Intake and Infiltration: Substantial Costs for Municipalities and Utilities
What is I&I (Intake and Infiltration) & Sensors as a Solution
I&I describes what happens when stormwater (inflow) and groundwater (infiltration) enter a wastewater system. This water, which ideally should drain into the ground or be routed to storm drains, can easily overload wastewater systems – causing higher energy waste-water treatment costs, sewage overflows, backups and impaired or unplanned operation shutdowns, shorter capital equipment lives, among other challenges. Wireless, intelligent sensors can play an important role in preventing and mitigating I&I. For example, manhole cover sensors can detect and alert when manhole covers have been tampered, damaged, or removed. Pump monitoring sensors can detect and alert when pump run-times are longer than expected as well as monitoring more frequent starts and stops. Sensors along with data analytics can detect when pipe segments are likely to fail (e.g. cracks, leaky joints), enabling crews to prioritize and repair pipes before they allow for infiltration.
Inflow
Inflow is stormwater that enters the sewer collection system through direct connections such as roof leaders, yard drains, catch basins, defective manhole covers and frame seals, un-secured or removed manhole covers, sump pumps or throughout indirect connections with storm sewers. It can also be caused when foundation drains are improperly connected to a sewer line.
Inflow occurs as a result of heavy storm events such as rainfall, snowfall and/or snow melt, each of which contribute to excessive sewer flows – resulting in hydraulic backups and the pooling of water. Inflow is generally measured during wet weather.
Infiltration
Infiltration is groundwater that enters sewer pipes (e.g., interceptors, collectors, manholes or side sewers) through cracks, leaky pipe joints, connection failures and deteriorated manhole covers. Infiltration amounts vary by season and in response to groundwater levels. Storm events can trigger a rise in groundwater levels and increase infiltration flows.
Because they are designed as direct connections, sump pumps and foundation drains are considered inflow sources. Yet, they act very similar to infiltration due to their nature of draining the groundwater surrounding a structure.
The highest infiltration flows often result from significant storm events or extended precipitation. It’s generally measured in wet weather seasons during seasonally high groundwater conditions.
You may have an underlying I&I issue if you experience either of the following warning signs:
Your lift station pumps run continuously; they start and stop. There may be an issue if your lift station pumps run for a long and continuous time after a rain event, or if your pumps start and stop frequently after a significant rain event. Each likely means stormwater has entered your sanitary sewer system, is on its way to be treated and is perhaps taxing its capacity.
Your pipes are backed up. Backed up pipes are often a clear indicator of an impending I&I issue. There is likely an issue at hand if, during a rain event, manholes are spilling wastewater on to local roadways or green space, rain water isn’t draining into sewer systems and/or various residential or business basements begin to flood. These issues need to be identified and addressed quickly.
You see significant spikes in flow. As you measure and evaluate the effectiveness of your wastewater treatment plant during precipitation or high groundwater conditions, readings that return spikes in flow likely indicate an I&I issue. While small amounts of I&I are to be expected, significant spikes rarely happen unless there is a deeper issue at hand. The two motion images above highlight a “spike” in flow that would have created more than 4 million gallons of I&I over the course of a year if left untreated.