Asaf Pekdeger

Persistence and transport of bacteria and viruses in groundwater — a conceptual evaluation

Abstract The results of an interdisciplinary research program on the subsurface persistence and transport of pathogenic bacteria and viruses are evaluated on the basis of an expanded advection-dispersion model which considers the persistence of these microorganisms under the conditions found within an aquifer, the retardation by adsorption-desorption processes and the role of filtration processes. The model indicates that the principal controls are filtration processes, the microorganisms being fixed on the filter media are ultimately eliminated or inactivated by biological, chemical and physical processes.

Anthropogenic gadolinium as a conservative tracer in hydrology

Abstract Surface water and in some cases also groundwaters of industrialised and highly populated areas show REE patterns with outstanding positive Gd anomalies. These are formed by using gadopentetic acid (Gd-DTPA) as a contrast medium in magnetic resonance imaging. This Gd complex is very stable under natural conditions. It is an anion and so not adsorbed onto clay mineral surfaces or particulate organic matter, in contrast to free rare earth element (REE) ions ions. Thus, this complex is a pseudo-natural marker, and allows the study of the origin of certain waters and their fate during mixing processes.

Sulfide oxidation and sulfate reduction in a shallow groundwater system (Oderbruch Aquifer, Germany)

Abstract Detailed groundwater monitoring was carried out over a period of two years in an anoxic, river recharged aquifer of the Oderbruch polder, north-eastern Germany. Isotope data from wells located in a 5 km transect along the flow direction was used to determine sources and sinks of SO 4 2− in the aquifer. The SO 4 2− originates from river water infiltration and from oxidative dissolution of FeS 2 within the alluvial loam covering the aquifer sands. A change of confined hydraulic conditions near the river to unconfined conditions in the central polder effects the hydrochemistry of the aquifer. The confined areas are dominated by sulfate reduction. Increasing δ 34 S −SO 4 values suggest continuous but slow ( t 1/2 =50 years) sulfate reduction from the beginning of inflow onwards with δ 34 S −SO 4 values ranging from +1.8 to +44.7‰ versus CDT and an enrichment factor of −33‰. A zone with a strong sulfate depletion ( δ 34 S −SO 4 of up to +85.7‰) exists in a shallow microenvironment rich in solid-phase organic carbon between river and levee. In the unconfined areas of the central polder, a SO 4 2− plume with concentrations exceeding the original river water content indicates FeS 2 oxidation by O 2 and/or NO 3 − within the alluvial loam. The lowered δ 34 S −SO 4 value reflects the input of the isotopically lighter SO 4 2− from the sulfide.

Modelling the removal of p-TSA (para-toluenesulfonamide) during rapid sand filtration used for drinking water treatment.

A finite element model was set-up to determine degradation rate constants for p-TSA during rapid sand filtration (RSF). Data used for the model originated from a column experiment carried out in the filter hall of a drinking water treatment plant in Berlin (Germany). Aerated abstracted groundwater was passed through a 1.6m long column-shaped experimental sand filter applying infiltration rates from 2 to 6mh(-1). Model results were fitted to measured profiles and breakthrough curves of p-TSA for different infiltration rates using both first-order reaction kinetics and Michaelis-Menten kinetics. Both approaches showed that degradation rates varied both in space and time. Higher degradation rates were observed in the upper part of the column, probably related to higher microbial activity in this zone. Measured and simulated breakthrough curves revealed an adaption phase with lower degradation rates after infiltration rates were changed, followed by an adapted phase with more elevated degradation rates. Irrespective of the mathematical approach and the infiltration rate, degradation rates were very high, probably owing to the fact that filter sands have been in operation for decades, receiving high p-TSA concentrations with the raw water.

Numerical investigations of fault-induced seawater circulation in the Seferihisar-Balçova Geothermal system, western Turkey

The Seferihisar-Balçova Geothermal system (SBG), Turkey, is characterized by temperature and hydrochemical anomalies along the faults: thermal waters in northern Balçova are heated meteoric freshwater, whereas the hot springs of the southern Seferihisar region have a strong seawater contribution. Previous numerical simulations of fluid flow and heat transport indicated that focused upsurge of hot water in faults induces a convective-like flow motion in surrounding units. Salt transport is fully coupled to thermally driven flow to study whether fault-induced convection cells could be responsible for seawater encroachment in the SBG. Isotope data are presented to support the numerical findings. The results show that fault-induced convection cells generate seawater plumes that extend from the seafloor toward the faults. At fault intersections, seawater mixes with rising hot thermal waters. The resulting saline fluids ascend to the surface along the fault, driven by buoyant forces. In Balçova, thick alluvium, minor faults and regional flow prevent ascending salty water from spreading at the surface, whereas the weak recharge flow in the thin alluvium of the southern SBG is not sufficient to flush the ascending hot salty waters. These mechanisms could develop in any faulted geothermal system, with implications for minerals and energy migration in sedimentary basins.ResumeLe système géothermal de Seferihisar-Balçova (SGSB), en Turquie, est caracterisé par des anomalies thermiques et hydrochimiques le long de failles : les eaux thermales dans la Balçova du Nord sont des eaux douces météoriques réchauffées, tandis que les sources chaudes de la région de Seferihisar ont une contribution forte de l’eau de mer. Des simulations numériques antérieures des écoulements de fluide et du transport de chaleur indiquent que des venues d’eau chaude dans les failles provoquent un mouvement de l’eau de type convectif dans les terrains alentours. Le transport du sel est complètement couplé avec le calcul des écoulements induits par la chaleur pour étudier si les cellules de convection crées par les failles pouvaient être responsables de l’invasion marine dans le SGBS. Les données isotopiques sont présentées pour appuyer les conclusions des calculs numériques. Les résultats montrent que la convection induite par les failles crée un panache d’eau salée qui s’étend du fond de la mer vers les failles. A l’intersection avec les failles, l’eau de mer se mélange avec l’eau des sources chaudes. Les fluides salins qui en résultent montent et atteignent la surface le long des failles, sous l’effet de la poussée d’Archimèdes. A Balçova, des alluvions épaisses, des failles mineures et l’écoulement régional empêchent l’eau salée qui remonte de s’étaler en surface, alors que la faible recharge des alluvions peu épaisses du sud du SGBS est insuffisante pour repousser l’eau chaude salée en mouvement ascendant. Ces mécanismes pourraient se développer dans n’importe quel système faillé géothermal, avec des implications sur la migration des minéraux et de l’énergie dans les bassins sédimentaires.ResumenEl sistema geotermal de Seferihisar-Balçova (SBG), Turquía, está caracterizado por anomalías de la temperaturas e hidroquímicas a lo largo de las fallas: las aguas termales en el norte de Balçova son agua dulces meteóricas calientes, mientras que los manantiales calientes de la región del sur de Seferihisar tienen una fuerte contribución de agua de mar. Las simulaciones numéricas previas del flujo del fluido y el transporte de calor indicaban que la surgencia focalizada de agua caliente en las fallas inducen un movimiento de flujo convectivo en las unidades circundantes. El transporte de sales se acopla totalmente al flujo térmicamente forzado para estudiar si las celdas de convección inducidas por las fallas podrían ser responsables de la invasión de agua de mar en el SBG. Se presentan los datos de isótopos para respaldar los hallazgos numéricos. Los resultados muestran que las celdas de convección inducidas por las fallas generan plumas de agua de mar que se extienden desde el fondo del mar hacia las fallas. En las intersecciones de las fallas, el agua de mar se mezcla con las aguas termales calientes surgentes. Los flujos salinos resultantes ascienden a la superficie a lo largo de la fallas, forzados por las fuerzas de flotación. En Balçova el grueso aluvio, las fallas menores y el flujo regional impiden que el agua salada ascendente se propague en la superficie, mientras que el flujo débil de la recarga en el aluvio delgado del sur del SBG no es suficiente para barrer el flujo ascendente de las aguas saladas. Estos mecanismos podrían desarrollarse en cualquier sistema geotermal fallado, con implicancias para la migración de minerales y de energía en las cuencas sedimentarias.摘要土耳其Seferihisar-Balçova(SBG)地热系统表现为沿着断裂的温度和水化学异常:北部Balçova地区的热水来源于大气降水,南部Seferihisar地区热水海水来源较多。前期水流场和热传导的数值模拟表明断裂里热水的集中涌出导致邻近单元里出现对流。盐分运移模拟耦合了热导致的水流,用于研究SBG地热系统中断层导致的对流是否产生了海水入侵。同位素数据用于为模拟结果提供依据。结果表明断裂导致的对流产生了海水晕,且其从海底直接延伸至断裂处。在断裂交汇处,海水与上升的热水发生混合。在浮力作用下,形成的咸水沿着断裂上升至地表。在Balçova地区较厚的冲积层处,基本上没有断裂和区域水流阻碍上升的咸水扩展到地表,而南部SBG地热系统中薄层冲积层里的补给较差的水流不足以冲散上升的咸水。这些过程在任何有断裂的地热系统中都能产生,也能应用于沉积盆地中矿物和能源的运移研究。RiassuntoLe falde acquifere del sistema geotermico del Seferihisar-Balçova (SBG), Turchia, sono caratterizzate da anomalie termiche e chimiche lungo le faglie: le acque termali a Nord di Balcova sono acque meteoriche riscaldate mentre le sorgenti di acqua calda nella regione meridionale di Seferihisar hanno salinità molto elevate. Simulazioni numeriche di flussi idrici e di calore hanno indicato che la fuoriuscita di acque termali focalizzata nelle faglie induce una circolazione convettiva negli acquiferi circostanti. Il trasporto di sale viene ora accoppiato ai flussi idrici indotti termicamente per studiare se questi flussi convettivi possano essere responsabili delle intrusioni marine nel SBG. Dati isotopici vengono presentati a sostegno dei risultati numerici. Questi ultimi mostrano che le cellule convettive indotte dalle faglie generano piume di acqua marina che si estendono dal fondo marino verso le faglie stesse. All’intersezione delle faglie, l’acqua marina si mescola con le acque termali ascendenti. I fluidi salini risultanti da questa miscela raggiungono la superficie lungo le faglie grazie alle forze di galleggiamento. In Balcova, lo spesso strato di sedimenti alluvionali, le faglie minori e il flusso idrico regionale impediscono alle acque termali ascendenti di diffondersi mentre le deboli ricariche idriche nel sottile deposito alluvionale nel SBG meridionale non sono sufficienti a diluire le acque termali ascendenti. Questi meccanismi possono svilupparsi in qualsiasi sistema geotermico con faglie, il che ha implicazioni per il trasporto di minerali ed energia in bacini sedimentari.ResumoO sistema Geotérmico de Seferihisar-Balçova (SBG), na Turquia, é caracterizado por anomalias hidroquímicas e de temperatura ao longo das falhas: as águas termais no norte de Balçova são águas quentes de origem meteórica, ao passo que as fontes termais da região sul de Seferihisar têm uma forte contribuição de água do mar. Anteriores simulações numéricas de fluxo de fluidos e transporte de calor indicaram que a ascenção localizada de água quente nas falhas induz um movimento de fluxo de tipo convectivo nas unidades vizinhas. O transporte do sal foi totalmente associado ao fluxo termo-induzido para estudar de que modo as células de convecção induzidas pelas falhas poderiam ser responsáveis pela invasão da água do mar no SBG. São apresentados dados isotópicos para apoiar as constatações numéricas. Os resultados mostram que as células de convecção induzidas pelas falhas geraram plumas de água salgada que se estendem desde o fundo do mar em direção às falhas. Nos cruzamentos de falhas, a água do mar mistura-se com as águas termais quentes ascendentes. Os fluidos salinos resultantes ascendem até à superfície ao longo das falhas, actuados por forças de impulsão. Em Balçova, as aluviões espessas, as falhas menores e o fluxo regional evitam que a água salgada ascendente se espalhe até à superfície, enquanto que o fraco fluxo de recarga na fina camada de aluvião no sul do SBG não é suficiente para repelir as águas salgadas quentes ascendentes. Estes mecanismos podem desenvolver-se em qualquer sistema de falhas geotérmicas, com implicações na migração de minerais e energia em bacias sedimentares.ÖZTürkiye’nin batısındaki Seferihisar-Balçova Jeotermal Sistemi (SBJS), faylar boyunca oluşan sıcaklık ve hidrokimyasal anomalilerle tanımlanır. Seferihisar bölgesinde sıcak su kaynaklarında güçlü bir deniz suyu katkısı varken Balçova’da sıcak sular, ısınmış meteorik tatlı sulardan meydana gelmektedir. Önceki akışkan akımı ve ısı taşınım sayısal modellemeleri, faylardaki sıcak sulardaki yükselmenin çevre birimlerde konvektif akım benzeri harekete neden olduğunu belirtmektedir. SBJS’de faylarla kontrol edilen konveksiyon hücrelerinin, deniz suyu girişiminden sorumlu olup olmadığını araştırmak için tuz taşınımı tamamen sıcak su kontrollü akımla birleştirilmiştir. İzotop verileri de, sayısal sonuçları desteklemek için sunulmuştur. Sonuçlar, fay kontrollü konveksiyon hücrelerinin, deniztabanından faylara doğru uzanan denizsuyu girişimini yarattığını göstermiştir. Fay arayüzeylerinde deniz suları, yükselen sıcak sular ile karışmaktadır. Sonuçta oluşan tuzlu akışkanlar, sıcaklık farkı ile oluşan kuvvetlerle faylar boyunca yükselmektedir. Seferihisar’da ince alüvyondaki zayıf akımlar yükselen sıcak tuzlu sular üzerinde etkisiz kalırken, Balçova’da kalın alüvyon, faylar ve bölgesel akım tuzlu suyun yükselerek yüzeyden çıkmasına engel olmaktadır. Bu mekanizmalar sedimanter havzalardaki mineral ve enerji göçünün oluştuğu herhangi bir faylı jeotermal sistemde gelişebilir.

The impact of cemented layers and hardpans on oxygen diffusivity in mining waste heaps A field study of the Halsbrücke lead-zinc mine tailings (Germany).

This article reports fibre-optic oxygen measurements on a reactive mine waste heap located in the polymetallic sulphide mine district of Freiberg in south-eastern Germany. The heaped material consists of sulphide-bearing tailings from a processing plant of a lead-zinc mine. Mine waste material was deposited in the water phase after separation of mining ores in a flotation process. The tailing impoundment is partly covered with coarse sand and topsoil. Oxygen profiles were monitored during one year at eleven locations showing different physical and mineralogical compositions. At each location a borehole was drilled where the optic sensors were installed at 2-5 different depths. After installation the oxygen profiles were monitored seven times during one year from 2006-2007 and three to five oxygen profiles at each location were obtained. Oxygen measurements were accompanied by physical, chemical and mineralogical data of the tailing material. Additionally, a detailed mineralogical profile was analysed at a location representative for the central part of the heap, where the cemented layers show lateral continuity. Results showed that cemented layers have a significant influence on natural attenuation of the toxic As and Pb species owing to their capacity of water retention. The measured oxygen profiles are controlled by the zone of active pyrite weathering as well as by the higher water content in the cemented layers which reduces gaseous atmospheric oxygen supply. In contrast, gypsum bearing hardpans detected at three other locations have no detectable influence on oxygen profiles. Furthermore, the grain size distribution was proved to have a major effect on oxygen diffusivity due to its control on the water saturation. Temporal changes of the oxygen profiles were only observed at locations with coarse sediment material indicating also an important advective part of gas flux.

Simultaneous determination of psychoactive substances and their metabolites in aqueous matrices by ultrahigh-performance liquid chromatography-tandem mass spectrometry

An analytical method was developed and validated for the simultaneous determination of six psychoactive compounds (meprobamate, primidone, phenobarbital, pyrithyldione, diazepam, and oxazepam) and a metabolite of primidone (phenylethylmalonamide) in environmental water samples. The method involves pre-concentration and clean-up by solid phase extraction (SPE) followed by ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), using electrospray ionization (ESI) in both positive and negative modes. Limits of quantification (LOQs) were between 0.02 and 0.03 µg L−1 in groundwater and between 0.1 and 0.15 µg L−1 in wastewater. With a few exceptions, relative recoveries of the analytes exceeded 80%. The described method was used to analyze the selected psychoactive drugs in groundwater that had been affected by sewage irrigation for several decades ago and treated and untreated wastewater from Berlin (Germany). Highest values were found in groundwater with concentrations reaching up to 1.35 µg L−1 in the case of phenobarbital.

The impact of hardpans and cemented layers on oxygen diffusivity in mining waste heaps: diffusion experiments and modelling studies.

This study reports column tests and modelling results to assess the impact of hardpans and cemented layers on oxygen supply in mine waste sediments. The analysed sediment samples were obtained from a low-sulphide and low-carbonate polymetallic mine waste tailings impoundment located in the Freiberg mining district in Germany. The three samples were characterised by different degrees and types of cementation. After physical and mineralogical properties of the samples had been determined, breakthrough curves of oxygen were measured in column studies at different degrees of water saturation, and the diffusivities were assessed using a numerical modelling approach. Results demonstrate that cemented layers and hardpans in undisturbed sediments associated with fine-grained material operate as preferential pathways for diffusive gas transport during rewetting, leading to higher oxygen diffusivities compared to disturbed sediments. Under air-dry conditions, the disturbed samples show higher diffusivities than the undisturbed sample, indicating clogging of the porosity by precipitation of secondary minerals such as trivalent Fe oxyhydroxides acting as a barrier and thereby decreasing the diffusivity of the undisturbed sample. In contrast to sediments without cementation, diffusion experiments of sediments with cemented layers used in this study yield similar tortuosities in spite of their different grain size distributions, pointing to the important role of these heterogeneities for gas diffusion.

Spatial structure of hydraulic conductivity in various porous media — problems and experiences

Geostatistical simulation techniques, both Gaussian as well as indicator simulation are practical tools to generate spatial realizations of aquifer parameters such as hydraulic conductivity for further use in deterministic groundwater-flow and — transport models. The application of simulation methods require modeling of the spatial variability of the considered parameter, i.e. the variogram and pdf models must be derived a priori. In actual cases of groundwater contamination generally only sparse information on hydraulic parameters is available. Their spatial structure is often completely unknown. The main scope of our work is to describe the spatial structure of hydraulic conductivity for some typical aquifers and scales in order to use this information in geologically comparable cases.

Geochemical changes under variably saturated conditions during artificial recharge via ponded infiltration — A field study

Artificial groundwater recharge by percolation through the unsaturated zone is an important technique to enhance the water quality for drinking water supplies. Purification of the infiltration water results mainly from microbially mediated redox-reactions that involve the degradation of a wide range of organic substances. The aim of this study was to identify the spatial and temporal distribution of the redox zones that develop beneath an artificial recharge pond, a system that is characterised by regular hydraulic changes between the saturated and unsaturated condition within every operational cycle. The most significant hydraulic changes result from the formation and removal of a clogging layer at the pond’s bottom. Geochemical analyses of suction cup water as well as oxygen and hydraulic measurements showed that generally nitrate and manganese reducing conditions dominated below the pond as long as water saturated conditions prevailed. Iron and sulphate reduction occurred only in patchily distributed zones directly below the clogging layer and resulted from chemical and physical heterogeneity. When the sediment below the clogging layer became unsaturated, atmospheric oxygen penetrated from the pond fringes into this region, allowing re-oxidation of previously formed sulphide minerals.