Preventing Infiltration and Inflow

Nov. 13, 2002
Manhole Testing

The most effective solution for eliminating infiltration and exfiltration is to accurately test sewer lines and manholes. The two commonly used methods to test sewer lines and manholes are with water and pressure. Pressure testing is a proven method of testing sanitary sewer systems.

Water Testing

Historically, water testing of pipe was the norm up until the mid- to late-1960s. In regards to manholes, water testing was common through the mid-1990s. Some areas today still allow testing of new pipes and manholes using water through either an infiltration or exfiltration test. In an infiltration test, groundwater entering into the pipe is monitored through the use of a weir. Conversely, in an exfiltration test, water is introduced into the pipeline or manhole, and the water level is monitored over a specified period of time, usually 24 hours.

Water testing for infiltration presents problems. For instance, a faulty segment of pipe could pass the test due to no groundwater being present. Also, it is difficult to use the metering equipment to measure water flow.

Water exfiltration tests also present certain problems. First, a water test is impacted by the moisture content of the soil—for instance, if the groundwater pressure is greater than the test pressure in the manhole or pipe, no water will leak out, thus giving a false passing reading.

Secondly, use of water also is much more costly to the contractor and city and is lengthy to conduct (24 hours). All water must be brought to the job site and be pumped out after the test. In either case, once it is determined that there is a leak, there is no method of determining where the leak is.

Pressure Testing

Conducting a low-pressure air test on new sewer lines will ensure pipe joints are tight and leak-free. Performing vacuum tests on new manholes ensure that they are structurally sound, correctly installed and leak free.

It is recommended that all sewer lines are pressure tested to verify the integrity of pipe (line acceptance test). A line acceptance test generally is performed to establish the tightness of a section of newly laid sewer pipe. A specific drop in air pressure within a pipe section over a specified length of time determines acceptance or failure of the line in question. Typically, a test can be accomplished in a matter of minutes compared to a 24-hour exfiltration test.

When a drop in pressure is recognized, two plugs can be used to isolate the leak to within five feet of pipe (leak location test). Leak location testing also can be done in a matter of minutes.

It is recommended that a vacuum test be given to verify the integrity of all manholes. Manhole testing is performed by creating a vacuum in the manhole and monitoring a gauge for vacuum loss. Vacuum testing identifies potential infiltration and exfiltration problems. A manhole testing system allows you to test manholes in approximately 20 minutes from start to finish compared to a 24-hour water exfiltration test. It provides immediate leak detection, before or after ring installation and backfilling, while also eliminating expensive/time-consuming water tests. Vacuum testing is an efficient, accurate and cost-effective method of testing new, existing and rehabilitated manholes.

Low-pressure air testing successfully has been used in the United States to test pipelines for more than 35 years. Vacuum testing, introduced in the last 15 years, now is the primary method for testing manholes. These methods of testing have proven to be a fast, economical and accurate method for testing newly installed sanitary systems.              WWD

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