The purpose of smoke testing is to find potential points of inflow and infiltration in the wastewater system. Smoke testing can also help locate the following points of groundwater or surface water intrusion into the wastewater system, any cross connections between sanitary wastewater systems and storm drains, and defective sewer connections that could allow sewer gases into a building.
During smoke testing, field crews blow air and smoke into the wastewater system in the street and monitor where smoke escapes the system. The smoke under pressure will fill the main line as well as any connections and then follow the path of any leak to the ground surface, quickly revealing the source of the problem. For instance, if smoke permeates up through a yard, it indicates breaks in the sewer line. Only enough force to overcome atmospheric pressure is required, and smoke should escape from building roof vents.