This report details the geophysical prospecting works carried out for hydrogeological purposes on a property located 19 km north of Tartagal, Santa Fe. The objective of the work is to locate areas with potential underground water storage with aptitude for cattle watering. The property has an area of approximately 13 km2.
Location
Figure 1 shows the location of the investigated site and Figure 2 shows the parametric transect. This site was chosen because it has the presence of groundwater in quality and quantity according to that required. In Figure 3, Figure 4 and Figure 5 the transects on which the exploratory studies were carried out are shown. The method implemented was that of tomography. electrical resistivity
Figure 1. Satellite image with the location of the studied site
Figure 2. Electrical resistivity tomography transect ERT 001 (parametric)
Figure 3. Electrical resistivity tomography transect ERT 002
Figure 4. Electrical resistivity tomography transect ERT 003
Figure 5. Electrical resistivity tomography transect ERT 004
The property has a group of reservoirs for the accumulation of rainwater. It has a hole on the access road to the house that is dry. According to the owner, other perforations made on the property illuminate water with high salinity, not suitable for livestock watering.
1 ERT
Measurements were carried out using the GD-10 equipment from GEOMATIVE, using different methods for data collection (arrangements). The separation between electrodes was 10 m for a total of 24 electrodes for the ERT001, ERT003 and 48 electrodes for the ERT002 and ERT004. The line length used for the ERT001 and ERT003 scans was 230m while for the ERT002 and ERT004 it was 470m. The arrangements used were Wenner Alpha and Wenner-Schlumberger and Dipole-Dipole.
For data interpretation and investment, the RES2DINV program was used.
Below are the images of the tomographies, where Figure 10 and Figure 11 show the profiles of the real resistivity obtained vs depth, after the inversion carried out using the interpretation program for ERT001 and Figure 12 and Figure 13 show the corresponding to ERT002. The reiteration of measurements in different arrangements for each transect allows evaluating the interpretive homogeneity and the best performance of the software with the minimization of errors..
Figura 6. ERT001, Wenner Alpha array.
Figura 7. ERT00, Schlumberger array.
Figura 8. ERT001, arreglo Wenner-Schlumberger array.
Figura 9. ERT002, Wenner alpha array.
Figura 10. ERT002, Wenner-Schlumberger array.
Figura 11. ERT003, Wenner Alpha array.
Figura 12. ERT003, Wenner-Schlumberger array
Figura 13. ERT003, Dipolo-Dipolo array.
Figura 14. ERT004, Wenner Alpha array.
Figura 15. ERT004, arreglo Wenner-Schlumberger array.
Figura 16. ERT004, Dipolo-Dipolo array.
Figure 17, Figure 18, Figure 19 and Figure 20 shows, on a satellite image, the electrical resistivity models obtained.
Figure 17. ERT001, Wenner-Schlumberger array.
Figure 18. ERT002, Wenner-Schlumberger array.
Figure 19. ERT003, Wenner-Schlumberger array.
Figure 20. 003 Wenner-Schlumberger array.
1.ERT001
The tomography was carried out in order to determine the geoelectric characteristics that would correspond to the areas where there is a presence of groundwater with low salinity. It was carried out in the EW direction. The Wenner Alpha array reached a depth of exploration of around 40m while the Schlumberger and Wenner Schlumberger reached 48m. The error in the adjustment of the first model was 1.26% 1.49% in the second in the third it was 1.27%. Progressive 0 is to the west. In the images obtained using the three arrangements, it is observed, in general, that the behavior of the apparent resistivity is quite homogeneous. The site of interest, where there is a catchment work, corresponds to the progressive 190. At that site, the behavior of the variable in question reaches its maximum, around 10 ohm.m. This resistivity value could be due to the fact that the subsoil, in this sector, contains stored water with lower conductivity. The anomaly extends to depths of 24 m. From that depth, the image shows a very low resistivity behavior that would correspond to the brackish aquifer.
2.ERT002
The tomography was carried out in the SE-NW direction. The Wenner Alpha array reached an exploration depth of around 91.2m while the WennerSchlumberger reached 104.8m. The error in the adjustment of the first model was 1.37%, while that of the second was 1.76%. A two-layer behavior is observed. The first, with a thickness of around 13m, has average resistivity values, no greater than 4 ohm.m. The lower layer has low resistivities, with values less than 1.5 ohm.m. The brackish aquifer would be housed in this.
3.ERT003
The tomography was carried out in the SSO-NNO direction. The Wenner Alpha array reached an exploration depth of 39.6 m, the Wenner-Schlumberger reached 48 m and the Dipole-Dipole only 31.9 m. The error in the adjustment of the first model was 1.72%, of the second, 2%, while that corresponding to the third was high, 12.1%. A two-layer behavior is observed. Like TRE002, the first layer, with a thickness of around 13m, has average resistivity values, no greater than 4 ohm.m. The lower layer has low resistivities, with values less than 1.5 ohm.m. The brackish aquifer would be housed in this. In this transect, two points of interest were marked on the ground, an issue that will be discussed later.
4.ERT004
he tomography was carried out in the SW-NW direction. The Wenner Alpha array reached an exploration depth of 91.2 m, the Wenner-Schlumberger reached 104.8 m and the Dipole-Dipole only 24.9 m. The error in the adjustment of the first model was 2.9%, of the second, 5.7%, while that of the third was high, 11%. Again a two-layer behavior is observed. The first layer in this case is more heterogeneous, with varying thicknesses from 13 to 25 m. This layer has medium to high resistivity values, not greater than 7 ohm.m. The lower layer has low resistivities, with values less than 1.5 ohm.m. The brackish aquifer would be housed in this. In this transect, two points of interest were marked on the ground with stakes, an issue that will be discussed later.
Below is a table with the coordinates of the sites of interest located from the studies carried out in advance. In it is the order of priority where it is advisable to drill.
The order of priority is a function of the depth recommended for the wells, so point P1 would be the most recommended site for drilling. It is recommended to carry out surveys prior to drilling in conventional diameter to ensure the success of the drilling. As a suggestion, the possibility of making curb-type wells, hand-carved, built directly at each point, should be evaluated in such a way that only the less brackish water can be intercepted and stored without connecting to the salty aquifer, thus conserving its quality.
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