a gravity situation eastside trunk sewer · 5/5/2017 · regional wwtp • adwf: 3.3 mgd • pwwf:...

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

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiXy7Oe_vXKAhVLzGMKHRIGA0gQjRwIBw&url=http://www.rohnertparkchamber.org/city-of-rohnert-park.html&psig=AFQjCNGs6QGfW-r33g-HCMl-E7_9cWkgtQ&ust=1455495712279579


Presentation agenda

• Background

• Planning and Design

• Construction

• Conclusions and What’s Next

Background


Rohnert Park

• Located in Sonoma County

• Population ~ 45,000

• Incorporated in 1962

City of Rohnert Park, California


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


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


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


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


Rohnert Park trunk sewers


Eastside trunk sewer (2008-2015)

Planning and Design


Geotechnical Setting

Berkeley

Rohnert Park


Geotechnical Setting


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


Gravity trunk sewers

• Utility conflicts

• Highway, railroad, and waterway crossings

• Flat and/or hilly terrain – deep trenching

• High groundwater and poor soils

• Community impacts


An alternative – pumped system

• Shallower trenching

• Fewer potential utility conflicts

However…

• Pump station capital and O&M costs

• Local collection system needs

• Community impacts


Gravity or pumped system?

• Useful life of construction materials

• O&M costs

• System reliability


LOW I/I / Corrosion / Community Impacts HIGH


Corrosive atmosphere in manhole

Unlined manhole Fiberglass base liner


Lined or unlined manholes?


Construction materials

• Integrated manhole systems

• Pipeline materials

• Trench materials


Integrated manhole systems

• Water-tight design

• Improved quality control with factory fabrication

• Increased construction efficiency

• Reduced manhole diameter

Construction



Phase 1 (2007) Manhole Base

• Precast with HDPE liner, polymer concrete coating, and “boot”

connection


Phases 2 and 3 (2013) Manhole Base

• Precast with fiberglass insert and gasketed connection




Phases 2 and 3 (2013) Manhole Base

• Gasketed pipe connections



Wall Liner

• Phases 1 and 2 – GSE StudLiner

• Phase 3 – Agru Sure-Grip Liner



Wall Liner

• Welded liner joints, including HDPE to fiberglass



Manhole Chimney

• Phases 1 and 2 – HDPE, wrap

• Phase 3 – fiberglass collar



Inside Lateral Drop Connections

• Welded joints

• Boot connection


Pipeline materials

• Phase 1 – HDPE-lined Concrete, double gasket

• Phases 2 and 3 – AWWA C905 PVC


Trench materials

• Controlled Low Strength Material (CLSM)

• Crushed rock bedding (3/4”)


Construction techniques

• Positive utility verification (potholing)

• Dewatering, shoring, soil stabilization

• Controlled low strength material (CLSM)

• CCTV inspection – allowable “bellies”

• Manholes testing


Positive utility verification

• Complete enough potholes to

identify alignment challenges

ahead of construction

• Coordinate with utility

companies

• Allow time for utility relocation

or modification


Dewatering, shoring, soil stabilization

• Dewatering wells at 50 to 100 foot spacing

• Shoring with soil stabilization


Manhole testing

• Manhole liner spark testing

• Manhole pressure testing


Pipe testing

• Joint Testing: vacuum, air testing

• Video: bellies

Conclusions and What’s Next


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


What’s next?

• Planning and assessment

• I/I rehabilitation

• Construction materials:

– Integrated manhole systems

– Pipelines: HDPE, plastic, fiberglass

– Trenches: CLSM

• Construction techniques

• Laterals


www.ghd.com

a gravity situation eastside trunk sewer · 5/5/2017 · regional wwtp • adwf: 3.3 mgd • pwwf:...

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