Attach 8 - Dexter GBR Update Amend0002.pdf

GEOTECHNICAL BASELINE REPORT

Dexter Adult Fish Collection Facility Upgrade

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TABLE OF CONTENTS

PART 1 - GENERAL

1.1 GENERAL INFORMATION

1.2 DESCRIPTION OF WORK

1.3 SCOPE

1.4 INTENDED METHODS, RECOMMENDATIONS, AND CLARIFICATIONS

1.4.1 General

1.4.2 Material Percentages

1.4.3 SPT Values

1.5 REFERENCES

1.6 SOURCES OF INFORMATION

1.7 AUTHORIZATION AND HISTORICAL PERSPECTIVE

1.8 GEOTECHNICAL EXPLORATIONS AND TESTING

1.8.1 General

1.8.2 Pre-Dam Drill Holes

1.8.3 2013 Explorations

PART 2 - SITE CONDITIONS AND GEOTECHNICAL BASELINE DATA

2.1 GEOLOGIC CONDITIONS

2.1.1 General

2.1.2 Overburden

2.1.3 Existing Fills

2.1.4 Bedrock

2.1.5 Surface Water

2.1.6 Groundwater

2.2 GEOTECHNICAL PROPERTIES AND CONSIDERATIONS

2.2.1 General

2.2.2 Existing Fill

2.2.3 Bedrock

2.2.4 Geotechnical Parameters

2.2.5 Excavations

2.2.6 Utilization of Excavated Materials

2.3 RIVER CONDITIONS

2.4 EXISTING UNDERGROUNDUTILITIES

PART 3 - CONSTRUCTION CONSIDERATIONS

3.1 GENERAL

3.2 LOWER FISH LADDER AND AUX. WATER SUPPLY DIFFUSION CHAMBER

3.3 UPPER FISH LADDER

3.3.1 Near the Fish Ladder Crossing

3.3.2 Alongside the Existing Asphalt Pond

3.4 PRE-SORT POOL

3.5 SORTING FACILITY AND OTHER LIGHT BUILDINGS

3.6 POST-SORT POOLS

3.7 HOPPER CRANE STRUCTURE

3.8 WATER SUPPLY PIPING

3.8.1 New FWS Pipe

3.8.2 AWS Return Pipe

3.12 TEMPORARY COFFERDAMS

3.13 ELECTRICAL DUCT BANKS

FOUNDATION DRAINS

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ACRONYMS

ASTM -American Society of Testing and Materials AWS -Auxiliary Water Supply DDR- Design Documentation Report GBR- Geotechnical Baseline Report GIS- Geographic Information System LiDAR- Light Detection and Ranging NMFS- National Marine Fisheries Service OHWM- Ordinary High-Water Mark SPF - Standard Project Flood SPT- Standard Penetration Test TIN- Triangulated Irregular Network USACE- US Army Corps of Engineers

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PART 1 - GENERAL

1.1 GENERAL INFORMATION

(a) This Geotechnical Baseline Report (GBR) is part of the contract documents for the Dexter Fish Collection Facility.

(b) This GBR presents the Government's interpretation of the anticipated subsurface conditions to be encountered during construction. This report shall be considered the sole source of the Government's interpretation of the geotechnical conditions for the proposed structures. The sources of the geotechnical data on which this report is based are referenced in paragraphs 1.5 and 1.6.

(c) The purpose of this GBR is to provide interpretive information on the anticipated materials to be encountered during construction and their behavior. This report is intended to aid prospective bidders in preparing their bids; the successful bidder in performing the work; the Government's and Contractor's staff in providing construction surveillance; and establish the geotechnical baseline that serves as the basis for identification of differing site conditions.

(d) This GBR is limited to site conditions within the proposed Dexter Adult Fish Collection Facility

Improvement construction boundaries, as shown on the Contract drawings. The geologic and geotechnical information provided herein is not intended to be used outside these construction boundaries. This GBR does not include the “boat launch” area; no explorations have been completed in the boat launch area for this project.

(e) This GBR is a part of the Contract Documents. The Contract Specifications and Drawings take precedence over this GBR. Accordingly, in the administration of the Differing Site Conditions clause in the contract (Section 00700 paragraph 52.236-2), subsurface conditions indicated or described in this report shall be construed as "indicated in this contract."

1.2 DESCRIPTION OF WORK

Geotechnical work to be performed in this contract will take place adjacent to and along the north shore of the Middle Fork Willamette River, downstream of Dexter Dam and west of the Dexter Dam Powerhouse shown in the drawings. The facility will utilize portions of the original Adult Fish Facility and will provide modern fish collection, sorting, holding, and truck transport features. The work will involve overburden and rock excavation and engineered fill to foundation grades or to final grades. The facility will have the following major features:

1) New Fish Ladder

2) New Auxiliary Water System (AWS) Chambers

3) New Facility Water System (FWS) piping

4) Fish Ladder Crossing

5) New Pre-Sort Pool and New Sorting Area

6) New Post-Sort Pools and Hopper Crane

7) New Truck Loading Area and Roads

8) New AWS Return Pipe

9) New Buildings

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Excavation of overburden materials, fill, and bedrock will be to the specified slopes or grades, or to those grades specified by the contracting officer. Construction of temporary cofferdams during the in-water work period will be required in the area of the new AWS chambers and lower fish ladder. Shoring in locations where deep excavations are present will likely be required.

1.3 SCOPE

This report provides geologic and geotechnical information related to the project area, with emphasis on the geotechnical conditions that may be encountered during excavation and construction. This report also presents general river and groundwater conditions to be expected.

1.4 INTENDED METHODS, RECOMMENDATIONS AND CLARIFICATIONS

1.4.1 General

(a) The material and unit descriptions presented in this report are based primarily on exploration logs and nearby outcrop exposures. Other information relied on for this report includes published geologic maps and reports, surficial observations, and design reports for the existing dam facility.

(b) The test pits and drill hole logs and related information depict generalized subsurface conditions only at these specific locations and at the particular time the subsurface explorations were completed. Soil, rock and groundwater conditions at other locations may differ from the conditions at these hole locations.

The passage of time may result in a change in the soil, rock and groundwater conditions at the site.

(c) The Contract indicates temporary cut slopes at 1 horizontal to 1 vertical (lH:lV) in overburden. This slope grade represents the maximum temporary stable slope for the overburden materials anticipated at the site, assuming drained conditions. The actual stability of the side slopes will depend on the cut heights, material properties, the length of time the cuts are open, and the moisture conditions. If excavations are to be open for long periods of time or during wet conditions, the cut slope angles should be flattened or shored accordingly.

1.4.2 Material Percentages

The percentages given for the various materials are approximate and are based on visual estimates or gradation testing. Visually determined percentages are expected to vary by +/-20% of the value shown.

An estimated value of 50% can therefore vary from 40 to 60%. An estimated value of 25% can vary from 20 to 30%. An estimated value of 10% can vary from 8 to 12%.

1.4.3 SPT Values

Standard Penetration Test (SPT) values are shown on the included drill1ogs and used to help estimate baseline parameters. These values are not corrected for overburden pressures and are loosely equal to uncorrected SPT N values. However, some of the values may be bias due to the presence of gravels, cobbles, and boulders in the fills and alluvial materials.

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1.5 REFERENCES

ASTM D 653-96, Standard Terminology Relating to Soil, Rock, and Contained Fluids.

ASTM D 2487-93, Classification of Soils for Engineering Purposes (Unified Soil Classification System).

ASTM D 2488-93, Standard Practice for Description and Identification of Soils (Visual-Manual Procedure).

Beaulieu, J.D., 1974, Environmental Geology of Western Linn County, Oregon; Oregon Department of Geology and Mineral Industries, Bulletin No. 84, 117 p., maps.

US Army Corps of Engineers, September 2010, 90% Design Documentation Report, Dexter Dam Adult Fish Facility Upgrade, Goldfinger, C., 1991, Evolution of the Corvallis fault and implications for the Oregon Coast Range:

Oregon State University, unpublished M.S. thesis, 129 p., 2 pis.

USACE, 2009, Regional seismic hazard assessment; Willamette Valley in the Pacific Northwest region:

Engineering Circular EC-1110-2-6000, 261 p.

Yeats, R. S., Graven, E. P., Werner, K. S., Goldfinger, C., and Popowski, T. A., 1996, Tectonics of the Willamette Valley, Oregon: U.S. Geological Survey Professional Paper 1560, p. 183-222, maps.

NAVFAC Design Manual 7.2 (1982) Foundations and Earth Structures

1.6 SOURCES OF INFORMATION

• Along with the references cited above, the following references represent the sources of geotechnical information used for the preparation of this report.

• Dexter Reregulating Dam, Analysis for Design for Non-Overflow Section, Powerhouse, and

Spillway (Dated April 1953)

• Dexter Dam Lookout Point Project Foundation Report (Dated January 1958)

• Geotechnical Data Report, Dexter Dam Adult Fish Facility Upgrades, prepared by Cornforth

Consultants for The US Army Corps of Engineers Portland District, April 2013

1.7 AUTHORIZATION AND HISTORICAL PERSPECTIVE

Dexter Dam provides reregulation for the Lookout Point Project which was authorized by the Flood Control Act of June 28, 1938, as described in Public Law 761, House Resolution 10618. The Dexter Project was authorized by the Flood Control Act of 1950, Public Law 516, Eighty-first Congress, House Resolution 5472 approved on May 17, 1950. The Dexter Project was completed in 1958.

The existing authorized purpose for Dexter Dam includes flood control, power generation, navigation, irrigation, water quality and recreation. The Willamette Project system of 13 USACE dams and reservoirs, including Dexter Dam, was authorized with the full recognition that it would cut off extensive areas of upstream habitat. To compensate, fish hatcheries and other measures were authorized. The Dexter Fish Facility Upgrade is in response to the July 2008 NMFS Biological Opinion, which requires that the Dexter Dam Adult Fish Facility be upgraded in accordance with the requirements of the 2008 NMFS Anadromous Salmonid Passage Facility Design Document and the best available technology.

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1.8 GEOTECHNICAL EXPLORATIONS AND TESTING

1.8.1 General

Subsurface explorations at Dexter Dam were conducted in the early 1950's during the design phase of the project. A total of 68 exploration drill holes were completed into foundation and overburden materials at that time. The drill holes and test pit locations were selected to gain a better understanding of material types in the area of the proposed structures and to assist in the project design. Results and boring logs from the 1950’s exploration project are found in Exhibit A.

In 2013, explorations were completed for this contract work by Cornforth Consultants and US Army Corps of Engineers. The explorations consisted of drilling twelve drill holes to depths ranging from 10 to 50 feet below the ground surface. In addition, two exploratory test pits were completed, each to very shallow depths due to rock encountered. Results of the Cornforth and USACE explorations are found in Exhibit B.

1.8.2 Pre-Dam Drill Holes

Prior to construction of Dexter Dam, a total of 68 exploratory drill holes were bored into the foundations and overburden materials at the site. Of the 68 drill holes, fifteen were completed in the fish facility project area. The locations of these historical borings and stick logs completed in project area are provided in historical documents referenced in this report. In general, the logs describe the materials encountered as lapilli tuff, basalt breccias, or intrusive basalt overlain by various thicknesses of silty sand with gravel.

During the 1952 exploration, the basalt found on the western end of the fish facility was mostly covered by a thin layer of silty clay with some talus and roots. Prior to original construction, rock debris and loose weathered rock was removed from the construction area, and blasting was employed for the removal of bedrock to create the area on which the fish facility is constructed.

A large pocket of soft pyroclastic rock of undetermined depth lies between the downstream flank of the right abutment and the intrusive basalt in the western portion of the fish facility area. The tuff is apparently shaped as a narrow trench and the original construction excavated into this material plus an additional several feet into the basaltic bedrock beneath. The basaltic bedrock surface dips southward under the fish holding pond area.

1.8.3 2013 Explorations

Drilling for exploratory borings was performed by Hardcore Drilling of Dundee, Oregon between February 27 and March 4, 2013 and the Omaha District of the US Army Corps of Engineers from August 12-16 and November 7-11, 2013. Borings were drilled with a track-mounted CME 850 drill rig using mud rotary and HQ3 core drilling techniques (Hardcore) and a Pech 1300C Wheeled Hydraulic Rig (USACE).

Subsurface materials encountered are presented on Summary Boring Logs in Figure B-2, Exhibit B. A one-inch diameter standpipe piezometer well was installed in Borings B-7 and B-11 to monitor groundwater levels. Remaining borings were backfilled with bentonite chips following completion of drilling. Test pits were excavated by Wheeler Construction of Eugene, Oregon using a small track-mounted excavator with a two-foot wide bucket equipped with ripping teeth. The two test pits were excavated on March 11, 2013.

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PART 2 - SITE CONDITIONS AND GEOTECHNICAL BASELINE DATA

2.1 GEOLOGIC CONDITIONS

2.1.1 General

Dexter Dam lies near the western lower reaches of the Middle Fork Willamette River Basin. Drainage from the basin flows from the summit of the Cascade Mountain Range northwestward toward the head of the Willamette Valley. The pattern of drainage is typical with valleys developed by fault control.

The Western Cascade Mountains in this area were elevated by regional tectonic uplift, and by both intrusive and extrusive tectonic activity. Their uplift has been accompanied by both faulting and folding to a moderate degree. Fossil plant evidence indicates that the age or the rocks in the vicinity of the dam range from Eocene to Miocene. Valley alluvium is of late Pleistocene age. The construction area is in a transitional zone between a typical deeply incised channel of the Cascades and the more open filled valleys of the Lower Willamette Basin.

The Middle Fork Willamette River forms a northwest linear which is believed to be controlled by the Upper Willamette River fault zone, which marks the northwestern end of the Eugene-Denio fault zone.

The fault zone is marked by regional lineaments mostly expressed as linear stream valleys, such as the Middle Fork Willamette River.

During the original construction of the dam, the overburden encountered was generally shallow, consisting of loose, sandy gravel containing cobbles and occasional boulders. Cemented gravel and boulders were encountered in the fault-controlled channel beneath the upstream training wall. At the base of the right abutment a shallow residual slope of clay and talus was found to underlie the alluvial gravel.

The river channel existing before the start of construction was essentially free of overburden except for a few boulders and cobbles mantling the bedrock surface. Exhibit C shows photos during construction.

2.1.2 Overburden

Based on test pit and boring explorations in the proposed project area, subsurface soils conditions at the site are typically similar across the site, since much of the site was leveled by blasting prior to being brought to grade by placing the silty sand with gravel fill that is present. Most of the site is covered by this fill, up to approximately 25 to 30 feet in some locations (deepest appears to be on the eastern side of the site). There is a very thin topsoil layer covering the underlying fill.

Nearing the location of the northern fish ladder crossing, it appears that the site has the deepest locations of fill before reaching a lapilli tuff layer. This is likely due to the deepest cuts being made in this area for the construction and placement of the fish ladder and the large FWS water pipe that rests at approximately 20 to 26 feet below finish grade, just north of the fish ladder crossing.

2.1.3 Existing Fills

As discussed above, the entire site is mantled by up to approximately 30 feet of existing fill which was placed during construction of the original Dexter Dam Fish Facility in the 1950's. The fills generally consist of medium dense to dense, silty to sandy gravel, with some greater silt, sand, and crushed rock zones. Based on pre-dam topography, finished grades along the upper riverbank may currently be 2 to 20 feet higher in some locations than the original grades. Across the site where grass grows, the upper approximately 4 to 6 inches of the fill consists of soft to firm organic, sandy silt with some fines, which was apparently placed to promote lawn growth.

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In general, most of the fill material is well graded and relatively dense. However, there is no indication that this material was placed and compacted in a manner suitable to be considered structural fill, therefore none of the existing fill in this area should be considered for reuse as such. Most of the existing fill material at the site is not considered suitable to support structural loads.

2.1.4 Bedrock

General historical geological studies reveal bedrock in the fish facility area consisting of a series of pyroclastic rocks which have been intruded by a dense basalt. The pyroclastic rocks range from tuff through lapilli tuff to tuff breccia. A poorly bonded, slaggy tuffaceous basalt, adjoins the intrusive in several places. The intrusive basalt is extremely hard and fine-grained. It is part of a stock extending along the north side of the valley (at the fish facility location). Many fingers of the basalt intrude the pyroclastic rocks. Attitudes of the pyroclastic rooks are variable because of their irregular deposition and the subsequent local disturbance by the intrusion which was accompanied by warping and faulting.

Geologic maps and sections of the area can be found in Exhibit D, which show the locations and structural relationships of the rock units in the foundation. Correlation of several drill holes downstream from the right abutment indicate that the pyroclastic rocks in that area have a moderate southward dip away from the abutment.

2.1.5 Surface Water

The site is generally flat to very slightly sloping (1 to 3%), with no well-developed drainage pathways.

The paved areas generally slope gently to the south to the river or fish ladder. Surface water in the lawn area east of the existing fruit tree orchard generally pools and infiltrates into the ground surface.

2.1.6 Groundwater

Shallow groundwater within overburden sediments originates primarily from infiltration of rainfall and storm water runoff from higher elevations to the north, and from the river to the south. Groundwater concentrates on-top of the bedrock surface, or on less permeable soil interbeds, and flows to the south, towards the river. In the project area, the shallow groundwater aquifer is highly influenced by the tailwater elevation of the river, and the groundwater table fluctuates with the river elevation.

Piezometers were installed at boring locations B-7 and B-11. Data from the piezometers was collected for almost two years and is shown in Figure 1 and 2. Based on the data it appears that PZ-11 is sensitive to tailwater elevation, but PZ-7 appears to be influenced by precipitation and infiltration from upland areas to the north of the site. Groundwater elevations in PZ-7 fluctuates between approximately El. 651 and 657 feet (NAVD88) (approximately 2 to 3 feet below ground surface) with highest groundwater recorded during the winter months. The permeable nature of the sandy gravel fill and rock layers underlying the site allow for relatively rapid aquifer response to increased or decreased river elevations.

Groundwater is anticipated to periodically be present in the deepest excavations, particularly during high tailwater elevations, and therefore dewatering measures may be required. A dewatering plan will be developed by the contractor and reviewed by the contracting officer’s representative prior to construction.

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Figure 1: Locations of piezometers PZ-7 and PZ-11.

Figure 2: Piezometer data collected from PZ-7 and PZ-11.

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2.2 GEOTECHNICAL PROPERTIES AND CONSIDERATIONS

2.2.1 General

Existing materials at the site originated by a number of natural and synthetic processes and have different geotechnical properties. The major units at the site include:

1. Loose to medium dense, silty sand with clay organic topsoil

2. Medium dense to dense, silty to sandy gravely and fill

3. Volcaniclastic deposits (Lapilli Tuff), bedrock

4. Basaltic bedrock

2.2.2 Existing Fill

Most of the existing fills at the site are non-structural in nature and were originally placed following dam construction to level the site and to dispose of excavated material. In general, these fills consist of medium dense to dense, silty sand with gravel, but they can be highly variable in different areas of the site in both consistency and depth. There is no detailed information about the nature of the fill materials, or the methods of placement and compaction found in original construction documents.

2.2.3 Bedrock

Recent geotechnical exploration reveals bedrock ranging from very hard and dense basalt in the area of the proposed post sort pools to a very weathered lapilli tuff in the area of the proposed AWS chambers nearest the powerhouse. Mechanical excavation (rock breakers, hydraulic hammers, etc.) will be required in areas where the foundations of structures or pipes will extend into the basalt. The lapilli tuff varies by location and depth and appears to become softer moving eastward toward the powerhouse. Refer to the boring logs found in the Appendixes for details pertaining to the characteristics of the rock.

2.2.4 Geotechnical Parameters

During the 2013 geotechnical investigation, rock was found to be close to the surface across much of the site, with a mixed silty sand with gravel fill overlaying the rock. This fill is not to be considered to be appropriate for the placement of structures as structural fill and will be completely excavated where encountered for the placement of proper structural fill imported from offsite. Strengths of the rock will vary as well. Based on general attributes, the basalt in the area has an allowable bearing pressure of approximately 80 tons per square foot, and the lapilli tuff, approximately 10 tons per square foot.

2.2.5 Excavations

It should be assumed that much of the excavation operations across the entirety of the construction site will extend into bedrock. Estimates for schedule, labor, and equipment wear should reflect this possibility.

According to visual inspection of the rock cores obtained during the most recent Geotechnical Data Report (Exhibit B), the rock quality designation indicates that the upper reaches of the basalt could be excavated with rippers or large buckets, however, the basalt bedrock becomes more intact and more difficult to break as depths increase. Blasting is not permitted at the site so the deeper, more intact bedrock will likely require mechanical excavation with hydraulic hammers/rock breakers.

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Excavation and laybacks for construction will follow stringent guidelines for both safety and design of structures. Specifications for construction have been written in a way that allows for conservative estimates for the removal of overburden and bedrock material in order to achieve the specific required construction parameters.

Shoring and other temporary soil retaining methods will likely be required to some extent, given the difficult to reach elevations of the fish ladder and the surrounding soils. Removal of the existing FWS water pipe will be a considerable task given the extent of soil excavation expected and the pipe’s depth.

Removal and rerouting of the existing hanging power lines should be reviewed for the excavation process well into construction due to the possibility of excavation equipment interference both overhead and at the poles along the line of construction.

Most of the overburden materials can be excavated with standard equipment (dozers, backhoes and trackhoes). Where larger rock boulders are encountered larger excavators (45,000 pound plus) may be required. Much of the tuffacious bedrock material at the site is weathered and can be ripped with large excavation equipment. Excavator mounted rock hammers may be required where rock is less weathered and jointed. If basaltic bedrock is encountered, rock breakers will likely be required.

2.2.6 Utilization of Excavated Materials

The existing gravelly fill will not be reused as structural fills. The material will be removed from the site and disposed of in a location approved of by the Contracting Officer. This area will likely be near the abandoned sewage lagoon located to the west of the site.

2.3 RIVER CONDITIONS

The ordinary high-water mark (OHWM) is defined as the point on the stream bank at which the presence and action of surface water is so continuous as to leave a distinct mark by erosion, destruction or prevention of woody terrestrial vegetation, predominance of aquatic vegetation, or other easily recognized characteristic. The OHWM is often defined as the 2-year flood elevation. Below Dexter Dam the 2-year recurrence interval peak flow corresponds to about 20,700 cfs. Using this tailwater discharge yields an OHWM of 645 feet. Based on water temperature measurements from 2004 to 2012, the tailwater water temperature ranges from approximately 38 degrees Fahrenheit to 65 degrees Fahrenheit, with the coldest water temperatures typically recorded in late January to early February of each year.

2.4 EXISTING UNDERGROUND UTILITIES

Underground utilities are present throughout the site and include irrigation, water, sewer, stormwater, and electric lines. Information about the location and design of many of these utility lines can be found in the Drawings and Reference Documents of the Contract package. Other utility lines may be present that are not identified in the Contract package, including a number of irrigation lines in the house area. Utility locates will be required prior to excavation, including the use of geophysical methods, to identity and verify the locations of underground utilities.

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PART 3 - CONSTRUCTION CONSIDERATIONS

3.1 GENERAL

Construction of the Dexter Fish Collection Facility will involve excavation with variable soil, rock, and groundwater conditions. Detailed geotechnical and geologic observations and inspections will be required to ensure that adequate bearing material has been encountered and will be used for the placement of structures. There are two main foundation bearing scenarios for this site depending on locations and conditions encountered:

Scenario 1: Placement of foundation on rock: This scenario will require the removal of the existing overburden and weathered rock encountered in order to reach the required elevation depth and the placement of the foundation of structures or pipes on a competent material, such as lapilli tuff or basalt.

Twelve inches of select backfill aggregate will be applied to the rock surface for leveling and drainage for this scenario before foundations are placed.

Scenario 2: Placement of foundation on imported structural fill: This scenario will require the removal of the existing overburden and the placement of compacted imported structural fill to the required elevation depth for the foundation of structures and pipes. Six inches of select backfill aggregate will be applied to the compacted surface for leveling and drainage for this scenario before foundations are placed.

3.2 LOWER FISH LADDER AND AUXILLARY WATER SUPPLY (AWS) DIFFUSION

CHAMBER

The new AWS chambers are to be located at the farthest eastern extents of the job site, near the powerhouse and the fish ladder entrance. This system is being built into the existing parking lot where there are already several complex water pipe systems in place. Much of the access for the replacement of existing pipes and construction of the new AWS chamber diffusion system will be through existing fill. It can be assumed that construction in this area will encounter existing fill and pipe trench bedding, and that excavation in this area will be difficult due to the presence of both existing utilities and rock that slopes downwards in elevation towards the river. Rock is apparently present at the lower levels of this area as shown in some of the existing drawings, though exact depths are unclear from the historical construction documents and as-built drawings. The latest geotechnical investigations reveal lapilli tuff at depths between 17 to 25 feet from current grade, though some fingers of rock may be encountered sporadically through this excavation.

Due to the necessity of removal and replacement of existing pipes connecting to the new AWS system, construction sequencing will be complicated. It has been considered that full excavation north of the existing gravity wall adjacent to the fish ladder be accomplished and temporarily shored for construction purposes so that removal and replacement of pipes at design elevations can be accomplished. Continuous soil retention such as shoring is recommended from the area involving the AWS Chambers and pipe placement straight across to the west towards the transition to the upper fish ladder nearing the existing asphalt pond to retain the slope and maintain travel along the access road on the northern side of the excavation near the substation to the powerhouse.

Additional deep shoring and temporary soil retention will be required where the existing AWS pipe will be connected to the new construction. This area is located further east towards the powerhouse. The existing counterfort wall located on the southern side of the parking lot area will require removal. The new AWS chamber and new counterfort foundation is at an elevation approximately 8 to 10 feet deeper than the existing. This excavation can expect to encounter tuff and basalt that may require some excavation and leveling of the rock surface with hydraulic hammers.

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Excavation up to the existing powerhouse for the replacement of the AWS pipe will be complicated and will require shoring on both sides of the excavation. Stability of the powerhouse and adjacent gravity wall should be double-checked with both Corps of Engineers Structural Design and Dam Safety personnel.

The new fish ladder construction nearest the ladder entrance is expected to encounter bedrock and concrete at foundation elevations. Additionally, excavations are present in the as-builts below operation elevations very near to this area to remove fault gouge so that the tailrace wall and gravity wall could be founded on competent rock. The Contractor should be aware that the rock surface in this area does not account for the original construction necessity to fill to operational elevation with concrete, and that this concrete fill near the fish ladder entrance may be encountered during excavation. Over-excavation down to or into bedrock and replacement with approved backfill will be required after demolition of the existing ladder is accomplished. Select backfill aggregate will also be used for placement as a base material under the new ladder structure.

Management of groundwater and seepage from the adjacent cofferdam will be a major consideration and all action should be taken to prevent flooding of the work area along the foundations of the AWS Chambers and the lower fish ladder as it gains in elevation to the corner of the asphalt pond.

3.3 UPPER FISH LADDER

Moving westward, fish ladder elevations continue to rise, eventually with the foundations above the present grade leading to the Pre-Sort Pool. Demolition and replacement of the fish ladder along the design path is very complicated. Soil retention will be a major concern along both sides of the ladder to accommodate for construction, as the area falls between two slopes before reaching the asphalt pond.

3.3.1 Near the Fish Ladder Crossing

Shoring or other soil retention of the area around the access crossing will likely be required not only for the ladder construction, but also for the removal and replacement of the water system pipes within the northern slope.

Excavation of this area will likely encounter existing fill to the ladder foundation elevation, underlain by lapilli tuff or possibly basalt, as this area is a transitional area between the two rock zones. Construction sequencing should build from the bottom elevation upwards, compacting imported approved structural fill to reach design finish grade elevations, accommodating acceptable foundations for the new pipes making adjustments as needed.

3.3.2 Alongside the Existing Asphalt Pond

As the ladder construction rises in elevation and reaches further west along the asphalt pond, the existing retaining wall built to support the asphalt pond on the south side of the ladder is to remain intact, as this wall provides support of the existing asphalt pond that is to remain operational and undamaged. Great care must be taken at all times to ensure the support of this wall and prevent collapse of the soil surrounding the asphalt pond. Bracing of this wall during demolition and replacement of the fish ladder is essential in order to prevent catastrophic shearing failure. Sequencing plans of the construction of this area will be required prior to beginning work.

Materials under the ladder alignment moving westward are best shown by Exhibit E, which depicts the profile of the rock layer under the ladder from entrance to exit. As shown, the existing rock line dips at approximate station F2+50 to F3+07, where coarse gravels have been filled to meet the required ladder elevation.

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On the north side of the ladder construction, excavation to remove the existing pipe and placement of the new pipes will be required. Considering the close proximity of the slope on the north side of this area, additional shoring or soil retention will likely be required for the safe construction of both the ladder and pipe features.

Excavation of the area surrounding the ladder can expect to encounter the existing fill; however, this area extends into the basalt as described earlier in this report and will require much more effort to remove if necessary. Boring B-4a encountered basalt at a depth of approximately three feet below the existing surface. Because of the close proximity of the existing pipe, it could be assumed that the pipe trench was removed by blasting during original for placement of the pipe at design depth. This is also very likely for the placement of the original fish ladder.

3.4 PRE-SORT POOL

Excavation of existing fill to bedrock (basalt) may be required along this section leading up to the presort pool. Boring B-4a lies very close to the foundation location of the upper fish ladder and Pre-sort Pool.

This boring revealed basalt at a depth of approximately three feet below existing grade. Further to the west, Boring B-5 confirmed the depth of the basalt to be located at approximately three feet below existing grade. Test Pit #2, however, found fractured basalt at a depth of approximately one foot below existing grade. Therefore, it can be assumed that the foundation of the pre-sort pool and upper fish ladder will rest on the basalt in this area. All overburden—both topsoil and existing fill—is to be removed for the placement of the foundation, which will include 12 inches of select backfill aggregate under the structure and into the rock for leveling and stability. Mechanical vaults are designed to be placed within close proximity to the pre-sort pool and will bear on the basalt and 12 inches of select backfill aggregate after excavation of the existing overburden.

3.5 SORTING FACILITY AND OTHER LIGHT BUILDINGS

The light buildings include the Maintenance and Office Building, the Mechanical and Electrical Building, the Sort Facility roof and slab, and the Pre-Sort Pool roof. These buildings are in an area with approximately 1 to 6 feet of overburden consisting of the existing silty sand and gravels, underlain by basalt. Because of the unknown characteristics of the existing soil in place, over-excavation to the competent rock contact will be required and backfilled with imported, approved compacted backfill to finish grade elevations required. Groundwater is anticipated to periodically be present in the deepest excavations, particularly during high tailwater elevations, and therefore dewatering measures may be required.

3.6 POST-SORT POOLS

The bottom foundation elevation of the Post-Sort Pools will be approximately 8-12 feet below existing grades, with the hopper pit foundation being approximately 15-19 feet below existing grades. The foundation bearing material for the Post-Sort Pools and Hopper Pit will be very hard basalt. The excavation will extend through approximately 2 to 6 feet of existing fill; underlain by weathered, fractured basalt, underlain by solid rock that continues to an unknown depth. Boring B-9 located just to the north of the post-sort area revealed basalt with Rock Quality Designation (RQD) of up to 94% and continued to 50 feet deep.

The Post-Sort area lies just to the north of the existing holding ponds that must remain operational during construction distance between this structure and the Post-Sort Hopper construction area is approximately 6 to 8 feet. Protection of the ponds from any damage is required. Shoring efforts, if required, must also be approved by the contracting officer. A construction sequencing plan will be required prior to this work.

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Groundwater is anticipated to be present in this area, at depths that will likely vary due to perched water table action and aquifer flows southward from the slope to the river and can fluctuate greatly, particularly during high tailwater elevations and storm events. Dewatering measures will likely be required. The Hopper Pit foundation in particular will likely extend below the groundwater table throughout much of the year, and therefore dewatering of this excavation will most likely be required during construction.

3.7 HOPPER CRANE STRUCTURE

The eastern end of the hopper crane structure will be supported on the post - sorting pool and hopper Pit structure discussed above. The western end of this structure will be supported on spread footings embedded approximately four feet below existing grade. At this depth the footing will be supported on imported, compacted structural fill that has been built up around the post-sort pool excavation. Loads on these western footings will be generally light, and six inches of select backfill aggregate will be required for leveling and stability under this footing as shown in the contract drawings.

Groundwater is anticipated to be below the western footing elevations during all but the most extreme tailwater conditions. Groundwater is not anticipated in this excavation, with the exception of minor seepage along perched interbeds during rainy conditions, which may require dewatering.

3.8 WATER SUPPLY PIPING

Various sizing of water supply piping will be installed across the site. Refer to the contract drawings for specific trenching requirements.

3.8.1 New FWS Pipe

The new underground FWS Pipe to replace the existing pipe will extend from Dexter Dam west of the Powerhouse, trend westward to feed the new AWS chambers, then extend westward along the north side of the lower fish ladder and along the upper fish ladder until it connects to feed the pre-sort pool. It then continues westward and to the north, avoiding interaction with footings and other pipes and foundations around the Sorting Area, then turns southward to make the connection at the original outlet at the holding ponds. Excavation will generally be in existing fills along its eastern extent, then transition into underlying bedrock along its western extent.

Shoring or soil retention and slope protection will be necessary along the pipe excavation for much of the pipe placement. In the parking lot area near the AWS chambers, shoring and bracing will be required on both sides of the excavation to locate and connect the new pipe to the existing outlet nearest the powerhouse. Moving westward, shoring and bracing will be required along the northern edge of the parking lot area, allowing constant vehicle access to the powerhouse and keeping the existing Lane Electric substation intact without damage due to undermining.

This pipe is part of the first phase of construction and must be completed and running at the end of the first scheduled fish facility shutdown. Construction around this pipe while it is running will be complicated and will require strict coordination and approved construction sequencing in order for the project to be successful.

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Nearing the fish ladder crossing, the design elevations suggest placement on top of imported, compacted structural fill that is being built up from the bottom of the excavation after removal of the existing FWS pipe. Shoring and bracing of the soils to the north of the excavation will be required, as layback areas will not be available due to the access road that must remain operational.

The same methods will be required moving westward along the upper fish ladder that lies between the existing asphalt pond and the slope that upholds the access road. Excavation around this area will be transitioning into the basalt found onsite and may require heavy excavation practices to remove the rock that will be present as the pipe continues westward. Along the northern most path near the sort area, the pipe will likely encounter basalt at depths of 1-3 feet as it runs along the slope upholding the access road to the north. Slope protection during excavation and construction work will likely be required.

Shallow, perched groundwater should be expected which may require dewatering. Close monitoring of the piezometers located at Borings B-7 and B-11 will be required.

3.8.2 AWS Return Pipe

This pipe begins at the inlet located at the existing fish ladder and continues along the same path with the new FWS pipe, flowing eastward to its outlet at the AWS chambers. Excavations for this pipe will be the same as the new FWS, as the pathways are parallel.

3.9 TEMPORARY COFFERDAMS

During construction, three cofferdams will need to be constructed:

1) To dewater the area of the AWS Chambers through the Lower Fish Ladder near the Fish Ladder

Crossing and prevent seepage problems through to the upper reaches of the fish ladder as it gains in elevation towards the asphalt pond. Tying into the existing riverbank slope will require removal of the riprap that is present and then forming a water-tight seal within the current road embankment at the foundation to keep water from moving under the cofferdam. The road embankment consists mostly of granular soils (fill) and cutting off the water infiltration will be required as part of keeping the work area dewatered.

2) To dewater the area around the return to river pipe outfall. Though the final design for this feature is not yet completed as of the date of this document, the Contractor should expect to encounter structural fill within the road embankment under the erosion protection that is present up to approximately 15 feet, where exploratory drilling met refusal in rock. Underwater, the bedrock will likely be overlain by gravels, cobbles, and boulders mantling the surface.

3) To dewater the area around the foundation, drain outfall. Similar to the return to river pipe outfall above, the final design for this feature is not yet completed as of the date of this document, and the Contractor should expect to encounter structural fill within the road embankment under the erosion protection that is present up to approximately 15 feet, where exploratory drilling upstream met refusal in rock. Underwater, the bedrock will likely be overlain by gravels, cobbles, and boulders mantling the surface.

The contract documents require submittal of the work plan involved with building and maintaining the integrity of the cofferdams including contingencies involving the possibility of encountering various types of soil during construction. It is anticipated that bedrock will be encountered in the river channel at relatively shallow depths and will require some over-excavation of gravels and boulders to form a seal required for the placement of the cofferdam. At the time of this document, no bathymetry was available.

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3.10 ELECTRICAL DUCT BANKS

At the time of this document creation, no designs have been generated to depict the locations or pathway of the estimated 2x2’ electrical duct bank that will be required for construction. Placement of this feature should be near the locations of the pipe placements, and reference to the expectations of these excavations should be noted. It may be required that alignment of the duct bank or other pipes could require deeper placement than expected, which move into the underlying basalts. This excavation will likely require rock breaking or other heavy effort for removal and placement of designed features.

3.11 FOUNDATION DRAINS

Refer to Contract Drawings for placement of facility foundation drains. Excavations of foundation drains are to be placed no deeper than the expected water table influence elevation.

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Exhibit A

Historic Exploration Logs

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Exhibit B

Geotechnical Data Report

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Figure B-1: Boring Locations Specific to This Contract – See Contract Drawings For Historical Data

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Figure B-2: Summary logs of 2013 exploratory borings.

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REPORT

May 2013

US ARMY CORPS OF ENGINEERS

PORTLAND DISTRICT

GEOTECHNICAL DATA REPORT

DEXTER DAM ADULT

FISH FACILITY UPGRADES

Lowell, Oregon

CORNFORTH

C O N S U L T A N T S

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May 10, 2013 2262

Mr. Stephen Eagar, P. E.

U.S. Army Corps of Engineers, Portland District P.O. Box 2946 Portland, OR 97208-2946

Geotechnical Data Report Dexter Dam Adult Fish Facility Upgrades Lowell, Oregon

Dear Mr. Eagar:

In accordance with our authorized scope of work, we have completed the geotechnical explorations for the proposed upgrades at the Dexter Dam adult fish facilities. Our work was completed in response to the Detailed Statement of Work for Contract No. W9127N-10-D-0001, Task Order No. 0017. This letter summarizes the results of the site explorations and laboratory testing that were completed as outlined in the Statement of Work.

Background and Scope of Work We understand that the U.S. Army Corps of Engineers, Portland District (CENWP) is tasked with designing upgrades for the adult fish facilities at Dexter Dam. Subsurface conditions and geotechnical parameters are required for structure foundation and site grading designs for the new facilities.

The scope of work for this task order included the following items:

• Advance seven exploratory borings to depths between 20 and 30 feet below the existing ground surface, or a minimum of 5 feet into hard bedrock at the locations selected by

CENWP.

• Excavate two test pits to depths of 15 feet each below the existing ground, or to refusal at the locations selected by CENWP.

• Collect photographs of materials encountered or sampled during the explorations.

• Install a standpipe piezometer at locations selected by CENWP.

• Mark the locations of all explorations at the completion of work.

• Perform laboratory testing on selected soil samples as outlined in the Detailed Statement of Work.

• Summarize the results of the site explorations and laboratory testing in a data report.

May 10, 2013 2 Cornforth Consultants, Inc.

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Site and Project Description The proposed facility improvements will be located on the downstream right abutment side of Dexter Dam, which is approximately 20 miles southeast of Eugene, Oregon immediately off of State Highway 58. The location of the project is shown on a Vicinity Map in Figure 1. New structures would be constructed on the right bank of the Middle Fork of the Willamette River.

Many of the new structures would be constructed adjacent to the existing fish facilities, on a relatively flat terrace created during construction of the original facilities. Vegetation consists of lawn areas around the existing fish facility structures, small to medium fruit trees near the fish facility manager’s residence, and medium-sized deciduous and evergreen trees in clusters on the margins of the site.

Subsurface Explorations The field explorations for this work included seven borings and two test pits. The approximate location of the borings and test pits are shown on a Site Plan on Figure 2. Photographs were taken during the fieldwork of soil and rock recovered during the explorations. A few representative photographs are grouped together by exploration and included in Appendix A of this report. As required by the Statement of Work, all photographs collected during this investigation are included in digital format on a separate compact disc provided to the CENWP.

Borings. Drilling for all exploratory borings was performed by Hardcore Drilling of Dundee, Oregon between February 27 and March 4, 2013. Borings were drilled with a track-mounted CME 850 drill rig using mud rotary and HQ3 core drilling techniques. A geologist from our office was present throughout the exploration program to coordinate field activities and complete a field log of subsurface conditions. Disturbed samples were collected in conjunction with Standard Penetration Tests (SPTs). Planned undisturbed samples (Shelby tubes) were not collected at the site as no fine-grained soils suitable for sampling were encountered during the drilling. Details of the drilling conditions and subsurface materials encountered are presented on Summary Boring Logs on attached Figures 3 through 9. A one-inch diameter standpipe piezometer well was installed in Boring B-7 to measure groundwater levels. Details of the sandpack around the piezometer tip and the ground surface seal are provided on the Summary Boring Log for B-7.