The theory sounds great: Whenever a building permit is issued, part of the due diligence on part of the building contractor is to figure out, if the grounds first must be searched for unexploded ordnances (UXOs). A central authority maintains and updates a state-of-the-art GIS to classify regions as potentially dangerous. The GIS also specifies a 'bomb horizon', a maximum depth in which aerial bombs are expected to be buried depending on the soil conditions. In other words, suspect sites are defined in 3-dimensional space.
Companies specializing in locating UXOs surveys employ a variety of technologies to scan suspect areas. The most convenient and least costly above-surface screening
methods, however, are only able to reliably detect warfare agents that are buried a few meters under the surface. Bomb horizons often reach into depths of more than 15 - 20 m necessitating the use of more intrusive scanning methods. The most common technique is to drill a vertical hole with a small diameter of, say, 10 cm and insert a magnetometer, which "takes real time readings of the amplitude of the Earth’s magnetic field. Buried ferrous items [...] are manifested as anomalies in the data that are invaluable for locating buried metal objects such as tanks, drums, pipes or bombs." (see full article)
 |
| Magnetometer plot indicating a UXO or ferrous item at 3 m depth (source: www.conepenetration.com) |
Here comes the chicken-and-egg
problem: Do you first drill the hole and then scan it or do you scan first and
then drill step-by-step each time reinserting the magnetometer? The latter practice allows you to only
drill into grounds that have previously been surveyed and "signed free" by a field expert. In practice,
however, this is a very time-consuming and costly process. Therefore, it is common practice for companies to drill the hole first, thereby risking
that their drilling tools directly and unknowingly penetrate potential UXOs, and then insert their magnetometers in order to scan the
surrounding building ground! In fact, since my company (Neidhardt Grundbau GmbH) is a leading provider of geotechnical engineering services, I have witnessed this practice many times first hand.
German government authorities have long turned a blind eye
toward the warfare agent detection methods employed in the private industry.
The problem exacerbates when the circumstances become even trickier: In the rapid rebuilding efforts post WW2, buildings, tunnels, and bridges were erected without regard for the potential hazards buried underneath. Building projects in urban areas often require the intrusion of neighboring building grounds to install pipes, drill ground anchors, etc. Especially ground anchors, often measuring 30+ m in length, can reach far underneath adjacent building structures that literally sit on a ticking bomb. Traditional survey methods fail under these circumstances as magnetometric readings become too distorted by surrounding "noise", i.e. ferrous foundation plates. Until now, government has largely ignored the threat giving permission to building companies to carry out their tasks in spite of the apparent threat because no solution yet existed.
A new proprietary GIS technology that is supposed
to circumvent this problem has for the first time been successfully tested on a
site in Hamburg, Germany, last year. A GIS based detection device is introduced
into the bore hole as the drilling tools perforate the building ground
allowing for real-time uninterrupted scanning and drilling at the
same time. The precise GPS coordinates are then automatically transferred
to a warfare agent specialist on the site, who monitors the resulting readings
and prompts for a production halt whenever a potential hazard is being
discovered. The data is then fed to local authorities in order to update the
governmental warfare agent mapping database.
