[en] The Ilimaussaq intrusion contains the water soluble mineral Villiaumite (NaF). The estimated content is 21 000 ton of NaF (10 000 ton of F). An estimated 175 Ton NaF is transported annually to the Narssaq bay through the Narssaq river. A measurement programme was set up before the tunnel work was begun and the programme was conducted until one year after in order to demonstrate wether the concentration of NaF in the river water was increased by the tunnel work. The concentration was measured periodically up streams and down streams of the working area. It was found that the concentrations in the two points varied greatly over the year. In summertime with high water discharge the concentration was around 2.5 ppm F, whereas in wintertime with low water discharge the concentrations reach values as high as 30 ppm F in both points. However the ratio between the concentrations in the two points was fairly constant through the whole period. This indicates that the tunnel work has not caused any measurable increase in the concentration of F in the river water. Only in seepage from the waste tip underneath the tunnel higher than normal concentrations of F can be found. (author)