Temperature as an indicator of flow in fractured rocks near Oracle, Arizona

Abstract

Knowledge of flow patterns in fractured rocks is important in understanding hydrology and contaminant transport. Methods of locating flow zones based on geophysical measurements are unreliable because of a lack of correlation between fracture density and hydraulic conductivity. In this work, analysis of data from natural temperature profiles, longterm heating tests, and three-hole recirculation thermal tracer experiments in saturated fractured granite indicates that temperature measurements can be used to identify local flow paths and flow directions in fractured systems. However, adequate controls on background noise and sufficient supplementary information must be incorporated into the testing procedure. Although thermal tracer tests at the Oracle site were inconclusive due to insufficient heat input, the use of heat as a tracer to define larger-scale flow patterns is found to be potentially useful in situations where ample supplies of warmer or cooler water are available.