| Abstrak/Abstract |
Geomorphological (landform) aspects have long been known to control groundwater conditions
in an area. Thus, combining the hydrogeological and geomorphological aspects
(lithology, genesis, and morphology) becomes a prospective approach for understanding
and delineating the hydrogeochemical processes in an area. The idea is then applied in
Kulonprogo, Java, Indonesia, that consists of several landforms with minimum anthropogenic
influence, in order to identify and quantify the hydrogeochemical processes that are
responsible for hydrogeochemical facies changes in each landform. The groundwater facies
based on Kurlov classification in each landform are strongly influenced by the water–rock
interaction process as it presented in the Gibbs curve. The magnitude of saturation indices
and mass transfer is also diverse that caused a distinction of hydrogeochemical facies and
processes in each landform. For instance, the evolution of groundwater in the denudational
hill to the fluviomarine plain occurs from Ca–HCO3 to Na + K–Ca–HCO3. The analysis
of Durov diagram and inverse modeling—using PHREEQ—reveals that the hydrogeochemical
processes that occur in most of the landform are ion exchange, weathering or
dissolution, and precipitation. Further, oxidation–reduction and mixing only occur in few
landforms. The further investigation from mass balance calculation that constructs from
inverse modeling reveals some interesting findings and hypotheses, such as the construction
of gypsum probably found in the deeper layer on swale as a result of pyrite dissolution
of 1.074 × 10?3 mmol, and it is responsible in escalating Ca2+ and SO42?. Another finding
is that although the calcite mineral mostly related to the past-marine environment, such
as in the east denudational hill, the calcite in the west part is formed as a breakdown of
3.225 × 10?3 mmol anorthite. |
