashon ice sheet. The valley drained through Indian Creek until about 8,000 to 10,000 years ago when a massive landslide created a natural dam on the modern-day east side of the lake (Logan and Schuster, 1991; Judd, 2014). Today, the lake drains toward the north into the Lyre River, over the Lyre River Falls.

Variable thicknesses of talus and colluvial sediments (slope deposits) overlie the bedrock in the project area. Several landslides are mapped by Schasse (2003) in the Crescent Formation around Lake Crescent, including the one that dammed the Indian Creek Valley to create the lake. In more recent times, cuts and fills were made along the project alignment during construction of the Spruce Railroad in the mid-1910s. The railroad track was used until the early 1950s. At that time, the track was taken up for salvage. Since then, the corridor has become a year-round, non-motorized, multiple-use trail.

After the trail improvements are constructed, it is anticipated that the variety of trail users’ ability will increase along with the volume of trail users. The improvements may also imply a different level of safety than previously perceived along the trail. Considerations of hazards need to be balanced with the wilderness context of the trail corridor.

GEOLOGIC HAZARDS

Geologic hazards along Segment A of the Spruce Railroad Trail generally include areas of erosion, landslides, and rock fall. Areas of potential erosion hazard were identified where existing drainage patterns cause water to cross the trail in an uncontrolled manner, either over the trail via sheet flow, or through the trail in eroded channels or deteriorated culverts. Areas of potential landslide hazards were identified where topography, drainage, and other features indicate the presence of existing landslides, and where proposed trail improvements could trigger new landslides (i.e., by cutting into existing soil/talus slopes). Areas of potential rock fall were identified along portions of the trail that lie below existing rock cut slopes where observed joint and fracture patterns are likely to yield unstable blocks. The site is also susceptible to seismic events which have the potential to exacerbate both landslide and rock fall hazards.

In order to differentiate the geologic hazards of the project site, we provide the following definitions for geologic hazard terminology used in this report:

Slump: A mass movement process consisting of a relatively shallow surficial slope failure.

Landslide: The movement of a relatively large mass of rock, debris, or earth down a slope.

Creep: Slow downslope movement of particles that occurs on every slope covered with loose, weathered material. Creep may also refer to slow movement of relatively unstable large landslides in this project.

Erosion - Erosion is the process by which soil and rock particles are worn away and moved elsewhere by gravity, or by a moving transport agent – wind, water or ice. For example, erosion of soil or rock particles may occur as water flows down a steep cut slope.

GEOTECHNICAL SITE RECONNAISSANCE AND RECOMMEDNATIONS

A Shannon & Wilson geotechnical engineer performed a reconnaissance of the site on November 3, 2016. Two Shannon & Wilson engineering geologists performed a separate reconnaissance of the site on February 14, 2017.

The following sections present our combined observations, recommendations, and evaluations of risk for the various features and geologic hazard areas we identified along the project alignment during our reconnaissance visits. The features and areas are organized by approximate stationing, which corresponds to the stationing presented on the Site Plan, Figure 2.

Approximate stationing was determined in the field through the combined use of iPhone-based GPS and the alignment shown on project plans dated January 25, 2017.

Approximate Station: 11+10

Feature Type: Drainage Ravine

Hazard Type: Erosion / Slope Instability

Typical Photograph:

Reconnaissance Notes:

The alignment crosses a drainage ravine, and we did not observe a culvert or other means to convey surface water beneath the fill placed for the railroad embankment.

We also did not observe evidence of active erosion or slope instability in this area, so the existing drainage may be adequate.

Recommendations:

Since we did not observe evidence of active erosion or drainage problems, we recommend doing nothing. If maintenance of the trail at this location becomes troublesome due to poor drainage, we recommend installing a culvert to convey water underneath the upper and lower trails.

Risks:

Trail erosion may occur during periods of heavy precipitation and snow melt.

Oversaturation of the ground could lead to slope instability.

Approximate Stations: 19+75, 26+20, 31+15, and 27+40

Feature Type: Failing Culverts

Hazard Type: Erosion / Slope Instability

Typical Photographs:

We observed deteriorating wooden culverts at three locations. Portions of some of the culverts have collapsed, creating sinkholes or depressions in the trail. We also observed a sinkhole at a fourth location (Station 27+40) that may have been caused by a failing culvert that is otherwise not visible at the surface.

Recommendations:

Replace the existing culverts at Stations 19+75, 26+20, and 31+15. At each location, excavate and remove the existing wooden culvert, and install a minimum 24-inch diameter culvert per WFLHD standard detail.

Remove the culvert or void at Station 27+40 and backfill the excavation with suitable material.

Risks:

Failure to replace the culverts could lead to additional sinkholes and depressions in the trail, as well as erosion below or through the trail. If drainage becomes blocked, slope stability may be reduced by oversaturation of the ground.

May 3, 2017

Final Spruce Trail Geotechnical Memorandum 24-1-04087-001

Approximate Station: 36+30 to 40+40

Feature Type: Drainage Incisions and Landslide

Hazard Type: Erosion / Slope Instability

Typical Photographs:

Reconnaissance Notes:

Several drainage channels are eroded through the trail alignment in this area, and sheet flow over the trail is apparent at some locations.

Topography within and adjacent to the trail in this area is consistent with that of a landslide. However, there are many mature trees that are not significantly leaning, suggesting that the slide is not moving rapidly at this time.

Recommendations:

In areas where water flows over the trail or is cutting through it, such as between Station approximately 36+30 and 40+40, improve drainage along the trail by excavating down to the bottom of the deepest incised drainage. Place a nonwoven geotextile (Class 1, Type A) on the exposed surface and then use riprap to build the grade back to the desired elevation. Class 2 riprap may be used for this construction. The riprap slope can be constructed by 1.5H: 1V slope. Place the non-woven geotextile on top of the riprap, and use the non-woven geotextile to wrap the subgrade above the riprap to prevent fines in the subgrade from washing out. Install minimum 24-inch diameter culverts just downstream of each riprap section. The goal would be to allow surface water in this area to drain through both the riprap and through the culverts. Refer to the conceptual diagram below.

A 3-foot deep ditch may be constructed to increase catchment storage and allow for easier maintenance.

AECOM

May 3, 2017

Approximate Station: 36+30 to 40+40 (Continued)

Risks:

Regardless of drainage improvements, the trail grade in this area may change over time as the landslide continues to creep downhill. If the trail is paved, pavement cracking should be anticipated. Placement of additional fill should be minimized between Station 36+30 and 40+40, as adding significant weight could exacerbate slope instability.

Approximate Station: 43+30 to 43+80 Feature Type: Possible Landslide / Slump Failure

Hazard Type: Slope Instability

We observed a possible slump failure in the cut slope north of the trail alignment.

There is a precariously positioned boulder at the top of the head scarp.

It appears that the scarp feature may actually have been created or the slide initiated when a tree cluster fell across the trail. The root wad of the tree cluster remains at the toe of the slope.

Recommendations:

Remove the boulder at the top of the scarp so that it doesn’t roll onto the trail.

The root wad at the toe of the slope may be removed.

Smooth the scarp back into the slope and, within 5 feet of the scarp, cut the existing trees off near the ground surface, leaving the roots in place.

If trail widening is required, excavate into the slope south of the trail.

Risks:

If not removed, ongoing erosion will undercut the boulder at the top of the scarp and it will roll onto the trail. Soil from the slide area may continue to slough onto the trail, particularly if it is undercut for trail widening.

Approximate Station: 47+00 to 48+60

Feature Type: Rock Cut Slope

Hazard Type: Rock fall

Typical Photograph:

This section of rock cut slope is approximately 160 feet long, 30 feet high, and cut between about 75 degrees and near-vertical.

There is a collection of talus and colluvial soil at the bottom of the cut.

Joints in the rock mass are closely spaced, and some joints are open. Apparent rock fall generally consists of blocks that are 1 foot in diameter and smaller.

Recommendations:

Trees and vegetation within approximately 5 feet of the top of the slope should be cut and removed to prevent roots from wedging the rock apart. Stumps may be left in place. We understand that removal of the tree will be evaluated for inclusion with the subsequent Segment B contract.

Loose rock should be scaled from the slope (approximately 2 days of effort) wherever the toe of the slope is within 20 feet of the proposed edge of the trail. Hand scaling generally is expected. We understand that scaling will be evaluated for inclusion with the subsequent Segment B contract.

Talus and soil may be removed up to the rock face as it is not providing toe support to the rock slope. Where there is sufficient room to accommodate the trail, existing talus may be reformed into a catchment berm that would reduce the number of blocks that roll out onto the trail. Refer to the conceptual diagram below.

Risks:

Minor rock fall of blocks less than 1 foot in diameter is likely to occur even after scaling and tree removal. Using a talus berm and keeping the trail away from the base of the slope will reduce risks to users. Risks could be reduced further with additional mitigation measures such as draping a wire mesh over the slope.

Approximate Station: 48+60 to 50+75

Feature Type: Rock Cut Slope / Rock Slide

Hazard Type: Rock fall / Rock Slide

This section of rock cut slope is approximately 215 feet long, 60 to 70 feet high, and cut between about 70 degrees and near-vertical.

There is a collection of talus and colluvial soil at the bottom of the cut and a rock slide that has extended across the trail alignment near Station 49+00.

Joint patterns are variable through this part of the cut. Some joints are smooth and persistent for 20 feet or more, creating car-sized intact rock blocks observed in the slide debris. In other areas, joints are shorter and more closely spaced, creating approximately 4-inch to 1-foot diameter blocks.

Adjacent to the existing slide, visible in the photo on the left, there is an approximately 100-cubic-yard volume of material on the slope that appears prone to failure in the future.

Recommendations:

Trees and vegetation within approximately 5 feet of the top of the slope should be cut and removed to prevent roots from wedging the rock apart. Roots are visible in the rock slide surface in the photo on the left. During tree removal, stumps may be left in place. We understand that removal of the tree will be evaluated for inclusion with the subsequent Segment B.

Loose rock should be scaled from the slope (approximately 2 days of effort) wherever the toe of the slope is within 20 feet of the proposed edge of the trail. Hand scaling generally is expected. We understand that scaling will be evaluated for inclusion with the subsequent Segment B contract.

After Segment A is constructed, evaluations of the slope to the east of the existing rock should be performed for the need for rock bolts or dowels. If needed, bolts or dowels could be included with the subsequent Segment B contract. Rock bolts (about 4 to 6) could be installed in the slope to the east of the existing rock slide to reduce the risk of future rock slides in this area. The rock bolts should be at least 10 feet long. We anticipate that each rock bolt may be 15 to 20 feet long for this site. We recommend that the contractor be required to submit a plan for rock bolt installation locations and details for review.

Talus and soil may be removed up to the rock face as it is not providing significant toe support to the rock slope. Removal of the rock slide debris may require splitting or blasting to break up intact blocks of rock. Where there is sufficient room to accommodate the trail, existing talus or rock slide debris may be reformed into a catchment berm that would reduce the amount of blocks that roll out onto the trail. Refer to the conceptual diagram presented for Station 47+00 to 48+60.

Risks:

If left unmitigated, the unstable blocks east of Station 49+00 could fail without warning.

This poses a hazard to trail users and would likely impact the trail itself.

Minor rock fall of blocks less than about 1 foot in diameter is likely to occur even after scaling and tree removal. Using a talus berm and keeping the trail away from the base of the slope will reduce risks to users. Risks could be reduced further with additional mitigation measures such as draping a wire mesh over the slope.

Approximate Station: 50+80

Feature Type: Narrow Trail Adjacent to Soil Slope

Hazard Type: Slope Instability / Erosion

Trail widening may require cutting into adjacent soil/talus slope or building out toward the lake.

It appears that there is a natural drainage in this area, and water flows over the existing trail during periods of intense precipitation or snow melt.

Recommendations:

In our opinion, the soil/talus cut that would be required in this area to achieve the desired trail width is minimal and poses low risk of significant slope failures. A 1 horizontal:1 vertical (1H:1V) cut slope may be acceptable if the original slope is close to 1H:1V.

However, there is a potential risk of erosion and local slump failures along the steep cut slopes during the wet winter months. Risks of increased maintenance associated with erosion and slump failures are relatively higher for 1H:1V slopes than for flatter cut slopes, such as 1.5H:1V. If the Agency does not accept such potential risk, a retaining wall, such as rockery wall or soil nail wall, may be required to retaining the steep cut slope. The wall would be approximately 50 feet long.

Current flow of water over the trail has not yet led to significant erosion. If the condition worsens, a culvert could be installed, but in our opinion, it does not appear necessary at this time.

Risks:

Cutting into the soil/talus slope may reduce slope stability and lead to failures that impact the trail, though this risk appears minimal at this location.

Flow through the drainage above the trail may eventually erode the trail and slope below.

This risk could be mitigated in the future by installing a trench drain and culvert.

Approximate Station: 51+65 to 52+85

Feature Type: Rock Cut Slope

This section of rock cut slope is approximately 120 feet long, 75 to 80 feet high, and cut between about 80 degrees and near-vertical.

A major flow contact appears to cross the cut slope in this area.

There is a collection of talus and colluvial soil at the bottom of the cut.

Apparent rock fall consists of blocks that average less than 6 inches in diameter, but some blocks up to 2 feet in diameter are present.

Recommendations:

Trees and vegetation within approximately 5 feet of the top of the slope should be cut and removed to prevent roots from wedging the rock apart. Stumps may be left in place. We understand that removal of the trees will be evaluated for inclusion with the subsequent Segment B contract.

Protruding rock knobs, such as the one near the middle of the photo on the right, appear unstable and should be removed.

Loose rock should be scaled from the slope (approximately 2 days of effort including knob removal) wherever the toe of the slope is within 20 feet of the proposed edge of the trail. Areas that are largely moss covered with tight joints are not apparently active sources of rock fall and will require minimal scaling effort. Hand scaling generally is expected. We understand that scaling will be included with the Segment B contract in the following year.

Talus and soil may be removed up to the rock face as it is not providing toe support to the rock slope. Where there is sufficient room to accommodate the trail, existing talus may be reformed into a catchment berm that would reduce the amount of blocks that roll out onto the trail. Refer to the conceptual diagram presented for Station 47+00 to 48+60. In this area, from Station 51+65 to 52+85, there appears to be ample room to cut into the berm on the south side of the trail for widening, allowing ample room for installation of a catchment berm to the north.

Risks:

Minor rock fall of blocks less than about 1 foot in diameter is likely to occur even after scaling and tree removal. Using a talus berm and keeping the trail away from the base of the slope will reduce risks to users.

Approximate Station: 52+85 to 54+00

Feature Type: Rock Cut Slope

This section of rock cut slope is approximately 115 feet long, 80 to 85 feet high, and cut between about 75 degrees and near-vertical.

Some western portions of the slope are moss covered and do not appear to be active sources of rock fall.

Near Station 53+50, there is an overhanging block (about 40 to 50 cubic yards of material) that appears to be unstable. It is visible near the middle of the photo on the right.

Apparent rock fall generally consists of blocks that are 1 foot in diameter and smaller.

Recommendations:

Trees and vegetation within approximately 5 feet of the top of the slope should be cut and removed to prevent roots from wedging the rock apart. Stumps may be left in place. We understand that removal of the trees will be evaluated for inclusion with the subsequent Segment B contract.

Loose rock should be scaled from the slope (approximately 2 days of effort) wherever the toe of the slope is within 20 feet of the proposed edge of the trail. Hand scaling generally is expected. We understand that scaling will be evaluated for inclusion with the subsequent Segment B contract.

The block of rock in the photo on the right, near Station 53+50, should either be removed or stabilized with rock bolts (about 4 to 6). The rock bolts should be at least 10 feet long.

We anticipate that each rock bolt may be 15 to 20 feet long for this site. We recommend that the contractor be required to submit a plan for rock bolt installation locations and details for review.

After scaling is complete, additional spot bolting may be needed.

Talus and soil may be removed up to the rock face as it is not providing any toe support to the rock slope. Where there is sufficient room to accommodate the trail, existing talus may be reformed into a catchment berm that would reduce the number of blocks that roll out onto the trail. Refer to the conceptual diagram presented for Station 47+00 to 48+60.

Risks:

If left unmitigated, the overhanging rock block near Station 53+50 may fall without warning. This poses a hazard to trail users and would likely impact the trail itself.

Minor rock fall of blocks less than about 1 foot in diameter is likely to occur even after scaling and tree removal. Using a talus berm and keeping the trail away from the base of the slope will reduce risks to users. Risks could be reduced further with additional mitigation measures such as draping a wire mesh over the slope.

Approximate Station: 54+00 to 55+00

Feature Type: Narrow Trail Between Existing Rockery Wall and Soil Slope

Hazard Type: Slope Instability

Trail widening may require cutting into adjacent soil/talus slope or building out toward the lake.

Recommendations:

It may be possible to cut into the soil/talus slope for trail widening, but this could result in future slope instability and slump or ravelling failures that impact the trail. A 1H:1V cut slope may be acceptable. However, there is a potential risk of erosion and local slump failures along the steep cut slopes during the wet winter months. Risks of increased maintenance associated with erosion and slump failures are relatively higher for 1H:1V slopes than for flatter cut slopes, such as 1.5H:1V. If the Agency does not accept such potential risk, a retaining wall, such as rockery wall or soil nail wall, may be required to retaining the steep cut slope.

Risks:

Cutting into the soil/talus slope may reduce slope stability and lead to failures that impact the trail.

Summary of Recommendations

Geologic hazards identified along Segment A of the Spruce Railroad Trail generally include areas of erosion, landslides, and rock fall. Erosion hazards can be reduced, as noted above, by replacing failing wooden culverts and installing new culverts and a drainage layer of riprap or quarry spalls in the existing landslide area between Station 36+30 and 40+40. The existing landslide between Station 36+20 and 41+50 appears to be slow moving, but the recommended drainage improvements in the area will not reduce ongoing movement of this landslide through the trail. The trail grade in this area will likely deform as the slide continues to creep down-slope. The trail construction requires cut and fill construction. A 1H:1V cut and fill slope may be acceptable. However, there is a potential risk of erosion and local slump failures along the steep cut and fill slopes during the wet winter months. Cutting steeply into the soil slope near Station 50+80 and between Stations 54+00 and 55+00 for trail widening has the potential to produce areas prone to erosion and slump failures that may impact the trail. If this risk is unacceptable, it is our opinion that the trail could be widened by constructing retaining walls along the cut areas.

The existing rock cut slopes, located intermittently along the alignment east of approximate Station 47+00, present a general rock fall hazard. We generally recommend evaluating, for inclusion in the subsequent Segment B contract, removal of trees and vegetation on and within approximately 5 feet of the tops of the slopes to prevent roots from wedging the rock apart and generating rock fall. Stumps may remain in place. Tree and vegetation removal should be done prior to scaling. We recommend scaling in several areas between approximate Stations 47+00 and 54+00 and estimate a total scaling effort of about 8 days. The estimated number of scaling days does not include tree removal, as the degree of effort needed to remove the trees will depend on issues such as access to the top of the slope and whether the cut trees will need to be hauled off site. In addition, we identified two areas, one near Station 49+00 and one near Station 53+50, where we recommend placing some rock bolts to improve trail safety (approximately 4 to 6 bolts at each location). Additional locations that would benefit from spot-bolting may become apparent during scaling. We recommend that a Shannon & Wilson representative be on site during the scaling effort to identify areas where additional spot-bolting may be necessary. Along much of the trail where rock cuts are present, safety could be significantly improved by rearranging the existing talus at the bottom of the slope into a 3-foot-high catchment berm (refer to conceptual diagram presented for Station 47+00 to 48+60). In most areas, there appears to be sufficient room to construct the talus catchment berm and complete trail widening toward the south.

Rock slopes are inherently hazardous, and no cost-effective mitigation measures can completely eliminate all risks associated with rock fall. Minor rock fall of blocks less than about 1 foot in diameter is likely to occur even after scaling and tree removal. We anticipate that ice-wedging will continue to induce rock fall along most of the existing rock cuts, and that preventative scaling will likely be necessary every 5 years or so to keep rock fall rates acceptably low. Using the talus berm mitigation described in this report and keeping the trail away from the base of the slope will reduce risks to users. If desired, risks could be reduced further with additional mitigation measures such as draping a wire mesh over the slope.

LIMITATIONS AND CLOSURE

The analyses, conclusions, and recommendations contained in this report are based on observed surface conditions as they existed at the time of our site visits. Within the limitations of 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. These conclusions and recommendations were based on our understanding of the project as described in this report and the observed site conditions.

Unanticipated conditions are commonly encountered in rock slopes during scaling and construction, and cannot be fully determined in advance by limited visual reconnaissance from the bottom of the slope. Such unexpected conditions frequently require that additional expenditures be made to attain a properly constructed project. Therefore, some contingency fund is recommended to accommodate such potential extra costs.

This report was prepared for the exclusive use of WFLHD and AECOM in the design of the subject trail. Our report, conclusions, and interpretations should not be construed as a warranty of surface or subsurface conditions.

Shannon & Wilson has prepared and included as Appendix A, “Important Information About Your Geotechnical/Environmental Report,” to assist you and others in understanding the use and limitations of our report.

May 3, 2017 Page 23 of24

SHANNON &WILSON, INC.

We appreciate the opportunity to be of service to AECOM and Wes tern Federal Lands. If you have questions or comments regarding this report, please contact Park Piao at (503) 210-4760.

Sincerely, SHANNON & WILSON, INC.

exp; l'l5 5/t)/t<J

I Adrian A.J. Holmes I

Adrian A.J. Holmes, LEG Senior Engineering Geologist

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Enc: Figure 1 - Vicinity Map Figure 2 - Site Plan

Risheng "Park" Piao, PE, GE Vice President I Geotechnical Engineer

Appendix A -Important Information About Your Geotechnical/Environmental Report

Final Spruce Trail Geotechnical Memorandum 24-1-04087-00 I

REFERENCES

Judd, R., 2014, Our deep lakes incite curiosity and conjure legends: in The Seattle Times, Available: http://www.seattletimes.com/life/lifestyle/our-deep-lakes-incite-curiosity-and-conjure-legends/, Accessed: February 20, 2017.

Logan, R. L.; Schuster, R. L., 1991, Lakes divided—The Origin of Lake Crescent and Lake Sutherland, Clallam County, Washington: Washington Geology, v. 19, no. 1, p. 38-42.

Porter, S.C., and Swanson, T.W., 1998, Radiocarbon age constraints on rate of advance and retreat of the Puget Lobe of the Cordilleran ice sheet during the last glaciation: Quaternary Research, v. 50, p. 205–213.

Schasse, H.W., 2003, Geologic Map of the Washington Portion of the Port Angeles 1:100,000 Quadrangle: Washington Division of Geology and Earth Resources Open File Report 2003- 6, scale 1:100,000.

SITE

LOCATION

Spruce Railroad Trail Segment A

Clallam County, Washington

VICINITY MAP

FIG. 1

February 2017 24-1-04087-001

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0 1 20.5

Scale in Miles

FIG. 1 £

Site Location

British Columbia

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Service Layer Credits: Copyright:© 2013 National Geographic Society, i-cubed Content may not reflect National Geographic's current map policy. Sources: National Geographic, Esri, DeLorme, HERE, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, increment P Corp.

Site Location

Drainage Ravine (Sta. 11+10)

24-1-04087-001

SITE PLAN

FIG. 2

Spruce Railroad Trail Segment A

Clallam County, Washington

February 2017

SHANNON & WILSON, INC.

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Approximate Scale in Feet

NOTES

Base map is from drawing "olym 201601_fa.dgn" dated January 25, 2017, provided in PDF format by AECOM.

Failing Culvert (Sta. 19+75)

Failing Culvert (Sta. 26+20)

Sinkhole Possibly Related to Failing Culvert (Sta. 27+40)

24-1-04087-001

SITE PLAN

FIG. 2

Spruce Railroad Trail Segment A

Clallam County, Washington

February 2017

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Approximate Scale in Feet

NOTES

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Failing Culvert (Sta. 31+15)

Landslide Area (Sta. 36+20 to 41+50)

Slump Failure (Sta. 43+30 to 43+80)

24-1-04087-001

SITE PLAN

FIG. 2

Spruce Railroad Trail Segment A

Clallam County, Washington

February 2017

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(Sheet 3 of 4)

0 100 200

Approximate Scale in Feet

NOTES

Base map is from drawing "olym 201601_fc.dgn" dated January 23, 2017, provided in PDF format by AECOM.

Slump Failure (Sta. 43+30 to 43+80)

Narrow Trail Between Existing Rockery Wall and Soil Slope (Sta. 54+00 to 55+00)

Existing Rock Cut Slope (Sta. 47+00 to 54+00)

24-1-04087-001

SITE PLAN

FIG. 2

Spruce Railroad Trail Segment A

Clallam County, Washington

February 2017

0 100 200

Approximate Scale in Feet

SHANNON & WILSON, INC.

Fi le

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Base map is from drawing "olym 201601_fd.dgn" dated

(Sheet 4 of 4)

24-1-04087-001

APPENDIX A

IMPORTANT INFORMATION ABOUT YOUR

GEOTECHNICAL / ENVIRONMENTAL REPORT

Page 1 of 2 1/2016

SHANNON & WILSON, INC.

Geotechnical and Environmental Consultants

Attachment to and part of Report: 24-1-04087-001 Geotechnical Memorandum

WFL Spruce Railroad Trail, Segment A Date: May 2017 To: AECOM Attn: Mr. Tom Gut, PE

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 1/2016

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