French Sea Trials on Chemical Dispersion: DEPOL 04 & 05

Abstract

In 2004 and 2005, Cedre organized sea trials off the coast of Brittany with the French Navy and in collaboration with the French Customs. While the 2004 trials were large experiments looking for global assessment of the technique of dispersion, the 2005 sea trials were small scale sea trials focused on the efficiency of the dispersant product itself. The 2004 sea trials, DEPOL 04, involved three controlled oil discharges which were treated with two chemical dispersants using aerial spraying equipment, (Cessna equipped with a spraying POD) and shipborne spraying equipment. The slicks’ evolution was monitored with remote sensing techniques, sampled for analysis and measured in-situ with spectrofluorometry. The objectives of these sea trials were:

• To study the natural weathering of the slicks

• To assess the chemical dispersion of the slicks

• To assess the operational possibilities of the spraying systems

• To run the annual Bonnex intercalibration exercise of the remote sensing means of the Bonn Agreement members

• To test new remote sensing devices under development

• To test roughly an oil recovery device purchased recently by the French Navy, (Sweeping Arm), to equip its spill control vessels.

The 2005 sea trials, DEPOL 05, aimed to establish an at sea testing procedure on small oil slicks to assess the real efficiency of dispersants versus different oil types. This paper presents these sea trials and their results considering mainly the chemical dispersion. For DEPOL 04, the dispersant treatment gave positive results despite the very calm meteorological conditions:

• Although the first slick was not totally treated with dispersant, most of the oil was dispersed.

• The comparison of the last two slicks’ evolution tends to show either a significant advantage of the aerial treatment over the ship-borne one, or a higher efficiency of one dispersant over the other one.

For DEPOL 05, an operational incident forced the planned testing program to stop prematurely, but the proposed procedure proved to be promising: such a testing method will allow the running of an important number of comparative tests while working with controlled application conditions especially the dispersant-oil-ratio.