A soft spot in the lawn that the mower sinks into, a depression that appears after rain, a crack across the driveway that keeps widening, or a hole that opens overnight all have one thing in common: soil has gone somewhere. Water carried it, and the most likely water in a residential yard is a sewer lateral leaking at a joint, a crack or a hole. Water leaving the pipe takes fine soil with it, the ground above loses its support, and eventually it drops. A sewer camera inspection is the cheapest way to confirm or rule out the lateral before anyone starts digging exploratory holes, and the sonde locate from the leak is what tells you whether the soft spot and the defect line up.
Quick answer: a sinkhole or soft spot above or near the line of the sewer lateral is a leaking sewer until proven otherwise. The camera finds the joint, crack or hole, and a sonde locate from the head at that point marks the surface above it. If the mark lands on or beside the soft spot, the cause is found. If the lateral is sound, the water main, a storm drain, a downspout or natural soil settlement are the next candidates. The repair is to fix the pipe and fill and compact the void, in that order.
How a sewer leak makes a hole
Every use of the house sends water through the lateral, and at a leaking joint a little of it leaves the pipe. The water flows through the bedding and the soil around it, carrying the finest particles with it, into the pipe through the same gap or into any gravel bed nearby. Over months the soil around the joint is replaced by a void. The ground above the void holds for a while by arching, then collapses when it gets wet or when a load passes over it. The process is slow and silent, and the first sign at the surface is often years after the leak began. The holes and voids guide describes what the camera sees at the leak.
Where to look
Along the line of the lateral between the house and the street, especially at the foundation wall where the pipe leaves the building, at any point where the lateral passes under a driveway or a path, near large trees, and at the connection to the main. A soft spot that is not on that line is less likely to be the sewer and more likely to be a storm pipe, a water service or a downspout drain. If the lateral’s route is unknown, the camera’s sonde traces it: push the head in, locate it every 15 or 20 ft, and paint the dots. Tracing a lateral across a yard covers the method.
What the camera finds
A joint with a gap, a crack or a hole, usually with soil or gravel visible through it and often with a void of blackness beyond where the LEDs find nothing to light. Roots, because they follow the leak. A scour mark on the wall where water has been leaving. Sometimes a section that has dropped into the void it created, which is a belly or a separated joint. Dim the LEDs, slow down at every joint, and watch the invert. Record the distance at each opening. The infiltration guide covers the wet-weather signs at the same joints.
Confirming the connection
With the head at the suspect opening, locate it from the surface with the receiver and mark the ground. Take a second locate from a different approach. If the marks fall on or within a few feet of the soft spot, the sewer is the cause. Probe the soft spot with a rod to feel the void. If the lateral is sound from end to end, the camera has ruled it out and the search moves to the other buried pipes. Marking a dig with a 512 Hz locator covers the locate.
The repair order
Pipe first, void second. Excavate at the mark, repair or replace the leaking section, then fill the void with compacted material and restore the surface. Filling the hole without fixing the pipe means the hole returns. Fixing the pipe without filling the void means the surface still drops. A camera pass after the repair confirms the joint is sealed, and the sinkhole stops growing. Spot repair vs full replacement helps size the dig.
When it is not the sewer
A water main leak saturates the ground rather than draining it, and the soft spot is wet rather than hollow. A storm drain or a downspout line leaks only in rain. Natural settlement of fill, especially over an old trench or a removed tree stump, drops evenly without a void. Buried debris rotting away leaves a hole with no pipe nearby. The camera inspection that rules out the sewer is still worth doing, because it is the cheapest of the investigations and the sewer is the most common cause.
Common questions
Can a sewer leak cause a sinkhole?
Yes, and it is the most common cause in a residential yard. The leak carries soil away and the ground above drops.
Will the camera show the void?
It shows the opening and, through it, the blackness of the void where the lights find nothing. The void itself is confirmed by probing at the surface mark.
Should I fill the hole first?
No. Fix the pipe, then fill. A filled hole over a leaking pipe reopens.
Related guides
See separated joints on camera, the best sewer cameras for excavation planning, and sewer line settlement after construction.