Wastewater utilities rely on lift stations in gravity systems to lift sewage from point to point until it reaches the treatment facility. Lift stations are essential to maintaining an efficient sewer system. One of the most significant (and often underestimated) challenges utilities face is inflow and infiltration (I&I). Evaluating I&I is not just a technical exercise; it directly affects costs, system reliability, and environmental protection.
What is Inflow and Infiltration?
Inflow refers to stormwater that enters the sanitary sewer system through direct connections such as manholes, sump pumps, or improperly tied-in storm drains. Inflow is typically characterized by a sharp spike in influent flow into the sewer system, either during or immediately after a heavy rainfall event. Infiltration, on the other hand, occurs when groundwater seeps into sewer pipes through cracks, defective joints, or other aging infrastructure-related pathways. The increase in influent flow caused by groundwater infiltration is subtle and can be either acute or chronic. Acute infiltration is typically associated with rain events and sudden rises in groundwater, and it is easily detected. Chronic infiltration occurs over long periods where increased flow is hard to detect without long-term, frequent monitoring. Together, both inflow and infiltration can dramatically increase the volume of wastewater that lift stations must handle, especially during heavy rain or high groundwater events.
Operational and Financial Impacts
Lift stations are designed to move a maximum volume of wastewater. Operators of these stations use predefined “level setpoints” that determine when pumps turn on and off. Therefore, excess I&I forces pumps to run longer to cycle more often, raising electricity consumption, shortening equipment life, and increasing maintenance needs, leading to costly emergency repairs. Higher-than-designed flows also increase treatment plant loads, thereby raising chemical and energy costs. Utilities that pay for treatment based on flow rates can face steep financial penalties when I&I drives volumes beyond contractual limits.
Environmental and Regulatory Concerns
Uncontrolled I&I can cause sanitary sewer overflows (SSO), which release untreated wastewater into streets, waterways, and groundwater. SSO events not only impact ecosystems but also put public health at risk and can often trigger regulatory fines. Evaluating and controlling I&I, therefore, is a critical endeavor for meeting state and federal discharge requirements.
Benefits of a Strong I&I Evaluation Program
I&I detection can be done either through direct physical tests that identify where extraneous water enters the system or by utilizing advanced analytics from SCADA (or other) data. The first method entails smoke testing, dye testing, and CCTV footage inspections to determine the physical source of the I&I. The second method relies on continuous, frequent data collection of the influent flow rate over time. By identifying sources of I&I and determining the impact that I&I is having on the system, utilities supported by SCADA monitoring can prioritize where physical inspections and tests should occur, optimizing efforts and focusing repairs, whether that means sealing pipe joints, replacing old mains, or disconnecting illicit stormwater connections. Implementing these proactive assessments helps utilities plan capital improvements and justify budgets to governing boards and the public.
Conclusion
Evaluating inflow and infiltration is more than a maintenance task; it is a foundational responsibility of wastewater management. Utilities that rigorously measure and control I&I protect their infrastructure, maintain lift station health, reduce unnecessary treatment costs and regulatory penalties, and safeguard the environment. Particularly at lift stations, where excess flow directly increases pumping and mechanical stress, early detection and targeted remediation of I&I yield long-term savings and resilience.
For more information, please contact Chad Morris at cmorris@arudrra.com or Manal Alduraibi at malduraibi@ardurra.com.
