The groundwater at Gardermoen is in a gravel bed left behind by the last Ice Age some 10,000 years ago. Groundwater is formed by precipitation seeping down through the gravel and filling the spaces between the gravel with water. The size of the groundwater reservoir therefore varies from year to year, depending on the amount of precipitation.
The part of the gravel bed that permanently contains water is called the saturated zone. Between the earth’s surface and the groundwater is a zone that is not filled with water. This is called the unsaturated zone. The boundary between the saturated zone and the unsaturated zone is called the water table. The water table is not flat. To put it simply, we can say that it roughly follows the contours of the terrain.
The highest point in the water table is called the groundwater divide. The divide runs as a ridge right across the airport area. The groundwater southwest of the divide flows into an area with ravines. Northeast of the divide the groundwater flows toward Lake Hersjøen and the kettle lakes. The groundwater reservoir in the Romerike district measures about 100 km2. The airport area lies above one tenth of the reservoir. The depth of the groundwater inside the airport area varies from 5 to 25 m. Flow rate varies, but is usually around 1-2 m a day within the airport area.
The ground alongside the runway and taxiway systems functions as a soil infiltration plant for aircraft and runway de-icing fluids used in the winter season. Most of the chemicals are broken down in the ground by microbiological processes before they reach the groundwater. In other words, the natural bacteria in the soil break down the chemicals that seep into it. In order to monitor these processes, fertilisers are added to the soil and checks are carried out. Research projects have also been carried out for a number of years to determine the critical loads, i.e. to determine how much de-icing fluid the soil is capable of breaking down.
The groundwater in the whole groundwater reservoir has a high level of minerals and is low in oxygen and does not meet the requirements of the drinking water regulations. However, this is the natural state of the groundwater here, the main problem being a high level of certain cations because of the natural solution of minerals. The sediments in the ground at Gardermoen are particularly rich in calcium and iron and manganese-rich minerals. In some places, the groundwater is also still affected by activities performed here before the airport was built, especially military operations and the Second World War.
Operation of the airport has had very little impact on the quality of the groundwater. This is documented by an extensive monitoring programme.
Requirements from the environmental authorities
Operation of the airport is subject to very strict environmental requirements. The Norwegian Pollution Control Authority (SFT) and the Norwegian Water Resources and Energy Directorate (NVE) have granted OSL discharge permits on the basis of the Pollution Control Act and the Water Resources Act respectively. The Norwegian Pollution Control Authority (SFT) has given the airport a permit to de-ice aircraft and runway systems and to discharge the de-icing chemicals to the ground alongside the runways and taxiways. The ground acts as a soil infiltration system, on the condition that the groundwater and waterways around the airport are not affected. SFT has also granted permission for a system for refuelling aircraft.
The Norwegian Water Resources and Energy Directorate (NVE) has granted permission for restricted lowering of the watertable within the airport area and discharge of pumped-out groundwater to the river Sogna, which runs to the west of the airport. One of the conditions of the discharge permit is that this does not affect the groundwater balance outside the airport area or the natural erosion processes in the ravines.
Waterways and the natural environment around the airport
The rivers Sogna and Vikka run through the area to the west of the airport. These are small tributaries of the river Leira. Parts of the Sogna’s drainage basin are located within the Romerike conservation area, which is an area with natural ravines that warrant protection. Both the Sogna and the Vikka receive groundwater that flows out of the groundwater reservoir. Natural erosion processes and the landscape are thus affected by how the groundwater flows out from the Gardermoen area. This is why the Norwegian Water Resources and Energy Directorate (NVE) has made it a condition that operation of the airport must not affect the natural erosion processes in the ravine area. These processes have been monitored for ten years, and it has been established that the development and operation of Oslo Airport have not affected the ravine system.
OSL monitors water quality in the river Sogna. The findings show that the river is polluted, especially in terms of its content of nutrients, bacteria and particles. The evidence shows that the main source of this pollution is agricultural activities in the catchment area of the Sogna. During thaws in winter, small amounts of de-icing chemicals are transported into the Sogna. However, these amounts are negligible and do not affect water quality. The river has a high content of organic material from natural drainage and erosion in the catchment area. The results from the monitoring work show that OSL’s discharges do not affect the waterway more than the other sources of pollution.
To the east and northeast of the airport are a number of small lakes called kettle lakes, which are protected. These lakes are situated in depressions in the landscape formed at the end of the last Ice Age some 10,000 years ago. Most of the kettle lakes are or have been in contact with the groundwater, i.e. there is contact between the groundwater and the water in the lakes. Other lakes are not and have not been in contact with the groundwater. There are then many different ecological systems in this area that are sensitive to external influences. It is important that operation of Oslo Airport does not affect these systems. Monitoring shows that the airport does not have an impact on the ecosystems.