Lambok M. Hutasoit

Controlling factors and driving mechanisms of nitrate contamination in groundwater system of Bandung Basin, Indonesia, deduced by combined use of stable isotope ratios, CFC age dating, and socioeconomic parameters

Number of populations, industry, and economic activities in Indonesia are growing rapidly and these impacts on natural environments raise awareness about water quality issue over the country. Bandung Basin, one of the most growing rapidity urban areas in Indonesia, was assessed for NO3- contamination in groundwater systems, and its controlling factors and driving mechanisms were investigated with the aim to demonstrate novelty on the use of combination of parameters of stable isotope ratios in nitrate (δ15N and δ18O in NO3-), groundwater age (using CFC-12 age tracer), and socioeconomic parameters (land-use, population, and economic database). Groundwater NO3- concentrations at present time did not exceed HWO limit for all the analyzed samples (3.00 mg/L in average with maximum value of 20.69 mg/L, n = 102). Dual stable isotopic analysis together with CFC-12 groundwater age determination suggest that anthropogenic activities are the major causes for increasing NO3- concentrations in groundwater. Those activities under respective land-use are industrial and domestic wastes for urban areas and chemical fertilizers for paddy and plantations areas. In general shallow unconfined aquifer is more vulnerable to NO3- contamination compared with deep confined aquifer because denitrification partly occurs in deep anoxic aquifer and this led attenuation of NO3- pollution in groundwater flowing. However, it seems likely at groundwater depression cones in urban areas that more concentrated waters are transported from shallow aquifer into deep aquifer system through downward vertical fluxes due to excessive pumping. Principal component analysis (PCA) on NO3- concentrations with socioeconomic parameters indicated that industrial and population growths are the main factors related to groundwater NO3- contamination. This result corresponds to CFC-age dating which shows younger (more recently recharged) groundwaters as being more contaminated than older ones do. Our study implies that NO3- contamination in this area may become more severe in future with a lack of necessary controls and treatment for human-induced nitrogen sources. Proposed approach is useful to understand how the NO3- contaminant behaves in large basin aquifer system under urban environments and might be applicable in other developing regions too because increasing populations may be associated with increasing nitrogen loadings.

Impact of excessive groundwater pumping on rejuvenation processes in the Bandung basin (Indonesia) as determined by hydrogeochemistry and modeling

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 14C 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.ResumeDans le bassin de Bandung, Indonésie, le pompage excessif des eaux souterraines dû à une augmentation rapide de l’industrialisation et de la croissance démographique a entraîné des problèmes environnementaux au niveau du sous-sol, tels qu’un abaissement excessif des eaux souterraines et des affaissements de terrain. Dans cette étude, de multiples techniques hydrogéochimiques et de modélisation numérique ont été appliquées pour évaluer les processus de recharge et l’âge des eaux souterraines (renouvellement). Bien que toutes les eaux souterraines du bassin de Bandung soient rechargées à la même altitude à la périphérie du bassin, le type d’eau et le temps de résidence des eaux souterraines de surface et profondes pourraient clairement être différenciés. Cependant, il y avait un rabattement important des eaux souterraines dans toutes les zones de dépression et il y a des preuves de mélange des eaux souterraines entre les eaux souterraines de surface et profondes. Le mélange des eaux souterraines a été retracé à partir des concentrations élevées de dichlorodifluorométhane (CFC-12) dans certains échantillons d’eaux souterraines profondes et en estimant le taux de renouvellement (R) dans certains piézomètres représentatifs. L’importance de la concentration de CFC-12, en tant qu’indicateur des eaux souterraines jeunes, montre une bonne corrélation avec R, déterminé en utilisant l’activité 14C dans des échantillons prélevés entre 2008 et 2012. Ces corrélations ont été confirmées avec l’estimation du flux vertical descendant des aquifères les moins profonds en utilisant la modélisation numérique. De plus, la variation du flux vertical est. affectée par la modification du pompage des eaux souterraines. Depuis les années 1970, le flux vertical a augmenté de manière significative et a atteint environ 15% de la quantité totale des pompages au cours des années 2000, car il a compensé le pompage des eaux souterraines. Cette étude a clairement révélé les processus d’impact des eaux souterraines causés par un pompage excessif des eaux souterraines à l’aide d’une combinaison de méthodes hydrogéochimiques et de modélisation.ResumenEn la cuenca de Bandung, Indonesia, el bombeo excesivo del agua subterránea originado por los rápidos aumentos en la industrialización y el crecimiento de la población ha causado problemas ambientales en el subsuelo, como el drenaje excesivo del agua subterránea y la subsidencia del terreno. En este estudio, se han aplicado múltiples técnicas hidrogeoquímicas y modelos numéricos para evaluar los procesos de recarga y la edad del agua subterránea (rejuvenecimiento). Aunque toda el agua subterránea en la cuenca de Bandung se recarga a una misma elevación en la periferia de la cuenca, el tipo de agua y el tiempo de residencia del agua subterránea somera y profunda podrían diferenciarse claramente. Sin embargo, hubo una importante profundización de los niveles del agua subterránea en todas las áreas de depresión y hay evidencias de la mezcla de agua entre el agua subterránea somera y profunda. La mezcla de agua subterránea se evidencia en las altas concentraciones de diclorodifluorometano (CFC-12) en algunas muestras de agua subterránea profunda y en la estimación de la relación de rejuvenecimiento (R) en algunos pozos de observación representativos. La magnitud de la concentración de CFC-12, como indicador de aguas subterráneas jóvenes, mostró una buena correlación con R, determinada mediante la actividad 14C en muestras tomadas entre 2008 y 2012. Estas correlaciones se confirmaron con la estimación del flujo descendente vertical desde acuíferos someros a profundos usando un modelado numérico. Además, el cambio en el flujo vertical se ve afectado por el cambio en el bombeo de aguas subterráneas. Desde la década de 1970, el flujo vertical aumentó significativamente y alcanzó aproximadamente el 15% de la cantidad total de bombeo durante la década de 2000, ya que compensó el bombeo de agua subterránea. Este estudio reveló claramente los procesos de impacto del agua subterránea causados por el bombeo excesivo del agua subterránea mediante una combinación de métodos hidrogeoquímicos y modelado.摘要在印度尼西亚万隆盆地,工业化迅速发展及人口增长引起的地下水过度开采导致地表以下出现环境问题,诸如地下水位下降及地面沉降。在本研究中,应用水文地质化学技术及数值建模评估补给过程和地下水年龄(恢复期)。尽管万隆盆地的所有地下水在盆地边缘同意高度得到补给,但浅层和深层地下水的水类型和滞留时间明显有区别。然而,在所有的低洼去地下水位都有大幅下降,有浅层地下水和深层地下水混合的证据。通过地下水水样中的二氟二氯甲烷(CFC-12)很高的含量及通过估算一些代表性的观测井中的恢复比(R)可追踪地下水的混合。作为年轻地下水指示的CFC-12含量量级与2008年到2012年间采用样品中的14C活度所确定的R具有很好的相关性。这些相关性通过数值模拟估算从浅层地下水到深层地下水垂直向下的通量得到了确认。此外,垂直通量的变化受地下水抽水的影响。自20世纪70年代,垂直通量显著增加,在二十一世纪前十年,大约达到总抽水量的15%,以补偿地下水的抽取。本研究采用水文地质化学方法和建模方法清晰地揭示了地下水过度抽取引起的地下水影响的过程。ResumoNa bacia de Bandung, Indonésia, o bombeamento excessivo de águas subterrâneas causado pelo rápido aumento no crescimento industrial e populacional tem causado problemas ambientais de subsuperfície, como declínios excessivos nas águas subterrâneas e subsidência de terreno. Nesse estudo, múltiplas técnicas hidrogeoquímicas e modelagem numérica foram aplicadas para avaliar o processo de recarga e datação das águas subterrâneas (rejuvenescimento). Apesar de toda águas subterrâneas da bacia de Bandung ser recarregada na mesma elevação na periferia da bacia, o tipo de água e o tempo de residência das águas subterrâneas rasas e profundas puderam ser claramente diferenciados. Entretanto, houve um rebaixamento significativo das águas subterrâneas em todas as áreas de depressão e existe uma evidencia de mistura de águas subterrâneas entre as águas subterrâneas rasas e profundas. A mistura das águas subterrâneas foi rastreada pelas altas concentrações de diclorodifluorometano (CFC-12) em algumas amostras de águas subterrâneas profundas e pela estimativa da razão de rejuvenescimento (R) em alguns poços de observação representativos. A magnitude da concentração de CFC-12, como um indicador de águas jovens, mostrou uma boa correlação com R, determinada usando a atividade de 14C nas amostras coletadas entre 2008 e 2012. Essas correlações foram confirmadas com a estimativa do fluxo descendente vertical dos aquíferos mais rasos para os mais profundos usando modelagem numérica. Além disso, a mudança no fluxo vertical é afetada pela mudança no bombeamento das águas subterrâneas. Desde os anos 1970, o fluxo vertical aumentou significativamente e alcançou aproximadamente 15% do montante total bombeado durante os anos 2000, uma vez que isso compensou o bombeamento das águas subterrâneas. O estudo revelou claramente o processo de impacto das águas subterrâneas causado pelo bombeamento excessivo das águas subterrâneas usando uma combinação e métodos hidrogeoquímico e modelagem.