Damage prevention
Why utility strikes still happen
The Common Ground Alliance counted 221,717 unique damage reports across the United States and Canada in 2025. Only 22.3% of the reports with a known root cause involved nobody calling 811. This page covers what the standards require, what a locate mark physically measures, and the conditions under which a correctly placed mark still puts the pipe somewhere else.
What the rules require, and what they do not
Federal law sets a floor and leaves the detail to the states. 49 CFR 198.37 describes the one-call damage prevention program a state must adopt — a system an excavator must notify before digging — covering every area of the state containing underground pipeline facilities. The excavator gives the centre their name, address and telephone number, and the specific location, starting date and description of the work. Emergency work may begin first, with notification “at the earliest practicable moment”. Two federal rules reach the excavator directly. OSHA’s excavation standard, 29 CFR 1926.651(b), requires the estimated location of underground utilities to be determined before an excavation is opened, and the exact location to be determined “by safe and acceptable means” as the work approaches them. 49 CFR Part 196 sets minimum requirements for anyone digging near a pipeline, which PHMSA enforces itself in states whose own enforcement it has found inadequate. Everything past that is state law, and it varies.
The consensus figure comes from CGA Best Practice 5-19 (Best Practices Guide, Version 22.0). The tolerance zone — the strip of ground around a marked utility where digging is limited to careful methods such as hand digging and vacuum excavation — is “the width of the facility plus 18 in. on either side of the outside edge of the underground facility on a horizontal plane”, and the practice states it is not meant to preempt states that already require more.
Some states do. Michigan’s equivalent, the “caution zone”, is 48 inches either side of the facility marks (MCL 460.723). California Government Code §4216(u) sets 24 inches each side of the field marking, and §4216.4(a)(1) then requires the excavator to “determine the exact location of the subsurface installations in conflict with the excavation using hand tools before using any power-driven excavation or boring equipment” inside that zone. A drill rig is boring equipment. Vacuum excavation may be substituted only if the excavator declared that intent when the ticket was obtained and the operator agreed; the other exceptions cover breaking out pavement with no installation in it, and equipment the state’s Dig Safe Board approves by regulation. CGA 5-20 lists the methods to consider generally: pot holing, hand digging, soft digging, vacuum excavation, pneumatic hand tools, or other mechanical methods with the facility owner’s approval.
Note what none of it covers. The tolerance zone is defined on a horizontal plane. OSHA’s bulletin on directional drilling states the position plainly: “Underground service locators typically cannot provide depth information for utility lines.” A ticket tells you where a line is in plan. It gives you nothing to build a profile on.
What a locate mark is a measurement of
Radiodetection puts it in one sentence: “Electromagnetic locators do not locate pipes and cables; they locate alternating magnetic fields.”
A current I in a long straight conductor produces a field at distance r of B = μ₀I / (2πr) — inversely proportional to distance. The receiver is a coil reading that field, and depth comes from reading it twice at once. In a twin-aerial instrument the coils sit about 400 mm (16 in) apart on a vertical axis. With the lower coil a distance d above the line and the coils x apart, the readings go as I/d and I/(d + x), and the instrument solves
d = x · Et / (Eb − Et)
where Et is the top coil and Eb the bottom. That arithmetic assumes one straight isolated conductor in an undistorted field. Radiodetection puts most location problems down to fields that are not like that, with the instrument’s own resolution setting a floor under the rest, and publishes the consequences as a percentage of the line’s own depth d:
| Ideal | Long straight isolated line, limited only by instrument resolution: single horizontal aerial ±10% of depth; vertical aerial and twin horizontal aerials ±5%. |
|---|---|
| Near a 90° bend | Twin horizontal aerials reach 16% plan error; a single horizontal aerial 25%; a vertical aerial 33%, with its 10% error band extending 5d either side of the bend. |
| Parallel lines, opposing currents | Similar signals running in opposite directions. Twin horizontal aerials reach 50% of depth, falling to 10% once the lines are 1.2d apart. A vertical aerial can be 100% out. |
Put a number on the bad case. Two parallel lines 4 ft down carrying similar signals in opposite directions, less than 1.2 × 4 ft = 4.8 ft apart: the plan error can reach 50% of 4 ft, which is 24 in. A 2 in line whose centreline sits 24 in from the paint lies wholly outside an 18 in tolerance zone drawn around that paint, and on the very edge of California’s 24 in zone — half of it outside, if the mark does not state the size — while the mark looks exactly like a good locate.
CGA Best Practice 4-12 covers how the signal is applied, which decides how much of this you suffer. Direct connection — a lead from the transmitter to the facility itself, with a ground lead to a ground point completing the circuit — gives the strongest signal and is least likely to bleed onto adjacent lines. An induction clamp is next. Broadcast induction, with the transmitter simply set on the ground, is worst: “a weak signal that will ‘bleed over’ to any conductor in the area.” CGA says to use the lowest frequency at the lowest power output that completes the locate; Radiodetection gives the reason, which is that higher frequencies couple more easily onto other conductors nearby.
On plastic pipe, you are locating a wire
Polyethylene is not conductive and produces no field. 49 CFR 192.321(e) requires unencased plastic pipe to have “an electrically conducting wire or other means of locating the pipe while it is underground”, with tracer wire or other metallic locating elements resistant to corrosion; 192.361(g) extends that to non-metallic service lines. So the locate on a plastic gas main is normally a locate of a tracer wire laid with it. If the wire is broken or corroded through, the signal fades at the break, and what the receiver follows beyond it may be signal that has coupled onto a neighbouring metallic line. The mark is then correct for the wrong object.
Abandoned lines are the same problem from another direction. CGA 4-11 states that abandonment, damage, or limited access points “may render an abandoned line non-locatable”, and that once located or exposed it is treated as live. CGA 4-23 exists for the case where the locator arrives and cannot establish the tolerance zone with confidence at all; it calls for escalation to vacuum truck, line tracer, ground penetrating radar or in-line 3D gyro mapping before the required marking date. Radar is the fallback where there is nothing to trace, and CGA gives its working band as 200–900 MHz, higher frequencies buying resolution at the cost of penetration, with conductive soils obscuring the return.
CGA’s 2021 damage report names the effect: “Locator Error can be considered a general ‘catch-all’ root cause that masks deeper root causes such as bad maps, tracer wire and abandoned facility issues.”
Depth is not a constant
Minimum cover for gas pipe comes from 49 CFR 192.327 and 192.361(a). These are minima, not design depths:
| Transmission, Class 1 | 30 in (762 mm) normal soil, 18 in (457 mm) consolidated rock |
|---|---|
| Transmission, Class 2–4 | 36 in (914 mm) normal soil, 24 in (610 mm) rock |
| Buried main | 24 in (610 mm) |
| Service line | 12 in (305 mm) in private property, 18 in (457 mm) in streets and roads |
192.327(c) then permits less cover on a transmission line or main “where an underground structure prevents the installation” at the minimum, provided it gets additional protection to withstand anticipated external loads. 192.361(a) makes the same allowance for a service line, and 192.327(d) lets a main go shallower than 24 in where state or municipal law sets a lower minimum for mains laid in a common trench with other utilities. A gas service crossing a front yard at 12 in is code-compliant. A main that dived under a storm drain and never came back up is code-compliant. After installation the ground moves: OSHA lists lines that “are buried at depths different from code requirements, or are in a different position from initial installation due to ground settling”, and regrading, resurfacing and erosion all change cover after the as-built was filed.
What the damage data says
CGA’s 2025 DIRT Data Summary & Trends, published July 2026: 221,717 unique damage reports, and the CGA Index — CGA’s statistically modelled measure of year-over-year damage levels in the United States — at a record 102, eight points above 2023. Telecom and cable TV accounted for 51% of facilities damaged, natural gas 36%, electric 8%, water and sewer 5%. The top ten root causes covered 86% of reports with an identified root cause. No notification to 811 remained the largest single one, at 22.3%. Next came the excavator failing to maintain clearance after verifying the marks (14.8%), the facility not marked because of locator error (14.2%), and marks placed inaccurately because of locator error (9.2%). Digging before verifying the marks by potholing was fifth, at 7.2%.
For directional drilling, CGA’s 2021 report analysed the 9,054 reports where HDD was the equipment. Contractors were 95% of known excavator types, most of them, CGA judged, likely working for a utility; its conclusion was that most HDD damages are facility operators and their contractors damaging each other and themselves. Locating practices was the leading root cause group; within excavation practices, failure to pothole and to maintain clearance led. CGA states the structural problem with the method directly: “unless potholing is performed, there is no visual verification that the drill path has successfully crossed existing buried facilities with no contact. Additionally, if the drill does damage another buried facility, some time may pass before it is realized.”
That delay is not hypothetical. The Gas Technology Institute records an HDD machine damaging a 12 in high-pressure natural gas transmission line at Asheville, North Carolina in 2003; the pipe failed on 10 January 2014, more than ten years later. The same GTI document defines damage as “any impact or contact with an underground facility, its appurtenances or its protective coating, or any weakening of the support for the facility or protective housing which requires repair”. A gouge through the coating of a steel pipe leaves bare steel in the ground, and the leak that follows can arrive years later on someone else’s shift.
And potholing only proves what is in the hole. OSHA’s account of the February 2013 Kansas City explosion: hand-dug potholes along the planned drill path found two lines two feet down. The crew presumed one was the gas line they were avoiding, though it sat shallower than expected. Both were electrical. Without verifying that, they drilled deeper and struck the gas line below. A restaurant worker was killed and three HDD workers were severely injured.
The planning consequence
All of the above is uncertainty with a known shape: a plan position carrying a tolerance zone of 18 in or more, a position error that grows near bends and parallel runs, a facility that may be a tracer wire rather than the pipe, and a cover figure that was a legal minimum decades ago. A profile that records those quantities separately can be checked. One that records a single depth per utility cannot.
BorePlanner Coming soon is our Android and Windows tool for that work: bore path depth profile, utility clearance and bend-radius checks, with USGS lidar elevation cached for offline use on site. Utilities go in by station, depth to top and size, and the clearance check measures to the wall of the reamed hole rather than to the pilot rod. On Android, survey points can be taken from the phone’s own GNSS receiver or through RTK corrections, and points taken with the GPS buttons are tagged with how they were measured — plain GNSS, RTK float or RTK fixed — so a plain phone fix is not mistaken for an RTK one.
See also: potholing and vacuum excavation — when exposure is required and how much clearance survives reaming.
Sources
49 CFR 198.37; 49 CFR Part 196; 49 CFR 192.321, 192.327, 192.361; 29 CFR 1926.651. CGA Best Practices Guide Version 22.0, March 2026, practices 4-11, 4-12, 4-23, 5-19, 5-20. CGA DIRT: 2025 Data Summary & Trends, July 2026; 2021 DIRT Report, Horizontal Directional Drilling section. California Government Code §4216 and §4216.4. Michigan Compiled Laws §460.723. OSHA SHIB 03-13-2018, Avoiding Underground Utilities during Horizontal Directional Drilling Operations. Gas Technology Institute, Trenchless Best Practices for Damage Prevention, Version 17 Final, 3 May 2016. Radiodetection, The Theory of Buried Cable and Pipe Location, sections 4, 10, 11 and 14.