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Abstract: Air injection into porous media is investigated by laboratory experiments and numerical modelling. Typical applications of air injection into a granular bed are aerated bio-filters and air sparging of aquifers. The first stage of the dynamic process consists of air injection into a fixed or a quasi-fixed water-saturated granular bed. Later stages could include stages of movable beds as well, but are not further investigated here. A series of laboratory experiments were conducted in a two-dimensional box of the size 60cm×38cm×0.55cm consisting of glass walls and using glass beads of diameter 0.4–0.6mm as granular material. The development of the air flow pattern was optically observed and registered using a digital video camera. The resulting transient air flow pattern can be characterized as channelled flow in a fixed porous medium with dynamic tree-like evolution behaviour. Attempts are undertaken to model the air injection process. Multiphase pore-scale modelling is currently disregarded since it is restricted to very small scales. Invasion percolation models taking into account gravity effects are usually restricted to slow processes. On the other hand a continuum-type two-phase flow modelling approach is not able to simulate the observed air flow pattern. Instead a stochastic continuum-type approach is discussed here, which incorporates pore-scale features on a subscale, relevant for the immiscible processes involved. Consequently, the physical process can be modelled in a stochastic manner only, where the single experiment represents one of many possible realizations. However, the present procedure retains realistic water and air saturation patterns and therefore produces similar finger lengths and widths as observed in the experiments. Monte Carlo type modelling leads to ensemble mean water saturation and the related variance. [Copyright &y& Elsevier]

Abstract: Investigations in outcrops of non-homogeneous gravel deposits in north-eastern Switzerland by Jussel et al. [Jussel P, Stauffer F, Dracos T. Transport modeling in heterogeneous aquifers: 1. Statistical description and numerical generation of gravel deposits. Water Resour Res 1994;30:1803–17] revealed distinct sedimentary structures or facies elements appearing as more or less horizontal lenses and layers embedded in extended patches of background gravel material. One of the observed sediment units consists of highly permeable inclined sequences of gravel layers. This inclination manifests itself as a strong anisotropy of the hydraulic conductivity with inclined principal directions. In this paper, the role of highly conductive sediment units with inclined bedding is investigated by a series of three-dimensional numerical flow and advective transport experiments. A typical single lens with inclined principal axes of the hydraulic conductivity tensor is investigated, which is embedded in homogeneous background matrix material. Particle tracking shows pronounced lateral (horizontal and vertical) distortions of the flow path depending on the angles of the bedding of the lens. The results allow better understanding of the flow and transport phenomena that are finally responsible for macrodispersion effects in similar gravel aquifers. [Copyright &y& Elsevier]

A method is proposed to estimate the uncertainty of the location of pathlines in two-dimensional, steady-state confined or unconfined flow in aquifers due to the uncertainty of the spatially variable unconditional hydraulic conductivity or transmissivity field. The method is based on concepts of the semianalytical first-order theory given in Stauffer et al. (2002, 2004) , which allows estimates of the lateral second moment (variance) of the location of a moving particle. However, this method is reformulated in order to account for nonuniform recharge and nonuniform aquifer thickness. One prominent application is the uncertainty estimation of the catchment of a pumping well by considering the boundary pathlines starting at a stagnation point. In this method, the advective transport of particles is considered, based on the velocity field. In the case of a well catchment, backtracking is applied by using the reversed velocity field. Spatial variability of hydraulic conductivity or transmissivity is considered by taking into account an isotropic exponential covariance function of log-transformed values with parameters describing the variance and correlation length. The method allows postprocessing of results from ground water models with respect to uncertainty estimation. The code PPPath, which was developed for this purpose, provides a postprocessing of pathline computations under PMWIN, which is based on MODFLOW. In order to test the methodology, it was applied to results from Monte Carlo simulations for catchments of pumping wells. The results correspond well. Practical applications illustrate the use of the method in aquifers. [ABSTRACT FROM AUTHOR]

This paper is concerned about aquifer models that are affected by the uncertainty on hydraulic conductivity and recharge. In particular, we study the impact of these sources of uncertainty on the stochastic characterization of drinking water well capture zones. The estimation of a drinking water well capture zone is important for the design of a protection zone around the well. The estimation is associated with uncertainty due to imperfect knowledge of the input parameters of the groundwater flow and mass transport equations. A first synthetic study shows that the uncertainty of the mean recharge has a larger impact on the well catchment uncertainty than the uncertainty of the spatial variability of recharge. Therefore, it is concluded that in practice the recharge can be estimated for one zone or a limited number of zones, without the need to estimate the recharge on the grid cell scale. The sequential self-calibrated method for the Monte Carlo type inverse modelling of groundwater flow and mass transport was extended for the estimation of recharge rates. Recharge rates can be estimated together with hydraulic conductivities, and possibly other parameters, using both head and concentration data. In a second synthetic study the joint estimation of transmissivities and recharge rates is illustrated. It is found that the transmissivity, hydraulic head and recharge fields are better characterised after the inverse conditioning. In order to stabilize the inverse estimation, it is essential that a regularization term is included in the objective function in case parameters are estimated zone-wise. [Copyright &y& Elsevier]

We present the comparison of two control criteria for the real-time management of a water well field. The criteria were used to simulate the operation of the Hardhof well field in the city of Zurich, Switzerland. This well field is threatened by diffuse pollution in the subsurface of the surrounding city area. The risk of attracting pollutants is higher if the pumping rates in four horizontal wells are increased, and can be reduced by increasing artificial recharge in several recharge basins and infiltration wells or by modifying the artificial recharge distribution. A three-dimensional finite elements flow model was built for the Hardhof site. The first control criterion used hydraulic head differences (Δh-criterion) to control the management of the well field and the second criterion used a path line method (%s-criterion) to control the percentage of inflowing water from the city area. Both control methods adapt the allocation of artificial recharge (AR) for given pumping rates in time. The simulation results show that (1) historical management decisions were less effective compared to the optimal control according to the two different criteria and (2) the distribution of artificial recharge calculated with the two control criteria also differ from each other with the %s-criterion giving better results compared to the Δh-criterion. The recharge management with the %s-criterion requires a smaller amount of water to be recharged. The ratio between average artificial recharge and average abstraction is 1.7 for the Δh-criterion and 1.5 for the %s-criterion. Both criteria were tested online. The methodologies were extended to a real-time control method using the Ensemble Kalman Filter method for assimilating 87 online available groundwater head measurements to update the model in real-time. The results of the operational implementation are also satisfying in regard of a reduced risk of well contamination. [Copyright &y& Elsevier]

Background: Reprocessing of medical devices, beingclassified as semi-critical B is recommended to be performed in a washer-disinfector. In order to estimate, whether the expected contaminants of the various medical disciplines can be effectively removed by this washer-disinfector, different so called "test soils" have been proposed to be tested as a marker of cleaning efficacy of the disinfector. Todays described test soils are optimised for the testingof contaminations occurring in surgical procedures, but not for dental procedures. Methods: In this study the test soils being proposed in the EN 15883-5 (e.g. KMNEsoil, recipe by Koller and coagulated sheep's blood) were compared with 8 reference substances used in the conservative-pros-thetic dental practice. The success of the cleaning efficacy in the washer-disinfector was checked visually and by determiningthe residual protein concentration on the contaminated instruments after the cleaning procedure. Results: It could be shown that in contrast to the proposed test soils of the EN 15883-5, the used reference substances of the dental practice could not be removed by the washer-disinfector. Removal of these ref-erence substances was only possible after manual or ultrasonic cleaning. Conclusions: Since blood plays a subordinate role as a contaminant of instruments during conservative-prosthetic dental treatments, testing of thecleaningefficacy of the washer-disinfector with test soils according to the proposals of the EN 15883-5 is not representative in this discip-line of dentistry. Most of the materials used in dental practice can only be removed manually or with the help of the ultrasound bath. [ABSTRACT FROM AUTHOR]

The main goal of this work is to implement and validate a visualization method with a given temporal/spatial resolution to obtain the dynamic three-dimensional (3D) structure of an air plume injected into a deformable liquid-saturated porous medium. The air plume develops via continuous air injection through an orifice at the bottom of a loose packing of crushed silica grains. The packing is saturated by a glycerin-water solution having the same refractive index and placed in a rectangular glass container. By using high-speed image acquisition through laser scanning, the dynamic air plume is recorded by sequential tomographic imaging. Due to the overlap between adjacent laser sheets and the light reflection, air bubbles are multiply exposed in the imaging along the scanning direction. Four image processing methods are presented for the removal of these redundant pixels arising from multiple exposure. The respective results are discussed by comparing the reconstructed air plume volume with the injected one and by evaluating the morphological consistency of the obtained air plume. After processing, a 3D dynamic air flow pattern can be obtained, allowing a quantitative analysis of the air flow dynamics on pore-scale. In the present experimental configuration, the temporal resolution is 0.1 s and the spatial resolution is 0.17 mm in plane and about 1 mm out of plane of the laser sheet. [ABSTRACT FROM AUTHOR]

Abstract: Laboratory air injection experiments in a two-dimensional vertically placed cell filled with a water-saturated packing of spherical glass beads show a particular transition of air flow patterns at different length scales, tree-like fingering with pore-scale drainage, a local fluidization of beads with finger-scale channeled air flow, and an oscillating irregular channel with finger-scale air flow, where the channel is formed by pushing beads aside. The tree-like pattern shows a parabola-like growth with vertical height, while both the top and the bottom lateral width of the pattern increase linearly for the small injection rate, then stay more or less constant for further increasing injection rates. By tracing the vertical position of maximum advance of the fluidized pattern with time, the evolution of the fluidized pattern is characterized by two dynamic regimes, the pattern not reaching or reaching the injection orifice, respectively, using small and medium injection rates. As the injection rate increases further, the fluidized pattern shows up immediately after air is injected. Via physical conceptual models using local forces or pressure gradient balances, we derive a series of characteristics that describe the width of the tree-like air plume, the width of a single channel, and the starting vertical position of the fluidized pattern. [Copyright &y& Elsevier]

Abstract: Injecting air into two-dimensional vertical liquid-saturated assemblies of grains causes a rearrangement of the grains. The interaction of the air flow injected at the bottom with the grains and the liquid leads to a mobilization of the grains, in which air channels migrate and grain clusters undergo shearing. The channel migration comes to a stop after some time, leaving one thin and stable preferential channel for air flow. Furthermore, the grain packing is compacted due to a rearrangement process caused by the pulsating movement of air channels. The compaction process is found to obey a slow exponential growth law. Additionally, the pulsation introduces size segregation in the packing. This is visualized by a set of tracing experiments showing that the coarser grains tend to accumulate at the downstream end of the preferential air pathway. However, the pulsating strength decreases sharply as the grain size increases. Therefore no segregation was observed in the coarse packing. A stabilization process of the preferential air channel can be described by a lower bound of critical channel size assuming the validity of Hagen–Poiseuille air flow inside the channel. Nevertheless, the channel size could not exceed an upper size which is determined by the capillary instability, assuming a quasi-static equilibrium of the dilating process of the air channel. [Copyright &y& Elsevier]

Abstract: A set of two-dimensional laboratory visualization experiments reveals a previously unrecognized gas-flow instability in a porous medium saturated with a glycerine–water solution. The medium is a non-fixed vertically placed packing of grains of crushed fused silica glass. The interaction of the injected air flow and the medium structure leads to mobilization of the medium and an instability, which causes the air channel to migrate. This instability is dominated by a dimensionless number , which can be interpreted as a normalization of a critical velocity with a dipole velocity for saturated conditions. The channel migration appears as a sequence of previous channels collapsing and new channels opening. The channel migration comes to a stop after some time, leaving one thin and stable channel. The process is studied by calculating the cumulated lateral movement distance of a channel and the lateral width of the area affected by the migration, both scaled by with an empirical power of 0.25. Another dimensionless number f is defined to qualify the migration under different grain size, height of bed, and air flow rate. [Copyright &y& Elsevier]

Evapotranspiration from a phreatic groundwater table is an important input parameter for hydrological models. This parameter, however, is difficult to determine in the field, since plants take their water from various depths and the penetration depth of direct evaporation is unknown. We present a method to estimate evapotranspiration rates based on diurnal groundwater level fluctuations observed in the Okavango Delta, Botswana. To this end, the regional setting as well as the local processes in the unsaturated zone have to be analysed. Resulting estimates for the evapotranspiration rate range from 0.06 to 4.3 mm/day, for varying local vegetation cover and soil characteristics. [Copyright &y& Elsevier]

The Sloan Digital Sky Survey (SDSS) has been active for approximately 15 years as of this writing. SDSS continues to produce large amounts of data, effectively daily. SDSS needs an effective system for data transfer and management that can operate essentially free of human intervention. In 2008, with the commencement of the third phase of SDSS, SDSS-III, new needs and opportunities motivated a fresh look at the data transfer infrastructure. We have constructed and are releasing a Python package, transfer, that contains all the automation needed for daily data transfer operations. This package has been tested and used successfully for several years. Significant portions of this code will continue to be used as SDSS transitions to its fourth phase, SDSS-IV. [ABSTRACT FROM AUTHOR]

Background: Currently, to our knowledge, quality of output water of dental chair units is not covered by specific regulations in the European Union, and national recommendations are heterogeneous. In Germany, water used in dental chair units must follow drinking water quality. In the United States of America, testingfor aerobic heterotrophic bacteria is recommended. The present study was performed to evaluate whether the counts of aerobic heterotrophic bacteria correlate with the presence of potentially pathogenic bacteria such as Legionella spp. or Pseudomonas aeruginosa. Methods: 71 samples were collected from 26 dental chair units with integrated disinfection device and 31 samples from 15 outlets of the water distribution pipework within the department were examined. Samples were tested for aerobic heterotrophic bacteria at 35°C and 22°C using different culture media and for Legionella spp. and for Pseudomonas aeruginosa. Additionally, strains of Legionella pneumo-phila serogroup 1 were typed with monoclonal antibodies and repre-sentative samples of Legionella pneumophila serogroup 1 were typed by sequence based typing. Results: Our results showed a correlation between different agars for aerobic heterotrophic bacteria but no correlation for the count of aerobic heterotrophic bacteria and the presence of Legionella spp. or Pseudo-monas aeruginosa. Conclusion: Testingfor aerobic heterotrophic bacteria in output water or water distribution pipework within the departments alone is without any value for predicting whether the water is contaminated with poten-tially pathogenic bacteria like Legionella spp. or Pseudomonas aeru-ginosa. [ABSTRACT FROM AUTHOR]

We present an optimal real-time control approach for the management of drinking water well fields. The methodology is applied to the Hardhof field in the city of Zurich, Switzerland, which is threatened by diffuse pollution. The risk of attracting pollutants is higher if the pumping rate is increased and can be reduced by increasing artificial recharge (AR) or by adaptive allocation of the AR. The method was first tested in offline simulations with a three-dimensional finite element variably saturated subsurface flow model for the period January 2004-August 2005. The simulations revealed that (1) optimal control results were more effective than the historical control results and (2) the spatial distribution of AR should be different from the historical one. Next, the methodology was extended to a real-time control method based on the Ensemble Kalman Filter method, using 87 online groundwater head measurements, and tested at the site. The real-time control of the well field resulted in a decrease of the electrical conductivity of the water at critical measurement points which indicates a reduced inflow of water originating from contaminated sites. It can be concluded that the simulation and the application confirm the feasibility of the real-time control concept. [ABSTRACT FROM AUTHOR]

Summary: In groundwater flow modelling, the interaction between rivers and aquifers is usually modelled with spatially and temporally constant leakage coefficients. We used conventional model calibration techniques to investigate the time-varying river–aquifer interactions in the sandy gravel aquifer of the upper Limmat valley in Zurich (Switzerland). The aim of the study was to determine whether the leakage coefficients have to be treated as time-dependent in order to adequately model the dynamics of the groundwater flow. A transient horizontal two-dimensional groundwater flow model was established together with a one-dimensional hydraulic model for river flow, as well as a scheme calculating groundwater recharge and lateral inflow from meteorological data and a soil water balance model. The groundwater flow model was calibrated using hydraulic head data from May and June 2004 and July and August 2005. The verification period covered 13years using hydraulic head data from 90piezometers. The comparison of the model results with the measurements in the verification period revealed three phenomena concerning river–aquifer interaction which all showed up as systematic deviations between model and observations. (1) The major flood event in May 1999 had a significant and persistent influence on the river–aquifer interaction. In an impounded river section upstream of a weir, the infiltration of river water was enhanced by the flooding probably due to erosion processes. (2) Seasonal river water temperature fluctuations influenced the infiltration rate, due to the temperature dependence of hydraulic conductivity of the river bed. (3) Depending on geometry and hydraulic characteristics of the riverbanks the leakage coefficient can be a function of the river stage. With higher water levels, additional areas can contribute to the infiltration of river water. Therefore, in modelling groundwater flow with strong river–aquifer interactions, it can become necessary to consider dynamic leakage coefficients and to recalibrate periodically. [Copyright &y& Elsevier]