Groundwater and volcanoes: examples from the Azores archipelago

Groundwater at the Azores archipelago is a strategic resource for the freshwater supply. Freshwater, mineral and thermal water discharges occur in the archipelago, and especially at the Fogo and Furnas volcanoes (São Miguel). These discharges provide data for case studies of groundwater chemistry from volcanic monitoring due to the stable composition of the sampled waters. The mineral and thermal discharges are mainly of sodium bicarbonate types and present a large range of temperatures, from cold springs to waters at about 90 °C. Some boiling discharges have a sulfate-dominated composition, suggesting a steam-heating mechanism. Geochemical studies on these mineral and thermal waters began in the 19th century. Data gathered since these earlier studies provide a baseline for pH, temperature, CO₂ and major-element composition. Weekly measurements of pH and temperature also denote a rather stable behavior.     

Finite element simulation of seawater intrusion into a quarry-site coastal aquifer,Kocaeli-Darıca,Turkey

A numerical simulation has been carried out to investigate the effects of below-sea-level (b.s.l.) excavation on the raw material quality of a cement quarry in Turkey. The model simulates variations in the hydrodynamic and hydrogeochemical mechanisms in the coastal aquifer upon BSL excavation. In this context, behavior of the seawater intrusion zone, changes in water levels, and salt concentrations have been simulated. In the development of the model, previous geological and hydrogeological reports of the quarry site and the near vicinity have been considered. Eleven new wells (BH-1,...BH-11) have been drilled to reveal hydrogeological features of the area and also for periodical observations of the water levels and hydrogeochemical monitoring. These wells were utilized to develop and calibrate the model to the field conditions. Physical and hydrogeochemical parameters used in the model have been evaluated using available hydrogeological data, the field test results and the related literature. The model has been verified using the field observations. It is based on the virgin conditions of the aquifer as well as on the data for years 1990 and 2001. An average raw material production rate for the cement factory was considered during development of the model, and for making future predictions. Two alternative production scenarios have been considered and probable effects of above-sea-level (a.s.l.) and b.s.l. excavations on seawater intrusion into the aquifer have been studied. Future prediction studies are based on these two production scenarios that assume 43 years of total production (30 years of a.s.l. and 13 years of b.s.l. production) in the quarry. The first scenario, Scenario I, assumes that starting from 2001, the next 30 years would be devoted only to ASL and then the remaining 13 years would be used for b.s.l. production. Scenario II, on the other hand, assumes simultaneous operations both at a.s.l. and b.s.l. levels for the next 43 years after 2001. Effects of b.s.l. production in the quarry site have been simulated accordingly, and seawater intrusion into the aquifer as well as water discharge rates have been predicted for –10, –20 and –30 m production levels.     

Dissolved oxygen and nitrate of groundwater in Choshui Fan-Delta,western Taiwan

Dissolved oxygen (DO) and nitrate concentrations of groundwater from a total of 191 new monitoring wells, with a maximum depth up to 300 m, in the Choshui fan delta of Taiwan were measured to delineate the regional patterns of the two components. Unconfined aquifers of the proximal part of the fan delta contain 1~7 mg/l of DO, and a 250-m deep well still has an unusual value of 1.83 mg/l. DO concentrations decrease downgradient along flow paths to below detection limit (0.01 mg/l) in shallow confined aquifers during the last 40 years, possibly due to oxidation of organic matters in sediments. A plume of high nitrate-N concentrations (0.5–17 mg/l) originating from the proximal part of the fan delta has been developing, possibly since 1956, due to agricultural fertilizers. From 1997 to 2001, the concentration has increased at a rate of ca. 0.28 mg/l per year.     

Improving groundwater-flow modeling using optimal zoning methods

Hydraulic conductivity sometimes exhibits complicated spatial variation over a site. A thorough understanding of the spatial distributions of hydraulic conductivity helps to make deterministic models of groundwater more accurate. This study presents a novel procedure that combines simulated annealing algorithms (SA) and the shortest distance method (SD) with the modular three-dimensional groundwater flow model (MODFLOW). The procedure is applied to a hypothetical site with groundwater-monitoring wells to minimize the difference between simulated and observed hydraulic head for optimal zoning of the spatial distribution of hydraulic conductivity. The results of this optimal zoning method indicate that this new procedure not only improves the efficiency of optimization, but also increases the probability of finding the global optimum, minimizing the errors of the hydraulic head simulated by MODFLOW in two scenarios, one with known and the other with unknown hydraulic conductivity. The results also illustrated that the procedure can effectively determine and delineate hydrogeological zones.     

GIS-based determination of the mean long-term groundwater recharge in Lower Saxony

This paper presents the findings of a collaborative research project of the Geological Survey of Lower Saxony (NLfB) and the Programme Group Systems Analysis and Technology Evaluation (STE) of Research Centre Jülich on the GIS-based determination of the mean long-term groundwater recharge in Lower Saxony using high-resolution digital data (Dörhöfer and others 2001). The model calculations were performed on the basis of the water-balance model GROWA (Kunkel and Wendland 2002) with a spatial resolution of 100x100 m². The accuracy of the calculated groundwater recharge values for the period 1961–1990 was verified on the basis of data from gauging stations and displayed a good agreement between observed runoff values and model results.     

Weathering of sulfidic shale and copper mine waste: secondary minerals and metal cycling in Great Smoky Mountains National Park,Tennessee, and North Carolina,USA

Metal cycling via physical and chemical weathering of discrete sources (copper mines) and regional (non-point) sources (sulfide-rich shale) is evaluated by examining the mineralogy and chemistry of weathering products in Great Smoky Mountains National Park, Tennessee, and North Carolina, USA. The elements in copper mine waste, secondary minerals, stream sediments, and waters that are most likely to have negative impacts on aquatic ecosystems are aluminum, copper, zinc, and arsenic because these elements locally exceed toxicity guidelines for surface waters or for stream sediments. Acid-mine drainage has not developed in streams draining inactive copper mines. Acid-rock drainage and chemical weathering processes that accompany debris flows or human disturbances of sulfidic rocks are comparable to processes that develop acid-mine drainage elsewhere. Despite the high rainfall in the mountain range, sheltered areas and intermittent dry spells provide local venues for development of secondary weathering products that can impact aquatic ecosystems.Electronic Supplementary Material  Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.

Geophysical response of filled sinkholes,soil pipes and associated bedrock fractures in thinly mantled karst,east-central Illinois

Karst aquifers are often protected by a thin mantle of unconsolidated sediment. Soil pipes and sinkholes may breach this natural protective barrier and open pathways for contaminants to quickly reach bedrock aquifers. Geophysical surveys offer a quick and noninvasive way to identify these features; such surveys may also be sequenced to reveal increasing detail in critical areas. At a study site in east-central Illinois, electromagnetic (EM) surveys mapped high conductivity anomalies over filled sinkholes and soil pipes that penetrated the unconsolidated cover. Two-dimensional inverted resistivity sections, made over these anomalies, depict filled sinkholes and soil pipes as conductive zones above deeply weathered bedrock fractures. Borings verified the geophysical models and suggest high conductivities associated with the filled sinkholes are the result of enhanced moisture near active soil pipes. EM surveys also identified conductive zones in the overburden above a probable bedrock fracture linking sinkhole areas 0.5 km apart. Resistivity and EM methods, used in a phased and sequential manner, thus proved useful in mapping filled sinkholes and in delineating the vertical and lateral connections between soil pipes and hydraulically active bedrock fractures.     

GIS-based spatial and temporal prediction system development for regional land subsidence hazard mitigation

An integrated GIS-based approach for establishing a spatial and temporal prediction system for groundwater flow and land subsidence is proposed and applied to a subsidence-progressed Japanese coastal plain. Various kinds of fundamental data relating to groundwater flow and land subsidence are digitized and entered into a GIS database. A surface water hydrological cycle simulation is performed using a GIS spatial data operation for the entire plain, and the spatial and temporal groundwater infiltration quantity is hereby obtained. Through the data transformation from the GIS database to a groundwater flow code (MODFLOW), a 3D groundwater flow model is established and unsteady groundwater flow simulation for the past 21 years is conducted with results which compare satisfactorily with observed results. Finally, a Visual Basic code is developed for land subsidence calculations considering aquifer and aquitard deformation. Future land subsidence in the plain is predicted assuming different water pumping scenarios, and the results provide important information for land subsidence mitigation decision-making.     

Modeling Biogeochemistry,the Key for Understanding Environmental Chemistry of a Semi－Arid Soil in Egypt

1IntroductionThecomponentsoftheenvironmentaredamagedbyagriculturalpractices.Soilslosstheirfer tilityandwaterdeterioratesduetopollution .Chemicalweatheringofmineralandsoiloccursattheinterfacesbetweentheliquidandsolidphases;consequentlythesurfaceareaandcompositionofthemineralsplayanimportantroleinthisprocess.GarrelsandMackenzie ( 1 96 7)suggestedthatincon gruentweatheringreactionswouldproducedissolvedspeciesandnewsolidsthataremorestableintheweatheringenvironmentthantheoriginalbedrockminerals.Ro…     

Rare-earth element mobility during ore-forming hydrothermal alteration: A case study of Dongping gold deposit Hebei Province,China

REE mobility during hydrothermal ore-forming processes has been extensively investigated in recent years and the potential of REE to provide information about ore forming processes has commonly been recognized.The Dongping gold deposit,which is located in northwestern Hebei Province,China,occurring in the inner contact zone of the Shuiquangou syenite complex,is spatially,and probably genetically,related to the syenite,the deposit was formed under the moderate to high temperature(220℃ to 320℃),weakly acidic to weakly alkaline,rather high fo2(lgfo2=-30～-34)environment.The REE study of the host rocks,altered wall rocks,ores and gangue minerals from the deposit suggests that the REEs have been mobilized and differentiated during K-feldspathization and silicification.The extremely altered syenite enveloping auriferous quartz vein shows positive Ce anomaly and larger LREE/HREE ratio than that of the unaltered syenite.The REE concentrations and patterns of the ores are determined by the ore types and mineral assemblages,LREE/HREE ratios in the gangue quartz and hydrothermal Kfeldspars are relatively low.The most significant observation is that the gangue quartz shows significant positive Eu anomaly,whereas the hydrothermal K-feldspars show less significant or no positive Eu anomaly at all relative to the primary feldspar in the unaltered syenite. It is evident that the REEs are mobile during K-feldspathization and silicification in the ore forming process.Weak to moderate K-feldspathization caused REE mobility without apparent differentiation with the exception of extreme K-feldspathization and silicification which resulted in significant depletion of HREE and Eu and relative enrichment of Ce.The REE,Y,U,Th and Au contents of the syenite decrease as the degrees of K-feldspathization and silicification of the rocks increase towards the auriferous quartz veins.As the ores were deposited under a rather oxidized environment,Ce^4 predominated over Ce^3 .The precipitation of the former in the form of CeO2 or absorpted onto the secondary mineral assemblage resulted in the inconsistent removal of the REE and the relative Ce enrichment in the strongly altered rocks.in contrast,Eu was present mainly in a low valence state (Eu^2 ).The geochemical differences from the other REE^3 and much less sites in the secondary minerals to accommodate the Eu released form the original minerals resulted in the enrichment of Eu in the fluids.The mobility and differentiation of REE and the coherent mobilities of Y,U,Th and Au also support the argument that the syenite is one of the source rocks for gold mineralization.The REE contents and patterns of the altered rocks enveloping the auriferous quartz vein could be used as a guide for locating ore veins in mineral exploration.