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We test the integration of ground-penetrating radar (GPR) borehole investigation and electromagnetic flowmeter surveys to characterize fissured or complex aquifers. Borehole GPR investigation allows assessment of the lateral continuity of the porous and permeable zones between closely spaced boreholes, whereas flowmeter tests are adopted to identify the inflow–outflow zones in the boreholes. We apply the coupled approach in a portion (between 10 and 20 m below ground surface) of a complex aquifer hosted in a calcareous–gypsiferous formation. The hydro-geophysical characterization was aimed to detect the most conductive levels and to estimate the hydrodynamic properties of the aquifer. The integration of single-hole flowmeters and GPR measurements accurately distinguished different productive levels of high porosity and permeability in the aquifer. Two aquifer systems characterized by a complex geometry of fissures and permeable layers have been recognized, establishing the role of the drilled boreholes in the short-circuiting of the two systems. Interpretation of the GPR survey in cross-hole configuration gave values of total porosity of the order of 0.35 and 0.5 in the two more productive levels, which were detected by the flowmeter investigation.

Tracer tests often give ambiguous interpretations that may be due to the erroneous location of sampling points and/or the lack of flow rate measurements through the sampler. To obtain more reliable tracer test results, we propose a methodology that optimizes the design and analysis of tracer tests in a cross borehole mode by using vertical borehole flow rate measurements. Experiments using this approach, herein defined as the Bh-flow tracer test, have been performed by implementing three sequential steps: (1) single-hole flowmeter test, (2) cross-hole flowmeter test, and (3) tracer test. At the experimental site, core logging, pumping tests, and static water-level measurements were previously carried out to determine stratigraphy, fracture characteristics, and bulk hydraulic conductivity. Single-hole flowmeter testing makes it possible to detect the presence of vertical flows as well as inflow and outflow zones, whereas cross-hole flowmeter testing detects the presence of connections along sets of flow conduits or discontinuities intercepted by boreholes. Finally, the specific pathways and rates of groundwater flow through selected flowpaths are determined by tracer testing. We conclude that the combined use of single and cross-borehole flowmeter tests is fundamental to the formulation of the tracer test strategy and interpretation of the tracer test results.

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