Non-invasive characterization of water-bearing strata using a combination of geophysical techniques

Abstract

Hydrogeological investigations were carried out in an arid area of Inner-Mongolia to determine the locations of future water supply resources. The first geophysical survey was conducted near Baiqi to identify favorable boreholes using magnetic resonance sounding (MRS). The yield capacities of 43 sites were investigated, and the extent of the potential groundwater storage was determined. Previous studies have indicated that a major tectonic structure may have a significant impact on the groundwater flow and well yield in the study area. Therefore, high-resolution seismic surveys were applied in the second stage of the investigation to determine the fault locations. After the regional identification, a major structure was investigated in detail to map the fracture patterns. Based on the assumption that the hydraulic conductivity of this formation is similar along the entire strike of the fracture, we proposed drilling a borehole (BQ3) in the zone. However, this well has a yield of only 0.8 L/s, falling short of the required flow rate of 3.0 L/s. Therefore, the objective of the final stage of exploration was to accurately define the attitude and extension of the aquifer and to select a more favorable borehole site that would meet the required water flow rate. The geophysical exploration was carried out using time-domain electromagnetic (TDEM) and MRS methods. The MRS results suggest optimal locations for water supply boreholes within the subsurface structures mapped by the TDEM inversion method. The data obtained by drilling and coring are in agreement with the predicted aquifer thickness from the TDEM data. Pumping tests indicate that the water discharge of borehole BQ4 was 3.5 L/s. Our results demonstrate that the delineation of the groundwater body using a combined application of three geophysical methods (the MRS, TDEM and 2D seismic methods) was successful. ► A well was determined using 2D seismic method, but, it has a yield of only 0.8 L/s. ► TDEM provides geoelectrical distribution in fracture zones identified by 2D seismic. ► Joint use of MRS and TDEM is useful for determining aquifer layers when SNR is low. ► QT inversion of MRS can get optimum spatial resolution of water content distribution. ► A combined use of three geophysical methods was successful to delineate groundwater.