The distribution of dumped ammunition in lake Mjøsa – autumn 2022 mapping

Following a decree from the Norwegian Environment Agency to the Norwegian Ministry of Defence (MoD), the Norwegian Defence Research Establishment (FFI) was tasked by the MoD to conduct a survey in lake Mjøsa to better establish where ammunition had been dumped. The survey was conducted using FFI’s autonomous underwater vehicle (AUV) “HUGIN HUS”, assisted by FFI’s autonomous surface vehicle “Ratatosk” from 7th to 19th of November 2022. Most of the dumped ammunition has been left in areas with a soft, muddy bottom and active sedimentation. Thus, much of the smaller crates and grenades are covered with mud and sediment. The survey shows that ammunition has been dumped in a large area outside Totenvika, covering approximately 7.1 km2. This is almost 10 times larger than the area marked in a map by Raufoss Ammunisjonsfabrikk (RA), the munitions factory that dumped the ammunition. The area is comparable in size to similar known dumping areas in the sea. Moreover, it might even be somewhat larger because our mapping was only conducted in areas deeper than 50 m. The dumping area between Gjøvik and Mengshol follows a ferry lane, and the surveyed area suggests a dumping area of 0.11 km2. However, we have indications that ammunition has also been dumped fairly close to the ferry landing, and if so, the area is closer to 0.31 km2. In the impact area of the shooting range, we observed a large number of Sidewinder missiles. They are all confined in an area of 1.3 km2 east of the Totenvika dumping ground. After an overall assessment, FFI recommends that all ammunition should be left in place. The ammunition is already covered or partly covered by mud and sediment, and this covering will continue in the future and gradually reduce any contamination. Furthermore, there are no indications of explosive compounds in the water today. FFI therefore does not recommend any measures be taken because disturbance may lead to dispersion of any contaminants and would constitute a safety risk. From an economical and sustainable point of view, it is hard to justify implementing any actions to retrieve or cover the ammunition. FFI recommends mapping the contamination in the dumping ground outside Totenvika, where no previous measurements have been done. Based on those results, the need for further mapping and monitoring of the dumping ground should be assessed. If the results are similar to those from Gjøvik, no ordinary monitoring is needed. FFI considers monitoring at intervals of 10–20 years will be sufficient.