THE MODIFIED CHEMICAL CONSTITUENT OF SEA WATER INTRUDING INTO THE COASTAL AQUIFER

Abstract

Intruding sea water into the aquifer often has different chemical composition from that of original sea water. Such phenomena are observed in the coastal region of Beppu Spa and explained by the process of cation exchange between intruding sea water and soil being in contact with thermal water for a long time before salt contamination. As the result, mixing sea water becomes rich in Ca ion and poor in Na ion in the period of initial stage of sea water intrusion, but recovers to the original sea water with progress of intrusion. Concentrations of iodine in intruding sea water are found to be much larger than those in the ocean from the observations in Beppu and Obama Spas. However, ratios of Br/Cl or I/Cl in thermal water containing large salt concentrations are found to be usefull as the index of contamination by the sea water.