Ground-penetrating radar transmits electromagnetic pulses into concrete or soil and reads the reflections. In concrete, GPR reliably locates rebar, post-tension tendons, conduits, and voids near the surface. In soil, it can locate utilities, tanks, disturbed ground, and subsurface anomalies — with more variability.
GPR does not produce X-ray vision. Detection depends on soil conductivity and moisture, target depth and material, antenna frequency, surface access, and the contrast between a target and its surroundings. Wet clay soils, common in parts of Hawaiʻi, attenuate signals quickly; dry sandy soils scan much deeper.
A professional GPR provider tells you the confidence and limitations of each finding rather than presenting every mark as certainty. Findings should be GPS-referenced and, ideally, integrated with GIS, survey, and CAD data so they remain usable after the crew leaves.
Scanning before drilling, cutting, or excavation is cheap insurance: hitting a post-tension tendon or a primary electrical duct costs orders of magnitude more than the scan that would have found it.
HAVE THIS EXACT PROBLEM?
Start with a one-hour technical assessment at $199 — you keep the diagnosis either way.
RELATED ANSWERS
This article is general information, not engineering, legal, or safety advice for any specific project. Site-specific conclusions require assessment by qualified — and where required, licensed — professionals.