What is being done to ensure quality work on the water main?
By David Brunsting and Nick Tremmel
When a community is investing in a large project such as the
NORWEJ water main in DeMotte, quality of the workmanship is essential. It is
certainly of the utmost importance to Abonmarche Consultants as well. Engineers
and inspectors have a few tools at their disposal to ensure the main has been
installed without any faults. Those tools come in the form of tests, principally
a timed hydrostatic leakage test and a bacteria test. The municipal water main
must pass these tests to ensure that it is ready for service prior to allowing
the public connect to the main. We at Abonmarche oversee these tests. The pressure testing portion is outlined in this post.
Leaks in a municipal water main
are problematic and can be costly. First, a water leak is essentially money
being dumped into the ground. When water is pulled out of the municipal well it
costs the system in the form of wear and tear on equipment and energy to run
the equipment. Since the processed water leaking into the ground will not go
through a water meter the costs of treatment cannot be recouped. Even small
leaks can cost municipalities tens of thousands of dollars per year if left
unattended. Second, leaks can be destructive to existing infrastructure. Even
small leaks can undermine and collapse roads and other structures. Additionally
a leak invites the possibility (albeit a slim one) for contamination of the
water in the line; whereas a sealed system provides a physical barrier to
contaminating bacteria.
If the water main could be installed above ground,
inspection for leaks would be very simple. Just fill the main with water under
system pressure and look for drips. Obviously, water main cannot be installed
above ground and must be buried so the question becomes, how do we ensure the
connections are acceptable? The answer is pressure testing indicates any leaks
and bacteriological testing indicates any contamination from the installation.
The way it works is rather simple. The main to be tested is
filled with water and air is expelled by opening hydrants along the way. Once
the pipe is completely filled with water from a clean well and almost all of
the air is out then the contractor connects a hydrostatic pump to the main. The
hydrostatic pump will bring the pressure of the entire line up to the test
pressure which in our case is 100 pounds per square inch. This test pressure is
roughly two times the system working pressure of 50 PSI. The pump is turned off
and the main is held at test pressure for a period of two hours. Because it is
almost impossible to get 100% of the air out of a water main the pressure will
begin to lower slightly, as seen in the picture. These minor losses are
expected, and they are the result of the remaining air trapped in the main,
temperature differences, minute movement of the pipe itself and other very
miniscule factors. The minor losses do not necessarily indicate a leak, but we
have to be sure. There are specifications that lay out (based on hypothesis and
empirical data) which draw a line, so to speak, between acceptable and
unacceptable pressure losses. After the two hours have passed and there has
been a drop in pressure the contractor has to pump the main back up to 100 PSI.
The specifications (in our case American Water Works Association, AWWA, C605)
outline an allowable amount of water to be used to return the line being tested
to the original pressure. This make up water typically amounts to 1 to 2
gallons depending on the length and diameter of the line being tested. Should
they go over the allowable amount the test fails and the contractor is
responsible for correcting the issue. It is common for a line to initially fail
a pressure test but pass on a subsequent attempt. This is most commonly the
result of excess air in the main. Though quite rare, on occasion a leak can be
found; the cause of the leak could be any number of things, be it material
issues or improper instillation or something else altogether. 
