HomeMy WebLinkAbout2018 FINAL REPORT - Kennydale Lakeline Sewer Improvements Ph II
City of Renton
Kennydale Lake Line Sewer System Evaluation
Report No. 1
PHASE 2B AND 3 COMBINED
SUMMARY
FINAL | July 2019
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019| i
pw:\\Carollo/Documents\Client/WA/Renton/10418B00/Deliverables/2018 Report 1\2018 Report No 1.docx
Contents
Chapter 1 - Introduction
1.1 Purpose of This Report 1-1
1.2 Background 1-1
1.3 Historical Documentation 1-2
1.3.1 Sewer System Evaluation 1-2
1.4 Report Content 1-4
1.5 Report Contributors 1-5
Chapter 2 - Phase 2B Public Involvement
2.1 Public Involvement 2-1
2.2 Mail Notifications 2-1
2.3 Door Hanging 2-1
2.4 Website Updates 2-2
2.5 Calls and Emails 2-2
2.6 EnviroLytical Database 2-2
2.7 Lessons Learned 2-2
Chapter 3 - Phase 2B Permitting
3.1 Permitting 3-1
3.1.1 The City of Renton Shoreline and SEPA 3-1
3.1.2 City of Renton Shoreline Master Program 3-1
3.1.3 SEPA 3-1
3.2 WDFW HPA and Ecology 401 Water Quality Certification 3-2
3.2.1 WDFW HPA 3-2
3.2.2 Ecology 401 Water Quality Certification 3-2
3.3 USACE NWP 12 and ESA Section 7 3-2
3.3.1 NWP 12 Utility Line Activities 3-3
3.3.2 ESA Section 7 Consultation 3-3
3.4 Lessons Learned 3-3
3.4.1 Project Definition and Description 3-3
3.4.2 Project Schedule 3-4
3.4.3 Emergency Activities 3-4
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3.4.4 HPA Permit 3-4
Chapter 4 - Phase 2B Design Activities
4.1 Design Activities 4-1
4.1.1 Pre-design 4-1
4.1.2 Survey 4-2
4.1.3 Emergency Order 4-2
4.1.4 Pre-Bid Tour 4-2
4.1.5 Contract Documents 4-2
4.2 Bid Support 4-3
4.3 Lessons Learned 4-3
4.3.1 Impacts of Emergency Work on Contractor Risk 4-3
4.3.2 Impact of Preselecting Contractor 4-3
4.3.3 Long Precast Concrete Manhole Procurement Time 4-3
4.3.4 Seal on Existing Nautilus Style Manhole 4-3
Chapter 5 - Phase 2B Construction Activities
5.1 Construction Activities 5-1
5.2 Pre-Procurement 5-1
5.3 Emergency Response Plan 5-1
5.4 Construction Support Services 5-1
5.5 Construction Observation and Inspection 5-2
5.6 Water Quality Monitoring 5-2
5.7 Installation of Temporary Manholes 5-2
5.8 Use of Existing Submerged Manholes 5-2
5.9 Construction Cost 5-3
5.10 Lessons Learned 5-4
5.10.1 Tidal Delays on Mobilization 5-4
5.10.2 Major Impacts from Shallow Water 5-4
5.10.3 Limited Use of Excavator 5-5
5.10.4 Transient Hydraulic Conditions during Temporary Connections 5-5
5.10.5 Issues connecting the Temporary Manhole to the Lake Line 5-5
5.10.6 Improvements to the Temporary Manhole 5-5
5.10.7 Field Mixed Fish Mix 5-6
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5.10.8 Successful HPA Permit Extensions 5-6
5.10.9 Consider Annual Ballard Locks Closure 5-6
5.10.10 Decanting Wastewater Worked Well 5-6
Chapter 6 - Condition Assessment
6.1 Condition Assessment 6-1
6.1.1 Visual Observations/ Dive Video 6-1
6.1.2 CCTV 6-5
6.1.3 Coupon Tests 6-7
6.1.4 Revised Ultrasonic Thickness Testing Results 6-13
6.1.5 RUL Results 6-13
6.2 Lessons Learned 6-17
6.2.1 Identifying the Location of Defects 6-17
6.2.2 Measurement of External Pitting Depth 6-18
6.2.3 Visibility in Submerged Sections 6-18
Chapter 7 - Cleaning Effectiveness
7.1 Pre-Cleaning CCTV Inspection 7-1
7.2 Effectiveness of Land-Based Hydro-Jetting 7-6
7.3 Cleaning Activities 7-6
7.4 Evaluation of Partial Blockages 7-13
7.4.1 Partial Blockage Severity 7-13
7.4.2 Location of Partial Blockages 7-14
7.4.3 Field Verifying Location the Partial Blockage 7-19
Chapter 8 - Near-Term Options for Uncleaned Sections
8.1 General Description of Methods 8-1
8.1.1 Hydro-Jet Cleaning 8-1
8.1.2 High-Velocity Flushing 8-2
8.1.3 Pipe Replacement 8-3
8.2 Hydro-Jet Cleaning at Individual Sites 8-5
8.2.1 Site A 8-5
8.2.2 Site B 8-7
8.3 High-Velocity Flushing of Entire Lake Line 8-13
8.3.1 Potential to Damage the Lake Line 8-13
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8.3.2 Flushing Velocity 8-13
8.3.3 Temporary Pumping at Lift Station and Flush Station 8-14
8.3.4 Alternative Flushing Location 8-14
8.3.5 Lateral Isolation 8-15
8.3.6 Lake Line Pressures during Flushing 8-18
8.3.7 Risk of Unsuccessful High-Velocity Flushing in a Partially Blocked Lake Line 8-19
8.3.8 Debris in Manholes 8-19
8.3.9 Cost 8-20
8.4 Pipe Replacement for Identified Sections with Partial Blockages 8-22
8.4.1 Cost 8-22
8.5 Cleaning Analysis Conclusion 8-22
8.5.1 Site A Cleaning Analysis Conclusions 8-22
8.5.2 Site B Cleaning Analysis Conclusions 8-23
Chapter 9 - Phase 3 Lake Line Replacement Alternatives
9.1 Gravity Sewer in Lake 9-1
9.1.1 Alignment 9-1
9.1.2 Profile 9-2
9.1.3 Lateral Installation 9-5
9.1.4 Operation and Maintenance Considerations 9-5
9.1.5 Permitting 9-5
9.1.6 Environmental Risk Reduction 9-5
9.1.7 Conceptual Planning-Level Budget 9-5
9.2 Gravity Sewer on Land 9-6
9.2.1 Alignment 9-6
9.2.2 Profile 9-8
9.2.3 Lateral Installation 9-8
9.2.4 Operation and Maintenance Considerations 9-9
9.2.5 Environmental Risk Reduction 9-9
9.2.6 Conceptual Planning-Level Budget 9-9
9.3 Replace-in-Place in Lake 9-9
9.3.1 Mainline Installation 9-10
9.3.2 Lateral Installation 9-10
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9.3.3 Operation and Maintenance Considerations 9-11
9.3.4 Permitting 9-11
9.3.5 Environmental Risk Reduction 9-11
9.3.6 Conceptual Planning-Level Budget 9-11
9.4 Replace in New Shoreline 9-14
9.5 Vacuum Sewer on Land 9-14
9.5.1 Alignment 9-14
9.5.2 Lateral Installation 9-14
9.5.3 Operation and Maintenance Considerations 9-15
9.5.4 Environmental Risk 9-15
9.6 Grinder Pumps on Land 9-17
9.6.1 Alignment 9-17
9.6.2 Profile 9-17
9.6.3 Lateral Installation 9-17
9.6.4 Easements 9-17
9.6.5 Operation and Maintenance Considerations 9-17
9.6.6 Conceptual Planning-Level Budget 9-19
9.7 Alternative Summary and Conclusion 9-20
Appendices
Appendix A Public Outreach Materials
Appendix B Permit Documents
Appendix C Contract Documents
Appendix D Submittal / Request for Information
Appendix E Construction Daily Reports / Water Quality Monitoring
Appendix F V&A Consulting Engineers Report
Tables
Table 3.1 Lake Line Permit Summary 3-1
Table 5.1 Final Construction Cost 5-4
Table 6.2 Limits of the CCTV Inspection Videos 6-5
Table 6.1 Remaining Useful Life for Pipe Samples 6-11
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Table 6.3 Ultrasonic Thickness Data and Remaining Useful Life
Summary (Revised 2018) 6-14
Table 8.1 Cost for Land-based installation and hydro-jetting of a temporary in-
water manhole 8-11
Table 8.2 Cost for Installation and hydro-jetting from a Permanent in-water
manhole on Kennydale Beach Park’s dock 8-12
Table 8.3 Cost for Installation and hydro-jetting from In-Water Temporary Manhole 8-13
Table 8.4 Cost for High-Velocity Flushing 8-20
Table 9.1 Gravity Sewer In-Lake Estimated Budgetary Placeholder Cost 9-6
Table 9.2 Length of Main and Lateral Replace-in-Place Lake Line Sewer
Replacement 9-10
Table 9.3 Replace in Place Estimated Conceptual Planning-Level Budget 9-13
Table 9.4 Grinder Pump Estimated Conceptual Planning-Level Budget 9-19
Table 9.5 Replace in Place Estimated Conceptual Planning-Level Budget 9-20
Figures
Figure 6.1-1 As-Found Condition of Mainline with Minor Corrosion Tubercles 6-2
Figure 6.1-2 Area of Scaling and Tuberculation on Mainline; Large Rocks Around
Mainline at 2811 Mountain View Avenue North 6-2
Figure 6.1-3 Surface of Mainline after Scaling and Corrosion Removed 6-2
Figure 6.1-4 Moderate Pitting and Graphitized Layer After Wire-Brushing Surface 6-3
Figure 6.1-5 Pitting and Graphitization 6-3
Figure 6.1-6 Typical Pipe Surface 6-3
Figure 6.1-7 Typical Bell and Spigot Joints Between Pipe Segments 6-4
Figure 6.1-8 Typical Mechanical Joints at Wye and Tee Fittings for Lateral Connections 6-4
Figure 6.1-9 Rip-Rap Directly Adjacent to and Above Lake Line at
2811 Mountain View Avenue North 6-4
Figure 6.1-10 Unsupported Bottom of Lake Line where Shoreline has Steep Drop-Offs 6-5
Figure 6.2-1 Typical Lining Delamination with Smooth Metal Surface Behind 6-6
Figure 6.2-2 Debris and Sediment, Some of which Appears to be Chunks of Cement
Mortar Lining Material 6-6
Figure 6.2-3 Typical Moderate to Significant Corrosion at High Point (Brown Area);
Black Area Appears to be Stained Mortar Lining 6-6
Figure 6.2-4 Typical Moderate to Significant Corrosion at High Points (Brown Area) 6-7
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Figure 6.3-1 Typical Dimple Pattern on Mainline Samples and Coupon; However, this
Is Cast Iron Pipe 6-8
Figure 6.3-2 Graphitization on Interior Surface of Manhole 4 Sample 6-8
Figure 6.3-3 Exterior Surface of Manhole 4 Sample with a Few Scattered Minor Pits 6-9
Figure 6.3-4 Cement Mortar Lining on Interior of Manhole 5 Sample 6-9
Figure 6.3-5 Corroded Surfaces near Joint of Manhole 5 Sample; Lining Failed
around Joint 6-9
Figure 6.3-6 Exterior Surface of Manhole 5 Sample with Scattered Minor Pitting 6-10
Figure 6.3-7 Deteriorated Cement Mortar Lining on Lateral Coupon 6-10
Figure 6.3-8 Exterior Surface of Lateral Coupon with Minor Pitting Corrosion 6-10
Figure 6.4 Three-inch Diameter Pipe Coupon as Received by Laboratory 6-12
Figure 6.5 Lake Line Remaining Useful Life by Location 6-15
Figure 6.6 Remaining Useful Life Cumulative Distribution Function 6-17
Figure 7.1 2018 Lake Line CCTV Pre-Cleaning Map Extent and Results 7-3
Figure 7.2 2018 Lake Line CCTV Pre-Cleaning Profile Extent and Results 7-5
Figure 7.3 2018 Lake Line CCTV Post-Cleaning Map Extent and Results 7-9
Figure 7.4 2018 Lake Line CCTV Post-Cleaning Profile Extent and Results 7-11
Figure 7.5 Visibility conditions encountered by CCTV 7-12
Figure 7.6 Model Results for Three Scenarios 7-15
Figure 7.7 Site A and Site B Evaluated with Debris and/or Partial Blockage of
Lake Line 7-17
Figure 8.1 Cleaning Schematic for High Velocity Flushing 8-4
Figure 8.2 Lake Line at Site A 8-5
Figure 8.3 Distance from Lake Line to Kennydale Beach Park 8-7
Figure 8.4 In-Lake Cleanout Installed in Mercer Island 8-10
Figure 8.5 Flush Station with Temporary Pump Configuration for High-Velocity
Flushing 8-16
Figure 8.6 Lift Station with Temporary Pump Configuration to Support High-
Velocity Flushing 8-17
Figure 8.7 Pressures from Lake Line Flushing 8-21
Figure 9.1 Lake Washington Bathymetry Offshore of the Kennydale Area 9-2
Figure 9.2 Southern Conceptual Lake Line Gravity Sewer Alignment Offshore in
Lake Washington 9-3
Figure 9.3 Northern Conceptual Lake Line Gravity Sewer Alignment Offshore in
Lake Washington 9-4
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Figure 9.4 Conceptual Alignment of On-Land Gravity Sewer 9-7
Figure 9.5 Profile of Conceptual On-land Gravity Sewer 9-8
Figure 9.6 Replace-In-Place Lake Line Sewer Infrastructure 9-12
Figure 9.7 Location of Potential Access Manholes in Replace-in-Place Alternative 9-13
Figure 9.8 Vacuum Sewer Preferred Elevation Range 9-15
Figure 9.9 Vacuum Sewer Alternative Alignment 9-16
Figure 9.10 Grinder Pump Lateral and Force Main Alignment 9-18
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Abbreviations
ANSI American National Standards Institute
APPS Aquatic Protection Permitting System
AWWA American Water Works Association
BMC Ballard Marine Construction
C.O. change order
Carollo Carollo Engineers, Inc.
CCTV closed-circuit television
CDF Cumulative Distribution Function
City City of Renton
CRM customer relationship management
Ecology Washington State Department of Ecology
ESA Endangered Species Act
FOG fats, oils, and greases
gpm gallons per minute
HDPE high-density polyethylene
HGL hydraulic grade line
HPA Hydraulic Project Approval
in. inch(es)
in./yr. inches per year
JARPA Joint Aquatic Resource Permit
Lake Line Kennydale Lake Line
LF linear foot
LS lump sum
MH manhole
NMFS National Marine Fisheries Services
NWP 12 Nationwide Permit 12 covering Utility Line Activities
O&M operation and maintenance
pct. percent
Project Kennydale Lake Line Sewer System Evaluation
psi pounds per square inch
PVC polyvinyl chloride
RCW Revised Code of Washington
RUL remaining useful life
SEPA Washington State Environmental Policy Act
SSO sanitary sewer overflow
State State of Washington
USACE US Army Corps of Engineers
USFWS US Fish and Wildlife Service
UT ultimate tensile
UTM universal testing machine
V&A V&A Consulting Engineers
WAC Washington State Administrative Code
WDFW Washington State Department of Fish and Wildlife
WSDOT Washington State Department of Transportation
yr. year
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Chapter 1
INTRODUCTION
1.1 Purpose of This Report
In 2018, the City of Renton (City) completed a condition assessment and conducted emergency
cleaning of the Kennydale Lake Line (Lake Line) System. This report documents the results of
the construction, inspection, and cleaning conducted on the Lake Line. It includes revised
estimates of the Lake Line's remaining useful life (RUL) based on updated information. It also
documents and evaluates potential methods to access and clean the remaining Lake Line
segments that were not reached in the 2018 efforts, considering both on-land and in-water
access.
In addition, this report investigates potential Lake Line replacement alternatives to help the City
make informed decisions regarding long-term planning for the Lake Line replacement. On-land
and in-lake options were considered independently to highlight the benefits and challenges
associated with each.
1.2 Background
The Lake Line is an 8-inch line in Lake Washington that serves two small residential
neighborhoods along the lake in the City. The 4,700-foot-long line begins at a flush station at the
north end of Gene Coulon Park and ends at the lift station and force main near
North 40th Street. The original construction did not install in-line maintenance access points to
the Lake Line. Where the pipe is buried, the depth of cover typically does not exceed three feet.
The top of the pipe is exposed above the lake bed along portions of the alignment. Boaters and
contractors have snagged the pipe multiple times resulting in pipe breaks.
Because of these maintenance challenges and uncertainty regarding the pipe's condition, in
1999, the City prepared a predesign to upgrade or replace the Lake Line. For this, ultrasonic
thickness testing was performed on exposed portions of the pipeline, dye testing was performed
from the flush station, and a geotechnical assessment was conducted on the lake bed adjacent
to the pipe. The analysis evaluated Lake Line system replacement through in-lake and on-land
alternatives (Tetra Tech/KCM, 2000).
According to the predesign report, nothing definitively indicated that the Lake Line system
would reach the risk of failure in the next 20 years; however, it was noted only part of the
pipeline was not accessed and tested.
Interim cleaning solutions were recommended to maintain the existing Lake Line for the rest of
its service life. Recommendations included installing new maintenance access points,
implementing a new cleaning program, repairing a hole in the Lake Line, tagging docks over the
Lake Line to mark its location for future surveys, and launching a community information
program to inform residents about the Lake Line, its location, and operational best practices to
extend its longevity.
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In 2004, three new maintenance access manholes were installed: two offshore from the LaValley
residence at 3713 Mountain View Avenue North, and one near 3713 Lake Washington Boulevard.
Improvements to the flush station were implemented in 2005.
Through a risk-based repair and replacement program for City Lift Stations, the City identified
the Lake Washington No. 2 lift station as a high-risk facility and the flush station as a moderately
high-risk facility (Carollo Engineers, Inc. [Carollo], 2016). Given the uncertainty in the Lake Line
system’s service life and difficult maintenance conditions, the City elected to conduct a
comprehensive condition assessment before implementing risk mitigation measures.
1.3 Historical Documentation
The following plans and studies provide a detailed account of the development of the existing
Lake Line system:
• Sanitary Sewer L.I.D. 270, Construction Drawings, and Technical Provisions (City of
Renton, 1972).
• Kennydale – Lake Washington Lake Front Sanitary Collection Sewer As-Built Survey and
Study Project (Horton Dennis & Associates, Inc., 1988).
• City of Renton 1992 Lift Station Improvements, Schedule B Lake Washington No. 2
Lift Station, Record Drawings (RH2 Engineers, Planners, Scientists, 1994).
• Kennydale Lakefront Sewer Predesign Report (Tetra Tech/KCM, Inc., 2000).
• Kennydale Lakefront Sewer Improvement (Tetra Tech, 2003).
• City of Renton 2004 Lift Station Rehabilitation (Flush Station) Record Drawings
(RH2 Engineers, Planners, Scientists, 2006).
• City of Renton Existing Force Main Condition Assessment and Lift Station Evaluation
System Technical Memorandum – System Inventory and Risk Assessment Summary
(Carollo, 2016).
• City of Renton Kennydale Lake Line Sewer System Evaluation Phase 1 Existing
Conditions Technical Memorandum 1 (Carollo, et al., 2017).
• City of Renton Kennydale Lake Line Sewer System Evaluation Phase 2 Condition
Assessment Report (Carollo, et al., 2018).
1.3.1 Sewer System Evaluation
The Kennydale Lake Line Sewer System Evaluation (Project) began in 2016 and has consisted of
the following phases:
• Phase 1 gathered data on the existing system. As part of this effort, the Consultant team
worked with City crews’ biennial maintenance on the Lake Line was documented and
analyzed. Phase 1 also included a condition assessment of the flush station and lift
station.
• Phase 2A collected additional existing system data on the condition and location of the
pipeline, the connecting sewer laterals, and bulkheads.
• Phase 2B, documented in this Report, completed further condition assessment in 2018
and added two temporary manholes and cleaned the Lake Line.
• Phase 3, documented in this Report, recommends further cleaning and analyze
alternatives for the eventual replacement of the Lake Line (Documented in this report).
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1.3.1.1 Phase 1 and Phase 2A
During Phase 1, the sites and structures of the flush station and lift station were surveyed, and
then, in Phase 2A, an additional survey better defined the Lake Line’s profile and alignment. A
survey team then confirmed the Lake Line’s alignment and surveyed properties served by the
Lake Line including docks, bulkheads, building finished floors, sewer cleanouts, and lateral
alignments.
More specifically, the Phase 2A condition assessment included the following:
• Closed-circuit television (CCTV) inspection of all accessible laterals. Limited sections of
the Lake Line were captures as part of the lateral inspections.
• Pipe coupon collection and testing: A partial sample of the Lake Line pipe, referred to as
a coupon, was taken adjacent to the flush station after excavation to the pipe. However,
this pipe segment may have been replaced during a water main rehabilitation in 2001
and as a result may not be representative of the rest of the Lake Line.
• Ultrasonic thickness testing: This testing was conducted at exposed locations on the
Lake Line and two laterals. Wall thickness measurements were used to estimate the
RUL of each pipe segment tested, and corrosion rates were calculated according to the
installation date of 1972 and measured pipe wall thickness at that time.
• Visual inspection of bulkheads: A geotechnical engineer completed this inspection to
provide input on potential sewer system vulnerabilities associated with bulkheads. All
but two properties were found to have a low bulkhead failure risk.
• Development of a hydraulic simulation model to investigate the hydraulics of the
Lake Line system. The model assessed the existing conditions, as well as evaluate future
alternatives.
1.3.1.2 Partial Blockages Identified
During Phase 2B, a hydraulic model was used to evaluate differences between conditions
observed in the field and the theoretical hydraulic capacity of the Lake Line system. With the
flush station offline, model results generally matched the field-estimated hydraulic grade
line (HGL). However, with the flush station running, the model did not match higher HGL
observed in the field. This indicated that there are likely restrictions in the Lake Line due to a
combination of sediment; fats, oils, and greases (FOG); and pipeline structural defects.
The model matched the field-estimated HGL data when the flush station ran with two simulated
partial blockages. Though the number and locations of actual partial blockages were unknown,
this evaluation modeled two partial blockages: one near 3009 Mountain View Avenue North and
one near 3711 Lake Washington Boulevard North. It was recognized that a combination of
multiple partial blockages could have a cumulative effect equal to that of the two partial
blockages modeled.
Because of the risk of interruption of service to the properties if partial blockages were to
worsen, the City pursued hydro-jet cleaning of the entire Lake Line system in 2018.
1.3.1.3 Phase 2B
A full cleaning of the Lake Line was pursued to address the partial blockages identified in
Phase 2A. This effort is documented and evaluated in this Report. In 2018, the City declared an
emergency, secured permits, and contracted out the cleaning of the Lake Line using in-water
manhole access. The Lake Line was cleaned from two temporary manhole locations and
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three existing in-water manholes. Hydro-jetting was performed from a vacuum truck loaded on a
floating barge. According to post-cleaning CCTV inspection, the Lake Line was free of major
debris where it was cleaned. However, due to obstacles in the Lake Line, this cleaning did not
reach the entire Lake Line.
In parallel to the cleaning, additional condition assessment of the Lake Line and lateral was
performed from removed pipe segments and coupons collected during the 2018 construction
work.
This report documents the planning, design, construction, condition assessment, and cleaning
effectiveness of Phase 2B activities. The report also reviews multiple options to address sections
of the Lake Line not reached in the 2018 cleanings to remove potential remaining partial
blockages, referred to as Sites A and B in this report. Three general approaches are assessed:
• Hydro-jet cleaning at two sites.
• High-velocity flushing of the entire Lake Line.
• Pipe replacement at identified segments with partial blockages.
1.3.1.4 Phase 3
Phase 3 investigates Lake Line replacement alternatives to aid in long-term City planning for the
pipeline replacement, including securing easements and financial resources. The conceptual
alternatives analysis considered replacing the Lake Line in-place, as well as moving it further
offshore in the lake and multiple options for on-land sewer service. For each alternative, the
report includes a description, conceptual sizing, and a high-level budgetary placeholder.
1.4 Report Content
This report is an overview of the work completed in 2018. Major tasks are documented in the
following chapters:
• Chapter 1 – Introduction.
• Chapter 2 – Phase 2B Public Involvement.
• Chapter 3 – Phase 2B Permitting.
• Chapter 4 – Phase 2B Design Activities.
• Chapter 5 – Phase 2B Construction Activities.
• Chapter 6 – Condition Assessment.
• Chapter 7 – Cleaning Effectiveness.
• Chapter 8 – Near-Term Options for Uncleaned Sections.
• Chapter 9 – Phase 3 Lake Line Replacement Alternatives.
• Appendices:
Appendix A Public Outreach Materials.
Appendix B Permit Documents.
Appendix C Contract Documents.
Appendix D Submittal / Request for Information.
Appendix E Construction Daily Reports / Water Quality Monitoring.
Appendix F V&A Consulting Engineers Report.
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1.5 Report Contributors
This report compiles work from City staff and the consulting team, which included the following
firms:
• Carollo Engineers, Inc.: Project Lead.
• Tetra Tech: Technical Lead.
• Confluence Environmental: Environmental Assessment and Permitting.
• EnviroIssues: Public Outreach and Communication.
• V&A Consulting Engineers (V&A): Pipe Condition Assessment.
City staff was instrumental in completing the Project. We commend the following staff members
and thank them for their assistance:
• Richard Marshall: Surface Water / Wastewater Special Operations Service Manager.
• Stan Job: Surface Water / Wastewater Special Operations Service Supervisor.
• Rocky Sittner: Lead Maintenance Worker.
• Travis Hamblin: Maintenance Services Worker III.
• Kevin Hiatt: Maintenance Services Worker III.
• Jacob Lundquist: Maintenance Services Worker III.
• Reed Pagel: Maintenance Services Worker II.
• Roger Rowland: Maintenance Services Worker II.
• Shane Couty: Lift Station Technician.
• Jayson Gallaway: Lift Station Technician.
• Dave Christensen: Utility Engineering Manager Waste Water.
• Michael Benoit: Civil Engineer III.
• John Hobson: Civil Engineer III.
• Don Ellis: Engineering Specialist III.
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Chapter 2
PHASE 2B PUBLIC INVOLVEMENT
In 2018, Phase 2B construction and condition assessment activities were performed directly
offshore of residences. To engage and involve the Lake Line customers, the City conducted
extensive public outreach. This chapter outlines the activities performed for public involvement.
2.1 Public Involvement
Public outreach for the Project's Phase 2B (summer and fall 2018) built on outreach efforts
completed over the last several years. During those efforts, the City partnered with property
owners and residents to access properties to maintain the Lake Line and completed a condition
assessment.
The goal of the 2018 outreach efforts was to keep all Lake Line residents and interested parties
informed about the Project’s activities and progression. In addition, outreach focused on
reaching out to residents and property owners closest to the concentrated work, specifically
those near the manhole installations, cleaning access sites, flush station, and lift station. The
outreach was meant to proactively communicate with residents directly affected by the project
of upcoming work, address questions, and continue to build productive relationships.
Public involvement consultant EnviroIssues led these outreach efforts. From June to July 2018,
EnviroIssues updated the public involvement plan for Phase 2B efforts, which included updating
key messaging and developing outreach materials. The following example outreach materials
are attached in Appendix A:
• Phase 2B Public Involvement Plan, including key messaging.
• Frequently asked questions from the project website.
• Letters sent to Lake Line neighbors and nearby residences.
• A door hanger for public notification activities.
• Back-pocket cards for crew members to give to members of the public who had
questions.
2.2 Mail Notifications
To keep residents informed, notifications were sent to all Lake Line residents on August 2, 2018.
Two versions of the letter, along with an enclosed project area map, were sent out. The first
letter was general, showing an overview map with areas where work would be concentrated, and
mailed to most residents within the project area (54 addresses). The second letter was sent to
the 11 properties adjacent to manhole sites and included property-specific images with the
potential location of work barges adjacent to work sites.
2.3 Door Hanging
Door hangers were delivered prior to specific work efforts:
• June 4, 2018: Door hangers were delivered to six properties before survey work was
done from June 7 to 8.
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• October 4, 2018: Door hangers were delivered to nine properties before condition
assessment fieldwork began.
• October 26, 2018: Door hangers were delivered to three properties to notify about
weekend work done from October 27 to 28.
2.4 Website Updates
In addition to mailing notifications to Lake Line residents, the project website was updated at
the beginning of the 2018 work and refreshed periodically to keep it current. The website also
hosted a “Frequently Asked Questions” document that was updated for the 2018 work.
Specifically, the website updates were submitted to the City on July 25, September 20,
October 11, and October 25 of 2018.
2.5 Calls and Emails
To reach the residents and property owners closest to the concentrated work, the project team
contacted specific property owners and gave them advance notice of work. Individual
communication via phone and email occurred on August 12, September 7, October 6, and
October 11 of 2018.
The City also met with the owners of one property on October 1, 2018, to provide updates and
answer questions in person.
2.6 EnviroLytical Database
Project communications were maintained in the EnviroLytical database, which is provided in
Appendix A, along with a copy of the EnviroLytical customer relationship management (CRM)
database to date. The database holds the following four types of data recorded, with a file for
each type:
1. Contacts: the people contacted during the project.
2. Communications: communications with contacts, including fieldwork notes from 2017.
3. Activities: outreach efforts, including mailings, phone calls, site visits, and door hanging.
4. Parcels: properties in the project area.
2.7 Lessons Learned
Project outreach in 2018 went smoothly, thanks largely to the City’s successful engagement in
previous years. The population of Lake Line neighbors was mostly familiar with the project, was
well-educated, could access online project updates, and was open and receptive to project
outreach. In fact, some crew members reported happy and satisfied comments from community
members they encountered during work.
The City understands the value of public outreach and makes diligent efforts to stay connected
with its customers and community members. However, because many of these connections
were developed without involving the outreach consultant, certain interactions were not
recorded in the outreach database in as much detail.
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
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Chapter 3
PHASE 2B PERMITTING
3.1 Permitting
This chapter addresses the environmental permits associated with the Phase 2B of the project,
which cleaned the pipeline and evaluated pipeline conditions at multiple locations in
Lake Washington. For the condition evaluation, pipeline coupons were collected and temporary
access was created at several existing in-water manholes to clean the Lake Line.
As shown in Table 3.1, the Project required several natural resource and land use permits from
local, state, and federal entities. Appendix B includes applications and approvals.
Table 3.1 Lake Line Permit Summary
Permit Permit Submitted Permit Issued Application
Duration
The City of Renton Shoreline Master
Program and State Environmental Policy
Act (SEPA).
April 20, 2018 June 8, 2018 49 days
Washington Department of Fish and
Wildlife’s (WDFW) Hydraulic Project
Approval (HPA) and Washington
Department of Ecology’s (Ecology)
401 Water Quality Certification.
May 25, 2018 June 18, 2018 24 days
US Army Corps of Engineers’ (USACE)
Nationwide Permit 12 covering Utility Line
Activities (NWP 12) and Section 7 of the
Endangered Species Act (ESA)
February 15, 2018 August 9, 2018 175 days
3.1.1 The City of Renton Shoreline and SEPA
Several City permits and administrative approvals were required, including compliance with
SEPA and the Shoreline Management Act as defined by the City’s Shoreline Master Program.
3.1.2 City of Renton Shoreline Master Program
Work within 200 feet of State of Washington (State) shorelines must comply with the local
jurisdiction of the Shoreline Master Program and often requires a Shoreline Substantial
Development Permit. The Project qualified for an exemption from this permit, because it
primarily consisted of normal maintenance and repair of existing structures or developments,
according to Washington State Administrative Code (WAC) 173.27.040 (2)(b). The Shoreline
Exemption was issued on June 8, 2018.
3.1.3 SEPA
SEPA identifies and analyzes the environmental effects associated with governmental decisions.
In this case, the City’s issuance of a Shoreline Exemption required SEPA review. Thus, a SEPA
checklist was prepared for the Project and submitted to the City.
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On May 25, 2018, the City, which was the assessment agency, determined that the project would
not likely adversely affect the environment and issued a Determination of Non-Significance.
3.2 WDFW HPA and Ecology 401 Water Quality Certification
The Project fell under several State regulations, primarily for the project’s activities in
Lake Washington. These reviews were completed and approval obtained. Under State regulation
(Revised Code of Washington [RCW] 77.55), construction activities in or near State waters are
required to obtain an HPA from the WDFW.
Ecology also has review and approval authority over certain aspects of the Project. Under
Section 401 of the Clean Water Act, a Water Quality Certification was required to ensure that the
Project complied with State water quality standards. Additionally, Ecology has review authority
over local shoreline management act decisions.
3.2.1 WDFW HPA
The State Hydraulic Code and the HPA requirements are defined in RCW 77.55.011. A hydraulic
project is defined as “the construction of performance of work that will use, divert, obstruct, or
change the natural flow or bed of any of the salt or freshwaters of the state.” In this definition,
"bed" means “the land below the ordinary high water lines of state waters.”
The Project included elements that changed Lake Washington’s bed through in-water
excavation, required to access the existing sewer line for coupon collection and new clean-out
installations. Thus, the project required an HPA.
Application materials for the HPA were submitted to WDFW using the online Aquatic Protection
Permitting System (APPS) on May 25, 2018. An HPA was issued on June 18, 2018. Because
subsequent Project-required activities continued beyond the specified construction window, an
extended in-water construction window was required. Two modifications were made to the
HPA, issued on September 24 and October 11, 2018, respectively. With the modifications, the
HPA was extended from September 31, 2018 to October 31, 2018.
3.2.2 Ecology 401 Water Quality Certification
The Project was required to comply with state water quality standards, which are typically
satisfied through a 401 Water Quality Certification from Ecology. However, because the Project
was approved under the USACE’s NWP 12, an individual Water Quality Certification was not
required so long as the project complied with additional State conditions.
Ultimately, additional review and approval by Ecology for NWP 12 were not required, since the
Project met the State's conditions.
3.3 USACE NWP 12 and ESA Section 7
The Project area included locations within Lake Washington, which is considered a Water of the
United States. As a result, it falls under the USACE's regulatory jurisdiction under Section 404 of
the Clean Water Act and Section 10 of the Rivers and Harbors Act. Thus, the Project required a
Department of the Army permit covering these two statutes.
The issuance of a federal permit is considered a “federal action,” which further requires the
Project to be reviewed under Section 7 of the ESA. ESA Section 7 requires federal agencies to
consult with the National Marine Fisheries Services (NMFS) and the US Fish and Wildlife
Service (USFWS) to ensure their actions do not jeopardize the continued existence of species
listed as threatened or endangered or otherwise adversely modify designated critical habitat.
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3.3.1 NWP 12 Utility Line Activities
The Project activities conducted in Lake Washington required approval under USACE’s NWP 12.
NWP 12 authorizes activities required for the construction, maintenance, repair, and removal of
utility lines and associated facilities in Waters of the United States, provided the activity does not
result in the loss of greater than half an acre of Waters of the United States for each single and
complete project.
The Project’s activities complied with the NWP 12 requirements, and USACE issued a letter of
verification on August 9, 2018 (Reference # NWS-2018-197).
3.3.2 ESA Section 7 Consultation
The Project was evaluated for potential effects to ESA’s listed species and designated critical
habitats in a project-specific Biological Evaluation prepared by the City, submitted to the
USACE, and used for the ESA Section 7 consultation with NMFS and USFWS. The Biological
Evaluation determined that the Project “may affect, but not likely to adversely affect” listed
species and designated critical habitat.
On August 6, 2018, the USFWS provided a Letter of Concurrence for this finding (USFWS
reference # 01EWFW00-2018-I-13891). The NMFS provided a Letter of Concurrence for this
finding on August 7, 2018 (NMFS reference # WCR-2018-10281). These concurrences satisfied
the requirements under ESA Section 7.
3.4 Lessons Learned
This Project faced various challenges while the required permits and approvals were obtained.
This section details some of the lessons learned from that experience, which may facilitate
similar efforts in the future.
3.4.1 Project Definition and Description
To gain regulatory approvals, a clear and concise project definition and description must first be
developed. This effort is the foundation of the required permit application documents (e.g., Joint
Aquatic Resource Permit Application [JARPA], WDFW APPS information, Biological Evaluation,
etc.).
The definition and description include project locations, methodologies, equipment used, and
schedules, as well as quantifiable project effects on sensitive or regulated resources. By
establishing the definition and description as early as possible during project design, permit
application submittals can be submitted in a timely manner and application documents are more
consistent.
The key challenge is identifying when to develop the definition and description. Specifically,
enough design information must be available for its content, and future designs must not
extensively change or update it.
Because an important part of the Project’s early steps was to identify the Lake Line’s condition
and locations where sampling and cleaning were required, the Project presented some
additional challenges in gaining the approvals.
To identify locations, the team first identified preferred locations from a technical standpoint
and then reviewed those locations from a permitting standpoint to finalize them. The team
wanted to describe the Project and its processes in adequate detail while giving the contractor
some flexibility. To foster that flexibility, additional assessment locations were permitted in case
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a location could not be accessed or additional funding became available to expand the
assessments.
3.4.2 Project Schedule
The Project faced multiple challenges related to scheduling. Initially, permit applications were
submitted with long lead times to allow regulatory agencies enough time to process the
application and issue permits. While most of the permits at the State and local levels were issued
within their expected timelines with no delays, staff resource challenges at the USACE
contributed to the prolonged review process. Since the project qualified for NWP 12 and used
methods consistent with a previously approved project in Lake Washington, the extended
timeline was an unexpected hurdle.
Ultimately, the USACE’s supervisory staff took over the project review, and the permit was
subsequently issued rapidly. In the case that an agency’s regulatory staff does not meet timeline
expectations, future projects are recommended to elevate the review to supervisory staff early
on.
The Project’s schedule was also complicated by work windows for in-water construction. Within
Lake Washington, several regulatory restrictions on in-water construction activities overlap.
More specifically, ESA-listed species are protected by in-water work closures during key months
associated with certain life-history stages (e.g., juvenile salmonid outmigration, adult salmonid
spawning, etc.). The City’s shoreline work windows associated with ESA-listed species allowed
in-water work to begin only after July 15, 2018, and close work on September 30, 2018.
Fortunately, the Project’s conservation measures planned ahead of time to isolate certain work
areas. In the end, WDFW agreed to allow continued in-water work through October 31, 2018, in
areas isolated from the rest of the Lake. Future projects are recommended to give the contractor
a realistic schedule and to develop a detailed contingency plan that maintains in-water work
schedules.
3.4.3 Emergency Activities
During the Project’s early phases, the existing sewer line was indicated to be substantially
obstructed and, without cleaning, might have overflowed and released untreated sewage into
Lake Washington or backed up into shoreline homes. Thus, the team requested the associated
permitting agencies to expedite the permit issuance.
All of these agencies agreed on the Project’s state of emergency, except for the USACE. Though
the USACE did not explain why it did not agree, it issued the required permit before this topic
required additional consideration.
Future projects in similar situations are recommended to take these important matters to the
USACE’s supervisors early on and to request a permit issuance deadline that will appropriately
deal with the emergency’s risks.
3.4.4 HPA Permit
Future cleaning efforts on the permanent manholes may require an HPA, even if no excavation is
performed. Installation of temporary access risers on the existing submerged manholes could be
interpreted to “use, divert, obstruct, or change the natural flow” of Lake Washington. This
interpretation is inconsistent with the City’s current understanding of the permit needs to access
their existing manholes. Therefore, the City is advised to consult with their attorney in
coordination with state agencies for a more formal determination on this topic.
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Chapter 4
PHASE 2B DESIGN ACTIVITIES
Temporary manholes installation and Lake Line cleaning were designed as part of the Phase 2B
activities. The initial permanent precast manhole design approach was changed based on issues
with pre-procuring the manholes and feedback from the contractor, Ballard Marine
Construction (BMC).
This chapter outlines major design activities and summarizes lessons learned for future projects.
4.1 Design Activities
The following activities occurred during design:
• 90-percent design was completed (permanent manhole): June 8, 2018.
• An emergency order was issued: June 11, 2018.
• Request for price proposal for precast manhole supply received no bids: June 22, 2018.
• Decision was made to use a temporary manhole: July 5, 2018.
• Bid set was submitted: July 11, 2018:
Bid Addendum No. 1 was submitted: July 25, 2018.
• The pricing proposal was accepted: July 28, 2018:
Change Order No. 1 was made: July 28, 2018.
• The revised pricing proposal was accepted: July 31, 2018.
Appendix C includes design documents.
4.1.1 Pre-design
The pre-design considered multiple in-lake access structures for the Lake Line:
• Nautilus-style permanent manholes: Concrete manholes designed to match the existing
manholes that allow access with aluminum caisson riser sections. Given the shallow
depths in the southern reaches of the Lake Line, the manholes would have been buried
after the work to avoid safety and navigation concerns.
• Temporary steel manholes: Steel column that connects to the Lake Line to act as a
manhole. External weights extend from the temporary manhole to counter buoyancy.
• In-line cleanout: a length of Lake Line would be replaced with a combination of wye and
tee joints to allow access from a variety of directions. Temporary riser pipes would be
used to extend access from the cleanouts above the lake surface. External weights and
bracing for the riser would be needed to counter buoyancy forces and other forces from
cleaning. This was City operators’ least preferred option due to concerns that the small
diameter of the riser might be difficult to use during cleaning.
The City initially selected the nautilus-style manhole for design. However, the project team could
not find a manufacturer that could make custom manholes in time for the scheduled work, so
contract documents were modified to use temporary steel manholes.
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4.1.2 Survey
As shown in the bid set, the two proposed locations for Manholes (MH) 4 and 5 were mapped
and added to the Project’s base map developed during Phase 2A. The proposed manhole
locations were mapped with approximately 100 feet on either side. Prior to construction,
surveyors staked manhole locations.
4.1.3 Emergency Order
On May 30, 2018, the City’s mayor issued a written Declaration of Emergency to complete
necessary improvements to the Lake Line sewer system. The declaration was made to prevent
potential substantial sanitary sewer overflows into Lake Washington and the adjacent properties
served by the system. The emergency declaration allowed more flexibility in bidding and
contracting to make improvements in a timely manner.
The Renton City Council approved Resolution 4345, ratifying the Emergency Declaration on
June 11, 2018.
4.1.4 Pre-Bid Tour
On June 8, 2018, a pre-bid tour of the existing manholes and proposed temporary manholes was
conducted with representatives from the City, Carollo, Tetra Tech, and BMC. During the tour,
measurements and dives were taken to investigate the condition of the existing manholes.
4.1.5 Contract Documents
Tetra Tech prepared the following contract documents: drawings, specifications, and a probable
opinion of construction cost.
Initial sets of drawings and specifications were prepared assuming that permanent precast
concrete manholes would be installed. As previously stated, the custom manholes could not be
procured within the scheduled work window, so contract documents were modified to use
temporary steel manholes.
The final contract documents were issued on July 10, 2018, and are detailed in the sections
below.
4.1.5.1 Drawings
Eight drawings were prepared, including site plans, details, a sewer cleaning plan, and a sewer
profile.
4.1.5.2 Specifications
Specifications were prepared based on Washington State Department of
Transportation’s (WSDOT’s) Standard Specifications for Road, Bridge, and Municipal
Construction (2016 edition). Special provisions were issued with additions or modifications to the
standard specifications.
The City provided front-end specifications, including the pricing requirements, contract forms,
conditions of the contract, and Division 1.
4.1.5.3 Probable Opinion of Costs
On July 18, 2018, Tetra Tech issued a total cost estimate of $783,200.
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On July 25, 2018, BMC issued an initial price proposal with a total estimated cost of $790,185.
Contract documents were modified to include steel temporary manholes before BMC submitted
its price proposal. On July 28, 2018, an addendum was issued.
On July 30, 2018, a second proposal was submitted with a total estimated cost of $910,030. The
second proposal had an increased price that accounted for surveys, staking, as-built drawings,
excavation safety systems, and pipe cleaning.
4.2 Bid Support
BMC was pre-selected as the contractor for the Project based on its strong qualifications for
aquatic constructions work, experience with lake line repair for other municipalities in
Lake Washington, and familiarity with the Renton Lake Line and qualifications, so no bid was
held.
4.3 Lessons Learned
4.3.1 Impacts of Emergency Work on Contractor Risk
Due to the emergency declaration, BMC was pre-selected without a public bidding process. To
encourage the contractor to use their standard rate sheet, bid items were typically on a “unit
basis” (typically days). While this approach may have kept costs down, it also effectively reduced
the contractor’s risk. In the future, the City would like to structure the bid to shift more risk of
unanticipated issues to the contractor.
4.3.2 Impact of Preselecting Contractor
Future work is anticipated to occur through a public bid process, not the pre-selection used in
2018 activities. A public bid may result in more competitive pricing.
The prequalification language was relatively generic in the 2018 specifications. Thus, the City is
recommended to consider a more specialized pre-qualification of bidders for future public bids,
given the highly specialized nature of in-water work.
4.3.3 Long Precast Concrete Manhole Procurement Time
The initial design was for nautilus-style submerged manholes that would be accessed using
King County caisson risers. Because this special-order structure took longer to procure than
anticipated, the design was changed to a temporary manhole.
According to precast concrete manhole manufactures contacted, embedding the stainless steel
elements and, to a lesser extent, using a custom framework were major factors in the long
procurement timing. Therefore, if selected for future improvements a longer procurement
period in advance of in-water work windows should be allowed. Given the normal work window
starting on July 15, the City it is recommended to beginning pre-procuring custom manholes no
later than January 1. Note that QCP constructed the existing manholes in 2003.
4.3.4 Seal on Existing Nautilus Style Manhole
The pre-bid tour showed a steel ring seat for the seal that was not in the existing manhole
as-builts. This ring seat was beneficial in creating a smooth surface for sealing the King County
Access Caisson in the 2018 cleaning activities. Thus, adding the steel ring seat in future
nautilus-style manholes is recommended.
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Chapter 5
PHASE 2B CONSTRUCTION ACTIVITIES
BMC was contracted to execute the 2018 field activities discussed in previous sections, and BMC
subcontracted Bravo Environmental to conduct the cleaning activities. On-site construction
activities were conducted between September 24, 2018, and October 28, 2018.
Chapter 5 describes key aspects of the construction activities and lessons learned. Information
collected during the construction activities is used for the evaluation of pipe condition (Chapter 6)
and to effectiveness of the cleaning (Chapter 7).
5.1 Construction Activities
During construction, the following activities occurred:
• Pre-construction meeting: August 21, 2018.
• Mobilization: September 4, 2018.
• Submittals: September 20, 2018.
• On-site construction began: September 24, 2018.
• On-site work ended: October 28, 2018.
• Demobilization was complete: November 2, 2018.
5.2 Pre-Procurement
The consultant team prepared cleaning contract documents while permits were being issued.
While attempting to procure permanent precast concrete manholes, the team found that the
manholes would not be available in time for the expected permit window due to the extremely
busy construction market and special requirements for the watertight manholes.
Instead, the plan was changed to procure temporary steel manholes. Cleaning would be done
from each of the two temporary manhole locations and from the three existing permanent
manholes.
5.3 Emergency Response Plan
Prior to construction, an emergency response plan was completed (see Appendix E).
5.4 Construction Support Services
5.4.1.1 Submittals
The consultant responded to the following submittals:
• Pipe and fittings.
• Temporary manhole shop drawing.
• Fish-mix material.
• Dive operations plan.
• Emergency management plan.
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The ductile iron pipes submitted by the contractor in compliance with the specification received
no exceptions in the review process.
Due to supply constraints, the contractor mixed 1.5-inch gravel with 3/8-inch gravel in the field to
meet the specification for the fish mix gravel. Submittals and Requests for Information are
provided in Appendix D.
5.5 Construction Observation and Inspection
The Consultant team provided full time on-site construction observation, as well as specialty
inspections. The Construction observations are provided in daily reports provided in Appendix D.
5.6 Water Quality Monitoring
Throughout construction, turbidity samples were taken at various locations outside the silt
curtain at regular intervals, ranging from just outside the silt curtain to the point of compliance
150 feet away from the silt curtain. Turbidity never reached a point of non-compliance. Water
quality samples are documented within the Daily Construction Reports in Appendix D.
5.7 Installation of Temporary Manholes
Temporary steel manholes were installed at two locations, MH-4 and MH-5. Temporary MH-4
was constructed offshore of 2905 Mountain View Ave North and MH-5 was constructed offshore
of 3119 Mountain View Ave North. To contain turbidity, the work area was surrounded by a
floating silt curtain. Then, excavation using a suction dredge was completed to the existing
Lake Line, and measurements of the Lake Line’s elevations were taken.
The temporary manhole locations were excavated, and manholes were placed with concrete
blocks that control the buoyancy of the manhole and pipe. To allow the team to inspect and
clean the pipeline, temporary connections to the manholes were also made.
The temporary manholes were disconnected after cleaning and inspection. New ductile iron
spools were installed to replace the pipe segments removed during the manhole installation. The
excavated areas were then backfilled with native material, and a fish-friendly spawning gravel
mixture was spread across the work areas’ surfaces.
5.8 Use of Existing Submerged Manholes
To allow the team to inspect and clean the pipeline, aluminum access caissons were temporarily
placed on the existing in-water manholes and were removed afterward. The contractor was
allowed to leave the caissons in place overnight given several conditions:
• Place a secure lid on the caisson when not in use.
• Provide visual beacons to alert nearby boaters.
• Restrict boating access to the caisson using the adjacent work barges to the extent
possible.
• Conduct direct outreach to properties adjacent to the work areas to alert them of the
caissons.
MH-1 and MH-2’s conditions necessitated placing work barges on the lake side (west) of the
manholes. With MH-3, the barge was placed to restrict boating access from the north. Access to
the west was kept open to allow the adjacent property owner use of their boat and dock.
No issues arose from nearby boaters during construction.
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5.9 Construction Cost
The final cost for the construction activities was $949,168.37. A breakdown of construction costs
is shown in Table 5.1.
The following is a breakdown of the construction elements:
Mobilization and Demobilization:
• Furnishing and installing complete and in-place work and all work and materials
necessary to move and organize equipment and personnel onto the job site.
• Providing and maintaining all necessary support facilities and utilities.
• Obtaining all necessary permits, licenses, bonds, and insurance.
• Preparing all necessary submittals.
• Preparing the site for construction operations.
• Maintaining the site and surrounding areas during construction.
• Providing protection for the existing utilities.
• Conducting final clean-up of the site, all in conformance with the contract documents.
Minor Change: Described in Section 1-09.6 of the Specifications for Force Account.
Construction Surveying, Staking, and As-builts:
• Verifying and expanding the project control network provided by the owner.
• Staking proposed manhole locations.
• Measuring top of pipe elevations at connection points.
• Measuring final pipe elevations prior to backfill activities.
• Taking original grades to guide backfill activities.
• Providing settlement monitoring prior to, during, and after excavation and backfill
activities.
Excavation Safety System: All labor, materials, hauling, planning, design, engineering,
submittals, and equipment necessary to furnish, install, remove, and dispose of adequate
shoring and support for all excavations to provide safe access for workers, prevent soil sloughing,
soil loss, and damage to pavement, structures, utilities, and ground adjacent to the excavation.
Temporary Manhole and Installation: All labor, materials, equipment, manufacturing of one
temporary access manhole, hauling, provision of silt curtain, excavation, pipe liquid level
monitoring, bypass pumping, transportation of city/engineer/assistant/inspector to and from
working platforms, placement and pipe connection of the manhole, pipe, fittings, joint
restraints, salvage of the removed pipe segment to the City shops, removal of the manhole,
placement of a new segment of ductile iron pipe, disposal of excess excavation soil, backfill,
blasting/painting the access tube after construction, and return of the access manhole to the City
shops.
Manhole Installation, Extra Days: All extra days of labor, materials, equipment, excavation,
pipe/pipe connections, pipe and manhole connections, and other necessary work to complete
that is not provided in temporary manhole and installation.
Pipe Cleaning: All labor, equipment, materials, cleaning, root cutting, internal removal of
protruding laterals, removal of hanging gaskets, tankage, transportation, manufacture and
installation of a rock catcher at the downstream pump station, daily cleaning of the rock catcher,
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decanting of sewer liquids to the City’s sewer system, and disposal of sewer solids to an
approved upland disposal site.
Sewer Pipe Inspection by CCTV: All labor, equipment, materials for both pre- and post-cleaning
CCTV inspection, provision of record DVDs and report to the City and Carollo.
Spawning Gravel: All labor, equipment, and materials necessary for placing a 6-inch layer of
spawning gravel across the full limits of each temporary manhole work area and fine grading to
return the areas to their original grade.
Bulkhead/Rockery Repair: All labor, equipment, and materials to reconstruct bulkheads/rockeries
that have settled as a result of adjacent pipe or manhole excavation.
Table 5.1 Final Construction Cost
Project Element Cost
Mobilization and Demobilization $80,200
Minor Change $25,000
Construction Surveying, Staking and As-Builts $31,800
Excavation Safety System $2,430
Temporary Manhole Installation $71,800
Manhole Installation, Extra Days $74,100
Pipe Cleaning $343,800
Sewer Pipe Inspection by CCTV $145,200
Spawning Gravel $11,750
Bulkhead/Rockery Repair $0
C.O #1(1) $76,800.34
Subtotal $862,880.34
Total with 10% Sales Tax $949,168.37
Note:
(1) C.O.: change order.
5.10 Lessons Learned
5.10.1 Tidal Delays on Mobilization
At the time of mobilization, large tidal fluctuations at the loading site on the Duwamish River
(Boyer Logistics) slowed barge loading. Because the work had to be done from barges and only
lightweight materials could be delivered from land, the barges could not depart for the work site
until nearly all materials were loaded.
5.10.2 Major Impacts from Shallow Water
The existing sewer pipe was in very shallow water at MH-5, the first location of the temporary
manhole. The contractor had estimated the water depth at this location prior to mobilization;
however, the lake level was regulated at the Ballard Locks and lowered nearly two feet with the
later start to construction in late summer. The water was so shallow that the barges could reach
only a point of 50 to 60 feet from the existing pipeline.
As a result, the temporary manhole was set near the barge and temporary piping was extended
from the existing pipe to the manhole. Future projects should clearly document the anticipated
range of water levels.
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 5-5
5.10.3 Limited Use of Excavator
The contractor mobilized an excavator on one of the two barges expecting to be able to use it to
excavate the manhole sites, lift the temporary manholes into place, and backfill the sites.
However, the excavator could not reach the MH-5 manhole location and was thus used to place
and remove the temporary steel manhole in its adjusted location.
At the Site 4 location, the second temporary manhole location, the barge came close to the
pipeline but not close enough to excavate parallel to the pipeline. As such, this equipment’s use
for excavation was limited, although it did place and remove the temporary manhole in line with
the existing pipeline.
The contractor noted that, under those project conditions, a crane with more reach would be
more helpful than an excavator. Specifically, a crane equipped for use with a clamshell excavator
would be best.
5.10.4 Transient Hydraulic Conditions during Temporary Connections
There is a risk of an inrush of water during the cutting and installation of temporary connections
to the Lake Line. This inrush of water has the potential to cause transient hydraulic conditions
creating temporary surcharging that could cause a sanitary sewer overflow (SSO). However, no
impacts from transient conditions were observed during construction. This may have been due
to Contractor methods that reduced the inrush of water, including:
• Construction methods were used to quickly seal the exposed pipe and limit the volume
of inrush water.
• Connections were made when the Lake Line was “empty” – the flush station had not
been run in some time – providing a storage volume to effectively reduce or eliminate
effects of the inrush.
Similar precautions are recommended during future construction.
5.10.5 Issues connecting the Temporary Manhole to the Lake Line
Because MH-5’s location was adjusted, the connecting piping required multiple bends through
which both the CCTV camera tractor and the cleaning nozzles had difficulty maneuvering. All
bends were made with 8-inch polyvinyl chloride (PVC), 45-degree bends.
According to the contractor, in hindsight, using a maximum bend angle of 22.5 degrees would
have greatly improved access. The contractor also recommended using high-pressure flexible
hoses with flanges for any future offsets required for temporary access since they eliminate
sharp bends and the flanges are much easier for divers to assemble in the water.
5.10.6 Improvements to the Temporary Manhole
The temporary manhole generally worked well. Several improvements were recommended for
the structure after the construction effort:
• Flexible piping to connect the temporary manhole and the Lake Line would provide
additional tolerance for both horizontal and vertical offsets. The initial connection at
MH-4 leaked due to a horizontal offset in the Lake Line. The pipe segment removed
included a deflected joint thought to have allowed the offset in the Lake Line. The
contractor resolved this leak through repositioning the manhole; however, it took
approximately a day to resolve the issue.
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
5-6 | JULY 2019 | DRAFT
• The temporary manhole tended to shift slightly during the work effort, so additional
stabilization was suggested for future work efforts. The contractor constructed a
wooden bridge from the barge to the temporary manhole that limited movement and
provided easier access for cleaning, but the construction barge had to remain in close
proximity to the manhole. To provide more flexibility, the contractor suggested welding
several plates outward (parallel to the bottom of the manhole) to provide a way for
super sacks or other weights to directly stabilize the bottom of the structure.
• Anchor weights were thought to help counter buoyancy forces; however, in some cases,
the available connection points restricted the anchors' use or effectiveness. The
contractor suggested adding additional anchor connection points at both the top and
middle of the temporary manhole to provide more options to place anchors.
• The contractor constructed an approximately 3-foot wooden deck around the manhole
with a railing to provide a better work area for cleaning activities. Including a similar
work area is recommended in future efforts. According to the contractor, bracing and
connection points for the decking could be welded onto the temporary manhole to
facilitate future installation.
5.10.7 Field Mixed Fish Mix
The fish-mix submittal initially proposed 3/8-inch pea gravel as fish mix. However, this mix was
not accepted, since it was too small and too poorly graded to be effective. Nonetheless, when
the submittal was returned, the Contractor’s work boat had already left for the job site with pea
gravel on board. Thus, as an improvised fish mix, the contractor proposed field-mixing the pea
gravel with imported 1.5-inch gravel. The engineer could not verify whether 1.5-inch and 3/8-inch
gravel were adequately mixed in the field.
5.10.8 Successful HPA Permit Extensions
Given the late start and variety of delays in the work’s progress, the project required
two extensions for the WDFW’s HPA permit. The first granted an extension of approximately
two weeks from the normal September closure of the fish window. A second extension was
granted until the end of October and came with additional conditions.
5.10.9 Consider Annual Ballard Locks Closure
With the fish window closing at the end of October, all in-water work needed to be completed.
Then, the annual inspection and cleaning of a fish barrier at the Ballard Locks imposed additional
time constraints on the contractor.
In late October, the Contractor reported that the Ballard Locks would be closed for annual
maintenance starting Monday, October 29, at 5:00 p.m. A subsequent notice changed this time
to 5:00 a.m. The closure was scheduled to last approximately three weeks. This annual closure
should be considered in future planning.
If the barges were not moved through the locks in time, the contractor would have been liable
for three additional weeks of rental time for the barges and the excavator, and the cleaning
sub-contractor would not have had access to one of its trucks.
5.10.10 Decanting Wastewater Worked Well
The contractor’s second barge had a full-sized vacuum truck and two portable steel Baker-style
tanks. When the vacuum truck was full of water, it was decanted to the two tanks. When the
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 5-7
two tanks were full, a manifold system was used to empty them together into the Lake Line at
the same rate to maintain the barge’s stability.
The manifold system collected water and sewage from the middle of the water column in the
tank to retain FOG and other floatables, as well as heavy solids and sediment. The manifold
system was then directed to the nearest Lake Line manhole available, from which clear water
and sewage were discharged downstream. No problems or negative effects on the Lake Line or
the work were noted with this configuration.
The Contract also called to cover the tanks for odor control. Two samples of sludge and solids
removed from the tanks indicated that anoxic conditions predominated in the tanks. The
contractor reported extreme odors when they were cleaned. However, no odor complaints were
received from adjacent home owners.
5.10.10.1 Quantifying Solids Removed
Finally, the contractor reported that approximately 2 tons of pipe-cleaning debris were disposed
of at the landfill. Assuming a fully saturated condition, this amount equates to 1 cubic yard of
debris.
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 6-1
Chapter 6
CONDITION ASSESSMENT
6.1 Condition Assessment
The following chapter details Carollo and V&A’s collaborative effort to conduct a condition
assessment of the Lake Line for the City. The assessment of the Lake Line was performed in
two phases, Phase 2A and Phase 2B, as described in the subsequent sections.
This report presents the results of both phases of the condition assessment to determine if the
Lake Line has at least 10 years of RUL. Further information on the condition assessment is
located in Appendix F, which contains the entire V&A Report.
6.1.1 Visual Observations/ Dive Video
V&A conducted qualitative visual assessments from shallow water depths, the shoreline, and the
boat (to the extent possible). Where the pipe was in deeper water (greater than approximately
three feet), V&A directed BMC to investigate conditions using a video monitor and audio
communications from the dive boat.
Visual assessments focused on the condition of the metallic pipe surface, joints, and any fittings
that were exposed. Defects, such as metallic corrosion, pitting, coating blisters, and coating
failures were documented with digital photographs, as applicable (shown in Appendix F). Visual
assessments are subjective in nature and made according to V&A’s experience in evaluating
metallic pipelines in water and soil environments.
As part of the 2018 construction activities and as part of the 2017 Phase 2a investigations, visual
observations and dive videos of the Lake Line and its laterals were collected where they were
exposed. Figure 6.1 shows example photographs and observations from the condition
assessment. Generally, the top half or the off-shore side of the pipe were exposed at these
locations. Given this exposure condition, electrolytic corrosion is likely occurring on the
Lake Line’s metal surface.
Lake Line laterals were assessed at two parcels, 3501 and 3717 Lake Washington Boulevard North.
The lateral at 3501 had a bell and spigot joint exposed along its run and a mechanical joint at the
connection to the Lake Line. The laterals exhibited minor to moderate surface corrosion. Most of
the Lake Line joints between individual pipe segments appeared to be bell and spigot (push-on)
joints. Meanwhile, observed lateral connections were joined to the mainline with mechanical
joints, either with wye or tee fittings. The bolts and gland rings of these connections exhibited
corrosion but, when corrosion and surface debris was removed, they were in fair to good
condition. Figures 6.1-7 through 6.1-10 outline the joint conditions of the mainline. However,
whether or not all lateral connections to the Lake Line have mechanical joints is unknown.
Appendix F includes additional photos and information from the visual observations of the
Lake Line.
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
6-2 | JULY 2019 | DRAFT
Figure 6.1-1 As-Found Condition of Mainline with Minor Corrosion Tubercles
Figure 6.1-2 Area of Scaling and Tuberculation on Mainline; Large Rocks Around Mainline at
2811 Mountain View Avenue North
Figure 6.1-3 Surface of Mainline after Scaling and Corrosion Removed
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 6-3
Figure 6.1-4 Moderate Pitting and Graphitized Layer After Wire-Brushing Surface
Figure 6.1-5 Pitting and Graphitization
Figure 6.1-6 Typical Pipe Surface
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
6-4 | JULY 2019 | DRAFT
Figure 6.1-7 Typical Bell and Spigot Joints Between Pipe Segments
Figure 6.1-8 Typical Mechanical Joints at Wye and Tee Fittings for Lateral Connections
Figure 6.1-9 Rip-Rap Directly Adjacent to and Above Lake Line at 2811 Mountain View Avenue North
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 6-5
Figure 6.1-10 Unsupported Bottom of Lake Line where Shoreline has Steep Drop-Offs
6.1.2 CCTV
Lake Line mainline was assessed using CCTV inspection by Bravo Environmental. A total of
3,211 feet of mainline CCTV video that was reviewed, approximately 50 percent of the video had
poor visibility due to the camera being submerged at sags in the mainline. V&A reviewed the
video files and reports and commented on the structural condition of the pipe.
Several cases of cement mortar lining delamination were found, some such areas appearing
smooth and free of corrosion. This suggests that previous Lake Line cleaning may have removed
some of the loose lining materials. At high points within the partial pipe flow, moderate to
significant corrosion was observed; in these cases, sewer gases could have deteriorated the
lining and corroded the metal substrate below.
Corrosion deposits were commonly observed near joints, even in areas where the lining
appeared intact. This is because the lining was discontinuous or roughly applied at the pipe ends,
creating weak spots allowed for corrosion. Meanwhile, some segments of the Lake Line saw
partial joint separation, offsets, and deflections. Table 6.1 summarizes the limits of the CCTV
inspection videos as reviewed by V&A.
Table 6.1 Limits of the CCTV Inspection Videos
Section No.
Upstream
Manhole
Downstream
Manhole
Direction of
Survey
Length of
Survey, feet
4 Flush Station New MH-5 Upstream 329
6 New MH-5 New MH-4 Downstream 257
9 New MH-5 New MH-4 Upstream 565
12 New MH-4 MH-3 Downstream 484
15 New MH-4 MH-3 Upstream 509
17 MH-2 MH-1 Downstream 635
18 MH-2 MH-1 Upstream 210
22 MH-1 Pump Station Downstream 222
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
6-6 | JULY 2019 | DRAFT
Figure 6.2-1 Typical Lining Delamination with Smooth Metal Surface Behind
Figure 6.2-2 Debris and Sediment, Some of which Appears to be Chunks of Cement Mortar
Lining Material
Figure 6.2-3 Typical Moderate to Significant Corrosion at High Point (Brown Area); Black Area
Appears to be Stained Mortar Lining
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 6-7
Figure 6.2-4 Typical Moderate to Significant Corrosion at High Points (Brown Area)
6.1.3 Coupon Tests
6.1.3.1 Phase 2A (2017)
The City excavated and exposed the Lake Line at one on-shore location just outside of the
Flush Station in 2017. One 3-inch-diameter pipe coupon was drilled from the top of the Lake Line
and sent to a laboratory for analysis. The coupon was evaluated by the following laboratory
procedures: visual examination, metallography, chemical analysis, mechanical testing – tensile
test, mechanical testing – Charpy V-notch impact test, and Brinell hardness testing.
The results of the laboratory analysis indicate that the pipe coupon is made of a ductile iron
material that meets the mechanical property requirements of American Water Works
Association (AWWA) C151-81 (American National Standards Institute [ANSI] A21.51-81),
Grade 60-42-10. The average wall thickness of the coupon was 0.349 inches.
6.1.3.2 Phase 2B (2018)
V&A received two mainline pipe samples and one lateral coupon from BMC. The samples and
coupon are described below:
•MH-4 sample: 8-inch-diameter, 40-inch-long mainline sample cut from the 20-foot
segment removed when constructing MH-4.
•MH-5 sample: 8-inch-diameter, 40-inch-long mainline sample cut from the 20-foot
segment removed when constructing MH-5. This sample included a bell-and-spigot
(rubber gasket) joint.
•Lateral coupon: 3-inch-diameter coupon from 6-inch-diameter lateral. The specific
location is unknown.
Visual Inspection:
Qualitative visual assessments were conducted on the mainline pipe samples and lateral pipe
coupon. Defects, such as metallic corrosion, pitting, and lining defects, were documented with
digital photographs.
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
6-8 | JULY 2019 | DRAFT
The mainline samples and lateral coupon exhibited a dimpling pattern on the exterior surface
that is typical of pipes made of a ductile iron material (Figure 6.1-1); however, laboratory testing
showed that the pipe was made of cast iron. Figures 6.3-1 – 6.3-8 shows additional examples of
visual deficiencies found during Phase 2B while Appendix F includes additional descriptions.
Figure 6.3-1 Typical Dimple Pattern on Mainline Samples and Coupon; However, this Is Cast Iron Pipe
Figure 6.3-2 Graphitization on Interior Surface of Manhole 4 Sample
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 6-9
Figure 6.3-3 Exterior Surface of Manhole 4 Sample with a Few Scattered Minor Pits
Figure 6.3-4 Cement Mortar Lining on Interior of Manhole 5 Sample
Figure 6.3-5 Corroded Surfaces near Joint of Manhole 5 Sample; Lining Failed around Joint
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
6-10 | JULY 2019 | DRAFT
Figure 6.3-6 Exterior Surface of Manhole 5 Sample with Scattered Minor Pitting
Figure 6.3-7 Deteriorated Cement Mortar Lining on Lateral Coupon
Figure 6.3-8 Exterior Surface of Lateral Coupon with Minor Pitting Corrosion
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 6-11
6.1.3.3 Joint Sample and Pull Test
Testing was performed on the MH-5 joint samples. The laboratory, Voss, performed a pull test to
document the maximum load required to separate the bell end from the spigot end and to view
the internal joint surface and gasket. Voss used a universal testing machine (UTM) to perform
the test. The UTM reached 8,750 pounds when the spigot end of the pipe failed at one of the bolt
holes used to hold the joint in the machine. The pipe joint pulled apart approximately 0.5 inches
at the time of the failure. V&A believes that the excessive load was required to pull the joint
apart because the internal joint surfaces were corroded.
6.1.3.4 Lab Analysis
Laboratory tests on the mainline samples and lateral coupon included microstructural
examination (metallography), wall thickness measurements, pit depth measurements, chemical
composition testing, Charpy impact testing, hardness testing, tensile strength testing, modulus
of rupture testing, and secant modulus of elasticity testing. The samples and coupon were
initially tested according to AWWA C151-81 (ANSI A21.51-81), which is mean for ductile iron
pipes. However, optical micrographs (microstructural examination) and the Charpy impact tests
indicated that the mainline samples and lateral coupon were made from gray cast iron.
Therefore, Talbot strip tests, a strength test specific to cast iron pipes (per ANSI A21.6), were
also conducted. Appendix F includes additional information on these tests.
The wall thickness of the specimens was measured using point micrometers. The interior and
exterior surfaces of the specimens were also examined for corrosion pitting. Then, the RUL for
the Phase 2B pipe samples was calculated from the wall thickness, results which are shown in
Table 6.2.
Table 6.2 Remaining Useful Life for Pipe Samples
Pipe Sample
Min.
Remaining
Thickness,
in.
Max.
Measured
Thickness,
in.
Max.
Thickness
Loss, in.
Max.
Thickness
Loss, pct.
Corrosion
Rate,
in./yr.
Remaining
Useful Life,
yr.
Manhole 4 0.228 0.376 0.148 39% 0.0033 69
Manhole 5 spigot 0.353 0.398 0.045 11% 0.0010 353
Manhole 5 bell 0.301 0.376 0.075 20% 0.0017 181
Lateral coupon 0.373 0.420 0.047 11% 0.0010 357
Note:
(1)in./yr.: inches per year; pct.: percent.
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
6-12 | JULY 2019 | DRAFT
Figure 6.4 Three-inch Diameter Pipe Coupon as Received by Laboratory
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 6-13
6.1.4 Revised Ultrasonic Thickness Testing Results
Ultrasonic Thickness (UT) testing was completed at exposed locations along the lake line as part
of Phase 2a. UT testing provides a non-invasive method to measure wall thickness
measurements from the exterior of the pipe. These measurements can be used to calculate the
corrosion rate of metal if the thickness at a previous point in time (such as the time of
installation) and the elapsed time are known. For this study, corrosion rates in inches per year
were calculated using the installation date of 1972 and the year of construction for the Lake Line
and laterals. The corrosion rate can then be extrapolated to determine when the pipe will reach
the minimum required thickness for the given service conditions. Appendix F includes additional
information on the assumptions made for this analysis.
The RUL analysis was revised according to the results of Phase 2B, which showed that the
pipeline, except at the Flush Station, is probably made of cast iron, rather than ductile iron, as
was assumed in Phase 2A. The UT analysis was revised to account for the change in material,
which caused minor changes in RUL, typically less than two years difference.
Table 6.3 summarizes the field ultrasonic thickness measurements and RUL estimates. For the
updates made in Phase 2B to these calculations, the “current year” was not updated, so the RUL
runs from 2017. The minimum calculated RUL estimate is 18 years (from 2017) for the Lake Line
test locations and 10 years (from 2017) for the test locations on the laterals.
These estimates are strongly influenced by the assumption that a 1/8-inch-deep pitting exists at
each test location. The actual pit depth coinciding with low ultrasonic thickness measurements
may be less. If the pitting were assumed to be negligible at each ultrasonic test location, the
minimum calculated RUL estimates would be 46 to 66 years.
6.1.5 RUL Results
At the end of RUL, pipes are anticipated to leak from holes caused by corrosion, resulting in
increased inflow and infiltration. Through these leaks, wastewater can exfiltrate to the Lake
when under pressure, such as when the flush station runs. For this reason, any hole is considered
by the City to be a pipe failure and, in this study, the RUL was defined by potential leaks, not a
collapse of the pipe or other major defects.
RUL estimates from UT measurements and pipe coupons are summarized in Figures 6.5 and 6.6.
Figure 6.5 shows the condition assessment sites geographically, where UT samples typically
were measured closely together on exposed pipe sections. The map illustrates the variability in
RUL in relatively short sections of pipe. Figure 6.6 provides a statistical summary of RUL
independent of location. It can be used to estimate extent of the Lake Line and laterals that are
likely to need to be repaired or replaced in any given time frame. For example, approximately
25 percent of the Lake Line and laterals will leak (reach the end of useful life) in 36 years and
50 percent in 50 years. While the graph is useful in conveying the RUL in general, the actual RUL
of the Lake Line and laterals may vary from this relationship. Factors that could impact the
actual RUL include:
• Relatively few lateral samples were considered; however, lateral RUL values were
assumed to be similar to the Lake Line given the samples’ similarities in age, material,
construction technique, and environment.
• Sensitivity analyses identified the RUL measurements from UT tests (the majority of
samples) were highly dependent on the assumed exterior pitting.
• Additionally, the estimated RUL values were calculated assuming a linear corrosion rate,
but corrosion rates can slow over time, which would present a longer RUL.
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
6-14 | JULY 2019 | DRAFT
Table 6.3 Ultrasonic Thickness Data and Remaining Useful Life Summary (Revised 2018)
Site/Street
Number Type
Measured Thickness Readings, in. Assumed Pipe Data Max.
Thickness
Loss, in.(1)
Max.
Thickness
Loss, pct.(1)
Max
Corrosion
Rate,
in./yr.(1)
Min.
Remaining
Useful Life,
yr.(1, 2)
Year
Taken Min. Avg. Max. Number Class
Nom.
Thickness,
in.
Main
Flush
Station
Pipe 2017 0.270 0.332 0.358 9 53 0.36 0.215 60% 0.0048 30
2811 Pipe 2017 0.338 0.404 0.428 13 23 0.44 0.227 52% 0.0050 42
3001 Pipe 2017 0.268 0.360 0.396 11 20 – 22 0.35 – 0.41 0.207 59% 0.0046 31
3411 Pipe 2017 0.260 0.305 0.362 11 20 0.35 0.215 61% 0.0048 28
3703 Pipe 2017 0.300 0.376 0.416 12 22 0.41 0.235 57% 0.0052 34
3703 Wye 2017 0.679 0.679 0.679 1 – 0.60 0.046 8% 0.0010 542
3719/3805 Pipe 2017 0.298 0.379 0.452 19 20 – 23 0.35 – 0.44 0.193 51% 0.0043 44
3719/3805 Wye 2017 0.622 0.622 0.622 1 – 0.60 0.103 17% 0.0023 217
3825/3827 Pipe (S) 2017 0.244 0.356 0.432 38 21 – 22 0.38 – 0.41 0.291 71% 0.0065 18
3825/3827 Wye 2017 0.658 0.658 0.658 2 – 0.60 0.067 11% 0.0015 358
3825/3827 Pipe (N) 2017 0.358 0.389 0.414 3 22 0.41 0.177 43% 0.0039 59
Laterals
3501 Pipe 2017 0.192 0.280 0.388 15 21 – 22 0.35 – 0.38 0.313 82% 0.0070 10
3717 Pipe 2017 0.280 0.283 0.286 3 21 0.35 0.195 56% 0.0043 36
Notes:
(1) Thickness loss includes 1/8-inch-deep pitting. The corrosion rate and remaining useful life were calculated from the resulting thickness loss values.
(2) The remaining useful life estimates run from 2017, the year the testing was performed, not from the time of this Phase 2B update.
(3) Thickness measurements based on cast iron pipe material.
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 6-15
Figure 6.5 Lake Line Remaining Useful Life by Location
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 6-17
Figure 6.6 Remaining Useful Life Cumulative Distribution Function
6.2 Lessons Learned
6.2.1 Identifying the Location of Defects
In a typical gravity sewer, initial pipe defects in pipe segments that are reaching the end of their
usable life would be identified through CCTV inspection and repaired or replaced through point
repairs. To an extent this may be possible for the Lake Line, such as sections of de-lined pipe
observed in the 2018 CCTV inspection. However, lack of access to and the submerged conditions
in the Lake Line makes this approach difficult and likely not able to identify minor defects in
many sections of the pipe. Alternatively, increasing defects and resulting leaks can be identified
through increasing inflows to the lift station over time. However, this approach does not provide
the location of specific leaks and may not enable the number and size of leaks to be
distinguished.
Periodic condition assessment activities (i.e., CCTV Inspection, UT Testing, and coupon testing)
can assist in identifying pipe defects. Based on the RUL, it is recommended additional condition
assessment occur within 10 years. However, given the cost of condition assessment activities,
the City may consider if conducting larger scale repair and replacement activities is more cost
effective.
0
0.25
0.5
0.75
1
0 20 40 60 80 100
Pr
o
b
a
b
i
l
i
t
y
RUL (years)
Remaining Useful Life CDF
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
6-18 | JULY 2019 | DRAFT
6.2.2 Measurement of External Pitting Depth
The RUL results were highly sensitive to the external pitting depth assumption. The RUL of UT
samples were calculated using a direct pipe wall thickness measurement and an assumption of
the depth of external pittings. In future assessments, the depth of external pitting should be
measured for each sample location, when possible. Measurement of smaller pits may have
limited accuracy due to their being underwater.
Given the resulting samples, additional statistical analysis should be conducted to determine the
effect of the varying measurements on the overall pipe RUL.
6.2.3 Visibility in Submerged Sections
Operators from Bravo Environmental conducted CCTV inspections and noted that the clarity of
submerged sections varies depending on the timing of the flows from the flush station, where
flows from the flush station appeared to increase turbidity in submerged sections and obscure
CCTV inspections. With that being said, operators reported a relatively-clear, submerged CCTV
inspection in several afternoons when the flush station was run in the morning, allowing turbidity
to settle. While clarity was increased, the inspection quality was still less in these areas than in
dry sections, since. Additionally, increasing wastewater content in the pipe from prolonged
periods without flushing also obscured CCTV inspections. The City is recommended to consider
these findings when planning future Lake Line CCTV inspections.
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 7-1
Chapter 7
CLEANING EFFECTIVENESS
The Lake Line sewer is not self-cleaning, and, when City’s crews clean it, they cannot reach the
entire pipeline. While the City has cleaned over 90 percent of the Lake Line in recent years,
observations of the HGL indicate partial blockages remain in the Lake Line; likely in the form of
either thin, broadly-distributed layers of sediment or other material or thicker local partial
blockages. The resulting reduction in Lake Line capacity could increase the risk of sewer
overflows into Lake Washington and backups into homes.
This chapter evaluates the 2018 Lake Line cleaning practices and evaluates the nature of partial
blockages in the pipeline.
7.1 Pre-Cleaning CCTV Inspection
A pre-cleaning CCTV inspection was conducted in 2018 to the extent possible. Because gravel
and accumulated debris existed in the pipelines, much of the Lake Line could not be accessed for
inspection. Figures 7.1 and 7.2 show the extent of the Lake Line’s sections that could be seen via
CCTV inspection:
• No Debris (orange line): Pipe sections free of major debris allowing CCTV inspection.
• Unknown sections (green line): Pipe sections that were not reached in 2018.
• Debris (blue line): Pipe Sections inaccessible due to debris, rocks, and encrustation or
due to obstructions caused by pipe size, geometry, or infrastructure. Pipe beyond initial
debris/obstruction cannot be assessed.
Where initial debris/obstructions prevented pre-cleaning CCTV the pre-cleaned condition could
not be determined.
The City and Contractor agreed that operators implement caution in their inspections due to the
extreme difficulty in recovering lost CCTV equipment in the Lake Line. More effort was placed in
post-cleaning CCTV Inspections that were thought to have less risk of CCTV equipment loss.
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Figure 7.1 2018 Lake Line CCTV Pre-Cleaning Map Extent and Results
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Figure 7.2 2018 Lake Line CCTV Pre-Cleaning Profile Extent and Results
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7.2 Effectiveness of Land-Based Hydro-Jetting
The City periodically cleans the Lake Line using hydro-jetting from four land-based access points
on the Lake Line, listed below. These activities are documented and evaluated in detail in the
Kennydale Lake Line Sewer System Evaluation Phase 1 Existing Conditions Technical
Memorandum 1 (Carollo, et al., 2017) and the Kennydale Lake Line Sewer System Evaluation
Phase 2 Condition Assessment Report (Carollo, et al., 2018). The effectiveness of land-based
hydro-jetting of the Lake Line was evaluated using pre-cleaning CCTV inspections from 2018
activities:
• The Flush Station.
• Lake Washington Lift Station No. 2.
• LaValley (3507 Mountain View Avenue North).
• Kennydale Beach Park (3501 Lake Washington Boulevard North).
Pre-cleaning inspections of CCTV showed substantial debris upstream of the
LaValley (3507 Mountain View Avenue North) cleaning lateral, indicating that the City’s previous
land-based cleaning is likely not effectively removing freed solids at the LaValley site.
Presumably, freed solids are not able to be moved up the cleaning lateral and are depositing
between MH-2 and -3.
Prior evaluations cautioned solids loosened by land-based cleaning may not have been removed
from the Lake Line, especially at LaValley and Kennydale Beach Park sites. These locations do
not have in-line access to remove solids and crews noted in 2016 that little solids were being
removed. At the Flush Station and Lift Station, where the pipe is accessed from a wet well or
vault, water and solids are brought back to the access point and removed with a vacuum truck.
The Kennydale Beach Park location was not CCTV inspected in 2018 and debris deposits at that
location cannot be confirmed.
7.3 Cleaning Activities
The Lake Line sewer was cleaned from the two temporary manhole locations and from the
three existing in-water manholes. To clean the sewer, 600 to 700 pounds per square inch (psi) of
water pressure was directed through a pipe-cleaning nozzle, first to pull the nozzle and hose into
the pipe and then to suspend and pull sediments back to the insertion manhole.
At some locations, where the jet nozzle could not pass a bend or joint in the pipe, the water
pressure was increased to move the nozzle along. After the nozzle passed the restriction, the
water pressure was lowered again to prevent damaging the inside of the pipe and to reduce the
chances of opening up pipe joints.
Figures 7.3 and 7.4 show the cleaning conducted in the CCTV-accessible areas:
• Cleaned sections (orange line) were verified to be cleaned and free of major debris by
CCTV inspections in 2018.
• Unknown, non-inspected sections (green line) may have been cleaned in 2016 or 2018;
however, CCTV inspections were not available to verify the cleaning's effectiveness.
• Non-cleaned sections (blue line) were not cleaned in 2016 or 2018. Specifically, in 2018,
debris stopped CCTV inspections from proceeding into these areas. Conditions beyond
the initial obstructions are unknown.
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Figure 7.4 details the cleaning profile of this work. Approximately 80 percent of the Lake Line
was accessible and debris-free (marked in orange) and showed significant improvements
compared to pre-cleaning conditions, shown in Figure 7.2.
Though cleaning improved CCTV accessibility, assessing the pipe remained difficult. Significant
portions of the debris-free and accessible areas were still submerged allowing limited
assessment. Figures 7.4 and 7.5 show the various stationing and elevations of the pipe that 1) did
not undergo CCTV inspection (marked in gray); 2) did undergo CCTV inspection and were visible
(marked in orange); and 3) did undergo CCTV inspection, but were not visible under water
(marked in blue).
Overall, the cleaning was successful where it reached. As discussed in Chapter 5, improvements
in construction techniques may increase the extent of cleaning in subsequent work efforts.
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Figure 7.3 2018 Lake Line CCTV Post-Cleaning Map Extent and Results
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Figure 7.4 2018 Lake Line CCTV Post-Cleaning Profile Extent and Results
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Figure 7.5 Visibility conditions encountered by CCTV
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7.4 Evaluation of Partial Blockages
According to City staff's observations after the cleaning in 2018, the cleaning did not
substantially affect the Lake Line’s hydraulics. City staff made the following observations in late
2018 with the flush station running at approximately 60 gallons per minute (gpm):
• Laterals for residences from 2805 to 2809 Mountain View Avenue North appeared to be
pressurized; City staff did not measure levels due to concerns of causing an SSO.
• Surcharging reached within about a foot of the surface at
3001 Mountain View Avenue North.
• Typical water levels were observed at Coleman Point
(3013 Mountain View Avenue North).
These observations were consistent with the pre-cleaning Lake Line operations, which indicated
that system hydraulics were influenced by one or more remaining partial blockages.
Post-cleaning CCTV inspection showed cleaning was effective in sections reached; however, not
all sections could be reached. The 2018 cleaning and CCTV inspection substantially narrowed the
potential location of partial blockages; therefore, hydraulic analyses were updated to evaluate
the severity and location of the partial blockages.
7.4.1 Partial Blockage Severity
To determine the potential severity of the partial blockage, varying degrees of partial blockage
were modeled using the hydraulic model developed in Phase 2a to replicate the 2018 field
observations of HGL. Three scenarios were considered:
1. Scenario 1, Clean pipe: No deposits or partial blockages.
2. Scenario 2, Deposits but No Significant Partial Blockages: Deposits filling up to one-third
of the pipe in the Lake Line’s uncleaned sections, but no additional significant partial
blockages.
3. Scenario 3, Deposits and One or More Significant Partial Blockages: Deposits filling up
to one-third of the pipe and one or more significant partial blockages (filling
approximately 80 percent of the pipe) in the Lake Line’s uncleaned sections.
The model simulated the HGL produced from potential deposits and partial blockages in the
Lake Line conditions for the current Flush Station operations (pumping rate of 60 gpm). As
shown in Figure 7.6, the results for the three scenarios were as follows:
• Scenario 1, Clean Pipe: The clean pipe scenario showed that the HGL would not
surcharge above the highest point of the pipe, except in early sections, due to
pressurization from the flush station. This was inconsistent with City staff’s observations
of surcharging.
• Scenario 2, Deposits but No Significant Partial Blockages: The model indicated that this
scenario would cause surcharging but not as much as what has been observed in the
field. This scenario was inconsistent with observed surcharging at 2805 and
3001 Mountain View Avenue North.
• Scenario 3, Deposits and One or More Significant Partial Blockages: This scenario
simulated field-observed surcharging at 2805 and 3001 Mountain View Avenue North.
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Thus, the hydraulic analysis indicated that at least one significant partial blockage is located in
the northern, uncleaned Lake Line section and that lesser deposits have not been fully removed.
However, multiple moderate partial blockages could also be creating the same effect.
Based on CCTV inspections, the Lake Line has greater than typical pipe roughness and minor
losses from joints. Modeling indicates that these losses and other smaller deposits do not restrict
the current low flow rates (60 gpm). However, they may have greater effects in the future if the
Lake Line is operated at higher flow rates. As flows increase above 60 gpm, deposits and partial
blockages will likely cause a large increase in HGL, which could cause SSOs and home backups.
7.4.2 Location of Partial Blockages
The 2018 activities cleaned both locations where partial blockages were assumed in the 2017
modeling, and post-cleaning CCTV inspection verified that no partial blockages were present at
those locations. Therefore, the hydraulic model was updated to explore other possible locations
of the partial blockages.
As shown in Figure 7.7, updated modeling assumed partial blockages at two locations in areas
that were not cleaned:
• Site A, in the sag near 2805 Mountain View Avenue North:
Moderate debris stopped the CCTV inspection at 2815 Mountain View Avenue North, and
a partial blockage could be located anywhere between 2805 and
2815 Mountain View Avenue North, where cleaning could not be verified in 2018. The
location at 2805 Mountain View Avenue North was chosen for evaluation given the
presence of a relatively large sag that likely has not been cleaned in recent cleanings.
• Site B, upstream of the cleaning lateral at Kennydale Beach Park
(3501 Lake Washington Boulevard North):
To replicate the surcharging observed at 3001 Mountain View Avenue and
Coleman Point, a partial blockage was simulated upstream at
3501 Lake Washington Boulevard North. The 2018 CCTV inspection showed the pipe
between 3001 and 3411 to be free of deposits. The partial blockage could be anywhere in
the uncleaned section between 3411 and 3703 Lake Washington Boulevard North. Site B
was assumed for the following reasons:
CCTV inspection found substantial debris upstream of the LaValley cleaning lateral.
Therefore, similar debris could have been deposited upstream of the
Kennydale Beach Park cleaning lateral.
The site corresponds to the deepest sag in the uncleaned section.
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Figure 7.6 Model Results for Three Scenarios
Site A
Site B
Deposits and Partial
Blockage
Deposits Only
Clean
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Figure 7.7 Site A and Site B Evaluated with Debris and/or Partial Blockage of Lake Line
Site A
2805 Mountain View Avenue North
Site B
3501 Lake Washington Boulevard North
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The partial blockage modeled at Site A had a relatively minor effect on the model’s results. Given
the lack of HGL measurements at the location, the model’s precision was limited and the
presence of a partial blockage could not be determined at this location. However, partial
blockage could also not be ruled out; therefore, cleaning is recommended at the location.
Most of the modeled surcharging resulted from Site B’s partial blockage. Modeling of a partial
blockage there generated results consistent with the limited field data. However, partial
blockage locations further downstream could also produce these results. Additional
measurements of HGL would be required to confirm sections further downstream are free of
partial blockages, as discussed in the next section.
The City is strongly recommended to maintain the current, low-flushing rates in the
Lake Line given the likely presence of deposits or a partial blockage. As flows increase above
60 gpm, the deposits and partial blockages can cause a large increase in HGL that could
cause SSOs and home backups.
7.4.3 Field Verifying Location the Partial Blockage
Sufficient information is not available for the model to precisely locate partial blockages. As a
result, this section presents various methods for field verifying the locations. It is recommended
that the City field verify partial blockage locations to the extent possible to support near-term
cleaning of uncleaned sections described in Chapter 8.
7.4.3.1 Identifying the Downstream End of Blockages
When the flush station is running, a partial blockage causes surcharging in the pipe. The
downstream extent of the blockage can be identified by a drop in the hydraulic grade. Two
general options are available to identify the hydraulic grade in the pipe:
• Estimate it using water levels in laterals, which are based on CCTV footage or other
direct measurements.
• Install pressure gauges at regular intervals in the Lake Line, which would require the
Lake Line to be uncovered.
Note that, in the field, the drop-off in HGL may be less pronounced than in the modeling,
depending on the severity and extent of the partial blockages.
7.4.3.2 Identifying the Upstream End of Blockages
The upstream extent of the partial blockage may not be identified by measuring the HGL since
the downstream extent of the partial blockage controls the hydraulics. Thus, the City will likely
need to conduct CCTV inspections of the Lake Line to determine the upstream extent of the
partial blockage. The City can attempt to gain CCTV access to the Lake Line from laterals.
Note: In 2017, the City conducted a CCTV inspection of laterals, showing push cameras typically
becoming submerged near the Lake Line. Additionally, operators were generally unable to
control the direction of travel in the Lake Line from the lateral, which was largely due to the
configuration of the tie-in of the lateral and Lake Line.
As described in Chapter 5, the City is recommended to operate the flush station to improve
visibility to the greatest extent possible and to use CCTV inspection technologies that may
maintain the camera higher in the pipe. Even with these recommendations, the CCTV
inspections may not provide the quality of information needed to identify the upstream end of
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the partial blockage. Otherwise, the City will need to construct additional access points into the
Lake Line.
Note that caution is strongly encouraged when conducting CCTV inspections of the laterals and
Lake Line since access points are limited to help free or retrieve from obstructions.
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Chapter 8
NEAR-TERM OPTIONS FOR UNCLEANED
SECTIONS
This chapter reviews options to address sections of the Lake Line not reached in recent cleanings
Site A and Site B), where partial blockages are believed to occur and increase the Lake Line’s
HGL. Three general approaches are assessed:
• Hydro-jet cleaning at Site A and Site B.
• High-velocity flushing of the entire Lake Line.
• Pipe replacement at identified sections with partial blockages.
The Chapter first discusses the general approaches in Section 8.1 and then details
implementation at Sites A and B in Sections 8.2 through 8.4.
8.1 General Description of Methods
8.1.1 Hydro-Jet Cleaning
Hydro-jet cleaning is an industry-standard method for cleaning gravity sewers. Typically, 600
to 700 psi of water pressure is directed through a pipe-cleaning nozzle, first to pull the nozzle and
hose into the pipe and then to suspend and pull sediments back to the insertion manhole. A
vacuum truck is typically used to supply jetting water and collect jetting water and sediment to
remove solids from the system.
Hydro-jetting has several benefits for the Lake Line:
• It generally removes solids and FOG from the pipeline with in-line access, such as a
manhole.
• It does not interrupt sewer service.
• Access needed for hydro-jetting also usually provides CCTV Inspection access that can
be used to verify the cleaning's effectiveness.
With that being said, hydro-jetting also has some disadvantages:
• It requires using existing and temporary in-water submerged access points, which
requires expensive barge-based cleaning.
• At some locations, bends or joints in the pipe provide obstacles for jetting. This is more
common in the Lake Line than in a traditional gravity sewer due to the Lake Line’s
profile and has, in past efforts, limited the length of hydro-jet activities to approximately
200 feet at some locations.
• It can be relatively damaging to pipe liners. There are indications that recent
hydro-jetting of the Lake Line has removed loose pipe liner at multiple locations.
Sites A and B have not been hydro-jetted in previous cleanings due to lack of access to the pipe
sections.
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8.1.2 High-Velocity Flushing
High-velocity flushing is an option for cleaning without in-lake access. Pumping high flows into
the Lake Line creates high velocities that are capable of scouring settled solids and other debris.
This approach would clean the entire Lake Line, with high flows being pumped from the flush
station and collected at the lift station. The high-velocity flushing would require isolating laterals
to prevent SSOs or home backups. Any home backups would likely result in large claims since
they’d likely be on the first floor (kitchen, living room, etc.) of the lakefront homes.
Figure 8.1 shows a schematic of the flushing approach. For this approach, the steps are as
follows:
• A City hydrant supplies flushing water to the flush station’s wet well, and an air gap is
provided to prevent the potential for a cross-connection.
• Temporary flush station pumps provide approximately 800 gpm of flushing flows to the
Lake Line to reach a 5 feet per second scouring velocity.
• The City isolates laterals using either a gate valve or inflatable plug valve to prevent
SSOs or home backups.
• Temporary pumps at the lift station convey the flushing flows to King County through
the existing force main.
High-velocity flushing has several benefits for the Lake Line:
• It does not require in-lake work, substantially reducing the effort related to
hydro-jetting.
• It is generally less damaging to the pipe lining than hydro-jetting.
However, it also has some disadvantages:
• Pipes and joints could move under high flows and pressure, creating new leaks. Severe
pipe movement and deflection could result in causing sewage to discharge into the lake.
• Pipe movement due to higher pressure against bulkheads or dock pylons would pose a
risk of damage to the Lake Line and laterals.
• It is generally less effective at removing FOG than hydro-jetting is. FOG may harden on
pipe walls and resist removal by flushing.
• Lateral isolation would require constructing new infrastructure in the Lake Line
customers’ backyards. Furthermore, operators would need to access the laterals during
flushing activities.
• Sewer service would be interrupted for 6 to 12 hours; bypass pumping may be required
for some customers.
• Sediment, especially larger debris, could become piled at pipe offsets and other pipe
obstructions during flushing.
• It doesn’t provide access to the Lake Line to confirm the cleaning’s effectiveness
through CCTV inspection.
8.1.2.1 History of Causing SSOs
In 1986, the City attempted to perform a high-flow, high-velocity flushing of the Lake Line. The
higher flows pressurized the Lake Line, requiring the laterals to be sealed to avoid potential
SSOs and backups into homes. Ball valves were installed and used during the flushing; however,
they did not seat effectively. Thus, during an initial attempt of high-velocity flushing of the line, a
significant amount of sewage backed up into the basement of one home, and the process was
not tried again.
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The City of Bellevue has also attempted a similar high-velocity flushing of a Lake Line and
experienced a SSO. The details of the City of Bellevue’s flushing are not known; however, it does
provide further antidotal evidence of lateral isolation being a key challenge in high velocity
flushing of the Lake Line.
8.1.3 Pipe Replacement
Instead of conducting cleaning activities, the City could potentially replace in place the existing
pipe with a new clean pipe. This could both address potential partial blockages and replace in
poor condition. Replacing a specific segment of piping can be completed using open-cut
methods. Past projects have cost-effectively replaced short segments of pipe using only a work
boat, saving the costs associated with barges/equipment needed in other cleaning approaches.
However, these cost savings are likely only available in certain conditions. Increased cost of pipe
replacement is anticipated to be driven by two considerations:
• Excavation Conditions: The effort to excavate a pipeline varies widely based on water
depth, excavation depth, surrounding sediment (ranging from loose sands/gravels to
consolidated clays), and adjacent obstacles (i.e., bulkheads, dock piers, buried debris,
etc.). Challenging conditions may result in less efficient excavation or require heavy
equipment and staging/material barges.
• Restoration of Disturbed Areas: Permit Agencies will likely require all disturbed areas to
be restored to the original grade and covered with sediment appropriate for salmonid
spawning (“Fish Mix”). Restoration of larger areas may require expensive
staging/material barges and potentially barge mounted heavy equipment.
For short segments of pipe in less challenging conditions, contractors may be able to use only a
suction dredge from a work boat. Heavy equipment and staging/material barges may be
required for more challenging conditions; resulting in much higher costs than using only a work
boat. Due to the highly variability conditions in the Lake, longer pipe replacement projects will
likely encounter more challenging conditions and require heavy equipment and staging/material
barges.
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Figure 8.1 Cleaning Schematic for High Velocity Flushing
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8.2 Hydro-Jet Cleaning at Individual Sites
8.2.1 Site A
The 2018 activities were unable to clean Site A from 2805 to 2811 Mountain View Avenue North.
Reported cleaning lengths indicate that a single pass of the hydro-jet was made through some of
this section; however, the effectiveness of this cleaning is unknown.
CCTV inspections were stopped at 2811 Mountain View Avenue North due to moderate sand and
pea gravel deposits. Thus, no CCTV inspection information is available for the relatively large
sag, which could contain additional deposits including a substantial partial blockage.
According to the City, the laterals at these homes are pressurized. Thus, the City is
recommended to attempt a CCTV inspection at this pipe section, followed by cleaning, if
required.
8.2.1.1 Access Options
Site A extends from 2805 to 2811 Mountain View Avenue North and, as shown in Figure 8.2, is
directly downstream of where the Lake Line turns into the lake. Previous attempts to clean from
the flush station were blocked by an obstruction near the lakeward turn. The following sections
describe several options to access Site A.
Figure 8.2 Lake Line at Site A
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Option 1: New or Modified Cleanout
Installing an access point on land may allow the City to bypass the obstruction that previously
limited CCTV inspection and hydro-jetting. According to City staff, two cleanouts on the site
could be modified to serve as an access point. If required, a new cleanout could also be installed.
A new cleanout may create a dead end and should be valved off to prevent odor and
maintenance concerns. In addition, a new easement may be required for a new cleanout and
piping.
According to the profile of the pipe, the section downstream of 2801 Mountain View Avenue North
has a relatively deep sag. The sag may make removing solids through hydro-jetting from land less
effective. Still, on-land CCTV and cleaning are recommended, given the less relative effort required
to create in-lake access.
Note that an approximately 50-foot section of the pipe was not located during survey activities in
earlier phases. This pipe section could be under a bulkhead (likely built after the Lake Line was
installed) or on land. However, even if found, this section is not anticipated to provide
meaningful access due to limited access between houses and the likely restoration costs if
accessed.
Option 2: Manhole in Street
To provide a larger access point, the City could install a standard manhole in the street that
connects with the Lake Line, on land. Once constructed, this would allow crews typical access to
the pipe without entering a customer’s property. Similar to the cleanout, the manhole would
create a dead end and should be valved off.
A new easement may be required for the proposed manhole and piping. Whether the manhole
would be located in a City street or a private drive would require further research. Thus, the City
should identify the need for an easement and potential restoration as part of project planning.
Option 3: In-Lake Manhole
Installing a submerged manhole would be difficult in this section of pipe. The Lake Line runs near
or under bulkheads, which would likely require shoring or rebuilding a portion of the bulkhead
after constructing the submerged manhole. Due to these constraints, attempting on-land access
before in-lake access is recommended. Potential in-lake access locations can be identified based
on Lake Line location, water depth, and bulkhead location and material.
8.2.1.2 Cost
On-Land
On-land access cleanouts or manholes may be installed by City staff or potentially through a
small works contractor. The anticipated costs for construction are provided below.
• Cleanout: can be installed in a one to two-day period with $4,000 or less in materials.
• Manhole: can be installed for $12,000 or less, assuming the patching of asphalt.
Additional site restoration costs may be incurred, depending on the location of the cleanout or
manhole. City staff could complete CCTV inspection and hydro-jet cleaning from an on-land
cleanout or manhole in several hours.
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In-Lake
Using in-lake access via a temporary manhole would take substantial effort. Based on the 2018
activities, the in-lake manhole would cost over $400,000, not including potential substantial
costs for excavation shoring, repair of bulkheads and docks, and property restoration.
Furthermore, permitting and design may take up to two years with construction limited to the
summer work window.
8.2.2 Site B
Site B’s uncleaned section of the Lake Line, believed to have a partial blockage, begins just south
of the Kennydale Beach Park at 3411 Lake Washington Boulevard North and extends to
3703 Lake Washington Boulevard North. This section of pipe is a relative high spot in the
Lake Line.
While the partial blockage could occur anywhere in this section, the City should focus initial
efforts on Kennydale Beach Park (3501 Lake Washington Boulevard North). Prior cleanings may
have inadvertently piled debris near the on-land cleaning lateral at this location, causing a partial
blockage.
The Lake Line at Kennydale Beach Park is approximately 30 to 50 feet offshore, as shown in
Figure 8.3, and is in approximately seven feet of water. The Lake Line crosses through the swim
area and likely under the park dock. The site has two laterals: the southern cleaning lateral (no
sanitary flow) and the northern lateral (sanitary flows from the park bathroom). The
Kennydale Beach Park has vehicle access from a relatively narrow road from the north.
Pedestrian access is through a stairway from Lake Washington Boulevard North. Note, the
wastewater utility would need to obtain permission from the Parks Department for any
construction and future cleanings in this park.
Figure 8.3 Distance from Lake Line to Kennydale Beach Park
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Hydro-jet cleaning at Site B would require additional access to the Lake Line, which demands
some in-water work. Because high costs were incurred when installing access from barges in
2018, the following alternative access methods were identified:
• Land-based installation of a temporary in-water manhole.
• Permanent in-water manhole on Kennydale Beach Park’s dock.
• Permanent in-lake cleanout access.
• In-water, temporary manhole installation.
Using one of these access options, the City or its contractor would hydro-jet the uncleaned
section of the Lake Line. Pre- and post-cleaning CCTV could be conducted to evaluate the
effectiveness of the cleaning.
8.2.2.1 Access Options
Land-based installation of a temporary in-water manhole
Kennydale Beach Park provides an opportunity to install a temporary in-water manhole and
hydro-jet from the equipment staged in the park, which would reduce overall costs for
construction and cleaning. 30 to 50 feet from shore, the Lake Line may be reached with a
truck-mounted boom crane with a boom length between 60 feet to 100 feet in length. A work
boat and divers would be required for in-water construction, whereas a work barge may not be
required.
This option presents several challenges:
• The work period would be limited to several weeks in September that meets both
permitted work windows and is outside of swim season at the popular park (a likely
request from the Parks Department).
• Heavy equipment may damage the access road, park surfaces, and retaining structures.
Wide loads may not be able to access the location due to the narrowed access road.
• Additional geotechnical work may be required to support the crane or other heavy
equipment.
• In 2018, a barge was used to stabilize the temporary manhole structure. Without the
barge, the City would likely need to alter the temporary manhole to provide greater
stability (See Chapter 5).
Hydro-jetting and solids removal would need to originate from a vacuum truck on the shore. This
is not expected to be a major concern as long as the temporary manhole provides a stable area
to conduct hydro-jetting from.
Note that a permanent submerged manhole outside the Park swim area, rather than a
temporary manhole, could be installed as part of this alternative to reduce the effort of future
cleanings. However, a permanent manhole in the lake would need to address navigation hazards
and risks to visitors at the park.
Kennydale Beach Park Dock Manhole
A permanent manhole could be built in or directly adjacent to Kennydale Beach Park’s dock. The
sealed or locked manhole would extend above the lake level and be incorporated into the dock
for safety and park aesthetics. The dock-based manhole would provide direct, land-based
access, making future maintenance easier. Furthermore, the City could install level monitoring
equipment in the manhole to better understand the Lake Line's operation.
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This option would require approval from the Parks Department, and the wastewater utility
would likely need to replace at least part of the dock when incorporating the manhole. Note,
changes to the dock may require the entire dock to be brought up to current code.
A downside of the dock manhole is that it would be located in a relative high spot in the
Lake Line. Cleaning effectiveness from that location may be reduced since the hydro-jet would
need to pass through upstream and downstream sags if extended more than several hundred
feet in either direction.
Permanent In-lake cleanout access
The City can install an in-line cleanout on a section of the Lake Line to provide access for
hydro-jet cleaning from equipment staged in the Park. Figure 8.4 shows a diagram and pictures
of a similar cleanout constructed for Mercer Island. The cleanout replaces approximately 20 feet
of pipe with a variety of ports that can be accessed using risers to the surface, which can be
customized to the City’s preferences.
Note that the City chose not to use this type of cleanout for the 2018 cleaning due to concerns
that it might cause pipe movement when hydro-jetting. This was a possibility because segments
of the Lake Line were unconstrained due to being exposed or in loose soil. Additionally,
operators were concerned they wouldn't be able to conduct hydro-jetting through a pipe riser
with a relatively small diameter.
In-water Temporary Manhole Installation
In-water temporary manhole installation where both construction and cleaning are completed
from barges is not recommended due to cost, unless on-land access or construction is not
feasible. This effort would be similar to the 2018 activities described in Report No. 1 (Carollo et
al., 2018).
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
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Figure 8.4 In-Lake Cleanout Installed in Mercer Island
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8.2.2.2 Cost
Conceptual costs were developed for Site B’s hydro-jetting access options. These costs represent
a budgetary placeholder and should be reevaluated during pre-design.
Soft cost estimates were made based on the 2018 cleaning. Depending on the scope and timing
of the work, these soft costs may be substantially reduced. As a conceptual cost estimate,
a 30 percent design contingency was included.
Land-based installation of a temporary in-water manhole
Table 8.1 presents conceptual costs to set up a temporary manhole and hydro-jet from
Kennydale Beach Park.
Table 8.1 Cost for Land-based installation and hydro-jetting of a temporary in-water manhole
Description Quantity Unit Unit Price Total Cost
Contractor Mobilization/Demobilization 1 LS $20,000 $20,000
Install Temporary Manholes 1 Manhole $130,000 $130,000
Contractor Cleaning Effort 1 LS $50,000 $50,000
Bulkhead Improvements 25 LF $1,000 $25,000
Park Restoration 1 LS $20,000 $20,000
Construction Subtotal $245,000
Contingency 30% $73,500
Construction with Contingency Subtotal $318,500
Sales Tax 10% $31,850
Construction Contract Amount (including Tax) $350,350
Permitting/Public Outreach 15% $47,775
Design/Bidding 20% $63,700
Construction Management 10% $31,850
City PM/Admin 10% $31,850
Soft Cost $175,175
Total Cost $525,525
Note:
(1) LF – linear foot; LS – lump sum.
Permanent in-water manhole on Kennydale Beach Park’s dock.
Table 8.2 presents conceptual costs to construct a dock manhole and hydro-jet from
Kennydale Beach Park.
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Table 8.2 Cost for Installation and hydro-jetting from a Permanent in-water manhole on
Kennydale Beach Park’s dock
Description Quantity Unit Unit Price Total Cost
Contractor Mobilization/Demobilization 1 Barge $20,000 $20,000
Install Manhole 1 Manhole $200,000 $200,000
Bulkhead Improvements 25 LF $1,000 $25,000
Park Restoration 1 LS $20,000 $20,000
Construction Subtotal $265,000
Contingency 30% $79,500
Construction with Contingency Subtotal $344,500
Sales Tax 10% $34,450
Construction Contract Amount (including Tax) $378,950
Permitting/Public Outreach 15% $56,843
Design/Bidding 20% $75,790
Construction Management 10% $37,895
City PM/Admin 10% $37,895
Soft Cost $208,423
Total Cost $587,373
Similar to the land-based construction, this option would reduce costs associated with
mobilization and demobilization of construction barges. Construction of the dock manhole was
conceptually budgeted at $200,000, which includes $130,000 for the manhole installation,
$20,000 for to-be-determined custom manhole features (exterior coverings, etc.), and $50,000
to replace the existing dock.
The area of Kennydale Beach Park near the dock is a sand beach with a concrete bulkhead and a
picnic shelter. The bulkhead improvements and park restoration were assumed to be required to
tie in the potential new dock.
The costs were derived assuming that the City would conduct hydro-jet cleaning since the work
effort would be similar to what has already been conducted at the Kennydale Beach Park lateral.
Therefore, no costs for cleaning were included in this option.
Permanent In-lake cleanout access
Installing a cleanout would have significantly lower construction costs than installing a manhole.
The Mercer Island cleanout had a construction cost of $75,000 using only divers and a workboat.
However, since the City did not prefer this option, costs were not estimated in detail.
In-Water Temporary Manhole Installation
Based on the 2018 work, the in-water installation of a single temporary manhole and cleaning
cost, presented in Table 8.3, would be approximately 40 percent more expensive than on-land
options.
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
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Table 8.3 Cost for Installation and hydro-jetting from In-Water Temporary Manhole
Description Quantity Unit Unit Price Total Cost
Contractor Mobilization/Demobilization 2 Barges $90,000 $180,000
Install Temporary Manhole 1 Manhole $130,000 $130,000
Contractor Cleaning Effort 1 Manhole $100,000 $100,000
Construction Subtotal $410,000
Contingency 30% $123,000
Construction with Contingency Subtotal $533,000
Sales Tax 10% $53,300
Construction Contract Amount (including Tax) $586,300
Permitting/Public Outreach 15% $87,945
Design/Bidding 20% $117,260
Construction Management 10% $58,630
City PM/Admin 10% $58,630
Soft Cost $322,465
Total Cost $908,765
8.3 High-Velocity Flushing of Entire Lake Line
This section evaluates the option to conduct a high-velocity flush of the entire Lake Line to scour
settled solids and other debris. The advantages and disadvantages of this potential approach
and conceptual costs are outline in Section 8.1.
8.3.1 Potential to Damage the Lake Line
According to construction specifications, the Lake Line should have been pressure-tested at
construction; however, no record of such a test exists. Whether the laterals were pressure-tested
is also unclear.
High pressures could cause pipes and joints to move thus creating additional leaks. Movement
against bulkheads, especially for laterals, or dock pylons poses a greater risk of damage to the
pipeline. Severe pipe movement and deflection could even result in sewage being discharged
into the lake. Given the age and lack of information on pressure testing, determining the
maximum pressure that can be used without causing damage is not possible.
Furthermore, the extent of issues that could result from pressurization is unknown. Overall,
pressurizing the pipe likely would reduce the Lake Line’s remaining useful life.
8.3.2 Flushing Velocity
Given the representative solids collected during the 2018 cleaning, achieving a flow velocity
between 5 and 7 feet per second is recommended when flushing. The collected solids were sent
to a laboratory for sieve testing, which revealed sands and pea gravel.
To move these sizes of materials, typically, flushing velocities between 5 and 7 feet per second
are required. To achieve 5 feet per second, the 8-inch Lake Line would require flushing flows of
approximately 800 gpm. While this flow rate is recommended, the flow rates may not be able to
be achieved
Standard practice for high-velocity flushing of potable water systems is to flush for a duration
equivalent to three to five pipe volumes, while no standard practice exists for wastewater.
Assuming five pipe volumes and 800 gpm, high-velocity flushing pumping would be required for
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80 minutes. However, lateral isolation will likely be needed for at least three hours to allow time
to isolate the system and the Lake Line surcharging to subside after the flushing.
8.3.3 Temporary Pumping at Lift Station and Flush Station
The existing lift station and flush station are unable to pump the 800 gpm needed to flush the
Lake Line. Instead of upgrading the capacity of the stations, the City is recommended to rent
temporary pumps. Temporary diesel pumps for non-potable water, such as the Godwin NC150S
Dri-Prime Pump or comparable, are widely available and typically self-contained on a trailer or
skid mount. Initial calculations show the existing force main can convey the flushing flows.
Additionally, if necessary, temporary piping can be extended to the City’s gravity system on the
east side of Lake Washington Boulevard North.
The temporary pumps would need to be field-fitted to the flush and lift stations, as shown in
Figure 8.5 and Figure 8.6. The flush station intake from the lake would need to be blocked to
keep chlorinated water from discharging into the lake.
The City plans to upgrade the flush station and lift station in the coming years. For those
projects, installing flushing ports is recommended to provide a dedicated connection for
temporary pumps. These dedicated ports would reduce the time required for installation and the
risk of poor field fittings.
8.3.4 Alternative Flushing Location
To reduce the logistical challenges of isolating the entire Lake Line for high-velocity flushing, the
City could begin or end the flush at In-Lake Manhole #2, which is less than 20 feet offshore of
3411 Lake Washington Boulevard North in shallow water. Flushing at this location would split the
system, where approximately 40 percent of the Lake Line (19 laterals versus 33 for the entire
Lake Line) are upstream of the manhole (toward the Flush Station) and 60 percent are
downstream (toward the Lift Station). A similar approach as flushing would be used with flows
traveling from the Flush Station to the Manhole #2 or from Manhole #2 to the Lift Station.
However, it would also present the following logistical challenges:
• Caisson risers or other means would be needed to access the manhole.
• Field fitting to create an isolating pressure seal on the inlet or outlet pipe may require
alternations to the manhole.
• A small baker tank would likely be needed to provide an air gap between the hydrant
and temporary pump.
• No publicly owned large staging area exists directly adjacent to the manhole. However,
there is one near the right of way on Mountain View Avenue North, and there is publicly
owned land on the County rail and trail directly uphill of the site.
These logistical challenges should be weighed against the benefits of the shorter flushing length.
Thus, this alternative flushing location was not costed.
Finally, if the manhole is used to pump out flushing flows, they may be disposed of in the
City-owned gravity sewer across Lake Washington Boulevard North. However, an additional
investigation is needed to confirm the receiving sewer capacity. This would require placing the
temporary pump and temporary piping across Lake Washington Boulevard North during the
flushing activities.
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
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8.3.5 Lateral Isolation
High-velocity flushing requires isolating customer laterals to prevent SSOs or home backups.
The existing plug valves were not considered a feasible option due to their age and the failure of
the 1986 high-velocity flushing activity.
Removing the existing valves and cleanouts would be a challenge since they have been encased
in rebar and concrete. Additionally, homeowners have covered in some cases some cleanouts or
valves with decking and other obstacles, which would require substantial costs to restore.
For these reasons, any lateral isolation effort is expected to avoid or minimize removal of the
existing valves. Other options for lateral isolation are described below.
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Figure 8.5 Flush Station with Temporary Pump Configuration for High-Velocity Flushing
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DRAFT | JULY 2019 | 8-17
Figure 8.6 Lift Station with Temporary Pump Configuration to Support High-Velocity Flushing
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8.3.5.1 Permanent Gate Valves
The City could install gate valves to reliably isolate the laterals. Gate valves would require
excavation for installation of the valve vault, and vegetation restoration. Once installed, valves
would also need to be periodically exercised to keep them in good working order for future
flushing events. Since homeowners historically have buried or covered existing valves and
cleanouts, this option’s maintenance may be a challenge. As a result, City staff does not prefer
this option.
8.3.5.2 Temporary Inflatable Plugs
Inflatable plugs could isolate laterals without a permanent valve at a cleanout in the lateral. A
major advantage of this approach is that the cleanout could be sealed and potentially buried
following the flushing effort. No ongoing efforts would be required between flushings, such as
exercising valves. Additionally, the City would not need to alter or remove existing valves.
However, if the seal is ineffective, then SSOs and home backups could occur. Backup claims
could be much larger than flushing costs since they would likely be on the first floor (kitchen,
living room, etc.) of lakefront homes.
Concerns about backups could be somewhat mitigated with the following approaches:
• Replace a segment of pipe on each side of the cleanout with a new smooth plastic pipe
to facilitate a tight seal. The roughness of the existing pipes may make a tight seal
challenging.
• Install two temporary plugs per cleanout to provide redundant seals.
• Visually observe the seal at the cleanout during flushing and make corrections or use
vacuum trucks to limit the volume of SSO or backup at a faulty seal.
When using inflatable plugs, the time required to install the plugs must be considered. At least
eight workers would be needed to install and remove temporary plugs to flush the Lake Line in
an eight-hour timeframe. This requires 33 total sites, a two to four-hour flush time, and
temporary plug installation or removal at 20 minutes per lateral. The installation and removal
time takes into account that operators would not be able to walk with multiple plugs from lateral
to lateral due to weight of the temporary plugs and the required pump weigh (approximately
30 pounds).
Per discussions with the City, inflatable plugs were preferred and thus used to cost this
alternative.
8.3.6 Lake Line Pressures during Flushing
Lake Line operation during flushing was evaluated using the hydraulic model to show likely
pressures with a clean Lake Line (no partial blockages). At the desired 800 gpm flushing flows,
pipe roughness and minor losses have a large effect.
According to initial pump sizing calculations, pressures between 60 psi and 80 psi at the flush
station would be required to achieve the flushing rates. At 60 psi, flows between 600 gpm and
800 gpm may be achieved, depending on the headloss in the Lake Line. This range reflects the
uncertainty in the current hydraulic capacity of the Lake Line, which has not been operated at
these flow rates in decades. Lower flow rates and corresponding velocities may limit the scour
and transport of larger materials.
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The hydraulic model modeled a conservative amount of loss resulting in a 600-gpm flushing flow
(which would achieve a velocity of only about 3.5 feet per second) with 60 psi at the flush station.
The pressures shown for 600 gpm are considered applicable up to 800 gpm if the actual pipe has
less roughness and minor losses than modeled.
According to the analysis, the vast majority of the Lake Line would surcharge and require
isolating laterals against high pressures. Pipe pressures would decrease from 60 psi to 20 psi
throughout the first approximately 2,600 of the Lake Line, as shown in Figure 8.7.
8.3.7 Risk of Unsuccessful High-Velocity Flushing in a Partially Blocked Lake Line
According to the hydraulic model, partial blockages significantly increase HGL as flows increase
above the existing flushing rate of 60 gpm without increased pump discharge pressure.
Theoretically, a partial blockage reduces the effective cross-sectional area in the pipe, achieving
scouring velocities at lower flow rates than the clean pipe.
As the partial blockage is gradually reduced, flows can be increased to account for the increased
pipe capacity. However, this may not occur in practice if the partial blockage is made from
difficult-to-scour materials, such as FOG, partially cemented sediment, heavy debris. In this case,
the City would not be able to increase flows, and the high-velocity flushing activity may fail to
achieve its goals.
With a partial blockage, flows must be ramped up slowly to reduce the chance of transitory
effects that could create high pressures. Installing pressure gauges on laterals throughout the
Lake Line is recommended to monitor pipe pressures and ceasing activities when pressures
increase unacceptably.
The temporary pump could be controlled according to downstream pressures so that pressures
do not exceed the operating range deemed acceptable to the City (assuming no transitory
effects). However, with a partial blockage, operations will be relatively hard to control initially as
the reduction of the partial blockages impacts pipe capacities and pressures (creates a moving
target).
High pressures, rather than decreasing as shown in Figure 8.7, will likely extend from the location
of the partial blockage to the flush station until the partial blockage is cleared. This would
increase the risk of pipe damage and movement versus a clean-pipe condition.
8.3.8 Debris in Manholes
The existing submerged manholes in the Lake Line would likely collect debris during flushing
since velocities would decrease in the manhole chamber. At the proposed flow rates, water from
the manhole inlet would likely jet through the manhole channel and, in theory, keep the channel
free of debris.
Some flow will exit the channel into the manhole chamber and deposit any entrained solids in
the manhole. These deposits may create odor issues as they decay. However, the amount of
deposition cannot be estimated without more extensive analysis. Computational fluid dynamic
modeling can be conducted as part of pre-cleaning efforts to estimate deposition, or the City
may take a “wait and see” approach.
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8.3.9 Cost
Table 8.4 shows the estimated cost of flushing. This conceptual estimate represents a budgetary
placeholder to be reevaluated in pre-design. Soft costs are estimated based on the 2018
cleaning. Because the scope of private property restoration is uncertain, a 50-percent design
contingency was included.
For this estimate, a contractor was assumed to conduct the flushing effort. However, City staff
could lead and execute the Lake Line flushing given sufficient staff availability.
The City recommended a budgetary placeholder of $200,000 for restoration, which is
approximately 60 percent of the conceptual construction costs. The City may consider a
performance-based specification or alternative project delivery mechanisms (design/build,
construction manager at-risk, etc.) that may limit design costs associated with the restoration.
Table 8.4 Cost for High-Velocity Flushing
Description Quantity Unit Unit Price Total Cost
Lateral Tee Installation 33 Lateral $2,000 $66,000
Temporary Plugs 33 Lateral $1,200 $39,600
Temporary Pumps 1 LS $10,000 $10,000
Installation of Pumps and Plugs 1 LS $20,000 $20,000
Restoration 1 LS $200,000 $200,000
Construction Subtotal $335,600
Contingency 50% $167,800
Construction with Contingency Subtotal $503,400
Sales Tax 10% $50,340
Construction Contract Amount (including Tax) $553,740
Permitting/Public Outreach 15% $83,061
Design/Bidding 20% $110,748
Construction Management 10% $55,374
City PM/Admin 10% $55,374
Soft Cost $304,557
Total Cost $858,297
FUTURE CLEANING OPTIONS AND REPLACEMENT ALTERNATIVE ANALYSIS | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 8-21
Figure 8.7 Pressures from Lake Line Flushing
15 37
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
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8.4 Pipe Replacement for Identified Sections with Partial Blockages
According to the condition assessment, widespread, minor pipe failures (leaks) may occur in the
Lake Line in 20 to 30 years. To provide a segment of clean Lake Line, the City could begin
replacing short segments of the Lake Line rather than cleaning them. This alternative is
particularly appealing if the City can identify a specific location for the partial blockage.
If the pipe is in poor condition, the new pipe would also address those condition issues.
8.4.1 Cost
Without knowing the location of partial blockage, the City may need to replace longer lengths of
the Lake Line, which is anticipated to be challenging and potentially costly. Thus, given the
uncertainty in scope, no costs were calculated for this option. In general, the estimated
construction costs to replace Lake Line segments in-place were $1,200 per LF. Replacing longer
sections of Lake Line may provide some economies of scale, especially for soft costs (design,
permitting, etc.).
Several challenges could have major effects on project costs:
• Permitting and design are anticipated to take up to two years, since permits may be
required for geotechnical investigations during design and for construction.
• The effort required to excavate the Lake Line is highly variable, depending on the lake’s
sediment material and water depth. This makes estimating costs difficult for small pipe
segments.
• Permit conditions and City standards may require the new pipe to be buried (2 to 3 feet).
Where the pipe is exposed, this may add substantial excavation to the Project.
• The existing pipe exceeds modern standards for pipe deflections and depth of bury. The
design would need to mitigate these issues and may require different pipe materials
(i.e., ductile iron, PVC, high-density polyethylene [HDPE], etc.).
• The area north of Kennydale Beach Park has closely spaced docks, likely limiting the
equipment that can be used to replace the Lake Line in this area.
8.5 Cleaning Analysis Conclusion
Future cleaning options for Sites A and B of the Lake Line are provided below.
8.5.1 Site A Cleaning Analysis Conclusions
Site A is focused at 2805 Mountain View Avenue North and may extend to
2811 Mountain View Avenue North. This section is directly downstream of where the Lake Line
turns into the lake. Previous attempts to clean from the flush station have been blocked by an
obstruction near the lakeward turn.
Based on the analysis of options, the City is recommended to attempt a CCTV inspection of this
pipe section to confirm the presence of debris or partial blockage, followed by cleaning, if
required. The City is also recommended to first attempt land access of the Lake Line using a new
or modified cleanout at 2811 Mountain View Avenue North or a new manhole in the street due to
the anticipated difficulty of creating in-lake access.
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A new easement may be required for these access points. If required, cleaning may be conducted
using hydro-jetting from the land access point or system-wide, high-velocity flushing. In-lake
access for hydro-jetting or replacement of pipe segments is anticipated to be difficult in this
section and should be avoided if possible.
8.5.2 Site B Cleaning Analysis Conclusions
Site B is located at Kennydale Beach Park near 3411 Lake Washington Boulevard North where
prior cleanings may have inadvertently piled debris near the on-land cleaning lateral, thus
causing a partial blockage. However, a partial blockage could occur anywhere between
Kennydale Beach Park and 3703 Lake Washington Boulevard North.
The Lake Line is approximately 30 to 50 feet offshore and is in approximately seven feet of water
at the Kennydale Beach Park. As a result, some in-lake work effort will be required to access the
Lake Line to perform hydro-jetting or pipe replacement. Three potential cleaning methods are
provided below.
8.5.2.1 Hydro-jetting
Hydro-jet cleaning can be conducted through in-lake access to improve solids removal. The
report identified three approaches to establishing access with construction staged from land or
entirely in-water using barges, similar to the 2018 work effort:
• Kennydale Beach Park dock permanent manhole: Conceptual total cost of $587,373.
• Land-based installation of a temporary in-water manhole: Conceptual total cost of
$525,525.
• In-water temporary manhole installation: Conceptual total cost of $908,765.
A permanent manhole could be built into Kennydale Beach Park’s dock or directly adjacent to
the dock. If approved by the Parks Department, the manhole would provide direct land-based
access for cleaning and other long-term O&M for a capital cost that is only slightly greater than
that of a temporary manhole. Any manhole would need to be sealed and locked and address
safety concerns and park aesthetics. Based on these O&M benefits, this option is expected to be
explored further and is a viable alternative to temporary manhole installation options.
Installing the temporary in-water manhole by land or in-water will both equally clean and restore
pipe. No major permanent improvements will be made to the Lake Line. Due to the substantially
less total costs, the City is anticipated to first consider land-based construction before executing
the in-water alternative.
Note that the conceptual total costs include those for construction, a construction contingency
of 30 percent, sales tax, permitting and public outreach, design and bidding support,
construction management, and the City’s project management and administration.
8.5.2.2 High-velocity Flushing
As previously discussed, pumping high flows into the Lake Line will create high velocities capable
of scouring settled solids and other debris. Temporary pumps will provide up to 800 gpm of
flushing flows to the Lake Line and pump them to King County via the existing force main.
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The main benefit of high-velocity flushing is that it can clean the entire line without in-lake
access. However, this option has major challenges and risks that should also be considered:
• The high flow rate will increase pressure to approximately ten times the typical
discharge pressure, requiring laterals to be isolated to prevent SSOs or home backups.
Home backups, as mentioned before, would likely result in large claims.
• High pressures associated with flushing can cause pipe movement that, if severe, could
cause sewage to be emitted into the lake. The extent of issues is impossible to know;
however, pressurizing the pipe will likely reduce the Lake Line’s RUL.
• Without prior hydro-jet cleaning or pipe replacement of suspected partial blockages, the
flushing activity may not achieve the target velocity within the acceptable pressure
ranges. Furthermore, partial blockages will likely make the flushing activities more
difficult to control, causing rapid increases in pressure.
The anticipated conceptual total costs for high-velocity flushing are $858,297, which may be
higher than the costs for hydro-jetting Site A and B. Property restoration accounts for
approximately 60 percent of the conceptual construction costs.
The City may consider a performance-based specification or alternative project delivery
mechanisms (design and build, construction manager at-risk, etc.) that may limit the design and
construction costs associated with the restoration.
8.5.2.3 Pipe Replacement
According to the condition assessment from earlier phases, the Lake Line and lateral near
Kennydale Beach Park had a relatively low RUL between 10 and 30 years. Therefore, rather than
cleaning the Lake Line, the City could replace-in-place the Lake Line to address condition issues
and provide a segment of clean Lake Line.
This alternative is particularly appealing if the City can identify a specific location for the partial
blockage based on future fieldwork. Without knowing the location of the partial blockage, the
City may need to replace longer lengths of the Lake Line, which is anticipated to be challenging
and potentially costly.
Given this uncertainty in scope, no costs were calculated for this option. In general, construction
costs to replace the Lake Line segment in-place are anticipated to be approximately
$1,200 per LF. Replacing longer segments of Lake Line may provide some economies of scale,
especially for soft costs (design, permitting, etc.).
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
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Chapter 9
PHASE 3 LAKE LINE REPLACEMENT
ALTERNATIVES
This section documents Phase 3 of the Lake Line Sewer Evaluation. The following Lake Line
replacement alternatives were investigated to give the City enough information to conduct long-
term planning for the pipeline replacement, including securing easements and financial
resources:
1. Gravity sewer in lake.
2. Gravity sewer on land.
3. Replace-in-place in lake.
4. Replace in new shoreline.
5. Vacuum sewer on land.
6. Grinder pumps on land.
For each alternative, the chapter includes a description, conceptual sizing, and a high-level
budgetary placeholder. All infrastructure alignments are conceptual and should be revised in
future predesign activities.
9.1 Gravity Sewer in Lake
A true gravity Lake Line sewer would slope downward between the upstream and downstream
ends to eliminate sags and be designed to maintain self-cleaning characteristics. Furthermore,
the new Lake Line would follow lake bathymetry to minimize in-lake excavation.
According to lake bathymetry from King County’s iMap, presented in Figure 9.1, lake bed slopes
vary between north and south of Coleman Point. The northern portion of the lake bed has a
shallower slope than the southern portion. Shallower-sloped portions may allow the Lake Line to
be constructed outside of the inner harbor line, avoiding the need for private easements and
minimizing effects on existing boat docks.
A new deep lift station would be constructed to pump the collected sewage to the City’s gravity
sewers east of Lake Washington Boulevard North. Laterals would need to be extended farther
offshore to connect to the new Lake Line. If the flush station were retained, the Lake Line could
be flushed to increase pipe velocities without raising the HGL enough to risk flooding homes.
9.1.1 Alignment
As shown in Figure 9.2 and Figure 9.3, the proposed alignment would be just offshore of the
existing private docks. This location would allow bulk dredging without needing to work beneath
and between docks and place the work in slightly deeper water. Pipelines would run from the
north and south ends to a potential pump station at Kennydale Beach Park.
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
9-2 | JULY 2019 | DRAFT
While the ideal pump station location would be about halfway along the Lake Line to limit depth,
the park is the nearest publicly owned parcel to the halfway point. The proposed alignment is
based on iMap bathymetry; a more detailed survey could push the alignment further offshore.
Figure 9.1 Lake Washington Bathymetry Offshore of the Kennydale Area
9.1.2 Profile
The pipeline would be designed for a minimum of 2 feet of cover. At the north end, this would be
at an elevation of 0.0 feet or at about 18 feet of water depth. The pipeline would run south
toward the pump station site at a minimum grade of 0.004 feet per foot (per Ecology’s
Orange Book for 8-inch gravity sewers) for a distance of about 1,850 feet, ending at the pump
station at an elevation of -9.0 feet.
From the south end, the pipe would start at elevation -5.0 feet to remain outside of the line of
docks. The southern alignment is approximately 3,200 feet to the pump station site, so the wet
well would be about elevation -20 feet. The elevation at the pump station site is approximately
25 feet. Allowing 5 feet of active storage depth, the required pump station would be 50 feet
below the beach park’s ground surface.
Lake bathymetry from
King County iMap.
Coleman Point
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 9-3
Figure 9.2 Southern Conceptual Lake Line Gravity Sewer Alignment Offshore in Lake Washington
Lift
Station
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
9-4 | JULY 2019 | DRAFT
Figure 9.3 Northern Conceptual Lake Line Gravity Sewer Alignment Offshore in Lake Washington
Lift
Station
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 9-5
9.1.3 Lateral Installation
Each of the existing 33 laterals would need to be connected to the new Lake Line at an average
of 250 feet offshore. Laterals would be extended from the main to the existing lateral locations,
assuming a connection and new cleanouts above the lakeshore or bulkheads.
Existing laterals would need to be rehabilitated or replaced to create a consistently new system.
The flush station and the four southern-most homes on land are anticipated to also be
connected in the current configuration.
9.1.4 Operation and Maintenance Considerations
The in-lake gravity sewer would provide operation and maintenance (O&M) benefits and
challenges. For example, it could be self-cleaning given sufficient flow. Unlike the existing
Lake Line, the gravity sewer could be designed to allow flushing flows with less risk of
surcharging that causes SSOs and home backups.
However, due to the distance of the gravity Lake Line offshore (typically 250 feet), the sewer
main would continue to be difficult to access. Additionally, the proposed lift station would
be 50-feet deep, potentially creating difficult infrastructure to access and maintain.
9.1.5 Permitting
City, state, and federal permits would be required to construct and operate a new Lake Line. The
existing Lake Line is under non-conforming land use, and there is no guarantee a new Lake Line
would be allowed under the same land-use rules. Thus, if this option is selected, utility staff are
recommended to meet with City planners early in the pre-design process to better understand
this issue.
Federal rules mandate analyzing “practicable alternatives” to determine the lowest impact on
the aquatic ecosystem. Therefore, practicable on-land alternatives would likely need to be ruled
out to permit this alternative.
9.1.6 Environmental Risk Reduction
The proposed in-lake gravity sewer would not mitigate the environmental risk of having a sewer
main in Lake Washington. With the new gravity main’s improved O&M, the City could better
manage the risk posed by the facility.
9.1.7 Conceptual Planning-Level Budget
Based on the assumptions above, the Project would be similar to the 2011 Mercer Island Sewer
Lake Line Project (Mercer Island Project). An estimate was developed by adjusting the lump sum
quantities from Mercer Island according to the scale of that project and adjusting the pipe
lengths to match the Project. Prices were escalated at 3 percent to 2019 dollars. Some amount of
bulkhead restoration was included in the Mercer Island bid prices, but a specific allowance was
made in this estimate.
A 50 percent scope contingency was applied to address currently unknown differences between
the Mercer Island Project and the Lake Line gravity sewer option. Table 9.1 shows conceptual
planning-level costs.
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
9-6 | JULY 2019 | DRAFT
Table 9.1 Gravity Sewer In-Lake Estimated Budgetary Placeholder Cost
Description Quantity Unit Unit Price Total Cost
Offshore Pipeline, Cleanouts, and Laterals 1 LS $14,425,000 $14,425,000
Bulkhead Replacements 660 LF $1,000 $660,000
Pump Station 1 LS $4,900,000 $4,900,000
Construction Subtotal $19,985,000
Contingency 50% $9,993,000
Construction with Contingency Subtotal $29,978,000
Sales Tax 10% $2,998,000
Construction Contract Amount (including Tax) $32,975,000
Permitting 10% $3,298,000
Design 20% $6,595,000
Construction Management 15% $4,946,000
City PM/Admin 10% $3,298,000
Soft Cost $18,137,000
Total Cost $51,112,000 $51,112,000
9.2 Gravity Sewer on Land
To reduce the environmental risk of facilities in the lake, the Lake Line could be replaced with a
gravity sewer on land. This alternative would construct a deep gravity sewer on the upland
side (east) of the homes, likely in the public right-of-way, where possible.
New laterals would connect the existing cleanouts along the lakeshore to the new gravity sewer.
Due to the lack of space between homes and the depth of the proposed gravity sewer, the new
laterals would be installed using trenchless technologies.
A new deep lift station would be constructed at Kennydale Beach Park to pump the collected
sewage to the City gravity sewers east of Lake Washington Boulevard North.
9.2.1 Alignment
Figure 9.4 shows the alignment of the on-land gravity sewer. The 8-inch gravity sewer could be
aligned mostly along Mountain View Avenue North and the access road west of
Lake Washington Boulevard North. Where no road is present (at 3307, 3401, 3405, 3411, and
3501 Lake Washington Boulevard North), the proposed gravity sewer may be placed east of the
current homes. A County-owned trail (former railway) is approximately 10 feet higher in
elevation in this section and, therefore, was not considered in conceptual planning.
The existing 33 Lake Line laterals would be re-routed east to the new gravity sewer alignment.
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 9-7
Figure 9.4 Conceptual Alignment of On-Land Gravity Sewer
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
9-8 | JULY 2019 | DRAFT
9.2.2 Profile
As shown in Figure 9.5, the conceptual profile of the Lake Line's on-land gravity sewer
replacement was developed using the above alignment. The land elevation for the alignment
was generated in GIS from King County’s 5-foot elevation contours, where elevations range from
approximately 22 feet to 41 feet.
The existing lateral cleanouts would be located near the shoreline at an approximate elevation of
19 feet to 26 feet. The minimum upstream sewer depth of 11 feet was calculated assuming the
following:
• A land elevation of 19 feet.
• Lateral depth of 3 feet.
• Assumed 200 foot lateral with a slope of 2.5 percent.
The gravity sewer depth was calculated assuming the following:
• Start at the minimum upstream depth.
• A shallow (0.5 percent) slope toward the Kennydale Beach Park.
• Lift station at Kennydale Beach Park.
The resulting gravity sewer would be mostly 20 feet to 40 feet in depth, likely requiring extensive
shoring. The lift station would be approximately 25-feet deep, which is less than the in-lake
option.
Figure 9.5 Profile of Conceptual On-land Gravity Sewer
9.2.3 Lateral Installation
At this time, the feasibility of installing laterals is unknown. Given the depth of the sewer, open-
cut installation between homes would be infeasible. Trenchless installation from the upland side
(access road) would require deep and long launch pits that are likely infeasible due to high costs.
-5
0
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0 1000 2000 3000 4000 5000
El
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Distance(ft)
Land Elevation(ft)
Gravity Sewer (ft)
Lift Station at
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PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 9-9
This leaves the option of installing the lateral from the existing cleanout at the shoreline.
However, in some cases, insufficient space exists between the cleanout and lake for trenchless
lateral installation.
Conceptually, flows could be routed along the shoreline to locations where laterals could be
installed without trenches, using fewer than the 33 existing Lake Line laterals. However,
installing new side sewers would likely require deeper cleanouts and expanded launch pit
requirements for trenchless installation. A detailed evaluation is required to determine if this
approach is feasible.
9.2.4 Operation and Maintenance Considerations
The City is well equipped and has experienced staff to operate and maintain the gravity sewer.
The on-land sewer would have the significant benefit of being on-land and, thus, offering easier
access.
The combined low-flow and shallow-slope gravity main might not be self-cleaning, thus will
likely require periodic cleaning. With appropriate safety precautions, the deep sewer could be
accessed and cleaned like the rest of the gravity system.
Additionally, advanced technologies could be deployed to monitor the sewer and better time
maintenance activities. Similarly, the lift station could be maintained similarly to other City
facilities.
9.2.5 Environmental Risk Reduction
The on-land gravity sewer alternative would eliminate the environmental risk of a sewer in the
lake. Additionally, as a gravity sewer, no special requirements would be needed for residents to
avoid clogs and other maintenance concerns that may lead to SSOs.
9.2.6 Conceptual Planning-Level Budget
No estimate could be developed for this alternative since installing laterals may be infeasible. In
general, this option was assumed to have costs similar in order of magnitude to the in-lake
gravity sewer alternative, given the difficulty of installing deep gravity sewers, laterals, and a lift
station.
9.3 Replace-in-Place in Lake
The existing Lake Line could be replaced in-place, likely through a combination of trenchless
methods and open-cut replacement. The new pipe, likely HDPE, would provide the City with
approximately 75 years of useful life and be resistant to corrosion. Lake Line operation would
likely continue in a manner similar to current operations.
This alternative could provide additional access points to allow more periodic cleaning and
maintenance; however, in-lake maintenance activities would continue to require relatively high
effort. Furthermore, this alternative would likely not reduce the potential environmental risk of
having a sewer in the lake, which is a major disadvantage.
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
9-10 | JULY 2019 | DRAFT
9.3.1 Mainline Installation
The replace-in-place option would use a combination of open-cut and trenchless installation.
Table 9.2 shows the length of the mainline and laterals. Due to the difficulty of in-water
excavation, trenchless technologies would be less costly than open-cut replacement where
appropriate. Additionally, trenchless replacement would likely allow construction to avoid some
existing docks and other in-water obstructions.
Table 9.2 Length of Main and Lateral Replace-in-Place Lake Line Sewer Replacement
Description Length (feet) Properties with Restoration Required
Lake Line Replacement 4,800 5 (on-land section)
Laterals 2,900 33
Lift Station NA 1
Various trenchless technologies may be employed:
• Slip-lining.
• Pipe-splitting.
• Cured-in-place pipe (particularly for laterals).
A smaller-diameter pipe (6-inch or 7-inch) could be used to allow slip-lining and reduce
challenges in construction causes by potential ground heaving from pipe-splitting. Excavation
would be required at each lateral tie-in and at locations that exceed the horizontal or vertical
angle limits of the trenchless method.
Pipe-splitting is similar to slip-lining, except the existing pipe is physically split to allow slip-lining
under a greater range of conditions. This technique may reduce the number of excavation
locations required. The choice to pipe-split or slip-line may be driven by the depth of cover and
buoyancy issues, where more depth of cover favors slip-lining.
Open-cut installation in the lake would likely be required where access for trenchless installation
is not practical. Relatively long sections of the Lake Line are likely partially or completely
unconstrained by the surrounding soil. These sections may benefit from being re-buried to
reduce the risk of damage, address increased buoyancy of the HDPE pipe, and reduce the
potential effects of construction. Additionally, minor shifts in alignment, likely using open-cut
installation, may be required to avoid potential obstructions and hazards.
9.3.2 Lateral Installation
Laterals may be replaced using similar approaches as those used to install the Lake Line,
especially in the lake. The transition from land to lake under the bulkheads is variable and
presents a number of construction-related concerns, such as steep slopes of lateral piping.
For this study, the transition was assumed to be open-cut, and the entire property bulkhead
would be replaced. This conservative assumption should be re-evaluated in pre-design, if this
alternative moves forward.
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 9-11
9.3.3 Operation and Maintenance Considerations
New access points could be installed in the replacement Lake Line to help with future
maintenance. As shown in Figure 9.6 and Figure 9.7, this idea was conceptualized as installing
submerged manholes every 400 feet at lateral tie-in locations. Adding a manhole or other access
point would require relatively little additional effort since excavation would already be required
for the pipe replacement. During pre-design, this reduced effort should be weighed against the
potential loss of efficiency in cleaning when not located in a sag.
9.3.4 Permitting
City, state, and federal permits are required to construct and operate a new Lake Line. The
existing Lake Line is a non-conforming land use, and a replacement may not be allowed under
future regulations. Thus, if this option is selected, utility staff is recommended to meet with City
planners early in the pre-design process to better understand this issue.
Federal rules require analyzing “practicable alternatives” to determine a project’s lowest effect
on the aquatic ecosystem. Therefore, practicable on-land alternatives would likely need to be
ruled out to permit this alternative.
9.3.5 Environmental Risk Reduction
The replace-in-place alternative would address the risk of SSOs by increasing access for cleaning
but would not change the environmental risk associated with a having a facility in the lake.
9.3.6 Conceptual Planning-Level Budget
Table 9.3 shows a conceptual planning-level budget for the replace-in-place alternative. The cost
estimate should be considered a budgetary placeholder, which will be updated during
pre-design. Costs for open-cut construction were estimated according to the 2018 construction
activities, during which approximately seven days of in-water work were required to remove,
replace, and restore 40 feet of the Lake Line.
Lake Line pipe-splitting and lateral pipe-splitting costs are included as placeholders; more
detailed designs are required to revise these estimates. Manhole installation and lateral tie costs
were also estimated based on the 2018 activities.
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
9-12 | JULY 2019 | DRAFT
Figure 9.6 Replace-In-Place Lake Line Sewer Infrastructure
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 9-13
Figure 9.7 Location of Potential Access Manholes in Replace-in-Place Alternative
Table 9.3 Replace in Place Estimated Conceptual Planning-Level Budget
Description Quantity Unit Unit Price Total Cost
Open Cut Lake Line 1,000 LF $1,500 $1,500,000
Lake Line Pipe Splitting 3,800 LF $200 $760,000
Lateral Pipe Splitting 2,900 LF $200 $580,000
Manhole Installation 11 Each $130,000 $1,430,000
Lateral Tie In 24 Each $130,000 $3,120,000
Lateral Cleanout Installation 33 Property $2,000 $66,000
Restoration 1 LS $200,000 $200,000
Bulkhead replacement 500 LF $1,000 $500,000
Lift Station/Flush Station Renewal 1 LS $1,500,000 $1,500,000
Construction Subtotal $9,656,000
Contingency 50% $4,828,000
Construction with Contingency Subtotal $14,484,000
Sales Tax 10% $1,448,400
Construction Contract Amount (including Tax) $15,932,400
Permitting/Public Outreach 15% $2,389,860
Design/Bidding 20% $3,186,480
Construction Management 10% $1,593,240
City PM/Admin 10% $1,593,240
Soft Cost $8,762,820
Total Cost $24,695,220
0.00
5.00
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+10+00 20+00 30+00 40+00 50+00
El
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Stationing
Profile Renton Kennydale Lake line New Manhole
Locations
New Manhole
Lakeline
Existing Manhole
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
9-14 | JULY 2019 | DRAFT
9.4 Replace in New Shoreline
Replacing the Lake Line in a new shoreline was an “outside-the-box” alternative conceived as a
potential middle ground between in-lake and on-land alternatives. This alternative would create
a new shoreline beyond the existing bulkheads that would contain the Lake Line and include
habitat features and ecological enhancements.
This alternative was considered fatally flawed and was not developed in detail. Confluence
Environmental, the Project’s permit specialist, believes that a new shoreline would not likely be
permitted, although they couldn't rule it out entirely. Furthermore, several permit conditions
would likely be unacceptable to property owners, including large view-blocking vegetation and
changes to existing dock structures.
9.5 Vacuum Sewer on Land
Vacuum sewers are commonly used to convey sewerage for flat areas, such as around lakes.
These sewers use suction to pull sewage to a central vacuum and lift station, rather than pushing
sewage, which is done with traditional pressure conveyance. Lateral flows collect in valve pits
that regulate the intake of sewage into the vacuum line.
Vacuum valves do not require power and can serve up to four residential customers. However,
they have limited capacity for elevation change, which limits their application in many locations.
Vacuum sewer mains use a “saw-tooth” profile when elevation increases, helping them maintain
relatively shallow mains. This profile would require any laterals between the shoreline and access
roads to be open cut, likely requiring extensive restoration.
9.5.1 Alignment
Vacuum sewer technology is typically limited to 13 feet of elevation gain. Figure 9.8 compares
the land elevation profile along the alignment of the on-land gravity sewer alternative against
the 13-foot elevation gain (assuming laterals at 16-feet elevation).
Due to excessive elevation gain, the vacuum sewer main cannot be placed on
Mountain View Avenue North south of Kennydale Beach Park. Therefore, the vacuum main
would need to run along the shoreline, which would require extensive easements and
restoration. North of Kennydale Beach Park, largely acceptable elevation gain exists. Figure 9.9
shows the resulting alignment.
A combined vacuum and lift station could be constructed at Kennydale Beach Park. Flows would
be conveyed to City gravity sewers on the east side of Lake Washington Boulevard North.
Relatively low, existing Lake Line flow rates may allow a standard vacuum station and lift station
design to be used.
9.5.2 Lateral Installation
Laterals would be installed using a saw-tooth profile to climb the slope between the shoreline
cleanouts and the access road north of Kennydale Beach Park. According to a cursory review,
some lateral slopes might exceed typical design requirements. The City is recommended to
consider these slopes further in pre-design with a manufacturer if this alternative moves
forward. If necessary, laterals might need to be extended to combine multiple homes in
locations where laterals can be constructed.
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 9-15
9.5.3 Operation and Maintenance Considerations
Vacuum sewers require prompt maintenance since the loss of vacuum at one location can cause
failure throughout the entire line. Vacuum valves also require regular maintenance to continue
functioning properly. Although the valves are relatively robust, they can become stuck open by
debris, which may lead to a loss of vacuum pressure.
Most manufacturers provide system monitoring to help identify and respond to these
maintenance issues.
9.5.4 Environmental Risk
Given their system reliability features, vacuum sewers would reduce the environmental risk of
discharges into the lake. Sewer infrastructure will be located on-land, rather than in the Lake.
Furthermore, vacuum sewer valve pits typically include some emergency overflow storage in
case of loss of vacuum or operational issues. In addition, vacuum stations have relatively low
power demands and typically have small back-up generators to maintain sewer service during
power outages.
Figure 9.8 Vacuum Sewer Preferred Elevation Range
10
15
20
25
30
35
40
45
0 1000 2000 3000 4000 5000
El
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Beach Park
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
9-16 | JULY 2019 | DRAFT
Figure 9.9 Vacuum Sewer Alternative Alignment
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 9-17
9.6 Grinder Pumps on Land
In King County, grinder pumps provide sewer service adjacent to many lakes and other low-lying
areas. Grinder pumps would be installed at all 33 lateral locations, each one pumping through a
small HDPE lateral to a mainline HDPE pipe in the street upland of the homes.
When included in new construction, grinder pumps often receive electrical power from the
houses they serve. To avoid the complexities of connecting to private electrical panels especially
if there are multiple instances of shared laterals, the proposed system would include an electrical
distribution system that serves each grinder pump installation and a standby generator for the
entire system.
9.6.1 Alignment
The mainline would be in three sections — north, center, and south — each with a separate
discharge to the upland gravity sewer along Lake Washington Boulevard North, as shown in
Figure 9.10. The north section would consist of two branches meeting at the northern-most
roadway access. Meanwhile, the center section would serve four houses just south of
Kennydale Beach Park. Finally, the south section would consist of a single branch leaving the
lakefront roadway at the north end.
Mainlines would start at 1.5 inches and increase according to the number of homes connected.
The south branch would include pipes up to 3 inches.
9.6.2 Profile
The mainline would be installed at a shallow depth, likely about 4 feet, to be beneath other
utilities. To self-clean, it would operate at high velocities.
Grinder pumps have near-vertical pump curves, allowing high headlosses with a limited effect on
the discharge rate. As such, the mainline profile can follow topography.
9.6.3 Lateral Installation
The profiles of the laterals can largely follow topography. Installation would be done through
directional drilling and include both the lateral and a conduit for the electrical service, which
would limit the excavation's footprint. Connections would be made to the grinder pump basin
discharge and to the mainline.
9.6.4 Easements
New easements would likely be required to install the grinder pumps and the laterals. If
easements cannot be obtained, this alternative may be infeasible.
9.6.5 Operation and Maintenance Considerations
Commercial grinder pump systems typically operate on simple level controls using a float or
other simple device. Some systems have operational monitoring, alarms, and other warnings to
help maintain the system. Typically, grinder pump systems have a number of operational
safeguards, including a small overflow storage volume and dual check valves to limit the risk of
surcharging into houses.
Grinder pumps would need periodic maintenance, such as pump inspection and cleaning, similar
to, but on a smaller scale, than the City’s lift stations. Because of the low cost of pumps, some
utilities simply switch out pumps in the field and conduct all mechanical maintenance at the shop.
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
9-18 | JULY 2019 | DRAFT
Figure 9.10 Grinder Pump Lateral and Force Main Alignment
PHASE 2B AND 3 COMBINED SUMMARY | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | CITY OF RENTON
DRAFT | JULY 2019 | 9-19
Homeowner education on the pumps would be important since the pumps can be clogged by
large materials, non-flushable wipes, etc. However, the grinding action and relatively high
velocity in force mains make grinder systems less susceptible to clogging from FOG and normal
sewage. The mainline could also be fitted with flushing ports at the end of each pipe section to
allow the City to flush the sewer force main for periodic maintenance.
9.6.6 Conceptual Planning-Level Budget
Table 9.4 shows the conceptual planning-level budget for the grinder pump alternative. The cost
estimate is a budgetary placeholder that will be updated during pre-design. Costs for grinder
pumps were estimated using previous system designs.
The sewer force main costs include the purchase of the force main, installation, and road
resurfacing. New laterals from the shoreline cleanouts to sewer force main in the upland access
road were assumed to be installed using trenchless approaches.
The grinder pumps' cost represents the average cost of installing a pre-engineered system. The
grinders are anticipated to be powered by a reliable electrical service independent of the
customers, which is the second largest cost for the grinder pump system.
A budgetary placeholder was included for restoration costs, which are anticipated to be
relatively high to incorporate the grinder pump systems into the lakefront yards.
A 50-percent scope contingency associated with the location and restoration of the grinder
pump system was applied. Permitting costs are anticipated to be 5 percent of the construction
cost, which is substantially lower than that of the in-water alternatives.
Note, no land or easement costs have been included in the cost estimate.
Table 9.4 Grinder Pump Estimated Conceptual Planning-Level Budget
Description Quantity Unit Unit Price Cost
Contractor Mobilization/ Demobilization 1 LS $300,000 $300,000
Sewer Force Main 3,730 LF $171 $638,418
Laterals 4,125 LF $75 $309,375
Grinder Pump Assembly 33 Each $8,000 $264,000
Electrical Service 1 LS $600,000 $600,000
Restoration 1 LS $500,000 $500,000
Construction Subtotal
$2,611,793
Contingency
50% $1,305,897
Construction with Contingency Subtotal
$3,917,690
Sales Tax
10% $391,769
Construction Contract Amount (including Tax)
$4,309,459
Permitting/Public Outreach
5% $195,884.49
Design/Bidding
15% $587,653.47
Construction Management
15% $587,653.47
City PM/Admin
10% $391,768.98
Soft Cost
$1,762,960
Total Cost
$6,072,419
CITY OF RENTON | KENNYDALE LAKE LINE SEWER SYSTEM EVALUATION | PHASE 2B AND 3 COMBINED SUMMARY
9-20 | JULY 2019 | DRAFT
9.7 Alternative Summary and Conclusion
Three Lake Line replacement alternatives were found to be feasible. Thus, conceptual
planning-level costs were developed for each one. Table 9.5 compares the three alternatives.
Table 9.5 Replace in Place Estimated Conceptual Planning-Level Budget
Alternative Environmental Risk
Construction
Challenges
O&M
Considerations
Conceptual
Planning-
Level Cost
Gravity
Sewer in
Lake
Unchanged.
• Discharge into lake
during pipe failure.
• Potential for SSO
at lateral cleanout.
• Requires
construction of deep
pump stations on
shoreline.
• Sewer main in lake.
• Laterals extended
250 feet into lake.
• Gravity sewer
facilitates cleaning.
• Access manholes are
offshore.
~$51 million
Replace-in-
Place in
Lake
Unchanged.
• Discharge into lake
during pipe failure.
• Potential for SSO
at lateral cleanout.
• In lake construction
near shoreline and
under docks.
• Trenchless methods
in lake unproven.
• Exposed pipe
segments may
impact construction
methods.
• Provides additional
access.
• Requires periodic
in-lake cleaning.
• Plastic pipe resistant
to corrosion.
~$25 million
Grinder
Pumps on
Land
Reduced.
• SSO may occur at
grinder pump.
• Stations include
small volume of
overflow storage
• Construction
impacts on
residents.
• Restoration
requirements likely
extensive.
• New easements
required.
• New pumps for City to
operate and maintain.
• Eliminates flush and
lift station.
• Grinder pumps require
regular maintenance.
~$6 million
(No land or
easement
costs
included)
The grinder pump alternative would have substantially lower costs than in-lake alternatives and
would reduce environmental risk. However, it would pose new O&M challenges. New easements
would likely need to be required to install the grinder pumps and laterals; without them, this
alternative may be infeasible. Other on-land alternatives, such as vacuum sewer and gravity
sewer, may not be technically feasible and would likely have greater costs.
While technically feasible, in-lake alternatives are anticipated to have high costs. Additionally,
practicable on-land alternatives would likely need to be ruled out before the in-lake alternatives
can be permitted.
The City is recommended to pre-design the grinder pump alternative to better understand its
costs and requirements. If the grinder pump system appears implementable and at an affordable
cost, the City may consider replacing the Lake Line rather than pursuing the near-term options
presented in Chapter 8.