Karst aquifers are very easily contaminated because of the surficial features that commonly exist in karst terranes. Pollutant releases into sinkholes, sinking streams, and/or losing streams commonly result in concentrated solutes rapidly infiltrating and migrating through the subsurface to eventually discharge at downgradient springs unless intercepted by production wells, but slow percolation through soils also may result in serious contamination of karst aquifers. The unique features of karst terranes tend to cause significant problems in the interpretation of results obtained from water-quality grab samples of karst groundwater. To obtain more representative samples, event-driven sampling was proposed some decades ago, but event-driven sampling can be difficult and expensive to implement. In this paper, application of passive-sampling strategies is advocated as a means for effectively obtaining representative water-quality samples from karst aquifers. A passive-sampling methodology may be particularly useful for karst aquifers that may be found in complexly folded and faulted terranes. For example, a groundwater tracing investigation of a contaminated site in a karst terrane confirmed that several offsite springs and wells are connected to the contaminated site. Tracer recoveries suggested transport rates that were relatively slow for flow in a karstic aquifer (~0.02 m/s). Breakthrough curves were erratic and spiky. To obtain representative groundwater samples, a passive-sampling methodology is recommended.

[Abstract] Groundwater availability, management and protection are great challenges for the sustainability of groundwater resources in the scattered rural areas of the Atlantic regions of Europe where groundwater is the only option for water supply. This report presents a hydrogeological study of the coastal granitic area of Oia in northwestern Spain, which has unique geomorphological and hydrogeological features with steep slopes favoring the erosion of the weathered granite. The hydrogeological conceptual model of the study area includes: (1) the regolith layer, which is present only in the flat summit of the mountains; (2) the slope debris and the colluvial deposits, which are present in the intermediate and lowest parts of the hillside; (3) the marine terrace; and (4) the underlying fractured granite. Groundwater recharge from rainfall infiltration varies spatially due to variations in terrain slope, geology and land use. The mean annual recharge estimated with a hydrological water balance model ranges from 75 mm in the steepest zone to 135 mm in the lowest flat areas. Groundwater flows mostly through the regolith and the detrital formations, which have the largest hydraulic conductivities. Groundwater discharges in seepage areas, springs, along the main creeks and into the sea. The conceptual hydrogeological model has been implemented in a groundwater flow model, which later has been used to select the best pumping scenario. Model results show that the future water needs for domestic and tourist water supply can be safely provided with eight pumping wells with a maximum pumping rate of 700 m3/day. | [Résumé] La disponibilité, la gestion et la protection des eaux souterraines sont de grands défis pour la durabilité de ces ressources en eaux dans les zones rurales dispersées des régions atlantiques de l’Europe où l’eau souterraine est la seule option pour l’approvisionnement en eau. Cet article présente une étude hydrogéologique de la zone granitique côtière d’Oia dans le nord-ouest de l’Espagne, qui présente des caractéristiques géomorphologiques et hydrogéologiques uniques avec des pentes fortes favorisant l’érosion du granite altéré. Le modèle conceptuel hydrogéologique de la zone d’étude comprend: (1) la couche de régolithe présente seulement sous le sommet plat des montagnes; (2) les débris de pente et les dépôts colluviaux présents dans les parties intermédiaires et les plus basses du versant; (3) la terrasse marine; et (4) le granite fracturé sous-jacent. La recharge des eaux souterraines par l’infiltration des précipitations varie dans l’espace en raison des variations de la pente du terrain, de la géologie et de l’occupation des sols. La recharge annuelle moyenne estimée à l’aide d’un modèle hydrologique de bilan en eau varie de 75 mm dans la zone la plus abrupte à 135 mm dans les zones plates les plus basses. Les eaux souterraines s’écoulent principalement à travers le régolithe et les formations détritiques, qui ont les plus fortes conductivités hydrauliques. Les eaux souterraines émergent dans les zones de suintement, aux sources, le long des principaux ruisseaux et en mer. Le modèle hydrogéologique conceptuel a été mis en œuvre dans un modèle d’écoulement des eaux souterraines, qui a ensuite été utilisé pour sélectionner le meilleur scénario de pompage. Les résultats du modèle montrent que les futurs besoins en eau pour l’approvisionnement en eau domestique et touristique peuvent être fournis en toute sécurité avec huit puits de pompage d’un débit maximum de 700 m3/jour. | [Resumen] La disponibilidad, la gestión y la protección de las aguas subterráneas es un gran reto para la sostenibilidad de los recursos hídricos subterráneos en las zonas rurales dispersas de las regiones atlánticas de Europa en las que las aguas subterráneas son la única opción para el suministro de agua. En este artículo se presenta un estudio hidrogeológico de la zona granítica costera de Oia en Galicia en el noroeste de España, con unas especiales características geomorfológicas e hidrogeológicas y pendientes que favorecen la erosión del granito meteorizado. El modelo conceptual hidrogeológico de la zona de estudio incluye: (1) la capa de regolito presente en la cumbre plana de la sierra costera; (2) los derrubios de ladera y los depósitos coluviales en las partes intermedias y bajas de la ladera; (3) la terraza marina; y (4) el granito fracturado subyacente. La recarga por infiltración de la precipitación varía espacialmente debido a la variabilidad espacial de la pendiente del terreno, la geología y el uso del suelo. La recarga media anual estimada con un modelo hidrológico de balance de agua oscila entre 75 mm en las zonas de mayor pendiente y 135 mm en las zonas llanas más bajas. El flujo subterráneo discurre principalmente a través del regolito y las formaciones detríticas que presentan las mayores conductividades hidráulicas. La descarga subterránea se produce en las zonas de rezume, los manantiales, los principales arroyos y en el mar. El modelo conceptual hidrogeológico se ha implementado en un modelo numérico de flujo subterráneo que posteriormente se ha utilizado para seleccionar el escenario óptimo de bombeo. Los resultados del modelo muestran que la futura demanda de agua para el abastecimiento doméstico y turístico se puede satisfacer de forma segura mediante ocho pozos de bombeo con un caudal punta de 700 m3/día. | [摘要] 地下水的可利用性, 管理和保护是欧洲大西洋地区分散的农村地区地下水资源可持续性的重要议题, 而地下水是这些地区唯一的供水选择。本文介绍了西班牙西北部Oia沿海花岗岩区的水文地质研究, 该地区具有独特的地貌和水文地质特征, 其陡峭的斜坡有利于风化花岗岩的侵蚀。研究区的水文地质概念模型包括:(1)仅存在于扁平化山峰的风化层; (2)山坡中部和最低处存在的坡积碎屑和崩积物; (3)海成阶地; (4)下伏的破碎花岗岩。由于地形坡度,地质和土地利用的变化, 地下水的降雨入渗补给在空间上也不同。采用水文水平衡模型估算的年均补给量从最陡的75 mm到最低平地的135 mm之间变化。地下水主要沿渗透系数最大的风化层和碎屑岩层流动。地下水排泄形式包括渗出区, 泉和沿小溪流入大海。概念性水文地质模型已用于建立地下水流模型, 之后用于优化抽水方案。模型结果表明采用八口开采井可以安全地满足生活和旅游用水的未来用水需求, 最高开采量可达700 m3/day。 | [Resumo] Disponibilidade, gestão e proteção das águas subterrâneas são grandes desafios para a sustentabilidade dos recursos hídricos subterrâneos nas áreas rurais dispersas das regiões atlânticas da Europa onde as águas subterrâneas são a única opção de abastecimento. Esse artigo apresenta um estudo hidrogeológico da área granítica costeira de Oia, no noroeste da Espanha, que apresenta características geomorfologias e hidrogeológicas únicas com encostas íngremes que favorecem a erosão do granito intemperizado. O modelo conceitual hidrogeológico da área de estudo inclui: (1) a camada regolítica, que está presente apenas no cume plano das montanhas; (2) os entulhos de encosta e os depósitos coluviais, que estão presentes nas partes intermediarias e mais baixas da encosta; (3) o terraço marinho; e (4) o granito fraturado subjacente. A recarga das águas subterrâneas pela infiltração da chuva varia espacialmente devido a variações na inclinação do terreno, geologia e uso da terra. A recarga média anual estimada com um modelo de balanço hídrico varia de 75 mm na zona mais íngreme a 135 mm nas áreas planas mais baixas. A água subterrânea flui principalmente através do regolito e das formações detríticas, que possuem as maiores condutividades. As águas subterrâneas descarregam em áreas de infiltração, nascentes, ao longo dos riachos principais e no mar. O modelo hidrogeológico conceitual foi implementado em um modelo de fluxo de água subterrânea, que posteriormente foi usado para selecionar o melhor cenário de bombeamento. Os resultados do modelo mostram que as necessidades futuras de água para abastecimento doméstico e turístico podem ser fornecidas com segurança com oito poços de bombeamento com uma vazão máxima de 700 m3/dia. | This work has been funded by the Water Authority of the Galician Regional Government (Xunta de Galicia), the Spanish Ministry of Economy and Competitiveness (Project PID2019-109544RB-I00), FEDER funds and the Galician Regional Government, Xunta de Galicia (Grant number ED431C 2017/57) from “Consolidación e estruturación de unidades de investigación competitivas”, Grupos de referencia competitiva | Xunta de Galicia; ED431C 2017/57

Closed-form analytical solutions for assessing the consequences of climate change on fresh groundwater oceanic island lenses have been developed by hydrogeologists during the last decade. Based on existing equations, this study focuses on the case of strip oceanic islands when three combined effects of climate change are observed to affect the freshwater lens volume and its groundwater resource renewal: sea-level rise, erosion, and change in groundwater recharge rates. New equations, integrating these combined effects of climate change on fresh groundwater resources are provided. These equations are solved by a novel methodology based on a Dupuit-Forchheimer groundwater flow model that allows for determination of the hydrogeological parameters included in the equations. The approach is illustrated with the strip island of Savary, which is located along the Pacific Coast of Canada in the province of British Columbia. This example illustrates, on the one hand, the volume depletion of the island freshwater lens and, on the other hand, the decrease of the renewal rate of groundwater. The proposed approach can be applied to any strip islands worldwide to assess the cumulative effects of sea-level rise and shore erosion on groundwater resources, depending on the predicted climate change scenarios. The results can then help decision-makers to anticipate the effects of climate change on the groundwater availability in strip oceanic islands and plan future groundwater use accordingly.

Water sustainability is a major challenge on the Loess Plateau of China, since the drying of soil and loss of surface water is threatening regional water security. Fundamental to effective water management is an understanding of groundwater recharge mechanisms. Based on a time series of stable isotopes data for precipitation, surface water and groundwater, the groundwater recharge ratios and water transmission times were quantitatively identified for the studied region. The results showed that groundwater discharge to surface water was a common phenomenon during the dry and wet seasons. However, groundwater could also be recharged by precipitation and surface water during specific months when experiencing large precipitation events. Over shorter time scales (<1 year), groundwater was mainly recharged by surface water, while the groundwater recharge ratio from rainfall during the wet season was higher than that from melting snow during the dry season. Over longer time scales (>1 year), precipitation was the primary recharge source of groundwater in small watersheds due to the general flow direction of groundwater to surface water. Groundwater recharge by precipitation mostly occurred through a combination of piston flow and preferential flow, where preferential flow was the primary recharge mechanism for groundwater replenished by precipitation in this region. Surface water could quickly recharge groundwater by lateral flow through fractures in the aquifer and vertical piston flow. These findings could, therefore, be used to provide a reference for the utilization and protection of groundwater resources in the small watersheds of the loess hilly regions of the Loess Plateau.

Alpine karst aquifers control the availability and longevity of some water resources, but are not well understood. A conceptual model of the alpine karst aquifer system in the Bear River Range of northern Utah (USA) has been developed by geochemical analysis (major ions, δ¹⁸O, δ²H and δ¹³C values) of seasonal water samples from seven perennial springs, and residence-time assessment (³H and CFCs) of two low- and two high-discharge springs. All spring data can be explained by reaction paths dominated by the dissolution of calcian dolomite. The δ¹³C values align well with reaction paths for open-system dissolution. Saturation indices and low Ca:Mg molar ratios indicate that incongruent dissolution exerts a strong control on water–rock interactions, complicating interpretation of natural solute tracers. Values of δ¹⁸O and δ²H in springs follow the Utah meteoric water line. Snow δ¹⁸O values correlate with elevation, but not with increasing rainout distance, providing qualitative estimates of recharge elevation that generally align with previous dye-traces to five of the seven springs. Concentrations of ³H and CFCs likely are best described by binary mixing of subannual recharge with 60–65-year-old groundwater, suggesting that the alpine karst aquifer system in the Bear River Range is best represented by a double-porosity model. Subannual recharge documented by dye traces implies that caverns are the primary flowpaths to the springs, but the presence of decadal-age water may indicate that lower permeability flowpaths dominate during baseflow. No evidence was found for a longer-residing flow component, suggesting high sensitivity to future climate variability.

The sustainable management of groundwater resources is essential to municipalities worldwide due to increasing water demand. Planning for the optimized use of groundwater resources requires reliable estimation of hydraulic parameters such as hydraulic conductivity (K) and specific storage (Sₛ). However, estimation of hydraulic parameters can be difficult with dedicated pumping tests while municipal wells are in operation. In this study, the K and Sₛ of a highly heterogeneous, multi-aquifer/aquitard system are estimated through the inverse modeling of water-level data from observation wells collected during municipal well operations. In particular, four different geological models are calibrated by coupling HydroGeoSphere (HGS) with the parameter estimation code PEST. The joint analysis of water-level records resulting from fluctuating pumping and injection operations amounts to a hydraulic tomography (HT) analysis. The four geological models are well calibrated and yield reliable estimates that are consistent with previously studies. Overall, this research reveals that: (1) the HT analysis of municipal well records is feasible and yields reliable K and Sₛ estimates for individual geological units where drawdown records are available; (2) these estimates are obtained at the scale of intended use, unlike small-scale estimates typically obtained through other characterization methods; (3) the HT analysis can be conducted using existing data, which leads to substantial cost savings; and (4) data collected during municipal well operations can be used in the development of new groundwater models or in the calibration of existing groundwater models, thus they are valuable and should be archived.

Stable hydrogen and oxygen isotope signatures of waters within Church and Inkwell blue holes are measured on San Salvador Island (Bahamas) to identify the origin of their fresh and saline waters. Stable isotope data, paired with a suite of physicochemical water parameters measured throughout the blue holes, as a function of both time and depth, provide a detailed understanding of the tidally influenced groundwater interactions on the island. Blue holes are prominent karst features in carbonate environments which serve as windows into subterranean hydrologic processes. Carbonate island hydrology is often complicated by complex interactions between the marine and meteoric water systems, as tidal pumping and water mixing result in diagenetic alteration of the bedrock, that in turn influence dissolution rates and preferential flow paths. Although the blue holes on the island are physically influenced by tidal forcing, the stable isotope data indicate that both their fresh and saline waters are of a meteoric origin rather than seawater, where the meteoric water is likely becoming saline through enrichment by aerosol-derived sea salts. Additionally, the physical profiles of each blue hole indicate differences in mixing processes driven by wind and tidal forcing, where stronger mixing can result in a disruption of the freshwater lens. The implications of this study are important for assessing mixing corrosion processes and dissolution effects, but more research and longer data sets are needed to show whether these results are applicable to other coastal carbonate environments.

Effective management of groundwater resources during drought is essential. How is groundwater currently managed during droughts, and in the face of environmental change, what should be the future priorities? Four themes are explored, from the perspective of groundwater management in England (UK): (1) integration of drought definitions; (2) enhanced fundamental monitoring; (3) integrated modelling of groundwater in the water cycle; and (4) better information sharing. Whilst these themes are considered in the context of England, globally, they are relevant wherever groundwater is affected by drought.

The dynamics related to evolution of nitrate-contaminated groundwater are analyzed with focus on the impact of intrinsic aquifer properties, agricultural activities and restoration measures at Campina de Faro aquifer (M12), southern Portugal. Agricultural practices in the region developed in the 1970s and resulted in high abstraction rates, nitrate contamination and salinization. Despite the implementation of the European Union (EU) Nitrates Directive since 1997, nitrate levels still show increasing trends at some locations, constituting a threat to the chemical status of M12 and consequent nitrate discharge to Ria Formosa coastal lagoon. Simultaneously, groundwater levels are not dropping consistently, despite apparent overexploitation. A groundwater flow and mass transport model is developed for M12 to assess the evolution of nitrate under different scenarios. Model results reveal that M12 has a hydraulic connection with northernmost aquifers, a process not properly assessed so far. Results further show that nitrate contamination in the upper Plio-Quaternary layer of M12 is extremely persistent and mostly linked to unbalanced fertilizer application practices and irrigation return flows. The response of M12 to implementation of good agricultural practices in compliance with EU policies is slow, indicating that good qualitative status would be impossible to reach by the required EU deadlines. Integration of climate change scenarios into the transport model reveals that despite the implementation of restoration measures, there could be a retardation of the nitrate levels’ decrease in the upper aquifer as a result of enhanced evapoconcentration caused by lower recharge, higher water demands and incomplete mixing within the aquifer.