On the island of Java, groundwater use has significantly increased because of population growth and industrial development. Mt. Karang (a volcano in West Java, Indonesia) has the potential to be a significant groundwater source. Samples were collected twice from springs, dug wells and rivers (rainy and dry seasons). We used information about the aquifer system, hydrogeological conditions and hydro-chemical data to investigate groundwater sources and their associated recharge processes. Chemical data showed that samples belonged to the Ca-Na-HCO3 type in both seasons. The dominant Ca2+ indicates that this water may have flowed through a rock formation composed of andesitic-basaltic rocks with Ca-plagioclase minerals. HCO3- originates from either infiltration of rain water that has been equilibrated with CO2 in the atmosphere, or from CO2 that has been generated by respiration of organic material. Several groundwater samples shows the isotopes values were lighter in the rainy season than in the dry season, which may indicate evaporation during infiltration in the recharge area. There are two types of water isotopically; one is relatively deep circulated water with consistent δD values, the other is of shallow circulated one affected by evaporation. We reconstructed a conceptual model of the groundwater flow systems and recharge mechanisms in Mt. Karang, based on hydrogeological, hydro-chemical and stable isotope data. This model will give an improved understanding of the region's hydrogeological condition.
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