USING GIS TO EVALUATE FEASIBILITY OF GEOTHERMAL ENERGY USE IN NEW HAMPSHIRE

The potential for geothermal energy in New Hampshire, both in terms of heating systems and power generation, is explored using heat flow and water table data from across the state. This study, which is done in cooperation with the New Hampshire Geological Survey, employs a variety of GIS tools to produce a depth-to-water table profile of the entire state, using well data provided by the Survey. Additionally, the spatial correlation of heat flow, conductivity, and gradient data from Jaupart et al. (1982), Hoag and Stewart (1977), Birch et al. (1968) and Roy et al. (1968) to the bedrock geology is statistically analyzed and used to designate the most significant areas of geothermal potential in the state. These sites are then correlated with bedrock type by overlaying the data on the digital bedrock map of New Hampshire (Lyons et al., 1997).

This state-wide assessment of the geothermal potential then leads to a more localized study of the areas identified by GIS. Chief among these areas is the Conway Granite, noteworthy for its high radioactivity and thermal conductivity. Heat produced from the decay of radiogenic elements is the primary reason for elevated heat flow in rock units such as the Conway Granite, and careful consideration of the concentrations of elements such as uranium and thorium, which often are a function of the rocks' mineralogy, help to identify the hottest areas within the regions themselves. In addition, modeled batholith shape and fracture and joint patterns are taken into account to arrive at a comprehensive geologic understanding of the rock units.

Modeling of geothermal systems is then performed using the specific physical properties identified for each of the regions of interest. This modeling, including constraints for heat flow and porosity, shows whether or not temperatures high enough for geothermal power generation (minimum 100˚C) can be reached at a reasonable depth, as well as the sustainability of the temperatures with time. However this study turns out, the extraction and use of the crust's heat in New Hampshire has the potential to play a significant role in the reduction of our reliance on fossil fuels.