Sources of Chlorine in Groundwater

Chloride is perhaps the most informative ion from a hydrochemical perspective, as it is common in groundwater, has a limited number of identifiable sources, and is hydrochemically conservative. These properties turn chlorine into a most useful hydrochemical marker. 

Three basic sources of chlorine in groundwater have to be considered in every case study  

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15 Evapotranspiration Index Calculation Based on Chlorine as a Hydrochemical Marker 

Chloride is unique as being most conservative among the common ions. Once it is introduced into the groundwater it stays in it, as there exists no water-rock interaction that can remove chlorine from groundwater. Bromide and lithium are similarly conservative, but their concentrations are low in fresh groundwater, and hence they are seldom analyzed. 

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Sea-derived airborne salts. Also called atmospheric salts, these are the most common source of chlorine in groundwater. The phenomenon was described in the previous section. Atmospheric chlorine is of major importance in all cases where the other sources can be ruled out. Thus atmospheric chlorine dominates in groundwaters that are fresh and are more than a few kilometers distant from the seashore (and in many cases up to the shore as well). Marine abundance ratios of various ions to chlorine supply direct evidence for their origin from atmospheric sea-derived salts, as discussed in section 6.13. 

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