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While hydraulic tomography (HT) is a mature aquifer characterization technology, its applications to characterize hydrogeology of kilometer-scale fault and fracture zones are rare. This paper sequentially analyzes datasets from two new pumping tests as well as those from two previous pumping tests analyzed by Illman et al. (2009) at a fractured granite site in Mizunami, Japan. Results of this analysis show that datasets from two previous pumping tests at one side of a fault zone as used in the previous study led to inaccurate mapping of fracture and fault zones. Inclusion of the datasets from the two new pumping tests (one of which was conducted on the other side of the fault) yields locations of the fault zone consistent with those based on geological mapping. The new datasets also produce a detailed image of the irregular fault zone, which is not available from geological investigation alone and the previous study. As a result, we conclude that if prior knowledge about geological structures at a field site is considered during the design of HT surveys, valuable non-redundant datasets about the fracture and fault zones can be collected. Only with these non-redundant data sets, can HT then be a viable and robust tool for delineating fracture and fault distributions over kilometer scales, even when only a limited number of boreholes are available. In essence, this paper proves that HT is a new tool for geologists, geophysicists, and engineers for mapping large-scale fracture and fault zone distributions.

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Open fractures are primary conduits for groundwater flow and thus constitute preferential transport pathways for dissolved contaminants. Fracture internal variability, caused, for example, by shearing, leads to significant variability in the in-plane groundwater velocity field (Egert et al., 2021;Zou et al., 2017), which in turn affects mass exchange processes with the stagnant water in the bordering porous rock matrix . Fracture filling minerals, that might have precipitated during past hydrothermal events, add more pieces to this already complex puzzle. In fact they might alter the local velocity field and react with some of the dissolved species. A thorough characterization of in-plane groundwater flow and reactive transport processes occurring at the scale of a single fracture has a direct impact on applications such as the remediation of a polluted site or the safety assessment study of a deep geological repository for nuclear waste.Groundwater channeling occurring at the scale of a single fracture was assessed by different experimental and numerical works. Brown et al. (1998) assessed in-plane channeling by injecting dye into a water-saturated precise replica of a natural fracture. The visual analysis of dye concentration shows the dye entering the fracture preferentially through a single large channel. The authors found the velocity contrast (i.e., the ratio between maximum and average velocity) to be within a factor of 5. Watanabe et al. (2009) performed experimental and numerical analyses on flow through shear (Mode II) fractures, which were generated by direct shear on granite under different constant normal load. Two different shear displacements (1 and 5 mm) were considered. The authors found that contact areas occupy around 30%-70% of the fracture plane, depending on the confining pressure. Numerical simulations, performed using the depth-average Reynolds equation, showed that only around 10%-30% of the non-contact areas contribute to fluid flow. More recently, Zou et al. ( 2017) used a laser-scanned real rock sample to assess the effect of roughness and variability in fracture aperture on radionuclide transport. The numerical models, which were based on the Navier-Stokes

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