Porirua Wastewater Master Plan Whaitua Committee discussion · 12/1/2016 · • To provide an...
Transcript of Porirua Wastewater Master Plan Whaitua Committee discussion · 12/1/2016 · • To provide an...
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Porirua Wastewater Master Plan –Whaitua Committee discussion
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Purpose
• To provide an update on the Stage 2 Master Plan work
• To seek input on potential improvement options and solution development
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Structure
1. Water quality issues from wastewater2. High Level Master Plan3. Inflow and Infiltration issues4. Growth5. Stage 2 Master Plan findings to date6. Improvement options7. Solution design – levels of service8. Next steps
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Wastewater effects on water quality
• Dry weather pollution Illegal cross connections Cracked or leaking pipes
• Wet weather overflows System designed for 4 x ADWF Inflow and infiltration can exceed capacity Porirua system has limited spare capacity
• Differences in receiving environments Streams / Harbour / Coastal
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Water Quality Monitoring
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Master Plan
• Guidance for wastewater asset development• Objectives• Challenges: Growth Inflow / Infiltration Capacity
• Council LTP• Level of Service
Safeguard public health
Protect environment
Reliable network
Provide reliable customer and regulatory needs
sustainable delivery of wastewater collection
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Porirua Wastewater Network
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Initial High Level Master Plan
• Three flow monitors• High level model developed• Key Inflow + Infiltration areas identified• Initial conceptual options developed• Further modelling + calibration recommended: Stage 2 Master Plan 2015‐17
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Inflow and Infiltration – High Level
• Significant I/I in: Cannons Creek Duck Creek Linden
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Inflow and Infiltration causes
• Direct inflow of stormwater Illegal down pipe connections Stormwater overflowing into gully traps
• Infiltration of groundwater Cracked pipes and ineffective joints Manhole sealing and old connections
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Growth planning projections
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12
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Stage 2 monitoring
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Inflow and Infiltration ‐ Stage 2
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Flow Monitoring ‐ day
Rainfall
Flow level
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Flow Monitoring ‐ year
Rainfall
Flow level
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Model Calibration
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CBD Overflow Chamber
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Current performance – high level
10/yr
4/yr
4/yr
4/yr
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Current performance ‐ detailed
Orange pipes ‐ approaching capacity during heavy rain eventsRed pipes – too small during heavy rain events
Predicted overflows small to large (blue > green > purple > red dots)Dark blue dots ‐ confirmed overflows
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• Conveyance• Storage• Screening• Treatment• Source reduction
– I&I reduction– Laterals renewal– Greywater re‐use
• New technologies– Pressure sewers?
Potential Options
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• Discharge factors– Overflow frequency – Overflow volume
• Impacts:– Environmental– Cultural– Public Health– Amenity– Economic
Solution framework – future Level of Service
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Solution framework considerations‐ Future Level of Service
• How do wastewater discharges fit within community priorities?
• Do we sufficiently understand impacts?
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Next steps
• Model outputs input to Whaitua CMP• Level of service to be developed• LTP cost estimates required• Consenting decisions• Stakeholder input• Treatment plant development