Tellus environment - Cartographier l'invisible pour agir

Gas cylinder detection at Le Blanc-Mesnil (Seine-Saint-Denis)

Published in Environment

  • Client: SIAAP
  • Domaine: Sites & sols pollués
  • Moyens utilisés: Le magnétomètre GSM19 à effet Overhauser


For the construction of a wastewater treatment plant, on behalf of the SIAAP (water management institution for the Parisian region), it is necessary to remove gas cylinders buried on a 5000 m2 site at Le Blanc-Mesnil. The DI Service company entrusts to Tellus Environment the task of diagnosing and mapping the underground.


The mission takes place in 2 successive stages. The first stage consists in a georeferenced measuring session of 2 magnetic quantities, i.e. total field and vertical gradient. The second stage consists in exploiting as quickly as possible the recorded magnetic data, by using the Magsalia process. The issue lies in locating in latitude, longitude and depth the ferrous magnetic masses, which could indicate the presence of buried gas cylinders.


Methods and equipment

The measuring equipment used for the mission is a dual Overhauser effect GSM19 magnetometer, developed by the GEM company, and equipped with a decimetric GPS antenna used for locating the measures. This equipment has been rented from the Abem-France company.

An initial shaping of the maps in total field and gradient could thus be produced with the provided software and equipment.


Results and customer benefits

The Magsalia process produces two types of tomographic pictures, using magnetic data. First type pictures locate, in a three-dimensional system, magnetic targets, whether isolated or extensive. Second type tomographic pictures locate, in three dimensions, magnetic masses. The juxtaposition of the two pieces of information induces a pre-classification of targets (magnetic anomalies) and makes easier their interpretation.

The survey lasted 2 days and was followed by a quick extrication of the magnetic anomalies. 24 anomalies have been pegged on the field. The files recording and inversion through the Magsalia process has allowed to produce maps, with a sufficient precision to extricate cylinders, fragments of cylinders and other ferrous and cumbersome objects with a mass comparable to, or of the same order of magnitude as the mass of a gas cylinder, or with a lower mass.



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