Geochemical Approach for Seawater Intrusion Assessment in the Area around Yogyakarta International Airport, Indonesia

Abstract

A total of 10 groundwater samples were obtained from groundwater wells with depths of around 8-10 meters distributed around Yogyakarta International Airport, Indonesia to test the geochemical of groundwater for assessing the seawater intrusion. Samples were taken into polyethylene bottles with a volume of 1000 ml. These bottles were rinsed to reduce the risk of any contamination prior to their filing with sampled water. Piper Diagram is used to evaluate seawater intrusion by plotting the percentages of cations and anions (in mEq/L) as a single point on the triangle. The groundwater facies' in the study area are CaHCO3 and CaNaHCO3. It suggests that the origins of the elements Ca and Na were estimated to derive from the dissolution of the plagioclase, hornblende, and pyroxene minerals found in the sand sediment, while the elements of HCO3 were estimated from the dissolution of carbonate minerals or the decomposition of organic matter and root respiration in the soil zone may enrich their concentration. The wells affected by slightly freshening were ZAM-04, ZAM-05, ZAM-06, ZAM-08, and ZAM-10. While the wells that are not affected by the intrusion or fresh were ZAM-01, ZAM-03, ZAM-07, and ZAM-09. However, ZAM-02 well which is close to the coastline and the closest to the airport development area was the only well that affected significantly by freshening, comparing with other wells. Another expected controlling factor was the fault in the northern part which continuously leads that location. By supported a flow pattern or large river, it was concluded the alluvial deposits buried the fault, and it was estimated to continue to that location.