Willamette Pump Station and Force Main Final 2022-04-29 FULL - Appendix C corrected-compressed.pdf

Willamette Pump Station and Force Main

Alternatives Analysis and Concept Design

FINAL | April 29, 2022

Clackamas Water Environment Services

Document Title

Client Name i

Willamette Pump Station and Force Main Alternatives Analysis and Concept Design

Project No: 672585CH.03.30.20.19

Document Status: Final

Date: April 29, 2022

Client Name: Clackamas Water Environment Services

Jessica Rinner, PE

Lynne Chicoine, PE

Author: Sven MacAller, PE

Shad Roundy, PE

Jacobs

2020 SW Fourth Avenue

3rd Floor

Portland, OR 97201

United States

T +1.503.235.5000 www.jacobs.com

© Copyright 2019 Jacobs. The concepts and information contained in this document are the property of Jacobs. Use or copying of this document in whole or in part without the written permission of Jacobs constitutes an infringement of copyright.

Limitation: This document has been prepared on behalf of, and for the exclusive use of Jacobs’ client, and is subject to, and issued in accordance with, the provisions of the contract between Jacobs and the client. Jacobs accepts no liability or responsibility whatsoever for, or in respect of, any use of, or reliance upon, this document by any third party.

Document history and status

Revision Date Description Author Checked Reviewed Approved

4/29 Draft to Final SJR ii

Contents

1. Introduction

2. Background

2.1 Existing Infrastructure

2.2 Design Flow Rates

2.3 Design Criteria

2.4 Cost Criteria

3. Alternatives Evaluation

3.1 Master Planning Alternatives

3.2 River Crossing Alternatives Evaluation

3.2.1 River Crossing Construction Methods

3.2.1.1 Construction Methods for Pipelines

3.2.1.2 Geotechnical Challenges for Trenchless Technologies

3.2.2 Alternative 4.1

3.2.3 Alternative 4.2

3.2.4 Alternative 4.3

3.2.5 Alternative 4.4

3.2.6 Cost Comparison

3.2.7 Preferred River Crossing Alternative

3.3 Upstream Force Main Routing Evaluation

3.4 Other River Crossing Alternatives and Force Main Routing Option Considerations

3.4.1 Soils and Flood Plain

3.4.2 Environmental Impacts

3.4.3 Utilities

3.4.4 Land Ownership

3.4.5 Potential Coordination with Other Infrastructure Projects

4. Conceptual Design

4.1 Pump Station

4.1.1 Pump Station Rehabilitation/Expansion vs Pump Station Replacement

4.1.2 Pump Station Siting

4.2 Force Main Alignment and Sizing

4.2.1 Force Main Coordination with Transportation Projects

4.2.2 Force Main Alignment from the Pump Station Site on Willamette Falls Drive to Sunset Avenue

4.2.3 Force Main Alignment from Sunset Avenue to the I-205/Abernethy Bridge

4.2.4 I-205/Abernethy Bridge Crossing

iii

4.3 Preliminary Pump Selection

4.3.1 Pump Configuration 1 – Flygt NP3231/735 3~480

4.3.2 Pump Configuration 2 –Flygt NP3231/765 3~480

4.3.3 Pump Configuration 3 – Flygt NP 3312/865 3~670

4.3.4 Preliminary Pump Recommendation

4.4 New Force Main Surge Analysis

4.5 Combination Air Valves

4.5.1 Combination Air Valves on the I-205/Abernethy Bridge

4.6 Class 4 Cost Estimate

4.7 Project Phasing

4.7.1 Use of Existing Force Main

4.7.2 Willamette Force Main Condition Assessment

4.7.3 Existing Force Main Hydraulics

5. References

Appendix A. Examples of Trenchless Crossings of the Willamette River

Appendix B. Hydraulics and Surge Analysis, I-205/Abernethy Bridge Crossing

Appendix C. Pump Selection Manufacturer Information

Appendix D. I-205/Abernethy Bridge Force Main Design (basis of design)

Appendix E. I-205/Abernethy Bridge Force Main Design (drawings)

Appendix F, Existing Willamette Pump Station and Force Main As-builts and Other Facility

Documentation

Appendix G. Willamette Pump Station and Force Main Alternatives and Concept Design - Workshop

Presentations

1. Introduction

A new Willamette Pump Station and Force Main were identified as capital improvements in the Clackamas

Water Environment Services (WES) Sanitary Sewer Master Plan (SSMP, Jacobs, 2019) to serve areas of the

City of West Linn, Oregon on the west side of the Willamette River. This report documents an alternatives analysis for the new Willamette Pump Station and Force Main improvements and a conceptual design for a preferred improvement alternative. The alternatives analysis addresses force main alignment options and

Willamette River pipeline crossing options for the new force main. Within the analysis, opportunities were also evaluated for redundant Willamette River pipeline crossings for the Bolton and River Street Pump

Stations which also serve the City of West Linn.

As the alternatives analysis was occurring, an immediate opportunity was identified to coordinate with the

Oregon Department of Transportation (ODOT) to design and construct the Willamette River pipeline crossing on the Abernethy Bridge (I-205 Bridge), saving WES millions of dollars compared to an under-river crossing. The design of the Abernethy Bridge pipeline crossing has since been completed and is referenced in this report. Based on elevation, the bridge pipeline crossing will connect in the future to the new Willamette Pump Station and Force Main but cannot not serve as a redundant pipeline river crossing for the Bolton and River Street Pump Stations due to its elevation.

The conceptual design in this report for the Willamette Pump Station and Force Main includes preliminary pump selection, pump station configuration, and the preferred alignment for the force main upstream of the Abernethy Bridge pipeline crossing.

2. Background

The background section of this document includes information about existing infrastructure in the project area, design flows, cost criteria, and design criteria used for the alternative analysis.

2.1 Existing Infrastructure

An overview of existing infrastructure for the Willamette Pump Station and Force Main is shown in Figure

2.1. Components relevant to this project are the Willamette, Bolton and River Street Pump Stations and

Force mains and the Willamette Interceptor where the pump stations currently and ultimately discharge.

The Bolton and River Street Pump Stations are included because of a potential to consider a redundant river crossing pipe associated with a new Willamette Force Main.

• The Willamette Pump Station and Force Main serve areas on the west side of the Willamette River including the southwest portion of West Linn. The existing pump station is located on 4th Street between the Willamette River and Willamette Falls Drive. Existing firm capacity (largest pump out of service) is 4.4 million gallons per day (mgd) with a total capacity of 5.5 mgd. A pump and system curve for the existing pump station is shown in Figure 2.2.

• The existing 18-inch Willamette Force Main roughly follows Willamette Falls Drive. The force main transitions to a gravity flow near a high point on Willamette Falls Drive. Existing force main length is

6,170 feet. A force main profile is shown in Figure 2.3.

• The Willamette Force Main discharges to the West Linn Interceptor (21 to 24-inch diameter) which follows Willamette Falls Drive and Mill Street before crossing the river on the Oregon City / Arch

Bridge (18-inch diameter across bridge) just downstream of Willamette Falls. After crossings the bridge, a drop structure conveys flow into the Willamette Interceptor on the east side of the river.

• The Bolton and River Street Pump Stations serve the north and east areas of West Linn. The Bolton

Force Main (16-inch diameter) is 6,180 feet and the River Street Force Main (12-inch to 16-inch diameter) is 2,600 feet. Both force mains cross under the Willamette River and discharge to a single

30-inch gravity sewer (Oregon City Interceptor) near Highway 99. The Oregon City Interceptor transitions to 42-inch diameter and discharges into the Willamette Interceptor. Existing firm capacity at the Bolton Pump Station was recently expanded to approximately 4.8 mgd and no additional capacity expansions are planned. Existing firm capacity at River Street Pump Station is 2.8 mgd and no capacity expansions are planned. Pipeline profiles and pump/system curves for the Bolton and River

Street Pump Stations are shown in Figures 2.4 through 2.7.

• The Willamette Interceptor is a large gravity interceptor with diameter ranging from 30-inches at the

Arch Bridge and confluence with the West Linn Interceptor to 72-inches where the Bolton and River

Street Pump Stations discharge flows enter the interceptor. The Willamette Interceptor conveys combined wastewater flows for the Cities of West Linn, Oregon City, and Gladstone to the Tri-City

Water Resource Recovery Facility (WRRF).

• Elevations presented in this document are in NGVD 29 vertical datum.

Figure 2.1. Study Area and Infrastructure Map (PS=pump station, FM=force main)

I-205

Transition from pressurized force main to West Linn

Interceptor

West Linn and

Willamette

Interceptors

Capacity Limited Willamette PS and

FM identified for improvement

Recent FM re-route, pump replacement

Existing Arch

Bridge Pipe

Crossing

River Crossings for Bolton and

River St Pump

Stations (12 and 16-inch)

Figure 2.2. Existing Willamette Pump and System Curve

0 2 4 6 8 10

H e a d

F e e t)

Flow (gpm)

Willamette Pump Station

Pump Curve - 1 Pump Pump Curve - 2 Pumps

Pump Curve - 3 Pumps System Curve (Hazen Williams C=120)

Firm Capacity =

4.4 mgd

Figure 2.3. Willamette Force Main Profile

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

El ev at io n fe et

Station

Pipe Invert

Pipe Crown

Rim

Tran sitio n to

G ravity

W illam e tte Fo rce m ain

H igh

P o in t

W illam e tte P u m p Statio n

18-inch 21-inch

Existing gravity sewer

Existing force main

Willamette Falls Drive

Ground

Figure 2.4. Bolton Force Main Profile

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+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

+0

El ev at io n fe et

Pipe Invert

Pipe Crown

Rim

Fo rce m ain H igh P o in t

Pipe Trestle

River Crossing

B o lto n

P u m p

Statio n

Start o f gravity se w e r

G lad sto n e Fo rce M ain

W illam e tte In tercep to r

B u rn s Street

Figure 2.5. Existing Bolton Pump and System Curve

0 1 2 3 4 5 6 7 8 9 10

H ea d

Fe et

Flow (mgd)

Bolton Pump Station

Pump Curve - 1 Pump Pump Curve - 2 Pumps

Pump Curve - 3 Pumps System Curve (Hazen Williams =120)

Firm Capacity =

4.8 mgd

Figure 2.6. River Street Force Main Profile

+0

+0

+0

+0

+0

+0

+0

El ev at io n fe et

Pipe Invert

Pipe Crown

Rim

River Crossing

R iver Street P u m p Statio n

G lad sto n e Fo rce M ain

Start o f gravity sew er

W illam e tte In tercep to r

B u rn s Street

Figure 2.7. River Street Pump and System Curve

0 1 2 3 4 5 6

H ea d

Fe et

Flow (mgd)

River Street Pump Station

Pump Curve - 1 Pump Pump Curve - 2 Pumps

Pump Curve - 3 Pumps System Curve (Hazen Williams C=120)

Firm

Capacity =

2.8 mgd

2.2 Design Flow Rates

Design flow rates for the Willamette Pump Station, Force Main and river crossing evaluations are based on the flow methodology from the SSMP as summarized below:

• Population and employment forecasts were developed by EcoNorthwest (EcoNothwest, 2016) from

Oregon Metro and Portland State University Population Research Center data.

• Existing dry weather flow (DWF) rates were developed by calibrating the collection system model average dry weather flow rates and existing system diurnal patterns to localized flow monitoring data.

• Future dry weather flow rates were developed by applying average per capita (67 gallons per capita per day) and per employee wastewater rates (50 gallons per employee per day) to population and employment forecasts. The future average dry weather flow rates were modeled using calibrated diurnal patterns to calculate peak dry weather flow rates.

• Existing wet weather flow (WWF) rates were developed by calibrating the collection system model rainfall derived and inflow and infiltration (RDI/I) unit hydrographs to localized flow monitoring data.

The model was then simulated with a historic precipitation event (November 2011) that produces a minimum 5-year rainfall and flow frequency in the system.

• Future wet weather flow rates were developed by applying calibrated unit hydrographs to future growth areas and simulating the historic precipitation event that produces a minimum 5-year rainfall and flow frequency. A second storm event that produces a minimum 10-year rainfall and flow frequency was also simulated for sizing gravity infrastructure improvements. System degradation was considered for aging infrastructure by increasing RDI/I response over time. An evaluation was performed to determine cost-effective RDI/I reduction levels relative to increased conveyance and treatment capacity. Based on the evaluation, targeted RDI/I reduction was recommended in sub-basins with excessive wet weather flow contributions including areas upstream of the Willamette

Pump Station.

Design flow rates are summarized in Table 2.1 for key infrastructure locations for this evaluation.

Table 2.1. Pump Station Design Flow Rates and Existing Capacity

Infrastructure

Existing

Firm

Capacity

(mgd)

Existing

Total

Capacity

(mgd)

2020 Peak

Hour Dry

Weather

Flow (mgd)

2020 Peak

Hour Flow

(mgd)1

2040 Peak

Hour Dry

Weather

Flow (mgd)2

2040 Peak

Hour Flow

(mgd)1, 2

Willamette

Pump Station

4.4 5.8 2.5 7.7 2.7 10.6

Bolton Pump

Station

4.8 5.5 0.7 4.5 0.9 4.8

River Street

Pump Station

2.8 3.1 0.2 0.8 0.2 0.7

Notes:

1 Peak hour flow during 5-year design storm event.

2 2040 approximates buildout condition.

2.3 Design Criteria

Criteria used to evaluate gravity, force main and pump station capacity, and size new infrastructure are defined as follows:

• Gravity Trunk (wet maximum) – For existing gravity trunk sewers, minimum 2 feet of freeboard to ground surface required during peak flow conditions during the 5-year design storm event. New gravity trunk sewers are sized to full flow capacity (no surcharging) during the 5-year design storm event. Minimal surcharging may be allowed if oversizing creates a scouring velocity issue in the near-term for dry weather flow conditions. Sensitivity flow rates (greater degradation and less wet weather flow reduction) are used to test sizing to ensure that the system does not overflow and that surcharging does not result in less than 2 feet of freeboard in the long-term.

• Gravity Trunk (dry maximum) – Maximum flow depth does not exceed 80-percent of pipe diameter for peak dry weather flow conditions. Excess capacity in the pipeline allows for controlled release of odors at the nearest downstream pump station or treatment facility and minimizes corrosion risks

• Gravity Trunk (scouring) - Sizing and pipe slope to consider near-term scouring velocity of 2 feet per second (fps) to avoid solids deposition during dry weather flows.

• Gravity Trunk (depth) - Sewer profile depth avoids excavation in excess of 15 feet while considering depth of existing and future service connections

• Pump Station (wet maximum) – Pump station operates with a firm capacity (largest pump out of service) equal to or greater than the peak hour flow during the 5-year design storm event.

• Force main (maximum) – Maximum velocity in the force main does not result in excessive friction losses and excessive total dynamic head (TDH) requirements for the pump station. Typically, maximum velocities are in the 5 to 8 fps range to minimize TDH.

• Force main (minimum) – Minimum velocity of 3.5 fps to re-suspend solids.

2.4 Cost Criteria

Cost estimates for the conceptual design were developed using Class 4 budget estimates, as established by the American Association of Cost Engineers (AACE). This preliminary estimate class is used for feasibility screening and assumes project definition maturity level between one and fifteen percent. The expected accuracy range is -15 to -30 percent on the low end, and +20 to +50 percent on the high end.

Cost estimates are intended to be used as guidance in establishing funding requirements at the project concept level based on information available at the time of the estimate. Estimates exclude land acquisition, financing, and inflation. The unit costs were developed in 2021 dollars for the conceptual design. Bid tabs for similar projects were specifically reviewed to establish factors for wetland construction and trenchless construction techniques.

Cost assumption details are summarized as follows:

• Pump station capital costs were developed from pump station cost curves populated from other similar Portland area wastewater pump station projects.

• Pipeline capital costs were developed for force mains and gravity pipes. An environmental factor of 40 to 100-percent was applied to construction in sensitive areas to account for environmental permitting, surface restoration, and construction matting.

• The force main costs include pipe materials, installation costs, and surface restoration. Unit costs assume that force mains are installed at no more than 10-foot depths, using American Water Works

Association (AWWA) C900 pipe and restrained joints. The force main costs were derived from ODOT and City of Portland cost referencing.

• Gravity sewer unit costs include pipe material (assumed to be PVC for diameters up to 36-inch and reinforced concrete pipe for larger pipes), installation, manholes at an average interval of 400 feet, bypass pumping where applicable, and surface restoration. Material costs are based on City of

Portland cost referencing and Ogden Oldcastle quotes. Installation and surface restoration costs are based on previous project experience in the area including ODOT and City of Portland project costs.

• Trenchless construction costs including micro-tunneling, horizontal directional drilling, auger bore, and pipe ram construction techniques were estimated between $2,500 and $8,000 per lineal-foot for large diameter improvements (>=24-inch) depending on complexity of the construction and complexity of river crossings. Actual costs vary based on mobilization and availability of construction equipment.

• Unit capital cost estimates for a pipeline bridge crossing (20 to 24-inch diameter) is approximately

$1,300 per lineal-foot.

• All costs were marked up using a uniform cost basis for factors and fees as shown in Table 2.2 including a composite contingency and indirect construction cost multiplier of 1.95.

Table 2.2. Contingency and Indirect Cost Multipliers

Cost Item Cost Multipliers

Construction Contingency 30%

Indirect Costs:

Design/Permitting/Public Involvement 25%

Construction Management

General Conditions 25%

Contractor Overhead & Profit

Total Indirect Costs 50%

Contingency and Indirect Multiplier 1.95

3. Alternatives Evaluation

The alternatives evaluation includes information from preliminary work performed as part of the 2019

Clackamas WES SSMP (Jacobs, 2019) and updated analysis for a new pump station, force main alignment and river crossing to convey flows from the Willamette Pump Station to the Tri-City WRRF.

3.1 Master Planning Alternatives

The SSMP (Jacobs, 2019) identified capacity deficiencies in the Willamette Pump Station, West Linn

Interceptor, and Willamette Interceptor. As shown in Section 2, Table 2.1, the Willamette Pump Station estimated peak hour inflow during the 5-year design storm exceeds the existing station firm capacity (4.4 mgd vs 7.7 mgd inflow). Additionally, the downstream gravity interceptors (West Linn Interceptor including Arch Bridge Pipeline and Willamette Interceptors) were identified as capacity deficient if the

Willamette Pump Station is improved to increase firm capacity (see profile in Figure 3.1). During the

SSMP, WES staff considered a range of RDI/I reduction targets and eventually selected a target of 65-percent wet weather flow reduction for subbasins upstream of the Willamette Pump Station. Even with targeted reduction by 2040, the Willamette Pump Station and the downstream interceptors were identified as deficient. In addition to the targeted RDI/I reduction, multiple alternatives were identified in the SSMP to address the capacity limitations for the pump station and interceptors as described below and shown in Figure 3.2.

• Master Plan Alternative 1 - Upgrades to the existing pump station and force main including the Arch

Bridge pipeline crossing. The alternative was eliminated because of the limitations of the Arch Bridge structural capacity and requirement to also improve the middle segment of the Willamette Interceptor immediately downstream of the confluence with the West Linn Interceptor. The Willamette Interceptor is located in downtown Oregon City and adjacent to the Willamette River Sea Wall which makes construction and access challenging.

• Master Plan Alternative 2 – Wet Weather Storage Facility adjacent to the Willamette Pump Station at the Blue Heron Site. The alternative was eliminated when WES sold the Blue Heron site.

• Master Plan Alternative 3 - Upgrades to the existing pump station and rehabilitation of an abandoned

Blue Heron River Crossing pipeline. The alternative was eliminated because of the condition of the existing river crossing pipeline and likely loss of capacity from rehabilitation of the pipe. Also, the alternative would have required improvement of the upper and middle segments of the Willamette

Interceptor.

• Master Plan Alternative 4 – Upgrades or replacement of the existing pump station and new force main with a Willamette River pipeline crossing adjacent to the Abernethy Bridge. Alternative 4 was selected as the preferred alternative for the following reasons.

• Ability to provide additional river crossing (redundancy)

• Limits impact to critical capacity sections of the Willamette Interceptor (Alternative 1)

• No storage facility to maintain (Alternative 2)

• Avoids risk involved in using the old Blue Heron Line (Alternative 3)

In Alternative 4, a new larger diameter force main was selected instead of an extension of the existing

18-inch force main. The existing force main size, with future design flows, experiences excessive velocities and headloss and increases pump head requirements.

The preferred alternative, SSMP Alternative 4, was further evaluated for alignment and river crossing sub-alternatives as documented in Section 3.2 and Section 3.3.

Figure 3.1. Capacity Limitations West Linn and Willamette Interceptors

West Linn and Willamette Interceptor Profiles

West Linn

Interceptor deficient by 2040 with Willamette

Pump Station

Discharge

West Linn

Interceptor and

Arch Bridge Pipe existing and 2040 deficiency with expanded

Willamette Pump

Station

Willamette

Interceptor existing and 2040 deficiency with expanded

Willamette Pump

Station

Figure 3.2. Sanitary Sewer Master Plan Alternatives (Jacobs, 2019)

3.2 River Crossing Alternatives Evaluation

Four sub-alternatives were included in the alternatives analysis for the portion of the force main crossing the Willamette River, near I-205/Abernethy Bridge to the Willamette Interceptor, as described below and shown in Figure 3.2. Alternatives 4.1, 4.2 and 4.3 cross under the river and include trenchless and open cut construction methods.

• Alternative 4.1 - Crosses under the river adjacent to the existing River Street and Bolton Force Mains.

• Alternative 4.2 - Crosses under the river between the existing Bolton and River Street crossing and the

I-205/ Abernethy bridge.

• Alternative 4.3 - Crosses under the river adjacent to the Abernethy Bridge.

During the initial work to evaluate the three alternatives under the river, a fourth alternative was identified for an above ground bridge crossing associated with immediate work being performed by ODOT to design an expanded I-205/Abernethy Bridge from West Linn to Oregon City. The timing of the bridge project presented an opportunity to coordinate design of a sewer crossing utilizing the bridge structure.

• Alternative 4.4 - Crosses over the river on the I-205/Abernethy Bridge.

Because of the accelerated timing of the bridge project and the cost savings identified for Alternative 4.4, the review of the other three river crossing alternatives was suspended and Alternative 4.4 was selected for immediate design and implementation. The scope of the bridge crossing design was limited to the bridge approach, bridge crossing, and bridge descent section to the Willamette Interceptor.

All river crossing alternatives are described in Section 3 to provide documentation of the early alternative’s evaluation and the ultimate selection of Alternative 4.4. Once selected, Alternative 4.4 became the focus of the concept design including how to integrate the bridge crossing with the upstream segments of the Willamette Force Main and Pump Station.

Figure 3.2. Willamette River Crossing Alternatives Overview

Transition from pressurized force main to gravity/siphon flow

New Willamette Pump

Station

Connection to

Emergency Crossing for Bolton and River St

Pump Stations

Start

Alternative 4.3

(under river)

Existing Force Main

Route – Option 1

(green)

Force main Route –

Option 3

Start

Alternative 4.1

(under river)

Force main

Route –

Option 2

Start Alternative 4.4

I-205/Abernethy Bridge

Crossing

Start

Alternative 4.2

(under river)

End

Alternative

4.4

End Alternatives

4.2 & 4.3

End Alternatives

4.1

River Crossing, Alt 4.2

River Crossing, Alt 4.3

River Crossing, Alt 4.4

Force Main Route

Options

Existing Force Main

Route Option

River Crossing, Alt 4.1

3.2.1 River Crossing Construction Methods

This section describes construction methods and risks with an emphasis on risks associated with pipeline construction under the Willamette River for Alternatives 4.1, 4.2, and 4.3. This section was prepared prior to the decision to construct the force main on the Abernethy Bridge (Alternative 4.4) but has been retained for informational purposes.

3.2.1.1 Construction Methods for Pipelines

The following construction and excavation methods were considered for pipeline construction under the

Willamette River. Definitions of each method and example river crossing projects for the Willamette River are provided in Appendix A.

• Open Trench River Crossing - Open trench construction through the river. This method includes trench excavation, trench backfill and compaction. Excavation equipment is located on a floating barge and excavates the river bottom. Pipelines are typically weighted down to ensure they do not float to the surface. Open trench in water work is more complicated than on land but less complex than trenchless river crossing methods. Permitting can be more challenging due to disturbance of aquatic ecosystems and construction timing is typically limited to times where water levels are low.

• Micro-tunneling – Trenchless construction technique that utilizes a remotely operated boring machine for tunneling for lengths greater than 300 feet and accurate slope specifications. Considerations for

Micro-Tunneling related to a Willamette River Crossing include:

• Extensive excavation and dewatering for sending and receiving pits may be required.

• Expensive mobilization based on other construction activities and transportation routes.

• Most expensive construction technique.

• Geotechnical conditions may be unfavorable for micro-tunneling in some soils layers.

• Limited casing sizes available reduces flexibility in pipe sizing and configuration.

• The presence of large cobbles in geology of the area would likely require a large and powerful micro-tunneling machine.

• Extensive geotechnical work required to determine suitability of crossing locations and to reduce project risk during construction.

• Horizontal Direction Drilling (HDD) - Horizontal directional drilling is a method to install pipelines by drilling a pilot hole and then pulling a pipeline back through the drilled pilot hole. Considerations for

HDD related to a Willamette River Crossing include:

• HDD requires drilling mud and alluvial gravel. Alluvial gravel formations found near the

Willamette River can be very challenging for HDD due to potential loss of drilling fluid.

• Ideally pullback of pipeline should be completed in one pull, requiring space for set-up of pipeline, up to 150% of actual drilling distance. This would likely require staging in the river.

• Pipeline could be floated into place if space is not available onshore

• Lower cost than other trenchless technologies.

• HDD crossings of the Willamette River have been completed successfully including the Lake

Oswego Tigard crossing downstream of the Abernethy bridge, however a carrier pipe was required due to drilling through mud and alluvial deposits. The HDD drilling required multiple attempts prior to success.

• The primary concern in using HDD is the containment of drilling mud in the alluvial deposits found in the Willamette River corridor. Techniques to contain drilling mud have been used to successfully complete HDD crossings of the river but they add complexity to HDD projects.

• Extensive geotechnical work required to determine suitability of crossing locations and to reduce project risk during construction.

3.2.1.2 Geotechnical Challenges for Trenchless Technologies

Trenchless technologies are used to establish underground infrastructure without excavation from the surface for installation. One commonality between all trenchless technologies is that the success or failure of construction is highly dependent on geotechnical conditions.

The area around the Willamette River and the riverbed is an alluvial deposit, meaning the layers of soil and gravel have been deposited by water. The exact nature of the deposits varies from site to site but in general the potential project area for a Willamette River pipeline crossing has four main layers (from upper to lower: fill, sand and silt alluvium, gravel alluvium, and alluvial deposits from a series of major geological events called the Missoula Floods. Alluvial deposits are not solid consolidated materials like a sedimentary rock but a loose sediment deposit. A geotechnical profile of the area adjacent to the

Abernethy Bridge in Oregon City is shown in Figure 3.3. This geotechnical investigation was performed for the bridge expansion but is a general representation of the conditions found in this area.

Figure 3.3- Example Geotechnical profile for Willamette River (Shannon and Wilson Inc., 2019)

Any trenchless crossing of the Willamette River would likely require some excavation in the upper fill layer.

Depending on the depth of excavation this requires some type of shoring. For deeper excavations that extend below the ground water table the shoring would need to be watertight to prevent flooding of the excavation. This could be achieved through secant piling or sheet piles.

Tunneling or drilling in the sand and silt alluvium is less problematic than other layers as it is a finer material and could retain drilling fluid if required and does not contain as many large rocks, cobbles, and boulders as other layers. Any trenchless technology used for a Willamette River Crossing would encounter the sand silt alluvium either in the boring process or in excavation if a deep access shaft was established.

The gravel alluvium is made up of materials that are generally larger than 2 millimeters (mm) but smaller than 100 mm (Lindeburg, 2012). These deposits are especially challenging for any trenchless technologies that require a drilling fluid as the fluid will leak out from the drill head into the surrounding deposits. In other trenchless crossings of the Willamette River, drilling contractors have struggled with

Missoula

Flood

Deposits

Gravel Alluvium

Sand Alluvium

River Surface Abernethy Bridge

Fill

Rock gravel alluvium deposits and have been forced to install additional carrier pipes to help retain drilling fluid adding to project costs and time. Larger rocks within the gravel alluvium can pose additional challenges when drilling or tunneling. To ensure that the drill or tunnel profile can be completed, larger equipment can be used that has more power to drill or tunnel through these larger rocks.

The Missoula Flood deposits contain sand, silt clay, gravel and larger rocks and cobbles. Depending on the texture in a specific location, these deposits can pose the same challenges in terms of retaining hydraulic drilling fluid as the gravel alluvium. The riverbed of the Willamette River in the project area for a pipeline river crossing is primarily Missoula flood deposit and it extends to a significant depth below the riverbed

(O’Connor et.al., 2001). Drilling or tunneling under these challenging deposits is not a feasible option.

Extensive geotechnical investigations and sampling would be required before trenchless technologies were pursued. In general, the geotechnical conditions in the area for trenchless river crossings present a high construction risk and potential for increased cost or failure.

3.2.2 Alternative 4.1

One potential location for an under-river crossing is adjacent to the existing Bolton/River Street Force

Main Crossings. This alignment requires the longest force main length from the Willamette Pump Station.

The alignment requires easement on lands owned by Oregon Parks, the City of West Linn and privately-owned lands within West Linn. The pipeline also crosses under the I-205 Bridge requiring coordination with ODOT. Topography is favorable for this alignment as the gradient is generally downhill from the high point of the force main to the existing crossing location. The river crossing may be constructed using open cut or (in-river) or trenchless methods (micro-tunnel or HDD), although all methods present critical construction risks and staging is complex. This alternative provides opportunities to construct a second pipeline in the same alignment as a redundant crossing for Bolton and River Street without topographical challenges or new pumps. After crossing the river, pipelines may tie into existing gravity infrastructure tributary to the Willamette Interceptor. Part of the floodway could potentially be used for stagging pipe for an HDD crossing. On the east side of the river some construction would be required in park lands owned by

Oregon City with requirement to permit construction within the Jon Storm Park.

Pro:

• Favorable for establishment of redundant River Street and Bolton Crossing (second pipe in common alignment and using common trench or trenchless approach)

• Shortest crossing distance

Con:

• Requires new gravity infrastructure though properties owned by West Linn, ODOT, Oregon Parks, Oregon City and private landowners in established river front neighborhood

• Utility conflicts throughout alignment and major transportation infrastructure

• Limited space for construction staging or staging for trenchless crossing

• Potential staging for river crossing construction in floodway or in the river using barges

• Unknown geotechnical conditions but likely challenging based on information from nearby crossing locations

• Permitting of construction in Willamette River and Jon Storm Park

• No maintenance access to the pipeline

• Pipeline under river is seismically vulnerable due to liquefaction risks.

3.2.3 Alternative 4.2

A crossing at approximately the midpoint between the existing River Street and Bolton Crossing and the I-

205 Bridge is a second potential under-river crossing location. This alternative provides opportunities to construct a second pipeline in the same alignment as a redundant crossing for Bolton and River Street without topographical challenges or new pumps. This potential alignment crosses from the midpoint location on the west bank of the river to approximately the location of the proposed new Willamette

Outfall and provides options for staging a pipe pull back in the river due to the angle of the crossing for

HDD construction. On the east side of the river there is potential for coordination with the outfall project to connect to the existing trunk line in Main Street as this corridor will also be used for the outfall. The construction adjacent to the outfall may be open cut (in-river).

Similar challenges are present in this alignment including land ownership, utility conflicts and geotechnical conditions as with Alternative 4.1.

Pro:

• Favorable for establishment of redundant River Street and Bolton Crossing (second pipe in common alignment and using common trench or trenchless approach)

• Option to stage in river based on construction angle

Con:

• Requires new gravity infrastructure though properties owned by West Linn, ODOT, Oregon Parks and

Recreation, Oregon City and private landowners in established river front neighborhood

• Utility conflicts throughout alignment and major transportation infrastructure

• Unknown geotechnical conditions but likely challenging based on information from nearby crossing locations

• Permitting of construction in Willamette River and Jon Storm Park

• No maintenance access to the pipeline

• Pipeline under river is seismically vulnerable due to liquefaction risks.

3.2.4 Alternative 4.3

An under-river crossing near the I-205/Abernethy Bridge provides the shortest gravity approach from the

Willamette Pump Station. If constructed under the river, this location can still provide a redundant crossing as a second pipeline for the River Street and Bolton Force Mains. Transportation, utility conflict, construction staging present similar challenges as Alternatives 4.1 and 4.2. Construction methods include trenchless (micro-tunnelling, HDD) or open cut (in-river). The crossing location provides an opportunity to coordinate the pipeline project with the new outfall project including common construction pit on the east side of the river. The additional of the pipeline project requires ODOT coordination related to the I-

205/Abernethy Bridge widening project.

Pro:

• Favorable for establishment of redundant River Street and Bolton Crossing (second pipe in common alignment and using common trench or trenchless approach)

• Coordination with the Willamette Outfall Project

Con:

• Requires new gravity infrastructure though properties owned by West Linn, ODOT, Oregon Parks and

Recreation, Oregon City and private landowners in established river front neighborhood

• Utility conflicts throughout alignment and major transportation infrastructure

• Very limited space for construction staging or staging for trenchless crossings

• Unknown geotechnical conditions but likely challenging based on information from nearby crossing locations

• Permitting on construction in the Willamette River and Jon Storm Park

• Potential conflicts with in-river work for the I-205/Abernethy Bridge widening project

• No maintenance access to the pipeline.

• Pipeline under river is seismically vulnerable due to liquefaction risk.

3.2.5 Alternative 4.4

The I-205/Abernethy Bridge crosses from West Linn to Oregon City just downstream of the current West

Linn Interceptor crossing at the Oregon City Bridge. The bridge has six lanes of traffic and is approximately

2,700 feet long. The bridge currently has a city of West Linn-owned water pipeline under the bridge deck.

A major bridge expansion project is being designed and implemented by ODOT, including an additional water pipeline. Alternative 4.4 routes the Willamette Force Main as a suspended pipeline along the bridge.

The timing of the bridge project and additional water line presented an opportunity to coordinate design of a sewer crossing utilizing the bridge structure. The primary challenges related to this crossing site include the approach to the bridge and transition from a buried pipeline to a pipeline suspended under the bridge and the transition back to an underground pipeline on the opposite side of the bridge. The slope of the bridge is also set, and any suspended pipelines must have the same slope as the bridge deck.

On the Oregon City side of the bridge the sewer line is significantly higher than Willamette Interceptor and a drop structure would be required to connect to the existing trunk.

A crossing suspended on the I-205/Abernethy Bridge deck would not provide the option for redundant service for Bolton or River Street Force Mains as the elevation of the bridge exceeds the available design head for the Bolton and River Street Pump Stations existing pumps. Additional there is inadequate space on the bridge for a second pipeline. A 24-inch redundant crossing for the Willamette Force Main, Bolton

Force Main, and River Street Force Main is assumed to be constructed under the river adjacent to the existing Bolton and River Street Force Mains at a future date for this alternative.

Pro:

• No trenchless river crossing (cost reduction and construction risk reduction)

• Reduced impact to local neighborhoods and landowners with new gravity sewers

• Limited new gravity piping to connect to existing Willamette Interceptor

• Maintenance access to the pipeline on the bridge

• Pipeline on the bridge is seismically resilient

Con:

• Vulnerability of suspended pipeline (weather, seismic)

• No redundant service for Bolton or River Street Force Mains

• Hydraulics limited by bridge elevations and slope

• Limited access to bridge piping after installation

• Timing dictated by bridge project and water line project (reduced schedule for design)

3.2.6 Cost Comparison

A high-level capital cost comparison (2020 dollars) is provided for the river crossing alternatives. The costs include the river crossing portion of the Willamette Force Main and redundant crossing options for the Bolton, River Street, and Willamette Force Mains. The costs exclude the Willamette Pump Station and the force main upstream of the river crossing.

• Alternatives 4.1, 4.2, and 4.3 include a 24-inch pipeline crossing for the Willamette Force Main

(trenchless or open cut, in-river construction); a second 24-inch pipeline crossing to create redundancy for the River Street, Bolton, and Willamette Force Mains River Crossings (trenchless or in-river open cut construction); a connecting 24-inch pipeline between the River Street and Bolton Force

Mains or the Willamette Force Main to the redundant river crossing.

o 24-inch pipeline river crossing (trenchless or open cut, in-river) = $11-14 million o 24-inch pipeline redundant river crossing (trenchless or open cut, in-river) = $11-14 million o 24-inch connecting pipeline for redundancy (open-cut) = $ 2-3 million

Total = $24-31 million

• Alternative 4.4 includes a 24-inch pipeline crossing for the Willamette Force Main (suspended on the

I-205/Abernethy Bridge); a second 24-inch pipeline crossing to create redundancy for the River

Street, Bolton, and Willamette Force Mains River Crossings; a connecting 24-inch pipeline between the

Willamette Force Main to the redundant river crossing.

o 24-inch pipeline bridge crossing (suspended) = $ 6-8 million o 24-inch pipeline redundant river crossing (trenchless or open cut, in-river) = $11-14 million o 24-inch connecting pipeline for redundancy (open-cut) = $ 2-3 million

Total = $19-25 million

The option to build a suspended pipeline across the I-205/Abernethy Bridge (Alternative 4.4) represents a

$5 to 6-million-dollar costs savings (20-25-percent) when compared with a trenchless or in-river (open cut) pipeline under the Willamette River (Alternatives 4.1, 4.2, and 4.3).

3.2.7 Preferred River Crossing Alternative

During the alternative’s evaluation, the selection of a preferred alternative for an under-river crossing was preempted by discussions with ODOT about opportunities to implement Alternative 4.4 (I-205/Abernethy

Bridge Crossing) with the near-term bridge widening project. Trenchless or open cut crossings of the river posed significant construction risks, and a bridge crossing was identified to be the most economical and feasible alternative. ODOT agreed to collaborate on the suspended pipeline design across the bridge and

WES hired Murraysmith to work with Quincy Engineering, the ODOT bridge designer, to design the pipeline. Because of the accelerated schedule associated with the bridge widening, the portion of the force main crossing the I-205/Abernethy Bridge was designed with the overall bridge package and will be constructed prior to the other upgrades to the Willamette Pump Station and the upstream portion of the

Willamette Force Main. See Appendix D for the Basis of Design Report for the Willamette Force Main I-

205/Abernethy Bridge Crossing. See Appendix E for the drawings for the Willamette Force Main I-

205/Abernethy Bridge Crossing.

WES elected to not proceed with a redundant service for the River Street, Bolton, and Willamette Force

Mains, however a redundant crossing for those pump stations may be added in the future. Future redundant river crossings will likely be adjacent to the existing River Street and Bolton River Crossings. Any additional crossings will have the same construction challenges as outlined in this section including:

• Geotechnical conditions for trenchless crossing methods

• Land ownership coordination and right-of-way on both sides of the river

• Limited space for construction staging

• Utility conflicts

• Permitting for construction in the Willamette River and in Jon Storm Park

Prior to construction of the redundant crossing, in an emergency, there is the potential to use either the

River Street Force Main or Bolton Force Main as the river crossing for the opposite pump station. The additional flow from a second pump station significantly increases head to the point where existing pumps may not be operable for simultaneous pump station operation. Any emergency operation would require an alternating pumping strategy and use of wet well storage so that only one pump station would be utilizing the available force main crossing at any given time. For the Willamette Pump Station, the existing force main, West Linn Interceptor and gravity pipe on the Arch Bridge will provide some level of redundancy in case the new I-205/Abernethy Bridge pipeline is inoperable.

3.3 Upstream Force Main Routing Evaluation

Several force main alignments were considered for the Willamette Pump Station Force Main upstream of the Willamette River Crossing as described below (also see Figure 3.2).

• Force Main Alignment - Option 1 – The first force main alignment (from upstream to downstream) is parallel to the existing Willamette Force Main located within public right-of-way on 5th Avenue, through private property on an existing Portland General Electric (PG&E) easement, within public right-of-way on Willamette Falls Drive and Mill Street, and then onto ODOT right-of-way for the I-

205/Abernethy Bridge Crossing. The existing PG&E easement associated with Option 1 may be too narrow for both the existing 18-inch and new 24-inch force mains.

• Force Main Alignment - Option 2 – The second force main alignment (from upstream to downstream) is similar to Option 1 but avoids the private property and the existing Portland General Electric easement. From the pump station, the route follows 4th Street north to Willamette Falls Drive and remains within public right-of-way on Willamette Falls Drive and Mill Street before reaching ODOT right-of-way for the I-205/Abernethy Bridge Crossing.

• Force Main Alignment – Option 3 – The third force main alignment (from upstream to downstream) follows closely the bank of the Willamette River on access roads for PG&E and the Willamette Paper

Company before ascending to Willamette Falls Drive, Mill Street, and ODOT right-of-way. The route was considered as an option to reduce the static head requirements for the pump station, however due to existing PG&E and Willamette Paper Company infrastructure, the alternate alignment only reduced the maximum elevation by fewer than 10 feet. The Option 3 alignment requires negotiation of new easements with PG&E and the Willamette Paper Company. Additional construction permitting may be required due to proximity of the force main alignment to the river. Force main air valve operation will also be interrupted when the river water surface elevation reaches the 100-year flood stage. Due to the added complexity/risk and the limited reduction in static head, option 3 was eliminated from consideration.

WES staff preferred Option 2 which locates most of the force main upstream of the bridge crossing in public right-of-way on 4th Street, Willamette Falls Drive and Mill Street. WES staff also requested that

Option 1 move forward as a future design alternative with further research into the width of the existing

PG&E easement.

3.4 Other River Crossing Alternatives and Force Main Routing Option

Considerations

This section describes other factors considered for the river crossing alternatives and force main options including soil types, flood plains, environmental areas, utility conflicts, land ownership and early review of opportunities to coordinate with other projects. This section was prepared prior to selection of a preferred river crossing alternative and the two force main options. The section has been retained for informational purposes. For discussion, the force main is subdivided into four areas along the potential project as shown in Figure 3.4.

Figure 3.4. Additional Consideration Area Definition

3.4.1 Soils and Flood Plain

Soils and floodplain impacts are described below and referenced in Figure 3.5.

• Upstream Force Main o Soils are primarily very stony silt loam with areas of steep slopes (greater than 25%).

o Areas around existing pump station are silty clay loam and are within the 100-year floodplain.

o Very stony soils may limit trenchless methods however construction will likely be open cut.

Upstream Force

Main Area

Abernethy Bridge

Area

East Bank

Area

West Bank

Area

• Abernethy Bridge o Soils are primarily very stony silt loam with areas of steep slopes (greater than 25%).

o Areas closer to river are characterized as fine sandy loam.

• West Bank o Areas adjacent to river are characterized as river wash, high ground water levels may impact construction.

o In the River Street neighborhood soils are classified as fine sandy loam.

• East Bank o Adjacent to the river soils are characterized as gravelly sandy loam.

o Areas east of Highway 99E are characterized as urban lands. This area is highly developed and upper soil layers are primarily fill.

Figure 3.5. Soils Map (NRCS, Soils Data)

E

Stony Silt Loam

Silty Clay Loam

Sandy Loam

Willamette PS and FM

3.4.2 Environmental Impacts

Environmental impacts are described below and referenced in Figure 3.6.

• Upstream Force Main o Force main alignments will cross areas designated as wetlands, classified vegetation areas and steep slopes. Impact will be minimized by utilizing existing right of ways and easements and new disturbance of wetlands and vegetation will be avoided.

• Abernethy Bridge o Park areas adjacent to the Abernethy Bridge are designated as vegetation.

o Areas adjacent to river are designated as wetlands including an area under the Abernethy Bridge that is a potential corridor for new sewer infrastructure.

• West…