A combined hydrochemical-statistical analysis of Saq aquifer, northwestern part of the Kingdom of Saudi Arabia

The present study includes detailed hydrochemical assessment of groundwater resources of Saq aquifer. The Saq aquifer covers a large area (about 375,000 km 2 ) and lies in the arid region with low annual rainfall and extremely high evaporation. In the study area, groundwater serves as the major source for agricultural activity and for domestic usages. A total of 295 groundwater samples collected and were analyzed for physico-chemical parameters such as hydrogen ion concentration (pH), total dissolved solids (TDS) and electrical conductivity (EC), sodium (Na + ), potassium (K + ), magnesium (Mg 2+ ), and calcium (Ca 2+ ), bicarbonate (HCO 3 ) chloride (Cl − ), sulfate (SO 4 2− ) and nitrate (NO 3 ). The goal and challenge for the statistical overview was to delineate chemical distributions in a complex, heterogeneous set of data spanning over a large geographic range. After de-clustering to create a uniform spatial sample distribution with 295 samples, histograms and quantile-quantile (Q-Q) plots were employed to delineate subpopulations that have coherent chemical affinities. The elements showing significantly higher positive correlation are: TDS with EC; Ca with EC, TDS; Mg and EC, TDS, Ca, K; Cl and EC, TDS, Mg, Na, Ca; SO 4 and EC, TDS, Ca, Cl, Na, Mg. The distribution of major ions in the groundwater is Na + > Ca ++ > Mg ++ > K + and Cl − > SO 4 −2 >HCO 3 − >NO 3 − . Ionic abundance plot of alkalis with Ca and Mg is suggestive of mix type trends of concentrations as evident by moderate correlation (r = 0.57). About 60% of the total samples have alkalis abundance and rests have more Ca + Mg concentrations than alkalis. Taking both results of cluster tree and geochemical features of variables into consideration, the authors classify the elements into two major groups, the first includes TDS, Na, EC, Cl, Ca, SO 4 , and Mg, where the relationship within the group are strong. The second group includes K, HCO 3 , pH, and NO 3 . This group has close relationship with group 1 demonstrate that, the increase in the concentration to some elements could be the same. Some of the analyzed parameters approach a normal distribution, as both their skewnesses and kurtoses reach close to “0”. The study revealed that, all of the element pairs exhibit positive relations.