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SariPenurunan permukaan air tanah yang cukup signifikan akibat pengambilan air tanah dilaporkan telah terjadi di daerah Bandung dan sekitarnya. Salah satu metode yang cukup potensial untuk memulihkan kondisi air tanah di daerah ini adalah peresapan buatan, mengingat daerah ini mempunyai curah hujan yang cukup tinggi. Dalam penelitian ini dilakukan simulasi numerik untuk memprediksi kondisi air tanah pada lima tahun ke depan, jika: 1) tidak dilakukan upaya pemulihan (do-nothing) (Skenario 1), dan 2) dilakukan peresapan buatan (Skenario 2). Dari hasil rekonstruksi hidrogeologi, yang diperlukan untuk membangun sistem fisik daerah simulasi, diketahui bahwa akuifer utama di daerah penelitian adalah Formasi Cibeureum yang disusun oleh kipas-kipas vulkanik; akuitar utama adalah Formasi Kosambi yang terdiri atas endapan danau, sementara batuan dasar hidrogeologi tersusun oleh Formasi Cikapundung, batuan vulkanik Kuarter yang lain selain Formasi Cibeureum, dan batu-batuan Tersier. Daerah resapan di daerah ini adalah daerah-daerah tempat Formasi Cibeureum tersingkap. Hasil simulasi numerik Skenario 1 menunjukkan bahwa jika tidak dilakukan pemulihan terhadap kondisi air tanah, maka pada tahun 2013 akan terjadi penambahan Zona Kritis sebesar 116 % dan Zona Rusak sebesar 570 %. Hasil skenario ini juga menunjukkan bahwa akan terjadi groundwater mining di beberapa Zona Rusak seluas 244 km 2 atau 41 % dari total luas akuifer terkekang di daerah penelitian. Hasil simulasi numerik Skenario 2 menunjukkan bahwa peresapan buatan di Zona Kritis dan Zona Rusak dapat dengan efektif memulih kan kondisi permukaan air tanah di tahun 2013, yaitu seluruh daerah penelitian menjadi Zona Aman. Jumlah peresapan buatan yang harus disediakan adalah sebesar 164 juta m 3 /tahun dan dimulai dari tahun 2009. Peresapan buatan ini dapat berarti sumur resapan, reservoir permukaan, atau parit resapan tempat Formasi Cibeureum tersingkap, atau sumur injeksi di kawasan Formasi Cibeureum tidak tersingkap.Kata kunci: permukaan air tanah, Bandung, resapan buatan, simulasi numerik AbstrAct Significant groundwater level drawdown caused by groundwater abstractions has been reported to occur in Bandung and its surrounding area. One potential method to recover the groundwater condition is artifical recharge, considering high quantity of rainfall in this area. In this research, numerical simulation has been performed in order to predict groundwater condition in the next five years, if: 1) no recovery action is taken (do-nothing) (Scenario 1), and 2) artificial recharge is performed (Scenario 2

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In the Bandung basin, Indonesia, excessive groundwater pumping caused by rapid increases in industrialization and population growth has caused subsurface environmental problems, such as excessive groundwater drawdown and land subsidence. In this study, multiple hydrogeochemical techniques and numerical modeling have been applied to evaluate the recharge processes and groundwater age (rejuvenation). Although all the groundwater in the Bandung basin is recharged at the same elevation at the periphery of the basin, the water type and residence time of the shallow and deep groundwater could be clearly differentiated. However, there was significant groundwater drawdown in all the depression areas and there is evidence of groundwater mixing between the shallow and deep groundwater. The groundwater mixing was traced from the high dichlorodifluoromethane (CFC-12) concentrations in some deep groundwater samples and by estimating the rejuvenation ratio (R) in some representative observation wells. The magnitude of CFC-12 concentration, as an indicator of young groundwater, showed a good correlation with R, determined using 14 C activity in samples taken between 2008 and 2012. These correlations were confirmed with the estimation of vertical downward flux from shallower to deeper aquifers using numerical modeling. Furthermore, the change in vertical flux is affected by the change in groundwater pumping. Since the 1970s, the vertical flux increased significantly and reached approximately 15% of the total pumping amount during the 2000s, as it compensated the groundwater pumping. This study clearly revealed the processes of groundwater impact caused by excessive groundwater pumping using a combination of hydrogeochemical methods and modeling.

DOI:10.17014/ijog.7.3.273-289Land subsidence is the lowering of ground surface due to natural and/or anthropogenic processes. Land subsidence in the Semarang-Demak plain has been going on for more than thirty years, however the contribution of natural and anthropogenic causes is relatively unknown. The Semarang-Demak plain has only been formed recently, as a result of rapid sedimentation during the Holocene. The basin mainly consists of underconsolidated thick clay, vulnerable to excessive settlement due to its own weight and additional pressures. The rate of natural subsidence is quantified by modelling the delayed dissipation of measured overpressure and the resulting vertical deformation, resulting in natural compaction rate of less than 0.8 cm/year in Semarang City and more than 0.8 cm/year in Demak Regency. The subsidence computed for parts of the Semarang-Demak plain were compared to the measured geodetic rate, and the relative contributions of natural and anthropogenic causes are derived. Modelling results show that natural subsidence is more significant at the eastern part of the plain (Demak region) with compaction rate reaching 0.9 - 2.2 cm/year that counts for 48 - 92% of the total land subsidence.