January 6, 2025
Picture of the month prepared by Andrew Stone, Hydrogeologist, andrewstone@gmail.com
WELLS IN BEDROCK FRACTURES
How often do you get to see a cross-section of what was until very recently a subsurface drill hole intercepting a bedrock fracture?
The photo of 1.4 billion old Silver Plume granite was taken on the I-70 frontage road in Mount Vernon Canyon just west of Golden, Colorado.
Photo Credit: Peter Barkmann, Colorado Geological Survey
The photograph shows a now exposed section view of a drill hole intercepting bedrock fractures in granite bedrock. When occurring below the water table, saturated fractures in bedrock can transmit and store water. To be successful, a bedrock well should intercept saturated fracture systems that are interconnected. In many cases, fracture systems that are connected to recharge zones, such as overlying layers of sediment, have the best chance of producing a reliable sustainable yield. There are millions successful bedrock wells providing water to homes, farms and businesses throughout the USA. Some bedrock wells have limited connection to groundwater and yield may decline seasonally or in times of drought. Aerial imagery and geophysical techniques can be effective in identifying the orientation and density of fractures and optimizing the chances of selecting a site for a successful water well.
