Nobody plans to dig into the sewer. The fence contractor does not know where the lateral runs, the homeowner planting a tree assumes it is deeper than it is, and the deck builder’s auger goes down until it hits something. A residential lateral is often only two or three feet down, it runs under the lawn where all of this happens, and in most houses nobody has a drawing. The result is a break that shows up as a slow drain weeks later, long after the post is set in concrete over the broken pipe, and a camera inspection that ends at a wall of soil and a sonde locate that lands squarely on the new fence.
Quick answer: fence posts, deck and shed footings, tree planting, retaining walls, irrigation trenches and pool excavation all reach lateral depth, and each produces a characteristic finding: a pierced pipe with the auger’s hole, a crushed section where a footing sits on it, a sheared joint where a trench cut the bedding, or a severed line filled with soil. The camera finds the break and the sonde locate identifies the feature above it. Prevention is an hour’s work: trace the lateral with a sonde and mark it before anyone digs.
Post holes and augers
A post hole auger drills a hole the width of the post and as deep as the fence needs, and a lateral at that depth is pierced or shattered. The camera shows a round hole in the crown or side of the pipe with soil or concrete in it, sometimes with the post itself visible, in clay or cast iron a shattered section, in plastic a hole with the edges pushed in. Flow continues past it, so the symptom is a slow leak into the soil and a root entry later rather than an immediate backup. The sonde locate lands on the fence line. The holes and voids guide covers the finding.
Footings
A deck, shed or addition footing poured on or beside the lateral loads it permanently. Plastic deflects under it; clay and cast iron crack; any pipe settles beside it as the footing’s own excavation disturbs the bedding. The camera shows an oval or crushed section, a circumferential crack, or an offset joint, with the locate on the footing. A footing cannot be moved, so the repair is a sleeve or a re-route. The ovality guide describes the plastic case.
Trenches
An irrigation line, a drainage pipe, a conduit for lights or a planting trench cut across the lateral either severs it or removes the bedding beside it. A severed line shows on camera as the pipe ending in soil, often with the other pipe or the cable visible through the break. A trench that only disturbed the bedding shows as a new belly or offset at the crossing. The separated joint guide covers the bedding case.
Trees, walls and pools
A tree planted over the lateral is a root problem in ten years and a damaged pipe today if the planting hole reached it. A retaining wall’s footing and drainage are a trench and a footing combined. A pool excavation is the largest dig most properties ever see, and the lateral is often re-routed around it, well or badly; the camera finds the re-route’s joints. The tree species guide covers the slow version of the first case.
Finding the culprit
Camera the lateral from the cleanout to the break, with the counter running. Note the distance. Activate the sonde and locate the head from the surface. The mark lands on, or within a foot or two of, the fence post, the footing, the tree or the trench. Photograph the mark with the feature in frame. That is the evidence for the conversation with whoever dug, and the specification for the repair. Marking a dig with a 512 Hz locator covers the locate.
Prevention
Before any digging, trace the lateral with a sonde camera and paint the route. Call 811 for the public utilities as well, because the lateral is private and 811 will not mark it. Give the contractor the route in writing. Keep posts, footings and trenches off it by at least a few feet, and where a crossing is unavoidable, dig it by hand. The cost is an hour with a camera; the saving is the repair, the fence and the argument. Calling 811 before digging and tracing a lateral across a yard cover the procedure.
What to record
The distance of the break, the surface mark, the feature above it, dated footage and a photograph of the mark. Any earlier footage of the same lateral for comparison. The contractor’s name and the date of the work. A repair quote built on that record is a specification; a complaint without it is a dispute.
Depth is the surprise
Homeowners assume the lateral is deep. On many lots it is not: two to three feet near the house, sometimes less where a slab house’s building drain exits, and a post hole auger or a tree spade reaches that in a minute. The sonde’s depth estimate during the trace is the number to write on the painted line, because a contractor who sees “2 ft” beside the paint will dig differently from one who assumes six.
Common questions
Can a fence post break a sewer line?
Yes. An auger reaches lateral depth on most lots and pierces or shatters the pipe.
Will 811 mark my sewer lateral?
No. 811 marks public utilities to the property line. The private lateral is yours to locate.
How do I find my lateral before digging?
A camera with a 512 Hz sonde, located from the surface every 10 or 15 ft, and paint.
Related guides
See inspection before major landscaping, the best sewer cameras for landscapers, and the best sewer locators for plastic pipes.