A great thickness (approx 1 km) of Lower Lias sediments occurs in the southern part of the North Minch basin, E of Lewis, Scotland. The Minch fault forms the western margin of the Permian-Tertiary rocks and is parallel to the Outer Isle thrust. The outcrop E of the fault in the N North Minch is no older than Middle Jurassic and may even include Cretaceous sediments. -R.A.H.
Abstract Catchment-scale (>40 km 2 ) contamination of the Chalk aquifer of Hertfordshire by bromate, emanating from a disused industrial site north of St Albans, represents the largest occurrence of point-source groundwater contamination in the UK. The influences of ‘double porosity’ diffusive exchange and rapid transport along solution-enhanced conduits complicate predictive modelling of contaminant transport to threatened public supply wells. Tracer testing indicates that solution-enhanced flow routes exist beyond the surface distribution of dissolution features in Hertfordshire, more extensively than previously thought. A quantitative conceptual understanding of this flow system has been incorporated into a spatially distributed equivalent porous media representation in MODFLOW and MT3D-MS. The calibrated model reproduces essential features of the aquifer system, including heads and flows, seasonal responses, and the timing and spatial distribution of observed tracer breakthroughs in the solution-enhanced aquifer, but does not fully capture the magnitude and form of tracer and bromate advance. Due to the influence of local solution enhancement and matrix effects, detailed breakthroughs at receptors cannot be resolved at the coarse grid scale. However, the model is able to simulate general trends.
Abstract This paper summarizes the findings of a recent research project on groundwater contamination from leaking sewers, which was completed for the Construction Industry Research and Information Association. Fifty‐four incidents were identified in England and Wales from a combined questionnaire survey and literature review. In addition to recorded incidents, the poor quality of many urban groundwaters suggests some effects from leaking sewers. Age is considered to be the most significant characteristic governing leakage from sewers; ground conditions (predominantly aquifer vulnerability) and usage (private versus public ownership) are also important factors relating to the likelihood of groundwater pollution from leaking sewers. Recommended strategies for reducing groundwater contamination include (a) modification of existing criteria for the service performance grading of existing sewers, (b) improved construction of new sewers in appropriate areas, (c) increased groundwater monitoring, and (d) risk assessments for new groundwater sources.
Abstract A regional ground‐water quality survey from 28 wells in the Coventry area of the United Kingdom identified widespread ground‐water pollution. Chlorinated hydrocarbon solvents (CHSs) were detected at concentrations exceeding l microgram per liter (μg/I) in all industrial and public water supply wells within the urban area. Of the CHSs analyzed, trichloroethene was most ubiquitous and was also detected at the highest concentrations, reaching a maximum of 547 μg/I at the industrial “Site A” during this study. By comparison with CHS pollution, inorganic and trace element concentrations were elevated relative to assumed baseline levels only in some industrial wells. The limited extent of inorganic contamination may be due to (1) retention of pollutants within the unsaturated zone, (2) ground‐water mixing in wells, (3) ferric hydroxide precipitation resulting in heavy metal coprecipitation, and (4) sorption on sand grains coated with ferric hydroxide. For inorganic determinants, a pollution index was devised which ranked zinc and boron as primary indicators of inorganic contamination. Regionally, concentrations of CHS and inorganic determinants did not reveal any significant correlation with depth.
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