Bedrock Groundwater

Water accumulates in the fractures and cavities in bedrock, which is often the major source of water for sparsely populated areas. Drilling a well in the most ordinary of rock will usually provide enough water for a farm, house or cottage.
Ground water flows out of a fracture in Bogen in Ofoten. Photo: Ø. Jæger, NGU

Bedrock groundwater is an important source of water supply for isolated dwellings.

Water seeps into fractures and channels found in non-porous rock. Therefore, we are prefer to refer to this as a fractured-rock aquifer than a pore aquifer, which is the most common aquifer found in large parts of Europe. The only porous rock found on the mainland of Norway is Brumunddal sandstone, a rock that is currently being drilled and pumped by and Ringsaker Water Works.

Boreholes must drilled in the bedrock perpendicular to the main fractures and channels.  The bedrock may often be heavily fractured, however, but these fractures may be clogged with clay minerals which prevent groundwater from being released when drilling.

It becomes gradually less likely to strike water as drilling depth increases due compression from the  weight of the overlying rock.  Therefore it is not usual to drill groundwater wells deeper than 100 meters. If a borehole produces little water because it does not cross the fractured rock, production could be increased by applying pressure.  This technique involves injecting water in the borehole under high pressure so that the fractures are jacked open and thus made more transmissive.

A water table is surface of the aquifer  -- the surface where the water pressure head is equal to the atmospheric pressure.  Below the water table, the aquifer is completely saturated with water. The distance down to the ground water table may vary from zero meters to several tens of meters, depending on whether it is being drilled in the valley or on higher hill. The height of water table also varies with climate and season.

In areas where the bedrock is made up of marble and other calcareous rocks, the water from the rainfall, streams and rivers can dissolve rock, which can result in  caves and underground streams and rivers. In such areas, bedrock boreholes drill provide a lot of water, but it's presence could be temporary as what rapidly flows out into any open channels.

On the islands and along the coastlines of Norway, saltwater intrusion is a problem. Fresh groundwater floats over the salt water like a large bubble, hence, the danger of saltwater intrusions increased borehole depth and with increasing withdrawal of water.

The infiltration of groundwater can cause problems when operating mines and constructing and operating tunnels.  Application of geological knowledge could help identify the fractures in the bedrock, where water might leak through.  A thorough investigation could help reduce costs related to damages, prevent injuries and prevent loss of life.

Under the Water Resource Act , all well drilling activities and groundwater studies, must be reported to NGU. The data is entered into the national groundwater database (GRANADA) which can be then accessed on-line through an interactive map and as fact-sheets. NGU will continue to gather data on groundwater boreholes and groundwater study, thereby contributing to a broad knowledge base of where bedrock groundwater is located and how it behaves.

In drilling wells the water will flow into the well along a few cracks cut by the borehole. This film shows a marked water..