USE OF SINGLE- AND CROSS-HOLE FLOWMETER LOGGING FOR INVESTIGATIONS IN CONTAMINATED FRACTURED-ROCK AQUIFERS

Single- and cross-hole flowmeter logging are valuable methods for investigating contaminated fractured rock. Flowmeter logs collected in single boreholes under ambient and stressed conditions are used to identify vertical flow and the most transmissive fractures that intersect the borehole. Using numerical modeling methods and single-hole flowmeter data, the transmissivity and head of discrete fracture intervals can be estimated. In addition, cross-hole flowmeter tests can be used to identify and characterize the hydraulic connections between the boreholes, by logging transient flow in one borehole while pumping or injecting from another borehole.

Three case studies demonstrate the importance of single- and cross-hole flowmeter methods for improved site characterization. In the first case, the single-hole tests were used to characterize discrete-interval head and transmissivity. Flowmeter methods produced transmissivity and head values similar to hydraulic tests that used straddle packers for the most transmissive fractures in the borehole. In the second case, cross-hole flowmeter logging was used to produce more robust interpretations of open-hole pumping test data conducted in a well field. The transient flow response was used to identify and characterize a hydraulic connection that was not obvious from the open-hole water-level response to pumping from a nearby extraction well. In the third case, the flowmeter methods were used to identify and hydraulically characterize aquifer flow zones at a fractured-rock site that was to be treated with chemical oxidation methods. In each case, flowmeter methods provided valuable information for 1) site characterization, 2) conceptual modeling of ground-water flow and advective transport, 3) evaluation of cross-connections within boreholes and the potential impact on open-hole sampling, and 4) characterization of hydraulic connections between the boreholes. Collectively, these data are critical for effective design and implementation of monitoring and remediation programs.