Smoke Testing Reveals Storm Connections in a Sanitary Basin
A utility is under a consent-order deadline to reduce infiltration/inflow (I/I) in a 1950s-era sanitary basin of about 60 miles of pipe. The utility runs smoke testing on a 12-block area. Results: 14 suspected roof-drain or foundation-drain connections, 6 suspected storm-drain cross-connections, and 3 smoke reports inside homes (one at a floor drain, two at sump pumps). Flow monitoring before testing showed dry-weather flow of 1.8 mgd and wet-weather peaks of 6.5 mgd in the basin. The utility has a limited rehabilitation budget and a mandate to show measurable I/I reduction within 18 months. The engineering consultant recommends lining all 60 miles. The operations superintendent disagrees.
1. How should the superintendent frame the decision about where to spend the limited rehabilitation budget, and what data supports that framing?
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The superintendent should frame the decision around cost-effective removal of inflow versus infiltration, using the flow data and smoke results rather than a blanket lining program. The gap between 1.8 mgd dry and 6.5 mgd wet (a 4.7 mgd swing) shows the basin is dominated by rainfall-dependent inflow, not steady groundwater infiltration. Smoke testing identified discrete, addressable sources - roof/foundation drains and storm cross-connections - which are typically the highest-yield, lowest-cost fixes. Lining all 60 miles is a capital-intensive approach that addresses infiltration but may not target the dominant inflow sources and cannot be completed within 18 months. The superintendent's argument is that the program should prioritize source removal (private-property connections, cross-connections) and targeted lining of the worst pipe segments identified by flow monitoring and CCTV, so measurable reduction is achievable within the deadline.
2. What must the utility do about the three smoke reports inside homes, and how does that affect the program?
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Smoke entering homes indicates a direct pathway between the sewer and the building interior - a serious public-health and safety issue that must be addressed promptly, not deferred to the capital plan. The utility should verify each report, notify the property owner in writing, and require correction of the defect (e.g., dry floor drain traps, defective sump connections, or broken building sewer). These findings also carry a safety message: smoke in a home means sewer gas can enter, and the utility should advise occupants. Programmatically, the in-home findings are evidence that private-property sources are significant and may require a private-side inspection/repair program with clear authority and funding. The judgment point is that the utility cannot treat private-side defects as outside its problem when they are contributing to the I/I the consent order targets.
3. How should the superintendent measure and report progress to satisfy the 18-month mandate?
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Progress should be measured with the same flow monitoring that established the baseline: re-monitor dry-weather and wet-weather flow at comparable points and compare rainfall-normalized peaks, not just raw numbers from different storms. The utility should track a small set of indicators - number of inflow sources removed, linear feet of pipe rehabilitated, and measured flow reduction per dollar spent - and report them against the consent-order milestones. Reporting should distinguish inflow removal from infiltration reduction so the regulator can see which measures are working. The superintendent should also document the decision rationale for prioritizing source removal over blanket lining, because if the regulator expects a certain level of lining, the utility needs a defensible explanation tied to the flow data. The key judgment is that "measurable reduction" requires a before/after monitoring plan designed up front, not an after-the-fact claim.