Major ion distribution in Khobar aquifer, Eastern Saudi Arabia

Major ion distribution maps are very common and they have been previously plotted for almost all of the Saudi Arabian aquifers. However, commonly, hydrochemical data is prone to instrumental and human errors. So it is very important to look for a consistent data set in analyzing an aquifer's hydrochemical setting. In order to get a consistent data out of a set for Khobar aquifer's chemical analyses data in Eastern Saudi Arabia, three successive screening steps were undertaken. The resultant data set is presented in isocons of major cations and anions. Major cations in Khobar aquifer show similar patterns. Although they differ in their magnitudes below the latitude 20° 30′, all the three cations increase downstream (towards the Arabian Gulf). The distribution maps of the anions show big differences. Chloride has a more or less similar distribution pattern as sodium. Bicarbonate concentration is high in the Wadi Al Miyah and Hofuf areas; whereas sulfate shows a stream of low sulfate concentration (26° 30′ - 27° 00′) area bordered by two high sulfate areas. Generally, Khobar aquifer water shows sulfate/sulfate-chloride type water in the upstream, evolving into chloride type water in the discharge area. There are interruptions of this general pattern which involve mixing of waters, cation exchange, and localized dissolution of, probably, disseminated sulfate minerals. Based on the trilinear plot, there are five hydrogeochemical facies in the Khobar aquifer.