A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
A Gravity Situation –
Eastside Trunk Sewer
Rohnert Park, CA
Art da Rosa, PE | Civil Engineer | City of Rohnert Park
Matt Winkelman, PE | Civil Engineer | GHD Inc.
Jim Winter, PE | Construction Manager | GHD Inc.
Dru Nielson, CEG | Geologist | McMillen Jacobs Associates
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Presentation agenda
• Background
• Planning and Design
• Construction
• Conclusions and What’s Next
Background
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Rohnert Park
• Located in Sonoma County
• Population ~ 45,000
• Incorporated in 1962
City of Rohnert Park, California
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Rohnert Park collection system - overview
• 80 miles of 6- to 42-inch gravity sewer
• 16 inverted siphons
• 1 collection system lift station
• All flow conveyed to Main Pump Station, which pumps flow to the
regional WWTP
• ADWF: 3.3 mgd
• PWWF: 14 mgd
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Rohnert Park collection system goals
• Minimize the use of pump stations
• Reduce life cycle costs associated with I/I
• Improve collection system reliability
• Build critical infrastructure with a longer useful life compared to local
collector sewers
• Minimize impacts to the public
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
System evaluation: 2003 - 2005
• Flow monitoring and field reconnaissance
• Hydraulic modeling and assessment
• Hydraulic deficiencies identified
• Opportunity identified to alleviate deficiencies by constructing a new,
gravity trunk sewer
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
System evaluation: the result
• Construct a 3.5 mile trunk sewer to relieve capacity deficiencies in
the eastern portion of the collection system
• Convey up to 12.7 mgd to the Main Pump Station
• Project split into three phases
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Rohnert Park trunk sewers
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Eastside trunk sewer (2008-2015)
Planning and Design
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Geotechnical Setting
Berkeley
Rohnert Park
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Geotechnical Setting
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Geotechnical Setting
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Geotechnical Setting
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Geotechnical Setting
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
A Gravity Situation
• What is the challenge?
• Is construction feasible?
• Does the project make financial sense?
• What are the project/municipality objectives?
• Comprehensive planning, then design
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Gravity trunk sewers
• Utility conflicts
• Highway, railroad, and waterway crossings
• Flat and/or hilly terrain – deep trenching
• High groundwater and poor soils
• Community impacts
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
An alternative – pumped system
• Shallower trenching
• Fewer potential utility conflicts
However…
• Pump station capital and O&M costs
• Local collection system needs
• Community impacts
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Gravity or pumped system?
• Useful life of construction materials
• O&M costs
• System reliability
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
LOW I/I / Corrosion / Community Impacts HIGH
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
LOW I/I / Corrosion / Community Impacts HIGH
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
LOW I/I / Corrosion / Community Impacts HIGH
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Corrosive atmosphere in manhole
Unlined manhole Fiberglass base liner
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Lined or unlined manholes?
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Lined or unlined manholes?
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Lined or unlined manholes?
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Lined or unlined manholes?
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Lined or unlined manholes?
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Construction materials
• Integrated manhole systems
• Pipeline materials
• Trench materials
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Integrated manhole systems
• Water-tight design
• Improved quality control with factory fabrication
• Increased construction efficiency
• Reduced manhole diameter
Construction
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Integrated manhole systems
Phase 1 (2007) Manhole Base
• Precast with HDPE liner, polymer concrete coating, and “boot”
connection
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Phases 2 and 3 (2013) Manhole Base
• Precast with fiberglass insert and gasketed connection
Integrated manhole systems
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Integrated manhole systems
Phases 2 and 3 (2013) Manhole Base
• Gasketed pipe connections
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Integrated manhole systems
Wall Liner
• Phases 1 and 2 – GSE StudLiner
• Phase 3 – Agru Sure-Grip Liner
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Integrated manhole systems
Wall Liner
• Welded liner joints, including HDPE to fiberglass
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Integrated manhole systems
Manhole Chimney
• Phases 1 and 2 – HDPE, wrap
• Phase 3 – fiberglass collar
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Integrated manhole systems
Inside Lateral Drop Connections
• Welded joints
• Boot connection
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Pipeline materials
• Phase 1 – HDPE-lined Concrete, double gasket
• Phases 2 and 3 – AWWA C905 PVC
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Trench materials
• Controlled Low Strength Material (CLSM)
• Crushed rock bedding (3/4”)
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Construction techniques
• Positive utility verification (potholing)
• Dewatering, shoring, soil stabilization
• Controlled low strength material (CLSM)
• CCTV inspection – allowable “bellies”
• Manholes testing
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Positive utility verification
• Complete enough potholes to
identify alignment challenges
ahead of construction
• Coordinate with utility
companies
• Allow time for utility relocation
or modification
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Dewatering, shoring, soil stabilization
• Dewatering wells at 50 to 100 foot spacing
• Shoring with soil stabilization
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Manhole testing
• Manhole liner spark testing
• Manhole pressure testing
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Pipe testing
• Joint Testing: vacuum, air testing
• Video: bellies
Conclusions and What’s Next
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
Conclusions
• Determine if system rehabilitation or conveyance is appropriate
• Evaluate life cycle costs for alternatives
• Evaluate available materials and techniques during project planning
• Learning curve for contractors
• I/I rehabilitation program could take 10 to 20 years to show tangible
benefits
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
What’s next?
• Planning and assessment
• I/I rehabilitation
• Construction materials:
– Integrated manhole systems
– Pipelines: HDPE, plastic, fiberglass
– Trenches: CLSM
• Construction techniques
• Laterals
A Gravity Situation – Eastside Trunk Sewer, Rohnert Park, CA
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