Assessing the Environmental Hazard of Using Seawater for Ore Processing at the Lasail Mine Site in the Sultanate of Oman

The Lasail mining area (Sultanate of Oman) was contaminated by acid mine drainage during the exploitation and processing of local and imported copper ore and the subsequent deposition of sulphide-bearing waste material into an unsealed tailings dump. In this arid environment, the use of seawater in the initial stages of ore processing caused saline contamination of the fresh groundwater downstream of the tailings dump. After detection of the contamination in the 1980s, different source-controlled remediation activities were conducted including a seepage water collection system and, in 2005, surface sealing of the tailings dump using an HDPE-liner to prevent further infiltration of meteoric water. We have been assessing the benefits of the remediation actions undertaken so far. We present chemical and isotopic (δ18O, δ 2H, 3H) groundwater data from a long-term survey (8–16 years) of the Wadi Suq aquifer along a 28 km profile from the tailings dump to the Gulf of Oman. Over this period, most metal concentrations in the Wadi Suq groundwater decreased below detection limits. In addition, in the first boreholes downstream of the tailings pond, the salinity contamination has decreased by 30 % since 2005. This decrease appears to be related to the surface coverage of the tailings pond, which reduces flushing of the tailings by the sporadic, but commonly heavy, precipitation events. Despite generally low metal concentrations and the decreased salinity, groundwater quality still does not meet the WHO drinking water guidelines in more than 90 % of the Wadi Suq aquifer area. The observations show that under arid conditions, use of seawater for ore processing or any other industrial activity has the potential to contaminate aquifers for decades.

Recharge Areas and Geochemical Evolution of Groundwater in an Alluvial Aquifer System in the Sultanate of Oman

A regional hydrogeochemical model was developed to evaluate the geochemical evolution of different groundwaters in an alluvial aquifer system in the Interior of Oman. In combination with environmental isotopes the model is able to extract qualitative and quantitative information about recharge, groundwater flow paths and hydraulic connections between different aquifers. The main source of water to the alluvial aquifer along the flow paths ofWadi Abyadh andWadi M’uaydin in the piedmont is groundwater from the high-altitude areas of the Jabal Akhdar and local infiltration along the wadi channels. In contrast, the piedmont alluvial aquifer alongWadi Halfayn is primarily replenished by lateral recharge from the ophiolite foothills to the east besides smaller contributions from the Jabal Akhdar and local infiltration. Further down gradient in the Southern Alluvial Plain aquifer a significant source of recharge is direct infiltration of rain and surface runoff, originating from a moisture source that approaches Oman from the south. The model shows that the main geochemical evolution of the alluvial groundwaters occurs along the flow path from the piedmont to the Southern Alluvial Plain, where dedolomitization is responsible for the observed changes in the chemical and carbon isotope composition in these waters.

Helium transfer from water into quartz crystals: A new approach for porewater dating

Several important fundamental and applied problems require a quantification of slow rates of groundwater flow. To resolve these problems helium appears to be a promising tracer. In this contribution we discuss a new approach, which gives the helium inventory in a rock – pore water system by using the relevant mineral record, i.e., without extraction and investigation of the porewater samples. Some U- and Th-poor minerals such as quartz (quartz separates from Permo-Carboniferous Formation, sandstone–shale interlayering, Molasses Basin, Northern Switzerland, hereafter PCF, are used in this study) contain excessive helium having migrated into their internal helium-accessible volume (HAV) from the surrounding porewater [I.N. Tolstikhin, B.E. Lehmann, H.H. Loosli, A. Gautschi, Helium and argon isotopes in rocks, minerals and related groundwaters: a case study in Northern Switzerland, Geochim. Cosmochim. Acta 60 (1996) 1497–1514]. These volumes are estimated by using helium as a nano-size penetrating tool, i.e., by saturation of the minerals with helium under controlled pressure–temperature conditions and subsequent measurements of the helium-saturated concentrations. In the quartz separates HAV/total volume ratios vary from 0.017% to 0.16%; along with the measured initial (unsaturated) He concentration the HAV gives the internal helium pressure, the mean value obtained for 7 samples (25 sample aliquots) is P=0.45F0.15 atm (1 r). The product of helium pressure and solubility (7.35_10_3 cc STP He/cc H2O for the temperature and salinity of PCF aquifers reported in [F.J. Pearson, W. Balderer, H.H. Loosli, B.E. Lehmann, A. Matter, T. Peters, H. Schmassmann, A. Gautschi, Applied Isotope Hydrogeology–A Case Study in Northern Switzerland, Elsevier Amsterdam, 1991, 439 pp.]) is the mineral-derived He concentration in the respective porewater, CPW=0.0035F0.0017 cc He/cc H2O. This value is in full accord with measured He concentrations in PCF aquifers, CPCF, varying from 0.0045 to 0.0016 cc He/cc H2O. This agreement validates the proposed approach and also shows that the mineral–porewater helium–concentration equilibrium has been established. Indeed, estimates of the He-migration rates through our quartz samples show that in ~6000 years the internal pressure should equilibrate with He-concentration in related porewater of PCF, and this time interval is short compared to independent estimates [I.N. Tolstikhin, B.E. Lehmann, H.H. Loosli, A. Gautschi, Helium and argon isotopes in rocks, minerals and related groundwaters: a case study in Northern Switzerland, Geochim. Cosmochim. Acta 60 (1996) 1497–1514]. The helium inventory in the rock–porewater assemblage shows that helium abundance in pore waters is indeed important. In shale samples (with ~15% porosity) porewaters contain more helium than the host minerals altogether. Porewater heliumconcentration profiles, available from the mineral record, along with helium production rates are input parameters allowing model(s) of helium migration through a hydrological structure to be developed. Quite high helium concentrations in PCF porewaters imply slow removal mechanisms, which will be discussed elsewhere.

Continental degassing of 4He by surficial discharge of deep groundwater

Radiogenic He is produced by the decay of uranium and thorium in the Earth’s mantle and crust. From here, it is degassed to the atmosphere and eventually escapes to space. Assuming that all of the 4He produced is degassed, about 70% of the total He degassed from Earth comes from the continental crust. However, the outgoing flux of crustal He has not been directly measured at the Earth’s surface and the migration pathways are poorly understood. Here we present measurements of helium isotopes and the long-lived cosmogenic radio-isotope Kr in the deep, continental-scale Guarani aquifer in Brazil and show that crustal He reaches the atmosphere primarily by the surficial discharge of deep groundwater. We estimate that He in Guarani groundwater discharge accounts for about 20% of the assumed global flux from continental crust, and that other large aquifers may account for about 33%. Old groundwater ages suggest that He in the Guarani aquifer accumulates over half- to one-millionyear timescales. We conclude that He degassing from the continents is regulated by groundwater discharge, rather than episodic tectonic events, and suggest that the assumed steady state between crustal production and degassing of He, and its resulting atmospheric residence time, should be re-examined.

Time-lapse pressure tomography for characterizing CO2 plume evolution in a deep saline aquifer

A time-lapse pressure tomography inversion approach is applied to characterize the CO2 plume development in a virtual deep saline aquifer. Deep CO2 injection leads to flow properties of the mixed-phase, which vary depending on the CO2 saturation. Analogous to the crossed ray paths of a seismic tomographic experiment, pressure tomography creates streamline patterns by injecting brine prior to CO2 injection or by injecting small amounts of CO2 into the two-phase (brine and CO2) system at different depths. In a first step, the introduced pressure responses at observation locations are utilized for a computationally rapid and efficient eikonal equation based inversion to reconstruct the heterogeneity of the subsurface with diffusivity (D) tomograms. Information about the plume shape can be derived by comparing D-tomograms of the aquifer at different times. In a second step, the aquifer is subdivided into two zones of constant values of hydraulic conductivity (K) and specific storage (Ss) through a clustering approach. For the CO2 plume, mixed-phase K and Ss values are estimated by minimizing the difference between calculated and “true” pressure responses using a single-phase flow simulator to reduce the computing complexity. Finally, the estimated flow property is converted to gas saturation by a single-phase proxy, which represents an integrated value of the plume. This novel approach is tested first with a doublet well configuration, and it reveals a great potential of pressure tomography based concepts for characterizing and monitoring deep aquifers, as well as the evolution of a CO2 plume. Still, field-testing will be required for better assessing the applicability of this approach.

Constraining age distributions of groundwater from public supply wells in diverse hydrogeological settings in Scania, Sweden

Twenty-five public supply wells throughout the hydrogeologically diverse region of Scania, southern Sweden are subjected to environmental tracer analysis (³H–³He,⁴He, CFCs, SF₆ and for one well only also ⁸⁵Kr and ³⁹Ar) to study well and aquifer vulnerability and evaluate possibilities of groundwater age distribution assessment. We find CFC and SF₆ concentrations well above solubility equilibrium with modern atmosphere, indicating local contamination, as well as indications of CFC degradation. The tracer-specific complications considerably constrain possibilities for sound quantitative regional ground- water age distribution assessment and demonstrate the importance of initial qualitative assessment of tracer-specific reliability, as well a need for additional, complementary tracers (e.g. ⁸⁵Kr,³⁹Ar and potentially also ¹⁴C). Lumped parameter modelling yields credible age distribution assessments for representative wells in four type aquifers. Pollution vulnerability of the aquifer types was based on the selected LPM models and qualitative age characterisation. Most vulnerable are unconfined dual porosity and fractured bedrock aquifers, due to a large component of very young groundwater. Unconfined sedimentary aquifers are vulnerable due to young groundwater and a small pre-modern component. Less vulnerable are semi-confined sedimentary or dual-porosity aquifers, due to older age of the modern component and a larger pre-modern component. Confined aquifers appear least vulnerable, due an entirely pre-modern groundwater age distribution (recharged before 1963). Tracer complications aside, environmental tracer analyses and lumped parameter modelling aid in vulnerability assessment and protection of regional groundwater resources.

Sediment mobilization deposits from episodic subsurface fluid flow—A new tool to reveal long-term earthquake records?

Subsurface fluid flow can be affected by earthquakes; increased spring activity, mud vol- cano eruptions, groundwater fluctuations, changes in geyser frequency, and other forms of altered subsurface fluid flow have been documented during, after, or even prior to seismic shaking. Recently discovered giant pockmarks on the bottom of Lake Neuchâtel, Switzerland, are the lake-floor expression of subsurface fluid flow. They discharge groundwater from the Jura Mountains karstic aquifers and experience episodically increased subsurface fluid flow documented by subsurface sediment mobilization deposits at the levees of the pockmarks. In this study, we present the spatio-temporal distribution of event deposits from these phases of sediment expulsion and of multiple time-correlative mass-transport deposits. We report five striking instances of concurrent multiple subsurface sediment deposits and multiple mass- transport deposits since late glacial times, for which we propose past earthquakes as a trigger. Comparison of this new event catalogue with historic earthquakes and other independent paleoseismic records suggests that initiation of sediment expulsion requires a minimum mac- roseismic intensity of VII. Thus, our study presents for the first time sedimentary deposits resulting from increased subsurface fluid flow as a paleoseismic proxy.

Isolation and Characterization of a Microorganism from Groundwater that Reduces Arsenate

This is an investigation into the microbially mediated processes involved in the transformation of arsenic. With the recent change in the Federal Maximum Contaminant Level for arsenic in drinking water, an increasing amount of resources are being devoted to understanding the mechanisms involved in the movement of arsenic. Arsenic in drinking water typically comes from natural sources, but the triggers that result in increased release of arsenic from parent material are poorly understood. Knowledge of these processes is necessary in order to make sound engineering decisions regarding drinking water management practices. Recent years have brought forth the idea that bacteria play a significant role in arsenic cycling. Groundwater is a major source of potable water in this and many other countries. To date, no reports have been made indicating the presence and activity of arsenate reducing bacteria in groundwater settings, which may increase dissolved arsenic concentrations. This research was designed to address this question and has shown that these bacteria are present in Maine groundwater. Two Maine wells were sampled in order to culture resident bacteria that are capable of dissimilatory arsenate reduction. Samples were collected using anaerobic techniques fiom wells in Northport and Green Lake. These samples were amended with specific compounds to enrich the resident population of arsenate utilizing bacteria. These cultures were monitored over time to establish rates of arsenate reduction. Cultures fiom both sites exhibited arsenate reduction in initial enrichment cultures. Isolates obtained fiom the Green Lake enrichments, however, did not reduce arsenate. This indicates either that a symbiotic relationship was required for the observed arsenate reduction or that fast-growing fermentative organisms that could survive in high arsenate media were picked in the isolation procedure. The Northport cultures exhibited continued arsenate reduction after isolation and successive transfers into fiesh media. The cultured bacteria reduced the majority of 1 a arsenate solutions in less than one week, accompanied by a corresponding oxidation of lactate. The 16s rRNA fiom the isolate was arnplifled and sequenced. The results of the DNA sequence analysis indicate that the rRNA sequence of the bacteria isolated at the Northport site is unique. This means that this strain of bacteria has not been reported before. It is in the same taxonomic subgroup as two previously described arsenate respirers. The implications of this study are significant. The fact that resident bacteria are capable of reducing arsenate has implications for water management practices. Reduction of arsenate to arsenite increases the mobility of the compound, as well as the toxicity. An understanding of the activity of these types of organisms is necessary in order to understand the contribution they are making to arsenic concentrations in drinking water. The next step in this work would be to quantitj the actual loading of dissolved arsenic present in aquifers because of these organisms.

AN ASSESSMENT OF THE RELATION OF CANCER MORTALITY RATES AND SOURCES OF DRINKING WATER IN TEXAS

The geographic distribution of average annual age-adjusted mortality rates (1964-1976) for four types of cancer (all cancer sites combined, gastrointestinal, urinary, and lung cancer) were compared by sources of drinking water for 254 Texas counties and county rural areas and 301 Texas cities. Exposure variables considered were surface versus ground water, public water supplies versus individuals wells, and trihalomethane levels in municipal water supplies. Each general source of "surface" and "ground" water was further divided by aggregating ground water using areas by aquifers and surface water using study areas by river basins. Potential confounding variables taken into account included median education, employment in cancer risk industries, population mobility, ethnicity, and urbanicity. A pattern of higher and lower cancer mortality rates was found for populations using some aquifers and river basins. Further study is required to determine whether the differences in cancer mortality rates that were observed are related to drinking water content or are coincidental with differences in personal characteristics which could not be taken into account in this ecologic study design. ^

Hydrogeological investigations in the upper Ouémé catchment in Benin, West Africa

The scope of this PhD thesis was the hydrogeological conceptualisation of the Upper Ouémé river catchment in Benin. The study area exceeds 14,500 km**2 and is underlain by a crystalline basement. At this setting the typical sequence of aquifers - a regolith aquifer at the top and a fractured bedrock aquifer at the bottom - is encountered, which is found in basement areas all over Africa and elsewhere in the world. The chosen regional approach revealed important information about the hydrochemistry and hydrogeology of this catchment. Based on the regional conceptual model a numerical groundwater flow model was designed. The numerical model was used to estimate the impact of climate change on the regional groundwater resources. This study was realised within the framework of the German interdisciplinary research project IMPETUS (English translation: "Integrated approach to the efficient management of scarce water resources in West Africa"), which is jointly managed by the German universities of Bonn and Cologne. Since the year 2000 the Upper Ouémé catchment was the principal target for investigations into the relevant processes of the regional water cycle. A first study from 2000 to 2003 (Fass, 2004, http://nbn-resolving.de/urn:nbn:de:hbz:5n-03849) focused on the hydrogeology of a small local catchment (~30 km**2). In the course of this thesis five field campaigns were underdone from the year 2004 to 2006. In the beginning of 2004 a groundwater monitoring net was installed based on 12 automatic data loggers. Manual piezometric measurements and the sampling of groundwater and surface water were realised for each campaign throughout the whole study area. Water samples were analysed for major ions, for a choice of heavy metals and for their composition by deuterium, oxygen-18 and tritium. The numerical model was performed with FEFLOW. The hydraulic and hydrochemical characteristics were described for the regolith aquifer and the bedrock aquifer. The regolith aquifer plays the role of the groundwater stock with low conductivity while the fractures of the bedrock may conduct water relatively fast towards extraction points. Flow in fractures of the bedrock depends on the connectivity of the fracture network which might be of local to subregional importance. Stable isotopes in combination with hydrochemistry proved that recharge occurs on catchment scale and exclusively by precipitation. Influx of groundwater from distant areas along dominant structures like the Kandi fault or from the Atacora mountain chain is excluded. The analysis of tritium in groundwater from different depths revealed the interesting fact of the strongly rising groundwater ages. Bedrock groundwater may possibly be much older than 50 years. Equilibrium phases of the silicate weathering products kaolinite and montmorillonite showed that the deeper part of the regolith aquifer and the bedrock aquifer feature either stagnant or less mobile groundwater while the shallow aquifer level is influenced by seasonal groundwater table fluctuations. The hydrochemical data characterised this zone by the progressive change of the hydrochemical facies of recently infiltrated rainwater on its flow path into deeper parts of the aquifers. Surprisingly it was found out that seasonal influences on groundwater hydrochemistry are minor, mainly because they affect only the groundwater levels close to the surface. The transfer of the hydrogeological features of the Upper Ouémé catchment into a regional numerical model demanded a strong simplification. Groundwater tables are a reprint of the general surface morphology. Pumping or other types of groundwater extraction would have only very local impact on the available groundwater resources. It was possible to integrate IMPETUS scenario data into the groundwater model. As a result it was shown that the impact of climate change on the groundwater resources until the year 2025 under the given conditions will be negligible due to the little share of precipitation needed for recharge and the low water needs for domestic use. Reason for concern is the groundwater quality on water points in the vicinity of settlements because of contamination by human activities as shown for the village of Dogué. Nitrate concentrations achieved in many places already alerting levels. Health risks from fluoride or heavy metals were excluded for the Upper Ouémé area.

Tab. 1 Mole % CO2 and 13C values of CO2 at baseline and at the final monitoring event for the eight observation wells

During CO2 storage operations in mature oilfields or saline aquifers it is desirable to trace the movement of injected CO2 for verification and safety purposes. We demonstrate the successful use of carbon isotope abundance ratios for tracing the movement of CO2 injected at the Cardium CO2 Storage Monitoring project in Alberta between 2005 and 2007. Injected CO2 had a d13C value of -4.6±1.1 per mil that was more than 10 per mil higher than the carbon isotope ratios of casing gas CO2 prior to CO2 injection with average d13C values ranging from -15.9 to -23.5 per mil. After commencement of CO2 injection, d13C values of casing gas CO2 increased in all observation wells towards those of the injected CO2 consistent with a two-source end-member mixing model. At four wells located in a NE-SW trend with respect to the injection wells, breakthrough of injected CO2 was registered chemically (>50 mol % CO2) and isotopically 1-6 months after commencement of CO2 injection resulting in cumulative CO2 fluxes exceeding 100000 m**3 during the observation period. At four other wells, casing gas CO2 contents remained below 5 mol % resulting in low cumulative CO2 fluxes (<2000 m**3) throughout the entire observation period, but carbon isotope ratios indicated contributions between <30 and 80% of injected CO2. Therefore, we conclude that monitoring the movement of CO2 in the injection reservoir with geochemical and isotopic techniques is an effective approach to determine plume expansion and to identify potential preferential flow paths provided that the isotopic composition of injected CO2 is constant and distinct from that of baseline CO2.

Características físico-químicas y aptitud agronómica de aguas subterráneas período 1997-2001 (Mendoza-Argentina)

El objetivo del presente estudio fue establecer las características físico-químicas y la aptitud agronómica de aguas subterráneas de la Provincia de Mendoza, correspondientes a perforaciones realizadas en el período 1997/ 2001. Se analizaron 206 muestras de aguas subterráneas provenientes de 15 departamentos de la provincia, para determinar -analíticamente o por cálculo- diversos parámetros fisicoquímicos y de aptitud agronómica. El 90 % de las aguas estudiadas resultó apto para el riego de todo tipo de cultivos y fue considerado de buena calidad de acuerdo con los criterios utilizados. En el Este de la provincia, debido a la contaminación de los acuíferos superficiales, se determinó que se requiere mayor profundidad para acceder a calidades aceptables. Los departamentos de Tupungato, Tunuyán y San Carlos, del Valle de Uco, poseen las aguas de mejor calidad, sobresaliendo Tunuyán. Excluida dicha zona, la mayor aptitud agronómica del agua se detectó en Maipú, mientras que la peor la detentan los departamentos de La Paz y General Alvear.

Impactos en el agua subterránea de un sistema de efluentes para riego : el Sistema Paramillos (Lavalle, Mendoza, Argentina)

En este trabajo se evalúa el impacto de un sistema de aprovechamiento de efluentes domésticos para riego en la calidad del agua subterránea. Los puntos de muestreo seleccionados son parte de un monitoreo a mayor escala del cual sólo se incluyeron aquellos relacionados con el sistema de la planta depuradora Paramillos, ubicada al Norte del aglomerado Mendoza. Esta planta consiste en una laguna de estabilización facultativa. Los resultados, presentados en gráficos, mapas y tablas, se discuten a partir del comportamiento de tres componentes del sistema hídrico: agua superficial (efluente), agua subterránea del nivel superior del acuífero (freática) y agua subterránea del acuífero profundo (confinado/ semiconfinado) y su interacción con el perfil del suelo. Se concluye que el acuífero profundo no es alcanzado por nitratos ni nitritos productos de la degradación biológica de la materia orgánica del efluente, lo que se atribuye a la capa impermeable subyacente. En el nivel superior o freático, el perfil del suelo remueve parte del N total y P total ingresado, entre el 39 y 90%. La remoción de DBO varía entre 30 y 90% y la remoción de E. coli remanente en efluente es total.

Evaluación de la contaminación de acuíferos producida por actividades de saneamiento y re-uso de efluentes en el norte de la provincia de Mendoza

En la zona norte de la provincia de Mendoza se desarrollan actividades que pueden afectar la calidad natural del agua subterránea: disposición y re-uso de efluentes industriales para riego agrícola, utilización de fertilizantes, saneamiento in-situ, fugas de redes de alcantarillado, etc. En esta región, surcada superficialmente por los ríos Mendoza y Tunuyán, la sedimentación cuaternaria determinó la formación de dos grandes unidades hidrogeológicas: acuíferos libres (sector de conos aluviales), y acuífero freático superior y acuíferos subyacentes confinados y/o semiconfinados. El área de estudio se encuentra ubicada en esta última unidad hidrogeológica donde se ha detectado contaminación de acuíferos por nitratos. El objetivo de este trabajo es identificar el origen de la contaminación, utilizando metodología hidroquímica mediante la evaluación de diversos parámetros físicoquímicos y biológicos, y técnicas isotópicas para corroborar la procedencia del agua subterránea y el origen de los nitratos. Los resultados obtenidos muestran que la presencia de nitratos en los acuíferos semiconfinado y confinado no proviene de la influencia del acuífero libre suprayacente, afectado por el re-uso de efluentes, sino que se relaciona con el ingreso de flujo horizontal de aguas subterráneas contaminadas provenientes del área del Gran Mendoza, debido a las pérdidas en las redes de alcantarillado y obras de saneamiento in situ.

Determinación de parámetros hidráulicos en columnas experimentales de suelos del sudeste de la provincia de Buenos Aires

La cuenca del Río Quequén Grande constituye una región representativa de los sistemas agrícolas pampeanos. El acuífero en esta región es la principal fuente de abastecimiento de agua para todos los usos, lo que pone de manifiesto la importancia de desarrollar los elementos necesarios para el estudio de la movilidad de los contaminantes a través de los suelos hacia la zona saturada. El objetivo del presente trabajo fue obtener parámetros hidráulicos bajo condiciones de saturación en columnas intactas de distintos tipos de suelos de la región, contemplando suelos de uso agrícola y natural. Se estudiaron dos series de suelo: Serie Azul y Serie Semillero Buck, con muestras tomadas en dos sectores próximos a las localidades de Lobería y La Dulce, respectivamente. Las columnas fueron eluidas con una solución acuosa de iones cloruro y se midió el incremento progresivo de conductividad. A partir de las curvas de arribo obtenidas, se ajustó la ecuación de transporte, obteniendo los valores de dispersividad y porosidad. Dichos parámetros no presentaron diferencias significativas según el uso para los suelos de Lobería, de textura franco arcillosa, indicando que la labranza no produciría modificaciones evidentes en el perfil del suelo. En La Dulce, donde los suelos poseen una textura más arenosa, los parámetros variaron según el uso del suelo, presentando una mayor dispersividad y menor porosidad del suelo bajo explotación agrícola extensiva.