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Few hydrology studies have investigated glacial till older than Illinoian time (> 300,000 BP) despite these older tills overlying a large portion of North America. An 8- and 6-well monitoring well nest installed into a 31 m thick pre-Illinoian till sequence near Cedar Rapids, Iowa was characterized using traditional hydrologic methods and chemical tracers. The aquitard system consists of about 9 m of fine-grained oxidized pre-Illinoian till overlying 22 m of unoxidized till and Devonian dolomite bedrock. Hydraulic conductivity ranged from 10−7 m/s in oxidized till and 10−10 m/s in unoxidized till. Hydraulic head relations indicated downward groundwater flow through the till profile with hydraulic gradients steepest near the unoxidized till/bedrock interface. Tritium and nitrate concentrations indicated recent (< 50 years old) recharge to a depth of 9–12 m below land surface. 18O and 2H results ranged between −6.2 to −7.9% and −38.0 to −50.9%, respectively, and plotted near the local Meteoric Water Line. A 1 per mil shift toward less negative 18O values with depth may suggest a climate change signal contained in the till water but more data are needed to verify this trend. Vertical groundwater velocity through the unoxidized till was estimated to range from 0.4 to 5.7 cm/year. The thickness of unoxidized pre-Illinoian till in Linn County was estimated from available records and contoured against vertical travel times to evaluate the effectiveness of pre-Illinoian till in preventing nitrate migration to underlying bedrock aquifers. 相似文献
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《China Geology》2021,4(3):463-475
Ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and anaerobic ammoniaoxidation (anammox) bacteria are very important contributors to nitrogen cycling in natural environments. Functional gene abundances of these microbes were believed to be well relevant to N-cycling in groundwater systems, especially in the Pearl River Delta (PRD) groundwater with unique high intrinsic ammonia concentrations. In this research, 20 sediment samples from two in the PRD were collected for porewater chemistry analysis and quantification of N-cycling related genes, including archaeal and bacterial amoA gene and anammox 16S ribosomal Ribonucleic Acid (rRNA) gene. Quantitative Polymerase Chain Reaction (qPCR) results showed that gene abundances of AOA, AOB, and anammox bacteria ranged from 3.13×105 to 3.21×107, 1.83×104 to 2.74×106, and 9.27×104 to 8.96×106 copies/g in the sediment of the groundwater system, respectively. Anammox bacteria and AOA dominated in aquitards and aquifers, respectively, meanwhile, the aquitard-aquifer interfaces were demonstrated as ammonium-oxidizing hotspots in the aspect of gene numbers. Gene abundances of nitrifiers were analyzed with geochemistry profiles. Correlations between gene numbers and environmental variables indicated that the gene abundances were impacted by hydrogeological conditions, and microbial-derived ammonium loss was dominated by AOA in the northwest PRD and by anammox bacteria in the southeast PRD.© 2021 China Geology Editorial Office. 相似文献
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Alain Prinzhofer Jean Pierre Girard Stphane Buschaert Yvon Huiban Sonia Noirez 《Chemical Geology》2009,260(3-4):269-277
A methodology has been developed to determine chemical and carbon isotopic compositions of trace amounts of hydrocarbon gas compounds (methane, ethane, propane, iso- and normal-butane) present as dissolved compounds in the porewater of the low permeability Callovo-Oxfordian argillites in eastern Paris Basin, France. Results indicate that the studied hydrocarbons contain significant amounts of ethane, butane and propane, in addition to methane. Carbon isotopic compositions reflect primarily thermogenic origin (thermal cracking of organic matter), and lack of any significant biodegradation. Because temperature did not exceed 50 °C in the studied argillites, investigated hydrocarbons must have originated in hotter/deeper organic-bearing formations, possibly Stephanian coals. Data supports the predominance of high maturity thermogenic gas in the upper part of the Callovo-Oxfordian, and low maturity thermogenic gas mixed with minor bacterially produced methane in the lower part of the formation. A mixing between three end-member gases models quite well the data: one thermogenic gas with a low maturity (42% methane, with a δ13C of − 53‰), a gas with higher maturity (55% methane, with a δ13C of − 47‰) and a bacterial gas (99.45% methane, with a δ13C of − 80‰). This study illustrates that migration of hydrocarbon gases can take place in rocks with very low permeability and porosity, such as compacted mudrocks, given enough time. It further suggests that the studied fluid migration and transfer in aquitards would help characterization and understanding of fluid movements in sedimentary basins, as a complement to studies focused on water aquifers and hydrocarbon reservoirs. Chemical and isotopic composition of dissolved hydrocarbons in porewater can be used as natural tracers of fluid circulation in sedimentary basins, in addition to more conventional tracers. 相似文献
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Jan Cools Yves Meyus Solomon Tuccu Woldeamlak Okke Batelaan Florimond De Smedt 《Environmental Geology》2006,50(8):1201-1209
For the implementation of the European Union Water Framework Directive (WFD), technological and scientific support are required. This paper presents a methodology to support a first step of the implementation of WFD, which is the delineation of groundwater bodies. The methodology consists of (1) the development of a complete and generally-accepted hydrogeological classification system for Flanders, named the HCOV code, (2) the development of a geographic information systems (GIS)-managed borehole database, and (3) the development of aquifer and aquitard models by means of a solid modeling approach. For each unit of the hydrogeological classification code for Flanders unit, GIS maps are generated for the three basic characteristics of hydrogeological layers: extent, base level and thickness, such that combined, the volume and extent of a hydrogeological layer is unambiguously defined. This GIS-based hydrogeological database has become a useful tool for groundwater management purposes and to provide the input for groundwater modeling. 相似文献
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D.?H.?PhillipsEmail author A.?O.?Thomas K.?Forde K.?Dickson S.?Plant G.?Norris B.?Bone R.?M.?Kalin 《Environmental Geology》2007,52(6):1117-1131
Volatile organic compound (VOC) contamination of subsurface geological material and groundwater was discovered on the Nortel
Monkstown industrial site, Belfast, Northern Ireland. The objectives of this study were to (1) investigate the characteristics
of the geological material and its influences on contaminated groundwater flow across the site using borehole logs and hydrological
evaluations, and (2) identify the contaminants and examine their distribution in the subsurface geological material and groundwater
using chemical analysis. This report focuses on the eastern car park (ECP) which was a former storage area associated with
trichloroethene (TCE) degreasing operations. This is where the greatest amount of volatile organic compounds (VOCs), particularly
TCE, were detected. The study site is on a complex deposit of clayey glacial till with discontinuous coarser grained lenses,
mainly silts, sands and gravel, which occur at 0.45–7.82 m below ground level (bgl). The lenses overall form an elongated
formation that acts as a small unconfined shallow aquifer. There is a continuous low permeable stiff clayey till layer beneath
the lenses that performs as an aquitard to the groundwater. Highest concentrations of VOCs, mainly TCE, in the geological
material and groundwater are in these coarser lenses at ∼4.5–7 m bgl. Highest TCE measurements at 390,000 μg L−1 for groundwater and at 39,000 μg kg−1 at 5.7 m for geological material were in borehole GA19 in the coarse lens zone. It is assumed that TCE gained entrance to
the subsurface near this borehole where the clayey till was thin to absent above coarse lenses which provided little retardation
to the vertical migration of this dense non-aqueous phase liquid (DNAPL) into the groundwater. However, TCE is present in
low concentrations in the geological material overlying the coarse lens zone. Additionally, VOCs appear to be associated with
poorly drained layers and in peat <3.0 m bgl in the ECP. Some indication of natural attenuation as VOCs degradation products
vinyl chloride (VC) and dichloromethane (DCM) also occur on the site. 相似文献
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Groundwater As concentrations >WHO limit (10 μg/L) are frequently found in the Po Plain (N. Italy). Although several hypotheses on As mobilization exist (i.e., reductive dissolution driven by peat degradation), the mechanisms of As release and subsequent attenuation acting in the multilayer aquifer in the Po Plain were poorly understood.The present work aims at implementing a reactive transport modeling of the aquifer system in Cremona, affected by As <183 μg/L, in order to quantify and test the feasibility of As release by the reductive dissolution of Fe-oxides driven by the degradation of peat contained in leaky aquitards and As attenuation downstream by the co-precipitation in iron sulfides.The model, based on a partial equilibrium approach, revealed that the observed As, Fe and Mn chemistry could be mostly explained by the simultaneous equilibrium between Fe-oxide and sulfate reduction and FeS precipitation and by the equilibrium of rhodochrosite precipitation/dissolution. Model results, together with litholog analysis, supported the assumption of peat as the likely source of organic matter driving As release. The model fitted to measured data showed that the peak in the organic carbon degradation rate at 20–40 m below surface (average of 0.67 mM/y), corresponding to the shallow peaty aquitard and the upper portion of the underlying semiconfined aquifer, is associated with the peak of net release of As (average of 0.32 μM/y) that is followed just downstream by a net precipitation in iron sulfides at 40–60 m below surface (average of 0.30 μM/y). These results support the assumptions of peaty aquifers as drivers of As release and iron sulfides as As traps. The model also outlined the following aspects that could have a broad applicability in other alluvial As affected aquifers worldwide: (a) shallow peaty aquitards may have a greater role in driving the As release since they likely have young and more reactive organic matter; (b) the occurrence of Fe-oxide reduction and FeS precipitation, that represent the As source and sink, together with sulfate reduction occurring simultaneously close to equilibrium may restrict the As mobility limiting the extent of contamination just downstream the source of organic matter that drives its release. 相似文献
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Radial reactive transport is investigated in an aquifer–aquitard system considering the important processes such as advection, radial and vertical dispersions for the aquifer, vertical advection and dispersion for the aquitards, and first-order biodegradation or radioactive decay. We solved the coupled governing equations of transport in the aquifer and the aquitards by honoring the continuity of concentration and mass flux across the aquifer–aquitard interfaces and recognizing the concentration variation along the aquifer thickness. This effort improved the averaged-approximation (AA) model, which dealt with radial dispersion in an aquifer–aquitard system by excluding the aquitard advection. To compare with our new solution, we expanded the AA model by including the aquitard advection. The expanded AA model considerably overestimated the mass in the upper aquitard when an upward advection existed there. The rates of mass change in the upper aquitard from the new solution and the AA model solution increased with time following sub-linear fashions. The times corresponding to the peak values of the residence time distributions for the AA model, the expanded AA model, and the new model were almost the same. The residence time distributions seemed to follow the Maxwell–Boltzmann distribution closely when plotting the time in logarithmic scale. In addition, we developed a finite-element COMSOL Multiphysics simulation of the problem, and found that the COMSOL solution agreed with the new solution well. 相似文献
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R.?Huizar-AlvarezEmail author J.?J.?Carrillo-Rivera G.?ángeles-Serrano T.?Hergt A.?Cardona 《Hydrogeology Journal》2004,12(4):436-450
An alternative procedure of pumping test data interpretation is used through a joint analysis of the standard time-drawdown curve and simultaneous field measurements of total dissolved solids (TDS); additional support is also provided by the temperature of extracted groundwater and the chemical composition of extracted water. The overall information was applied to characterise the groundwater flow system and its sources, the hydraulic conditions of the aquifer and hydraulic response of extraction boreholes. The analysis of this information suggests the presence of: (i) a local flow system that circulates at shallow depth through basalt units interstratified with fine grained sediments and pyroclastics; these materials contain water with TDS of 127–600 mg/L and Na of 24–178 mg/L, and temperature of 18–19.5 °C; (ii) intermediate flow in granular material under reducing conditions by the oxidation of organic matter in aquitard sediments; this water has TDS and Na values of 203–940 and 30–370 mg/L, respectively, and temperatures of about 20–22 °C; (iii) regional flow through volcanic rocks and limestone, with TDS content of 300–700 mg/L, Na of 80–230 mg/L and temperature of 23.0–24.8 °C. The hydraulic response and the chemical composition of the water produced by some boreholes are affected by the seepage inflow from sewage effluents, the input from an overlying aquitard unit and the inducement of regional flow. The conception of the flow regime thus obtained allowed the recognition of hydraulic conditions which were more consistent with the hydrogeological setting, than if only a time vs. drawdown test analysis would have been carried out.
Resumen La interpretación conjunta de la gráfica de prueba de bombeo, valores de temperatura y sólidos totales disueltos (STD) del agua subterránea extraída, medidos simultáneamente en campo y la composición química del agua extraída como apoyo adicional; se utilizó como un procedimiento alternativo para interpretar los datos de pruebas de bombeo. Toda esa información fue aplicada para caracterizar el sistema de flujo subterráneo y el origen de éste, las condiciones hidráulicas del acuífero y la respuesta hidráulica de los pozos de extracción. El análisis de la información indica la presencia de: (i) flujo local con temperatura de 18–19.5 °C, STD de 127–600, y Na de 24–178 mg/L; (ii) flujo intermedio con temperatura de 20–22 °C, los STD y Na son de (203–940 y 30–370 mg/L), respectivamente; (iii) regional con STD de 300–700 y Na de 80–230 mg/L, y temperatura de 23–24.8 °C. En el primer caso el agua circula a través de rocas basálticas, en el segundo viaja por material granular y materia orgánica en sedimentos del acuitado. El flujo regional circula por material volcánico y rocas calizas. La respuesta hidráulica y la composición química del agua extraída por algunos pozos, es afectada por infiltración de efluentes de agua residual, entrada de agua del acuitardo sobreyacente y la inducción de flujo regional. La concepción del régimen de flujo obtenida, permitió reconocer a las condiciones hidráulicas de los pozos, más correspondientes con el contexto hidrogeológico, que sí únicamente se hubieran analizado los datos de abatimiento vs tiempo.
Résumé Linterprétation simultanée de pompages dessais, des données de température et résidu sec (RS) de Leau souterraine pompée, mesurées simultanément sur le terrain et la composition chimique de Leau pompée comme un aide additionnelle, est utilisée comme une différent procédure pour interpréter les pompages dessais. La procédure a été appliquée pour caractériser le système découlement souterraine et sa source, les conditions hydrauliques de laquifère et la réponse hydraulique des puits considéré. L› analyse de cette information suggérer la présence des systèmes découlement suivantes. (i) local avec18 et 19.5 °C de température, RS de 127–600 mg/L, et Na de 24–178 mg/L, (ii) intermédiaire avec une température de 20 á 22 °C, le RS de 203–940 mg/L et Na 30–370 mg/L, (iii) régional avec 300 à 700 mg/L de RS et 80 à 230 mg/L de Na, une température de 23 à 24.8 °C. Dans le premier cas, leau traverse des roches basaltiques, dans le deuxième, des sédiments clastiques avec matière organique de laquitard, dans le troisième, des roches volcaniques et calcaires. La chimie de leau des quelques puits et sa réponse hydraulique met en évidence linfluence de leau de Laquitard, des effluents de surface et écoulement régional. La conception du régime d› écoulement obtenu, a permis reconnaître les conditions hydrauliques des puits plus correspondantes au contexte hydrogéologique, que si uniquement les données rabattement vs temps auraient été analysé相似文献
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