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.