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Crude influent sewages were collected from 30 English wastewater treatment works representing rural, urban and industrial catchments as part of a screening study to assess the significance of the concentrations of substances from the Water Framework Directive priority pollutants list in crude sewage. Composite samples were analysed for a range of determinands including metals and organic compounds. Of the determinands quantified, the pesticides were almost exclusively below the limit of detection. Most trace metals (with the exception of mercury) were detectable in all wastewaters, reflecting their ubiquitous nature. Organic determinands detected in the influent at μg/L levels included surfactants (linear alkylbenzene sulphonates and nonylphenol ethoxylates), phthalates (diethylhexyl phthalate), polynuclear hydrocarbons and solvents. Trace concentrations of trichlorobenzene, tributyltin and polychlorinated biphenyl 153 were detected in a limited number of works. Little correlation was observed between runoff or trade effluent inputs entering the works and determinand concentration (chromium being the only exception).

Regional groundwater resource models are often built to improve confidence in predicted groundwater abstraction impacts on river flows and groundwater levels. By explicitly representing the aquifer system geometry, properties and boundaries, together with transient recharge and abstraction pressures, such models provide a robust platform to support abstraction impact assessment, alongside evidence from field data and investigations. Regulatory drivers include the European Union Habitats and Water Framework Directives and other abstraction licensing decisions. This paper presents examples of the spatial and temporal patterns of groundwater abstraction impacts predicted by several models. A variety of presentation formats are used to illustrate the simulated flow impacts of abstractions both individually, and in combination with other surface water abstractions and discharges. Model predictions from a range of abstraction, aquifer, and river settings are often more complex than would be suggested by simpler tools and approaches. In many cases, absolute low-flow impacts are less than long-term groundwater abstraction rates. The ‘real world’ hydrogeological mechanisms behind these impact patterns are discussed. The paper also recommends a protocol for using regional models to assess individual licensed groundwater abstraction impacts across the full range of historic climate conditions (typically, as monitored since 1970) and in the context of other operational artificial influences.

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The ability of NaCI and MgSO 4 to impair the performance of Portland cement, blended cements containing slag and fly ash and of a permeable backfill have been measured. Performance is determined by decrease in pH, changes in mineralogy and loss of physical coherence. Experiments have been made at 250, 550 and 85'C and extensively backed up by chemical models of cement performance. NaCI, up to 1.5M, has a comparatively slight impact on performance but MgSO 4 rapidly and almost quantitatively reacts, lowering system pH's to < 10, conditioned by mixtures of Mg(OH) 2 and magnesium silicates with gypsum.

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