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    Interactive Tool

    Where Does the I&I Actually Come From?

    Find out how much infiltration and inflow enters through private property and service laterals instead of public mainlines, drawn from numerous published studies, program reports and surveys.

    Private Property Share

    43% to 80%

    Share of total I&I from private property

    Private Lateral Share

    40%

    Median share from private service laterals

    Adding Laterals

    17% to 67%

    Peak flow reduction once laterals are added

    Measured, Not Estimated

    29%

    Utilities that based their split on flow data

    Data Explorer

    Private Property Share of Total I&I

    Share of total infiltration and inflow each utility attributes to private property: laterals, foundation drains, sump pumps, downspouts and area drains together.

    • Field-Tested Pilot
    • Utility Estimate
    • Conceptual Estimate
    • Bound At Least or Up To
    • Range
    • Survey Median
    • Span of All Estimates
    0%25%50%75%100%
    Rehabilitation Outcomes

    Adding Laterals Raised the Reduction in Each Comparison Below

    Each row compares a public-only program with one that also rehabilitated private laterals, in the same study. Most figures are projected design-storm peaks, not measured volumes, and the label says which.

    • Public Only
    • With Laterals
    • Other Scope
    • Public Range
    0%25%50%75%100%

    Program Results

    Reported reductions from programs that included private property work.

    • Rockford, IL

      Over 65%

      Wet weather inflow removed by a public and private program. Post-rehab monitoring only.

    • Johnson County, KS

      41.7% to 71.1%

      I&I reduction, private disconnections plus sewer work

    • Wauwatosa, WI

      75%

      Drop in lateral I&I after lateral lining (laterals only, not total)

    • Duluth, MN

      49%

      5-year peak RDII cut by foundation and roof drain removal

    Key Findings

    What the Evidence Supports

    43% to 80%

    Of total I&I from private property

    Private Property Is Consistently a Large Share

    Every utility estimate in this set falls between 43% and 80% of total I&I. In northern systems much of that comes from foundation drains and sump pumps, not the lateral pipe itself.

    17% to 67%

    Projected peak reduction once laterals are added

    Adding Laterals Raises Projected Reduction

    Projected peak reduction rose from 17% to 67% in WERF's case studies and from 11% to 88% in Sweet Home, Oregon. Partial lateral work, such as wye grouting alone, has shown no benefit.

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