Proses hidrogeokimia pengontrol salinitas air tanah tidak tertekan di utara Cekungan Air Tanah Jakarta

Abstract

ABSTRAK
Analisis fasies air tanah dan diagram bivariat berbagai parameter hidrokimia sangat bermanfaat untuk mengetahui proses-proses yang mengontrol salinitas air tanah tidak tertekan di utara Cekungan Air Tanah Jakarta. Hasil penelitian menunjukkan bahwa pembentukan fasies air tanah tidak tertekan terutama dipengaruhi oleh proses-proses hidrogeokimia berupa pencucian air tanah oleh perkolasi air hujan, tukar kation, dan penyusupan air laut. Pada Endapan Pematang Pantai (Qbr), pencucian air tanah oleh perkolasi air hujan berlangsung
relatif cepat disertai oleh tukar kation antara ion Ca2+ dan Mg2+ oleh ion Na+, sehingga air tanah didominasi oleh fasies Ca-HCO3, Mg-HCO3, dan Na-HCO3 dengan karakter air bersifat tawar hingga sedikit asin. Pada Endapan Aluvial (Qa), pencucian air tanah oleh perkolasi air hujan dan proses tukar kation antara ion Ca2+ dan Mg2+ oleh ion Na+ berlangsung relatif lambat sehingga air tanah didominasi oleh fasies Na-HCO3 dan Na-Cl dengan karakter air bersifat sedikit asin hingga asin. Pada daerah pantai, beberapa lokasi menunjukkan adanya indikasi penyusupan air laut.
Kata kunci: pencucian air tanah, tukar kation, penyusupan air laut, Jakarta

ABSTRACT
Groundwater facies and bivariate analysis of various hydrochemistry parameters were very useful to know the processes that control the groundwater salinity at the northern part of Jakarta Groundwater Basin. The results show that the formation of groundwater facies mainly influenced by hydrogeochemical processes such as groundwater leaching due to rainwater percolation, cation exchange, and seawater intrusion. At the Beach Ridge Deposits (Qbr), groundwater leaching process due to rainwater percolation was relatively fast accompanied by cation exchange between Ca2+ and Mg2+ ions replaced by Na+ ions. The groundwater was dominated by Ca-HCO3, Mg-HCO3 facies and Na-HCO3 with fresh to slightly saline character. On Alluvial Deposits (Qa), the groundwater leaching process by rainwater percolation and cation exchange between Ca2+ and Mg2+ ions replaced by Na+ ions was relatively slow, so that the groundwater was dominated by Na-HCO3 facies and Na-Cl with slightly to moderately saline characters. In areas which are relatively close to the coast, some of them show the presence of seawater intrusion.
Keywords: groundwater leaching, cation exchange, seawater intrusion, Jakarta