Dasapta Erwin Irawan
Lecturer/researcher, Applied Geology Research Division, Faculty of Earth Sciences and Technology, Institut Teknologi Bandung
The estimated groundwater potential in Indonesia is about 100 billion m3, circulated in 421 groundwater basins. Most of the basins are composed of volcanic deposits. The porous and fracture system deposits perform as productive aquifers, shown by the emergence of spring belt at the foot slopes with enormous discharge and excellent quality. As part ring of ﬁre, Indonesia is encircled with volcanic belt. There are 128 volcanoes or 13–17% of total volcanoes in the world. These volcanoes produce volcanic deposit cover a total area of 33,000 km2 or one sixth of Indonesia’s land (Department of Mining and Energy, 1979). Therefore the hydrogeological setting of volcanic deposit is very interesting to be studied.
Thesis and Dissertation
For the last 15 years, I have worked in volcanic areas for academic research. I worked in Southern Bandung area for my undergraduate final project and Mount Ciremai area for master and PhD thesis. The result of each project have been published in refereed journal and presented in several conferences. For my undergraduate project, I have written the geological condition of Southern Bandung area which has many small volcanic vents (Irawan et al., 2000) and . In the paper, I also proposed geological mapping technique to identify volcanic aquifer system.
In my master thesis and PhD dissertation, I worked in Mount Ciremai, a solitaire-strato volcano with elevation of 3072 masl. It situated in Majalengka (west flank) and Kuningan Regency (East flank), 20 km south of Cirebon. The diameter of this volcano, from the peak to the foot slope is about 10 km. Many studies have been conducted at the area, consists of regional geology and hydrogeology in large scale. There are at least 119 springs with variable discharge, from 10 L/s to nearly 100 L/s (Bappeda of Kuningan Regency, 2000). The availability of data and groundwater information, is fundamental to understanding the conditions necessary to support the planning of ground water utilization of ground water to achieve optimum utilization of groundwater and its sustainability.
I identified three main aquifer units: pyroclastic breccias, lava, and laharic breccias. All of the observed-aquifers are unconfined aquifers. They feed water to spring zone encircling Ciremai. The spring zone is interpreted to be controlled by slope morphology. However, the morphology forms two slope breaks: at 750 masl (average 4o of slope difference) and at 1350 masl (19o of slope difference) (Irawan et al., 2003). I also found three factors to control the spring emergence (Irawan et al., 2006). First factor is the change of rock distribution from lava to laharic breccias. Morphological features in the form of ridges and valleys also contribute to control groundwater flow pattern. The second factor is fracture system in lava flows and continuous conduits in laharic breccias. The third factor is the intensive weathering processes in the study area. The process produces thick residual soil and high final infiltration rate. The residual soil is very potential in storing and transmitting water.
In another paper, I have tested 25 samples of thermal waters of various sources. I found that the thermal system is reflected by groundwater chemical properties. The characteristics shift from meteoric-dominated waters to formation-dominated waters (Irawan and Puradimaja, 2006). Moreover, I have conducted hydrogeochemical analysis on the area based on 119 spring locations in at Mount Ciremai area. Using Cluster analysis on 14 parameters, I have successfully extracted three clusters (Irawan et al., 2009b). Cluster 1 (112 springs) is distinguished by normal temperatures, low TDS, EC, and high bicarbonate concentrations. Cluster 2 (five springs) has moderately high temperature, TDS, EC, and high concentration of chloride. Cluster 3 (two springs) exhibits high temperature, anomalous high TDS, EC, and chloride concentration. Three hydrogeological systems have been pictured based on the 3 clusters consecutively. The first system is developed in shallow unconfined aquifer, with domination of high bicarbonate (4.2 me/L) meteoric water. The second system is predominated with mixing processes, between groundwater in unconfined aquifer and hot groundwater from deeper aquifers. The third system is primarily dominated by groundwater flow from deep formation. The hot – deep seated groundwater flow also carries mud particles. It has anomalous high TDS (>1000 mg/L), EC (515 S/cm), and chloride (99 me/L) from interaction between groundwater with clay formations, interpreted as Kaliwangu Formation. The identification of water quality and the hydrogeological role of certain area is important to regional planning. It will assist the groundwater spring and well protection measures (Irawan et al., 2009a).
It is very important as sources of fresh water in Indonesia. Land use changes such as advancement of agriculture or inhabitation upslope results in changes in the local hydrological systems. This influences quantity and quality of groundwater. In Bandung Basin, volcanic deposit is the most productive aquifer system. On the other hand, they exhibit large spatial heterogeneity with generally no single structural geological direction. This complex subsurface architecture influences the flow patterns as well as the groundwater quality.
Based on current condition, part of my current focus is how to provide the hydrostratigraphy of volcanic aquifers in Bandung area. The research is based on environmental isotope measurement in groundwater and morphometry. In 2011, I have selected to receive two research grants from ITB, entitled: The Hydrostratigraphy of Bandung Basin based on Deuterium, Oxygen-18, and Tritium and Morphometry Analysis and Field Permeability Value of Northern Bandung Area.
My work on these projects consists of two major measurements: hydrochemistry parameter as well as environmental isotope contents and field permeability (final infiltration rate). These techniques will allow us to estimate of spring or well capture zone and to link recharge areas and discharge areas with sufficient precision. I will also rely on classic multivariate statistical methods and data mining techniques. This provides a more quantitative foundation for the analysis, allows the establishment of more accurate models, and gives more insight into an groundwater behaviour.
I plan to continue my efforts in learning groundwater tracer technology and hydrometry. The synergy of these two techniques will allow me to fingerprint groundwater movement and behaviour. I will also seek an active cooperation with colleagues in both areas, in order to gain a better understanding of the dynamic process of learning.
In cooperation with Dr. T. Bogaard at Delft University (The Netherlands), I will continue my current efforts to evaluate the result of my research, and also to write joint paper. At the same time, it will provide myself an excellent and diverse opportunity widen my insight about the advancement of hydrogeology in general.
Bappeda of Kuningan Regency, 2000. Groundwater Resources of Kuningan Regency Report, Board of Regional Planning (Bappeda) of Kuningan Regency.
Department of Mining and Energy, 1979. The Database of Volcanoes in Indonesia, Department of Mining and Energy.
Irawan, D.E. and Puradimaja, D.J., 2006. The Differentiation of Hyperthermal Groundwater Origin by using Multivariate Statistics On Water Chemistry. Jurnal Geoaplika, 1(2).
Irawan, D.E., Puradimaja, D.J. and Bogaard, T., 2006. Spatial Analysis of Volcanic Hydrogeology at Gunung Ciremai, West Java, Indonesia, Persidangan Bersama Geosains. Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia.
Irawan, D.E., Puradimaja, D.J. and Hutasoit, L.M., 2003. Geological Control to Spring Emergence. Case Study: East Slope of Mt. Ciremai, Buletin Geologi. Buletin Geologi, 35 (1): 8.
Irawan, D.E., Puradimaja, D.J., Notosiswoyo, S. and Soemintadiredja, P., 2009a. Hydrochemical tracers to map hydrogeological setting at Mount Ciremai. Warta Bapeda
Irawan, D.E., Puradimaja, D.J., Notosiswoyo, S. and Soemintadiredja, P., 2009b. Hydrogeochemistry of Volcanic Hydrogeology based on Cluster Analysis of Mount Ciremai, West Java, Indonesia. Journal of Hydrology.
Irawan, D.E., Puradimaja, D.J., Yuwono, S. and Syaifullah, T.A., 2000. Geological Mapping of Volcanic Deposit for Volcanic Aquifer System Identification. Case Study: Pasir Jambu-Situwangi Soreang, Bandung Regency, West Java. Buletin Geologi, 3.