Throughout the world, unexploded ordnance (UXO) pose a severe threat to all people and the environment.  The United States Department of Defense (US DOD) has owned and/or operated on over 100 million acres in the US, as well as thousands more acres in other countries.  The militaries of many other nations, as well as paramilitary and rebel groups, have also owned or controlled millions of acres all over the world.  In the US, DOD sites include former military installations or FUDS (Formerly Used Defense Sites), installations undergoing Base Realignment and Closure (BRAC), and currently active installations.  Overseas, there are similar active and former military sites, as well as active and former war zones.

Subsurface UXO can range in size from less than 20 mm projectiles to 2000-pound bombs, come in myriad shapes, and can be buried at depths of inches to tens of feet. UXO items occur singly, as well as in clusters or massive caches.  They have been fired, dropped, intentionally set (e.g. land mines), or disposed-of (either officially or clandestinely) a day ago to more than a century ago.  In addition, UXO sites are not limited to land, but include underwater firing ranges, mine fields, and disposal areas.

With their primarily metal construction, detection of UXO items is usually less difficult than discrimination and identification (an exception is modern nonmetallic land mines).  That is, real expertise lies in the abilities to discriminate between UXO items and (for instance) soup cans, fire extinguishers, bicycle seats, or any of the other common debris items that are ubiquitous in developed areas, and to identify the type of a buried UXO item. Discrimination is critical for reducing false positive UXO identifications (no one wants to spend the money and time required to dig an innocuous oil filter as if it were a live grenade), while identification allows others to choose the proper “render-safe”, “blow-in-place”, or removal procedure.

Enviroscan employs a range of geophysical methods to detect, discriminate, and identify buried UXO. The simplest detection methods involve field-screening with handheld metal detectors or magnetometers, with real-time marking of buried targets (the classic mag and flag method).  On sites where a permanent record of target locations and signatures is desired, or if discrimination/identification are to be attempted, Enviroscan performs digital geophysical mapping using total field or full vector magnetometry (MAG) and time- or frequency-domain electromagnetics (EM) with hand-held systems or vehicle-towed, multi-sensor arrays.  We have performed MAG and EM mapping surveys on land, underwater, and from the air on sites ranging from less than 500 square feet to hundreds of acres, and have generated dig sheets with only a few to over 15,000 targets.

Because of the small size of many UXO items, precise navigation is required to map and relocate targets. Therefore, Enviroscan attains high-resolution location control using global positioning systems (GPS), auto-tracking robotic total stations, and where necessary, low-tech lane marking with a tape and transit.  In all cases, measurement stations or lane end points, as well as survey grid corners are tied-in to any geospatial coordinate system specified by the client.

In order to provide the best available technology for UXO discrimination and identification, we employ the latest MAG and EM data fusion and analysis methods, as well as ground penetrating radar (GPR).  Targets are classified by calculating various instrument response ratios, and comparing them with generic UXO signature catalogs or site-specific signatures from onsite test grids containing most-probable munitions.  Target depths are estimated using MAG and EM depth inversion based on anomaly wavelengths, and where applicable, GPR travel times (calibrated in the onsite test grid where available).

Enviroscan personnel all have specific, formal UXO training and experience, and are not just adapting other or general geophysical knowledge to UXO sites. Our UXO training, experience, and on-the-job activities remain focused not just on the performance metrics of accurate detection, discrimination and identification of UXO, but even more importantly, on safety.