Verifying Wet Weather CSOSSO Capacity Assurance

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Verifying Wet Weather CSO/SSO Capacity Assurance

• Andy Lukas, BC
• Milwaukee, WI

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Presentation Overview

• Capacity Assurance Programs for Combined Systems
• Capacity Assurance Programs in Concept
• Major Goals of CAPs
• Approach for Using Monitoring and Modeling to
  Validate CAPs
• Example Analyses Using Monitoring/Modeling
  Approach
• Conclusions

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Capacity Assurance for Combined Systems

• Preservation of status wrt Nine Minimum Controls
• Performance relative to LTCP control objectives
• Requires tracking of capacity allocations
• Connections
• Satellite flows
• Regardless of whether in sanitary or combined
  sewer area
• Requires post-event analysis and annual summary
• Putting actual events in perspective
• capture calculation or activation frequency
• Are you relying on Green Infrastructure? How is
  it Doing?

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MMSD System Performance
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MMSD System Performance
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Capacity Assurance for Separate Systems

• The Wet Weather Plan was written to achieve
• No SSOs in 5-yr, 24-hr storm, or
• SSO frequency of no more than 1 per 5 years, or
• ???
• How do you know it was achieved?
• How do you know you are protecting it?
• Are you relying on I/I reduction?

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Capacity Assurance Programs in Concept for
Sanitary Systems

• Maintain Capacity-Related Level of Service
• Equivalent Terms
• Capacity Assurance Programs
• Concurrency Management Programs
• I/I Mitigation Banks
• Capacity Credits
• Sewer Futures?

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Regulatory Drivers for Capacity Assurance Program

• NPDES or Collection System Permits
• Risk of enforcement action for SSOsthat are
  preventable throughI/I reduction or increased
  capacity
• EPA Administrative Order

Consequences of overflows explicit in the DENR
(NC) permit
DENR may void local sewer permitting program,
issue NOV, penalties and/or moratorium if
capacity-related SSOs continue.
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Responsive Rehabilitation and Capital Projects
Program Make it Better Policy
Options if no available capacity

• No new connections
• Enhance capacity so that available capacity is
  new connection request
• Rehab to offset flow from new request by a factor
  of X
• Developer funded rehab or capital projects

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Typical CAP Goals

• Formal, fully developed, and documented business
  process
• Approval system for new connections
• Approval to ensure that the proposed flow does
  not negatively impact the collection system
• Meet regulatory requirements 
• Establish service connection application,
  evaluation, and approval processes.
• Provide program documentation to regulatory
  agency

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Example Administrative OrderRequired CAP
Components

• Determine adequate collection, transmission and
  treatment capacity
• Evaluate impacts of projected flows
• Protocols for implementation of the CAP
• Certification of adequate capacity by a
  registered PE
• Integrate applications for new services or
  increased flows from existing connections with
  CAP
• Information management system to monitor and
  track adequate capacity

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Primary Program Components
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Primary Program Components
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Adequate Capacity is Needed for New Connections
Peak Flow (demand)
SystemCapacity

Wastewater flow Inflow Infiltration
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Primary Program Components
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Tracking Net Changes Over Time
Capacity from Capacity Enhancement Projects
Flow Commitments for Approved Connections
Starting Available Capacity
Available Capacity

-

• Track flow commitments and certifications
• Capacity Accounting
• Capacity Certification
• Capacity from capacity enhancement projects
  updated on a project by project basis
• True-up available capacity periodically with
  monitoring and modeling

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Approach for Using Monitoring and Modeling to
Validate CAPs

• When flow reductions are depended upon to
  recover system capacity
• Assumptions concerning capacity credits can
  mislead
• Sufficient monitoring and appropriate modeling
  can validate the status of credits
• Example from Milwaukee (MMSD)

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Approach for Using Monitoring and Modeling to
Validate CAPs

• Community Requests Additional Capacity in Basin
  Where Allocation Has Been Met
• Community Has Proof of I/I Reduction Activities
• Community or MMSD Has Collected Sufficient Flow
  and Rainfall Data
• Analysis to Confirm Current Flow Conditions
  Warrant Approval

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Approach for Using Monitoring and Modeling to
Validate CAPs
Collect Flow and Rainfall Data for 1 Year
Review Records Concerning I/I Reduction Efforts
Within Basin
Establish Existing Sewer Basin Land Use Data
Calibrate Sewer Flow Model to Current Conditions
- Dry Weather
Determine Current 5-year Peak Day Flow
Compare to Facilities Plan Capacity Allocation
Calibrate Sewer Flow Model to Current Conditions
- Wet Weather
Perform Sewer Flow Model Long-Term Simulations
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Statistical Comparison of Hourly Peak Flows
I/I Flows
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Summary of Long Term Simulation Statistical
Analysis After Rehabilitation

• Rehab created
• 1.07 mgd of peak day flow
• 1.21 mgd of peak hour flow

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Conclusions

• CAPs Are An Important Component of CMOM and Wet
  Weather Compliance Programs
• Tools/Approaches Are Available To Go From
  Accounting Exercises to Verified Programs
• Start Collecting Data Early to Position for
  Appropriate Analysis When You Need It