Comparison of transmissivities from MRS and pumping tests in Denmark

International audience

إنجليزي. In Denmark, hydrogeophysical mapping is performed intensively in accordance with the Danish Government's environmental plans of ensuring a high quality drinking water supply. Previously the magnetic resonance sounding (MRS) method has been proven to improve the hydrogeological characterization from geophysical surface measurements in Denmark. In order to implement hydraulic parameters estimated from MRS together with hydraulic parameters obtained from pumping tests, it is necessary to analyse and compare the hydraulic parameters from the two data sources. These parameters are determined very differently with uncertainties arising from very different sources and the comparison requires an analysis in each specific case with attention on the investigated volumes. Several comparisons of transmissivities from MRS and pumping tests in Denmark show that the pumping test transmissivity value corresponds to the MRS transmissivity accumulated over depth intervals determined by the screen position depth interval in the borehole. When specific determinations of these depth intervals are performed, very good correlation is obtained between transmissivities from MRS and pumping tests. Comparisons of transmissivities from MRS and pumping tests will also lead to the determination of MRS calibration coefficients. MRS calibration is essential for quantitative use of MRS transmissivities. Sixteen calibration coefficients in different survey areas have been calculated. If these calibration coefficients can be categorized according to the different Danish survey locations and hydrogeological conditions in which they are obtained, these categorized calibration coefficients could be used in future MRS surveys without the need of calibrating with pumping tests in each survey. However, only a slight tendency of increasing calibration coefficient with increasing transmissivity and increasing grain size is observed. The present study shows that in general only little dispersion is observed around an average calibration coefficient for the different Danish survey locations and hydrogeological conditions.