Greg Lawrence, Cherne Industries, Inc.
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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
