Inflow and Infiltration
TQI Approach to I/I Reduction
We prefer to locate and eliminate the most significant sources of inflow (rapid response to rainfall) which are key causes of basement flooding and treatment plant bypasses. These are generally more economic to eliminate than sources of infiltration (low rates of extraneous flow sustained for long durations). If a significant source of inflow can be located and eliminated, then there is usually little point in modeling it. Our intention is to locate where you can make the biggest strides in reducing the problem for the least cost.
We have developed numerous proprietary tools that we utilize as appropriate in different I/I reduction projects. These include flow monitoring approaches, peak level recording devices, battery operated all season rain gauges, modeling programs, analytic and plotting software, etc. These tools have been utilized across Canada for a range of municipality sizes (small hamlet to major cities).
For a list of I/I samples found by TQI click here.
Our innovative work in this field and its application to a problem area in Belleville were recognized by the ACEC with an “Award of Merit” in their annual national engineering awards program.
Our proprietary custom compound weir monitoring system is customized for each location to address low and high flow situations. This system can also address surcharge situations with the addition of a velocity sensor. A big advantage is that at near surcharge situations, the velocity sensor can be calibrated by the weir. Also with the A/V meter in place, we are able to develop a stage discharge curve which extends into the surcharge region of flow. This combination of abilities allows for cleaner data over sustained periods of time at a much lower cost than commercially available A/V type monitors. It has been used across the country (St. John’s Newfoundland to Vancouver Island).
We have allowed SFE Global (a western Canadian firm) to apply our technology there, and also in much of the United States.
From our numerous projects we have encountered a great number of types of inflow sources and developed appropriate solutions. It is important to remember that unlike storm sewers, sanitary sewers are not supposed to respond to rainfall. Thus when looking for sources of I/I, you are looking for something that is not supposed to exist. Reviewing system plans is useful to gain knowledge of how a system is intended to function but it should be remembered that in many cases, problems exist because the system in the ground differs in some aspects from that shown on the plans. In some cases the source of the problem is not even in the sanitary sewer system, but rather in the storm drainage system. An I/I project manager is unlikely to uncover the problem by simply working in the office. For this reason our senior hydrotechnical engineers are actively involved in the I/I fieldwork.
When we encounter a community with an I/I problem, we find it useful to first meet with a range of people familiar with different aspects of the system (mixture of supervisors and field personnel). We make a presentation concerning I/I, review selected projects we have carried out and show examples of types of sources we have encountered (complete with humorous anecdotes).
We find that seeing the types of things encountered in other municipalities often “triggers” additional ideas of what may be happening in your system from your own personnel. We can then summarize the range of theories and interactively develop an investigative plan to prove or disprove the various theories. We come with rough costs and marginal costs prepared, so that we can usually provide a budget cost “on the spot.” This further helps to arrive at an appropriate investigative plan, specific project scope specifications and budget by the end of the session.