How to Decide Between Jetting, Cabling and Excavation

Why this matters

The common way this decision gets made is by counting failures: cable it, and when it comes back often enough, dig. That is a scoreboard, not a diagnosis, and it means the customer pays for the education. Excavation is not the escalation of failed cleaning. It answers a different question entirely, which is whether the conduit itself is intact and correctly graded, and a cleaning method applied to a structural defect will go on succeeding on the day and failing on the interval for as long as anyone is willing to keep paying for it.

So the decision runs on a classification, not on a count. Three questions, in a fixed order, and the order is fixed because each answer changes what the next question means.

Before any of the three: the hazards each option adds

Cleaning hazards belong to the sibling card and are not repeated here beyond one line: jetting aerosolizes wastewater and needs a full face shield plus ventilation of an enclosed space, and cabling runs on a foot pedal with a cable mitt.

Excavation adds hazards that are categorically different and are the reason a shop does not drift into digging:

• Locate the underground utilities before the first shovel or machine bucket goes in, through the regional one-call service, and hand-dig within the tolerance zone around a marked line rather than machine-digging it. On a construction site this is a requirement of 29 CFR 1926 Subpart P.
• A trench 5 feet or more deep requires a protective system, sloping, benching, shoring or a shield, unless it is entirely in stable rock, under 29 CFR 1926.652, and below 5 feet a protective system is still required where a competent person examining the ground sees a potential cave-in. Nobody enters an unprotected trench to "just look".
• Keep spoil and equipment set back from the edge rather than piled at it, because the surcharge load at the lip is what turns a marginal wall into a collapse, and a competent person inspects the excavation daily and after any rainfall under the same Subpart.
• A manhole, wet well or interceptor you might open during the work is a permit-required confined space under 29 CFR 1910.146 in general industry or 29 CFR 1926 Subpart AA on a construction site, and the entry setup, atmospheric testing and attendant obligations attach before anyone's shoulders pass the plane of the opening.

Question one: can this line take energy at all?

Both cleaning tools deliver energy to the inside of the pipe, and both of them do harm when the wall cannot receive it. If you have recovered pipe fragments, if the customer reports a sinkhole or a soft spot in the yard, or if the line has no history and no record at all, this question is answered by a camera before a tool, not by trying gently.

The reason this comes first rather than second is that a jet into an open joint washes bedding out through the defect and creates a void under the pipe, which converts a repairable defect into a repair plus a settlement problem. The classification you are about to do in question two is worth nothing if question one has already made the line worse.

Question two: what class is the defect?

Three classes, and the whole decision turns on which one you are looking at.

Class A, an obstruction in an intact conduit. A root mass, a foreign object, a discrete plug. The pipe is fine; something is in it. Cabling is the tool because it engages the object and brings a sample back.

Class B, accumulation on an intact wall. Grease, scale, silt, a general loss of bore over a length. The pipe is fine; its cross-section has been reduced. Jetting is the tool because it works the circumference and restores area.

Class C, a defect of the conduit itself. A belly, a separated joint, an offset, a crack, a partial collapse, a reversed or flat grade, a broken or intruding tap. Nothing in the pipe is the problem; the pipe is the problem. Neither cleaning tool addresses this class, and both of them will appear to.

Class C is the one that gets misread, because a Class C defect produces Class A and Class B symptoms continuously. A belly collects solids, so a camera run after the deposition looks like an accumulation problem. Clear it and the geometry that caused the deposition is untouched.

Question three: does a trenchless route exist?

Only Class C reaches this question. A defect of the conduit can sometimes be repaired without opening the ground, and what a liner can and cannot do is a sibling card's subject, so the short version here is the part that governs the decision: a liner restores the wall and inherits the geometry. That single sentence sorts most of Class C.

• Cracks, corroded wall, root-admitting joints, a deteriorated but correctly graded pipe: a trenchless route is on the table.
• A belly, a reversed grade, a settled section, a collapse, a missing section: the geometry is the defect, and lining a bad shape gives you a smooth-walled bad shape.

Access, length, bends, diameter changes and the number of laterals all constrain this further, and those are questions for the lining contractor rather than for you.

The comparison

Worked example: three successful calls and a belly

A 4 inch building sewer from a residence, cast iron to the property line. Three service calls in 14 months, each cleared on the day.

Camera run on the fourth call, entering at the outside cleanout:

• Standing water first observed at 38 feet on the counter, water clearing at 49 feet
• Water depth at the deepest point, read against the camera head, roughly 40 percent of the pipe diameter
• Wall condition through the section: sound, no open joint, no fragments, solids lying in the low point

Question one clears: the wall took the camera and shows no defect that would pass energy into the soil. Question two classifies it as Class C, because the standing water is present with no obstruction, which is geometry rather than accumulation. Question three: a belly is a shape, so lining is out and excavation is the route.

Now the counter arithmetic, which is where crews get the dig wrong. A camera footage counter's error is stated as a percentage of reading, not a fixed count, so it grows with distance, and on a single run with a single instrument it behaves as a systematic offset rather than a random spread. Take 2 percent of reading:

• Length of the defective segment: 49 - 38 = 11 feet. Because both readings come from the same instrument in the same run, the offset cancels in the difference, leaving 2 percent of the 11 foot difference, which is 0.22 feet. That number is trustworthy.
• Absolute position of the upstream end for the dig: 38 feet, carrying the full 2 percent of reading, which is 0.76 feet, and at the downstream end 2 percent of 49 feet is 0.98 feet.

So the length is good to a quarter of a foot and the position is good to about a foot at each end, which is why the dig gets located with a sonde and a receiver from the surface rather than by measuring the counter reading off along the lawn. Mark both ends with the sonde, and treat the counter as the thing that told you how long the defect is, not where it is.

The labor comparison, in one currency. Stated as field labor hours so the two sides are the same kind of hour, and excluding restoration, permits and equipment on both sides:

• Cleaning intervals: 5, 4 and 5 months, mean = 14 / 3 = 4.67 months
• Visits per year: 12 / 4.67 = 2.6
• At 1.5 labor hours per visit: 3.9 labor hours per year, indefinitely
• Depth at the point of work, from the invert at the cleanout plus the run's own fall plus the rise in ground surface over the 38 feet: 5.4 feet, so 29 CFR 1926.652 attaches and the trench carries a protective system rather than a ladder alone
• Point repair of an 11 foot segment: two techs for 6 hours = 12 labor hours, plus 2 labor hours setting and pulling the shield = 14 labor hours, once
• Break-even: 14 / 3.9 = 3.6 years

One qualifier has to be applied to that figure rather than left in the prose, and it belongs to the slope-fault card rather than to this one. A belly deepens its own problem: deposited solids raise the effective invert, which lowers velocity further, which increases deposition. The interval therefore shortens over time rather than holding at 4.67 months, so the annual cleaning hours rise and the break-even arrives sooner. The honest form is <= 3.6 years, one inequality sign, no interval, because 3.6 is the case where nothing gets worse and nothing about a belly stays the same.

The failure mode of skipping the classification is visible in the three earlier tickets. Each one recorded a cleared line and a satisfied customer. None recorded standing water, because on those visits the tech never ran a camera, and the defect only exists in a picture taken between clearings rather than during one.

Confirming the classification before the shovel

Two checks, both cheap, both done before anyone quotes a dig.

Camera the line after a clearing, not before it. A run through a line full of solids shows you solids. A run through a freshly cleared line shows you the pipe, and standing water in a freshly cleared line is the single clearest evidence of Class C there is, because there is nothing left in the pipe to hold it.

Confirm the low point with water, not with the picture. Run the fixture group and watch the camera head at the low point: water that flows through and leaves a residual depth behind it is a belly, water that backs up and then releases is an obstruction downstream of the head. Techs read a standing pool on a camera as a belly when it is sometimes just the pool above a restriction the camera has not reached, and one flow test separates them.

What flips the answer

A property line or a public main. The segment's owner changes the decision, because a defect on the utility's side of the connection is the utility's repair and the correct action is a report with the sonde-located position rather than a quote.

Depth and what is above the pipe. A belly 3 feet down in a lawn and the same belly 9 feet down under a driveway are the same defect and completely different jobs, and at 9 feet the trench needs a protective system under 29 CFR 1926.652 that the shallow one may not, so depth changes both the method and who is qualified to do it.

A line that is going to be replaced for another reason. If the customer is already opening the ground for a service upgrade or a foundation repair, a Class B accumulation that would normally be jetted may be worth replacing while the trench is open, and that is a scheduling decision rather than a drainage one.

References

• 29 CFR 1926 Subpart P, excavations, including 29 CFR 1926.652 protective systems; construction
• 29 CFR 1910.146, permit-required confined spaces, general industry; 29 CFR 1926 Subpart AA in construction
• Camera and locator manufacturer documentation for footage counter accuracy and sonde depth range
• See related: Why Jetting and Cabling Solve Different Problems; What a Lining Repair Can and Cannot Fix
• See related: Sewer Camera Inspection Reference; Why a Drainage Fault Is Usually a Slope Fault in Disguise