Dye water flooding consists of forcing nontoxic, brightly colored dye into manholes to assist in locating defects. Photos: R.A. Smith National
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    A sewer performance map prepared for the New Berlin Water & Wastewater Division identifies areas of low, moderate, and high infiltration and inflow.

In addition to observing defects, smoke testing identifies illegal connections to the sanitary sewer system on private property. Unlike CCTV or manhole inspections, smoke testing will reveal potential I/I sources that cannot otherwise be seen. Typically performed as a part of a survey rather than a routinely scheduled inspection task, smoke testing is usually outsourced.

Nontoxic smoke is forced through a sealed-off sewer segment, creating smoke plumes where defects exist. The location of the smoke plume will help determine if the defect is causing infiltration and if it is a result of an illegal connection such as a downspout or sump pump. Smoke testing should be performed during seasonally dry weather, as rain events or high ground-water can prevent smoke from seeping through defects.

Defects that can be identified by smoke testing include cracked or broken pipes, open joints, holes or poorly fitting manhole covers, and lateral cleanouts with cracked or missing covers. Typical illegal connections found by smoke testing include footing drains, sump pumps, down spouts, and storm sewer or yard inlets. Defective plumbing systems, or dry traps, may allow smoke into properties, but that does not necessarily mean there is a defect at that location. Properly installed plumbing will prevent smoke from entering the house by redirecting it out the plumbing vents.

Smoke plumes are most commonly noted using measurements from stationary landmarks, addresses, and photographs. A crew of two or three tracks the sources of smoke emissions during the testing. The workers photograph smoking areas and identify them in a report that can be used to locate the source again in the future. The results of the smoke testing can be entered into asset-management software for future use.


Often performed in conjunction with structure or CCTV inspection, dye water flooding can confirm potential I/I sources identified by other investigation methods. Dye water flooding also can reveal a previously invisible defect by showing system performance under the stresses of water pressure. Dye water flooding helps quantify specific defects during an evaluation.

The procedure consists of forcing non-toxic, brightly colored dye into specific defects. The path of the dye is observed and defects are located and documented. Examples of defects include manholes with evidence of I/I, mainline defects, cross-connections, and roof drains.


With a few exceptions, the SSES investigation tasks may be completed in any sequence or concurrently. Specific features such as age, construction material, operation, and suspected illegal service connections may change the order of the investigations performed, but the following are a few key points to remember when preparing the SSES schedule.

  • CCTV and manhole inspection are best performed during seasonally high groundwater, or the wet-weather season. This allows the inspector to witness I/I defects in an active stage, providing the best recommendation for repair or rehabilitation.
  • Smoke testing should be performed during seasonally dry weather, as rain events or high groundwater can prevent smoke from seeping through defects. Dry weather allows the smoke to emit from sources such as rain gutters, downspouts, and the ground.
  • Flow monitoring is typically the longest process, as continuous monitoring during all periods is necessary for an accurate picture of system performance.
  • — Stamborski is a project engineer for the Municipal Services Division, R.A. Smith National, Brookfield, Wis.