A portable nuclear gauge used to test soil and pavement sat unattended at a Hampton Roads Bridge-Tunnel job site for about 25 hours before it was recovered undamaged. The Nuclear Regulatory Commission logged the lapse as event 58493 after Virginia’s radioactive materials program reported it on Oct. 13. The state and the licensee reported no apparent exposures, and a formal state investigation is planned.
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The device was a Troxler model 3440 moisture and density gauge, serial number 31062, which holds two radioactive sources. It belonged to DMY Engineering Consultants, and the lapse began when an employee went back to the office with only the carrying case.
How a gauge ended up alone on a job site
Under the NRC event report, the authorized user returned to the office on Oct. 11 with the empty case and left the gauge itself at the Hampton Roads Bridge-Tunnel site. The general contractor told the licensee about the gauge at about 8 a.m. EDT on Oct. 12. The gauge had been unattended from about 8 a.m. on Oct. 11 to about 9 a.m. on Oct. 12, and it was recovered at about 9 a.m. that morning. Put plainly, the lapse lasted roughly a day, with the case back at the office and the instrument itself on the site, and the fix that followed was a return to the licensee for leak testing. The licensee’s radiation safety officer reported the event to the state by telephone within 24 hours.
The licensee is listed as DMY Engineering Consultants of Hampton Roads, under license 107-540-1. Virginia assigned incident number VA260006, and Tyler Hale made the report on behalf of the state’s program, according to the NRC record. The material is rated “Less than Cat 3,” which is how the report classifies the material involved.
Cesium-137 and americium-241 inside a Troxler 3440
The record lists two sealed sources in the gauge: 8 millicuries of cesium-137, serial number 750-5681, and 40 millicuries of americium-241/beryllium, serial number 47-10729. A millicurie is a thousandth of a curie, and the curie is defined as 37 billion decays per second. Those sources do different jobs. As the entry on nuclear density gauges explains, cesium-137 supplies the gamma rays used to measure density of shallow layers such as roads, while an americium-241/beryllium source supplies neutrons whose slowing by hydrogen reveals moisture.
The Environmental Protection Agency’s cesium-137 page gives a half-life of about 30 years and says a large external exposure to a strong industrial source could cause burns, acute radiation sickness and death, and that its gamma radiation raises cancer risk. Those are the outcomes sealed-source rules exist to prevent. Those effects describe large exposures to strong sources; the report finds none of that here, but a gauge left alone overnight is still a lapse in control of licensed material, and that is why it was reported.
The gauge works by positioning a source against the ground and counting the radiation that comes back or passes through. The entry on density gauges describes two modes: direct transmission, in which a retractable rod is lowered into a pre-drilled hole and a denser material gives a lower detector count, and backscatter, in which the rod stays level with the detector and a denser material scatters more radiation back. Crews use the readings to judge how well soil, gravel or asphalt has been compacted, which is routine work on roadway projects and is the reason such gauges travel between job sites.
What the survey and the state found
According to the report, the gauge was undamaged and appeared untampered with, and both sources remained in their shielded or intact positions. A survey measured 0.05 millirem per hour at 1 meter. The device was returned to the licensee for leak testing, which checks that the sealed sources are not shedding material. The report states: “There were no apparent exposures as a result of this incident.”
Virginia’s program, which the NRC record labels an Agreement State report, will conduct a formal investigation. Nothing in the record says what the contractor’s site looked like overnight, whether the gauge was in a vehicle or on the ground, or whether anyone approached it, and those are likely questions for the state. The NRC’s record was last updated Oct. 13.
The Hampton Roads Bridge-Tunnel is a busy crossing between Hampton and Norfolk that is undergoing a multibillion-dollar expansion, so job sites in the area are active. The entry on the crossing puts the expansion, which adds two new two-lane bridge-tunnels and widens the corridor to four lanes in each direction, at $3.3 billion, with completion moved to February 2027. That is background for the setting only. Nothing in the gauge report links the licensee to that program. The NRC record does not tie the gauge to any particular contractor or phase of that work, and the report calls the location only a Hampton Roads Bridge-Tunnel job site.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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