Vulnerability of regional crystalline rock aquifers to fluoride contaminaton: a case study from southern Sri Lanka

Paper presented at Groundwater and Climate in Africa, an International Conference, Kampala, Uganda, 24-28 June 200

Isotope and reactive transport modelling of denitrification in the Lincolnshire Limestone aquifer, eastern England

Groundwater within the outcrop area of the Lincolnshire Limestone aquifer in eastern England is characterized by high (>50 mg l–1) nitrate concentrations, whereas in the confined zone c. 15 km further east, nitrate concentrations are low

Application of a combined hydrochemical and stable isotope approach to the study of the interaction between irrigation canal water and groundwater in southern Sri Lanka. [Abstract only].

In International Symposium, Sustainable Agriculture for Prosperity, Faculty of Agriculture, University of Ruhuna, Sri Lanka, 16 November 2010. Proceedings, Part 1 - Keynote speeches and abstracts. Kamburupitiya, Sri Lanka: University of Ruhuna. Faculty of Agricultur

Mapping the potential human health implications of groundwater pollution in southern Sri Lanka

In southern Sri Lanka, irrigation influences the concentrations of faecal bacteria and inorganic toxic contaminants in groundwater. We develop a groundwater vulnerability map describing the potential human health implications of harmful constituents in the Uda Walawe Basin, by overlaying geological and land use data with information describing the irrigation system, the oxygen isotope composition of water bodies, and the concentrations of selected contaminants. Given the limited data available, we examine the spatial distribution of harmful constituents and the potential human health risks. Fluoride poisoning from groundwater is the greatest health threat in our study area, where fluoride concentrations ranging from 0.1 to 9.2 mg/L are associated with a geologic origin. Arsenic occurs in high concentrations, up to 0.4 mg/L, in areas with low recharge, although the source of arsenic is not clear. Nitrate concentrations are low, ranging from 0.4 to 23 mg/L, despite high fertilizer inputs, except in areas with low recharge and non-favourable reducing conditions, where concentrations up to 136 mg/L are found. Faecal bacteria decrease from surface water via shallow groundwater to deep groundwater. Irrigation water appears to play a major role in increasing microbial contamination and diluting inorganic constituents in groundwater. Hence, the most important determinants for mapping groundwater vulnerability are local geology and infiltration of irrigation water. The method we present provides a qualitative, yet practical, alternative to commonly used vulnerability mapping techniques for countries where high human health risk via consumption of groundwater is inevitable, and thus acts as a tool for selecting preventive and curative measures

Finite-elment model simulation of nitrate transport behaviour in saturated fractured porous media

A finite-element reactive transport model is developed and applied to study the transport behaviour of nitrate under the effect of denitrification in saturated fractured media. The reduction of nitrate is considered to be undertaken by a heterotrophic population of bacteria present on the fracture walls and in the pore space of the porous matrix. The bacterial metabolic activity is controlled by the availability of an electron donor (organic matter) and electron acceptors (nitrate and oxygen). Model equations are developed assuming 1D advective–dispersive transport in a set of parallel fractures with 2D diffusive transport in the adjacent porous matrix. The bacterial reaction in these equations is represented by dual Monod kinetic terms and the bacterial growth is represented by a single linear kinetic equation. The equations are discretized by the finite-element Galerkin method and the resultant set of non-linear algebraic equations is solved by an iterative scheme. The model is used to explore the effect of denitrification on fracture and porous matrix nitrate concentration profiles for different values of fracture aperture size, advective velocity, porous matrix width, porosity, and dispersion and diffusion coefficients. The effect of the presence of oxygen in limiting rates of bacterial nitrate reduction is also assessed. Overall, it is concluded that in fractured media with good porous matrix diffusion properties and favourable properties for bacterial growth, denitrification in the porous matrix can be more significant than in the fracture set in the reduction of nitrate mass

Stable isotope evidence for the hydrogeological characteristics of clay-rich till in northern East Anglia

The intrinsic vulnerability of the Chalk aquifer in East Anglia in eastern England to surface-derived contamination is dependent on the nature and juxtaposition of overlying Quaternary deposits. The study presented here is a direct investigation of the physical characteristics and pore water isotope composition of the glacial deposits found overlying the Chalk at five drilled locations in north Norfolk. The pore water isotopic composition demonstrated a range of d18O values from -8.13 to -6.47‰, similar to the range for Chalk groundwater in the area of -8.18 to -7.01‰. A lithology-dependent model is developed that recognizes the presence of isotopically depleted palaeowater of late Pleistocene origin contained within layers of clay-rich till, adjacent to pore water containing modern meteoric water within layers of sand-rich till. The presence of (weathered) vertical fractures and intercalated lenses of sand-and gravel-rich layers is inferred to explain the occurrence of isotopically enriched water within the general mass of clay-rich till. It is apparent that groundwater movement in the heterogeneous lodgement till is controlled by advection in the more permeable sand-rich layers, whereas in the mass of clay-rich till, diffusion is more dominant. At one confined site, the observed pore water isotopic profile is modelled as having developed by downward diffusion of modern meteoric water during the past 5-10 ka

Beneath the surface of global change: Impacts of climate change on groundwater

Global change encompasses changes in the characteristics of inter-related climate variables in space and time, and derived changes in terrestrial processes, including human activities that affect the environment. As such, projected global change includes groundwater systems. Here, groundwater is defined as all subsurface water including soil water, deeper vadose zone water, and unconfined and confined aquifer waters. Potential effects of climate change combined with land and water management on surface waters have been studied in some detail. Equivalent studies of groundwater systems have lagged behind these advances, but research and broader interest in projected climate effects on groundwater have been accelerating in recent years. In this paper, we provide an overview and synthesis of the key aspects of subsurface hydrology, including water quantity and quality, related to global change. Adaptation to global change must include prudent management of groundwater as a renewable, but slow-feedback resource in most cases. Groundwater storage is already over-tapped in many regions, yet available subsurface storage may be a key to meeting the combined demands of agriculture, industry, municipal and domestic water supply, and ecosystems during times of shortage. The future intensity and frequency of dry periods combined with warming trends need to be addressed in the context of groundwater resources, even though projections in space and time are fraught with uncertainty. Finally, potential impacts of groundwater on the global climate system are largely unknown. Research to improve our understanding of the joint behaviors of climate and groundwater is needed, and spin-off benefits on each discipline are likely

Attenuation of groundwater pollution by bank filtration

Bank filtration, either natural or induced through the river bed by pumping from a system of connected lateral or vertical wells, provides a means of obtaining public water supplies. The success of such schemes is dependent on the microbial activity and chemical transformations that are commonly enhanced in the colmation layer within the river bed compared to those that take place in surface or ground waters. The actual biogeochemical interactions that sustain the quality of the pumped bank filtrate depend on numerous factors including aquifer mineralogy, shape of the aquifer, oxygen and nitrate concentrations in the surface water, types of organic matter in the surface and ground water environments, and land use in the local catchment area. This paper provides an introduction to a series of nine papers contained in this Special Issue that highlight these factors and finishes with a list of recommendations for co-ordinated research into attenuation of groundwater pollution by bank filtration