Jon P. Jones

A simple method to assess unsaturated zone time lag in the travel time from ground surface to receptor

In contaminant travel from ground surface to groundwater receptors, the time taken in travelling through the unsaturated zone is known as the unsaturated zone time lag. Depending on the situation, this time lag may or may not be significant within the context of the overall problem. A method is presented for assessing the importance of the unsaturated zone in the travel time from source to receptor in terms of estimates of both the absolute and the relative advective times. A choice of different techniques for both unsaturated and saturated travel time estimation is provided. This method may be useful for practitioners to decide whether to incorporate unsaturated processes in conceptual and numerical models and can also be used to roughly estimate the total travel time between points near ground surface and a groundwater receptor. This method was applied to a field site located in a glacial aquifer system in Ontario, Canada. Advective travel times were estimated using techniques with different levels of sophistication. The application of the proposed method indicates that the time lag in the unsaturated zone is significant at this field site and should be taken into account. For this case, sophisticated and simplified techniques lead to similar assessments when the same knowledge of the hydraulic conductivity field is assumed. When there is significant uncertainty regarding the hydraulic conductivity, simplified calculations did not lead to a conclusive decision.

Assessing the impact of large-scale dewatering on fault-controlled aquifer systems: a case study in the Acque Albule basin (Tivoli, central Italy)

The development of large-scale bedrock quarry operations often requires high-volume and long-term groundwater extraction to maintain a sustainable working environment. These dewatering activities often influence groundwater levels and flow patterns regionally. In the present study, the influence of the dewatering of the travertine quarry operations near the city of Tivoli, Italy, are quantitatively investigated through an integrated analysis of field data and numerical modeling. Lowering of regional groundwater levels in the vicinity of the quarry has led to destructive land subsidence and alterations to the flow system sustaining a hot-spring area. The study employs a finite element numerical model (FEFLOW) to evaluate and quantify the impact of the extensive dewatering on fault-controlled regional groundwater flow in the Acque Albule basin. By incorporating the physical field data and historical hydrologic information, the numerical model was calibrated against three groundwater scenarios, reproducing the effects of different exploitation activities, coupled with natural changes over the course of the quarry operation. The results indicate that groundwater withdrawals by the mining industry and by “Terme di Roma” spa resulted in the cessation of flow from the primary thermal spring and a drop in the phreatic level in the area consequently affected by land subsidence.RésuméL’exploitation à grande échelle de carrières de pierres de taille nécessite souvent d’extraire un volume d’eau souterraine important sur le long terme, afin de fournir un environnement de travail stable. Ces activités de dénoyage influencent souvent les niveaux piézométriques ainsi que les caractéristiques des écoulements régionaux. Dans la présente étude, l’influence du dénoyage lors d’une exploitation de carrière de travertin, près de la ville de Tivoli, Italie, a été étudiée quantitativement par analyse de données de terrains et modélisation numérique. L’abaissement des niveaux piézométriques régionaux à proximité de la carrière a entraîné une subsidence de terrain destructrice et des altérations du système d’écoulement alimentant une zone de sources chaudes. L’étude emploie un modèle à éléments finis (FEFLOW) pour évaluer et quantifier l’impact du dénoyage important du flux de la nappe souterraine du bassin contrôlé par faille dans le bassin d’Acque Albule. En incorporant les paramètres physiques et l’information hydrologique historique, le modèle numérique a été calibré pour trois scénarios reproduisant les effets de différentes activités d’exploitation, couplés à des modifications normales du mode d’opération de la carrière. Les résultats montrent que les prélèvements d’eau souterraine par l’industrie extractive et par le “Terme di Roma” spa aboutissent à l’arrêt de l’écoulement de la source thermale primaire et à un abaissement du niveau piézométrique dans la zone par suite affectée par la subsidence.ResumenEl desarrollo de operaciones a gran escala de excavaciones de rocas de base a menudo requiere la extracción de grandes volúmenes de agua subterránea por largos plazos para mantener un ambiente de trabajo sustentable. Estas actividades de drenaje a menudo influyen en los niveles de agua subterránea y en los patrones de flujo regional. En el presente estudio, se investiga cuantitativamente la influencia del drenaje en las operaciones de excavaciones de travertino en las cercanías de la ciudad de Tivoli, Italia, a través de un análisis integrado de datos de campo y de modelados numéricos.El descenso de los niveles regionales de agua subterránea en las vecindades de las excavaciones ha provocado una subsidencia destructiva del terreno y alteraciones en el sistema de flujo que sustenta un área de manantiales termales. El estudio emplea un modelo numérico de elementos finitos (FEFLOW) para evaluar y cuantificar el impacto del drenaje extensivo en el flujo subterráneo regional controlado por fallas en la cuenca Acque Albule. Para la incorporación de los datos físicos de campo y la información hidrológica histórica, el modelo numérico fue calibrado con respecto de tres escenarios de agua subterránea, reproduciendo los efectos de las diferentes actividades de explotación, acoplados con cambios naturales sobre el curso de la operación de la excavación. Los resultados indican que la extracción de agua subterránea para la industria minera y para el spa “Terme di Roma” resultaron en la cese del flujo proveniente del manantial termal primario y una caída en el nivel freático en el área consecuentemente afectada por la subsidencia del terreno.摘要进行大型基岩采石作业往往需要大量和长期排除地下水来维持可持续的工作环境。这些抽水活动往往会影响区域地下水水位和地下水流动模式。在本次研究中,通过现场数据的综合分析和数值模拟对意大利帝沃利附近石灰华采石场抽水作业的影响进行了定量研究。降低采石场附近区域地下水位已导致破坏性的地面沉降,也改变了维持温泉区域的地下水流系统。本次研究采用有限元数值模型(FEFLOW)来评价和量化大量抽取地下水对Acque Albule盆地由断层控制的区域地下水流的影响。通过结合物理场数据和历史水文资料,根据三种不同的地下水开采方案对数值模型进行了校正,再现不同地下水开采活动的影响和在采石作业过程中的自然变化。研究结果表明,采矿业和Terme di Roma水疗中心大量抽取地下水造成主要温泉的地下水流的中断和受地面沉降影响的区域潜水位的下降。RiassuntoL’estrazione di materiali litoidi su larga scala spesso necessita di emungimenti consistenti e duraturi, per consentire le operazioni di coltivazione sotto falda. Tali attività possono determinare un generale abbassamento dei livelli piezometrici ed alterare il deflusso idrico sotterraneo a scala regionale. Nel presente studio viene proposta un’analisi dei dati di campo, integrata con una modellazione numerica, per quantificare l’effetto degli emungimenti delle cave di travertino prossime all’abitato di Tivoli (Italia). Gli abbassamenti dei livelli di falda regionale, osservati nelle aree di coltivazione del travertino, hanno innescato fenomeni di subsidenza e alterazioni del regime idraulico di sorgenti termali. L’indagine utilizza un modello numerico ad elementi finiti (FEFLOW) per valutare e quantificare l’impatto dei prelievi idrici sull’acquifero regionale, nel bacino delle Acque Albule, abbinato alla presenza di sistemi di faglie in grado di determinare direttrici di flusso preferenziali. Il modello e’ stato calibrato su tre scenari di impatto antropico, utilizzando dati di campo e informazioni storiche sull’idrologia dell’area, per simulare l’effetto dei prelievi idrici con l’evolversi delle condizioni ambientali. I prelievi idrici indotti dall’industria mineraria e dalle “Terme di Roma” hanno determinato la cessazione del deflusso idrico delle principali sorgenti termali e abbassamenti piezometrici nell’area interessata da fenomeni di subsidenza.ResumoO desenvolvimento de operações de extração de pedra a grande escala requere, frequentemente, a extração de grandes volumes de água subterrânea durante longos períodos, de modo a manter um ambiente de trabalho sustentável. Estas atividades de drenagem influenciam muitas vezes os níveis de água subterrânea e os padrões de fluxo à escala regional. Neste estudo investigou-se quantitativamente a influência da drenagem de travertino explorado numa pedreira, perto da cidade de Tivoli, Itália, através de uma análise integrada de dados de campo e modelação numérica. A descida dos níveis regionais de água subterrânea nas imediações da pedreira conduziu à subsidência destrutiva do terreno e induziu alterações no sistema de fluxo que alimenta uma área de nascentes termais. O estudo aplica um modelo numérico de elementos finitos (FEFLOW) para avaliar e quantificar o impacte da drenagem intensiva no fluxo subterrâneo regional, controlado por falhas, na bacia de Acque Albule. Através da incorporação de dados físicos de campo e de informação hidrológica histórica, o modelo numérico foi calibrado comparando três cenários de água subterrânea, reproduzindo os efeitos das diferentes atividades de exploração, tendo em conta as variações naturais que decorrem durante a operação da pedreira. Os resultados indicam que as extrações de água subterrânea pela indústria mineira e pelo estabelecimento termal “Terme di Roma” resultaram na cessação do fluxo da fonte termal primária e numa descida do nível freático na área consequentemente afetada pela subsidência do terreno.

Delineating baseflow contribution areas for streams – A model and methods comparison

This study addresses the delineation of areas that contribute baseflow to a stream reach, also known as stream capture zones. Such areas can be delineated using standard well capture zone delineation methods, with three important differences: (1) natural gradients are smaller compared to those produced by supply wells and are therefore subject to greater numerical errors, (2) stream discharge varies seasonally, and (3) stream discharge varies spatially. This study focuses on model-related uncertainties due to model characteristics, discretization schemes, delineation methods, and particle tracking algorithms. The methodology is applied to the Alder Creek watershed in southwestern Ontario. Four different model codes are compared: HydroGeoSphere, WATFLOW, MODFLOW, and FEFLOW. In addition, two delineation methods are compared: reverse particle tracking and reverse transport, where the latter considers local-scale parameter uncertainty by using a macrodispersion term to produce a capture probability plume. The results from this study indicate that different models can calibrate acceptably well to the same data and produce very similar distributions of hydraulic head, but can produce different capture zones. The stream capture zone is found to be highly sensitive to the particle tracking algorithm. It was also found that particle tracking by itself, if applied to complex systems such as the Alder Creek watershed, would require considerable subjective judgement in the delineation of stream capture zones. Reverse transport is an alternative and more reliable approach that provides probability intervals for the baseflow contribution areas, taking uncertainty into account. The two approaches can be used together to enhance the confidence in the final outcome.

Understanding the water balance paradox in the Athabasca River Basin, Canada

Aquanty, Inc., 564 Weber Street North, Waterloo, Ontario, Canada Department of Earth and Environmental Sciences, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada Suncor Energy Inc., 150 6 Avenue SW, Calgary, Alberta, Canada Correspondence Hyoun‐Tae Hwang, Aquanty, Inc., 564 Weber Street North, Waterloo, Ontario, Canada. Email: hthwang@aquanty.com Funding information Suncor Energy Inc.