Identifying cross-well fracture connections using the dissolved oxygen alteration method

Abstract

Determining how wells in fractured crystalline bedrock are interconnected is essential in defining contaminant flow paths and in interpreting water quality data from wells. Although various tracers and geophysical techniques have been used with success, the high cost or logistics may restrict their implementation. This study demonstrates a low-cost technique for identifying fracture connections between wells by combining the dissolved oxygen alteration method (DOAM) with cross borehole hydraulic pumping tests. Following the alteration of the dissolved oxygen (DO) profile in the observation well through bubbler aeration, an interconnected well is pumped, which results in changes in borehole flow in the aerated observation well. The DO profile in the observation well is monitored over time to characterize the changes in borehole flow and identify fractures that hydraulically connect to the pumping well. The method was demonstrated at three test sites in Storrs, Connecticut. Each site has two or three interconnecting wells in fractured crystalline bedrock and varying flow conditions. The DOAM successfully identified interconnecting fractures in wells 15–84 m apart.