Storage and pumping of jet-fuel have caused a severe contamination of soil and groundwater at a military facility in Denmark. The contamination was detected in 2001. The Danish Defence has conducted 3 a series of investigations and set up a skimmer system, that has recovered approximately 25 m of jetfuel. In 2005, the recovery stopped, and the remaining jet-fuel is trapped as a residual light non-aqueous 3 2 phase liquid (LNAPL) comprising approximately 45 m jet-fuel in a 1000 m source area. In the ground water downstream of the source area, there is an extensive diving plume of contaminants. In part of the source area, the Danish Defence and NIRAS have launched a pilot Scale Surfactant Enhanced Aquifer Remediation (SEAR) in order to demonstrate mobilization of LNAPL from the sedi® ment. The pilot remediation was carried out using non-ionic surfactants (Ivey-sol ) from Ivey International Inc. for injection in a line of injections wells. The mobilized oil and injected surfactants were recovered from a downstream line of extraction wells. The recovered oil/ground water was treated on site, and the treated water was re-injected up-gradient in a line of hydraulic control wells. The effect of the pilot SEAR was monitored by sampling and analyzing the ground water from the extraction wells and by estimation of trapped jet-fuel in an oil-water separator as part of the on-site treatment, supplemented by post soil sampling/analyses from boreholes. The 3 different methods gave different results for the mass balance, and the estimated effect of the pilot remediation ranged from 25 kg to 150 kg of hydrocarbons.