# Innovative Hydrogeophysical Approaches as Aids to Assess Hungarian Groundwater Bodies
## 4 Discussion and Conclusions
Their shaliness was estimated by iteratively reweighted factor analysis, while their hydraulic properties were directly derived from the electrical resistivity log as demonstrated through a thermal-water exploration example. For the exploration of formation shaliness and hydraulic conductivity using classical (maximum-likelihood method-based) factor analysis were previously applied [64; 65], which confirmed the validity of multivariate statistical methods that were further improved in this study. The porosity, water-saturation, shale content and the fractional volume of rock matrix were earlier estimated by the interval inversion method [66], which allowed not just the automated determination of volumetric parameters, but the layer-boundaries, some zone parameters (i.e., physical properties of fluid and matrix components, textural properties, such as Archie's constants and other functional constants of probe response equations) as well as the uncertainty of the estimated model parameters. An application for the cooperative use of inverse modeling and factor analysis was published [67], which showed the advantages of the joint application of these two approaches for more accurate and reliable reservoir characterization. On the basis of theoretical considerations and the presented field results, the following recommendations for geophysical surveying programs in different groundwater bodies can be given. To resolve problems where vertical electrical resistivity variations must be followed, that is to present layered structures, water table or large rock units (challenges 1 and 6 and partially 2, which may mainly occur in shallow porous, porous and porous thermal groundwater bodies), traditional geoelectric ERT measurement with WS array is satisfactory. WS measurements can give the depth, thickness and resistivity of the layers enabling their geological interpretation. Well-logging methods can verify ERT results and can be used to determine the petrophysical and hydraulic properties of the layers. In addition to this, the above presented multivariate statistical interpretation of wireline logs using robust cluster analysis allows a reliable lithological separation of potential aquifers and the estimation of their shaliness. Thus, their application is recommended to handle challenges 1 and 2, and especially the 3 and 5 ones (Table 1). In order to get a more detailed image of the subsurface, in particular, if the aim is to describe horizontal resistivity variations, which may be, e.g., due to faults, fractures, fracture zones, or holes (challenges 2-4, which may mostly occur in shallow upland, upland, karstic and thermal karts groundwater bodies) traditional Dp ERT measurements are recommended completed by \(\gamma_{11\text{n}}\) ERT ones. It was shown that the \(\gamma_{11\text{n}}\) array could verify the results of the traditional WS and DP arrays and often complete with important information. They enabled more accurate localization of faults and fractures and better delineation and description of fracture zones, thus improving the input parameters of hydrogeological modeling and improving the yield of wells. Since drilling a well only a small distance from a fracture may drastically decrease the quantity of the exploitable water, accurate localization of the fractures is extremely important. If the aim is to get a detailed image of the subsurface, from surface measurements, Dp and \(\gamma_{113}\), \(\gamma_{115}\) measurements and the joint interpretation of their results seem to be a very good combination. The advanced interpretation of wireline logs using robust statistical analysis of in situ data may further improve the results enabling the construction of better hydrogeological models serving with more accurate input parameters. Its application is expected to localize water wells better, thus producing more water. Vulnerable areas can also be better delineated by better characterizing fractures and fracture zones, which are the key parameters in water circulation. Conceptualization, P.S.