Manganese concentrations in Scottish groundwater

Groundwater is increasingly being used for public and private water supplies in Scotland, but there is growing evidence that manganese (Mn) concentrations in many groundwater supplies exceed the national drinking water limit of 0.05 mg l^− 1. This study examines the extent and magnitude of high Mn concentrations in groundwater in Scotland and investigates the factors controlling Mn concentrations. A dataset containing 475 high quality groundwater samples was compiled using new data from Baseline Scotland supplemented with additional high quality data where available. Concentrations ranged up to 1.9 mg l^− 1; median Mn concentration was 0.013 mg l^− 1 with 25th and 75th percentiles 0.0014 and 0.072 mg l^− 1 respectively. The Scottish drinking water limit (0.05 mg l^− 1) was exceeded for 30% of samples and the WHO health guideline (0.4 mg l^− 1) by 9%; concentrations were highest in the Carboniferous sedimentary aquifer in central Scotland, the Devonian sedimentary aquifer of Morayshire, and superficial aquifers. Further analysis using 137 samples from the Devonian aquifers indicated strong redox and pH controls (pH, Eh and dissolved oxygen accounted for 58% of variance in Mn concentrations). In addition, an independent relationship between Fe and Mn was observed, suggesting that Fe behaviour in groundwater may affect Mn solubility. Given the redox status and pH of Scottish groundwaters the most likely explanation is sorption of Mn to Fe oxides, which are released into solution when Fe is reduced.Since the occurrence of elevated Mn concentrations is widespread in groundwaters from all aquifer types, consideration should be given to monitoring Mn more widely in both public and private groundwater supplies in Scotland and by implication elsewhere.     

Groundwater Exploitation and Development: Some Current Issues in Scotland

The increasing cost of water in public supply is providing renewed interest in groundwater from industry and other intensive water-users. At present, groundwater in Scotland enjoys considerable advantages: over surface water. However, there are also disadvantages: in some areas groundwater quality is poor due either to anthropogenic activity or the natural occurrence of acidic groundwaters. The future groundwater development and management policy for Scotland is being formed around the Water Resources Framework Directive and the Groundwater Action Programme. However, there are several policy constraints which urgently need to be addressed; these include (a) the role of the Water Order and (b) the need for a licensing system to control abstraction from selected aquifer units.     

Grundwasserströmung und -beschaffenheit im Einzugsgebiet der Eckernförder Bucht, Schleswig-Holstein

Within the scope of the Sub-GATE-project (Submarine Groundwater Fluxes and Transport Processes from Methane Rich Coastal Sedimentary Environments), hydrogeology of the catchment area of the Eckernfoerde Bay within gehe whole Pleistocene succession down to the up-permost continous Tertiary aquitard was studied. This aquitard usually consists of clays of the Miocene Vierland-Stufe, which occur at 160 to 190 m bsl. Regional catchment areas of the most important aquifers and their main characteristics were estimated by evaluation of hydraulic and hydrochemical data from wells in this region. Groundwater in the Miocene aquifer in general is more reduced than groundwater in the Pleistocene aquifer, mainly due to the advanced activity of microorganisms. Recharge areas of the Pleistocene aquifer occur NW and S of Eckernfoerde, while recharge areas of the Miocene aquifer are situated in the SW of the study area and at the southern coast of the Eckernfoerde Bay. Some uncertainty arising from data aquisation at different times used in geostatistical regionalisation was accounted for by application of a fuzzy-kriging-procedure.     

Nitrate contamination of shallow groundwaters in Ontario,Canada

Highly elevated concentrations of NO₃^? have been found in the groundwaters from shallow aquifers at several locations in Ontario. The nitrate is derived either from the fertilizers applied to the agricultural soils, or from industrial point sources, and should be regarded as a major water quality problem. However, the nitrate levels may be reduced by denitrification processes under reducing conditions in the aquifer. The distributions of ammonia, chloride, dissolved oxygen, redox potential, methane, calcium and magnesium are presented and related to the hydrogeochemical changes undergone by the pollutant nitrate during flux along the groundwater flow systems.     

Movement of heavy metals into a shallow aquifer by leakage from sewage oxidation ponds

The concentrations of Mn, Ni, Cu, Cd and Cr were measured in a shallow perched groundwater aquifer which underlies the Dan Region Sewage Reclamation Project (Israel). The contribution of effluents to the groundwaters has been evaluated on the basis of chloride concentration. Groundwater which are estimated to contain more than 60% effluents showed a hundred-fold decrease in Cu and Mn at a distance of 650 m away from the ponds, as compared with the near ponds samples. Ni and Cd showed only a small decrease in concentration over a distance of 150 m, and then stayed constant. The concentrations of Cu and particularly of Mn in the groundwaters near the oxidation ponds is equivalent to or greater than in the ponds themselves. It is suggested that Cu and Mn are mobilized from the precipitated sludge into the interstitial waters. They percolate into the groundwater near the ponds and then are precipitated by increasing aeration during the movement of the water away from the pond area. Cd and Ni form stable soluble organic chelates which are only slightly removed by interaction with the sandy soil of the aquifer.     

Grundwasserfließgeschehen Mecklenburg-Vorpommerns – Geohydraulische Modellierung mit Detrended Kriging

Groundwater heads were mapped for the entire State of Mecklenburg-Western Pomerania by applying a Detrended Kriging method based on a numerical geohydraulic model. The general groundwater flow system (trend surface) was represented by a two-dimensional horizontal flow model. Thus deviations of observed groundwater heads from simulated groundwater heads are no longer subject to a regional trend and can be interpolated by means of Ordinary Kriging. Subsequently, the groundwater heads were obtained from the sum of the simulated trend surface and interpolated residuals. Furthermore, the described procedure allowed a plausibility check of observed groundwater heads by comparing them to results of the hydraulic model. If significant deviations were seen, the observation wells could be allocated to different aquifers. The final results are two hydraulically established groundwater head distributions – one for the regional main aquifer and one for the upper aquifer which may differ locally from the main aquifer.     

GROUNDWATER IN A WATER-RICH ENVIRONMENT: WALES, A LAND OF PLENTY

Traditionally, Wales has relied on surface water, with only 8% of the total public supply currently derived from groundwater sources. There are various significant aquifers in Wales, including the Carboniferous Limestone in South and North-East Wales and the Triassic aquifer in the Vale of Clwyd, as well as superficial granular deposits that are of particular importance in West Wales. Groundwater quality is generally good and minimal treatment is required. Hydrogeological data in the public domain for Wales are scarce: the Carboniferous Limestone, for example, is particularly poorly documented. Despite this lack of information there are some notable groundwater schemes, but current legislative aspects now require a better overall understanding of the hydrogeology of Wales. A key recommendation is the preparation of public domain data-sets and a comprehensive report on the hydrogeology of Wales.     

The significance of colloids in the transport of pesticides through Chalk

Agrochemical contamination in groundwater poses a significant long term threat to water quality and is of concern for legislators, water utilities and consumers alike. In the dual porosity, dual permeability aquifers such as the Chalk aquifer, movement of pesticides and their metabolites through the unsaturated zone to groundwater is generally considered to be through one of two pathways; a rapid by-pass flow and a slower 'piston-flow' route via the rock matrix. However, the dissolved form or 'colloidal species' in which pesticides move within the water body is poorly understood. Following heavy rainfall, very high peaks in pesticide concentration have been observed in shallow Chalk aquifers. These concentrations might be well explained by colloidal transport of pesticides. We have sampled a Chalk groundwater beneath a deep (30 m) unsaturated zone known to be contaminated with the pesticide diuron. Using a tangential flow filtration technique we have produced colloidal fractions from 0.45 microm to 1 kDa. In addition, we have applied agricultural grade diuron to a typical Chalk soil and created a soil water suspension which was also subsequently fractionated using the same filtration system. The deep groundwater sample showed no evidence of association between colloidal material and pesticide concentration. In comparison, despite some evidence of particle trapping or sorption to the filters, the soil water clearly showed an association between the <0.45 microm and <0.1 microm colloidal fractions which displayed significantly higher pesticide concentrations than the unfiltered sample. Degradation products were also observed and found to behave in a similar manner to the parent compound. Although relatively large colloids can be generated in the Chalk soil zone, it appears transport to depth in a colloidal-bound form does not occur. Comparison with other field and monitoring studies suggests that rapid by-pass flow is unlikely to occur beneath 4-5 m. Therefore, shallow groundwaters are most at risk from rapid transport of high concentrations of pesticide-colloidal complexes. The presence of a deep unsaturated zone will mean that most of the colloidal-complexes will be filtered by the narrow Chalk pores and the majority of pesticide transport will occur in a 'dissolved' form through the more gradual 'piston-flow' route.     

Sources and controls for the mobility of arsenic in oxidizing groundwaters from loess-type sediments in arid/semi-arid dry climates - evidence from the Chaco-Pampean plain (Argentina)

In oxidizing aquifers, arsenic (As) mobilization from sediments into groundwater is controlled by pH-dependent As desorption from and dissolution of mineral phases. If climate is dry, then the process of evaporative concentration contributes further to the total concentration of dissolved As. In this paper the principal As mobility controls under these conditions have been demonstrated for Salí River alluvial basin in NW Argentina (Tucumán Province; 7000 km²), which is representative for other basins or areas of the predominantly semi-arid Chaco-Pampean plain (1,000,000 km²) which is one of the world’s largest regions affected by high As concentrations in groundwater. Detailed hydrogeochemical studies have been performed in the Salí River basin where 85 groundwater samples from shallow aquifers (42 samples), deep samples (26 samples) and artesian aquifers (17 samples) have been collected. Arsenic concentrations range from 11.4 to 1660 μg L⁻¹ leaving 100% of the investigated waters above the provisional WHO guideline value of 10 μg L⁻¹. A strong positive correlation among As, F, and V in shallow groundwaters was found. The correlations among those trace elements and U, B and Mo have less significance. High pH (up to 9.2) and high bicarbonate (HCO₃) concentrations favour leaching from pyroclastic materials, including volcanic glass which is present to 20-25% in the loess-type aquifer sediments and yield higher trace element concentrations in groundwater from shallow aquifers compared to deep and artesian aquifers. The significant increase in minor and trace element concentrations and salinity in shallow aquifers is related to strong evaporation under semi-arid climatic conditions. Sorption of As and associated minor and trace elements (F, U, B, Mo and V) onto the surface of Fe-, Al- and Mn-oxides and oxi-hydroxides, restricts the mobilization of these elements into groundwater. Nevertheless, this does not hold in the case of the shallow unconfined groundwaters with high pH and high concentrations of potential competitors for adsorption sites (HCO₃, V, P, etc.). Under these geochemical conditions, desorption of the above mentioned anions and oxyanions occurs as a key process for As mobilization, resulting in an increase of minor and trace element concentrations. These geochemical processes that control the concentrations of dissolved As and other trace elements and which determine the groundwater quality especially in the shallow aquifers, are comparable to other areas with high As concentrations in groundwater of oxidizing aquifers and semi-arid or arid climate, which are found in many parts of the world, such as the western sectors of the USA, Mexico, northern Chile, Turkey, Mongolia, central and northern China, and central and northwestern Argentina.     

Hydrogeologie des Kabul-Beckens (Afghanistan), Teil I: Grundwasserleiter und Hydrologie

Shallow groundwater currently represents the main source for water supply in Kabul. Detailed information on the hydrogeology of the Kabul basin is therefore needed to improve the supply situation and to develop sustainable concepts of groundwater use. The basin is situated at the intersection of three major fault systems and comprises three major aquifers, all consisting of coarse sandy to gravely material originating from the surrounding mountains. The aquifers were deposited by several rivers draining the basin. Marl is the basal layer of the aquifers. Usually the aquifers are covered by loess loams which are an important feature in groundwater protection. The coarse aquifer material has high permeability. Deeper parts are affected by cementation of pore spaces, resulting in formation of semi-diagenetic conglomerates which decrease well yields. The main groundwater recharge occurs after the snowmelt from direct exfiltration from the rivers and from foothill infiltration. The high withdrawals of the last few years and a steadily rising population have led to a strong overexploitation of the groundwater resource as indicated by falling groundwater levels and deteriorating groundwater quality.     

An Unsteady Regional Multilayered Aquifer Model for Microcomputers

Groundwater quality and quantity modeling in regional aquifer systems has developed very rapidly within the last twenty years. The new computational methods introduced to this field offer flexible tools to practicing engineers to analyze complex problems that otherwise would have been unfeasible to solve. Recent advances made in microcomputer technology introduce a new phase to this progress since such computational facilities are now readily available to most engineers, and the existing groundwater models can be implemented on these computers for efficient and reliable simulation. The study summarized here is an extension of an earlier steady-state groundwater Now model developed by the first author. The numerical model discussed here is developed for an IBM-AT or compatible system with 640K core memory capacity. The FORTRAN code is compiled using the Microsoft version 3.2 FORTUNE Compiler (MS-FORTRAN Compiler) which runs under version 1.25 of the Microsoft Disk Operating System (MS-DOS). For fast numeric processing an 8087 coprocessing environment is suggested but such a processor is not necessary for proper execution. The unsteady multilayer aquifer model developed here is verified based on analytical solutions for multilayer aquifers available in the literature. The computer code generated is identified as MUCF1 (Multilayer-Unsteady-Groundwater-Flow) model.     

下辽河平原南部咸水入侵的数值模拟

建立了地下水水流与溶质的耦合模型,应用FEFLOW软件,对研究区的水位与水质进行了模拟预测.预测结果表明,区内大部分地区明化镇组含水层地下水C1ˉ质量浓度为50～120mg/L,馆陶组为20 ～50 mg,/L.地下水开采15年后咸水界面明显向内陆运移,咸水区北部运移距离大,速度快;咸水区两侧运移距离小,速度慢.模拟预...     

Grundwasser in Nürnberg: Wichtige Einheiten und deren Nutzbarkeit

The use and protection of urban – area aquifers such as the groundwater resources below the city of Nuremberg is becoming increasingly important. Hence, we present a stratigraphic and hydrogeologic overview of the “Nuremberg Syncline”.The Nuremberg Syncline regional aquifer system can be divided into seven units. Geochemical and stable isotope investigations have shown that strict hydraulic separations between aquifers and aquitards do not always exist. Connections may be enhanced, for example, via tectonic discontinuities that enable the rise of CO₂-rich groundwaters from deeper units. This is confirmed by frequent occurrences of artesian well conditions. Important subsurface structures in the near-surface aquifers include four palaeo-valleys that cut deep into the stratigraphic units of Keuper sandstones (Keuper Group; Middle and Late Triassic). These remarkable palaeo-valleys have been investigated with more than 2400 boreholes. The gravel and sand deposits of these aquifers offer, for instance, ideal possibilities for both heating and cooling of buildings by geothermal heat pumps.     

Significance of biomass support particles in laboratory studies on microbial degradation of organic chemicals in aquifers

In degradation studies of xenobiotics in groundwater environments from where only water samples can be obtained (e.g. established deep groundwater wells, inhomogeneous formations as boulder aquifers, or consolidated aquifers), solids might be added as biomass support materials. The importance of biomass support materials as quartz sand, rock wool and crushed tiles on the degradation of 8 aromatic hydrocarbons (benzene, toluene, o-xylene, 1,2-dichlorobenzene (1,2-DCB), 1,4-dichlorobenzene (1,4-DCB), naphthalene, biphenyl and nitrobenzene) was investigated in experiments with groundwater collected from two aerobic aquifers (Vejen and Grindsted, Denmark). Experiments with only groundwater as well as groundwater suspensions with aquifer sediment were run as references. It was impossible to adjust pH to the desired level in the experiments with crushed tiles, where also substantial sorption of the test compounds and server clogging of filters used in sampling occurred, and this material was therefore useless as biomass support material. Presence of rock wool supported growth of bacteria and increased the degradation (in terms of rates and number of compounds degraded) compared with experiments with groundwater only. However, the degradation was less and the degradation patterns varied more than in the presence of aquifer sediment. Quartz sand gave the most promising results with respect to growth of bacteria, and the degradation patterns of most of the compounds were similar to those obtained in experiments including aquifer sediments, although the latter showed the most substantial degradation. This study suggests that in case aquifer sediment is not available, quartz sand should be added as biomass support material in studies on degradation of organic xenobiotics in groundwater environments.     

Chlorinated Solvents in UK Aquifers

The paper reviews background data on chlorinated solvents and all published data on chlorinated solvents in UK groundwaters. New data from an aquifer-wide survey of the organic water quality of the Birmingham aquifer (carried out by the University of Birmingham and the Water Research Centre (WRc)) show that contamination by chlorinated solvents is extensive and is greater than that observed in previously published UK studies. Trichloroethylene contamination is particularly apparent in the Birmingham aquifer, with 40% of the boreholes sampled containing waters above the new UK limit for this contaminant. Fortunately the Birmingham aquifer is not used for public supply. Land use and hydrogeological factors are shown to influence the contamination observed in particular boreholes. The difficulties associated with locating contaminated zones in aquifers, due to the immiscible flow of chlorinated solvents, are indicated. It is concluded that the occurrence of chlorinated solvents in groundwaters makes a significant contribution to the poor water quality of many UK aquifers that underlie, or are close to, urban and industrial areas.     

Integrated Catchment Modelling as a Water Resources Management Tool

Groundwater models are becoming increasingly important in water resources management. Most aquifers in the UK are closely linked with river systems, to which they contribute baseflow from seepages and springs. As a result, major groundwater abstractions almost inevitably affect river flows. To assess with confidence the effect of utilizing ground-water resources, an aquifer and river system has to be linked within an integrated model which can simulate varying hydrogeological conditions throughout the catchment.
The main features of an integrated catchment management model, which links aquifer and river systems, are described in this paper. The model has been applied to a number of catchments in southern England including the River Darent in Kent, which is probably the most well-known and worst-affected of all rivers identified nationally as suffering from over-abstraction.
The process of model preparation and calibration is illustrated with reference to the River Darent. Twenty years of river flow and groundwater hydrograph records were used in producing a close simulation of modelled and actual hydrological conditions. The model was then operated to assess a large number of possible options for restoring flows to the river. Examples of various management strategy simulations are given, leading to formulation of a water resources management plan for the Darent. This involved (a) reductions in selected abstractions, (b) flow augmentation using river support boreholes, and (c) meeting peak groundwater supply demands in drought periods.     

Hydrogeochemistry of groundwater in coastal wetlands: implications for coastal conservation in Scotland

Groundwater in a shallow coastal aquifer in north east Scotland was monitored over the hydrological year October 1996-September 1997. Groundwater flow from inland areas sustained freshwater conditions in a dune-wetland complex of conservation importance. In particular, seasonal flooding of the coastal wetlands due to water table rise provided important roosting and breeding habitats for waterfowl. Hydrogeochemical analysis revealed that groundwater in the shallow sand aquifer was circum-neutral, and non-saline, despite being within 50 m of the sea and only 1 m above the mean high water mark. Calcium and HCO3 were the dominant cation and anion respectively, reflecting weathering processes in the aquifer. Use of the geochemical code NETPATH indicated that calcite weathering in shell fragments within the sand was the primary source of Ca and alkalinity generation. The concentrations of Na and Cl were also important, though these can be explained primarily by atmospheric inputs from precipitation. In detail, the spatial and temporal variation in groundwater chemistry was remarkably complex for what intuitively appeared a simple aquifer system. Temporal variations in groundwater chemistry mainly related to the seasonal event of groundwater recharge. Thus, the main period of rising groundwater levels resulted in a marked dilution of solutes in the aquifer, implying that water storage greatly increased in a relatively short period. A period of several weeks appeared to be required for dissolution processes to proceed to equilibrium. Spatial variation in groundwater chemistry appears to relate to the spatial distribution of geochemical processes in different hydrogeological units. Sulphate reduction, alkalinity generation and Fe precipitation appear to be locally important processes. The chemistry of groundwater maintains the wetland habitat by providing freshwater conditions that allow populations of various plant species to flourish. The potentially large recharge catchments of coastal wetlands, together with increasing pressures in the coastal zone, dictate that pollution can threaten the integrity of hydrochemical processes and requires careful monitoring if freshwater wetlands are to maintain their conservation importance.     

The East Kent Chalk Aquifer during the 1988-92 Drought

Groundwater resources of Chalk aquifers may become depleted during drought periods; major causes of this depletion include reductions in the aquifer transmissivity and the interaction between aquifers and rivers. In the East Kent aquifer there are certain catchments where difficulties are encountered in maintaining yields but, in other catchments, drought periods have little effect on the available resources. A mathematical model is developed to help understand the flow processes within the aquifer system, and the model is used to predict the consequences of possible abstraction scenarios.     

Temporal variability of organic C and nitrate in a shallow aquifer

The loading of organic substrates into shallow aquifers may follow seasonal cycles, which will impact the transport and fate of agrichemicals. The objective of this research was to measure temporal changes in the groundwater dissolved organic C (DOC) and nitrate concentrations. Groundwater monitoring wells were installed and sediment samples from the aquifer were collected in 1991. Sediment samples were used to evaluate denitrification potentials, while water samples were collected at periodic intervals in 1992 and 1993 from the surface of the aquifer. Water samples were analyzed for nitrate-N and DOC-C. Denitrification was observed in sediment amended with nitrate and incubated under anaerobic conditions at 10°C. Addition of algae lazed biomass increased denitrification, establishing that denitrification was substrate limited. In the aquifer, DOC concentrations followed seasonal patterns. DOC concentrations were highest following spring recharge and then decreased. Peak timing indicates that freezing and thawing were responsible for seasonal DOC patterns. These findings show that seasonally driven physical processes, such as freezing and thawing, influence organic substrate transport from surface to subsurface environments, and that this process should be taken into account when assessing agrichemical detoxification rates in shallow aquifers.