Antonella Baiocchi

Impact of groundwater withdrawals on the interaction of multi-layered aquifers in the Viterbo geothermal area (central Italy)

The impact of groundwater withdrawals on the interaction between multi-layered aquifers with different water qualities in the Viterbo geothermal area (central Italy) was studied. In this area, deep thermal waters are used to supply thermal spas and public pools. A shallow overlying aquifer carries cold and fresh water, used for irrigation and the local drinking-water supply. Starting with a conceptual hydrogeological model, two simplified numerical models were implemented: a steady-state flow model of the entire groundwater system, and a steady-state flow and heat transport model of a representative area, which included complex interactions between the aquifers. The impact of increased withdrawals associated with potential future development of the thermal aquifer must be considered in terms of the water temperature of the existing thermal sources. However, withdrawals from the shallow aquifer might also influence the discharge of thermal sources and quality of the water withdrawn from the shallow wells. The exploitation of the two aquifers is dependent on the hydraulic conductivity and thickness of the intervening aquitard, which maintains the delicate hydrogeological equilibrium. Effective methods to control this equilibrium include monitoring the vertical gradient between the two aquifers and the residual discharge of natural thermal springs.RésuméL’impact des prélèvements d’eau souterraine sur l’interaction entre un complexe d’aquifères comprenant différentes qualités d’eau dans la zone géothermique de Viterbo (Centre de l’Italie) a été étudié. Dans cette zone, les eaux thermales profondes sont utilisées pour alimenter des thermes et des piscines publiques. Un aquifère supérieur peu profond transporte des eaux douces froides, utilisées pour l’irrigation et pour l’alimentation en eau potable. A partir d’un modèle conceptuel hydrogéologique, deux modèles numériques simplifiés ont été mises en œuvre : un modèle d’écoulements en régime permanent pour la totalité du système aquifère, et un modèle en régime permanent pour les flux et le transport de chaleur d’une zone représentative, comprenant les interactions complexes entre les aquifères. L’impact de l’augmentation des prélèvements associée au développement potentiel futur de l’aquifère thermal doit être considéré en termes de température des sources thermales existantes. Cependant, les prélèvements de l’aquifère superficiel peut aussi influencer le débit des sources thermales et la qualité de l’eau prélevée au niveau des puits peu profonds. L’exploitation des deux aquifères est dépendante de la conductivité hydraulique et de l’épaisseur de l’aquitard intervenant, qui maintient l’équilibre hydrogéologique fragile. Des méthodes efficaces de contrôle de cet aquifère comprend le suivi du gradient vertical entre les deux aquifères et le débit résiduel des sources thermales naturelles.ResumenSe estudió el impacto de las extracciones de agua subterránea en la interacción entre acuíferos multicapas con diferentes calidades del agua en el área geotermal de Viterbo (Italia Central). En esta área, las aguas termales profundas son usadas para el abastecimiento de spas y natatorios públicos termales. Un acuífero somero suprayacente transporta agua fría y dulce, usada para irrigación y el abastecimiento local de agua potable. Comenzando con un modelo hidrogeológico conceptual, se implementaron dos modelos numéricos simplificados: un modelo de flujo en estado estacionario sobre la totalidad del sistema de agua subterránea, y un modelo en estado transitorio de flujo y transporte de calor de un área representativa, que incluyó las complejas interacciones entre los acuíferos. El impacto de las crecientes extracciones asociadas con un futuro desarrollo potencial del acuífero termal debe ser considerado en función de la temperatura del agua de las fuentes termales existentes. Sin embargo, las extracciones provenientes del acuífero somero podrían también influenciar la descarga de las fuentes termales y la calidad del agua extraída desde los pozos someros. La explotación de los dos acuíferos es depende de la conductividad hidráulica y espesor del acuitardo interviniente, el cual mantiene el delicado equilibrio hidrogeológico. Los métodos efectivos para controlar este equilibrio incluyen el monitoreo del gradiente vertical entre los dos acuíferos y la descarga residual de los manantiales naturales termales.摘要本文研究了地下水开采对viterbo地热区不同水质多层含水层之间相互作用的影响。在这一地区,深层地热水主要用于当地的温泉洗浴和公共泳池。上覆浅层含水层中的冷淡水主要用于灌溉和当地的饮用水供水。基于水文地质概念模型,两种简化的数值模型应用于本次研究,分别为整个地下水系统的稳定流模型和包含含水层间复杂相互作用的典型区稳定流和热运移模型。与潜在深层热含水层未来开发有关的地下水开采量增加影响必须从现有热源中地下水温度来考虑。然而,浅层地下水开采也可能影响热源的排泄量及浅层井中水的水质。上、下含水层的开采量主要取决于能使两个含水层形成微妙平衡的水文地质参数,即渗透系数和含水层间弱透水层的厚度。有效控制上述平衡的办法包括监测含水层间垂向水力梯度和天然热泉的剩余排泄量。ResumoFoi estudado o impacte das extrações de água subterrânea na interação entre aquíferos multicamada com diferentes qualidades de água na área geotérmica de Viterbo (Itália central). Nesta área, águas termais profundas são usadas para abastecimento de termas e piscinas públicas. Um aquífero livre superficial com água doce a temperatura normal é usado para rega e para o abastecimento doméstico local. Começando por um modelo hidrogeológico concetual, foram implementados dois modelos numéricos simplificados: um modelo de fluxo estacionário de todo o sistema hidrogeológico e um modelo de fluxo estacionário e de transporte de calor de uma área representativa que incluiu interações complexas entre os aquíferos. O impacte do incremento das extrações, associado ao potencial desenvolvimento futuro do aquífero termal, deve ser considerado em termos da temperatura da água das fontes termais existentes. No entanto, as extrações a partir do aquífero livre podem também influenciar a descarga das fontes termais e a qualidade da água extraída dos poços superficiais. A exploração dos dois aquíferos está dependente da condutividade hidráulica e da espessura do aquitardo, o qual mantém o delicado equilíbrio hidrogeológico. Métodos efetivos de controlo deste equilíbrio incluem a monitorização do gradiente vertical entre os dois aquíferos e da descarga residual das nascentes termais naturais.

Comparison of pumping at constant head and at a constant rate for determining the sustainable yield of a well

Determining the yield of a production well remains one of the main problems in hydrogeological studies. Starting from the results of a 3-year-long monitoring of a continuously exploited well functioning at constant head (i.e., at a variable discharge rate), a new pumping style has been examined using numerical models. The objective is to control the impact of pumping on the aquifer in accordance with the principle of sustainability. Different models were developed in a transient state and were calibrated using discharge data of the well during the recession periods. Successively, the trends of the residual outflow from the aquifer system with the well operating at variable discharge and at constant discharge were simulated. The results indicate that the ratio of the volume of water pumped from the well to the volume of residual outflow is a significant indicator of the sustainability of groundwater withdrawals. Modeling confirms that a constant discharge rate can be derived from the information gained through a preliminary production phase of a well at constant head. This approach appears to be particularly useful when the problem is determining the sustainable yield of a single well from aquifers with low hydraulic diffusivity.

Estimation of rock mass permeability using variation in hydraulic conductivity with depth: experiences in hard rocks of western Turkey

Determining permeability of fractured rocks is a focal point in engineering projects. Many methods have been developed for direct in situ determination of the hydraulic parameter; nevertheless, especially in the preliminary stages of rock mass characterization, empirical correlations are used to estimate the rock permeability. This study proposes a relationship between rock mass depth and permeability that may be useful for initial hydraulic characterization of fractured media. For this purpose, results of core drilling, injection tests, and geophysical prospecting carried out in fractured hard rocks—mainly andesites and secondly metamorphites—of western Turkey were considered. A decrease in rock mass permeability with depth is evident from the results of injection tests. Within the depth of investigation (the first 100 m), hydraulic conductivity shows an exponential declining trend with depth and depends on the surface value of the hydraulic parameter. No correlation is evident between discontinuity spacing and depth or rock quality designation (RQD) and depth. The applicability of the relationship found requires a hydrostructural homogeneity of the rock mass, which can be verified through inexpensive geological survey and geophysical prospecting.

Reply to Comment on “Impact of groundwater withdrawals on the interaction of multi-layered aquifers in the Viterbo geothermal area (central Italy)”: report published in Hydrogeology Journal (2013) 21:1339–1353, by Antonella Baiocchi, Francesca Lotti and Vincenzo Piscopo

The Comment concerns directly the subject article of Baiocchi et al. (2013) and indirectly the article of Baiocchi et al. (2012). These two articles present the results of two research projects on the hydrothermal area of Viterbo, central Italy, funded by the Regione Lazio and the Ministry of Education, Universities and Research. The hydrogeology group in the Department of Biological and Ecological Sciences at the University of Tuscia has conducted investigations and measurements authorized by Regione Lazio, that is, the body that governs the mining and thermal waters permits. In the period 2008–2010:

Sessione S 30. Groundwater resource among human needs, reuse and environmental requirements

Abstract from 88th Congress of the Italian Geological Society, 2016-09-07 - 2016-09-09, NaplesAbstract from 88th Congress of the Italian Geological Society, 2016-09-07, 2016-09-09, Naplesbook Edited by D. Calcaterra, S. Mazzoli, F.M. Petti, B. Carmina & A. Zuccari doi: 10.3301/ROL.2016.79

Hydrogeological site characterization of marly-silici-calcareous rocks through surveys of discontinuities and pumping tests

One of the challenges in the characterization of fractured aquifers is to define whether the approximation to a porous medium is valid or not. In this context, the present study concerns the hydrogeological characterization of a small area constituted by densely fractured marly-silici-calcareous rocks. The hydrogeological investigations included fracture network surveys and pumping tests. The survey of the outcrops showed a rock mass characterized by a high number of persistent discontinuities with a wide spatial distribution, high frequency and a wide range of values of the aperture in the different systems. These characteristics imply the possibility of considering the rock mass as an equivalent porous medium at the outcrop scale. Pumping tests highlighted a consistent reaction of the various monitoring points and a similar trend of the drawdown-time curve, resulting in considering the aquifer as continuous medium at the scale of the volume influenced by pumping. The drawdown maps seems to be related to a weak anisotropy of the aquifer in the horizontal plane with the major axis of the ellipse aligned along the direction NE-SW, consistent with the directions of the principal components of the hydraulic conductivity resulting from the hydraulic model of the rock mass. Although the aquifer can be considered an equivalent anisotropic porous medium at the scale of the study, the comparison between the results of pumping tests and of the rock mass survey indicates that this approach would be not sufficient to characterize groundwater movement.