Identifying and Managing Annual I&I Issues Where does the sand in wastewater treatment plants come from?  The answer is the collection system.  Determining whether or not there is an I&I (inflow and infiltration) issue can be the real challenge.  Spring is just around the corner, and with it, the time of year when most of the country’s rainfall usually occurs.  Throughout the wet season, an increase in flow into a WWTP can be due to inflow and not an increase in domestic wastewater collected.  Increase in flow is also a potentially a reliable indicator that treatment capacity has been compromised and may need to be restored. Over time, sand seeps into pipes and lift stations and is eventually transported to WWTP infrastructure.  Sand, unlike other debris such as rag material, FOGs, and grit, is an unintended consequence of increased inflow into collection systems.  During heavy rainfall, wastewater collection pipes receive an inflow of rainwater which seeps into the pipes transporting sand.  Seepage bringing sand usually occurs without notice until the associated problems have become acute and require immediate attention. I&I issues tend to be out of sight, out of mind.  The consequences of I&I tend to go undetected due to the fact that pipes are buried underground.  Since the water in tanks at facilities are not see-through, accumulated sand at the bottom of these tanks remain unseen and unnoticed. Eventually, the increase of sand into wastewater treatment infrastructure can reduce treatment volume and increase energy use.  Consider instead the value of restoring capacity versus replacing capacity.  When the sand is removed, capacity is restored in the structure at the WWTP.  Consider also the capital cost to repair or replace pipe segments that may have high inflows.  Often, the first solution to solve I&I issues is to repair or replace the pipes.  However, the cost-benefit of removing sand from the WWTP may be more cost-effective than fixing the pipes.  For example, if the annual cost of maintenance is less than the cost of borrowing the capital to do the repair or replacement project, then removing sand at the WWTP may make more sense.  Finally, the benefit of reducing the amount of energy required to run blowers by removing sand can be significant. When average daily wet season flows increase significantly compared to the dry season, then sand transported into the collection and treatment systems may be accumulating until it gets your attention. Don’t be taken by surprise;