Application of geophysical methods in environmental and municipal engineering. Theoretical study

This report includes the fundamental theoretical aspects of geophysics applied in environmental surveys. The main emphasis is put on analysing of electrical, electromagnetic, and soil temperature measurements. Petrophysical basis necessary for quantitative interpretation and modelling is covered. Some theoretical formulas and laboratory measurements of water samples indicate that the salinity(TDS) can be interpreted from surface measurements and that TDS is a relatively reliable indicator of groundwater contamination. Geophysical methods can be successfully used both before waste disposal operations for evaluation of site characteristics and for monitoring of possible leachate flow. When galvanic electrical survey takes place some forth of sounding-profiling array is superior in the sense of earth section coverage and cost effectiveness. Among the many possibilities, the set - Wenner-B, pole-dipole and pole-polearrays - was chosen. Layered earth and three-dimensional modelling indicate that the combination of arrays covers the depth range of 0 - 30 metres. Direct inversion methods and aspects in layer model interpretation are discussed. It was also noted that the self-potential method may offer new possibilities in the detection of leakage points. Electromagnetic methods from another variety of tools for earth probing purposes. After fundamental concepts the selected three-layer earth models are analysed in frequency and time domain and for loop(dipole) and plane wave excitation. The same models are used as with galvanic electrical methods to allow easy comparison. Dielectric effects are taken into account and the apparent resistivity sounding curves are also calculated. The results of the EM-theory indicate that the EM-sounding methods would be powerful techniques to be used together with electrical methods in detecting near-surface structures, but the instrumentation currently available does not cover high frequencies or the early time transients required. The possibilities of plane wave methods in the detection of lateral resistivity changes are also discussed. The results of the VLF-theory indicate strongly the dominating and masking effects of shallow soil structures. The possibilities of using the soil temperature measurements in evaluating hydrogeologic conditions in groundwater flow systems is studied by means of a case study example from the existing landfill site in Tuusula. The results were not found encouraging due to complicated interpretational points of view.