MULTISCALE FRACTURE CHARACTERIZATION OF THE IDAHO BATHOLITH, BOISE, IDAHO

Groundwater recharge to deep Boise valley aquifers is derived from several sources. Geochemical and residence time studies have estimated that the contribution to recharge from the fractured biotite-quartz monzonite Atlanta Lobe of the Idaho Batholith, situated N-NE of Boise, is important but the quantity of recharge from this source is unclear (Hutchings and Petrich, 2002). Field reconnaissance has identified joint sets aligned in three principal directions: 345, 60NE; 15, 60NW; and 308, 83NE. Lineament extraction indicates a fracture density of .11 fractures per square meter and a mean fracture length of 116 meters. The fracture sets will be modeled using the discrete fracture network models available in the FracWorks XP ® software to obtain hydraulic properties of the fracture network. Detailed mapping and modeling of the fracture network for the batholith along the Boise Front is performed at multiple scales to provide hydraulic parameters that will lead to quantifying recharge from this source.

Hutchings, J., Petrich, C. R., 2002. Report: Groundwater recharge and flow in the regional Treasure Valley aquifer system: Geochemistry and Isotope Study. Submitted to The Idaho Department of Water Resources by The Idaho Water Resources Research Institute.