Flow Metering from USG

Sewer lines are more than simply a place to dump dirty toilet water and forget about it. The water that enters sewers is sent off to a Wastewater Treatment Plant, where it is cleaned for reuse or release into the environment. This treatment process comes at a cost to local municipalities, which is paid by local residents through sewer bills, local government taxes, or funding from state and federal agencies.
A significant portion of these costs can be reduced by preventing clean water, such as stormwater or groundwater, from entering sewer systems unnecessarily. This begs the question: how can this be done? The first step for local municipalities and infrastructure owners to stop overpaying to treat clean water is by monitoring sewer systems through an inflow and infiltration (I&I) investigation technique called Flow Metering. During flow metering, measuring devices are installed to collect data on the volume of water entering the system. Using this data, owners can identify where unwanted water is entering the sewer system and take steps to address it.

How Does Unwanted Water Enter Sewer Systems?

Stormwater and other clean water can enter into a sewer system through several means. Sometimes this excess water is a result of infiltration, which is allowed in through cracks, joints, or other defects in sewer infrastructure. During heavy rain events, this water seeps into aging or compromised sewer lines, increasing overall system flow. Additionally, inflow occurs through stormwater conveyance systems or sump pumps from residential homes that are sometimes illegally connected, discharging directly into sewer systems. This extra water must then be sent off to a Wastewater Treatment Plant, or WWTP, where it undergoes a costly process of sanitation before it can be safely used or released.

The Flow Metering Process

Devices are installed within strategically selected manholes or drainage basins throughout the sewer system, where they collect data over a defined monitoring period. These sensors continuously measure flow rates and water levels within the sewer line, capturing how the system performs during both dry-weather conditions and wet-weather events.
The data collected is then analyzed to identify trends, fluctuations, and abnormal increases in flow. By interpreting this information, infrastructure owners can better understand when excess water is entering the system and how it correlates to rainfall or system usage, allowing them to pinpoint likely sources of inflow or infiltration and prioritize next steps.
A flow metering service can help determine exactly how and when this unwanted water is entering a line based on the flow characteristics observed in the data. The flow data is plotted into graphs and analyzed to identify patterns over time. Distinct flow patterns, such as spikes during rain events (inflow), or gradual increases following rainfall events (infiltration), can help infrastructure managers determine whether the issue is caused by inflow and infiltration or illegal connections.

What Comes After Flow Metering?

Once flow metering data identifies abnormal increases in system flow, additional investigation is often required to confirm the exact source and location of the problem. These next steps allow municipalities and private infrastructure owners to move beyond data trends and visually verify where inflow or infiltration is occurring.
One common follow up method is wet weather surveys, which involve observing manholes and sewer structures during or immediately after rainfall events. By inspecting these access points while the system is under stress, crews can identify active inflow points such as leaking manhole covers, defective joints, or surface water entering the system directly.
Closed circuit television (CCTV) inspections are also frequently used to evaluate the interior condition of sewer lines. Cameras are sent through the pipe to identify cracks, joint separations, root intrusion, or structural defects that may allow groundwater to infiltrate the system. These inspections provide a clear visual record of pipe conditions and help prioritize areas in need of repair.
In some cases, smoke testing is performed to locate illegal connections, surface level defects, or direct stormwater connections. Non-toxic smoke is introduced into the sewer system and observed at ground level. Smoke escaping from yards, buildings, or stormwater structures can indicate cross connections or breaks in the system that allow unwanted water to enter.
Together, these investigative methods provide a comprehensive understanding of how and where excess water is entering the sewer system, allowing infrastructure owners to develop targeted, cost-effective rehabilitation strategies rather than relying on broad or reactive repairs.

USG: The Intersection of People, Safety, Service, and Technology

When unwanted water enters a sewer system, the cost extends far beyond the pipe itself. By combining flow metering with targeted investigative methods, infrastructure owners gain the insight needed to make informed decisions, reduce unnecessary treatment costs, and protect the long-term performance of their systems. Rather than relying on broad repairs or assumptions, this data-driven approach allows solutions to be applied exactly where they are needed. With a focus on accuracy, efficiency, and responsible infrastructure management, USG helps clients move from identification to action with confidence. When it comes to protecting critical sewer systems, USG stands at the intersection of people, safety, service, and technology. Contact USG today to learn how our investigative and rehabilitation services can support your infrastructure goals.