Last updated 2026-07-17
A tank sweep is a non-invasive scan of a property to find out whether an underground storage tank (UST) is buried on it. In New Jersey — where tens of thousands of homes once heated with oil — it has become a standard step in buying an older house, right alongside the home inspection and the radon test.
Nothing is dug up. A technician walks the property with detection equipment, checks the house for tell-tale plumbing, and issues a written report, usually the same day.
From the 1930s through the 1980s, heating oil was the default fuel across much of NJ. The oil lived in a steel tank, very often buried in the yard for convenience. As natural gas lines spread, homeowners converted their furnaces — and in many cases simply disconnected the old tank and left it in the ground.
Decades later, those forgotten steel tanks are at or past the end of their service life. NJDEP classifies residential heating oil tanks as unregulated USTs — the state does not require owners to register or remove them — so there is no official inventory. The only way to know whether a specific property has one is to look. That is the sweep.
Magnetometer (the screening tool). A magnetometer senses disturbances in the local magnetic field caused by buried ferrous metal. A 550-gallon steel tank produces a large, distinctive signature. The technician walks a grid across the lawn, driveway edges, and foundation perimeter, watching for spikes. It is fast and covers ground efficiently — but it cannot tell a tank from a buried car hood or a cluster of construction debris.
Ground-penetrating radar (the confirmation tool). GPR sends radar pulses into the soil and reads the reflections, producing a cross-section image of what is below. Over a magnetometer “hit,” GPR can show a tank-shaped object at tank-like depth — or reveal that the anomaly is a pipe, boulder, or scattered metal. Many NJ sweep firms now include GPR follow-up in their standard price.
The eyes-on checks. Equipment aside, experienced technicians look for physical evidence: fill and vent pipes at the foundation (sometimes cut off at grade and buried under mulch), copper supply lines entering the basement wall, patched holes near the furnace, and records of an oil-to-gas conversion. A sweep that skips the interior check is incomplete.
| Method | What it does well | What it can’t do |
|---|---|---|
| Magnetometer | Fast full-lot screening for buried steel | Can’t distinguish a tank from other metal |
| GPR | Images shape/depth of an anomaly; finds non-steel voids | Slower; interpretation requires skill |
| Visual/interior inspection | Finds pipes, lines, conversion evidence | Only catches what’s visible |
A proper sweep report states the areas scanned, the equipment used, and any anomalies found, usually with a sketch or photos. Two honest limits:
This is where NJ’s contract mechanics matter. After the three-business-day attorney review, standard NJ contracts give buyers roughly a 10–14 day inspection window. A tank discovered in that window is a negotiable inspection issue. Typical paths, in rough order of frequency:
If a removal happens and a leak is discovered, New Jersey law requires the discharge to be reported immediately to NJDEP at 1-877-WARNDEP (1-877-927-6337), and the cleanup path runs through the state’s Unregulated Heating Oil Tank (UHOT) program — covered in our leaking tank guide.
New Jersey certifies UST contractors — categories under N.J.A.C. 7:14B include tank closure and subsurface evaluation — but there is no state certification for the sweep itself. So vet on substance: full-lot coverage, magnetometer plus GPR capability, interior inspection, a written same-day report, and independence (a firm that profits from removals has an incentive a pure sweep company does not). Sweeps in NJ generally run $200–$500; see our sweep cost guide for the breakdown.
A sweep detects buried metal masses and subsurface anomalies consistent with an underground storage tank. It flags the likely presence and location of a tank; it does not tell you the tank's condition or whether it ever leaked.
They answer different questions. A magnetometer finds buried ferrous metal quickly across a whole yard; GPR images the shape and depth of an anomaly so you can tell a tank from buried debris. The strongest sweeps use the magnetometer to screen and GPR to confirm.
No. NJDEP certifies UST contractors for activities like closure and subsurface evaluation under N.J.A.C. 7:14B, but a geophysical sweep itself is not a certified category. Vet sweep companies on equipment, experience, and whether they issue a written report — and note whether they also hold NJDEP UST certifications for follow-on work.
No law forces a seller to remove a non-leaking tank, so it comes down to negotiation during your inspection contingency. In practice many NJ deals resolve with the seller removing the tank with permits and providing soil results, because most buyers, attorneys, and some lenders will not proceed otherwise.
It is uncommon with a thorough sweep, but possible — tanks under additions, decks, or deep interference can be obscured, and a sweep only covers accessible ground. That is one reason to hire a firm that scans the full lot and checks the house interior for old oil lines, not just the perimeter.
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