Suchergebnisse

ABSTRACTUrban areas can impose significant loads of nitrogen, as ammonium or nitrate, onto the underlying groundwater. There are many sources of nitrogen pollution, including diffuse sources (parks and gardens), intense point sources (industrial chemical spills), and multi‐point sources (leaking sewers). Data on the loadings associated with the various sources are scarce, although an estimate of the overall load is available for Nottingham. For other cities, a total load could be estimated by factoring the Nottingham result, or by considering each component of the load separately. Both approaches are described, and the integrated method is recommended for its simplicity.

AbstractThe effluent from a former coal‐carbonisation plant in Nottinghamshire has contaminated the underlying aquifer with ammonium and organic compounds. In terms of flow and contamination, the site has experienced a complex history. MODFLOW has been used to unravel the past flow directions and to provide a basis for solute transport and biodegradation modelling. The modelling has shown that a fine grid is required to represent local flows to prevent incorrect site interpretations. A telescopic mesh technique was essential for this study to enable the site features to be adequately represented while including the regional hydrogeological influences. The influence of grid size to numerical dispersion was investigated for the MT3D computer program. The 'method of characteristics'and 'hybrid method of characteristics'modules of MT3D were found to be relatively free from numerical dispersion for all the grid sizes investigated. However, the 'modified method of characteristics'suffered extensively, and a linear relationship between grid size and numerical dispersion was demonstrated for this complex model.

ABSTRACTThe serious pollution of groundwater under cities is demonstrated with data from Coventry (UK), Madras (India) and Birmingham (UK). Microbiological organisms, nitrates, and organic chemicals are common, but many other pollutants are also found. The main sources are industry and inadequate sewerage. The provision of sewerage must remain a priority, on health grounds, for cities in the developing world. Virtually all industrial sites pollute the soil and groundwater through careless handling of chemicals. Industrial sites should be treated like landfills: contained and carefully monitored. If industrialists had to use groundwater from below their own sites, they would suffer the consequences of any pollution. This would also clean up the aquifer by pumping out polluted water.

ABSTRACTThe 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.

AbstractWe review published references on 'deculverting' (also known as 'daylighting') projects in the United Kingdom and internationally. The aim of the review was to assess the objectives of implemented projects and to establish where evidence exists for the purported social, economic and environmental benefits of deculverting. The outcomes highlight the need for collaboration to collate detailed information on such projects, to support the further development of evidence‐based policy. It is clear that deculverting schemes can indeed exert considerable positive impacts, including ecological benefits, reduced flood risks, recreation for local communities and a stimulus for regeneration, but that the evidence for these impacts is sparse. We conclude that improvements in policy will help to maximise these opportunities, by encouraging the implementation of good practices.

AbstractThis paper provides a method of identifying land contaminated with chlorinated hydrocarbon solvents by sampling and analysing soil gas. Relationships are presented which enable levels of soil gas contamination to be related to levels of soil and groundwater pollution. Two case studies are presented. Soil gas surveying of an industrial site with severe groundwater pollution demonstrated that standards for contaminated land are insufficient to protect groundwater. Solvent levels in groundwater were one to two orders of magnitude higher than UK permitted concentrations in drinking water, whereas soil contamination values did not reach polluted levels. Surveying of a site occupied by a disused fire station showed significant differences in patterns of soil gas and groundwater pollution. This is explained by direct pollution of groundwater though the well at the site and/or possible flow of polluted groundwater to the site from adjacent areas.