Inflow success stories


Wastewater utilities and water utilities are intrinsically linked.  Wastewater utilities often discharge to water bodies that are water supplies for downstream water plants.  In other cases, wastewater plants provide additional supply options to reduce water demands in the form of reclaimed water.  However as a wastewater utility, costs are often associated with power- pumping and aeration, which can be 30% or more of the utility’s costs in the worst cases.  However, substantial savings in operations can be achieved by reducing the amount of wastewater that must be pumped and treated and in some cases that reduction also is associated with water quality benefits for the reuse of reclaimed water.  Utilities have long dealt with the infiltration and inflow (I and I) issues in their system by televising their pipes and identifying leak points, but this primarily addresses only the infiltration part of I and I.  Inflow and infiltration are not the same thing – they are very different and must be addressed differently.  Inflow causes hydraulic issues during rain events – like sanitary sewer overflows and basement flooding.  Both subject the utility liability from lawsuits and/or regulatory fines.  Inflow is the risk issue that must be addressed to protect the utility.  A cost effective solution to inflow involves low tech, low cost methods can identify the problems that can corrected easily.  Removing the inflow portion from I and I, often leads to a more focused plan for infiltration correction.  What are those tools?  Smoke testing, cleanout repairs, sealing manholes and manhole dishes.  But each of these needs to be carefully selected.  Because these solutions, pipe that leak can be seen through another low tech solution – a midnight monitoring event.  Recent efforts here in south Florida indicate that only 15-20% of the pipes in a sewer system need to be televised and within those, about half the leaky pipes are actually not leaking – they are broke laterals.  Laterals are one of the most ignored parts of the sewer system – often they are small pipes and much of the piping is on private property so the utility does not address those pipes.  And in many utilities these are the pipes in the worst condition.

Other things that our efforts have shown are that new pipe can leak, just like old pipe, clay is not the only pipe that leaks and that the inflow solutions can be very helpful.  Figures 1-4  show how the solutions affected three lift stations and one community.  The graphs show rainfall vs flow.  Before these efforts, the flows increased with rainfall events.  After, they did not.  Hence this utility was able to resolve its risk for overflows at a cost of under $500/manhole.  That is relatively inexpensive.

LS 52 db LS 54 LS 53

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