Sewer laterals often don’t get much attention during regular CCTV inspections. Because municipalities are not responsible for them, they’re rarely on the usual schedule. This can leave a large portion of a collection system un-inspected, un-repaired and ready to cause problems. When laterals do end up on the docket, it’s usually for one of three reasons:
- Cross bore detection. While the burden of preventing and repairing cross bores falls mainly on the utilities who create them (generally gas and telecom utilities), cities may find themselves performing lateral inspections to locate cross bores.
- Pre-acceptance. When a city is about to take responsibility for a new section of pipe, it will perform lateral inspections to ensure all construction was done to spec. Cities don’t have the budget to manage improperly installed lines.
- Blame assignment. When a ratepayer experiences a backup, they often want to avoid paying for an expensive sewer repair. To ensure the responsible party covers the cost, cities will perform a lateral sewer inspection to locate the problem and determine who should shoulder the expense.
Outside of these three scenarios, cities generally do not perform lateral inspections. Nevertheless, degraded laterals can have a major impact on the collection system as a whole. Private sewer laterals typically make up about half the total length of a sewer system and can account for roughly 40% of a system’s inflow and infiltration (I&I). Given the recent push to eliminate sources of I&I, municipalities may be driven to identify all sources, not just ones the city is responsible for. Ensuring sewer mains are clear and intact is only half the job.
In fact, neglecting laterals has such a major impact on the entire collection system that it can negate many of the benefits of mains improvement. For example, EPA studiesshow that repairing mains can cause the water table to rise as groundwater loses escape routes, causing unforeseen I&I in laterals. Additionally, while lateral repair may not initially seem cost-effective, the effects can have cascading benefits. If repairing laterals “prevents peak flows from exceeding maximum design flows at lift stations or at the wastewater treatment plant (WWTP), or if it eliminates the need to upsize parts of the collection system,” it’s likely worth the cost.
Ultimately, the choice of whether to inspect or not comes down to time, expense and focus, and utilities must have a plan in place for what to do with inspection data once they have it. To learn more about why cities should inspect and what it means for their operations, check out this resource from the EPA: