SPATIAL-TEMPORAL HYDROCHEMICAL ANALYSIS OF UNCONFINED GROUNDWATER IN NORTH JAKARTA AND SURROUNDING AREA

• Main Author: Aprilia Putra, Dita
• Format: Final Project
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/69835
• Institution: Institut Teknologi Bandung

The research area focuses on the northern coastal plain area of Jakarta. Administratively, the research area is located in North Jakarta with an estimated area is about 295,2 km2. Problems that commonly occur in coastal areas are contamination of freshwater by saltwater and degradation of groundwater quality due to the influence of human activities. Nitrates and ammonium can be used as indicators of contamination of unconfined groundwater by human activities. High levels of nitrate and ammonium in groundwater can have a negative impact on human health also the ecosystems. The purpose of this research was to identify the physical and chemical parameters of unconfined groundwater in the research area, determine the distribution of nitrate and ammonium contaminants, and evaluate the quality of unconfined groundwater using the WQI (Water Quality Index) method. The research area consists of two geomorphological units, namely the Coastal Plain Geomorphological Unit and the Bogor Volcano Fan Geomorphology Unit. The geology of the research area from old to young consists of Banten Tuff, Alluvial Fan Deposit, Beach Ridge Deposit, and Alluvial. The hydrogeology of the research area consists of aquifers with flow through inter-grain spaces consisting of several sandstone aquifers. Determination of the physical and chemical characteristics of groundwater was carried out in 10 wells sourced from the Jakarta Groundwater Conservation Center in the range of 2018 – 2020. All wells are assumed to be in an unconfined aquifer system. Based on TDS, groundwater in the research area is grouped into freshwater in the south, freshwater - brackish in the center, and brackish water in the north with a range of pH that is neutral - slightly alkaline. There were no significant changes to the TDS and pH values during 2018 - 2020. The chemical composition of groundwater in the research area has a trend of cations and anions Na+ > Ca2+ > Mg2+ > K+ > NH4 + and Cl- > HCO3 - > SO4 2- > NO3 -. Nitrate values in the research area is ranging from 0 - 44 mg/L. Indications of high nitrate contamination were found in 3 groundwater samples in 2020 which were located in the center of the research area. Ammonium values ranged from 0 – 13 mg/L. Indications of ammonium contamination were found in 3 samples of groundwater in the period 2018 – 2020. The groundwater facies in the research area are sodium chloride, sodium bicarbonate, and calcium bicarbonate types. The chemical composition of groundwater in the research area is influenced by interactions with saltwater in the north, precipitation and evaporation, interactions with rocks, and anthropogenic activities in the south. Groundwater quality based on the WQI method can be grouped as excellent, good, bad, very bad, and unsuitable for consumption. Good groundwater quality during 2018 - 2020 was found in 2 samples located in the southern and central parts of the research area. However, the sample indicated the presence of nitrate contamination.