GIS based correlation between groundwater quality parameters and geological units


The degree of fluoride contamination and identification of hydrogeochemical process in mobilising the fluoride contamination for this study area has been published by Keshari and Dhiman (2001).



By using the GIS and a statistical package a significant correlation is found between the groundwater quality parameters and the geological units in the Western Indian Aquifer system. The statistical parameters for groundwater chemical species (in meq/L) are shown in Table 1.



Table 1 reveals that the range for calcium lies between 1 to 3.5 meq/L, fluoride lies between 0.05 to 0.17 meq/L, bicarbonates between 3.69 to 6.2 meq/L and the pH range in the study area is between 7.34 to 7.77. The low standard error exists for all the parameters considered for the analysis.

The correlation coefficients between groundwater quality parameters and the geological units as obtained are shown in Table 2.

A high negative correlation (-0.84) exists between calcium and ultrabasic rock, whereas a moderate negative correlation (-0.55) is observed with the schist and a low positive correlation 0.19 with gneiss for the calcium. A high positive correlation (0.8) exists between fluoride with ultrabasic rock, and a moderate positive correlation with gneiss and quartzite and quaztzite schist. However, fluoride is showing a very poor correlation with schists. A moderately high positive correlation of 0.6 exists between bicarbonate and ultrabasic rocks and a moderate positive correlation of 0.3 with schist and moderately low 0.18 with quartzite and quartz-schists, and a very low correlation of 0.06 with gneiss. A very high positive correlation of pH with gneiss (0.94) and schists (0.93), whereas a moderately high with quartzite and quartz-schist (0.79) and ultrabasic rock (0.62).

Conclusion
Geographical information system based correlation analysis has been carried out to establish the relation between the concentration of the chemical species and the geological units in a spatial domain. Results for the study area reveal that there exists a high negative correlation between calcium and ultrabasic rock, a high positive correlation between fluoride and ultrabasic rock, and a moderately high correlation between bicarbonate and ultrabasic rock and a very high correlation between pH and gneiss and schists. Such studies within GIS environment help in understanding the water-rock interactions and thus will prove useful in formulating numerical models to study transport mechanisms of various chemical species in different hydrogeologic and chemical environments.

References
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