When You Should Consider Smoke Testing Your Collection System
Identifying leaks and defects in a sanitary sewer or stormwater collection system requires more than routine inspections. Undetected leaks can lead to inflow and infiltration (I&I) issues, structural failures, environmental contamination, and costly regulatory penalties. Traditional diagnostic methods like CCTV inspections or dye testing have limitations in pinpointing hidden defects, particularly in private laterals or unsealed connections. Smoke testing is one of the most efficient and cost-effective ways to detect leaks, cross-connections, and illicit discharges in a collection system.
But when is the right time to conduct smoke testing? Understanding the conditions that warrant this approach can help municipalities, utilities, and facility managers proactively address vulnerabilities before they escalate into larger problems.
What is smoke testing?
Smoke testing is a diagnostic procedure used to identify unauthorized connections, structural defects, and sources of inflow in a sewer or stormwater system. During testing, a nontoxic, artificially generated smoke is introduced into the system through maintenance holes or cleanouts using a high-powered blower. The smoke follows the path of least resistance, escaping through cracks, open connections, uncapped cleanouts, and defective seals.
Technicians monitor the test area and document points where the smoke emerges — whether from the ground, building foundations, roof leaders, or storm drains. These findings provide a detailed map of leaks and unauthorized connections that would otherwise be difficult to detect through visual inspection alone.
When should you consider smoke testing?
Smoke testing is not a one-size-fits-all diagnostic tool. It is most effective when used strategically to address specific concerns within a collection system. Below are key situations where smoke testing is the best approach.
Persistent I&I issues
Smoke testing is especially helpful in diagnosing inflow and infiltration problems. Inflow refers to the direct entry of stormwater into the sewer system through defects such as roof drains, uncapped laterals, and improperly connected catch basins. Infiltration occurs when groundwater enters the system through cracks, pipe joints, and deteriorated manholes.
Municipalities experiencing frequent wet-weather surcharging, sewer overflows, or unexplained increases in flow at treatment plants should consider smoke testing to identify the root cause of excessive I&I. By locating inflow sources and leaks, utilities can prioritize repairs and reduce the hydraulic burden on wastewater treatment facilities.
Unexplained sewer odors or gas intrusion
Sanitary sewer systems should be airtight, preventing the escape of sewer gases into streets or buildings. If residents or businesses report persistent sewer odors, it could indicate leaking pipe joints, damaged vent stacks, or untrapped lateral connections.
Because smoke behaves similarly to sewer gases, it provides a reliable way to detect faulty plumbing connections, defective vent stacks, and dry traps. When smoke is observed inside buildings during testing, it confirms the presence of leaks that could allow methane, hydrogen sulfide, and other dangerous gases to enter occupied spaces.
Cross-connection investigations
Unintentional cross-connections between stormwater and sanitary sewer systems can cause significant problems, including regulatory violations, capacity overloads, and untreated wastewater discharges. During heavy rainfall, improperly connected storm drains and roof leaders can introduce large volumes of water into the sanitary system, contributing to overflows.
Smoke testing helps pinpoint where these unauthorized connections exist by forcing smoke into one system and monitoring whether it appears in unintended locations. This method is particularly useful for detecting illegal stormwater connections in commercial or industrial properties where improper plumbing modifications may have occurred.
Pre- and post-rehabilitation assessments
Before undertaking major sewer rehabilitation projects, municipalities should conduct smoke testing to establish a baseline condition of the system. Identifying and addressing leaks beforehand can prevent costly rework and ensure that new linings, joint seals, or replacement pipes are properly integrated with existing infrastructure.
Similarly, post-rehabilitation smoke testing confirms the effectiveness of repairs. If smoke appears in areas that were recently lined or replaced, it may indicate failed gaskets, defective liners, or construction errors that require correction.
Regulatory compliance
Under the EPA’s Capacity, Management, Operation, and Maintenance (CMOM) framework, utilities are required to demonstrate that they are actively managing their collection systems to minimize overflows and maintain compliance with National Pollutant Discharge Elimination System (NPDES) permits.
Smoke testing is frequently used as part of proactive I&I reduction programs required by regulatory agencies. Utilities that conduct regular smoke testing and document findings can provide evidence of due diligence in infrastructure management, helping to avoid costly enforcement actions.
A strategic tool for collection system maintenance
Smoke testing is one of the most effective diagnostic tools for identifying leaks, cross-connections, and inflow sources in sanitary and stormwater collection systems. However, its success depends on proper timing, execution, and interpretation of results.
