Proximity vs positive read — the cost of the shortcut on private-side sweeps

A proximity read and a positive read look similar on a mark-out sheet. Both produce a point on plan and a depth estimate; both produce a coverage row on the closeout. The difference is what the field team actually did, and it shows up the first time a contractor excavates against a mark-out that read as proximity rather than positive. A proximity read says a line is near here. A positive read says a line is here, and the team induced a signal and watched the receiver respond at this mark. The two reads are not interchangeable, and treating them as interchangeable is the shortcut that compounds into strike risk.

The shorthand is that proximity reads happen when the field team cannot induce a clean signal on the target line — typically because the access does not allow direct connection, because the material response is masked by adjacent assets, or because the receiver is being used in a mode that records response curves rather than discrete target reads. A team running a proximity read will still mark a point on plan; the receiver is responding to something in the corridor, just not necessarily to the target the corridor was supposed to locate. The mark-out ends up ambiguous, and the ambiguity is what the contractor inherits.

The methodology fix is to name the read-state on every mark. A target that the team induced a signal on and read positively at the mark is recorded as a positive read with the depth estimate that came with the read. A target that the team cannot induce a clean signal on, but where the receiver is responding to an adjacent asset in the corridor, is recorded as a proximity read and flagged for re-attempt with a complementary method. A target that the team cannot read at all is recorded as undetermined, and an undetermined asset in a planned excavation corridor is treated as a potholed-and-confirmed point before the contractor is mobilized.

What changes about pre-field intelligence is the up-front honesty. A program team that runs a single-method sweep on a complex corridor will default to proximity reads, and the mark-out will read as a coverage row rather than as a per-asset verification. The shift to multi-method verification — picking the method up front that lets the team read each target positively rather than proximately — is the shift that turns the closeout into a contractor-ready artifact. The cost of the shortcut is paid by the contractor who excavates against an ambiguous mark, not by the team that produced the mark, and the compounding is exactly what the SureTrace framework is designed to displace.