Borehole and surface-based hydrogeophysics

Excerpt

To better identify underground water resources, one needs to assess with sufficient accuracy the characteristics of the water in storage, its chemical and biological quality and its possible flow properties. Drilled holes cannot be used to attain all of these objectives. They permit core sampling, in situ tests, piezometric measurements but are invasive, modify water circulation (and thus the information lost during the drilling operation can never be recovered), are expensive to carry out and cannot be achieved with a fine mesh grid. On the contrary, the different geophysical techniques are non-invasive, cheap and can be performed with a high spatial sampling. In practice, direct measurements (such as outcrop properties, core sampling, and logging) are often necessary for interpreting geochemical data, and to determine known geological features. In some cases, geophysical prospecting allows one to interpolate the results obtained from boreholes or piezometers (subsurface exploration) and the characterization of ground features (detailed exploration). Thus geophysical techniques have an enormous potential for supplementing the data obtained by invasive methods provided the geophysical measurements can be expressed in terms of hydrogeological information (Purvance and Andricevic 2000). It requires, however that the relationships between physical properties of soils and rocks and hydraulic parameters be established. This essay is a forward-looking description of borehole and surface-based geophysics applied to hydrogeology. First, it reviews common physical properties, specific properties of the water molecule and water monitoring available when applying geophysical surveys to hydrogeologic problems. Second, comments on recent published studies in hydrogeophysics are presented. Finally, a prospective of future geophysical work in hydrogeology is proposed. …