INVESTIGATING THE CHROMATOGRAPHIC EFFECT OF CHEMICAL SPECIES IN GROUNDWATER
The chromatographic effect is exhibited by the concentration anomalies of anion species SO42- , Cl-, and HCO3-, and elements As, Ca, Cd, Ni, and Pb of unknown speciation. The concentration anomalies of individual ion species passing through two monitoring wells separated by 660 m could be used to evaluate the speed of migration of that species. Based on these anomalies, the speeds for SO42- and HCO3- are estimated to be 110 m/year or 0.32 m/day. Similar migration speeds were derived for Cl- and As. A hydraulic conductivity of 110 m/year was obtained by groundwater modeling in 1995. In order to refine migration speed evaluations, a higher-resolution record of the duration of anomalies must be obtained through more frequent groundwater sampling. The migration speed of these chemical species through the aquifer follows an increasing sequence: Ca>As=Cl->HCO3-=SO42- . Other elements such as Cd, Ni, and Pb have multiple anomalies and may indicate the existence of multiple species. In addition, significant changes in concentrations of Cl- and Ca down piezometric gradient are observed while SO42 - and HCO3- remain relatively unchanged. The chromatographic effect of the migration of these chemical species through an aquifer can only be observed by a long-term study.