It is raining good quality drinking water
According to a 2008 survey in Norway, the water purifying facilities of Øvre Årdal municipality produce the best quality drinking water from an underground water source in Norway.
The water purifying facilities in Øvre Årdal were built in an area close to the Årdal lake.
It was neither a matter of luck or a coincidence that resulted to the top results for the Øvre Årdal purifying facilities in the survey. Several thorough ground investigations and extended calculations/numerical hydrological models were conducted before the purifying facilities were constructed. Simply, a digital test model of the whole purifying facility was built before the construction work started.
The Øvre Årdal municipality lies on top of a well formed aquifer which contain large quantities of water that run trough sand and gravel deposits from the last ice age. The water that runs though the deposits is already physically cleaned on the way to the aquifer. Several test boreholes and pile wells were drilled before construction started. The results from these tests formed the basis for a ground water model of the aquifer.
There were not so many different alternatives for building the purifying facilities. The final choice was on a location just by the side of the Årdal lake. One of the challenges that the designer phased, was whether it would be possible to pump large water amounts from the aquifer without the influx of lake water, which is of lower quality, into the aquifer.
The chosen location is also very close to an outlet for another cleaning municipal facility and lies on top of an old wasteland. As a consequence of this choice, the public health authorities were in doubt whether this was an acceptable location and the local municipal administrators were not convinced before NGI showed them their work. This work consisted of hydrological data of the area, as well as extended ground water modeling that showed in details what would happen to the quality of the drinking water if intense pumping of the aquifer for up 500 liters per second take place.
The ground water modeling that was performed was based on the results of the test boreholes and pile wells and shows the characteristics of underwater stream. It was also shown in the modeling work, that the aquifer has a relative high pressure, which prevents influx of the lake water or polluted water fromm the municipal cleaning facilities.
The aquifer can be considered as an "underground river" in the sense that the groundwater that streams, towards the pumping well, is both narrow and concentrated. Nevertheless, the aquifer lies at a depth of about 50 m which means that this drinking water resource is self protected and very safe.
The results also showed that it was not necessary to create artificial barriers between the aquifer and the purifying facility and that we could pump up to 500 lt/sec without reducing the quality of drinking water. The purifying facility is dimensioned to pump a maximum 100 lt/sec.
The manager of the purifying facility, Arne Kjos proudly says that - The quality of our water is as good as or even better from the bottle water - and continues - It is really both unexpectable and impressing to see that people are willing to pay 30 NoK/liter for bottle water while in Øvre Årdal are producing water of very high quality fro just 1 cent NoK /liter.
In this project, NGI's participation was mainly the creation and development of a credible and reliable underground water model that considers all available hydrogeological input data. Hydrogeologists at NGI have several years experience to find and develop the ground water resources.
Miljøgeologi AS was responsible for all testing of the test boreholes as well as the geochemistry aspects. The difficult drilling trough the loose deposits and waste landfill was undertaken by the drilling specialist company Brødrene Mhyre AS. Tveiten As was the project leader for the Årdal municipality.
Read a presentation of the project in the Norwegian magazine Kommunalteknikk.