Roger Thunvik

Geochemical characterisation of shallow aquifer sediments of Matlab Upazila, Southeastern Bangladesh — Implications for targeting low-As aquifers

High arsenic (As) concentrations in groundwater pose a serious threat to the health of millions of people in Bangladesh. Reductive dissolution of Fe(III)-oxyhydroxides and release of its adsorbed As is considered to be the principal mechanism responsible for mobilisation of As. The distribution of As is extremely heterogeneous both laterally and vertically. Groundwater abstracted from oxidised reddish sediments, in contrast to greyish reducing sediments, contains significantly lower amount of dissolved arsenic and can be a source of safe water. In order to study the sustainability of that mitigation option, this study describes the lithofacies and genesis of the sediments within 60 m depth and establishes a relationship between aqueous and solid phase geochemistry. Oxalate extractable Fe and Mn contents are higher in the reduced unit than in the oxidised unit, where Fe and Mn are present in more crystalline mineral phases. Equilibrium modelling of saturation indices suggest that the concentrations of dissolved Fe, Mn and PO(4)(3-)-tot in groundwater is influenced by secondary mineral phases in addition to redox processes. Simulating As(III) adsorption on hydroferric oxides using the Diffuse Layer Model and analytical data gave realistic concentrations of dissolved and adsorbed As(III) for the reducing aquifer and we speculate that the presence of high PO(4)(3-)-tot in combination with reductive dissolution results in the high-As groundwater. The study confirms high mobility of As in reducing aquifers with typically dark colour of sediments found in previous studies and thus validates the approach for location of wells used by local drillers based on sediment colour. A more systematic and standardised colour description and similar studies at more locations are necessary for wider application of the approach.

Determination of formation permeability by double-packer tests

Abstract The double-packer test is a classical field method for in situ determination of formation permeability. The formulae used in this calculation are based on the assumption that the formation is continuous, homogeneous and isotropic, and that the borehole is cased (impervious) except for the region of injection between the packers. These ideal conditions are rarely realized in practice, and the present paper deals with the error which thus in the calculated permeability is included, for an inhomogeneous, anisotropic or discontinuous formation, as well as for an uncased (pervious) borehole. The investigation takes the form of a numerical simulation of double-packer tests in hypothetical formations of a priori known permeability, with the rate of flow and the water overpressure at quasi steady state measured as in a real packer test. This information is subsequently used as input for calculating the permeability in the idealized model, and the calculated permeabilities are compared with the actual ones. It has been shown that for homogeneous and isotropic formations, Dagans, Hvorslevs and Moyes formulae yield similar results, cased and uncased boreholes show practically the same permeability value, and a low permeability around the borehole accounts for a significant distortion of the representative value for the formation as a whole. For an anisotropic formation with horizontal vertical principal axes of anisotropy, the calculated results more or less coincide with the horizontal value.

Environmental health practices, constraints and possible interventions in peri-urban settlements in developing countries--a review of Kampala, Uganda.

Like most cities in developing countries, Ugandas capital city, Kampala, is experiencing urbanisation leading to an increase in population, and rapid development of peri-urban (informal) settlements. More than 60% of the citys population resides in these settlements which have the lowest basic service levels (sanitation, water supply, solid waste collection, stormwater and greywater disposal). A review of earlier studies on infrastructure development and sustainability within Kampalas peri-urban settlements, field surveys in a typical peri-urban settlement in the city (Bwaise III Parish), and structured interviews with key personnel from the National Water and Sewerage Corporation (NWSC), Kampala City Council (KCC), and the National Environment Management Authority (NEMA) were undertaken. Findings on current environmental health practices as well as perspectives of local communities and interviewed institutions on problems, constraints and possible solutions to basic service provision are presented. The implications of these viewpoints for possible environmental health interventions are presented.

On the use of continuum approximations for regional modeling of groundwater flow through crystalline rocks

Abstract Two main issues associated with the application of the stochastic continuum approach to numerical modeling of regional groundwater flow and mass transport through crystalline rocks is addressed. First, the problem of conductivity upscaling from a highly heterogeneous subgrid (measurement) conductivity field to a less heterogeneous supragrid (model) one is studied. Secondly, the question of whether the intervening rock masses between major fracture zones can allow for a sufficient spatial homogenization of a dispersion phenomenon as required by invoking the ergodic hypothesis is studied. For the sake of this paper, it is assumed that the observed spatial variability of apparent conductivity data, determined by 3m double-packer tests, obeys a statistically isotropic and stationary lognormal random function in two dimensions with a logconductivity variance σ 2 ln K of 16. The result of the numerical simulations undertaken suggests that the upscaling of a highly heterogeneous subgrid conductivity field may benefit from considering the anisotropy characteristics caused by an insufficient homogenization of the subgrid heterogeneity on the scale of a supragrid model block. Concerning the spreading of a conservative solute the treatment was restricted to a single realization with a characteristic field dimension of 32 λ ln K , where λ ln K is the logconductivity integral scale. The solute dispersion was studied in two orthogonal directions by particle tracking. Despite an isotropic logconductivity field, the particle tracking produces different dispersivities, which demonstrates that the particular realization studied was not large enough to provide ergodicity.

Water Transport, Retention, and Survival of Escherichia coli in Unsaturated Porous Media : A Comprehensive Review of Processes, Models, and Factors

The vadose zone can function as both a filter and a passage for bacteria. This review evaluates when and why either effect will apply based on available literature. It summarizes theories and experimental research that address the related, underlying bacterial attenuation processes, the applied macro-scale modeling approaches, and the influencing factors - including the cell, soil, solution and system characteristics. Results point to that the relative importance of each removal mechanism depends on the moisture content and the solution ionic strength. The limitations of available modeling approaches are discussed. It remains unclear in which contexts these are reliable for predictions. The temporal first-order kinetic Escherichia coli (E. coli) removal coefficient ranges three orders of magnitude, from 10−4 to 10−1/min. Results suggest that this rate depends on the pore-water velocity. Spatial filtration of E. coli increases with slower flow and higher collector surface heterogeneity. It could be insignificant in the case of heavy and sudden infiltration and subsequent transport in preferential flow paths, induced, for example, by plant roots or cracks in clayey soils. Future research thus needs to address transport as an effect of extreme weather events such as droughts and subsequent floods.

Geogenic arsenic and other trace elements in the shallow hydrogeologic system of Southern Poopó Basin, Bolivian Altiplano.

Environmental settings in the southern area of Lake Poopó in the Bolivian highlands, the Altiplano, have generated elevated amounts of arsenic (As) in the water. The area is characterised by a semiarid climate, slow hydrological flow and geologic formations of predominantly volcanic origin. The present study aimed at mapping the extent of the water contamination in the area and to investigate the geogenic sources and processes involved in the release of As to the groundwater. Ground- and surface-water samples were collected from 24 different sites, including drinking water wells and rivers, in the southern Poopó basin in two different field campaigns during the dry and rainy seasons. The results revealed variable levels of As in shallow drinking water wells and average concentration exceeding the WHO guidelines value. Arsenic concentrations range from below 5.2 μg/L (the detection level) to 207 μg/L and averages 72 μg/L. Additionally, high boron (B) concentrations (average 1902 μg/L), and high salinity are further serious concerns for deteriorating the groundwater quality and rendering it unsuitable for drinking. Groundwater is predominantly of the Na-Cl-HCO3 type or the Ca-Na-HCO3 type with neutral or slightly alkaline pH and oxidising character. While farmers are seriously concerned about the water scarcity, and on a few occasions about salinity, there are no concerns about As and B present at levels exceeding the WHO guidelines, and causing negative long term effects on human health. Sediment samples from two soil profiles and a river bed along with fourteen rock samples were also collected and analysed. Sequential extractions of the sediments together with the calculation of the mineral saturation indices indicate that iron oxides and hydroxides are the important secondary minerals phases which are important adsorbents for As. High pH values, and the competition of As with HCO3 and dissolved silica for the adsorption sites probably seems to be an important process for the mobilisation of As in the shallow groundwaters of the region. Continuous monitoring and expansion of monitoring systems are necessary prerequisites for better understanding of the pattern of As mobilisation in the Southern Poopó Basin.

Arsenic-enriched groundwaters of India, Bangladesh and Taiwan—Comparison of hydrochemical characteristics and mobility constraints

Arsenic (As) enrichment in groundwater has become a major global environmental disaster. Groundwater samples were collected from 64 sites located in the districts of 24-Parganas (S), and Nadia in West Bengal, India (Bhagirathi sub-basin), and 51 sites located in the districts of Comilla, Noakhali, Magura, Brahman baria, Laxmipur, Munshiganj, Faridpur and Jhenaida in Bangladesh (Padma-Meghna sub-basin). Groundwater samples were also collected from two As-affected areas (Chianan and Lanyang plains) of Taiwan (n = 26). The concentrations of major solutes in groundwater of the Padma-Meghna sub-basin are more variable than the Bhagirathi sub-basin, suggesting variations in the depositional and hydrological settings. Arsenic concentrations in groundwaters of the studied areas showed large variations, with mean As concentrations of 125 μg/L (range: 0.20 to 1,301 μg/L) in Bhagirathi sub-basin, 145 μg/L (range: 0.20 to 891 μg/L) in Padma-Meghna sub-basin, 209 μg/L (range: 1.3 to 575 μg/L) in Chianan plain, and 102 μg/L (range: 2.5 to 348 μg/L) in Lanyang plain groundwater. The concentrations of Fe, and Mn are also highly variable, and are mostly above the WHO-recommended guideline values and local (Indian and Bangladeshi) drinking water standard. Piper plot shows that groundwaters of both Bhagirathi and Padma-Meghna sub-basins are of Ca-HCO(3) type. The Chianan plain groundwaters are of Na-Cl type, suggesting seawater intrusion, whereas Lanyang plain groundwaters are mostly of Na-HCO(3) type. The study shows that reductive dissolution of Fe(III)-oxyhydroxides is the dominant geochemical process releasing As from sediment to groundwater in all studied areas.

Prevalence of microbiological contaminants in groundwater sources and risk factor assessment in Juba, South Sudan

In low-income regions, drinking water is often derived from groundwater sources, which might spread diarrheal disease if they are microbiologically polluted. This study aimed to investigate the occurrence of fecal contamination in 147 improved groundwater sources in Juba, South Sudan and to assess potential contributing risk factors, based on bivariate statistical analysis. Thermotolerant coliforms (TTCs) were detected in 66% of the investigated sources, including 95 boreholes, breaching the health-based recommendations for drinking water. A significant association (p<0.05) was determined between the presence of TTCs and the depth of cumulative, long-term prior precipitation (both within the previous five days and within the past month). No such link was found to short-term rainfall, the presence of latrines or damages in the borehole apron. However, the risk factor analysis further suggested, to a lesser degree, that the local topography and on-site hygiene were additionally significant. In summary, the analysis indicated that an important contamination mechanism was fecal pollution of the contributing groundwater, which was unlikely due to the presence of latrines; instead, infiltration from contaminated surface water was more probable. The reduction in fecal sources in the environment in Juba is thus recommended, for example, through constructing latrines or designating protection areas near water sources. The study results contribute to the understanding of microbiological contamination of groundwater sources in areas with low incomes and high population densities, tropical climates and weathered basement complex environments, which are common in urban sub-Saharan Africa.

Using geovisualisation to support participatory problem structuring and decision making for an urban water utility in Uganda

This paper describes the application of geovisualisation to facilitate participatory identification and structuring of problems in an urban water supply system in Uganda. The city of Kampala has ex ...

Development of decision support tools for decentralised urban water supply management in Uganda : An action research approach

This paper presents a study in which four real-life problem situations are used to explore the challenges of developing and implementing decision support tools within an urban water utility. In the study, an Action Research approach is used, with theoretical considerations leading to specific actions being implemented, which in turn yield results that are used to reflect upon the original theoretical assumptions. Results of the study emphasize the need for proper problem-structuring prior to the formulation of actions; the challenges of moving from planning to action; the importance of user involvement in the development of tools; and how a good match of people, problem-structuring, proactiveness and participatory tools development is required for effective decision support provision. The study also highlights the challenges of embedding decision support within existing work systems in organizations. The Action Research approach is shown to be useful in bridging the gap between theory and practice, aiding the development of decision support tools of immediate and practical benefit to organizations.