Academic Conference on Natural Science for Master and Ph. D students From Cambodia Laos Vietnam



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Fig. 5. The VES interpretation with calculated data fitting observed data, which obtained from middle part of Champhon (S-2, S-7, S-8, S-9, S-11, and S-35)



Fig. 6. The VES interpretation with calculated data fitting observed data, which obtained from western of Champhon District (S-21, S-26, S-27, S-30, S-31, and S-32)

In addition, contour maps of apparent resistivity at half current electrode spacing of 1.5 m, 10 m, 20 m and 30 m was plotted in order to show resistivity in this area. A high resistivity zone of greater than 100 ohm-m appears in almost parts of study area at small current electrode spacing of 1.5 m and some parts of the area at electrode spacing of 10 m, 20 m and 30 m (Figure 7), low resistivity zone of less 10 ohm-m (blue color) at the middle part of the study area, my be caused by thick salt deposit in this area and moderate resistivity of 30 to 100 ohm-m was observed in the western and northeastern of this area.




Fig. 7. Apparent resistivity maps of Champhon District at different half current electrode spacing (1.5, 10, 20, and 30m)
Similar as contour maps of apparent resistivity at half current electrode spacing of 45 m, 60 m, 90 m and 150 m (Figure 8). Low resistivities of less than 10 ohm-m appears in the middle part of study area indicated that conductive ground layers extend to downward in the study area and found moderate resistivity of 30 to 100 ohm-m appear in the western and eastern part of this area.

Fig. 8. Apparent resistivity maps of Champhon District at different half current electrode spacing (45, 60, 90, and 150m)

True resistivity contour maps at different depths obtained from interpretation of VES curves was plotted in order to classify resistivity value zones (Figures 9). These maps show high resistivity of greater than 100 ohm-m at ground surface and moderate resistivities of 25 to 100 ohm-m in southwestern and eastern parts of the study area at 5, 10 and 15 m depths. Low resistivities of less than 8 ohm-m appear in middle part of the study area from 5 to 30 meters depth whereas low resistivity decrease area at 40 to 50 meters depth as shown in Figure 10. However, moderate resistivities of 25 to 100 ohm-m are found in the southwestern and eastern parts of the study area, indicating suitable zones for good quality groundwater this area.



Fig. 9. True resistivity contour maps of Champhon District at different depths (0, 5, 10, and 15m)




Fig. 10. True resistivity contour maps of Champhon District at different depths (20, 30, 40 and 50m)

The resistivity models of sounding points S-27 was compared with geological logs of wells Lk-268 (Figure 11) in order to determine a correlation between lithological information and resistivity model. The four -layer earth model obtained from the resistivity interpretation of sounding point S-27 was compared with the geological logs of well Lk-268. The first layer of 170 ohm-m and 0.7 meters thick corresponds with the thin top soil, the second and third layers of 25 to 32.2 ohm-m in resistivity model at 0.7 to 66 meters depth corresponds with claystone, siltstone, and sandstone layers at 1.8 to 73.94 m depth and thin layer of anhydrite below at depths 73.94 to 77.5 m of this well. Found very low resistivity to 0.6 ohm-m at the bottom layer of resistivity model with 66 m depth corresponds with the top of the halite layer at depths 77.5 to 188.8 m with a thin layer of sand and anhydrite interbedded at depths of 188.8 to 196.2 m.



Fig. 11. Correlation of VES-result at sounding point S-27 with the known lithology of well Lk-268

  1. CONCLUSIONS

The results of present work showed that found low resistivity of less than 8 ohm-m from observed data curves at the middle part of the study area similar as true resistivity contour maps, showed low resistivity zones of less than 8 ohm-m in the same part of this area. In addition, contour maps of apparent resistivity showed that low resistivity zones of less than 8 ohm-m appear in the middle part of the study area, low resistivity zones are considered to be sand bearing with clay, silt layers or thick salt deposit in this area, indicated that high salinity water in this zone, its thickness of thick salt extends downward to 75 meters depth, obtained from apparent resistivity contour maps. However, moderate resistivity range from 25-100 ohm-m in southwestern and eastern parts of the study area at 5-75 meters depth, indicating suitable areas for good quality groundwater.

  1. ACKNOWLEDGMENTS

We would like to thanks to the International Programme in Physical Sciences (IPPS) of Uppsala University, Sweden and Assoc. Prof. Dr. Ernst van Groningen, the director of IPPS, for research grant for research work. The authors acknowledge Physics Department, Faculty of Science, National University of Laos for document that related to fieldwork and Department of Geology and Mines of Laos for geological map and borehole data in the study area. I specially thanks to Mr. Khampheua Phaxayaphet, local authority for facility document and joining in fieldwork in Champhon District, Savannakhet Province.

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