Data Series 728
1U.S. Geological Survey.
2New Hampshire Geological Survey.
The U.S. Geological Survey, in cooperation with the New Hampshire Geological Survey, measured the fluid temperature of groundwater in deep bedrock wells in the State of New Hampshire in order to characterize geothermal gradients in bedrock. All wells selected for the study had low water yields, which correspond to low groundwater flow from fractures. This reduced the potential for flow-induced temperature changes that would mask the natural geothermal gradient in the bedrock. All the wells included in this study were privately owned, and permission to use the wells was obtained from homeowners before logging.
Maximum groundwater temperatures at the bottom of the logs were between 11.7 and 17.3 degrees Celsius. Geothermal gradients were generally higher than typically reported for other water wells in the United States. Some of the high gradients were associated with high natural gamma emissions. Groundwater flow was discernible in 5 of the 10 wells studied but only obscured the portion of the geothermal gradient signal where groundwater actually flowed through the well. Temperature gradients varied by mapped bedrock type but can also vary by differences in mineralogy or rock type within the wells.
First posted November 1, 2012
For additional information contact:
Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.
Degnan, J.R., Barker, Gregory, Olson, Neil, and Wilder, Leland, 2012, Temperature logging of groundwater in bedrock wells for geothermal gradient characterization in New Hampshire, 2012: U.S. Geological Survey Data Series 728, 19 p., available only at http://pubs.usgs.gov/ds/728/.
Purpose and Scope
Temperature and Other Borehole Logs