The Department of Defense (DoD) needs better tools to help its personnel involved in remediation of unexploded ordnance (UXO) and nonhazardous items to more quickly and safely identify filler materials. This ability would significantly lower the dangers to personnel and the cost of remediation.

This new filler identification (ID) technology utilizes acoustic waves to identify the materials inside sealed UXO. Acoustic waves are high-frequency pressure fluctuations that travel through materials (sound). Small sensors clamped to the outside of the ordnance item send low-energy acoustic waves through the shell walls and filler material. The received signals are processed to determine the characteristic acoustic properties of the filler material. These properties are then compared to a database of properties for known filler materials.

Currently, no cost-effective instrument is in routine use to identify the fillers in UXO. The demonstrated technology would permit personnel to quickly identify hazardous items and optimize remediation efforts. Significant cost savings can be achieved through more efficient procedures and reduction of false identifications.

The only known technology being developed for filler ID relies on detection of gamma rays emitted by stimulating the ordnance item with a neutron beam. One system that uses this technology is termed pulsed elemental analysis with neutrons (PELAN). PELAN is a man-portable system for explosives detection based on the principle that explosives contain various chemical elements such as H, C, N, O, etc. in quantities and ratios that differentiate them from other innocuous substances. Although PELAN can provide accurate filler ID for larger UXO, it often gives false readings for smaller ordnance because the signal from the explosive is overwhelmed by signals from the surrounding environment.


The objective of this work was to demonstrate and validate a new technology to identify the filler material in UXO. This technology, developed under a two-year Strategic Environmental Research and Development Program (SERDP) project (MR-1382), has been tested at several DoD lab and range facilities. The ability to correctly identify important inert filler types has been demonstrated on actual ordnance. The purpose of this ESTCP demonstration was to conduct field tests at an active test site to validate filler ID under field conditions.

Demonstration Results

The acoustic technique was tested in March 2009 at an active remediation site in Vieques, Puerto Rico. Unfortunately, these tests were disappointing because, even with the 3-month “set-aside” effort, the number of ordnance items in the correct size range was very limited. During the test week, the acoustic system was moved from one site to another testing any items that were near the targeted size range. Over a total of about 10 field sites with smaller ordnance, the demonstrators were able to test about 20 items. Unfortunately, many of these were very corroded and no acoustic signals were received at all through these items.

The multi-year ESTCP field tests showed that, although the technology will not identify all ordnance types and filler materials, it provides a simple, low-cost way to ID some of the most common inert filler materials. The technology works best on fillers that are cast into the shell body and are intimately bonded to the metal walls. Thus, plaster of paris (POP), wax, and cement fillers provide good signals for identification, whereas loose sand and gravel do not. Although signals for other cast filler materials have been measured, high explosive (HE) fillers do not provide strong signals for ID. Although corrosion reduces the amplitude of the received signals, good signals were received in the laboratory for a number of highly corroded items filled with cement and POP. However, as learned during the Vieques tests, the acoustic technique will not work for heavily corroded shells where the case has burst and swollen beyond the nominal outer diameter

Implementation Issues

Unfortunately, because of the limitations of the active test site, this study did not provide an adequate validation of the acoustic filler ID technology. The Vieques, Puerto Rico, site just did not provide inert-filled UXO of the required size for testing the acoustic technique. In addition, all efforts to identify an alternate field site with appropriate UXO have failed.

Although some of the test results were encouraging (MK82 cement bombs), much more field data is required to adequately evaluate the acoustic technique. Suitable testing of the current acoustic technology would require a large number of small (less than 90 mm) inert filled items that had low corrosion (case is not swollen and burst open).