Smoke Testing for Municipal Inflow and Infiltration Programs: EPA Compliance and Field Protocol

Inflow and infiltration represent two of the most expensive and most preventable problems in municipal sanitary sewer systems. Inflow is stormwater that enters the sewer through direct connections such as roof drains, yard drains, downspouts, and foundation drains. Infiltration is groundwater that seeps into the collection system through cracked pipes, deteriorated joints, and failed manhole barrel sections. Together, I&I adds unnecessary hydraulic load that can overwhelm treatment plant capacity, trigger sanitary sewer overflows (SSOs), and result in permit violations with serious regulatory consequences. Smoke testing is the standard, cost-effective field method for locating inflow sources across a collection system, and it is the first step in any defensible I&I reduction program. For municipalities and contractors sourcing the non-toxic cold-burn emitters required for occupied-area sewer smoke testing, Shutter Bombs provides SDS-documented options with the chemical safety profile required for testing in residential and commercial service areas.

Regulatory Context: Why Municipalities Must Address I&I

Municipal collection systems operating under a National Pollutant Discharge Elimination System (NPDES) permit are required under the Clean Water Act to manage their systems in a manner that prevents SSOs. The U.S. Environmental Protection Agency's framework for collection system management, known as the Capacity, Management, Operation and Maintenance (CMOM) program, explicitly addresses I&I as a primary source of wet-weather SSOs. EPA's guidance on sanitary sewer overflows, available at epa.gov/npdes/sanitary-sewer-overflows-ssos, makes clear that permit holders are expected to demonstrate active efforts to identify and eliminate I&I sources as part of their collection system management program.

In consent decrees and administrative orders, EPA commonly requires municipalities to conduct systematic I&I investigations that include smoke testing of identified problem basins, followed by documented repair programs with measurable flow reduction targets. Smoke testing results that are properly documented, mapped, and submitted to the regulating authority provide the evidentiary foundation for demonstrating good-faith compliance with I&I reduction requirements. Municipalities that cannot produce field documentation of their I&I investigation methodology face significant challenges defending their NPDES permit status during regulatory audits.

State regulatory agencies also impose I&I requirements through state revolving fund (SRF) loan programs. Many state environmental agencies require borrowers to complete an I&I analysis and demonstrate cost-effectiveness of removal before approving SRF funding for capacity expansion projects. In these programs, a completed smoke testing survey of the contributing service area is often a prerequisite for project approval, making the documentation of smoke testing results a direct financial concern rather than a compliance formality.

What Smoke Testing Finds in an I&I Investigation

Smoke testing in an I&I context is specifically targeted at inflow sources. Infiltration (groundwater through pipe cracks) is invisible to smoke testing because the flow pathway is from outside the pipe inward, not from the surface downward. Smoke testing excels at identifying direct inflow connections, which are the highest-impact and most cost-effective I&I removal opportunities.

Common inflow sources identified during municipal smoke testing programs include illegal downspout connections to sanitary sewer cleanouts, sump pump discharge connections routed to sanitary rather than storm sewer, cross-connections between sanitary and storm sewer catch basins, deteriorated manhole covers and frames that allow surface water entry during storm events, area drain connections in parking lots and around building foundations, and basement floor drain connections in older structures where the sanitary and storm systems were not separated at original construction. Each of these categories produces smoke emergence at a specific, documentable surface location when the connected sewer segment is pressurized.

A well-executed smoke test identifies not only the location but the likely ownership of the inflow source. Smoke emerging at a specific downspout, foundation drain, or area drain connection can be attributed to a specific parcel and the property owner can be notified of the illegal connection and required to remove it. This parcel-level identification is the basis for I&I source removal programs and is what distinguishes smoke testing from other I&I investigation methods that can only measure total flow rather than locate specific sources.

Pre-Test Planning and Notification Protocol

Municipal I&I smoke testing requires more extensive advance planning than contractor-initiated HVAC or plumbing diagnostics because it involves testing across entire collection system basins, often affecting hundreds of properties simultaneously.

Basin Selection and System Review

The first step is identifying which collection system basins show hydraulic signatures consistent with high I&I loading. Flow monitoring data from wet-weather events is the primary tool for basin prioritization. Basins where measured wet-weather flow exceeds 1.5 times dry-weather baseflow by volume (a commonly used threshold, though specific criteria vary by permit) are candidates for smoke testing investigation. Smoke testing the entire system simultaneously is neither practical nor cost-effective; basin prioritization ensures that field resources are concentrated where documented I&I loading is highest.

Review available system maps before scheduling smoke tests. Identify the upstream and downstream limits of the basin to be tested, all manhole locations within the test zone, and any known private sewer laterals, building connections, or utility conflicts. Systems with aging infrastructure or incomplete documentation may have unmapped connections that complicate test execution; allocating additional time for fieldwork in poorly documented service areas reduces the risk of incomplete coverage.

Public Notification Requirements

Public notification before a municipal smoke testing program is not optional. Smoke entering homes and businesses through plumbing fixtures is a foreseeable and common consequence of sanitary sewer smoke testing. Without advance notice, occupants who see smoke inside a building will call 911, which halts the testing program, generates public relations problems, and diverts emergency resources unnecessarily. Proper notification eliminates the false alarm risk and converts potential complaints into community cooperation.

Standard notification elements for a municipal I&I smoke testing program include: door hangers distributed to all properties within the test zone at least 48 hours before testing begins; press release or local media notification in communities where news coverage is standard practice; coordination with the local fire department and police dispatch so that any 911 calls about smoke inside buildings can be immediately routed to the testing crew; and a field crew phone number available to the public through all notification channels so property occupants can reach someone who can confirm whether a smoke test is in progress at their address.

Properties with known wet plumbing traps (floor drains, basement toilets, utility sinks that are used infrequently) are at the highest risk of smoke entry through dried trap seals. Notification materials should advise property owners to run water in all floor drains and basement fixtures before the scheduled test date to restore trap seals. Many municipalities include this instruction in notification language to reduce interior smoke incidents and build positive public response to the program.

Fire Department Coordination

Coordinate with the fire department shift commander for every test day to confirm that responding units understand what smoke testing is, why smoke may appear in structures, and that the non-toxic cold-burn emitters being used do not create fire or inhalation risk. Provide the fire department with a written description of the smoke devices being used, including the SDS. Some municipalities provide a laminated one-page test summary to each station in the affected service area. This coordination ensures that if a 911 response does occur despite notification, responding units arrive with accurate information rather than treating the event as an active structure fire.

Equipment and Emitter Specification for Municipal I&I Testing

Municipal sewer smoke testing uses a high-CFM blower unit to pressurize the sewer mainline segment under test through a manhole opening. Smoke is introduced into the pressurized segment, either through the blower intake or through a separate introduction point, and the positive pressure within the sewer forces smoke upward through any connection between the sewer and the surface. The key equipment components are the sewer blower, the smoke emitters, and the field documentation kit.

Sewer blowers for mainline pressurization are typically rated at 2,500 to 4,000 CFM for standard 8-inch to 12-inch sewer mains. Larger diameter mains require higher-CFM units or multiple blowers positioned at the same manhole. The blower is sealed at the manhole opening using a neoprene inflatable plug or a fabricated cover plate matched to the manhole frame diameter. The smoke is introduced upstream of the blower intake so that the entire air volume entering the sewer carries smoke at a consistent concentration.

Smoke emitter selection for municipal I&I testing is governed by the same chemical safety criteria as building diagnostic applications: the emitter must be non-toxic, cold-burn, and documented by an SDS confirming the absence of hexachloroethane, sulfur compounds, and heavy metal colorants. Unlike building applications where a single emitter serves a small enclosed volume, municipal sewer testing requires multiple emitters per test segment because the sewer network volume is substantially larger than any building cavity. A standard 8-inch mainline test segment of 500 feet between manholes requires sustained smoke introduction throughout the test period to maintain signal quality at remote lateral connections. Shutter Bombs bulk procurement options are available for municipalities and contractors running extended testing programs across multiple basins and test days. Sourcing smoke emitters in multi-pack quantities reduces per-unit cost and ensures consistent device chemistry across an entire survey, which is important when submitting SDS documentation to regulatory agencies.

Field documentation equipment should include GPS-enabled tablets or smartphones loaded with the GIS sewer map layer, flagging materials and temporary marking paint for surface location marking, and a photography protocol that captures each smoke emergence point with enough context to identify the location on a map. Many municipalities use third-party I&I investigation platforms that integrate GPS location with photo documentation and generate a formatted report suitable for regulatory submission.

Field Execution: Segment-by-Segment Testing Protocol

Municipal I&I smoke testing is organized around sewer segments, with each segment defined by two adjacent manholes. The testing crew works systematically through the test basin, completing each segment before advancing to the next, to ensure complete coverage without gaps or duplicate testing.

1. Segment setup: Position the blower unit over the downstream manhole of the segment. Seal the manhole frame. Close the downstream manhole plug or use a pipe plug to isolate the test segment from the downstream network. This isolation ensures that smoke pressure builds within the target segment rather than dissipating through the downstream collection system.
2. Smoke introduction and pressurization: Start the blower unit and introduce the first smoke emitter at the blower intake. Allow 30 to 60 seconds for pressure to build within the segment. The upstream manhole (segment terminus) should begin showing smoke emergence within the first minute of operation if the segment is isolated correctly.
3. Surface observation: Field observers spread out across the surface area served by the test segment. The coverage zone for a standard residential street segment includes all properties with private laterals connected to the segment, the street surface above the main, and any adjacent storm sewer inlets or catch basins that may have cross-connections. Observers watch for smoke emergence at ground-level openings, building foundation vents, window wells, downspout cleanouts, and area drains.
4. Documentation: Each smoke emergence point is photographed, GPS-marked, and logged by address or parcel ID. Note the specific opening type (downspout, area drain, cleanout, etc.) for each emergence point, as this information determines the likely repair method and responsible party.
5. No-smoke confirmation: Segments where no smoke emergence is observed at any surface location after five to seven minutes of sustained pressurization are documented as confirmed no-defect segments. This documentation is as important as finding defects: the regulatory record of a complete I&I investigation requires evidence that the entire basin was tested, not just the segments where problems were found.
6. Advance to next segment: Remove pipe plugs, advance the blower to the next manhole, and repeat. A typical field crew of three technicians can complete six to eight segments per day in a standard residential service area with good prior notification and accessible manholes.

Post-Survey Reporting and Regulatory Submission

The deliverable from a municipal I&I smoke testing survey is a formal investigation report suitable for submission to the state environmental agency or EPA regional office as evidence of CMOM compliance. Standard report elements include a survey area map with all test segments numbered and color-coded by result (tested and clear, inflow source identified, access problem that prevented testing), a tabular summary of all inflow sources identified by address or parcel ID and opening type, photographs of each identified source keyed to the segment map, a summary of emitter SDS documentation confirming the smoke materials used comply with non-toxic certification requirements, and a recommended follow-up action for each identified source (property owner notification, lateral inspection, storm-sanitary separation).

Municipalities with active consent decrees or administrative orders typically submit I&I investigation reports on a schedule specified in the agreement. The report establishes the baseline condition of the basin and sets the starting point against which subsequent flow monitoring data is compared to demonstrate I&I reduction. Inaccurate or incomplete field documentation undermines the evidentiary value of the survey and may require repeat testing at additional cost.

For contractors bidding municipal I&I smoke testing contracts, the ability to produce a complete regulatory-quality deliverable is as important as the field execution capability. Municipalities that have experienced inadequate deliverables from prior contractors increasingly specify report format requirements and field documentation standards in the bid documents. Contractors who can demonstrate experience producing EPA-compliant I&I investigation reports have a significant competitive advantage in municipal procurement.

For background on smoke testing method selection and the scenarios where pressure testing complements smoke testing in a comprehensive I&I program, the smoke testing vs. pressure testing comparison guide provides the decision framework. For detailed field protocol for contractor-initiated sewer smoke testing, the sewer smoke testing contractor guide covers the complete setup and execution workflow. Additional context on inspection efficiency and how smoke diagnostics reduce total investigation time across complex collection systems is available in the smoke diagnostics inspection efficiency guide.