Modelling and variability of selected chemical properties of shallow water wells using GIS in Wasit and Dhi Qar provinces/Iraq

Abstract

This study was conducted to model several chemical properties of shallow well waters and to investigate the spatial variability of these properties in different regions over two provinces in Iraq - Wasit and Dhi-Qar. Eleven wells were chosen to evaluate the quality of their water and its suitability for agricultural, civil engineering and human applications and uses. Samples were taken in January 2018 from Giazna (1, 2, 3, and 4 ), Karthiya, Badra, Dujaili, Shaikhsaad, Muwafaqiya, Hay, in Wasit province and from Fajr in Dhi-Qar province. The water samples were subjected to chemical analysis to measure the concentrations of sodium (Na 1+ ), calcium (Ca 2+ ), magnesium (Mg 2+ ), pH, electrical conductivity (Ec), and total dissolved solids (TDS). Results were undergone several descriptive statistics Minimum (Min.), Maximum (Max.), standard deviation (std), skewness (skew.), and Kurtosis, (Kurt.) and coefficient of variation (CV%). Mathematical models were generated using Data Fit (9.3) software to predict sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) depending on chemical properties. The predicted values of SAR and ESP were validated using several validation indices including the factor of determination R 2 , root mean squared error (RMSE), absolute mean error (MAE), relative error (RE), correlation coefficient (r) and standard error (s). A GIS program was used to map the studied chemical properties. The results showed that the SAR model (SAR = a 1 × Na 1+ + a 2 × Ca 2+ + a 3 × Mg 2+ + a 4 × ESP + a 5 × X east + a 6 × Y north + a 7 ) which with (R 2 =0.999, SEE=5.30, RMSE=0.000, MAE=0.000, and RE=0.000) and the ESP model (ESP = Exp(a 1 × Na 1+ + a 2 × Ca 2+ + a 3 × Mg 2+ + a 4 × X east + a 5 × Y north + a 6 )) which with ( R 2 =0.9827, SEE=5.55, RMSE=0.037,MAE=0.026 and RE=0.003) were the best for predicting SAR and ESP values for the selected wells. The Well water quality index (WWQI) was determined and accordingly the water was classified as poor. As a result, the water of the studied wells was considered unsuitable for human consumption as drinking water and irrigation; except the well of Fajr which was found critically suitable for irrigation purposes.