USGS Digital Elevation Model showing fractured bedrock

USGS Digital Elevation Model showing fractured bedrock

Fractured bedrock aquifers, are the most common source of groundwater in mountainous terrain.  Nearly vertical fractures, and systems of fractures, can extend hundreds of meters below the surface, and can be present over great distances.  It is these fractures in which water accumulates, moves, and ultimately can be recovered from, for use as a source of water supply to wells.

Conversely, aquifers comprised of inter-layered strata of sand, gravel, silts and clays that have accumulated in basins as sediment derived by erosion of those same mountains, are generally classified as alluvial aquifers.  Alluvial aquifers represent a vast storage system for groundwater, and are quite prolific in their supply and extent.  The majority of human endeavors that rely upon groundwater, rely upon groundwater from alluvial aquifers.

Finding water in either aquifer type has its own requirements, and challenges.  Alluvial aquifers tend to have large volumes of economically available water, but can have naturally or man-made pollutants present in them.  Fractured bedrock aquifers have fewer quality challenges (they do occur) but have far smaller quantities of water available to them.  As such, locating wells in fractured bedrock aquifers requires an understanding of not only the geology and hydrogeology, but of meteorology so that rainfall can be accounted for and recharge may be improved, along with several other factors ranging from water quality to site engineering issues.

In general, locating wells in fractured bedrock aquifers requires solid geologic an hydrogeologic work, in the form of a fracture trace analysis (FTA).  Completing a FTA significantly reduces the risk of drilling a well with unacceptable low-yield, poor recharge, or impaired water quality.

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