Bedrock Groundwater

In sparsely populated areas in Norway groundwater from boreholes in bedrock is the major source of water supply. Groundwater accumulates in fractures and cavities in bedrock. Drilling a well in the most ordinary of rock types will usually provide enough water for a farm, house or cottage.
Ground water flows out of a fracture in Bogen in Ofoten. Photo: Øystein 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. We differentiate aquifers in crystalline fractured rock from aquifers in porous fluvial or glaciofluvial deposits. 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.

The water table

Boreholes should be drilled in the bedrock perpendicular to the main fractures to yield the most water. The bedrock may often be heavily fractured, but these fractures may be clogged with clay minerals which prevent groundwater from being released when drilling. Commonly, groundwater wells in bedrock are drilled down to 100 meters depth. If a borehole has a low water yield because it does not intersect / cross the fractures in the rock, production could be increased by applying pressure. This technique, called fracking, 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.

Mines and tunnels

Coastal areas of Norway may have problems with saltwater intrusion. 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.

Groundwater is regarded as a problem with regards to mines and tunnels. Water leakage is unpredictable and may be costly to prevent or reduce. To reduce water leakage into subsurface constructions geological and geophysical mapping in feasibility studies will reduce the risk and 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.